Johnson-Cook材料模型参数的实验测定

介绍了一种通过Hopkinson拉伸实验、圆筒爆炸试验和计算机仿真来确定Johnson-Cook材料模型中相关常数的方法。

相变增韧陶瓷平面应变Ⅰ型定常扩展裂纹的渐近分析(Ⅱ)

本文采用一种考虑相交剪切变形的陶瓷材料本构关系，对平面应变Ⅰ型定常扩展裂纹尖端场进行渐近分析．给出了裂纹尖端附近环形域内的应力、速率分布以及应力奇异性指数．对不同材料参数下的变化规律进行了详细的分析和讨论．

Effects of temperature on the threshold of phosphorus for algal blooms

Algal blooms, worsening marine ecosystems and causing great economic loss, have been paid much attention to for a long time. Such environmental factors as light penetration, water temperature, and nutrient concentration are crucial in blooms processes. Among them, only nutrients can be controlled. Therefore, the threshold of nutrients for algal blooms is of great concern. To begin with, a dynamic eutrophication model has been constructed to simulate the algal growth and phosphorus cycling. The model encapsulates the essential biological processes of algal growth and decay, and phosphorus regeneration due to algal decay. The nutrient limitation is based upon commonly used Monod's kinetics. The effects of temperature and phosphorus limitation are particularly addressed. Then, we have endeavored to elucidate the threshold of phosphorus at different temperature for algal blooms. Based on the numerical simulation, the isoquant contours of change rate of alga as shown in the figure are obtained, which obviously demonstrate the threshold of nutrient at an arbitrary reasonable temperature. The larger the change rate is, the more rapidly the alga grows. If the phosphorus concentration at a given temperature remains larger than the threshold the algal biomass may increase monotonically, leading to the algal blooming. With the rising of temperature, the threshold is apparently reduced, which may explain why likely red tide disasters occur in a fine summer day. So, high temperature and sufficient phosphorus supply are the major factors which result in algal growth and blowout of red tide.

计算空气动力学

  《计算空气动力学》总结了多年来作者在计算空气动力学方面的主要研究工作．介绍了采用差分方法求解气体动力学方程，数值模拟航天飞行器的跨声速、超声速和高超声速绕流的研究工作．
    书中既给出了在实际工作中作者提出的计算方法，也给出了采用各种计算方法解决实际问题的实例．内容重点是解决实际问题，也简述了各种计算方法的理论基础，而且尽可能地反映了当前计算空气动力学的最新成果．
    《计算空气动力学》可供大专院校流体力学专业的本科生、研究生、教师和从事这方面研究工作的科学工作者参考．

甲型H1N1/2009 流感病毒的种属跨越机制

摘要在世界范围流行的甲型H1N1/2009 流感病毒具有下述3 个重要特征: 可寄生于人 体, 易感人群很多, 患者年龄偏低. 本研究确定了病毒蛋白中的一块关键区域. 该区域对病 毒所寄生的物种的种属范围起决定性作用, 并且是全球性流感病毒的一个标志性区域. 正是 该区域氨基酸的特性导致了上述3 个特点. 具体来说, 对宿主的免疫系统而言, 病毒蛋白质 结构的变化会形成新的标靶结构, 并且可以进一步导致宿主范围的变化. 基于多肽链发生致 病性结构转换的概率, 本研究确定了甲型流感病毒中对控制宿主范围起决定性作用的氨基 酸的位置. 研究发现甲型H1N1/2009 流感病毒中处于这些位点的多肽链在本质上可以在寄 生于人的毒株中表达, 而之前仅在宿主为禽、猪的毒株中被发现. 其与另一氨基酸短串的协 同构象改变对于甲型H1N1/2009 流感病毒的种属跨越具有重要作用. 人体对这些关键位点 的免疫缺陷导致了甲型H1N1/2009 流感病毒宿主人群多和青年人易致病的特点.

Relativistic channel-coupling focusing enhanced nonlinear guiding of an intense laser beam in a plasma channel

We employ the variational method to study the optical guiding of an intense laser beam in a preformed plasma channel without using the weakly relativistic approximation. Apart from the dependence on the laser power and the nonlinear channel strength parameter, the beam focusing properties is shown also to be governed by the laser intensity. Relativistic channel-coupling focusing, arising from the coupling between relativistic self-focusing and linear channel focusing, can enhance relativistic self-focusing but its strength is weaker than that of linear channel focusing. (C) 2008 Elsevier B.V. All rights reserved.

A planar waveguide Nd : YAG laser using active Q-switching of a hybrid unstable resonator

A planar waveguide laser operating in a negative branch unstable resonator is Q-switched by an acoustooptic mod latorin anew configuration, providing effective, high-speed switching. The laser using a 200-mu m Nd:YAG core, face pumped by 10 laser diode bars, has produced 100-W output in a good beam quality at 100-kHz pulse rate, and 4.5 mJ at lower frequency with 15-ns pulse duration.

Infrared to visible upconversion fluorescence in Yb,Tm : YAG single crystal

Absorption spectrum from 400 to 2000 run and upconversion fluorescence spectra under 940 nm pumping of YAG single crystal codoped with 5 at.% Yb3+ and 4 at.% Tm3+ were studied at room temperature. The blue upconversion emission centered at 483 nm corresponds to the transition (1)G(4) -> H-3(6), the emission band around 646 nm corresponds to the transition (1)G(4) -> F-3(4) of Tm3+. Energy transfer from Yb3+ to Tm3+ is mainly nonradiative and the transfer efficiency was experimentally assessed. The line strengths, transition probabilities and radiative lifetimes of (1)G(4) level were calculated by using Judd-Ofelt theory. Gain coefficient calculated from spectra shows that the upconversion corresponding with transitions (1)G(4) -> H-3(6) in YAG doped with Yb3+ and Tm3+ is potentially useful for blue light Output. (c) 2006 Elsevier B.V. All rights reserved.

Sm:GdVO_4晶体的生长及光谱性能研究

应用中频感应提拉法生长出掺杂浓度为2%原子分数的Sm:GdVO4晶体,研究了室温下c轴方向Sm:GdVO4晶体的吸收和荧光光谱。通过J-O理论计算出强度参数(Ωt),同时计算了对应于4G5/2能级的自发跃迁几率、荧光分支比和辐射寿命。通过荧光光谱计算了对应于566、604和646nm三个发射峰对应的发射截面,结果表明,Sm:GdVO4在604nm的发射截面最大,是掺Sm:YAP在607nm处发射截面的4.4倍。

Crystal growth and spectral properties of Sm:GdVO4

The 2 at.% Sm:GdVO4 crystal was grown by the Czochralski method. The segregation coefficient of Sm3+ ion in this crystal is 0.98. The crystal structure of the Sm:GdVO4 crystal was determined by X-ray diffraction analysis. Judd-Ofelt theory was used to calculate the intensity parameters (Omega(i)), the spontaneous emission probability, the luminary branching ratio and the radiative lifetime of the state (4)G(5/2). The stimulated emission cross-sections at 567, 604 and 646 nm are calculated to be 5.92 x 10(-21), 7.62 x 10(-21) and 5.88 x 10(-21) cm(2), respectively. The emission cross-section at 604 nm is 4.4 times lager than that in Sm: YAP at 607 nm. (C) 2007 Elsevier B.V. All rights reserved.