Numerical Investigation of Toroidal Shock Wave Focusing

In this paper,focusing of a toroidal shock wave propagating from a shock tube of an- nular cross-section into a cylindrical chamber was investigated numerically with the dispersion- controlled scheme. For CFD validation, the numerical code was rst applied to calculate both viscous and inviscid ows at a low Mach number of 1.5, which was compared with the experi- ment results and got better consistency. Then the validated code was used to calculate several cases for high Mach numbers. From the result, several major factors that in uent the ow, such as the Mach number and the viscosity, were analyzed detailedly and along with the high Mach number some unusual ow structure was observed and explained theoretically

稻属Oryza rufipogon和Oryza nivara的遗传多样性和居群分化研究

普通野生稻(Oryza rufipogon Griff.)和尼瓦拉野生稻(O. nivara Sharma et Shastry)是亚洲栽培稻的最近缘野生种，是亚洲栽培稻育种和遗传改良的重要基因库。由于人类的破坏、生境片段化及亚洲栽培稻的遗传渐渗等因素，这两种野生稻处于濒危状态而急需保护。本文用微卫星标记研究中国普通野生稻居群的遗传多样性和居群分化，用核基因序列研究了全分布区的普通野生稻和尼瓦拉野生稻的遗传变异及模式，同时发现了巴布亚新几内亚普通野生稻的特殊分子变异。主要结果如下： 取自中国普通野生稻四个主要分布区的12个天然居群，共237份个体材料，利用10对微卫星引物对遗传多样性进行比较研究。结果表明这些居群的遗传多样性处于中高水平，其中每个位点的等位基因数之在2至18之间不等，平均10.6个，多态位点比率P从最低40.0%最高100%，平均为83.3%。观察杂合度在 (HO) 0.163-0.550变化，平均为0.332, 期望杂合度(HE) 在0.164- 0.648，平均 0.413，从地区来看，广西居群的遗传多样性水平是最高的，其次是广东、海南居群，江西的最低。这些结果与以前用其他分子标记得到的结果基本一致。但是本研究得到的居群间遗传分化却相对较高，分化系数RST为 0.5199，θ为 0.491，这表明一半左右的遗传变异存在于居群之间。两两居群之间的分化系数(pairwise θ)与地理距离呈正相关(r = 0.464)，这表明中国普通野生稻居群之间的遗传分化是由于地理的隔离造成的。造成目前这种遗传结构和分化模式的主要原因在于普通野生稻生境的破坏和生境的片段化。 选择6个普通野生稻居群，5个尼瓦拉野生稻居群共11个居群105个个体材料为研究对象，取样覆盖两个野生稻的主要分布区，用核基因片段Lhs1研究了这两种野生稻的序列水平的变异，探讨了它们的遗传结构和基因流方向。结果表明，普通野生稻的核苷酸多样性，无论在居群还是物种水平上，均显著高于尼瓦拉野生稻的。在居群水平上，普通野生稻的核苷酸多样性(Hd = 0.712; θsil = 0.0017)是尼瓦拉野生稻的2-3倍(Hd = 0.306; θsil = 0.0005)。AMOVA的结果表明，尼瓦拉野生稻居群之间的遗传分化(78.2%)显著高于普通野生稻居群间的分化(52.3%)。造成这种不同层次的遗传多样性和完全不同的遗传分化模式的原因在于这两种野生稻差异显著的生活史和交配系统。普通野生稻是多年生、异交的野生种，营养与有性繁殖混合，尼瓦拉野生稻为一年生的自交种，靠种子繁殖。模拟分析表明，二者之间的基因流方向是单向的，明显是从自交的尼瓦拉野生稻到异交的普通野生稻，基因流在这两个野生 稻遗传多样性模式的形成上，扮演至关重要的角色。 对于稻属A基因组物种的进化和多样性来说, 巴布亚新几内亚(PNG)是个很重要的地方。我们用两个核基因和一个叶绿体基因，对巴布亚新几内亚的普通野生稻样品进行了序列分析，结果发现来自巴布亚新几内亚北部Sepik河谷的普通野生稻样品在核基因Os0053位点和叶绿体基因序列上与其他地区的样品有很大的差异。巴布亚新几内亚北部的普通野生稻在Os0053位点上杂合的，其中一条等位基因与普通野生稻基本一致，另一条等位基因则与A基因组的另一个物种O. meridionalis基本一致，证明巴布亚新几内亚北部的普通野生稻实际上是亚洲典型普通野生稻与澳洲野生稻O. meridionalis种间进行天然渐渗杂交的后代。这个结果从分子序列上验证了前人有关巴布亚新几内亚北部的普通野生稻是比较特殊的观点。

