Descripción: Purification of the ethanolic extract of the starfish L. annulatus led to the isolation of two sulfated glycosides and a pentahydroxylated steroid. One of the saponins contains a novel pentasaccharide chain attached to C-6 of the steroidal aglycone.

Descripción: We review some of the recent results obtained in MHD turbulence, as encountered in many astrophysical objects.We focus attention on the lack of universality in such flows, including in the simplest case (no externally imposed magnetic field, no forcing, unit magnetic Prandtl number). Several parameters can foster such a breakdown of classical Kolmogorov scaling, such as the presence of velocity-magnetic field correlations, or of magnetic helicity and the role of the interplay between nonlinear eddies and Alfven waves. A link with avalanche processes is also discussed. These findings have led to the conjecture of the emergence of a new paradigm for MHD turbulence, as a possibly unsettled competition between several dynamical phenomena. © International Astronomical Union 2011.

Descripción: Chagas' disease, caused by Trypanosoma cruzi, affects about 18 million people in Latin America, and no effective treatment is available to date. To acquire sialic acid from the host glycoconjugates, T. cruzi expresses an unusual surface sialidase with trans-sialidase activity (TcTS) that transfers the sugar to parasite mucins. Surface sialic acid was shown to have relevant functions in protection of the parasite against the lysis by complement and in mammalian host cell invasion. The recently determined 3D structure of TcTS allowed a detailed analysis of its catalytic site and showed the presence of a lactose-binding site where the β-linked galactose accepting the sialic acid is placed. In this article, the acceptor substrate specificity of lactose derivatives was studied by high pH anion-exchange chromatography with pulse amperometric detection. The lactose open chain derivatives lactitol and lactobionic acid, as well as other derivatives, were found to be good acceptors of sialic acid. Lactitol, which was the best of the ones tested, effectively inhibited the transfer of sialic acid to N-acetyllactosamine. Furthermore, lactitol inhibited parasite mucins re-sialylation when incubated with live trypanosomes and TcTS. Lactitol also diminished the T. cruzi infection in cultured Vero cells by 20-27%. These results indicate that compounds directed to the lactose binding site might be good inhibitors of TcTS. © Oxford University Press 2004; all rights reserved.

Descripción: The lower section of Canadon Asfalto Formation (Callovian-Oxfordian) is located at Las Chacritas, Cerro Condor area, on the middle course of Chubut River. It is represented by lacustrine carbonate faciès with interbedded volcanic layers accumulated in the rift system of the Somuncura-Canadon Asfalto Basin. Eight microfacies (MF), defining the lake environments, and three biohermal faciès (MFB) corresponding to an extensive microbialitic belt overlying eulittoral sediments have been recognized: The microfacies are: MF1, mudstone with microbial lamination, related to supralittoral shallow ponds; MF2, biohermal intraclastic floatstone linked to storm episodes; culminating with evaporitic levels; MF3, mudstone with evidence of dessication formed in stagnant water; MF4, microbial-peloidal mudstone/wackestone with evidence of sporadic wave currents, in a eulittoral environment; MF5, intraclastic grainstone/rudstone with pedogenic alterations showing evidence of wave action in a eulittoral area; MF6, oncoidal floatstone interpreted as an hiperconcentrated flow; MF7: Bio-intra-siliciclastic packstone/wackestone accumulated in infralittoral conditions and MF8, silicified bulbous stromatolites related to the outlet of fluvial channels. The biohermal faciès are: MFB9, mudstone with stromatolites and wackestone levels; MFB10, planar stromatolites and MFB11, hemispherical stromatolites with chalk crust. Behind the biohermal belt, palustrine limestones locally show layers with episodic storm floods. The microfacial and facial distribution represents expansion and contraction cycles of a closed lake, controlled mainly by the precipitations. ©1999 Asociacián Gcológica Argentina.

Descripción: We study the existence of periodic solutions for a nonlinear second order system of ordinary differential equations of p-Laplacian type. Assuming suitable Nagumo and Landesman-Lazer type conditions we prove the existence of at least one solution applying topological degree methods. We extend a celebrated result by Nirenberg for resonant systems. © 2006 Elsevier Inc. All rights reserved.

Descripción: We present a theoretical study on the inner-shell ionization of Au, Pb, and Bi. A collective response model, the shellwise local plasma approximation (SLPA), is employed, which works within the dielectric formalism. The wave functions and binding energies were obtained in fully-relativistic way by solving numerically the Dirac equation. The theoretical results describe nicely the experimental data for M-shell ionization of Au and Bi above 2MeV/amu, and for L-shell ionization of Au and Pb above 10 MeV/amu. The SLPA tends to underestimate the data for energies below the range of validity of the model and approach to them for higher energies.

