Characterization of metallocene Epdm terpolymers with high diene and propylene content crosslinked by dicumyl peroxide and β-radiation Nicolás, Javier; Ressia, Jorge Aníbal; Valles, Enrique Marcelo; Merino, Juan Carlos; Pastor, José María Two metallocene EPDMs with the same weight fraction of ethylene but differing in diene content were crosslinked, either by dicumyl peroxide (DCP) or β-radiation. The effect of different diene and propylene content on the molecular structure and the mechanical properties once the materials were crosslinked was studied. The final gel content was very high due to the large level of unsaturations. The crosslinking process was monitored by FTIR spectroscopy by following the decay of unsaturations and the variation of the carbonyl groups that are related to the oxidation grade. It was found that β-radiation crosslinked samples exhibited a lower oxidation grade than those crosslinked by DCP. An oscillant disc rheometer was employed to follow the evolution of the rheological properties, the scorch time, and the time corresponding to full cure during the crosslinking reaction with DCP. In addition, in order to characterize the state of cure we have studied the rheological properties in shear employing a dynamic parallel plate geometry. These results were correlated with those obtained from the molecular characterization of the soluble fraction by size exclusion chromatography. The experiments indicate that, at low irradiation doses, there is a high rate of chain scission reactions that cause an important decrease in storage modulus. Whereas, at high irradiation doses the rate of chain scission reactions diminishes, thus the storage modulus increases but it still remains at lower levels than those corresponding to the original terpolymers. The tensile properties, hardness (Shore A) and compression set tests also suggest the presence of chain scission reactions.

Provenance and Evolution of the Guarguaráz Complex, Cordillera Frontal, Argentina López, Vanina Lucrecia; Gregori, Daniel Alfredo The Guarguaráz Complex, basement of the Cordillera Frontal, included in the proposed Chilenia Terrane, consists of metasedimentary rocks deposited in clastic and carbonatic platforms. Turbiditic sequences point out to slope or external platform environments. According to geochemical data, the sedimentary protoliths derived through erosion of a mature cratonic continental basement. Volcanic and subvolcanic rocks with N and E-MORB signature were interbeded in the metasedimentary rocks during basin development. A compressional stage, starting with progressive deformation and metamorphism, followed this extensional stage. Continuing deformation led to the emplacement of slices of oceanic crust, conforming an accretionary prism during Late Devonian. The Guarguaráz Complex and equivalent units in western Precordillera and also in the Chilean Coastal Cordillera share common evolutional stages, widely represented along the western Gondwana margin. These evidences imply that Chilenia is not an allochthonous terrane to Gondwana, but a portion of its Early Paleozoic margin. Regional configuration indicates that the Guarguaráz Complex and equivalent units represent the accretionary prism of the Famatinian arc (Middle Ordovician-Late Devonian).

A simple method for domestic animal identification in Argentina using PCR-RFLP analysis of cytochrome b gene Bravi, Claudio Marcelo; Liron, Juan Pedro; Mirol, Patricia Monica; Ripoli, María Verónica; Peral Garcia, Pilar; Giovambattista, Guillermo We developed a simple, quick assay in order to discriminate forensic samples among human, and common domestic and livestock species of the Pampean region, Argentina. A mitochondrial cytochrome b fragment amplified with universal primers was separately digested with three restriction enzymes (AluI, HaeIII, and HinfI) and the resulting fragments were resolved through electrophoresis in polyacrylamide gels. This PCR-RFLP method allowed us to identify the target species and worked on degraded samples. The assay was successfully applied in livestock robbery cases in Argentine, and may be useful when attempting a first assessment as to the specific status of a forensic evidence. © 2004 Elsevier Ireland Ltd. All rights reserved.

