Hartree-Fock dynamics in highly excited quantum dots

Time-dependent Hartree-Fock theory is used to describe density oscillations of symmetry-unrestricted two-dimensional nanostructures. In the small amplitude limit the results reproduce those obtained within a perturbative approach such as the linearized time-dependent Hartree-Fock one. The nonlinear regime is explored by studying large amplitude oscillations in a non-parabolic potential, which are shown to introduce a strong coupling with internal degrees of freedom. This excitation of internal modes, mainly of monopole and quadrupole character, results in sizeable modifications of the dipole absorption.Comment: 4 pages, 4 embedded figure

Band alignment at metal/ferroelectric interfaces: insights and artifacts from first principles

Based on recent advances in first-principles theory, we develop a general model of the band offset at metal/ferroelectric interfaces. We show that, depending on the polarization of the film, a pathological regime might occur where the metallic carriers populate the energy bands of the insulator, making it metallic. As the most common approximations of density functional theory are affected by a systematic underestimation of the fundamental band gap of insulators, this scenario is likely to be an artifact of the simulation. We provide a number of rigorous criteria, together with extensive practical examples, to systematically identify this problematic situation in the calculated electronic and structural properties of ferroelectric systems. We discuss our findings in the context of earlier literature studies, where the issues described in this work have often been overlooked. We also discuss formal analogies to the physics of polarity compensation at LaAlO3/SrTiO3 interfaces, and suggest promising avenues for future research.Comment: 29 pages, 23 figure

La transfixión percutánea cúbito-carpiana en las fracturas inestables de la extremidad distal del radio

Se expone una alternativa terapéutica para las fracturas inestables de la extremidad distal del radio, consistente en estabilizar la reducción mediante una aguja de Kirschner que atravesando oblícuamente la extremidad distal del cúbito se ancla en el carpo. Se precisan los detalles de la técnica que, en una valoración inicial sobre más de cien casos, aporta resultados constantemente satisfactorios. Se hace énfasis en la sencillez del procedimiento, que al propiciar una ejecución muy rápida, cobra ventaja frente a otras modalidades (fijador externo, osteosíntesis abierta, etc.) y especialmente ante traumatismos asociados del mismo miembro.A therapeutic alternative for the unstable fractures of the distal extremity of the radius is presented. The technique consists in stabilizing the fracture reduction by means of one Kirschner's wire that crosses obliquely the distal extremity of the ulnar and anchors in the carpus. The details of this technique are described. This technique has constantly provided satisfactory results in an initial evaluation on more than one hundred cases. Emphasis is made upon the simplicity of the procedure which surpasses other technical procedures (external fixation, open osteosynthesis, etc.) due to the fact that it propitiates a quicker execution, and it surpasses other technical procedures specially with associated injuries in the same limb

Reducing side lobes of antenna array by the binomial method

This paper explores optimization and synthesis of linear, which prints antennas arrays. The developed synthesis bases on an optimization binomial method. The objective of this paper is to adapt the binomial method to reduce the side lobe level. The application of this formalism gives terrific results

Design and implementation of a technology planar 4x4 butler matrix for networks application

In this paper, switched beam smart antenna systems are investigated to improve the performance of wireless networks. The microstrip technology of antenna arrays with Butler matrix topology as a beam-former is used to implement the switched beam smart antenna system. The optimum design of a 4x4 planar Butler matrix array, operating at 5.6 GHz for WLAN applications. System’s design and optimization was based on computer simulations

Quiste óseo aneurismático poliostótico

Se presenta un caso de quiste óseo aneurismático de localización bifocal, correspondiente a una niña de 12 años de edad. La primera lesión diagnosticada se localizó en la metáfisis proximal de la tibia izquierda y dos años más tarde, se descubrió una lesión similar en el calcáneo derecho. El estudio individualizado de estas lesiones no demuestra diferencias significativas respecto a las clásicamente descritas para los quistes óseos aneurismáticos genuinos, monostó- ticos. En una amplia revisión bibliográfica sólo hemos podido encontrar un caso de localización plurifocal.A bifocal aneurysmatic bone cyst presenting in a 12-year-old is reported. The first lesion detected was situated in the proximal metaphysis of the left tibia; the second lesion was diagnosed two years later in the right calcaneus. Individual evaluation of these lesions discovered no significant differences with respect to classical monostotic, true aneurysmatic bone cysts. An exhaustive review of the literature yielded only one case exhibiting plurifocal location

Three strongly correlated charged bosons in a one-dimensional harmonic trap: natural orbital occupancies

We study a one-dimensional system composed of three charged bosons confined in an external harmonic potential. More precisely, we investigate the ground-state correlation properties of the system, paying particular attention to the strong-interaction limit. We explain for the first time the nature of the degeneracies appearing in this limit in the spectrum of the reduced density matrix. An explicit representation of the asymptotic natural orbitals and their occupancies is given in terms of some integral equations.Comment: 6 pages, 4 figures, To appear in European Physical Journal