Resumen:

A comprehensive study of nonstoichiometry titanium oxide thin films (TiOx, 0.3≤x≤2) prepared by ion beam deposition technique is reported. The physical properties of the material are studied by ultraviolet and x-ray photoelectron, Raman, and Fourier transform infrared spectroscopies, and atomic force microscopy. An abrupt transition from metallic characteristics to a wide gap semiconductor is observed in a very narrow range of oxygen variation. Concomitantly with this change the crystal structure and morphology suffer remarkable physical properties modifications. This transformation is ascribed to surface-volume energy minimization due to the influence of oxygen determining the size of the TiO2 particles during coalescence. © 2010 American Institute of Physics.

Afiliación de los autores: Marchi, M.C. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Afiliación de los autores: Bilmes, S.A. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Afiliación de los autores: Alvarez, F. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales; Argentina.

Resumen:

Explanations for gene tree discordance with respect to a species tree are commonly attributed to deep coalescence (also known as incomplete lineage sorting [ILS]), as well as different evolutionary processes such as hybridization, horizontal gene transfer and gene duplication. Among these, deep coalescence is usually quantified as the number of extra linages and has been studied as the principal source of discordance among gene trees, while the other processes that could contribute to gene tree discordance have not been fully explored. This is an important issue for hybridization because interspecific gene flow is well documented and widespread across many plant and animal groups. Here, we propose a new way to detect gene flow when ILS is present that evaluates the likelihood of different models with various levels of gene flow, by comparing the expected gene tree discordance, using the number of extra lineages. This approach consists of proposing a model, simulating a set of gene trees to infer a distribution of expected extra lineages given the model, and calculating a likelihood function by comparing the fit of the real gene trees to the simulated distribution. To count extra lineages, the gene tree is first reconciled within the species tree, and for a given species tree branch the number of gene lineages minus one is counted. We develop a set of r functions to parallelize software to allow simulations, and to compare hypotheses via a likelihood ratio test to evaluate the presence of gene flow when ILS is present, in a fast and simple way. Our results show high accuracy under very challenging scenarios of high impact of ILS and low gene flow levels, even using a modest dataset of 5–10 loci and 5–10 individuals per species. We present a powerful and fast method to detect hybridization in the presence of ILS. We discuss its advantage with large dataset (such as genomic scale), and also identifies possible issues that should be explored with more complex models in future studies.

Afiliación de los autores: Olave, Melisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico para el Estudio de los Ecosistemas Continentales; Argentina. University of Konstanz; Alemania

Afiliación de los autores: Avila, Luciano Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico para el Estudio de los Ecosistemas Continentales; Argentina

Afiliación de los autores: Sites, Jack W.. Brigham Young University; Estados Unidos

Afiliación de los autores: Morando, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Centro Nacional Patagónico. Instituto Patagónico para el Estudio de los Ecosistemas Continentales; Argentina

Resumen:

Coating strategies of inorganic nanoparticles (NPs) can provide properties unavailable to the NP core alone, such as targeting, specific sensing, and increased biocompatibility. Non-covalent amphiphilic NP capping polymers function via hydrophobic interactions with surface ligands and are extensively used to transfer NPs to aqueous media. For applications of coated NPs as actuators (sensors, markers, or for drug delivery) in a complex environment, such as biological systems, it is important to achieve a deep understanding of the factors affecting coating stability and behavior. We have designed a system that tests the coating stability of amphiphilic polymers through a simple fluorescent readout using either polarity sensing ESIPT (excited state intramolecular proton transfer) dyes or NP FRET (Förster resonance energy transfer). The stability of the coating was determined in response to changes in polarity, pH and ionic strength in the medium. Using the ESIPT system we observed linear changes in signal up to ∼20-25% v/v of co-solvent addition, constituting a break point. Based on such data, we propose a model for coating instability and the important adjustable parameters, such as the electrical charge distribution. FRET data provided confirmatory evidence for the model. The ESIPT dyes and FRET based methods represent new, simple tools for testing NP coating stability in complex environments.