Tefroestratigrafía (40 000-2000 a. P.) en el sector caribe de los volcanes Barva, Congo y Hule, Cordillera Central, Costa Rica Alvarado, Guillermo; Salani, Flavia Maria El área de estudio se ubica en el flanco norte de la Cordillera Volcánica Central, en las inmediaciones de los volcanes Poás (históricamente activo), Von Frantizius (activo por lo menos hace 40 000 años), Congo (activo hace unos 6000 años) y comprende la caldera explosiva de la Laguna Hule, que explotó hace 2800 años posiblemente con periodos eruptivos menores hace 1700 y 670 años a.P. y el volcán Barva. Las capas de pómez plinianas (caída y flujos) aflorantes en ambas márgenes del río Sarapiquí son antiguas (> 40 000 años). Se encontraron capas piroclásticas (tobas freatomagmáticas y lapilli pliniano) holocenas con fragmentos líticos y juveniles, procedentes de los volcanes Congo y Hule. Entre las facies asociadas con Congo, se identificaron facies de caída de naturaleza andesítica, correspondientes con distintas erupciones (C1 y C2); facies de flujo piroclástico (pumíceos y menos frecuentemente de bloques y ceniza) y una facies lahárica (datada en 6030 años). Dentro del evento explosivo relacionado con el centro volcánico Hule, se encuentran además de la facies de caída pliniana, depósitos de tobas estratificadas y lapillitas vinculados con procesos de oleadas piroclásticas basales y oleadas asociadas con nubes de cenizas.; The area is located in the north side of the Central Volcanic Range, near the Poás (historically active), Von Frantzius (active at least 40 000 years B.P.) and Congo (active about 6000 years B.P.) volcanoes. It comprises the Hule maar that exploded 2800 years ago and possibly showed some minor eruptive periods about 1700 and 670 years B.P., and the Barva volcano. Pumice sheets (airfall and flow) which crop out in both margins of the Sarapiquí river are older than 40 000 years. Field survey showed the existence of thick pyroclastic sheets (phreatomagmatic tuffs and plinian lapilli) from the Congo and Hule volcanoes. Among the facies associated with Congo we identified airfall facies of andesitic composition and corresponding to different eruptions (C1 y C2); pumice and -less frequent- block and ash pyroclastic flow facies and a lahar facies with a radiocarbon age of 6030 years. Within the explosive event related with the Hule volcanic center, besides the plinian airfall facies, there are stratified tuffs and lapilli deposits corresponding to base surges and ash cloud surges.

Dynamics of the tuning process between singers Urteaga, Raul; Bolcatto, Pablo Guillermo We present a dynamical model describing a predictable human behavior like the tuning process between singers. The purpose, inspired in physiological and behavioral grounds of human beings, is sensitive to all Fourier spectrum of each sound emitted and it contemplates an asymmetric coupling between individuals. We have recorded several tuning exercises and we have confronted the experimental evidence with the results of the model finding a very well agreement between calculated and experimental sonograms.

Keeping dry and crossing membranes Fernandez, Ariel Water sustains life but also imposes constraints on what life should be like. Its high dipole moment, proton donor-acceptor dual nature and rotational freedom make it a powerful former of hydrogen bonds. In solu- ble proteins, this property places stringent constraints on the way proteins interact (1-4) and fold (5). I argue here that the manipulation of intramolecularly underdehydrated or underwrapped electrostatic interactions in proteins can be exploited in engineering strategies to create molecules with an enhanced ability to traverse biological membranes, with potential implications for oral delivery of peptide-based drugs.

Multipeaked polarons in soft potentials Fuentes, Miguel Angel; Maniadis, P.; Kalosakas, G.; Rasmussen, K.; Bishop,A. R.; Kenkre, V. M.; Gaidedei, Yu B. We consider a minimal coupled charge/excitation-lattice model capturing a competition between linear polaronic self-trapping and the self-focusing effects of a soft nonlinear on-site potential. The standard singlehumped polaron ceases to exist above a critical value of the coupling strength, closely related to the inflection point in the nonlinear potential. For couplings beyond this critical value, we find that successive multihumped polaronic solutions correspond to the lowest-energy stationary states of the system, which may admit interesting quantum resonance behavior.

Alkaline phosphatase activity sensitive to environmental salinity and dopamine in muscle of the euryhaline crab Cyrtograpsus angulatus Pinoni, Silvina Andrea; Lopez Mañanes, Alejandra Antonia The occurrence, characteristics and response to environmental salinity and dopamine of alkaline phosphatase (AP) activity were studied in chela muscle of the euryhaline crab Cyrtograpsus angulatus from Mar Chiquita coastal lagoon (Buenos Aires Province, Argentina). Chela muscle exhibited a high AP activity with a Michaelis –Menten kinetic (Km=1.21 mM). AP activity was strongly inhibited by EDTA (I50=2.26 mM). AP activity appeared to be sensitive to environmental salinity. In crabs acclimated to low salinity (10x) AP activity was lower than in 35x salinity. Upon an abrupt change to reduced salinity a short-term decrease of AP activity occurred, concomitant with the transition to hyperregulation. Furthermore, AP activity appeared to be under hormonal control since it was inhibited ‘‘in vivo’’ by 10 4 M dopamine. The response to both environmental salinity and dopamine suggests that AP activity could be a component of muscle regulatory mechanisms at the biochemical level secondary to hyperregulation of C. angulatus. The possible functional relationship of AP activity with Na+ /K+ ATPase in muscle is discussed.

