Simulation of a turbulent premixed open V-shaped flame using contour advection with surgery

Despite its capability of high spatial resolution, simulation of turbulent flows with traditional Lagrangian (front tracking) scheme is often discouraged by numerical instability caused by clustering of marker nodes and topological changes of fronts. Contour advection surgery (CAS), being a robust front tracking scheme, can limit the growth of front complexity during simulation without jeopardizing accuracy or efficiency. This allows it to open up an advantage over traditional front-tracking schemes. It has already been demonstrated that CAS, with incorporation of the reaction sheet model, can accurately simulate the propagation and advection of a turbulent premixed V-shaped flame. In this study, it is further tested with 10 values of vortex circulation. A range of upstream turbulence levels of 1.8–19.8% was obtained. Results indicate that upstream turbulence increase the average flame length, flame zone area and the overall burning rate. Flame surface density Σ was also estimated. Maximum values of Σ obtained lie in the range 0.1–1.4 mm⁻¹. Skewness towards the burnt region was observed in all profiles of Σ. Similar to results from laboratory experiments, it was found that Σ values decreases with upstream turbulence. From this study, the ability of CAS to cope with intense turbulence is demonstrated and a better quantitative understanding on the scheme has also been acquired.     

V型河谷地应力研究

介绍了河谷地应力研究现状 ,利用弹性理论和变分原理 ,研究了V型河谷岩体地应力问题 ,得到了河谷岩体中由于自重应力和构造应力引起的复杂应力场。应用本文结果 ,不仅可以方便绘制各种应力图件 ,而且可以较为精确地得到河谷区域任意指定点的应力值 ,从而为区域稳定性和岩体稳定性评价 ,为水电工程、地下硐室设计以及边坡工程等提供必要的岩体力学资料。本文方法数值实现简单 ,编程容易 ,计算快 ,精度高 ,可应用推广.     

Modification of the fracture criterion for V-shaped notches (plane problem). Relationship between toughness and strength and structural parameters

A fracture criterion of the type of the Neuber-Novozhilov criterion is proposed to describe the fracture in the vicinity of the tip of a V-shaped notch under tensile and shear loading. In the proposed criterion, the limits of averaging of the stresses along the notch axis depend on the presence, location, and size of the initial defects in the material. The crystal lattice parameter of the initial material is chosen for the characteristic linear size. For a V-shaped notch subjected to tension and shear, simple equations are obtained that relate the stress intensity factors for the modified singularity coefficients, the singularity coefficients themselves, and the theoretical tensile and shear strengths of a single crystal of the material taking into account the damage to the material in the vicinity of the notch tip. The equations obtained allow a passage to the limit from a notch to a crack. It is shown that the classical critical stress intensity factor used in the strength analysis of cracked solids is not a material constant.Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 1, pp. 106–115, January–February, 2005.     

V形固体激光腔的动力学分析与改进

对通用的V形固体激光腔进行了全面的动力学分析，指出了它的优缺点，它的致命缺点是在动力学因子1ft≈1l1-f附近出现高损耗的运行区，激光器无法运行.为了克服这一缺点，在一种改进的V形腔基础上提出了一种更为紧凑的V形改进腔. 关键词： 固体激光腔 V形固体激光腔 改进的V形腔     

Electric field induced non-linear multisubband electron mobility in V-shaped asymmetric double quantum well structure

ABSTRACT

We study the effect of the external electric field F_ext on the low-temperature electron mobility μ in an asymmetrically doped Al_xGa_1-xAs based V-shaped double quantum well (VDQW) structure. We show that nonlinearity of µ occurs under double subband occupancy on account of intersubband effects. The field F_ext alters the VDQW potential leading to transfer of subband wave functions between the wells, which affects the scattering potentials and hence μ. In the VDQW structure, due to the alloy channel layer, the alloy disorder (Al-) scattering happens to be significant along with the ionised impurity (Imp-) scattering. The non-linear behaviour of μ is because of μ^Imp, while the overall magnitude of μ is mostly due to μ^Al. The increase of difference in the doping concentrations of the outer barriers increases the nonlinearity of μ. The oscillatory character of μ is amended by varying the width of the well and barrier and also the height of the VDQW. Our results can be used to study VDQW based nanoscale field effect transistor structures.     

