Finite Rotations

We present an elementary discussion of two basic properties of angular displacements, namely, the anticommutation of finite rotations and the commutation of infinitesimal rotations, and show how commutation is achieved as the angular displacements get smaller and smaller

Interplay between disorder, quantum and thermal fluctuations in ferromagnetic alloys: The case of UCu2Si(2-x)Ge(x)

We consider, theoretically and experimentally, the effects of structural disorder, quantum and thermal fluctuations in the magnetic and transport properties of certain ferromagnetic alloys.We study the particular case of UCu2Si(2-x)Ge(x). The low temperature resistivity, rho(T,x), exhibits Fermi liquid (FL) behavior as a function of temperature T for all values of x, which can be interpreted as a result of the magnetic scattering of the conduction electrons from the localized U spins. The residual resistivity, rho(0,x), follows the behavior of a disordered binary alloy. The observed non-monotonic dependence of the Curie temperature, Tc(x), with x can be explained within a model of localized spins interacting with an electronic bath whose transport properties cross-over from ballistic to diffusive regimes. Our results clearly show that the Curie temperature of certain alloys can be enhanced due to the interplay between quantum and thermal fluctuations with disorder.Comment: 4 pages, 3 figures, to appear in Phys. Rev. Let

Flag-Dipole Spinor Fields in ESK Gravities

We consider the Riemann-Cartan geometry as a basis for the Einstein-Sciama-Kibble theory coupled to spinor fields: we focus on $f(R)$ and conformal gravities, regarding the flag-dipole spinor fields, type-(4) spinor fields under the Lounesto classification. We study such theories in specific cases given for instance by cosmological scenarios: we find that in such background the Dirac equation admits solutions that are not Dirac spinor fields, but in fact the aforementioned flag-dipoles ones. These solutions are important from a theoretical perspective, as they evince that spinor fields are not necessarily determined by their dynamics, but also a discussion on their structural (algebraic) properties must be carried off. Furthermore, the phenomenological point of view is shown to be also relevant, since for isotropic Universes they circumvent the question whether spinor fields do undergo the Cosmological Principle.Comment: 18 pages, improved versio

MODELING OF THE KINETIC OF SALICYLIC ACID ADSORPTION IN POLYMERIC AND ACTIVATED CHARCOAL ADSORBENTS

The understanding of adsorption mechanisms of compounds utilized in many medications and prescription drugs represents an important step for the development of different separation processes of such substances. The adsorption kinetic study of such chemical compounds through the application of new models permits a better comprehension of the involved mechanisms, leading to the estimation of important parameters that will be incorporated in the equipment design. In this work a kinetic model of irreversible adsorption is implemented, which is dependent on both solute and site concentrations. It showed to be very effective correlating the simulated results with the adsorption experiments of salicylic acid through three adsorbents in different temperature conditions. The application of an inverse problem approach, with the minimization of the squared residues cost function, was successful in determining the kinetic parameters. The increase in the kinetic constants obtained with the temperature increase was followed by a reduction in the adsorption capacity of the adsorbents. Thermodynamic parameters were also estimated, leading to the comprehension about the equilibrium states of the adsorption systems considered

Rendimento de massa e características morfológicas de Crotalaria ochroleuca em populações de plantas.

JIPE 2013