具有梯度结构表层301不锈钢的压缩性能

利用表面机械研磨处理技术,在301奥氏体不锈钢中得到晶粒尺度呈梯度分布的变形表层,进行了压缩试验和微观组织观察。结果表明,变形表层中晶粒可细化至100nm。相比原始态的屈服强度236MPa,具有变形梯度表层后屈服强度增加到436MPa,变形后的加工硬化指数为0.31,经400和700℃的退火后分别增加到0.32和0.35。另外,随着应变速率的增加,流变应力增大而加工硬化能力降低.

利用Cyanex 301萃取体系制备纳米硫化物的研究

溶剂萃取由于具有处理量大、操作简单、易于连续化等优点，被广泛应用于湿法冶金工业。而溶剂萃取过程通常都伴随着有机相微乳体系的形成、变化、甚至完全破乳的过程以及萃合物分子聚集状态的不断变化，因此可以认为，液－液萃取体系提供了一系列可调控的微乳体系。相对于液液萃取在金属分离方面的广泛应用，液液萃取过程中形成的微乳体系在材料制备方面的应用研究还处于起始阶段。本论文在广泛调研文献资料的基础上，开展了利用硫代有机膦萃取剂Cyanex 301萃取体系制备纳米硫化物的研究，取得了一些有意义的结果。该工作的开展将对促进溶剂萃取分离与纳米材料制备一体化研究起到一定的作用，并为寻找简便易行且适用于大规模生产的纳米材料制备新方法提供思路。主要内容如下： 1. 通过两相热法，利用Cyanex 301－AgNO3两相萃取体系制备了尺寸均匀、分散性好的Ag2S纳米粒子。并且发现了与通常纳米材料制备过程不一样的现象，即Ag2S产物的粒径随着反应温度的升高逐渐增大，这与通常观察到的产物颗粒随反应温度升高而变小的现象完全不同。通过红外谱图分析，确定了反应机理，并提出了影响产物粒径的可能机制，认为产物粒径的变化是Cyanex 301作为硫源与作为表面修饰剂相互竞争的结果。 2. 通过两步法合成了四面体、类六角锥和六角片型的Ag2S/CdS纳米复合材料。Ag2S纳米粒子在产物的形成中起到了晶种与模板导向作用，溶剂对产物的形貌也起到诱导作用。 3. 利用两相热法，一步合成了CuS微米花和微米球自组装结构，产物的形貌随水相金属离子浓度的改变而发生变化。

Experimental Study Of Vortex-Induced Vibrations Of A Pipeline Near An Erodible Sandy Seabed

Based on similarity analyses, a series of experiments have been conducted with a newly established hydro-elastic facility to investigate the transverse vortex-induced vibrations (VIVs) of a submarine pipeline near an erodible sandy seabed under the influence of ocean currents. Typical characteristics of coupling processes between pipe vibration and soil scour in the currents have been summarized for Case 1: pipe is laid above seabed and Case 11: pipe is partially embedded in seabed on the basis of the experimental observations. Pipe vibration and the corresponding local scour are usually two coupled physical processes leading to an equilibrium state. The influence of initial gap-to-diameter ratio (e(0)/D) on the interaction between pipe vibration and local scour has been studied. Experimental results show that the critical values of V-r for the initiation of VIVs of the pipe near an erodible sand bed get bigger with decreasing initial gap-to-diameter ratio within the examined range of e(0)/D (-0.25 < e(0)/D < 0.75). The comparison of the pipe vibrations near an erodible soil with those near a rigid boundary and under wall-free conditions indicates that the vibration amplitudes of the pipe near an erodible sand bed are close to the curve fit under wall-free conditions; nevertheless, for the same stability parameter, the maximum amplitudes for the VIV coupled with local scour increase with the increase of initial gap-to-diameter ratio. (c) 2007 Elsevier Ltd. All rights reserved.

On the formation of well-aligned ZnO nanowall networks by catalyst-free thermal evaporation method

Two-dimensional ZnO nanowall networks were grown on ZnO-coated silicon by thermal evaporation at low temperature without catalysts or additives. All of the results from scanning electronic spectroscope, X-ray diffraction and Raman scattering confirmed that the ZnO nanowalls were vertically aligned and c-axis oriented. The room-temperature photoluminescence spectra showed a dominated UV peak at 378 nm, and a much suppressed orange emission centered at similar to 590 nm. This demonstrates fairly good crystal quality and optical properties of the product. A possible three-step, zinc vapor-controlled process was proposed to explain the growth of well-aligned ZnO nanowall networks. The pre-coated ZnO template layer plays a key role during the synthesis process, which guides the growth direction of the synthesized products. (C) 2007 Elsevier B.V. All rights reserved.

