Descripción: The potential energy of the lowest 1 ∑u + state of the hydrogen molecule is given as a function of the internuclear distance. Calculations were carried out by the valence bond method using Slater 1s and 2p atomic Orbitals. Both ionic and covalent structures were considered. The 1s orbitals of the ionic and covalent functions included a variational parameter but the orbital exponent of the 2p orbital was kept constant. It is found that the introduction of the 2p orbital into the wave function results in a considerable improvement of the dissociation energy and that further the state is essentially covalent in character rather than ionic, as previously reported.

Descripción: These concretions form discrete spherical bodies 2 to 20 cm in sizes, within medium grained massive sandstone (arkosic arenite). Three concentric zones are recognized: a) dark green to black core composed of quartz and feldespar cemented by illite and roscoellite, b) an intermediate pale red zone of hematite-coated quartz, and c) a white, iron-leached outer zone. Edax and ICP analyses reveal high concentrations of vanadium mainly in zones a) and b) (60340 and 2582 ppm respectivily), uranium (237 and 163 ppm), rubidium (252ppm) and copper (178ppm). The concretions are interpreted as formed under eodiagenetic conditions before the development of haematite cement which gave the red colour to the host rock.

Descripción: An equation proposed by H. Mechetti to describe the permittivity of very dilute polar/nonpolar solutions as a function of concentration was used to calculate the molecular dipole moment of the solutes. The procedure is very simple, and the results are in good agreement with those obtained through more elaborate known methods. Furthermore, an adequate choice of solvents leads to results that are in very good agreement with the corresponding vapor-phase values. © 1985 American Chemical Society.

Descripción: A database of daily extreme temperature was created for as many stations as possible for Uruguay, as far back as possible. This is the first attempt to gather all the different data sources together, perform a quality control and homogeneity assessment. We work with seven stations; it should be taken into account that Uruguay is a small country (around 177 000 km2) and this represents most of the available data. There are three old series with starting dates in 1930, and four that start around 1950. From this database, a set of four extreme temperature indices was constructed for the oldest five stations, warm days (TX90), cold days (TX10), warm nights (TN90) and cold nights (TN10). The index TN10 shows the largest significant negative trend for the period 1960-2002, while TN90 shows a positive but not significant trend for this period indicating a strong warming of nighttime temperature. A spectral analysis was performed using the multi taper methods (MTM) to the de-trended annual, summer Dec-Feb (DJF) and winter Jun-Aug (JJA) indices time-series. This analysis shows that on inter-annual timescales, the most significant range of frequencies is from 2 to 2.5 years and from 3 to 6 years. Low frequencies of variability were detected when the MTM was applied to de-trended smoothed annual time-series, around the range of frequencies of 15-25 years for almost all the indices analysed. Links with global sea surface temperature (SST) were studied for two stations (Paysandu and Rocha), and it was found that the indices showed largest correlations with SST anomalies in the Pacific Ocean. We detected changes in the response of the TN10 index for Rocha station when the series was split up into two different periods (1942-1976 and 1977-2005). Copyright © 2007 Royal Meteorological Society.

Descripción: This study analyses heating degree-days (HDDs) in Argentina during the period 1900-2008. Gridded temperature data provided by the University of Delaware were analysed to calculate monthly and annual cumulative HDDs. Mean, maximum and minimum values as well as the average duration of the heating season are used to characterize the mean features of the region. Spatial variations are driven by latitude and altitude. The analysis of the temporal distribution of HDDs reveals that the centre of the mean heating season varies from mid-June to mid-July. The length of the cold season grows with increasing latitude and westward with increasing altitude. In the high Andes, the heating season extends all year round. S-mode principal component analysis is used to identify sub-groups of grid points with similar temporal variability. Negative trends in annual cumulative HDDs are detected in most of the country. Linear and nonlinear trends as well as temporal statistics are examined for inter- and intra-annual variability of HDDs to discuss its potential incidence on residential use of natural gas. Seasonal increases in natural gas consumption in the country, including the effect of regional price benefits, could be now better explained not only by population growth but also by the spatial and temporal characterization of the HDD season. © 2012 Royal Meteorological Society.

Descripción: A honeybee's waggle dance is an intriguing example of multisensory convergence, central processing and symbolic information transfer. It conveys to bees and human observers the position of a relatively small area at the endpoint of an average vector in a two-dimensional system of coordinates. This vector is often computed from a collection of waggle phases from the same or different dancers. The question remains, however, of how informative a small sample of waggle phases can be to the bees, and how the spatial information encoded in the dance is actually mapped to the followers' searches in the field. Certainly, it is the variability of a dancer's performance that initially defines the level of uncertainty that followers must cope with if they were to successfully decode information in the dance. Understanding how a dancer's behaviour is mapped to that of its followers initially relies on the analysis of both the accuracy and precision with which the dancer encodes spatial information in the dance. Here we describe within-individual variations in the encoding of the distance to and direction of a goal. We show that variations in the number of a dancer's wagging movements, a measure that correlates well with the distance to the goal, do not depend upon the dancer's travelled distance, meaning that there is a constant variance of wagging movements around the mean. We also show that the duration of the waggle phases and the angular dispersion and divergence of successive waggle phases co-vary with a dancer's orientation in space. Finally, using data from dances recorded through high-speed video techniques, we present the first analysis of the accuracy and precision with which an increasing number of waggle phases conveys spatial information to a human observer.

