Descripción: I. Rehabilitation of Alvaradoa subovata Cronquist (Simaroubaceae), the correct scientific name for the "pichi blanco". II. Roupala cataractarum Sleumer is a synonym of Roupala brasiliensis Klotzch (Proteaceae). A brief account regarding the validated nomenclature, Roupala brasiliensis and Alvaradoa subovata, for both taxa is given. Pollen observations obtained from SEM, in order to complement the identifications, are also given.

Descripción: The holotypes and isotypes of 20 Hypoxylon taxa described by Spegazzini have been examined and their taxonomic positions and nomenclatural problems are discussed. Two new combinations, Annulohypoxylon apiahynum comb. nov. and A. subeffusum comb. nov., are proposed. H. goliath is considered a synonym of Rosellinia bunodes. H. albostigmatosum and H. guarapiense are synonyms of H. anthochroum, H. anthracoderma of H. monticulosum, H. mbaiense of H. notatum, H. paulistanum of H. diatrypeoides, H. plumbeum and H. rubiginosum var. microcarpum of H. perforatum. H. porteri and H. intermedium belong in Biscogniauxia capnodes, H. puiggarii in Annulophypoxylon subeffusum, H. subvinosum. in H. lenormandii, H. turbinatum var. guaraniticum in Phylacia turbinata and H. valsarioides in Creosphaeria sassafras. H. leptascum is transferred to A. leptascum, H. circostomum to Nemania circostoma and H. latissimum to N. latissima. The holotype of H. albostigmatosum has been recovered, thus the lectotypification by Shear no longer is needed. H. subnigricans and H. umbilicatum are confirmed as good taxa. H. anthochroum and H. lenormandii are reported as first records from Argentina (Tucumán). © 2009 by The Mycological Society of America, Lawrence, KS 66044-8897.

Descripción: We investigated the taxonomic status of two sympatric morphospecies of squat lobsters from southern South America (Beagle Channel, Strait of Magellan, and Burdwood Bank), Munida gregaria and Munida subrugosa, by DNA sequence analysis of three mitochondrial (mt)DNA gene fragments [416 bp of 16S rDNA(165), 566 bp of cytochrome c oxidase subunit I(COI) and 418 bp of NADH dehydrogenase subunit 1 (ND1)]; and the nuclear rDNA internal transcribed spacer (ITS) 1 (883-952 bp). We obtained a total of 79 sequences from 32 individuals. The 16S sequences of all M. gregaria and M. subrugosa were invariant and identical, whereas COI and ND1 showed 12 and 15 variable sites, respectively. These polymorphisms were shared between morphospecies. Interspecific Tamura-Nei distances for COI and ND1 sequences were 0.0024 and 0.0032, respectively, and were not significantly different from intraspecific distances (Kruskal-Wallis tests: P = 0.58 and P = 0.69, for COI and ND1, respectively). Similar to the results obtained from the mtDNA sequences, no relationship was found between the ITS1 maximum parsimony tree topology and the morphologic classification of specimens in M. gregaria and M. subrugosa. We conclude that M. gregaria and M. subrugosa from southern South America may either represent a case of a dimorphic species, or a case of incomplete lineage sorting. The fact that these two morphospecies did not show fixed differences over a total of 1947 bp analysed reinforces the hypothesis of a single dimorphic species. © 2008 The Linnean Society of London.

Descripción: Taxonomic characters of the genera Echinochaete and Polyporus s. str. from southern South America are summarized based on examination of 350 collections, including 88 holotypes from different herbaria. The research revealed one species of Echinochaete and nineteen species and one variety of Polyporus s. str. representing four established subgenera (Polyporus, Melanopus, Polyporellus, Favolus). and the new subgenus, Austropolyporus, proposed here to accommodate P. gayanus. Pseudofavolus is considered a synonym of Polyporus s. str. Polyporus arcularioides is accepted as a separate taxon. Polyporus brumalis was not found in the area studied. Polyporus saltensis, considered an autonomous taxon, differs from P. tenuiculus in lacking clamp connections. Polyporus tucumanensis is recognized as a separate species distinct from P. ciliatus. Polyporus maculatissimus, usually considered within Polyporus s. str., belongs in Neolentiporus.

Descripción: A variety of methods have been developed for determination of drugs of abuse in urine, plasm/serum, bilis, hair and others in clinical and forensic samples. Relevance of the application of the technique of gas-liquid chromatography and different types of mass spectrometry are discussed in this paper, being sample preparation emphasized. Amphetamines, cannabinoids, cocaine and benzoylecgonine, morphine and metabolites, phenciclidine, benzodiazepines, tricyclic antidepressants, barbiturates, opiates, local anesthetics and methadone were properly analysed and quantified by means of this methodology. © 2007 Federación Bioquímica de la Provincia de Buenos Aires.

Descripción: The Gondwana margin contained some Triassic basins that together constitute a regionally northwest-trending extensional system. The Cuyana rift Basin is internally composed of a family of hemigrabens filled with thick piles of sedimentary clastic and epiclastic rocks that can reach more than three thousand meters. In particular the Rincón Blanco sub-basin, one of the northernmost depocenter of this rift, is bounded by a linked through-going normal fault that usually displays an en-échèlon map view. Along strike existence of discrete depocenters and alternation of sedimentary wedges of different types suggest a linkage origin for some of them separated by a transfer zone. The infilling was strongly controlled by tectonics which in term produced distinctive features along the whole sedimentary sequence. An immediate consequence of this latter is that the architecture of the fill resulted from the geometry and the displacement of the bounding normal faults. Using lithology and structural data the infilling was subdivided into packages of genetically linked units bounded by regional extended surfaces. Hence, three depositional sequences or tectono- stratigraphic units separated by regional unconformities have been recognized. They were interpreted as a result of a major reactivation of the extensional system that could have evolved along strike as segments of fault that linked together and/or as laterally propagating faults. Using these basic concepts it was possible to reconstruct the geometry and the history of the infilling of the east margin of the hemigraben, buried under several backthrusts. Additionally, it could be possible to separate a sequence of rock, the Marachemill Unit, from the Rincón Blanco Group and to understand their tectonosedimentary relationships.

Descripción: The Huecú basin is located at the central part of the large Loncopué retroarc trough. Its volcanic, volcaniclastic, lacustrine and fluvial filling is directly related to neotectonic activity in the area. The basaltic eruptions are reflecting different pulses associated with the development of extensional faults and tensional fractures. Geophysical potential methods have identified basement involvement in the extensional deformation that affected the Tertiary sequences of the area during the last 5 Mys. Neotectonic features in Quaternary volcanic sequences suggest the persistence of these subsidence mechanisms in the Huecú depocenter. These faults are directly connected to the basement segmentation identified by gravimetric and mag-netometric studies. The historical floods produced by the Agrio river damming, are related to fisural eruptions and demons-trate the high probability that retroarc volcanic eruptions may occur again. The recognition of flooded areas that are forming the youngest sedimentary levels in the Huecú depocenter shows potential areas of active retroarc spreading in the Neuquén area associated with neotectonic and seismic processes.

Descripción: The analyses of the main parameters controlling the present Chile-type and Marianas-type tectonic settings developed along the eastern Pacific region show four different tectonic regimes: (1) a nearly neutral regime in the Oregon subduction zone; (2) major extensional regimes as the Nicaragua subduction zone developed in continental crust; (3) a Marianas setting in the Sandwich subduction zone with ocean floored back-arc basin with a unique west-dipping subduction zone and (4) the classic and dominant Chile-type under compression. The magmatic, structural and sedimentary behaviours of these four settings are discussed to understand the past tectonic regimes in the Mesozoic Andes based on their present geological and tectonic characteristics. The evaluation of the different parameters that governed the past and present tectonic regimes indicates that absolute motion of the upper plate relative to the hotspot frame and the consequent trench roll-back velocity are the first order parameters that control the deformation. Locally, the influences of the trench fill, linked to the dominant climate in the forearc, and the age of the subducted oceanic crust, have secondary roles. Ridge collisions of seismic and seismic oceanic ridges as well as fracture zone collisions have also a local outcome, and may produce an increase in coupling that reinforces compressional deformation. Local strain variations in the past and present Andes are not related with changes in the relative convergence rate, which is less important than the absolute motion relative to the Pacific hotspot frame, or changes in the thermal state of the upper plate. Changes in the slab dip, mainly those linked to steepening subduction zones, produce significant variations in the thermal state, that are important to generate extreme deformation in the foreland. © 2009 John Wiley & Sons, Ltd.

Descripción: A Singular value decomposition (SVD) analysis was performed jointly on the daily intensity of extreme rainfall (DIER) over Argentina and the sea surface temperature (SST) of all the oceans from 17.5°N to 90°S in order to identify the large-scale variability of the SSTs related to extreme rainfall, in the period 1962-2005. The main objective of the article is to objectively recognize regions of the tropical and subtropical oceans that could be related with the extreme rainfall over Argentina. Spring is the season that is best represented by the first mode, accounting for up to 45% of the covariance between the DIER and SST. The first SVD mode of spring, summer and autumn presents a pattern of SST relating to the El Niño-Southern Oscillations (ENSO) phenomena with an enhanced DIER in different zones of centre and east of Argentina. In the second SVD mode of spring and summer, the SST patterns show cold conditions in the tropical and subtropical Atlantic and near Indonesia with an enhancement of the DIER in the centre and east of Argentina. These modes show a significant decadal variability. In the third SVD mode of spring and summer, the SST patterns present warm and cold conditions in the Indian Ocean and the centre and western Pacific Ocean (PO) with decreased rainfall in the northern and eastern portion of Argentina, respectively. This mode shows a significant period of temporal variability of around 14 years. The third mode of autumn presents warm conditions in the tropical Atlantic and the southwest PO with a low DIER in the centre and east of Argentina. This mode also presents temporal variability of around 14 years. The correlation between each mode derived from analysis of SVD and climate indices related with SST were computed. © 2012 Royal Meteorological Society.