盲肠回流的水流运动特性

本文在总结和分析现有研究成果的基础上，系统地论述了盲肠回流的形成原因和运动机理。描述了盲肠回流运动系统的物理模式。根据水槽模型试验结果，对回流的流速分布特性、水面形态、以及影响回流运动强度的因素等进行了分析，并近似求解了盲肠回流的平面流速场。

流速对高气压电激励CO_2激光器输出功率的影响

<正> 过去我们研究了运转压力为20Torr时,较大流速(20～340m/s)对激光器性能的影响,也探讨了固定流速为70m/s时,运转压力为40Torr～2atm范围内高压CW CO_2激光器特性。本文将进一步在高压(40～760Torr)和更大的流速范围(30～340m/s)内研究流速和气压对CO_2激光器特性的综合影响,以期探索发挥高气压器件的潜力。 所考虑的装置见图1。计算的模型和方程与[1]同。假定电子密度n_e在正柱区内沿x方向均匀分布,将一维理想气体的守恒方程和三振型系统的弛豫方程联立求解,在满足一定的稳

平板集热器铁管板式集热板的最佳化

本文利用平板集热器管板式集热板的最佳化数学模型,计算得到了我国目前应用较广泛的铁管板式集热板的最佳化参数——在最小成本/效率参数时的最佳管间距、最佳板厚以及最佳管径。

非线性流动稳定性理论

<正> 流体的湍流运动普遍存在于大气、海洋、飞行器周围、推进装置和流体机械中,探讨湍流形成的条件和过程是流动稳定性理论的研究对象。 早在1843年,Stokes就预见到流体状态转捩的原因是失稳。整整100年前(1883年),Reynolds让液体流入不同口径的圆管,并在对称轴上注入一股纤细的颜色水,以便明显、敏感地观察到湍流的发生。他发现: (1)流速较低时,可以看到层次分明的层流,流速增加到一定程度后,就转变成高度无序的湍流状态;

Air flow over a mountain and the convective boundary-layer

In this paper, the analytical model coupling the convective boundary layer (CBL) with the free atmosphere developed by Qi and Fu (1992) is improved. And by this improved model, the interaction between airflow over a mountain and the CBL is further discussed. The conclusions demonstrate: (1) The perturbation potential temperatures in the free atmosphere can counteract the effect of orographic thermal forcing through entraining and mixing in the CBL. If u(M)BAR > u(F)BAR, the feedback of the perturbation potential temperatures in the free atmosphere is more important than orographic thermal forcing, which promotes the effect of interfacial waves. If u(M)BAR < u(F)BAR, orographic thermal forcing is more important, which makes the interfacial height and the topographic height identical in phase, and the horizontal speeds are a maximum at the top of the mountain. (2) The internal gravity waves propagating vertically in the free atmosphere cause a strong downslope wind to become established above the lee slope in the CBL and result in the hydraulic jump at the top of the CBL. (3) With the CBL deepening, the interfacial gravity waves induced by the potential temperature jump at the top of the CBL cause the airflow in the CBL to be subcritical.

The asymptotic near-tip solution for mode-iii crack in steady growth in power hardening media

Two local solutions, one perpendicular and one parallel to the direction of solar gravitational field, are discussed. The influence of gravity on the gas-dynamical process driven by the piston is discussed in terms of characteristic theory, and the flow field is given quantitatively. For a typical piston trajectory similar to the one for an eruptive prominence, the velocity of the shock front which locates ahead the transient front is nearly constant or slightly accelerated, and the width of the compressed flow region may be kept nearly constant or increased linearly, depending on the velocity distribution of the piston. Based on these results, the major features of the transient may be explained. Some of the fine structure of the transient is also shown, which may be compared in detail with observations.

化学反应和球面聚心爆轰波的相互作用

考察球面爆轰波聚心传播过程中，波阵面附近压力和温度不断升高引起化学反应进程的改变；对比氢氧可燃气体与氮气的数值模拟结果，分析化学反应对波面温度和压力的影响，从而考察Zeldovich理论预测聚心爆轰波后参数的精确性．数值结果表明，爆轰波聚心传播初期，放热的燃烧反应对波后热力学参数起主导作用；传播后期，波阵面趋近于对称中心时，吸热的气体解离反应变得非常活跃，解离反应对后期的汇聚压力影响不大，但会在很大程度上限制汇聚温度的升高．

Adiabatic shear localization: occurrence, theories, and applications