Selective incorporation of Si along step edges during delta-doping on MOVPE-grown GaAs (001) vicinal surfaces

We investigated the delta-doping (δ-doping) of Si using SiH₄ on MOVPE-grown GaAs (001) vicinal surfaces to explore the possibility of selective incorporation of Si along atomic steps, and to demonstrate doping quantum wires by the combination of multiatomic steps and wire-like doping. It was found that the doping density on vicinal surfaces was enhanced as the misorientation angle was increased, which suggested the enhanced decomposition of SiH₄ and the selective incorporation of Si at step edges. It was also found that this selective incorporation could be enhanced by annealing the surface prior to the δ-doping, which resulted from the reduced incorporation of Si at the terrace regions. Anisotropic electron transport properties which are expected from the wire-like incorporation along step edges are also discussed.     

Eigenvalue estimation of dominant electromechanical modes based on synchronous measurement and generator grouping technique

The authors have been studying a new approach for modal analysis of large power systems that utilizes GPS‐based synchronous measurement technology. The approach is based on the identification of a linearized multi‐input multi‐output model of power system. Since the identified model expresses approximately the electromechanical dynamics of an actual power system, modal frequencies, dampings, and mode shapes corresponding to electromechanical modes can be estimated as eigenvalues and eigenvectors of the identified model. In the paper, in order to advance our approach to a practical technique, it is mainly discussed how to select a small number of machines suitable for measurement locations to estimate eigenvalues associated with dominant slow modes. Such machines can be detected by identifying coherent groups related to the slow modes. The reference generators that behave representatively in each coherent group are the optimal ones to be measured. Therefore, the slow modes can be obtained by observing one generator from each group. The verification of the new modal analysis and coherency‐based machine selection is done through simulation studies using the IEEJ EAST 10‐machine system model. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(4): 24–32, 2008; Published online in Wiley InterScience ( www.interscience. wiley.com ). DOI 10.1002/eej.20428     

Calculation of distribution system voltage and power flow state using measured values

This paper describes a techique of calculating voltage and power flow state of a distribution system using the information measured with two or more switches with sensors installed in a distribution system. In the proposed technique, a set of the power distribution section where two or more switches with a sensor are connected is defined as the large section, and the active power and reactive power consumption in the large section are calculated based on measurement information, voltage (RMS), current (RMS), and power factor. Using the simple distribution system model consisting of the large sections, the power consumption of the large section is calculated by the power flow calculation to separate power consumption and power distribution loss. It is distributed to the small sections that constitute the large section, and detailed power flow calculation is performed. Verification of the proposed technique and basic estimation of the calculation error were performed using the simple power distribution system model. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 164(4): 33–42, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20416     

A triangle lattice model that predicts transmembrane helix configuration using a polar jigsaw puzzle

We developed a method of predicting the tertiary structuresof seven transmembrane helical proteins in triangle latticemodels, assuming that the configuration of helices is stabilizedby polar interactions. Triangle lattice models having 12 or11 nearest neighbor pairs were used as general templates ofa seven-helix system, then the orientation angles of all heliceswere varied at intervals of 15°. The polar interaction energyfor all possible positions of each helix was estimated usingthe calculated polar indices of transmembrane helices. An automatedsystem was constructed and applied to bacteriorhodopsin, a typicalmembrane protein with seven transmembrane helices. The predictedoptimal and actual structures were similar. The top 100 predictedhelical configurations indicated that the helix-triangle, CFG,occurred at the highest frequency. In fact, this helix-triangleof bacteriorhodopsin forms an active proton-pumping site, suggestingthat the present method can identify functionally importanthelices in membrane proteins. The possibility of studying thestructure change of bacteriorhodopsin during the functionalprocess by this method is discussed, and may serve to explainthe experimental structures of photointermediate states.     

Plasma-Resistant Dense Yttrium Oxide Film Prepared by Aerosol Deposition Process

Dense yttrium oxide film was prepared on a quartz substrate by the aerosol deposition process at the room temperature. The deposition rate was very high, 60 m/h. Thick film of 10 m was easily achievable on the quartz substrate. Transmission electron microscopy showed that the film was highly dense without voids and was composed of randomly oriented Y₂O₃ crystallites of sizes smaller than 20 nm. The interface between the film layer and the quartz substrate was homogeneous. The film (2-m thick) had a high transmittance (55–85%) in the wavelength region of 250-800 nm. The mechanical properties of the film were very good. The adhesion force of the interface between the Y₂O₃ layer and the quartz substrate was over 80 MPa. The Vickers hardness of the film was 7.7 GPa. The film also had an excellent plasma resistance in a gas mixture of CF₄/O₂. Outstanding results were noted in eroded depth, surface roughness, nanostructure, and transmittance change after plasma exposure of the film.     

城市降雨径流模型-修正RRL法及其改进

对修正RRL法进行改进，在修正RRL法中加入非线性水库方程来描述地面径流汇流过程，管道汇流采用能够考虑压力水头的非恒定流方程来代替修正RRL法中的简化无压管流模型，使得改进后的模型可以处理自由水面或压力管流问题。通过实例研究，验证了改进后的模型的可应用性和有效性。     

Highly Efficient Photoelectrocatalytic Decomposition of Biomass Compounds Using a Nanoporous Semiconductor Photoanode and an O2-Reducing Cathode with Quantum Efficiency Over 100

UV light-activated highly efficient photoelectrocatalytic decomposition of biorelated compounds and biowastes was successfully achieved by a Biophotochemical Cell (BPCC) comprising a nanoporous semiconductor film photoanode and an O₂-reducing cathode with high internal quantum efficiency over 100. Major decomposition reaction was dark auto-oxidation of the activated substrate radicals (R^?) by the bulk O₂ into CO₂ or/and to N₂. Photocatalytic decomposition of aqueous solutions of urea, ammonia, pig urine, and oxalic acid was investigated. Combination cells were fabricated comprising a photoanode/cathode unit for activation of organic compounds and a large volume chamber for autooxidation of activated substrates.     

Evaluation on high temperature fracture toughness of CrMoV cast steel by small punch testing

Toughness of CrMoV cast steel for steam turbine casings operated at elevated temperature can be degraded during the operation. It is important to measure the degradation under operation to estimate the damage and the maintenance interval. However, conventional testing methods for fracture toughness require large specimens and it is impractical for successive operation after sampling these specimens.     

Polarization Engineering on Buffer Layer in GaN-Based Heterojunction FETs

To improve the pinched-off characteristics of an AlGaN/GaN heterojunction field effect transistor (HJFET), the conduction band potential of an incorporated AL_xGa_1-xN buffer is designed to be upwardly convex in a band diagram. This approach utilizes the polarization effects specific to GaN-based materials by lowering the Al content x from 30% to 5% almost linearly toward the front side. Fabricated field effect transistors (FETs) adopting the designed buffer have demonstrated the following advanced characteristics in comparison to those of a FET adopting a conventional GaN buffer: less than one-tenth of the buffer leakage current, a gate-to-drain breakdown voltage BV_gd twice or more as high, and remarkably improved carrier confinement and pinched-off behavior. The FETs are operated in an enhancement mode with a gate-to-channel distance thick enough to prevent tunneling current through the gate.