Rheological properties of a two phase lipid monolayer at the air/water interface: Effect of the composition of the mixture Wilke, Natalia; Vega Mercado, Franco; Maggio, Bruno Many biologically relevant monolayers show coexistence of discrete domains of a long-range ordered condensed phase dispersed in a continuous, disordered, liquid-expanded phase. In this work, we determined the viscous and elastic components of the compressibility modulus and the shear viscosity of monolayers exhibiting phase coexistence with the aim at elucidating the contribution of each phase to the observed monolayer mechanical properties. To this purpose, mixed monolayers with different proportions of distearoylphosphatidylcholine (DSPC) and dimyristoylphosphatidylcholine (DMPC) were prepared and their rheological properties were analyzed. The relationship between the phase diagram of the mixture at 10 mN m-1 and the rheological properties was studied. We found that the monolayer shear viscosity is highly dependent on the presence of domains and on the domain density. In turn, the monolayer compressibility is only influenced by the presence of domains for high domain densities. For monolayers that look homogeneous on the micrometer scale (DSPC amount lower that 23 mol %), all the analyzed rheological properties remain similar to those observed for pure DMPC monolayers, indicating that in this proportion range the DSPC molecules contribute as DMPC to the surface rheology in spite of having hydrocarbon chains four carbons longer.

Contratos de estado, inversión extranjera y derecho internacional público Castillo Argañarás, Luis Fernando El objetivo de éste artículo es responder al siguiente interrogante: ¿Es posible aplicar Derecho Internacional Público a los contratos de Estado? En ese sentido, se analizará la naturaleza jurídica de estos contratos y luego la vinculación de éste tipo de instrumentos jurídicos con el Derecho Internacional Público. También se considerará el arbitraje internacional.; O objetivo deste artigo é responder à seguinte questão: É possível aplicar o Direito Internacional Público a contratos do Estado. Nesse sentido, vamos analisar a natureza jurídica dos contratos do Estado e, a seguir, relacionar estes tipos de contratos com o Direito Internacional. Também ser considerada uma arbitragem internacional.; The purpose of this paper is to answer the following question: Is it possible to apply Public International Law to State Contracts? In this sense, the legal nature of State contracts will be analysed and then the link between Public International Law and this type of contracts will be established. International arbitration will be considered.

Experiencias y discursos sobre organización política y laboral de las y los jóvenes. Un acercamiento histórico-etnográfico a los procesos de socialización-apropiación contemporáneos Scarfó, Gabriela Fernanda; Enrique, Iara Nuria El objetivo de este artículo consiste en analizar, desde un enfoque histórico-antropológico, la particularidad de algunas experiencias y reflexiones relativas a la vida política y laboral de las y los jóvenes adolescentes, en dos contextos de socialización diferenciados: una organización no gubernamental dedicada a la formación de la juventud en el mundo del trabajo y una organización de segundo grado que procura aglutinar al llamado movimiento estudiantil secundario en la Ciudad de Buenos Aires.; The aim of this paper is to analyze from a historical-anthropological approach the particularity of some experiences and reflections relative to the political life and the world of the work of the young people in two different contexts of socialization: an non-governmental organization dedicated to the education of young people in the world of work and an organization of the second degree that tries to agglutinate the so called student secondary movement in the City of Buenos Aires.

Evaluación y calidad en los programas y cursos online en la enseñanza superior; Evaluation and quality at programmes and specific courses in higher education Constantino, Gustavo Daniel; Llull, Laura La Educación a Distancia (EAD) ha sido siempre considerada con cierto escepticismo en cuanto a la calidad de los programas en contraste con la enseñanza en presencia. La EAD basada en redes telemáticas ha logrado disminuir el recelo, pero no lo ha hecho desaparecer.La evaluación, como aspecto crítico de la calidad, hasta hoy no ha sido objeto de un examen profundo en relación a los nuevos contextos y en general se trasvasan los sistemas de evaluación convencionales y propios de la formación en presencia a los entornos online. Sin embargo, existe una intuición extendida en que tales sistemas no son del todo congruentes con la naturaleza de la enseñanza y del aprendizaje en comunidades virtuales, aspecto que ha sido particularmente sensible en el caso del Proyecto Alfa-Miforcal, ilustrándose con un par de ejemplos. El escenario de la educación online está cambiando dramáticamente con el surgimiento de nuevas formas de enseñar y aprender, pasando de modelos de reproducción de conocimientos a modelos del aprendizaje colaborativo y conocimiento compartido centrados en la actividad del estudiante en Comunidades Virtuales de Aprendizaje. En estas se puede llegar a un grado de interacción en el que la evaluación formativa alcanza niveles semejantes a los de la mejor orientación del aprendizaje en presencia.; Distance Education has been always considered with certain skepticism for the quality of the programs in contrast with the education in presence. The distance education based on virtual networks has managed to diminish the mistrust, but it has not made it disappear. The evaluation, as critical aspect of the quality, up to today has not been an object of a deep examination in relation to the new contexts, which implies that the conventional and proper systems of evaluation of the formation in presence are applied to the environments online. Nevertheless, there exists a widespread intuition in which such systems do not correspond completely to the nature of the education and of learning in virtual communities, Aspect that has been particularly sensitive in case of the Project Alfa-Miforcal, illustrated with a pair of examples. The scenario of the education online is changing dramatically with the emergence of new ways of teaching and of learning, going on from models of reproduction of knowledge to models of collaborative learning and shared knowledge focused on the activity of the student in Learning Virtual Communities. In these, it is possible to come to a grade of interaction in which the formative evaluation reaches similar levels to those of the best orientation of learning in presence.