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

Descripción: A hybrid, named tricepiro, was obtained in 1972, by crossing a hexaploid triticale (2n=6×=42) and an octoploid trigopiro (2n=8×=56). The lines achieved include the tricepiro Don René INTA, which has shriveled kernels, and FA-L2, which has smooth ones. The relationship between the heterochromatin content of the rye chromosomes, the seed weight, the presence of meiotic abnormalities and the kernel shriveling has been documented previously in other intergeneric hybrids. The purpose of this study was to determine the average percentage of heterochromatin content in the rye chromosomes of the two tricepiro lines mentioned above and to relate this feature to some characteristics of the meiosis and seeds. We confirmed that the two lines have the same total chromosome number (2n=42) and the same number of rye chromosomes (14). We found that both lines have a complete chromosome mating until late diakinesis, but differ in the percentage of cells with univalents outside the equatorial plate in Metaphase I (Don René 42.85% and FA-L2 14.00%). In addition, the two lines differed in their meiotic index (Don René 66.47% and FA-L2 87.90%) and seed weight (Don René 0.029 ± 0.000 g and FA-L2 0.038 ± 0.001 g). The C-banding in rye chromosomes in mitotic metaphase indicated that the average percentage of heterochromatin content did not differ significantly between the two lines. In contrast to our expectations, the meiotic behavior and seed characteristics were not related to the heterochromatin percentage of the rye chromosomes of the tricepiro lines studied.

Descripción: Laboratory-reared larvae of Limnoperna fortunei (Dunker) were monitored until the morula stage at 26°C, and from there on until settlement at 20, 25 and 28°C. The first polar lobe is produced c. 40 min after spawning, and the first division occurs 14 min later. Slightly over an hour after spawning, the second polar lobe appears and the second division yields a 4-cell stage. The third division occurs 90 min after spawning, and the fourth 115 min after spawning. The morula stage is reached 3.5 h after spawning. The trochophore stage (size: 95-110 μm) is reached 20, 6.3 and 6 h after spawning at 20, 25 and 28°C, respectively. Straight-hinged veligers (115-175 μm) start appearing at 45, 26, and 24 h after spawning; umboned veligers (156-220 μm) at 287, 165 and 118 h after spawning; and pediveligers (>200 μm) at 480, 313 and 265 h after spawning. Implications of these findings for the dispersion of the species and for its fouling impact are discussed. © The Malacological Society of London 2005, all rights reserved.

Descripción: The objective of this research is to study the main variability modes of the frequency of extreme temperatures in the south of South Amenica, their relation to sea surface temperatures (SSTs), and some indices of atmospheric circulation in the Southern Hemisphere. Observational data and reanalysis data were used for this purpose over the 1964-2003 period. An initial analysis showed that between the months of March and June, the frequency of wann events (especially warm nights) is highly associated with the SST in coastal zones. A wavelet analysis showed that the main variability mode found at a seasonal scale was an 8-year wave signal present in spning that remains active until the 1990s; it was noticeable in the analysis of cold nights, Atlantic SSTs, Pacific SSTs, and the Southern Annular Mode (SAM). A cross-wavelet analysis among them reflected this signal as a common variability mode, with the positive phase of the SAM congruent with the warmest conditions in the coastal zones of the Atlantic Ocean and lower cases with cold nights at the reference meteorological stations analyzed. Although longer series are desirable for low-frequency variability analysis, the results agree with previous studies that take into account an 8-year periodicity of the baroclinic waves at the Southern Hemisphere, supporting the relevance of the 8-year signal. Copyright 2008 by the American Geophysical Union.

Descripción: The nature of telencephalic control over premotor and motor circuits is debated. Hypotheses range from complete usurping of downstream circuitry to highly interactive mechanisms of control. We show theoretically and experimentally, that telencephalic song motor control in canaries is consistent with a highly interactive strategy. As predicted from a theoretical model of respiratory control, mild cooling of a forebrain nucleus (HVC) led to song stretching, but further cooling caused progressive restructuring of song, consistent with the hypothesis that respiratory gestures are subharmonic responses to a timescale present in the output of HVC. This interaction between a life-sustaining motor function (respiration) and telencephalic song motor control suggests a more general mechanism of how nonlinear integration of evolutionarily new brain structures into existing circuitry gives rise to diverse, new behavior. © 2013 Goldin et al.

Descripción: The inversion polymorphism of the cactophilic fly Drosophila buzzatii was studied in two natural populations. We assessed the temporal changes and microspatial population structure. We observed a significant increase in the frequency of arrangement 2J at the expense of 2ST in both populations. These gene arrangements appear to affect the life-history of flies differently. Environmental heterogeneity explains the karyotype coexistence in nature. The analysis of population structure showed that differentiation of inversion frequencies among individual breeding sites, the rotting clacodes of Opuntia vulgaris, was highly significant. The karyotypic frequencies did not depart significantly from Hardy-Weinberg expectations, neither in individual rots nor in the total population. These results suggest that the observed population structure can be easily accounted by random genetic drift.

Descripción: This paper presents the results of the application of terrestrial magnetometry in the study of waste deposits. The area chosen for the pilot study was located toward the south of the town of Gualeguaychú, in the southeastern Entre Rios province. This location was selected because it was known that operations were to cease and local authorities had an interest in verifying the presence of anomalies indicative of potentially dangerous environmental pollutants. Interpretation of the magnetic signal suggests that buried objects of high magnetic susceptibility are not large (smaller than containers of 1m in height). For that reason we discount the presence of drums of standard dimensions, the possible containers of toxic elements. The estimated depth of the objects of high susceptibility increases with the distance from the access road to the the area. © 2004 Asociación Geológica Argentina.

Descripción: We discuss the matching of the quark model to the effective mass operator of the 1/Nc expansion using the permutation group SN. As an illustration of the general procedure we perform the matching of the Isgur-Karl model for the spectrum of the negative parity L=1 excited baryons. Assuming the most general two-body quark Hamiltonian, we derive two correlations among the masses and mixing angles of these states which should hold in any quark model. These correlations constrain the mixing angles and can be used to test for the presence of three-body quark forces. © 2010 American Institute of Physics.

Descripción: We tested the applicability of Allen ' s rule in 47 species and 32 unnamed forms (populations that are probably good species or undefined taxa within a superspecies or species group) of the South American subterranean Hystricomorph rodents of the genus Ctenomys (tuco-tucos) (Rodentia: Ctenomyidae) by analyzing tail length in relation with head and body length, and body mass. Tail length allometry was analyzed by Reduced Major Axis regression while the possible correlation of relative tail length with temperature, precipitation and evapotranspiration variables was explored through Simultaneous Autoregression to account for spatial autocorrelations. Our results indicate that tuco-tucos do not follow Allen ' s rule but its converse, tail proportion relative to body mass increasing with latitude while body size decreases in the same direction (the trend is similar for tail length relative to head and body length but not statistically significant). Regarding climatic variables, the main predictors of relative tail length were temperature and evapotranspiration variables with trends confirming the positive (non-Allenian) correlation of relative tail length with latitude. We conclude that tuco-tucos, being almost fully subterranean, thermoregulate behaviorally by maintaining constant temperatures within their burrows independent of geographic location. The former confirms previous results that indicated that Ctenomys follows the converse to Bergmann ' s rule. Relative tail length variation would be a result of simple allometric growth. © 2011 by Walter de Gruyter.

Descripción: Samples obtained from four wells located at Bancalari, Buenos Aires Province, have been analysed in order to define textural parameters, petrofacies, palaeoenvironments and palaeoclimate evolution. The samples were obtained from the upper part of the Puelches Formation and from the Pampean and Postpampean sediments; in particular this paper highlights the informally named Preensenadense interval. Six textural groups (I to VI) and two petrofacies (A and B) have been recognised. Groups I to III represent fluvial sands (I), gradually overlain by backswamp and lake deposits (II -III), generated on very low slope and well-drained floodplains, with oxidizing conditions. Groups II and III are assigned to Preensenadense interval. The three groups are included in petrofacies A (Qt:F:L = 43:49:8), of sedimentary and basement provenance, which has an igneous metamorphic heavy suite, scarce hornblende and dominance of smectite over illite. By contrast the upper groups (IV to VI) show more varied depositional settings, including aeolian, fluvial and marine environments. Group IV is loessic and corresponds to the Ensenada Formation. Group V, the Lujan Formation (Río Salado Member), is composed of fluvial plain deposits deposited during a wet and temperate climate. Marine silts and clays (group VI) represent a transgression over terrestrial environments and record of the so-called Querandino event. The three upper groups are included in petrofacies B (12:56:32), and have a magmatic arc provenance, with plagioclase dominance and contributions of volcaniclastic and vitroclastic material. It contains a heavy-mineral suite mainly composed of hornblende and it has more illite than smectite. © 2005 Asociación Geológica Argentina.

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

Descripción: A recently proposed local Fukui function is used to predict the binding site of atomic hydrogen on silicon clusters. To validate the predictions, an extensive search for the more stable Sin H (n=3-10) clusters has been done using a modified genetic algorithm. In all cases, the isomer predicted by the Fukui function is found by the search, but it is not always the most stable one. It is discussed that in the cases where the geometrical structure of the bare silicon cluster suffers a considerable change due to the addition of one hydrogen atom, the situation is more complicated and the relaxation effects should be considered. © 2005 American Institute of Physics.

Descripción: A theoretical study of the relation between the relativistic formulation of the nuclear magnetic shielding and spin-rotation tensors is presented. To this end a theoretical expression of the relativistic spin-rotation tensor is formulated, considering a molecular Hamiltonian of relativistic electrons and non-relativistic nuclei. Molecular rotation effects are introduced considering the terms of the Born-Oppenheimer decomposition, which couple the electrons and nuclei dynamics. The loss of the simple relation linking both spectral parameters in the non-relativistic formulation is further analyzed carrying out a perturbative expansion of relativistic effects by means of the linear response within the elimination of the small component approach. It is concluded that relativistic effects on the spin-rotation tensor are less important than those of the nuclear magnetic shielding tensor. © 2012 American Institute of Physics.

Descripción: In the present work, numerical results of the nuclear spin-rotation (SR) tensor in the series of compounds HX (X=H,F,Cl,Br,I) within relativistic 4-component expressions obtained by Aucar [J. Chem. Phys. 136, 204119 (2012)10.1063/1.4721627] are presented. The SR tensors of both the H and X nuclei are discussed. Calculations were carried out within the relativistic Linear Response formalism at the Random Phase Approximation with the DIRAC program. For the halogen nucleus X, correlation effects on the non-relativistic values are shown to be of similar magnitude and opposite sign to relativistic effects. For the light H nucleus, by means of the linear response within the elimination of the small component approach it is shown that the whole relativistic effect is given by the spin-orbit operator combined with the Fermi contact operator. Comparison of "best estimate" calculated values with experimental results yield differences smaller than 2-3 in all cases. The validity of "Flygares relation" linking the SR tensor and the NMR nuclear magnetic shielding tensor in the present series of compounds is analyzed. © 2013 American Institute of Physics.

