Snap-through and pull-in instabilities of an arch-shaped beam under an electrostatic loading

The snap-through and pull-in instabilities of the micromachined arch-shaped beams under an electrostatic loading are studied both theoretically and experimentally. The pull-in instability that results in a system collision with an electrode substrate may lead to a system failure and, thus, limits the system maximum displacement. The beam/plate structure with a flat initial configuration under an electrostatic loading can only experience the pull-in instability. With the different arch configurations, the structure may experience either only the pull-in instability or the snap-through and pull-in instabilities together. As shown in our computation and experiment, those arch-shaped beams with the snap-through instability have the larger maximum displacement compared with the arch-shaped beams with only the pull-in stability and those with the flat initial configuration. The snap-through occurs by exerting a fixed load, and the structure experiences a discontinuous displacement jump without consuming power. Furthermore, after the snap-through jump, the structures are demonstrated to have the capacity to withstand further electrostatic loading without pull-in. Those properties of consuming no power and increasing the structure deflection range without pull-in is very useful in microelectromechanical systems design, which can offer better sensitivity and tuning range.

SNAP-23蛋白在鲈鱼巨噬细胞白细胞介素1β分泌过程中的功能

SNARE蛋白家族是所有真核细胞胞吐及分泌作用中的关键因子，由其介导的运输囊泡膜与靶膜的锚靠、融合为胞内蛋白的运出提供了一条重要途径。体外试验表明，Syntaxin6-Syntaxin7-Vti1b，SNAP-23-Syntaxin4等SNARE核心蛋白之间精确的相互作用是哺乳动物巨噬细胞肿瘤坏死因子α (TNF-α)运输和分泌的必备条件，在机体非特异性免疫应答反应过程中起重要作用。 本研究受上述启示，旨在揭示SNARE蛋白在海洋鱼类免疫细胞内重要细胞因子白细胞介素1β (IL-1β)的分泌过程中的作用。参照Percoll密度梯度离心技术，从鲈鱼头肾组织分离纯化巨噬细胞进行稳定培养；利用RT-PCR方法克隆出鲈鱼t-SNARE蛋白SNAP-23和Syntaxin3的部分cDNA序列，再结合先前克隆的VAMP2和已知的鲈鱼IL-1β，TNF-α和IL-8的基因序列，设计特异性引物。利用Real-time PCR技术在mRNA水平上精确测定鲈鱼巨噬细胞中上述6种基因在革兰氏阴性菌脂多糖(LPS)分子刺激下的表达变化，发现SNAP-23基因与三种细胞因子基因的表达正相关；通过免疫印迹检测SNAP-23蛋白表达变化，利用酶联免疫吸附试验(ELISA)检测IL-1β的分泌水平，在蛋白水平上验证了SNAP-23表达与IL-1β分泌的正相关性；利用5`RACE和3`RACE技术克隆出鲈鱼SNAP-23全长基因，结合定点突变策略和靶向PCR克隆手段，构建鲈鱼SNAP-23野生型融合质粒pEGFP-SNAP-23wt，Cys缺失突变融合质粒pEGFP-SNAP-23ΔCys和模拟E型肉毒神经毒素(BoNT/E)切割突变融合质粒pEGFP-SNAP-23ΔBoNT/E，以及鲈鱼IL-1β野生型融合表达质粒IL-1β-pEGFP和IL-1β-pEYFP。所有融合蛋白均在鲈鱼巨噬细胞内成功表达，结合ELISA实验结果发现，SNAP-23野生型的表达对IL-1β的分泌有促进作用，而Cys缺失突变体的表达则抑制IL-1β向胞外分泌。首次证实了鱼类巨噬细胞内SNAP-23蛋白在IL-1β分泌过程中的重要作用。此外通过与GFP共表达，定位了IL-1β分子在巨噬细胞内的分布，发现新合成的IL-1β分子很可能像TNFα一样经“内质网－胞质－伪足－胞外” 的分泌路径运出胞外。

