Stress and couple stress in foams

Even in the range of small elastic deformations the behavior of foams is not well described by only two elastic constants. Usually the manufacturers give values of the material parameters depending on the loading conditions. This problem is investigated on a microscopic scale by a simple beam model. It has been found that this approach shows the size effect that cannot be described within the framework of the standard continuum mechanical setting. The size effect within this model can be explained by independent rotations which do not scale with the displacement field.

A homogenization procedure is proposed that allows for the determination of macroscopic quantities like stress and couple stress in terms of volumetrical averages. The homogenized results of the microscopic model are compared to the results obtained by an enhanced macroscopic model, namely a Cosserat model. Both approaches show good agreement.     

Interdiffusion in the solid couple AgI-CuI

Interdiffusion measurements were calculated using the Boltzmann-Mattano analysis of concentration profiles and by following the thickness and resistance of the diffusion cell as a function of time. The results for the equimolar solid solution Ag_0.5Cu_0.5I were coincident for the three methods, the values of the interdiffusion coefficients being of the order of 10^–7 cm² s^–1 for the temperature range 570–620 K.     

The mortality of companies

The firm is a fundamental economic unit of contemporary human societies. Studies on the general quantitative and statistical character of firms have produced mixed results regarding their lifespans and mortality. We examine a comprehensive database of more than 25 000 publicly traded North American companies, from 1950 to 2009, to derive the statistics of firm lifespans. Based on detailed survival analysis, we show that the mortality of publicly traded companies manifests an approximately constant hazard rate over long periods of observation. This regularity indicates that mortality rates are independent of a company''s age. We show that the typical half-life of a publicly traded company is about a decade, regardless of business sector. Our results shed new light on the dynamics of births and deaths of publicly traded companies and identify some of the necessary ingredients of a general theory of firms.     

猪圈做腊味 出租屋制"日本酱油"

据报道,广州市质监人员在广州市白云区进行突击查处行动时,现场所见令人触目惊心:猪圈做腊味、双氧水泡鱼翅、农民制造"日本酱油".     

Tribospectroscopic study of a steel-steel friction couple

The force of friction between a steel plate and a steel sample oscillating at a frequency of 60–70 kHz has been studied as a function of the oscillation amplitude. The static friction force rapidly decays when the oscillation amplitude increases from zero to 0.1 μm. Then, the force decreases only slightly as the amplitude grows further up to about 0.5 μm. The experimental data are interpreted within the framework of a theoretical model comprising two bodies moving in a random potential and coupled by a randomly oscillating bond. An analysis of this model shows that the oscillation amplitude at which the behavior of the friction force exhibits a qualitative change corresponds to a spatial scale producing a maximum contribution to the frictional force. From this, it is concluded that friction in the steel-steel couple originates on a scale of about 50 nm.     

Porous slider bearing with couple stress fluid

Summary Theoretical study of porous slider bearing with couple stress fluid as lubricant is made and the lubrication qualities of couple stress fluid are examined. The lower surface is covered by a thin porous material and the upper one, having arbitrary shape, moves in its own plane with constant velocity. Analytical expressions for load capacity, frictional force and the centre of pressure are derived. It yields increase in, load capacity and ensures the decrease in coefficient of friction. The problem is also discussed in the context of various geometries viz, (1) Rayleigh step bearings and (2) inclined slider bearings. Bounds on flow rate, frictional coefficient, centre of pressure and time-height relation are obtained and compared with classical case, Gross [1]. Suitable design parameters are predicted for the efficient lubrication of slider bearings.     

Diffusion couple preparation using cast coating technique

A novel diffusion couple preparation technique suitable for the measurement of diffusivities in molten metals and semiconductors via the long capillary method has been developed. The so-called cast coating technique involves casting of a molten alloy, which contains the impurity element to be diffused, on top of the pure solvent rods. Planar, oxide and defect free interfaces were produced at the alloy/solvent junction of the diffusion couple following basic solidification principles and a controlled atmosphere. It was noted that the thermal properties of both the molten alloy and the mould were critical in determining the location and planarity of the diffusion couple interface. The Sn/Sn-1 wt% Au and Pb/Pb-1 wt% Au diffusion couples in conjunction with moulds machined from graphite, porous graphite and a machinable ceramic were chosen as a case study.