Detection and Characterization of Long-Pulse Low-Velocity Impact Damage in Plastic Bonded Explosives

Damage not only degrades the mechanical properties of explosives, but also influences the shock sensitivity, combustion and even detonation behavior of explosives. The study of impact damage is crucial in the vulnerability evaluation of explosives. A long-pulse low-velocity gas gun with a gas buffer was developed and used to induce impact damage in a hot pressed plastic bonded explosive. Various methods were used to detect and characterize the impact damage of the explosive. The microstructure was examined by use of polarized light microscopy. Fractal analysis of the micrographs was conducted by use of box counting method. The correlation between the fractal dimensions and microstructures was analyzed. Ultrasonic testing was conducted using a pulse through-transmission method to obtain the ultrasonic velocity and ultrasonic attenuation. Spectra analyses were carried out for recorded ultrasonic signals using fast Fourier transform. The correlations between the impact damage and ultrasonic parameters including ultrasonic velocities and attenuation coefficients were also analyzed. To quantitatively assess the impact induced explosive crystal fractures, particle size distribution analyses of explosive crystals were conducted by using a thorough etching technique, in which the explosives samples were soaked in a solution for enough time that the binder was totally removed. Impact induces a large extent of explosive crystal fractures and a large number of microcracks. The ultrasonic velocity decreases and attenuation coefficients increase with the presence of impact damage. Both ultrasonic parameters and fractal dimension can be used to quantitatively assess the impact damage of plastic bonded explosives.

Numerical Simulation of Pulsed Liquid Fluidized Bed and Its Experimental Validation

The pulsed liquid fluidized bed was studied using numerical simulation and experimental methods, The area-averaged two-fluid model (TFM) was used to simulate the pulsed fluidization. The bed expansion and collapse processes were simulated first and the phenomena obtained from the calculation were consistent with our previous experiments and observations. In the pulsed fluidization, the variation of bed height, the variations of particle velocity and concentration distribution were obtained and analyzed. Experiments were carried out to validate the simulation results. The pressure variation with time at different locations was measured using pressure transducers and compared with the simulated results. The variations of bed height and particle concentration distribution were recorded using a digital video camera recorder. The results were consistent with the simulation results as a whole.

李敏华院士传略

<正>李敏华,女,1917年11月2日出生于江苏省吴县(苏州市)的职员家庭。母亲思想比较开明,毕业于杭州女子师范中学,支持李敏华姐妹自小读书。1925年,李敏华刚到上海不久便发生了"五卅惨案",上海滩上,英国巡捕随便打杀中国人,外国军舰在黄浦江上耀武扬威的种种事实,给少年的李敏华留下深刻的印象。1931年,日本侵略军侵略我国东北三省。李

Self-compression of femtosecond pulses in argon with a power close to the self-focusing threshold

Self-compression of femtosecond pulses in noble gases with an input power close to the self-focusing threshold has been investigated experimentally and theoretically. It is demonstrated that either multiphoton ionization (MPI) or space time focusing and self-steepening effects can induce pulse shortening, but they predominate at different beam intensities during the propagation. The latter effects play a key role in the final pulse self-compression. By choosing an appropriate focusing parameter, action distance of the space time focusing and self-steepening effects can be lengthened, which can promote a shock pulse structure with a duration as short as two optical cycles. It is also found that, for our calculation cases in which an input pulse power is close to the self-focusing threshold, either group velocity dispersion (GVD) or multiphoton absorption (MPA) has a negligible influence on pulse characteristics in the propagation process.

光学领域里的一对奇葩——介绍2005年诺贝尔物理学奖

2005年诺贝尔物理学奖授于了光学研究领域里的两项原创性工作：1963年美国物理学家罗伊·格劳伯（R．J．Glauber 1925～）提出的“相干性量子理论”，以及1983年美国物理学家约翰·霍尔（J．L．Hall．1934～）和德国物理学家特奥多尔·亨施（T．W．Hansch．1941～）利用激光的特性对精确测量技术所作的发展。近些年来诺贝尔物理学奖频频惠顾光学研究领域。如2001年诺贝尔物理学奖授予了从事玻色一爱因斯坦凝聚的相关研究、1997年诺贝尔物理学奖授予华裔科学家朱棣文从事的激光冷却和俘获原子

Grating-encoded multichannel photorefractive incoherent-to-coherent optical conversion

A dynamic multichannel incoherent-to-coherent optical converter based on the photorefractive effect of SBN:Ce is described. A number of grating-encoded input images, illuminated by incoherent light, are projected onto the crystal to yield photoinduced phase gratings. Coherent positive replicas of these images are simultaneously reconstructed by a coherent read beam. A simple theoretical description of this converter and corresponding experimental results are presented.

铒镱共掺磷酸盐玻璃的激光性质

制备了镱铒共掺的磷酸盐玻璃并研究了室温下LD泵浦的连续激光输出性质。在泵浦功率为496mW时实现了最大输出功率77mW。讨论了在不同玻璃样品厚度和谐振腔长度时的斜率效率的变化以及在不同玻璃样品厚度，泵浦功率和谐振腔长度时的不同激光模式竞争的动力学行为。结果表明：激光光谱受到光学增益和光学损耗相对大小的限制。

飞秒激光辐照ZnO晶体

利用飞秒激光对ZnO晶体进行辐照，对辐照前后的晶体样品进行发光光谱及拉曼光谱检测。辐照后发光光谱的某些发光峰强度有明显增强，但未产生新的发光峰，表明没有新的缺陷结构产生，但晶体内锌空位、间隙位锌、间隙位缺陷浓度增加。拉曼光谱结果表明，辐照后ZnO晶体未产生相变，但随着辐照激光功率的增大，拉曼峰327 cm-1，437 cm-1强度明显减弱，表明在飞秒激光辐照作用下氧化锌的结晶程度下降。但574 cm-1峰值却随着辐照功率的增大而变大，分析表明该拉曼峰很可能是由于晶体内间隙位缺陷所致。同时实验过程中观察到飞