Descripción: We define a type of crossed product over braided Hopf algebras, which generalizes the ones introduced by Blattner, Cohen, and Montgomery, and Doi and Takeuchi, and we study some of its properties. For instance, we prove Maschke's Theorem for these new crossed products and we construct a natural Morita context which extends the one obtained by Cohen, Fischman, and Montgomery. © 2003 Elsevier Science (USA). All rights reserved.

Descripción: A harmonic oscillator model for reactive chemical collisions is proposed. The model is solved rigorously for the reaction H2 + H = H + H2. The results show the appearance of quite narrow resonance peaks for the reaction cross sections.

Descripción: We study a cost function for the aggregate behavior of all the agents involved in the minority game (MG) or the bar attendance model (BAM). The cost function allows us to define a deterministic, synchronous dynamic that yields results that have the main relevant features than those of the probabilistic, sequential dynamics used for the MG or the BAM. We define a temperature through a Langevin approach in terms of the fluctuations of the average attendance. We prove that the cost function is an extensive quantity that can play the role of an internal energy of the many-agent system while the temperature so defined is an intensive parameter. We compare the results of the thermal perturbation to the deterministic dynamics and prove that they agree with those obtained with the MG or BAM in the limit of very low temperature. © 2002 The American Physical Society.

Descripción: The characterization and the mechanical stability of charged thin shells with spherical symmetry are analyzed in the context of Einstein-Born-Infeld theory. The study of stability is performed by considering linearized perturbations preserving the symmetry of the static configurations. It is found that as the charge increases, the shells can be stable for a wider range of the parameters. © 2012 American Institute of Physics.

Descripción: 1. 1. The reaction between 5,5′-dithio-bis-(2-nitrobenzoic acid) (DTNB) and the SH groups of soybean callus succinyl-CoA synthetase has been investigated. At pH 8-6 and 25° C, four SH groups are titrable with DTNB in the native enzyme. No additional thiol groups have been revealed after unfolding of the protein with 8 M urea. 2. 2. The loss of enzymatic activity paralleled the decrease in the number of free SH groups. As with p-mercuribenzoate and other mercurials, reaction with DTNB also resulted in dissociation of the enzyme into subunits. © 1974.

Descripción: Our previously developed analytical infinite order sudden (IOS) quantum theory of triatomic photodissociation is extended to describe indirect photodissociation processes through a real or virtual intermediate state. The theory uses the IOS approximation for the dynamics in the final dissociative channels and an Airy function approximation for the continuum states. These approximations enable us to evaluate the multi-dimensional non-separable transition amplitudes analytically (as one-dimensional quadratures), despite the different natural coordinates for the initial bound, the intermediate resonant, and the final dissociative states. The fragment internal energy distributions are described as a function of the initial and final quantum states and the photon excitation energy. The theory readily permits the evaluation of rotational distributions for high values of the total angular momentum J in the initial bound molecular state, a feature that would be very difficult with close-coupled methods. In paper II we apply the theory to describe the photofragment yield spectrum of NOCl in the region of the T1(13A″)→S0(11A′) transition. © 1997 American Institute of Physics.

Descripción: Our previously developed analytical infinite order sudden quantum theory of triatomic photodissociation is generalized to compute fragment internal energy distributions when the initial triatomic rotational state has K ≠ 0. The dependence of product rotational energy distributions on initial rotational and vibrational state is illustrated through model computations for the direct NOCl photodissociation from the ground to the T1(1 3A″) potential energy surface. The calculations consider all J,K ≤ 9 and employ a repulsive potential that is fit to ab initio computations. Comparisons of fragment rotational distributions with previous semiclassical approximations further elucidate the role of the mapping of the initial state bending wave function onto the fragment rotational distributions and the influence of parent rotations on this mapping. The infinite order sudden quantum-mechanical distributions exhibit a more complex structure, but upon thermal averaging they are already transformed at T = 3 K into fairly broad rotational distributions. The present theory readily permits the calculations of energy distributions for initial states of high J and K. © 1994 American Institute of Physics.

Descripción: A Three-Dimensional Finite Volume Arbitrary Lagrangian-Eulerian simulation code was developed to study different plasma physics problems in 3D+t. The code is based on a complex multi-component species program with transport and radiation terms written and applied to plasma and fusion physics problems. Three different examples are shown: double-base chemical propellant combustion, ignition and propagation of a thermonuclear detonation wave, and, the development of the Kelvin-Helmholtz (KH) instability in local plane slab models of the magnetopause, showing the response of a background equilibrium to the excitation by finite amplitude perturbations generated upstream. © 2006 American Institute of Physics.

Descripción: Three-dimensional measurements of the ion flux along the filter of a magnetically filtered d-c vacuum arc are presented. The device includes a metallic plasma-generating chamber with cooper electrodes coupled to a substrate chamber through a quarter-torus magnetic filter. The filtering magnetic field was high enough to magnetize the electrons but not the ions. The ion current distribution was studied using a multi-element Cu probes, placed at three different positions along the filter. The ion saturation current of each probe was measured by biasing the probe at -70V with respect the grounded anode. Preliminary results of the three dimensional ion flux distribution and the floating potential of the plasma as functions of the bias filter voltage and magnetic field intensity are reported. © 2006 American Institute of Physics.

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

Descripción: Turbulent flows take place in a large variety of astrophysical objects, and often times are the source of dynamo generated magnetic fields. Much of the progress in our understanding of dynamo mechanisms, has been made within the theoretical framework of magnetohydrodynamics (MHD). However, for sufficiently diffuse media, the Hall effect eventually becomes non-negligible. We present results from simulations of the Hall-MHD equations. The simulations are performed with a pseudospectral code to achieve exponentially fast convergence. We study the role of the Hall effect in the dynamo efficiency for different values of the Hall parameter. © 2011 International Astronomical Union.

Descripción: The structures of three new polymeric lanthanide complexes, poly[[bis-(2,2′-bipyridine)-μ4-itaconato-di-μ3-itaconato- digadolinium(III)] tetra-hydrate], {[Gd 2(C 5H 4O 4) 3(C 10H 8N 2) 2]̇4H 2O} n , (I),poly[diaqua-(2,2′- bipyridine)di-μ3-itaconato-μ2-ita-conato-digadolinium(III)], [Gd 2(C 5H 404) 3(C 10H 8N 2)(H 2O) 2] n , (II), and poly-[[bis-(2,2′-bipyridine)-μ4-itaconato-di-μ3-itaconato-di- holmium(III)] dihydrate], {[Ho 2(C 5H 4O 4) 3(C 10H 8N 2) 2]̇2H2O} n , (III), have been solved from twinned specimens. Compound (I) presents a two-dimensional polymeric structure parallel to (011) built up around two independent nine-coordinated Gd centres displaying similar GdO 7N 2 environments, with both N-donor atoms in each provided by a chelating 2,2′-bipyridine (bpy) unit. The coord-inating O atoms are from three different itaconate (ita) anions (itaconic acid is 2-methyl-idene-butane-dioic acid). Compound (II) also presents two independent Gd centres (one ten- and the other ight-coordinated), but the overall formula and individual coordinations are different from those of (I). The chemical unit is in this case completed by one bpy ligand, three ita anions (one of them displaying a new, hitherto unreported, mu;3-O,O′:O′,O′′: O′′′ binding mode) and two aqua ligands. The whole structure is built up around a twofold rotation axis passing through both cations, as well as through the centre of the bpy ligand and one of the ita anions, thus making only half of the chemical unit independent. Finally, compound (III) presents a single independent Ho centre, a bpy unit and one and a half ita anions (one of them bisected by a twofold rotation axis) in the asymmetric unit, plus two (disordered) nonbonded solvent water mol-ecules. In compounds (II) and (III), those ita anions bisected by a symmetry element incompatible with the inter-nal symmetry of the ligand exhibit disorder in the C=CH 2 group. © 2009 International Union of Crystallography.

Descripción: We consider R and NS spectral flow sectors of type IIB superstring theory on AdS 3 × S 3 × T 4 in the context of the AdS 3/CFT 2 correspondence. We present a derivation of the vertex operators creating spectral flow images of chiral primary states previously proposed in the literature. We compute spectral flow conserving three-point functions involving these operators on the sphere. Using the bulk-to-boundary dictionary, we compare the results with the corresponding correlators in the dual conformal field theory, the symmetric product orbifold of T 4. In the limit of small string coupling, agreement is found in all the cases considered. © SISSA 2009.

Descripción: We determine how the differences in the treatment of the subfilter-scale physics affect the properties of the flow for three closely related regularizations of Navier-Stokes. The consequences on the applicability of the regularizations as subgrid-scale (SGS) models are also shown by examining their effects on superfilter-scale properties. Numerical solutions of the Clark-α model are compared to two previously employed regularizations, the Lagrangian-averaged Navier-Stokes α-model (LANS-α) and Leray-α, albeit at significantly higher Reynolds number than previous studies, namely, Re≈3300, Taylor Reynolds number of Re≈790, and to a direct numerical simulation (DNS) of the Navier-Stokes equations. We derive the de Kármán-Howarth equation for both the Clark-α and Leray-α models. We confirm one of two possible scalings resulting from this equation for Clark-α as well as its associated k-1 energy spectrum. At subfilter scales, Clark-α possesses similar total dissipation and characteristic time to reach a statistical turbulent steady state as Navier-Stokes, but exhibits greater intermittency. As a SGS model, Clark-α reproduces the large-scale energy spectrum and intermittency properties of the DNS. For the Leray-α model, increasing the filter width α decreases the nonlinearity and, hence, the effective Reynolds number is substantially decreased. Therefore, even for the smallest value of α studied Leray-α was inadequate as a SGS model. The LANS-α energy spectrum ∼k1, consistent with its so-called "rigid bodies," precludes a reproduction of the large-scale energy spectrum of the DNS at high Re while achieving a large reduction in numerical resolution. We find, however, that this same feature reduces its intermittency compared to Clark-α (which shares a similar de Kármán-Howarth equation). Clark-α is found to be the best approximation for reproducing the total dissipation rate and the energy spectrum at scales larger than α, whereas high-order intermittency properties for larger values of α are best reproduced by LANS-α. © 2008 American Institute of Physics.

