Descripción: A paleomagnetic study, carried out on 9 sites of the La Flecha Formation (facies Los Sapitos, Upper Cambrian, Marjuman-Steptoean) exposed along the la Angostura creek, Precordillera of La Rioja (29.5°S, 68.7°W), permitted to determine two magnetic components. One is postectonic and of low coercivities and unblocking temperatures (A, Dec: 7.5°, Inc: -40.3°, a95: 10.1°, N: 6), being interpreted as a recent remanence of probable viscous origin. A second, pretectonic, component was isolated in seven sites with opposite polarities and is likely carried by magnetite (B, Dec: 206.9°, Inc: 63.3°, a95: 12.8°, N: 7). The paleomagnetic pole position for this component (Lat: 63.8°S, Long: 244.6°E, dp: 15.9°, dm: 20.2°) suggests that the remanence was acquired by the end of the Permian and it is interpreted as produced by the regional remagnetization associated with the San Rafael orogenic phase found in other units of the Precordillera. An analysis of pole positions, type of magnetizations, polarities and geographic distribution of the remagnetized units suggests a pattern of time-space migration of the remagnetization from west to east, between the Early Permian and the Permian-Triassic. This pattern is consistent with a model of remagnetization by migration of fluids expelled from the orogenic area that reached rocks not involved directly in the deformation. The pole position obtained for La Flecha Formation also suggests the lack of major tectonic rotations in the study area since the Permian. © 2005 Asociación Geológica Argentina.

Descripción: Synthetic Aperture Radar (SAR) images are dificult to segment due to their characteristic noise, called speckle, which is multiplicative, non-gaussian and has a low signal to noise ratio. In this work we use the GH distribution to model the SAR data from the different regions of the image. We estimate their statistical parameters and use them in a segmentation algorithm based on multiregion competition. We then apply this algorithm to segment simulated as well as real SAR images and evaluate the accuracy of the segmentation results obtained. © 2009 Springer-Verlag Berlin Heidelberg.

Descripción: The general form of a Lagrangian concomitant of a metric and a curvature form is found, improving substantially a previous result. © 1989 American Institute of Physics.

Descripción: The effect of rotation is considered to become important when the Rossby number is sufficiently small, as is the case in many geophysical and astrophysical flows. Here we present direct numerical simulations to study the effect of rotation in flows with moderate Rossby numbers (down to Ro ≈ 0.03) but at Reynolds numbers large enough to observe the beginning of a turbulent scaling at scales smaller than the energy injection scale. We use coherent forcing at intermediate scales, leaving enough room in the spectral space for an inverse cascade of energy to also develop. We analyze the spectral behavior of the simulations, the shell-to-shell energy transfer, scaling laws and intermittency, as well as the geometry and the anisotropy of the structures in the flow. At late times, the direct transfer of energy at small scales is mediated by interactions with the largest scale in the system, the energy containing eddies with k⊥ ≈ 1, where ⊥ refers to wavevectors perpendicular the axis of rotation. The transfer between modes with wavevector parallel to the rotation is strongly quenched. The inverse cascade of energy at scales larger than the energy injection scale is nonlocal, and energy is transferred directly from small scales to the largest available scale. We observe both a direct and inverse cascade of energy at high rotation rate, indicative that these cascades can take place simultaneously. Also, as time evolves and the energy piles up at the large scales, the intermittency of the direct cascade of energy is preserved while corrections due to intermittency are found to be the same (within error bars) as in homogeneous nonrotating turbulence. © 2009 American Institute of Physics.

Descripción: Fil:Dmitruk, P. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: Towards the northeast of the Sierra de San Luis several wolfram ore deposits occur. In San Martín district they are divided into three groups: Los Avestruces, La Esperanza and Cerrito Blanco. The geology of this area is formed of the Conlara metamorphic complex composed of schists (with a strike of 300° north), granitoids and pegmatites. In the same area subsaturated chalco-alkaline lamprophyres also appear as subvertical bodies with NW-NE strikes. Toward the boundaries of these rocks, the amount of biotite rises gradually from 80 to 90% developing a biotitite rock due to metasomatic processes and the superimposed deformation. This biotitite is rich in K, Rb and W among other elements. The scheelite mineralization (with quartz, biotite and tourmaline as non ore minerals) occurs in veins that are usually hosted between the lamprophyres and the wall rocks. Scheelite also appears between the schist planes of the biotitite rocks as well as disseminated crystals in quartz aggregates. This mineralization took place from fluids with XH2O: 0.87/0.82 - XCO2: 0.11/0.16 - XNaCl: 0.015/0.013 - (CH4) meanwhile the scheelite, according to the fluid inclusions studies, precipitated from unmixing processes below 320°C and 2.3 kb. Achaliana orogeny and the intrusion of Las Chacras-Piedras Coloradas batholiths (Devonian-Carboniferous) were the responsible for the slight rise of the fluids from the basement, the generation of fault structures through which they rose, the metasomatism and the mineralization.

Descripción: Plasma temperature and radial density profiles of the plasma species in a high energy density cutting arc have been obtained by using a quantitative schlieren technique. A Z-type two-mirror schlieren system was used in this research. Due to its great sensibility such technique allows measuring plasma composition and temperature from the arc axis to the surrounding medium by processing the gray-level contrast values of digital schlieren images recorded at the observation plane for a given position of a transverse knife located at the exit focal plane of the system. The technique has provided a good visualization of the plasma flow emerging from the nozzle and its interactions with the surrounding medium and the anode. The obtained temperature values are in good agreement with those values previously obtained by the authors on the same torch using Langmuir probes. © 2010 American Institute of Physics.

Descripción: We investigate the potential impact of forthcoming Jefferson Lab semi-inclusive polarized deep inelastic scattering proton measurements in the determination of the sea quark polarization in the nucleons by means of a next to leading order global QCD analysis. Specifically, we estimate the resulting improvement in the constraints on polarized parton densities for different flavors, which is found to be significant for up and strange quarks, and the correlation between remaining uncertainty ranges for each of the parton species.

Descripción: We studied the dietary niche of the Barn Owl (Tyto alba) in temperate agroecosystems of central Argentina by describing seasonal and geographic variation in the food habits of this owl in four districts of the Pampean region (Flooding, Inland, Rolling, and Southern Pampas). We identified 21,925 prey items from samples of fresh pellets collected in summer (n = 23) and winter (n = 26). Mammals,' mostly sigmodontine rodents, were the main prey items (91.9%), followed by amphibians (6.5%) and birds (1.6%). Arthropods were also a common prey item (found in 45% of the samples). The consumption of arthropods and amphibians was higher in summer than in winter, indicating that seasonal changes in prey abundances are reflected in the Barn Owl diet. We found no differences in food-niche breadth among the four study districts, but food-niche breadth varied between seasons, being higher during summer. Six rodent species were common to all districts: Calomys spp., Akodon azarae, Oligoryzomys flavescens, Mus musculus, Rattus spp., and Holochilus brasiliensis. Calomys spp. was numerically dominant in 46 of the 49 samples, and together with A. azarae and O. flavescens comprised the bulk of the diet (> 80%). Predation on rodents may reflect population dynamics of the prey species with high predation rates when peaks in abundance of sigmodontine rodents occurred (autumn-winter). © The Neotropical Ornithological Society.

Descripción: In Buenos Aires, the most crowded city of Argentina, there is a potential risk of dengue virus transmission by the mosquito Aedes aegypti during late summer. The temporal patterns of oviposition activity and abundance of breeding sites of this vector were studied in two cemeteries of the city. Between September 1998 and August 1999, we examined 142 ovitraps weekly and a total of 18,010 water-filled containers. Both study areas showed remarkable differences in the percentages of positive ovitraps (19% vs 8%) and breeding sites (18% vs 1%), but similar temporal abundance patterns. The percentage of breeding sites was higher in summer and autumn than in spring and winter, and the percentage of positive ovitraps was higher in summer than in the other three seasons. Immatures were recorded from the first week of October to the second week of July, and oviposition activity from the third week of October until the end of April. In both cemeteries and with both methodologies the highest infestation levels were registered in March (ovitraps: 41.8% and 20.6%, breeding sites : 39.2% and 3.4%). These highest abundances took place after several months with mean temperatures above 20°C and accumulated rainfalls above 150 mm. A sharp decline in oviposition activity was observed when monthly mean temperature decreased to 16.5°C, and no eggs were found below 14.8°C. Seasonal fluctuation of Ae. aegypti abundances in mid-latitudes like Buenos Aires would allow reduction of the egg mosquito population through the elimination of containers during the coldest months, which are free of adults.

Descripción: Sedimentology and paleoenvironments of the Patagoniano and its transition to the Santa Cruz Formation south of Lago Argentino, southern Patagonia. Detailed sedimentological analysis of the Patagoniano and its transition to the Santa Cruz Formation has been carried out south of Lago Argentino, in southern Patagonia. The 180 meters thick succession of fossiliferous sandstones was subdivided into twelve lithofacies, grouped in three facies associations. From base to top we defined the facies association I, dominated by massive, bioturbated and fossiliferous sandstones; the facies association II, dominated by fining upward cycles of cross-stratified sandstones and heterolithic facies; and the facies association III dominated by thin conglomeratic levels interbedded with mudstones rich in plant remains and paleosoils. The facies association I is interpreted as the deposit of a transgressive, shallow sea with oyster rich biogenic accumulations, finally evolving to a coastal plain paleoenvironment. A new transgression originated the discontinuity underlying the facies association II, which was interpreted as a progradational estuarine system. Finally, the ongoing progradation produced the fluvial meandering system of facies association III, assigned to the Santa Cruz Formation. The new name "Estancia 25 de Mayo" is formalized here for the Patagoniano in the southernmost Cordillera Patagónica, instead of the problematic name Centinela Formation. The Estancia 25 de Mayo Formation was subdivided in two members: the lower Quién Sabe Member, equivalent to the facies association I, and the upper Bandurrias Member, equivalent to the (facies association II).

Descripción: The study of the carbonate-ramp deposits of La Manga Formation has allowed us to recognize three facies associations. The lithofacies association A is composed by five lithofacies (A1-A5). This association represents part of the transgressive systems tract. It corresponds to external ramp deposits, accumulated below the storm-wave base. The A facies association appears in cycles of centimetric to decimetric thickness and belong to a retrograding parasequence set of 5th order. The lithofacies B association starts after an abrupt facies contact. It is characterized by six lithofacies (B1-B6). They are coarsening upward beds that form metric-scale cycles. These are interpreted as middle-ramp deposits dominated by storms. It corresponds to 4th order sequences. The lithofacies C includes three lithofacies (C1-C3). The small scale cycles were controlled by storm events, while the medium and large scale ones were likely originated by eustasy. The studied stratigraphic sections of La Manga Formation are included in two depostitional sequences SD-2 and SD-3. An abrupt discontinuity marks the beginning of the depositional sequence SD-2, which constitutes a transgressive system-tract, composed by a coarsening upward parasequence stacking set. Above a maximum flooding surface, manifested by a drastic change of facies, a low rate accommodation space period and a sea-level fall (characterized by a lowstand systems tract) are evidenced. The third depositional sequence SD-3 is composed by lagoon deposits. It starts after a paleokarstic surface, characterized by the development of a sheet-cake breccia and an intense vadose diagenesis.

Descripción: Structural anatomy of seedlings of Cupressus lusitanica Mill., C. macrocarpa Hartw. and C. sempervirens L. (Cypress) cultivated in Argentina was studied. Seedlings of these species were fixed at eigth different stages of the germination process. Anatomical features of root, hypocotyl, cotyledonary node, cotyledons and epicotyl were described. The root-hypocotyl-cotyledon vascular transition was analized. In the root and in most of the hypocotyl length, the protoxylem exhibits exarch position. At the cotyledonary node the metaxylem differentiates gradual- and laterally divergent from the protoxylem. In sections of the upper zone of the hypocotyl, close to the cotyledonary node, the protoxylem shows an endarch position. In the epicotyl, the undifferentiated procambium alternates with the cotyledonary vascular bundles. The number of xylematic poles is equal to the number of cotyledons in thr three species.

Descripción: The Euterpe edulis embryo consists of a prominent single cotyledon, a very short radicle-hypocotyl axis and an epicotyl. The epicotyl is obliquely angled with respect to the cotyledon; consequently it corresponds to one of the two categories recognized for palm seeds by DeMason (1988). Parenchyma, protoderm and procambium can be distinguished on the basis of position and shape of their cells, which are highly vacuolated with one central vacuole and the cytoplasm restricted to a thin parietal layer. Initial cells from both apical meristems are also vacuolated but they have small vacuoles distributed around the nuclei. Silica occurs in cell walls of some protodermal cells. Raphides, silica bodies and tannins all occur occasionally in vacuoles, especially in the basal cotyledon region. Most embryo cells lack storage reserves and exhibit an active state, with numerous mitochondria, RER cisternae and Golgi apparatus, indicating a strategy of continuous development without the interposition, at maturity, of a dry state. The endosperm consists of living cells with very large nuclei and thickened cell walls. Similar to the endosperm of other studied palm species, their cells exhibit a quiescent appearance with lipid, protein, minerals (in the cytoplasm) and mannans (in the cell walls) as the insoluble storage reserves. © 2004 The Linnean Society of London.

Descripción: In this communication, the genesis of great anomalous seismic activity registered during austral summer 2003/2004 on Deception Island (Antarctica) is discussed, and related with changes on the chemical composition of fumarolic gases and vent deposits. Here we present a comparative analysis performed to explain this activity. We propose a possible parcial seal of the microfracture system. This effect allows an increase on pressure follow by reopening of microfractures, resulting on a sequence of seismic events and changes on the chemical composition of fumarolic emissions.

Descripción: Fil:Prezzi, C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: Mice harboring three mouse mammary tumor virus (MMTV) variants develop pregnancy-dependent (PD) tumors that progress to pregnancy-independent (PI) behavior through successive passages. Herein, we identified 10 predominant insertions in PI transplants from 8 independent tumor lines. These mutations were also detected in small cell populations in the early PD passages. In addition, we identified a new viral insertion upstream of the gene Rspo3, which is overexpressed in three of the eight independent tumor lines and codes for a protein very similar to the recently described protein encoded by Int7. This study suggests that during progression towards hormone independence, clonal expansion of cells with specific mutations might be more relevant than the occurrence of new MMTV insertions. Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Descripción: A clique in a graph is a complete subgraph maximal under inclusion. The clique graph of a graph is the intersection graph of its cliques. A graph is self-clique when it is isomorphic to its clique graph. A circular-arc graph is the intersection graph of a family of arcs of a circle. A Helly circular-arc graph is a circular-arc graph admitting a model whose arcs satisfy the Helly property. In this note, we describe all the self-clique Helly circular-arc graphs. © 2006 Elsevier B.V. All rights reserved.

Descripción: The competition between chemical equilibrium, for example protonation, and physical interactions determines the molecular organization and functionality of biological and synthetic systems. Charge regulation by displacement of acid-base equilibrium induced by changes in the local environment provides a feedback mechanism that controls the balance between electrostatic, van der Waals, steric interactions and molecular organization. Which strategies do responsive systems follow to globally optimize chemical equilibrium and physical interactions? We address this question by theoretically studying model layers of end-grafted polyacids. These layers spontaneously form self-assembled aggregates, presenting domains of controlled local pH and whose morphologies can be manipulated by the composition of the solution in contact with the film. Charge regulation stabilizes micellar domains over a wide range of pH by reducing the local charge in the aggregate at the cost of chemical free energy and gaining in hydrophobic interactions. This balance determines the boundaries between different aggregate morphologies. We show that a qualitatively new form of organization arises from the coupling between physical interactions and protonation equilibrium. This optimization strategy presents itself with polyelectrolytes coexisting in two different and well-defined protonation states. Our results underline the need of considering the coupling between chemical equilibrium and physical interactions due to their highly nonadditive behavior. The predictions provide guidelines for the creation of responsive polymer layers presenting self-organized patterns with functional properties and they give insights for the understanding of competing interactions in highly inhomogeneous and constrained environments such as those relevant in nanotechnology and those responsible for biological cells function.

Descripción: Fil:Ponce-Dawson, S. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: We investigate the evolution of the ridge produced by the convergent motion of two substrates, on which a layer of a non-Newtonian power-law liquid rests. We focus on the self-similar regimes that occur in this process. For short times, within the linear regime, the height and the width increase as t 1/2, independently of the rheology of the liquid. In the self- similar regime for large time, the height and the width of the ridge follow power laws whose exponents depend on the rheological index. © 2009 IOP Publishing Ltd.

Descripción: We investigate the evolution of the ridge produced by the non-symmetrical convergent motion of two substrates over which an initially uniform layer of a Newtonian liquid rests. The lack of symmetry of the flow arises because the substrates move with different velocities. We focus on the self-similar regimes that occur in this process. For short times, within the linear regime, the height and the width increase as t1/2 and the profile is symmetric, independently of degree of asymmetry of the motion of the substrates. In the self-similar regime for large time, the height and the width of the ridge follow the same power laws as in the symmetric case, but the profiles are asymmetric. © 2009 IOP Publishing Ltd.

Descripción: The fidelity amplitude (FA) is a quantity of paramount importance in echo-type experiments. We use semiclassical theory to study the average FA for quantum chaotic systems under external perturbation. We explain analytically two extreme cases: the random dynamics limit-attained approximately by strongly chaotic systems-and the random perturbation limit, which shows a Lyapunov decay. Numerical simulations help us to bridge the gap between both the extreme cases. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Descripción: We have calculated the electrical conductivity in the current-in-plane geometry of multilayered granular alloys composed of Co clusters embedded in Ag alternating with pure Ag layers. In particular, we have paid attention to the conductivity behavior as a function of Ag layer thickness, Co clusters' size, and degree of percolation. The electronic structure is self-consistently calculated within the unrestricted Hartree-Fock approximation using a parametrized tight binding Hamiltonian which includes a Hubbard-like term. The conductivity tensor is obtained by using the semiclassical Boltzmann equation in the anisotropic relaxation time approximation. We have used a s-d Mott-like scattering model for the electronic mean free path taking into account the Sondheimer's picture for electronic transport in thin films. We find that the experimental conductivity behavior at coalescence can be explained through the electronic band contribution. The conductivity behavior of continuous multilayers is already attained in the very early stage of percolation, as in the experiments. © 2007 American Institute of Physics.

Descripción: Semiconductor lasers with optical feedback present a regime in which power dropouts are observed. Although this regime has been extensively studied, there is no agreement about whether the dropouts are deterministically or stochastically generated. In this paper we will study the statistics of time intervals between dropouts assuming noise-driven simple excitable models. We explain the appearance of characteristic times in the first return maps. © 1999 The American Physical Society.

Descripción: The excited states of the double hydrogen bond in the adenine-thymine nucleotide base pair has been investigated in the semiempirical CNDO/S-CI approximation. Double-minimum potential curves are obtained for several nuclear configurations characterizing simultaneous tautomeric rearrangements of the NH⋯N and O⋯HN bonds. The energy profiles for the coupled movement of the hydrogen bonding show that the Watson-Crick configuration of the adenine-thymine base pair is the most stable for all of the excited states studied. Estimates are made within the WKB approximation of the tunneling rate and tunneling probability. The results indicate that increasing the energy of the excited states would increase the probability of double protonic transfer by tunnel effect and thus for irreversible mutation. A comparison of the composition of the potentials for the single movement of the protons with the double-minimum potential of the concerted movement shows that the potential is nonseparable. The shortcomings that follow from the WKB approximation as applied to the present problem are discussed. © 1981 American Chemical Society.

