Thermionic arc breakdown in small discharge gaps: model andapplications

A model for thermionically induced breakdown is developed which predicts the voltage levels experienced in low-voltage discharges. Initially, electron emission across an active discharge minigap must be established. Prior to breakdown, emitted electrons populate the cathode space-charge region and the remaining gap is unionized. Breakdown criteria and a means for estimating the reduced breakdown voltage in the bulk gas are derived in terms of conventional Townsend ionization mechanisms, wherein multistep or cumulative ionization must be active. Since the cathode space-charge region is replete with emitted electrons, positive ions traversing it release to the bulk gas considerably more electrons than would be available with the conventional Townsend γ mechanism at the cathode surface. This equivalently higher γ significantly shifts the Paschen curve toward lower minima. One practical thermionic assisting device is a tungsten light-bulb-grade filament, which shunts the primary discharge electrodes and, within the filament's minigaps, breakdown occurs. Thermionic arc breakdown has been implemented in the starting of arc devices for lamps and in thermionic power converters; an application to ionization chambers in electrostatic thrusters is also discussed     

Explicit Ziv-Zakai lower bound for bearing estimation

The extended Ziv-Zakai bound for vector parameters is used to develop a lower bound on the mean square error in estimating the 2-D bearing of a narrowband planewave signal using planar arrays of arbitrary geometry. The bound has a simple closed-form expression that is a function of the signal wavelength, the signal-to-noise ratio (SNR), the number of data snapshots, the number of sensors in the array, and the array configuration. Analysis of the bound suggests that there are several regions of operation, and expressions for the thresholds separating the regions are provided. In the asymptotic region where the number of snapshots and/or SNR are large, estimation errors are small, and the bound approaches the inverse Fisher information. This is the same as the asymptotic performance predicted by the local Cramer-Rao bound for each value of bearing. In the a priori performance region where the number of snapshots or SNR is small, estimation errors are distributed throughout the a priori parameter space and the bound approaches the a priori covariance. In the transition region, both small and large errors occur, and the bound varies smoothly between the two extremes. Simulations of the maximum likelihood estimator (MLE) demonstrate that the bound closely predicts the performance of the MLE in all regions     

Thermal and Optical Properties of Yb3+- and Nd3+-Doped Phosphate Glasses Determined by Thermal Lens Technique

In this work, we study the thermal and optical properties of ion-doped phosphates glasses using the thermal lens (TL) technique. Three samples were characterized: Nd³⁺-doped Q-98; Nd³⁺-doped Q-100; and Yb³⁺-doped QX. We report multiwavelength TL measurements for a more accuracy determination of the fluorescence quantum efficiency and temperature coefficient of the optical path length change (ds/dT). In Nd-doped glasses, it was carried out using four discrete excitation wavelengths (between 514 and 872 nm) chosen to match with the ion absorption lines. In Yb-doped glass, the spectrum of heat generated along the Yb³⁺ transition (² F _5/2rarr² F _7/2) was obtained. In addition, parameters as thermal diffusivity and conductivity, thermal loading, etc were achieved. The advantages to obtain fluorescence quantum efficiency using the TL technique, mainly in Yb³⁺ doped materials, which are normally overestimated due to radiation trapping effect, are presented. The accuracy knowledge of these parameters is very important for design of high-power solid-state lasers, since these properties are directly related to the heat generation.     

Two-dimensional profiles of fumonisin B1 production by Fusarium moniliforme and Fusarium proliferatum in relation to environmental factors and potential for modelling toxin formation in maize grain

This study has examined in detail the effect of temperature (7-37 degrees C) and water availability (water activity, a(w), 0.89-0.97) on fumonisin B1 (FB1) production by an isolate of Fusarium moniliforme and F. proliferatum on irradiated maize grain after incubation for 28 days. The optimum conditions for F. moniliforme and F. proliferatum were 30 degrees C at 0.97 a(w) and 15 degrees C at 0.97 a(w), respectively. The maximum concentrations were 2861 mg kg(-1) and 17,628 mg kg(-1) dry wt. maize grain, respectively. At marginal a(w)/temperature conditions for growth (e.g. 0.89-0.91 a(w)) no FB1 was detected (<0.1 mg kg(-1)). A high variability was found between replicates for F. moniliforme, but not for F. proliferatum. These data were used to construct two-dimensional diagrams of all the a(w) x temperature conditions favourable for FB1 production for the first time. The data were also subjected to a polynomical regression, which demonstrated that there was a very good fit for the 15-30 degrees C range of temperature and at 0.97 a(w). However, at marginal environmental conditions this was not possible. This suggests that it may be possible to predict within a limited environmental range the potential for significant FB1 production.     

