Preparation and characterization of thin films of electrodeposited CdTe semiconductors

Thin films of CdTe semiconductors were prepared by electrodeposition technique in aqueous solutions. The deposition mechanism was investigated by cyclic voltammetry. The potential regions for the formation of the n-CdTe and p-CdTe films were determined. The structure, composition and morphology characteristics of as-deposited thin films of CdTe grown on SnO₂/glass and CdS/SnO₂/glass were investigated by XRD, EDAX and SEM techniques. The optical properties were measured to determine the absorption coefficient and band gap values. The as-deposited CdTe films grown on SnO₂/glass contained free Te while those grown on CdS/SnO₂/Glass did not contain this phase. The CdTe has the cubic structure with strong (111) orientation. The EDAX analysis showed a nearly stiochiometric Cd:Te ratio. The band gap has a value of 1.48 eV, which is in a good accordance with those reported in the literature. The effect of annealing at 350 and 400°C after CdCl₂ treatment on the structure and morphology was also examined.     

Decentralized stabilization of large electric power systems

This paper considers the problem of stabilizing the dynamics of a large electric power system, represented by a linear time invariant system of equations, by using several decentralized (or local) state feedback control laws. The stabilization problem is formulated into a functional minimization problem which implicitly controls the closed-loop eigenvalues of the controlled system. The constraint of decentralization is tackled in the minimization algorithm by using the method of feasible directions. To illustrate the application of the algorithm, it is used to stabilize a three machine electric power system.     

An efficient decision feedback with center sampling differential detector for restricted bandwidth fast Rayleigh channels

An efficient decision feedback technique (EDF) is proposed to improve the performance of premodulation Gaussian minimum shift keying (GMSK) signals. Center sampling differential detector (CSDD) over restricted bandwidth (BW) fast Rayleigh channels is employed. The intersymbol interference (ISI) is partially eliminated by using the conventional decision feedback (CDF) technique. In the present modification ISI is drastically eliminated by using EDF technique resulting in the minimization of probability of error. The new receiver structure, is useful in mobile radio (MR) and mobile satellite communications where power efficiency, synchronization and implementation complexity are of primary concern. Numerical results show that the receiver structure under consideration yields a superior performance in narrowband channels where conventional differential detector (CDD) becomes unusable.     

On the convergence acceleration of iterative processes

In this note, a method is proposed for accelerating the convergence of iterative processes based on the method of successive substitution. The proposed method can be considered as a different way of implementing the general dominant eigenvalue method (GDEM) of Crow & Nishio.     

Ceramic-based chemical sensors, probes and field-tests in automobile engines

The monitoring and control of combustion-related emissions is a top priority in many industries. The major methods used to detect combustion gases fall short of practical applications for in-situ measurements in industrial environments involving high temperature and chemical contaminants. The real challenge is not only to develop highly sensitive and selective sensors, but to maintain long-term stability in such aggressive environments. This article presents an overview of a multidisciplinary research effort in ceramic-based chemical sensors, highlighting opportunities as well as challenges. The group of sensors (CO, NO _x , O₂, and CO₂) selected for this article can, in general, be used to determine the state of combustion in a wide variety of applications. Fabrication of sensor probes and their field-test results in automobile engines are also presented.     

Power flow solution using the modified quasilinearization method

In this paper a method for solving power system load flow is developed. The proposed method is very simple, and is based on formulating the problem in rectangular coordinates, as a nonlinear programming problem. The solution is carried out using the modified quasilinearization method.

To examine the effectiveness of the proposed method, a comparison with a direct search optimization algorithm is carried out. The results are analysed in detail with the main result being that the proposed technique tested, is superior as far as computer memory and time is concerned.     

Intrasplenic venous flow patterns demonstrated by Doppler ultrasound in patients with portal hypertension

The flow pattern in the splenic vein has been previously reported in patients with portal hypertension, but with no reference to the flow within the intrasplenic venous radicles. Using Doppler ultrasound, this study describes the intrasplenic venous flow direction in 176 adult patients with intrahepatic portal hypertension. In our series, a normal flow pattern was maintained in all except four patients (2.3%) who had either reversed or dual venous drainage patterns resulting in trans-splenic portosystemic shunts. These abnormal patterns are Doppler signs of portal hypertension which might be associated with a higher risk of oesophageal variceal bleeding. It is recommended that the intrasplenic venous flow pattern should be assessed before surgical intervention involving the spleen in patients with portal hypertension.     

Study of electrical and optical properties of Cd1 − x Zn x S thin films

Thin films of Cd_0.9Zn_0.1S and CdS were prepared by thermal evaporation under vacuum of 10^–6 Torr and with deposition rate of 60 nm/min. X ray diffraction studies confirm the hexagonal structure of both CdS and Cd_0.9Zn_0.1S films. The effect of heat treatments with or without CdCl₂ enhances the grain size growth and improves the crystalline of the films. Moreover, the activation energy is decreased by heat treatment with or without CdCl₂ for all thin films. The optical absorption coefficient of Cd_0.9Zn_0.1S thin films were determined from measured transmittance and reflectance in the wavelength range of 300 to 2500 nm. The optical absorption spectra reveal the existence of direct energy gap for these films. It was found that the optical energy gap decreases upon annealing or CdCl₂ treatments.