Hydride Vapor Phase Epitaxy of GaN Thick Films by the Consecutive Deposition Process Using GaCl3

GaN buffer and main layers were grown by the conventional hydride vapor phase epitaxy technique using GaCl₃ consecutively. The deposited buffer layers were investigated by atomic force microscopy and X-ray analysis. To examine the behavior of the buffer layers at main layer growth temperature, heat treatment was conducted at 900°C. Based on the results of the buffer layer study, GaN thick films were grown at 1050°C. Optimum deposition conditions of buffer layer from the buffer and main layer studies generally coincided. On the φ scanning pattern, the GaN films grown on (0001) Al₂O₃ were single-crystalline. Band-edge emission dominated photoluminescence was observed at room temperature.     

Control of circulating current in two parallel three-phase boost rectifiers

One unique feature in parallel three-phase converters is a potential zero-sequence circulating current. To avoid the circulating current, most present technology uses an isolation approach, such as transformers or separate power supplies. This paper proposes a parallel system where individual converters connect both AC and DC sides directly without additional passive components to reduce size and cost of the overall parallel system. In this case, the control of the circulating current becomes an important objective in the converter design. This paper: (1) develops an averaged model of the parallel converters based on a phase-leg averaging technique; (2) a zero-sequence model is then developed to predict the dynamics of the zero-sequence current; (3) based on the zero-sequence model, this paper introduces a new control variable, which is associated with space-vector modulation; (4) a strong zero-sequence current control loop is designed to suppress the circulating current; and (5) simulation and experimental results validate the developed model and the proposed control scheme.     

Substrate transport and cocaine binding of human dopamine transporter is reduced by substitution of carboxyl tail with that of bovine dopamine transporter

A chimeric dopamine transporter (DAT) cDNA encoding mutant human DAT (hDAT) protein in which the intracellular carboxyl-terminal tail is replaced by that of the bovine dopamine transporter (bDAT) was constructed. The chimeric hDAT cDNA was expressed in COS-7 cells, and [3H]dopamine and [3H]MPP+ uptake and [3H]CFT binding capacities were assessed. Substrate transport and ligand binding of bDAT were reduced by 32-43% as a result of substitution of the carboxyl tail in hDAT, suggesting that the functional characteristics of bDAT arise from differences in the carboxyl tail between human and bovine DAT. Thus, it appears that the sequences encoded within the carboxyl terminal of DAT would be one of the important determinants for its functions.     

Aerodynamic effect on natural frequency and flutter instability in rotating optical disks

 Experimental studies on the aerodynamic coupling effect on natural frequencies and flutter instability of rotating disks are investigated in this paper. The experiments performed using a vacuum chamber and optical disks give two main results. One is that the aerodynamic effect by surrounding air reduces the natural frequencies and critical speeds of the vibration modes in pre-flutter regions. The other is that the natural frequency of the disk rotating at ambient atmospheric pressure is equal to that in vacuum at the flutter onset speed where the disk experiences aero-induced flutter. In post-flutter regions, the aerodynamic coupling between the disk and surrounding air increases the natural frequencies of the disk. Received: 17 June 2002/Accepted: 7 October 2002 The work was supported by Grant No. R11-1997-042-090001-0 of the Center for Information Storage Devices designated by the Korea Science & Engineering Foundation. Paper presented at the 13th Annual Symposium on Information Storage and Processing Systems, Santa Clara, CA, USA, 17–18 June, 2002     

The effects of carrier-velocity saturation on high-current BJToutput resistance

Modern bipolar junction transistors (BJTs) tend to operate with saturated carrier velocity in the collector space-charge region. A physical analysis of the effects of velocity saturation on the output resistance of BJTs, especially for high current levels is presented. Physical analyses show that when the collector current density approaches a critical value, the Early voltage can increase significantly due to carrier-velocity saturation as the resulting base push-out partially offsets base-width modulation. This effect is also demonstrated in simulations with PISCES and MMSPICE     

Degradation of junction leakage in devices subjected to gateoxidation in nitrous oxide [MOS transistors]

Nitrided gate oxides offer several electrical and reliability advantages over conventional oxides and also provide a good barrier against impurity diffusion. Oxidation in nitrous oxide (N₂O) has been very successful in overcoming some of the problems associated with nitridation in ammonia. The authors have observed that the extent of N₂O oxidation has a strong detrimental effect on the drain leakage current of MOS transistors in the off state. This phenomenon has been identified to be caused by an increase in the active area junction leakage current     

An efficient assumed strain element model with six DOF per node for geometrically non-linear shells

The present paper describes an assumed strain finite element model with six degrees of freedom per node designed for geometrically non-linear shell analysis. An important feature of the present paper is the discussion on the spurious kinematic modes and the assumed strain field in the geometrically non-linear setting. The kinematics of deformation is described by using vector components in contrast to the conventional formulation which requires the use of trigonometric functions of rotational angles. Accordingly, converged solutions can be obtained for load or displacement increments that are much larger than possible with the conventional formulation with rotational angles. In addition, a detailed study of the spurious kinematic modes and the choice of assumed strain field reveals that the same assumed strain field can be used for both geometrically linear and non-linear cases to alleviate element locking while maintaining kinematic stability. It is strongly recommended that the element models, described in the present paper, be used instead of the conventional shell element models that employ rotational angles.     

Experience with Applying Formal Methods to Protocol Specification and System Architecture

In the last three years or so we at Enterprise Platforms Group at Intel Corporation have been applying formal methods to various problems that arose during the process of defining platform architectures for Intel's processor families. In this paper we give an overview of some of the problems we have worked on, the results we have obtained, and the lessons we have learned. The last topic is addressed mainly from the perspective of platform architects.     

Structure and dynamics of suspensions of silica particles in liquidcrystals under a low frequency AC applied voltage

Silica particles dispersed in liquid crystals exhibit a novel behavior such as a unique migrating behavior and alignment. These characteristics are found to depend on the size of the nanoparticles, the surface state of nanoparticles, the liquid crystal (LC) phases, the amplitude and the frequency of applied voltage. These are discussed in terms of anisotropic particle-particle and particle-LC molecules interactions in the anisotropic environment of liquid crystal matrix