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Mattea F.,National University of Cordoba | Romero M.R.,National University of Cordoba | Vedelago J.,National University of Cordoba | Vedelago J.,Institute Fisica Enrique Gaviola | And 5 more authors.
Applied Radiation and Isotopes | Year: 2015

Polymer gel dosimeters have specific advantages for recording 3D radiation dose distribution in diagnostic and therapeutic medical applications. But, even in systems where the 3D structure is usually maintained for long periods of time after irradiation, it is still not possible to eliminate the diffusion of the different species in the regions of dose gradients within the gel. As a consequence, information of the dose loses quality over time. In the pursuit of a solution and to improve the understanding of this phenomenon a novel system based on itaconic acid and N-N'-methylene-bisacrylamide (BIS) is hereby proposed. Effects of changes in the chemical structure of the monomers over the dosimetric sensitivity and over the post-irradiation diffusion of species was studied. In this study, one of the carboxylic groups of the itaconic acid molecule was modified with aniline to obtain molecules with similar reactivity but different molecular sizes. Then, dosimeters based on these modified species and on the original ITA molecules were irradiated in an X-ray tomography apparatus at different doses up to 173. Gy. Afterwards, the resulting dosimeters were characterized by Raman spectroscopy and optical absorbance in order to study their feasibility and capabilities as dosimetric systems, and by optical-CT to analyze the post irradiation diffusion. © 2015 Elsevier Ltd.

Cattena C.J.,Institute Fisica Enrique Gaviola | Fernandez-Alcazar L.J.,Institute Fisica Enrique Gaviola | Bustos-Marun R.A.,Institute Fisica Enrique Gaviola | Bustos-Marun R.A.,National University of Cordoba | And 2 more authors.
Journal of Physics Condensed Matter | Year: 2014

Decoherent transport in mesoscopic and nanoscopic systems can be formulated in terms of the D'Amato-Pastawski (DP) model. This generalizes the Landauer-Büttiker picture by considering a distribution of local decoherent processes. However, its generalization for multi-terminal set-ups is lacking. We first review the original two-terminal DP model for decoherent transport. Then, we extend it to a matrix formulation capable of dealing with multi-terminal problems. We also introduce recursive algorithms to evaluate the Green's functions for general banded Hamiltonians as well as local density of states, effective conductances and voltage profiles. We finally illustrate the method by analyzing two problems of current relevance. (1) Assessing the role of decoherence in a model for phonon lasers (SASER). (2) Obtaining the classical limit of giant magnetoresistance from a spin-dependent Hamiltonian. The presented methods should pave the way for computationally demanding calculations of transport through nanodevices, bridging the gap between fully coherent quantum schemes and semiclassical ones. © 2014 IOP Publishing Ltd.

Gleiser R.J.,Institute Fisica Enrique Gaviola | Ramirez M.A.,Institute Fisica Enrique Gaviola
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2012

In this paper we consider some aspects of the relativistic dynamics of a cylindrical shell of counterrotating particles. In some sense these are the simplest systems with a physically acceptable matter content that display in a well-defined sense an interaction with the radiative modes of the gravitational field. These systems have been analyzed previously, but in most cases resorting to approximations, or considering a particular form for the initial value data. Here we show that there exists a family of solutions where the space time inside the shell is flat and the equation of motion of the shell decouples completely from the gravitational modes. The motion of the shell is governed by an equation of the same form as that of a particle in a time-independent one-dimensional potential. We find that under appropriate initial conditions one can have collapsing, bounded periodic, and unbounded motions. We analyze and solve also the linearized equations that describe the dynamics of the system near a stable static solutions, keeping a regular interior. The surprising result here is that the motion of the shell is completely determined by the configuration of the radiative modes of the gravitational field. In particular, there are oscillating solutions for any chosen period, in contrast with the "approximately Newtonian plus small radiative corrections" motion expectation. We comment on the physical meaning of these results and provide some explicit examples. We also discuss the relation of our results to the initial value problem for the linearized dynamics of the shell. © 2012 American Physical Society.

Dain S.,Institute Fisica Enrique Gaviola | De Austria I.G.,Institute Fisica Enrique Gaviola
Classical and Quantum Gravity | Year: 2015

We obtain remarkably simple integral bounds for axially symmetric linear perturbations for the extreme Kerr black hole in terms of conserved energies. From these estimates we deduce pointwise bounds for the perturbations outside the horizon. © 2015 IOP Publishing Ltd.

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