一种基于分布式交叉认证的证书验证代理的设计

阐述了一种用于减轻客户端负担的证书验证代理服务器的设计,描述了该代理服务器的总体框架.该设计在支持分布式交叉认证的混合信任模型的基础上,提出了一种优化的路径构建方法,给出了详细算法和主要数据结构,并对路径验证过程进行了描述.该代理服务器的应用将使得客户端与繁琐复杂的证书验证处理相分离,构建出真正的瘦客户端,提高客户端应用程序效率.     

基于对称旋转不变性的非圆相干分布源直接定位算法

针对现有相干分布源直接定位方法中存在的依赖分布模型、计算复杂等问题,该文提出一种基于非圆信号特征的对称旋转不变直接定位算法。该方法首先根据分布源参数化假设建立基于数据域信息的直接位置估计模型,并利用非圆信号特征扩展接收信号的协方差矩阵。然后针对中心对称阵列,证明了相干分布源的确定性角信号分布函数矢量具有对称特性,基于这一特征建立了扩展方向矢量的旋转不变关系;构造了融合多个观测站信息的目标函数,直接估计目标位置,避免了对分布模型的依赖,且降低了待估计参数维度。仿真结果表明,与现有相干分布源定位算法相比,所提算法提高了分布源位置估计精度和效率,避免了对分布模型的依赖,更具实用价值。

     

分布式信源数据域直接位置估计方法

针对目前信号数据域直接位置估计方法对分布式信号源进行直接定位存在精度下降问题,该文提出分布式信源数据域直接位置估计方法。首先构建分布式信源直接位置估计模型,然后分别基于最大似然准则和特征结构分解思想给出分布式信源高精度直接位置估计的两种方法分布源最大似然估计方法和广义子空间方法。最后通过多维搜索完成对于分布式信源的直接位置估计。仿真分析表明,该文算法对分布式信源进行直接位置估计的精度较传统直接位置估计算法明显提升,能够在较低信噪比下逼近克拉美罗界;分布源最大似然估计方法在低信噪比下定位精度优于广义子空间方法,而广义子空间方法复杂度更低。     

一种基于维度加权盲K近邻算法的数字预失真技术

传统的数字预失真(DPD)模型通常在所有的输入信号功率上采用单一多项式模型和单一记忆深度对功率放大器(PA)进行线性化矫正。然而,功率放大器在不同的功率水平下会呈现出不同的非线性特性,并产生不同的记忆效应。针对这一问题,该文提出一种基于维度加权盲K近邻(KNN)算法的数字预失真模型,所提模型根据功放当前输入信号以及记忆输入信号的幅度进行维度加权的KNN分类,组成维度加权盲KNN记忆多项式(WKMP)模型,并为每一类输入信号序列建立子模型。所提方法用Doherty功率放大器进行实验验证,使用带宽为30 MHz、频点为2.2 GHz的3载波长期演进(LTE)信号作为输入,反馈端使用122.88 MHz的采样率进行采样。实验结果表明,所提维度加权盲KNN分类方法与记忆多项式(MP)模型结合时,功放正向建模效果和数字预失真效果均超过了广义记忆多项式(GMP)模型,并远超记忆多项式模型的效果,实验结果验证了所提模型的优良性能。     

印尼国会社会结构分析

印尼议会在其民主化进程中具有重要地位,从宗教构成等垂直分层社会结构因素解析印尼议会有其合理性。分析印尼1999年人民代表会议（DPR）、2004年人民代表会议（DPR）及2004年地方人民代表会议（DPD）的宗教构成,印尼议员可分为世俗与非世俗两大类,两大类所占比例基本相当。在非世俗议员中,又存在传统派伊斯兰、现代派伊斯兰和非伊斯兰宗教（基督教）的区分,其中两派伊斯兰之间的政治力量也大体相当。同时,印尼议会宗教构成与地域因素亦紧密关联。印尼议会宗教构成呈现出异质性及多样化特征,这种特征暗示了印尼国内政治的世俗性及外交的温和伊斯兰路线。     

U型微乳水相增溶过程微观结构的模拟

利用耗散粒子动力学（DPD）方法对丁酸乙酯/无水乙醇/Tween80/水四组份微乳体系形成过程进行了模拟,其模拟内容包括水相增溶过程中微乳体系的微观结构和微乳液滴的形态特征变化、微乳体系内有效区域与无效区域的分界线等。模拟结果表明：水相增溶过程中,微乳体系能够在含水量为50%和70%时发生相的转变以及微乳液滴形态结构的变化：柱状→球状→柱状→球状。在油相与表面活性剂质量比小于等于5：5时,微乳体系水相可无限增溶;当油相与表面活性剂质量比为10：0,9：1,8：2,7：3,6：4时,微乳体系的最大增溶水量分别为25%,30%,35%,45%和50%,均为油包水型微乳,当水容量大于最大增溶水量时,微乳体系被破坏,分层。试验结果也发现：当含水量小于55%时,微乳体系电导率表明,微乳体系为油包水型;当含水量为55%-70%时,微乳体系为双连续型;当含水量大于70%时,微乳体系为水包油型。微乳体系的三相图也显示出微乳的有效区域。试验结果很好的吻合了模拟结果。     

