磁性稀土材料在VM制冷机中的应用

介绍用液氮作中间冷却剂产生１０Ｋ低温的ＶＭ制冷机。介绍了磁性回热材料的选择以及磁性稀土材料在制冷机中的应用与发展。在回热器中用低温下比热值较大的磁性稀土材料Ｅｒ（Ｎｉ０．７９Ｃｏ０．２１）２部分代替铅丸进行试验，无负荷温度降低，在２０Ｋ时间测得制冷量增加，证明了回热器的效率有所提高。     

An alternating method based on the VNA solution for analysis of damaged solid containing arbitrarily distributed elliptical microcracks

This paper presents the development of an alternating method for the interaction analysis of arbitrary distributed numerous elliptical microcracks. The complete analytical solutions (VNA solutions) for a single elliptical crack in an infinite solid, subject to arbitrary crack-face tractions, are implemented in the present alternating method, together with the coordinate transformations for stress tensors. First, the present method is verified by solving the problems of two interacting cracks for which accurate numerical solutions have been obtained previously. Next, the present method demonstrates obtaining efficient and accurate solutions for the problems of many interacting elliptical cracks, which cannot be solved in a practical sense by the ordinary numerical methods such as the finite element method. Furthermore, damaged solids containing periodically distributed elliptical microcracks are analyzed by the present alternating method. The effective elastic moduli are evaluated for varying microcrack density. Detailed structures of the interactions in the damaged solids are visualized and clarified. This revised version was published online in July 2006 with corrections to the Cover Date.     

Analytical study of effects of finger-growth velocity on reaction characteristics of reactive miscible viscous fingering by using a convection-diffusion-reaction model

Reactive miscible viscous fingering occurs when a reactive and miscible less-viscous liquid displaces a more-viscous liquid. Effects of bulk finger-growth velocity on reaction characteristics of miscible viscous fingering with a chemical reaction were studied analytically by using a convection-diffusion-reaction model. The model assumes the existence of a distinct interface between both liquids, assumes the existence of a two-dimensional, steady, stagnated flow field in the less-viscous liquid, and assumes an infinite chemical reaction rate. The model was then used to determine the reaction characteristics, such as the location of the reaction surface and the profile of the product, as functions of the velocity and initial reactant concentrations. The results reveal that the effects of the velocity on the reaction characteristics can be divided into low-, intermediate-, and high-velocity regions. In the low-velocity region, the reaction characteristics strongly depend on the reactant concentrations. In the intermediate-velocity region, the dependence of the reaction characteristics on the reactant concentrations decreases with increasing velocity. In the high-velocity region, the reaction characteristics are nearly independent of the reactant concentrations. Experiments confirm the existence of these three velocity regions predicted by the model.     

Gain scheduling control of variable speed WTG under widely varying turbulence loading

Probabilistic paradigms for wind turbine controller design have been gaining attention. Motivation derives from the need to replace outdated empirical-based designs with more physically relevant models. This paper proposes an adaptive controller in the form of a linear quadratic Gaussian (LQG) for control of a stall-regulated, variable speed wind turbine generator (WTG). In the control scheme, the strategy is twofold: maximization of energy captured from the wind and minimization of the damage caused by mechanical fatigue due to variation of torque peaks generated by wind gusts. Estimated aerodynamic torque and rotational speed are used to determine the most favorable control strategy to stabilize the plant at all operating points (OPs). The performance of the proposed controller is compared with the classical proportional-integral-derivative (PID) controller. The LQG is seen to be significantly more efficient especially in the alleviation of high aerodynamic torque variations and hence mechanical stresses on the plant drive train. Simulation results validate the effectiveness of the proposed method.     

Effects of alkali or acid treatment on the isomerization of amino acids

The effect of alkali treatment on the isomerization of amino acids was investigated. The 100×D/(D+L) values of amino acids from peptide increased with increase in the number of constituent amino acid residues. Furthermore, the N-terminal amino acid of a dipeptide was isomerized to a greater extent than the C-terminal residue.     

Electrical properties of Zn+-doped (AlGa)As prepared by molecular beam epitaxy and its use in shallow junction solar cells

In conventional molecular beam epitaxy the p-type dopant zinc cannot be incorporated into GaAs because of its high vapour pressure. In the present work, zinc atoms were ionized to increase the sticking coefficient and zinc-doped p-type (AlGa)As was prepared by molecular beam epitaxy for the first time. The p-type layer with hole concentrations of $\text{10}{}^{16}\text{?10}{}^{19}\text{cm}{}^{\mathrm{?3}}$ is readily produced by this technique. Measurements of the Hall effect, the impurity distribution profile and the photoluminescence showed that Zn⁺-doped GaAs and (AlGa)As layers have a good quality comparable with that of layers doped with other impurities such as magnesium and beryllium. The epitaxial p-GaAs thin films were used to prepare shallow junction solar cells. The electrical characteristics showed a reduction of the surface recombination effect, and an energy conversion efficiency of up to 12.6% was obtained.