Descripción: Water resources management and agriculture planning models require a statistical synthesis of some rainfall features, in particular those representing dry atmospheric conditions. The bigger the basin, the more important these features become, as is the case of the La Plata Basin (LPB). This paper focuses on the precipitation variability in the large LPB in South America, analysing the number of months per year with low rainfall and the sequences of months with low rainfall, their theoretical distributions and stability, which are needed as input for the models mentioned above. Long time series are used to analyse the low-frequency variability and the relative importance of decadal variability. Changes are evident in the number of months per year with low rainfall, with a decrease of about 20% in the period after 1970. Theoretical distribution models (binomial and geometric) are fitted to these empirical distributions, and the regional variability of the fitting parameters is shown. In practically the entire region, the goodness-of-fit of the two theoretical models considered is statistically satisfactory. The temporal variability of the parameters of the theoretical binomial (p) and geometric (α) distributions is analysed, in excluding sub-periods of 10 and 5 years, respectively. The results show low-frequency variability overlapped on a decadal variability, with low homogeneous regional behaviour. The distribution models have proven to be efficient for frequency adjustments of the rainfall properties studied. These results are an acceptable and necessary input to decision models in LPB. They also make it possible to infer effects of climate change. Copyright © 2008 Royal Meteorological Society.

Descripción: Odour-guided behaviour is a quantitative trait determined by many genes that are sensitive to gene-environment interactions. Different natural populations are likely to experience different selection pressures on the genetic underpinnings of chemosensory behaviour. However, few studies have reported comparisons of the quantitative genetic basis of olfactory behaviour in geographically distinct populations. We generated isofemale lines of Drosophila melanogaster from six populations in Argentina and measured larval and adult responses to benzaldehyde. There was significant variation within populations for both larval and adult olfactory behaviour and a significant genotype × sex interaction (GSI) for adult olfactory behaviour. However, there is substantial variation in the contribution of GSI to the total phenotypic variance among populations. Estimates of evolvability are orders of magnitude higher for larvae than for adults. Our results suggest that the potential for evolutionary adaptation to the chemosensory environment is greater at the larval feeding stage than at the adult reproductive stage. © 2008 The Authors.

Descripción: Aims. We analyze the consistency of different astronomical data of the variation in the fine-structure constant obtained with Keck and VLT. Methods. We tested the consistency using the Student test and confidence intervals. We splited the data sets into smaller intervals and grouped them according to redshift and angular position. Another statistical analysis is proposed that considers phenomenological models for the variation in α. Results. Results show consistency for the reduced intervals for each pair of data sets and suggests that the variation in α is significant at higher redshifts. Conclusions. Even though the dipole model seems to be the most accurate phenomenological model, the statistical analyses indicate that the variation in α might be depending on both redshift and angular position. © 2013 ESO.

Descripción: Sjögren's syndrome (SS) is a chronic autoimmune disease characterized by a progressive oral and ocular dryness that correlates poorly with the autoimmune damage of the glands. It has been proposed that a loss of homeostatic equilibrium in the glands is partly responsible for salivary dysfunction with acinar cells involved actively in the pathogenesis of SS. The non-obese diabetic (NOD) mouse model of Sjögren's syndrome develops secretory dysfunction and early loss of glandular homeostatic mechanisms, with mild infiltration of the glands. Based on the vasodilator, prosecretory and trophic effects of the vasoactive intestinal peptide (VIP) on acini as well as its anti-inflammatory properties we hypothesized that the local expression of VIP/vasoactive intestinal peptide receptor (VPAC) system in salivary glands could have a role in acinar cell apoptosis and macrophage function thus influencing gland homeostasis. Here we show a progressive decline of VIP expression in submandibular glands of NOD mice with no changes in VPAC receptor expression compared with normal mice. The deep loss of endogenous VIP was associated with a loss of acinar cells through apoptotic mechanisms that could be induced further by tumour necrosis factor (TNF)-α and reversed by VIP through a cyclic adenosine-5'-monophosphate (cAMP)/protein kinase A (PKA)-mediated pathway. The clearance of apoptotic acinar cells by macrophages was impaired for NOD macrophages but a shift from inflammatory to regulatory phenotype was induced in macrophages during phagocytosis of apoptotic acinar cells. These results support that the decline in endogenous VIP/VPAC local levels might influence the survival/apoptosis intracellular set point in NOD acinar cells and their clearance, thus contributing to gland homeostasis loss. © 2011 The Authors. Clinical and Experimental Immunology © 2011 British Society for Immunology.

