Electric fields in the rheology of disperse systems

In the present survey, the influence of electric fields on the structure and rheological properties of disperse systems as well as the effect of deformations on their electrical characteristics are discussed. The properties of these systems are considered in terms of the dielectric permittivity and electrification potential. The considerable thickness of the double electric layer around the disperse phase particles, which is characteristic of disperse systems with nonpolar hydrocarbon dispersion media, provides the possibility for strong electric fields to produce an electric nonuniformity on the surface of the disperse phase particles. The formation of hydrate layers on the particles creates the possibility of polarization of the disperse phase. In plastic disperse systems such as greases, a strong orientation effect is observed, which contributes to the creation of frozen flow patterns when the flow is suddenly stopped. The survey is concluded with a consideration of the process of formation of chain structures in the direction of the lines of force of the electric field whose orientation is normal to the direction of flow, which can lead to complete stoppage of the flow.     

Convex duality for finite-fuel problems in singular stochastic control

Upon introducing a finite-fuel constraint in a stochastic control system, the convex duality formulation can be set up to represent the original singular control problem as a minimization problem over the space of vector measures at each level of available fuel. This minimization problem is imbedded tightly into a related weak problem, which is actually a mathematical programming problem over a convex,w*-compact space of vector-valued Radon measures. Then, through the Fenchel duality principle, the dual for the finite-fuel control problems is to seek the maximum of smooth subsolutions to a dynamic programming variational inequality. The approach is basically in the spirit of Fleming and Vermes, and the results of this paper extend those of Vinter and Lewis in deterministic control problems to the finite-fuel problems in singular stochastic control. Meanwhile, we also obtain the characterization of the value function as a solution to the dynamic programming variational inequality in the sense of the Schwartz distribution.The author is much indebted to Professor Wendell H. Fleming for his constant support and many helpful discussions during the preparation of this paper.     

Generalized projection and approximation of fixed points of nonself maps

Let K be a nonempty closed convex proper subset of a real uniformly convex and uniformly smooth Banach space E; T:K→E be an asymptotically weakly suppressive, asymptotically weakly contractive or asymptotically nonextensive map with F(T){xK: Tx=x}≠. Using the notion of generalized projection, iterative methods for approximating fixed points of T are studied. Convergence theorems with estimates of convergence rates are proved. Furthermore, the stability of the methods with respect to perturbations of the operators and with respect to perturbations of the constraint sets are also established.     

论光滑粒子流体动力学(SPH)方法

“光滑粒子流体动力学(SPH-SmoothedParticleHydrodynamics)”是近20多年来发展起来的一种新的纯Lagrange方法.SPH是一种质点方法,有点类似质点网格法,但根本的不同点在于SPH方法中计算空间导数时不需要使用任何网格,而被插值公式中的解析微分式子所替代,从而避免了高维拉氏差分网格法中网格缠结和扭曲等最令人头痛的问题.这种方法另一个突出的优点是表现在对缺乏对称性和内含真空的三维系统的计算特别有效.因为利用网格建立的所有传统的差分方法,随着网格数目的增加,到了三维情形变得难以招架,真空区域的网格剖分造成内存储量的大量浪费又实在令人可惜,而SPH恰能克服上述的缺点.本论文重点介绍了该方法的理论基础和SPH执行过程等有关问题.     

Lipschitz局部严格伪压缩映象的迭代逼近

设Ｋ是一致光滑Ｂａｎａｃｈ空间Ｋ的非空子集，Ｔ：Ｋ→Ｘ是Ｌｉｐｓｃｈｉｔｚ局部严格伪压缩映象。本文给出一个迭代序列强收敛到Ｔ的唯一不动点，并给出一个涉及Ｌｉｐｓｃｈｉｔｚ局部强增殖映象Ｔ的非线性方程Ｔｘ＝ｆ的解的迭代逼近。     

Near-i.r. Absorption of H2O and D2O in the liquid and supercooled range

Summary Results are reported on near-i.r. absorption spectra of H₂O and D₂O down to the temperature region of supercooled liquid. No anomalous behaviour is observed when the absorbance at any given frequency is studied as a function of temperature. A critical-exponent behaviour strikingly correlating with that exhibited by transport properties is instead observed when spectral deconvolution methods are used. Results are discussed in relation with current views on water structure, based on molecular-dynamics simulation results and connectivity calculations.

