Nucleon-to-Delta axial transition form factors in relativistic baryon chiral perturbation theory

We report a theoretical study of the axial Nucleon to Delta(1232) ($N\to\Delta$) transition form factors up to one-loop order in relativistic baryon chiral perturbation theory. We adopt a formalism in which the $\Delta$ couplings obey the spin-3/2 gauge symmetry and, therefore, decouple the unphysical spin-1/2 fields. We compare the results with phenomenological form factors obtained from neutrino bubble chamber data and in quark models.Comment: A few clarifying remarks added; version to appear in Physical Review

Impurity in a granular gas under nonlinear Couette flow

We study in this work the transport properties of an impurity immersed in a granular gas under stationary nonlinear Couette flow. The starting point is a kinetic model for low-density granular mixtures recently proposed by the authors [Vega Reyes F et al. 2007 Phys. Rev. E 75 061306]. Two routes have been considered. First, a hydrodynamic or normal solution is found by exploiting a formal mapping between the kinetic equations for the gas particles and for the impurity. We show that the transport properties of the impurity are characterized by the ratio between the temperatures of the impurity and gas particles and by five generalized transport coefficients: three related to the momentum flux (a nonlinear shear viscosity and two normal stress differences) and two related to the heat flux (a nonlinear thermal conductivity and a cross coefficient measuring a component of the heat flux orthogonal to the thermal gradient). Second, by means of a Monte Carlo simulation method we numerically solve the kinetic equations and show that our hydrodynamic solution is valid in the bulk of the fluid when realistic boundary conditions are used. Furthermore, the hydrodynamic solution applies to arbitrarily (inside the continuum regime) large values of the shear rate, of the inelasticity, and of the rest of parameters of the system. Preliminary simulation results of the true Boltzmann description show the reliability of the nonlinear hydrodynamic solution of the kinetic model. This shows again the validity of a hydrodynamic description for granular flows, even under extreme conditions, beyond the Navier-Stokes domain.Comment: 23 pages, 11 figures; v2: Preliminary DSMC results from the Boltzmann equation included, Fig. 11 is ne

Radio-frequency performance comparison of several H-plane rectangular waveguide filters loaded with circular dielectric posts

This paper is a postprint of a paper submitted to and accepted for publication in IET Microwaves Antennas and Propagation and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at IET Digital LibraryThe study presents a radio-frequency performance comparison between several H-plane geometry filters based on rectangular waveguide technology. The basic all-metal filter of resonant cavities is compared with filters loaded with circular dielectric resonators, either in propagative or evanescent mode. The use of these resonators is claimed to reduce the length of the filter, increase the rejection band until the first spurious frequency and to improve the voltage magnification factor (VMF), at the cost of increasing the losses. Therefore, in order to properly assess and quantify the possible advantages of these filters, an accurate analysis of six of them has been developed. All the filters have been designed to have the same electrical response, and the length, losses, rejection band, VMF, and fabrication cost for all the filters are compared.Our acknowledgement to the Val Space Consortium for its contribution - Laboratories co-funded by the European Regional Development Fund - A way of making Europe.Bachiller Martin, MC.; Esteban González, H.; Diaz, F.; Morro, JV.; Boria Esbert, VE. (2016). Radio-frequency performance comparison of several H-plane rectangular waveguide filters loaded with circular dielectric posts. IET Microwaves Antennas and Propagation. 10(5):536-545. doi:10.1049/iet-map.2014.0738S53654510

Transport coefficients for inelastic Maxwell mixtures

The Boltzmann equation for inelastic Maxwell models is used to determine the Navier-Stokes transport coefficients of a granular binary mixture in $d$ dimensions. The Chapman-Enskog method is applied to solve the Boltzmann equation for states near the (local) homogeneous cooling state. The mass, heat, and momentum fluxes are obtained to first order in the spatial gradients of the hydrodynamic fields, and the corresponding transport coefficients are identified. There are seven relevant transport coefficients: the mutual diffusion, the pressure diffusion, the thermal diffusion, the shear viscosity, the Dufour coefficient, the pressure energy coefficient, and the thermal conductivity. All these coefficients are {\em exactly} obtained in terms of the coefficients of restitution and the ratios of mass, concentration, and particle sizes. The results are compared with known transport coefficients of inelastic hard spheres obtained analytically in the leading Sonine approximation and by means of Monte Carlo simulations. The comparison shows a reasonably good agreement between both interaction models for not too strong dissipation, especially in the case of the transport coefficients associated with the mass flux.Comment: 9 figures, to be published in J. Stat. Phy

Navier-Stokes transport coefficients of dd-dimensional granular binary mixtures at low density

The Navier-Stokes transport coefficients for binary mixtures of smooth inelastic hard disks or spheres under gravity are determined from the Boltzmann kinetic theory by application of the Chapman-Enskog method for states near the local homogeneous cooling state. It is shown that the Navier-Stokes transport coefficients are not affected by the presence of gravity. As in the elastic case, the transport coefficients of the mixture verify a set of coupled linear integral equations that are approximately solved by using the leading terms in a Sonine polynomial expansion. The results reported here extend previous calculations [V. Garz\'o and J. W. Dufty, Phys. Fluids {\bf 14}, 1476 (2002)] to an arbitrary number of dimensions. To check the accuracy of the Chapman-Enskog results, the inelastic Boltzmann equation is also numerically solved by means of the direct simulation Monte Carlo method to evaluate the diffusion and shear viscosity coefficients for hard disks. The comparison shows a good agreement over a wide range of values of the coefficients of restitution and the parameters of the mixture (masses and sizes).Comment: 6 figures, to be published in J. Stat. Phy