Descripción: In the region of the Main Andes of San Juan, exists a high concentration of landslide deposits that can originate natural dams. The outburst of these dams generated by slide is a common process in this morphology. The analyses of satellite imagery and air photos of previous years allow reconstructing the characteristics and the origin of the slides that formed those natural dams. In this region of the Main Andes, the rapid uplift and erosion of the mountain chain has created abrupt slopes and an internal structure in the materials that determined an increase of the susceptibility to the slope collapse without triggers as the seismic activity or precipitations. The objectives of the present work are (1) to analyze the causes that formed the natural dam and produced the landslide dam and development of the Los Erizos lagoon in the middle course of the Santa Cruz river; (2) the outburst of the dam and their consequent flood; and (3) the morphologic characteristic of the study region. The temporary comparison between air photos with satellite imageries indicates that the natural dam was generated by slip of the western hillside of the Santa Cruz mountain range, located below the Cerro Estrella. However, the constant water flow to the lagoon, has increased its water level until reaching the maximum benchmark of the dam, produced the beginning of the lake drainage and weakening of the dam causing the outburst and its consequent flood. Based on satellite imagery, a temporary analysis of the lagoon is presented, indicating that monitoring is an important tool to alert in the whole San Juan river basin for possible natural dikes, preventing hazards to the populations down water. The alluvium of November 12 of 2005, discharged 32.100.000 m3 in 67 minutes and traveled 254 km in less than 12 hours.

Descripción: Large landslides of different types not previously recorded are located in the left bank of the Río Curri Leuvú valley, north of the Tricao Malal village. There are situated among the Cerro Palao and the Palao pond and Riscos Negros site to the north. The largest landslides (Malal Cura and Arroyo Mogolillo landslides) correspond to the multiple rotational progressive type. They are developed on Mesozoic sedimentary rocks, covered by Cenozoic basalt flows. The debris and earth flows are developed in areas covered by the volcanic rocks of the Charilehue Formation (Middle Miocene) and continue north of study reaching the latitudes of the Grande and Medio streams and also the Colimamil stream valley southeast of Cerro Domuyo. The impact of these phenomena in the fluvial system was important and produced ephemeral and permanent blocking as seen in the La Turbia stream with coeval ponding. It is hypothesized that the landslide occurrence is related to excess or long-lasting periods of rain in postglacial times. It is also indicated the presence of rock glaciers in the Cerro Palao.

Descripción: Langmuir probe measurements in an atmospheric pressure direct current (dc) plasma jet are reported. Sweeping probes were used. The experiment was carried out using a dc non-transferred arc torch with a rod-type cathode and an anode of 5 mm diameter. The torch was operated at a nominal power level of 15 kW with a nitrogen flow rate of 25 Nl min -1. A flat ion saturation region was found in the current-voltage curve of the probe. The ion saturation current to a cylindrical probe in a high-pressure non local thermal equilibrium (LTE) plasma was modeled. Thermal effects and ionization/recombination processes inside the probe perturbed region were taken into account. Averaged radial profiles of the electron and heavy particle temperatures as well as the electron density were obtained. An electron temperature around 11 000 K, a heavy particle temperature around 9500 K and an electron density of about 4 × 10 22 m -3, were found at the jet centre at 3.5 mm downstream from the torch exit. Large deviations from kinetic equilibrium were found throughout the plasma jet. The electron and heavy particle temperature profiles showed good agreement with those reported in the literature by using spectroscopic techniques. It was also found that the temperature radial profile based on LTE was very close to that of the electrons. The calculations have shown that this method is particularly useful for studying spraying-type plasma jets characterized by electron temperatures in the range 9000-14 000 K. © 2012 American Institute of Physics.

Descripción: Above the southern Andes range and its prolongation in the Antarctic Peninsula, large-amplitude mountain and shear gravity waves observed with Weather Research and Forecasting (WRF) mesoscale model simulations during winter 2009 are analyzed. Two specific reasons motivated this study: (1) a decade of satellite observations of temperature fluctuations in the stratosphere, allowing us to infer that this region may be launching the largest-amplitude gravity waves into the upper atmosphere, and (2) the recent design of a research program to investigate these features in detail, the Southern Andes Antarctic Gravity wave Initiative (SAANGRIA). The simulations are forced with ERA-Interim data from the European Centre for Medium-Range Weather Forecasts. The approach selected for the regional downscaling is based on consecutive integrations with weekly reinitialization with 24 h of spin-up, and the outputs during this period are excluded from the analysis. From 1 June to 31 August 2009, five case studies were selected on the basis of their outstanding characteristics and large wave amplitudes. In general, one or two prevailing modes of oscillation are identified after applying continuous wavelet transforms at constant pressure levels and perpendicularly to the nominal orientation of the dominant wave crests. In all cases, the dominant modes are characterized by horizontal wavelengths around 50 km. Their vertical wavelengths, depending on a usually strong background wind shear, are estimated to be between 2 and 11 km. The corresponding intrinsic periods range between 10 and 140 min. In general, the estimated vertical wavelength (intrinsic period) maximizes (minimizes) around 250-300 hPa. The synoptic circulation for each case is described. Zonal and meridional components of the vertical flux of horizontal momentum are shown in detail for each case, including possible horizontal wavelengths between 12 and 400 km. Large values of this flux are observed at higher pressure levels, decreasing with increasing height after a progressive deposition of momentum by different mechanisms. As expected, in the wintertime upper troposphere and lower stratosphere in this region, a prevailing zonal component is negative almost everywhere, with the exception of one case above the northern tip of the Antarctic Peninsula. A comparison with previous experimental results reported in the region from in situ and remote sensing measurements suggests a good agreement with the momentum flux profiles computed from the simulations. Partial wave reflection near the tropopause was found, as considerable departures from equipartition between potential and kinetic wave energy are obtained in all cases and at all pressure levels. This ratio was always less than 1 below the lower stratosphere. Copyright 2012 by the American Geophysical Union.

