Strategic spectrum occupancy for secondary users in cognitive radio networks with retrials

This article investigates joining strategies and admission control policy for secondary users (SUs) with retrial behavior in a cognitive radio (CR) system where a single primary user (PU) coexists with multiple SUs. Under a certain reward‐cost structure, SUs opportunistically access the PU band when it is not occupied by the PU. If the band is available upon arrival, an SU decides with a probability either to use the band immediately or to balk the system. If the band is occupied, the SU must decide whether to enter the system as a retrial customer or to leave the system. Once the PU requests for service, the service of SU being served, if any, will be interrupted, and the interrupted SU leaves the band and retries for service after a random amount of time. In this article, we study the equilibrium behavior of non‐cooperative SUs who want to maximize their benefit in a selfish, distributed manner with delay‐sensitive utility function. The socially optimal strategies of SUs are also derived. To utilize the PU band more efficiently and rationally, an admission control policy is proposed to regulate SUs who enter the system in order to eliminate the gap between the individually and socially optimal strategies.     

基于行为复合机制的结构化图形动画技术的研究与实践

在各类计算机动画中 ,角色动画可满足实时性及交互性的需要 ,其核心技术在于角色的建模技术。该文主要介绍了作者所研制的角色动画制作系统———“网动王 98” (简称Net_Anim系统 )中所采用的角色建模机制及其相关技术 ,内容包括 :角色的对象模型及其运行机制 ;角色复合行为的实现算法及相关的关键问题 ;应用示例 :Net_Anim系统的特色和有待进一步研究和解决的相关问题。     

一类非线性系统的浑沌与次谐波

本文利用Melnikov方法讨论了一类非Hamilton可积方程的周期激励系统,得到了该系统存在浑沌解与次谐波分支的充分条件。     

一种基于熵值的装备维修性评价模型

本文提出了一种基于熵值的装备维修性综合评价模型,该模型包括评价指标的熵值度量模型、装备维修信息结构图和行为控制图以及基于熵值的评价指标聚合模型等3个方面。本研究首先在分析装备维修一般过程和维修性评价内容的基础上,构建了定性指标和定量指标相结合的装备维修性评价指标体系,分析了维修任务复杂度、维修保障复杂度和基于熵值的维修效果的涵义;其次,给出了定性指标的熵值、定量指标的熵值以及基于权值的装备维修性熵值等计算方法;最后,给出一个装备维修性熵值评价的算例。算例结果表明,所提方法能够结合综合维修任务、维修保障和维修效果等多种影响因素进行装备维修性评价,不仅可以根据熵值大小对装备维修性水平进行高低排序,还可以分析影响装备维修性水平的瓶颈因素。     

Experimental investigation on enhanced damage to fuel tanks by reactive projectiles impact

Enhanced damage to the full-filled fuel tank,impacted by the cold pressed and sintered PTFE/AL/W reactive material projectile(RMP)with a density of 7.8 g/cm3,is investigated experimentally and theoretically.The fuel tank is a rectangular structure,welded by six pieces of 2024 aluminum plate with a thickness of 6 mm,and filled with RP-3 aviation kerosene.Experimental results show that the kerosene is ignited by the RMP impact at a velocity above 1062 m/s,and a novel interior ignition phenomenon which is closely related to the rupture effect of the fuel tank is observed.However,the traditional steel projectile with the same mass and dimension requires a velocity up to 1649 m/s to ignite the kerosene.Based on the experimental results,the radial pressure field is considered to be the main reason for the shear failure of weld.For mechanism considerations,the chemical energy released by the RMP enhances the hydrodynamic ram(HRAM)effect and provides additional ignition sources inside the fuel tank,thereby enhancing both rupture and ignition effects.Moreover,to further understand the enhanced ignition effect of RMP,the reactive debris temperature inside the kerosene is analyzed theoretically.The initiated reactive debris with high temperature provides effective interior ignition sources to ignite the kerosene,resulting in the enhanced ignition of the kerosene.     