基于协议分析的IM阻断策略及算法分析

本文根据即时通讯（IM）的协议模型，在TCP层和即时通讯协议层分析了阻断即时通讯的可能性，分别提出了基于TCP层和即时通讯协议层的协议分析的阻断策略．在TCP层，通过插入FIN报文或RST报文，以关闭TCP连接（特别是与登录服务器的连接）；在即时通讯协议层，通过对相应字段的值进行设置，使客户端进入不活动状态．为使阻断策略能够有效地实施，本文也提出了一个消息驱动的实现算法．通过对Yahoo! Messenger的阻断实验，证明了本文提出的方法能够高效地完成阻断任务（平均数据包量不超过2．5个）．用统计分析的方法对它们的性能进行比较，结果表明各种方法的效率在不同的背景流量下没有显著的差异，通过消息驱动算法实现的基于协议分析的阻断策略，其工作效率不受背景流量的影响．另外，即时通讯数据的触发方式，使得发送的阻断包的数量与背景流量无关，也不对网络负载造成明显的影响．本文的工作为实施即时通讯的阻断提供了有效的解决方案．

Observation of N-Shaped Negative Differential Resistance in GaAs-Based Modulation-Doped Field Effect Transistor with InAs Quantum Dots

N-shaped negative differential resistance (NDR) with a high peak-to-valley ratio (PVR) is observed in a GaAs-based modulation-doped field effect transistor (MODFET) with InAs quantum dots (QDs) in the barrier layer (QDFET) compared with a GaAs MODFET. The NDR is explained as the real-space transfer (RST) of high-mobility electrons in a channel into nearby barrier layers with low mobility, and the PVR is enhanced dramatically upon inserting the QD layer. It is also revealed that the QD layer traps holes and acts as a positively charged nano-floating gate after a brief optical illumination, while it acts as a negatively charged nano-floating gate and depletes the adjacent channel when charged by the electrons. The NDR suggests a promising application in memory or high-speed logic devices for the QDFET structure.

