The critical pressure and impeding pressure of Al evaporation during induction skull melting processing of TiAl

In this article, two key pressures, the critical pressure P _crit and the impeding pressure P _impe of elemental evaporation, are defined and studied based on the calculation relationship between the evaporation loss rate N _m and the chamber pressure P during melting of titanium-aluminum alloys. When the chamber pressure is below P _crit or above P _impe, N _m tends to the maximum or the minimum value and remains almost unchanged. However, if P _crit<P<P _impe, with the increase of the chamber pressure, N _m declines sharply. A method has been put forward to calculate P _crit and P _impe of Al evaporation in a Ti-XAl (at pct) (X=25 to 50) melt. The calculation result shows that P _crit or P _impe is a second-order function of the molar percentage of Al and the melt temperature.     

100 mm一等量块自动测量仪测量不确定度评定

分析了100mm一等量块自动测量仪的误差来源，确定了测量量块的合成标准不确定度和扩展不确定度。     

科技期刊编辑专业化和学者化是保证期刊学术质量的关键

一般科技期刊刊载的论文内容都具有很强的专业性,这就要求科技期刊编辑必须具有丰富的专业知识和较高的学术水平才能胜任编辑工作.从编辑过程的选题组稿、论文初审、选择审稿专家和编辑加工四个方面对此进行了阐述,指出了提高科技期刊编辑的相关专业知识和学术水平的措施.     

Observation and Analysis of Gypsum Particleboard using SEM

The microstructures of gypsum board and gypsum particleboard were observed by SEM. The effects of retarder and waterproof agent on the shape and the average dimension of the gypsum crystal were discussed. The mechanism was investigated as well. Four typical instances, i e, the gypsum crystal shape, the gypsum combined with particles on the particles surface, the gypsum combined with particles on the wood cross section and the gypsum combined with particles inside the wood cell cavity were selected and observed. Furthermore, the agglomeration and cementation mechanism between gypsum and particle were studied.     

西北江三角洲来水来沙的非线性分形特征

根据西、北江干流高要、石角及西北江三角洲网河区顶点马口、三水四个水文站的流量和含沙量资料 ,应用非线性分形原理的R S方法 ,计算西北江干流及西北江网河区顶点四个水文站的流量、含沙量的赫斯特数H和分形维数D ;探讨西、北江干流来水来沙的分形特征及西北江三角洲的分水分沙规律。结果表明 ,流量的分维数略大于含沙量的分维数 ,三水站流量及含沙量的分维数与其上游的石角站流量、含沙量的分维数相差较大 ,与思贤的分水分沙造成西北江的水沙交换有关     

国外大型调水工程渠道运行控制综述

与常规的以经验为主的运行方式相比，考虑了水动力学影响、以多渠池串联的整个渠道系统为研究对象的渠道运行控制在增加调水工程的安全性、降低运行成本、提高输水效率等方面能取得更佳的效果。国外关于调水工程渠道控制的研究起步较早，基于非线性偏微分圣维南方程组发展了多种离散化、线性化等简化方法，建立了相应的控制模型，并从不同角度确定了其控制方法以及控制算法。参考已有的研究思路和方法，总结国外渠道运行控制的成果，对我国南水北调工程的运行控制有着重要的借鉴意义。     

国内外钻探用金刚石复合片性能的研究

主要介绍国内外金刚石复合片性能及采用四高复合片钻探硬岩的初试,为快速钻探提供一个新的途径.     

土酸溶液中溴化十六烷基吡啶对锌的缓蚀作用及吸附热力学研究

用失重法研究了土酸溶液中溴化十六烷基吡啶对锌的缓蚀作用，发现溴化十六烷基吡啶在锌表面上的吸附是产生缓蚀作用的重要原因，且吸附规律服从Langmuir吸附等温式。用Sekine方法处理实验数据，从而获得了吸附过程△H^0、△S^0和△G^0等一系列重要热力学参数。     

Bandwidth‐guaranteed QoS routing of multiple parallel paths in CDMA/TDMA ad hoc wireless networks

This paper investigates the issues of QoS routing in CDMA/TDMA ad hoc networks. Since the available bandwidth is very limited in ad hoc networks, a QoS request between two nodes will be blocked if there does not exist a path that can meet the QoS requirements, even though there is enough free bandwidth in the whole system. In this paper, we propose a new scheme of using multiple paths between two nodes as the route for a QoS call. The aggregate bandwidth of the multiple paths can meet the bandwidth requirement of the call and the delays of these paths are within the required bound of the call. We also propose three strategies by which to choose a set of paths as the route, namely, shortest path first (SPF), largest bandwidth first (LBF), and largest hop‐bandwidth first (LHBF). Extensive simulations have been conducted to evaluate the performance of the three strategies in comparison with a traditional single path routing algorithm. The simulation results show that the proposed multiple paths routing scheme significantly reduces the system blocking rates in various network environments, especially when the network load is heavy. Copyright © 2005 John Wiley & Sons, Ltd.     

MHD simulation of high-current subsonic vacuum arc under different distributed axial magnetic fields

Based on two-temperature magnetic hydrodynamic (MHD) model, the influence of saddle-shaped distributed axial magnetic field (AMF, linearly increases along radial position) and bell-shaped distributed AMF (linearly decreases along radial position) on plasma loss and heat flux density to anode in subsonic high-current vacuum arc (HCVA) is simulated and analyzed. According to the simulation results, the saddle-shaped AMF can more effectively inhibit plasma loss from arc column than that of bell-shaped AMF. Comparisons between simulation results and experimental results further verify the correctness of model and simulation.