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

Descripción: The Kelvin-Helmoltz instability (KH) with formation of vortices appears in a wide variety of terrestrial, interplanetary, and astrophysical contexts. We study a series of iterated rolled-up coherent plasma structures (15) that flow in the equatorial Earth's boundary layer (BL), observed on October 24, 2001. The data were recorded during a 1.5 hour-long Wind crossing of the BL at the dawn magnetospheric flank, tailward of the terminator (X≈-13 RE). The interplanetary magnetic field (IMF) was radially directed, almost antiparallel to the magnetosheath (MS) flow. This configuration is expected to be adverse to the KH instability because of the collinearity of field and flow, and the high compressibility of the MS. We analyze the BL stability with compressible MHD theory using continuous profiles for the physical quantities. Upstream, at near Earth sites, we input parameters derived from an exact MHD solution for collinear flows. Further downtail at Wind position we input measured parameters. The BL is found KH unstable in spite of unfavorable features of the external flow. On the experimental side, the passage of vortices is inferred from the presence of low density - hot plasma being accelerated to speeds higher than that of the contiguous MS. It is further supported by the peculiar correlation of relative motions (in the bulk velocity frame): cold-dense plasma drifts sunward, while hot-tenuous plasma moves tailward. This event differs from many other studies that reported BL vortices under strongly northward IMF orientations. This is a case of KH vortices observed under an almost radial IMF, with implicit significance for the more common Parker's spiral fields, and the problem of plasma entry in the magnetosphere.

Descripción: The thermohaline structure across the tidal fronts of the continental shelf off Patagonia is analyzed using historical and recent summer hydrographic sections. The near-summer tidal front location is determined on the basis of the magnitude of vertical stratification of the water column as measured by the Simpson parameter. Sea surface and air CO2 partial pressures based on data from eleven transects collected in summer and fall from 2000 to 2004 are used to estimate CO2 fluxes over the shelf. The near-shore waters are a source of CO2 to the atmosphere while the midshelf region is a CO2 sink. The transition between source and sink regions closely follows the location of tidal fronts, suggesting a link between vertical stratification of the water column and the regional CO2 balance. The highest surface values of Chl a are associated with the strongest CO2 sinks. The colocation of lowest CO2 partial pressure (pCO2) and highest Chl a suggests that phytoplankton blooms on the stratified side of the fronts draw the ocean's CO2 to very low levels. The mean shelf sea-air difference in pCO2 (ΔpCO2) is -24 μatm and rises to -29 μatm if the shelf break front is included. Peaks in ΔpCO2 of -110 μatm, among the highest observed in the global ocean, are observed. The estimated summer mean CO2 flux over the shelf is -4.4 mmol m-2 d-1 and rises to -5.7 mmol m-2 d-1 when the shelf break area is taken into account. Thus, during the warm season the shelf off Patagonia is a significant atmospheric CO2 sink. Copyright 2005 by the American Geophysical Union.

Descripción: Different immunomodulatory activities present in Trichilia glabra (TG) leaf extracts have already been described. Particularly, chloroform-methanol extracts were responsible for an in-vivo anti-inflammatory effect. The effect of such extracts on the infectivity of enveloped and naked viruses were investigated. Methanolic fraction extracts were active against herpes simplex virus type 1 (HSV-1) and vesicular stomatitis virus (VSV), while no activity against poliovirus type 3 was observed. VSV was slightly more affected than HSV-1: 2.8 log10 reduction in VSV titer against 2.4 log10 reduction in HSV-1 titer when 0.25 mg/ml F2 fraction was tested and a reduction of 2.7 log10 in VSV virus titer and of 1.5 log10 in HSV-1 virus titer was observed when 0.25 mg/ml F3 fraction was tested. Results obtained in this work suggest a potential pharmaceutical use of TG extract components.