Tris(pyrazolyl)methane ligands: Syntheses and structures of monometallic and metallodendritic complexes Sánchez Méndez, Alberto Horacio; Silbestri, Gustavo Fabián; de Jesús, Ernesto; de La Mata, F. Javier; Flores, Juan C.; Gómez, Rafael; Gómez-Sal, Pilar The substituted ligands Me3SiC(pz)3 and Me 3SiOCH2C(pz)3 (2) have been prepared starting from HC(pz)3 and HOCH2C(pz)3. The molecular structure of compound 1 has been determined by X-ray diffraction studies, which show a propeller-like conformation of the pyrazolyl rings. Compound 2 has been found to be useful for the synthesis of [Mo(CO)3{Me 3SiOCH2C(pz)3}] (3), [TiCl2(NtBu) {Me3SiOCH2C(pz)3}] (4), and [PdCl 2{Me3SiOCH2C(pz)3}] (5), through ligand exchange reactions. The characterization of the new complexes is compatible with a tridentate coordination of the ligands in complexes 3 and 4, and a bidentate coordination in 5 as confirmed by an X-ray analysis carried out with the palladium complex. The procedure has been extended for the synthesis of the carbosilane G1-[OCH2C(pz)3]4 (6) and the tetrametallic compound G1-[OCH2C(pz)3Mo(CO) 3]4 (7) (G1 = Si(CH2CH2CH 2Me2Si)4-).

Determinacion de las funciones dielectricas del semiconductor PbI2 Naudi, Andrés Alberto; Albanesi, Eduardo Aldo Presentamos un estudio de las funciones dielectricas del ioduro de plomo, basado en calculos realizados  con un metodo Full Potential Linearized Augmented Plane Wave (FP-LAPW), dentro de la teoria de la funcional densidad (DFT). Los resultados de la estructura electronica indican un band gap directo en el borde de la zona de Brillouin correspondiente al eje mayor de este cristal hexagonal. En el entorno de este punto, tanto la banda de valencia superior como la banda de conduccion inferior tienen un comportamiento parabolico, resultando que el tope de la banda de valencia es principalmente s-Pb, con cierta hibridizacion p-I. Las bandas obtenidas muestran el  comportamiento de un material estructurado en capas, a partir de las cuales hemos obtenido funciones dielectricas anisotropicas, propias de un cristal uniaxial. Nuestros calculos resultan satisfactorios en comparacion con los datos experimentales.

Flavonoids from shoots and roots of Trifolium repens (white clover) grown in presence or absence of the arbuscular mycorrhizal fungus Glomus intraradices Ponce, María Alejandra; Scervino, Jose Martin; Erra Balsells, Rosa; Ocampo, Juan A.; Godeas, Alicia Margarita White clover (Trifolium repens) plants were grown in the presence or absence of the arbuscular mycorrhizal fungus Glomus intraradices. Flavones, 4?,5,6,7,8-pentahydroxy-3-methoxyflavone and 5,6,7,8-tetrahydroxy-3-methoxyflavone, as well as two flavones 3,7-dihydroxy-4´-methoxyflavone and 5,6,7,8-tetrahydroxy-4?-methoxyflavone never previously reported in plants, were isolated. The known 3,5,6,7,8-pentahydroxy-4´-methoxyflavone, 2´,3´,4´,5?,6?-pentahydroxy-chalcone, 6-hydroxykaempferol, 4?,5,6,7,8-pentahydroxyflavone and 3,4?-dimethoxykaempferol were also obtained. Analysis of extracts obtained from roots and shoots revealed that the compositions of the flavonoid mixtures varied with growing conditions. Quercetin, acacetin and rhamnetin accumulated in roots of inoculated plants, whereas they were not detected in non-inoculated plants.

On the universal bahavior of sorption isotherms in disordered mesoporous solids Cordero Sánchez, Salomon; Domínguez, Armando; Kornhauser, Isaac; López, Raúl Horacio; Rojas González, Fernando; Vidales, Ana Maria; Zgrablich, Jorge Andres Adsorption–desorption isotherms in disordered mesoporous solids, described by the Dual Site-Bond Model, are obtained through Monte Carlo simulations and their behavior is correlated to the topological properties of the porous networks and to their percolation properties, extending previous results to the general case of variable connectivity networks. A quasi-universal curve is found which may be useful in the problem of obtaining pore size distributions from the analysis of experimental Adsorption–desorption isotherms.

