University Nac

San Carlos de Bariloche, Argentina

University Nac

San Carlos de Bariloche, Argentina
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Querales-Flores J.D.,Bariloche Atomic Center | Querales-Flores J.D.,University Nac | Ventura C.I.,Bariloche Atomic Center | Ventura C.I.,University Nac | And 2 more authors.
Physica B: Condensed Matter | Year: 2016

A good description of the electronic structure of BiS2-based superconductors is essential to understand their phase diagram, normal state and superconducting properties. To describe the first reports of normal state electronic structure features from angle resolved photoemission spectroscopy (ARPES) in LaO1-x Fx BiS2, we used a minimal microscopic model to study their low energy properties. It includes the two effective tight-binding bands proposed by Usui et al., Phys. Rev. B, 86, 2012, 220501(R), and we added moderate intra- A nd inter-orbital electron correlations related to Bi-(pY, pX) and S-(pY, pX) orbitals. We calculated the electron Green's functions using their equations of motion, which we decoupled in second-order of perturbations on the correlations. We determined the normal state spectral density function and total density of states for LaO1-x Fx BiS2, focusing on the description of the k-dependence, effect of doping, and the prediction of the temperature dependence of spectral properties. Including moderate electron correlations, improves the description of the few experimental ARPES and soft X-ray photoemission data available for LaO1-x Fx BiS2. Our analytical approximation enabled us to calculate the spectral density around the conduction band minimum at k→0=(0.45π,0.45π), and to predict the temperature dependence of the spectral properties at different BZ points, which might be verified by temperature-dependent ARPES. © 2016 Elsevier B.V. All rights reserved.

Sofia Nanni A.,University Nac | Ortiz P.E.,National University of Tucuman | Ortiz P.E.,CONICET | Pablo Jayat J.,University Nac | And 2 more authors.
Hornero | Year: 2012

We studied the diet of the Common Barn-Owl (Tyto alba) in the Dry Chaco of Santiago del Estero, Argentina. From 332 pellets collected between 2007 and 2009 we analyzed the seasonal variation in number and biomass of prey-items, diversity, and trophic niche width. We identified 1170 individuals belonging to 14 prey-items, corresponding to mammals (87%), birds (7%) and insects (6%). Cricetid rodents were the most frequent group (85%) with the highest biomass contribution (>75%), being Calomys spp. the most abundant item. During the dry season of the first year, the abundance of micromammals reached the highest values while birds and insects showed the opposite pattern. Diversity and trophic niche width showed their highest values during the wet season and niche overlap was lower between samples of different seasons. Seasonal variation in biomass was mostly due to a higher consumption of birds during the wet season of 2008. In the wet season of the second year the diet showed an anomalous behaviour, in some cases showing the opposite of the expected patterns, probably related to a pronounced decrease in rainfall. The results of this study allow us to confirm a generalist-opportunistic diet, with high consumption of micromammals during the dry season probably explained by their high population sizes. Environmental modifications could be explaining the extreme dominance of Calomys spp., as it has been documented in other regions of Argentina.

Monteserin A.,University Nac | Monteserin A.,CONICET | Schiaffino S.,University Nac | Schiaffino S.,CONICET | And 2 more authors.
Computers and Education | Year: 2010

In CSCL systems, students who are solving problems in group have to negotiate with each other by exchanging proposals and arguments in order to resolve the conflicts and generate a shared solution. In this context, argument construction assistance is necessary to facilitate reaching to a consensus. This assistance is usually provided with isolated arguments by demand, but this does not offer students a real and integral view of the conflicts. In this work, we study the utilisation of argumentation plans to assist a student during the argumentation. The actions of an argumentation plan represent the arguments that a student might use during the argumentation process. Moreover, these plans can be integrated with the tasks needed to reach a shared solution. These plans give the student an integral and intuitive view of the problem resolution and the conflict that must be resolved. We evaluated our proposal with students of an Artificial Intelligence course. This evaluation was carried out by comparing three different assistance scenarios in which students had to solve exercises: no assistance, assistance with isolated arguments, and assistance with argumentation plans. The results obtained show that reaching consensus was easier for the students when the assistance was provided using argumentations plans. © 2009 Elsevier Ltd. All rights reserved.

Leconte M.C.,University Nac | Mazzarino M.J.,CONICET | Satti P.,CONICET | Crego M.P.,CONICET
Biology and Fertility of Soils | Year: 2011

Rice hulls and sawdust are commonly used to compost poultry manure in several countries. We studied the effects of these two bulking agents and different sizes of compost particles on the release of N and P from poultry manure composts. Five composts, produced with a 2:1 and 1:1 ratio of sawdust or rice hulls to poultry manure and 1:1:1 of all three materials, were separated into fractions >10, 5-10, 1-5, and <1 mm. The >10-mm fraction was less than 1. 5% and was not further analyzed. In all other fractions, pH, electrical conductivity, organic C, lignin, cellulose, and total N, P, Ca, K, and Si were determined and related to N and P release in 16-week incubations of a sandy soil amended with 40 g kg -1 of each fraction. Nitrogen release with composts containing sawdust was higher than with rice hull composts (114-189 vs. 78-127 mg kg -1 at week 16), and this was highly correlated with TN (1. 9-3. 7% vs. 1. 4-2. 7%) and negatively with pH (5. 5-6. 2 vs. 6. 7-6. 9). Extractable P was very high (85-340 mg kg -1 at week 16), and the highest values were associated with the composts with more proportion of poultry manure. An increase in stability with decreasing particle size was apparent from the gradient of N and P dynamics: from net P release and an exponential pattern of net N mineralization with the coarsest fraction to net P retention and a linear pattern of N mineralization with the smallest one. Despite its higher fertilizer value, the 5- to 10-mm fraction posed the highest environmental risk due to elevated P release over time. © 2011 Springer-Verlag.

Gonzalez M.,National University of Tucuman | Tereschuk M.L.,National University of Tucuman | Criado S.,National University of Rio Cuarto | Reynoso E.,National University of Rio Cuarto | And 6 more authors.
Redox Report | Year: 2015

Objectives: The study was focused on the activity of propolis from Amaicha del Valle, Argentina (ProAV) as a promoter and scavenger of Riboflavin (Rf) – photogenerated reactive oxygen species (ROS). Methods: Through a kinetic and mechanistic study, employing stationary and time-resolved photochemical and electrochemical techniques, the protecting activity of ProAV was investigated. Results: In the absence of light and Rf, ProAV exerted a relatively efficient inhibitory effect on 1,1-diphenyl-2- picrylhydrazyl radicals and acts as a protector of artificially promoted linoleic acid oxidation. Under aerobic visible-light-irradiation conditions, in the presence of Rf as the only light-absorber species, a complex picture of competitive processes takes place, starting with the quenching of singlet and triplet electronically excited states of Rf by ProAV. The species O2(1 g), O2 •−, H2O2, and OH• are generated and interact with ProAV. Discussion: ProAV behaves as an efficient ROS scavenger. It is scarcely photo-oxidized by interaction with the mentioned ROS. Quantitative results indicate that ProAV is even more resistant to photo-oxidation than the recognized antioxidant trolox. Two dihydroxychalcones, mostly present in the ProAV composition, are responsible for the protecting activity of the propolis. © W. S. Maney & Son Ltd 2015.

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