Training sequence design and channel estimation of OFDM-CDMA broadband wireless access networks with diversity techniques

In this paper, an OFDM-CDMA system employing various diversity schemes is considered for a possible candidate of broadband wireless access networks and broadcasting applications. With an emphasis on a preamble design for multi-channel separation, we address a channel estimation based on the time-domain windowing and its imperfectness in OFDM-based multiple-antenna transmission systems. By properly designing each preamble for multiple antennas to be orthogonal in the time domain, the channel estimation can be applied to the HIPERLAN/2 and IEEE 802.11a standards in the case of more than two transmit antennas. Also, the effect of diversity techniques on the performance of OFDM-CDMA based broadband wireless access networks is investigated and the maximum achievable diversity gain for a two-path Rayleigh fading environment is evaluated. Simulation results show that the OFDM-CDMA system applying a space-time-frequency diversity with a full-rate full diversity code can give the diversity of D=4 and D=8 for both multi-user cases of maximum user and half user capacities, respectively.     

非接触型光外差轮廓仪

本文介绍一种纳米级非接触型高精度光外差轮廓仪,它是基于普通光路的光外差干涉仪。工件表面被两束有微小频差的激光束所照射,其中一束经聚焦后用作测量光探针来扫描工件表面,另一束则用作参考光束。两束光经表面反射后产生干涉。测量信号和参考信号的相位差与表面的微不平值成正比。仪器的横向分辨率为2μm,高度分辨率为1 nm,它不需要对试样作大范围的调整,且可用试样自身作参考面。信号经光电转换后由微型计算机进行处理,它能快速完成测量、计算、显示及打印出各种参数和曲线。     

支持专业知识获取的中间件的研究

 分析了如何利用中间件技术支持专业知识获取的问题．提出了基于XML，SOAP，UDDI和WSDL的web服务技术的专业知识获取的中间件应用模式，它可以有效解决消息传送、服务功能的抽象描述以及服务在网络上的发布与发现等问题。以固定瓦推力滑动轴承的性能参数计算Web服务为实例，指出web服务是分布式设计知识获取和知识资源集成的有效途径．     

高档工作面顶板管理的几点做法

介绍了9号、10号、11号煤层开采中顶板管理的具体做法，对特殊时期的初采初放和末采回收也做了阐述，并对特殊地质条件下的顶板管理提出了可行的方法。     

丰满流域可能最大暴雨与可能最大洪水分析研究

依据丰满漉域的水文气象资料,计算丰满流域可能最大暴雨,推求白丰区间的可能最大洪水并进行成果合理性分析.     

Formation and surface modification of self-assembled films with acrylated hyperbranched poly(ester-amine) as the outmost layer

An acrylated hyperbranched poly(ester-amine) (HPEA) synthesized from piperazine and trimethylolpropanetriacrylate at a molar ratio of 1:1.42 was used as the polycation to form self-assembled films by layer-by-layer dipping with poly(sodium-p-styrenesulfonate) as the polyanion. The surface morphology and hydrophilicity of the films with HPEA as the outmost layer were controlled by adjusting the solution pH of HPEA. Due to the existence of many acrylate groups, the films with HPEA as the outmost layer were further reacted with a series of reagents, including piperazine, piperidine, laurylamine and p-phenylenediamine. The surface reactions of the films depended on both the nature of the reagents and the morphology of the initial surface. In the presence of the strong basic amines, piperazine and piperidine, the films dissolved extensively into the solution. In the case of laurylamine, a modified film with an opaque appearance was obtained due to the crystallization of long alkyl chains. With the weak basic amine p-phenylenediamine as the reactant, the film was effectively modified without any change in the surface morphology.     

基于传感器信息的机器人精密装配作业分析

介绍了一个应用力传感器组成的智能机器人精密装配作业的宏／微操作系统，它能够完成一般凸形销孔零件沿任意方向的精密装配作业。     

Multistage amplifier topologies with nested Gm-Ccompensation

This paper presents a multistage amplifier for low-voltage applications (<2 V). The amplifier consists of simple (noncascode) low gain stages and is stabilized using a nested transconductance-capacitance compensation (NGCC) scheme. The resulting topology is similar to the well known nested Miller compensation (NMC) multistage amplifier, except that the proposed topology contains extra G _m feedforward stages which are used to enhance the amplifier performance. The NGCC simplifies the transfer function of the proposed multistage amplifier which, in turn, simplifies its stability conditions. A comparison between the NGCC and NMC shows that the NGCC has wider bandwidth and is easier to stabilize. A four-stage NGCC amplifier has been fabricated using a 2-μm CMOS process and is tested using a ±1.0 V power supply. A dc gain of 100 dB has been measured. A gain bandwidth product of 1 MHz with 58° of phase margin and power of 1.4 mW can be achieved. The op amp occupies an active area of 0.22 mm². Step response shows that the op amp is stable     

Boundary Constrained Swept Surfaces for Modelling and Animation

Due to their simplicity and intuitiveness, swept surfaces are widely used in many surface modelling applications. In this paper, we present a versatile swept surface technique called the boundary constrained swept surfaces. The most distinct feature is its ability to satisfy boundary constraints, including the shape and tangent conditions at the boundaries of a swept surface. This permits significantly varying surfaces to be both modelled and smoothly assembled, leading to the construction of complex objects. The representation, similar to an ordinary swept surface, is analytical in nature and thus it is light in storage cost and numerically very stable to compute. We also introduce a number of useful shape manipulation tools, such as sculpting forces, to deform a surface both locally and globally. In addition to being a complementary method to the mainstream surface modelling and deformation techniques, we have found it very effective in automatically rebuilding existing complex models. Model reconstruction is arguably one of the most laborious and expensive tasks in modelling complex animated characters. We demonstrate how our technique can be used to automate this process.