邻—(4—乙基苯甲酰基)苯甲酸的研究

本文阐述了通过Friedel-Crafts反应合成邻-(4-乙基苯甲酰基)苯甲酸的方法.研究了影响产物质量的因素,提出了适宜的工艺条件.     

Bezier曲线树

本文提出Ｂｅｚｉｅｒ样条曲线树结构用以高效地实现对曲边几何体的各种几何运算。对任意一条Ｂｅｚｉｅｒ样条曲线，用ｄｅＣａｓｔｅｌｊａｕ算法进行分割后，将分割结果用一平衡二叉树来存储。此后，对于该曲线所作的各种几何运算可以一种逼近等级的方式来进行。先以粗糙的逼近来进行计算，必要时增加精密度，从而提高各种运算的效率。     

基于工作站和EUCLID－IS的计算机组装结构CAD系统研究

随着集成电路技术的发展及计算机性能的不断提高，计算机组装结构设计在计算机，总体设计中的地位越来越重要，它直接影响到计算机性能的提高。本文针对一个基于工作站和ＥＵＣＬＩＤ－ＩＳ软件的电子计算机组结构ＣＡＤ系统，从软、硬件平台，系统功能及实现等方面进行了讨论，旨在为电子计算机组装结构设计提供一种强有力的、方便的设计工具，有利于增强国产计算机的市场竞争能力。     

本地七号公共信令网实施的若干问题

本文主要讨论本地七号公共信令网实施的若干问题，如信令转发点的设置，链路设置和路由选择，话路网和信令网的关系，不同制式七号公共信令的互通问题等。     

Evidence for two types of spatial representations: Hemispheric specialization for categorical and coordinate relations.

Analyses of human object recognition abilities led to the hypothesis that 2 kinds of spatial relation representations are used in human vision. Evidence for the distinction between abstract categorical spatial relation representations and specific coordinate spatial relation representations was provided in 4 experiments. These results indicate that Ss make categorical judgments—on/off, left/right, and above/below—faster when stimuli are initially presented to the left cerebral hemisphere, whereas they make evaluations of distance—in relation to 2 mm, 3 mm, or 1 in. (2.54 cm)—faster when stimuli are initially presented to the right cerebral hemisphere. In addition, there was evidence that categorical representations developed with practice. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The zinc-rich corner of the Zn-Fe-Ni-Si quaternary system at 450 °C

Following up on recent studies of the Zn-rich corners of the Zn-Fe-Ni and Zn-Fe-Si ternary systems, a 450 °C isothermal section of the Zn-Fe-Ni-Si quaternary phase diagram with the Zn composition being fixed at 93 at.% was determined experimentally using optical microscopy, scanning electron microscopy (SEM) coupled with energy dispersive x-ray spectroscopy (EDS), and x-ray diffractometry (XRD). FeSi was found to be in equilibrium with almost all phases in the section, including the T, ζ, Ni-δ, NiSi₂, and FeSi₂ phases, as well as the liquid phase (L). Silicon solubilities in the T, ζ, and Ni-δ phases were rather limited. However, the solubilities of Fe and Zn in the NiSi₂ phase, at 4.5 at.% and 7.2 at.%, respectively, were appreciable. The existence of the (L+NiSi₂+Ni-δ) three-phase equilibrium state apparently prevents other Ni-Si compounds from entering equilibrium with the liquid at 450 °C. No true quaternary compound was found in the study.     

飞机液压系统污染及控制

本文全面分析了收音机液压系统污染的危害和主要原因，并在此基础上有针对性地提出了预防措施。     

Measurement of Thermal Diffusivity at Low Temperatures Using an Optical Reflectivity Technique

An experimental arrangement has been developed for measuring the transient temperature responses and the thermal diffusivities of foil materials in the range of 10 to 300K by using the optical reflectivity technique. The cryogenic system with optical windows is designed to provide temperatures from 10 to 300 K. The front surface of a foil specimen is heated by a pulsed Nd:YAG laser. In situ measurement of the reflectivity of a continuous-wave He–Ne laser at the rear surface is conducted on the microsecond time scale. Using the temperature dependence of reflectivity, the transient temperature response is deduced. The thermal diffusivity is obtained by fitting Parker's formulae to the experimental data on temperature rise. Stainless-steel foils are chosen as samples and are studied in the region from 10 to 300 K. The accuracy is examined by comparing the present results with the theoretical temperature responses and thermal diffusivity data from the literature. Good agreement is observed.     

LDPC-based space-time coded OFDM systems over correlated fadingchannels: Performance analysis and receiver design

We consider a space-time coded (STC) orthogonal frequency-division multiplexing (OFDM) system with multiple transmitter and receiver antennas over correlated frequency- and time-selective fading channels. It is shown that the product of the time-selectivity order and the frequency-selectivity order is a key parameter to characterize the outage capacity of the correlated fading channel. It is also observed that STCs with large effective lengths and ideal built-in interleavers are more effective in exploiting the natural diversity in multiple-antenna correlated fading channels. We then propose a low-density parity-check (LDPC)-code-based STC-OFDM system. Compared with the conventional space-time trellis code (STTC), the LDPC-based STC can significantly improve the system performance by exploiting both the spatial diversity and the selective-fading diversity in wireless channels. Compared with the previously proposed turbo-code-based STC scheme, LDPC-based STC exhibits lower receiver complexity and more flexible scalability. We also consider receiver design for LDPC-based STC-OFDM systems in unknown fast fading channels and propose a novel turbo receiver employing a maximum a posteriori expectation-maximization (MAP-EM) demodulator and a soft LDPC decoder, which can significantly reduce the error floor in fast fading channels with a modest computational complexity. With such a turbo receiver, the proposed LDPC-based STC-OFDM system is a promising solution to highly efficient data transmission over selective-fading mobile wireless channels