Symmetries and Ambiguities in the linear sigma model with light quarks

We investigate the role of undetermined finite contributions generated by radiative corrections in a $SU(2)\times SU(2)$ linear sigma model with quarks. Although some of such terms can be absorbed in the renormalization procedure, one such contribution is left in the expression for the pion decay constant. This arbitrariness is eliminated by chiral symmetry.Comment: 9 pages. Added references through the text; an author was added due to an important contribution; corrected typos; the title also was changed. Submitted to Modern Physics Letter

Cobertura morta de leguminosas no controle de ervas invasoras em sistema de cultivo em faixas (Alley cropping).

bitstream/item/32692/1/CPATU-BP137.pd

Effects of Inelastic Neutrino-Nucleus Scattering on Supernova Dynamics and Radiated Neutrino Spectra

Based on the shell model for Gamow-Teller and the Random Phase Approximation for forbidden transitions, we have calculated reaction rates for inelastic neutrino-nucleus scattering (INNS) under supernova (SN) conditions, assuming a matter composition given by Nuclear Statistical Equilibrium. The rates have been incorporated into state-of-the-art stellar core-collapse simulations with detailed energy-dependent neutrino transport. While no significant effect on the SN dynamics is observed, INNS increases the neutrino opacities noticeably and strongly reduces the high-energy tail of the neutrino spectrum emitted in the neutrino burst at shock breakout. Relatedly the expected event rates for the observation of such neutrinos by earthbound detectors are reduced by up to about 60%.Comment: 4 pages, 2 figures, 1 tabl

Skyrmion morphology in ultrathin magnetic films

Nitrogen-vacancy magnetic microscopy is employed in quenching mode as a non-invasive, high resolution tool to investigate the morphology of isolated skyrmions in ultrathin magnetic films. The skyrmion size and shape are found to be strongly affected by local pinning effects and magnetic field history. Micromagnetic simulations including static disorder, based on a physical model of grain-to-grain thickness variations, reproduce all experimental observations and reveal the key role of disorder and magnetic history in the stabilization of skyrmions in ultrathin magnetic films. This work opens the way to an in-depth understanding of skyrmion dynamics in real, disordered media.Comment: 9 pages, 8 figures, including supplementary information

Regularization Independent Analysis of the Origin of Two Loop Contributions to N=1 Super Yang-Mills Beta Function

We present a both ultraviolet and infrared regularization independent analysis in a symmetry preserving framework for the N=1 Super Yang-Mills beta function to two loop order. We show explicitly that off-shell infrared divergences as well as the overall two loop ultraviolet divergence cancel out whilst the beta function receives contributions of infrared modes.Comment: 7 pages, 2 figures, typos correcte

Casimir energy and a cosmological bounce

We review different computation methods for the renormalised energy momentum tensor of a quantised scalar field in an Einstein Static Universe. For the extensively studied conformally coupled case we check their equivalence; for different couplings we discuss violation of different energy conditions. In particular, there is a family of masses and couplings which violate the weak and strong energy conditions but do not lead to spacelike propagation. Amongst these cases is that of a minimally coupled massless scalar field with no potential. We also point out a particular coupling for which a massless scalar field has vanishing renormalised energy momentum tensor. We discuss the backreaction problem and in particular the possibility that this Casimir energy could both source a short inflationary epoch and avoid the big bang singularity through a bounce.Comment: 13 pages, LaTeX, 8 figure

Evolution of the eyes of vipers with and without infrared-sensing pit organs

We examined lens and brille transmittance, photoreceptors, visual pigments, and visual opsin gene sequences of viperid snakes with and without infrared-sensing pit organs. Ocular media transmittance is high in both groups. Contrary to previous reports, small as well as large single cones occur in pit vipers. Non-pit vipers differ from pit vipers in having a twotiered retina, but few taxa have been examined for this poorly understood feature. All vipers sampled express rh1, sws1 and lws visual opsin genes. Opsin spectral tuning varies but not in accordance with the presence/absence of pit organs, and not always as predicted from gene sequences. The visual opsin genes were generally under purifying selection, with positive selection at spectral tuning amino acids in RH1 and SWS1 opsins, and at retinal pocket stabilization sites in RH1 or LWS (and without substantial differences between pit and nonpit vipers). Lack of evidence for sensory trade-off between viperid eyes (in the aspects examined) and pit organs might be explained by the high degree of neural integration of vision and infrared detection; the latter representing an elaboration of an existing sense with addition of a novel sense organ, rather than involving the evolution of a wholly novel sensory system

TRANSIENT HEAT TRANSFER ANALYSIS UP TO DRYOUT IN 3D FUEL RODS UNDER UNIDEAL CONDITIONS THROUGH THE DEVELOPMENT OF A COMPUTER CODE