Afiliación de los autores: Azcárate, Julio César. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina

Afiliación de los autores: Díaz, Sebastián A.. Max Planck Institute For Biophysical Chemistry; Alemania

Afiliación de los autores: Fauerbach, Jonathan Arturo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Centro de Investigaciones en Hidratos de Carbono. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Centro de Investigaciones en Hidratos de Carbono; Argentina

Afiliación de los autores: Gillanders, Florencia. Max Planck Institute For Biophysical Chemistry; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Centro de Investigaciones en Bionanociencias ; Argentina

Afiliación de los autores: Rubert, Aldo Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina

Afiliación de los autores: Jares Erijman, Elizabeth A.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Química Orgánica; Argentina

Afiliación de los autores: Jovin, Thomas M.. Max Planck Institute For Biophysical Chemistry; Alemania

Afiliación de los autores: Fonticelli, Mariano Hernan. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina

Resumen:

The objective of this work was to obtain water-in-oil (w/o) emulsions with polyglycerol polyricinoleate (PGPR) as emulsifier and to study the effect of the addition of calcium in the dispersed aqueous phase on the stability of these systems. Emulsions were formulated with 0.2, 0.5 and 1.0% w/w PGPR and 10% w/w water containing calcium chloride at varied concentrations or other salts (calcium lactate or carbonate; sodium, magnesium or potassium chloride). The stability of these systems was studied with a vertical scan analyzer during 15 days; coalescence and sedimentation were observed as simultaneous destabilization processes. The increase of PGPR concentration and/or calcium chloride content gave more stable emulsions. The stabilizing effect of calcium salt was attributed to the diminution of the water droplets size, the decrease of the attractive force between water droplets and the increase of the adsorption density of the emulsifier. The viscoelastic parameters of the interfacial film were decreased with increasing calcium and PGPR concentrations. Calcium chloride produced a higher increase of stability than calcium salts with lower dissociation degree. The presence of any assayed salt in the aqueous phase also allowed the stabilization of w/o emulsions with higher water contents. © 2009 Elsevier Inc. All rights reserved.

Afiliación de los autores: Márquez, Andrés Leonardo. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigación y Desarrollo en Criotecnología de Alimentos. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de Investigación y Desarrollo en Criotecnología de Alimentos; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentina

Afiliación de los autores: Medrano, Alejandra. Universidad de la República; Uruguay

Afiliación de los autores: Panizzolo, Luis A.. Universidad de la República; Uruguay

Afiliación de los autores: Wagner, Jorge Ricardo. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Resumen:

La coalescencia parcial de las emulsiones o/w puede inducirse por agitación, debido a la presencia de cristales de grasa en las gotas. En este trabajo se estudió el efecto de la agitación sobre el comportamiento reológico de emulsiones tipo crema preparadas con leche de soja reconstituida (5% y 10%), aceite de girasol y grasa láctea de alto punto de fusión comparativamente con una nata comercial. Las cremas, inicialmente líquidas, aumentaron progresivamente la consistencia durante la agitación cuando el contenido de fase lipídica fue del 40%. Aunque se requirió un mayor tiempo de agitación en cremas con leche más concentrada (a igual proporción de fase lipídica) se registró un aumento más pronunciado de la viscoelasticidad. Por otra parte, al aumentar la concentración de grasa láctea en la fase lipídica se requirió un tiempo de agitación menor por verse favorecida la coalescencia parcial. Independientemente del contenido en grasa láctea, las emulsiones con fases lipídicas relativamente bajas (20%) no aumentaron su consistencia por agitación.

In o/w emulsions, partial coalescence can be induced by stirring, due to the presence of fat crystals in oil droplets. In this work, effect of stirring on rheological behaviour of cream-like emulsions prepared with reconstituted soybean milk, sunflower oil and milk fat (high melting fraction) was analysed. Commercial milk cream sample was used as control. During stirring, progressive increase of consistency of 40% lipid phase emulsions was observed. Although a high stirring time was required in emulsions prepared with more concentrated soybean milk, a pronounced enhance of its viscoelasticity was observed. On the other hand, when milk fat concentration was increased in lipid phase, it was required a low stirring time value as consequence of promoted partial coalescence. Independently of the milk fat content, in emulsions with relatively low lipid phase content (20%) an increase of consistency was not observed.

