高雷诺数流动的控制方程体系和扩散抛物化Navier-Stokes方程组的意义和用途

在计算机发达的时代,高雷诺(Re)数绕流计算中有无必要使用简化NS方程组,本文讨论这个问题.主要内容如下:(1)高Re数绕流包含3种基本流动:所有方向对流占优流动、所有方向对流扩散竞争流动和部分方向对流占优部分方向对流扩散竞争流动(简称干扰剪切流动),3个基本流动的特征彼此不同且在流场中所占领域大小彼此相差悬殊,NS方程区域很小,它们的最简单控制方程组Euler、Navier-Stokes(NS)和扩散抛物化(DP)NS方程组的数学性质彼此不同,因此利用Euler-DPNS-NS方程组体系分析计算高Re数绕流流动就是一个合乎逻辑的选择,该法与利用单一NS方程组的常用方法可以彼此检验和补充.(2)流体之间以及流体与外界的动量、能量和质量交换,流态从层流到湍流的演化主要发生在干扰剪切流动中,干扰剪切流及其最简单控制方程--DPNS方程组具有基础意义;DPNS方程组笔者在1967年已提出.(3)诸简化NS方程组:DPNS、抛物化(P)NS、薄层(TL)NS、黏性层(VL)NS方程组的发展、相互关系,它们的历史贡献和今后的用途;它们的数学性质均为扩散抛物型,但它们包含的黏性项彼此有所不同;从流体力学角度来看,它们中只有DPNS方程组能够准确描述干扰剪切流动.提出把诸简化NS方程组统一为DPNS方程组的建议.(4)干扰剪切流--DPNS方程组与无干扰剪切流--边界层方程组之间的关系以及进一步研究干扰剪切流的意义.

高效率,窄脉冲1198.5nm Ba(NO_3)_2喇曼激光器(英文)

利用1 064 nm的Nd∶YAG激光抽运振荡腔内的硝酸钡晶体,获得高效率、窄脉冲的喇曼激光输出.硝酸钡晶体由水溶液降温法生长,长度为48 mm.喇曼振荡腔由对抽运光、一阶、二阶斯托克斯光有不同反射率的双色平面镜构成.当抽运光功率达到4.5 W时,获得最高的一阶斯托克斯喇曼激光功率为1.48 W,相应的转换效率为32.9%,并测得斜率效率为40%.由于受激喇曼散射的作用,喇曼脉冲光由抽运脉冲光的19.8 ns压缩为2.4 ns,获得的喇曼激光脉冲波形具有的＂上升沿陡峭、下降沿缓慢＂的特性,对其形成过程作了

InAs/GaAs单量子点中电子/空穴自旋弛豫

利用分子束外延制备了三种类型量子点样品,它们分别是:未掺杂样品、n型Si调制掺杂样品和p型Be调制掺杂样品.在5 K温度下,采用共聚焦显微镜系统,测量了单量子点的光致发光谱和时间分辨光谱, 研究了单量子点中三种类型激子(本征激子、负电荷激子和正电荷激子)的电子/空穴自旋翻转时间.它们的自旋翻转时间常数分别为: 本征激子的自旋翻转时间约16 ns, 正电荷激子中电子的自旋翻转时间约2 ns, 负电荷激子中空穴的自旋翻转时间约50 ps.

~(209)Fr的能级结构研究

利用能量为 90— 1 0 5MeV的16 O束流 ,通过197Au( 16 O ,4n)反应研究了2 0 9　Fr的高自旋态能级结构 .进行了γ射线的激发函数、γ γ延迟符合及γ射线的角分布测量 .首次建立了由 2 1条γ射线构成的2 0 9Fr的能级纲图 ,其中包括一个半寿命为 ( 52± 2 0 )ns的同质异能态 .基于2 0 9Fr与2 0 8Rn低位能级结构的相似性 ,用一个h9/ 2 价质子与2 0 8Rn激发态的弱耦合解释了2 0 9Fr的低位能级结构 .