Descripción: This work extends the concept of seniority number, which has been widely used for classifying N-electron Slater determinants, to wave functions of N electrons and spin S, as well as to N-electron spin-adapted Hilbert spaces. We propose a spin-free formulation of the seniority number operator and perform a study on the behavior of the expectation values of this operator under transformations of the molecular basis sets. This study leads to propose a quantitative evaluation for the convergence of the expansions of the wave functions in terms of Slater determinants. The non-invariant character of the seniority number operator expectation value of a wave function with respect to a unitary transformation of the molecular orbital basis set, allows us to search for a change of basis which minimizes that expectation value. The results found in the description of wave functions of selected atoms and molecules show that the expansions expressed in these bases exhibit a more rapid convergence than those formulated in the canonical molecular orbital bases and even in the natural orbital ones. © 2013 AIP Publishing LLC.

Descripción: Riboflavin, an essential cofactor for all organisms, is biosynthesized in plants, fungi and microorganisms. The penultimate step in the pathway is catalyzed by the enzyme lumazine synthase. One of the most distinctive characteristics of this enzyme is that it is found in different species in two different quaternary structures, pentameric and icosahedral, built from practically the same structural monomeric unit. In fact, the icosahedral structure is best described as a capsid of twelve pentamers. Despite this noticeable difference, the active sites are virtually identical in all structurally studied members. Furthermore, the main regions involved in the catalysis are located at the interface between adjacent subunits in the pentamer. Thus, the two quaternary forms of the enzyme must meet similar structural requirements to achieve their function, but, at the same time, they should differ in the sequence traits responsible for the different quaternary structures observed. Here, we present a combined analysis that includes sequence-structure and evolutionary studies to find the sequence determinants of the different quaternary assemblies of this enzyme. A data set containing 86 sequences of the lumazine synthase family was recovered by sequence similarity searches. Seven of them had resolved three-dimensional structures. A subsequent phylogenetic reconstruction by maximum parsimony (MP) allowed division of the total set into two clusters in accord with their quaternary structure. The comparison between the patterns of three-dimensional contacts derived from the known three-dimensional structures and variation in sequence conservation revealed a significant shift in structural constraints of certain positions. Also, to explore the changes in functional constraints between the two groups, site-specific evolutionary rate shifts were analyzed. We found that the positions involved in icosahedral contacts suffer a larger increase in constraints than the rest. We found eight sequence sites that would be the most important icosahedral sequence determinants. We discuss our results and compare them with previous work. These findings should contribute to refinement of the current structural data, to the design of assays that explore the role of these positions, to the structural characterization of new sequences, and to initiation of a study of the underlying evolutionary mechanisms.

Descripción: In the present work, we have used the papillomavirus E7 oncoprotein to pursue structure-function and evolutionary studies that take into account intrinsic disorder and the conformational diversity of globular domains. The intrinsically disordered (E7N) and globular (E7C) domains of E7 show similar degrees of conservation and co-evolution. We found that E7N can be described in terms of conserved and coevolving linear motifs separated by variable linkers, while sequence evolution of E7C is compatible with the known homodimeric structure yet suggests other activities for the domain. Within E7N, inter-residue relationships such as residue co-evolution and restricted intermotif distances map functional coupling and co-occurrence of linear motifs that evolve in a coordinate manner. Within E7C, additional cysteine residues proximal to the zinc-binding site may allow redox regulation of E7 function. Moreover, we describe a conserved binding site for disordered domains on the surface of E7C and suggest a putative target linear motif. Both homodimerization and peptide binding activities of E7C are also present in the distantly related host PHD domains, showing that these two proteins share not only structural homology but also functional similarities, and strengthening the view that they evolved from a common ancestor. Finally, we integrate the multiple activities and conformations of E7 into a hierarchy of structure-function relationships. © 2012 Chemes et al.

Descripción: Protein modification by conjugation of small ubiquitin-related modifier (SUMO) is involved in diverse biological functions, such as transcription regulation, subcellular partitioning, stress response, DNA damage repair, and chromatin remodeling. Here, we show that the serine/arginine-rich protein SF2/ASF, a factor involved in splicing regulation and other RNA metabolism-related processes, is a regulator of the sumoylation pathway. The overexpression of this protein stimulates, but its knockdown inhibits SUMO conjugation. SF2/ASF interacts with Ubc9 and enhances sumoylation of specific substrates, sharing characteristics with already described SUMO E3 ligases. In addition, SF2/ASF interacts with the SUMO E3 ligase PIAS1 (protein inhibitor of activated STAT-1), regulating PIAS1-induced overall protein sumoylation. The RNA recognition motif 2 of SF2/ASF is necessary and sufficient for sumoylation enhancement. Moreover, SF2/ASF has a role in heat shock-induced sumoylation and promotes SUMO conjugation to RNA processing factors. These results add a component to the sumoylation pathway and a previously unexplored role for the multifunctional SR protein SF2/ASF.

Descripción: We present a detailed structural and surface-enhanced Raman scattering (SERS) study of poly(allylamine) modified with Os (byp)2 ClPyCHO (PAH-Os) and gold nanoparticles self-assembled multilayers [PAH-Os+ (Au-nanoparticlesPAH-Os)n, n=1 and 5]. Atomic force microscopy and variable-angle spectroscopic ellipsometry measurements indicate that the first nanoparticle layer grows homogenously by partially covering the substrate without clustering. Analyzing the sample thickness and roughness we infer that the growth process advances thereafter by filling with nanoparticles the interstitial spaces between the previously adsorbed nanoparticles. After five immersion steps the multilayers reach a more compact structure. The interaction between plasmons of near-gold nanoparticles provides a new optical absorption around 650 nm which, in addition, allows a more effective SERS process in that spectral region than at the single-plasmon resonance (∼530 nm). We compare the electronic resonance Raman and SERS amplification mechanisms in these self-assembled multilayers analyzing Raman resonance scans and Raman intensity micromaps. As a function of nanoparticle coverage we observe large changes in the Raman intensity scans, with maxima that shift from the electronic transitions, to the plasmon resonance, and finally to the coupled-plasmon absorption. The Raman micromaps, on the other hand, evidence huge intensity inhomogeneities which we relate to "hot spots." Numerical discrete dipole approximation calculations including the interaction between gold nanoparticles are presented, providing a qualitative model for the coupled-plasmon absorption and redshifted Raman hot spots in these samples. © 2005 American Institute of Physics.

Descripción: A population of Belostoma sp. polymorphic for the sex chromosome determining system has been analyzed. The fundamental karyotype of the species is 2n = 16 = 14 + XY (male), and at different times individuals 2n = 17 have been encountered in a low frequency (27% and 16%, respectively). Sex chromosome area measurements confirm that the original X chromosome of the XY system has fragmented into two unequal-sized chromosomes (X1 and X2). At male metaphase II, the sex univalents associate in a pseudotrivalent that can show different arrangements (in a chain, in a double-plate, or in other transitional arrangements). Their frequency varies among individuals. The present polymorphic population represents a direct evidence of a multiple sex chromosome system originating through fragmentation of the single X. The different kinds of arrangement of the three sex chromosomes at male metaphase II, and their frequency within each individual suggest that some forces are acting to achieve a double plate arrangement and a regular meiotic behaviour. The maintenance of the polymorphism during more than three years seems to indicate that the new chromosomal variant is neutral, or even could be selectively advantageous.

Descripción: We examined diurnal and nocturnal nectar secretion across sexual stages in protandrous Alstroemeria aurea, a bumble bee-pollinated herb with long-lived flowers native to the southern Andes. We found the following patterns: (1) most nectar was produced diurnally and (2) three times more sugar was secreted during the male than female phase, not only because the male phase lasted longer but also because the rate of nectar production was higher. This 3:1 ratio in nectar production matched the ratio of the minimum number of bumble bee visits required on average to saturate male (pollen removal) vs. female (seed set) functions. Standing crop of nectar, on the other hand, did not differ greatly between male- and female-stage flowers left open to visitors, because the high-production male-phase flowers were visited more frequently than female-phase flowers. In an experiment concurrent with the repeated nectar sampling of individual flowers over their life-span, we removed pollen from anthers or deposited pollen on stigmas by hand. Neither treatment, designed to mimic effects of visits by Alstroemeria's native bumble bee pollinator, affected nectar production. The absence of plasticity in nectar secretion in relation to pollination events may reflect a low cost of nectar production, or may result from developmental constraints related to the evolution of the synchronous protandry that characterizes A. aurea.

Descripción: Factors affecting mating behaviour in the bug Triatoma infestans were quantitatively studied in the laboratory. Experimental conditions were established so that the probability of copulation increased with the time elapsed since the first adult meal. Copulatory attempts by males did not vary as a function of time, but rejections by females became significantly less frequent with the post feeding time. Non-receptive females displayed four types of rejection behaviour, i.e. flattening, stridulation, evasion and abdominal movements. The occurrence of stridulation performed by females in a sexual context was observed in a regular fashion and was quantified for the first time in this species.

Descripción: The factors affecting the sexual behaviour of Panstrongylus megistus were studied under laboratory conditions. A general description of mating behaviour is presented for this species. The effect of the time elapsed after the first imaginal feeding on the mating frequency, the motivation of males to mate and the rejection behaviour by females, were analyzed. We also determined the number of copulas accepted by females of this species. Finally, the possible existence of a sexual chemical signal promoting male aggregation around mating couples was evaluated. Results showed that mating frequency increased with the time elapsed since the first adult meal. Despite the number of male copulatory attempts did not change as a function of time, the rejection behaviour of females became gradually less frequent. Females rejected mating by means of body flattening on the substrate, abdominal movements, evasion or stridulation. After a single copula, females did not usually accept to mate again. Neither male nor female aggregation around mating couples was observed, suggesting the absence of a sexual assembling pheromone in P. megistus.

Descripción: Fil:Massoni, V. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: Despite the interest in applying environmentally friendly control methods such as sterile insect technique (SIT) against Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae), information about its biology, taxonomy, and behavior is still insufficient. To increase this information, the present study aims to evaluate the performance of wild flies under field cage conditions through the study of sexual competitiveness among males (sexual selection). A wild population from Horco Molle, Tucumán, Argentina was sampled. Mature virgin males and females were released into outdoor field cages to compete for mating. Morphometric analyses were applied to determine the relationship between the multivariate phenotype and copulatory success. Successful and unsuccessful males were measured for 8 traits: head width (HW), face width (FW), eye length (EL), thorax length (THL), wing length (WL), wing width (WW), femur length (FL), and tibia length (TIL). Combinations of different multivariate statistical methods and graphical analyses were used to evaluate sexual selection on male phenotype. The results indicated that wing width and thorax length would be the most probable targets of sexual selection. They describe a nonlinear association between expected fitness and each of these 2 traits. This nonlinear relation suggests that observed selection could maintain the diversity related to body size.

Descripción: The large-scale dynamics of plasmas is well described within the framework of magnetohydrodynamics (MHD). However, whenever the ion density of the plasma becomes sufficiently low, the Hall effect is likely to become important. The role of the Hall effect has been studied in several astrophysical plasma processes, such as magnetic reconnection, magnetic dynamo, MHD turbulence, or MHD instabilities. In particular, the development of small-scale instabilities is essential to understand the transport properties in a number of astrophysical plasmas. The magneto-rotational instability (MRI), which takes place in differentially rotating accretion disks embedded in relatively weak magnetic fields, is just one example. The influence of the large-scale velocity flows on small-scale instabilities is often approximated by a linear shear flow. In this paper, we quantitatively study the role of the Hall effect on plasmas embedded in large-scale shear flows. More precisely, we show that an instability develops when the Hall effect is present, which we therefore term as the Hall magneto-shear instability. As a particular case, we recover the so-called MRI and quantitatively assess the role of the Hall effect on its development and evolution. © 2011 The American Astronomical Society. All rights reserved.

Descripción: A procedure, based on a continuous transformation of the origin of the (quantum mechanical) current density that sets the diamagnetic contribution to zero (CTOCD-DZ) all over the molecular domain, is applied to determine shielding polarizabilities to first order in a perturbing electric field. In any calculations relying on the algebraic approximation, irrespective of size and quality of the (gaugeless) basis set employed, all the components of the CTOCD-DZ magnetic shielding polarizability are origin independent, and the constraints for charge and current conservation are exactly satisfied. The effects of a static uniform electric field on the nuclear magnetic resonance (NMR) shielding of H2O2, F2, H2C2, H2CO, NH3, HCN, and HNC molecules have been investigated within the CTOCD-DZ method, and compared with the conventional results evaluated via the same basis sets, and with theoretical results taken from the literature. © 2000 American Institute of Physics.

Descripción: In this article we extend the theory of shift-invariant spaces to the context of LCA groups. We introduce the notion of H-invariant space for a countable discrete subgroup H of an LCA group G, and show that the concept of range function and the techniques of fiberization are valid in this context. As a consequence of this generalization we prove characterizations of frames and Riesz bases of these spaces extending previous results, that were known for Rd and the lattice Zd. © 2009 Elsevier Inc. All rights reserved.

Descripción: The coastline position in Claromecó, Buenos Aires province was determined, featuring character elements identified in relation to the position of the shoreline. In comparison on the determination of coastline and shoreline, it appears that the first results of the geomorphologic interpretation, while the position of the shoreline is subject to a number of uncertainties if there are no long-term measurements. The nomenclature for the coastal areas is not always clear, hampering the interpretation of the processes occurring in the coast and shore. The correct identification is important technical, scientific and legal. Current legislation states that the boundary between public and private territory corresponds to the shoreline. The use of plant species in the determination of the coastline and shoreline, by itself is not determinative if not accompanied by the geomorphologic reconnaissance of the area. The exact determination of shoreline and coastline is essential in the implementation of geological surveys of major importance for the proper planning and development of the coastal area. In the task of delimitation of the coastal area beach ridges were found; one located about 5 m a.s.l has an age of 4,370 years BP.

Descripción: We study experimentally and theoretically the controlled transfer f harmonically trapped ultracold gases between different quantum states. n particular, we experimentally demonstrate a fast decompression anddisplacement of both a non-interacting gas and an interacting Bose-Einstein ondensate, which are initially at equilibrium. The decompression parameters re engineered such that the final state is identical to that obtained after a erfectly adiabatic transformation despite the fact that the fast decompression is erformed in the strongly non-adiabatic regime. During the transfer the atomic ample goes through strongly out-of-equilibrium states, while the external onfinement is modified until the system reaches the desired stationary state. The cheme is theoretically based on the invariants of motion and scaling equation echniques and can be generalized to decompression trajectories including an rbitrary deformation of the trap. It is also directly applicable to arbitrary initial on-equilibrium states. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Descripción: Vertical excitation and electron detachment energies associated with the optical absorption of iodide ions dissolved in supercritical ammonia at 420 K have been calculated in two limiting scenarios: as a solvated free I- ion and forming a K+ I- contact ion pair (CIP). The evolution of the transition energies as a result of the gradual building up of the solvation structure was studied for each absorbing species as the solvent's density increased, i.e., changing the N H3 supercritical thermodynamic state. In both cases, if the solvent density is sufficiently high, photon absorption produces a spatially extended electron charge beyond the volume occupied by the solvated solute core; this excited state resembles a typical charge-transfer-to-solvent (CTTS) state. A combination of classical molecular dynamics simulations followed by quantum mechanical calculations for the ground, first-excited, and electron-detached electronic states have been carried out for the system consisting of one donor species (free I- ion or K+ I- CIP) surrounded by ammonia molecules. Vertical excitation and electron detachment energies were obtained by averaging 100 randomly chosen microconfigurations along the molecular dynamics trajectory computed for each thermodynamic condition (fluid density). Short- and long-range contributions of the solvent-donor interaction upon the CTTS states of I- and K+ I- were identified by performing additional electronic structure calculations where only the solvent interaction due to the first neighbor molecules was taken into account. These computations, together with previous experimental evidence that we collected for the system, have been used to analyze the solvent effects on the CTTS transition. In this paper we have established the following: (i) the CTTS electron of free I- ion or K+ I- CIP presents similar features, and it gradually localizes in close proximity of the iodine parent atom when the ammonia density is increased; (ii) for the free I- ion, the short-range solvent interaction contributes to the stabilization of the ground state more than it does for the CTTS excited state, which is evidenced experimentally as a blueshift in the maximum absorption of the CTTS transition when the density is increased; (iii) this effect is less noticeable for the K+ I- ion pair, because in this case a tight solvation structure, formed by four N H3 molecules wedged between the ions, appears at very low density and is very little affected by changes in the density; (iv) the long-range contribution to the solvent stabilization can be neglected for the K+ I- CIP, since the main features of its electronic transition can be explained on the basis of the vicinity of the cation; (v) however, the long-range solvent field contribution is essential for the free I- ion to become an efficient CTTS donor upon photoexcitation, and this establishes a difference in the CTTS behavior of I- in bulk and in clusters. © 2007 American Institute of Physics.

Descripción: In the mammalian inner ear, the gain control of auditory inputs is exerted by medial olivocochlear (MOC) neurons that innervate cochlear outer hair cells (OHCs). OHCs mechanically amplify the incoming sound waves by virtue of their electromotile properties while the MOC system reduces the gain of auditory inputs by inhibiting OHC function. How this process is orchestrated at the synaptic level remains unknown. In the present study, MOC firing was evoked by electrical stimulation in an isolated mouse cochlear preparation, while OHCs postsynaptic responses were monitored by whole-cell recordings. These recordings confirmed that electrically evoked IPSCs (eIPSCs) are mediated solely by α9β10 nAChRs functionally coupled to calcium-activated SK2 channels. Synaptic release occurred with low probability when MOC-OHC synapses were stimulated at 1 Hz. However, as the stimulation frequency was raised, the reliability of release increased due to presynaptic facilitation. In addition, the relatively slow decay of eIPSCs gave rise to temporal summation at stimulation frequencies >10 Hz. The combined effect of facilitation and summation resulted in a frequency-dependent increase in the average amplitude of inhibitory currents in OHCs. Thus, we have demonstrated that short-term plasticity is responsible for shaping MOC inhibition and, therefore, encodes the transfer function from efferent firing frequency to the gain of the cochlear amplifier. © 2011 the authors.

Descripción: Short-time decay of the Loschmidt echo was discussed. It is used to measure the sensitivity to perturbations of quantum evolutions. It was found that the characteristic time of the regime is well described by the inverse of the width of the local density of states.

