Optical absorption spectrum in disordered semiconductor multilayers

The effects of chemical disorder on the electronic and optical properties of semiconductor alloy multilayers are studied based on the tight-binding theory and single-site coherent potential approximation. Due to the quantum confinement of the system, the electronic spectrum breaks into a set of subbands and the electronic density of states and hence the optical absorption spectrum become layer-dependent. We find that, the values of absorption depend on the alloy concentration, the strength of disorder, and the layer number. The absorption spectrum in all layers is broadened because of the influence of disorder and in the case of strong disorder regime, two optical absorption bands appear. In the process of absorption, most of the photon energy is absorbed by the interior layers of the system. The results may be useful for the development of optoelectronic nanodevices.Comment: 6 pages, 6 EPS figures, revised versio

Image Segmentation from RGBD Images by 3D Point Cloud Attributes and High-Level Features

In this paper, an approach is developed for segmenting an image into major surfaces and potential objects using RGBD images and 3D point cloud data retrieved from a Kinect sensor. In the proposed segmentation algorithm, depth and RGB data are mapped together. Color, texture, XYZ world coordinates, and normal-, surface-, and graph-based segmentation index features are then generated for each pixel point. These attributes are used to cluster similar points together and segment the image. The inclusion of new depth-related features provided improved segmentation performance over RGB-only algorithms by resolving illumination and occlusion problems that cannot be handled using graph-based segmentation algorithms, as well as accurately identifying pixels associated with the main structure components of rooms (walls, ceilings, floors). Since each segment is a potential object or structure, the output of this algorithm is intended to be used for object recognition. The algorithm has been tested on commercial building images and results show the usability of the algorithm in real time applications

Laboratory-scale Investigation of Two-phase Relative Permeability

We present experimental investigations of two-phase (oil and water) relative permeability of laboratory scale rock cores through a joint use of direct X-ray measurement and flow-through investigations. The study is motivated by the observation that appropriate modeling of oil and water displacement in porous media or fractured rocks requires to be firmly grounded on accurate and representative core flood experiments and their appropriate interpretation. Experimental data embed key information relating relative permeability to observables. In this context, direct measurement of in-situ fluid saturation through X-Ray techniques has the unprecedented ability to characterize key processes occurring during the displacement of immiscible fluids through natural permeable materials. Water saturation profiles determined by X-ray scanner can then be linked to relative permeability curves stemming from two-phase flow experiments. We illustrate the benefit of employing direct X-Ray measurements of fluid saturation through a set of laboratory experiments targeted to the estimate of two-phase relative permeabilities of homogeneous samples (sand pack and Berea sandston core). Data are obtained for a range of diverse fractional flow rates and provide information at saturations ranging from irreducible water content to residual oil saturation. Our X-Ray saturation data are consistent with an interpretation of measured relative permeabilities as associated with water-wet rock conditions. The comparison of different preamble samples result high displacement efficiency and recovery factor corresponds to the high permeable and well-connected pores

Illicit methylphenidate use among Iranian medical students: prevalence and knowledge

Afshin Habibzadeh1 Mahasti Alizadeh2 Ayoub Malek3 Leili Maghbooli1 Mohammadali M Shoja4 Kamyar Ghabili41Students' Research Committee, 2Department of Community Medicine, 3Department of Psychiatry, 4Tuberculosis and Lung Disease Research Center, Tabriz University of Medical Sciences, Tabriz, IranBackground: Methylphenidate, a medication prescribed for individuals suffering from attention-deficit/hyperactivity disorder, is increasingly being misused by students.Objective: The aims of this study were to evaluate the frequency of methylphenidate use among a group of Iranian medical students and to assess their knowledge of methylphenidate.Methods: Anonymous, self-administered questionnaires were completed by all medical students entering the university between 2000 and 2007.Results: Methylphenidate users’ mean knowledge score was higher than that of nonusers (15.83 ± 3.14 vs 13.66 ± 3.10, P = 0.008). Age, gender, and school year were positively correlated with knowledge score (P < 0.05). Data analysis demonstrated that 27 participants (8.7%) had taken methylphenidate at least once in their lifetime. The respondents believed that the most common motive for methylphenidate use among youths was that it aided concentration and therefore ability to study.Conclusion: This study indicates a relatively low level of knowledge about methylphenidate among Iranian medical students. More educational programs regarding the use of methylphenidate are required and should be focused on the student suppliers, clinicians, pharmacists, and medical students.Keywords: methylphenidate, medical student, prevalence, Ira