四气门发动机可变涡流稀薄燃烧特性研究

本文研究了可变涡流对四气门发动机稀薄燃烧特性的影响情况。在稀薄燃烧情况下,发动机负荷大小对CO和HC排放的影响不大,对NOx排放的影响主要表现在对13～17空燃比范围内NOx排放的影响,负荷越大,NOx排放越大;对空燃比小于13或大于17以后的NOx排放影响较小。阀片位置对发动机排放特性的影响较小,对发动机的燃油经济性存在一定影响,这是因为不同阀片位置的进气涡流比不同所致,同时也表明较强的涡流运动对燃油经济性更有利。涡流运动在不同转速条件下对发动机燃油经济性的影响情况不同,它更有利于改善低速条件下的燃油经济性。     

三维光晶格中玻色凝聚气体基态波函数及干涉演化

基于Gross-Pitaevskii方程，运用有效化学势概念，研究了囚禁在组合势(由磁阱和三维光 晶格组成)中玻色凝聚气体在三维光晶格中的分布规律，并由此得到玻色凝聚气体的归 一化基态波函数.在取消组合势和仅取消光晶格而保留磁阱的两种情况下，运用传播子方 法求解出玻色凝聚气体密度分布的解析表达式.取消组合势后，理论计算所得到的玻色凝聚 气体聚随时间的演化规律与Greiner等的实验结果相一致.仅取消光晶格而保留磁阱时，研 究表明玻色凝聚气体的干涉模式呈现周期性的振荡行为.此外，在磁阱为各向异性的情况下 ， 关键词： 玻色凝聚气体 磁阱 光晶格 干涉模式     

激光限制结晶技术制备nc-Si/SiO2多层膜

在等离子体增强化学气相淀积系统中，采用aSi:H层淀积和原位等离子体氧化相结合的逐层生长技术制备了aSi:H/SiO_2多层膜.在激光诱导限制结晶原理基础上，使用KrF准分子脉冲激光为辐照源，对aSi:H/SiO_2多层膜进行辐照，使纳米级厚度的aSi:H子层晶化.Raman散射谱和电子衍射谱的结果表明，经过激光辐照后纳米Si颗粒在原始的aSi:H子层内形成，晶粒尺寸可以根据aSi:H层的厚度精确控制.还研究了样品的光致发光（PL）特性以及激光辐照能量密度对PL性质的影响. 关键词： 脉冲激光 多层膜 限制结晶     

Self-assembly of Carboxyl Functionalized Polystyrene Nanospheres into Close-packed Monolayers via Chemical Adsorption

The polyacrylic acid functionalized polystyrene nanospheres were synthesized and self-assembled into irregular, densely packed monolayers in non-aqueous media. The polymer nanoparticles were chemically adhered to substrates. The morphologies of the resulting films were investigated. The impact of the volume fraction of alcohol in the mixed solvents on the particle adsorption and fabrication of nanosphere assembled films was examined.     

Periodic solutions for a Lotka–Volterra mutualism system with several delays

In the present paper, a Lotka–Volterra type mutualism system with several delays is studied. Some new and interesting sufficient conditions are obtained for the global existence of positive periodic solutions of the mutualism system. Our method is based on Mawhin’s coincidence degree and novel estimation techniques for the a priori bounds of unknown solutions. Our results are different from the existing ones such as those in of Yang et al. [F. Yang, D. Jiang, A. Ying, Existence of positive solution of multidelays facultative mutualism system, J. Eng. Math. 3 (2002) 64–68] and Chen et al. [F. Chen, J. Shi, X. Chen, Periodicity in a Lotka–Volterra facultative mutualism system with several delays, J. Eng. Math. 21 (3) (2004) 403–409].     

Multiple periodic solutions of a delayed stage-structured predator–prey model with non-monotone functional responses

A delayed stage-structured predator–prey model with non-monotone functional responses is proposed. It is assumed that immature individuals and mature individuals of the predator are divided by a fixed age, and that immature predators do not have the ability to attack prey. Some new and interesting sufficient conditions are obtained for the global existence of multiple positive periodic solutions of the stage-structured predator–prey model. Our method is based on Mawhin’s coincidence degree and novel estimation techniques for the a priori bounds of unknown solutions to Lx = λNx. An example is given to illustrate the feasibility of our main result.     

First-Principles Study on the Electronic Structures for Y^3＋：PbWO4 Crystals

The possible defect models of Y^3＋：PbWO4 crystals are discussed by defect chemistry and the most possible substituting positions of the impurity Y^3＋ ions are studied by using the general utility lattice program （GULP）. The calculated results indicate that in the lightly doped Y^3＋ ：PWO crystal, the main compensating mechanism is [2Ypb^＋ ＋ VPb^2-], and in the heavily doped Y^3＋ ：PWO crystal, it will bring interstitial oxygen ions to compensate the positive electricity caused by YPb^＋, forming defect clusters of [2Ypb^＋ ＋Oi^2-] in the crystal. The electronic structures of Y3＋ ：PWO with different defect models are calculated using the DV-Xα method. It can be concluded from the electronic structures that, for lightly doped cases, the energy gap of the crystal would be broadened and the 420nm absorption band will be restricted; for heavily doped cases, because of the existence of interstitial oxygen ions, it can bring a new absorption band and reduce the radiation hardness of the crystal.     

Periodic solutions of a second order forced sublinear differential equation with delay

In this paper, existence criteria are established for the existence of periodic solutions of a second order sublinear differential equation with delay and forcing function. Our method is based on careful a priori estimation and continuation theorems, and our sublinear condition is an improvement of the boundedness condition in some recent results.     

变In组分沟道的MM-HEMT材料电子输运特性研究

在变缓冲层高迁移率晶体管（MM_HEMT）器件中，二维电子气的输运性质对器件性能起着决定作用.通过低温下二维电子气横向电阻的量子振荡现象，结合变温度的Hall测量，系统研究了不同In组分沟道MM_HEMT器件中子带电子迁移率和浓度随温度的变化关系.结果表明，沟道中In组分为0.65的样品，材料电学性能最好，In组分高于0.65的样品，严重的晶格失配将产生位错，引起迁移率下降，大大影响材料和器件的性能. 关键词： 变缓冲层高迁移率晶体管 Shubnikov_de Hass 振荡