Descripción: Fil:Ferrari, H. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: It is now recognized that in addition to its activity upon erythroid progenitor cells, erythropoietin (Epo) is capable of stimulating survival of different non-erythroid cells. Since stimulation of erythropoiesis is unwanted for neuroprotection, Epo-like compounds with a more selective action are under investigation. Although the carbamylated derivative of erythropoietin (cEpo) has demonstrated non-hematopoietic tissue protection without erythropoietic effect, little is known about differential mechanisms between Epo and cEpo. Therefore, we investigated signaling pathways which play a key role in Epo-induced proliferation. Here we show that cEpo blocked FOXO3a phosphorylation, allowing expression of downstream target p27kip1 in UT-7 and TF-1 cells capable of erythroid differentiation. This is consistent with the involvement of cEpo in slowing down G1-to-S-phase progression compared with the effect of Epo upon cell cycle. In contrast, similar antiapoptotic actions of cEpo and Epo were observed in neuronal SH-SY5Y cells. Inhibition and competition assays suggest that Epo may act through both, the homodimeric (EpoR/EpoR) and the heterodimeric (EpoR/βcR) receptors in neuronal SH-SY5Y cells and probably in the TF-1 cell type as well. Results also indicate that cEpo needs both the EpoR and βcR subunits to prevent apoptosis of neuronal cells. Based on evidence suggesting that cell proliferation pathways were involved in the differential effect of Epo and cEpo, we went forward to studying downstream signals. Here we provide the first evidence that unlike Epo, cEpo failed to induce FOXO3a inactivation and subsequent p27kip1 downregulation, which is clearly shown in the incapacity of cEpo to induce erythroid cell growth. © 2013 Elsevier B.V.

Descripción: Natural time series usually show either a combination of periodic phenomena with stochastic components or chaotic behavior. In many cases, when nonlinear characteristics are computed, they will essentially indicate the most remarkable effects and the results will underestimate or overestimate the real complexity of the system. For that reason signal separation of the frequency bands representing well known phenomena, like periodic or almost periodic behaviors, allows comprehension of the hidden nonlinear or stochastic phenomena involved. In this work a signal separation method based on trigonometric wavelet packets is described. The method has been applied, as an example, to a time series of daily mean discharges of the Atuel river in Argentina, that presents strong annual and semiannual oscillations due to meteorological effects. The correlation dimension and the maximum Lyapunov exponent of the residual time series were obtained taking away its known almost periodic components.

Descripción: Spectral analyses performed on records of cosmogenic nuclides reveal a group of dominant spectral components during the Holocene period. Only a few of them are related to known solar cycles, i.e., the De Vries/Suess, Gleissberg and Hallstatt cycles. The origin of the others remains uncertain. On the other hand, time series of North Atlantic atmospheric/sea surface temperatures during the last ice age display the existence of repeated large-scale warming events, called Dansgaard-Oeschger (DO) events, spaced around multiples of 1470 years. The De Vries/Suess and Gleissberg cycles with periods close to 1470/7 (∼210) and 1470/17 (∼86.5) years have been proposed to explain these observations. In this work we found that a conceptual bistable model forced with the De Vries/Suess and Gleissberg cycles plus noise displays a group of dominant frequencies similar to those obtained in the Fourier spectra from paleo-climate during the Holocene. Moreover, we show that simply changing the noise amplitude in the model we obtain similar power spectra to those corresponding to GISP2 δ18O (Greenland Ice Sheet Project 2) during the last ice age. These results give a general dynamical framework which allows us to interpret the main characteristic of paleoclimate records from the last 100 000 years. © 2010 Author(s).

Descripción: We present a new approach to simple homotopy theory of polyhedra using finite topological spaces. We define the concept of collapse of a finite space and prove that this new notion corresponds exactly to the concept of a simplicial collapse. More precisely, we show that a collapse X ↘ Y of finite spaces induces a simplicial collapse K (X) ↘ K (Y) of their associated simplicial complexes. Moreover, a simplicial collapse K ↘ L induces a collapse X (K) ↘ X (L) of the associated finite spaces. This establishes a one-to-one correspondence between simple homotopy types of finite simplicial complexes and simple equivalence classes of finite spaces. We also prove a similar result for maps: We give a complete characterization of the class of maps between finite spaces which induce simple homotopy equivalences between the associated polyhedra. This class describes all maps coming from simple homotopy equivalences at the level of complexes. The advantage of this theory is that the elementary move of finite spaces is much simpler than the elementary move of simplicial complexes: It consists of removing (or adding) just a single point of the space. © 2007 Elsevier Inc. All rights reserved.

Descripción: A simple model based on an approximation of the dropletlike model is formulated for studying adsorption of fluids into cylindrical pores. This model yields a nearly universal description of capillary condensation transitions for noble gases confined by alkali metals. The system’s thermodynamical behavior is predicted from the values of two dimensionless parameters: [formula presented] (the reduced asymptotic strength of the fluid-adsorber interaction, a function of temperature) and [formula presented] (the reduced radius of the pore). The phenomenon of hysteresis inherently related to capillary condensation is discussed. The connection to a previously proposed universality for cylindrical pores is also established. © 2002 The American Physical Society.

Descripción: Landscape simulators are widely applied in landscape ecology for generating landscape patterns. These models can be divided into two categories: pattern-based models that generate spatial patterns irrespective of the processes that shape them, and process-based models that attempt to generate patterns based on the processes that shape them. The latter often tend toward complexity in an attempt to obtain high predictive precision, but are rarely used for generic or theoretical purposes. Here we show that a simple process-based simulator can generate a variety of spatial patterns including realistic ones, typifying landscapes fragmented by anthropogenic activities. The model "G-RaFFe" generates roads and fields to reproduce the processes in which forests are converted into arable lands. For a selected level of habitat cover, three factors dominate its outcomes: the number of roads (accessibility), maximum field size (accounting for land ownership patterns), and maximum field disconnection (which enables field to be detached from roads). We compared the performance of G-RaFFe to three other models: Simmap (neutral model), Qrule (fractal-based) and Dinamica EGO (with 4 model versions differing in complexity). A PCA-based analysis indicated G-RaFFe and Dinamica version 4 (most complex) to perform best in matching realistic spatial patterns, but an alternative analysis which considers model variability identified G-RaFFe and Qrule as performing best. We also found model performance to be affected by habitat cover and the actual land-uses, the latter reflecting on land ownership patterns. We suggest that simple process-based generators such as G-RaFFe can be used to generate spatial patterns as templates for theoretical analyses, as well as for gaining better understanding of the relation between spatial processes and patterns. We suggest caution in applying neutral or fractal-based approaches, since spatial patterns that typify anthropogenic landscapes are often non-fractal in nature. © 2013 Pe'er et al.

Descripción: Fil:Velázquez, P.F. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: We study the asymptotic behavior of a semi-discrete numerical approximation for a pair of heat equations ut = Δu, vt = Δv in Ω × (0, T); fully coupled by the boundary conditions ∂u/∂η = up11vp12, ∂v/∂η = up21vp22 on ∂Ω × (0, T), where Ω is a bounded smooth domain in ℝd. We focus in the existence or not of non-simultaneous blow-up for a semi-discrete approximation (U, V). We prove that if U blows up in finite time then V can fail to blow up if and only if p11 > 1 and p21 < 2(p11 - 1), which is the same condition as the one for non-simultaneous blow-up in the continuous problem. Moreover, we find that if the continuous problem has non-simultaneous blow-up then the same is true for the discrete one. We also prove some results about the convergence of the scheme and the convergence of the blow-up times.

Descripción: We discuss a semiclassical treatment to inflationary models from Kaluza-Klein theory without the cylinder condition. We conclude that the evolution of the early universe could be described by a geodesic trajectory of a cosmological 5D metric here proposed, so that the effective 4D FRW background metric should be a hypersurface on a constant fifth dimension. © 2003 Elsevier B.V. All rights reserved.

Descripción: A logarithmic 1-form on ℂℙn can be written as ω = (Π0m Fj) ∑0m λi dFi/Fi = λ0F̂ 0dF0 +⋯+ λmF̂ mdFm with F̂i = (Π0 m Fj)/Fi for some homogeneous polynomials Fi of degree di and constants λi ∈ ℂ* such that ∑ λidi = 0. For general Fi, λi, the singularities of ω consist of a schematic union of the codimension 2 subvarieties Fi = Fj = 0 together with, possibly, finitely many isolated points. This is the case when all Fi are smooth and in general position. In this situation, we give a formula which prescribes the number of isolated singularities. © Foundation Compositio Mathematica 2006.

Descripción: Gonads in the tropical lucinid bivalves Ctena orbiculata, Codakia orbicularis, and Lucina pensylvanica are located in the cephalopodial mass above the foot and behind the gills. Age estimates for Lucina pensylvanica suggest that individuals less than one year old are immature, as also is C. orbicularis, and that both males and females mature at two years. For Ctena orbiculata, we have no age data, but we consider that this species may also have early development. In July 2002 when water temperatures were high, mature individuals of all three species were spawning or in resorption, and oocyte envelopes were present. Parasites were found in the digestive diverticula of C. orbiculata and L. pensylvanica. External ultrastructure of the spermatozoon shows differences between the three species. Codakia orbicularis and L. pensylvanica have a long-headed spermatozoa, whereas Ctena orbiculata has a middle-size head. Codakia orbicularis possesses a flagellum with a lateral undulating membrane, absent from the two other species.

Descripción: Changes in promoter structure and occupation have been shown to modify the splicing pattern of several genes, evidencing a coupling between transcription and alternative splicing. It has been proposed that the promoter effect involves modulation of RNA pol II elongation rates. The C4 point mutation of the Drosophila pol II largest subunit confers on the enzyme a lower elongation rate. Here we show that expression of a human equivalent to Drosophila's C4 pol II in human cultured cells affects alternative splicing of the fibronectin EDI exon and adenovirus E1a pre-mRNA. Most importantly, resplicing of the Hox gene Ultrabithorax is stimulated in Drosophila embryos mutant for C4, which demonstrates the transcriptional control of alternative splicing on an endogenous gene. These results provide a direct proof for the elongation control of alternative splicing in vivo.

Descripción: Sviluppo e Studi Superior! in Sardegna (CRS4). The geometries, interaction energies, and harmonic vibrational frequencies of water clusters (with up to 8 molecules) have been studied using density functional theory (DFT) at the gradient corrected level. The water monomer and water dimer calculations have been used as benchmarks to investigate different choices for basis sets and density functionals. Our results for larger clusters agree with both available high-level ab initio calculations and experimental information. The calculations of the vibrational frequencies and IR absorption intensities for the larger clusters, for which no other reliable quantum-chemical calculation is available, are presented to facilitate the frequency assignment of experimental spectra.

Descripción: For α in (0, 1], a subset E of R2 is called a Furstenberg set of type α or Fα-set if for each direction e in the unit circle there is a line segment ℓe in the direction of e such that the Hausdorff dimension of the set E∩ℓe is greater than or equal to α. In this paper we use generalized Hausdorff measures to give estimates on the size of these sets. Our main result is to obtain a sharp dimension estimate for a whole class of zero-dimensional Furstenberg type sets. Namely, for hγ(x)=log-γ(1x), γ>0, we construct a set Eγ∈Fhγ of Hausdorff dimension not greater than 12. Since in a previous work we showed that 12 is a lower bound for the Hausdorff dimension of any E∈Fhγ, with the present construction, the value 12 is sharp for the whole class of Furstenberg sets associated to the zero dimensional functionshγ. © 2012 Elsevier Ltd.

Descripción: We study small random perturbations by additive white-noise of a spatial discretization of a reaction-diffusion equation with a stable equilibrium and solutions that blow up in finite time. We prove that the perturbed system blows up with total probability and establish its order of magnitude and asymptotic distribution. For initial data in the domain of explosion we prove that the explosion time converges to the deterministic one while for initial data in the domain of attraction of the stable equilibrium we show that the system exhibits metastable behavior. © 2011 Elsevier Inc.

Descripción: We prove that if C is a cocommutative k-coalgebra such that dimk(ke Λ ke) < N for all group-like elements e εo C ⊗ k, then smoothness of C is equivalent to the condition Hoch*(C) = 0 for all * ≥ N. © 2002 Elsevier Science B.V. All rights reserved.

Descripción: In this work we describe for the first time the social and reproductive behavior of the Neotropical fish Cichlasoma dimerus (Heckel, 1840) [Perciformes: Cichlidae], endemic to the Paraná River basin, using a comprehensive-integral approach, including morphological and physiological features. This substrate breeding fish has biparental care of the fry and presents a dominance hierarchy that determines access to breeding territories among males, and to males with territories among females. Gregarious behavior associated with a pale body color, was observed before reproductive behaviors started. Afterwards, a dominance hierarchy was established through aggressive interactions. Territorial individuals had bright body color patterns and non territorial an opaque grey one. Black ventral coloration was associated with reproductive individuals. Courtship displays, which were similar to threatening displays, had the common effect of increasing the visible area of the individual. The dominant male was always the largest one suggesting that size is probably a major factor determining the hierarchy establishment and that these intra-sexually selected traits may have been reinforced by inter-sexual selection. Reproductive males had higher pituitary levels of β-follicle stimulating hormone (β-FSH) and somatolactin (SL) than non reproductive ones, while no differences were found among females. No differences were found among male gonadosomatic indexes. Non reproductive individuals had higher plasma cortisol levels for both sexes. It is possible that dominant reproductive individuals may be inhibiting reproduction of subordinate fish through physical contact, increasing their cortisol levels and diminishing FSH and SL pituitary content. However, this was not reflected as an inhibition at the gonadal level in our experimental design. © 2011 Sociedade Brasileira de Ictiologia.

Descripción: We compute the threshold-resummed cross section for pseudo-scalar MSSM Higgs boson production by gluon fusion at hadron colliders. The calculation is performed at next-to-next-to leading logarithmic accuracy. We present results for both the LHC and Tevatron Run II. We analyze the factorization and renormalization scale dependence of the results, finding that after performing the resummation the corresponding cross section can be computed with an accuracy better than 10%. © 2007 Elsevier B.V. All rights reserved.

Descripción: We have used a tabletop soft-x-ray laser and a wave-front division interferometer to probe the plasma of a pinch discharge. A very compact capillary discharge-pumped Ne-like Ar laser emitting at 46.9 nm was combined with a wave division interferometer based on Lloyd's mirror and Sc-Si multilayer-coated optics to map the electron density in the cathode region of the discharge. This demonstration of the use of tabletop soft-x-ray laser in plasma interferometry could lead to the widespread use of these lasers in the diagnostics of dense plasmas. ©1999 The American Physical Society.

Descripción: On June 2, 2003, SOHO/LASCO coronagraph observed two CMEs at the West limb of the Sun, at 00.30 and 08:54 UT, respectively, which appeared to originate from the same source region. Both CMEs show the typical three-part structure. These events have been also observed by SOHO/UVCS, allowing us to infer their physical parameters. We also looked for interplanetary signatures of the CMEs in ACE 'in situ' observations but we did not find evidence of the ejected flux rope; however, the solar wind appeared significantly distorted, probably as a consequence of the influence of both CMEs on their surrounding interplanetary plasma. © 2010 American Institute of Physics.

Descripción: The relationships between landscapes features evolution and soil genesis and distribution are studied. The area is located in southern Entre Rios province (33o00'-33o45'S and 58o30'-59o17'W). The Parana River Delta, has a complex genetic evolution, due to river processes, marine ingressions and aeolian actions. These processes resulted in an unstable landscape, that imprinted its particular features in soils. Nine geomorphic units were recognized: 1) Gualeguay river alluvial plain and terraces, 2) Arroyo Ñancay aluvial plain and terrazes, 3) Minor streams aluvial plains, 4) Gualeguay river delta, 5) Deltaic plain, 6) Beach ridges, 7) Old lagoon and tidal plain, 8) Loessic plain and 9) Dunes. Soils are mainly Entisols, Inceptisols and Mollisols, and a spatial trend is recognized in the Delta Region. Soil evolution is controlled by a) an active morphodynamic, b) soil landscape features that resulted in a dominant aquic regime of soils and c) Late Quaternary climatic fluctuations that resulted in sea level variations. Finally, soil development, soil features and distribution and soil drainage are studied in relation with landscape main features and evolution. © 2004 Asociación Geológica Argentina.

Descripción: Factors of soils formation, parent material, and relief in western part of Santa Cruz province (southermost Patagonia) were studied in rio de las Vueltas valley beetween Laguna del Desierto and Lago Viedma (49oS-49o30′S y a 73o W). There is great soil variability related to a strong north-west-south-east bioclimatic and geomorphic gradient. Soils were studied in a NW-SE transect, where three different sectors could be distinguished. The western area, including the Patagonian Andean Cordillera and piedmont is characterised by strong landscape variations due to glacial processes, colluvial, glacial, cineritc and glacifluvial parent materials, a udic-xeric regime and Nothofagus woodlands. The landscape of the eastern area is mainly of glacial-fluvioglacial, fluvial origin, with aeolian landforms, an and regime, grassland-shrub steppe and large flat structural plain landscape. Because of their different landscape-relief features and parent materials, both areas have different soils associations. The western area is characterized by a distrudepts, udivitrands/hapludands and haploxerolls sequence, meanwhile the eastern by an haplargides, torriortents and haplocalcides trends. In the western area, podzolisation features were recognized. In the north-western sector, Bs and E horizons were recognized, and low pH base saturation values, due to climatic conditions, indicate ongoing podzolization. Elsewhere in the south-eastern sector calcium carbonate from the surface, basic pH and total saturation are soils main features. © 2004 Asociación Geológica Argentina.

Descripción: The objective of this work was to assess the soil oribatid mite communities in four sites of the Upper Paraná Bosque Atlántico, in the Iguazú National Park, Argentina and in surrounding areas: bamboo forest, palm forest and two mixed forests. A comparison between each pair of sites, based on the presence-absence of oribatid species, was performed using Jaccard's index. This is the first systematic sampling of oribatid mites in this area. A total of 56 genera and 96 oribatid species were found, 25 and 49 of them, respectively, are new citation for Argentina. The highest similarity was found between mixed forests. Almost 68% and 34% of the genera were cited for similar biotopes in Brazil and Paraguay, respectively.

Descripción: The study area is located in central-western Santa Cruz including El Chaltén town between 49°00'and 49°36'S - 73°30'and 72°00'W. Environmental variability, relief, parent material, altitude, climate, vegetation and soils were recognized. According to characteristics of the soils, it is possible to differentiate three sectors: western, central and eastern. Inceptisols, Spodosols and Andisols dominate in the first, meanwhile in Central area the main soils are Molisolls and Entisols. Aridisols and aridic Entisols dominate in the Eastern sector. A west-east variation trend, in relation to soil features could be established: an increase in pH, CEC, exchangeable bases and % of CaCO3. Inversely there is an increase % C, pHNaF (in udic regime soils) and divalent/monovalent cations relationship.

Descripción: Active regions (ARs), involved in the Halloween events during October-November 2003, were the source of unusual activity during the following solar rotation. The flares on 18-20 November 2003 that occur in the AR NOAA10501 were accompanied by coronal mass ejections associated to some particularly geoeffective magnetic clouds. Our analysis of the magnetic flux and helicity injection revealed that a new emerging bipole and consequent shearing motions continuously energized the region during its disk passage. The stored energy was eventually released through the interaction of the various systems of magnetic loops by several magnetic reconnection events. Active events on November 18 (filament eruptions and CMEs) were originated by shearing motions along a section of the filament channel that injected magnetic helicity with sign opposite to that of the AR. Two homologous flares, that occurred on November 20, were apparently triggered by different mechanisms as inferred from the flare ribbons evolution (filament eruption and CMEs). We studied in detail the behaviour of two North-South oriented filaments on November 20 2003. They merged and split following a process suggestive of 'sling-shot' reconnection between two coronal flux ropes. We successfully tested this scenario in a 3D MHD simulation that is presented in this paper. © International Astronomical Union 2011.

