Diet selection by goats on a semi-arid shrubland in central Argentina Pisani, Jorge Marcelo; Distel, Roberto Alejandro; Bontti, Eliana E. The objective of this study was to determine diet selection by goats on a semi-arid shrubland in the central part of Argentina. Ten goats grazed on a pasture for 10-days periods in winter, spring, and summer. The botanical composition of the pasture was estimated by a combined measure of cover and biomass, whereas the botanical composition of the diet was determined by the microhistological technique complemented with direct observation. Two shrub species (Condalia microphylla and Prosopis caldenia) and five soft grasses (Piptochaetium napostaense, Poa spp., Stipa tennis, S. clarazii, and Pappophorum spp.) were highly selected by goats. Shrubs represented 32%, 40% and 74% of goat diets in winter, spring and summer, respectively. For each season, the rest of goat diets was composed by the soft grasses. Although coarse grasses represented most (> 80%) of the available biomass in all seasons, they were always highly avoided by goats. The results showed that goats behave as mixed-feeders (eat grasses and shrubs) on semi-arid shrublands in central Argentina.

Thermal behavior and hydration properties of yeast proteins from Saccharomyces cerevisiae and Kluyveromyces fragilis Otero, Miguel A.; Wagner, Jorge Ricardo; Vasallo, María C.; García, Lourdes; Añon, Maria Cristina High pressure homogenization of yeast cells followed by incubation at 50°C for the dissociation of ribonucleic acid-protein complexes resulted in a high denaturation degree of isolated proteins. Proteins in intact cells exhibited an ample endothermic peak with peak temperatures (T(P)) at 66.66 and 63.67°C for S. cerevisiae and K. fragilis, respectively. No differences were found with respect to the associated enthalpy changes for both studied species. The isolation of proteins from its biomass shifts T(P) to values around 50°C. Impurities such as nucleic acid, polysaccharides and other intracellular components seem to play a protective role upon denaturation. Isolated proteins showed solubilities lower than 40% but exhibited water retention properties and wettability from 3.5 to 7.0 ml of water/g of protein.

Clinical and epidemiologic characteristics of respiratory syncytial virus subgroups A and B infections in Santa Fe, Argentina Imaz, María S.; Sequeira, María D.; Videla, Cristina Mónica; Veronessi, Inés; Cociglio, Raquel; Zerbini, Elsa Virginia; Carballal, Guadalupe Respiratory Syncytial Virus (RSV) has two major antigenic groups, A and B. The implications of these variants in the epidemiology and pathogenesis of RSV infection are not well defined. This study was undertaken to compare the two RSV subgroups in patients admitted to hospital. Clinical and epidemiologic features of RSV subgroups in children under 30 months of age with proven RSV acute lower respiratory infections were examined during 4 winters from 1993 to 1996 in Santa Fe, Argentina. RSV typing was carried out with monoclonal antibodies in nasopharyngeal cells by indirect immunofluorescence. Of the 177 RSV positive nasopharyngeal aspirates obtained from 1993 to 1996, 85 (48%) were available for typing. Seventy-three (85.9%) specimens were identified as Subgroup A and 12 (14.1%) as Subgroup B. Except in 1993, in which only Subgroup A was detected, both variants circulated throughout the epidemic season. Subgroup A infections produced more severe disease than Subgroup B infections, as assessed by the length of the hospital stay and the use of respiratory support. This difference was age related, being evident in infants 0-6 months old. Patients with Subgroup B infections were also significantly less frequently breast-fed (95% vs. 75% for A and B subgroups, respectively; P = 0.04). It is concluded that the severity of disease in Argentinian patients admitted with acute RSV infections may be associated with Subgroup A strains as determined by a serogrouping method.