Frequency Sensitivity and Electromechanical Propagation Simulation Study in Large Power Systems

A global view of power system's frequency behavior opens up a new window for analyzing system's dynamics. With the aid of global positioning system, measurements from different locations would have synchronous time; therefore a system-wide observation and analysis would be possible. As part of the US-wide power frequency monitoring network project this paper focus on simulation study results of power frequency dynamics of the Eastern U.S. system. The study assesses the frequency measurement accuracy needed to observe frequency dynamics from events such as remote generation drops. Electromechanical-wave propagation phenomena during system disturbances have been observed. The speeds of electromechanical-wave propagation in different areas of the U.S. systems were estimated and their characteristics were discussed.     

KeyStone内存架构

随着全球大量的资料强烈冲击无线和有线网络,营运商面临着严峻的挑战,需要不断推出能满足当前与未来需求的网络。因此,通信基础建设设备制造商致力于降低每bit成本和功耗的同时,也不断寻求能够满足当前及未来需求的核心技术。TI最新推出的新型KeyStone多核心SoC架构即能满足这些挑战。     

The Effectiveness of Test in Controlling Quality Costs: A Conformability Analysis Based Approach

Test and inspection are an increasingly costly element of electronic system design and manufacture and so it is critical that the cost effectiveness of test and inspection are well understood. This paper presents techniques which may be used to assess test capability and hence the implied test quality costs of PCB level electronic circuits. The techniques presented are based on the electronic Conformability Analysis (eCA) approach which combines process capability indices and Failure Modes and Effects Analysis with a cost mapping procedure. It introduces a new measure of test capability based on the widely used process capability measure C _pk. This analysis allows the quality costs associated with design and manufacture induced faults to be estimated and the effectiveness of test strategies in reducing these costs to be determined. It allows the trade-off between quality costs and the component, manufacturing process and test costs to be explored. The technique has been applied to analogue & mixed signal, safety critical circuits from automotive systems.     

Tolerance of the diapausing stages of four species of Lepidoptera to methyl bromide

The diapausing stages exposed to methyl bromide were larvae of Ephestia elutella (Hübner) and Plodia interpunctella (Hübner), pupae of Pieris brassicae (L.) and eggs of Bombyx mori (L.). Diapausing larvae of Ephestia elutella were highly tolerant, a few surviving to the adult stage after exposure to concentration-time (CT) products of up to 150 mg hr/l at 25°C and 260 mg hr/l at 15°C. Diapausing larvae of Plodia interpunctella were tolerant at low temperatures but quite susceptible at 25°C. In both species, larvae in diapause were four to six times more tolerant than other larvae at 15°C or below, and strains recently collected from the field were more tolerant than laboratory reared stocks.In E. elutella, differences in the method of induction, maintenance or termination of diapause did not affect tolerance to fumigation. P. interpunctella larvae reared at high population density were more susceptible than those reared at low density. Among strains of these species, a correlation was observed between the duration of larval diapause and tolerance to methyl bromide. Adults emerging after fumigation of diapausing larvae were of lowered fertility but rarely sterile. The CT products required for the complete control of moths in diapause were higher than those currently recommended for the disinfestation of stored products.Diapausing pupae of an outdoor species Pieris brassicae required the very high CT product of 403 mg hr/l for complete control at 25°C and were at least six times more tolerant than non-diapausing pupae. Diapausing eggs of Bombyx mori required 179 mg hr/l for complete control, while non-diapausing eggs were all killed by 125 mg hr/l.     

阿尔卡特呼叫中心解决方案

阿尔卡特呼叫中心解决方案基于局域网,采用ＣＳＴＡ作为主导通信协议,其Ａ４４００ＣＣｘ产品系列包括呼叫中心分配器Ａ４４００ ＣＣＤ、监管系统Ａ４４００ ＣＣＳ１管理器Ａ４４００ＣＣＭ、座席应用组件Ａ４４００ ＣＣＡ、万维网服务器Ａ４４００ ＣＣＷ以及语音应答、语音记录和其它配套设备。其中阿尔卡特４４００综合业务交换平台的基本结构采用阿尔卡特晶体结构技术;而公司的专利技术－－矩阵化分配方式则运用于呼叫     

Technical challenges to a decentralized phone system

Changes that followed in the wake of the divestiture of AT&T are examined. One of these is the growth of new services, particularly ISDN and Switching System No.7 (SS7) services. Another is that setting standards has become a public and global, rather than strictly AT&T-determined, process. Waiting for standards is slowing innovations in the networks, because major equipment vendors to not want to take risks in developing new features, functions, and capabilities before standards are decided on. Service gains and lags in the new environment are discussed