双羟基Gemini表面活性剂的溶液性能及其聚集形态

以1-溴十二烷、2-甲氨基乙醇、1,3-二溴丙烷、1,4-二溴丁烷、1,6-二溴己烷、1,8-二溴辛烷、1,10-二溴癸烷和1,12-二溴十二烷为原料,制得含有双羟基的Gemini表面活性剂〔缩写为12(OH)-s-12(OH),其中s=3、4、6、8、10和12〕。并测定了双羟基Gemini表面活性剂的热稳定性及其在水溶液中的表面张力及泡沫性能;采用耗散粒子动力学(DPD)方法预测了Gemini表面活性剂在水溶液中的聚集形态。结果表明,该类型Gemini表面活性剂具有较好的热稳定性和泡沫性能,随着连接基团长度的增加(s≤6),其在水溶液中的临界胶束浓度(CMC)从0.62mmol/L(s=3)降至0.21mmol/L(s=6)左右,且当连接基团长度s6后CMC基本不变。随着Gemini表面活性剂摩尔分数的增加,胶束形态从球状胶束→棒状胶束→层状胶束→反胶束网络结构逐渐转变,且连接基团长度的改变几乎不影响其在水溶液中的胶束形态转变。     

Dissipative particle dynamics studies on the interface of incompatible A/B homopolymer blends in the presence of nanorods

Dissipative particle dynamics (DPD) simulations are used to investigate the effect of nanorods on the interface of immiscible A/B homopolymer blends. The nanorods are constructed by a string of beads connected through the spring forces, and then their rigidity is achieved depending on the angle forces. For the low volume fraction and/or aspect ratio, nanorods lead to broaden the interfacial width, D and decrease the interfacial tension, γ_S with the increase of the volume fraction. There is also a pronounced linear relationship. For the high volume fraction and/or aspect ratio, the variation of D and γ_S is found to depend on Onsager’s dimensionless parameter ψν, where ψ and ν are the volume fraction and aspect ratio of nanorods in the systems, respectively. Two scaling D ∼ (ψν)³ and γ_S ∼ (ψν)² are constructed. These results indicate that nanorods can indeed be used as a compatibilizing agent of immiscible blends as mentioned in reference [J. Chem. Phys. 2008, 128, 054901] and improve the interfacial characteristics, only when the parameters (ψν) in the correct range are chosen.     

Dissipative particle dynamics simulations of electroosmotic flow in nano-fluidic devices

When modeling the hydrodynamics of nanofluidic systems, it is often essential to include molecular-level information such as molecular fluctuations. To this effect, we present a mesoscopic approach which combines a fluctuating hydrodynamics formulation with an efficient implementation of Electroosmotic flow (EOF) in the small Debye length limit. The resulting approach, whose major ingredient is Dissipative Particle Dynamics, is sufficiently coarse-grained to allow efficient simulation of the hydrodynamics of micro/nanofluidic devices of sizes that are too large to be simulated by ab initio methods such as Molecular Dynamics. Within our formulation, EOF is efficiently generated using the recently proven similitude between velocity and electric field under appropriate conditions. More specifically, EOF is generated using an effective boundary condition, akin to a moving wall, thus avoiding evaluation of the computationally expensive electrostatic forces. Our method is used for simulating EOFs and DNA molecular sieving in simple and complex two-dimensional (2D) and 3D geometries frequently used in nano-fluidic devices. The numerical data obtained from our model are in very good agreement with theoretical results.     

Digital techniques to mitigate feedback impairment and noise of look‐up table digital predistortion

In this article, some new effects of feedback impairment and noise on look‐up table (LUT) digital predistortion (DPD) are presented. Several digital techniques are proposed to mitigate these effects. A smoothing filter (SMF) for LUTs is used to eliminate fluctuations of the transfer function of the overall DPD amplification system. By combining SMF method with iterative average (IA) method, the LUTs iterative process becomes stable and well converged. A postcompensator is established according to the proposed two‐box model for feedback impairment. For the demonstration, both simulation and experiments are carried out based on a Hammerstein‐type PA. Simulation results give some preliminary cognition of these new effects and the effectiveness of proposed techniques. Experimental tests are performed on an S‐band amplifier excited with single‐carrier WCDMA signal. The adjacent channel power ratio (ACPR) at 5‐MHz offset is ?48 dBc after DPD with SMF method and postcompensator. A total of 8 dB extra improvement of ACPR is obtained compared with that with neither SMF nor postcompensator. The result clearly shows that the proposed digital techniques are qualified for LUT DPD system, especially when it suffers significant feedback impairment and noise. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011.