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471.
令$BS(G,f)=\sum\limits_{uv\in E(G)}|f(u)-f(v)|$, 其中$f$为$V(G)\rightarrow\{1,2,\cdots,|V(G)|\}$的双射, 并称$BS(G)=\min\limits_{f}BS(G,f)$为图$G$的带宽和. 讨论顶点数为$n$的简单图$G$加上一条边$e\in\overline{E(G)}$后, 带宽和$BS(G+e)$与$BS(G)$的关系, 得其关系式$BS(G)+1\leq BS(G+e)\leq BS(G)+n-1$. 并证明此不等式中等号可取到, 即存在图$G_{1}$和$G_{2}$使得$BS(G_{1}+e)=BS(G_{1})+1$, $BS(G_{2}+e)=BS(G_{2})+n-1$. 相似文献
472.
473.
474.
分别在直流偏置和交流偏置下,对大功率GaN基LED的电学和光学特性进行了研究。结果显示,通过改变靠近p型层的量子垒(也就是最后一个量子垒)中的In组分可以调控有源区中的载流子分布。有源区内积累的电子会引起负电容效应。而通过降低有源区量子垒的势垒高度,可以改善LED中载流子传输特性,并实现载流子复合速率及通信调制带宽20%的提高。这个工作将有助于理解GaN基LED中载流子分布对频率特性的影响,并为设计适用于可见光通信的大功率高速LED奠定基础。 相似文献
475.
Characteristic analysis of the optical delay in frequency response of resonant cavity enhanced (RCE) photodetectors 下载免费PDF全文
With consideration of the modulation frequency of the input
lightwave itself, we present a new model to calculate the quantum
efficiency of RCE p-i-n photodetectors (PD) by superimposition of
multiple reflected lightwaves. For the first time, the optical
delay, another important factor limiting the electrical bandwidth of
RCE p-i-n PD excluding the transit time of the carriers and RCd
response of the photodetector, is analyzed and discussed in detail.
The optical delay dominates the bandwidth of RCE p-i-n PD when its
active layer is thinner than several 10~nm. These three limiting
factors must be considered exactly for design of ultra-high-speed
RCE p-i-n PD. 相似文献
476.
T. Gomti Devi 《Journal of Raman spectroscopy : JRS》2008,39(3):427-432
The isotropic Raman component of the C = O stretching mode of ethyl acetate (EA) was analyzed using various polar and nonpolar solvents. It was found that the bandshape approaches towards Lorentzian at high dilution using the curve‐fitting method. The isotropic Raman band was also analyzed by estimating the correlation coefficient with reference to the Lorentzian lineshape using a simple method of linear‐curve fitting. The effects of dispersion and hydrodynamic forces on bandwidth were studied in details. The vibrational relaxation rate was studied using certain parameters and it was found that the microscopic based parameter can explain the complexities occurring in solute–solvent interactions. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
477.
Jiu-sheng Li 《Optik》2008,119(1):19-22
A novel optical modulator using SiO2 waveguides on a silicon substrate is proposed. The modulator is analyzed and designed with the finite element method. The numerical results have shown that an optimally designed modulator can give a broad bandwidth, good impedance match, and low cost. The proposed modulator can be fabricated easily using Si-based very large-scale integrated technology, and it is very suitable for opto-electronic integrated circuits. 相似文献
478.
介绍了一个利用2种不同编码方法实现数字化视频传输的光纤系统。简述了光纤传输中线路编码、数据串行化的方法和构成,通过选择一种大位宽的串行器/解串行器电路,实现并行数据的复用(串行化)/解复用以及不同的编码功能。论述了这2种数据编码方法的优点和不足,给出了这2种编码方法相对于传统编码的优势以及不同编码方法对系统接收性能的影响,提供了每种编码方法信号连接的示意图及特殊数据的编码表,同时给出了用多层线路板所构成系统的性能以及应用场合。 相似文献
479.
Improvement on the wave absorbing property of a lossy frequency selective surface absorber using a magnetic substrate 下载免费PDF全文
An equivalent-circuit model is used to analyse the improvement of the wave absorbing performance of the lossy frequency selective surface(FSS) absorber by using a magnetic substrate,showing that it is possible to widen the wave absorbing bandwidth.Three pieces of magnetic substrates are prepared.According to the complex permittivity and permeability,the reflectivity of the corresponding absorber is calculated by the finite difference time-domain(FDTD) method,and the bandwidth of the reflectivity below 10 dB is optimized by genetic algorithm.The calculated results indicate that the wave absorbing performance is significantly improved by increasing the complex permeability of the substrate;the reflectivity bandwidth below 10 dB of the single layer FSS absorber can reach 3.6-18 GHz with a thickness of 5 mm,which is wider than that with a dielectric substrate.The density of the FSS absorber is only 0.92 g/cm 3.Additionally,the absorption band can be further widened by inserting a second lossy FSS.Finally,a double layer lossy FSS absorber with a magnetic substrate is fabricated based on the design result.The experimental result is consistent with the design one. 相似文献
480.
In an ATM network, bandwidth is allocated at different levels and in different stages. At the physical level, the ATM topology can be dynamically reconfigured by adding/removing truns between ATM switches. This allocation of bandwidth is made possible by the SONET Synchronous Transfer Mode (STM) infrastructure equipped with Digital Cross Connect Systems (DCSs). We will refer to this allocation asSTM allocation. At the ATM level, we can allocate bandwidth to individual Virtual Circuits (ATM-VC allocation) as well as to Virtual Paths (ATM-VP allocation). For example, in order to implement the Connectionless Network Access layer functions we find it convenient to organize the Virtual Paths in a Connectionless Overlay Network. This introduces another type of bandwidth allocation (CLS allocation). In this paper, we address and formulate the above bandwidth allocation problems, and propose efficient techniques for their solution. We illustrate these techniques with examples based on STM and CLS allocation, respectively.This work was jointly supported by the Brazilian National Science Council (CNPq) and NSF. 相似文献