Descripción: Background. Micro RNAs (miRs) constitute a large group of endogenous small RNAs that have crucial roles in many important plant functions. Virus infection and transgenic expression of viral proteins alter accumulation and activity of miRs and so far, most of the published evidence involves post-transcriptional regulations. Results. Using transgenic plants expressing a reporter gene under the promoter region of a characterized miR (P-miR164a), we monitored the reporter gene expression in different tissues and during Arabidopsis development. Strong expression was detected in both vascular tissues and hydathodes. P-miR164a activity was developmentally regulated in plants with a maximum expression at stages 1.12 to 5.1 (according to Boyes, 2001) along the transition from vegetative to reproductive growth. Upon quantification of P-miR164a-derived GUS activity after Tobacco mosaic virus Cg or Oilseed rape mosaic virus (ORMV) infection and after hormone treatments, we demonstrated that ORMV and gibberellic acid elevated P-miR164a activity. Accordingly, total mature miR164, precursor of miR164a and CUC1 mRNA (a miR164 target) levels increased after virus infection and interestingly the most severe virus (ORMV) produced the strongest promoter induction. Conclusion. This work shows for the first time that the alteration of miR pathways produced by viral infections possesses a transcriptional component. In addition, the degree of miR alteration correlates with virus severity since a more severe virus produces a stronger P-miR164a induction. © 2009 Bazzini et al; licensee BioMed Central Ltd.

Descripción: Escape responses to directly approaching predators represent one instance of an animal's ability to avoid collision. Usually, such responses can be easily evoked in the laboratory using two-dimensional computer simulations of approaching objects, known as looming stimuli. Therefore, escape behaviors are considered useful models for the study of computations performed by the brain to efficiently transform visual information into organized motor patterns. The escape response of the crab Neohelice (previously Chasmagnathus) granulata offers an opportunity to investigate the processing of looming stimuli and its transformation into complex motor patterns. Here we studied the escape performance of this crab to a variety of different looming stimuli. The response always consisted of a vigorous run away from the stimulus. However, the moment at which it was initiated, as well as the developed speed, closely matched the expansion dynamics of each particular stimulus. Thus, we analyzed the response events as a function of several variables that could theoretically be used by the crab (angular size, angular velocity, etc.). Our main findings were that: (1) the decision to initiate the escape run is made when the stimulus angular size increases by 7 deg; (2) the escape run is not a ballistic kind of response, as its speed is adjusted concurrently with changes in the optical stimulus variables; and (3) the speed of the escape run can be faithfully described by a phenomenological input-output relationship based on the stimulus angular increment and the angular velocity of the stimulus. © 2012. Published by The Company of Biologists Ltd.

Descripción: Nitrogen compounds like urea and melamine are known to be commonly used for milk adulteration resulting in undesired intoxication; a well-known example is the Chinese episode occurred in 2008. The development of a rapid, reliable and economic test is of relevance in order to improve adulterated milk identification. Cyclic voltammetry studies using an Au working electrode were performed on adulterated and non-adulterated milk samples from different independent manufacturers. Voltammetric data and their first derivative were subjected to functional principal component analysis (f-PCA) and correctly classified by the KNN classifier. The adulterated and non-adulterated milk samples showed significant differences. Best results of prediction were obtained with first derivative data. Detection limits in milk samples adulterated with 1% of its total nitrogen derived from melamine or urea were as low as 85.0 mg·L-1 and 121.4 mg·L-1, respectively. We present this method as a fast and robust screening method for milk adulteration analysis and prevention of food intoxication. © 2012 by the authors; licensee MDPI, Basel, Switzerland.

Descripción: Vortex configurations in the two-dimensional torus are considered in noncommutative space. We analyze the BPS equations of the Abelian Higgs model. Numerical solutions are constructed for the self-dual and anti-self dual cases by extending an algorithm originally developed for ordinary commutative space. We work within the Fock space approach to noncommutative theories and the Moyal-Weyl connection is used in the final stage to express the solutions in configuration space. © SISSA 2006.

Descripción: The motion of a single vortex originates chaos in the quantum fluid defined in Bohm's interpretation of quantum mechanics. Here we analize this situation in a very simple case: one single vortex in a rectangular billiard. © 2007 American Institute of Physics.

Descripción: According to the global predictions by the International Panel of Climate Change (IPCC), the sea-level rise due to ocean thermal expansion and glacier mass loss will average 0.09 - 0.88 m between 1990 and 2100, with a trend toward an increasing rise rate. Potential impacts of this increasing rise rate relate to changes in the coastal area, including floods, increased coastal retreat, and saline intrusion in the coastal acquiferous and estuaries. In order to achieve an appropriate coastal management scheme in the Province of Río Negro, the area was divided into zones to show information of the level of hazard on a simple map. To identify areas of geological hazard related to permanent and/ or episodic floods, a database was prepared. The threatened or in-danger areas were identified by means of coastal vulnerability indices, also called susceptibility indices, which were calculated by means of an algorithm that relates different variables obtained from coastal geology, and oceanographic and climatological information. This index is defined by seven variables and can be used to identify areas in risk of erosion or permanent/temporary flood. The most vulnerable areas to sea level rise are Balneario El Salado (Playas Doradas), San Antonio Oeste - San Antonio Este, Caleta de los Loros, and the Río Negro mouth. By contrast, vulnerability of the coastal area located to the south of Punta Pórfido is low. © 2004 Asociación Geológica Argentina.