Descripción: A method is developed to solve Laplace's equation with Dirichlet's or Neumann's conditions in plane, single-connected regions bounded by arbitrary single curves. It is based on the existence of a conformal transformation that reduces the original problem to another whose solution is known. The main advantage of the method is that it does not require the knowledge of the transformation itself, so it is applicable even when no transformation is available. The solution and its higher-order derivatives are expressed in terms of explicit quadratures easy to evaluate numerically or even analytically. © 1990 American Institute of Physics.

Descripción: If Ω ⊂ Rn is a bounded domain, the existence of solutions u ∈ W01, p (Ω) of div u = f for f ∈ Lp (Ω) with vanishing mean value and 1 < p < ∞, is a basic result in the analysis of the Stokes equations. It is known that the result holds when Ω is a Lipschitz domain and that it is not valid for domains with external cusps. In this paper we prove that the result holds for John domains. Our proof is constructive: the solution u is given by an explicit integral operator acting on f. To prove that u ∈ W01, p (Ω) we make use of the Calderón-Zygmund singular integral operator theory and the Hardy-Littlewood maximal function. For domains satisfying the separation property introduced in [S. Buckley, P. Koskela, Sobolev-Poincaré implies John, Math. Res. Lett. 2 (5) (1995) 577-593], and 1 < p < n, we also prove a converse result, thus characterizing in this case the domains for which a continuous right inverse of the divergence exists. In particular, our result applies to simply connected planar domains because they satisfy the separation property. © 2005 Elsevier Inc. All rights reserved.

Descripción: We study by topological methods a nonlinear differential equation generalizing the Black-Scholes formula for an option pricing model with stochastic volatility. We prove the existence of at least a solution of the stationary Dirichlet problem applying an upper and lower solutions method. Moreover, we construct a solution by an iterative procedure. © 2002 Elsevier Science (USA). All rights reserved.

Descripción: We study H-systems with a Dirichlet boundary data g. Under some conditions, we show that if the problem admits a solution for some (H0, g 0), then it can be solved for any (H,g) close enough to (H 0,g0). Moreover, we construct a solution of the problem applying a Newton iteration.

Descripción: New insights into equilibrium and dynamical aspects of electron photodetachment reactions in small water clusters were given. It focuses on assessing the effects of thermal and polarization fluctuations provided by three cluster environments with different extents of spatial confinement, on the microscopic mechanisms that drive the reaction. These fluctuations, in turn, determine the characteristics of the electron localization and the subsequent detachment following photoexcitation of the probe.

Descripción: Solvation of excess electrons in supercritical ammonia along the T = 450 K isotherm was investigated. Equilibrium aspects of solvation were analyzed using combined path integral-molecular dynamics techniques. Observations showed transition from localized to quasifree states at approximately one fourth of the triple point density.

Descripción: This paper presents a new generalization of the graph multicoloring problem. We propose a Branch-and-Cut algorithm based on a new integer programming formulation. The cuts used are valid inequalities that we could identify to the polytope associated with the model. The Branch-and-Cut system includes separation heuristics for the valid inequalities, specific initial and primal heuristics, branching and pruning rules. We report on computational experience with random instances. © 2009 Elsevier B.V. All rights reserved.

Descripción: We prove that the zero set of a 4-nomial in n variables in the positive orthant has at most three connected components. This bound, which does not depend on the degree of the polynomial, not only improves the best previously known bound (which was 10) but is optimal as well. In the general case we prove that the number of connected components of the zero set of an m-nomial in n variables in the positive orthant is lower than or equal to (n+1) m-121 + (m - 1)(m - 2)/2, improving slightly the known bounds. Finally, we show that for generic exponents, the number of non-compact connected components of the zero set of a 5-nomial in three variables in the positive octant is at most 12. This strongly improves the best previously known bound, which was 10,384. All the bounds obtained in this paper continue to hold for real exponents. © 2005 Springer Science+Business Media, Inc.

Descripción: In this paper we propose an extended family of almost orthogonal spline wavelets with compact support. These functions provide snug bases for L2 (ℛ), preserving semiorthogonal properties. As it is well known, orthogonality is a desirable quality while finite support has attractive features for numerical applications. This work represents an effort to combine these conditions in the spline case and to enhance previous results of Chui and Unser et al. We start by reviewing the concept of semiorthogonal wavelets and we discuss their performance. Next, we give a brief description of the general technique for computing compactly supported spline wavelets. Finally we expose these functions. We also develop several formulas in accord with our purposes. © 1996 Academic Press, Inc.

Descripción: After an appropriate restatement of the Gelfand-Naimark-Segal construction for topological* -algebras we prove that there exists an isomorphism among the set Cycl (A) of weakly continuous strongly cyclic* -representations of a barreled dual-separable* -algebra with unit A, the space HilbA (A*) of the Hilbert spaces that are continuously embedded in A* and are* -invariant under the dual left regular action of A, and the set of the corresponding reproducing kernels. We show that these isomorphisms are cone morphisms and we prove many interesting results that follow from this fact. We discuss how these results can be used to describe cyclic representations on more general inner product spaces. © 2008 American Institute of Physics.

Descripción: We study the boundedness of the one-sided operator g λ,φ + between the weighted spaces L p(M - w) and L p(w) for every weight w. If λ = 2/p whenever 1 < p < 2, and in the case p = 1 for λ > 2, we prove the weak type of g λ,φ + For every λ > 1 and p = 2, or λ > 2/p and 1 < p < 2, the boundedness of this operator is obtained. For p > 2 and λ > 1, we obtain the boundedness of g λ,φ + from L p((M -) [p/2]+1w) to L p(w), where (M -) k denotes the operator M - iterated k times.

Descripción: The Oligo-Miocene Somuncura province is the largest (∼55 000 km2) back-arc mafic volcanic field in Patagonia, and one of Earth's largest with no clear link to a hotspot or major extension. Major and trace element and Sr-Nd-Pb isotopic data suggest involvement of a plume-like component in the mantle magma source mixed with hydrous, but not high field strength element (HFSE)-depleted components, from a disintegrating subducting plate. Magmatism is attributed to mantle upwelling related to disturbances during plate reorganization, possibly at a time when the South America plate was nearly stationary over the underlying mantle. Melting was enhanced by hydration of the mantle during Paleogene subduction. Crustal contamination was minimal in a refractory crust that had been extensively melted in the Jurassic. Eruption began with low-volume intraplate alkaline mafic flows with depleted Nd-Sr isotopic signatures. These were followed by voluminous ∼29-25 Ma tholeiitic mafic flows with flat light and steep heavy rare earth element (REE) patterns, intraplate-like La/Ta ratios, arc-like Ba/La ratios and enriched Sr-Nd isotopic signatures. Their source can be explained by mixing EM1-Tristan da Cunha-like and depleted mantle components with subduction-related components. Post-plateau ∼24-17 Ma alkaline flows with steep REE patterns, high incompatible element abundances, and depleted Sr-Nd isotopic signatures mark the ebbing of the mantle upwelling. Copyright © 2007 Oxford University Press.

Descripción: The fundamental space ζ is defined as the set of entire analytic functions [test functions φ(z)], which are rapidly decreasing on the real axis. The variable z corresponds to the complex energy plane. The conjugate or dual space ζ′ is the set of continuous linear functionals (distributions) on ζ. Among those distributions are the propagators, determined by the poles implied by the equations of motion and the contour of integration implied by the boundary conditions. All propagators can be represented as linear combinations of elementary (one pole) functionals. The algebra of convolution products is also determined. The Fourier transformed space ζ̃ contains test functions φ̃(x). These functions are extra-rapidly decreasing, so that the exponentially increasing solutions of higher-order equations are distributions on ζ̃. © 1994 American Institute of Physics.

Descripción: We studied the spatial and temporal distribution of Hantavirus Pulmonary Syndrome (HPS) cases from 1998 to 2001 in the Buenos Aires Province, Argentina. HPS is a severe viral disease whose natural reservoir are rodents of the subfamily Sigmodontinae (Muridae) and which occurs in many countries of South and North America. We considered two spatial arrangements: cells of 18.5 x 18.5 km2; and departments, the political subdivisions of the province, as spatial units. We tested the departure from a Poisson distribution of the number of cases per cell and per month with the Variance/Mean index, while the interaction between spatial and temporal clustering was tested by means of the Knox and Mantel tests. We constructed probability maps in which the HPS rates per department were considered Poisson variates according to population, area and the product of population and area. We analysed the relation between rodent distribution, environmental and demographic variables and HPS cases conducting preliminary univariate analysis from which we selected variables to enter in general linearized models. We found that both the spatial and temporal distribution of cases is strongly aggregated. The spatiotemporal interaction appears to be related to a strong seasonality and the existence of particular ecological conditions rather than epidemic transmission of the disease. The main explanatory variables for the distribution of HPS cases among the departments of the Buenos Aires Province were human population, the distribution of the rodent Oxymycterus rufus and evapotranspiration. The last two variables are probably indicators of favourable ecological conditions for the reservoirs, which encompass other variables not taken into account in this study.

Descripción: Monthly lower stratosphere temperature anomalies in a layer centred about 70 hPa, from the MSU data set are analysed for the period 1979-1997. T-mode approach principal component analysis (PCA) is used in order to obtain the leading spatial anomaly patterns and their sequences of occurrence throughout the period under study. Five principal components (PCs) are significantly different from the spatial distribution of noisy data. The patterns given by the PC scores represent ten typical spatial anomaly patterns: five correspond to the direct mode, that is to say anomaly fields with the same sign as the PC score patterns, and five have the opposite sign. The first three PCs represent simple spatial temperature anomaly distributions, with zonal wave 0 to wave 2 wave structures. The following significant PCs, orders four and five, display a more complex spatial behaviour, with wave 3 wave structures. The first two PC's frequency distribution in time, given by the PC loadings time series, do not show noticeable changes throughout the period analysed. The remaining three PCs show changes in their frequency of occurrence that might be associated with the negative trends in the lower stratosphere temperature, as well as to the other different features observed in the real temperature anomaly time series for the grid points in the Southern Hemisphere. The latter are studied with the PCA in the S-mode approach in the companion paper (Compagnucci et al., 2001. International Journal of Climatology 21: 419-437). Copyright © 2001 Royal Meteorological Society.

Descripción: The extent and seasonality of nutrient limitation of Posidonia oceanica (L.) Delile in the Costa Brava littoral (NW Mediterranean) in 5 meadows was investigated by means of repeated nutrient additions along a year cycle. Nutrient additions had a modest effect on leaf growth. The response to fertilization varied considerably among meadows, with those meadows consistently maintaining low (300 μM dissolved inorganic nitrogen and 9 μM soluble reactive phosphorus) dissolved inorganic nutrient concentrations in sediment pore waters showing the greatest response to fertilization. The seasonality of the growth response to fertilization was consistent with calculated nutrient deficiencies, which were greatest in late spring and summer. Nutrient deficiency was alleviated in the fall, partially due to reduced growth, but also to nutrient reclamation from old leaves, which represented 20% and 18% of the annual nitrogen and phosphorus incorporation, respectively. The relative deficiency of nitrogen and phosphorus differed among sites, with the highest response found in P-deficient meadows. Nutrient limitation of P. oceanica meadows was greatest in late spring and summer, but differed greatly in magnitude and nature (nitrogen vs phosphorus) depending on local nutrient regimes.

Descripción: Many grasshopper species are considered of agronomical importance because they cause damage to pastures and crops. Comprehension of pest population dynamics requires a clear understanding of the genetic diversity and spatial structure of populations. In this study we report on patterns of genetic variation in the South American grasshopper Dichroplus elongatus which is an agricultural pest of crops and forage grasses of great economic significance in Argentina. We use Direct Amplification of Minisatellite Regions (DAMD) and partial sequences of the cytochrome oxydase 1 (COI) mitochondrial gene to investigate intraspecific structure, demographic history and gene flow patterns in twenty Argentinean populations of this species belonging to different geographic and biogeographic regions. DAMD data suggest that, although genetic drift and migration occur within and between populations, measurable relatedness among neighbouring populations declines with distance and dispersal over distances greater than 200 km is not typical, whereas effective gene flow may occur for populations separated by less than 100 km. Landscape analysis was useful to detect genetic discontinuities associated with environmental heterogeneity reflecting the changing agroecosystem. The COI results indicate the existence of strong genetic differentiation between two groups of populations located at both margins of the Paraná River which became separated during climate oscillations of the Middle Pleistocene, suggesting a significant restriction in effective dispersion mediated by females and large scale geographic differentiation. The number of migrants between populations estimated through mitochondrial and DAMD markers suggest that gene flow is low prompting a non-homogeneous spatial structure and justifying the variation through space. Moreover, the genetic analysis of both markers allows us to conclude that males appear to disperse more than females, reducing the chance of the genetic loss associated with recent anthropogenic fragmentation of the D. elongatus studied range. © 2012 Rosetti, Remis.

Descripción: The spatial stability of similarity solutions for an incompressible fluid flowing along a channel with porous walls and driven by constant uniform suction along the walls is analyzed. This work extends the results of Durlofsky and Brady [Phys. Fluids 27, 1068 (1984)] to a wider class of similarity solutions, and examines the spatial stability of small amplitude perturbations of arbitrary shape, generated at the entrance of the channel. It is found that antisymmetric perturbations are the best candidates to destabilize the solutions. Temporally stable asymmetric solutions with flow reversal presented by Zaturska, Drazin, and Banks [Fluid Dyn. Res. 4, 151 (1988)] are found to be spatially unstable. The perturbed similarity solutions are also compared with fully bidimensional ones obtained with a finite difference code. The results confirm the importance of similarity solutions and the validity of the stability analysis in a region whose distance to the center of the channel is more than three times the channel half-width. © 2000 American Institute of Physics.

Descripción: The relationship between annual rainfall totals and gauge elevation over Great Britain is re-examined using the recently developed technique of geographically weighted regression (GWR). This enables the spatial drift of regression parameters to be identified, estimated and mapped. It is shown that the rate of increase of precipitation with height, or height coefficient, varies from around 4.5 mm/m in the northwest to almost zero in the southeast. There is a particularly rapid change in this value across the English Midlands. The predicted sea level precipitation varies from 1250 mm to less than 600 mm in much the same way. Copyright © 2001 Royal Meteorological Society.

Descripción: In this work, we analyze the behavior of a neuronal network when it is stimulated by a synaptic train current with variable frequency. Using the fact that resonat (type II) neurons have a preferred input frequency, we constructed a network formed by two groups of neurons, each one responding to a different eigenfrequency. We show than even though every neuron is locally connected with neighbors of both groups, only those properly tuned to the input frequency fire synchronically with the incoming signal. In this sense, given a fixed sized network of heterogeneous neurons different subsets respond to the stimulus depending on its frequency. © 2007 American Institute of Physics.

Descripción: Specimens and eggs masses of the gastropod Trochita pileus were collected during a research cruise by bottom trawling at depths between 82 m and 120 m. Adult T. pileus were found attached to such hard substrata as the shells of scallops and oysters. The egg mass of T. pileus is composed of 7-8 transparent, triangular-shaped egg capsules fixed to the substratum with stalks. Four egg masses collected from brooding females, with a total number of 241 embryos, were examined. Trochita pileus is a protandrous hermaphrodite, and histological studies of the male, transitional, and female gonads were performed. The testicular portion of the gonad in both male and transitional individuals and the ovary of the female were studied by histological techniques. Spermatogenesis was observed for males and transitional individuals.

Descripción: Although the temperate regions of South America are known to have a diverse daphniid fauna, there has been no genetic evaluation of the existing taxonomic system or of the affinities between the North and South American faunas. The present study analyses mitochondrial DNA sequences and allozyme variation to investigate species diversity in 176 Daphnia populations from Argentina. This work established the presence of at least 15 species in Argentina, six of which are either undescribed or are currently misidentified and two of which represent range extensions of North American taxa. Eleven of the Argentine species appear endemic to South America, while the remaining four also occur in North America. In the latter cases, the close genetic similarity between populations from North and South America indicates the recent exchange of propagules between the continents. While biological interactions and habitat availability have undoubtedly contributed to the observed species distributions, chance dispersal has apparently played a dominant role in structuring large-scale biogeographical patterns in this genus and probably in other passively-dispersed organisms. © 2004 The Linnean Society of London.

Descripción: A subgrid-scale spectral model of rotating turbulent flows is tested against direct numerical simulations (DNSs). The case of Taylor-Green forcing is considered, a configuration that mimics the flow between two counter-rotating disks as often used in the laboratory. Computations are performed for moderate rotation down to Rossby numbers of 0.03, as can be encountered in the Earth's atmosphere. We provide several measures of the degree of anisotropy of the small scales and conclude that an isotropic model may suffice at moderate Rossby number. The model, developed previously [J. Baerenzung, H. Politano, Y. Ponty, and A. Pouquet, "Spectral modeling of turbulent flows and the role of helicity," Phys. Rev. E77, 046303 (2008)], incorporates eddy viscosity and eddy noise that depend dynamically on the index of the energy spectrum. We show that the model reproduces satisfactorily all large-scale properties of the DNS up to Reynolds numbers of ~104 and for long times after the onset of the inverse cascade of energy; it is also shown to behave better than either the Chollet-Lesieur eddy viscosity model [J. P. Chollet and M. Lesieur, "Parametrization of small scales of three-dimensional isotropic turbulence utilizing spectral closures," J. Atmos. Sci.38, 2747 (1981)] or an under-resolved DNS. © 2010 American Institute of Physics.

Descripción: Trypanosomatid parasites containing a metabolically unstable ornithine decarboxylase (ODC) are naturally resistant to high levels of α-difluoromethylornithine (DFMO) because this ODC inhibitor, though causing a drastic reduction of intracellular putrescine, elicits only a moderate decrease of the spermidine endogenous pool. In this study we have used a combination of DFMO with cyclohexylamine (CHA; bis-cyclohexylammonium sulfate), an inhibitor of spermidine synthase, to reach a more complete depletion of spermidine. Under these conditions we have observed the arrest of proliferation not only in trypanosomatids with stable ODC but also in parasites with an enzyme of high turnover rate. In all cases the reinitiation of proliferation occurred only after the addition of exogenous spermidine, and neither putrescine nor spermine were able to induce the same effect. © 2001 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All rights reserved.

Descripción: Three of the biggest barrier spits of Argentina are studied in order to determine the relationship between the coastal planform and littoral dynamics. The studied landforms are the spit of Cabo San Antonio of an age of the 5800 years BP, the north spit of Caleta Valdés with a maximum age of approximately 5700 years BP and El Páramo spit of San Sebastián bay with an inferred age of approximately 6000 years BP. The orientation regarding the coastal planform of the three spits, allows to establish the relationship between landforms and coastal dynamics, being obtained the predominant waves that gave origin to them. Also the possible consequences for the modification or erosion of these landforms, that they would take to the disappearance of coastal environments of significant ecological value and the submergence of some adjacent areas; just as it would happen in Caleta Valdés.