Gypsum-hydroboracite association in the sues formation (Miocene, NW Argentina): implications for the genesis of Mg-bearing borates Ortí, Federico; Alonso, Ricardo Narciso This paper deals with sedimentologic and diagenetic aspects of the evaporitic fades of the Sijes Formation (Miocene, central Andes, NW Argentina), which contains the largest known hydroboracite reserves in the world. In outcrop, the sulfate minerals are secondary gypsum and minor anhydrite, and the borate minerals are hydroboracite with subordinate inyoite and colemanite, and some ulexite. In the Monte Amarillo Member of the Sijes Formation it is possible to distinguish two coeval, shallow lacustrine subbasins, in which the gypsum accumulated in the margins and the hydroboracite in the centers, the intermediate zones being characterized by mixed gypsum-hydroboracite layers. In the depositional sequence, primary gypsum (gypsarenite) and syndepositional anhydrite, in association with limited amounts of calcium borates (colemanite, inyoite) precipitated first, followed by hydroboracite (calcium/magnesium borate). Alternations of gypsum and hydroboracite layers also formed. Hydroboracite is mainly a primary mineral, although it replaced some gypsum under synsedimentary conditions. The formation of colemanite, which occurred during early diagenesis, is linked to the precipitation of calcium sulfates (gypsum and anhydrite), whereas inyoite coexists with both calcium sulfates and magnesium-bearing borates. Transformations among the various borate minerals during burial diagenesis were not detected. Primary gypsum was transformed into anhydrite from early diagenesis to moderate burial diagenesis. The boron source of these deposits seems to be related to the volcanic/hydrothermal activity in the central Andes during the Miocene.

An improved method for the identification and cuantitation of polyamines and related compounds as benzoilated derivatives Hockl, Pablo Francisco; Thyssen, Sandra M; Libertun, Carlos A simple reversed phase HPLC method was developed for the determination of polyamines (putrescine, cadaverine, spermidine, spermine) and other polycations (n-acetyl putrescine, histamine, n-acetilspermine, agmatine), as their benzoylated derivatives. The advantages of this method,examined in various matrixes (hypothalamus, hypophyses, ovary, and seminal plasma), are its versatility, simplicity, and short time of determination of polyamines and related substances of importance in prokaryotes and eukaryotes, even in different matrixes, using a standard HPLC equipment (UV detection at 254 nm), with good resolution, sensitivity, and reproducibility.

Metal-insulator transition and magnetic properties of La(1-x)Eu(x)NiO3 (0 ≤ x ≤ 1) Sanchez, Rodolfo Daniel; Causa, Maria Teresa Beatriz; Seoane, A.; Rivas, J.; Rivadulla, F.; López Quintela, M. A.; Pérez Cacho, J. J.; Blasco, J.; García, J. This paper reports X-ray diffraction patterns, Rietveld fit profiles, electrical resistivity dc magnetic susceptibility, and electron paramagnetic resonance (EPR) measurements of La(1-x)EU(x)NiO3 (0 ≤ x ≤ 1). A shift to high temperature of the metal-insulator transition temperature with x and hysteresis in the electrical resistivity and magnetization versus temperature at intermediate concentration of the compound are observed. The antiferromagnetic order of the Ni sublattice can be observed after subtracting the magnetic contribution of the rare earth ions. A change in space group from R-3c to Pbnm for x ≥ 0.4 was detected, as was the appearance of magnetic order. Samples with 1% Gd3+ probe were studied by EPR. Drastic changes were observed in the shape of the lines with x, though the crystal field symmetry of the Gd sites remained constant in all the samples studied. We observed that when Eu substitution increases, the number of Gd ions that contribute to the crystal-field spectrum diminishes. A possible cause of this effect is a previously reported increase in the Ni-O covalence in the neighborhood of the Eu sites.