Analysis of Retinal Layers in Fibromyalgia Patients with Premium Protocol in Optical Tomography Coherence and Quality of Life

Purpose To evaluate the inner retinal layers in fibromyalgia (FM) patients compared to control subjects using posterior pole protocol (PPole) analysis in optical coherence tomography (OCT) and to correlate structural retinal changes with subjective quality of life. Methods Seventy-four eyes of healthy subjects and 55 eyes of those with FM were analyzed. All subjects underwent retinal evaluation using the PPole protocol for Spectralis OCT (Heidelberg Engineering) to obtain measurements of the retinal nerve fiber layer (RNFL) and the ganglion cell layer (GCL) in the macular area. The EuroQol (EQ-5D) questionnaire and Fibromyalgia Impact Questionnaire (FIQ) were performed to analyze health-related quality of life. Additionally, the FM group was divided into three groups depending on the disease phenotype (atypical, depressive, and biological). Results Patients with FM presented with a reduction of the RNFL thickness compared to controls in 17/64 cells of the PPole area, and a reduction of the GCL thickness in 47/64 cells. Depressive FM phenotype showed the greatest number of cells with significant reduction compared with the control group in both RNFL and GCL layers. A correlation between temporal-inferior cells of the GCL and the EuroQol 5D questionnaire results was observed. Conclusions Patients with FM present with a reduction of the inner retinal layers in the macular area. This degeneration correlates with disease severity/reduced quality of life in these patients. The PPole protocol for OCT is a non-invasive and fast tool that might help clinicians diagnose and monitor neurodegeneration in FM patients

Enumeration of minimal stoichiometric precursor sets in metabolic networks

Background: What an organism needs at least from its environment to produce a set of metabolites, e.g. target(s) of interest and/or biomass, has been called a minimal precursor set. Early approaches to enumerate all minimal precursor sets took into account only the topology of the metabolic network (topological precursor sets). Due to cycles and the stoichiometric values of the reactions, it is often not possible to produce the target(s) from a topological precursor set in the sense that there is no feasible flux. Although considering the stoichiometry makes the problem harder, it enables to obtain biologically reasonable precursor sets that we call stoichiometric. Recently a method to enumerate all minimal stoichiometric precursor sets was proposed in the literature. The relationship between topological and stoichiometric precursor sets had however not yet been studied. Results: Such relationship between topological and stoichiometric precursor sets is highlighted. We also present two algorithms that enumerate all minimal stoichiometric precursor sets. The first one is of theoretical interest only and is based on the above mentioned relationship. The second approach solves a series of mixed integer linear programming problems. We compared the computed minimal precursor sets to experimentally obtained growth media of several Escherichia coli strains using genome-scale metabolic networks. Conclusions: The results show that the second approach efficiently enumerates minimal precursor sets taking stoichiometry into account, and allows for broad in silico studies of strains or species interactions that may help to understand e.g. pathotype and niche-specific metabolic capabilities. sasita is written in Java, uses cplex as LP solver and can be downloaded together with all networks and input files used in this paper at http://www.sasita.gforge.inria.fr

Diffusion of impurities in a granular gas

Diffusion of impurities in a granular gas undergoing homogeneous cooling state is studied. The results are obtained by solving the Boltzmann--Lorentz equation by means of the Chapman--Enskog method. In the first order in the density gradient of impurities, the diffusion coefficient $D$ is determined as the solution of a linear integral equation which is approximately solved by making an expansion in Sonine polynomials. In this paper, we evaluate $D$ up to the second order in the Sonine expansion and get explicit expressions for $D$ in terms of the restitution coefficients for the impurity--gas and gas--gas collisions as well as the ratios of mass and particle sizes. To check the reliability of the Sonine polynomial solution, analytical results are compared with those obtained from numerical solutions of the Boltzmann equation by means of the direct simulation Monte Carlo (DSMC) method. In the simulations, the diffusion coefficient is measured via the mean square displacement of impurities. The comparison between theory and simulation shows in general an excellent agreement, except for the cases in which the gas particles are much heavier and/or much larger than impurities. In theses cases, the second Sonine approximation to $D$ improves significantly the qualitative predictions made from the first Sonine approximation. A discussion on the convergence of the Sonine polynomial expansion is also carried out.Comment: 9 figures. to appear in Phys. Rev.

Downward shortwave radiation trends in Europe since the 20th century: what we know from direct measurements and sunshine duration records?

Póster presentado en: AGU Fall Meeting celebrado en San Francisco del 15 al 19 de diciembre de 2014.This work was supported by the Ministry of Economy and Competitiveness of the Government of Spain through the projects NUCLIERSOL (CGL2010-18546) and HIDROCAES (CGL2011-27574-CO2-02). The first author was supported by the “Secretaria per a Universitats i Recerca del Departament d’Economia i Coneixement, de la Generalitat de Catalunya i del programa Cofund de les Accions Marie Curie del 7è Programa marc d’R+D de la Unión Europea” (2011 BP-B 00078) and the postdoctoral fellowship JCI-2012-12508. ASR received a grant from the FPU program (FPU AP2010-0917) of the Spanish Ministry of Education