Comparative study of defect states in light-soaked and high-temperature-annealed a-Si:H

The electrical conductivity, light-induced ESR (LESR) and constant photocurrent method (CPM) measurements were performed on a-Si:H films which had been high-temperature-annealed (HTA) and on those which had been light-soaked (LS) at room temperature. The results were compared for HTA and LS samples with similar levels of the neutral dangling bond density. It is found from the electrical measurements that LS samples exhibit more prominent decrease in the electrical conductivity, suggesting a change in the network structure besides the creation of neutral dangling bonds. It is also found from the LESR and CPM measurements for HTA and LS samples that the ratio of the density of neutral dangling bonds to that of charged ones is increased more prominently by light soaking than by high-temperature annealing.     

Microstructural characteristics of ultrafine-grained aluminum produced using equal-channel angular pressing

The shearing associated with equal-channel angular (ECA) pressing was examined using optical microscopy. Samples of pure A1 with a large grain size were subjected to ECA pressing to different strains and then examined on three orthogonal planes. Samples were pressed without any rotation or with rotations of either 90 or 180 deg between each consecutive pressing. The experimental observations are compared with models which predict the shearing characteristics associated with ECA pressing under different conditions. It is demonstrated that there is good agreement, in terms of both the grain elongation and the shearing within individual grains, between the experimental results and the predictions of the models. This article is based on a presentation made in the symposium “Mechanical Behavior of Bulk Nanocrystalline Solids,” presented at the 1997 Fall TMS Meeting and Materials Week, September 14–18, 1997, in Indianapolis, Indiana, under the auspices of the Mechanical Metallurgy (SMD), Powder Materials (MDMD), and Chemistry and Physics of Materials (EMPMD/SMD) Committees.     

Temperature dependence of fracture toughness of epoxy resins cured with diamines

The fracture toughness (critical stress intensity factor, K _Ic) of epoxy resins cured with four diamines has been measured as a function of temperature over the range from –35° C to above T _g. It was found that K _Ic for each epoxy-diamine system did not vary below room temperature, and in the higher temperature range K _Ic increased with increasing temperature to a maximum and then decreased. The temperature which maximized K _Ic, agreed with the temperature at which the flexural modulus of the epoxy resins abruptly dropped. This temperature was therefore considered as T _g. This temperature was found to be about 20° C lower than the heat deflection temperature under load (1.82 M Pa) of the resins.     

Hybridization between Si3N4 and SiC films by plasma CVD

Journal of Materials Science Letters -     

Classification and analysis of voltage stabilities in power systems

The voltage stability problem has long been studied by many researchers mainly by means of two approaches: the static approach in which voltage stability is considered as a load-flow problem; and the dynamic approach in which it is dealt with as a stability problem in dynamic systems. However, up to now, these separate approaches have not clarified sufficiently the overall aspect of the voltage problem. In fact, there are no proper criteria to determine which approach is suited to analyze voltage stability. Thus, a basic study seems to be needed under such a situation. This paper investigates the voltage stability problem from the viewpoint of mechanism causing voltage instability. Various dynamic factors which affect voltages are studied as much as possible. First, possible voltage instability patterns are classified based on singular perturbation theory. That is, four categories of instabilities are defined mathematically. Second, a method of stability assessment for each instability is presented. It is clarified that the determinant of the load-flow Jacobian is an effective index to approximately assess two types of instabilities. On the other hand, the remaining instabilities require eigenvalue analyses or direct nonlinear analyses. The validity of these results is verified through numerical simulations and eigenvalue analyses in which dynamic characteristics of generating units, loads and tap-changing transformers are taken into account.     

Thermal expansion of interlayer spacing and thermal vibrational displacement of carbon atoms in petroleum coke

On petroleum coke heat-treated at various temperatures in the range from 1600 to 3000°C, thermal expansion of the interlayer spacing and the mean-square displacement along the c-axis due to thermal vibration of carbon atoms were measured from room temperature to 1050°C by means of X-ray diffractometry. The static mean-square displacement due to imperfect crystallization was also estimated for each sample.The c-axis spacing increases linearly with temperature and the slopes had almost the same values (1.85×10^–4 to 1.89×10^–4Å/°C) for all samples. The mean-square thermal vibrational displacements of carbon atoms increased almost linearly from 0.012Ų at room temperature to 0.047Ų at 1000°C for all samples, except for the sample heat-treated at 1640°C.A mean free space between the layer planes, that is the interlayer spacing minus twice the total root-mean-square displacement of carbon atoms along the c-axis direction, was obtained in consideration of the mean-square thermal vibrational displacement and the mean-square static displacement. The mean free space increases abruptly with decrease of c-spacing from 6.86 to 6.85Å (heat-treatment temperatures of 1640 and 2100°C respectively), then decreases slowly and eventually again begins to increase with further decrease of c-axis spacing to 6.73Å.     

In-channel focusing of flowing microparticles utilizing hydrodynamic filtration

We present herein microfluidic systems to continuously focus the positions of flowing particles onto the center of a microchannel, which is indispensable to various applications for manipulating particles or cells such as flow cytometry and particle-based bioassay. A scheme called ‘hydrodynamic filtration’ is employed to repeatedly split fluid flows from a main stream, while remaining particles in the main stream. By re-injecting the split flows into the main channel, these flows work as sheath flows, focusing the positions of the particles onto the center of the microchannel without the help of sheath flows or complicated devices generating physical forces. In this study, we proposed two schemes, and compared the focusing efficiencies between the two schemes using particles 5.0 μm in diameter. Also, we confirmed that the flow speed did not affect the focusing efficiency, demonstrating the versatility and applicability of the presented systems. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.