Closing the SU(3)L⊗U(1)XSU(3)_L\otimes U(1)_X Symmetry at Electroweak Scale

We show that some models with $SU(3)_C\otimes SU(3)_L\otimes U(1)_X$ gauge symmetry can be realized at the electroweak scale and that this is a consequence of an approximate global $SU(2)_{L+R}$ symmetry. This symmetry implies a condition among the vacuum expectation value of one of the neutral Higgs scalars, the $U(1)_X$'s coupling constant, $g_X$, the sine of the weak mixing angle $\sin\theta_W$, and the mass of the $W$ boson, $M_W$. In the limit in which this symmetry is valid it avoids the tree level mixing of the $Z$ boson of the Standard Model with the extra $Z^\prime$ boson. We have verified that the oblique $T$ parameter is within the allowed range indicating that the radiative corrections that induce such a mixing at the 1-loop level are small. We also show that a $SU(3)_{L+R}$ custodial symmetry implies that in some of the models we have to include sterile (singlets of the 3-3-1 symmetry) right-handed neutrinos with Majorana masses, being the see-saw mechanism mandatory to obtain light active neutrinos. Moreover, the approximate $SU(2)_{L+R}\subset SU(3)_{L+R}$ symmetry implies that the extra non-standard particles of these 3-3-1 models can be considerably lighter than it had been thought before so that new physics can be really just around the corner.Comment: 32 pages, no figure, RevTeX. Some typos correcte

Evaluation of the greenhouse gas balance in the Eucalyptus globulus sector in Portugal

Este estudio evalúa el balance de gas invernadero en el sector del E. globulus en Portugal. Las eliminaciones y las emisiones de dióxido de carbono (CO2) y el metano (CH4) fueron calculadas a lo largo en todo el sector forestal, incluyendo el ecosistema forestal, el tratamiento industrial de madera y las etapas de empleo y la disposición final de productos forestales. El balance de gas invernadero fue calculado restándose la eliminación de carbono neto a las emisiones de carbono fósil y sumándose las emisiones de carbono como el CH4. El balance global de gas invernadero fue una eliminación neta de carbono que varió entre 401 y 1033 Gg Ceq yr-1, respectivamente con el cambio de reservas y los accesos de flujo atmosférico. La diferencia entre las dos estimaciones es equivalente al carbón exportado en productos de madera y forestales. Tanto productos forestales como forestales eran sumideros de carbono, como sus reservas han estado aumentando. Aproximadamente el 94 % del cambio total de reservas de carbono en el sector era debido al bosque, mientras que el papel era el producto forestal con la contribución principal al aumento de reservas de carbono. Emisiones de carbono de fósil consideradas para el 13 % de las emisiones totales de carbono en el sector y disminuido el retiro neto de carbono por 18 y el 34 %, respectivamente con el flujo atmosférico y los cambio de reservas. El carbón emitido como CH4 tuvo la importancia menor y, por consiguiente, era responsable de una disminución en el retiro neto de carbón de sólo 4 y el 8 %, respectivamente con el flujo atmosférico y los accesos de cambio de reservas.____________________________________This study evaluates the greenhouse gas balance in the E. globulus sector in Portugal. Removals and emissions of carbon dioxide (CO2) and methane (CH4) were calculated along the whole forest sector, including the forest ecosystem, the industrial processing of wood and the stages of use and final disposal of forest products. The greenhouse gas balance was calculated by subtracting to the net carbon removal, the fossil carbon emissions and the additional emissions of carbon as CH4. Two different approaches were applied for estimating the net carbon removal in the sector: the stock-change and the atmospheric-flow approach. The global greenhouse gas balance was a net removal of carbon that varied between 401 and 1033 Gg Ceq yr-1, respectively with the stock-change and the atmospheric-flow approaches. The difference between the two estimates is equivalent to the carbon exported in wood and forest products. Both forest and forest products were carbon sinks, as their stocks have been increasing. About 94% of the total change in carbon stocks in the sector was due to forest, whereas paper was the forest product with the major contribution to the increase of carbon stocks. Fossil carbon emissions accounted for 13% of the total carbon emissions in the sector and decreased the net carbon removal by 18 and 34%, respectively with the atmospheric-flow and the stock-change approaches. Carbon emitted as CH4 was of minor importance and, consequently, was responsible for a decrease in the net carbon removal of only 4 and 8%, respectively with the atmospheric-flow and the stock-change approaches