Molecular field theory for polar,biaxial bent-core nematics

We have studied a polar, biaxial nematic liquid crystal formed from bent-core molecules using molecular field theory. The model includes a simple Heisenberg-form dipolar intermolecular interaction in addition to the usual quadrupolar nematic interaction, and mimics a system consisting of nematogenic bent-core molecules with a large transverse dipole along the bisector of the two molecular arms. Such systems are regarded as good candidates for biaxial nematic liquid crystals. In principle, the molecular dipoles can align, thus stabilising the ordering of the minor axes. Our calculations predict that, for suitable values of the bent-core interarm angle, the biaxial nematic phase can be stabilised at higher temperatures than in the absence of the transverse dipole. In general, the transverse macroscopic polar order stabilises the biaxial nematic phase. In particular, for a large enough dipolar interaction, the Landau point in the pure biaxial nematic develops into a line of first-order polar biaxial nematic-to-isotropic phase transitions.     

Co−MOFs with 1,1′-(5-methyl-1,3-phenylene)bis(1H-imidazole) and aromatic carboxylates as coligands: synthesis,structure, and spectroscopic and thermal characterizations

Four cobalt(II) compounds, [Co(Bim)(IA)(H₂O)₂]_n·0.5nH₂O (1), [Co(Bim)(MA)(H₂O)₂]_n (2), [Co₂(Bim)₂(MA)₂]_n·nH₂O (3), and [Co₃(Bim)₄(TA)₂(H₂O)₂]_n·2.5nH₂O (4), have been synthesized by solvothermal reactions of cobalt(II) salts with 1,1′-(5-methyl-1,3-phenylene)bis(1H-imidazole) [Bim] and aromatic polycarboxylic acids (H₂IA = isophthalic acid, H₂MA = 5-methylisophthalic acid, and H₃TA = trimesic acid) as coligands. The four complexes were characterized by IR and UV?vis spectra, elemental analyses, X-ray powder and single-crystal diffractions, and thermogravimetric analyses (TGAs). 1 features a zigzag polymeric macrocycle chain containing a nanotubular channel, which is constructed by bridging the folded 20-membered macrocyclic [Co₂(Bim)₂] subunits with IA ligands. 2 represents a double-chain structure containing 18-membered macrocyclic [Co₂(Bim)(MA)] subunits. Both 3 and 4 are 2-D porous coordination polymers but have different architectures. In 3, cage-like [Co₄(Bim)₂(MA)₄] subunits are 4-connected nodes that are further bridged by another half-set of Bim ligands to form a 2-D helical structure containing one-dimensional achiral channels and alternately arranged left- and right-handed helical tubular channels. In 4, Bim ligands bridge three crystallographically independent Co centers into sharply distorted left- and right-handed helices which are further connected by TA ligands to form a meso layer about 3.0 nm monolayer thickness with a unique (3,4)-connected topology. The structural diversities of coordination polymers 1–4 are tuned by the flexible coordination number of Co and coligand polycarboxylates. Thermal analyses show that the main frameworks of all compounds remain stable to 352 °C. Moreover, the interesting color changes of crystals 1–4, varying from pink to purple and dark blue, result from the d → d* transitions of chromophoric Co²⁺ in different coordination geometries as determined by the UV–vis spectra in combination with crystal structure analyses.     

角度非均匀材料平面V形切口应力奇性分析

提出了一种确定角度非均匀材料平面V形切口尖端应力奇性指数的有效方法。首先,在弹性力学基本方程中引入V形切口尖端位移场的级数渐近展开,建立以位移为特征函数的变系数和非线性微分方程组。然后,采用微分求积法(DQM)求解微分方程组,可得到多阶应力奇性指数及其相对应的特征函数,该法具有公式简单、编程方便、计算量少和精度高等优点,可处理任意开口角度和任意材料组合的V形切口。典型算例验证了微分求积法的有效性和精确性。     

基于微悬臂梁生物传感器检测三磷酸腺苷

基于适配子构建了无标记检测三磷酸腺苷(ATP)的微悬臂梁生物传感器。 将ATP适配子修饰在微悬臂梁阵列中的传感悬臂镀金面上,用来识别ATP,而参比悬臂修饰巯基己醇(MCH)防止非特异性吸附。 ATP与其适配子发生特异性相互作用,使悬臂的上下两个表面产生应力差,导致传感悬臂产生偏转,扣除参比悬臂偏转后其偏转值与ATP的浓度在0.5~5 mmol/L范围内有良好的线性关系,相关系数为0.998,最低检出限为0.06 mmol/L。 该微悬臂梁生物传感器响应快速、操作简单,并且对ATP具有良好的特异性。