Facultad de Ciencias Exactas

Resumen:

En este trabajo se analizó el efecto de ciclos calentamientoenfriamiento sobre cremas preparadas a 60ºC con leche de soja en polvo reconstituida, aceite de girasol y grasa láctea y almacenadas posteriormente a 4ºC durante 3 horas. Los ciclos consistieron en un calentamiento a 40ºC o 50ºC (30 min) seguido de un enfriamiento a 4ºC (2 horas). En los ensayos realizados sobre cremas formuladas con 40% de fase lipídica se observó un aumento de los valores de G’ y G’’ después del ciclo 40ºC-4ºC, a pesar de no haberse observado un aumento en el contenido de grasa sólida. Estos resultados se atribuyen a la formación de agregados de gotas inducida por la fusión parcial, reordenamiento y recristalización de la grasa láctea en las gotas. Estudios de resonancia magnética nuclear de pulsos, calorimetría diferencial de barrido y distribución de tamaño de partícula por difracción de luz permitieron corroborar que el principal mecanismo de formación de agregados es la coalescencia parcial. Frente al mismo ciclo térmico, la crema con 20% de fase lipídica no aumentó su consistencia, dada la ausencia o formación insuficiente de agregados por el bajo número de gotas. Ensayos similares sobre la nata a 40ºC o sobre las cremas de leche de soja a 50ºC, no mostraron cambios reológicos, debido a la fusión casi total de la grasa.

In this work, the effect of temperature cycling on emulsions formulated with reconstituted soy milk, sunflower oil and high melting point milk fat was analysed. The emulsions were prepared at 60°C, stored at 4°C (3 h), warmed at 40°C or 50°C (30 min) and afterwards cooled at 4°C (2h). Although solid fat content of emulsions did not raised after tempering at 40°C, increase of G' and G″ was observed only in those formulated with 40% lipid phase. This phenomenon was attributed to droplet aggregation due to partial melting, recrystallization and reordering of fat crystals in oil droplets. The main droplet destabilization mechanism was the partial coalescence; it was corroborated by nuclear magnetic resonance, differential scanning calorimetry and droplet size distribution studies. On the other hand, the consistency of 20% of lipid phase emulsion did not increased. Low droplet concentration disfavoured the partial coalescence of droplets. Similar assays on cream at 40°C and cream-like soy milk emulsions at 50°C, did not show rheological modifications, due to almost total melting of milk fat during tempering.

Facultad de Ciencias Exactas

Resumen:

Lack of resolution in a phylogenetic tree is usually represented as a polytomy, and often adding more data (loci and taxa) resolves the species tree. These are the ‘soft’ polytomies, but in other cases additional data fail to resolve relationships; these are the ‘hard’ polytomies. This latter case is often interpreted as a simultaneous radiation of lineages in the history of a clade. Although hard polytomies are difficult to address, model-based approaches provide new tools to test these hypotheses. Here, we used a clade of 144 species of the South American lizard clade Eulaemus to estimate phylogenies using a traditional concatenated matrix and three species tree methods: *BEAST, BEST, and minimizing deep coalescences (MDC). The different species tree methods recovered largely discordant results, but all resolved the same polytomy (e.g. very short internodes amongst lineages and low nodal support in Bayesian methods). We simulated data sets under eight explicit evolutionary models (including hard polytomies), tested these against empirical data (a total of 14 loci), and found support for two polytomies as the most plausible hypothesis for diversification of this clade. We discuss the performance of these methods and their limitations under the challenging scenario of hard polytomies.

Afiliación de los autores: Olave, Melisa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina

Afiliación de los autores: Avila, Luciano Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina

Afiliación de los autores: Sites, Jack W.. University Brigham Young; Estados Unidos

Afiliación de los autores: Morando, Mariana. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina

Resumen:

In this work, we analyze some aspects of the macroscopic Gurson-Tvergaard-Needleman (GTN) constitutive model when it is addressed to solve ductile fracture problems by means of numerical simulations:(i) The analytical solutions of the material discontinuous bifurcation problem is performed.Closed and exact formulas are obtained. The so determined critical conditions and the developed strain localization mode are afterward studied and compared in crack growth problems. Even when this methodology of analysis is rather standard at the present, the conclusions drawn from this study differ significantly from that obtained with a similar analysis in quasi-brittle fracture problems.(ii) A new very robust numerical integration method for the GTN model, namely the Impl-Ex Method, is proposed. It is a low computational cost algorithm, equivalent to a linear problem per each integration step, with a reasonable precision for engineering purposes. Its accuracy and convergence rate is assessed by means of an error study applied to a ductile fracture test simulation.(iii) A detailed analysis of a plane strain ductile crack growth problem is performed in a material containing two size-scale of voids. In the analysis, particular attention is given to the mesh size dependence and to the coalescence of the larger void.