El entorno sudamericano y su significado en la política exterior de los gobiernos de Duhalde y Kirchner Torres, Miguel Agustín La crisis institucional y socioeconómica que afectó a Argentina a fines de 2001 y principios de 2002 no solo implicó el agotamiento del modelo neoliberal implementado desde el comienzo de la década del noventa sino que también significó la posibilidad de revisar el esquema de inserción internacional que lo complementó. Esta reformulación de la política exterior incluía la oportunidad de replantear los vínculos con los países sudamericano y el rol del país dentro de MERCOSUR. En este aporte se analiza el significado que se asignó a las relaciones con los actores subregionales y a MERCOSUR en la política y exterior argentina luego de la crisis del 2001.; A crise institucional e sócio-econômicos que a Argentina sofreu no final de 2001 e início de 2002, não só representou o esgotamento do modelo neoliberal aplicado desde o início dos anos noventa, também significou a possibilidade de rever o esquema de inserção internacional que acompanhou esse modelo. Esta reformulação da política externa incluída a oportunidade de repensar os laços com os países da América do Sul eo papel do país no Mercosul. Esta contribuição analisa os significados atribuídos às relações com os atores subregionais e ao Mercosul na política externa da Argentina após a crise de 2001.

Screening for antifungal activity in plants from central Argentina Palacios, Sara Maria; Ruiz, Gustavo; Carpinella, Maria Cecilia Ethanolic extracts from aerial parts of 71 native plants from Argentina were tested by bioautography on Thin Layer Chromatography (TLC) for their antifungal effects against pathogenic Fusarium verticillioides. The extracts of Aristolochia argentina (Aristolochiaceae), Flourensia oolepis (Asteraceae), Gaillardia megapotamica (Asteraceae), Salvia cuspidata (Lamiaceae) and Trichocline reptans (Asteraceae) at Minimum Inhibitory Concentrations (MICs) of 0.03 to 0.12 mg/spot were highly effective in inhibiting the fungal growth followed by extracts from Baccharis artemisioides (Asteraceae), Baccharis salicifolia (Asteraceae), Dalea elegans (Fabaceae), Heterothalamus alienus (Asteraceae), Lepechinia floribunda (Lamiaceae), Vernonia nudiflora (Asteraceae) and Zanthoxylum coco (Rutaceae) at MICs of 0.25 - 0.50 mg/spot. While, F. oolepis, T. reptans and A. argentina extracts proved most potent, with MICs of 0.03, 0.03 and 0.06 mg/spot, respectively. Further studies are required with extracts of the most active species in bioguided assay isolation to obtain new molecules with potent antifungal properties to control harmful fungi such as F. verticillioides.

Maximal operators, Riesz transforms and Littlewood–Paley functions associated with Bessel operators on BMO Betancor, J.J.; Chicco Ruiz, Anibal Leonardo; Fariña, J.C.; Rodríguez-Mesa, L. In this paper we study boundedness properties of certain harmonic analysis operators (maximal operators for heat and Poisson semigroups, Riesz transforms and Littlewood–Paley g-functions) associated with Bessel operators, on the space BMOo(R) that consists of the odd functions with bounded mean oscillation on R.

