IPv4到IPv6过渡策略研究

本文从IPv4的局限性和IPv6的优势入手,提出了IP协议从IPv4过渡到IPv6将成为历史的必然,重点研究了IPv4到IPv6的过渡策略及策略的选择。     

提高信号到达角估计精度的新方法

现有的基于矢量天线估计信号到达角的方法都没有利用阵列的孔径信息,这样的估计虽然是无模糊的,但精度不高.该文在现有估计方法的基础上进一步利用阵列的孔径信息,通过迭代搜索的方法改善到达角估计的精度,数值模拟结果证明该方法是有效的.     

基于ICGA的星载天线自适应调零算法

有效地抑制干扰,最大程度地保障正常通信,是卫星通信的一项关键技术.采用基于整数编码遗传算法(Integer Coded Genetic Algorithm ICGA )的卫星天线自适应调零算法,利用遗传算法不受初始值选择的局限,全局搜索及整数编码的快速性,可以实时实现天线调零.计算机仿真实验表明了该算法的有效性和鲁棒性.     

新型PTCDA/p-Si光电探测器

研制成功的PTCDA／p—Si新型光电探测器与型号为PHD714的PIN光电二极管的电参数进行了测试对比。结果表明,两者的光谱响应范围均为450～1100nm,峰值波长为930nm,对光的响应速度均小于10^-9s;在1000Lx及1．5V电压作用下,前者的光电流普遍大于100μA,后者光电流小于100μA,前者经高温（120℃）48h及低温（-80℃）12h 2次循环实验后测得其电参数稳定。表明,这种新型有机／无机光电探测器具有更优良的光敏性及可靠性。     

低磁场条件下Mn5(Ge3-xSbx)(x=0、0.1、0.2、3)合金磁热效应研究

用真空高频悬浮炉在高纯氩气保护下制备了Mn5（Ge3-xSbx）（x=0、0.1、0.2、3）合金系列样品,用直接测量方法测定了在永磁体提供的低磁场（H=1.3T）条件下样品的磁热效应曲线（ΔTad-T）,结果表明,用元素Sb替代Mn5Ge3合金中的Ge原子,不能增强合金的磁热效应,但对合金的居里温度有一定影响.     

新一代电信运营支持系统

文章论叙了电信运营中支持系统(新97系统)的产生背景、平台架构及系统的功能。     

基于EMD时频分析方法的性能研究

针对传统的时频分析方法存在的局限性,评述了一种最新的可适用于非平稳、非线性信号的时频分析法-Hilbert-Huang时频分析.研究了经验模态分解(Empirical Mode Decomposition,EMD)与希尔伯特变换(Hilbert Transformation,HT)相结合的提取信号瞬时特征的EMD/HS法,并对其性能进行了分析.仿真实验中通过与传统的时频分析效果的比较,表明该法具有理想的时频聚集性,并且消除了交叉干扰项.     

提高地层承压能力的钻井液堵漏作用机理

应用线弹性岩石力学和岩石断裂力学基本理论,揭示了钻井液堵漏阻止诱导裂缝延伸并提高裂缝重启压力从而提高地层承压能力的作用机理。通过分析承压堵漏后缝内压力分布,建立了封堵诱导裂缝的断裂力学模型,并给出承压堵漏阻止诱导裂缝延伸的必要条件;基于井周围岩裂缝诱导应力场的数学模型,提出了堵漏提高诱导裂缝重启压力的力学实质。理论研究表明,堵漏材料在裂缝入口后一定距离封堵为封堵诱导裂缝的最佳位置形式;裂缝尖端部分流体压力必须低于水平最小主应力,且该压力越低,越有利于裂缝的阻裂;诱导裂缝重启压力的提高依赖于周向诱导应力,堵漏材料必须支撑裂缝以维持周向诱导应力;承压堵漏作用机理包含密封和支撑裂缝两方面,堵漏材料应同时具有封堵性能和机械强度。     

Thermodynamic performances of [mmim]DMP/Methanol absorption refrigeration

In order to study the theoretical cycle characteristic of [mmim]DMP(1-methyl-3-methylimidazolium dimethylphosphate)/methanol absorption refrigeration,the modified UNIFAC group contribution model and the Wilson model are established through correlating the experimental vapor pressure data of [mmim]DMP/methanol at T=280～370K and methanol mole fraction x=0.529～0.965.Thermodynamic performances of absorption refrigeration utilizing [mmim]DMP/methanol,LiBr/H2O and H2O/NH3 are investigated and compared with each other under the same operating conditions.From the results,some conclusions are obtained as follows:1)the circulation ratio of the [mmim]DMP /methanol absorption refrigeration is higher than that of the LiBr/H2O absorption refrigeration,but still can be acceptable and tolerable.2)The COP of the [mmim]DMP/methanol absorption refrigeration is smaller than that of the LiBr/H2O absorption refrigeration,while it is higher than that of the H2O/NH3 absorption refrigeration under most operating conditions.3)The[mmim]DMP/methanol absorption refrigeration are still available with high COP when the heat source temperature is too high to drive LiBr/H2O absorption refrigeration.     

A look-up-table digital predistortion technique for high-voltage power amplifiers in ultrasonic applications

In this paper, we present a digital predistortion technique to improve the linearity and power efficiency of a high-voltage class-AB power amplifier (PA) for ultrasound transmitters. The system is composed of a digital-to-analog converter (DAC), an analog-to-digital converter (ADC), and a field-programmable gate array (FPGA) in which the digital predistortion (DPD) algorithm is implemented. The DPD algorithm updates the error, which is the difference between the ideal signal and the attenuated distorted output signal, in the look-up table (LUT) memory during each cycle of a sinusoidal signal using the least-mean-square (LMS) algorithm. On the next signal cycle, the error data are used to equalize the signal with negative harmonic components to cancel the amplifier's nonlinear response. The algorithm also includes a linear interpolation method applied to the windowed sinusoidal signals for the B-mode and Doppler modes. The measurement test bench uses an arbitrary function generator as the DAC to generate the input signal, an oscilloscope as the ADC to capture the output waveform, and software to implement the DPD algorithm. The measurement results show that the proposed system is able to reduce the second-order harmonic distortion (HD2) by 20 dB and the third-order harmonic distortion (HD3) by 14.5 dB, while at the same time improving the power efficiency by 18%.