Experimental study on two-phase gas-liquid flow patterns at normal and reduced gravity conditions

Experimental studies have been performed for horizontal two-phase air-water flows at normal and reduced gravity conditions in a square cross-section channel. The experiments at reduced gravity are conducted on board the Russian IL-76 reduced gravity airplane. Four flow patterns, namely bubble, slug, slug-annular transition and annular flows, are observed depending on the liquid and gas superficial velocities at both conditions. Semi-theoretical Weber number model is developed to include the shape influence on the slug-annular transition. It is shown that its prediction is in reasonable agreement with the experimental slug-annular transition under both conditions. For the case of two-phase gas-liquid flow with large value of the Froude number, the drift-flux model can predict well the observed boundary between bubble and slug flows.

牵拉力对共培养的表皮干细胞及成纤维细胞迁移行为的影响

国家自然科学基金项目(30730032)

适合于小飞机防撞系统的机载小型激光测距仪

报道了一种重量轻、功耗低、适合于小飞机防撞系统应用的小型激光测距仪。系统基于脉冲激光测距原理，采用905nm半导体脉冲激光器、电感升压式偏置高压电源和可编程逻辑器件（PLD），研制出重量不大于100g，功耗不大于625mW，测量范围100m，盲区3．0m，分辨率±1m的机载小型激光测距仪。实验测试结果表明，其各项技术性能指标符合无人驾驶小飞机防撞系统的应用要求。

克隆整合对植物竞争力和群落结构的影响

某些克隆植物通过克隆整合能够很好的适应逆境或快速扩张。基于克隆整合，研究克隆植物的抗逆性、入侵性及其对群落结构的影响在很多方面值得深入。本文主要应用实验生态学的方法，分别在野外或温室以沙鞭、空心莲子草和羊柴为主要研究对象，研究克隆整合对处于逆境生长条件下克隆植物生长的影响;克隆整合对入侵植物竞争力和被入侵植物群落组成的影响;克隆整合对沙地群落结构和初级生产力的影响，探讨克隆植物对风蚀和水淹的适应机制、入侵克隆植物的入侵机制以及对群落组成和结构的影响机制。主要结论如下： 1. 沙鞭分株的叶片数目和生物量跟沙鞭根状茎的埋藏深度高度正相关，当根状茎被暴露在空气中时，上面所依附的分株要么死亡，要么长势很弱。每样方内沙鞭的分株数目、叶片数目和总生物量随风蚀强度的增加而降低。在对照和短期风蚀中，根状茎连接并不影响上述指标，但是在长期风蚀下，根状茎连接的作用会增强。根状茎连接能够减轻风蚀对沙鞭的负面影响，这很有可能是因为遭受风蚀胁迫的分株从那些没有遭受风蚀侵害的分株那里获得了水分和光合产物的资助。本研究首次证实了保持根状茎连接有助于提高干旱区植物抵御风蚀的能力。 2. 水淹会降低空心莲子草先端分株的生长;克隆整合显著增强了空心莲子草先端分株的生长和繁殖，但降低了基端分株的生长和繁殖。最终，克隆整合并不影响整体空心莲子草克隆片段的生长表现，这预示当空心莲子草从陆地生境向水生生境扩散时，克隆整合对其总体没有净收益。我们认为空心莲子草在由陆地扩张到水域时，可能拥有一种“双刃剑”机制：当处于水生生境中的先端分株得到处于陆生生境中的基端分株的资源支持时，先端分株能够增强自身生长;当因外界扰动导致二者间相连匍匐茎断裂后，陆生生境中的基端分株能够快速增强自身的匍匐茎和分株生长。这种机制可能使得空心莲子草很好的适应高度干扰或高度异质生境，从而增强了其入侵性。 3. 竞争显著降低了空心莲子草先端分株的光系统II中的最大量子产额(Fv/Fm)和生长（生物量、分株数目、叶片数目、总匍匐茎长度和总叶面积），但并不影响高羊茅的生物量。匍匐茎连接显著增强了空心莲子草先端分株的最大量子产额和生长。然而，这种连接效应在竞争时的作用要比非竞争时的作用小的多，而且匍匐茎连接并没有改变空心莲子草的相对邻体效应。与非竞争环境相反，在竞争条件下匍匐茎连接会降低空心莲子草对根系的生物量投资。克隆整合可能对提高空心莲子草的竞争力帮助不大，但是对其开拓空旷领地却非常重要。这些结果预示空心莲子草的入侵性可能和其克隆整合作用有密切关系。 4. 克隆整合显著增强了空心莲子草在群落中的扩张能力，但并没有提高其抑制整体群落物种的能力。相比低密度播种群落，生长在高密度播种群落中的空心莲子草长势明显要弱，高密度播种群落具有更强的抵御入侵的能力。在低密度播种群落中，相比切断群落内外空心莲子草相连匍匐茎，如果保持其连接，优势物种的地上生物量会降低而次优势物种的地上生物量会增加，进而群落的丰富度会得到提高。实验结果预示克隆整合能够增强入侵物种在建植群落中的扩张速度，并能够修饰其在群落结构上的影响，改变群落中单个物种的生长表现。 5. 克隆整合显著增强了羊柴在沙地植物群落中的分株数目，但并没有提高其地上生物量。羊柴分株数目的变化受不同处理因素的影响，在加氮的处理中分株数目为最大，切断处理中为最小。在群落主要组成物种中，克隆整合显著影响了烛台虫实的地上生物量，而其它主要物种的地上生物量则不受处理因素影响。克隆整合并没有影响沙地群落的物种多样性，但会显著影响沙地群落的初级生产力，尤其是添加氮肥以后。