鳞毛蕨科、叉蕨科和藤蕨科的分子系统学研究

利用叶绿体rbcL和atpB基因对鳞毛蕨科、叉蕨科和藤蕨科进行了系统发育重建。对鳞毛蕨科的范畴和科下划分进行了重点研究，同时基于叶绿体rps4-trnS和trnL-F序列对该科三个东亚特有属（玉龙蕨属、柳叶蕨属和鞭叶蕨属）的分类等级进行了研究，基于rbcL、atpB和accD基因重新讨论了拟贯众属的系统位置。主要内容包括： 1.鳞毛蕨科的界定及三个东亚特有属的系统位置 利用rbcL和atpB基因，探讨了鳞毛蕨类及其近缘类群的系统发育关系。取样包括了鳞毛蕨类所有主要的分类群，尤其是增加了中国和东亚地区的类群代表。两个基因片段的联合分析较好地解决了鳞毛蕨类及其近缘类群的系统发育关系。研究结果显示广义鳞毛蕨科是个多系类群，传统上置于鳞毛蕨科中的蹄盖蕨类athyrioid、球子蕨类onocleoid和叉蕨类植物tectarioid均应该从鳞毛蕨科分出而独立成科。我们的研究结果支持Smith et al.（2006）对鳞毛蕨科的重新界定，但被作者暂时置于鳞毛蕨科的三个属：大膜盖蕨属Leucostegia、肿足蕨属Hypodematium和Didymochlaena应该从鳞毛蕨科分立出去;红腺蕨属Diacalpe、毛枝蕨属Leptorumohra和黔蕨属Phanerophlebiopsis应该作为鳞毛蕨科的成员，同时被Smith et al.（2006）保留在叉蕨科的黄腺羽蕨属Pleocnemia也应该作为鳞毛蕨科成员。鳞毛蕨科下分为四个主要的分支：鳞毛蕨支dryopteroids、耳蕨支polystichoids、肋毛蕨支ctenitoids和舌蕨支elaphoglossoids。鳞毛蕨支和耳蕨支互为姐妹群，舌蕨支是其他三个分支的姐妹群。 玉龙蕨属Sorolepidium、柳叶蕨属Cyrtogonellum和鞭叶蕨属Cyrtomidictyum是鳞毛蕨科中的三个东亚特有属，这三个特有属的分类等级和系统位置在不同的分类系统中存在争议。本文对rbcL基因进行分析并结合孢子扫描电镜观察，不支持玉龙蕨属成为一个独立的属，而应该作为耳蕨属的异名。利用rbcL、atpB、trnL-F和rps4-trnS四个DNA片段对柳叶蕨属和鞭叶蕨属进行的系统学分析，支持鞭叶蕨属作为一个独立的属，并且位于整个耳蕨类植物的基部位置。柳叶蕨属同耳蕨属近缘，尤其是同耳蕨属的细裂耳蕨组Sphaenopolystichum、半开羽耳蕨组Haplopolystichum和戟叶耳蕨组Crucifilix关系较近。但是柳叶蕨属的分类等级以及与耳蕨属的属间界限尚需要进一步研究。 2.叉蕨科的分子系统学研究 对rbcL和atpB两个基因片段的单独和联合分析均表明，秦仁昌定义的叉蕨科Tectariaceae不是一个自然的单系类群。在系统发育树上，肋毛蕨属Ctenitis、轴鳞蕨属Dryopsis、节毛蕨属Lastreopsis和黄腺羽蕨属Pleocnemia与鳞毛蕨科聚在一起构成一个强支持的分支。当把上述四个属排除以后，叉蕨属Tectaria、轴鳞蕨属Ctenitopsis、地耳蕨属Quercifilix、牙蕨属Pteridrys和沙皮蕨属Hemigramma形成一个单系类群，并得到很好的支持，该单系类群同条蕨科、骨碎补科和水龙骨科形成姐妹群关系。该单系类群同目前Smith et al.（2006）对叉蕨科的定义一致。在rbcL基因单独分析中，爬树蕨属Arthropteris同叉蕨属－沙皮蕨属聚在一起，但支持率较低。 3.藤蕨科的分子系统学研究及拟贯众属的系统位置 根据对薄囊蕨类114个分类群的rbcL基因和30个代表类群的rbcL、atpB和accD基因的系统发育分析，发现传统的藤蕨科Lomariopsidaceae不是单系类群，除了藤蕨属和Thysanosoria仍然为藤蕨科成员外，藤蕨科的主要成员（实蕨属Bolbitis、网藤蕨属Lomagramma、舌蕨属Elaphoglossum和Teratophyllum）同鳞毛蕨科植物聚在一起，因此应该被归并到鳞毛蕨科。根据Smith et al.（2006）对藤蕨科的最新定义，藤蕨科包括藤蕨属Lomariopsis、肾蕨属Nephrolepis等在内的4个属。但是本文的研究不支持把肾蕨属作为藤蕨科成员，而应该作为一个独立的分类单元，即成立肾蕨科更为合适。根据我们的分析，拟贯众属Cyclopeltis既不是鳞毛蕨科也不是叉蕨科成员，而与藤蕨属Lomariopsis聚成一个强支持的姐妹群。叶片奇数一回羽状、侧生羽片以关节着生于叶轴，叶脉游离等形态特征支持两者的近缘关系。