Descripción: Studies performed during the last five years have shown the existence of 74 prehistoric rock-avalanches in the northern Neuquén Andes (36°-38°S). These are mainly related to volcanic grounds of Pliocene to Pleistocene age corresponding to the Hualcupén Formation. In this work we describe their main characteristics and general homogeneous morphology. They are also characterized by a single tectonic control associated with the occurrence of their break-away and mainly postglacial ages, fact revealed by their systematic position into previous glacial valleys and limited radiometric ages. The obstruction produced by these features altered the shape of the valleys giving to local lakes. Eighteen percent of the cases are characterized by landslide dams preserved nowadays while only six percent by ephemeral ones. Two of the dams were actually catastrophically collapsed: the Cerro Pelán and Navarrete rock-avalanches: The former in Barrancas river valley with the consequent formation of the Carrilauquen lake and the later with the generation of Navarrete lake. The Carrilauquen's dam broke during historical times (29/12/1914) forming an outburst-flood that passed from the Barrancas valley to the Colorado river valley destroying their local economy and reaching after 1,500 km the Atlantic coast. The highest computed volumes in the entire region for the deposits related to rock-avalanches correspond to Varva Co Campos avalanche (3 km3). Cosmogenic isotopes have revealed its age and the age of the neighbor deposit of Varvar Co Tapia rock-avalanche, resulting in 30 ka and 60 ka respectively. Further cosmogenic isotope data revealed that the Cerro PeMn avalanche is only 2 ka. A wrong assumption, presently revaluated, was related to the assignment of these deposits to glacial accumulations because of their chaotic structure, their hummocky topography and the induced dams. Finally, several topographic, geomorphological and seismotectonic criteria are exposed to prove a seismic trigger for these avalanches. Graphics and one table are used to display the distribution of their deposits and its dose association with the orogenic front at these latitudes and the crustal seismicity of the region. © 2006 Asociación Geológica Argentina.

Descripción: We examine long-time properties of the ideal dynamics of three-dimensional flows, in the presence or not of an imposed solid-body rotation and with or without helicity (velocity-vorticity correlation). In all cases, the results agree with the isotropic predictions stemming from statistical mechanics. No accumulation of excitation occurs in the large scales, although, in the dissipative rotating case, anisotropy and accumulation, in the form of an inverse cascade of energy, are known to occur. We attribute this latter discrepancy to the linearity of the term responsible for the emergence of inertial waves. At intermediate times, inertial energy spectra emerge that differ somewhat from classical wave-turbulence expectations and with a trace of large-scale excitation that goes away for long times. These results are discussed in the context of partial two dimensionalization of the flow undergoing strong rotation as advocated by several authors. © 2011 American Physical Society.

Descripción: We extend the homogeneous modified Chaplygin cosmologies to large-scale perturbations by formulating a Zeldovich-like approximation. We show that the model interpolates between an epoch with a soft equation of state and a de Sitter phase, and that in the intermediate regime its matter content is simply the sum of dust and a cosmological constant. We then study how the large-scale inhomogeneities evolve and compare the results with cold dark matter (CDM), ΛCDM and generalized Chaplygin scenarios. We find that unlike that like the latter, our models resemble ΛCDM. © 2005 Elsevier B.V. All rights reserved.

Descripción: We study the large time behavior of nonnegative solutions of the Cauchy problem ut =R J(x,y)(u(y; t),u(x; t)) dy,up, u(x; 0) = u0(x) 2 L∞, where |x|αu0(x) → A < 0 as |x| → 1. One of our main goals is the study of the critical case p = 1+2=ff for 0 > ff > N, left open in previous articles, for which we prove that tff=2ju(x; t) , U(x; t)j → 0 where U is the solution of the heat equation with absorption with initial datum U(x; 0) = CA;N |x|,α. Our proof, involving sequences of rescalings of the solution, allows us to establish also the large time behavior of solutions having more general nonintegrable initial data u0 in the supercritical case and also in the critical case (p = 1 + 2=N) for bounded and integrable u0.