东北草甸棕壤的零电荷点和界面酸-碱反应特征平衡常数

分别采用电势滴定(Potentiometric titration)法,质量滴定(Mass titration)法和惰性电解质滴定(Inert electrolyte titra-tion)法测定了荷结构负电荷的东北草甸棕壤的零净电荷点(PZNC),研究表明荷结构负电荷的土壤依然存在与电解质浓度无关的零净电荷点,三种方法的实验结果分别为2.9,5.0和3.3.相比较而言,电势滴定法和惰性电解质滴定法的结果相近,而质量滴定法的结果偏高.对文献中推算表面质子活性位密度(Ns)的方法进行了改进,得到东北草甸棕壤样品的Ns为2.5 mmol·g-1.根据实验测定的pHPZNC,Ns和结构电荷密度(σst)值直接计算得出东北草甸棕壤样品的界面反应特征平衡常数即1-pK模型中的pK,2-pK模型中pKain1t和pKain2t,分别为3.37,2.42和4.32,与文献报道的沉积物和蒙脱土的值相吻合.

基于随机网络编码的无线广播重传方案及性能分析

针对自动最复重传(ARQ)机制在无线广播系统中吞吐量性能不佳的缺陷,提出一种基于随机网络编码的广播重传方案RNC-ARQ。对于广播节点,采用随机线性码对所有丢失包进行编码组合重传。对于接收节点,当接收的编码包累积到一定数量后可通过解码操作恢复出原始数据。该方案可有效减少重传次数,改善无线广播的吞吐量性能。基于Gilbert-Elliott模型描述的突发错误信道,建立了信道状态和节点接收处理流程合并的多状态马尔可夫模型,并以此为基础推导了RNC-ARQ方案的TQ吐量闭合解。最后,使用NS-2模拟器评估RNC-ARQ方案的性能,结果表明在突发差错信道下,基于随机网络编码重传方案的吞吐量优于传统的选择重传ARQ方案和基于异或编码的重传方案。

基于跨层的卫星网络协议研究

卫星网络的固有特性如大时延、高误码、链路不对称和资源匮乏等特点， 使得TCP/IP协议无法为卫星网络提供令人满意的服务，因此设计适应卫星网络的特点新型网络协议以是一个值得深入研究的问题。采用跨层设计思想可以减少层次网络的冗余性，实时获取网络状态信息，通过调整数据传输方式，使得网络具有自适应性，并能显著提高卫星网络的性能。本文提出了基于跨层的卫星网络协议SaclTCP，它针对TCP协议的拥塞控制策略提出改进：在物理层将链路有效带宽信息反馈给传输层，使传输层了解物理链路容量的大小，准确的设定拥塞窗口门限阈值；在数据链路层将链路丢包事件通知给传输层，使传输层对丢包原因做出正确的判断；在网络层对路由器缓冲队列进行管理，一方面以一定的概率发送显示拥塞通知，另一方面计算网络拥塞状况，传输层利用这些信息动态调节拥塞窗口的大小。最后，在NS-2环境下对SaclTCP仿真，并与传统TCP协议进行比较。实验结果表明，SaclTCP协议在传输性能上有大幅度提高，更适合卫星网络环境，同时也证明了基于跨层的卫星网络协议设计的正确性和可行性。