Synthesis of acetal (1,1-diethoxyethane) from ethanol and acetaldehyde over acidic catalysts Capeletti, Maria Rosa; Abovsky, Leandro; de la Puente, Gabriela; Laborde, Miguel Ángel; Sedran, Ulises Anselmo Various acidic catalysts (zeolitic and amorphous FCC catalysts, mordenite, montmorillonite, and sulfonic ion exchange resin) were tested for the synthesis of acetal from ethanol and acetaldehyde, at 4 and 20C and atmospheric pressure in batch stirred reactors. All the catalysts were active, but the exchange resin showed amuch better performance than the other catalysts, since it quickly reached equilibrium ethanol conversion values. The resin was also tested under different pressures and catalyst to reactants ratios. Clear relationships between the catalyst activity, the amount of acidity and the physical properties of the catalysts were not apparent. A possible reaction mechanism suggests that protonic acid sites are necessary. Water, a reaction product, seems to have an inhibitory effect on the reaction rate.

Increased sulfur tolerance of Pt/KL catalysts prepared by vapor-phase impregnation and containing a Tm promoter Jacobs, Gary; Ghadiali, Firoz; Pisanu, Adriana; Padro, Cristina; Borgna, Armando; Alvarez, Walter E.; Resasco, Daniel E. Pt/KL catalysts are highly active and selective for the aromatization of hexane, but they display a very high sensitivity to even small concentrations of sulfur in the feed. Tm-containing Pt/KL catalysts were prepared by incipient wetness impregnation (IWI), ion exchange (IE), and vapor-phase impregnation (VPI) methods. The platinum morphology resulting from the addition of thulium and platinum sequentially, using the VPI method, yielded the greatest enhancement to the aromatization performance of the Pt/KL catalysts. The presence of thulium in the sequential VPI Pt/Tm/KL catalyst resulted in a catalyst with higher platinum dispersion than that in an unpromoted VPI catalyst. VPI catalysts provided more finely dispersed Pt clusters than either than either conventional IWI or IE methods. From temperature programmed oxidation of poisoned catalysts, thulium acted as a getter for sulfur, thus, delaying the poisoning of platinum under sulfur-containing feeds. The initial activity of the Tm-promoted VPI catalysts was higher than that of the unpromoted Pt/KL VPI catalysts, suggesting that thulium may directly modify platinum or even participate in accelerating the aromatization reaction.

Receptor expression for IgG constant fraction in human umbilical vein endothelial cells. Alberto, Maria Fabiana; Bermejo, Emilse; Lazzari, María Ángela Endothelial cells (EC) lining the vasculatureform a natural barrier between the circu- immune complex levels, whereby patients with thelating blood and the underlying tissue. One highest disease scores tend to have the highest levelof the major functions of these cells is to prevent of immunocomplexes (IC) [4]. Moreover, patientsplatelet deposition and activation of the coagula- with active SLE contain IC that bind to EC oftion cascade [1].

Single agents and the set of many-to-one stable matching Martinez, Ruth; Massó, Jordi; Neme, Alejandro José; Oviedo, Jorge Armando Some properties of the set of many-to-one stable matchings for firms that have responsive preferences and quotas are not necessarily true when firms' preferences are substitutable. In particular, we provide examples in which firms have substitutable preferences but firms and workers may be "single" in one stable matching and matched in another one. We identify a set of axioms on firms' preferences guaranteeing that the set of unmatched agents is the same under every stable matching. We also propose a weaker condition than responsiveness, called separability with quotas or q-separability, that together with substitutability implies this set of axioms.