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Riassunto Si riportano risultati sugli spettri di assorbimento i.r. di H₂O e D₂O fino alla regione di temperature del liquido sopraraffreddato. L'andamento dell'assorbanza a frequenza costante in funzione della temperatura non mostra alcuna indicazione di comportamento anomalo. Al contrario, quando gli spettri sono analizzati con metodo di deconvoluzione, si osserva un comportamento di tipo esponente critico, che correla straordinariamente bene con quello mostrato dalle proprietà di trasporto. I risultati sono discussi anche in relazione ai piú recenti modelli di struttura dell'acqua, derivanti dai risultati di simulazione e dai calcoli di connettività.

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Резюме Приводятся результаты для спектров инфракрасного поглощения H₂O и D₂O для температур переохлажденной жидкости. Не обнаружено аномального поведения, когда поглощательная способность при заданной частоте изучается как функция темпетатуры. Напротив, при анализе спектров с помощью спектральных методов конволюции наблюдается поведение типа критической экспоненты, которое коррелирует с поведением, определяемым транспортыми свойствами. Полученные результаты обсуждаются в связи с недавними моделями структуры воды, полученными на основе моделирования молекулярной динамики и нычислений связности.

     

Effect of defects on the electronic structure of a PbI2/MoS2 van der Waals heterostructure: A first-principles study

PbI2/MoS2,as a typical van der Waals(vdW)heterostructure,has attracted intensive attention owing to its remarkable electronic and optoelectronic properties.In this work,the effect of defects on the electronic structures of a PbI2/MoS2 heterointerface has been systematically investigated.The manner in which the defects modulate the band structure of PbI2/MoS2,including the band gap,band edge,band alignment,and defect energy-level density within the band gap is discussed herein.It is shown that sulfur defects tune the band gaps,iodine defects shift the positions of the band edge and Fermi level,and lead defects realize the conversions between the straddling-gap band alignment and valence-band-aligned gap,thus enhancing the light-absorption ability of the material.     

Electronic and optical properties of Sr3X2 (X=N,P, As,Sb and Bi) compounds: first principles study

ABSTRACT

Direct bandgap semiconductors are very essential to fulfil the demand for the advancement in optoelectronic devices. Therefore it is important to predict new potential candidates having such unique features. In current work, Sr₃X₂ (X=N, P, As, Sb and Bi) compounds have been reported for the first time by well trusted FP-APW+lo method. For the better prediction of the energy band gap, mBJ is used alongwith routine generalised gradient approximation (GGA). The results show small and direct energy band gaps at Γ-Γ symmetry points with magnitude in the range from 0.62?eV (Sr₃P₂) to zero energy band gap (Sr₃Bi₂). In partial density of state Sr-d state and X-p state are contributed in the band structure. The compounds show mostly covalent bonding nature. The frequecy dependent optical properties in the linear optical range are also investigated.     

Mode structure in wideband waveguide radiofrequency CO2 lasers

We have analysed the mode structure of a wideband radiofrequency excited waveguide CO₂ laser by using different waveguide diameters and optical cavities. In particular we have observed the phase shift of some linear polarized waveguide modes in the transition region between the guided and the free Gaussian propagation.     

复杂势场量子弹球中疤痕态的量子化条件

量子疤痕是波函数在经典不稳定周期轨道周围反常凝聚的一种量子或波动现象.人们对疤痕态的量子化条件进行了大量研究,对深入理解半经典量子化起到了一定的促进作用.之前大部分研究工作主要集中在硬墙量子弹球上,即给定边界形状的无穷深量子势阱系统.本文研究具有光滑复杂势场的二维量子弹球系统,考察疤痕态的量子化条件及其重复出现的规律,得到了与硬墙弹球不一样的结果,对理解这类现象是一个有益的补充.这些结果将有助于理解具有无规长程杂质分布的二维电子系统的态密度谱和输运行为.