On state estimation in electric drives Leon, Enrique Andres; Solsona, Jorge Alberto This paper deals with state estimation in electric drives. On one hand a nonlinear observer is designed, whereas on the other hand the speed state is estimated by using the dirty derivative from the position measured. The dirty derivative is an approximate version of the perfect derivative which introduces an estimation error few times analyzed in drive applications. For this reason, our proposal in this work consists in illustrating several aspects on the performance of the dirty derivator in presence of both model uncertainties and noisy measurements. To this end, a case study is introduced. The case study considers rotor speed estimation in a permanent magnet stepper motor, by assuming that rotor position and electrical variables are measured. In addition, this paper presents comments about the connection between dirty derivators and observers, and advantages and disadvantages of both techniques are also remarked.

Phage adsorption to Lactobacillus plantarum: influence of physiological and environmental factors. Briggiler Marcó, Mariángeles; Reinheimer, Jorge Alberto; Quiberoni, Andrea del Lujan Bacteriophage infection of lactic acid bacteria (LAB) constitutes one of the major problems in the dairy industry, causing economic losses and a constant risk of low quality and/or unsafe foods. The first step in the phage biology is the adsorption on the host cell surface. In a previous study, a remarkable thermal, chemical and photocatalytic resistance was demonstrated by four phages of Lactobacillus plantarum (ATCC 8014-B1, ATCC 8014-B2, FAGK1 and FAGK2). In the present work, these phages were used to characterize the adsorption process on L. plantarum ATCC 8014. Clearly, the characterization of this process could increase the possibilities of design useful strategies in order to prevent phage infections. The influence of Ca(2+), temperature, pH and physiological cell state on phage adsorption was investigated. Burst sizes of phages ATCC 8014-B1 and ATCC 8014-B2 were 60 and 83 PFU/infective centre, respectively. The four phages exhibited a high infectivity even at pH 4 and pH 11. Calcium or magnesium ions were not indispensable for cell lysis and plaque formation, and more than 99% of phage particles were adsorbed either in the presence or absence of Ca(2+), after 15 min at 37 degrees C. Phage adsorption was only partially affected at 50 degrees C, while reached its maximum between 30 and 42 degrees C. The highest adsorption values (99.9%) were observed from pH 5 to 7, after 30 min at 37 degrees C. Adsorption rates decreased after the thermal inactivation of cells, though, when 20 microg/ml of chloramphenicol was used, adsorption values were similar on treated and untreated cells. All these results showed that the adsorption process was only partially affected by a few conditions: thermally killed host cells, an incubation temperature of 50 degrees C and pH values of 9 and 10. Nevertheless, and unfortunately, those conditions are not commonly applied during fermented food manufacturing, thus restricting highly the application of strategies currently available to reduce phage infections in industrial environments. This work also contributes to increase the currently knowledge on the biological aspects of L. plantarum bacteriophages.

Recorrido sobre las lenguas del Chaco y los aportes a la investigación lingüística Golluscio, Lucia Angela; Vidal, Alejandra Silvia El Chaco es una de las regiones más ricas de América del Sur, no sólo desde el punto de vista ecológico, sino en términos de su diversidad etnolingüística. Este artículo ofrece primero un panorama actualizado sobre las lenguas chaqueñas y su clasificación genealógica así como un estado del arte de las obras publicadas sobre las lenguas del Chaco argentino. Después de reseñar los estudios sobre sintaxis en las lenguas chaqueñas anteriores a este volumen de Amerindia, las autoras se centran en los planteos teóricos que emergen del estudio de la cláusula y las relaciones interclausales en esta área lingüística, haciendo hincapié en los sistemas de alineamiento, las clases de palabras, sus límites y superposiciones, la relacionalidad de los sustantivos, los distintos tipos de cláusulas y de predicados, los procesos de combinación de verbos y de enlace entre cláusulas a nivel oracional y discursivo. Por último, pasan revista a los aspectos en los cuales los trabajos compilados contribuyen a la discusión y profundización de todos esos temas.

Nonrandom assembly of bacterial populations in activated sludge flocs Ayarza, Joaquín M.; Guerrero, Leandro Demián; Erijman, Leonardo The aim of this work was to investigate the dynamics of assembly of bacterial populations in activated sludge flocs. We approached this question by following the development of active bacterial populations during floc development in four replicated lab-scale activated sludge reactors, in which solid retention time (SRT) was set at 4 days. The null hypothesis was that the similarities in community composition could be accounted for by the probability that the same organisms occur in more than one replicated reactor. Microscopic imaging showed that the size of flocs in reactors with biomass retention increased during the first few days until a steady-state size was reached. The diversity and community structure of the sludge in all reactors were analyzed during a period of up to ten SRT, using denaturing gradient gel electrophoresis (DGGE) of reverse-transcription polymerase chain reaction-amplified 16S rRNA. High rates of change in DGGE profiles from consecutive sampling points suggested a high level of dynamics in all reactors. This conclusion was confirmed by the application of the Raup and Crick probability-based similarity index (SRC) for the comparison of rRNA-based fingerprinting patterns, which indicated that bacterial communities within reactors were not significantly similar after three SRT (0.05 < SRC > 0.95) and became significantly dissimilar after five SRT (SRC < 0.05). More importantly, significant similarity between replicate reactors was observed at all times analyzed (SRC > 0.95). The fact that the patterns between replicates were more reproducible than expected by chance under highly dynamic conditions allowed us to reject the null hypothesis that activated sludge floc communities assemble randomly from the available source pool of bacteria. We suggest that communities progressively recruit from the available pool of bacterial species, each with particular ecological requirements that determine their time of emergence into the community. © 2009 Springer Science+Business Media, LLC.

