New insight into phase change memories

The switching mechanism in phase change memories was described on the basis of minimum switching unit: the commuton. A commuton is a minimum cluster of atoms that supports a reversible phase change from high to low electrical conduction state and back under the influence of an external signal. The switching process in a phase change chalcogenide film was modeled using two dimensional cellular automata approach. A system of 50 × 50 cells, each cell containing a commuton, was simulated. In the particular case of Ge₂Sb₂Te₅ (investigated here) this system corresponds to a 30 × 30 nm area. The formation of the percolation path as a function of phase change induced in commutons explains the switching phenomenon. The influence of the percent of defects in the material on the percolation threshold has been studied.     

The effects of temperature and frequency on the magnetization switching mode in circular MI sensors

This paper presents results computed using a meshless method in a point collocation formulation to investigate the effects of temperature and frequency on the magnetization switching mode in the circular amorphous magneto-impedance sensor (element). Specifically, the solutions characterizing the MI effect are solved from a set of coupled nonlinear equations consisting of the Maxwell’s equations, the Landau-Lifshitz-Gilbert equation, and the thermal diffusion equation. This coupled nonlinear space-time model predicts the formation and propagation of dynamic domain walls in switching and it is shown how they contribute to experimentally observed temperature and frequency effects. Computed results (that agree well with reported experimental data) suggest radial domain walls may play a larger role in the MI effect than originally believed even for the realistic conditions considered here at 1 MHz or more.     

Optimal seat allocation for two-flight problems with a flexible demand segment

In this paper, we study a two-flight model where there are two flights between two cities in a day (e.g., one departs at 9:00 am and another at 11:00 am) and booking requests in each fare class arrive according to a random process. There are three types of booking requests: the first and second types are respectively for the first and the second flight only; whereas the third type is flexible and willing to take either flight. Upon receiving a booking request, the airline has to decide whether to accept it, and in case a third type is accepted, which flight to accommodate it. This paper uncovers the structure of optimal booking policies through four monotone switching curves. We also present an extension of the basic model to multiple-flight case. Finally, a numerical example is used to illustrate the derivation and the dynamics of the optimal booking policies.     

开关电源新技术动态

本文介绍了开关电源的发展情况以及国外的最新成就，考察了各种新型开关电源，它们的主要优点及其存在的问题；综述了开关电源计算机辅助设计技术的研究和发展；最后简要介绍了国外目前正在研究的一些课题。     

Impact of Modulation Index on Homodyne Crosstalk in Optically Switched Networks

The impact of imperfect modulation depth on crosstalk induced penalty in optical switched systems is theoretically and experimentally investigated. A nonlinear relationship with a clear "knee" is observed, indicating an optimum modulation index of 8 dB.     

南京ATM宽带多媒体网络的建设

ＡＴＭ技术在经济ＩＴＵ－Ｔ和ＡＴＭ论坛多年的研究与论证后,已开始在多个领域得到广泛运用。本文介绍了南京市ＡＴＭ的网络的建设情况,包括基本组成、网络业务及网络的测试等。     

Switching stochastic models and applications in retrial queues

Some special classes of Switching Processes such as Recurrent Processes of a Semi-Markov type and Processes with Semi-Markov Switches are introduced. Limit theorems of Averaging Principle and Diffusion Approximation types are given. Applications to the asymptotic analysis of overloading state-dependent Markov and semi-Markov queueing modelsM _SM,Q /M _SM,Q /1/∞ and retrial queueing systemsM/G/1/w.r in transient conditions are studied. The paper was supported by INTAS Project 96-0828     

用于半导体器件瞬态特性研究的大幅度矩形纳秒脉冲发生器

本文提出了一个用于半导体激光器和其他高速器件瞬态特性研究的大幅度矩形纳秒脉冲发生器的设计.为了产生一对极性相反的高速同步脉冲,在设计中采用了我国发明的新功能器件──双向负阻晶体管(BNRT).为了获得高速大电流主脉冲输出,采用了同时触发的双雪崩晶体管串联组合电路.所研制的发生器的主脉冲输出,其电压幅度高达200V(在50Ω负载)、峰值电流为4A、上升时间约2ns、宽度5-100ns、晃动小于50ps.而且输出脉冲波形呈良好的矩形,其过冲和顶部不平坦度均小于±3％.     

一种带频率抖动功能的振荡器电路的设计

介绍了一种带频率抖动功能的振荡器,该振荡器结构简单、频率抖动效果明显,通过周期性改变振荡器内部比较器的比较阈值达到频率抖动的效果,可有效降低芯片电磁干扰.使用0.5 μm BCD工艺对电路进行仿真,在25℃,TT工艺角下,振荡器中心频率为66.87 kHz,频率抖动差值为±5.02 kHz,频率抖动重复频率约为1.046 kHz.电路适用于对电磁兼容性要求较高的开关电源芯片,具有很强的工程实用性.