Rigidity and flexibility of virtual polytopes

All 3-dimensional convex polytopes are known to be rigid. Still their Minkowski differences (virtual polytopes) can be flexible with any finite freedom degree. We derive some sufficient rigidity conditions for virtual polytopes and present some examples of flexible ones. For example, Bricard's first and second flexible octahedra can be supplied by the structure of a virtual polytope.     

PC104在工程中的应用

根据在宝钢铁水动态监测系统中使用PC104的经验,介绍了选用PC104的优点,同时,介绍了在工程实际中使用PC104的一些具体用法,对从事嵌入式应用开发者使用PC104具有一定的参考价值。     

DSP与PC间的数据通讯

DSP由于具有高性能和灵活可编程的优点而得到广泛的应用。文章给出了用PC机作主机 ,DSP作从机来实现DSP与PC机间有效、可靠通讯的实现方法。同时通过一个数据传输程序的例子来详细阐述如何使用VB6.0专业版作为开发工具 ,并利用DSP中的SCI(SerialCommunicationInter face)模块来实现DSP与微机间的数据传递方法。     

Fluid and diffusion limits for transient sojourn times of processor sharing queues with time varying rates

We provide an approximate analysis of the transient sojourn time for a processor sharing queue with time varying arrival and service rates, where the load can vary over time, including periods of overload. Using the same asymptotic technique as uniform acceleration as demonstrated in [12] and [13], we obtain fluid and diffusion limits for the sojourn time of the M_t/M_t/1 processor-sharing queue. Our analysis is enabled by the introduction of a “virtual customer” which differs from the notion of a “tagged customer” in that the former has no effect on the processing time of the other customers in the system. Our analysis generalizes to non-exponential service and interarrival times, when the fluid and diffusion limits for the queueing process are known.     

"一步建站"Web管理系统的探讨和实现

“一步建站”Web管理系统是指通过Web界面一次性提交用户资料，系统自动完成为上网建站用户开通虚拟服务器、进行域名解析、创建FTP维护账号及指定租用硬盘空间大小等一系列操作。同时，该系统还可对已开通的用户站点进行管理。     

On hyperbolic virtual polytopes and hyperbolic fans

Hyperbolic virtual polytopes arose originally as polytopal versions of counterexamples to the following A.D.Alexandrov’s uniqueness conjecture: Let K ⊂ ℝ³ be a smooth convex body. If for a constant C, at every point of ∂K, we have R ₁ ≤ C ≤ R ₂ then K is a ball. (R ₁ and R ₂ stand for the principal curvature radii of ∂K.) This paper gives a new (in comparison with the previous construction by Y.Martinez-Maure and by G.Panina) series of counterexamples to the conjecture. In particular, a hyperbolic virtual polytope (and therefore, a hyperbolic hérisson) with odd an number of horns is constructed. Moreover, various properties of hyperbolic virtual polytopes and their fans are discussed.     

Java语言及其虚拟机技术探讨

随着Internet的迅猛发展，Internet编程语言Java愈来愈成为计算机行业的焦点。本文在简述了Java的主要特点后，重点对Java最关键的技术──虚拟机进行了深入的探讨。     

气相色谱质谱联用仪与微机的数据传输和处理

报道了一种用于气相色谱质谱联用仪和微机之间实现数据传输和处理的方法。方法可更有效地利用质谱仪采集的数据，解决了工作站处理数据的局限性。经数据格式转换，原始数据可以在微机上实现色谱峰再现，从而为色谱条件的优化和定量数据处理创造了条件。     

A study of PBT/PC blends by modulated DSC and conventional DSC

Two poly(butylene terephthalate)/polycarbonate (PBT/PC) blends with different formulations were analyzed by modulated DSC (MDSC) and conventional DSC to determine differences in crystallization behavior. A significant difference (30°C in cold crystallization temperature) between the two samples was detectable by MDSC while no significant difference was seen by conventional DSC. That indicatesthe total heat flow from MDSC is not always equivalent to the heat flow from conventional DSC as we have assumed or seen before. The reason has not been fully understood, but may be related to unusual nucleation and crystallization induced by modulation. Alternative conventional DSC methods were developed and compared to the MDSC results.Dedicated to Professor Bernhard Wunderlich on the occasion of his 65th birthdayThe authors like to thank Drs. Bernhard Wunderlich and Robert Gallucci for helpful discussion, David Shaker and Mary Parsonage for some DSC experiments. Technical support from TA Instruments is also greatly appreciated.     

Application of the essential work of fracture concept to nanostructured polymer materials

The first part of the paper deals with a critical discussion of the methodical basis of essential work of fracture (EWF) concept with respect to the specimen geometry (especially the notch depth) and application to polymers. In the second part, an in situ testing device, which combines a tensile testing machine with an optical strain-field measuring system, has successfully demonstrated possibility of characterization of fracture behaviour of polystyrene-polybutadiene block copolymers and block copolymer/homopolymer blends as examples of nanostructured polymer materials. It has been shown that knowledge of the time evolution of the strain field close to the crack tips leads to a simple verification of the basic precondition for the applicability of the EWF concept, the precondition “plastic zone coalescence-before-stable crack propagation”.