Adiabatic theorems for dense point spectra

We prove adiabatic theorems in situations where the Hamiltonian has dense point spectrum. The gap condition of the standard adiabatic theorems is replaced by an appropriate condition on the ineffectiveness of resonances.Supported under NSF grant number DMS-8801548 and DMS-8416049     

Poro-viscoelastic properties of anisotropic cylindrical composite materials

A new poro-viscoelastic mechanical model, which is able to predict strain creep, stress relaxation and instant elasticity for anisotropic cylindrical composite materials based on the characteristics of dentinal biomaterials of cylindrical microstructures, is described. The model enables evaluation of the poro-viscoelastic properties of dentinal biomaterials with no cracks and with fatigue-cracks. The predicted poro-viscoelastic properties obtained from the present anisotropic constitutive model agree well with the available experimental data for both wet and dry situations. The present model can be applied to anisotropic cylindrical composite materials other than biomaterials.     

光波在左手材料中的菲涅尔公式和布儒斯特定律

根据Maxwell的电磁场理论，推导出单色平面光波入射到介电常量和磁导率分别为ε1、μ1和ε2、μ2的两种介质时的菲涅耳公式和反射率及透射率的普适表达形式.对于ε2<0 和，μ2<0的左手材料，普适菲涅耳公式同样适用.研究了光从右手材料入射到左手材料时反射和折射的特性，给出了反射光为全偏光时布儒斯特角应满足的条件,此条件说明,在左手材料中布儒斯特角不但与折射率有关而且与磁导率有关.     

Durability of sound absorbing materials for highway noise barriers

This paper presents the results of a research study into two properties of sound absorbing materials intended for highway noise barrier applications: their durability and their sound absorption coefficients before and after exposure to adverse weather. After surveying the products of 34 manufacturers, eight materials and one “absorption system” were tested in the field and the laboratory. Even though there is no single, accepted test for weather endurance for these kinds of material, the results of the study provide in ormation on their likely future behaviour when installed on a barrier. The results apply at least partially to other outdoor situations too, and augment the limited information presently available on sound absorptive materials for outdoor use.     

基于平均二次电子发射系数的航天器表面起电特征分析

为了进一步贴近航天器表面起电环境以得到更加可信的分析结果,针对航天器在恶劣充电环境下的表面起电问题,考虑空间等离子体双麦克斯韦分布情况,建立了基于平均二次电子发射系数的航天器表面起电阈值方程,可在入射电子能量连续分布情况下定量分析航天器表面起电特征,其中双麦分布可更好地描述磁层亚爆期间的恶劣充电环境。经过理论分析,归纳出双麦分布下的两种典型等离子体状态。通过仿真计算,得到了在两种典型等离子体状态下航天器表面电位随等离子体浓度和温度变化的特征。结果表明:电子温度越高,表面负带电电位越高,充电越严重,与此同时,双麦分布下等离子体两种电子组分的浓度比值对带电结果有重要影响。     

Comparative properties of systems involving dangling bonds

Abstract

The role of dangling bonds in tetrahedrally coordinated systems is analyzed in a variety of different physical situations: tricoordinated silicon atoms at the Si—SiO₂ interface or in a-Si, vacancies in covalent materials or in compounds, pinning of some impurity levels, dangling bonds at surfaces and interfaces. Emphasis is put on the common features that exist in all these apparently very different situations, resulting in a fairly simple and general understanding of the related physical properties.     

双源共蒸法制备非均匀膜的模型分析

探讨了双源共蒸法制备非均匀薄膜的堆积模型，并给出了非均匀膜的沉积速率与两种膜料沉积速率的关系.当两种膜料的沉积单分子大小近似相等或者小分子沉积速率远大于大分子时，可以近似认为混合介质膜的沉积速率等于两种膜料的沉积速率之和；当两种膜料的沉积单分子大小不满足近似相等且两种膜料的沉积速率可比较时，非均匀膜的沉积速率不能简单地用两种膜料的沉积速率之和来近似，它将随两种膜料沉积单分子的大小不同和沉积速率比不同按照不同的规律变化，并在文中给出了不同情况下的非均匀膜的沉积速率变化规律. 关键词： 非均匀膜 共蒸法 模型     

On the occurrence of naked singularity in spherically symmetric gravitational collapse

Generalizing earlier results of [1], we analyze here the spherically symmetric gravitational collapse of a matter cloud with a general form of matter for the formation of a naked singularity. It is shown that this is related basically to the choice of initial data to the Einstein field equations, and would therefore occur in generic situations from regular initial data within the general context considered here, subject to the matter satisfying the weak energy condition. The condition on initial data which leads to the formation of black hole is also characterized.     

Elastic consequences of a single plastic event: A step towards the microscopic modeling of the flow of yield stress fluids

With the eventual aim of describing flowing elasto-plastic materials, we focus here on the elementary process of such a flow, a plastic event, and compute the long-range perturbation it elastically induces in a medium submitted to a global shear strain. We characterize the effect of a nearby wall on this perturbation, and quantify the importance of finite-size effects. Although most of our explicit formulae refer to 2D situations, our statements hold for 3D situations as well.     

等离子体四波混频精确解反射光栅位形

给出了均匀磁化等离子体介质中的简并与近简并的寻常波四波混频形成反射光栅位形时的普适非线性耦合方程组。在不作无衰减抽运近似的情况下,得到了任意复耦合系数时的方程组的精确解。其解不仅可以推广到各种等离子体形态,而且可以推广到光致折射材料中去。对进一步理论研究四波混频相位共轭,发展新的非线性光学器件可能有所帮助。