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41.
The recent fabrication of optical traps using super-continuum light impresses the need for a theory of inter-particle interactions under such conditions. Development of the theory provides a basis for calculation of the observations expected under experimental conditions. An expression for the inter-particle potential energy induced by continuum states of light is first derived using quantum electrodynamics. This energy expression is cast as a function of the spectral irradiance of the light, and the electric susceptibility of the interacting particles. Specific results are derived for light with a Lorentzian spectrum. It is shown that by filtering part of the spectrum, it is possible to exert control over the length of linear particle chains organized along the Poynting vector. The results exhibit scope for the optical fabrication of moldable structures using broadband light. 相似文献
42.
城域WDM环网及其应用 总被引:1,自引:0,他引:1
文章阐述了城域WDM环网的节点结构、保护方式、波长转换器、子速率复用和光网络管理等,给出了WDM环网在城域应用时应考虑的一些因素,并分析了运营商所关心的系统成本问题。 相似文献
43.
针对无线通信中高误码率、高突发误帧、频谱资源紧张等特点,对多拒绝自动请求重传(MR-ARQ)协议相比于传统ARQ协议在提高系统吞吐量、降低系统平均传输时延和时延抖动等方面的优势性能进行了理论分析。在此基础上,针对不同业务传输时对误码率、传输时延和时延抖动的不同要求,研究了基于MR-ARQ协议的宽带无线接入系统(BWA)中多业务混合传输的服务质量保证(QoS)机制,提出了多速率重传策略、基于业务区分的多队列机制以及上行集中带宽分配等3种系统性能优化方案。最后对系统在采用上面3种方案前后的性能进行了仿真和比较分析,验证了方案的可行性和良好效果。 相似文献
44.
For shared access to a broadband communication network using the asynchronous transfer mode (ATM) a passive optical network (PON) has previously been proposed. A novel algorithm to evaluate the time division multiple access (TDMA) protocol which controls the traffic from the various subscribers towards the shared access equipment (upstream direction) is proposed. It uses counters to estimate the moment of a data packet arrival at the subscriber side. By this ‘look-ahead’ technique no extra upstream channels are needed to initiate the polling by the subscriber. The algorithm guarantees fair access for all subscribers and minimizes the necessary overhead. Both the maximum access delay and overhead may be readily calculated, and the obtained results were supported by numerical simulation. Applicability in the standard broadband network environment has been proved by hardware design simulation. 相似文献
45.
Jean-Pierre Coudreuse 《International Journal of Communication Systems》1988,1(4):213-221
The definition of broadband ISDN recently became a major topic of research and predevelopments. Fast packet technologies are widely recognized as the basis for BISDN. Even if international consensus has appeared far more quickly than could have been expected a few years ago, a lot of issues remain open. This paper is a contribution to discussions on some important topics relating to the definition of asynchronous transfer mode. 相似文献
46.
宽带光纤接入网及其发展展望 总被引:2,自引:0,他引:2
文章指出各种宽带光纤接入网都有其最佳使用场合和时机,宽带点到点有源光纤系统最适合企事业用户;宽带点到点有源以太网光纤系统适合在低密度用户分散地区应用;宽带点到多点无源光纤系统最适合新建或改建的密集用户区应用.文章认为中国宽带光纤接入网的发展将可能跨越ATM无源光网络(APON)、宽带无源光网络(BPON)和以太网无源光网络(EPON)阶段,从宽带点到点以太网光纤系统和千兆比特以太网无源光网络(GEPON)开始,较快地过渡到千兆比特无源光网络(GPON). 相似文献
47.
Takao Fukui 《General Relativity and Gravitation》2003,35(1):121-127
An accelerating flat universe with a variable cosmological term is obtained in the Robertson-Walker metric. The variable cosmological term is defined by the correction terms of the metric tensor field. Simple solutions of the scale factor and the cosmological term are shown. In this model of the universe, the magnitude-redshift relation is analytically studied to see if the model reproduces the tendency of the present observational data. The equation of state parameter is touched. 相似文献
48.
Novel Broadband Reflectarray Antenna with Windmill-Shaped Elements for Millimeter-Wave Application 总被引:1,自引:0,他引:1
Hua Li Bing-Zhong Wang Ping Du 《International Journal of Infrared and Millimeter Waves》2007,28(5):339-344
A novel broadband millimeter-wave reflectarray antenna composed of windmill-shaped elements of variable lengths is proposed.
Compared to the conventional single-layer reflectarray elements, the windmill-shaped elements can realize much larger phase
variation range (over 600°), leading to broader bandwidth. Using this technique, a 15°-beam-steering reflectarray operating
at 30 GHz is designed. The computed results demonstrate the agreement of the main beam steering with the design requirement,
and a 1-dB gain bandwidth close to 20% is obtained. The validity of the obtained results is verified by comparing the ones
generated by Ansoft High Frequency Structure Simulator (HFSS) with those produced by Ansoft Designer. The antenna is useful
for millimeter-wave applications.
This work was supported by the National Natural Science Foundation of China (No. 90505001), the High-Tech Research and Development
Program of China (No. 2006AA01Z275), and the Creative Research Group Program of UESTC. 相似文献
49.
在分析传统源极电感负反馈输入匹配结构缺陷的基础上,利用一个小值LC网络代替大感值的栅极电感,同时去掉源极负反馈电感。基于这种改进型输入匹配结构,设计了一种适用于无线接收机用的宽带CMOS低噪声放大器。结果表明,该LNA在工作频带内可达到15 dB的增益,2.75~3.65 dB的噪声系数,-10 dBm的1 dB压缩点,以及良好的稳定性。虽然输入匹配由于去除源极负反馈电感受到一定影响,但有利于降低噪声系数,并减小实际制作的芯片面积。 相似文献
50.
High Altitude Platform Station (HAPS): A Review of New Infrastructure Development for Future Wireless Communications 总被引:2,自引:1,他引:2
This paper looks into the relatively new field of high altitude platform stations. HAPS is seen as a ‘middle ground’ between
the terrestrial and satellite cases, and aims to exploit of the advantages of both types of system. Since HAPS is such a new
field, this paper focuses on the technology behind a HAPS communications system, how this has developed, and compares it to
the terrestrial and satellite equivalents. One important area that is being investigated is the applications for which HAPS
should be used. This is a critical issue if a significant business case is to be made for HAPS. Worldwide HAPS projects and
research issues are also highlighted. Finally, the review concludes with the remarks on the future of HAPS for wireless communications
systems. 相似文献