Electronic structure of semiconducting crystals under high stress

We present a calculation of the band structure of semiconducting crystals under arbitrarily high stress, in which all input parameters are determined from the properties of the unstressed crystal alone. The method is applied to obtain the band structure of Ge and Si at high stress, and the strain dependence of the energies and matrix elements of a number of critical-point transitions are presented.     

Tidal Effects on Groundwater Motions

Assuming a sharp interface between freshwater and seawater within a coastal aquifer, a theory is developed to account for the piezometric head movement of steady and unsteady components in terms of large- and small-time scales. Tidal fluctuations are simulated by a series of decomposed simple harmonic motions in time. Groundwater fluctuation induced by tidal motion is perturbed to the groundwater head of large-time scale. Ghyben–Herzberg formulation is applied for solutions of large-time scale and a unified formulation for various flows of small-time scale is derived (Strack, 1989). Approximate analytical solutions for amplitudes and phase lags of tidal groundwater motions and the freshwater–seawater interface for a coastal aquifer in a circular island are obtained. The induced fluctuation amplitude generally decays in distance with a parameter consisting of hydraulic conductivity, storage coefficient, thickness of aquifer and tidal period. The present approach can be applied to confined and unconfined aquifers, with only freshwater flows or interfacial flows. The theory is verified with some experimental results (Parlange, et al., 1984; Nielson, 1990). It can also used to determine physical parameters of an aquifer by monitoring the groundwater fluctuations due to tidal motions (Carr and van der Kamp, 1969).     

Generation of stable solitary waves by a piston-type wave maker

The focus of present study is on how to generate solitary waves as pure as possible by using a piston type wave maker. A meshless numerical model, which can simulate the trajectories of fluid particles in a wave motion exerted by the wave paddle, is established for the purpose of present study. The present numerical model is verified by the comparison with experimental data before it is employed to the focused problem. Various wave paddle motions are considered. The results show that solitary waves generated by applying Fenton’s solitary solution to the paddle motion proposed by Goring are purer than those generated by other paddle motions.     

Effects of solid and slotted baffles on the convection characteristics of backward-facing step flow in a channel

This study investigates the enhancement of the laminar forced convection characteristics of backward-facing step flow in a two-dimensional channel through the installation of solid and slotted baffles onto the channel wall. The effects of the height of baffle H _b, inclination of baffle installation ϕ_b, height of slot in baffle H _t, inclination of slot in baffle ϕ_t, and distance between the backward-facing step and baffle D on the flow structure, temperature distribution and Nusselt number variation for the system at various Re are numerically explored. Results show that a slotted baffle can enhance the average Nusselt number for the heating section of channel plate by the maximum 190% when Pr=0.7, H _s=0.5, L=5, H _b ≤ 0.3, W _b ≤ 0.2, 0.1 ≤ D ≤ 0.5, 0° ≤ ϕ_b ≤ 45°, H _t ≤ 0.1, 0° ≤ ϕ_t ≤ 45° and 50 ≤ Re ≤ 400. As for the solid baffle, the enhancement may be up by 230%. The solid baffle might cause the re-separation of main stream, and consequently result in poor local heat transfer coefficient in the end region of heating section. This disadvantage can be obviously improved as the baffle is slotted. Besides the penalty of increase in pressure drop due to the baffle installation is much higher for the situation with solid baffle.     

Combined heat and mass transfer in laminar gas stream flowing over an evaporating liquid film

A numerical analysis was carried out to study the detailed heat and mass transfer characteristics in laminar gas stream flowing over a falling liquid water film by solving the respective governing equations for the liquid film and gas stream together. It was observed that the cooling of the liquid film is mainly caused by the latent heat transfer connected with the vaporization of the liquid film. Significant liquid cooling results for the system with a high inlet liquid temperature, high gas stream velocity or a low liquid flowrate. Additionally, the predicted Nusselt and Sherwood numbers were correlated.     

Solution processed amorphous InGaZnO semiconductor thin films and transistors

Amorphous indium gallium zinc oxide (a-IGZO) semiconductor thin films and transistors were deposited on alkali-free glasses by the sol–gel route. The atomic ratio of In:Ga:Zn in the solution was 0.7:0.3:1. In this study, the effects of annealing temperature on the structural, surface condition, optical transmittance, and electrical resistivity of a-IGZO semiconductor thin films were investigated. GIXRD measurements and TEM-NBD analysis indicated that all annealed IGZO thin films had an amorphous phase structure. The dried IGZO sol–gel films annealed at a temperature higher than 425 °C had a flat surface and exhibited high transparency (>89%) in the visible region. According to results from TGA, FT-IR and XPS, the residual organic compounds in the dried IGZO sol–gel films were completely removed at the annealing temperatures higher than 450 °C. Therefore, we chose the 450 °C annealed thin film as the active channel layer in the bottom-gate, bottom-contact (BGBC) thin-film transistor (TFT) in the present study. Current–voltage (I–V) characteristics of the 450 °C annealed a-IGZO TFT revealed that it operated in n-type behavior with a positive threshold voltage (enhancement mode).     

Enhancement of pool boiling heat transfer in a horizontal water layer through surface roughness and screen coverage

An experimental investigation was carried out to study the augmentation of heat transfer in saturated pool boiling of a liquid water layer on a heated horizontal stainless steel plate by roughing the surface and/or covering it with a single layer of stainless steel screen. The results were presented in terms of the boiling curves. Effects of various parameters – the surface roughness, liquid level and size of the stainless steel mesh on the boiling heat transfer were examined in detail. The measured data clearly indicated that a lowering of the liquid level from 60 to 5?mm in water depth causes heat transfer reduction. Roughing the surface was found to sig- nificantly enhance the heat transfer. Use a layer of metal screen to cover the heated surface was shown to substantially augment the heat transfer especially for a shallow water layer if the mesh size is comparable with the bubble departure diameter. Covering the rough surface with the metal mesh, however, reduced the heat transfer.