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.     

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 Motivation derives from the need to replace outdated empirical-based designs with more physically relevant models.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.     

A novel flavin adenine dinucleotide (FAD) containing d-lactate dehydrogenase from the thermoacidophilic crenarchaeota Sulfolobus tokodaii strain 7: purification, characterization and expression in Escherichia coli

Dye-linked D-lactate dehydrogenase activity was found in the crude extract of a continental thermoacidophilic crenarchaeota, Sulfolobus tokodaii strain 7, and was purified 375-fold through four sequential chromatography steps. With a molecular mass of about 93 kDa, this enzyme was a homodimer comprised of identical subunits with molecular masses of about 48 kDa. The enzyme retained its full activity after incubation at 80 degrees C for 10 min and after incubation at pHs ranging from 6.5 to 10.0 for 30 min at 50 degrees C. The preferred substrate for this enzyme was D-lactate, with 2,6-dichloroindophenol serving as the electron acceptor. Using high-performance liquid chromatography (HPLC), the enzyme's prosthetic group was determined to be flavin adenine dinucleotide (FAD). Its N-terminal amino acid sequence was MLEGIEYSQGEEREDFVGFKIKPKI. Using that sequence and previously reported genome information, the gene encoding the enzyme (ST0649) was identified. It was subsequently cloned and expressed in Escherichia coli and found to encode a polypeptide of 440 amino acids with a calculated molecular weight of 49,715. The amino acid sequence of this dye-linked D-lactate dehydrogenase showed higher homology (39% identity) with that of a glycolate oxidase subunit homologue from Archaeoglobus fulgidus, but less similarity (32% identity) to D-lactate dehydrogenase from A. fulgidus. Taken together, our findings indicate that the dye-linked D-lactate dehydrogenase from S. tokodaii is a novel type of FAD containing D-lactate dehydrogenase.