Density and habitat use at different spatial scales of a guanaco population (Lama guanicoe) in the Monte desert of Argentina Acebes, Pablo; Traba, Juan; Malo, Juan E.; Ovejero Aguilar, Ramiro Jose Antonio; Borghi, Carlos Eduardo The first density estimates of a peripheral guanaco population and its habitat use at different spatial scales are presented for a protected area of Monte desert, Argentina. Transects were surveyed in the wet and dry seasons of 2005. All guanaco herds observed during systematic surveys using roads and tracks were GPS located and their habitat use was identified. Herd size differed significantly between the dry and wet seasons. Population densities differed between wet (0.10-0.12 individuals/km2) and dry seasons (0.60-0.75 individuals/km2). The population estimates ranged from 75 individuals (dry season) to 388 individuals (wet season). Guanacos showed differential habitat use, the first determinant being abiotic factors, such as topography, soil characteristics or microclimate conditions, animals being detected in rougher rocky substrata in the dry season and in open flat terrain in the wet season, followed by a mesoscale selection defined by plant communities. At the latter scale, guanaco preferentially used mixed creosote bushland and saltbush more intensively during the wet season, and open scrub and columnar-cactus slopes in the dry season. The estimated population of this protected area was small but its population density was within the range of other populations and was relatively high for this dry and unproductive area.

Cross-habitat variation in the phenology of a colonial spider: Insights from a reciprocal transplant study Fernández Campón, María Florencia In species with widespread distribution, populations found in markedly different environments can show differences in developmental traits. This, in time, can have an effect on reproductive success. Sources of variation in developmental traits can be genetic or environmentally induced. I examined the relationship between environmental and genetic influences on juvenile development in populations of the colonial spider, Parawixia bistriata, located at sites with different moisture regimes and associated environmental variables (e.g., prey availability). It was expected that individuals from different populations would show differences in developmental traits and that those differences will be associated with lower reproductive success at dry sites. I recorded the phenology and developmental traits of native and transplanted individuals in the field and estimated reproductive success based on clutch size. Colonies from wet versus dry sites showed different phenologies, with individuals at dry sites maturing later. Transplant results suggest plasticity in instar duration caused by environmental effects. Despite differences in resources and spider phenology, clutch sizes of native dry and wet populations were similar. Transplanted individuals, however, were differentially affected. Transplants from wet to dry sites (WD) showed lower growth rates and smaller clutches, whereas transplants from dry to wet sites had larger clutch sizes than in native habitat. Delayed maturation and failure to reproduce in WD individuals is associated with a lower tendency to capture prey in groups and less aggressive interactions during prey capture. Thus, despite negative environmental effects on development, dry native individuals have evolved non-developmental traits that allow successful reproduction.

Maximal operators, Riesz transforms and Littlewood-Paley functions associated with Bessel operators on BMO Betancor, J. J.; Chicco Ruiz, Anibal Leonardo; Fariña, J. C.; Rodriguez Mesa, L. In this paper we study boundedness properties of certain harmonic analysis operators (maximal operators for heat and Poisson semigroups, Riesz transforms and Littlewood– Paley g-functions) associated with Bessel operators, on the space BMOo(R) that consists of the odd functions with bounded mean oscillation on R.

El temor reverencial: un principio político en Hobbes y Vico Alarcón, Patricio Este artículo tiene como objetivo dilucidar la función que cumple el temor reverencial en el Leviatán de Thomas Hobbes y en la Scienza Nuova de Giambattista Vico como principio del mundo civil. Se centra la atención en la imaginación y en la religión como elementos fundantes de las instituciones humanas, analizando sus implicanciones.; This article aims to elucidate the role of ‘awe’ in Thomas Hobbes’s Leviathan and in Giambattista Vico’s Scienza Nuova as a principle of civilian world. The focus is on imagination and religion as foundational elements of human institutions, analyzing its implications.

