Noncommutative quantum mechanics and the Aharonov-Casher effect

In this work a new method is developed to investigate the Aharonov-Casher effect in a noncommutative space. It is shown that the holonomy receives non-trivial kinematical corrections.Comment: 8 pages, Plain Tex, to appear in Eur. Phys. J.

Aharonov-Casher effect for spin one particles in a noncommutative space

In this work the Aharonov-Casher (AC) phase is calculated for spin one particles in a noncommutative space. The AC phase has previously been calculated from the Dirac equation in a noncommutative space using a gauge-like technique [17]. In the spin-one, we use kemmer equation to calculate the phase in a similar manner. It is shown that the holonomy receives non-trivial kinematical corrections. By comparing the new result with the already known spin 1/2 case, one may conjecture a generalized formula for the corrections to holonomy for higher spins.Comment: 9 page

Empty singularities in higher-dimensional Gravity

We study the exact solution of Einstein's field equations consisting of a ($n+2$)-dimensional static and hyperplane symmetric thick slice of matter, with constant and positive energy density $\rho$ and thickness $d$, surrounded by two different vacua. We explicitly write down the pressure and the external gravitational fields in terms of $\rho$ and $d$, the pressure is positive and bounded, presenting a maximum at an asymmetrical position. And if $\sqrt{\rho}\,d$ is small enough, the dominant energy condition is satisfied all over the spacetime. We find that this solution presents many interesting features. In particular, it has an empty singular boundary in one of the vacua.Comment: 13 page

Space-Time Symmetries of Quantized Tensionless Strings

The tensionless limit of the free bosonic string is space-time conformally symmetric classically. Requiring invariance of the quantum theory in the light cone gauge tests the reparametrization symmetry needed to fix this gauge. The full conformal symmetry gives stronger constraints than the Poincar\'e subalgebra. We find that the symmetry may be preserved in any space-time dimension, but only if the spectrum is drastically reduced (part of this reduction is natural in a zero tension limit of the ordinary string spectrum). The quantum states are required to be symmetric ({\it i.e.} singlets) under space-time diffeomorphisms, except for the centre of mass wave function.Comment: 15pp, plain latex, USITP-92-

SU(2) Kinetic Mixing Terms and Spontaneous Symmetry Breaking

The non-abelian generalization of the Holdom model --{\it i.e.} a theory with two gauge fields coupled to the kinetic mixing term $g {tr}(F_{\mu \nu} (A) F_{\mu \nu} (B))$-- is considered. Contrarily to the abelian case, the group structure $G\times G$ is explicitly broken to $G$. For SU(2) this fact implies that the residual gauge symmetry as well as the Lorentz symmetry is spontaneusly broken. We show that this mechanism provides of masses for the involved particles. Also, the model presents instanton solutions with a redefined coupling constant.Comment: 9pp. typos and clarifications are adde

Bent crystal spectrometer for both frequency and wavenumber resolved x-ray scattering at a seeded free-electron laser

We present a cylindrically curved GaAs x-ray spectrometer with energy resolution $\Delta E/E = 1.1\cdot 10^{-4}$ and wave-number resolution of $\Delta k/k = 3\cdot 10^{-3}$, allowing plasmon scattering at the resolution limits of the Linac Coherent Light Source (LCLS) x-ray free-electron laser. It spans scattering wavenumbers of 3.6 to $5.2/$\AA\ in 100 separate bins, with only 0.34\% wavenumber blurring. The dispersion of 0.418~eV/$13.5\,\mu$m agrees with predictions within 1.3\%. The reflection homogeneity over the entire wavenumber range was measured and used to normalize the amplitude of scattering spectra. The proposed spectrometer is superior to a mosaic HAPG spectrometer when the energy resolution needs to be comparable to the LCLS seeded bandwidth of 1~eV and a significant range of wavenumbers must be covered in one exposure

Díganle a Julio que la guerra terminó*

Mientras trataba de retomar el alientoiba pensando en la lejana posibilidadde encontrarlo esta vez. Ya eranmuchos los intentos terminados en frustración,pero no se le ocurría desistir. Terminó deascender entre riscos espinosos y luego tuvoque luchar contra un camino arenisco que lehacía perder el equilibrio. Miró hacia el cielo,como intentando establecer una señal de ubicuidad,pero parecía estar enmarañado por lavegetación

Rubber Additions into Concrete and Gamma Radiation Effects on Mechanical Properties and Microwave Absorption Capacity

Rubber is the indispensable raw material for the manufacture of tires; it is obtained from plants, trees and currently can be produced synthetically. The tire rubber is mixed with compounds such as carbon black, sulfur, cement, paints, antioxidants, oils and fats, steel wire, almost etc., making impossible to recycle the tires itself. In this work, we investigate, the effects of the incorporation of ground rubber in concrete, mixture designed to establish the possibility of being used in the construction industry. The samples of concrete were addition with, 5 vol. %., 15 vol. % and 25 vol. % of rubber. Samples with different rubber addition were irradiated by a cobalt 60 gamma source to study the effect on their mechanical compression properties and microwave absorption capacity. Likewise, the microwave absorption capacity was studied for both irradiated and the non-irradiated. It was found that between 5 vol. % and 15 vol. % of rubber addition change the mechanical properties approximately 25 %, higher rubber additions result in a decrease in a 75 % of its mechanical properties. The fracture behavior is not the expected one due to as the curves of stress vs. strain show a double slope, which is associated with the concrete porosity and rubber content. The aging with the gamma rays generates loss of mechanical properties, especially at lower rubber addition, since at content greater than 15 Vol % the radiation effect is less. These rubber additions allow moderate deformations in compression, thus contributing to the care and preservation of the environment

Effect of design parameters on the mass of a variable-span morphing wing based on finite element structural analysis and optimization

In the past years, the development of morphing wing technologies has received a great deal of interest from the scientific community. These technologies potentially enable an increase in aircraft efficiency by changing the wing shape, thus allowing the aircraft to fly near its optimal performance point at different flight conditions. However, these technologies often present an undesired mass increase due to their inherent complexity. Therefore, the aim of the current work is to ascertain the influence of geometrical and inertial parameters on the structural mass of a Variable-span Wing (VSW). The structural mass prediction is based on a parametric study. A minimum mass optimization problem with stiffness and strength constraints is implemented and solved, being the design variables structural thicknesses and widths, using a parametric Finite Element Model (FEM) of the wing. The study is done for a conventional fixed wing and the VSW, which are then combined to ascertain the VSW mass increment, i.e., the mass penalization of the adopted morphing concept. Polynomials are found to produce good approximations of the wing mass. The effects of the various VSW design parameters in the structural mass are discussed. On one hand, it was found that the span and chord have the highest impact in the wing mass. On the other hand, the VSW to fixed wing mass ratio proved that the influence of span variation ratio in the wing mass is not trivial. It is found that the mass increase does not grow proportionally with span variation ratio increase and that for each combination of span and chord, exists a span variation ratio that minimizes the mass penalty. In the future, the developed polynomials could be used to create a mass prediction model to aid the design of morphing wings during the conceptual design phase