1940, un año en revisión. La Argentina y la repercusión regional de la Segunda Guerra Mundial Figallo, Beatriz Josefina Este trabajo pretende abordar la confluencia entre repercusiones producidas por la guerra en el cono sur, la neutralidad de la Argentina -postura que entonces compartió activamente con el resto de América- y los problemas que se suscitaron en el plano de la defensa hemisférica y de las vinculaciones con los países lindantes, entendiendo que son conocidos los aportes clásicos que han tratado aquellos días. Nuestra mirada revisa un año en particular, el de 1940, crucial como todos los de la guerra, aunque decisivo para la Argentina cuando crisis internacional, regional e institucional convergieron, con actitudes y decisiones que se explican mutuamente y se comprenden más, en la comparación.

Effect of the nature of the starting material on the formation of Mg2FeH6 Castro, F. J.; Gennari, Fabiana Cristina The compound Mg2FeH6 was synthesized in a single process by reactive mechanical alloying (RMA) a 2MgH2+Fe mixture under hydrogen atmosphere at room temperature. The process yield is 15.6 wt.% of Mg2FeH6, after 100 h of milling. The synthesis of Mg2FeH6 takes almost twice the time and gives nearly half the yield obtained when milling a 2Mg+Fe mixture under similar conditions. The differences observed are explained in terms of the contrast between the mechanical properties and the microstructures of the starting mixtures.

Isobornyl Methacrylate as a Reactive Solvent of Polyethylene Schnell, Matthias; Borrajo Fernandez, Julio; Williams, Roberto Juan Jose; Wolf, Bernhard A. Solutions containing 15 wt % of a low-molar-mass polyethylene (PE) in isobornyl methacrylate (IBoMA), containing 0, 5 or 10 wt % of 1,4 butanediol dimethacrylate (BDDMA) as crosslinker, were polymerized using either benzoyl peroxide (BPO), at 80 ºC, or dicumyl peroxide (DCPO), with a thermal cycle attaining 150 ºC, as initiators. Phase separation of an amorphous PE-rich phase took place when carrying out the reaction at temperatures higher than the PE melting temperature. Partial crystallization of PE was observed when cooling to room temperature. Depending on the initial amount of BDDMA, the fraction of PE that was phase separated varied between 57 % and 66 % of the initial amount, with crystalline fractions in the range of 15 % to 42 %. The use of IBoMA as a reactive solvent of PE has two main advantages over other reactive solvents reported in the literature: a) it has a very low vapor pressure, and b) its free-radical polymerization gives a polymer with a relatively high glass transition temperature.

DAWN en América Latina y el Caribe Gagliardino, Juan Jose Relativamente pocos estudios han examinado el impacto psicosocial de la diabetes. El programa DAWN (Diabetes, Attitudes, Wishes and Needs) trató este problema en un estudio en el que participaron personas con diabetes de 13 países. La conclusión fue que la depresión era mucho más común entre las personas con diabetes que entre quienes no tienen la afección, y se asoció a alteraciones del autocontrol y de la calidad de vida. Aunque los países de América Latina y el Caribe no participaron del estudio DAWN, sus concluisiones aplican a la atención de la diabetes de la región. En este artículo, Juan José Gagliardino nos habla de la aplicación de las conclusiones del programa DAWN dentro de un contexto latinoamericano y caribeño.

Metodología para evaluar riesgo de erosión hídrica en el suroeste de la provincia de Córdoba, Argentina; A methodology to evaluate water erosion risk in the southwest of Cordoba province, Argentina Cantu, Mario Pablo; Becker, Analia Rosa; Musso, Telma Belén The aim of this work was to prove a methodology to evaluate water erosion risk in La Colacha basin in the Southwest of Cordoba Province, Argentina. The susceptibility to soil erosion was established through the evaluation of parameters which are involved in water erosion such as geomorphologic, lithologic, previous erosion and soil parameters. In this area, changes in land use have produced an increment in water erosion processes due to the alteration of physical, chemical and biochemical soil conditions. This led us to consider these changes as the hazard. Erosion risk was considered as the product between susceptibility and hazard. Susceptibility, hazard and risk maps were obtained through a GIS. The results showed that La Colacha basin presented low water erosion risk in most of its area. Units with slopes lower than 1% under a beef cattle production system did not present water erosion risk. Areas with slopes higher than 3% under a conventional tillage crop production system showed a moderately water erosion risk. Low water erosion risk classes corresponded to sites with intermediate slopes. This methodology permits to obtain a rapid assessment of water erosion risk and can be used in a medium scale territorial and environmental planification. The method can be applied in other environments through assigning indexes according with the characteristics of the site and with a right evaluation of land use pressure. The advantage of this methodology is that it may be easily applied using only a soil map.