Descripción: Paralomis granulosa Jacquinot is a commercially fished lithodid crab species living in subantarctic and cold-temperate regions of southern South America. Its larval stages (Zoea I, II, Megalopa) are fully lecithotrophic, developing in the complete absence of food from hatching through metamorphosis; first feeding occurs in the first juvenile crab stage. In laboratory rearing experiments conducted at constant 1, 3, 6, 9, 12, and 15°C, we studied rates of larval and early juvenile survival and development in relation to temperature. At 1°C, many larvae (52%) reached the Megalopa stage almost 2 mo after hatching, but all died subsequently without passing through metamorphosis. Larval development was successfully completed at all other temperatures, with maximum survival at 6 to 9°C. The time of non-feeding larval development from hatching to metamorphosis lasted, on average, from 24 d (at 15°C) to almost 4 mo (117 d, at 3°C). When the experiment was terminated 1 yr after hatching, the 3rd (3°C) to 8th (15°C) juvenile crab instar had been reached. The relationship between the time of development through individual larval or juvenile stages (y) and temperature (T) was described as a power function (y = a × Tb, or log[y] = log[a] + b · log[T]; the same regression model was also used to describe the temperature-dependence of cumulative periods of development from hatching. The wide thermal tolerance window for successful larval development (at least 3 to 15°C) and the broad geographic range of this species show that the early life-cycle stages of P. granulosa are cold-eurythermal. This physiological trait together with larval independence of food indicate that this lithodid crab species is well adapted to severe conditions of cold in combination with the food-limitation in subantarctic regions. Since similar traits have been also observed in other Lithodidae, we suggest that early life-history adaptations to low temperatures and low planktonic productivity may explain the high number of lithodid species occurring at high latitudes and in the deep sea, i.e. in conditions under which other Decapoda show strongly reduced diversity.

Descripción: A rock-avalanche (named Las Cañas) was distinguished near the Potrero de Leyes rock-avalanche previously recognized in the southern Sierras Pampeanas. It is located on the western slope of the Sierra Grande de San Luis (San Luis Province), which is regarded as the range uplift front during the Andean tectonism. On account of its greater degradation than the Potrero de Leyes rock-avalanche, the deposits described here are considered to be older in age. Their morphometric attributes could be only roughly calculated, because fluvial erosion has removed a large portion of its initial shape and volume. The avalanche-related deposits form round-shaped hills, which can be distinguished from alluvial fan deposits by their higher altitude, photogeological signature and degree of degradation. Two fault sets have also modified its original surface configuration. It is considered that this phenomenon was also triggered by an earthquake. Hence, the recognition and analysis of these geomorphological processes provides a useful addition to palaeosismological analysis and is significant for an adequate evaluation of the the seismic hazard of this region. © 1998 Asociación Geológica Argentina.

Descripción: An approach was developed to determine triplet quantum yields, ΦT, which overcomes most of the difficulties usually encountered in flash photolysis studies of triplet states. The combined application of near-IR emission and optoacoustics yields ΦT values which are independent of the absorption properties of the triplets. Thus, the triplet energies derived from near-IR phosphorescence spectra together with the values of the heat stored by the triplets determined from optoacoustic experiments afforded ΦT = 0.3 ± 0.1 for porphycene (PO) and 0.4 ± 0.1 for its tetra-n-propyl derivative (TPrPO). Several calorimetric references for optoacoustic measurements in the red region were tested. The ΦT values, combined with flash photolysis data, yielded accurate triplet- minus ground-state absorption coefficients. The quantum yields for singlet molecular oxygen production determined by time-resolved phosphorescence were ΦΔ = 0.34 ± 0.05 for PO and 0.36 ± 0.03 for TPrPO which implies an efficiency near unity for O2(1Δ8) production upon collision of the triplet states of the porphycenes with ground-state O2. © 1990 American Chemical Society.

Descripción: We compute the four-quark plus three-gluon and six-quark plus one-gluon tree level amplitudes using on-shell recursion relations. They are needed for the calculation of the 5-jet cross-section at the Born level, and constitute an essential ingredient for next-to-leading order 4-jet and next-to-next-to-leading order 3-jet production at hadronic colliders. Very compact expressions for all possible helicity configurations are provided, allowing direct implementation in computer codes. With the results presented in this paper, the full set of seven-parton tree amplitudes becomes available. © SISSA 2006.

Descripción: The Cordillera de los Andes is the typical example of a subduction-related orogen. Its present topography is the result of post-Miocene uplift, however, Andean compressional deformation and uplift started in the Late Cretaceous, as increasingly recognized in different sectors of the mountain belt. We present evidences of a Late Cretaceous event of compressional deformation in the southern Central Andes (35oS), reflected in syn-orogenic foreland basin deposits assigned to the Neuquén Group in Argentina and the Brownish-Red Clastic Unit in Chile. Comparison of the facies of these units allows us to recognize a sector proximal to the Late Cretaceous orogenic front, a distal sector with sediment provenance from the forebulge and a western sector where the sediments where deposited within the Late Cretaceous mountain belt. On this basis, we assign the orogenic front to an inverted Jurassic normal fault, the Río del Cobre fault, and reconstruct the structure of the easternmost Late Cretaceous Andes at this latitude. The change in the location of the orogenic front north and south of 35oS allows us to recognize a long-lived change in behavior in Andean evolution in this sector, which correlates with a change in the shape and the deposits of Mesozoic Neuquén basin.

