浅析前期罗马帝国的边防政策

前期罗马帝国(公元前30年至公元283年)是罗马帝国的全盛时期,其边界从西北到东南的直线距离达数千公里.罗马帝国通过建设一支职业化的常备军队、建立大量缓冲国、设立永久性纵深防御体系、构筑永久性防御设施和创造出一套高效的军需供应体系,成功地保护了漫长的边界线.罗马帝国皇帝屋大维是这一系列边防政策的奠基者.但随着罗马社会经济的发展和外部环境的变化,上述曾一度为帝国长期和平与繁荣提供了有力保障的边防政策逐渐失效,并走到了自身的反面,最后在蛮族入侵面前土崩瓦解,退出了历史舞台.     

时域TEM喇叭天线的分析和设计

TEM喇叭是一种超宽带天线,但迄今为止大都是利用频域的概念来研究的。本节从波模理论出发,提出喇叭的开口阻抗不能看作真空波阻抗,它与喇叭尺寸、张角有关;由于冲激脉冲有时序性,反射只与局部结构有关。介绍了实际制作的TEM喇叭天线,并给出了实验结果,表明它具有良好的阻抗匹配特性和波形保真性,对时域天线的研究具有很好的理论和实用价值。     

Linear compound algorithms for the partitioning problem

For a given set S of nonnegative integers the partitioning problem asks for a partition of S into two disjoint subsets S₁ and S₂ such that the sum of elements in S₁ is equal to the sum of elements in S₂. If additionally two elements (the kernels) r₁, r₂ ∈ S are given which must not be assigned to the same set S_i, we get the partitioning problem with kernels. For these NP‐complete problems the authors present two compound algorithms which consist both of three linear greedylike algorithms running independently. It is shown that the worst‐case performance of the heuristic for the ordinary partitioning problem is 12/11, while the second procedure for partitioning with kernels has a bound of 8/7. © 2000 John Wiley & Sons, Inc. Naval Research Logistics 47: 593–601, 2000     

Spatial pricing and product allocation in online retailing

Spatial pricing means a retailer price discriminates its customers based on their geographic locations. In this article, we study how an online retailer should jointly allocate multiple products and facilitate spatial price discrimination to maximize profits. When deciding between a centralized product allocation ((i.e., different products are allocated to the same fulfillment center) and decentralized product allocation (ie, different products are allocated to different fulfillment centers), the retailer faces the tradeoff between shipment pooling (ie, shipping multiple products in one package), and demand localization (ie, stocking products to satisfy local demand) based on its understanding of customers' product valuations. In our basic model, we consider two widely used spatial pricing policies: free on board (FOB) pricing that charges each customer the exact amount of shipping cost, and uniform delivered (UD) pricing that provides free shipping. We propose a stylized model and find that centralized product allocation is preferred when demand localization effect is relatively low or shipment pooling benefit is relatively high under both spatial pricing policies. Moreover, centralized product allocation is more preferred under the FOB pricing which encourages the purchase of virtual bundles of multiple products. Furthermore, we respectively extend the UD and FOB pricing policies to flat rate shipping (ie, the firm charges a constant shipping fee for each purchase), and linear rate shipping (ie, the firm sets the shipping fee as a fixed proportion of firm's actual fulfillment costs). While similar observations from the basic model still hold, we find the firm can improve its profit by sharing the fulfillment cost with its customers via the flat rate or linear rate shipping fee structure.     

GSVM:一种支持Gather/Scatter的向量存储器

宽单指令多数据流(Single Instruction Multiple Data, SIMD)架构数字信号处理器一般都能高效支持地址连续或等距跨步等规则应用的向量访存,但对于科学与工程计算中广泛存在的不规则应用的数据访存则带宽利用率往往较低,从而大幅降低了其整体运算能效。为了提高不规则应用的向量访存性能,基于某SIMD数字信号处理器的体系结构,设计了一种支持Gather/Scatter访存的向量存储器GSVM。通过设计与SIMD宽度相匹配的向量地址计算单元和合适深度的冲突缓冲器阵列,实现了Gather/Scatter指令向量地址计算、仲裁与缓存的全流水访存操作。实验结果表明,相比以前不支持Gather/Scatter访存的存储器,GSVM在增加22%的硬件代价基础上,基于稀疏矩阵向量乘的测试程序集获得了2～8的性能加速比。     

不确定性作战任务形式化描述方法

针对复杂作战环境下作战任务的不可预知性特点,对不确定性任务的形式化描述方法进行了深入研究。分析不确定环境导致的任务分解和执行过程中存在的不确定性因素,从任务本身的不确定性、任务之间关系不确定性以及作战单元执行不确定性等方面,对不确定性任务进行了形式化描述,提出了不确定性任务形式化描述流程,最后通过一个实例对所提方法进行了验证。     

温升热源条件油气热着火关键因素探究

通过对影响油气受热着火的关键因素进行研究,为发展主动防护技术提供理论依据。基于系统的实验和分析,探究了快速氧化现象、热源加热速度、热源面积与爆燃空间比例对热着火发生时临界浓度、着火概率和着火延迟期的影响,提出了温升热源条件受限空间能否发生热着火的综合判据。该判据认为：如果油气体积分数低于2.4％,受限空间体积与热源面积比值小于0．64m,那么即使温度达到873K,湿度降低到18％～21％,着火也不会发生。     

石英晶体测试实验中干扰的消除

Ｙ－切石英晶体的各向异性物理特性,使它在正碰撞或平面冲击波作用条件下能产生压剪波的传播,为实现对材料的压剪加载实验研究提供了条件。由于石英晶体的压电效应,国外采用了ＶＩＳＡＲ技术进行测试。在我们的工作中,首次尝试用锰铜压阻法和电磁质速测量法进行测试。压电效应造成了明显的干扰,妨碍信号的获取。实验中用磁控溅射方法将石英晶体表面镀银层约１μｍ,达到了中和极化电荷、屏蔽极化电场的目的,比较成功地消除了压电干扰,获得了有效的测试信号。     

浅谈航空产品生产过程中的静电防护

静电给航空工业带来很大危害,我们应充分认识静电防护的重要性和必要性。本文列举了在我国航空企业静电控制过程中的一些常见问题,并对这些常见问题给出了相应的改进措施,并强调航空企业应把建立静电控制系统看成质量保证体系的一个重要组成部分。     

做好型号设计质量评价控制武器装备质量源头

型号设计阶段是装备质量形成的源头,质量评价是保证型号研制方案质量的重要手段。根据型号研制阶段设计质量评价新需求,应用现代产品质量理论及方法,阐述了型号设计质量评价的概念、特点、过程、方法体系及软件工具系统,为保证装备方案质量提供切实可行的技术途径,使装备质量持续改进成为可能。