Sequence stratigraphy of a tidally dominated carbonate-siliciclastic ramp; the Tithonian-Early Berriasian of the southern Neuquen Basin, Argentina Spalletti, Luis Antonio; Franzese, Juan Rafael; Matheos, Sergio Daniel; Schwarz, Ernesto The Tithonian-Berriasian Vaca Muerta, Carrin Cura and Picun Leufu formations in the southern Neuquen Basin were deposited on a tidally dominated, mixed carbonate-siliciclastic ramp. Basinal, outer, middle, shallow and back ramp facies associations are recognized and a sequence stratigraphic analysis reveals that the ramp record consists of three shallowing-upwards sequences (Ti1, Ti2 and Ti3) set within a lower-order progradational cycle. A higher order of cyclicity is superimposed on to the middle (Ti2) sequence. The majority of the ramp facies belong to the transgressive and highstand systems tracts; however, at the base of Ti2, a lowstand systems tract is identified, characterized by a basal unconformity and an abrupt basinward shift of the shallow marine lithofacies. Transgressive systems tracts were characterized by slow sedimentation rates and rapid sea-level rises that affected carbonate productivity. Highstand systems tracts show the greatest carbonate productivity and an increased progradation rate on account of a reduction in accommodation space generation. Palaeogeography played a major role in the development of the depositional systems. Partial isolation from the Pacific Ocean reflecting the growth of the Andean magmatic arc and geographic restriction due to tectonic inversion in the central part of the basin resulted in a meso-macrotidal regime that produced a tidally dominated sedimentary record in the shallow and back ramp environments. Coeval anoxic conditions in the central part of the Neuquen Basin favoured distal ramp and basinal black shale deposition during episodes of relative sea-level rise.

Ejemplares tipo de Asteraceae (=Compositae) de A.L. Cabrera. Freire, Susana Edith; Iharlegui, Laura El presente trabajo representa un catálogo de los ejemplares tipo de 426 especies y 82 variedades de Asteraceae descriptas por A. L. Cabrera entre los años 1931 y 1999. Los taxones se presentan en orden alfabético. Para cada taxón se indica: diagnosis original, tipo nomenclatural, categoría del tipo, herbario, etiqueta original y nombre actualizado.

Synthesis and properties of [Ru(tpy)(4,4'-X2bpy)H]+ (tpy = 2,2':6',2-terpyridine, bpy = 2,2'-bipyridine, X = H and MeO), and their reactions with CO2 Konno, Hideo; Kobayashi, Atsuo; Sakamoto, Kazuhiko; Fagalde, Florencia; Katz, Néstor Eduardo; Saitoh, Hideki; Ishitani, Osamu A novel type of hydrido complex [Ru(tpy)(4,4'-X2bpy)H]+ (X = H and MeO) was synthesized. The stronger hydridic character of the complexes compared with [Ru(bpy)2(L)H]+ type complexes (L = CO, PPh3 and AsPh3) was demonstrated by the relatively high chemical shifts of Ru-H in the 1H NMR spectra and by higher reactivities with CO2. The reactions of [Ru(tpy)(4,4'-X2bpy)H]+ with CO2 occurred at second-order rate constants varying from (4.69 ± 0.02) to (5.51 ± 0.04) x 10-3 M-1 s-1 depending on both solvent and X, giving the formato complexes [Ru(tpy)(4,4'-X2bpy)(OCHO)]+ quantitatively. The rate constant was increased with the increase of solvent acceptor number, and the reaction of [Ru(tpy){4,4'-(MeO)2bpy}H]+ with CO2 was found to be 3.6 times faster than that of [Ru(tpy)(bpy)H]+. These results suggest that nucleophilic attack of the hydride ligand to the carbon atom of CO2 is the rate determining step for the formation of the formato complex. The structure of the formato complex [Ru(tpy)(bpy)(OCHO)](PF6) was determined by X-ray crystallographic analysis.

Neurotensin inhibits neuronal Na+, K+-ATPase activity through high affinity peptide receptor López Ordieres, María Graciela; Rodriguez, Georgina Emma Neurotensin is a peptide present in mammalian CNS and peripheral tissues, which may play a major role in neurotransmission or neuromodulation, subserving diverse physiological functions. We studied the effect of added neurotensin on ATPase activities in synaptosomal membranes isolated from rat cerebral cortex. Neurotensin at 3 x 10-8-3 x 10-6 M concentration decreased 20-44% Na+, K+-ATPase activity but failed to modify Mg2+-ATPase activity; lower neurotensin concentrations (3 x 10-14-3 x 10-10 M) had no effect on enzyme activities. This inhibitory effect was abolished by neurotensin heating, by enzyme preincubation with neurotensin during periods exceeding 10 min, or by adding 1 x 10-6 M SR 48692, a high affinity neurotensin receptor antagonist. Levocabastine, which blocks low affinity neurotensin receptor, failed to alter enzyme inhibition by the peptide. It is suggested that the sodium pump may be a target for neurotensin effects at neuronal level involving the participation of high affinity neurotensin receptor. © 2000 Elsevier Science Inc.