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

Descripción: Scenarios and use cases are popular means for supporting requirements elicitation and elaboration. They provide examples of how the system-to-be and its environment can interact. However, such descriptions, when large, are cumbersome to reason about, particularly when they include conditional features such as scenario triggers and use case preconditions. One problem is that they are susceptible to being satisfied vacuously: a system that does not exhibit a scenario's trigger or a use case's precondition, need not provide the behaviour described by the scenario or use case. Vacuously satisfiable scenarios often indicate that the specification is partial and provide an opportunity for further elicitation. They may also indicate conflicting boundary conditions. In this paper we propose a systematic, semi-automated approach for detecting vacuously satisfiable scenarios (using model checking) and computing the scenarios needed to avoid vacuity (using machine learning). © 2012 Springer-Verlag Berlin Heidelberg.

Descripción: Chenopodium stuckertii is identified as Holmbergia tweedii and lectotypified.

Descripción: Strains derived from HfrH carrying the arcA2 null mutation exhibit a higher respiratory rate, enhanced glucose consumption, and a more-reduced intracellular redox state than arcA deletion mutants of a different lineage. The phenotype of the arcA2 mutants was due to the presence of a creC constitutive mutation introduced by P1 transduction. Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Descripción: Anastrepha fraterculus (Wiedemann) (Diptera: Tephritidae) displays a lek mating system. Males form groups in which they simultaneously display signals (acoustical, visual, or chemical) to attract females with the purpose of mating. Females visit the lek and choose among signaling and courting males to mate. Scarce information is available in A. fraterculus about the main factors involved in female choice and the behavior of displaying males. This information could be important within the context of pest control programs with a sterile insect technique (SIT) component, because departures from normal sexual behavior caused by artificial rearing could affect males' performance in the field. In this study we assessed A. fraterculus male behavior within the leks and analyzed the importance of behavioral and morphological traits on their copulatory success. The existence of preferred places for lek formation was evaluated in field cages with trees inside and analyzed by dividing the trees in sectors according to a 3-dimensional system. Males were individually weighed, marked, and observed every 15 min. Morphometric and behavioral characteristics of successful and unsuccessful males were compared. Most successful males grouped in a region of the tree characterized by the highest light intensity in the first 2 h of the morning. Results showed that pheromone calling activity is positively associated with copulatory success. Copulations were more frequent for males calling inside the lek, indicating that pheromone calling activity and presence in the lek are key factors for copulatory success. A positive association between copulatory success and eye length was found; some characteristics of the face were also associated with copula duration and latency.

Descripción: To investigate the expression of leptin receptors (Ob-R) in the rat hypothalamus-pituitary-ovarian axis, immature rats were treated with eCG/ hCG and Ob-R expression was evaluated by western blot analysis. The Ob-R expression increased 24 h after eCG administration in all the tissues assayed. In the hypothalamus, these levels immediately decreased to those obtained without treatment. In the pituitary, the Ob-R expression continued to be elevated 48 h after eCG administration, whereas the hCG injection did not modify these levels. Similar results were obtained with the ovarian long isoform. To assess the effect of leptin on its receptors, Ob-R was assessed in hypothalamus, pituitary and ovarian explants cultured in the presence or absence of leptin (0.3-500 ng/ml). In the hypothalamus, we found a biphasic effect: the Ob-R expression was either reduced or increased at low or high concentrations of leptin respectively. LH-releasing hormone secretion increased at 1 ng/ml. In the pituitary, Ob-R increased at 10 or 30 ng/ml of leptin for the long and short isoforms respectively. Leptin also induced an increase in LH release at 30 ng/ml. In the ovarian culture, the presence of leptin produced an increase in Ob-R expression at different ranges of concentrations and a dose-dependent biphasic effect on the progesterone, production. In conclusion, all these results clearly suggest that leptin is able to modulate the expression of its own receptors in the reproductive axis in a differential way. Moreover, the positive or negative effect that leptin exerts on the ovulatory process may be dependent on this regulation. © 2008 Society for Endocrinology.

