数字图书馆基于内容的检索技术研究与实现

基于内容的检索技术是数字图书馆研究的热点问题。本文分析了全文检索和图像检索的关键技术，提出图像检索应建立在相关反馈、视觉特征和对图像内容加注的文字进行全文检索相结合的基础上，并在原型系统上给出了实验结果。     

基于图像特征与心理感知量的伪装效果评价方法

目标的探测概率是伪装效果评价的重要指标,在以往的评价方法中忽略了判读人员的心理因素。在统计决策模型基础上,通过定义4 个图像特征相似度,建立了单个图像特征量与心理感知量的关系,进行了5 个心理实验,找出了目标探测概率与心理感知量的关系。经过综合判读实践验证,该模型能够客观地得到目标的探测概率,为伪装效果评价提供新的方法。     

四轨电磁发射器电枢-轨道初始接触特性分析

为探究四轨电磁发射器电枢-轨道初始接触特性,采用有限元法对电枢和轨道的初始接触特性进行分析,选择电枢最大等效应力、接触系数、接触压强均匀系数和相对接触压强系数为接触特性性能指标,探究电枢臂长度、过盈量和电枢臂尾部厚度对接触特性性能指标的影响规律。结果表明：不同的结构参量对性能指标的影响不同,过盈量对等效应力影响较大,电枢臂长度增加导致接触系数降低,电枢臂尾部厚度主要影响相对接触压强系数。     

碳含量及类型对镁碳耐火材料弹性模量的影响

采用声频法测量经不同热处理温度后镁碳耐火材料的弹性模量,并测量了气孔率以及常温弯曲强度,同时进行了热震实验,用XRD和SEM并辅助EDX分析了试样的物相组成及显微结构的变化,评估碳含量及类型对镁碳耐火材料抗热震性的影响。结果表明：随着石墨含量的降低,材料的弹性模量不断升高;含炭黑试样的弹性模量低于含石墨试样,使其具有更好的热震稳定性。随着热处理温度的升高,气孔率不断升高并导致弹性模量的不断降低;抗氧化剂Al粉与电熔镁砂反应生成的MgAl2O4相使得弹性模量在1 000,1 400 ℃出现稍许增加。     

Analysis of hydrodynamic characteristics of unmanned underwater vehicle moving close to the sea bottom

The accurate research on the hydrodynamics of unmanned underwater vehicle （UUV）, which moves close to the sea bottom, has a great significance for its maneuverability. The structured grid of the computational models with different distances to the sea bottom and attack angles is generated by Ansys ICEM, and the flow field near the sea bottom is simulated using CFX. The characteristics of the drag, lift, pitching moment influenced by the distance to sea bottom and the attack angle are studied. The result shows that the drag coefficient increases with the decrease of distance, while it increases with the increase of attack angle. There exists attraction force when UUV moves close to the sea bottom, and the attraction force increases with the decrease in distance. The lift coefficient increases with the increase in attack angle. The absolute value of the pitching moment coefficient increases with the decrease in distance and the increase in attack angle.     

AZ31B镁合金TIG焊焊接裂纹的产生及其特征分析

在厚度为8.0 mm 的AZ31B 镁合金板材上分别进行钨极氩弧焊 TIG 自熔焊和斜 Y 型坡口添丝焊焊接裂纹试验,研究焊接裂纹的产生原因和扩展特征,分析镁合金材料的裂纹敏感性。试验结果表明,在自拘束条件下,自熔焊焊缝区焊后立即产生焊接热裂纹,斜 Y 型坡口添丝焊焊缝区在焊接电流为170 A 和180 A 的情况下出现焊接热裂纹。自熔焊焊接热裂纹是沿晶扩展,添丝焊焊接热裂纹是沿晶与穿晶的混合扩展,裂纹在扩展过程中都存在分叉裂纹。未出现裂纹的焊接试件放置48 h 后仍然没有观察到任何形式的延迟裂纹。     