Structural requirements and reaction pathways in condensation reactions of alcohols on MgyAlOx catalysts Di Cosimo, Juana Isabel; Apesteguia, Carlos Rodolfo; Ginés, M. J. L.; Iglesia, E. The effect of composition and of surface properties on alcohol-coupling reactions was studied on MgyAlOx catalysts using C2H5OH or 13CH3OH/1–12C3H7OH mixtures as reactants. Samples with Mg/Al ratios of 0.5–9.0 were obtained by thermal decomposition of precipitated hydrotalcite precursors. The nature, density, and strength of surface basic sites were obtained by temperature-programmed desorption (TPD) of CO2 and by 13CO2/12CO isotopic switch methods, whereas the acid site densities were measured by TPD of NH3. The catalyst ability for activating H–H bonds was investigated by performing H2–D2 steady-state equilibration reactions. Isotopic tracer studies were carried out in order to probe chain growth pathways in the synthesis of isobutanol. The rates and product selectivity for C2H5OH or CH3OH/C3H7OH reactions strongly depended on the chemical composition of MgyAlOx samples. In turn, the chemical composition affected the acid–base properties of MgyAlOx samples by modifying surface acid and base site densities and the distribution of strength for such sites. The rate of alcohol dehydration to ethers and olefins increased with increasing Al content. Al-rich MgyAlOx samples contained a high density of Al3+–O2− site pairs and of moderate strength basic sites, the combination of which promoted the formation of ethylene or propylene from primary alcohols via E2 elimination pathways. The competitive dehydration to form ethers involved the adsorption of two alcohol molecules on neighboring active sites offering different acid–base properties. On MgyAlOx samples, the active acid sites for ether formation were probably the Al3+ cations, whereas the basic sites were the neighboring O2− ions. The abundance of surface Al3+–O2− pairs accounted for the high ether formation rates observed on Al2O3 and Al-rich MgyAlOx samples. The dehydrogenation of alcohols to aldehydes (C2H4O or C3H6O) involved the initial alkoxy intermediate formation on weak Lewis acid–strong Brønsted base site pairs. The synthesis of C2H4O or C3H6O was favored on Mg-rich MgyAlOx samples because these samples contained a much larger number of properly positioned Al3+ Lewis acid sites and Mg2+–O2− basic pairs, which are required for hydrogen abstraction steps leading to alkoxy intermediates. Pure MgO showed lower dehydrogenation rates than Mg-rich MgyAlOx samples because the predominant presence of isolated O2− hindered formation of alkoxy intermediates by alcohol dissociative adsorption. Aldol condensation reactions on MgyAlOx samples involved also the formation of a carbanion intermediate on Lewis acid–strong Brønsted base pair sites and yielded products containing a new C–C bond such as n-C4H8O (or n-C4H9OH) and iso-C4H8O (or iso-C4H9OH). Reactions leading to condensation products were also favored on Mg-rich samples, but they took place at much slower rates than those of the corresponding dehydrogenation reactions to aldehydes. This reflected the bimolecular and consecutive character of condensation reactions, which are affected not only by the catalyst acid–base properties but also by the chemical nature of the alcohols and steric factors.