Descripción: Using methods of non-equilibrium thermodynamics that extend and generalize the MHD energy principle of Bernstein et al. (1958, Proc. Roy. Soc. A, 244, 17) we develop a formalism in order to analyze the stability properties of prominence models considered as dissipative states i.e. states far form thermodynamic equilibrium. As an example, the criterion is applied to the Kippenhahn-Schlüter model (hereafter K-S) considering the addition of dissipative terms in the coupled system of equations: the balance of energy equation and the equation of motion. We show from this application, that periods corresponding to typical oscillations of the chromosphere and photosphere (3 and 5 min respectively), that were reported as observations of the prominence structure, can be explained as internal modes of the prominence itself. This is an alternative explanation to the one that supposes that the source of these perturbations are the cold foot chromospheric and photospheric basis.

Descripción: Aims. We study the modes and stability of non-isothermal coronal loop models with different intensity values of the equilibrium magnetic field. Methods. We use an energy principle obtained via non-equilibrium thermodynamic arguments. The principle is expressed in terms of Hermitian operators and allow to consider together the coupled system of equations: the balance of energy equation and the equation of motion. Results. We determine modes characterized as long - wavelength disturbances that are present in inhomogeneous media. This character of the system introduces additional difficulties for the stability analysis because the inhomogeneous nature of the medium determines the structure of the disturbance, which is no longer sinusoidal. Moreover, another complication is that we obtain a continuous spectrum of stable modes in addition to the discrete one. Conclusions. We obtain a unique unstable mode with a characteristic time that is comparable with the characteristic life-time observed for loops. The feasibility of wave-based and flow-based models is examined. © ESO 2006.

Descripción: Aims. We study the stability and modes of non - isothermal coronal loop models with different intensity values of equilibrium twisted magnetic field.Methods. We use an energy principle obtained by means of non - equilibrium thermodynamic arguments. The principle is expressed in terms of Hermitian operators and enables us to consider the coupled system of equations, the balance of energy equation and the equation of motion, to obtain modes and eigenmodes in a spectrum ranging from short to long-wavelength disturbances without using weak varying approximations of the equilibrium parameters. Long-wavelength perturbations introduce additional difficulties because the inhomogeneous nature of the medium produce disturbances corresponding to continuous intervals of eigenfrequencies, which cannot be considered as purely sinusoidal.Results. We analyze the modification of periods, modes structure, and stability when the helicity, the magnetic field strength, and the radius of the fluxtube are varied. The efficiency of the damping due to the resonant absorption mechanism is analyzed in terms of modes that can either impulsively release or store magnetic energy.Conclusions. We find that the onset of the instability is associated with a critical value of the helicity and the magnetic energy content has a determinant role on the instability of the system with respect to the stabilizing effect of the resonant absorption mechanism. © 2008 ESO.

Descripción: The nonlinear conditions for the development of helical vortex filaments in a circular tube are considered. The helical flow is assumed to be irrotational, except in a vortex filament of infinitesimal core area. By introducing an appropriate image for this helical vortex filament, the boundary condition on the material frontier is satisfied. By assuming an axisymmetric flow upstream and imposing the conservation laws, a dependence between the helix pitch and the nonlinear amplitude of the helical vortex developed downstream is obtained. Our results show that only helical flows with the pitch in a certain range of values are allowed. The dependence of this range on the swirl ratio and on the tube cross section is considered. We discuss the usefulness of the nonlinear analysis of the allowed flows to explain experimental results and to complement the usual linear study of stability. © 1999 American Institute of Physics.

Descripción: In this paper we develop and analyze a family of mixed finite element methods for the numerical solution of the Stokes problem in two space dimensions. In these schemes, the pressure is interpolated on a mesh of rectangular elements, while the velocity is approximated on a triangular mesh obtained by dividing each rectangle into four triangles by its diagonals. Continuous interpolations of degrees k for the velocity and l for the pressure are considered, so the new finite elements are called cross-grid Pk Ql. A stability analysis of these approximations is provided, based on the macroelement technique of Stenberg. The lowest order P1 Q1 and P2 Q1 cases are analyzed in detail; in the first case, a global spurious pressure mode is shown to exist, so this element is unstable. In the second case, however, stability is rigorously proved. Numerical results obtained in these two cases are also presented, which confirm the existence of the spurious pressure mode for the P1 Q1 element and the stability of the P2 Q1 element. © 2010 Elsevier B.V. All rights reserved.

Descripción: The stacking of positively charged (or doped) terthiophene oligomers and quaterthiophene polymers in solution is investigated applying a recently developed unified electrostatic and cavitation model for first-principles calculations in a continuum solvent. The thermodynamic and structural patterns of the dimerization are explored in different solvents, and the distinctive roles of polarity and surface tension are characterized and analyzed. Interestingly, we discover a saturation in the stabilization effect of the dielectric screening that takes place at rather small values of ε0. Moreover, we address the interactions in trimers of terthiophene cations, with the aim of generalizing the results obtained for the dimers to the case of higher-order stacks and nanoaggregates. © 2006 American Institute of Physics.

Descripción: The evolution of the energy distribution was studied for a stadium with moving balls. A one period driving cycle was considered, which was characterized by an amplitude A and a wall velocity V. The spreading mechanism was dominated by transitions between neighboring levels for an extremely slow wall velocity V, while for larger velocities, the spreading mechanism had both perturbative and nonperturbative features.

Descripción: This paper reports the standardization of methods used for processing and embedding various vertebrate brains of different sizes in paraffin. Other technical details developed for avoiding frequent difficulties arising during laboratory routine are also reported. Some modifications of the Nissl and Klüver-Barrera staining methods are proposed. These modifications include: 1) a Nissl stain solution with a rapid and efficient action with easier differentiation; 2) the use of a cheap microwave oven for the Klüver-Barrera stain. These procedures have the advantage of permitting Nissl and Klüver-Barrera staining of nervous tissue in about five and fifteen minutes respectively. The proposed procedures have been tested in brains obtained from fish, amphibians, reptiles and mammals of different body sizes. They are the result of our long experience in preparing slides for comparative studies. Serial sections of excellent quality were regularly obtained in all the specimens studied. These standardized methods, being simple and quick, are recommended for routine use in neurobiological laboratories.

Descripción: Fil:Dmitruk, P. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: This work is devoted to the exact statistical mechanics treatment of simple inhomogeneous few-body systems. The system of two hard spheres (HSs) confined in a hard spherical pore is systematically analyzed in terms of its dimensionality D. The canonical partition function and the one- and two-body distribution functions are analytically evaluated and a scheme of iterative construction of the D+1 system properties is presented. We analyze in detail both the effect of high confinement, when particles become caged, and the low density limit. Other confinement situations are also studied analytically and several relations between the two HSs in a spherical pore, two sticked HSs in a spherical pore, and two HSs on a spherical surface partition functions are traced. These relations make meaningful the limiting caging and low density behavior. Turning to the system of two HSs in a spherical pore, we also analytically evaluate the pressure tensor. The thermodynamic properties of the system are discussed. To accomplish this statement we purposely focus in the overall characteristics of the inhomogeneous fluid system, instead of concentrate in the peculiarities of a few-body system. Hence, we analyze the equation of state, the pressure at the wall, and the fluid-substrate surface tension. The consequences of new results about the spherically confined system of two HSs in D dimension on the confined many HS system are investigated. New constant coefficients involved in the low density limit properties of the open and closed systems of many HS in a spherical pore are obtained for arbitrary D. The complementary system of many HS which surrounds a HS (a cavity inside of a bulk HS system) is also discussed. © 2010 American Institute of Physics.

Descripción: Recent studies have compared properties of the magnetic field in simulations of Hall MHD turbulence with spacecraft data, focusing on methods used to identify classical discontinuities and intermittency statistics. Comparison of ACE solar wind data and simulations of 2D and 3D turbulence shows good agreement in waiting-time analysis of magnetic discontinuities, and in the related distribution of magnetic field increments. This supports the idea that the magnetic structures in the solar wind may emerge fast and locally from nonlinear dynamics that can be understood in the framework of nonlinear MHD theory. The analysis suggests that small scale current sheets form spontaneously and rapidly enough that some of the observed solar wind discontinuities may be locally generated, representing boundaries between interacting flux tubes. © 2010 American Institute of Physics.

Descripción: Stenurus globicephalae Baylis et Daubney, 1925 (Nematoda: Pseudaliidae) was found in the cranial air sinuses of a false killer whale, Pseudorca crassidens (Owen), stranded on the coast of Uruguay in 1999. Although this species has been reported once in P. crassidens from the North Atlantic, this is the first record for South America. A total of 920 specimens were obtained, of which 663 were females (body length: 4.34 ± 0.45 cm) and 257 were males (2.99 ± 0.18 cm). Morphometric details are presented for S. globicephalae in this host, which do not show significant differences from those parasitizing Globicephala melas (Traill), but are distinct from those parasitizing Peponocephala electra (Gray), The host's skull revealed loss of osseous mass with the disappearance of the left zygomatic arch, and the left jaw had three osseous fenestrations in the region related to the organ of acoustic reception. These lesions support the hypothesis that this infection, known as stenurosis, was related to the stranding.

Descripción: The three related 160-kDa proteins, SRC-1, TIF-2 and RAC-3, were initially identified as factors interacting with nuclear receptors. They have also been reported to potentiate the activity of other transcription factors such as AP-1 or NF-κB. The aim of this work was to identify whether SRC-1 interferes with the TGF-β/Smad signaling pathway, and if so, to identify its underlying mechanisms of action. Using transient cell transfection experiments performed in human dermal fibroblasts with the Smad3/4-specific (SBE) 4-lux reporter construct, as well as the human PAI-1 promoter, we determined that SRC-1 enhances TGF-β-induced, Smad-mediated, transcription. Likewise, SRC-1 overexpression potentiated TGF-β-induced upregulation of PAI-1 steady-state mRNA levels. Using a mammalian two-hybrid system, we demonstrated that SRC-1 interacts with the transcriptional co-activators p300/CBP, but not with Smad3. Overexpression of the adenovirus E1A oncoprotein, an inhibitor of CBP/p300 activity, prevented the enhancing effect of SRC-1 on Smad3/4-mediated transcription, indicating that p300/CBP may be required for SRC-1 effect. Such hypothesis was validated, as expression of a mutant form of SRC-1 lacking the CBP/p300-binding site failed to upregulate Smad3/4-dependent transcription, while full-length SRC-1 potentiated p300-Smad3 interactions. These results identify SRC-1 as a novel Smad3/4 transcriptional partner, facilitating the functional link between Smad3 and p300/CBP. © 2005 Nature Publishing Group All rights reserved.

Descripción: Background: LePRK1 and LePRK2 are two pollen receptor kinases localized to the plasma membrane, where they are present in a high molecular weight complex (LePRK complex). LePRK2 is phosphorylated in mature and germinated pollen, but is dephosphorylated when pollen membranes are incubated with tomato or tobacco style extracts.Results: Here we show that LePRK2 dephosphorylation is mediated by a heat-, acid-, base-, DTT- and protease-resistant component from tobacco styles. Using LePRK2 phosphorylation as a tracking assay for purification, style exudates were subjected to chloroform extraction, anionic exchange, and C18 reverse-phase chromatography columns. We finally obtained a single ~3,550 Da compound (as determined by UV-MALDI-TOF MS) that we named STIL (for Style Interactor for LePRKs). STIL increased pollen tube lengths of in vitro germinated pollen in a dose-dependent manner.Conclusion: We propose that the LePRK complex perceives STIL, resulting in LePRK2 dephosphorylation and an increase in pollen tube growth. © 2010 Wengier et al; licensee BioMed Central Ltd.

Descripción: A peptide from hindguts of the Triatoma hematophagous Chagas insect vector activates adenylyl cyclase activity in Trypanosoma cruzi epimastigote membranes and stimulates the in vitro differentiation of epimastigotes to metacyclic trypomastigotes. Hindguts were obtained from insects fed 2 days earlier with chicken blood. Purification was performed by gel filtration and HPLC on C18 and C4 columns. SDS/PAGE of the purified peptide showed a single band of about 10 kDa. The following sequence was determined for the 20 amino-terminal residues of this peptide: H 2N-Met-Leu-Thr-Ala-Glu-Asp-Lys-Lys-Leu-Ile-Gln-Gln-Ala-Trp-Glu-Lys- Ala-Ala-Ser-His. This sequence is identical to the amino terminus of chicken αD-globin. On a Western blot, the peptide immunoreacted with a polyclonal antibody against chicken globin D. A synthetic peptide corresponding to residues 1-40 of the αD-globin amino terminus also stimulated adenylyl cyclase activity and promoted differentiation. This 125I-labeled synthetic peptide bound specifically to T. cruzi epimastigote cells. Activation of epimastigote adenylyl cyclase by the hemoglobin-derived peptide may play an important role in T. cruzi differentiation and consequently in the transmission of Chagas disease.

Descripción: Fil:Passeron, E.J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: We present stopping power measurements of Zn for C and O ions and compare them with a theoretical description given by the Transport Cross Section - Extended Friedel Sum Rule (TCS-EFSR) for the valence electrons, and two different models for the inner-shells: the Shellwise Local Plasma Approximation (SLPA) and the CasP approach. The SLPA, which successfully applies to projectiles from H to B, is slightly high for C ions and clearly overestimates the data for O ions. On the other hand, total stopping results using the CasP description for the inner-shells show good agreement with the data for C and O ions, and also with the SRIM predictions. © Published under licence by IOP Publishing Ltd.

Descripción: Comparative studies on fatty acid and protein composition of the endosperm and embryo of palmito (Euterpe edulis Martius) were conducted using gas-liquid chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. On a dry weight basis, the embryo contained extremely lower amounts of lipids and proteins than did the endosperm, which was associated with the scarce lipid and protein bodies previously reported in axis and cotyledon. The fatty acid composition also exhibited differences between both tissues: (I) the fatty acid diversity was greater in embryo than in endosperm; (II) embryo and endosperm contained predominantly linoleic, palmitic, oleic and stearic acids even though the relative values were different for each tissue. As compared to other palm species, the higher fatty acid unsaturation in Euterpe edulis seed could be involved in the previously reported short longevity and recalcitrant behavior during storage. Proteins of both tissues were heterogeneous in molecular mass. Some proteins were tissue-specific, but other were common, among them a highly glycosylated protein which migrated at about 55 kDa. We hypothesize that the latter, also reported in all previously studied palm species, is one of the proteins characterizing the Arecaceae family.

Descripción: In this paper new geologic evidences allow us to complete the stratigraphy of Ramez de Velasco ranges. Granitoids of the igneous basement are included into the Ojo de Agua-Ambargasta complex as the Sumampa Granite which is composed of three facies: facies Para Yacu, Sumampa Viejo and Los Telares. Thin aplitic dykes were included into the same basement as the last magmatic event of the same geological setting. The geochemical signature of these rocks shows meta to peraluminous compositions, which evidence magmatic arc granitoides. Basic dykes, few meters wide and more than one kilometer long, also intrude these granitoids. They are composed of basalts and andesites with calcoalkaline signatures that were correlated with Balbuena formation due to their petrological features. Finally, few and small outcrops of sandstones appears as the only expression of the Neopaleozoic sedimentation. On the basis of all the data obtained we suggest that the Ramíez de Velasco ranges preserve evidences of several geologic processes that took place since the Paleozoic.

Descripción: In the right bank of the Arroyo Tapalqué (Salto de Piedra, Olavarría, Buenos Aires province) is a section through fluvial sediments of the Luján Formation (upper and lower members) and aeolian deposits of La Postrera Formation. A geological and geophysical study was carried out to determination the magnetic parameters of the sediments of both formations, in order to evaluate the environmental and climatic conditions at the time of deposition. Levels with high concentrations of ferromagnetic minerals are thought to be related to an increase in capacity of river transport probably due to higher rainfall. By contrast, a particular magnetic behaviour was detected in levels closely associated with pedogenetic processes (Suelo Puesto Callejón Viejo, SPCV, Suelo Puesto Berrondo, SPB and present soils). This behaviour is attributed to the partial dissolution of the ferromagnetic fraction (magnetic/titanomagnetite) and to possible formation of a high c oercitivity magnetic fraction (hematite?) as an associated process. These results are similar to those obtained for paleosols from the Buenos Aires Formation, probably because of parental material common to both. On the basis of present field and laboratory observations, together with previously available information, a detailed correlation is proposed between features observed in this section and palaeoclimatic fluctuations identified for Pleistocene/Holocene.

Descripción: Late Cretaceous and Paleogene sedimentary rocks of the Austral Basin crop out on the south-eastern margin of Lake Viedma. In the Barrancas Blancas section, 28 m of yellowish sandstone and mudstone of the La Asunción Member of the Anita Formation are transitionally covered by 390 m of greyish sandstone and mudstone of the Cerro Fortaleza Formation. The former represent a prograding barred nearshore system, whereas the latter correspond to paralic, fluvial and fluvial-tidal sedimentation. The evolution of the depositional sequences, sedimentary palaeoenvironments, sandstone provenance and palaeocurrents indicate that the sediments were deposited during the back-arc (sag) stage of the basin. At Cerro Piramides, Tertiary sedimentary rocks rest with fault contact on top of the Cerro Fortaleza Formation. The limited thickness (<1m) preserved of greenish sandstone of the Man Aike Formation precludes any attempt to interpret its depositional environment. Conglomerate, sandstone and mudstone (locally carbonaceous) of the Río Leona Formation (75 m) rest with erosional contact on the former. These rocks represent a rapid transition from a high energy to low energy fluvial systems that eventually graded into marginal marine environments represented by the fossiliferous sandstones of the Centinela Formation (<3m). The facies arrangement, evolution of the palaeoenvironments, and palaeocurrents suggest that these sediments were deposited during the foreland basin stage. © 2003 Asociación Geológica Argentina.

Descripción: Results of a detailed geologic survey of the Río Borbollón area, located in the Cordillera Principal of the province of Mendoza are presented. The stratigraphic record of the area corresponds to a Jurassic-early Cretaceous sedimentary succession, the products of Neogene igneous activity and Quaternary deposits. The Tres Esquinas and La Manga Formations of Jurassic age were recognized for the first time in the study area. The main structural features of the area are described and interpreted based on the obtained data and previous works. A balanced structural cross section of the Malargüe fold and thrust belt at 34°15'S depicts the structural style and the amount of orogenic shortening in this region of the Andes.