Descripción: Leptin, the 16-kDa protein product of the obese gene, was originally considered as an adipocyte-derived signaling molecule for the central control of metabolism. However, leptin has been suggested to be involved in other functions during pregnancy, particularly in placenta. In the present work, we studied a possible effect of leptin on trophoblastic cell proliferation, survival, and apoptosis. Recombinant human leptin added to JEG-3 and BeWo choriocarcinoma cell lines showed a stimulatory effect on cell proliferation up to 3 and 2.4 times, respectively, measured by 3H-thymidine incorporation and cell counting. These effects were time and dose dependent. Maximal effect was achieved at 250 ng leptin/ml for JEG-3 cells and 50 ng leptin/ml for BeWo cells. Moreover, by inhibiting endogenous leptin expression with 2 μM of an antisense oligonucleotide (AS), cell proliferation was diminished. We analyzed cell population distribution during the different stages of cell cycle by fluorescence-activated cell sorting, and we found that leptin treatment displaced the cells towards a G2/M phase. We also found that leptin upregulated cyclin D1 expression, one of the key cell cycle-signaling proteins. Since proliferation and death processes are intimately related, the effect of leptin on cell apoptosis was investigated. Treatment with 2 μM leptin AS increased the number of apoptotic cells 60 times, as assessed by annexin V-fluorescein isothiocyanate/propidium iodide staining, and the caspase-3 activity was increased more than 2 fold. This effect was prevented by the addition of 100 ng leptin/ml. In conclusion, we provide evidence that suggests that leptin is a trophic and mitogenic factor for trophoblastic cells by virtue of its inhibiting apoptosis and promoting proliferation. © 2007 by the Society for the Study of Reproduction, Inc.

Descripción: Leptin was originally considered as an adipocyte-derived signaling molecule for the central control of metabolism. However, pleiotropic effects of leptin have been identified in reproduction and pregnancy, particularly in placenta, where it may work as an autocrine hormone, mediating angiogenesis, growth, and immunomodulation. Leptin receptor (LEPR, also known as Ob-R) shows sequence homology to members of the class I cytokine receptor (gp130) superfamily. In fact, leptin may function as a proinflammatory cytokine. We have previously found that leptin is a trophic and mitogenic factor for trophoblastic cells. In order to further investigate the mechanism by which leptin stimulates cell growth in JEG-3 cells and trophoblastic cells, we studied the phosphorylation state of different proteins of the initiation stage of translation and the total protein synthesis by [3H]leucine incorporation in JEG-3 cells. We have found that leptin dose-dependently stimulates the phosphorylation and activation of the translation initiation factor EIF4E as well as the phosphorylation of the EIF4E binding protein EIF4EBP1 (PHAS-I), which releases EIF4E to form active complexes. Moreover, leptin dose-dependently stimulates protein synthesis, and this effect can be partially prevented by blocking mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3 kinase (PIK3) pathways. In conclusion, leptin stimulates protein synthesis, at least in part activating the translation machinery, via the activation of MAPK and PIK3 pathways. © 2009 by the Society for the Study of Reproduction, Inc.

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

Descripción: Leukemia inhibitory factor (LIF) and oncostatin M (OSM) induce DNA synthesis in Swiss 3T3 cells through common signaling mechanism(s), whereas other related cytokines such as interleukin-6 and ciliary neurotrophic factor do not cause this response. Induction of DNA replication by LIF or prostaglandin F 2α (PGF 2α) occurs, in part, through different signaling events. LIF and OSM specifically trigger STAT1 cytoplasmic to nuclear translocation, whereas PGF 2α fails to do so. However, LIF and PGF 2α can trigger increases in ERK1/2 activity, which are required for their mitogenic responses because U0126, a MEK1/2 inhibitor, prevents both ERK1/2 activation and induction of DNA synthesis by LIF or PGF 2α treatment. PGF 2α induces cyclin D expression and full phosphorylation of retinoblastoma protein. In contrast, LIF fails to promote increases in cyclin D mRNA/protein levels; consequently, LIF induces DNA synthesis without promoting full phosphorylation of retinoblastoma protein (Rb). However, both LIF and PGF 2α increase cyclin E expression. Furthermore, LIF mitogenic action does not involve protein kinase C (PKC) activation, because a PKC inhibitor does not block this effect. In contrast, PKC activity is required for PGF 2α mitogenic action. More importantly, the synergistic effect between LIF and PGF 2α to promote S phase entry is independent of PKC activation. These results show fundamental differences between LIF and PGF 2α-dependent mechanism(s) that induce cellular entry into S phase. These findings are critical in understanding how LIF and other related cytokine-regulated events participate in normal cell cycle control and may also provide clues to unravel crucial processes underlying cancerous cell division. © 2006 by The American Society for Biochemistry and Molecular Biology, Inc.

Descripción: Lichens and spore-derived cultured mycobionts of Teloschistes chrysophthalmus and Ramalina celastri were studied chemically, and results indicated that they produced, respectively, parietin and usnic acid as major secondary metabolites, which were purified and identified. Identification of the compounds was performed by high performance liquid chromatography and structural elucidation by nuclear magnetic resonance ( 1 H) and electron impact mass spectrometry. Usnic acid exhibited antiviral activity whereas parietin had a virucidal effect against the arenaviruses Junín and Tacaribe. © 2007 Verlag der Zeitschrift für Naturforschung.