In this paper we analyze a conjugated transient heat transfer problem consisting of a nuclear reactor’s fuel rod and its intrinsic coolant channel. Our analysis is made possible through a computer code being developed at the Instituto de Engenharia Nuclear (IEN/CNEN). This code is meant to study the temperature behavior in fuel rods which exhibit deviation from their ideal conditions, that is, rods in which the cladding is deformed or the fuel is dislocated. It is also designed to avoid the use of the computationally expensive Navier-Stokes equations. For these reasons, its physical model has as basis a three-dimensional fuel rod coupled to a one-dimensional coolant channel, which are discretized using the finite element method. Intending to study accidental conditions in which the coolant (light water) transcends its saturation temperature, turning into vapor, a homogeneous mixture is used to represent the two-phase flow, and so the coolant channel’s energy equation is described using enthalpy. Owing to the fact that temperature and enthalpy are used in the physical model, it became impractical to generate a fully coupled method for solving the pertinent equations. Thus, the conjugated heat transfer problem is solved in a segregated manner through the implementation of an iterative method. Finally, as study cases for this paper we present analyses concerning the behavior of the hottest fuel rod in a Pressurized Water Reactor during a shutdown wherein the residual heat removal system is lost (loss of the reactor’s coolant pumps). These studies contemplate cases in which the fuel rod’s geometry is ideal or curved. Analyses are also performed for two circumstances of positioning of the fuel inside the rod: concentric and eccentric.In this paper we analyze a conjugated transient heat transfer problem consisting of a nuclear reactor’s fuel rod and its intrinsic coolant channel. Our analysis is made possible through a computer code being developed at the Instituto de Engenharia Nuclear (IEN/CNEN). This code is meant to study the temperature behavior in fuel rods which exhibit deviation from their ideal conditions, that is, rods in which the cladding is deformed or the fuel is dislocated. It is also designed to avoid the use of the computationally expensive Navier-Stokes equations. For these reasons, its physical model has as basis a three-dimensional fuel rod coupled to a one-dimensional coolant channel, which are discretized using the finite element method. Intending to study accidental conditions in which the coolant (light water) transcends its saturation temperature, turning into vapor, a homogeneous mixture is used to represent the two-phase flow, and so the coolant channel’s energy equation is described using enthalpy. Owing to the fact that temperature and enthalpy are used in the physical model, it became impractical to generate a fully coupled method for solving the pertinent equations. Thus, the conjugated heat transfer problem is solved in a segregated manner through the implementation of an iterative method. Finally, as study cases for this paper we present analyses concerning the behavior of the hottest fuel rod in a Pressurized Water Reactor during a shutdown wherein the residual heat removal system is lost (loss of the reactor’s coolant pumps). These studies contemplate cases in which the fuel rod’s geometry is ideal or curved. Analyses are also performed for two circumstances of positioning of the fuel inside the rod: concentric and eccentric.In this paper we analyze a conjugated transient heat transfer problem consisting of a nuclear reactor’s fuel rod and its intrinsic coolant channel. Our analysis is made possible through a computer code being developed at the Instituto de Engenharia Nuclear (IEN/CNEN). This code is meant to study the temperature behavior in fuel rods which exhibit deviation from their ideal conditions, that is, rods in which the cladding is deformed or the fuel is dislocated. It is also designed to avoid the use of the computationally expensive Navier-Stokes equations. For these reasons, its physical model has as basis a three-dimensional fuel rod coupled to a one-dimensional coolant channel, which are discretized using the finite element method. Intending to study accidental conditions in which the coolant (light water) transcends its saturation temperature, turning into vapor, a homogeneous mixture is used to represent the two-phase flow, and so the coolant channel’s energy equation is described using enthalpy. Owing to the fact that temperature and enthalpy are used in the physical model, it became impractical to generate a fully coupled method for solving the pertinent equations. Thus, the conjugated heat transfer problem is solved in a segregated manner through the implementation of an iterative method. Finally, as study cases for this paper we present analyses concerning the behavior of the hottest fuel rod in a Pressurized Water Reactor during a shutdown wherein the residual heat removal system is lost (loss of the reactor’s coolant pumps). These studies contemplate cases in which the fuel rod’s geometry is ideal or curved. Analyses are also performed for two circumstances of positioning of the fuel inside the rod: concentric and eccentric

On the equivalence between Implicit Regularization and Constrained Differential Renormalization

Constrained Differential Renormalization (CDR) and the constrained version of Implicit Regularization (IR) are two regularization independent techniques that do not rely on dimensional continuation of the space-time. These two methods which have rather distinct basis have been successfully applied to several calculations which show that they can be trusted as practical, symmetry invariant frameworks (gauge and supersymmetry included) in perturbative computations even beyond one-loop order. In this paper, we show the equivalence between these two methods at one-loop order. We show that the configuration space rules of CDR can be mapped into the momentum space procedures of Implicit Regularization, the major principle behind this equivalence being the extension of the properties of regular distributions to the regularized ones.Comment: 16 page