A medium-access control protocol for a cellular packet CDMAcarrying multirate traffic

We propose and evaluate a medium-access control (MAC) protocol for synchronous cellular packet direct-sequence code-division multiple-access (DS/CDMA). The protocol is designed for handling a variety of multimedia traffic types in an integrated wireless-access network (IWAN). For instance, the protocol is suited for carrying multiple traffic types of different priorities. An analytical model for the equilibrium state has been developed for the proposed protocol. A comparative evaluation of the protocol is done for three different radio frequency bandwidths currently under consideration for personal communication services (PCS), i.e., 1.25 MHz, 5 MHz, and 10 MHz. Our results demonstrate that the proposed protocol is both robust and flexible for the intended IWAN applications. It offers a significant multiplexing gain as the bandwidth increases     

Internet网的服务方式与入网方式一览

目前，世界上最大的计算机网络Ｉｎｔｅｒｎｅｔ网，已成为通达１５０多个国家的国际互联网络。作为引导中国计算机用户进入Ｉｎｔｅｒｎｅｔ的中国公用计算机互联网ＣＨＩＮＡＮＥＴ也正迅速发展。本文就Ｉｎｔｅｒｎｅｔ网的服务方式和入网方式进行了综述。     

Tri-Gate Bulk MOSFET Design for CMOS Scaling to the End of the Roadmap

A tri-gate bulk MOSFET design utilizing a low-aspect-ratio channel is proposed to provide an evolutionary pathway for CMOS scaling to the end of the roadmap. 3-D device simulations indicate that this design offers the advantages of a multi-gate FET (reduced variability in performance and improved scalability) together with the advantages of a conventional planar MOSFET (low substrate cost and capability for dynamic threshold-voltage control).     

Reversible nonlinear conduction in high‐density polyethylene/acetylene carbon black composites at various ambient temperatures

The reversible nonlinear conduction (RNC) in of high‐density polyethylene/acetylene carbon black composites with different degrees of crosslinking was studied above room temperature and below the melting point of high‐density polyethylene (HDPE). The experimental current density‐electric field strength curves can be overlapped onto a master curve, suggesting that the microscopic mechanisms for the appearance of RNC exist regardless of the ambient temperature and the crosslinking degree of the HDPE matrix. The relationship between the crossover current density and the linear conductivity can be explained in the framework of the dynamic random‐resistor‐network model. According to these results, two electron‐tunneling models are suggested to interpret the microscopic conduction behavior. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1212–1217, 2004     

OFDM-MIMO系统及其频率同步分析

多媒体业务对无线通信的带宽与品质提出了更高的要求，OFDM和MIMO由于满足了这一需求被越来越多的无线通信标准采用所为底层的调制和传输技术。频率同步问题是OFDM—MIMO物理层设计中正确解调的前提和基础，本文介绍了OFDM—MIMO的原理、特点和频率同步问题的研究现状。     

Matlab在“计算机辅助电路分析”中的应用

"计算机辅助电路分析"课程,是通过计算机仿真实验来训练学生分析和解决电路问题的能力.实践证明,将Matlab软件,特别是其中的Simulink仿真模块作为电路分析工具,引入到计算机辅助电路分析课程教学中,收到了良好的教学效果.本文以二阶电路阶跃响应问题的求解为例,介绍了辅以Matlab的五种求解方法,并对这五种方法的特点进行了比较,说明了Matlab在电路分析方面的优越性.     

激光微焊接质量的模糊识别技术研究

讨论了激光微焊点焊接质量的模糊识别的概念，数学模型及其应用方法，并介绍了系统的硬件组成。     

一种简易可靠的射频激光调制器

采用ＰＩＮ电调衰减器、ＴＬ４９４等元件组成了射频（ＲＦ）大功率ＣＯ２激光调制器，调制频率、占空比和调制度单独可调。给出了电路的工作原理和测试结果。     

Formation of β‐iPP in isotactic polypropylene/ethylene–propylene rubber blends: Effects of preparation method,composition, and thermal condition

The effects of preparation method, composition, and thermal condition on formation of β‐iPP in isotactic polypropylene/ethylene–propylene rubber (iPP/EPR) blends were studied using modulated differential scanning calorimeter (MDSC), wide angle X‐ray diffraction (WAXD), and phase contrast microscopy (PCM). It was found that the α‐iPP and β‐iPP can simultaneity form in the melt‐blended samples, whereas only α‐iPP exists in the solution‐blended samples. The results show that the formation of β‐iPP in the melt‐blended samples is related to the crystallization temperature and the β‐iPP generally diminishes and finally vanishes when the crystallization temperature moves far from 125 °C. The phenomena that the lower critical temperature of β‐iPP in iPP/EPR obviously increases to 114 °C and the upper critical temperature decreases to 134 °C indicate the narrowing of temperature interval, facilitating the formation of β‐iPP in iPP/EPR. Furthermore, it was found that the amount of β‐iPP in melt‐blended iPP/EPR samples is dependent on the composition and the maximum amount of β‐iPP formed when the composition of iPP/EPR blends is 85:15 in weight. The results through examining the effect of annealing for iPP/EPR samples at melt state indicate that this annealing may eliminate the susceptibility to β‐crystallization of iPP. However, only α‐iPP can be observed in solution‐blended samples subjected to annealing for different time. The PCM images demonstrate that an obvious phase‐separation happens in both melt‐blended and solution‐blended iPP/EPR samples, implying that compared with the disperse degree of EPR in iPP, the preparation method plays a dominant role in formation of β‐iPP. It is suggested that the origin of formation of β‐iPP results from the thermomechanical history of the EPR component in iPP/EPR. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1704–1712, 2007     

聚苯硫醚／石墨基双极板复合材料性能的研究

以聚苯硫醚树脂和人造石墨为原料一次模压成型制备双极板复合材料.研究了模压成型过程中加压时机、冷却方式及人造石墨原料对复合材料电导率和弯曲强度的影响.结果表明,制备聚苯硫醚/石墨基双极板材料宜选用石墨化程度较高且结构密实的石墨粉料;采用保温后加压及空气中冷却方式制备的复合材料的综合性能较优.