Recent advances in insulated gate bipolar transistor technology

Device design of the insulated gate bipolar transistor (IGBT) has been optimized to reduce the distributed transmission-line effect. In addition, cell geometry is chosen to yield high latchup current capability and low forward-voltage drop simultaneously. The vertical structure is optimized to enhance both the turn-off speed and the safe operating area of the IGBTs. The turn-off time of the n-IGBT has been shortened to be as low as 40 ns. The p-channel IGBT latchup current has been improved four to six times over the previously reported results through innovative design and processes. An open-base bipolar transistor model has been implemented to investigate transient IGBT characteristics     

Admission Control Algorithms for Revenue Optimization with QoS Guarantees in Mobile Wireless Networks

We propose and analyze call admission control algorithms integrated with pricing for revenue optimization with QoS guarantees to serve multiple service classes in mobile wireless networks. Traditional admission control algorithms make acceptance decisions for new and handoff calls to satisfy certain QoS constraints such as the dropping probability of handoff calls and the blocking probability of new calls being lower than a pre-specified threshold. We analyze a class of partitioning and threshold-based admission control algorithms that make acceptance/rejection decisions not only to satisfy QoS requirements but also to optimize the revenue of the system by taking prices and arrival/departure information of service calls into account. We show that for a “charge-by-time” pricing scheme, there exist optimal resource allocation settings under which the partitioning and threshold-based admission control algorithms would produce the maximum revenue obtainable by the system without sacrificing QoS requirements. Further, we develop a new hybrid admission control algorithm which outperforms both partitioning and threshold-based admission control algorithms over a wide range of input parameters characterizing the operating environment and service workload conditions. Methods for utilizing of the analysis results for realtime admission control for revenue optimization with QoS guarantees are described with numerical data given to demonstrate the applicability.     

Stereoscopic view-dependent visualization of terrain height fields

Visualization of large geometric environments has always been an important problem of computer graphics. We present a framework for the stereoscopic view-dependent visualization of large scale terrain models. We use a quadtree based multiresolution representation for the terrain data. This structure is queried to obtain the view-dependent approximations of the terrain model at different levels of detail. In order not to lose depth information, which is crucial for the stereoscopic visualization, we make use of a different simplification criterion, namely, distance-based angular error threshold. We also present an algorithm for the construction of stereo pairs in order to speed up the view-dependent stereoscopic visualization. The approach we use is the simultaneous generation of the triangles for two stereo images using a single draw-list so that the view frustum culling and vertex activation is done only once for each frame. The cracking problem is solved using the dependency information stored for each vertex. We eliminate the popping artifacts that can occur while switching between different resolutions of the data using morphing. We implemented the proposed algorithms on personal computers and graphics workstations. Performance experiments show that the second eye image can be produced approximately 45 percent faster than drawing the two images separately and a smooth stereoscopic visualization can be achieved at interactive frame rates using continuous multiresolution representation of height fields     

Optimization and surface charge sensitivity of high-voltageblocking structures with shallow junctions

The most commonly used high-voltage blocking and termination structures-floating field limiting rings (FLR), lateral charge control HVIC devices, and junction termination extension (JTE) structures-are very sensitive to positive silicon and silicon dioxide interface charges. These high-voltage termination structures specifically designed for 1000-V blocking capability lose 25 to 50% of their voltage-blocking capability under 5×10¹¹ cm^-2 net interface state density. In contrast, optimized multiple-zone JTE (MZ-JTE), and offset multiple field plated and field-limiting ring (OFP-FLR) structures will lose only 5% of their respective voltage blocking capabilities under the same surface-charge condition. These improved high-voltage blocking structures do not require additional passivation and process complexities     

Elliptic cylinder geometry for distinguishability analysis in impedance tomography

