Comparison between two kinds of semiconductor absorbers for mode-locking in Nd : YVO4 laser

We have demonstrated passive mode-locking in a diode-end-pumped Nd:YVO4 laser using two kinds of semiconductor absorbers whose relaxation region comes from In0.25Ga0.75As grown at low temperature (LT) and GaAs/air interface respectively Mode-locking, using absorbers of the GaAs/air interface relaxation region, has the characteristics of less Q-switching tendency and higher average output power than that using absorbers of LT In0.25Ga0.75As relaxation region, but is not as stable as the latter.

Excitation transfer in vertically self-organized pairs of unequal-sized InAs/GaAs quantum dots

The excitation transfer processes in vertically self organized pairs of unequal-sized quantum dots (QD's), which are created in InAs/GaAs bilayers with different InAs deposition amounts in the first and second layers, have been investigated experimentally by photoluminescence technique. The distance between the two dot layers is varied from 3 to 12 nm. The optical properties of the formed pairs of unequal-sized QD's with clearly discernible ground-state transition energy depend on the spacer thickness. When the spacer layer of GaAs is thin enough, only one photoluminescence peak related to the large QD ensemble has been observed as a result of strong electronic coupling in the InAs QD pairs. The results provide evidence for nonresonant energy transfer from the smaller QDs in the second layer to the larger QD's in the first layer in such an asymmetric QD pair.

High phosphorous doping and morphological evolution during Si growth by gas source molecular beam epitaxy (GSMBE)

Uniform and high phosphorous doping has been demonstrated during Si growth by GSMBE using disilane and phosphine. The p-n diodes, which consist of a n-Si layer and a p-SiGe layer grown on Si substrate, show a normal I-V characteristic. A roughening transition during P-doped Si growth is found. Ex situ SEM results show that thinner film is specular. When the film becomes thicker, there are small pits of different sizes randomly distributed on the flat surface. The average pit size increases, the pit density decreases, and the size distribution is narrower for even thicker film. No extended defects are found at the substrate interface or in the epilayer. Possible causes for the morphological evolution are discussed. (C) 1999 Elsevier Science B.V. All rights reserved.

A two-step backoff scheme for improving the performance of the IEEE 802.11 distributed coordination function

This paper describes the binary exponential backoff mechanism of 802.11 distributed coordination function (DCF), and introduces some methods of modifying the backoff scheme. Then a novel backoff scheme, called Two-step Backoff scheme, is presented and illustrated. The simulation process in OPNET environment has been described also. At last, the analysis and simulation results show that the Two-step backoff scheme can enhance the performance of the IEEE 802.11 DCF.

MPI同步通信顺序模型死锁静态检测算法

静态检测MPI程序同步通信死锁比较困难,通常需要建立程序模型.顺序模型是其他所有复杂模型的基础.通过一种映射方法将顺序模型转化为字符串集合,将死锁检测问题转化为等价的多队列字符申匹配问题,从而设计并实现了一种MPI同步通信顺序模型的静态死锁检测算法.该算法的性能优于通常的环检测方法,并能适应动态消息流.

高效毛细管电泳安培检测的应用研究

毛细管电泳在生命科学，生物技术，医学药物和环境保护中显示了极其重要的应用前景，也被认为是人类进入纳米技术时代的一种富有重要潜在价值的手段。具有高效、快速，耗样量小等特点。而安培电化学恰恰适合毛细管电泳对检测器的要求。毛细管电泳-安培检测法在多方面发挥着不可忽视的作用。本文用此方法进行了一些分析。1. 毛细管区带电泳柱端安培检测抗癌药物巯嘌呤 报道了一种高效快速检测抗癌药物巯嘌呤的方法-毛细管区带电泳柱端安培检测。优化了检测条件，考察了巯嘌呤的电化学行为。在15kV电压下进样3s，在此电压下进行电泳分离，背景电解质为10mmol/L Na_2HPO_4，1.2V检测时，此药物的检测限为1 * 10~(-7)mol/L，线性范围为5 *　10~(-4)-5　* 10~(-6)mol/L，相关系数为0.995，重现性良好。并用该法检测了人体尿样及牛血清蛋白中的巯嘌呤，本工作具有一定的临床意义。2. 毛备管区带电泳柱端安培分离分析多种抗癌药物 通过毛细管区带电泳柱端安培检测法对8-氮鸟嘌呤，5-氟尿嘧啶，6-巯嘌呤，氨甲喋呤和6-硫鸟嘌呤五种抗癌药物进行了灵敏，高效，迅速的分离检测。实验采用33μm的碳纤维盘电极，在20min内分离检测了此五种药物的混合物。在1.2V的检测电位下，五种药物的线性范围超过了三个数量级，相关系数是0.992，这五种药物的检测限依次为5，3，5，9和5 * 10~(-7)mol/L。3. 三种噻唑衍生物的毛细管电泳安培分析 在碳纤维电极上检测三种噻唑衍生物，2-氨基噻唑，2-氨基苯并噻唑和2-巯基苯并噻唑。对应检测限分别为2.0，0.013，0.025 * 10~(-6)mol/L。它们的线性范围较宽，相关系数均在0.9995以上。分别考察了缓冲液pH值及其浓度，分离电压对电泳分离效果的影响，还对实际样品进行了分析。此工作具有一定的实用意义。

