Experimental investigation on anti-penetration performance of polyurea-coated ASTM1045 steel plate subjected to projectile impact

In this study, the anti-penetration performance of polyurea/ASTM1405-steel composite plate subjected to high velocity projectile was analyzed. Two kinds of modified polyurea material (AMMT-053 and AMMT-055) were selected and a ballistic impact testing system including speed measuring target system and high-speed camera was designed. This experiment was conducted with a rifle and 5.8 mm projectile to explore the effects by the polyurea coating thickness, the polyurea coating position and the glass-fiber cloth on the anti-penetration performance of polyurea/ASTM1405-steel composite plate. The result showed that the effects of polyurea coating position were different between two types of polyurea, and that the effects of glass-fiber position were disparate between two types of polyurea as well. For AMMT-053 polyurea material, it was better to be on front face than on rear face; whereas for AMMT-055 pol-yurea, it was better to be on rear surface although the difference was very subtle. Additionally, formulas had been given to describe the relationship between the effectiveness of polyurea and the thickness of polyurea coating. In general, AMMT-055 had better anti-penetration performance than AMMT-053. Furthermore, five typical damage modes including self-healing, crack, local bulge, spallation and local fragmentation were defined and the failure mechanism was analyzed with the results of SHPB test. Additionally, the bonding strength played an important role in the anti-penetration performance of polyurea/steel composite plate.     

运载火箭伺服机构故障检测与诊断的扩展多模型自适应方法

针对运载火箭伺服机构故障,提出一种基于扩展多模型自适应估计的故障检测与诊断算法。建立考虑伺服机构故障的运载火箭姿态动力学模型;将故障角度作为状态变量得到增广状态空间模型;利用扩展卡尔曼滤波器进行状态向量和故障参数的非线性估计,并基于传感器测量数据采用假设检验算法在线计算故障发生的概率;给出基于扩展多模型自适应估计的故障检测与诊断算法流程。仿真结果表明,该方法在无故障时可对伺服机构进行健康监测;在单台伺服机构故障下,可以及时准确判断出哪一台芯级伺服机构发生故障,并可准确估计出伺服机构故障下的发动机摆角角度。     

Synchronizing pricing and replenishment to serve forward-looking customers

We incorporate strategic customer waiting behavior in the classical economic order quantity (EOQ) setting. The seller determines not only the timing and quantities of the inventory replenishment, but also the selling prices over time. While similar ideas of market segmentation and intertemporal price discrimination can be carried over from the travel industries to other industries, inventory replenishment considerations common to retail outlets and supermarkets introduce additional features to the optimal pricing scheme. Specifically, our study provides concrete managerial recommendations that are against the conventional wisdom on “everyday low price” (EDLP) versus “high-low pricing” (Hi-Lo). We show that in the presence of inventory costs and strategic customers, Hi-Lo instead of EDLP is optimal when customers have homogeneous valuations. This result suggests that because of strategic customer behavior, the seller obtains a new source of flexibility—the ability to induce customers to wait—which always leads to a strictly positive increase of the seller's profit. Moreover, the optimal inventory policy may feature a dry period with zero inventory, but this period does not necessarily result in a loss of sales as customers strategically wait for the upcoming promotion. Furthermore, we derive the solution approach for the optimal policy under heterogeneous customer valuation setting. Under the optimal policy, the replenishments and price promotions are synchronized, and the seller adopts high selling prices when the inventory level is low and plans a discontinuous price discount at the replenishment point when inventory is the highest.     

基于双线性连接模型的超静定捆绑火箭助推器动力学响应分析

对于长径比较高的助推器来说,为了提高与芯级的连接可靠性,可采用超静定捆绑连接方式。这种捆绑连接方式增加了助推器动力学响应分析的难度。以超静定捆绑火箭助推器为研究对象,通过引入拉压双线性弹簧模拟捆绑连接装置,建立合理的动力学分析模型,对系统进行数值求解,获得径向冲击作用下助推器的动力学响应特性。通过与静定捆绑模型的对比,获得超静定捆绑助推器的广义位移、频谱和内力的响应,从而为工程应用提供一定的参考和理论支撑。     

美国网络安全人才培养机制

加强网络安全人才队伍建设已经成为世界主要国家抢占网络空间制高点的战略举措。近年来的研究表明,美国通过发布专门的网络安全人才培养国家战略,设立专门的网络安全人才培养卓越中心,开发专门的网络安全人才培养在线资源,形成了一套较为成熟的惠及全民的网安全人才培养机制。     

基于排挤机制改进的多目标进化算法

进化算法是求解多目标优化问题(MOP)重要而有效的方法。为加快收敛速度,提高收敛精度,在已有算法(NSGA-Ⅱ)的基础上,引进小生境思想,提出了更为合理的排挤机制。通过典型应用函数的计算测试,结果表明:上述改进不仅具有较高的计算效率,而且能够得到分布更为合理的解,且能保持解的多样性分布。     

试件水灰比和胶砂比对混凝土硫酸盐侵蚀速度影响

通过大量试验,采用强度指标研究了试件水灰比和胶砂比对硫酸盐侵蚀速度的影响.结果表明:试件的水灰比越大,胶砂比越小,侵蚀速度越快;为了加快硫酸盐侵蚀速度,宜采用大水灰比、小胶砂比的试件.在各种条件下,硫酸钠侵蚀破坏的速度比硫酸镁侵蚀快.对硫酸钠型侵蚀,采用抗折抗蚀系数作为判定指标较为合理,而对硫酸镁型侵蚀,应该综合考虑抗折抗蚀系数和抗压抗蚀系数.     

农村经济结构调整的动力机制分析

农村经济结构调整是一系列因素共同作用的结果 ,引致这种调整的动力机制包括政策导向动力机制、市场需求动力机制、科技发展动力机制和国际竞争动力机制。这四大动力机制共同作用 ,使农村经济结构的调整朝着符合国内外需求、优质高效的目标发展。     

碳化硼基3DMC材料抗弹性能的初步探讨

通过7.62穿甲燃烧弹的射击考核,分析了碳化硼基3DMC材料的抗弹性能,发现其综合抗弹性能优于等厚度的某型号装甲钢,并具有抗击连续打击的能力,认为该材料可以独立用于装甲防护。     

管道金属磁记忆检测技术现状分析及发展研究

针对管道无损检测问题,阐述了金属磁记忆效应的基本原理,与传统无损检测方式比较,归纳了磁记忆检测的基本特性。在磁记忆检测仪器研发现状的基础上,设计了新型管道磁记忆／漏磁综合检测仪。从检测机理、信号处理和缺陷识别3个方面对检测技术研究现状进行分析和总结。探讨了检测机理的局限性,提出管道磁记忆检测技术的研究新方向。