Self-assembly of a silylated steroid-based organogelator and its use as template for the in situ sol-gel polymerization of tetraethyl orthosilicate Edelsztein, Valeria Carolina; Burton, Gerardo; Di Chenna, Pablo Hector In this paper we report the synthesis of a new steroid-based low-molecular weight organogelator, the analysis of the self-assembled fibrilar network (SAFIN) and its use as template for the preparation of SiO2 nanotubes. This novel steroidal organogelator has a unique structure among the well known family of steroid-based organogelators, the most important characteristic of this molecule is the presence of a silyl ether group at C-3 together with a 6β,19-oxo bridge. It was capable to gelate hydrocarbons and tetraethyl orthosilicate at very low concentrations (<1 wt %). An insight into the aggregation mechanism is provided revealing that complementary interaction between an α-oriented hydrogen bond donor and a β-oriented acceptor on the steroid skeleton is the driving force for the primary 1D self-assembly. The SAFIN was successfully used as template to grow silica nanotubes (external diameter: 40-60 nm, internal diameter: 7 nm and several micrometers length) through a catalyst-free in situ co-assembly polymerization process. Hydrogen bond or electrostatic interactions between the anionic silicate intermediate species and the SAFIN are proposed to be the driving force for templating.

Lipase-catalyzed synthesis and characterization of a novel linear polyamidoamine oligomer Monsalve, Leandro Nicolas; Kaniz Fatema, M.; Nonami, Hiroshi; Erra Balsells, Rosa; Baldessari, Alicia A linear polyamidoamine oligomer was obtained by polymerization of ethyl acrylate and N-methyl-1,3-diaminopropane, catalyzed by the Candida antarctica lipase. Depending on the reaction conditions such as substrates concentration, solvent and enzyme:substrate ratio, the enzyme catalyzes the polymerization reaction or Michael adducts formation. The polymeric material, characterized by FTIR, 1H and 13C NMR and UV-MALDI-TOF-MS, shows low molecular weight and high monodispersity. The activity showed by C. antarctica lipase in the polymerization reaction is highly selective and allows to obtain a product with potential biomedical applications in mild condition reactions and low environmental impact.

Convexity properties of the condition number Beltran, Carlos; Dedieu, Jean Pierre; Malajovich, Gregorio; Shub, Michael Ira We define in the space of n×m matrices of rank n, n ≤ m, the condition Riemannian structure as follows: For a given matrix A the tangent space at A is equipped with the Hermitian inner product obtained by multiplying the usual Frobenius inner product by the inverse of the square of the smallest singular value of A denoted σ n(A). When this smallest singular value has multiplicity 1, the function A → log(σ n(A) -2) is a convex function with respect to the condition Riemannian structure that is t → log(σ n(A(t)) -2) is convex, in the usual sense for any geodesic A(t). In a more abstract setting, a function α defined on a Riemannian manifold (M, 〈, 〉) is said to be self-convex when log α(γ(t)) is convex for any geodesic in (M, α 〈, 〉). Necessary and sufficient conditions for self-convexity are given when α is C 2. When α(x) = d(x,N) -2, where d(x,N) is the distance from x to a C 2 submanifold N ⊂R j, we prove that α is self-convex when restricted to the largest open set of points x where there is a unique closest point in N to x. We also show, using this more general notion, that the square of the condition number ∥A∥ F /σ n(A) is self-convex in projective space and the solution variety.

Theoretical and experimental study of electrochemical reactors with three-dimensional bipolar electrodes Gonzalez Perez, Omar; Bisang, Jose Maria A mathematical model to represent three-dimensional bipolar electrodes is proposed taken into account the leakage current. The model is analytically solved when the electrochemical reaction has a mass-transfer control at low overpotentials, which represents a limiting case of the general mathematical treatment. For this simplified situation, expressions are deduced to evaluate the current and potential distribution and to calculate the leakage current. The effect on the leakage current of kinetic, electrochemical and geometric variables, which are lumped into one dimensionless number, is discussed. The influence of the leakage current on the optimal bed depth under limiting current conditions is also analyzed. Likewise, experimental data, using the deposition-dissolution of copper as test reaction, are compared with the theoretical prediction of the general treatment achieving a good agreement between both.

Successful experiment?: on Chile’s experience with territorial use rights in fisheries Orensanz, Jose Maria; Parma, Ana María Chile’s experience with territorial use rights in fi sheries shows their potential for the management of coastal resources, provided some simple safeguards are put in place.