Descripción: The three transition-metal complexes, (meso-5,7,7,12,14,14-hexa methyl-1,4,8,11-tetra azacyclo tetra decane-κ4 N)bis (perchlorato-κO)copper(II), [Cu(ClO4)2(C18H40N4)], (I), (meso-5,7,7,12,14,14-hexa methyl-1,4,8,11-tetra azacyclo tetra decane-κ4 N)bis (nitrato-κO)zinc(II), [Zn(NO3)2(C18H40N4)], (II), and aqua chlorido (meso-5,7,7,12,14,14-hexa methyl-1,4,8,11-tetraazacyclo tetra decane-κ4 N)copper(II) chloride, [CuCl(C18H40N4)(H2O)]Cl, (III), are described. The mol ecules display a very similarly distorted 4+2 octa hedral environment for the cation [located at an inversion centre in (I) and (II)], defined by the macrocycle N4 group in the equatorial sites and two further ligands in trans-axial positions [two O-ClO3 ligands in (I), two O-NO2 ligands in (II) and one chloride and one aqua ligand in (III)]. The most significant difference in mol ecular shape resides in these axial ligands, the effect of which on the intra- and inter molecular hydrogen bonding is discussed. In the case of (I), all strong hydrogen-bond donors are saturated in intra molecular inter actions, while weak inter molecular C - H⋯O contacts result in a three-dimensional network. In (II) and (III), instead, there are N - H and O - H donors left over for inter molecular inter actions, giving rise to the formation of strongly linked but weakly inter acting chains. © 2013 International Union of Crystallography.

Descripción: We study the resummation of large logarithmic QCD corrections for the process pp → H + X when the Higgs boson H is produced at high transverse momentum. The corrections arise near the threshold for partonic reaction and originate from soft gluon emission. We perform the all-order resummation at next-to-leading logarithmic accuracy and match the resummed result with the next-to-leading order perturbative predictions. The effect of resummation on the Higgs transverse momentum distribution at the LHC is discussed. © SISSA 2006.

Descripción: In this paper we propose a method, based on the Gabor transform, to quantify and visualize the time evolution of the traditional frequency bands defined in the analysis of electroencephalogram (EEG) series. The information obtained in this way can be used for the information transfer analyses of the epileptic seizure as well as for their characterization. We found an optimal correlation between EEG visual inspection and the proposed method in the characterization of paroxism, spikes, and other transient alterations of background activity. The dynamical changes during an epileptic seizure are shown through the phase portrait. The method proposed was examplified with EEG series obtained with depth electrodes in refractory epileptic patients. © 1995 The American Physical Society.

Descripción: In this paper we compare two methods, based on the Gabor and wavelet transforms, to quantify and visualize the time evolution of frequency contents of electroencephalogram (EEG) time series. We found an optimal correlation between EEG visual inspection and the proposed methods in the characterization of the frequency and energy content of characteristic activity during an epileptic seizure. The quasimonofrequency behavior observed in the epileptic EEG series, in a previous work using a Gabor analysis [J. Inst. Electr. Eng. 93, 429 (1946)], is confirmed with the analysis using a wavelet. Moreover, the method based on the wavelet transform allows us to build a detector of epileptic events. Both methods are exemplified with EEG series obtained with depth electrodes in refractory epileptic patients. © 1996 The American Physical Society.

Descripción: We exhibit a new method for showing lower bounds for time-space tradeoffs of polynomial evaluation procedures given by straight-line programs. From the tradeoff results obtained by this method we deduce lower space bounds for polynomial evaluation procedures running in optimal nonscalar time. Time, denoted by L, is measured in terms of nonscalar arithmetic operations and space, denoted by S, is measured by the maximal number of pebbles (registers) used during the given evaluation procedure. The time-space tradeoff function considered in this paper is LS2. We show that for "almost all" univariate polynomials of degree at most d our time-space tradeoff functions satisfy the inequality LS2≥d8. From this we conclude that for "almost all" degree d univariate polynomials, any nonscalar time optimal evaluation procedure requires space at least S≥cd, where c>0 is a suitable universal constant. The main part of this paper is devoted to the exhibition of specific families of univariate polynomials which are "hard to compute" in the sense of time-space tradeoff (this means that our tradeoff function increases linearly in the degree). © 2000 Academic Press.

Descripción: We put limits on the time variation of the electron mass in the early universe using observational primordial abundances of D, 4He, and 7Li, recent data from the cosmic microwave background, and the 2dFGRS power spectrum. Furthermore, we use these constraints together with other astronomical and geophysical bounds from the late universe to test the Barrow-Magueijo model for the variation in me. From our analysis we obtain -0.615 < Gω/c4 < -0.045 (3 σ interval), in disagreement with the result obtained in the original paper. © 2008. The American Astronomical Society. All rights reserved.

Descripción: Aims. We analyze different data of the variation of the fine structure constant obtained with different methods to check their consistency.Methods. We test consistency using the modified student test and confidence intervals. We split the data sets into smaller intervals. A criterion for this selection is proposed.Results. Results show consistency for reduced intervals for each pair of data sets considered.Conclusions. Results are at variance with the ones obtained considering mean values over the whole interval. © 2008 ESO.

Descripción: Aims.We calculate the bounds on the variation in the fine structure constant at the time of primordial nucleosynthesis and at the time of neutral hydrogen formation. We used these bounds and other bounds from the late universe to test the Bekenstein model.Methods.We modified the Kawano code, CAMB, and CosmoMC to include the possible variation in the fine structure constant. We used observational primordial abundances of D, He, and Li, recent data from the cosmic microwave background, and the 2dFGRS power spectrum, to obtain bounds on the variation in . We calculated a piecewise solution to the scalar field equation of the Bekenstein model in two different regimes: i) matter and radiation, ii) matter and cosmological constant. We match both solutions with the appropriate boundary conditions. We performed a statistical analysis, using the bounds obtained from the early universe and other bounds from the late universe to constrain the free parameters of the model.Results.Results are consistent with no variation in for the early universe. Limits on are inconsistent with the scale length of the theory being larger than the Planck scale.Conclusions.In order to fit all observational and experimental data, the assumption > implied in Bekenstein's model has to be relaxed. © 2008 ESO.

Descripción: In plant sexual reproduction, water and solute movement are tightly regulated, suggesting the involvement of aquaporins. We previously identified TIP5;1 and TIP1;3 as the only Arabidopsis aquaporin genes that are selectively and highly expressed in mature pollen, and showed that they can transport both water and urea when expressed in Xenopus oocytes. Here, we show that TIP5;1 has unusual characteristics, as its water transport activity is regulated by pH. Analysis of the water transport activity of a mutant version of TIP5;1 (TIP5;1-H131A) and amino acid alignment with other plant aquaporins regulated by pH suggested that a conserved motif is involved in pH sensing. GFP-TIP5;1 is located in the mitochondria of pollen tubes. The single mutants tip1;3 and tip5;1, as well as the tip1;3 tip5;1 double mutant, are fertile, but all mutants had shorter than normal pollen tubes when germinated in vitro in the absence of exogenous nitrogen. Thus, we propose that TIP5;1 and TIP1;3 are involved in nitrogen recycling in pollen tubes of Arabidopsis thaliana. © 2010 The Authors. The Plant Journal © 2010 Blackwell Publishing Ltd.

Descripción: Used vehicle tires are a source of mosquito vectors and a means of their introduction and expansion. With the aim of assessing the effects of urbanisation on the main mosquito vectors in temperate Argentina, the infestation levels of Aedes aegypti (L.) and Culex pipiens L. were studied in used tires from highly urbanised cities to low-urbanised small towns in Buenos Aires. Immatures of both species accounted for 96% of the 9,722 individuals collected; the total individuals collected represented seven species. The percentage of water-filled tires containing mosquitoes [container index (CI)] was 33% and the percentage of infested sites [site index (SI)] was 65.2%. These indexes decreased significantly from low to high urbanisation levels for both mosquito species. The relative abundance (RA) of Ae. aegypti immatures was slightly higher toward large cities, but showed no difference for Cx. pipiens. The CI of shaded tires was significantly higher than the CI of exposed tires for both mosquito species. There was no difference in RA values between shaded and sunlit tires. The CI and the SI were highest during the summer across the urbanisation levels, except for Cx. pipiens, which continued to increase during the autumn in small towns. Results related to urbanisation gradient, sunlit exposure and seasonality are discussed.

Descripción: The use of 5-aminolaevulinic acid (ALA) is gaining increasing attention for photosensitization in photodynamic therapy of superficially localized tumours. The aim of this work was to determine the kinetics of porphyrin generation in tissues after topical application of ALA delivered in different vehicles on the skin overlying the tumour and normal skin of mice. Maximal accumulation was found in tumour 3 h after ALA application in both cream and lotion preparations. Normal and overlying tumour skin tissues showed different kinetic patterns, reflecting histological changes when the latter is invaded by tumour cells. Liver, kidney, spleen and blood porphyrins also raised from basal levels, showing that ALA and/or ALA-induced porphyrins reach all tissues after topical application. During the first 24 h of ALA topical application, precursors and porphyrins are excreted by both urine and faeces. ALA lotion applied on the skin overlying the tumour induced higher accumulation of tumoural porphyrins than cream, and lotion applied on normal skin appeared to be the most efficient upon inducing total body porphyrins. This work has demonstrated the great influence of the formulation of ALA vehicle on penetration through the skin. Knowledge of the kinetics of porphyrin generation after different conditions of ALA application is needed for the optimization of diagnosis and phototherapy in human tumours.