Afiliación de los autores: Sánchez, Pablo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

Afiliación de los autores: Oliver, Juan Pablo. Technical University of Catalonia; España

Afiliación de los autores: Huespe, Alfredo Edmundo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química. Universidad Nacional del Litoral. Instituto de Desarrollo Tecnológico para la Industria Química; Argentina

Resumen:

Partial coalescence was studied in double (W1/O/W2) emulsions prepared with skimmed milk, polyglycerol polyricinoleate (PGPR) as lipophilic emulsifier, and different fats. Microstructural and rheological analyses were performed. Encapsulation efficiency (as a parameter of inner water retention) and solid fat content were estimated by differential scanning calorimetry. The presence of PGPR in dispersed lipid phase promoted partial coalescence especially at higher concentration. This promotion of partial coalescence may have been produced by the increase of collision frequency due to protein displacement by PGPR at the outer interface and/or the increase of capture efficiency due to the modification of fat crystals by PGPR. Partial coalescence was also favored when inner water droplets were released as a consequence of an osmotic unbalance between inner and outer aqueous phases. Thus, the addition of glucose in dispersed aqueous phase decreased the partial coalescence degree due to the higher encapsulation efficiency given by the balanced osmotic pressures. With respect to the effect of the employed fat on partial coalescence, the obtained data indicate that the phenomenon was favored at higher solid fat content in lipid phase. Results led to the conclusion that inner osmolality, encapsulation efficiency, and inhibition of partial coalescence were correlated.

Afiliación de los autores: Pérez, María Paula. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Investigación en Funcionalidad y Tecnología de Alimentos; Argentina

Afiliación de los autores: Wagner, Jorge Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Investigación en Funcionalidad y Tecnología de Alimentos; Argentina

Afiliación de los autores: Márquez, Andrés Leonardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional de Quilmes. Departamento de Ciencia y Tecnología. Laboratorio de Investigación en Funcionalidad y Tecnología de Alimentos; Argentina

Resumen:

A clear understanding of the structural foundations underlying protein aggregation is an elusive goal of central biomedical importance. A step toward this aim is exemplified by the β- barrel motif represented by the intestinal fatty acid binding protein (IFABP) and two abridged all-β sheet forms (δ98δ and δ78δ). At odds with the established notion that a perturbation of the native fold should necessarily favor a buildup of intermediate forms with an enhanced tendency to aggregate, the intrinsic stability (δG°H2O) of these proteins does not bear a straightforward correlation with their trifluoroethanol (TFE)-induced aggregation propensity. In view of this fact, we found it more insightful to delve into the connection between structure and stability under sub-aggregating conditions (10% TFE). In the absence of the co-solvent, the abridged variants display a common native-like region decorated with a disordered Cterminal stretch. Upon TFE addition, an increase in secondary structure content is observed, assimilating them to the parent protein. In this sense, TFE perturbs a common native like region while exerting a global compaction effect. Importantly, in all cases, fatty acid binding function is preserved. Interestingly, energetic as well as structural diversity in aqueous solution evolves into a common conformational ensemble more akin in stability. These facts reconcile apparent paradoxical findings related to stability and rates of aggregation. This scenario likely mimics the accrual of aggregation-prone species in the population, an early critical event for the development of fibrillation.

Afiliación de los autores: Angelani, Carla Romina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Físico-Química Biológicas "Prof. Alejandro C. Paladini". Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Físico-Química Biológicas; Argentina

Afiliación de los autores: Caramelo, Julio Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Bioquímicas de Buenos Aires. Fundación Instituto Leloir. Instituto de Investigaciones Bioquímicas de Buenos Aires; Argentina

Afiliación de los autores: Curto, Lucrecia María. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Físico-Química Biológicas "Prof. Alejandro C. Paladini". Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Físico-Química Biológicas; Argentina

Afiliación de los autores: Delfino, Jose Maria. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Instituto de Química y Físico-Química Biológicas "Prof. Alejandro C. Paladini". Universidad de Buenos Aires. Facultad de Farmacia y Bioquímica. Instituto de Química y Físico-Química Biológicas; Argentina