梯度堆焊合金层界面组织特征及性能

在Q235A基体上采用药芯焊丝埋弧焊和自保护明弧焊方式,依次堆焊包含"20Cr2Mn12Ni Mo N韧性过渡层+Cr12W3Mn塑性缓冲层+Cr20Ti Mn Si高铬耐磨层"结构的堆焊合金。借助光学显微镜、扫描电镜、X线衍射仪和显微硬度计等研究堆焊合金层的界面组织特征及性能。结果表明,增加韧性过渡层和塑性缓冲层形成了梯度硬度结构的堆焊合金层,不仅可减小残余应力,而且抑制母材成分的稀释影响,规避网状碳化物和共晶等脆性组织形成。     

Burning characteristics of microcellular combustible objects

Microcellular combustible objects for application of combustible case, caseless ammunition or combustible detonator-holding tubes are fabricated through one-step foaming process, in which supercritical CO2 is used as foaming agent. The formulations consist of inert polymer binder and ultra fine RDX. For the inner porous structures of microcellular combustible objects, the cell sizes present a unimodal or bimodal distribution by adjusting the foaming conditions. Closed bomb test is to investigate the influence of both porous structure style and RDX content on burning behavior. The sample with bimodal distribution of cell sizes burns faster than that with unimodal distribution, and the concentration of RDX can influence the burning characteristics in a positive manner. In addition, the translation of laminar burning to convective burning is determined by burning rate versus pressure curves of samples at two different loading densities, and the resulting transition pressure is 30 MPa. Moreover, the samples with bigger sample size present higher burning rate, resulting in providing deeper convective depth. Dynamic vivacity of samples is also studied. The results show that the vivacity increases with RDX content and varies with inner structure.     

Laval型雾化器气液流动特性研究

喷嘴出口气流速度和气液质量流率比是影响液态金属雾化效果的两个主要因素。为改善雾化效果,对现有环缝型雾化器进行改进,出口采用Laval型。建立了喷嘴出口速度、气体与金属质量流率的表达式,获得稳定气、液质量流率比的坩埚背压与金属液面高度的关系。通过实验方法建立了采用限制型Laval喷嘴导流管出口负压值与雾化压力之间的关系。     

Formation of explosively formed penetrator with fins and its flight characteristics

The ultimate goal of weapon system employing an explosively formed penetrator （EFP） is to defeat a target at the longest standoff. In order to do this, an EFP must be aerodynamically stable so as to strike the target at a small angle of obliquity, and the decay velocity per meter of EFP must be smaller at extended standoff. As the angle of attack increases, the penetration ability of EFP greatly reduces. The fins improve the EFP aeroballistic characteristics and decrease the flight drag of EFP as well, EFP with fins formed by three-point initiation is presented. The for- mation of EFP with fins is studied by LS-DYNA, and the aeroballistics is studied through experiment. The experimental results show that the decay velocity per meter of EFP with fins is much smaller than that of normal EFP, and the attitude angle steadily decreases.     

Cu-Cr-RE合金的冷变形及时效特性研究

针对纯铜材料具有高的导电性但强度非常低的不足,通过添加Cr、稀土Y等合金化元素,以及形变强化和时效处理等手段制备Cu-Cr-RE合金,以期达到提高铜基合金的强度而电导率无明显下降的目的。     

多孔硅/高氯酸钠复合材料合成与爆炸特性研究

采用电化学阳极氧化法制备多孔硅,考察不同阳极氧化条件下多孔硅孔隙率及膜厚变化规律,分析阳极氧化条件、高氯酸钠溶液浓度及多孔硅贮存方法等对多孔硅/高氯酸钠复合材料爆炸特性的影响。结果表明,多孔硅孔隙率随阳极氧化电流密度增加而增大,当电流密度达到50mA.cm-2时趋于稳定,当氢氟酸浓度增加时多孔硅孔隙率反而减小,而阳极氧化时间延长时多孔硅孔隙率呈先增加后减小现象,且氧化时间为30min时孔隙率最大;多孔硅膜厚随时间增加而增大,其生长速度为2μm.min-1左右;当新鲜多孔硅形成后,其表面出现微裂缝,内部含大量长度为40μm,宽度为2～3μm硅柱;当新鲜或乙醇贮存7天内的多孔硅浸入浓度不小于0.1g.mL-1NaClO4甲醇溶液后,形成的多孔硅/高氯酸钠复合材料能够发生爆炸。