Descripción: Endothelial cells, at the cell-cell borders, express PECAM-1, and have been implicated in vascular functions. The monoclonal antibody MEC 13.3 recognizes PECAM-1 molecule from mouse vessels and allows to analyze the ontogeny of mouse endothelium. At the present, little is known about the molecular basis of differentiation pathways of endothelial cells, that enables its morphological heterogeneity. The purpose of this study was to analyze the pattern of PECAM-1 expression, employing monoclonal antibody MEC 13.3, in cellular suspensions obtained from different mouse organs at pre and postnatal stages. Fluorescence activated cell sorter analysis showed a different profile of the glycoprotein expression in a cell population with size and granularity selected by 1G11 endothelial cell line. The expression differs from prenatal to postnatal developmental stages in a given organ, and among the organs studied. Another cell population, with a size and granularity higher than 1G11 endothelial cell line, coexists in cellular suspensions obtained from liver, gut and brain. These cells could be related to those detected by means of immunoenzyme methods which showed a non-differentiated morphology. The different PECAM-1 pattern expression could reflect potential organ-specific differentiation pathways during development and according to organs environment. The existence of another cell population with a size and granularity higher than 1G11 endothelial cell line required a phenotypic characterization.

Descripción: Brucella spp., like other pathogens, must cope with the environment of diverse host niches during the infection process. In doing this, pathogens evolved different type of transport systems to help them survive and disseminate within the host. Members of the TolC family have been shown to be involved in the export of chemically diverse molecules ranging from large protein toxins to small toxic compounds. The role of proteins from the TolC family in Brucella and other α-2-proteobacteria has been explored little. The gene encoding the unique member of the TolC family from Brucella suis (BepC) was cloned and expressed in an Escherichia coli mutant disrupted in the gene encoding TolC, which has the peculiarity of being involved in diverse transport functions. BepC fully complemented the resistance to drugs such as chloramphenicol and acriflavine but was incapable of restoring hemolysin secretion in the tolC mutant of & coli. An insertional mutation in the bepC gene strongly affected the resistance phenotype of B. suis to bile salts and toxic chemicals such as ethidium bromide and rhodamine and significantly decreased the resistance to antibiotics such as erythromycin, ampicillin, tetracycline, and norfloxacin. Moreover, the B. suis bepC mutant was attenuated in the mouse model of infection. Taken together, these results suggest that BepC-dependent efflux processes of toxic compounds contribute to B. suis survival inside the host. Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Descripción: The small community of the Tomárâho, an ethnic group culturally derived from the Zamucos, have become known in the South American and world anthropological scenario in recent times. This group, far from the banks of the Paraguay river, remained concealed from organized modern societies for many years. Like any other groups of people in close contact with nature, the Tomárâho developed a profound and rich world-view which parallels other more widely researched aboriginal cultures as well as showing distinctive features of their own. This is also apparent in their imagery of the sky and of the characters that are closely connected with the celestial sphere. This paper is based on the lengthy anthropological studies of G. Sequera. We have recently undertaken a project to carry out a detailed analysis of the different astronomical elements present in the imagined sky of the Tomárâho and other Chamacoco ethnic groups. We will briefly review some aspects of this aboriginal culture: places where they live, regions of influence in the past, their linguistic family, their living habits and how the advancement of civilization affected their culture and survival. We will later mention the fieldwork carried out for decades and some of the existing studies and publications. We will also make a brief description of the methodology of this work and special anthropological practices. Last but not least, we will focus on the Tomárâho conception of the sky and describe the research work we have been doing in recent times. © International Astronomical Union 2011.

Descripción: In this study, carried out in San Antonio Bay (Northern Argentinean Patagonia), we aimed to understand the relative importance of bottom-up and top-down controls on macroalgal blooms in a macrotidal system with high nutrient supply and high consumer abundance. Our results show that nutrients, pH, and O 2 concentrations were higher during low tide. A field experiment showed that the biomass accumulation rate of Ulva lactuca ranged from 6 to 12% d -1 and was reduced by herbivory by 60%. The biomass accumulation rate did not differ in thalli with different initial internal nutrient pools. There was a negative relationship between the percentage of algae consumed and the N content in algal tissues, suggesting compensatory feeding by herbivores. Herbivory reduced the biomass accumulation rate of U. lactuca when PO 4 3- or no nutrients were added, but not when NO 3 - was added. In the absence of herbivory, the addition of nutrients did not increase U. lactuca biomass accumulation rate. These results suggest that nutrients remain high enough for adequate time intervals to be assimilated by macroalgae and support blooms. Large water exchange during tidal changes, however, can diminish the potential negative effects of macroalgal accumulation (oxygen depletion, high ammonium concentrations) on herbivores such that herbivores can have a large impact on macroalgae. © Inter-Research 2011.

Descripción: This field experimental study simultaneously analysed the effects of predation (top-down) and nutrients (bottom-up) on planktonic communities (phytoplankton, zooplankton, heterotrophic nanoflagellates and ciliates) in a warm temperate wetland in South America. The top-down and bottom-up controls were investigated by assessing the impact of omnivorous-planktivorous fish (Jenynsia sp.) and the effects of nutrient input from natural lake sediments, respectively. Three treatments and a control were run in triplicate in mesocosms and samples were taken at Days 0, 3, 7 and 15. The control contained all the planktonic components while treatments included all planktonic components plus the addition of either planktivorous fish (F), natural wetland sediments in dialysis bags (S) or both of them (SF). A bottom-up effect due to nutrient release from sediment (mainly total phosphorus) was noticed in treatments S and SF. Phytoplankton abundance increased in all treatments compared with the control. Thus, phytoplankton appeared to be bottom-up controlled while fish exerted a strong predation pressure on zooplankton (top-down), because treatments F and SF showed a marked decrease in mesozooplankton abundance. The results obtained in this study agree with the hypothesis that phytoplankton regulation by zooplankton might be weaker in warm temperate systems than in temperate ones.

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

Descripción: A chaotic three-dimensional flow can be described through the topological organization of the periodic orbits shadowed by an attractor. If only a scalar variable is available, this description requires the embedding of the data. In this work we report an example in which the reconstructed topology of the flow depends on the chosen embedding. © 1995 The American Physical Society.

Descripción: A recent paper [1] claims that topologically massive gravity contains only chiral boundary excitations at a particular value of the Chern-Simons coupling. On the other hand, propagating bulk degrees of freedom with negative norm were found even at the chiral point in [2]. The two references use very different methods, making comparison of their respective claims difficult. In this letter, we use the method of [1] to construct a tower of physical propagating bulk states satisfying standard AdS boundary conditions. Our states have finite norm, with sign opposite to that of right-moving boundary excitations. Our results thus agree with [2] and disagree with [1]. © 2008 SISSA.

Descripción: Toric dynamical systems are known as complex balancing mass action systems in the mathematical chemistry literature, where many of their remarkable properties have been established. They include as special cases all deficiency zero systems and all detailed balancing systems. One feature is that the steady state locus of a toric dynamical system is a toric variety, which has a unique point within each invariant polyhedron. We develop the basic theory of toric dynamical systems in the context of computational algebraic geometry and show that the associated moduli space is also a toric variety. It is conjectured that the complex balancing state is a global attractor. We prove this for detailed balancing systems whose invariant polyhedron is two-dimensional and bounded. © 2009 Elsevier Ltd. All rights reserved.

Descripción: We pose the problem of generalizing Dupire's equation for the price of call options on a basket of underlying assets. We present an analogue of Dupire's equation that holds in the case of several underlying assets provided the volatility is time dependent but not asset-price dependent. We deduce it from a relation that seems to be of interest on its own. © 2009 Elsevier Inc. All rights reserved.

Descripción: We derive an asymptotic formula for the eigenvalues of the Aharonov-Bohm annular billiard (ABAB) that improves and corrects previous estimates. Employing semiclassical arguments we relate the limitations of the procedure to the topology of the classical phase space of the system. © 2001 American Institute of Physics.

Descripción: The insect tracheal system is a continuous tubular network that ramifies into progressively thinner branches to provide air directly to every organ and tissue throughout the body. During embryogenesis the basic architecture of the tracheal system develops in a stereotypical and genetically controlled manner. Later, in larval stages, the tracheal system becomes plastic, and adapts to particular oxygen needs of the different tissues of the body. Oxygen sensing is mediated by specific prolyl-4-hydroxylases that regulate protein stability of the alpha subunit of oxygen-responsive transcription factors from the HIF family. Tracheal cells are exquisitely sensitive to oxygen levels, modulating the expression of hypoxia-inducible proteins that mediate sprouting of tracheal branches in direction to oxygen-deprived tissues. © 2009 Elsevier Ltd. All rights reserved.

Descripción: Biological invasions are excellent opportunities to study the evolutionary forces leading to the adaptation of a species to a new habitat. Knowledge of the introduction history of colonizing species helps tracking colonizing routes and assists in defining management strategies for invasive species. The Palearctic species Drosophila subobscura is a good model organism for tracking colonizations since it was detected in Chile and western North America three decades ago and later on in the Atlantic coast of Argentina. To unravel the origin of the Argentinean colonizers two populations have been analysed with several genetic markers. Chromosomal arrangements and microsatellite alleles found in Argentina are almost similar to those observed in Chile and USA. The lethal allelism test demonstrates that the lethal gene associated with the O5 inversions in Argentina is identical to that found in Chile and USA, strongly supporting the hypothesis that all the American colonizing populations originated from the same colonization event. A secondary bottleneck is detected in the Argentinean populations and the genetic markers suggest that these populations originated from the invasion of 80-150 founding individuals from Chile. © 2008 European Society For Evolutionary Biology.

Descripción: Chemical trails have been shown to act as an orientation cue in some ant species. Here, I report that the trail-laying behaviour in the nectar-feeding ant, Camponotus rufipes, varies with the concentration of the sucrose solutions collected. Single workers collected solutions of different sucrose concentrations (5, 20, and 40 in weight) during 4 consecutive visits to the resource, and their trail-marking behaviour was recorded on soot-coated slides during their first and last visits. Results suggest that these chemical trails provide both an orientation cue between the nest and the food source, as previously suggested for Camponotus ants, as well as information about food quality. © 2011 Pablo E. Schilman.