一氧化氮(NO)调节白皮松花粉管生长和细胞壁构建的研究

花粉管是种子植物受精过程中的雄性生殖单位载体，具有典型的顶端极性生长特点，因此成为近年来研究植物细胞间相互识别、胞内外信号传递的模式系统。裸子植物花粉管与被子植物花粉管相比具有萌发时间长、生长缓慢等特点。一氧化氮（NO）作为一个重要的胞内信号分子，参与调节植物生长发育和多种生理过程，但是，有关NO对花粉管生长的作用机制目前尚不清楚。本研究以裸子植物白皮松(Pinus bungeana)花粉为材料，应用不同浓度的NO释放剂SNAP和SNP, NO清除剂cPTIO和哺乳动物一氧化氮合酶抑制剂L-NNA处理，对白皮松花粉萌发和花粉管伸长进行了细胞学研究，从而为进一步揭示NO调控裸子植物花粉管生长机理提供参考。 本论文首先研究了NO释放剂、清除剂及NOS抑制剂对白皮松花粉萌发和花粉管生长的影响。结果显示，SNAP和SNP能够促进白皮松花粉萌发和花粉管伸长，并具有浓度效用，但对其花粉管的形态特征无明显影响；cPTIO和L-NNA能够抑制白皮松花粉萌发和花粉管生长，并且具有浓度效应，同时还可使花粉管顶端膨大呈球形，并丧失花粉管的极性生长。运用NO特异探针DAF-2DA标记显示，SNAP和SNP处理可促进花粉管胞内NO产生；经cPTIO和L-NNA处理后，花粉管内荧光强度比对照花粉管明显减弱。上述结果表明，NO参与裸子植物花粉管极性生长，并且适量NO可以促进花粉管的生长。 用显微注射技术将Ca2+特异探针注射入白皮松花粉管，以检测白皮松花粉管胞内Ca2+浓度梯度。结果显示，SNAP和SNP处理后，NO荧光增加的同时，花粉管顶端Ca2+浓度梯度增加。与此相反，cPTIO和L-NNA处理后，NO荧光降低的同时，花粉管顶端Ca2+浓度梯度也相应降低。应用非损伤微测技术测定花粉管胞外Ca2+内流，结果显示，SNAP和SNP促进胞外Ca2+内流，而cPTIO和L-NNA则抑制胞外Ca2+内流。据此，我们推测，在白皮松花粉管中，NO可能通过调节胞外Ca2+内流来调节胞内Ca2+浓度梯度，然而，我们不能排除在NO信号传递过程中，胞内Ca2+库可能影响胞内Ca2+浓度梯度。 通过微丝特异探针标记的白皮松花粉管显示，SNAP和SNP可使花粉管顶端细微丝束解聚，而cPTIO和L-NNA处理后，花粉管中微丝聚合，尤其在花粉管顶端形成粗的微丝束，并一直延伸到花粉管的最顶端。结合上述Ca2+结果，我们认为，经NO处理后，白皮松花粉管微丝骨架的动态变化，可能是通过Ca2+浓度来进行调控的。通过FM4-64探针标记显示，正常生长白皮松花粉管胞吞作用主要集中在顶端和亚顶端，并且形成倒“V”形的分布模式，SNAP与SNP处理后荧光分布模式与对照花粉管类似，但达到饱和所用时间相对较短；而L-NNA处理后顶端膨大丧失极性的花粉管，荧光分布在膨大花粉管靠近质膜的区域，未见倒“V”形分布模式；经L-NNA处理后，顶端没有膨大的花粉管，荧光几乎均匀分布于整个花粉管，并且L-NNA处理后达到饱和的时间较对照长。上述结果表明，适量NO能够促进白皮松花粉管胞吞。 免疫抗体标记技术分析发现，对照花粉管的酯化果胶质和AGPs都集中在顶端，酸性果胶质分布在侧壁，胼胝质均匀分布在整个花粉管壁上。L-NNA处理后的花粉管，在其顶端出现酸性果胶和酯化果胶，以及有胼胝质积累，而AGPs则分布在花粉管的基部。运用傅里叶红外光谱技术（Fourier Transform Infared Spectroscopy, FTIR）技术分析白皮松花粉管顶端细胞壁成分，结果显示，SNAP处理后花粉管顶端酯化果胶增加而酸性果胶降低；与之相反，经L-NNA处理后的花粉管，其顶端酯化果胶降低而酸性果胶增加。 综上所述，在白皮松花粉管中，NO促进胞外Ca2+内流，从而维持胞内Ca2+浓度梯度，进而影响花粉管顶端微丝骨架的组装，促进囊泡运输，使花粉管顶端酯化果胶累积，最终促进花粉管的正常生长。

支持EJB动态分布的组件迁移模型与算法

Web应用服务器是Web计算环境下的新型中间件，为基于组件的分布式Web应用提供了基础运行平台．组件静态分布限制了事务性Web应用在运行期间适应执行环境变化的能力．为了满足Web应用的动态分布需求，Web应用服务器需在底层为组件提供一种动态迁移的能力．如何维持组件迁移前后的一致性是组件迁移中最棘手的问题之一．为解决此问题，定义了组件迁移一致性约束CMC(component migration constrains)，并给出了在 J2EE(Java 2 platform enterprise edition)应用服务器中支持EJB(enterprise Java Bean)动态分布的组件迁移模型和 sLB_Copy,SFB_Copy,EB-Copy 3个迁移算法．分析得出sLB_Copy,SFB_copy和EB_copy均满足CMC约束．迁移模型和算法已在自主研制的Web应用服务器WebFrame2．0中实现，并已应用到自适应负载平衡、失效恢复等多个方面．