Descripción: The Cerro Cóndor depocenter represents the most complete stratigraphic sequence of the continental Jurassic of the Cañadón Asfalto basin and southern South America. It is situated in extraandean Patagonia, on both sides of the middle Chubut river valley. The sedimentation in this pull-apart basin begins early in the Middle Jurassic, accompanied by effusions of olivinic basalts. The prevailing lacustrine deposits are characterized by carbonatic and siliciclastic facies associations, interfingering with volcanic deposits grading from lavic in the base to predominantly pyroclastic towards the top. The facies evolution from north to south is described, embracing the sections of farm El Torito and the canyons of Los Loros, Las Chacritas, Carrizal, Asfalto and Lahuincó. The carbonatic facies/microfacies are represented by mudstones, wackestones, packstones, grainstones and microbialitic limestones, characteristic of littoral/marginal and palustrine environments. In the Cañadón Asfalto Formation are distinguished a lower member (Las Chacritas composed by limestones, shales, sandstones and conglomerates intercalated with olivinic basalts, and an upper member (Puesto Almada) composed by tuffs, tuffites, shales and sandstones. The first is bearing a palynologic assemblage of Bajocian-Bathonian age and the second dinosaurs of Tithonian age. The stratigraphic sections of both members of the formation are described and illustrated at their type localities cañadón Las Chacritas and farm El Torito and the paleoenvironments of the depocenter, from the Aalenian to the Tithonian are described and illustrated. The age of the Puesto Almada Member at its type locality was obtained by radiometric dating (K/Ar) of biotites from a thin layer of volcanic tuff (147.1 + 3.3 Ma, Tithonian) from the upper part of the unit.

Descripción: The stratigraphy of Cretaceous marine mudstones in the Fuegian Andes, roughly equivalent to Charles Darwin's clay-slate formation, remains a still unsolved problem. Previous records of Albian, Turonian-Coniacian, and Santonian-Campanian bivalves are combined with new findings of the Late Albian inoceramid Inoceramus anglicus Woods, and the Maastrichtian ammonites Diplomoceras sp., Anagaudryceras sp., Maorites densicostatus (Kilian and Reboul), Maorites sp., and Pachydiscus (Neodesmoceras) sp. to further constrain the Cretaceous stratigraphy of the eastern Fuegian Andes. In addition, new records of distinctive trace fossils and ichnofabric are meaningful for stratigraphic division and delineation of paleoenvironmental settings in these Cretaceous mudstones. The Lower Cretaceous ichnoassemblage of Chondrites targioni (Brongniart) and Zoophycos isp. is consistent with the inferred slope-volcaniclastic apron settings of the Yahgan Formation; Nereites missouriensis (Weller) reflects distal basin plain depositional settings for the Beauvoir Formation. In the Upper Cretaceous, the "Estratos de Buen Suceso" record the earliest extensively bioturbated horizons, reflecting prolonged well-oxygenated bottom conditions. In the Bahía Thetis Formation, organic-rich, channel margin or distal basin slaty mudstones record the last occurrence of inoceramid bivalves in the Austral Basin; the generalized absence of trace fossils is consistent with dysoxic bottom conditions. The thoroughly bioturbated Policarpo Formation, records a marked change in paleoceanographic conditions. The strong contrast in the intensity of bioturbation between the Upper Campanian-Maastrichtian Bahía Thetis Formation, almost devoid of trace fossils, and the highly bioturbated Maastrichtian-Danian Policarpo Formation reflects a change from dysoxic-anoxic to well ventilated conditions, probably associated with a cooling trend of bottom waters in the austral deep oceans.

Descripción: The Huecú depocenter is located in the central sector of the Loncopué trough in western Neuquén. This basin is composed of volcanic, volcaniclastic, fluvial and lacustrine deposits, younger than 1.6 Ma encompassing postglacial and even historical sediments and lavas. During most of its evolution, the Huecú depocenter has constituted a small closed depression (pullapart basin) restricted to the Loncopué trough, a major extensional retroarc basin in the Central and Patagonian Andes. This basin was fed from the north since the beginning of its evolution by a series of big amalgamated post-Pliocene stratovolcanoes located in the Mandolegüe Cordillera. The basin was also filled by fissural lava flows originated in the Agrio caldera located to the east grouped in the Escorial Basalt of 1.6 to 0.8 Ma. Polygenetic volcanic products form in the region big stratovolcanoes among which the Trolón and Colorado volcanic centers were the most prominent. These centers of Pleistocene age were highly eroded by the last glacial activity that affected the region. Nearly at the end of the glacial period two fissural volcanic fields covered the Huecú depocenter corresponding to the Rankül-Lom Basalt and preglacial Tres Hermanos basalts. Finally postglacial volcanic lavas covered most of the Huecú depocenter. These were grouped in the Cerro Artillería Basalts and postglacial Tres Hermanos basalt, which have recurrently dammed the main fluvial basins in the area. The fluvial and lacustrine deposits are represented by El Huecú and Mar Pequeño Formations.

Descripción: The Central Precordillera of San Juan is a thin-skinned fold and thrust belt bounded to the east by the thick-skinned structures of the Eastern Precordillera. The objective of this study is to describe and interpret the structural features found at the southern end of this fold and thrust belt. The lomas de Andapaico's folds are of asymmetric, open chevron type, and are genetically related to fault propagation. Toward the north, the folding becomes tighter and broken by faults. The regional structure consists of an imbricated fan of an array of separated to overlapping fault propagation folds, and out-of-sequence structures related to the Eastern Precordillera uplift. The major décollement thrust is located near the top of the San Juan Formation limestone. Deformation occurred in two main stages. First, an imbricate array of fault-propagation folds was developed as the thrust front migrated toward the foreland. Then, the uplift of the eastern Precordillera impeded the migration of the thrust front and may have caused the development of out-of-sequence structures in the Central Precordillera. The minimum horizontal shortening calculated is 4.8 km, and the whole structure shows a southward decreasing shortening that is shown by structures of different orders and a variety of styles of deformation.

Descripción: The scope of the present review focuses on the interfacial properties of cell membranes that may establish a link between the membrane and the cytosolic components. We present evidences that the current view of the membrane as a barrier of permeability that contains an aqueous solution of macromolecules may be replaced by one in which the membrane plays a structural and functional role. Although this idea has been previously suggested, the present is the first systematic work that puts into relevance the relation water-membrane in terms of thermodynamic and structural properties of the interphases that cannot be ignored in the understanding of cell function. To pursue this aim, we introduce a new definition of interphase, in which the water is organized in different levels on the surface with different binding energies. Altogether determines the surface free energy necessary for the structural response to changes in the surrounding media. The physical chemical properties of this region are interpreted in terms of hydration water and confined water, which explain the interaction with proteins and could affect the modulation of enzyme activity. Information provided by several methodologies indicates that the organization of the hydration states is not restricted to the membrane plane albeit to a region extending into the cytoplasm, in which polar head groups play a relevant role. In addition, dynamic properties studied by cyclic voltammetry allow one to deduce the energetics of the conformational changes of the lipid head group in relation to the head-head interactions due to the presence of carbonyls and phosphates at the interphase. These groups are, apparently, surrounded by more than one layer of water molecules: a tightly bound shell, that mostly contributes to the dipole potential, and a second one that may be displaced by proteins and osmotic stress. Hydration water around carbonyl and phosphate groups may change by the presence of polyhydroxylated compounds or by changing the chemical groups esterified to the phosphates, mainly choline, ethanolamine or glycerol. Thus, surface membrane properties, such as the dipole potential and the surface pressure, are modulated by the water at the interphase region by changing the structure of the membrane components. An understanding of the properties of the structural water located at the hydration sites and the functional water confined around the polar head groups modulated by the hydrocarbon chains is helpful to interpret and analyze the consequences of water loss at the membranes of dehydrated cells. In this regard, a correlation between the effects of water activity on cell growth and the lipid composition is discussed in terms of the recovery of the cell volume and their viability. Critical analyses of the properties of water at the interface of lipid membranes merging from these results and others from the literature suggest that the interface links the membrane with the aqueous soluble proteins in a functional unit in which the cell may be considered as a complex structure stabilized by water rather than a water solution of macromolecules surrounded by a semi permeable barrier. © 2008 Elsevier B.V. All rights reserved.

Descripción: Located at the transitional southern end (33o S) of the Pampean flat-slab, the Tertiary volcanic belt records the eastward migration of the Andean volcanic arc due to the flattening of the Nazca Plate in Mio-Pliocene times. The tertiary volcanic belt encompasses several very important metallogenetic districts in the San Luis Pampean Ranges. Volcanic rocks and associated ore-deposits crop out following a NW-WNW trending belt at La Carolina, Cañada Honda - Cerros Largos, Cerros del Rosario and El Morro volcanic fields. The available geochronological data indicate that the volcanic activity began early at the western end of the belt and ended ~ 10 Ma later at its eastern border. Cañada Honda district represents the oldest and longest-lived volcanic field of the tertiary volcanic belt. It records eruptive events and related hydrothermal alteration from 12-13 Ma to 7.3 Ma, including lavas and volcaniclastic products. Preliminary structural analysis shows that previous structures have strongly controlled, either directly or indirectly, the emplacement of volcanic rocks and related mineral deposits. Kinematic and strain fabric analyses allow to recognize two volcano-tectonic associations. One of these associations would be related to dextral reactivations of structures parallel to basement foliation. On the other hand, the main one would be linked with the generation of two volcano-tectonic depressions which are aligned in a NW-WNW direction. Their dominant structures trend NW-WNW and reveal sinistral-normal motions, both at local and Tertiary volcanic belt scales.

Descripción: The main mineralizations of the Sierra Pintada uranium district, San Rafael Massif, Mendoza, are associated with the Choiyoi volcanic province. In the lower section of this magmatic cycle uranium deposits hosted by epiclastic sandstones are predominant. In the upper section, small vein-type deposits of low economic significance are found instead. During the emplacement of these Permian volcanic and sedimentary sequences two different stress regimes, which conditioned the mineralizing systems, were dominant: transpressional (San Rafael orogenic phase) and transtensional (post-orogenic stage). A strain fabric analyses was performed in an attempt to evaluate the control exerted by the structures in the distribution of the uranium mineralizations during these two stages of deformation. So that, a contribution to a better understanding of the genesis of these deposits will aid to the generation of new exploration guides for uranium in the Choiyoi province. In the case of the deposits related to the lower Choiyoi, three orders of magnitude could be defined for the structural control. The fabric of the structures determining the distribution of these mineralizations reflects the structural grain of the San Rafael orogeny. The deposition of uranium hosted by the upper Choiyoi sequences was directly or indirectly influenced by the structures generated under the post-sanrafaelic stress field.

Descripción: Little attention has been paid to small copepods and other zooplankton inhabiting pelagic ecosystems of the Southwestern Atlantic Ocean under the influence of the Antarctic Circumpolar Current circulation, despite their important role in the trophic chain and fisheries. This study gives a synoptic view (January 2001) of the micro and mesoplankton size fractions and normalized biomass size spectra (NBSS) in upper waters of five different ecological domains (shelf and oceanic Subantarctic and Antarctic waters) including the Brazil-Malvinas confluence (BMC). Copepods were always the main component of the zooplankton; the <300-μm fraction represented between 70 and 99% in terms of numbers and from 20 to 88% in terms of biomass. Other zooplankton contributed with <40% to total zooplankton densities, though showing some biomass peaks (>50%). Chlorophyll a, sea surface temperature and salinity were the environmental variables that best explained the distribution trend of zooplankton, mainly that of the <300-μm fraction. For all the domains, NBSS revealed flat slopes (-0.6 to-1), suggesting a higher proportion of large organisms than expected at equilibrium. A dome-shape feature was detected in the BMC. Total biomass and trophic levels of the system were related to the composition of the community and the hydrological conditions of the domains covered. © 2013 The Author.

Descripción: Molecular dynamics simulations have been carried out to investigate the structure and dynamics of liquid methanol confined in 3.3 nm diameter cylindrical silica pores. Three cavities differing in the characteristics of the functional groups at their walls have been examined: (i) smooth hydrophobic pores in which dispersive forces prevail, (ii) hydrophilic cavities with surfaces covered by polar silanol groups, and (iii) a much more rugged pore in which 60% of the previous interfacial hydroxyl groups were replaced by the bulkier trimethylsilyl ones. Confinement promotes a considerable structure at the vicinity of the pore walls which is enhanced in the case of hydroxylated surfaces. Moreover, in the presence of the trimethylsilyl groups, the propagation of this interface-induced spatial ordering extends down to the central region of the pore. Concerning the dynamical modes, we observed an overall slowdown in both the translational and rotational motions. An analysis of these mobilities from a local perspective shows that the largest retardations operate at the vicinity of the interfaces. The gross features of the rotational dynamics were analyzed in terms of contributions arising from bulk and surface states. Compared to the bulk dynamical behavior, the characteristic timescales associated with the rotational motions show the most dramatic increments. A dynamical analysis of hydrogen bond formation and breaking processes is also included. © 2010 American Institute of Physics.

Descripción: Congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency is the most frequent inborn error of metabolism, and accounts for 90-95% of CAH cases. The affected enzyme, P450C21, is encoded by the CYP21A2 gene, located together with a 98% nucleotide sequence identity CYP21A1P pseudogene, on chromosome 6p21.3. Even though most patients carry CYP21A1P-derived mutations, an increasing number of novel and rare mutations in disease causing alleles were found in the last years. In the present work, we describe five CYP21A2 novel mutations, p.R132C, p.149C, p.M283V, p.E431K and a frameshift g.2511_2512delGG, in four non-classical and one salt wasting patients from Argentina. All novel point mutations are located in CYP21 protein residues that are conserved throughout mammalian species, and none of them were found in control individuals. The putative pathogenic mechanisms of the novel variants were analyzed in silico. A three-dimensional CYP21 structure was generated by homology modeling and the protein design algorithm FoldX was used to calculate changes in stability of CYP21A2 protein. Our analysis revealed changes in protein stability or in the surface charge of the mutant enzymes, which could be related to the clinical manifestation found in patients. © 2011 Minutolo et al.

Descripción: A numerical solution for the metallic-plasma-neutral-gas structure generated in a low-pressure arc is presented. The equations correspond to a spherically symmetric fluid-like steady model, valid for the outer region of the arc, and describe the ion slowing down by elastic scattering with the neutral particles. Technically, the obtention of the profiles of different magnitudes is complicated due to the existence of a critical point in the steady-state system of equations. The proposed approach to overcome this difficulty is to solve instead a pseudotransient system of equations which rapidly and efficiently relax to the stationary state. By employing this numerical method of second-order accuracy in space, the plasma and neutral gas density, the electron and ion drift velocities, the electron and neutral temperatures, and the electrostatic potential profiles are obtained from the border of the arc channel up to the discharge chamber wall. It is found that the value of the neutral gas filling pressure strongly influences the plasma density and plasma potential distributions. An important result is that metallic ions emitted from the arc channel deliver their kinetic energy to the filling gas in a gradual manner, up to a pressure-dependent point beyond which they move to the walls sustained against collisions with the gas by a self-consistent electric field. Near the mentioned point, the metallic ion density presents a peculiar behavior, showing an increase that is more pronounced at high pressures; a pattern also evident in the electrostatic potential. © 2000 American Institute of Physics.

Descripción: Fil:Galloni, E.E. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: The Sierras Bayas Group of Late Precambrian age is formed by sedimentary Villa Mónica, Cerro Largo and Loma Negra formations. It is located in the northwest area of Sierras Septentrionales of Buenos Aires Province. The outcrops of this group are located around Olavarría city, mainly in the low isolated hills of Sierras Bayas and also though in a limited way, in the Barker city area. The morphstructure of these sedimentary rocks in the Northern sector of Sierras Bayas is defined by an asymmetric basin subtly tilted to south-southwest. Two interfering fold systems, F1(NE) and F2(NW) which define a type 1 domes and basins pattern, were recognized based on systematic structural mapping of de Sierras Bayas Group formations. Both F1 and F2 foldings with interference angles between 70° to 90° have subvertical axial planes and subhorizontal B axis. In adopted mapping scales, folding systems were observed in three fold orders which exert a direct control over natural an artificial outcrops of the Sierras Bayas Group. The less important local faulting exerts a poor control over the attitude of Late Precambrian folded Sierras Bayas Group and field relationships supports that it's initial activity postdates folding deformation. Ductile deformation of Sierras Bayas Group sedimentary cover, as was locally observed, is thought to be associated with a tectonic reactivation of the basement, Buenos Aires Complex, furnished by pre-existing planar anisotropies of the mylonitized granitic rock mass. The resemblance F1 and F2 patterns of foldings, the overall basin morphostructure and absence of a clear interference sequence between the foldings could be related with a sole episode of constrictional deformation. But also, a type 1 folding interference pattern could have been formed by two regional, orthogonal contractional deformations, in rehologic conditions of low ductility contrast. Folding interference of SBG is considered a result of tectonic activity occurred during Late Precambrian to Lower Early Paleozoic, and predates Cambro - Ordovicic Balcarce Formation of the Sierras Septentrionales. The ductile deformation of Sierras Bayas Group with basement involvement by reactivation of main penetrative anisotropies is correlated with comparable structural patterns owing to Pan African Tectonics, in coetaneous Damara Sequence and Nama Group of Southwest Africa. © 2005 Asociación Geológica Argentina.

Descripción: The major cAMP receptors in eukaryotes are the regulatory (R) subunits of PKA, an allosteric enzyme conserved in fungi through mammals. While mammals have four R-subunit genes, Saccharomyces cerevisiae has only one, Bcy1. To achieve a molecular understanding of PKA activation in yeast and to explore the evolution of cyclic-nucleotide binding (CNB) domains, we solved the structure of cAMP-bound Bcy1(168-416). Surprisingly, the relative orientation of the two CNB domains in Bcy1 is very different from mammalian R-subunits. This quaternary structure is defined primarily by a fungi-specific sequence in the hinge between the αB/αC helices of the CNB-A domain. The unique interface between the two CNB domains in Bcy1 defines the allosteric mechanism for cooperative activation of PKA by cAMP. Some interface motifs are isoform-specific while others, although conserved, play surprisingly different roles in each R-subunit. Phylogenetic analysis shows that structural differences in Bcy1 are shared by fungi of the subphylum Saccharomycotina. © 2010 Elsevier Ltd.

Descripción: The southern part of the Ñirihuau basin at the valley of the Cushamen River region, is deformed and uplifted forming a prominent Precordillera Patagónica fold and thrust belt, east of the Patagonian Andes. The Ñirihuau Basin infill is represented by Oligocene to Miocene sedimentary to volcaniclastic rocks gathered in eleven litho types belonging to four members. These foreland sequences are exposed by a combination of thin-skinned deformation whose shortening is transferred to the basement in the west beneath the Cordón del Maitén. The entire Ñirihuau section as well as the overlying Collón Cura Formation is characterized by the occurrence of progressive unconformities, fact that implies synorogenic sedimentation at the time of the Cordón del Maitén range uplift. This belt is formed by an east-verging basement wedge associated with a series of backthrusts. The reactivation of the deformation associated with growth strata, indicates that the basin has evolved in a wedge-top of a foreland system in different pulses of deformation.

Descripción: Enrollments into first-year university biology courses may be very large, and therefore evaluating student learning can represent quite a challenge. In this article, we present our experience in assessing students by means of an assessment instrument called "Understand Before Choosing" (UBC). It has been used for six semesters, and its performance has been compared with two other common means of assessment, the use of multiple-choice questions and the use of open-ended questions. UBC consists of a text (100 lines, nearly 700 words) on the subject being tested, and a set of carefully worded questions that require the selection of one of five crafted options to be answered. To choose the best option, a student needs to understand the concepts embedded in the text. © 2008 by The International Union of Biochemistry and Molecular Biology.

