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。     

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。     

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。     

不锈钢与碳钢在液固两相流中冲刷腐蚀特性的研究

研究了不锈钢与碳钢在液固两相流中的冲刷腐蚀特性和冲刷腐蚀交互作用。实验表明 :( 1)提高冲刷速度和浆料温度都大大加剧了材料的损伤和破坏 ,T8钢冲刷腐蚀失重率远大于 18- 8不锈钢。两者均在冲击角度为 4 5°时出现极大值 ,表明冲击角度在 4 5°时 ,对材料产生的损伤强度最大 ,因此在设计管道时应尽量避免 4 5°冲击角结构 ;( 2 ) 18- 8不锈钢以冲刷失重为主 ,T8钢以腐蚀失重为主 ,两者的冲刷腐蚀交互作用失重率占其总失重率的 6 0 %以上 ,表明耐蚀不耐磨的 18- 8不锈钢和耐磨不耐蚀的T8钢在冲刷腐蚀工况中均难以胜任 ;( 3)T8钢的冲刷腐蚀失重率和交互作用失重率均是 18- 8不锈钢的 6倍以上 ,表明在液固两相流冲刷腐蚀工况中 ,材料必须首先具有一定的耐蚀性 ,然后再考虑提高材料的硬度和耐磨性 ,这样才能有效地提高材料的耐冲刷腐蚀性能     

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.     

注射成形钨合金弹芯材料的性能与组织特征

研究开发低成本钨合金的近净成形技术是钨合金的一个重要发展方向。针对直径较大(Φ20～25mm)的钨棒弹芯和钨环散弹弹芯材料的注射成形,对粘结剂进行一系列的改进。采用一种粘度适中、流动性好、流变稳定性好的油+少量蜡组成的新型半固态塑料体系粘结剂,和多组元低分子混合溶剂快速脱除注射坯中60％以上的粘结剂,再采用热脱脂脱除其余的粘结剂,然后烧结,制备了性能很高的钨环和钨棒弹芯材料。研究了弹芯材料的性能和组织特征。结果表明,由弹芯加工成的冲击试样断口和拉伸试样断口形貌呈显著的钨晶粒穿晶解理断裂。采用注射成形工艺可以得到具有较高综合力学性能的钨合金弹芯。对于大截面的钨棒弹芯,弹芯材料的拉伸性能、延伸率和冲击性能分别达到σ_b=965MPa,δ=23％,A_k=54.4J/cm~2。