Asymptotic fields at the tip of a cohesive crack

Recently, the authors (Xiao and Karihaloo, J Mech Mater Struct 1:881–910, 2006) obtained universal asymptotic expansions at a cohesive crack tip, analogous to the Williams (ASME J Appl Mech 24:109–114, 1957) expansions at a traction-free crack tip for any normal cohesion-separation law (i.e. softening law) that can be expressed in a special polynomial. This special form ensures that the radial and angular variations of the asymptotic fields are separable as in the Williams expansions. The coefficients of the expansions of course depend nonlinearly on the softening law and the boundary conditions. They demonstrated that many commonly-used cohesion-separation laws, e.g., rectangular, linear, bilinear and exponential, can indeed be expressed very accurately in this special form. They also obtained universal asymptotic expansions when the cohesive crack faces are subjected to Coulomb friction. The special polynomial involves fractional powers which seem rather contrived. In this paper, we will show that the asymptotic expansions can be obtained in a separable form even when the cohesion-separation law is in a special polynomial form involving only integer powers.     

Design and performance of the solar-powered floor heating system in a green building

In the green building of Shanghai Research Institute of Building Science, the evacuated tubular solar collectors with a total area of 150 m² were installed to provide heating for the covered area of 460 m². The floor heating coil pipes were made of high-quality pure copper with the dimension of Φ 12 × 0.7 mm. Under typical weather condition of Shanghai, the average heating capacity was 25.04 kW during the working hours from 9:00 to 17:00, which was sufficient to keep indoor thermal environment. The average electric COP of the floor heating system was 19.76 during the system operation. Compared with the widely used air-source heat pump heating systems with the electric COP of 3.5 in Shanghai, the solar-powered floor heating system shows great potential in energy conservation in winter. With respect to the whole heating period, the solar fraction was 56%. According to the performance analysis of the system with ambient parameters, it was observed that the system performance could be greatly enhanced with the increase of daily solar insolation. However, the system performance varied slightly with average ambient temperature. Compared with average ambient temperature, daily solar insolation had a more distinct influence on the performance of the solar-powered floor heating system.     

Conductivity and Magnetic Susceptibility of Nanotube/Polypyrrole Nanocomposites

A method has been developed to produce a carbon nanotube/conducting polymer nano-composite through in-situ polymerization of pyrrole in the carbon nanotube template. The nano-composites of carbon nanotube and polypyrrole have been characterized by SEM, TEM, XRD, Raman Scattering. The thermal stability was studied by TGA (Thermal Gravity Analysis). The measurements of conductivity and magnetic susceptibility of the composites have been studied.     

Probing the time course of representational momentum.

Observers saw a rectangle at three orientations along a path of rotation. They attempted to remember the third orientation and were then tested with a fourth orientation that was either the same as, or slightly different from, the third. As in previous representational momentum studies we find that memory for position is distorted in the direction of the implied motion, in analogy to physical momentum. We now report that memory shift increases with retention interval for small intervals, as predicted by the analogy. However, instead of reaching some asymptotic value, the memory shift then decreases with retention interval. The results U-shaped curve may be considered the result of two competing effects: a positive memory shift attributable to representational momentum, which dominates at short intervals, and a negative shift attributable to memory averaging effects, which dominates at longer intervals. The memory averaging effect increases with retention interval and is strongest for faster presentation rates. For very short retention intervals the rate of increase in memory shift is proportional to the implied velocity of the inducing display, as predicted from the analogy to physical momentum. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of VDT data entry work on operators

The before/after study of physiological and biochemical parameters was used to delineate the effects of VDT data entry work on operators. Twenty-nine healthy Chinese students were chosen and divided at random into the simple and the complicated data entry group. The subjects were instructed to work as quickly and correctly as possible according to the 'Data Entry Work Programme' for 150 min. Work performance (correct entry) was automatically recorded once every 10 min. The before/after parameters were tested respectively. The results showed that performance fluctuated over time. It decreased obviously after 50-60 min of work, followed by a rebound, and there was a terminal motivation phenomenon at the end of the test, which was associated with the auto-arousal and cerebral compensatory effort. Changes in physiological parameters revealed that operators were fatigued after data entry work. The adrenaline excretion in urine showed a tendency to increase after simple data entry work. The noradrenaline excretion showed a tendency to decrease after complicated data entry work. The differences in performance, diastolic blood pressure in a standing position and neurobehaviour between two groups indicated that much stress was experienced when performing complicated data entry work.     

Ion-milled waveguide lenses and lens arrays in GaAs

The authors discuss ion-milled planar waveguide lenses in GaAs which exhibit a considerably higher efficiency than that previously reported for those lenses and near diffraction-limited spot size. The authors also report the performance characteristics of these latest lenses, including single lenses and lens array of analog Fresnel, chirp grating, and hybrid types as well as a collimation-Fourier transformation lens-pair, together with the detailed design and fabrication procedures. A simple theoretical model for the lens efficiency is also formulated to assist in the lens design. Ion milling has been shown to be a simple and versatile technique for fabrication of waveguide lenses in GaAs and applicable to any other substrate material. Such ion-milled waveguide lenses should facilitate realization of a variety of monolithically integrated optic device modules and circuits in GaAs and other related substrates with applications to communications, signal processing, and computing     

The relationships between resistance and thermoelectric properties caused by impurities in metals

A set of linear relationships between resistance and thermoelectric properties caused by impurities in metals have been derived from Matthiessen's rule and the Mott theory. These are the linear relationships between temperature coefficient of resistance and thermoelectric power or motive force, the change in resistance ratio and impurity concentration, and the change in temperature coefficient of resistance and impurity concentration etc. In terms of these linear relationships we have interpreted the empirical formulae and experimental results of platinum containing impurities in detail.