基于DSP+CPLD的高精度信号发生器

介绍了基于直接数字式频率合成(DDS)原理的全数字信号发生器(DSP),利用DSP芯片快速、高精度的运算优势以及CPLD芯片灵活的编程逻辑、大容量存储功能的特点,采用通用可编程芯片以及数字波形合成技术,形成高稳定、高精度、高动态的数字合成信号.该信号发生器可产生0～25 kHz的正弦波、三角波和方波,输出电压峰峰值为0～5 V,频率步进1 Hz,幅度步进0.001 V.     

基于PCI总线的高速多路数据传输卡设计

介绍了一套基于外部设备互连(PCI)总线的高速多路数据传输卡的设计,采用基于PCI内核与PCI用户逻辑相结合的新型设计方案,在顶层通过仿真来验证PCI接口以及用户逻辑设计正确与否.降低了设计的复杂程度,提高了电路的集成度和系统的性能,并根据PCI卡对外部设备驱动能力较弱的特点,在传输卡中加入了长线驱动功能,采用低电压差分信号(LVDS)技术,既降低了系统功耗,又实现长距离的计算机双向通信.     

硫酸盐浆厂污水处理工程及单元技术特点

本文简略介绍云南某硫酸盐浆厂污水处理工程采用的国内不多见的污水单元技术，并对其先进性和实用性效果进行评价和探讨。     

位相连续变化型毫米波衍射天线的性能分析

报道了一种新型毫米波天线—衍射天线的测量结果．经分析讨论说明，这种天线具有良好的电性能．     

Study and design of step-index channel waveguide bends withlarge-angle and low-loss characteristics

By using micro-prisms, improved three-dimensional (3-D) bends of the embedded and buried waveguides of step-index profile are proposed. A simple phase compensation rule for the optimal design of the micro-prism is also presented. Through the simulation of 3-D semivectorial finite-difference beam propagation method, the transmission characteristics of the improved bends are shown to have been enhanced dramatically as compared with those of the conventional ones. Even for a bend angle of as large as 10°, the normalized transmitted power can still be greater than 95%. These results of 3-D bends are then compared with those of the two-dimensional (2-D) ones which are simplified from 3-D structures by the effective index method, and physical explanation of the discrepancy between the 3-D and 2-D results is introduced. The influences of waveguide structures and prism parameters on the transmission characteristics are discussed in detail. Some criteria for the design of large-angle low-loss 3-D improved bends are also accessed     

一种产生式系统的并行推理模型

1.引言 在人工智能领域中,产生式系统是一种比较有效的知识表示方法,并得到了广泛应用。目前许多较为成功的专家系统都是用产生式系统实现的~[1]。随着应用领域的不断扩士其知识座的抓橄称渐增     

Performance model of interactive video-on-demand systems

An interactive video-on-demand (VoD) system allows users to access video services, such as movies, electronic encyclopedia, interactive games, and educational videos from video servers on a broadband network. This paper develops a performance evaluation tool for the system design. In particular, a user activity model is developed to describe the usage of system resources, i.e., network bandwidth and video server usage, by a user as it interacts with the service. In addition, we allow batching of user requests, and the effect of such batching is captured in a batching model. Our proposed queueing model integrates both the user activity and the batching model. This model can be used to determine the requirements of network bandwidth and video server and, hence, the trade-off in communication and storage costs for different system resource configurations     

A BiCMOS dynamic carry lookahead adder circuit for VLSIimplementation of high-speed arithmetic unit

A BiCMOS dynamic carry lookahead circuit that is free from race problems is presented. A 16 b full-adder test circuit, which has been designed based on a 2 μm BiCMOS technology, shows a more than five times improvement in speed as compared to the CMOS Manchester carry lookahead (MCLA) circuit. The speed advantage of the BiCMOS dynamic carry lookahead circuit is even greater in a 32- or 64-b adder     

STRL33, A novel chemokine receptor-like protein, functions as a fusion cofactor for both macrophage-tropic and T cell line-tropic HIV-1

The chemokine receptors CXCR4, CCR2B, CCR3, and CCR5 have recently been shown to serve along with CD4 as coreceptors for HIV-1. The tropisms of HIV-1 strains for subgroups of CD4(+) cells can be explained, at least partly, by the selective use of G protein-coupled receptors (GPCRs). We have identified a novel human gene, STRL33, located on chromosome 3 that encodes a GPCR with sequence similarity to chemokine receptors and to chemokine receptor-like orphan receptors. STRL33 is expressed in lymphoid tissues and activated T cells, and is induced in activated peripheral blood lymphocytes. When transfected into nonhuman NIH 3T3 cells expressing human CD4, the STRL33 cDNA rendered these cells competent to fuse with cells expressing HIV-1 envelope glycoproteins (Envs). Of greatest interest, STRL33, in contrast with CXCR4 or CCR5, was able to function as a cofactor for fusion mediated by Envs from both T cell line-tropic and macrophage-tropic HIV-1 strains. STRL33-transfected Jurkat cell lines also supported enhanced productive infection with HIV-1 compared with control Jurkat cells. Despite the sequence similarities between STRL33 and chemokine receptors, STRL33-transfected cell lines did not respond to any in a panel of chemokines. Based on the pattern of tissue expression of the STRL33 mRNA, and given the ability of STRL33 to function with Envs of differing tropisms, STRL33 may play a role in the establishment and/or progression of HIV-1 infection.