分布系统中多米诺效应的分析与消除

分布系统中发生故障后,错误信息在进程间的传播,以及由此引起的系统恢复过程中的多米诺效应是分布系统容错恢复技术所面临的最重要与最困难的问题.目前各种研究工作偏重于具体的系统动态恢复技术.本文的研究重点在于首次揭示多米诺效应本身固有的数量特征及其与分布系统技术参数间的联系,给出多米诺效应动态消除技术,引入系统额外开销的下限,并针对动态技术的缺点,探讨多米诺效应的静态消除技术,为解决困难开辟新途径.     

Some aspects of deformation behavior

The deformation behavior of several single- and two-phase coarse microstructures has been examined using microhardness measurements. It has been found that the strength response of a coarse phase in isolation is distinctly different from its response when it exists in a two-phase system. The second phase alters the mechanical state of the first one andvice versa even in the plastically undeformed condition. This phenomenon is explained in terms of the existence of an appreciable amount of residual stresses in two-phase coarse microstructures. These stresses primarily arise due to the difference in thermal expansion coefficients of the phases. The in- fluence of elastic stress field on microhardness response is shown with a new type of experiment to support the proposed explanation. The present results question the existing expressions for deformation modeling of multiphase materials because of the uncertainties in the estimation of the average strength of the phases in a two-phase system.     

模糊预测控制及其应用研究*

本文提出一种新的模糊预测控制算法。它将预测控制与模糊控制相结合,应用于一类复杂的工艺过程的终点控制,获得了优良的控制效果,如抗干扰性和模型失配等。本算法在对电弧炉炼钢的氧化过程控制的仿真研究中取得十分满意的效果,它对培养训练操作人员十分有效。     

利用低轨卫星星座的移动通信系统

本文介绍两种利用低轨地理卫星星座进行移动通信的系统。一种是英法联合研究提出的利用24颗低轨卫星组成的移动通信；另一种是美国研究提出的利用192颗低轨卫星组成的移动通信系统。最后将低轨卫星移动通信系统与同步卫星移动通信系统及高轨卫星移动通信系统进行了比较。     

反应烧结法制备MgAlON的合成机理及烧结行为的研究

通过对以Al2 O3、MgO和AlN为起始原料 ,在氮气气氛中反应烧结合成MgAlON材料合成机理的研究发现 :在 12 0 0℃以前 ,MgO与Al2 O3反应生成镁铝尖晶石 ,此后 ,随着温度的升高 ,Al2O3不断向所形成的尖晶石中固溶 ;在 130 0℃以前 ,AlN基本上不参与反应 ,而在更高的温度下 ,AlN开始向尖晶石中固溶形成MgAlON ,约在 15 5 0℃时形成单一的MgAlON相。用热膨胀仪检测了试样的线变化率随温度和时间的变化 ,用最小二乘法回归分析了试样线变化率的实验数据 ,并根据烧结理论对MgAlON材料烧结初期的动力学进行了探讨。结果表明 ,MgAlON材料烧结初期的烧结机理以体积扩散为主     

Pressurized fluidized-bed hydro retort ing of raw and beneficiated Eastern oil shales

Bench-scale tests were conducted with raw and beneficiated shales in an advanced multi-purpose research reactor. Raw Alabama shale and raw and beneficiated Indiana shales were retorted at 515 °C using hydrogen pressures of 4 and 7 MPa. Shale feed rates were 15 to 34 kg h⁻¹. High oil yields and carbon conversions were achieved in all tests. Oil yield from Alabama shale hydroretorted at 7 MPa was 200% of Fischer assay. Raw and beneficiated Indiana shales hydroretorted at 7 MPa produced oil yields of 170 and 195% of Fischer assay respectively. Total carbon conversions were >70% for all tests conducted at 7 MPa.     

Response of simulated propellant and explosives to projectile impact—II. Fragmentation

This paper is the second of a series concerned with the penetration and perforation phenomena in two types of propellant and explosive simulant, named Propergol, due to the impact at normal incidence of both blunt and conically-tipped steel strikers. The collision results in fragmentation, plug formation and generation of a cloud of debris that includes particles of measurable dimensions traveling with significant velocities. Both the fragment size and area as well as the ejecta mass are determined experimentally as a function of Propergol specimen thickness and impact velocity or energy. The cumulative number of fragments as a function of size for the Propergol is uniformly found to be a bi-linear semi-logarithmic relationship with the bifurcation occurring at the mean crystal radius. Individual crystals and the crater generated are examined by means of a scanning electron microscope.

A phenomenological model of the fragmentation process is constructed, based on an assumed spherical shape of the fragments and the bi-linear fragment distribution, using energy methods. This is combined with a perforation analysis that considers the process to be sequentially composed of initial indentation, fragmentation, and sliding and deflection of the Propergol disks. An evaluation of this model providing fragment volumes as a function of impact velocity is compared with experimental results and found to be in good agreement.     

Jitter in ATM networks and its impact on peak rate enforcement

Cells arriving to an ATM network experience random delays due to queueing in upstream multiplexing stages, notably in customer premises. This is the phenomenon of jitter and the aim of the present paper is to study its influence on peak rate enforcement. We first introduce some general characterizations of jitter and then, describe two models of jittered flows based on simple queueing systems. We discuss the objectives of peak rate enforcement and study the impact of jitter on the dimensioning of jumping window and leaky bucket mechanisms. A useful synthetic characterization of jitter appears to be a remote quantile of the cell delay distribution expressed in units of the initial inter-cell interval.