Descripción: 1. 1. A method for purifying human erythrocytes ALA-D, using a mixture of n-butanol and chloroform, which denature hemoglobin, followed by ammonium sulphate fractionation and affinity chromatography yielding a 1600-fold purified enzyme, is described. 2. 2. By oxidation of Sephadex G-25 with NaIO4, a polyaldehyde, is obtained which can be covalently bound to the ALA-D; however the immobilized enzyme is inactive, because essential ε{lunate}-amino groups at the active site were involved in the coupling. Similar experiments with another enzyme, Rhodanese, resulted in an active insolubilized preparation. 3. 3. By suspending the carrier-enzyme in buffer, slow solubilization with simultaneous release of protein occurs, indicating that this approach might find important therapeutical applications in the treatment of enzyme deficiencies. © 1980.

Descripción: 1. 1. A family investigation was performed in eleven cases of Porphyria Cutanea Tarda (PCT). 2. 2. By using clinical findings, quantitative measurements and thin layer chromatography (TLC) of urinary porphyrins, overt and subclinical PCT patients have been identified. 3. 3. In the overt type, skin manifestations are present, excretion of urinary porphyrins is increased and the TLC pattern of porphyrins in urine is characteristic for PCT. 4. 4. In the subclinical type, patients have no clinical symptoms, excretion of porphyrins in urine might be normal or enhanced and TLC pattern of urinary porphyrins is typical for PCT. 5. 5. By applying these criteria a clear distinction between hereditary and non-hereditary PCT was possible. 6. 6. Among the 11 families studied, in four families where PCT was hereditary, four members have the overt type and ten relatives the subclinical type. 7. 7. In seven families where PCT was non-hereditary only the propositus has overt PCT and not a single relative showed any clinical or biochemical abnormality. © 1980.

Descripción: Fil:del C. Batlle, A.M. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: Many characteristics of the South American teleost fish Cichlasoma dimerus (body size, easy breeding, undemanding maintenance) make it amenable to laboratory studies. In the last years, many of the fundamental aspects of its reproductive and developmental biology have been addressed in our laboratory. Rather recently, the immunohistochemical localization of pituitary hormones involved in reproduction and in background color adaptation has been described in both adult and developing individuals, and the role of FSH in ovarian differentiation has been established. These findings have been correlated with mapping of some of their brain-derived controlling hormones. The latter include brain-derived gonadotropins which were shown to be active in vitro in the control of pituitary hormone secretions. The emerging picture shows C. dimerus as an interesting species in which many of their basic features have already been investigated and which conform a solid platform for comparative studies correlating neurohormones, pituitary hormones and behavior, from the molecular to the organismic level.

Descripción: The use of plasma actuators is a recent technology that imposes a localized electric force that is used to control air flows. A suitable representation of actuation enables to undertake plasma actuators optimization, to design flow-control strategies, or to analyse the flow stabilization that can be attained by plasma forcing. The problem description may be clearly separated in two regions. An outer region, where the fluid is electrically neutral, in which the flow is described by the Navier-Stokes equation without any forcing term. An inner region, that forms a thin boundary layer, where the fluid is ionized and electric forces are predominant. The outer limit of the inner solution becomes the boundary condition for the outer problem. The outer problem can then be solved with a slip velocity that is issued from the inner solution. Although the solution for the inner problem is quite complex it can be contoured proposing pseudo-empirical models where the slip velocity of the outer problem is determined indirectly from experiments. This pseudo-empirical model approach has been recently tested in different cylinder flows and revealed quite adapted to describe actuated flow behaviour. In this work we determine experimentally the influence of the duty cycle on the slip velocity distribution. The velocity was measured by means of a pitot tube and flow visualizations of the starting vortex (i.e. the induced flow when actuation is activated in a quiescent air) have been done by means of the Schlieren technique. We also performed numerical experiments to simulate the outer region problem when actuation is activated in a quiescent air using a slip velocity distribution as a boundary condition. The experimental and numerical results are in good agreement showing the potential of this pseudo-empirical model approach to characterize the plasma actuation.

Descripción: In this work, we have study the EEG signals of birds during the first 6 weeks of life. The aim of the article is to perform a quantitative analysis of the dynamical changes observed in these signals due to the brain maturation effects. The signals' long scaling behaviour is study by Multifractal Detrended Fluctuation Analysis (MFDFA). This method allows the multifractal characterization of these EEG nonstationary time series and characterize the different stage of bird brain maturation. © 2007 American Institute of Physics.

Descripción: During the austral autumn of 1997, a sequence of record low ozone events with anomalous behavior occurred at subtropical latitudes to midlatitudes over southern South America, also known as the South Cone (Chile, Argentina, Uruguay, and Southern Brazil). The extreme low ozone events took place in May and early June 1997, i.e., at a time of the year when according to the climatological studies for Northern Hemisphere ozone miniholes, the most significant events would not be expected (if such studies could be simply extrapolated to the Southern Hemisphere). The first and most prominent ozone minihole, with a quasi-stationary evolution, reached values near 200 DU, i.e., a negative anomaly near 90 DU, close to 40°S. Simultaneously, extreme weather conditions were observed over the South Cone: three significant blocking events took place separated by short intervals. Both the behavior of the ozone layer over the region and the evolution of the blocking events were analyzed. As expected, the evolution of the total ozone column is shown to be linked to these perturbed weather conditions. Despite the apparently similar nature of the blocking events and of the ozone decrease during each of these events, the present study shows that the response of the UT/LS region is different in each case. The respective roles of the vertical displacement of the tropopause and the horizontal advection/divergence of ozone is discussed for the two most important events, showing how these two mechanisms combine in different ways to yield very low total ozone values. The vertical displacement of the tropopause, coupled to the size of the tropopause pressure gradient, appears to be the most efficient mechanism to modify the total ozone column amounts. Copyright 2002 by the American Geophysical Union.

Descripción: An experimental study of the plasma jet generated in a pulsed copper vacuum arc with an annular anode and operated with a linear magnetic filter is presented. Two types of filters were employed, one consisting of an insulating duct and the other of a conducting duct, both of them surrounded by an external coil, which generates the axial magnetic field. To improve the ion flux at the filter entrance another auxiliary magnetic field in the cathode region was applied (focusing field). Also, the cathode shape was modified to confine the cathode spot onto the front cathode surface. Operating the arc under vacuum conditions, probe measurements of the ion saturation current and the plasma potential at different axial positions along the ducts and for different filtering magnetic field values are reported. A comparison between both kinds of filters is also presented. © 2006 American Institute of Physics.

Descripción: Fil:Mininni, P.D. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: Longitudinal dependences of stratospheric gravity wave (GW) fluctuations and lower ionospheric irregularities (sporadic E) at midlatitudes are studied by means of radio occultation data of the Global Positioning System/Meteorology Experiment (GPS/MET) satellite mission. The zonal average of temperature variance of GW fluctuations with vertical scales less than 7 km at northern midlatitudes is observed to be similar to that at southern midlatitudes, but there is a significant interhemispheric difference in the longitudinal dependence of GW fluctuations. The GPS/MET data at northern midlatitudes show a rapid change of the gravity wave distribution from 25 to 35 km height, resulting in a broad maximum of temperature variance located over the Atlantic and Eurasia. We only find in the wave distribution at h = 25 km some weak traces of possible orographic effects. On the other hand, the distribution of GW fluctuations at southern midlatitudes has a strong and sharp maximum over Andes, which is obviously due to orographic wave generation by the interaction of surface wind with the Andean mountain ridge. This observation of the new GPS radio occultation technique is in agreement with previous measurements of spaceborne microwave and infrared limb sounders. The amplitude of the average wave field increases with height over Andes, while the amplitude maximum moves westward, against the prevailing wind. The temperature fluctuations have an apparent, dominant vertical wavelength of around 6 km. In situ measurements by a balloon-borne rawinsonde at Ushuaia, Argentina (54.7°S, 68.1°W) are compared to a simultaneous GPS/MET temperature profile. The balloon observations of temperature and horizontal wind are interpreted by a large amplitude mountain wave propagating to the upper stratosphere. Wave characteristics and atmospheric background conditions are investigated in detail for this mountain wave observation. Finally, the GPS/MET experiment indicates enhanced sporadic E in the lower ionosphere over Southern Andes. We assume that these plasma irregularities are generated by enhanced, upward wave flux due to the possible orographic ettect of Andes. Copyright 2002 by the American Geophysical Union.

Descripción: Longitudinal dependences of stratospheric gravity wave (GW) fluctuations and lower ionospheric irregularities (sporadic E) at midlatitudes are studied by means of radio occultation data of the Global Positioning System/Meteorology Experiment (GPS/MET) satellite mission. The zonal average of temperature variance of GW fluctuations with vertical scales less than 7 km at northern midlatitudes is observed to be similar to that at southern midlatitudes, but there is a significant interhemispheric difference in the longitudinal dependence of GW fluctuations. The GPS/MET data at northern midlatitudes show a rapid change of the gravity wave distribution from 25 to 35 km height, resulting in a broad maximum of temperature variance located over the Atlantic and Eurasia. We only find in the wave distribution at h = 25 km some weak traces of possible orographic effects. On the other hand, the distribution of GW fluctuations at southern midlatitudes has a strong and sharp maximum over Andes, which is obviously due to orographic wave generation by the interaction of surface wind with the Andean mountain ridge. This observation of the new GPS radio occultation technique is in agreement with previous measurements of spaceborne microwave and infrared limb sounders. The amplitude of the average wave field increases with height over Andes, while the amplitude maximum moves westward, against the prevailing wind. The temperature fluctuations have an apparent, dominant vertical wavelength of around 6 km. In situ measurements by a balloon-borne rawinsonde at Ushuaia, Argentina (54.7°S, 68.1°W) are compared to a simultaneous GPS/MET temperature profile. The balloon observations of temperature and horizontal wind are interpreted by a large amplitude mountain wave propagating to the upper stratosphere. Wave characteristics and atmospheric background conditions are investigated in detail for this mountain wave observation. Finally, the GPS/MET experiment indicates enhanced sporadic E in the lower ionosphere over Southern Andes. We assume that these plasma irregularities are generated by enhanced, upward wave flux due to the possible orographic effect of Andes. Copyright 2002 by the American Geophysical Union.

Descripción: In the present work, we studied the efficiency of a magnetic island filter for two vacuum arc designs, pulsed and continuous. The magnetic island filter consisted in a straight duct with an external solenoid and a magnet enclosed in a housing (magnetic island) located inside the duct on its axis, and both magnetic fields are in opposite direction. The housing of the magnetic island obstructs the line of sight between the cathode and the substrate. In this arrangement, the charged plasma components move along the curved magnetic field lines, around the magnetic island, but the macroparticles move in straight paths and deposit on the wall of the magnetic island housing. The performance of the filter was characterized for different external and internal field strengths. The plasma transport efficiency was analyzed by measuring the ion saturation current with Langmuir probes and the deposited mass rate. The ion transmission efficiency around the system axis achieved values around 25%. Observation of the coating surface morphology with optical microscopy determined that the macroparticles were effectively removed.

Descripción: This work describes a simple spatial decomposition of the first-order reduced density matrix corresponding to an N -electron system into first-order density matrices, each of them associated to an atomic domain defined in the theory of atoms in molecules. A study of the representability of the density matrices arisen from this decomposition is reported and analyzed. An appropriate treatment of the eigenvectors of the matrices defined over atomic domains or over unions of these domains allows one to describe satisfactorily molecular properties and chemical bondings within a determined molecule and among its fragments. Numerical determinations, performed in selected molecules, confirm the reliability of our proposal. © 2005 American Institute of Physics.

Descripción: In the cliffs of the Ladrillero cape, situated on the Atlantic coast of the Isla Grande de Tierra del Fuego, the uppermost records of the Austral or Magallanes foreland basin infill crop out. This locality contains Lower Miocene deposits informally named "Cabo Ladrillero beds" and "Cabo San Pablo beds" being the "upper Cabo Ladrillero beds" analyzed in this paper. This locality is situated around ten kilometers to the north of the emerging orogenic front (Punta Gruesa locality) where four facies association have been defined from gravitationally-driven supra batial to prograding and shallowing upward deltaic wedges. Deformed and massive beds by liquefaction processes and resedimentation are connected with abundant clastic dykes and synsedimentary faults. The statistic study suggests they are associated tectonic activity related to a transtensive episode rather than tectonic quiescence sometimes suggested in previous works. We conclude that microfossils documented in the area and used as a tool to support a deep marine environment are situated in underlying stratigraphic intervals that form part of the Desdémona Formation and the "lower Cabo Ladrillero beds" cropping out to the south of the study area. Sedimentological evidence are not conclusive respect to the batimetry but absence of classical turbidites, hyperpycnal flows and abundant deformed and resedimented deposits are more compatible with deltaic deposits, with high detritus supply generating unstable slopes rather than deep marine depositional settings, suggesting a more complex depositional evolution than the foraminiferal-based framework dominant in the literature.

Descripción: Fil:Behrens, N.H. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: FKBP51 and FKBP52 (FK506-binding protein 51 and 52) are tetratricopeptide repeat-domain immunophilins belonging to the tetratricopeptide- protein•hsp90•hsp70•p23 heterocomplex bound to steroid receptors. Immunophilins are related to receptor folding, subcellular localization, and hormonedependent transcription. Also, they bind the immunosuppressant macrolide FK506, which shows neuroregenerative and neuroprotective actions by a still unknown mechanism. In this study, we demonstrate that in both, undifferentiated neuroblastoma cells and embryonic hippocampal neurons, the FKBP52• hsp90•p23 heterocomplex concentrates in a perinuclear structure. Upon cell stimulation with FK506, this structure disassembles and this perinuclear area becomes transcriptionally active. The acquisition of a neuronal phenotype is accompanied by increased expression of bIII-tubulin, Map-2, Tau-1, but also hsp90, hsp70, p23, and FKBP52. During the early differentiation steps, the perinuclear heterocomplex redistributes along the cytoplasm and nascent neurites, p23 binds to intermediate filaments and microtubules acquired higher filamentary organization. While FKBP52 moves towards neurites and concentrates in arborization bodies and terminal axons, FKBP51, whose expression remains constant, replaces FKBP52 in the perinuclear structure. Importantly, neurite outgrowth is favored by FKBP52 over-expression or FKBP51 knock-down, and is impaired by FKBP52 knock-down or FKBP51 over-expression, indicating that the balance between these FK506-binding proteins plays a key role during the early mechanism of neuronal differentiation. © 2010 The Authors.

Descripción: The proopiomelanocortin gene (POMC) encodes several bioactive peptides, including adrenocorticotropin hormone, α-, β-, and γ-melanocyte-stimulating hormone, and the opioid peptide β-endorphin, which play key roles in vertebrate physiology. In the human, mouse, and chicken genomes, there is only one POMC gene. By searching public genome projects, we have found that Tetraodon (Tetraodon nigroviridis), Fugu (Takifugu rubripes), and zebrafish (Danio rerio) possess two POMC genes, which we called POMCα and POMCβ, and we present phylogenetic and mapping evidence that these paralogue genes originated in the whole-genome duplication specific to the teleost lineage over 300 MYA. In addition, we present evidence for two types of subfunction partitioning between the paralogues. First, in situ hybridization experiments indicate that the expression domains of the ancestral POMC gene have been subfunctionalized in Tetraodon, with POMCα expressed in the nucleus lateralis tuberis of the hypothalamus, as well as in the rostral pars distalis and pars intermedia (PI) of the pituitary, whereas POMCβ is expressed in the preoptic area of the brain and weakly in the pituitary PI. Second, POMCβ genes have a β-endorphin segment that lacks the consensus opioid signal and seems to be under neutral evolution in tetraodontids, whereas POMCα genes possess well-conserved peptide regions. Thus, POMC paralogues have experienced subfunctionalization of both expression and peptide domains during teleost evolution. The study of regulatory regions of fish POMC genes might shed light on the mechanisms of enhancer partitioning between duplicate genes, as well as the roles of POMC-derived peptides in fish physiology.

Descripción: The one-dimensional stationary full hydrodynamic model for semiconductor devices with non-isentropic pressure is studied. This model consists of the equations for the electron density, electron temperature, and electric field in a bounded domain supplemented with boundary conditions. The existence of a classical subsonic solution with positive particle density and positive temperature is shown in two situations: non-constant and constant heat conductivities. Moreover, we prove uniqueness of a classical solution in the latter case. The existence proofs are based on elliptic estimates, Stampacchia truncation methods, and fixed-point arguments. © 2001 Academic Press.

Descripción: Detailed study of Callovian carbonates of the Calabozo Formation (30 m) in western Argentina, reveals the abundance of benthic carbonates particles produced by organisms that are light dependent, and non-skeletal grains such as ooids and peloids. The biota consists of bivalves, dasyclads (Salpingoporella annulata Carozzi, Cylindroporella annulata Carozzi, and Heteroporella sp.), scleractinian corals, echinoderms, cyanobacteria (Cayeuxia (Rivularia) piae Rech-Frollo, and Cayeuxia (Rivularia) kurdistanensis Elliot), oncoids, gastropods, forams, and calcispheres as well as ostracods, and bryozoans in relatively minor quantities. Allochemical particles suggest for the shallow marine limestones of the Calabozo Formation a Photozoan Association under subtropical seawater conditions. The petrographic features allow to recognize seven microfacies, differentiated by particle types, fossils and depositional texture: 1) criptalgal bindstone; 2) bioclastic-peloidal wackestone; 3) bioclastic-intraclastic wackestone; 4) bioclastic-peloidal-terrigenous wackestone, 5) coral framestone, 6) peloidal-bioclastic-intraclastic packstone, and 7) oolitic-bioclastic-peloidal packstone-grainstone. The recognition of microfacies groups constitute two palaeoenvironmental associations: inner ramp and middle ramp settings. Diagenetic studies are based on examination of stained thin sections, through conventional petrography and under cathodoluminescence. Early diagenetic processes are micritization and precipitation of peloidal micrite and acicular calcite. These cements predate granular and syntaxial calcite cements. Cathodoluminescent petrography allows to identify three morphologic types of clear cements: (1) fine acicular crystals, (2) granular cements, and (3) syntaxial cement rims on echinoderm particles. Description of the CL signature has evolved to discrimination as either, non-luminescent, dully luminescent red/orange, or brightly luminescent yellow. The earlier acicular calcite cement is non-luminescent, on the other hand, the predominantly dully luminescent red/orange, or brightly luminescent yellow of interparticular and intraparticular granular calcite and syntaxial cements indicate a shallow burial meteoric-phreatic diagenetic environment.

