Influence of Al2O3 particles on the microstructure and mechanical properties of copper surface composites fabricated by friction stir processing

The influence of three factors, such as volume percentage of reinforcement particles (i.e. Al₂O₃), tool tilt angle and concave angle of shoulder, on the mechanical properties of Cu–Al₂O₃ surface composites fabricated via friction stir processing was studied. Taguchi method was used to optimize these factors for maximizing the mechanical properties of surface composites. The fabricated surface composites were examined by optical microscope for dispersion of reinforcement particles. It was found that Al₂O₃ particles are uniformly dispersed in the stir zone. The tensile properties of the surface composites increased with the increase in the volume percentage of the Al₂O₃ reinforcement particles. This is due to the addition of the reinforcement particles which increases the temperature of recrystallization by pinning the grain boundaries of the copper matrix and blocking the movement of the dislocations. The observed mechanical properties are correlated with microstructure and fracture features.     

数字电位器在P T100温度仿真中的应用

伴随高速可编程逻辑器件的广泛应用,实时快速可靠地对系统状态信号进行处理,实现对复杂机电系统运行状态的实时监控成为用户追求的目标。基于数字电位器由于可调精度高,控制方便,性能稳定等优点,给出了一种基于CPLD可编程器件,通过数字电位器实现在半实物仿真系统中对PT100热电阻的阻值变化进行等效模拟的工程应用。利用本研究内容,通过上位机界面对系统温度参数进行人工设定,即可轻易实现对PT100热电阻在不同温度下阻值的真实模拟,检验实际系统温度监测装置软硬件的可靠性,确保系统安全运行。     

天基预警系统资源调度问题分析

在介绍天基预警系统作战流程,以及天基预警系统资源和任务的分析和描述的基础上,提出天基预警系统资源调度问题,给出其输入输出结构,并以五元组的形式对该问题进行形式化描述。 关键词：天基预警系统、资源调度、形式化描述     

基于消防响应时间满意度的消防站布局优化研究

消防站布局是否合理是及时扑灭火灾的关键,当前城市消防站规划方法主观性较大,缺乏量化数据支持,研究科学合理的城市消防站布局优化方法,具有十分重要的意义。在吸收前人研究的基础上,运用区域火灾风险评估、ARCGIS、遗传算法等,在构建消防响应时间满意度函数的基础上,构建了基于消防响应时间满意度的消防站布局优化选址方法。该方法从消防需求角度对研究区域的消防站布局进行了规划,达到用最少的消防站覆盖全部的消防需求点,以实现消防资源的最优化配置。     

临近空间高超声速目标上升段拦截需求分析

针对临近空间高超声速目标(NSHT)防御问题,从NSHT的特点出发分析上升段拦截面临的难点,并建立了空基拦截模型,以此为基础分析拦截武器所需的能力并确定其指标,对于拦截系统的建设具有一定的借鉴意义。     

非相参三点源有源诱偏下ARM弹着点研究

非相参多点源诱偏技术是对抗反辐射导弹(ARM)的有效手段。以ARM目标分辨的二分组理论和双点源诱偏的仿真结果为依据,对等功率三点源诱偏的2种经典布局的ARM落点整体分布进行预测。通过对ARM落点和系统被击中概率曲线的分析及拟合处理,验证了预测的正确性及系统被击中概率与占地面积的相关性,为通信辐射源抗ARM的布设提供一定的参考。     

三相逆变器新型积分控制加状态反馈控制

三相逆变器在实际运行中,不平衡负载工况较为常见,原因是传统积分控制加状态反馈控制无法实现三相输出电压的对称性。针对该问题提出了不平衡负载条件下三相逆变器新型积分控制加状态反馈控制策略,并通过仿真和实验验证了该策略能有效降低不平衡负载时三相逆变器输出电压的不平衡度,从而获得对称的三相输出电压波形。     

环管型燃烧室喷雾燃烧DES模拟

为研究燃气轮机燃烧室内复杂的两相三维湍流燃烧问题,采用基于Realizable k-ε模型的分离涡模拟(DES)方法对环管型燃烧室进行喷雾燃烧数值模拟.数值模拟结果表明:DES模拟在燃烧区发挥出大涡模拟(LES)的作用,能获取结构复杂的流场、温度场和涡量场,其对流场内涡结构的捕捉和分辨能力明显强于传统的RANS(雷诺时均N-S方法)模拟.与实验数据对比发现,DES模拟所得燃烧产物含量和燃烧室出口温度分布更符合.因此,DES方法可用于复杂形状燃烧室的燃烧数值模拟,能够避免RANS模型对湍流脉动进行平均处理导致耗散过大、抹平涡结构的缺点,从而可获取更准确的计算结果.     

Initiating insurgencies abroad: French plans to ‘chouannise’ Britain and Ireland, 1793–1798

Secret French plans to launch guerrilla-style raids on the British Isles devised in the spring of 1796 were referred to as ‘chouanneries’. The name and concept behind these small-war operations were modelled on the irregular tactics used by the Chouan rebels in the Vendée, which the French state army had brutally quashed, but some wished to transfer into their institutional practice. Part of France's ongoing military strategy in the war against Britain, which included fomenting insurrection in Ireland, these irregular operations were to be manned partially by pardoned deserters and released convicts and prisoners of war. Of these, only Tate's brief invasion of Wales in 1797 was realised, but the surviving plans provide insightful historical lessons into an Anglophobic mindset shared by a small network of practitioners and policy deciders on the effectiveness of such shock and awe tactics. Largely motivated by the desire to take revenge for Britain's support of counter-revolutionaries in the Vendée, these plans could more aptly be referred to as counter-‘chouanneries’.     

Inventory control and replenishment with flexible delivery‐time upgrade

We consider a capacitated inventory model with flexible delivery upgrades, in which the seller allocates its on‐hand inventory to price‐ and delivery‐time‐sensitive customers. The seller has two decisions: inventory commitment and replenishment. The former addresses how the on‐hand inventories are allocated between the two classes of customers within an inventory cycle. The latter addresses how the inventory is replenished between inventory cycles. We develop optimal inventory allocation, upgrade, and replenishment policies and demonstrate that the optimal policy can be characterized by a set of switching curves. © 2014 Wiley Periodicals, Inc. Naval Research Logistics 61: 418–426, 2014