War Size Distribution: Empirical Regularities Behind Conflicts

This paper analyses the statistical distribution of war sizes. Using a new methodology we find moderate support for a Pareto-type distribution (power law), considering data from different sources (COW and UCDP) and periods. A power law is a plausible model for the size distribution of a pool of all wars and a sample of wars in many years, although the log-normal distribution is a plausible alternative model that we cannot reject. The random growth of conflicts could generate both types of distribution. We study the growth rates of battle deaths and random growth cannot be rejected for most of the distribution, although the results also reveal a clear decreasing pattern; the growth of deaths declines faster if the number of initial deaths is greater.     

Spatial Distribution of Minority Communities and Terrorism: Domestic Concentration versus Transnational Dispersion

Qualitative studies of terrorist movements frequently highlight the importance of diaspora communities as important factors in producing and sustaining terrorist activity in countries. The underlying theoretical argument is that bifurcation of tight-knit minority communities between countries nurtures separatist or irredentist sentiments among affected community members, thus prompting terrorist activity, while minority community members in other countries might mobilize financial and political resources to support terrorist activity among their compatriots. In this study, we empirically test whether transnational dispersion, versus domestic concentration, of minority communities in countries produces higher incidents of terrorism. Conducting a series of negative binomial estimations on a reshaped database of around 170 countries from 1981 to 2006, derived from the Minorities at Risk database and the Global Terrorism Database, we determine that both transnational dispersion of kin minority communities and domestic concentration of minorities within countries increase terrorism and that transnational dispersion is a particularly robust predictor of terrorist attacks.     

弹炮结合防空武器系统火力分配模型

火力分配是弹炮结合武器系统射击指挥中的重要环节。论文针对弹炮结合武器系统中防空导弹分系统和高炮分系统战术技术性能与作战特点,在具体分析火力分配考虑的主要因素——防空导弹分系统和高炮分系统的杀伤区与毁伤概率的基础上,确立了相应的火力优化分配原则,构建了实用的临近航路和过航点处火力分配模型,通过仿真表明该模型实时性好,能满足实际应用需要,对进一步研究提供了有益的参考。     

气泡输运方程及其应用

舰船尾流中含有大量的不同直径的气泡 ,尾流的几何特性与产生它的舰船大小、航行速度、海面风速等因素有很大的关系 ,对气泡规律的研究无论在理论还是在应用中都具有重要的意义。介绍了水中气泡分布函数 ,推导了分布函数所满足的输运方程 ,并给出了气泡输运方程的特征解。对影响分布函数的因素作了探讨 ,并利用输运方程对具体问题进行了计算。结果表明 ,运用气泡输运方程可解决气泡的分布、输运问题 ,并可对气泡分布与气泡半径、气泡所处深度的关系作出定量分析     

图像处理技术在桨叶表面应力分布试验中的应用

介绍图像处理技术在桨叶表面应力分布测试试验中的应用情况 ,对实际使用中的图像处理技术进行了较详细的分析讨论 .经过处理后的桨叶试验图像 ,不仅增加了图像的清晰程度 ,而且从中可获得半定量以至定量的参数 ,以帮助对桨叶表面应力分布进行分析     

一种新的动态分形海面模型及其电磁散射统计特性研究

给出了一种更符合海面实际情况的基于未充分发展海谱的分形海面模型(NDFFM),使用双尺度法计算了NDFFM海面的后向散射截面,并研究了动态散射场幅值分布。结果表明在大特征斜率下散射场服从K分布,随着特征斜率的下降,散射场分布向瑞利分布退化。最后将计算数据与传统的分形模型和实测雷达数据进行比对,证明了该模型的准确性和有效性。     

Experimental investigation on dynamic response and damage models of circular RC columns subjected to underwater explosions

Reinforced concrete (RC) columns are widely used as supporting structures for high-piled wharfs. The study of damage model of a RC column due to underwater explosion is a critical issue to assess the wharf’s antiknock security. In this study, the dynamic response and damage model of circular RC columns subjected to underwater explosions were investigated by means of scaled-down experiment models. Experiments were carried out in a 10.0 m diameter tank with the water depth of 2.25 m, under different explosive quantities (0.025 kg–1.6 kg), stand-off distances (0.0 m–7.0 m), and detonation depths (0.25 m–2.0 m). The shock wave load and dynamic response of experiment models were measured by configuring sensors of pressure, acceleration, strain, and displacement. Then, the load distribution characteristics, time history of test data, and damage models related to present conditions were obtained and discussed. Three damage models, including bending failure, bending-shear failure and punching failure, were identified. In addition, the experience model of shock wave loads on the surface of a RC column was proposed for engineering application.     