Descripción: The stress response involves complex physiological mechanisms that maximize behavioral efficacy during attack or defense and is highly conserved in all vertebrates. Key mediators of the stress response are pituitary hormones encoded by the proopiomelanocortin gene (POMC). Despite conservation of physiological function and expression pattern of POMC in all vertebrates, phylogenetic footprinting analyses at the POMC locus across vertebrates failed to detect conserved noncoding sequences with potential regulatory function. To investigate whether ortholog POMC promoters from extremely distant vertebrates are functionally conserved, we used 5′-flanking sequences of the teleost fish Tetraodon nigroviridis POMCα gene to produce transgenic mice. Tetraodon POMCα promoter targeted reporter gene expression exclusively to mouse pituitary cells that normally express Pomc. Importantly, transgenic expression in mouse corticotrophs was increased after adrenalectomy. To understand how conservation of precise gene expression mechanisms coexists with great sequence divergence, we investigated whether very short elements are still conserved in all vertebrate POMC promoters. Multiple local sequence alignments that consider phylogenetic relationships of ortholog regions identified a unique 10-bp motif GTGCTAA(T/G)CC that is usually present in two copies in POMC 5′-flanking sequences of all vertebrates. Underlined nucleotides represent totally conserved sequences. Deletion of these paired motifs from Tetraodon POMCα promoter markedly reduced its transcriptional activity in a mouse corticotropic cell line and in pituitary POMC cells of transgenic mice. In mammals, the conserved motifs correspond to reported binding sites for pituitary-specific nuclear proteins that participate in POMC transcriptional regulation. Together, these results demonstrate that mechanisms that participate in pituitary-specific and hormonally regulated expression of POMC have been preserved since mammals and teleosts diverged from a common ancestor 450 million years ago despite great promoter sequence divergence. Copyright © 2007 by The Endocrine Society.

Descripción: Background. Considering that sunflower production is expanding to arid regions, tolerance to abiotic stresses as drought, low temperatures and salinity arises as one of the main constrains nowadays. Differential organ-specific sunflower ESTs (expressed sequence tags) were previously generated by a subtractive hybridization method that included a considerable number of putative abiotic stress associated sequences. The objective of this work is to analyze concerted gene expression profiles of organ-specific ESTs by fluorescence microarray assay, in response to high sodium chloride concentration and chilling treatments with the aim to identify and follow up candidate genes for early responses to abiotic stress in sunflower. Results. Abiotic-related expressed genes were the target of this characterization through a gene expression analysis using an organ-specific cDNA fluorescence microarray approach in response to high salinity and low temperatures. The experiment included three independent replicates from leaf samples. We analyzed 317 unigenes previously isolated from differential organ-specific cDNA libraries from leaf, stem and flower at R1 and R4 developmental stage. A statistical analysis based on mean comparison by ANOVA and ordination by Principal Component Analysis allowed the detection of 80 candidate genes for either salinity and/or chilling stresses. Out of them, 50 genes were up or down regulated under both stresses, supporting common regulatory mechanisms and general responses to chilling and salinity. Interestingly 15 and 12 sequences were up regulated or down regulated specifically in one stress but not in the other, respectively. These genes are potentially involved in different regulatory mechanisms including transcription/translation/protein degradation/protein folding/ROS production or ROS-scavenging. Differential gene expression patterns were confirmed by qRT-PCR for 12.5% of the microarray candidate sequences. Conclusion. Eighty genes isolated from organ-specific cDNA libraries were identified as candidate genes for sunflower early response to low temperatures and salinity. Microarray profiling of chilling and NaCl-treated sunflower leaves revealed dynamic changes in transcript abundance, including transcription factors, defense/stress related proteins, and effectors of homeostasis, all of which highlight the complexity of both stress responses. This study not only allowed the identification of common transcriptional changes to both stress conditions but also lead to the detection of stress-specific genes not previously reported in sunflower. This is the first organ-specific cDNA fluorescence microarray study addressing a simultaneous evaluation of concerted transcriptional changes in response to chilling and salinity stress in cultivated sunflower.

Descripción: We studied the transepithelial potential difference (TEPD) and 22Na flux across isolated perfused gills (anterior pair 5 and posterior pairs 6-8) of the crab Chasmagnathus granulatus acclimated to either hypo- or hyper-osmotic conditions. The gills of crabs acclimated to low salinity, perfused and bathed with 10%‰ saline solutions, produced the following TEPDs (hemolymph side with respect to bath side): 0.4±0.7, -10.2±1.6, -10.8±1.3 and -6.7±1.3mV for gills 5, 6, 7 and 8, respectively. Gills 6, 7 and 8 did not differ significantly. Reducing the saline concentration of bath and perfusate from 30%‰ to 20%‰ or 10%‰ increased significantly the TEPDs of these gills. TEPDs of gill 6 (representative of posterior gills) were reduced by 69±5% and 60±5% after perfusion with ouabain or BaCl2 (5mmoll-1 each), respectively. The same gill showed a net ouabain-sensitive Na+ influx of 1150±290 μequiv g-1h-1. Gill 6 of crabs acclimated to high salinity produced TEPDs of -1.5±0.1 and -1.3±0.09mV after perfusion with 30%‰ or 40%‰ salines, respectively. Perfusion with ouabain or BaCl2 reduced TEPDs by 76±7% and 86±4%, respectively. A net ouabain-sensitive Na+ efflux of 2282±337 μequiv g-1h-1 was recorded in gill 6 perfused with 38%‰ saline.

Descripción: Nucleotide variation was studied in a 1.1 kb section of the coding region of an Esterase gene (Est-A) that maps in the center of the segments rearranged by polymorphic inversions in the cactophilic Drosophila buzzatii. We examine 30 homozygous second-chromosome lines differing in gene arrangement and three D. koepferae isofemale lines as outgroups. Our data show that Est-A is a highly polymorphic gene at both synonymous and replacement sites. Significant departures from homogeneity in the distribution of the ratio of silent polymorphism to divergence predicted by the neutral theory reveals a local excess of silent polymorphism. This is consistent with the presence of two apparent narrow peaks of elevated silent polymorphism surrounding nonconservative amino acid substitutions. These polymorphisms as well as others at synonymous and nonsynonymous sites are shared with D. koepferae. We suggest that the presence of shared nucleotide polymorphisms is probably due to interspecific gene flow and/or balancing selection acting on replacement variants and/or to a decreased probability of loss of ancestral polymorphisms caused by linkage to an adaptive inversion polymorphism. Recurrent mutation and persistence of neutral ancestral polymorphisms cannot, however, be ruled out. The analysis of the distribution of nucleotide variation among the three chromosomal arrangements sampled reveals that derived arrangements (J and JZ3) are less polymorphic than the ancestral ST, and that the widely distributed ST and J arrangements are genetically differentiated. However, a significant number of polymorphisms are shared between arrangements, suggesting frequent exchange either from gene conversion or from double crossovers in heterokaryotypes. Finally, our present results in combination with data of sequence variation at the breakpoints of inversion J suggest that this old gene arrangement has risen in frequency in relatively recent times.

Descripción: In this work, we explored theoretically the transport of organelles driven along microtubules by molecular motors of opposed polarities using a stochastic model that considers a Langevin dynamics for the cargo, independent cargo-motor linkers and stepping motion for the motors. It has been recently proposed that the stiffness of the motor plays an important role when multiple motors collectively transport a cargo. Therefore, we considered in our model the recently reported values for the stiffness of the cargo-motor linker determined in living cells (~0.01 pN/nm, [1]) which is significantly lower than the motor stiffness obtained in in vitro assays and used in previous studies. Our model could reproduce the multimodal velocity distributions and typical trajectory characteristics including the properties of the reversions in the overall direction of motion observed during melanosome transport along microtubules in Xenopus laevis melanophores. Moreover, we explored the contribution of the different motility states of the cargo-motor system to the different modes of the velocity distributions and could identify the microscopic mechanisms of transport leading to trajectories compatible with those observed in living cells. Finally, by changing the attachment and detachment rates, the model could reproduce the different velocity distributions observed during melanosome transport along microtubules in Xenopus laevis melanophores stimulated for aggregation and dispersion. Our analysis suggests that active tug-of-war processes with loose mechanical coupling can account for several aspects of cargo transport along microtubules in living cells. © 2012 Bouzat et al.

Descripción: The cellular resistance to tumor necrosis factor (TNF) of most cell types has been attributed to both a protective pathway induced by this cytokine and the preexistence of protective factors in the target cell. NF-κB has been postulated as one of the principal factors involved in antiapoptotic gene expression control on TNF-resistant cells. We have previously shown that glucocorticoids protect the naturally TNF-sensitive L-929 cells from apoptosis. Here we analyze the role of NF-κB and glucocorticoids on TNF-induced apoptosis in L-929 cells. We found that inhibition of NF-κB enhanced the sensitivity to TNF-induced apoptosis. Glucocorticoids inhibited NF-κB transactivation via IκB induction. Moreover, glucocorticoids protected from TNF-induced apoptosis even when NF-κB activity was inhibited by stable or transient expression of the superrepressor IκB. These results demonstrate that although glucocorticoids inhibit NF-κB transactivation in these cells, this is not required for their protection from TNF-induced apoptosis. (C) 2000 Elsevier Science B.V.

Descripción: The variability of atmospheric midlatitudinal ozone between 1980 and 2000 over the Southern Hemisphere is discussed. The distribution of ozone and ozone change during the seasonal cycle is discussed using Total Ozone Mapping Spectrometer Nimbus and Earth Probe data binned at 72 (30° longitude by 5° latitude) bins, between 60° and 30°S. Rather than using a standard trend approach, the annual mean time series for each bin were fitted with a cubic polynomial. The results show that in the zonal mean sense there is a sizable, latitude-dependent slowdown of the ozone loss from the early 1990s onward, but when individual bins are considered, significant longitudinal patterns of ozone change appear, with both positive (enhancement) and negative (depletion) changes in total ozone. Thus regional evolution remains important as an indicator both of chemical depletion evolution and the relation with climate. Such longitudinal behavior is limited in the subtropics and grows toward the subpolar edge of the sampled region. For example, a large decrease was observed over southern South America in the 1990s, but during the 1990s there was only a limited change. The analysis for January, June, and October over the 20-year period shows changes in the evolution along the year, both in time and space. Furthermore, such seasonally dependent changes reach a peak in October, as would be expected. The October pattern of interannual variability could be linked to Southern Annular Mode, though there probably are some other processes driving it. Copyright 2005 by the American Geophysical Union.

