The effect of carrier-induced change on the optical properties of AlGaAs-GaAs intermixed quantum wells

The carrier-induced effects in the change of absorption and refractive index on the AlGaAs-GaAs intermixing modified quantum wells (QW's) have been investigated theoretically. Band-filling, bandgap shrinkage, and free-carrier absorption have been included for various carrier concentrations. The Schrodinger and the Poisson equations have been considered self-consistently. The polarized absorption coefficients are calculated using the Kane k·p method for a four band model and followed by the Kramers-Kranig transformation to obtain the refractive index change. The results obtained show a more enhanced bandgap renormalization and change of absorption, but a reduced change in refractive index for the larger intermixing extents. It is important to know the carrier-induced optical parameter changes the intermixed QW's because of their recent interests in photonics.published_or_final_versio

Designing an external efficieny of over 30% for light emittingdiode

In designing high intensity LED's, substantial increase in efficiency can be achieved with the use of a textured surface, which is characterized by its external quantum efficiency and radiation pattern. We have found that the randomness of the inclined facade surfaces contributes substantially to the enhanced efficiency substantially. Such efficiency is strongly dependent upon the textured surface layer's thickness and its distance to the active layer of the diode. To attain the maximum efficiency, an optimal range for these parameters is required.published_or_final_versio

Optimization of Textured-surface Light Emitting Diode

We present an analysis of the efficiency and radiation pattern of the textured-surface LED by tracing the light rays that emits from the active layer. Through simulation, we discover that the efficiency depends on the thickness of the textured layer and its separation distance from the active layer. By carefully choosing these two parameters, maximum efficiency an be achieved. The radiation pattern of a texture-surface LED is found to be different from the flat-surfaced LED in that the textured surface has a wider angular spread.published_or_final_versio

Brain tumor boundary detection in MR image with generalized fuzzy operator

Boundary detection in MR image with brain tumor is an important image processing technique applied in radiology for 3D reconstruction. The nonhomogeneities density tissue of the brain with tumor can result in achieving the inaccurate location in any boundary detection algorithms. Recently, some studies using the contour deformable model with regional base technique, the performance is insufficient to obtain the fine edge in the tumor, and the considerable error in accuracy is existed. Moreover, even in some of the normal tissue region, edge created by this method has also been encompassed. In this paper, we propose a new approach to detect the boundary of brain tumor based on the generalized fuzzy operator (GFO). One typical example is used for evaluating this method with the contour deformable model.published_or_final_versio

Estimation of the gray level variations in soft and hard peri-implant tissue from X-ray images

In the treatment and assessment of periodontal disease periapical films are taken at regular intervals. The films are compared around the region of the implant to monitor the changes that have taken place. A computer-assisted method to automate this process is presented here. To compare two images, a pair of X-ray images are superimposed on top of each other. The images are normalized and transformed to obtain the best fit. These images are subtracted and the difference in pixel values are used as a basis for analysis. A method for improving the alignment accuracy and contrast compensation is highlighted.published_or_final_versio

Fast adaptive blind beamforming technique for cyclostationary signals

Castedo et al. (1995) have present a blind beamforming criterion based on the property of cyclostationary signals. A stochastic gradient-based algorithm, which needs to choose the step size suitably, was derived to compute the optimum weight vector. In this paper a fast adaptive algorithm is proposed. We show that the recursive least square techniques can be applied to solve this problem successfully by making an appropriate approximation. Simulation results demonstrate the effect of the theoretic analysis.published_or_final_versio

Thyroid cancer cells boundary location by a fuzzy edge detection method

Morphometric assessment of tumor cells is important in the prediction of biological behavior of thyroid cancer. In order to automate the process, the computer-based system has to recognize the boundary of the cells. Many methods for the boundary detection have appeared in the literature and some of them applied to microscopic slice analysis. However, there is no reliable method since the gray-levels in the nuclei are uneven and are similar to the background. In the paper, a fuzzy edge detection method is used and is based on an improved generalized fuzzy operator. The method enhances the nuclei and effectively separates the cells from the background.published_or_final_versio

Normalization of contrast in document images using generalized fuzzy operator with least square method

The visual effect of non-uniform contrast and brightness surrounds in the image is a very common problem in the applications of photocopying, IC manufacture and medicine. In using the digital/CCD camera to capture documents and photos based on non-uniform illumination condition, the poor image will be seen. The poor image can result in achieving the inaccurate reading from the optical character recognition (OCR) system. This paper present a new approach to normalize the local contrast in documentation based on the least square method and also enhance the object of interest using generalized fuzzy operator (GFO). Two typical examples are used for evaluating the method. © 2002 IEEE.published_or_final_versio

Influence of TCE concentration in thermal oxidation on reliability of SiC MOS capacitors under Fowler-Nordheim electron injection

The effects of trichloroethylene (TCE) concentration in SiC thermal oxidation on the reliability of MOS capacitors under Fowler-Nordheim (FN) electron injection have been investigated. It is found that TCE thermal oxidation can enhance the resistance of the SiO2/SiC interface against generation of interface states and oxide charges caused by FN electron injection, and the resistance increases with TCE ratio increasing from 0 to 0.1. As compared with the control sample based on dry-O2 oxidation, the interface-state generation at 0.25 eV below the conduction-band edge is 5, 23, and 170 times smaller for samples with TCE ratio of 0.01, 0.05 and 0.1 respectively. In addition, the interface traps and oxide-charge traps of fresh samples decrease with increasing TCE ratio for the ratio less than 0.01, and then increase for larger ratio. It is proposed that the enhanced resistance against the stress is attributed to the gettering or dislodging of electrical and physical defects by the chlorine atoms incorporated in the oxide during the TCE oxidation. © 2006.link_to_subscribed_fulltex

Electronic properties of a rough quantum film

We use the coherent potential approximation to study the effect of surface roughness on the electronic properties of electrons in a quasi-two-dimensional quantum film. Calculations of the local and average density of states and electrical conductivity are presented. © 1998 Elsevier Science Ltd. All rights reserved.link_to_subscribed_fulltex