Efficient CT Image Reconstruction in a GPU Parallel Environment.

Computed tomography is nowadays an indispensable tool in medicine used to diagnose multiple diseases. In clinical and emergency room environments, the speed of acquisition and information processing are crucial. CUDA is a software architecture used to work with NVIDIA graphics processing units. In this paper a methodology to accelerate tomographic image reconstruction based on maximum likelihood expectation maximization iterative algorithm and combined with the use of graphics processing units programmed in CUDA framework is presented. Implementations developed here are used to reconstruct images with clinical use. Timewise, parallel versions showed improvement with respect to serial implementations. These differences reached, in some cases, 2 orders of magnitude in time while preserving image quality. The image quality and reconstruction times were not affected significantly by the addition of Poisson noise to projections. Furthermore, our implementations showed good performance when compared with reconstruction methods provided by commercial software. One of the goals of this work was to provide a fast, portable, simple, and cheap image reconstruction system, and our results support the statement that the goal was achieved.

Nanoscale conductive pattern of the homoepitaxial AlGaN/GaN transistor.

The gallium nitride (GaN)-based buffer/barrier mode of growth and morphology, the transistor electrical response (25-310 °C) and the nanoscale pattern of a homoepitaxial AlGaN/GaN high electron mobility transistor (HEMT) have been investigated at the micro and nanoscale. The low channel sheet resistance and the enhanced heat dissipation allow a highly conductive HEMT transistor (Ids > 1 A mm(-1)) to be defined (0.5 A mm(-1) at 300 °C). The vertical breakdown voltage has been determined to be ∼850 V with the vertical drain-bulk (or gate-bulk) current following the hopping mechanism, with an activation energy of 350 meV. The conductive atomic force microscopy nanoscale current pattern does not unequivocally follow the molecular beam epitaxy AlGaN/GaN morphology but it suggests that the FS-GaN substrate presents a series of preferential conductive spots (conductive patches). Both the estimated patches density and the apparent random distribution appear to correlate with the edge-pit dislocations observed via cathodoluminescence. The sub-surface edge-pit dislocations originating in the FS-GaN substrate result in barrier height inhomogeneity within the HEMT Schottky gate producing a subthreshold current.

Nanoscale investigation of AlGaN/GaN-on-Si high electron mobility transistors.

AlGaN/GaN HEMTs are devices which are strongly influenced by surface properties such as donor states, roughness or any kind of inhomogeneity. The electron gas is only a few nanometers away from the surface and the transistor forward and reverse currents are considerably affected by any variation of surface property within the atomic scale. Consequently, we have used the technique known as conductive AFM (CAFM) to perform electrical characterization at the nanoscale. The AlGaN/GaN HEMT ohmic (drain and source) and Schottky (gate) contacts were investigated by the CAFM technique. The estimated area of these highly conductive pillars (each of them of approximately 20-50 nm radius) represents around 5% of the total contact area. Analogously, the reverse leakage of the gate Schottky contact at the nanoscale seems to correlate somehow with the topography of the narrow AlGaN barrier regions producing larger currents.

Diagnóstico de Peligros e Identificación de Riesgos de Desastres en México. Atlas Nacional de Riesgos de la República Mexicana / Diagnosis of Danger and Disaster Risks Indentification in México. National Atlas of Risks of the Mexican Republic

El presente "atlas de riesgos" tiene como propósito general difundir conocimientos sobre los peligros e identificación de los riesgos de desastres que se presentan en México derivados de los fenómenos de origen geológico, hidrometeorológico, químico, sanitario y socio-organizativo. Contenido: 1) Introducción: riesgo de desastres en México; la prevención de desastres; diagnóstico de riesgo; conceptos básico sobre prevención de desastres; estadísticas de daños. 2) Riesgos geológicos: sismos; tsunamis; volcanes; movimientos de la superficie del terreno natural. 3) Riesgos hidrometeorológicos: precipitación pluvial; tormentas de granizo y nieve; heladas; ciclones tropicales; escurrimiento; inundaciones; sequía; Erosión; viento; marea de tormenta. 4) Riesgos químicos: definición de los riesgos y accidentes de origen químico y estadísticas de accidentes mundiales; ubicación y características de las fuentes de peligro (zonas industriales, industria petroquímica, tubería de transporte de gas; estaciones de servicio; fuentes de materiales radiactivos); accidentes relacionados con sustancias químicas; residuos peligrosos; incendios forestales. 5) Otros riesgos: de origen sanitario y socio-organizativos. 6) Microzonificación del riesgo: aspectos generales; tecnologías; mapas municipales de riesgo y de escenarios. Céreditos, autorías y bibliografía