Qualitative analysis of mathematical arc models using Lyapunov theory

An approach is proposed to the study of the electric arc near current zero by means of mathematical models. The approach is based on Lyapunov's stability theory and allows a qualitative analysis of the nonlinear differential equations describing the phenomenon. The main results concern the determination of the set of conditions leading to arc extinction and their dependence on the physical parameters involved. The classical Mayr and Cassie models are studied using the method, and some numerical results are given.     

A Study of an Intelligent Battlefield Damage Assessment System Based on a Multi-agent System

Battlefield damage assessment is the key to Battlefield Damage Assessment and Repair (BDAR).We present an Intelligent Battlefield Damage Assessment System (IBDAS) based on multi-agent system technology. We first establish the system framework, and then study the interior structure and workflow of a problem allocation agent. The result shows that, there are many advantages to resolve the problem of battlefield damage assessment by applying multi-agent system technology, and it will bring significant military benefit.     

Linear-Dispersion Division Multiple-Access for MIMO systems

Comprehensive study on novel Linear-Dispersion Division Multiple-Access（LDDMA） for multi-user uplink Multiple-Input Multiple-Output（MIMO）systems is proposed.In the new multiplexing scheme,each user’s information symbol is dispersed by a User-Specific Matrix（USM）both in space and time domain and linearly combined at base-station side.And a simple random search algorithm,based on capacity maximization criteria,is developed to generate a bank of USMs.Simulation results are presented to demonstrate the advantages of LDDMA.When the Bit Error Rate（BER） reaches 10^–3,the performance gains are 3dB and 5dB,compared with Time-Division Linear Dispersion Codes（TD-LDC）and BLAST,respectively.     

IMPROVEMENT OF THE PERFORMANCE OF A SUPERCONDUCTING TURBOGENERATOR THROUGH USE OF A CONTROLLABLE REACTIVE POWER COMPENSATOR

ABSTRACT

This paper presents the dynamic performance of a superconducting turbo-generator which employes a thyristor controlled static reactive power compensator at its terminals. The application of the fast acting compensator external to the machine, in a power system, is foreseen as one possible alternative to alleviate the excitation problems which arise on account of the extremely large field time constant of a superconducting generator. This application is compatible with the fast development in the rating of static compensators and imminent use of superconducting machines in the future.

The paper dwells on the transient aspects of performance to evaluate the feasibility of use of an external controller for voltage and also incorporating stabilizing signals. Simulation of the load rejection and transient stability dynamic performance of the superconducting alternator with and without thyristor controlled static compensator brings out its superiority over the field forcing techniques usually used with the conventional generators.     

INVESTIGATION ON SELF-PROPAGATING HIGH-TEMPERATURE SYNTHESIS OF TiAl INTERMETALLIC COMPOUND

The self-propagating high-temperature syn-thesis method was used to synthesize the TiAl intermetalliccompound,and two kinds of synthesis modes were studied inthis paper.The results show that the thermal explosion modeis suitable for the synthesis of TiAI,the pre-heating tempera-ture has a great influence on the synthesis.Microstructurestudy show that the density of the sample fabricated by thermal explosion mode is higher than that fabricated by propa-gating mode.     

Stability and 2-D Simulation Studies of Avalanche Breakdown in 4H-SiC DMOSFETs With JTE

In this paper, the stability of n-channel 4H-silicon carbide (SiC) DMOSFETs with junction termination extension (JTE) was assessed by measuring the breakdown voltage (BV) of these devices before and after bias stress at a high temperature. The BV slumped after the DMOSFET was bias stressed at 1200 V for 2 h at 175degC, and the slumped BV dynamically recovered to the prestress value during the poststress period. Computer simulation suggests that the BV slump and its recovery are dominated by the positive charge trapping/detrapping phenomena at the SiC/fleld oxide interface in the JTE structure, rather than the trapping/detrapping at the SiC/gate oxide interface in the cell structure. A positive interface charge of approximately one-third of the sheet dopant concentration of the JTE region, lowers BV by 150 V, which is the typical measured BV slump of the DMOSFETs of this paper.     

The impact of data aggregation on the performance of wireless sensor networks

With the increasing need for different energy saving mechanisms in Wireless Sensor Networks (WSNs), data aggregation techniques for reducing the number of data transmissions by eliminating redundant information have been studied as a significant research problem. These studies have shown that data aggregation in WSNs may produce various trade‐offs among some network related performance metrics such as energy, latency, accuracy, fault‐tolerance and security. In this paper, we investigate the impact of data aggregation on these networking metrics by surveying the existing data aggregation protocols in WSNs. Our aim is twofold: First, providing a comprehensive summary and comparison of the existing data aggregation techniques with respect to different networking metrics. Second, pointing out both the possible future research issues and the need for collaboration between data management and networking research communities working on data aggregation in WSNs. Copyright © 2006 John Wiley & Sons, Ltd.