粗枝云杉( Picea asperata Mast.)天然群体的遗传变异

西南地区在我国的经济发展和生态环境建设中占重要地位，但也是我国生态环境最脆弱的地区之一，生态系统退化，生态功能减弱，严重制约着西南林业的可持续经营与发展。本项目采用DNA 分子标记SSR 研究不同生境条件下粗枝云杉群体的遗传变异及其时空分布格局，考察遗传变异与复杂的山地生态环境间的潜在联系，系统地揭示粗枝云杉天然群体与环境系统相互作用的生态适应与分子进化机制。粗枝云杉适应性强，生长迅速，在植树造林和工业用材方面占有重要地位，研究成果可为中国西南部亚高山天然林的可持续经营及退化生态系统的恢复与重建提供理论依据和科学指导。主要研究结果如下： 1. SSR 位点变异丰富，等位基因频率的分布格局多样。7 个SSR 标记全是多态位点，每位点的等位基因数变化范围为13~24，平均为19.9 个。SSR 位点的等位基因片段长度范围变化较大。73.1%的等位基因变异遵循逐步突变模型(SSM)而发生1 个重复基元的变化，22.3%和4.6%的变异分别按两阶段突变模型(TMP)发生1 个重复基元以上的变化和在SSR 位点侧翼区发生1 个碱基变化的插入-删除事件。 2. 粗枝云杉拥有中等偏高水平的遗传多样性和相对大的群体间遗传分化。通过分析代表10 个群体的250 个个体在7 个SSR位点的变化，调查了源自中国西南山区的粗枝云杉的微卫星变异。相当高的遗传多样性和强烈的群体分化发生在粗枝云杉中， 其群体平均Nei's 期望杂合度为0.707 ， 群体间遗传距离为0.121~0.224(FST)和0.100~0.537(RST)。然而，群体间遗传距离与地理距离之间无相关性，从而排除了简单的距离分离模式并暗示迁移不是影响粗枝云杉遗传变异格局的主要因素。事实上，使用私有等位基因估算的基因流数量非常低，仅等于0.753。等位基因置换检验(Allele permutation tests)揭示逐步突变及遗传漂变都对群体间分化有贡献。另外，在多数位点检测到显著的群体间遗传差异，这个结果说明自然选择，假设通过环境压力，是引起粗枝云杉微地理分化的主要因素之一。根据SSR基因型，250 个粗枝云杉个体的70%被正确地归类入其各自的来源群体，结果表明微卫星(SSR)对区分来自中国不同生态地理位点的粗枝云杉基因型是有效的。 3. 在SSR、RAPD 和AFLP 位点，显著的群体间遗传结构被发现的，但三种标记间遗传分化程度和群体遗传关系有差异。利用来自10 个群体的247 个个体，我们报告了关于样本粗枝云杉群体间遗传关系的总体看法。根据各自对评价遗传关系的信息能力和适用性，SSR、RAPD 和AFLP 标记被选用，三种技术非常有效地区别这些基因型。使用的SSR、RAPD 和AFLP 标记分别估计平均Dice 相似性系数。Mantel 检验产生显著但相对低的共表型适合度(RAPD = 0.63£AFLP = 0.60和SSR = 0.75)。比较三种标记系统，RAPD 和AFLP 共表型指数相对高地相关(r =0.59)，而RAPD 和SSR 及SSR 和AFLP 之间的相关系数分别是0.53 和0.35。所有系统树，包括不同标记资料结合获得的系统树，反映了多数群体依据它们的地理条件而成某种特定关系。结果暗示单个或结合标记系统能用来深入洞察粗枝云杉遗传研究，并且不同标记系统合并资料能提供更可靠的信息。 Southwestern region plays an important role in economic developmentand ecological construction in China. Yet, it is also one of the weak regionsof ecological environment in China with degraded ecosystem and imperfectfunction, which restricts the sustaining management and development ofsouthwestern forestry. The genetic variation and spatial distribution patternof P. asperata populations originating from different habitats wereinvestigated using SSR molecular markers in this study. The correlationsbetween genetic variation and ecological and environmental conditionswere detected, and the interaction between P. asperata populations andenvironmental system and the mechanism of ecological adaption -molecular evolution were revealed. Given the significant ecological andeconomic roles of the fast-growing and wide-adaptive species in reforestation and production of pulp wood and timber, the study couldprovide a strong theoretical evidence and scientific direction for thesustaining management of subalpine natural forest, and the afforestationand rehabilitation of degraded ecosystem. The results are as follows: 1. The genetic variation at SSR loci was abundant and the distributionof allelic frequencies was uneven. All seven loci were polymorphic, and thenumber of alleles per locus varied from 13 to 24 with a mean valueequaling 19.9. The allele sizes at SSR loci were found to vary widely.73.1% of allelic variation followed stepwise mutation model (SSM) whichresults increase or decrease by one repeat type, and 22.3% and 4.6% wereresulted from two-phase mutation model (TMP) with allele size varying bymore than one repeat type and from insertion-deletion events in theflanking regions at SSR loci with a single basepair changing, respectively. 2. P. asperata possessed a moderate to high level of genetic diversityand considerable genetic differentiation. Microsatellite variation of P.asperata. originating from the mountains of southwestern China wasinvestigated by analyzing variation at seven SSR loci in 250 individualsrepresenting ten populations. A fair degree of genetic diversity and strongpopulation subdivision occurred with the mean gene diversity (H) of 0.707,and genetic distances among populations varying between 0.121 and 0.224(FST) and between 0.100 and 0.537 (RST). However, inter-populationgenetic distances showed no correlation with geographic distances between the population sites. This ruled out a simple isolation by distance modeland suggested that migration does not have a great impact. In fact, theamount of gene flow, detected using private alleles, was very low, equalingonly 0.753. Allele permutation tests revealed that stepwise-like mutations,coupled with genetic drift, could contribute to population differentiation.Moreover, significant genetic differences between populations weredetected at most loci. The results indicate that natural selection, presumablythrough environmental stress, may be one of the main factors causingmicro-geographical differentiation in the genetic structure of P. asperata.Based on SSR genotypes, 70% of the 250 individuals were correctlyclassified into their sites of origin. This suggests that microsatellites (SSRs) are effective in distinguishing genotypes of P. asperata originating fromdiverse eco-geographical sites in China. 3. Using a set of 247 individuals from ten P. asperata populations wereport an overview on the genetic relationship among the sampled P.asperata populations. RAPD, AFLP and SSR were used in terms of theirinformativeness and applicability for evaluate relationship and all threetechniques discriminated the genotypes very effectively. Mean Dicesimilarities coefficient were estimated using RAPD, AFLP and SSR,respectively. The Mantel test resulted in a significant but relatively low fit(RAPD = 0.63, AFLP = 0.60 and SSR = 0.75) of cophenetic values.Comparing the three marker systems to each other, RAPD and AFLP cophenetic indices were highly correlated (r = 0.59), while correlationcoefficient between RAPD and SSR was r = 0.53 and between SSR andAFLP was r = 0.35. For all markers a relatively high similarity indendrogram topologies was obtained although some differences wereobserved. All the dendrograms, including that obtained by the combineduse of all the marker data, reflect some relationships for most of thepopulations according to their geographic conditions. The results indicatethat single or combined marker system could be used to insight into geneticstudy in P. asperata and the combined data of different marker systems canprovide more reliable information.

