NICALON SiC/Al 预制丝热膨胀特性研究

本文研究了NICALON SiC束丝纤维增强铝预制丝在15～400℃温度区间内的热膨胀特性。研究表明预制丝两次热循环后得到的膨胀曲线不一致,该曲线在15～400℃范围的平均热膨胀系数分别为3.2×10~(-6)℃~(-1)、4.1×10~(-6)℃~(-1)。本文对预制丝的热膨胀行为进行了理论分析和探讨,计算值和实验值较为符合。     

贫铀武器及其对人体健康的危害

贫铀基础知识铀自1896年发现铀的放射性后,铀作为核工业的基本原料,广泛应用于核动力(如发电、火箭和潜艇推进)、核武器(如原子弹、氢弹)、辐射能源(如宇宙飞船、人造卫星)等多个领域。铀在地壳中的平均含量为4×10~(-6)(相当1卡车泥土中有1大汤勺铀),在海水中含量为3.3×10~(-9),总量达45亿吨。人们每天都会通过空气、水和食物摄入一定量的铀,平均来说,每天通过食物和水摄     

一台200keV中子发生器

本文介绍一台200KeV中子发生器的调试结果:用200KeV,1.5mA氘束轰击氚钛靶,由(d,T)反应产生中子产额可达2×10~(11)n/s;有效直径为20mm质量好的新靶,在160Kev,0.8mA下,中子产额5×10~(10)n/s维持4小时。该发生器采用高频离子源,用普通高压电瓷绝缘环装配加连管,高压电源采用四级倍压回路、离子源和高压电源的供电频率50Hz,靶室用水冷却。     

622机的乘除法和溢出处理

在实时控制系统中,乘除法指令用的较多。DJS—130机无专门的乘除法指令,用子程序做乘、除法,每次需时150μS以上,即乘、除法运算速度每秒6700次。虽然加、减法运算速度可达每秒50万次,但平均速度并不高。若乘、除法指令占30％,平均执行一条指令的时间为:150×0.3+2×0.7=46.4μS即,速度只有1/(46.4×10~(-6))≈2万次/秒。 622机增加了专门的乘除法指令,每次乘、除法时间为18μS,平均执行一条指令的时     

一个实用的高速串行数据传输系统

本文根据雷达性能综合自动检测系统的要求,设计了一套实用的串行数据传输系统,其最大传输速率为1.5×10~5bit/s ,此系统可作为一个通用的串行数据传输系统,应用于传输速率≤1.5×10~5bit/s范围内的其它系统。     

装备零讯

美军第20批次U-2S高空侦察机采用新型座舱6月14日,一架第20批次的U-2S“龙女”(DragonLady)高空侦察机飞抵韩国乌山(Osan)空军基地。与早期的第10批次飞机相比,第20批次的U-2主要改进了座舱显示/控制系统。这项改进是该机以提高维护性和可靠性为目的的“侦察航空电子系统现代化计划”(PAMP)的一部分,可提高飞行员的态势感知能力和飞行安全性。改进后的座舱/显示控制系统利用一台新型机载计算机处理比以往多得多的信息,并将它们显示在3台150毫米×200毫米的大型多功能显示器和2台较小的显示器上,所显示的信息包括海拔高度和导航信息、发…     

国防要闻

美国具有精确能力的A-10对地攻击机12月首飞A-10对地攻击机A-10对地攻击机A-10对地攻击机美国《每日防务》2004年10月报道,洛克希德·马丁公司称,首架升级安装了洛·马公司开发的新式精确交战(PE)包的A-10对地攻击飞机将在今年12月飞上蓝天。洛·马A-10PE项目经理RogerIlGrande称,飞行试验计划12月进行。A-10升级内容包括数据链集成、1760标准数据总线兼容性、附加电源、增加一个先进瞄准吊舱和改进后的数字式座舱显示器和系统,通过升级该机将具有投放波音GPS/INS制导的联合直接攻击弹药(JDAM)及洛·马公司的风修正弹药布撒器(WC…     

民兵文摘

一、工资、薪金所得,其个人所得税计算方法如下:个人所得税额=全月应纳税所得额×超额累进税率=(每月收入额-800元)×(5％～45％) 注:全月应纳税所得额规定为每月收入额减去800元。 下面是个人所得税的超额累进税率表: (工资薪金所得适用)     

