高性能罗兰-C接收天线设计

为了提高罗兰-C磁天线的接收能力,设计了一种顺接串联多层线圈的磁天线。理论推导了顺接串联多层线圈磁天线的信噪比和灵敏度,最终设计的磁天线大小为150 mm×150 mm。远场测试接收到了较高信噪比的罗兰-C信号,在相同信号调理电路条件下,与单层单组线圈的磁天线相比,顺接串联多层线圈的磁天线接收到3.47 V的电压信号,且信噪比高达30.87 dB,灵敏度和信噪比分别提高了82.42%和63.20%。顺接串联多层线圈磁天线提高了罗兰-C磁天线的灵敏度和信噪比,对罗兰-C系统在定位方面的应用具有重要意义。     

基于HSI颜色空间的蔗糖结晶图像分割方法

针对煮糖过程蔗糖结晶图像的特点,采用颜色空间转换的方法,将图像从RGB颜色空间转换到HSI颜色空间,利用HSI颜色空间各分量相对独立性以及结晶颗粒和糖浆溶液的色调差异通过改进的大津法对H分量进行阈值分割,再通过数学形态学,中值滤波,孔洞填充,去除噪声颗粒,去除图像边界的非完整颗粒等方法进行后续处理,最终将结晶颗粒从复杂的图像信息中分割出来。实验证明该方法分割效果好,切实可行。     

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.     

钙钛矿氧化物La0.3Ca0.7MnO3的磁性质

采用固相反应法制备了样品La0.3Ca0.7MnO3. 通过测量样品的M-T曲线、 M-H曲线和ESR曲线, 研究了La0.3Ca0.7MnO3的磁性质. 结果表明 在262 K时形成电荷有序相(CO相). 当T＞262 K时, 表现为顺磁;当T＜190 K时, 表现为长程反铁磁(在AFM本底中存在少量FM成分);从262～190 K(TCO), 随温度降低在电荷有序态下从顺磁向反铁磁转变.     

优化连铸中间包控流装置的水模实验

对鞍钢第二炼钢厂板坯连铸中间包进行了控流装置优化的水模实验,发现结构合理的挡墙和湍流控制器能够明显改善中间包内的流体流动特性,使钢包长水口注流区上方的液面更加平稳,并且减轻钢包注流对耐火材料的冲刷与侵蚀.     

Large Magnetic Entropy Effect in La2／3Ca1／3MnO3

The magnetocaloric effect in the colossal magnetoresistance material La2/3Ca1/3MnO3 was studied. From the measurements of temperature dependence of magnetization in various magnetic fields, the large magnetic entropy change associated with the ferromagnetic-paramagnetie transition was discovered. This result suggests that perovskite manganites are suitable candidates as working substance in magnetie refrigeration technology.     

一种基于带宽的文件分块动态下载模型

讨论在并行下载期间服务器的输出带宽和客户机的输入带宽对并行下载效率的影响,以及一个客户机实施并行下载时能同时使用的服务器数量.提出一种文件分块动态并行下载模型,并在网格结点上进行模拟实验.实验结果表明,在对较大目标文件进行下载时,所提模型的并行下载性能优于一般的静态和动态并行下载模型.     

粒子系统在导弹飞行尾焰图形仿真中的应用

采用粒子系统原理,基于OpenGL平台实现了导弹飞行尾焰的实时图形仿真.文章根据粒子系统原理对导弹飞行尾焰进行了建模,并基于OpenGL平台实现了这种自然景物.计算机仿真结果表明,效果逼真且生成速度快,适合在实时的图形仿真中应用.     

对崇明岛引淡(水)工程的建议

崇明岛地势平坦,河网密集,根据总体规划、岛域水系特点、河网水系布局,经多年的整治和完善,已在岛内构成了“1环、5湖、29竖、27闸”、“南引北排”、“西水东调”的引排水格局,这些虽是建设生态岛的优势,但距离实现引淡（水）工程还任重而道远,因在崇明岛,虽家家户户都喝上了自来水,但由于水厂的取水口均在内河中,     

水泥熟料冷却机全面改善性维修方法初探

本文作者将多年从事水泥熟料冷却机全面改善性维修实践中,遇到的冷却机“通用问题”进行了分类。对各类问题进行了根本原因分析,并提出了相应的解决方案。