Performance of a modified polling strategy for broadband wireless lans in a harsh fading environment

In this paper, we consider a radio-based communication network in which a single, high speed radio channel is shared by some plurality of small portable notebooks. Such a system has the potential to provide LAN-like service within buildings, allowing the portable "notebooks" to access the CPU and data resources of a wired network. In this harsh indoor fading environment, a base-station approach is used. We propose a modified polling scheme for the indoor radio LAN channel. The base station regularly polls each remote, in response to which the remote either generates a "keep alive" packet or a request packet, allowing the base to fetch the requested information from the wired network and scheduling a reply to that remote. The efficiency of such a scheme is studied and the expected turn-around delay as a function of network loading is approximately obtained. A system stability under such a scheme is derived. For a polling cycle of 20 milliseconds and a network containing 10 or 50 users, for example, the maximum link efficiency is 97% and 87%, respectively, assuming that the link speed is 5 Mbps.The Center for Telecommunications Research is an NSF Engineering Research Center. This work was supported under NSF grant #ECD88-1 1111.     

梯形波脉冲筛板萃取柱传质性能

本文以UO_2(NO_3)_2—30％TBP(KO)为实验体系,进行了梯形波脉冲筛板柱传质性能的研究。实验中测量了两组分的两相稳态浓度剖面共13组,以扩散模型为基础,求得了梯形波脉冲柱的“真实”传质单元高度HTU_(ox),分散单元高度HDU及表观传质单元高度HTU_(oxp)。通过对实验结果进行分析,选择出了适于本实验体系的较好的操作条件。     

A New Heuristic Search Technique-Algorithm SA

In this paper, we present a new heuristic searching algorithm by introducing the statistical inference method on the basis of algorithm A (or A*). It is called algorithm SA. In a simplified search space, a uniform m-ary tree, we obtain the following result. Using algorithm SA, a goal node can be found with probability one, and its mean complexity is O(N·ln N) where N is the depth at which the goal is located.     

Synthesis of Single-Crystalline Silicon Nitride Nanobelts Via Catalyst-Assisted Pyrolysis of a Polysilazane

Recently, one-dimensional nanostructures have attracted extensive attention since they are potentially important for both applications and fundamental research. In this paper, we report the synthesis of ultra-long single crystal Si₃N₄ nanobelts via catalyst-assisted pyrolysis of polymeric precursors. The obtained products contain both α- and β-Si₃N₄ nanobelts, which are 50–100 nm in thickness, 400–1000 nm in width, and a few hundreds of micrometers to several millimeters in length. Different from previous techniques for synthesizing one-dimensional structures, the current nanobelts are synthesized through confined crystallization of an amorphous phase. A solid–liquid–gas–solid reaction/crystallization growth mechanism is proposed. The formation of nanobelts instead of nanowires is attributed to the anisotropy growth at an earlier stage.     

LDPE／EVA／CPE并用微孔鞋底料的研制

采用模压法研究了化学交联LPDE/EVA/CPE并用微孔鞋底料的制造方法,着重讨论了LDPE/EVA/CPE并用比,不同种类的橡胶改性剂以及发泡剂、交联剂、填充剂用量对微孔鞋底物理机械性能的影响。实验结果表明,采用国产原料CPE,当LDPE:EVA:CPE=50:30:20时,并配以超细碳酸钙20份和其他助剂,可制得性能较好的微孔鞋底材料。     

我国露天矿应用半连续开采工艺的现状与前景

介绍了半连续开采工艺在我国露天矿山的应用现状和特点,分析了采用该工艺的必要性,展望了半连续开采工艺的发展趋势,为加速发展我国露天矿山半连续开采工艺而提出几项建议。     

谈公共设施中的环境陶艺形态

探讨公共设施环境陶艺形态的类型、表现手法及特点,指出公共设施中的环境陶艺形态设计要强调实用与审美、环境相统一。     

钛酸铝陶瓷及其研究现状

本文简述了钛酸铝陶瓷的制备及性能,论述了钛酸铝陶瓷的稳定性、微裂纹、低热膨胀性,讨论了工艺条件及外加剂对钛酸铝材料性能的影响,最后提出了改善钛酸铝陶瓷性能的技术途径。     

Rainbow holographic aberrations and the bandwidth requirements

Rainbow holographic image resolution, primary aberrations, and bandwidth requirements are presented. The results obtained for the rainbow holographic process are rather general, for which the conventional holographic image resolution, aberrations, and bandwidth requirements, can be derived. The conditions for the elimination of the five primary rainbow holographic aberrations are also given. These conditions may be useful for the application of obtaining a high-quality rainbow hologram image. In terms of bandwidth requirements, we have shown that the bandwidth requirement for a rainbow holographic construction is usually several orders lower than that of a conventional holographic process. Therefore, a lower-resolution recording medium can generally be used for most of the rainbow holographic constructions.