On the dynamic behavior of gas bubbles in an inhomogeneous standing wave

The motion of gas bubbles in an inhomogeneous standing wave is examined. The nonlinear system of equations is solved by the averaging method. Stationary solutions (bubble clusters) are found, and the conditions for their stability are established __________ Translated from Prikladnaya Mekhanika, Vol. 42, No. 5, pp. 88–94, May 2006.     

L p-Perturbations of Invariant Subbundles for Linear Systems

We use Riccati's equations and the ordinary and exponential dichotomies to get simple recurrent formulae for the asymptotic integration of linear systems subjected to L _p -perturbations with arbitrary p 1. Moreover, we establish conditions which are necessary and sufficient for the persistence of one-dimensional invariant subbundles for the linear system under L _p -perturbations. In this way, we prove the sharp nature of the well known Levinson and Hartman–Wintner asymptotic theorems.     

Multiscale Structures to Describe Porous Media Part I: Theoretical Background and Invasion by Fluids

A porous medium with a broad pore-size distribution is described on the basis of the Multiscale Percolation System concept. The representative structure is the superposition of several constitutive elementary networks, of which mesh sizes are proportional to the diameter of the class of pores considered. To account for the contribution of each class to the connection of the medium, a recurrent building process, involving rescaling and superposition, is defined. This process leads to an equivalent monoscale network, involving elements representative of the various classes. Mercury intrusion at increasing pressure into a finite-size sample of this equivalent network is modelled. The inverse problem is solved, leading to the identification of the representative multiscale structure of a given material from the experimental intrusion curve.     

The effect of pore-structure on hysteresis in relative permeability and capillary pressure: Pore-level modeling

The effect of pore-structure upon two-phase relative permeability and capillary pressure of strongly-wetting systems at low capillary number is simulated. A pore-level model consisting of a network of pore-bodies interconnected by pore-throats is used to calculate scanning loops of hysteresis between primary drainage, imbibition and secondary drainage. The pore-body to pore-throat aspect ratio strongly influences the pattern of hysteresis. Changes in the patterns of hysteresis often attributed to consolidation can be understood in terms of changes in aspect ratio. Correlation between the sizes of neighboring pore-throats affects the shape of the relative permeability curves, while the width and shape of the pore-size distribution have only a minor influence.     

自重体积力作用下坡体张应力及坡面位移的变化规律

为了提高对边坡体力学行为的认识,借助于FLAC有限差分软件的数值模拟,并结和相似理论的推导验证,研究了在仅有自重体积力作用的条件下,线弹性边坡体的一些力学特征及其与相关变量或物理力学参数的相关关系。没有外载荷影响时边坡地表最大主应力和最小主应力分别平行和垂直于地表,当深度增加时,主应力的取向逐渐变成竖直和水平两个方向,坡面处既有张应力区也有拉应力区,坡脚处亦存在较大的张应力,这是自重体积力作用下边坡体应力分布的一般性特征,在本文和前人的研究中都能体现。本文还重点揭露了：坡角线性增加时坡顶最大张应力的变化速率表现为：快——慢——快; 沿坡顶面竖直向下张应力随深度增加线性减小; 小变形条件下边坡应力场与弹性模量无关; 最后验证了满足相似理论的坡体,坡面对应点的位移比是其几何尺寸比的平方倍。本文不仅是对既有研究成果的进一步补充,而且为以后研究复杂条件下边坡体的力学特征奠定了基础,对于理论和实践都有一定的启发意义。     

Exact solutions to the equations of perfect gases through Lie group analysis and substitution principles

In this paper we consider the equations that govern the motion of perfect gases. We explicitly characterize some classes of steady solutions in two and three space dimensions, by introducing invertible point transformations suggested by Lie group analysis; moreover, by using various transformations known as substitution principles, new steady and unsteady solutions are constructed.     

Nearly-Hamiltonian Structure for Water Waves with Constant Vorticity

We show that the governing equations for two-dimensional gravity water waves with constant non-zero vorticity have a nearly-Hamiltonian structure, which becomes Hamiltonian for steady waves.      

Tm3+/Yb3 :LiYF4单晶的高效近红外量子剪裁及其在光伏电池中的应用

采用改进的坩埚下降法成功地生长了Tm/Yb共掺氟化钇锂单晶. 该单晶体具有每吸收一个蓝色光子并能发射出2个1000 nm近红外光子的下转换发光效应. 测定了样品的激发光谱、发射光谱和荧光衰减曲线. 在465 nm蓝光激发下观察到由Yb³⁺：²F_5/2→²F_7/2能级跃迁所致的960～1050 nm 波段的发射带,此发光带源于Tm³ 对Yb³ 离子的能量下转换过程. 应用Inokuti-Hirayama模型,研究了晶体的能量转换过程,结果表明Tm³ 向Yb³ 的能量传递是一个电偶极子相互作用机制过程. 当Tm³ 与Yb³ 离子的掺杂浓度为0.49mol%与5.99mol%时,单晶的量子剪裁效率达到最大值167.5%.     

非晶碳氧化硅纳米线的合成与光致发光

利用直流电弧放电合成非晶碳氧化硅(SiCO)纳米线,不使用催化剂和模板,独立的SiCO 纳米线沉积在石墨锅的表面．通过XRD、SEM、TEM、XPS、FTIR等对SiCO纳米线进行了表征．结果表明,纳米线长度为20～100 μm,直径为10～100 nm,Si原子同C原子和氧原子分享成键组成SiCO单元．SiCO纳米线的光致发光谱在454和540 nm呈现了强而稳定的白色发光峰． SiCO纳米线的生长机制为等离子辅助气―固生长机制．     

纳米金刚石掺混纳米氧化锌的场发射特性

利用水热法制备了菊花状的氧化锌纳米棒,并进行表征,将纳米氧化锌掺入纳米金刚石中配制成电泳液,超声分散后电泳沉积到钛衬底上,再经热处理后进行场发射特性的测试.结果表明:未掺混的金刚石阴极样品的开启电场为7.3V/μm,在20V/μm的电场下,场发射电流密度为81μA/cm2;掺混后阴极样品的场发射开启电场降低到4.7~6.0V/μm,在20V/μm电场下,场发射电流密度提高到140~158μA/cm2.原因是纳米ZnO掺入后,增强了涂层的电子输运能力、增加了有效发射体数目,提高了场增强因子β,而金刚石保证了热处理后涂层与衬底的良好键合,形成了欧姆接触,降低了场发射电流的热效应.场发射电流的稳定性随掺混ZnO量的增加而下降,要兼顾场发射电流密度及其稳定性,适量掺入ZnO可有效提高纳米金刚石的场发射性能.