Descripción: The Ischigualasto-Villa Union basin developed as a consequence of processes taking place at the transition between Sierras Pampeanas and Precordillera, together with the Gondwana extension and ultimate break-up since the Upper Palaeozoic-Triassic (Lower Jurassic ?). In the Ischigualasto region the basin is characterized by accumulations of continental sediments and contemporaneous mafic magmatic rocks. This paper presents data on the basalts and trachytes, which are alkaline rocks of the basalt-trachybasalt-trachyte series. Petrology indicates high pressure and temperature involving the fractionation of olivine, magnetite (Ti-magnetite), ilmenite, cpx, Ca feldspar and apatite. Flows were extruded through fracture-related vents and/or monogenetic volcanoes constructed of piles of thick and viscous lavas. These rocks seem to correspond and are interpreted as being the product of fast magmatic ascent and subsequent intrusion or flow. Temporary storage in smaller chambers at intermediate depth could have been the mechanism for the differentiation process.

Descripción: Triassic clastic and volcanic rocks from the Precordillera were deposited in the Cuyana rift basin filling half-graben systems. Contractional/transpressional Andean tectonics leads to the almost complete inversion of some portions of the basin which resulted in present-day isolated, structurally controlled outcrops of these Triassic rocks. In the Southern Precordillera both the degree of Neogene tectonic inversion and structural compexities are variable. At the regional scale, these variations in Andean deformation are related to first order anisotropies like the Cuyana basin borders and previous shear zones of Permian age (San Rafael orogenic phase). This paper focuses on the kinematic analysis done in the Cerro Manantial thrust sheet area (Cordón San Bartolo, central sector of the South Precordillera) where tectonic inversion was not that strong and the influence of oblique strain zones is practically null. Four sets of extensional/ transtensional faults were recognized affecting Triassic sedimentary rocks of the El Cielo Formation (Uspallata Group) at the Quebrada El Salto. Fault displacements are of decimetric to metric scale. Mesoscopic kinematic indicators (en-échèlon tensional gashes, Riedel shear fractures, sigmoidal fractures) were measured. Once Andean deformation was restored, a NNE direction for the Triassic extension was determined. Considering a northern branch of the Cuyana basin trending NNW (Az. 150°) and oblique to the direction of extension (Az. 35-40°), a sinistral strike-slip component could be inferred for this portion of the basin.

Descripción: The Atuel depocentre corresponds to a Late Triassic - Early Jurassic NNW-trending subbasin, located in the northern sector of the Neuquén basin. Based on pre-existing stratigraphical data and present structural analysis we propose that the Atuel depocentre is bounded by the presence of two NNW-trending major normal faults, named Alumbre and La Manga. These faults are inferred to have controlled the development of two west-facing half-grabens: the Río Blanco, a completely emerged half-graben, and the western Arroyo Malo, a completely submerged half-graben. The structural model presented here is based on the assumption that both, the basement structural grain and the regional extension direction, exerted a first-order control in the development and evolution of the Atuel depocentre. During the early stage of rifting (pre-Rhaetian - Middle Hettangian) the pre-Triassic Alumbre and La Manga faults reactivated in an oblique mode. During the second episode of rifting, both Alumbre and La Manga faults continued to play, while WNW-trending normal fault developed in order to accommodate the strain inside both half-grabens. The third extensional event began with an abrupt marine rise inside the Arroyo Malo half-graben during late Middle Hettangian, as a result of the last displacement of the Alumbre fault, and finished with an abrupt marine drop associated with the desactivation of the La Manga fault.

Descripción: An entomological and serological survey was performed in three localities of the Department of Concepción, Province of Corrientes, Argentina in 1998 and 1999, to identify triatomines species involved in domestic and wild transmission of Chagas disease. Triatomines were collected by man/hour capture in 32 houses randomly selected and 44 nearby outdoor ecotopes. Trypanosoma cruzi infection in triatomines was assessed by direct microscopic observation (400x) of feces and polymerase chain reaction. Serological techniques used for people were Indirect Hemagglutination Test and Indirect Fluorescent Test. Triatomines were collected in 28.1% of the houses and 31.8% of the wild biotopes. Triatoma infestans (Klug 1834) was exclusively found indoors and T. cruzi infected 60% of them. Triatoma sordida (Stål 1859) was mainly found in extradomtestic ecotopes where trypanosome infection rate reached 12.7%. Serological study of 98 local people showed that 29.6% were seroreactive; most of their houses were closed to wild biotopes colonized by T. sordida. Results indicate that there is an active T. infestans mediated transmission of Chagas disease in this zone that yields important human prevalence and that the populations of T. sordida in wild biotopes not only sustain the wild T. cruzi cycle but also represent an actual risk for people living in the area.

Descripción: From a Lie algebra g satisfying Z(g)=0 and Λ2(g)g=0 (in particular, for g semisimple) we describe explicitly all Lie bialgebra structures on extensions of the form L=g×K{double-struck} in terms of Lie bialgebra structures on g (not necessarily factorizable nor quasi-triangular) and its biderivations, for any field K of characteristic different form 2, 3. If moreover, [g,g]=g, then we describe also all Lie bialgebra structures on extensions L=g×K{double-struck}n. In interesting cases we characterize the Lie algebra of biderivations. © 2013 Elsevier Inc.

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

Descripción: Argentine operational rawinsonde records spanning a 30-year period (1968-1997) were used to study the climatology of the tropopause from the subtropics to the southern mid-latitudes, approximately along the 60°W meridian. The thermal tropopause annual cycle as well as its variability was analyzed at three sites: Resistencia (RES), Ezeiza (EZE), and Comodoro Rivadavia (CRD). Single and double tropopause observations were studied, given the comparatively frequent occurrence of double tropopause events at all three sites. The tropopause behavior at RES and CRD is distinct, whereas at EZE it shows a winter evolution similar to the one at CRD and a summer evolution closer to the one at RES, in agreement with the annual evolution of the subtropical jet. The tropopause evolution is discussed under the light of the dynamic climatology of southern South America. In the presence of double tropopause events and in terms of potential temperature, it should be noted that the upper tropopause temperature is close to the 380 K isentropic, i.e. the tropical tropopause layer. Moreover, the lower tropopause and single tropopause events are fairly close together, i.e. coincident with the lowermost stratosphere. Considering previous research and results from the present analysis, a definition of Extratropical Tropopause Layer (ExTL) is introduced in this work. It is proposed that the lowermost stratosphere should be regarded as the ExTL. Copyright © 2006 Royal Meteorological Society.

Descripción: Trypanosoma cruzi, the aetiological agent of Chagas' disease, is exposed to extremely different environment conditions during its life cycle, and transporters are key molecules for its adaptive regulation. Amino acids, and particularly arginine, are essential components in T. cruzi metabolism. In this work, a novel T. cruzi arginine permease was identified by screening different members of the AAAP family (amino acid/auxin permeases) in yeast complementation assays using a toxic arginine analogue. One gene candidate, TcAAAP411, was characterized as a very specific, high-affinity, l-arginine permease. This work is the first identification of the molecular components involved specifically in amino acid transport in T. cruzi and provides new insights for further validation of the TcAAAP family as functional permeases. © 2010 Federation of European Microbiological Societies.

Descripción: By using improved pulsed field gel electrophoresis conditions, the molecular karyotype of the reference clone CL Brener selected for Trypanosoma cruzi genome project was established. A total of 20 uniform chromosomal bands ranging in size from 0.45 to 3.5 Megabase pairs (Mbp) were resolved in a single run. The weighted sum of the chromosomal bands was approximately 87 Mbp. Chromoblots were hybridized with 39 different homologous probes, 13 of which identified single chromosomes. Several markers showed linkage and four different linkage groups were identified, each comprising two markers. Densitometric analysis suggests that most of the chromosomal bands contain two or more chromosomes representing either homologous chromosomes and/or heterologous chromosomes with similar sizes.

Descripción: The protozoan parasite Trypanosoma cruzi, the agent of Chagas disease, has a large number of mucin molecules on its surface, whose expression is regulated during the life cycle. These mucins are the main acceptors of sialic acid, a monosaccharide that is required by the parasite to infect and survive in the mammalian host. A large mucin-like gene family named TcMUC containing about 500 members has been identified previously in T. cruzi. TcMUC can be divided into two subfamilies according to the presence or absence of tandem repeats in the central region of the genes. In this work, T. cruzi parasites were transfected with one tagged member of each subfamily. Only the product from the gene with repeats was highly O-glycosylated in vivo. The O-linked oligosaccharides consisted mainly of β-D-Galp(1→4)-GlcNAc and β-D-Galp(1→4)[β-D-Galp(1→6)]-D-GlcNAc. The same glycosyl moieties were found in endogenous mucins. The mature product was anchored by glycosylphosphatidylinositol to the plasma membrane and exposed to the medium. Sera from infected mice recognized the recombinant product of one repeats-containing gene thus showing that they are expressed during the infection. TcMUC genes encode a hypervariable region at the N terminus. We now show that the hypervariable region is indeed present in the exposed mature N termini of the mucins because sera from infected hosts recognized peptides having sequences from this region. The results are discussed in comparison with the mucins from the insect stages of the parasite (Di Noia, J. M., D'Orso, I., Sanchez, D. O., and Frasch, A. C. C. (2000) J. Biol. Chem. 275, 10218-10227) which do not have variable regions.

Descripción: A model is presented for generation of fast solar wind in coronal holes, relying on heating that is dominated by turbulent dissipation of MHD fluctuations transported upward in the solar atmosphere. Scale-separated transport equations include large-scale fields, transverse Alfvénic fluctuations, and a small compressive dissipation due to parallel shears near the transition region. The model accounts for proton temperature, density, wind speed, and fluctuation amplitude as observed in remote sensing and in situ satellite data. © 2010. The American Astronomical Society. All rights reserved..

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

Descripción: Magnetohydrodynamic turbulence has been proposed as a mechanism for the heating of coronal active regions, and has therefore been actively investigated in recent years. According to this scenario, a turbulent regime is driven by footpoint motions. The energy being pumped this way into active region loops, is efficiently transferred to small scales due to a direct energy cascade. The ensuing generation of fine scale structures, which is a natural outcome of turbulent regimes, helps to enhance the dissipation of either waves or DC currents. We present an updated overview of recent results on turbulent coronal heating. To illustrate this theoretical scenario, we simulate the internal dynamics of a coronal loop within the reduced MHD approximation. The application of a stationary velocity field at the photospheric boundary leads to a turbulent stationary regime after several photospheric turnover times. This regime is characterized by a broadband power spectrum and energy dissipation rate levels compatible with the heating requirements of active region loops. Also, the energy dissipation rate displays a complex superposition of impulsive events, which we associate to the so-called nanoflares. A statistical analysis yields a power law distribution as a function of their energies, which is consistent with those obtained from observations. We also study the distributions of peak dissipation rate and duration of these events. © 2008 International Astronomical Union.

