Light scattering models for describing the transmittance of transparent and translucent alumina and zirconia ceramics

The original Apetz-van-Bruggen model for predicting the transmittance of dense polycrystalline ceramics with randomly oriented birefringent crystallites is shown to be incorrect. In a correct Apetz-van-Bruggen equivalent composite model (ECM) the volume fraction must be 1/3 instead of 1/2 and the factor 2/3 in front of the maximum birefringence must be abandoned. This ECM is in good agreement with the simplified version of Pecharromán’s dense polycrystalline model (DPM) and can be improved by replacing the Jobst approximation (i.e. the large-size limit of the Rayleigh-Gans approximation) by the van-de-Hulst approximation. Similarly, a new DPM is proposed that combines the van-de-Hulst approximation with Pecharromán’s texture function. However, all these models fail for small grains. Therefore two new models (infimum-supremum-based ECM and DPM) are proposed, which combine the full Rayleigh-Gans approximation (for small grains) with the van-de-Hulst approximation (for large grains) and provide (for all grain sizes) predictions almost identical to Mie theory.     

扩展厢式展览车扩展壁板的设计

采用Shell 91和Shell 99 2种单元混合离散方法,对扩展厢式展览车的可扩展壁板进行了有限元计算分析,确定了满足展览车使用要求的壁板结构,对采用混合离散方法分析复合夹芯板承载特性的新方法进行探索,为类似结构的设计分析提供了有益参考.     

COMMENTS CONCERNING A SIMPLE EQUATION OF STATE OF THE VAN DER WAALS FORM

When the Carnahan-Starling equation of state for hard spheres is combined with a simple attractive term, the molecular size parameter b for argon (as obtained from critical data) is much closer to the “correct” value than that obtained from the empirical Redlich-Kwong equation

For the critical isotherm for argon, the best simple form of the attractive term lies between the two common forms, proposed by van der Waals and by Redlich. At constant temperature, the attractive contribution to the compressibility factor is proportional to (v + 0.2b)^?1 where v is the molar volume. This proportionality is in agreement with results for a square-well fluid recently reported by Sandier.     

铯原子与无缺陷金属表面间的范德瓦尔斯（vdw）作用势：特定量子态C3的数值计算

根据电偶极跃迁几率的定义和Wigner-Eckart定理,建立了计算铯原子与无缺陷金属表面间范德瓦尔斯（vdw）作用势的特定量子态的理论模型,并计算了铯原子基态、激发态各特定量子态C3的数值。     

Pulmonary dispersion formulations: The impact of dispersed powder properties on pressurized metered dose inhaler stability

Suspension-type metered dose inhaler formulations characteristically have a high degree of dispersion instability. This may occur as the result of any of a large number of formulation issues including phase separation, particle growth, agglomeration/flocculation, moisture ingress, and particle interactions with both the canister material and other particles. Many of these undesirable instabilities may arise as a result of the physical and chemical properties of the dispersed powder in the liquid propellant system. As such, this review provides a detailed understanding of the characteristics of the dispersed phase in the liquid propellant system necessary to ensure stability of the final formulation.     

Socially Inclusive Design in Denmark: The Maturing Landscape

With a tradition of social inclusion and innovative contemporary design, Denmark leads the way internationally in its architectural provision for an older population. Architect, author and researcher Terri Peters highlights some pioneering housing schemes in Denmark that use architecture to reduce the stigma of old age in the creation of environments that are overtly ‘homey’ or domestic – breaking away from the sanitised environment of the ‘nursing home’ – and that employ nature and landscape to positive effect, as a means of promoting healing and health.     

Close Up

The last two decades have brought with them unprecedented technological changes that have had a far-reaching impact on design ethos and culture. Hernan Diaz Alonso , Principal of Xefirotarch and Professor of Architecture at the Southern California Institute of Architecture (SCI-Arc), reflects on the nature of these changes: observing that as ‘criticality in architecture’ is ‘replaced by talent’ or ‘virtuosity’, there is a greater ‘focus on specific architectural or design problems’. This brings with it a shift from the design detail, reliant on technical expertise and precision, to ‘the close-up’ that is more concerned with resolution and the conceptual, bridging the gap between the intellectual and the physical.     

Everything We Need: Scarcity,Scale, Hyperobjects

Scarcity as a concept places an emphasis on limits and the restrictions that there might be on the supply of resources, energy and materials. Timothy Morton, who is Professor of English at the University of California, Davis, and has written extensively on philosophy and ecology, among other subjects, questions philosophically this emphasis on limits and the contemporary tendency to need to quantify everything around us. He urges us to ‘look beyond those artificial boundaries’ and ‘find abundance’.     

Van der Pol—Duffing系统共振双Hopf分岔

研究时滞反馈van der Pol-Duffing系统的共振双Hopf分岔,讨论时滞量和位移反馈增益变化对双Hopf分岔的影响。利用Hopf分岔定理得到系统出现1∶2共振双Hopf分岔的充要条件;借助中心流形定理和平均化方法约化了系统,从理论上分析共振双Hopf分岔点附近的动力学行为,得到共振双Hopf分岔引起的各种周期解的近似解析解和稳定性条件;通过数值实验,验证了理论分析的正确性。结果表明,时滞和位移反馈增益不仅导致共振双Hopf分岔,而且会使系统出现多稳态周期运动。     

谐和激励下强非线性杜芬-范德波振子的响应

为了研究力学与电子系统中典型强非线性系统的性质,提出求解强非线性刚度的杜芬-范德波振子谐和激励下响应的平均法.基于系统的哈密顿作用量及相位差是慢变量而角变量是快变量原理,通过对角变量的平均推导出系统共振时作用量及相位差的平均方程,给出不同参数时系统稳态响应的频响曲线,经过数字模拟研究了系统锁相运动的稳定性,得到了确定稳定域的近似公式并讨论了该近似公式的适用范围.数值仿真结果表明, 用该平均法预测系统的稳态响应具有很高的精度,且该方法可适用于非常强的非线性系统.