一个连长的模拟婚礼

环境主席台中央挂有一个大红双喜,上方挂有“×××先生和×××小姐结婚典礼”的横幅,周围装点着各色的气球、彩带和喜字,婚礼会场的四周摆放着桌子和座椅,桌上排放着饮料、点心、水果和炒货。主持人:各位领导、新人家长,各位亲朋好友、各位女士、各位小姐、各位先生、各位战友,中午好!在这春光明媚、大喜大庆的日子里,我们相聚在这里,隆重庆祝×××先生和×××小姐喜结良缘。今天我十分荣幸地接受新郎新娘的重托,为这对新人担任司仪。首先请允许我介绍一下今天的嘉宾。(略)尊敬的领导、战友和各位来宾,你们是友谊和吉祥的使者。你们的光…     

B—M型双联装30mm舰炮

性能数据系统发射率 2×800发/分初速 1400米/秒俯仰范围 -13°～+80°旋回范围无限高低瞄准速度 75°/秒高低瞄准加速度 100°/秒~2方向瞄准速度 120°/秒     

基于铽镝铁换能器的全保偏光纤磁场传感系统

制作了铽镝铁保偏光纤换能器,建立了全保偏马赫—曾德尔光纤干涉仪系统,采用工作点控制方法解调信号,实现了光纤磁场传感。该全保偏光纤干涉系统结构简单、抗干扰,有效解决了偏振不稳定问题。实验检测了系统对磁场幅度变化的响应特性,最小可测交流磁场信号为3×10-10T。     

Reliability of a 2‐dimensional k‐within‐consecutive‐r × s‐out‐of‐m × n:F system

A 2‐dimensional rectangular (cylindrical) k‐within‐consecutive‐r × s‐out‐of‐m × n:F system is the rectangular (cylindrical) m × n‐system if the system fails whenever k components in a r × s‐submatrix fail. This paper proposes a recursive algorithm for the reliability of the 2‐dimensional k‐within‐consecutive‐r × s‐out‐m × n:F system, in the rectangular case and the cylindrical case. This algorithm requires min ( O (mk^r(n?s)), O (nk^s(m?r))), and O (mk^rn) computing time in the rectangular case and the cylindrical case, respectively. The proposed algorithm will be demonstrated and some numerical examples will be shown. © 2001 John Wiley & Sons, Inc. Naval Research Logistics 48: 625–637, 2001.     

航空发动机在超声速引射系统中的应用分析

航空发动机可以对空气增压,并且增加气流温度,理论上存在应用于超声速引射系统的可能。分析了气源对引射器性能的影响以及引气对航空发动机的影响,介绍了3种航空发动机在超声速引射系统中可能的布局方案。针对某领域内的排气参数要求,分别对3种布局方案进行了计算分析。计算结果表明,当上游气体压强为0.044×10⁵ Pa和0.029 3×10⁵ Pa时,通过合理选择发动机的布局以及工作参数,发动机可以直接将上游气体排出或者作为驱动气源应用于超声速引射系统。     

The non-isothermal gravimetric method for study the thermal decomposition kinetic of HNBB and HNS explosives

The hexanitrostilben (HNS) is a thermally stable explosive that can be prepared from hexanitrobibenzyl (HNBB). Therefore, the investigation of thermal stability of HNBB can be important in the yield of preparation of HNS. The decomposition kinetic of HNBB and HNS are studied by non-isothermal gravimetric method. The TG/DTG curves in non-isothermal method are obtained in range of 25°C–400 °C at heating rates of 3 °C/min, 5 °C/min, 8 °C/min, 10 °C/min and 12 °C/min. The data of weight-temperature are used for calculation of activation energy (E_a) of thermal decomposition reactions by methods of Ozawa, Kissinger, Ozawa-Flynn-Wall (OFW) and Kissinger-Akahira-Sunose (KAS) as model-free methods and Strink's equation as model-fitting method. The compensation effect is used for prediction of mechanism and determination of pre-exponential factor (lnA) of the decomposition reaction. A reduction 60 kj/mol for the average of activation energy of thermal decomposition reaction of HNBB is obtained versus HNS. This result shows the lower thermal stability of HNBB in comparison to HNS. The Avrami equation (A_3/2) with function f(α) = 3/2(1-α)[-ln(1-α)]^1/3 indicates the predicted mechanism for thermal decomposition reaction both explosives.     

