Electronic States and Optical Transitions in Bulk and Quantum Well Structures of III-V Compound Semiconductors

In this work we apply the methods of band structure calculation combined with self-consistent treatment of the light-matter interaction to a variety of problems in bulk semiconductors and semiconductor heterostructures as well as in new optoelectronic devices. In particular, we utilize the 30- and 8-band k • p band structure calculation methods to study the electronic, magnetic, and optical properties of the diluted magnetic semiconductor, GaMnAs, in the mean-field Zener model. We calculate the anisotropic dielectric response of GaMnAs in the metallic regime and show that our model produces a good agreement with the experimental results of magneto-optical Kerr spectroscopy in the interband transition region. We also discuss the advantages of the 30-band k • p model for spin-polarized ferromagnetic GaMnAs. We present new methods for calculating electronic states in low-dimensional semiconductor heterostructures based on the real-space Hamiltonian. The formalism provides extreme simplicity of the numerical implementation and superior accuracy of the results. They are applicable to a general n-band k • p model and specifically tested in the 6-, 8-band k • p models, and a simple parabolic one band model. The transparency of the new method allows us to investigate the origin and elimination of spurious solutions in the unified manner. Spurious solutions have long been a major issue in low- dimensional band structure calculations. As an application of nonlinear optical interactions in two-dimensional semiconductor heterostructures, we calculate the upper limits on the efficiency of the passive terahertz difference frequency generation based on the intersubband resonant nonlinearity. Our approach incorporates electronic states together with propagating coupled fields through the self-consistent calculation of the Poisson equation, density matrix equations, and coupled wave equations. We develop optimal device geometries and systematically study the device performance as a function of various parameters. The results are compared with a simplified analytic solution

(E)-2,2′-[3-(2-Nitro­phen­yl)prop-2-ene-1,1-di­yl]bis­(3-hy­droxy­cyclo­hex-2-en-1-one)

In the title compound, C21H21NO6, each of the cyclo­hexenone rings adopts a half-chair conformation. Each of the pairs of hy­droxy and carbonyl O atoms are oriented to allow for the formation of intra­molecular O—H⋯O hydrogen bonds, which are typical of xanthene derivatives

Performance Improvement of a High Side Scroll Compressor by Thrust Surface Oil Groove

Performance analysis has been carried out on a high side scroll compressor having a fixed scroll equipped with a circular oil groove on its thrust surface. Oil is supplied to the oil groove through an intermittent opening from a high pressure oil reservoir formed inside the orbiting scroll hub. Oil in the groove is then delivered to both suction and back pressure chambers by pressure differentials and viscous pumping action of the orbiting scroll base plate. Mathematical modeling of this oil groove system has been incorporated into main compressor performance simulation program for optimum oil groove design. Pressure in the oil groove can be controlled by changing the oil passage area and oil groove configuration. With an enlarged oil passage, pressure in the oil groove increases due to increased flow rate, but pressure increase in the back pressure chamber is not that large, resulting in reduced friction loss at the thrust surface between the two scrolls. On the other hand, by increasing the oil passage area, oil content in the refrigerant flow increases, and the orbiting scroll stability could be negatively affected by oil groove pressure increase. Considering all these factors, EER could be improved by about 3.6% at ARI condition by optimum oil groove design

Mapa anisotrópico estadístico de imágenes de resonancia magnética funcional

En este trabajo presentamos un nuevo método para procesar imágenes de Resonancia Magnética Funcional (IRMf) del cerebro. El nuevo procedimiento esta basado en aplicar difusión anisotrópica robusta (DAR) a imágenes de resonancia magnética funcional ruidosa, para obtener mapas estadísticos de mayor relevancia. Las IRMf utilizan una serie de imágenes de resonancia magnética para mapear de forma no invasiva las áreas de actividad neuronal aumentada del cerebro humano. La baja relación señal ruido de las imágenes funcionales, hace necesario el uso de técnicas de procesamiento de imágenes sofisticadas como mapas estadísticos paramétricos (MEP). La aplicación del método propuesto permite obtener MEPs que incluyen valiosa información con respecto a la interrelación entre las series temporales correspondientes a cada elemento de volumen en un espacio 3-D (voxel) en el correspondiente MEP. Presentamos resultados de la técnica propuesta tanto en imágenes artificiales como en imágenes reales de resonancia magnética funcional de una experiencia basada en un estimulo visual en bloques.Eje: II - Workshop de computación gráfica, imágenes y visualizaciónRed de Universidades con Carreras en Informática (RedUNCI

Mapa anisotrópico estadístico de imágenes de resonancia magnética funcional

En este trabajo presentamos un nuevo método para procesar imágenes de Resonancia Magnética Funcional (IRMf) del cerebro. El nuevo procedimiento esta basado en aplicar difusión anisotrópica robusta (DAR) a imágenes de resonancia magnética funcional ruidosa, para obtener mapas estadísticos de mayor relevancia. Las IRMf utilizan una serie de imágenes de resonancia magnética para mapear de forma no invasiva las áreas de actividad neuronal aumentada del cerebro humano. La baja relación señal ruido de las imágenes funcionales, hace necesario el uso de técnicas de procesamiento de imágenes sofisticadas como mapas estadísticos paramétricos (MEP). La aplicación del método propuesto permite obtener MEPs que incluyen valiosa información con respecto a la interrelación entre las series temporales correspondientes a cada elemento de volumen en un espacio 3-D (voxel) en el correspondiente MEP. Presentamos resultados de la técnica propuesta tanto en imágenes artificiales como en imágenes reales de resonancia magnética funcional de una experiencia basada en un estimulo visual en bloques.Eje: II - Workshop de computación gráfica, imágenes y visualizaciónRed de Universidades con Carreras en Informática (RedUNCI

Violet-light spontaneous and stimulated emission from ultrathin In-rich InGaN/GaN multiple quantum wells grown by metalorganic chemical vapor deposition

We investigated the spontaneous and stimulated emission properties of violet-light-emitting ultrathin In-rich InGaN/GaN multiple quantum wells (MQWs) with indium content of 60%-70%. The Stokes shift was smaller than that of In-poor InGaN MQWs, and the emission peak position at 3.196 eV was kept constant with increasing pumping power, indicating negligible quantum confined Stark effect in ultrathin In-rich InGaN MQWs despite of high indium content. Optically pumped stimulated emission performed at room temperature was observed at 3.21 eV, the high-energy side of spontaneous emission, when the pumping power density exceeds ???31 kW/ cm2.open6

(E)-2,2′-[3-(2-Nitro­phen­yl)prop-2-ene-1,1-di­yl]bis­(3-hy­droxy-5,5-dimethyl­cyclo­hex-2-en-1-one)

In the title compound, C25H29NO6, each of the cyclo­hexenone rings adopts a half-chair conformation. Each of the pairs of hy­droxy and carbonyl O atoms are oriented to allow for the formation of intra­molecular O—H⋯O hydrogen bonds, which are typical of xanthene derivatives. The nitro group is rotationally disordered over two orientations in a 0.544 (6):0.456 (6) ratio. In the crystal, weak inter­molecualr C—H⋯O hydrogen bonds link mol­ecules into layers parallel to the ab plane