Charge-sensitive deep level transient spectroscopy of helium-ion-irradiated silicon, as-irradiated and after thermal annealing

Electrically active defects in the phosphor-doped single-crystal silicon, induced by helium-ion irradiation under thermal annealing, have been investigated. Isothermal charge-sensitive deep-level transient spectroscopy was employed to study the activation energy and capture cross-section of helium-induced defects in silicon samples. It was shown that the activation energy levels produced by helium-ion irradiation first increased with increasing annealing temperature, with the maximum value of the activation energy occurring at 873K, and reduced with further increase of the annealing temperature. The energy levels of defects in the samples annealed at 873 and 1073K are found to be located near the mid-forbidden energy gap level so that they can act as thermally stable carrier recombination centres.

Theoretical investigation on excitation, ionization and capture in H(1s, 2s)+H(1s, 2s) collisions

Cross sections of electron- loss in H( 1s)+ H( 1s) collisions and total collisional destruction of H( 2s) in H( 1s) + H( 2s) collisions are calculated by four- body classical- trajectory Monte Carlo ( CTMC) method and compared with previous theoretical and experimental data over the energy range of 4 - 100 keV. For the former a good agreement is obtained within di. erent four- body CTMC calculations, and for the incident energy Ep > 10 keV, comparison with the experimental data shows a better agreement than the results calculated by the impact parameter approximation. For the latter, our theory predicts the correct experimental behaviour, and the discrepancies between our results and experimental ones are less than 30%. Based on the successive comparison with experiments, the cross sections for excitation to H( 2p), single- and double- ionization and H- formation in H( 2s)+ H( 2s) collisions are calculated in the energy range of 4 - 100 keV for the. rst time, and compared with those in H( 1s)+ H( 1s) and H( 1s)+ H( 2s) collisions.