Fragment spatial distribution of prismatic casing under internal explosive loading

Non-cylindrical casings filled with explosives have undergone rapid development in warhead design and explosion control. The fragment spatial distribution of prismatic casings is more complex than that of traditional cylindrical casings. In this study, numerical and experimental investigations into the fragment spatial distribution of a prismatic casing were conducted. A new numerical method, which adds the Lagrangian marker points to the Eulerian grid, was proposed to track the multi-material interfaces and material dynamic fractures. Physical quantity mappings between the Lagrangian marker points and Eulerian grid were achieved by their topological relationship. Thereafter, the fragment spatial distributions of the prismatic casing with different fragment sizes, fragment shapes, and casing geometries were obtained using the numerical method. Moreover, fragment spatial distribution experiments were conducted on the prismatic casing with different fragment sizes and shapes, and the experimental data were compared with the numerical results. The effects of the fragment and casing geometry on the fragment spatial distributions were determined by analyzing the numerical results and experimental data. Finally, a formula including the casing geometry parameters was fitted to predict the fragment spatial distribution of the prismatic casing under internal explosive loading.     

Investigation on the spatial distribution characteristics of behind-armor debris formed by the perforation of EFP through steel target

The behind-armor debris (BAD) formed by the perforation of an EFP is the main damage factor for the secondary destruction to the behind-armor components. Aiming at investigating the BAD caused by EFP, flash X-ray radiography combined with an experimental witness plate test method was used, and the FEM-SPH adaptive conversion algorithm in LS-DYNA software was employed to model the perforation process. The simulation results of the debris cloud shape and number of debris were in good agreement with the flash X-ray radiographs and perforated holes on the witness plate, respectively. Three-dimensional numerical simulations of EFP's penetration under various impact conditions were conducted. The results show that, an ellipsoidal debris cloud, with the major-to-minor axis radio (a/b) smaller than that caused by shaped charge jets, was formed behind the target. With the increase of target thickness (h) and decrease of impact velocity (v₀) and obliquity (θ), the value of a/b decreases. The number of debris ejected from target is significantly higher than that from EFP. Based on the statistical analysis of the spatial distribution of the BAD, An engineering calculation model was established considering the influence of h, v₀ and θ. The model can with reasonable accuracy predict the quantity and velocity distribution characteristics of BAD formed by EFP.     

Effect of tool rotational speed on the particle distribution in friction stir welding of AA6092/17.5 SiCp-T6 composite plates and its consequences on the mechanical property of the joint

This study investigates the effect of tool rotational speed (TRS) on particle distribution in nugget zone (NZ) through quantitative approach and its consequences on the mechanical property of friction stir welded joints of AA6092/17.5 SiC_p-T6 composite. 6 mm thick plates are welded at a constant tool tilt angle of 2° and tool traverse speed of 1 mm/s by varying the TRS at 1000 rpm, 1500 rpm and 2000 rpm with a taper pin profiled tool. Microstructure analysis shows large quantity of uniformly shaped smaller size SiC particle with lower average particle area which are homogeneously distributed in the NZ. The fragmentation of bigger size particles has been observed because of abrading action of the hard tool and resulting shearing effect and severe stress generation due to the rotation of tool. The particles occupy maximum area in the matrix compared to that of the base material (BM) due to the redistribution of broken particles as an effect of TRS. The migration of particles towards the TMAZ-NZ transition zone has been also encountered at higher TRS (2000 rpm). The microhardness analysis depicts variation in average hardness from top to bottom of the NZ, minimum for 1500 rpm and maximum for 2000 rpm. The impact strength at 1000 rpm and 1500 rpm remains close to that of BM (21.6 J) while 2000 rpm shows the accountable reduction. The maximum joint efficiency has been achieved at 1500 rpm (84%) and minimum at 1000 rpm (68%) under tensile loading. Fractographic analysis shows mixed mode of failure for BM, 1000 rpm and 1500 rpm, whereas 2000 rpm shows the brittle mode of failure.