Electrical impedance tomography (EIT) is a technique that computes the cross-sectional impedance distribution within the body by using current and voltage measurements made on the body surface. It has been reported that the image reconstruction is distorted considerably when the boundary shape is considered to be more elliptical than circular as a more realistic shape for the measurement boundary. This paper describes an alternative framework for determining the distinguishability region with a finite measurement precision for different conductivity distributions in a body modeled by elliptic cylinder geometry. The distinguishable regions are compared in terms of modeling error for predefined inhomogeneities with elliptical and circular approaches for a noncircular measurement boundary at the body surface. Since most objects investigated by EIT are noncircular in shape, the analytical solution for the forward problem for the elliptical cross section approach is shown to be useful in order to reach a better assessment of the distinguishability region defined in a noncircular boundary. This paper is concentrated on centered elliptic inhomogeneity in the elliptical boundary and an analytic solution for this type of forward problem. The distinguishability performance of elliptical cross section with cosine injected current patterns is examined for different parameters of elliptical geometry.     

Unethical computer using behavior scale: A study of reliability and validity on Turkish university students

This study was carried out in a Turkish university with 216 undergraduate students of computer technology as respondents. The study aimed to develop a scale (UECUBS) to determine the unethical computer use behavior. A factor analysis of the related items revealed that the factors were can be divided under five headings; intellectual property, social impact, safety and quality, net integrity and information integrity.     

Effect of heat treatment in air on the thermal properties of SiC fibre-reinforced composite. Part 1: a barium osumilite (BMAS) matrix glass ceramic composite

The thermal properties have been studied on a glass ceramic composite comprised of a barium osumilite (BMAS) matrix reinforced with SiC (Tyranno) fibres which has been subjected to a heat treatment in air in the range of 700–1,200 °C. Microstructural studies were carried out especially on of the interface between fibre and matrix. The presence of a carbon thin layer in the interface is a typical observation in SiC fibre-reinforced glass ceramic matrix composite systems. The microstructural evaluation and thermal properties showed a degradation of interfacial layer occurred at low heat treatment temperatures, (700–800 °C) this was attributed to the fact that, at those heat treatment temperatures the carbon rich layer formed during processing was oxidised away leaving voids between fibre and matrix, which were linked by isolated silicon-rich bridges. After heat treatment at higher temperatures of 1,000–1,200 °C, the thermal properties were retained or even enhanced by leaving a thick interfacial layer.     

The existence and the determination of terminal equations for hybrid connected N-ports

A new procedure for the existence and the determination of terminal equations for the hybrid interconnection of two n-port networks is given. It is shown that this procedure generalizes the previous works of Duffin, Trapp and Mitra for the hybrid sum of terminal impedance matrices which are either Hermitian positive semi-definite (HSD) or arbitrary matrices with complex entries. For the application of the new procedure it is shown that each n-port need not be terminal solvable or well defined. In fact, even in the case of active RLC n-ports considered in sinusoidal steady-state, the previous results of Duffin, Mitra and Trapp established for HSD matrices or arbitrary complex matrices can still be utilized with the use of modified terminal equations, to obtain the terminal equations of the resulting n-port networks. It is also noted that the method introduced in this paper is independent of the choice of generalized inverses.     

A direct borohydride-peroxide fuel cell-LiPO hybrid motorcycle prototype: Investigation of short-term behavior of DBPFC stack – I

In the present study, a safer and more performance 270?W Direct Borohydride/Peroxide Fuel Cell (DBPFC) Stack has been constructed for an electrical hybrid motorbike application. Performance tests were carried out with single cell and 5–10–25?cell stacks. Performance loss has been not observed while stacking DBPFC because of the Independent Cell Liquid Distribution Network (ICLDN) system and special bipolar plate design. The power densities have been approximately 120?mWcm^?2 for a single DBPFC and 25-cell DBPFC stack without any stacking loss. Additionally, the stack temperature has been controlled by keeping the oxidant concentration low, and it has been maintained at approximately 52?°C without using a cooling system. The short-term performances of the 25-cell DBPFC stack have been tested over 25?min and 50?min, which showed that the performance and stack security of the DBPFC are highly related to the oxidant properties, such as the concentration, temperature and feed type.