Lipase-catalysed deacetylation of androstane and pregnane derivatives: Influence of ring D substitution Bruttomesso, Andrea; Baldessari, Alicia A series of acetoxy derivatives of androstane and pregnane was deacetylated in organic solvents by microbial lipases. The best results were obtained with lipase from Candida antarctica (CAL B), Candida rugosa (CRL) and Pseudomonas sp. (PSL). In some derivatives, CAL B and CRL showed a regioselective behaviour towards the removal of the 3β- or 16α/16β-acetyl group. The results of the enzymatic deacetylation of pregnanes and androstanes substituted by various groups containing an sp2-hybridised C-atom in ring D could suggest that CAL B activity seems to be conditioned by the occurrence of a polar carbon double bond in this part of the steroid skeleton. Ten new steroid derivatives were obtained through this approach.

Adrenal gland involvement in the regulation of renal 11beta-hydroxysteroid dehydrogenase 2 Zallocchi, Marisa Laura; Matkovic, Laura Beatriz; Calvo, Juan Carlos; Damasco, Maria Cristina Renal 11beta-hydroxysteroid dehydrogenase 2 (HSD2) catalyzes the conversion of active glucocorticoids to inert 11beta-keto compounds, thereby preventing the illicit binding of these hormones to mineralocorticoid receptors (MRs) and, thus, conferring aldosterone specificity. Absence or inhibition of HSD2 activity, originates a hypertensive syndrome with sodium retention and increased potassium elimination. Recent studies from our laboratory reported an increment of HSD2 activity in intact-stressed rats. To evaluate the adrenal involvement in this increase, we analyzed HSD2 activity and protein abundance in Intact, Sham-operated, and adrenalectomized rats under stress situations (gavage with an overload of 200 mM HCl (10 ml) and simulated gavage) or with corticosterone replacement. HSD2 activity was assessed in renal microsomal preparations obtained from different groups of animals. HSD2 protein abundance was measured by Western-blot. Circulating corticosterone was determined by radioimmunoassay. Sham-operated animals showed an increase in HSD2 activity and abundance compared to Intact and adrenalectomized rats suggesting the involvement of stress-related adrenal factors in HSD2 regulation. In the case of acidotic adrenalectomized animals, there was an increase in renal HSD2 activity when, along with the HCl overload, the rats were injected with corticosterone. This increment occurred without an increase in enzyme abundance. These results suggest the importance of circulating levels of glucocorticoids to respond to a metabolic acidosis, through regulation of HSD2 stimulation. The group subjected to a simulated gavage showed an increase in enzyme activity and protein abundance, thus demonstrating the need for both adrenal and extra-factors in the modulation of renal HSD2. The adrenalectomized animals injected with different doses of corticosterone, produced a progressive increase in enzyme activity and abundance, being significant for the dose of 68 microg corticosterone/100 g body weight. The highest dose (308 microg/100 g body weight) did not show any variation in activity and abundance compared to the control group. This biphasic effect of glucocorticoids could be explained taking into account their permissive and suppressive actions, depending on their blood levels. Knowing that stress induces multifactorial responses, it should not be surprising to observe a differential regulation in renal HSD2, confirming that different stressors act through different factors of both, adrenal and extra-adrenal origin.

Continuum approach to the numerical simulation of material failure in concrete Oliver, J.; Huespe, Alfredo Edmundo; Samaniego, E.; Chaves, E. W. V. Some new aspects of the continuum strong discontinuity approach (CSDA) to model material failure in geomaterials are addressed. A new global algorithm, for tracking multiple crack lines/surfaces in 2D/3D cases is proposed. It is based on solving a simple heat conduction-like problem accompanying the standard mechanical algorithm. A viscous perturbation method on the crack surface is also proposed to remedy the instabilities caused by mutual interactions of multiple developing cracks. A simple procedure to compute the critical time step that ensures algorithmic uniqueness is then provided. Numerical simulations of two and three-dimensional problems displaying a multi-crack pattern are finally presented