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

Descripción: The life cycle of Pygidiopsis crassus n. sp. was experimentally reproduced, starting from cercariae from naturally infected Littoridina parchappei collected from Lujan River and different ponds in Buenos Aires Province, Argentina. Metacercariae were found encysted in the body cavity of experimentally and naturally infected fishes Cnesterodon decemmaculatus and naturally infected Jenynsia lineata. Adults were obtained experimentally in chicks and mice. The natural host is unknown. The new species is compared with Pygidiopsis macrostomum Travassos 1928, from Rattus norvegicus and from Noctilio leporinus mastivus, differing in body and egg sizes, in the size relation of oral and ventral sucker and the shape of excretory vesicle.

Descripción: The life cycle of Ascocotyle (Leighia) hadra n. sp. was experimentally reproduced, starting from cercariae from naturally infected Littoridina parchappei, collected from Los Ranchos stream, near Mercedes city, Buenos Aires Province, Argentina. Metacercariae were found encysted in the liver and mesentery of experimentally and naturally infected fishes Cnesterodon decemmaculatus and Jenynsia lineata. Adults were obtained experimentally in chicks and mice. The natural host is unknown. The new species is compared with Ascocotyle (Leighia) mcintoshi Price 1936 as described by Leigh, 1974, differing in behavior and morphology of cercarial, metacercarial and adult stages.

Descripción: In this paper we present data on the nesting success and life history traits of the Scarlet-headed Blackbird (Amblyramphus holosericeus) nesting in the Argentinean pampas. During the 1995-1997 and 2001-2002 breeding seasons (September-December), we found 60 Scarlet-headed Blackbird nests. About 40% of these nests produced fledglings, and daily nest mortality did not differ among nesting stages (laying, incubation, nestling). Clutch size was 3 eggs, and the mean number of fledglings was 1.33 ± 0.78. Brood reduction was a common cause of nestling loss as 39% of nest with more than 1 nestling lost the last hatched one. Results obtained from experimental nests indicate that parent nest attention increases the probability of nest success as natural nests showed a lower predation rate. We suggest that the high nest attention detected in this species could be responsible for the higher nesting success compared to other sympatric marsh nesting species. However, high nest attendance could also imply an additional cost as it may constrain the time available to parents for foraging, thus limiting the food delivered to nestlings. © The Neotropical Ornithological Society.

Descripción: Rhizobium leguminosarum is a soil bacterium that infects root hairs and induces the formation of nitrogen-fixing nodules on leguminous plants. Light, oxygen, and voltage (LOV)-domain proteins are bluelight receptors found in higher plants and many algae, fungi, and bacteria. The genome of R. leguminosarum bv. viciae 3841, a peanodulating endosymbiont, encodes a sensor histidine kinase containing a LOV domain at the N-terminal end (R-LOV-HK). R-LOV-HK has a typical LOV domain absorption spectrum with broad bands in the blue and UV-A regions and shows a truncated photocycle. Here we show that the R-LOV-HK protein regulates attachment to an abiotic surface and production of flagellar proteins and exopolysaccharide in response to light. Also, illumination of bacterial cultures before inoculation of pea roots increases the number of nodules per plant and the number of intranodular bacteroids. The effects of light on nodulation are dependent on a functional lov gene. The results presented in this work suggest that light, sensed by R-LOV-HK, is an important environmental factor that controls adaptive responses and the symbiotic efficiency of R. leguminosarum.

Descripción: This is the first contribution to the lignicolous marine fungi from Mar Chiquita coastal lagoon, Argentina. Twelve species were collected from Spartina densiflora Brongn. and drift culms. Nine species of Ascomycotina were found: Chaetomastia typhicola (Karsten) Barr, Didymosphaeria lignomaris Strongman & Miller, Leptosphaeria australiensis (Cribb & Cribb) G.C. Hughes, L. oraemaris Linder, L. pelagica Jones, Passeriniella obiones (Crouan & Crouan) Hyde & Mouzouras, Phaeosphaeria spartinae (Ellis & Everhart) Shoemaker & Babcock, Ph. spartinicola Leuchtmann, Sphaerulina oraemaris Linder. Also, three species of Deuteromycotina were found: Phoma glomerata Wollenw. & Hochapfand, Zalerion maritimum (Linder) Anastasiou and Z. varium Anastasiou. Didymosphaeria lignomaris, L. australiensis, L. pelagica and S. oraemaris are new records for South America.

Descripción: Five species of lignicolous marine fungi from the coast of Buenos Aires province (Argentina) are described. Haligena salina Farrant & Jones, Nautosphaeria cristaminuta Jones and Ocostaspora apilongissima Jones, Johnson & Moss, were collected from driftwood and intertidal wood. Cumulospora marina I. Schmidt and Helicascus kanaloanus Kohlmeyer were found growing on Spartina densiflora Brongn. N. cristaminuta is a new record for Argentina, while the remaining ones are new records for South America.

Descripción: The present study describes a new species, Ligophorus uruguayense, parasitizing the gills of Mugil platanus Günther, 1880 from the coast of Uruguay. It differs from all other species of the genus mainly in the shape of the ventral bar, the thick process at the distal end of the inner root of ventral anchors, the J-shaped penis accessory piece and the vaginal tube showing transverse annulations at its distal end, the host species, and geographical distribution. This is the first description of a species of Ligophorus from a mullet in the South Atlantic Ocean. © 2009 Versita Warsaw and Springer-Verlag Berlin Heidelberg.