Bionic stab-resistant body armor based on triangular pyramid structure

A stab-resistant substrate was designed and realized with a triangular pyramidal structure, inspired by the biological armor model in nature. The stab-resistance behavior and dynamic response mechanisms were studied through numerical simulation and experimental testing of a knife impacting a substrate, and an optimal structural design was obtained accordingly, with a tilted angle of 22.5° and optimal thickness of 1.2 mm. It was shown that the triangular pyramidal structure generated twice the internal energy of the knife than the flat substrate due to the dispersing effect of the structure. The force parallel to the inclination caused a significant scratch on the substrate surface, while the force perpendicular caused obvious substrate deformation. A new riveting method was used to form the total layer, which passed the GA 68—2008 standard. The stab-resistant clothing coupled with the reduced wearing burden could provide effective protection and avoid fatal injuries on security personnel working in dangerous environments. The method provided may enlighten the future design and manufacturing of stab-resistant clothing.     

Partial penetration of annular grooved projectiles impacting ductile metal targets

Changing and optimizing the projectile nose shape is an important way to achieve specific ballistic performance. One special ballistic performance is the embedding effect, which can achieve a delayed high-explosive reaction on the target surface. This embedding effect includes a rebound phase that is significantly different from the traditional penetration process. To better study embedment behavior, this study proposed a novel nose shape called an annular grooved projectile and defined its interaction process with the ductile metal plate as partial penetration. Specifically, we conducted a series of low-velocity-ballistic tests in which these steel projectiles were used to strike 16-mm-thick target plates made with 2024-O aluminum alloy. We observed the dynamic evolution characteristics of this aluminum alloy near the impact craters and analyzed these characteristics by corresponding cross-sectional views and numerical simulations. The results indicated that the penetration resistance had a brief decrease that was influenced by its groove structure, but then it increased significantly-that is, the fluctuation of penetration resistance was affected by the irregular nose shape. Moreover, we visualized the distribution of the material in the groove and its inflow process through the rheology lines in microscopic tests and the highlighted mesh lines in simulations. The combination of these phenomena revealed the embed-ment mechanism of the annular grooved projectile and optimized the design of the groove shape to achieve a more firm embedment performance. The embedment was achieved primarily by the target material filled in the groove structure. Therefore, preventing the shear failure that occurred on the filling material was key to achieving this embedding effect.     

基于有限理性理论的虚拟士兵感知行为建模研究

针对当前虚拟士兵感知行为模型的缺陷,介绍有限理性理论和基于有限理性虚拟士兵的概念,分析了加入有限理性理论的虚拟士兵的特点,提出了基于有限理性虚拟士兵的感知行为模型。该模型包括有限视觉模型、有限听觉模型和有限记忆模型,基于该感知模型的虚拟士兵在感知、决策和运动能力方面与类似真实士兵具有较高的一致性。这对虚拟士兵的感知行为建模研究具有一定的探索意义。     

觉察压力、社会支持、健康行为关系的路径分析

目的：综合研究觉察压力、社会支持和健康行为间的关系。方法：在问卷调查的基础上采用路径分析的方法,建立三者之间的结构方程模型并进行验证。研究工具：调查问卷：觉察压力量表;领悟社会支持评价量表;报告健康行为量表。结果：①问卷内部一致性信度为：0.701-0.802。②模型各拟合指数为：χ^2/df=1.34（χ^2=104.481,df=78）;GFI（拟合优度指数）=0.898;AGFI（调整拟合优度指数）=0.900;NFI（规范拟合指数）=0.926,TLI（Tucker-Lewis指数）=0.897;CFI（比较拟合指数）=0.912;RMSEA（近似误差均方根）=0.051。说明模型拟合情况良好。结论：应综合开展包括：压力应对、建立社会支持环境、培养良好生活方式在内的心理健康教育。     

Virtools环境下虚拟装备行为控制方法

为解决当前基于Virtools的装备虚拟训练系统中外观模型与机理模型紧密耦合所导致的模型开发效率低、不可重用的问题,分析了虚拟装备仿真模型结构,提出了一种基于Virtools消息机制的虚拟装备行为控制方法,实现了机理模型与外观模型相互分离、彼此独立的开发和维护,提高了模型的可维护性和可重用性。基于该方法开发的“某高炮虚拟训练系统”,已推广至军事院校的教学、训练,其验证了该方法的可行性。