脉冲电流处理过程中的相变和再结晶细化晶粒(英文)

在室温下对铸态TiAl合金和冷轧TA15合金进行高密度脉冲电流处理。应用光学金相显微镜和透射电子显微镜研究脉冲电流处理前、后试样的显微组织。实验结果表明:通过脉冲电流处理可以细化铸态TiAl基合金的晶粒,从约1000μm的原始粗大层片组织,经脉冲电流处理后可以得到尺寸为3050μm细小、均匀的晶粒。对于冷轧TA15合金,脉冲电流处理后发生了完全的再结晶,晶粒组织由原始的α板条晶粒转变为细小的α等轴晶粒。研究结果表明,脉冲电流处理是一种有效的细化晶粒方法;由于不需要热机处理所要求的挤压等变形工序和高温加热、真空保护等条件,简化了工艺过程。     

声光调QCO_2激光器的理论计算和实验研究

采用谐振腔内插入声光调制器的方法进行了小型CO2激光器的调Q实验,并根据影响激光器输出的诸多因素,利用调Q脉冲激光器速率方程对该激光器输出的主要技术参数进行了理论计算,据此提出了声光调QCO2激光器优化设计的途径和方法。设计制成的声光调QCO2激光器获得峰值功率超过4000 W,激光脉冲宽度为180 ns,与理论计算基本一致。激光器脉冲重复频率调节范围1 Hz~100 kHz。理论分析和实验结果均证明,调Q晶体中超声场的渡越时间并不会影响输出激光的脉冲宽度,因此无需在腔内插入光学透镜进行光束直径的压缩变换;渡越时间的影响只是体现在延长了激光脉冲的建立时间上;激光器的最佳工作频率在1 kHz左右,这与CO2分子0001能级大约1 ms的辐射寿命相匹配,当频率超过1 kHz时,激光的脉冲宽度随着频率的增加而开始加宽。激光器通过光栅选线的设计方式实现了9.2~10.8μm的全波段波长调谐,测得激光输出谱线超过60条。     

超光滑光学基底表面原子力显微镜测试方法

原子力显微镜(AFM)是评价亚纳米级表面粗糙度σRMS最主要的测试仪器,但其测试结果会因采样条件(采样间距、采样点数)及测量点位置变化而改变。以AFM测试超光滑光学基底随机表面为例,应用累积功率谱理论建立了确定合理采样条件的方法,避免了采样条件选取不当带来的数据丢失或冗余;通过全局优化选取测量点和局部优化选取测量点相结合,降低了样品表面区域性差异给测试结果带来的不确定性,并大大减少了获得可靠测试结果所需的测试量。上述工作为超光滑光学基底AFM测试提供了有效方案。     

Dynamic response of gravity dam model with crack and damage detection

Gravity dam is a typical structure that has been frequently used in the fields of water conservancy engineering, and the safety of the structure has received widespread attention recently. Due to earthquakes or other reasons, gravity dams normally have damage such as cracks in practical service. Damage in the structures can alter the structural dynamic behavior and seriously affect structural performance. Maintaining safety and integrity of the gravity dam structures requires a better understanding of dynam...     

Influence of orifice-to-wall distance on synthetic jet vortex ring simpinging on a fixed wall

Two-dimensional particle image velocimetry (PIV) is used to investigate the influence of the orifice-to-wall distance on synthetic jet vortex rings impinging on a fixed wall. Both evolutions of vortical structures and statistical characteristics of flow fields at different orifice-to-wall distances are presented. It is found that different orifice-to-wall distances have different effects in terms of the vortex strength and impinging speed when the vortex rings are approaching the wall. The secondary vortex ring can be observed within the shear layer only when the dimensionless orifice-to-wall distance is close to or less than the dimensionless stroke length. Consequently, an appropriate orifice-to-wall distance plays a vital role in the sense of impingement effect. The statistical analysis of the flow field indicates that a wall jet forms after impingement, while both the decay rate of the maximum radial velocity and the spreading rate of the half-width decrease with the increasing orifice-to-wall distance. The non-dimensional wall jet velocity profiles at different orifice-to-wall distances all exhibit self-similar behaviors, which is consistent with the theoretical solution of the laminar wall jet.     

Fold-Hopf bifurcation in a simplified four-neuron BAM (bidirectional associative memory) neural network with two delays

The bidirectional associative memory (BAM) neural network with four neurons and two delays is considered in the present paper.A linear stability analysis for the trivial equilibrium is firstly employed to provide a possible critical point at which a zero and a pair of pure imaginary eigenvalues occur in the corresponding characteristic equation.A fold-Hopf bifurcation is proved to happen at this critical point by the nonlinear analysis.The coupling strength and the delay are considered as bifurcation parame...     

Application of SSOR-PCGM with improved iteration format in FEM simulation of massive concrete

In this study, for the purpose of improving the efficiency and accuracy of numerical simulation of massive concrete, the symmetric successive over relaxation-preconditioned conjugate gradient method (SSOR-PCGM) with an improved iteration format was derived and applied to solution of large sparse symmetric positive definite linear equations in the computational process of the finite element analysis. A three-dimensional simulation program for massive concrete was developed based on SSOR-PCGM with an improved...     

抗弹陶瓷的特殊耗能机制研究

以刚玉系抗弹陶瓷为研究对象 ,测定其防护系数和相关性能 ,通过结构分析研究其抗弹机理 ,并提出陶瓷的特殊耗能机制 ,试图揭示陶瓷具有优良抗弹能力的本质     

武汉鹦鹉洲长江大桥项目总控信息系统设计研究

目前大型桥梁项目在建设过程中给项目管理带来严峻的挑战,本文以武汉鹦鹉洲长江大桥为背景,分析了大桥的管理难点,并针对大桥的相关特点提出了鹦鹉洲大桥项目总控信息系统的建设目标。文章最后论述了鹦鹉洲大桥项目管理信息系统的结构和功能以及在工程中的应用。     

抗Chalara elegans烤烟品系及其杂交后代的田间特性

对4个烤烟育种品系(WAC 119,WAC 120,WAC 121,WTN 120)与来自AC Gayed(WAC 119,WAC 120,WAC 121)或来自TN 90 (WTN 120)的抗Chalara elegans的N.debneyi-型品种及其杂交后代,在标准烤烟田间管理条件下,按照半双列杂交设计在3块随机选定的田间生长情况进行了研究。11个品系和Wi?lica品种作为参照品种用于比较以下选定的生长参数:叶片数、茎杆上3个部位(中下部叶、烟叶、顶芽)的叶片尺寸、植株高度和原烟产量参数(每单位面积产量、高等级烟叶百分比、一公顷烟草作物的收益)。该试验选择了受Chalara elegans病害风险最低的地点进行,以便于能够对所研究品系及其杂交后代不受病害影响的潜能做出评估。