On the nature of the spin-polarized hole states in a quasi-two-dimensional GaMnAs ferromagnetic layer

A self-consistent calculation of the density of states and the spectral density function is performed in a two-dimensional spin-polarized hole system based on a multiple-scattering approximation. Using parameters corresponding to GaMnAs thin layers, a wide range of Mn concentrations and hole densities have been explored to understand the nature, localized or extended, of the spin-polarized holes at the Fermi level for several values of the average magnetization of the Mn ystem. We show that, for a certain interval of Mn and hole densities, an increase on the magnetic order of the Mn ions come together with a change of the nature of the states at the Fermi level. This fact provides a delocalization of spin-polarized extended states anti-aligned to the average Mn magnetization, and a higher spin-polarization of the hole gas. These results are consistent with the occurrence of ferromagnetism with relatively high transition temperatures observed in some thin film samples and multilayered structures of this material.Comment: 3 page

A semiquantitative approach to the impurity-band-related transport properties of GaMnAs nanolayers

We investigate the spin-polarized transport of GaMnAs nanolayers in which a ferromagnetic order exists below a certain transition temperature. Our calculation for the self-averaged resistivity takes into account the existence of an impurity band determining the extended ("metallic" transport) or localized (hopping by thermal excitation) nature of the states at and near the Fermi level. Magnetic order and resistivity are inter-related due to the influence of the spin polarization of the impurity band and the effect of the Zeeman splitting on the mobility edge. We obtain, for a given range of Mn concentration and carrier density, a "metallic" behavior in which the transport by extended carriers dominates at low temperature, and is dominated by the thermally excited localized carriers near and above the transition temperature. This gives rise to a conspicuous hump of the resistivity which has been experimentally observed and brings light onto the relationship between transport and magnetic properties of this material

On the Effects of Residual Stresses Induced by Coated and Uncoated Cutting Tools with Finite Edge Radii in Turning Operations

This paper presents an analysis of residual stresses in turning of AISI 316L and AISI 1045 steels with coated and uncoated tools having finite edge radii. An analytical predictive model, and experimental techniques involving X-ray diffraction and IR thermal imaging were used. Machining with coated tools produce higher superficial residual stresses, larger tensile layer thickness and higher residual stresses below the machined surface when using large cutting edge radii at low feed rates. This effect is correlated with the increase in the amount of heat conducted into the workpiece, and the associated generation of high tensile residual stresses and severe work-hardening.http://www.sciencedirect.com/science/article/B8CXH-4P37B21-X/1/ade5f4d85d7cb77cb37cbb62ae400bb

Half Quantization

A general dynamical system composed by two coupled sectors is considered. The initial time configuration of one of these sectors is described by a set of classical data while the other is described by standard quantum data. These dynamical systems will be named half quantum. The aim of this paper is to derive the dynamical evolution of a general half quantum system from its full quantum formulation. The standard approach would be to use quantum mechanics to make predictions for the time evolution of the half quantum initial data. The main problem is how can quantum mechanics be applied to a dynamical system whose initial time configuration is not described by a set of fully quantum data. A solution to this problem is presented and used, as a guideline to obtain a general formulation of coupled classical-quantum dynamics. Finally, a quantization prescription mapping a given classical theory to the correspondent half quantum one is presented.Comment: 20 pages, LaTex file, Substantially revised versio

Magnetic friction due to vortex fluctuation

We use Monte Carlo and molecular dynamics simulation to study a magnetic tip-sample interaction. Our interest is to understand the mechanism of heat dissipation when the forces involved in the system are magnetic in essence. We consider a magnetic crystalline substrate composed of several layers interacting magnetically with a tip. The set is put thermally in equilibrium at temperature T by using a numerical Monte Carlo technique. By using that configuration we study its dynamical evolution by integrating numerically the equations of motion. Our results suggests that the heat dissipation in this system is closed related to the appearing of vortices in the sample.Comment: 6 pages, 41 figure

Programmed buckling by controlled lateral swelling in a thin elastic sheet

Recent experiments have imposed controlled swelling patterns on thin polymer films, which subsequently buckle into three-dimensional shapes. We develop a solution to the design problem suggested by such systems, namely, if and how one can generate particular three-dimensional shapes from thin elastic sheets by mere imposition of a two-dimensional pattern of locally isotropic growth. Not every shape is possible. Several types of obstruction can arise, some of which depend on the sheet thickness. We provide some examples using the axisymmetric form of the problem, which is analytically tractable.Comment: 11 pages, 9 figure