南海东北部下地壳高速层的成因探讨

通过对南海北部大陆边缘地壳结构分析，指出南海东北部存在下地壳高速层，

Microarray Analyses of Gene Expression during the Tetrahymena thermophila Life Cycle

Background: The model eukaryote, Tetrahymena thermophila, is the first ciliated protozoan whose genome has been sequenced, enabling genome-wide analysis of gene expression. Methodology/Principal Findings: A genome-wide microarray platform containing the predicted coding sequences (putative genes) for T. thermophila is described, validated and used to study gene expression during the three major stages of the organism's life cycle: growth, starvation and conjugation. Conclusions/Significance: Of the,27,000 predicted open reading frames, transcripts homologous to only,5900 are not detectable in any of these life cycle stages, indicating that this single-celled organism does indeed contain a large number of functional genes. Transcripts from over 5000 predicted genes are expressed at levels >5x corrected background and 95 genes are expressed at >250x corrected background in all stages. Transcripts homologous to 91 predicted genes are specifically expressed and 155 more are highly up-regulated in growing cells, while 90 are specifically expressed and 616 are up-regulated during starvation. Strikingly, transcripts homologous to 1068 predicted genes are specifically expressed and 1753 are significantly up-regulated during conjugation. The patterns of gene expression during conjugation correlate well with the developmental stages of meiosis, nuclear differentiation and DNA elimination. The relationship between gene expression and chromosome fragmentation is analyzed. Genes encoding proteins known to interact or to function in complexes show similar expression patterns, indicating that co-ordinate expression with putative genes of known function can identify genes with related functions. New candidate genes associated with the RNAi-like process of DNA elimination and with meiosis are identified and the late stages of conjugation are shown to be characterized by specific expression of an unexpectedly large and diverse number of genes not involved in nuclear functions.

不同处理方式采伐剩余物的分解及其对森林更新的影响

采伐迹地上运走大径级的原木所剩下的枝桠物质是生态系统养分能量的来源；是动力，植物和微生物物栖息地。在本世纪五十年代就有人（A. A. Loman）对择伐和皆伐迹地上的枝桠进行了研究，用以比较它们树皮存留率的差异，但详细深入的研究是在八十年代以后，以R. L. Edmonds, C. E. Pertson为代表研究不同层次，不同径级研究枝桠的分解速率，我国在此领域的研究尚属空白。本文以长白山阔叶红松林带的四个树种：红松，白桦，落叶松，色木为对象探讨了它们枝桠的生物量，分解速率，分解过程中的养分动态以及枝桠堆对更新和火灾的影响。采伐后0-14后间，迹地上枝桠干重为31.96-9.60T/ha，通过对7个年代采伐迹地上枝桠堆面积估算后得知，枝桠堆平均占地为11.53%，以1CM直径累计值对应的枝桠堆的高度（Y：CM）为因变量，分解时间（X, yr）为自变量，则枝桠堆高度随时间变化的过程可以描述为：Y = 1.288 - 0.000889 X~2 r = -0.9896。本文以密度（Y: g/CM~3）随分解年令（X: yr）的变化来表示分解速率。四十年代样品用排水法求出来的密度与用园柱法求出的密度有如下相关关系：Y排 = 0.0129 +2.316 Y园，r = 0.94 Y表示密度（g/CM~3）。我们用单项指数模型描述分解速率：落叶松：Y = 0.4701 * exp (-0.01783 X) r = -0.927 色木: Y = 0.6742 * exp (-0.07824 X) r = -0.988 红松：Y = 0.5349 * exp (-0.03421 X) r = -0.927 桦树：Y = 0.5316 * exp (-0.1139 X) r = -0.992 红松树皮的分解模型近似于直线：Y = 0.5258 - 0.01133 X r = -0.984 落叶松，红松，色木，桦树的分解常数分别为：0.01783, 0.0.41, 0.0782, 0.1139。依此预测分解原密度的95%所需要的时间分别为：168年，87.6年，38.3年，26年。可以看出这四个树种分解从难到易的顺序为：落叶松 > 红松 > 色木 > 桦树。对枝桠密度的差民显著性检验可以说明：红松样品层次对分解的影响显著而径级对分解的影响仅在下层显著。随着分解的进行，样品的重量损失，我们也探讨了密度的降低与失重百分率之间的关系。桦树样品下层失重比上层快，说明淋溶作用对桦树样品失重的贡献不大。温湿度是影响分解的最主要的生态因子。枝桠堆上下层的湿度差异特别明显。分解时间越长，径级对含水量的影响越显著。水分含量（Y：%）随年代（X: yr）变化的趋势为：Y = 36.18 - 0.004337 X~2 (4-7cm径级）Y = 33.64 - 0.01097 X~2 (1-4cm径级） 温，湿度影响土壤动物及微生物种群分布及数量，进而影响到枝桠的分解速率，分解过程中元素动态变化是：C基本上恒定，全N含量趋于增高。径级对红松N的累积有影响。下层4-6cm径极累积最快，其次是上层4-6cm。层次的影响仅限于红松，除72年以外上层 > 下层。其它元素如P, Mg++， Ca++总的趋势是随分解过程而增加。土壤中的C元素含量受立地条件的影响，但是枝桠堆下面土壤C值高于对照。枝桠堆对森林更新和火灾均有影响。枝桠是林火的燃料，枝桠堆面积占采伐迹地的11.53%，这样减少更新面积。