Link-16数据链抗干扰性能分析与仿真

在部队通信服务问题的研究中,数据链仿真是数据链武器装备论证的重要研究内容和方法,对军队数据链建设具有重要意义.以美军现役战术数据链Link-16为背景,比较分析了数据链系统的四类信息传输方式,为提高抗干扰性能,介绍了主要的抗干扰技术.利用Simulink软件对数据链系统建立了链路仿真平台,重点构建了直序扩频模块和跳频模块,对在加性高斯白噪声和莱斯衰落影响下的信号传输进行了仿真并进行了抗干扰性能分析.通过仿真与分析可以看出,RS编码、直序扩频、跳频等技术保证了Link-16数据链的高抗干扰性能,使其满足军用通信要求.     

Photoshop的抠图技巧分析

本文介绍了抠图的概念,分析了选区在Photoshop图像处理过程中的关键作用,提出了选区创建的直接法与间接法,具体分析了各种操作方法的优缺点及使用的广泛性。     

Using visual and text features for direct marketing on multimedia messaging services domain

Traditionally, direct marketing companies have relied on pre-testing to select the best offers to send to their audience. Companies systematically dispatch the offers under consideration to a limited sample of potential buyers, rank them with respect to their performance and, based on this ranking, decide which offers to send to the wider population. Though this pre-testing process is simple and widely used, recently the industry has been under increased pressure to further optimize learning, in particular when facing severe time and learning space constraints. The main contribution of the present work is to demonstrate that direct marketing firms can exploit the information on visual content to optimize the learning phase. This paper proposes a two-phase learning strategy based on a cascade of regression methods that takes advantage of the visual and text features to improve and accelerate the learning process. Experiments in the domain of a commercial Multimedia Messaging Service (MMS) show the effectiveness of the proposed methods and a significant improvement over traditional learning techniques. The proposed approach can be used in any multimedia direct marketing domain in which offers comprise both a visual and text component.

Credit scoring using support vector machines with direct search for parameters selection

Support vector machines (SVM) is an effective tool for building good credit scoring models. However, the performance of the model depends on its parameters’ setting. In this study, we use direct search method to optimize the SVM-based credit scoring model and compare it with other three parameters optimization methods, such as grid search, method based on design of experiment (DOE) and genetic algorithm (GA). Two real-world credit datasets are selected to demonstrate the effectiveness and feasibility of the method. The results show that the direct search method can find the effective model with high classification accuracy and good robustness and keep less dependency on the initial search space or point setting.     

一种基于加法链的快速标量乘算法

给出一种标量的串长加法链算法来提高椭圆曲线标量乘法的效率。新的标量乘算法结合底层域直接计算2Q+P、2^nR+S算法,使用大小窗口法将串长算法和滑动窗口算法结合,加法链长度、存储空间和预计算都减少,其效率比二元法提高53%,比NAF法提高47.5%,比串长算法提高46.2%,比Windows法提高42.2%。     

基于RDMA的区块传输机制设计与实现

随着区块链技术的不断发展,区块的传输延迟成为区块链系统可扩展性的性能瓶颈。远程直接内存访问（RDMA）技术能够支持高带宽和低时延的数据传输,为低延迟区块传输提供了新的思路。因此,结合RDMA原语的特性,设计了用于区块信息共享的区块目录结构,并在此基础上设计并实现了区块传输的基本工作过程。实验结果表明,相较于基于TCP的方案,在1 MB大小的区块上基于RDMA的区块传输机制将节点间的区块传输延迟降低了44%,全网络的区块传输延迟降低了24.4%,在10 000节点规模的区块链上,区块链发生临时分叉的数量降低了22.6%。可见,基于RDMA的区块传输机制充分发挥了高速网络的性能优势,降低了区块传输延迟及临时分叉的数量,提高了现有区块链系统的可扩展性。     

交流电机变频调速中矢量控制与直接转矩控制的研究

随着交流电机在现代社会生产中的广泛应用,三相交流异步交流调速控制系统成为研究的热点,各种各样的变频调速方案相继出现,作为当前两种主要的交流电机变频控制方法,矢量控制和直接转机控制在实际中得到广泛的应用。本文以矢量控制与直接转矩控制比较为核心,对二者的控制原理、特性以及应用进行了分析与比较。同时,在分析的直接转矩控制原理的基础上,基于Simulink环境下对直接转矩控制系统进行仿真模型的搭建,并得到相应的仿真图象。     

反渗透阻垢剂的合成、应用及机理研究进展

投加阻垢剂是解决反渗透(Reverse osmosis,RO)膜结垢问题简单有效的方法。综述了RO系统中阻垢剂的合成应用、阻垢特征、机理及存在问题。含磷类阻垢剂因导致水体磷污染已经基本被其它几类阻垢剂替代,绿色环保类阻垢剂在阻垢效果和可降解性方面均比聚合物类好。但任何阻垢剂单独使用都难于满足(RO)系统阻垢的实际需求,阻垢剂的复配可相互弥补单一阻垢剂的缺陷,同时发挥其协同效应,而阻垢剂的特征改性具有更强的针对性和适用性。因此,阻垢剂的复配和改性是其研究的趋势和重点。     

Direct numerical simulations for assessment of gas-solid drag models in two-dimensional random arrays of particles

The momentum exchange between the phases plays a vital role in modelling of gas–solid flows and it is mathematically described by drag models. However, no consensus exists on which drag model gives the most accurate prediction of the drag force, and, despite the increase in available computing power, the same drag models are used in two-dimensional and three-dimensional simulations. In this study, direct numerical simulations of gas flow through multiple random configurations of static monodisperse particles are performed. The variations of solid volume fraction and particle Reynolds number are in the ranges of 0.05–0.4 and 13.7–136.9, respectively. The drag force exerted on particles is calculated and properly averaged. Based on the simulation results, thirteen drag models are compared and correction factors are introduced using the stochastic gradient descent algorithm. The correction factors provide a simple adjustment for the models to be used in 2D modelling.     

A numerical algorithm coupling a bifurcating indicator and a direct method for the computation of Hopf bifurcation points in fluid mechanics

This paper deals with the computation of Hopf bifurcation points in fluid mechanics. This computation is done by coupling a bifurcation indicator proposed recently (Cadou et al., 2006) [1] and a direct method (Jackson, 1987; Jepson, 1981) [2] and [3] which consists in solving an augmented system whose solutions are Hopf bifurcation points. The bifurcation indicator gives initial critical values (Reynolds number, Strouhal frequency) for the direct method iterations. Some classical numerical examples from fluid mechanics, in two dimensions, are studied to demonstrate the efficiency and the reliability of such an algorithm.