Vacancies in SiGe: Jahn–Teller distortion and spin effects

The electronic structure of a vacancy in silicon-germanium is studied using ab initio total-energy minimization methods. The calculations are based on density-functional theory in the local-spin-density approximation. We report ionic relaxations, defect formation energies and ionization levels of Si and Gevacancies in a zinc blende model structure (SiGe). The Gevacancy in SiGe is characterized by symmetry-lowering Jahn–Teller (JT) distortions and a negative-effective-U effect, in those respects resembling the vacancy in elemental silicon. For Si vacancy, the exchange-coupling energy is found to overcome the JT energy, and symmetric high-spin ground states are predicted.Peer reviewe

Seudomicetoma dermatofítico en un gato persa : aspectos clínicos, patológicos y evolutivos

En este trabajo presentamos los aspectos clínicos, anatomopatológicos y evolutivos de un caso de dermatitis piogranulomatosa múltiple causada por hongos del género Microsporum, también conocida como seudomicetoma dermatofítico, en un gato persa, no castrado, de un año de edad al comienzo de la enfermedad. Las lesiones se caracterizaron macroscópicamente por la formación de numerosos nódulos de diferentes tamaños, localizados en la cabeza y antebrazo derecho, extendiéndose posteriormente a zona dorso lateral del tronco. La evolución de estos nódulos, que se generalizaron en algo menos de un mes, era hacia la coalescencia y fistulización, con descarga de un material grumoso blanco-grisáceo. El estudio histopatológico reveló una dermatitis piogranulomatosa, supeficial y profunda, caracterizada por presentar en el centro de los granulomas agregados de hongos septados inmersos en una matriz acidófila. La extirpación quirúrgica de un gran número de nódulos proporcionó mejorías transitorias, aunque reaparecieron nuevas lesiones. En este trabajo se describe la evolución tras dos años de seguimiento clínico. Tras el tratamiento con griseofulvina no se detectan nuevas lesiones después de 6 meses de su aplicación y seguimiento.This paper reports the clinical and histopathological features of a case of pyogranulomatous dermatitis caused by Microsporum fungi, a condition also known as dermatophyte pseudomycetoma, in a eneyear-old Persian cat. Grossly apparent fistulized nodules of varying sizes displaying a granular discharge were localized on the head, back, elbow and tail. Microscopic analysis revealed a deep piogranulomatous dermatitis characterized by centrally-located clusters of fungi within an acidophilic matrix. In just under a month, nodules had beco me generalized. Partial surgical excision and non-specific treatment provided temporary improvement, but new lesions subsequentlyappeared

Phase-field model for Hele-Shaw flows with arbitrary viscosity contrast. II. Numerical study

We implement a phase-field simulation of the dynamics of two fluids with arbitrary viscosity contrast in a rectangular Hele-Shaw cell. We demonstrate the use of this technique in different situations including the linear regime, the stationary Saffman-Taylor fingers and the multifinger competition dynamics, for different viscosity contrasts. The method is quantitatively tested against analytical predictions and other numerical results. A detailed analysis of convergence to the sharp interface limit is performed for the linear dispersion results. We show that the method may be a useful alternative to more traditional methods.Comment: 13 pages in revtex, 5 PostScript figures. changes: 1 reference added, figs. 4 and 5 rearrange

Visual 3-D SLAM from UAVs

The aim of the paper is to present, test and discuss the implementation of Visual SLAM techniques to images taken from Unmanned Aerial Vehicles (UAVs) outdoors, in partially structured environments. Every issue of the whole process is discussed in order to obtain more accurate localization and mapping from UAVs flights. Firstly, the issues related to the visual features of objects in the scene, their distance to the UAV, and the related image acquisition system and their calibration are evaluated for improving the whole process. Other important, considered issues are related to the image processing techniques, such as interest point detection, the matching procedure and the scaling factor. The whole system has been tested using the COLIBRI mini UAV in partially structured environments. The results that have been obtained for localization, tested against the GPS information of the flights, show that Visual SLAM delivers reliable localization and mapping that makes it suitable for some outdoors applications when flying UAVs

ab initio modeling of open systems: charge transfer, electron conduction, and molecular switching of a C_{60} device

We present an {\it ab initio} analysis of electron conduction through a $C_{60}$ molecular device. Charge transfer from the device electrodes to the molecular region is found to play a crucial role in aligning the lowest unoccupied molecular orbital (LUMO) of the $C_{60}$ to the Fermi level of the electrodes. This alignment induces a substantial device conductance of $\sim 2.2 \times (2e^2/h)$. A gate potential can inhibit charge transfer and introduce a conductance gap near $E_F$, changing the current-voltage characteristics from metallic to semi-conducting, thereby producing a field effect molecular current switch

Cluster-based density-functional approach to quantum transport through molecular and atomic contacts

We present a cluster-based density-functional approach to model charge transport through molecular and atomic contacts. The electronic structure of the contacts is determined in the framework of density functional theory, and the parameters needed to describe transport are extracted from finite clusters. A similar procedure, restricted to nearest-neighbor interactions in the electrodes, has been presented by Damle et al. [Chem. Phys. 281, 171 (2002)]. Here, we show how to systematically improve the description of the electrodes by extracting bulk parameters from sufficiently large metal clusters. In this way we avoid problems arising from the use of nonorthogonal basis functions. For demonstration we apply our method to electron transport through Au contacts with various atomic-chain configurations and to a single-atom contact of Al.Comment: 18 pages, 13 figure

Phase-field model for Hele-Shaw flows with arbitrary viscosity contrast. I. Theoretical approach

We present a phase-field model for the dynamics of the interface between two inmiscible fluids with arbitrary viscosity contrast in a rectangular Hele-Shaw cell. With asymptotic matching techniques we check the model to yield the right Hele-Shaw equations in the sharp-interface limit and compute the corrections to these equations to first order in the interface thickness. We also compute the effect of such corrections on the linear dispersion relation of the planar interface. We discuss in detail the conditions on the interface thickness to control the accuracy and convergence of the phase-field model to the limiting Hele-Shaw dynamics. In particular, the convergence appears to be slower for high viscosity contrasts.Comment: 17 pages in revtex. changes: 1 reference adde

Resonant Andreev reflections in superconductor-carbon-nanotube devices

Resonant Andreev reflection through superconductor-carbon-nanotube devices was investigated theoretically with a focus on the superconducting proximity effect. Consistent with a recent experiment, we find that for high transparency devices on-resonance, the Andreev current is characterized by a large value and a resistance dip; low-transparency off-resonance devices give the opposite result. We also give evidence that the observed low-temperature transport anomaly may be a natural result of Andreev reflection process