陕北黄土丘陵沟壑区水土保持耕作及施肥下农田土壤种子库特征

为了探明多年免耕下农田恶性杂草发生的机理,提高保护性耕作下作物对农田恶性杂草持久稳定的抑制效果,依据陕西安塞田间4a的定位试验,采用小区调查取样和室内实验相结合的方法,从物种组成、密度特征、多样性以及相似性特征等方面,研究了黄土丘陵旱作农区大豆(Glycine max)、玉米(Zea mays)、红小豆(Semen Phaseoli)、马铃薯(Solanum tuberosum)在翻耕化肥(CF)、翻耕有机肥(CM)、翻耕无肥(CN)、免耕化肥(NF)、免耕有机肥(NM)、免耕无肥(NN)等水平下的农田土壤种子库。结果表明:(1)4种作物24种土样中共萌发出12个物种1965株幼苗,隶属于7科12属。1年生杂草占94%,棒头草(fugax nees ex steud)、苋菜(Acalypha australis)、马唐(Digitaria sanguinalis)、早熟禾(Poasphondylodes)为优势种,占87%。(2)在0～20cm土层不同处理间,土壤种子库的密度变动于(282.9±63.4)～(7482.5±1078.3)粒.m-2,其中,红小豆小区>马铃薯小区>大豆小区>玉米小区;翻耕小区>免...

不同前茬对设施黄瓜产量和品质及土壤酶活性的影响

试验研究了在延安日光温室不同前茬作物条件下,黄瓜随着生长季节的变化其产量和品质及土壤呼吸和酶活性的动态变化。结果表明,前茬为豇豆的黄瓜产量和土壤碱性磷酸酶活性较高,前茬为番茄的黄瓜可溶性糖含量和土壤呼吸强度较高,前茬为四季豆的黄瓜维生素C含量较高,前茬为翻青玉米的黄瓜硝酸盐含量和土壤脲酶活性较高,前茬为翻青黑豆的土壤蔗糖酶活性较高。从提高黄瓜产量的角度出发,豇豆-黄瓜是最佳模式,而从改善黄瓜品质的角度出发,番茄-黄瓜和四季豆-黄瓜是最优模式

A study on GaP/Si heterostructures grown by GS-MBE

GaP/Si is a promoting heterostructure for Si-based optoelectronic devices since lattice constants of GaP and Si are so closed that they can match with each other. GaP was successfully grow on (100) Si subtracts by Gas-Source Molecular Bean Epitaxy (GS-MBE) in the study. The GaP/Si heterostructure was characterized by X-ray double crystal diffraction, Anger electron spectrograph, X-ray photonic spectrograph and photoluminescence (PL) measurements. The results showed that the epitaxial GaP layers are single crystalline, in which a parallel to and a (perpendicular to)are 0.54322 and 0.54625 nm, respectively. The peaks in PL spectra of GaP epitaxial layer grown on Si are 650, 627 and 640 nm, respectively. The study demonstrated that GaP/Si is a kind of lattice matched heterostructures and will be a promoting materials for future integrated photonics.

Analytical method of predicating the instabilities of a micro arch-shaped beam under electrostatic loading

An arch-shaped beam with different configurations under electrostatic loading experiences either the direct pull-in instability or the snap-through first and then the pull-in instability. When the pull-in instability occurs, the system collides with the electrode and adheres to it, which usually causes the system failure. When the snap-through instability occurs, the system experiences a discontinuous displacement to flip over without colliding with the electrode. The snap-through instability is an ideal actuation mechanism because of the following reasons: (1) after snap-through the system regains the stability and capability of withstanding further loading; (2) the system flips back when the loading is reduced, i.e. the system can be used repetitively; and (3) when approaching snap-through instability the system effective stiffness reduces toward zero, which leads to a fast flipping-over response. To differentiate these two types of instability responses for an arch-shaped beam is vital for the actuator design. For an arch-shaped beam under electrostatic loading, the nonlinear terms of the mid-plane stretching and the electrostatic loading make the analytical solution extremely difficult if not impossible and the related numerical solution is rather complex. Using the one mode expansion approximation and the truncation of the higher-order terms of the Taylor series, we present an analytical solution here. However, the one mode approximation and the truncation error of the Taylor series can cause serious error in the solution. Therefore, an error-compensating mechanism is also proposed. The analytical results are compared with both the experimental data and the numerical multi-mode analysis. The analytical method presented here offers a simple yet efficient solution approach by retaining good accuracy to analyze the instability of an arch-shaped beam under electrostatic loading.

不同植被对土壤侵蚀及铜元素流失的影响

通过野外天然降雨产流及人工模拟降雨试验,研究不同植被对坡面土壤侵蚀及土壤铜元素流失的影响及降雨过程中铜元素的流失规律。结果表明:(1)紫花苜蓿、绿豆、荒草3种植被覆盖小区的年径流量为5183.8,5 366.2,3 867.3 m~3/km~2,比裸地减少33%,30.8%和50.1%;侵蚀模数为379.18.482.3,15.78 t/km~2,比裸地减少34.7%,16.4%和97.2%;全年全铜流失量为12.9,25.5,0.46 kg/km~2,有效铜流失量为6.22,11.01,0.15 kg/ km~2,分别比裸地减少67.3%,35.3%,98.8%和54.6%,19.6%,98.9%;(2)在模拟降雨过程中,农地小区的产流产沙强度过程呈现波动上升趋势,产沙过程波动较产流过程剧烈。铜元素流失强度过程与产流产沙强度过程相似,但其峰值多于产流产沙过程,且最高峰出现时间不同。有效铜流失强度变化率略高于全铜。