南黄海重磁资料处理与断裂系统研究

南黄海位于中国大陆和朝鲜半岛之间，北与北黄海相通，南与东海相连，是奠基于下扬子地台前震旦纪变质岩基底之上一个多旋回盆地的叠覆。 目前研究表明，南黄海兼跨中朝、扬子和华南3大构造单元，区域构造复杂，是我国近海唯一未获得工业性流油的海域，我国在该区与韩国尚存在海域及油气资源的划界争议问题。对南黄海开展研究，从开展理论研究、开发海洋资源、维护海洋权益等方面出发都有重大意义。由于我国在该区的勘探与研究成效不高，认识较浅，故应加大对该区的研究力度。 本文收集了南黄海重力与磁力资料，对这些资料进行了处理。通过对这些海洋重磁资料的常规处理，本文得到了该地区区域布格重力异常及磁异常的上下延拓图、导数异常图等常规成果图件，对研究区重磁异常进行了分区和特征解释；应用小波多尺度分解的方法对重磁数据进行了分析，并结合常规处理结果，对研究区的断裂系统进行了讨论；初步探讨了南黄海盆地的形成与演化。并获得如下几点结论： 1)研究区中断裂十分发育，优势走向为NE—NEE向，是太平洋板块挤压作用的结果，同时，研究区内不同方向（如NE、NW、EW和NS向等）的断裂相互交错，互有切割，有明显的多期活动的迹象； 2)证实了朝鲜半岛西缘断裂带的存在，其在靠近济州岛时表现的更为破碎；黄海中央断裂带为一条，走向为NNW，向南逐渐变为NW向延伸； 3)南黄海盆地是一个自晚元古代以来不断迁移叠合、并经多次改造而使原貌小完整的序列残留盆地，具有复杂的形成与演化过程。

THE CLEAVAGE REACTION OF THE MO-MO TRIPLE BOND - THE CRYSTAL-STRUCTURES OF MOLYBDENUM COMPLEXES [CPMO(CO)(2)(C(5)H(4)NS)], [CPMO(CO)(2)(C(9)H(6)NS)]O=PPH(3) AND [CPMO(CO)(2)(S(2)CNME(2)]

The reactions of [Cp2Mo2(CO)4] (1) with 2,2'-dipyridyl disulphide (C5H4NS-)2, 8,8'-diquinolyl disulphide (C9H6NS-)2 and tetramethyl thiuram disulphide (Me2NC(S)S-)2 in toluene solution resulted in the cleavage of the Mo-Mo triple bond to yield molybdenum complexes [CpMo(CO)2(C5H4NS)] (2), [CpMo(CO)2(C9H6NS)] (3) and [CpMo(CO)2(S2CNMe2)] (4), respectively. The molecular structures of 2, 3 . O=PPh3 and 4 were determined by X-ray diffraction studies. Crystals of 2 are monoclinic, space group P2(1)/n, with Z = 4, in a unit cell of dimensions a = 6.448(1), b = 12.616(2), c = 14.772(2) angstrom, beta = 92.85(1)-degrees. The structure was refined to R = 0.028 and R(w) = 0.039 for 1357 observed reflections. Crystals of 3 . O=PPh3 are triclinic, space group P1BAR, with Z = 2, in a unit cell of dimensions a = 11.351(3), b = 13.409(3), c = 9.895(2) angstrom, alpha = 94.59(2), beta = 90.35(2), gamma = 78.07(2)-degrees. The structure was refined to R = 0.033 and R(w) = 0.037 for 3260 observed reflections. Crystals of 4 are monoclinic, space group P2(1)/a and Z = 4 with a = 12.468(5), b = 7.637(2), c = 13.135(4) angstrom, beta = 96.62(3). The structure was refined to R = 0.032 and R(w) = 0.042 for 1698 observed reflections. Each of complexes 2-4 contains a cyclopentadienyl ligand, a cis pair of carbonyls and a chelate ligand (S,N donor or S,S donor). All the compounds have distorted square-pyramid structures.