Implementation of the IPPP–CLOPPA–INDO/S method for the study of indirect nuclear spin coupling constants and its application to molecules containing tin nuclei Botek, Edith L.; Aucar, Gustavo Adolfo; Cory, Marshall G.; Zerner, Michael C. The inner projection of the polarization propagator, using contributions from localized orbitals, IPPP–CLOPPA, and using the intermediate neglect of the differential overlap model parameterized for spectroscopy, INDO/S, was implemented and used to calculate indirect nuclear spin coupling constants. The resulting model was tested on a group of small- and medium-size model compounds by comparing its performance with that of other semi-empirical methods and experiments where available. It is shown that in general the INDO/S approximation with the use of S N 2 (0) and r N −3 atomic parameters taken from the INDO and AM1 approaches is the most suitable scheme to describe coupling constants. The introduction of atomic parameters for S N 2 (0) and r N −3 in the case of heavy nuclei like Sn, is a critical step. The correction of the bonding beta parameter for this nucleus was also necessary within the INDO/S approximation to improve the accuracy and to better account for indirect relativistic effects. The application of this parameterization was accomplished in a series of tetrastannacyclohexanes and different pathways for coupling transmission were analyzed.

Peptide models XXV. Side-chain conformational potential energy surface, E = E(χ1, χ2) of N-formyl-L-aspartic acidamide and its conjugate base N- formyl-L-aspartatamide in their γ(L) backbone conformations Salpietro, Salvatore J.; Perczel, Andràs; Farkas, Od̈ön; Enriz, Ricardo Daniel; Csizmadia, Imre Gyula Ab initio molecular computations were carried out on the γ(L) backbone conformation of N-formyl-L-aspartic acidamide and its conjugate base N- formyl-L-aspartatamide at the HF/3-21G level of theory. All side-chain conformations were explored for the parent amino acid diamide and its conjugate base. Propionate ion, propionic acid, 3,3-difluoropropionate ion and 3,3-difluoropropionic acid were used to model the side-chain in the anionic and neutral compounds.

Evaluation of hydrogen transfer in FCC catalysts. A new approach for cyclohexene as a test reactant de la Puente, Gabriela; Sedran, Ulises Anselmo The conversion of cyclohexene over different commercial FCC catalysts in a batch fluidized-bed reactor under very short contact times at 300°C, was described by means of a simple lumped kinetic model that accounted for the observed yield patterns. The main branch of reaction starting from the adsorption of cyclohexene was used to assess an index based on kinetic parameters that defines the relative significance of hydrogen transfer reactions in a set that also includes proton transfer and cracking reactions. Complementary experiments with pulses of reactant on a fixed-bed reactor allowed to establish the best temperature to obtain maximum sensitivity to hydrogen transfer. The same evolutions were observed for the relationships between the index of hydrogen transfer and the paired acid site density with the Y zeolite unit cell size, confirming that two regions can be defined separated by unit cell sizes of about 24.28–24.30 Å, the correlations being stronger at low values of this parameter.

Unitary quasifinite representations of W_{\infty} Kac, Victor; Liberati, Jose Ignacio We classify the unitary quasi-finite highest-weight modules over the Lie algebra W and realize them in terms of unitary highest-weight representations of the Lie algebra of infinite matrices with finitely many nonzero diagonals.

Mineral composition of perennial vegetation of shrub patches in northeastern Patagonia del Valle, Hector Francisco; Rosell, Ramon Antonio This study was conducted to (1) quantify the mineral composition of litter, new leaves, and stems of two plant species (Atriplex lampa and Prosopis alpataco) in shrub patches, occurring with common abundance in the northeastern Patagonian region, and (2) determine the spatial and temporal variabilities of the mineral elements. There were 240 vegetal samples collected from six different sites, all within about 15 km. The essential nature of 15 mineral elements for litter and plant parts was analyzed. Composition varied significantly for P, Ca, Mg, Na, K, Cu, Zn, Mo, and B between species; N between seasons; and S, Al, Fe, Mn, and Cd among sites. Also Na, K, and B showed secondary variations derived from a seasonal effect, as did P, Ca, Mg, Cu, Zn, and Mo, but associated with secondary differences among sites.