Electrical Properties of Ca<Subscript>9</Subscript>ZnLi(PO<Subscript>4</Subscript>)<Subscript>7</Subscript> Ceramics Prepared by Reactive Pressureless Sintering

Well-crystallized Ca₉ZnLi(PO₄)₇ ceramics were prepared by reactive pressureless sintering at atmospheric pressure. The single-phase Ca₉ZnLi(PO₄)₇ ceramics were confirmed by x-ray diffraction (XRD). The dielectric and electrical properties were investigated over a wide frequency range (1 Hz to 1 MHz) by complex impedance spectroscopy at different temperatures between 25°C and 600°C. A dielectric anomaly was observed at 440°C, which might be related to the phase transition. The impedance Cole–Cole plot was used to analyze the results of complex impedance measurements, revealing that the electrical properties depend strongly on frequency and temperature. Two relaxation dispersions of the electrical parameters were found and analyzed in terms of bulk and grain-boundary ionic transfer processes. The slope of the alternating-current (AC) conductivity over a wide range of temperatures provides activation energies from 0.48 eV to 1.69 eV. These results suggest that the conduction process is of the mixed type.     

Synthesis and Crystal Structure of 1,6:3,4-Bis(1,2-xylyiene) tetrahydro-imidazo[4,5-d]imidazole-2,5(1H,3H)-dione

The compound 1,6∶3,4-Bis(1,2-xylyiene)tetrahydro-imidazo[4,5-d]imidazole-2,5(1H,3H)-dione(C20H18N4O2, Mr=346.38) has been synthesized for the first time. Complete assignments were achieved by 1H NMR, IR, EI-MS, elemental analysis and single-crystal X-ray diffraction technique. The crystal belongs to monoclinic, space group P2(1)/n with a=10.266 0(16), b=11.298 5(18), c=1.452 20(20) nm, β=97.923(3), V=1.668 4(5) nm3, Z=4, Dc=1.379 g/cm3, μ(MoKα)=0.092 mm-1, F(000)=728, R=0.053 2 and wR=0.112 3 for 3632 observed reflections with I>2σ(I). X-ray analysis reveals dimeric aggregates are formed through hydrogen bond and offset π-π stacking. In addition, the compound assembles to a three-dimensional networking structure by other hydrogen bond.     

海面岛礁背景下舰船红外自动识别技术研究

为了提高岛礁背景下对红外目标的识别能力,提出了基于平均灰度的识别方法.红外探测器在对远距离舰船目标识别时,舰船附近与目标外型轮廓相似的海岛会给识别带来很大困难.通过对海岛和舰船的组成和红外特性的对比分析,以及从实地试验图像中得到的数据发现舰船的灰度平均值要高于海岛的灰度平均值.     

基于NiosⅡ的学习型遥控器设计

以AlteraFPGA系列CycloneEPlCl2Q240C8器件为载体,通过SoPC技术构建嵌入式软核NiosⅡ处理器平台,运用VerilogHDL硬件描述语言设计等精度测量载波频率IP核、红外信号解调IP核、红外编码脉宽测量IP核和红外发送调制逻辑电路,以实现载波的精确测量、红外信号解调、脉宽测量和调制功能,并给出了外围硬件电路和软件设计方案。实验表明,该遥控器解决了单片机因时钟频率低而无法对载波频率进行测量的瓶颈,实现了对任何一款普通遥控器的按键编码学习,真正完成了学习型遥控器的学习功能。     

基于信号和OCC表示的情感模型研究

情感模型的建立可以使计算机具备基本的情感识别和表达能力,在和谐人机交互方面有着广泛的应用.借助于Picard教授关于情感计算的理论,将线性系统理论和数字信号处理方法应用到情感信号与系统建模上,用信号很好地表示了人类的内在情感和情绪,并通过MATLAB仿真实验分析证明了模型的正确性.最后结合情感的高层次认知推理机制,将情感模型应用到情感虚拟人当中,形象地实现了情感对人脸表情变化的控制.     

中国3G市场调研

文章是针对目前中国3G的建设及市场需求进行分析,通过对3G发展的简介到目前中国三大营运商对3G建设的投入状况详细总结。概述了3G建网历次招标的情况及相关受益的设备厂商,并对中国3G带来的PCB行业机遇及挑战进行了分析。     

质量发展规划的探讨

文章从质量工作的现状分析中探求组织的不足和需要改进之处．运用克劳士比的质量成熟度理论开展质量的发展规划。提出了组织在不同质量成熟度的平台上为不同的市场和经济平台提供不同的能力保证。为了支持和配合组织各个阶段的经济目标实现,质量管理工作应在中长期规划中提出相应的成熟度目标,本文为组织制定质量工作发展规划提供了一种思路。     

A channel preemption model for vertical handoff in a WLAN-embedded cellular network

In this paper, a channel preemption model for vertical handoff in a WLAN-embedded cellular network is presented. In a heterogeneous networking environment, since many wireless LANs may be deployed within the coverage of a cellular network, horizontal handoffs among neighboring WLANs and vertical handoffs between a WLAN and the cellular network could occur frequently. Performance in terms of blocking probability of the cellular network can be seriously degraded if the channels are not appropriately allocated. The novelty of this paper is right in that a newly initiated mobile node (MN) outside the WLAN coverage can preempt the channels occupied by an MN inside the WLAN coverage when the cellular channels are completely used up. The channel preempted MN is forced to switch its network access to a WLAN. This proposed channel preemption scheme can effectively reduce the blocking probability while not disrupting any of the existing connections within WLANs. For the purpose of performance evaluation, we build a three-dimension Markov chains to analyze the proposed channel preemption mechanism. We derive the equations of move-in and move-out mobility rates based on the node speed and residence times, respectively. The network performance in terms of the number of active WLAN users, the channel utilization and the channel blocking probability of a cellular network, the preemption probability, and the preempted probability of an MN are calculated. From the analytical results, we observe the performance improvements by varying the node speed and the ratio of WLAN coverage.     

基于单片机AT89C51SND1C的MP3方案设计

提出一种基于单片机AT89C51SNDIC的MP3播放系统的设计方案.单片机集成了专用的解码器,使用K9F1208闪存作为外存储器,放音电路采用CS4330,存储文件通过播放器上的USB接口设备从PC机上直接下载,液晶显示采用LCD 1602.方案设计简单,性价比高,低功耗,易扩展.由于采用的是通用单片机实现的,可以很容易地移植到其他微控制器系统中,有很强的市场竞争能力和实用价值.