Optimizing the defensive characteristics of mild steel via the electrodeposition of ZnSi3N4 reinforcing particles

The effect of ZnSi₃N₄ deposition prepared via direct electrolytic co-deposition on mild steel was studied as a result its inherent vulnerability to corrosion in an aggressive environment and failure on the application of load. The experiment was conducted varying the mass concentration of silicon nitride (Si₃N₄) between 7 and 13 g at cell voltage of 0.3 and 0.5 V, at constant temperature of 45 °C. The morphologies of the coated surfaces were characterized using high resolution Nikon Optical Microscope and Scanning Electron Microscope (SEM) revealing that the particles of the ZnSi₃N₄ were homogeneously dispersed. The corrosion behaviour was studied using potentiodynamic polarization technique in 3.65% NaCl solution and the microhardness was examined using Brinell hardness testing technique. The result of the corrosion experiment confirmed an improved corrosion resistance with a reduction in corrosion rate from 9.7425 mm/year to 0.10847 mm/year, maximum coating efficiency of 98.9%, maximum polarization resistance of 1555.3 Ω and a very low current density of 9.33 × 10⁻⁶ A/cm². The negative shift in the E_corr revealed the cathodic protective nature of the coating. The microhardness was also found to have increased from 137.9 HBN for the unmodified steel to a maximum value of 263.3 HBN for the 0.5Zn13Si₃N₄ coated steel representing 90.9% increment in hardness as a result of the matrix grain refining and dispersion-strengthening ability of the incorporated Si₃N₄ particles.     

Rendezvous of three agents on the line

This paper considers a three‐person rendezvous problem on the line which was introduced earlier by the authors. Three agents are placed at three consecutive integer value points on the real line, say 1, 2, and 3. Each agent is randomly faced towards the right or left. Agents are blind and have a maximum speed of 1. Their common aim is to gather at a common location as quickly as possible. The main result is the proof that a strategy given by V. Baston is the unique minimax strategy. Baston's strategy ensures a three way rendezvous in time at most 3.5 for any of the 3!2³ = 48 possible initial configurations corresponding to positions and directions of each agent. A connection is established between the above rendezvous problem and a search problem of L. Thomas in which two parents search separately to find their lost child and then meet again. © 2002 Wiley Periodicals, Inc. Naval Research Logistics 49: 244–255, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/nav.10005     

1.25cm 体效应振荡器研制

文中讨论了一种1.25cm波段的波导型体效应振荡器。其主腔采用可调节的同轴减高波导座结构,使电路与二极管实现良好匹配。文中着重讨论了主腔各部尺寸对振荡器特性的影响。稳频腔采用高Q值的H_(011)模式圆柱腔,并采用线胀系数不同的金属材料进行温度补偿,提高了频率稳定度。利用WT55型体效应管,在23-25GH_2频带内,功率输出大于30mw,频率稳定度为5×10~(-5)。     

A solution for queues with instantaneous jockeying and other customer selection rules

This paper presents a general solution for the M/M/r queue with instantaneous jockeying and r > 1 servers. The solution is obtained in matrices in closed form without recourse to the generating function arguments usually used. The solution requires the inversion of two (Z^r?1) × (2^r?1) matrices. The method proposed is extended to allow different queue selection preferences of arriving customers, balking of arrivals, jockeying preference rules, and queue dependent selection along with jockeying. To illustrate the results, a problem previously published is studied to show how known results are obtained from the proposed general solution.     

Mathematical aspects of the 3 × n job-shop sequencing problem

The paper discusses mathematical properties of the well-known Bellman-Johnson 3 × n sequencing problem. Optimal rules for some special cases are developed. For the case min B_i ≥ maxA_j we find an optimal sequence of the 2 × n problem for machines B and C and move one item to the front of the sequence to minimize (7); when min B_i ≥ max C_j we solve a 2 × n problem for machines A and B and move one item to the end of the optimal sequence so as to minimize (9). There is also given a sufficient optimality condition for a solution obtained by Johnson's approximate method. This explains why this method so often produces an optimal solution.     

二维 DFT 和 DCT 的 Systolic 阵列

超级计算中一个活跃的研究领域是将某些有限和,如离散富里叶变换(DFT)、离散余弦变换(DCT),映射到多处理机阵列上。本文首先通过二维DFT的行列分解算法流程图,给出了计算二维DFT的二种Systolic阵列:一种是由N_1个处理器组成的线性阵列,所花时间步为O(N_1N_2)(设二维DFT为N_1×N_2长的),与行列分解算法在单处理机上顺序执行所花时间相比,加速比为O(N)(设N_1=N_2=N)。这一结果无论是在时间消耗,还是在PE数量上都是目前最优的。另一种是由N_1×N_2个处理器组成的矩形阵列,所需时间为O(N_1+N_2),与行列算法在单处理机上顺序运行所花时间相比,加速比为O(N~2)(这里仍假定N_1=N_2=N)。本文还给出了二维DCT的与二维DFT相似的Systoilc阵列结构。不难将上述阵列推广到多维的情况。