Analyses of Lattice Traffic Flow Model on a Gradient Highway

The optimal current difference lattice hydrodynamic model is extended to investigate the traffic flow dynamics on a unidirectional single lane gradient highway. The effect of slope on uphill/downhill highway is examined through linear stability analysis and shown that the slope significantly affects the stability region on the phase diagram.Using nonlinear stability analysis, the Burgers, Korteweg-deVries(KdV) and modified Korteweg-deVries(mKdV) equations are derived in stable, metastable and unstable region, respectively. The effect of reaction coefficient is examined and concluded that it plays an important role in suppressing the traffic jams on a gradient highway. The theoretical findings have been verified through numerical simulation which confirm that the slope on a gradient highway significantly influence the traffic dynamics and traffic jam can be suppressed efficiently by considering the optimal current difference effect in the new lattice model.     

Ab initio study of [001] GaN nanowires

We present the results of a study of structural, electronic, and optical properties of the unpassivated and H-passivated GaN nanowires having diameters in the range of 3.29 to 18.33 Å grown along [001] direction by employing the first-principles pseudopotential method within density functional theory in the local density approximation. Two types of nanowires having hexagonal and triangular cross-sections have been investigated. The binding energy increases with the diameter of the nanowire because of a decrease in the relative number of the unsaturated surface bonds. The binding energies of the triangular cross-sectional nanowires are somewhat smaller than those of the hexagonal cross-sectional nanowires in accordance with the Wulff’s rule except the smallest diameter triangular cross-sectional nanowire, where the binding energy is comparable with the corresponding hexagonal cross-sectional nanowires. The band gap varies rapidly with the diameter of the nanowire in the case of the smaller diameter nanowires, and quite slowly for the larger diameter nanowires. After atomic relaxation, appreciable distortion occurs in the nanowires, where the chains of Ga- and N-atoms are curved in different directions. These distortions are reduced with the diameters of the nanowires. The optical absorption in the GaN nanowires is quite strong in the ultra-violet region but an appreciable absorption is also present in the visible region for the larger diameter nanowires. The present results indicate the possibility of engineering the properties of nanowires by manipulating their diameter and surface structure. The presently predicted smaller diameter GaN nanowire possessing the triangular cross-section should be observable in the experiments.     

Al_2S_n~±(n=2—10)团簇结构特征和稳定性的密度泛函理论研究

采用密度泛函理论的B3LYP方法,在6-311G**水平上对Al2S±n(n=2—10)团簇的几何结构和电子结构进行了理论计算.讨论了铝硫二元离子混合团簇基态结构的变化规律、电荷转移和成键特征.结果表明,在S簇中掺杂Al原子会使Sn结构发生明显改变.Al2S±n团簇基态结构是以Al2S2四元环为骨架或桥梁,分别与S原子或S簇相结合形成单环到三环的平面和立体结构.结构中化学键键型和成键数目影响团簇的稳定性.通过对基态结构的解离能和能量二次差分值的分析得到了Al2S±n团簇的稳定性信息.     

复相系平衡条件及平衡稳定性条件的分析

复相系平衡条件及平衡稳定性条件的分析曾丹苓（重庆大学热力工程系重庆６３００４４）关键词复相系，平衡条件，平衡稳定性条件１引言汽液相变是工程上常见的现象，它是一个复杂的物理过程，涉及到传热传质、相转变、表面现象、流体流动及工质热物性等领域，但从热力学的...     

各向异性作用下合金定向凝固界面稳定性的渐近分析

采用渐近分析方法对考虑了界面能各向异性的单相二元合金平界面定向凝固过程进行了线性稳定性分析，得到了特定条件下的零级、一级渐近解，并通过对长波段渐近解的讨论得出了适用于整个波段的色散关系.分析表明零级渐近解等效于成分过冷理论，而一级渐近解则与M-S稳定性理论一致.在稳定状态控制参数(抽拉速度和温度梯度)的选择图中，界面能各向异性增大了不稳定区域，且在高速和高温度梯度时的影响更强.     

