Naganori Ishihara

The preparation conditions and characteristics of the Bi−Sr−Ca−Cu−O single crystals

The 7 K, (7+80) K and 80 K phase lli-Sr-Ca-Cu-O single crystals were prepared by changing the composition of the starting materials using a self-flux method. The results of AES (Auger electron spectroscopy) measurements indicate that a part of the Sr would be substituted by Ca in the 7 K phase crystal. Plate-like crystals were observed by SEM (scanning electron microscope) in the as-grown 80 K phase crystal surface. This may be due to the fact that the specimen has a layer structure.

Optimal Feedback Control Design Using Genetic Algorithm in Multimachine Power System

Abstract This paper introduces an application of genetic algorithm (GA) to design weighting matrices Q and R elements in Linear Quadratic Regulator (LQR) optimization process. The weighting matrices Q and R are the most important components in LQR optimization. The performance of matrices Q and R determines the output performances of the system. Commonly, a trial-and-error method has been used to construct the matrices Q and R elements. This method is very simple, but very difficult to produce good control performances. Also it takes a long time to choose the best values in its processing. Because of this, in order to improve control performances by selecting the elements of matrices Q and R, the Bryson method can be employed to give better results in shorter time than the previous method. In this paper, we use GA to construct the weighting matrices Q and R properly. We design the weighting matrices of a power system optimization by using the trial-and-error method, Bryson method, and GA method and compare the control performances. It is shown that the GA calculation is the most useful among the three methods to improve system performances via matrices Q and R design to minimize settling time of control. This idea gives a new alternative procedure in time varying feedback control to improve the stability performances.

Determining the arrangement of fictitious charges in charge simulation method using genetic algorithms

Abstract In this paper, we propose a method to decide the appropriate arrangement of fictitious charges in the charge simulation method (CSM) by using a direct search method. The appropriate arrangement is achieved by using genetic algorithms (GA) as a search method. We describe the arrangement of the charges as chromosomes and place fictitious point-charges at random on the rotational axis of a spheroidal electrode. The charge arrangement is adjusted by using GA until the potential reaches a specified value over the surface of the electrode.

The difference between 6H-SiC (0001) and (0001) faces observed by AES, LEED and ESCA

Abstract 6H-SiC has a hexagonal structure. The top most surfaces of (0001) and (000 1 ) are only covered with Si and C atoms, respectively. The former is called a Si-rich surface and the latter is called a C-rich surface. These different surface polarities show different surface characteristics. These can also be observed by surface analytical techniques. Here, SiC surfaces were heated to several temperatures (RT-1100°C) for 10 min in an ultra-high vacuum (UHV) chamber. Then the surfaces were observed by LEED (low energy electron diffraction) and AES (Auger electron spectroscopy). The surfaces heated to 1000°C showed the cleanest surfaces. C(KVV)/Si(LVV) AES peak to peak (p-p) height ratio showed a minimum value at 1000°C for all SiC surfaces; on average it is 0.26 on a Si face and 0.38 on a C face. LEED patterns which were heated at 1000°C showed (√3 × √3 - R30°) structure on a Si-rich face and (3 × 3) structure on a C-rich face. After LEED and AES, ESCA experiments were carried out on these samples. C1s/Si2p peak area ratios were 1.2 and 2.0 on Si and C-rich faces, respectively. However, after Ar-ion sputter etching, the differences could not be observed.

Automatic arrangement of fictitious charges and contour points in charge simulation method for two spherical electrodes

Abstract We propose a method to decide the appropriate arrangement of both fictitious charges and contour points in the charge simulation method for the case that the shape of electrodes can be expressed in the spherical coordinates. In this paper, we use genetic algorithm (GA), which is inspired by the mechanism of natural selection where stronger individuals are likely the winners in a competing environment, as a search method. We calculated the potential distribution around two spherical electrodes with different potentials above a grounded electrode plate. The surface potentials of the electrodes were assumed to be 5000 and 30 V , respectively, for example. The total number of the charges was 22 for the electrode system. First, we placed fictitious point-charges and contour points at random inside the electrodes and on the surfaces of electrodes, respectively. The arrangement was automatically adjusted by using GA until the potential reached the desired values at all the test points placed on the electrode surfaces. We show that the GA can be useful to determine the appropriate arrangement of both fictitious charges and contour points simultaneously.

