浅谈IEC电线及电缆标准

1引言 电线及电缆制造商在拓展全球市场时,都面临一项高难度的挑战,就是要同时符合不同市场的国家标准要求。即使是同一款的线型,制造商通常也因应不同国家的要求,生产不同的电线型号。这些电线在推向市场之前,必须通过多项测试和认证,而这些测试及认证,有时需要在全球各地的实验室和认证机构内进行。     

Analytical performance of M-ary time-hopping orthogonal PPM UWB systems under multiple access interference

In this paper, we extend the characteristic-function approach to derive an exact symbol error rate expression for the M-ary time-hopping orthogonal pulse position modulation (THPPM) ultra-wideband (UWB) system under the interference from multiple users. Monte Carlo simulations are then used to validate the analytical solutions. The results are found to be valid even when that the chip width is greater than the pulse duration. Moreover, the analytical results are compared to those found by Gaussian approximation and the Gaussian Quadrature Rule method. We further show that compared to a binary system, M-ary systems can produce better error rate performance.     

有机半导体ADN的DFT理论计算研究

采用密度泛函理论( DFT)方法对9,10-二(2-萘基)蒽(ADN)进行了B3LYP/6-31G水平上的分子结构优化、红外光谱、Raman光谱、紫外-可见光谱、分子前线轨道、Mulliken电荷等理论计算.研究结果表明:理论计算结果与实验数据吻合得较好,对IR、THz、UV-Vis吸收光谱和Raman散射光谱中的特征峰进行了归属,发现ADN在0.1～10 THz波谱范围内有5个明显的吸收峰,分别位于1.08、2.52、4.44、5.64及6.60 THz,其中5.64 THz的吸收是最强的,它是由萘环面外弯曲及蒽环面内摇摆振动产生的.ADN在紫外光波段有三个吸收峰,分别对应于386.34、352.98及352.50 nm,其中386.34 nm的紫外吸收峰最强.ADN理论计算能隙值为3.516 eV,比实验值3.2 eV略高.ADN的Mulliken电荷计算表明,所有H原子的Mulliken电荷皆为正电荷,C原子Mulliken电荷与其具体的化学环境相关.     

Metamorphic AlInAs/GaInAs HEMTs on GaAs Substrates by MOCVD

Metamorphic AlInAs/GaInAs high-electron mobility transistors with very good device performance have been grown by metal-organic chemical vapor deposition (MOCVD), with the introduction of an effective multistage buffering scheme. Measured room-temperature Hall mobilities of the 2-DEG were over 8000 cm²/V ldr s with sheet carrier densities larger than 4 times 10¹² cm^-2. Transistors with 1-mum gate length exhibited transconductance up to 626 mS/mm. The unity current gain cutoff frequency f_T and the maximum oscillation frequency f_max were 39.1 and 71 GHz, respectively. These results are very encouraging toward the manufacturing of metamorphic devices on GaAs substrates by MOCVD.     

A Tree-Based Data Collecting Network Structure for Wireless Sensor Networks

In a sensor network with a large number of densely populated sensor nodes, a single target of interest may be detected by multiple sensor nodes simultaneously. Data collected from the sensor nodes are usually highly correlated, and hence energy saving using in-network data fusion becomes possible. A traditional data fusion scheme starts with dividing the network into clusters, followed by electing a sensor node as cluster head in each cluster. A cluster head is responsible for collecting data from all its cluster members, performing data fusion on these data and transmitting the fused data to the base station. Assuming that a sensor node is only capable of handling a single node-to-node transmission at a time and each transmission takes T time-slots, a cluster head with n cluster members will take at least nT time-slots to collect data from all its cluster members. In this paper, a tree-based network structure and its formation algorithms are proposed. Simulation results show that the proposed network structure can greatly reduce the delay in data collection.     

Minimum norm mutual coupling compensation with applications in direction of arrival estimation

This paper introduces a new mutual coupling compensation method based on the minimum norm solution to an underdetermined system of equations. The crucial advantage over previous techniques is that the formulation is valid independent of the type of antenna element and provides good results in situations where signal strengths vary considerably. In using the matrix pencil algorithm to estimate the directions of arrival, the examples show that the proposed method results in significantly lower bias than the traditional open circuit method. The analysis of mutual coupling is also applied in the context of a code division multiple access communication system.     

On-demand learning for a wireless campus

The current Internet and wireless networks are harsh environments for transporting high-bandwidth multimedia data. We examine the technical issues involved, and describe an end-to-end solution to support a Web-based learn-on-demand system that operates in a wireless campus environment.     

Critical thickness of GaAs/InGaAs and AlGaAs/GaAsP strained quantum wells grown by organometallic chemical vapor deposition

In this paper we describe a study of strained quantum wells (QWs) as a means to experimentally observe the critical thickness (h _c) for the formation of interfacial misfit dislocations. Two material systems were investigated: GaAs/In_0.11Ga_0.89As, in which the QW layers are under biaxialcompression, and Al_0.35Ga_0.65As/GaAs_0.82P_0.18, in which the QW layers are under biaxialtension. Samples were grown by atmospheric pressure organometallic chemical vapor deposition, and characterized by low-temperature photoluminescence (PL), x-ray diffraction, optical microscopy, and Hall measurements. For both material systems, the observed onset of dislocation formation agrees well with the force-balance model assuming a double-kink mechanism. However, overall results indicate that the relaxation is inhomogeneous. Annealing at 800–850° C had no significant effect on the PL spectra, signifying that even layers that have exceededh _c and have undergone partial relaxation are thermodynamically stable against further dislocation propagation.     

Calculation of third order intermodulation spectrum

A fast method for calculating the third order intermodulation spectrum by convolution of the input power spectrum using the FFT method is presented. The computation time is reduced to seconds even for large numbers of carriers. The computation time is insensitive to the number of different carrier types (level and bandwidth).<>