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Buenos Aires, Argentina

Roura Bas P.,Comision Nacional de la Energia Atomica | Aligia A.A.,Bariloche Atomic Center
Journal of Physics Condensed Matter | Year: 2010

We study the singlet-triplet Anderson model (STAM) in which a configuration with a doublet is hybridized with another containing a singlet and a triplet, as a minimal model to describe two-level quantum dots coupled to two metallic leads in effectively a one-channel fashion. The model has a quantum phase transition which separates regions of a doublet and a singlet ground state. The limits of integer valence of the STAM (which include a model similar to the underscreened spin-1 Kondo model) are derived and used to predict the behavior of the conductance through the system on both sides of the transition, where it jumps abruptly. At a special quantum critical line, the STAM can be mapped to an infinite- U ordinary Anderson model (OAM) plus a free spin 1/2. We use this mapping to obtain the spectral densities of the STAM as a function of those of the OAM at the transition. Using the non-crossing approximation (NCA), we calculate the spectral densities and conductance through the system as a function of temperature and bias voltage, and determine the changes that take place at the quantum phase transition. The separation of the spectral density into a singlet and a triplet part allows us to shed light on the underlying physics and to explain a shoulder observed recently in the zero bias conductance as a function of temperature in transport measurements through a single fullerene molecule (Roch et al 2008 Nature 453 633). The structure with three peaks observed in nonequilibrium transport in these experiments is also explained. © 2009 IOP Publishing Ltd.

Perillo P.M.,Comision Nacional de la Energia Atomica
Materials Today Communications | Year: 2016

TiO2 membrane nanotubes prepared by anodization method was used for detection of d-butylamine (DBA) operating at low temperature. The TiO2 membrane nanotubes have an average diameter of 100 nm and a length of 12 μm. The flexible gas sensor was achieved using a flexible substrate onto which array interdigitated gold electrodes were obtained using conventional microfabrication procedure.The sensing characteristics were investigated by measuring the electrical resistance of the sensor in a test chamber as a function of gas concentration. This was used to detect DBA within a concentration range of 8-20 ppm.The results indicate that TiO2 membrane nanotubes has good potential in practical applications, due to its remarkable performance and facile synthesizing methods. © 2016 Elsevier Ltd.

Roncaroli F.,Comision Nacional de la Energia Atomica | Blesa M.A.,National University of San Martin of Argentina
Physical Chemistry Chemical Physics | Year: 2010

A FTIR-ATR kinetic study on the adsorption of carboxylic acids (oxalic, citric, malonic, succinic, gallic, EDTA and TTHA acids, where EDTA = ethylenediaminetetraacetate and TTHA = triethylenetetramine-N,N,N′, N′′,N′′′,N′′′-hexaacetate, in the concentration range 6 × 10-7 M-2 × 10-5 M on TiO2 (Degussa P25) by ATR-FT-IR is reported. The influence of carboxylic acid concentration, pH, ionic strength, TiO2 load in the film is presented. The adsorption processes follows pseudo-first-order kinetics at constant ligand concentration, even though several adsorption modes have been reported in the literature. Plots of the pseudo first order constant k obsvs. carboxylic acid concentration are linear for all the studied ligands. The slopes of these plots (a) are not very sensitive to the nature of the ligands; a decrease in a is observed as the size increases. The intercept (b) is inversely related to the stability of the surface complexes. We propose that both the rate of adsorption, and the desorption rate are controlled by the diffusion through the pores of the film, although in the case of (b), the desorption rate is modulated by the stability of the surface complex. These results are relevant for oxide dissolution, remediation of water, pollutants removal, sensors design and heterogeneous photocatalysis. © 2010 the Owner Societies.

Oppezzo O.J.,Comision Nacional de la Energia Atomica
Journal of Photochemistry and Photobiology B: Biology | Year: 2012

The contribution of different components of sunlight to the lethal action exerted by this radiation on bacteria was studied using Pseudomonas aeruginosa ATCC27853 as a model organism. When solar UVB was excluded from the incident radiation by filtering it through a naphthalene solution (cut off 327 nm), significant modifications were observed in the cell-death kinetics. These modifications were comparable to those expected for a reduction of 27-32% in the dose rate, according to the model used in the analysis of the survival curves, and were also observed when the effects of sunlight filtered through polyethylene terephthalate (cut off 331 nm) or polystyrene (cut off 298 nm) were compared. Viability of P. aeruginosa remained almost unchanged when the incident radiation was filtered through a sodium nitrite solution (cut off 406 nm) in order to exclude the UVA and UVB components of sunlight. Nevertheless, a delay in colony formation was detected in bacteria treated in this way, suggesting that a non-lethal effect was exerted by visible light. The results are not consistent with a generally accepted notion which attributes the lethal action of sunlight to the radiation with wavelengths above 320 nm. The characterization of UVB contribution to the lethal effect of sunlight on bacteria is relevant for understanding of the mechanism of cell death, and for improvement of dosimetry techniques and irradiation procedures. © 2012 Elsevier B.V. All rights reserved.

Roura-Bas P.,Comision Nacional de la Energia Atomica
Physical Review B - Condensed Matter and Materials Physics | Year: 2010

The universal scaling behavior is studied for nonequilibrium transport through a quantum dot. To describe the dot we use the standard Anderson impurity model and use the nonequilibrium noncrossing approximation in the limit of infinite Coulomb repulsion. After solving de Hamiltonian, we calculate the conductance through the system as a function of temperature T and bias voltage V in the Kondo and in the mixed valent regime. We obtain a good scaling function in both regimes. In particular, in the mixed valent regime, we find excellent agreement with recent experiments and previous theoretical works. © 2010 The American Physical Society.

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