云南拉市海高原湿地冬季水禽聚集情况变化

拉市海是云南省丽江县境内最大的高原湖泊，常年水面面积仅有９．３３ｋｍ２。但却记录有水禽７目１０科３１种．占全省水禽种数的２５．８％。其中冬候鸟２９种，与１９８４年的调查结果比较，１９９７年水禽的种数增加３倍。平均数量达２５０００多只，成为云南省重要的水禽越冬地之一。

Realization of MMI power splitter by UV-light imprinting technique using hybrid sol-gel SiO2 materials

An efficient fabrication scheme of buried ridge waveguide devices is demonstrated by UV-light imprinting technique using organic-in organic hybrid sol-gel Zr-doped SiO2 materials. The refractive indices of a guiding layer and a cladding layer for the buried ridge waveguide structure are 1.537 and 1.492 measured at 1550 nm, respectively. The tested results show more circular mode profiles clue to existence of the cladding layer. A buried ridge single-mode waveguide operating at 1550 nm has a low propagation loss (0.088 dB/cm) and the 1 x 2 MMI power splitter exhibits uniform outputs, with a very low splitting loss of 0.029 dB at 1549 nm.

Design, fabrication and characterization of a high-performance microring resonator in silicon-on-insulator

A high-performance microring resonator in a silicon-on-insulator rib waveguide is realized by using the electron beam lithography followed by inductively coupled plasma etching. The design and the experimental realization of this device are presented in detail. In addition to improving relevant processes to minimize propagation loss, the coupling efficiency between the ring and the bus is carefully chosen to approach a critical coupling for high performance operating. We have measured a quality factor of 21,200 and an extinction ratio of 12.5dB at a resonant wavelength of 1549.32nm. Meanwhile, a low propagation loss of 0.89dB/mm in a curved waveguide with a bending radius of 40 mu m is demonstrated as well.

精确的程序静态分析

程序的静态分析是程序语言和编译领域的一个重要研究方向，已经被研究了很多年。近年来，它也引起形式方法和软件工程领域的重视，被用于程序测试和正确性验证。文中从程序的语法特征、所关心的数据类型和程序性质等方面比较了一些静态分析技术。着重描述基于路径的分析方法，特别是符号执行技术，讨论了程序路径可行性分析问题及其分类、复杂度。针对程序分析精度的一种量化指标，说明了其计算方法。

Homoepitaxial Growth and Characterization of 4H-SiC Epilayers by Low-Pressure Hot-Wall Chemical Vapor Deposition

Horizontal air-cooled low-pressure hot-wall CVD (LP-HWCVD) system is developed to get highly qualitical 4H-SiC epilayers.Homoepitaxial growth of 4H-SiC on off-oriented Si-face (0001) 4H-SiC substrates is performed at 1500℃ with a pressure of 1.3×103Pa by using the step-controlled epitaxy.The growth rate is controlled to be about 1.0μm/h.The surface morphologies and structural and optical properties of 4H-SiC epilayers are characterized with Nomarski optical microscope,atomic force microscopy (AFM),X-ray diffraction,Raman scattering,and low temperature photoluminescence (LTPL).N-type 4H-SiC epilayers are obtained by in-situ doping of NH3 with the flow rate ranging from 0.1 to 3sccm.SiC p-n junctions are obtained on these epitaxial layers and their electrical and optical characteristics are presented.The obtained p-n junction diodes can be operated at the temperature up to 400℃,which provides a potential for high-temperature applications.