Efficient top-emitting white organic light emitting device with an extremely stable chromaticity and viewing-angle

In this paper,we report on the fabrication of a top-emitting electrophosphorescent p-i-n white organic lightemitting diode on the basis of a low-reflectivity Sm/Ag semi-transparent cathode together with a thickness-optimized ZnS out-coupling layer.With a 24-nm out-coupling layer,the reflectivity of the cathode is reduced to 8% at 492 nm and the mean reflectivity is 24% in the visible area.By introducing an efficient electron blocking layer tris(1phenylpyrazolato,N,C2 ’)iridium(III)(Ir(ppz) 3) to confine the exciton recombination area,the current efficiency and the colour stability of the device are effectively improved.A white emission with the Ir(ppz) 3 layer exhibits a maximum current efficiency of 9.8 cd/A at 8 V,and the Commission Internationale de L’Eclairage(CIE) chromaticity coordinates are almost constant during a large voltage change of 6 V-11 V.There is almost no viewing angular dependence in the spectrum when the viewing angle is no more than 45,with a CIE x,y coordinate variation of only(±0.0025,±0.0008).Even at a large viewing angle(75),the CIE x,y coordinate change is as small as(±0.0087,±0.0013).     

A NUMERICALLY STABLE BLOCK MODIFIED GRAM-SCHMIDT ALGORITHM FOR SOLVING STIFF WEIGHTED LEAST SQUARES PROBLEMS

Recently, Wei in proved that perturbed stiff weighted pseudoinverses and stiff weighted least squares problems are stable, if and only if the original and perturbed coefficient matrices A and A^- satisfy several row rank preservation conditions. According to these conditions, in this paper we show that in general, ordinary modified Gram-Schmidt with column pivoting is not numerically stable for solving the stiff weighted least squares problem. We then propose a row block modified Gram-Schmidt algorithm with column pivoting, and show that with appropriately chosen tolerance, this algorithm can correctly determine the numerical ranks of these row partitioned sub-matrices, and the computed QR factor R^- contains small roundoff error which is row stable. Several numerical experiments are also provided to compare the results of the ordinary Modified Gram-Schmidt algorithm with column pivoting and the row block Modified Gram-Schmidt algorithm with column pivoting.     

桁架结构稳定分析的几何非线性欧拉稳定理论

目前,桁架结构稳定分析有两个理论:经典的特征值理论和几何非线性临界点理论。前者发展较早,在许多结构力学书中都有叙述。但是经过工程应用检验,它过高地估计了结构抗稳定的能力。后者是20年前提出的,提出者认为适用于所有的扁桁架。经过几年的研究,作者连续提出三个稳定理论:线性与非线性欧拉理论;非线性临界点-欧拉理论和两个计算方法,进行桁架结构的线性和非线性截面优化设计。经过理论研究和对前人文献中数值例题的计算和比较,发现特征值理论不符合实际,临界点理论只适用于大扁度的桁架,而不适用于一切扁桁架。研究结果提供了若干有用的结论,给出了各种稳定理论的适用范围,指出了国际文献中若干例题的正确和错误,补充了桁架结构的稳定分析理论,使之更为完整和实用了。     

岩土材料应变局部化的有限元分析方法

采用有限单元法分析岩土材料的应变局部化时经常会遇到单元尺寸敏感性问题和网格锁定问题。自适应网格技术能够有效地解决网格锁定问题,但仍然无法克服计算结果对单元尺寸的依赖性,尽管在一维情况下被证明是可行的。复合体理论(均匀化理论)和弱非连续有限元方法可以成功地解决岩土材料的单元尺寸敏感性问题,在一维情况下两类方法实际上是一致的。本文针对岩土材料应变局部化的有限元新技术所存在的若干问题进行了详细的讨论,并给出了有关算例。     

基于特征值方法的旋翼尾迹稳定性分析

给出一个旋翼尾迹线性化稳定性分析的方法.在该方法中,尾迹涡线被离散为直线涡段,尾迹的扰动归结为涡元端点的扰动,考虑了桨尖涡的自诱导和涡线的互诱导以及桨尖涡与桨叶的实际干扰.使用该方法,分别以UH-1H和AH-1G模型旋翼为例,对悬停和前飞状态的旋翼尾迹的稳定性进行计算和分析.结果表明:旋翼尾迹运动存在大于0的特征值,是内在不稳定的,且最大发散率随波数变化呈现出一定规律性;前飞与悬停状态不同,其最大发散率减小,不稳定性减弱.