Descripción: Concentration gradients inside cells are involved in key processes such as cell division and morphogenesis. Here we show that a model of the enzymatic step catalized by phosphofructokinase (PFK), a step which is responsible for the appearance of homogeneous oscillations in the glycolytic pathway, displays Turing patterns with an intrinsic length-scale that is smaller than a typical cell size. All the parameter values are fully consistent with classic experiments on glycolytic oscillations and equal diffusion coefficients are assumed for ATP and ADP. We identify the enzyme concentration and the glycolytic flux as the possible regulators of the pattern. To the best of our knowledge, this is the first closed example of Turing pattern formation in a model of a vital step of the cell metabolism, with a built-in mechanism for changing the diffusion length of the reactants, and with parameter values that are compatible with experiments. Turing patterns inside cells could provide a check-point that combines mechanical and biochemical information to trigger events during the cell division process. © 2007 Strier, Ponce Dawson.

Descripción: In an unpublished manuscript, Alan Turing gave a computable construction to show that absolutely normal real numbers between 0 and 1 have Lebesgue measure 1; furthermore, he gave an algorithm for computing instances in this set. We complete his manuscript by giving full proofs and correcting minor errors. While doing this, we recreate Turing's ideas as accurately as possible. One of his original lemmas remained unproved, but we have replaced it with a weaker lemma that still allows us to maintain Turing's proof idea and obtain his result. © 2007 Elsevier Ltd. All rights reserved.

Descripción: We consider the generalization of two classical periodic problems to the context of time scales. On the one hand, we generalize a celebrated result by Castro for the forced pendulum equation. On the other hand, we extend a well-known result by Nirenberg to a resonant system of equations on time scales. Furthermore, the results are new even for classical difference equations. © 2007 Texas State University.

Descripción: Fil:De Asúa, L.J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Descripción: We discuss the production of two hadrons in e+e- annihilation within the framework of perturbative QCD. The cross section for this process is calculated to next-to-leading order accuracy with a selection of variables that allows the consideration of events where the two hadrons are detected in the same jet. In this configuration we contemplate the possibility that the hadrons come from a double fragmentation of a single parton. The double-fragmentation functions required to describe the transition of a parton to two hadrons, are also necessary to completely factorize all collinear singularities. We explicitly show that factorization applies to order αs in the case of two-hadron production. © 2003 Elsevier B.V. All rights reserved.

Descripción: The partition function of two hard spheres in a hard-wall pore is studied, appealing to a graph representation. The exact evaluation of the canonical partition function and the one-body distribution function in three different shaped pores are achieved. The analyzed simple geometries are the cuboidal, cylindrical, and ellipsoidal cavities. Results have been compared with two previously studied geometries; the spherical pore and the spherical pore with a hard core. The search of common features in the analytic structure of the partition functions in terms of their length parameters and their volumes, surface area, edges length, and curvatures is addressed too. A general framework for the exact thermodynamic analysis of systems with few and many particles in terms of a set of thermodynamic measures is discussed. We found that an exact thermodynamic description is feasible based on the adoption of an adequate set of measures and the search of the free energy dependence on the adopted measure set. A relation similar to the Laplace equation for the fluid-vapor interface is obtained, which expresses the equilibrium between magnitudes that in extended systems are intensive variables. This exact description is applied to study the thermodynamic behavior of the two hard spheres in a hard-wall pore for the analyzed different geometries. We obtain analytically the external reversible work, the pressure on the wall, the pressure in the homogeneous region, the wall-fluid surface tension, the line tension, and other similar properties. © 2010 American Institute of Physics.

Descripción: In this work we analytically evaluate, for the first time, the exact canonical partition function for two interacting spherical particles into a spherical pore. The interaction with the spherical substrate and between particles is described by an attractive square-well and a square-shoulder potential. In addition, we obtain exact expressions for both the one particle and an averaged two particle density distribution. We develop a thermodynamic approach to few-body systems by introducing a method based on thermodynamic measures [I. Urrutia, J. Chem. Phys. 134, 104503 (2010)] for nonhard interaction potentials. This analysis enables us to obtain expressions for the pressure, the surface tension, and the equivalent magnitudes for the total and Gaussian curvatures. As a by-product, we solve systems composed of two particles outside a fixed spherical obstacle. We study the low density limit for a many-body system confined to a spherical cavity and a many-body system surrounding a spherical obstacle. From this analysis we derive the exact first order dependence of the surface tension and Tolman length. Our findings show that the Tolman length goes to zero in the case of a purely hard wall spherical substrate, but contains a zero order term in density for square-well and square-shoulder wall-fluid potentials. This suggests that any nonhard wall-fluid potential should produce a non-null zero order term in the Tolman length. © 2011 American Institute of Physics.

Descripción: The isomorphous title compounds, [Tr(S4O6)(C 12H12N2)2]·2C 3H7NO (Tr = CdII and ZnII), consist of metal centres to which one tetrathionate and two 4,4′-dimethyl-2, 2′-bipyridine chelating ligands bind. The structures are completed by two symmetry-related dimethylformamide solvent molecules. Each metal-centred complex is bisected by a twofold axis running through the metal centre and halving the chelating tetrathionate dianion through the central S - S bond. The ancillary symmetry-related 4,4′-dimethyl-2,2′-bipyridine ligands act as chelates. This results in a distorted six-coordinate geometry, with similar Tr - O/N distances but central angles differing substantially from 90 and 180°. Both ligands are basically featureless from a geometric point of view, with torsion angles in both coordinated tetrathionate groups suggesting a trend linking metal size (covalent radius) and ligand 'openness'. Packing is directed by (C - H)aromatic⋯O bridges and π-π offset stacked interactions defining chains along [001], further linked by weaker (C - H)methyl⋯O bridges, some of them mediated by the dimethylformamide solvent molecules. © 2013 International Union of Crystallography.

Descripción: We present the two-loop virtual corrections to Standard Model Higgs boson pair production via gluon fusion gg→ HH in the heavy top quark limit. Based on this result, we evaluate the corresponding cross section at the LHC at 14 TeV in the next-to-next-to-leading order soft-virtual approximation. We find an inclusive K-factor of about 2.4, resulting in an increase close to 23% with respect to the previous available calculation at next-to-leading order. As expected, we observe a considerable reduction in the renormalization and factorization scale dependence. © 2013 Elsevier B.V.

Descripción: We study the following two phase elliptic singular perturbation problem:Δ uε = βε (uε) + fε, in Ω ⊂ RN, where ε > 0, βε (s) = frac(1, ε) β (frac(s, ε)), with β a Lipschitz function satisfying β > 0 in (0, 1), β ≡ 0 outside (0, 1) and ∫ β (s) d s = M. The functions uε and fε are uniformly bounded. One of the motivations for the study of this problem is that it appears in the analysis of the propagation of flames in the high activation energy limit, when sources are present. We obtain uniform estimates, we pass to the limit (ε → 0) and we show that limit functions are solutions to the two phase free boundary problem:Δ u = f χ{u ≢ 0} in  Ω {set minus} ∂ {u > 0},| ∇ u+ |2 - | ∇ u- |2 = 2 M on  Ω ∩ ∂ {u > 0}, where f = lim fε, in a viscosity sense and in a pointwise sense at regular free boundary points. In addition, we show that the free boundary is smooth and thus limit functions are classical solutions to the free boundary problem, under suitable assumptions. Some of the results obtained are new even in the case fε ≡ 0. The results in this paper also apply to other combustion models. For instance, models with nonlocal diffusion and/or transport. Several of these applications are discussed here and we get, in some cases, the full regularity of the free boundary. © 2006 Elsevier SAS. All rights reserved.

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

Descripción: Two copper complex solvatomorphs, namely (3,10-C-meso-3,5,7,7,10,12,14,14- octamethyl-1,4,8,11-tetraazacyclotetradecane)bis(perchlorato-κO)copper(II) 1.2-hydrate, [Cu(ClO4)2(C18H 40N4)]·1.2H2O, (I), and (3,10-C-meso-3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclotetradecane) bis(perchlorato-κO)copper(II), [Cu(ClO4)2(C 18H40N4)], (II), are described and compared with each other and with a third, already reported, anhydrous diastereomer, denoted (III). Both compounds present very similar centrosymmetic coordination environments, with the CuII cation lying on an inversion centre in a distorted 4+2 octahedral environment, defined by the macrocyclic N4 group in the equatorial sites and two perchlorate groups in trans-axial positions [one of the perchlorate ligands in (I) is partially disordered]. The most significant difference in molecular shape is seen in the orientation of the perchlorate anions, and the influence of this on the intramolecular hydrogen bonding is discussed. The (partially) hydrated state of (I) favours the formation of chains along [011], while the anhydrous character of (II) and (III) promotes loosely bound structures with low packing indices. © 2013 International Union of Crystallography.

Descripción: Lipid-protein interactions play an essential role in the regulation of biological function of integral membrane proteins; however, the underlying molecular mechanisms are not fully understood. Here we explore the modulation by phospholipids of the enzymatic activity of the plasma membrane calcium pump reconstituted in detergent-phospholipid mixed micelles of variable composition. The presence of increasing quantities of phospholipids in the micelles produced a cooperative increase in the ATPase activity of the enzyme. This activation effect was reversible and depended on the phospholipid/detergent ratio and not on the total lipid concentration. Enzyme activation was accompanied by a small structural change at the transmembrane domain reported by 1-aniline-8-naphtalenesulfonate fluorescence. In addition, the composition of the amphipilic environment sensed by the protein was evaluated by measuring the relative affinity of the assayed phospholipid for the transmembrane surface of the protein. The obtained results allow us to postulate a two-stage mechanistic model explaining the modulation of protein activity based on the exchange among non-structural amphiphiles at the hydrophobic transmembrane surface, and a lipid-induced conformational change. The model allowed to obtain a cooperativity coefficient reporting on the efficiency of the transduction step between lipid adsorption and catalytic site activation. This model can be easily applied to other phospholipid/detergent mixtures as well to other membrane proteins. The systematic quantitative evaluation of these systems could contribute to gain insight into the structure-activity relationships between proteins and lipids in biological membranes. © 2012 Dodes Traian et al.