Descripción: The cyclic AMP (cAMP)-dependent protein kinase A (PKA) signaling pathway plays a role in regulating development, growth, and virulence in a number of fungi. To determine whether PKA plays a similar function in zygomycete fungi, a mutant of Mucor circinelloides was generated that lacks pkaR1, one of the regulatory subunits of PKA. The mutant showed a reduction in growth and alterations in germination rates, cell volume, germ tube length, and asexual sporulation. The lack of pkaR1 gene resulted in a highly decreased, but not null, cAMP binding activity and in a protein kinase activity that was still dependent on cAMP, although with a higher -/+ cAMP activity ratio, suggesting the existence of other cAMP binding activities. Consequently, three proteins analogous to pkaR1 were predicted from the recently sequenced genome of M. circinelloides and were named pkaR2, pkaR3, and pkaR4. Two of the proteins, pkaR2 and pkaR3, with cAMP binding activity were isolated from the wild-type strain and identified by mass spectrometry. The expression of all genes was detected at the mRNA level by semiquantitative reverse transcription-PCR, and they showed a differential expression at different developmental stages. This is the first time that a fungus is reported to have more than one gene encoding the regulatory subunit of PKA. © 2009, American Society for Microbiology.

Descripción: Cemeteries are ideal urban areas to study the importance of different types of containers as breeding sites of Aedes aegypti (L.). In the present study, the suitability of plastic, glass, ceramic and metal containers was evaluated in four patches within a cemetery of Buenos Aires City, Argentina. Between October 1998 and May 2000, we found 215 breeding sites of Ae. aegypti out of 13,022 water-filled containers examined. In two patches containing microenvironments sheltered from the sun, the use of the different types of containers was proportional to the offer (correlation coefficient = 0.99, P < 0.05 in both cases). In the remaining patches, plastic and metal containers were the most and less frequent breeding sites, respectively (P < 0.001 in both cases). The number of immatures per breeding site (median = 4.5) did not show significant differences among the four types of containers examined (H3, 215 = 1.216, P = 0.749). Differences found in patches from a same cemetery suggest that different microenvironmental conditions affect the suitability of each type of container for Ae. aegypti breeding. Plastic containers appeared as key breeding sites that should be removed to reduce the Ae. aegypti population in the study area.

Descripción: Five disulfated steroids and a mixture of monosulfated steroids were isolated from the ethanolic extract of the antarctic ophiuroid Gorgonocephalus chilensis. The structures were determined by 1H-NMR, 13C-NMR and FABMS.

Descripción: Trypanosoma cruzi, the agent of Chagas disease contains a major cysteine proteinase, cruzipain (Cz), with an unusual carboxyl-terminal extension (C-T). We have previously reported the presence of sulfate groups in the N-linked oligosaccharide chains of this domain. In order to evaluate the immune responses to sulfated moieties on Cz, BALB/c mice were immunized with purified Cz and C-T prior and after desulfation treatment. The humoral immune response to sulfates on Cz or C-T was mainly IgG2b. Interestingly, the abolishment of IgG2b reactivity when desulfated antigens were used as immunogens demonstrates that esterified sulfate groups are absolutely required for eliciting IgG2b response to Cz. Sera from chronically T. cruzi -infected subjects with mild disease displayed higher levels of total IgG and IgG2 antibodies specific for sulfated epitopes compared with those in more severe forms of the disease. A significant reduction of C-T-specific delayed-type hypersensitivity reaction in C-T-immunized mice was observed when desulfated C-T was challenged, suggesting the involvement of sulfate groups in the generation of memory T-cell responses. Moreover, immunization with C-T in the absence of infection elicited ultrastructural abnormalities in heart tissue. Surprisingly, hearts from sulfate-depleted C-T-immunized mice did not present pathological alterations. This is the first report showing that sulfate-bearing glycoproteins from trypanosomatids are able to elicit specific humoral and cellular immune responses and appeared to be involved in the generation of heart tissue damage. These results represent a further step in the understanding of the role of Cz in the course of T. cruzi infection. © The Japanese Society for Immunology. 2008. All rights reserved.

Descripción: We present a generalization of fermionic fluiddynamics to the case of two trapped fermion species with a contact interaction. Within a mean field approximation, we derive coupled equations of motion for the particle densities, particle currents, and anomalous pair density. For an inhomogeneous system, the equilibrium situation with vanishing currents is described by a generalized Thomas-Fermi relation that includes the superfluid gap, together with a new nonlocal gap equation that replaces the usual BCS one. These equations are numericaly solved resorting to a local density approximation (LDA). Density and gap profiles are analyzed in terms of the scattering length, revealing that the current frame can exhibit microscopic details of quantum origin that are frequently absent in more macroscopic scenarios. © 2009 IOP Publishing Ltd.

Descripción: Compressibility has a strong influence on the stability of velocity shear layers when the difference of velocity ΔV across the flow becomes supersonic. The flanks of the Earth's magnetopause are normally supersonic Ms > 1, and super-Alfvénic MA > 1, depending on the distance from the dayside terminator (Ms and MA are the sonic and Alfvén Mach numbers of the magnetosheath plasma, respectively). The stability of MHD supersonic flows depends, also on several other features, such as the finite thickness Δ of the boundary layer, the relative orientation of velocity and magnetic fields, the density jump across the boundary and the magnetic shear angle. We analyze the MHD stability of some representative flank sites modeled after data from spacecraft crossings of the magnetopause under different interplanetary conditions, complementing these cases with extrapolations of likely conditions upstream, and downstream of the crossing site. Under northward interplanetary magnetic field conditions, there are solar wind regimes such that the near, but already supersonic, flank of the magnetopause may be locally stable. Stability is possible, e.g., when M s becomes larger than ∼1.2-1.4 while MA remains smaller than 1.2, and there is magnetic shear between the geomagnetic and the interplanetary magnetic field. Solar winds favouring local stability of the boundary layer are cold, not-too-dense plasmas, with strong magnetic fields, so that MA is smaller, while Ms is larger, than normal values of the magnetosheath flow. A gap between dayside and tail amplifying regions of Kelvin-Helmholtz disturbances over the magnetopause may exist when the above conditions are realized. © 2009 IOP Publishing Ltd.

Descripción: In addition to their role in DNA repair, recombination events are associated with processes aimed at providing the genetic variability needed for adaptation and evolution of a population. In bacteria, recombination is involved in the appearance of new variants by allowing the incorporation of exogenous DNA or the reshuffling of endogenous sequences. Here we show that HpMutS2, a protein belonging to the MutS2 family in Helicobacter pylori, is not involved in mismatch repair but inhibits homologous and homeologous recombination. Disruption of HpmutS2 leads to an increased efficiency of exogenous DNA incorporation. HpMutS2 has a selective affinity for DNA structures mimicking recombination intermediates with no specificity for homoduplex DNA or mismatches. The purified protein has an ATPase activity stimulated by the same DNA structures. Finally, we show that HpMutS2 inhibits DNA strand exchange reactions in vitro. Thus, MutS2 proteins are candidates for controlling recombination and therefore genetic diversity in bacteria.

Descripción: Nasal secretions were studied in 80 allergic adults patients: 16 with intermittent rhinitis and 64 with persistent rhinitis. The percentage of supranuclear stria of ciliated cells with regard to leucocytes was studied by nasal scraping. Four groups of patients were classified according to nasal leucocytic predominance: patients with eosinophilic predominance with eosinophils > 10% in Group A (N=23), patients with abundant neutrophils and eosinophils > 10% in Group B (N=15), patients with scant leucocytes in Group C (N=29), patients with neutrophilic predominance without eosinophils in Group D (N=13). An increase of supranuclear stria percentage was correlated to eosinophils > 10% and also correlated to scant leucocytes. Nevertheless, a significant decrease of supranuclear stria percentage was observed in neutrophilic leukocytosis of bacterial etiology.

Descripción: Survival of a potentially lethal high temperature stress is a genetically variable thermal adaptation trait in many organisms. Organisms cope with heat stress by basal or induced thermoresistance. Here, we tested quantitative trait loci (QTL) for heat stress survival (HSS) in Drosophila melanogaster, with and without a cyclic heat-hardening pre-treatment, for flies that were reared at low (LD) or high (HD) density. Mapping populations were two panels of recombinant inbred lines (RIL), which were previously constructed from heat stress-selected stocks: RIL-D48 and RIL-SH2, derived from backcrosses to stocks of low and high heat resistance, respectively. HSS increased with heat hardening in both LD and HD flies. In addition, HSS increased consistently with density in non-hardened flies. There was a significant interaction between heat hardening and density effects in RIL-D48. Several QTL were significant for both density and hardening treatments. Many QTL overlapped with thermotolerance QTL identified for other traits in previous studies based on LD cultures only. However, three new QTL were found in HD only (cytological ranges: 12E-16F6; 30A3-34C2; 49C-50C). Previously found thermotolerance QTL were also significant for flies from HD cultures. © 2012. Published by The Company of Biologists Ltd.

Descripción: Fil:Gürtler, R.E. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: Chagas disease remains a serious obstacle to health and economic development in Latin America, especially for the rural poor. We report the long-term effects of interventions in rural villages in northern Argentina during 1984-2006. Two community-wide campaigns of residual insecticide spraying immediately and strongly reduced domestic infestation and infection with Trypanosoma cruzi in Triatoma infestans bugs and dogs and more gradually reduced the seroprevalence of children <15 years of age. Because no effective surveillance and control actions followed the first campaign in 1985, transmission resurged in 2-3 years. Renewed interventions in 1992 followed by sustained, supervised, community-based vector control largely suppressed the reestablishment of domestic bug colonies and finally led to the interruption of local human T. cruzi transmission. Human incidence of infection was nearly an order of magnitude higher in peripheral rural areas under pulsed, unsupervised, community-based interventions, where human transmission became apparent in 2000. The sustained, supervised, community-based strategy nearly interrupted domestic transmission to dogs but did not eliminate T. infestans despite the absence of pyrethroid-insecticide resistance. T. infestans persisted in part because of the lack of major changes in housing construction and quality. Sustained community participation grew out of establishing a trusted relationship with the affected communities and the local schools. The process included health promotion and community mobilization, motivation, and supervision in close cooperation with locally nominated leaders. © 2007 by The National Academy of Sciences of the USA.

Descripción: Successful mammalian pregnancy relies upon acceptance of a semi-allogeneic fetus by the maternal immune system. Lessons learned from studies on protective immunity to microbial infections and tumours, prevention of autoimmunity, and allograft rejection have contributed to delineate the mechanisms leading to T-cell tolerance at the fetomaternal interface. Recent observations highlight the contribution of galectins, a family of endogenous glycan-binding proteins, to critical biological events occurring during mammalian gestation, including immune cell tolerance, inflammation, implantation, and angiogenesis. These multifunctional lectins can hierarchically control a cascade of immunoregulatory events including the expansion, recruitment, and function of regulatory T cells, the promotion of tolerogenic dendritic cells, and the execution of T-cell death programs. In addition, galectins can control cell adhesion and signaling events critical for implantation and are involved in fundamental processes linking tissue hypoxia to angiogenesis. In an attempt to integrate the regulatory roles of galectins to immunological and vascular programs operating during pregnancy. Here we outline the regulated expression and function of individual members of the galectin family within the fetoplacental unit and their biological implications for the development and preservation of successful pregnancies. © 2013 John Wiley & Sons A/S.

Descripción: In the moth, Agrotis ipsilon, newly mated males cease to be attracted to the female-produced sex pheromone, preventing them from re-mating until the next night, by which time they would have refilled their reproductive glands for a potential new ejaculate. The behavioural plasticity is accompanied by a decrease in neuron sensitivity within the primary olfactory centre, the antennal lobe (AL). However, it was not clear whether the lack of the sexually guided behaviour results from the absence of sex pheromone detection in the ALs, or if they ignore it in spite of detection, or if the sex pheromone itself inhibits attraction behaviour after mating. To test these hypotheses, we performed behavioural tests and intracellular recordings of AL neurons to non-pheromonal odours (flower volatiles), different doses of sex pheromone and their mixtures in virgin and newly mated males. Our results show that, although the behavioural and AL neuron responses to flower volatiles alone were similar between virgin and mated males, the behavioural response of mated males to flower odours was inhibited by adding pheromone doses above the detection threshold of central neurons. Moreover, we show that the sex pheromone becomes inhibitory by differential central processing: below a specific threshold, it is not detected within the AL; above this threshold, it becomes inhibitory, preventing newly mated males from responding even to plant odours. Mated male moths have thus evolved a strategy based on transient odour-selective central processing, which allows them to avoid the risk-taking, energy-consuming search for females and delay re-mating until the next night for a potential new ejaculate. © 2010. Published by The Company of Biologists Ltd.

Descripción: In 1853, Sylvester introduced a family of double sum expressions for two finite sets of indeterminates and showed that some members of the family are essentially the polynomial subresultants of the monic polynomials associated with these sets. In 2009, in a joint work with C. D'Andrea and H. Hong we gave the complete description of all the members of the family as expressions in the coefficients of these polynomials. More recently, M.-F. Roy and A.Szpirglas presented a new and natural inductive proof for the cases considered by Sylvester. Here we show how induction also allows to obtain the full description of Sylvester's double-sums. © 2012 Elsevier Ltd.

Descripción: In 1853 Sylvester introduced a family of double-sum expressions for two finite sets of indeterminates and showed that some members of the family are essentially the polynomial subresultants of the monic polynomials associated with these sets. A question naturally arises: What are the other members of the family? This paper provides a complete answer to this question. The technique that we developed to answer the question turns out to be general enough to characterize all members of the family, providing a uniform method. © 2009 Elsevier Ltd. All rights reserved.

Descripción: We introduce the symmetric Radon-Nikodỳm property (sRN property) for finitely generated s-tensor norms β of order n and prove a Lewis type theorem for s-tensor norms with this property. As a consequence, if β is a projective s-tensor norm with the sRN property, then for every Asplund space E, the canonical mapping {position indicator}~βn,sE'→({position indicator}~β'n,sE)' is a metric surjection. This can be rephrased as the isometric isomorphism Qmin(E)=Q(E) for some polynomial ideal Q. We also relate the sRN property of an s-tensor norm with the Asplund or Radon-Nikodỳm properties of different tensor products. As an application, results concerning the ideal of n-homogeneous extendible polynomials are obtained, as well as a new proof of the well-known isometric isomorphism between nuclear and integral polynomials on Asplund spaces. An analogous study is carried out for full tensor products. © 2010 Elsevier Inc.

Descripción: In this article we study symmetry properties of the extremals for the Sobolev trace embedding H1(B(0,μ))→Lq(∂B(0, μ)) with 1≤q≤2(N-1)/(N-2) for different values of μ. These extremals u are solutions of the problem Δu=uinB(0,μ),∂u∂η= λ|u|q-2uon∂B(0,μ). We find that, for 1≤q<2(N-1)/(N-2), there exists a unique normalized extremal u, which is positive and has to be radial, for μ small enough. For the critical case, q=2(N-1)/(N-2), as a consequence of the symmetry properties for small balls, we conclude the existence of radial extremals. Finally, for 1<q≤2, we show that a radial extremal exists for every ball. © 2004 Elsevier SAS. All rights reserved.

Descripción: Dichroplus pratensis has a complex system of Robertsonian rearrangements with central-marginal distribution; marginal populations are standard telocentric. Standard bivalents show a proximal-distal chiasma pattern in both sexes. In Robertsonian individuals a redistribution of chiasmata occurs: proximal chiasmata are suppressed in fusion trivalents and bivalents which usually display a single distal chiasma per chromosome arm. In this paper we studied the synaptic patterns of homologous chromosomes at prophase I of different Robertsonian status in order to find a mechanistic explanation for the observed phenomenon of redistribution of chiasmata. Synaptonemal complexes of males with different karyotypes were analysed by transmission electron microscopy in surface-spread preparations. The study of zygotene and early pachytene nuclei revealed that in the former, pericentromeric regions are the last to synapse in Robertsonian trivalents and bivalents and normally remain asynaptic at pachytene in the case of trivalents, but complete pairing in bivalents. Telocentric (standard) bivalents usually show complete synapsis at pachytene, but different degrees of interstitial asynapsis during zygotene, suggesting that synapsis starts in opposite (centromeric and distal) ends. The sequential nature of synapsis in the three types of configuration is directly related to their patterns of chiasma localisation at diplotene-metaphase I, and strongly supports our previous idea that Rb fusions instantly produce a redistribution of chiasmata towards chromosome ends by reducing the early pairing regions (which pair first, remain paired longer and thus would have a higher probability of forming chiasmata) from four to two (independently of the heterozygous or homozygous status of the fusion). Pericentrometric regions would pair the last, thus chiasma formation is strongly reduced in these areas contrary to what occurs in telocentric bivalents.

Descripción: We have previously described a murein hydrolase activity for the surface layer (S-layer) of Lactobacillus acidophilus ATCC 4356. Here we show that, in combination with nisin, this S-layer acts synergistically to inhibit the growth of pathogenic Gram-negative Salmonella enterica and potential pathogenic Gram-positive bacteria, Staphylococcus aureus and Bacillus cereus. In addition, bacteriolytic effects were observed for the Gram-positive species tested. We postulate that the S-layer enhances the access of nisin into the cell membrane by enabling it to cross the cell wall, while nisin provides the sudden ion-nonspecific dissipation of the proton motive force required to enhance the S-layer murein hydrolase activity. Copyright © 2010, American Society for Microbiology. All Rights Reserved.

Descripción: Four brassinosteroids analogs of homoteasterone and homotyphasterol bearing 5α-OH and 5α-F groups have been synthesized and their bioactivities evaluated.

Descripción: Fil:Martins Alho, M.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: New organophosphorus insecticides of dialkylsulphoximines derived with activity upon acetylcholinesterase were synthesized. The obtained compounds were characterized by NMR and IR, and anticholinesterase activity and toxicity was measured. A simulation through computer was done in order to establish the relationship between structure and activity.

Descripción: The synthesis of 2,3,5,6-tetra-O-benzyl-D-galactofuranose, a useful compound for α-glycosylation studies, is described. Direct anomeric O-alkylation of galactose was employed for alpha-allylation to yield pure allyl α-D-galactofuranoside, which is a versatile precursor for the synthesis of galactofuranose-containing oligosaccharides. Allyl removal of the benzylated galactofuranosyl derivative was performed using palladium (II) chloride as catalyst. ©ARKAT.

Descripción: 11α,12α-aziridinosteroids (2a, b, c) were prepared from 5β-H-11-pregnene-3, 20-dione (1) using different iminophenyliodinanes and cloramine aziridination reagents.

Descripción: 17(13→18)-Abeo and D-homo analogs of the natural neurosteroid 3α-hydroxy-5αH-pregnan-20-one were prepared by anionic or radical (mercury (II) hydride mediated) rearrangements of steroidal cyclopropylketones respectively.

Descripción: The synthesis of some isoxazolic compounds from carbohydrate derivatives is described. These products are obtained by 1,3-dipolar cycloaddition reaction and their functionalization leads to derivatives with potential biological activities.

Descripción: This paper reports a synthesis of novel diheteroarylethenes functionalized for coupling to biomolecules starting from indole derivatives. The strategy is based on the derivatization at the N-atom in the indole substructure. TBDMS protection proved to be superior over BOC protection schemes, leading to higher yields in the overall synthesis. The suitability of the new derivatives as acceptors for pcFRET was calculated for selected donors.