FlatLFS:一种面向海量小文件处理优化的轻量级文件系统

海量小文件的高效存储和访问是当前分布式文件系统面临的主要挑战之一。以GFS和HDFS为代表的分布式文件系统大多面向海量大文件的高效存储和访问设计,缺乏小文件处理的针对性优化,导致访问海量小文件时效率低下。针对分布式文件系统中海量小文件访问时的数据服务器优化问题,提出了一种采用扁平式数据存储方法的轻量级文件系统FlatLFS,取代传统文件系统对上层分布式文件系统提供数据存储和访问支持,提高了数据服务器处理小数据块时的I/O性能,从而提升了整个分布式文件系统的性能。实验表明,当数据块大小设定为1M时,FlatLFS的随机读性能分别比ext3、ext4、reiserfs高135%、112%和122%。     

The German wars of liberation 1807–1815: The restrained insurgency

In the Age of Napoleon, ‘small wars’ and ‘revolutionary war’ were closely connected. There were, however, different strands of this phenomenon: speaking professionally, conservative officers condemned small wars as an irregular regression to previous less disciplined forms of warfare. The Prussian state continually tried to discipline and regulate spontaneous risings. Yet the irregular character of small wars offered the opportunities for a less complex way of fighting, thus enabling the arming of the ‘people’ to fight. Individual undertakings, such as Ferdinand von Schill's doomed campaign in 1809, were designed to spark off a general popular uprising. But they were cheered by many and supported by few. Meanwhile, Neidhardt von Gneisenau conceived guerrilla-style Landsturm home-defence forces, which were designed for an irregular people's war. These concepts were put into practice in the ‘war of freedom’ – or ‘war of liberation’ – in 1813. Eventually both the mobilisation and the tactics remained regular, however, despite the emphatic appeal to a national ‘people's war’.     

舰炮弹丸对零航路捷径超声速导弹的侵彻分析

以零航路捷径下小口径舰炮弹丸对超声速反舰导弹的侵彻毁伤效果为研究方向,仿真计算了零航路捷径下小口径舰炮弹丸与超声速反舰导弹的交汇姿态,建立了反舰导弹模型,在此基础上就不同侵彻部位及交汇角度条件下小口径舰炮弹丸对超声速反舰导弹的侵彻毁伤效果进行了有限元仿真,得出了具有统计意义的仿真结果,总结了弹丸无法毁伤导弹战斗部的几点因素。研究对有效评价小口径舰炮弹丸对超声速反舰导弹的毁伤效果以及对导弹整体的易损性分析提供了理论参考。     

Contents and Author Index,Volume 20, 2013

The United States has multiple nuclear detection initiatives to secure against a terrorist nuclear attack, including the Container Security Initiative, installation of radiation detectors at U.S. border points of entry, and establishment of the Domestic Nuclear Detection Office (DNDO). The current nuclear detection system architecture falls short of being able to reliably catch fissile nuclear material in transit, specifically shielded Highly Enriched Uranium (HEU) and Plutonium (Pu), both within the US and abroad. Checkpoints at border crossings can be circumvented, and no adequate system is under development to deter the transport of fissile materials. Using nuclear link-budget calculations, we show why a network relying primarily on handhelds, fixed detectors, and portals is not sufficient. We examine the technical, economic, and operational feasibility of a comprehensive national network incorporating in-vehicle detectors to reliably detect and deter the transport of fissile material inside the vehicle itself.     

The dangerous myths and dubious promise of COIN

Counterinsurgency (COIN) has again emerged as a topic of both contemporary and historical interest in the age of what has been called a global counterinsurgency. However, little attention is being paid to the historical lineage of a COIN doctrine that is being rediscovered and promoted by an enthusiastic group of military intellectuals and commanders as the basis for US Army and Marine Corps doctrine. This article argues that historical claims for COIN success, based on courting popular gratitude by improving economic conditions, are at best anchored in selective historical memory, when not fantasy fabrications. The first argument of this article is that COIN does not constitute a distinct form of warfare, but merely a sub-set of minor tactics. Second, ‘hearts and minds’, so-called population-centric warfare, has seldom been a recipe for lasting stability. Rather, historically counterinsurgency succeeded when it has shattered and divided societies by severely disrupting civilian life. In fact, COIN is a nineteenth century legacy of empire whose uniqueness and impact was mythologized in its own day, and that is unlikely to prove a formula for strategic success in the twenty-first century.     

基于逆合成孔径成像激光雷达的自旋小目标成像系统

为了获得毫米级自旋小目标的清晰成像,采用逆合成孔径成像激光雷达技术设计了基于距离向数据与方位向数据相融合的图像重建系统。系统采用大带宽、窄线宽光纤激光器配合调制器实现激光脉冲的线性调频,利用光外差原理对回波信号进行采集处理。结合自旋目标的运动特性,给出了含有自旋分量的回波信号函数方程,并将该分量引入传统的R-D算法中实现了对自旋目标的ISAIL二维图像的重建。实验采用毫米级铝条构成被测小目标,通过步进电机及带倾角的转台完成运动及自旋模拟。实验结果显示,当目标固定时,可通过回波能量数据获得一维距离向图像,与被测目标的4个特征点位置一致。当目标运动时,通过数据压缩并代入自旋参量,最后通过R-D算法可以获得可识别的ISAIL二维图像,验证了系统符合自旋小目标成像的设计要求。     

多品种空投小件装载优化建模研究

针对空投小件装载率低下的现状,提出利用相关容重比平衡法,制定装载计划以充分利用飞机的载重能力及其使用面积,分别建立了单机和多机空投小件装载模型。该模型充分考虑了飞机的面积和载重量,对提高空投小件装载的利用率,起到良好应用效果。     

一种辐射屏蔽模拟计算的方法

本文论述了用蒙特卡罗方法直接模拟计算非带电粒子辐射的屏蔽穿透概率问题,讨论了粒子穿透概率无偏估计的两种实际情况,探讨了将粒子输运理论应用于解决实际辐射物理问题的途径。     

区域掩护高射炮最佳配置的数量分析

本文根据军事运筹学的有关理论,以现装备的高射炮作为主要的防空武器,针对实施区域掩护时为取得良好的掩护效果,从数量上对兵力兵器作了系统分析。     

硼介质／石墨水泥基材料电磁屏蔽性能实验研究

为增强水泥基材料的电磁屏蔽性能,通过混凝土骨料替换的方法,实验研究了碳化硼、硼砂及石墨组合对复合材料电磁屏蔽效能的影响规律。实验结果表明单纯的碳化硼或碳化硼一硼砂作为水泥基材料骨料时,样品电磁屏蔽性能提升有限,但在添加硼介质时引入适当比例的石墨能有效改善材料的电磁屏蔽性能;另外,硼砂的添加会造成样品明显的缓凝现象,并且会对石墨导电吸波机制产生负面影响。