磷酸盐激光玻璃聚（CH3）2Si（OC2H5）2防潮膜

以（CH3）2Si（OC2H5）2为前驱体，采用溶胶-凝胶与有机合成相结合的方法，制得稳定性良好的涂膜液。采用旋转涂膜法在掺钕磷酸盐激光玻璃棒端面涂制防潮膜，膜层固化后透过率达96．5％，获得的膜层表面粗糙度优良，均方根表面粗糙度（RMS）为1．659nm，平均粗糙度（RA）平均为1．321nm；在激光波长1053nm，脉冲宽度1 ns条件下膜层的激光破坏闽值可达10～14 J／cm^2。经过“神光Ⅱ”高功率激光器物理实验运行，膜层使用期为五年，并且已经在我国“神光Ⅲ”原型装置上试用。

Passive Q-switching of short-length Tm3+-doped silica fiber lasers by polycrystalline Cr2+:ZnSe microchips

We demonstrate passive Q-switching of short-length double-clad Tm3+-doped silica fiber lasers near 2 mu m pumped by a laser diode array (LDA) at 790 nm. Polycrystalline Cr2+:ZnSe microchips with thickness from 0.3 to 1 mm are adopted as the Q-switching elements. Pulse duration of 120 ns, pulse energy over 14 mu] and repetition rate of 53 kHz are obtained from a 5-cm long fiber laser. As high as 530 kHz repetition rate is achieved from a 50-cm long fiber laser at similar to 10-W pump power. The performance of the Q-switched fiber lasers as a function of fiber length is also analyzed. (c) 2008 Elsevier B.V. All rights reserved.

Investigation of damage threshold to TiO2 coatings at different laser wavelength and pulse duration

Laser-induced damages to TiO2 single layers and TiO2/SiO2 high reflectors at laser wavelength of 1064 nm, 800 run, 532 urn, and pulse width of 12 ns, 220 ps, 50 fs, 8 ns are investigated. All films are prepared by electron beam evaporation. The relations among microstructure, chemical composition, optical properties and laser-induced damage threshold (LIDT), have been researched. The dependence of damage mechanism on laser wavelength and pulse width is discussed. It is found that from 1064 nm to 532 nm, LIDT is mainly absorption related, which is determined by film's extinction coefficient and stoichiometric defects. The rapid decrease of LIDT at 800 nm is due to the pulse width factor. TiO2 coatings are mainly thermally by damaged at long pulse (tau >= 220 ps). The damage shows ablation feature at 50 fs. (C) 2007 Elsevier B.V. All rights reserved.

Influence of SiO2 additional layers on the laser induced damage threshold of Ta2O5 films

A series or Ta2O5 films with different SiO2 additional layers including overcoat, undercoat and interlayer was prepared by electron beam evaporation under the same deposition process. Absorption of samples was measured using the surface thermal lensing (STL) technique. The electric field distributions of the samples were theoretical predicted using thin film design software (TFCalc). The laser induced damage threshold (LIDT) was assessed using an Nd:YAG laser operating at 1064 nm with a pulse length of 12 ns. It was found that SiO2 additional layers resulted in a slight increase of the absorption, whereas they exerted little influence on the microdefects. The electric field distribution among the samples was unchanged by adding an SiO2 overcoat and undercoat, yet was changed by adding an interlayer. SiO2 undercoat. The interlayer improved the LIDT greatly, whereas the SiO2 overcoat had little effect on the LIDT. (C) 2007 Elsevier Ltd. All rights reserved.

High repetition rate Q-switched microchip Nd:YVO4 laser with pulse duration as short as 1.1 ns

We have demonstrated a compact and an efficient passively Q-switched microchip Nd:YVO4 laser by using a composite semiconductor absorber as well as an output coupler. The composite semiconductor absorber was composed of an LT (low-temperature grown) In0.25Ga0.75As absorber and a pure GaAs absorber. To our knowledge, it was the first demonstration of the special absorber for Q-switching operation of microchip lasers. Laser pulses with durations of 1.1 ns were generated with a 350 mu m thick laser crystal and the repetition rate of the pulses was as high as 4.6 MHz. The average output power was 120 mW at the pump power of 700 mW. Pulse duration can be varied from 1.1 to 15.7 ns by changing the cavity length from 0.45 to 5 mm. Pulses with duration of 1.67 and 2.41 ns were also obtained with a 0.7 mm, thick laser crystal and a 1 mm thick laser crystal, respectively. (C) 2007 Elsevier GmbH. All rights reserved.