Crystal Growth of Bi-Sr-Ca-Cu-O (c0=39 Å) Single Crystals

Bi-Sr-Ca-Cu-O (Bi-based) single crystals were prepared by the self-flux method with a temperature-holding process. The prepared Bi-based single crystals were platelike with a size of about 2×2 mm2. From the X-ray diffraction patterns, we found that the Bi-based single crystal had a c-axis unit cell length of about 39 A.

LEED-AES and XPS Studies of Bi-Sr-Ca-Cu-O Single Crystal Surfaces

The well-defined clean surface in the 80K-phase Bi-Sr-Ca-Cu-O single crystal was obtained by cleaving it in air and heating it at 350°C in ultrahigh vacuum (UHV). The low-energy electron diffraction (LEED) pattern from the clean surface showed the perfect single domain of a 1×5 structure. From the Auger electron spectroscopy (AES) measurements, the cleaved surface might be a Bi-O layer and O atoms will be removed more easily than the other elements of Sr, Ca and Cu by Ar+ sputter etching. In the clean surface of the single crystal, Cu2+ was dominant. The X-ray photoelectron spectroscopy (XPS) spectrum of O 1s consists of the OH(~531 eV) and OL(~529 eV) components, and the OH component is smaller than the OL component.

XPS Studies of Bi-Sr-Ca-Cu-O Single Crystal and Ceramics Surfaces

The XPS (X-ray photoelectron spectroscopy) spectra from (a) the cleaved surface of a single crystal, (b) the polished surface and (c) the Ar+-sputtered surface of the ceramics in Bi-Sr-Ca-Cu-O are mecnsured and compared. The chemical bond nature of Bi is the same in all three surfaces. Sr and Ca in (c) are more oxidized than those in (a). In (b), there are two kinds of Sr and Ca, one from a clean surface like the cleaved surface region, and the other, more oxidized Sr and Ca which exist in the Ar+-sputtered surface. Cu2+ is dominant in (a) and (b), while Cu+ is dominant in (c). The O 1s XPS spectrum from (c) is sharper and narrower than that from (a). This may be due to the existence of isolated metal oxides of Sr, Ca and Cu by Ar+-sputter etching.

Automatic arrangement of fictitious charges and contour points in charge simulation method for polar coordinate system

Abstract We have used genetic algorithms (GA) to decide an appropriate arrangement of both fictitious charges and contour points in charge simulation method (CSM) for 2D electrode system with asymmetrical structure. We calculated the potential distribution around two cylindrical electrodes above a grounded plate electrode. In this paper, an electrode differs remarkably from the other in the potential and the size in comparison with previous research. We describe the radial r - and direction angel θ -components of the charge positions and the θ -components of the contour-point positions as genes. First, we placed fictitious line-charges and contour points at random inside the electrodes and on the surface of electrodes, respectively. The arrangement was adjusted automatically by using GA. Also, the appropriate numbers of the charges and the contour points are assigned to each electrode.

A RHEED study of the initial growth of Ag on the Si(001) surface

Abstract The growth of Ag on Si(001) 2×1 surfaces was studied by reflection high-energy electron diffraction (RHEED). An oscillation of the specular beam intensity was observed using a nearly single domain surface of Si(001) 2 × 1 as a function of the Ag coverage at the substrate temperature T s = RT (room temperature). Streaks, along the [110] direction for the 2 × 1 surface, in the pattern, developed with increasing Ag coverage up to ~ 1 ML (monolayer). The intensity of the specular beam spot increased immediately after the start of Ag deposition, and decreased to a constant value beyond ~ 1 ML. The RHEED pattern revealed that one-dimensional Ag atomic chains were formed along the dimer rows of the Si surface. For more than ~ 1.5 ML coverage, Ag islands of the (111) orientation grew epitaxially.