Descripción: A process of stream piracy caused by the active retrograde erosion of Limay Chico stream - a tributary of Limay river- is described. It is located in the southern part of headwaters of the Alicurá drainage basin, tributary of Collon Cura river. It is supposed that the increment of the headward erosion is related to the postglacial climatic conditions and a coetaneous deepening of the Limay river channel, a process expressed by modern and lower erosion terraces. Moreover the retrograde erosion was enhanced by the special location of the Limay Chico valley along an important line of structural weakness, the Limay Chico fault. The fluvial capture and the consequent diversion of the Alicurá basin upper part showed previous favorable conditions: 1) the topographic lower disposition of Limay Chico stream and their base level; 2) its steeper slope and the location of Limay Chico valley along a zone of structural and litologicalk weakness; 3) transverse arrangement of the Alicurá river's headwaters; 4) its gentle slope and location of their basin and base level at a topographic higher level. Several wind gaps were recognized and were interpreted two probable elbows of capture and barbed pattern. Also the increment of discharge of Limay Chico stream caused in their basin local phenomena of static rejuvenation. It is suppose a close genetic relation between the landslides observed along the steep fault scarp promoted by the Limay Chico Fault and the postglacial climatic change and the local erosional deepening of Limay Chico valley. The slumps characterized by the coalescence of their scan, generated the irregular and ruged landscape of the western side of Limay Chico valley. On the eastern valley slope the slumps reach minor expression. Longitudinal profils and slopes of the analized streams are included.

Descripción: We calculated the influence of the limb-darkened finite-disk correction factor in the theory of radiation-driven winds from massive stars. We solved the one-dimensional m-CAK hydrodynamical equation of rotating radiation-driven winds for all three known solutions, i.e., fast, Ω-slow, and δ-slow. We found that for the fast solution, the mass-loss rate is increased by a factor of 10%, while the terminal velocity is reduced about 10%, when compared with the solution using a finite-disk correction factor from a uniformly bright star. For the other two slow solutions, the changes are almost negligible. Although we found that the limb darkening has no effects on the wind-momentum-luminosity relationship, it would affect the calculation of synthetic line profiles and the derivation of accurate wind parameters. © 2012. The American Astronomical Society. All rights reserved.

Descripción: In this paper we study the limit of Monge-Kantorovich mass transfer problems when the involved measures are supported in a small strip near the boundary of a bounded smooth domain, Ω. Given two absolutely continues measures (with respect to the surface measure) supported on the boundary ∂Ω, by performing a suitable extension of the measures to a strip of width ε near the boundary of the domain Ω we consider the mass transfer problem for the extensions. Then we study the limit as ε goes to zero of the Kantorovich potentials for the extensions and obtain that it coincides with a solution of the original mass transfer problem. Moreover we look for the possible approximations of these problems by solutions to equations involving the p-Laplacian for large values of p.

Descripción: We present a measure of string complexity, called I-complexity, computable in linear time and space. It counts the number of different substrings in a given string. The least complex strings are the runs of a single symbol, the most complex are the de Bruijn strings. Although the I-complexity of a string is not the length of any minimal description of the string, it satisfies many basic properties of classical description complexity. In particular, the number of strings with I-complexity up to a given value is bounded, and most strings of each length have high I-complexity. © 2012 Elsevier B.V. All rights reserved.

Descripción: We introduce the notion of a T-path within Petri nets, and propose to adopt the model of directed hypergraphs in order to determine properties of nets; in particular, we study the relationships between T-paths and firable sequences of transitions. Let us consider a Petri net P=〈P,T,A,M0〉 and the set of places with a positive marking in M0, i.e., P0=p|M0(p)>0. If we regard the net as a directed graph, the existence of a simple path from any place in P0 to a transition t is, of course, a necessary condition for the potential firability of t. This is sufficient only if the net is a state machine, where |•t|=|t•|=1 for all t∈T. In this paper we show that the existence of a T-path from any subset of P0 to a transition t is a more restrictive condition and is, again, a necessary condition for the potential firability of t. But, in this case: (a) if P is a conflict-free Petri net, this is also a sufficient condition, (b) if P is a general Petri net, t is potentially firable by increasing the number of tokens in P0. For conflict-free nets (CFPN) we consider the following problems: (a) determining the set of firable transitions, (b) determining the set of coverable places, (c) determining the set of live transitions, (d) deciding the boundedness of the net. For all these problems we provide algorithms requiring linear space and time, i.e., O(|P|+|T|+|A|), for a net P=〈P,T,A,M0〉. Previous results for this class of networks are given by Howell et al. (1987) [20], providing algorithms for solving problems in conflict-free nets in O(|P|×|T|) time and space. Given a Petri net and a marking M, the well-known coverability problem consists in finding a reachable marking M′ such that M′ ...ver más