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961.
C_(60),M@C_(60)电子传输特性研究 总被引:3,自引:2,他引:1
采用扩展的Hückel方法与格林函数方法,分析了双Au电极作用下,C60,M@C60(M=Si,Ge)富勒烯分子的电子结构与导电性,并对三种富勒烯分子的电子结构与电子输运特性进行了对比。研究结果表明,三种富勒烯分子与A u电极“接触”后,其最高占据分子轨道与最低未占据分子轨道间的能隙减小,它们与A u电极之间的结合既有共价键的成分,又有离子键的成分;三种富勒烯分子的电子输运性能依次具有Ge@C60>Si@C60>C60的顺序。 相似文献
962.
963.
分组网络上的视频流传输面临的挑战及对策 总被引:2,自引:0,他引:2
视频已成为通信、娱乐中十分重要的媒介,视频流传输在因特网上得到了快速发展及广泛应用。分组网络所呈现出的异构性、时变性等本质属性,使得基于分组网络的视频流传输面临许多挑战。首先,当分组从一个节点传输到另一个节点时,由于其所经历的实际网络路径不同,路由器及通信信道的性能和表示这些分组连接的参数(如带宽、分组丢失概率及分组延迟)也会彼此不同。甚至会出现几个数量级大的差异。此外,上述参数还会随着时间发生变化。本从端主机的角度出发,分析在分组网络视频流传输过程中面临的挑战,并提出相应对策。 相似文献
964.
在丽水市建立有线数字电视服务平台后,需要将有线数字电视传输到丽水市各县(市)、乡镇乃至农户家里,实现有线数字电视的全市覆盖。从丽水市的实际出发,提出利用SDH传输网和1550nm射频副载波调制干线光传输相结合的方法覆盖全市8个县(市)的具体方案。 相似文献
965.
966.
L. A. Ferrari 《Il Nuovo Cimento D》1993,15(7):957-967
Summary Several experimental artifacts which can cause traunsport in strongly scattering media to appear to depart from classically
expected behavior are discussed. In particular, scale-dependent transmission data in dielectric media consisting of either
alumina or polystyrene spheres that reveal two different absorption lengths are shown to be most likely due to the presence
of unscattered or coherent energy. A restricted geometry decreases the attenuation coefficient. This analysis requires the
application of the diffusion equation to thin samples, less than four mean free paths in thickness, which in turn requires
boundary conditions on the diffuse flux to be rederived. It is shown that in these thin samples, the coherentenergy contribution
to the measured transport is probably more important than the thin-sample corrections to diffusive transport. 相似文献
967.
By applying switch-signal theory, the interaction between MOS transmission switch-ing transistor and current signal in current-mode CMOS circuits is analyzed, and the theory oftransmission current-switches which is suitable to current-mode CMOS circuits is proposed. Thecircuits, such as ternary full-adder etc., designed by using this theory have simpler circuit struc-tures and correct logic functions. It is confirmed that this theory is efficient in guiding the logicdesign of current-mode CMOS circuits at switch level. 相似文献
968.
HUANG He~ CHEN Fushen~ JIANG Yi~ 《中国电子科技》2003,1(1)
A method for online dispersion monitoring by adding a single in-band subcarrier tone isintroduced.According to the theoretical analysis,the dispersion monitor and measurement range aredetermined by the specific frequency of the subcarrier tone.By using simulation tools,figures aboutrelationship between power of subcarrier tone and transmission distance in ideal condition are shown. 相似文献
969.
In an in-home digital network it may be expected that several data streams (audio, video) run simultaneously over a shared
communication device, e.g., a bus. The burstiness of a data stream can be reduced by buffering data at the sending and receiving
side, thereby allowing a lower bus share allocation for the stream. In this paper we present an algorithm that determines
how much of the bus capacity and buffer space should be allocated to each stream, in order to have a feasible transmission
schedule for each stream. Furthermore, the algorithm determines a transmission schedule for each stream, indicating how much
data is transmitted over time. We show how this multiple-stream problem can be solved by repeatedly solving single-stream
problems. We present efficient algorithms to solve these single-stream problems. Furthermore, we present some experimental
results.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
970.
We derive a new joint power and rate control rule with which we can minimize the mean transmission delay in CDMA networks for a given mean transmission power. We show that it is optimal to respectively control the power inverse‐linearly and the rate linearly to the square root of channel gain while maintaining the signal‐to‐interference ratio at a constant. We also show that the proposed joint power/rate control rule achieves excellent performance results in terms of the probability of the instantaneous delay being within a target delay against one‐dimensional control schemes. 相似文献