Stabilization control for multimachine system using decentralized H∞ excitation controller realizing terminal voltage control and damping control

In this paper, to achieve both damping of power system oscillation and terminal voltage control simultaneously on a multimachine power system, we propose a decentralized H_∞ excitation controller. In the proposed method, H_∞ control via the Normalized Coprime Factorization approach is used to achieve the proposed design idea. By the Normalized Coprime Factorization approach, the weighting function in H_∞ control design is simplified, and output feedback controllers that take into account the realities and constraints of the power systems are designed. The proposed controller is subjected to model reduction of H_∞ controllers, and is transformed to a discrete system to perform digital control by computer systems in consideration of application to a real system. We verify that the proposed excitation controller can achieve both damping of power system oscillation and terminal voltage control by computer simulations of a multimachine power system. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(1): 33–41, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10254     

10 Gbit/s, 100 km nonrepeatered fibre transmission experiment using a high-sensitivity semiconductor optical preamplifier

10 Gbit/s, 100 km nonrepeated fibre transmission has been demonstrated using a high-sensitivity receiver with two-stage cascade-connected semiconductor optical amplifiers and a pin PD front end. The sensitivity and its improvement were -23.5 dBm and 12.2 dB respectively, resulting in the allowable span-loss of 24.5 dB.<>     

Observation of Real Metal Surfaces by Tribostimulated Electron Emission and Its Relationship to the Analyses by XPS and Photoemission

The characteristics of tribostimulated electron emission (called TriboEE) have been studied for real metal surfaces subjected to rubbing with polytetrafluoroethylene (PTFE). A gas-flow Geiger counter with a counter gas called Q gas was used for observing the TriboEE. Metal samples used were as follows: Ti, Zr (group 4 in the periodic table); V, Nb, Ta (group 5); Mo, W (group 6); Fe (group 8); Co (group 9); Ni, Pd, Pt (group 10); Cu, Ag, Au (group 11); Zn (group 12); Al (group 13); and Sn (group 14). For metals in the same groups of 4, 5, 6, 10, and 11 the number of electrons ejected during rubbing time (called TriboEE total count) increased with an increase in the period for the metal. For the metals in the groups of 4, 10, and 11 the surface fluorine content originating from PTFE debris attached at the surfaces increased with an increase in the period for the metal. The TriboEE total count was almost independent of the photoelectric thresholds determined in photoemission (PE) experiment throughout the metals, while the amount of ejected electrons in the PE measurement tended to decrease with increasing threshold. The surface potential (SP) was almost unchanged before and after the TriboEE measurement. Based on the relation to XPS, PE, and SP results the TriboEE was explained as being associated with the release of electrons transported to the attached PTFE debris from the metal substrate by a surface electric field.     

Synchrotron X-Ray Study of the Crystal Structure and Hydrothermal Degradation of Yttria-Stabilized Tetragonal Zirconia Polycrystal

Structural study with synchrotron X-ray diffractometry was made on phase separation phenomena in 2, 3, and 4 mol% Y₂O₃-stabilized tetragonal ZrO₂ polycrystal (abbreviated as 2, 3, and 4Y-TZP, respectively). The sintered body of 3Y and 4Y-TZP underwent phase separation into high and low yttrium regions as sintering temperature increased, and the tetragonal phase was assigned to both regions. The sintering body is less separated, and a large monoclinic phase was detected in 2Y-TZP. Analysis of aging kinetics of tetragonal- to monoclinic-phase transition showed that the fraction of the transformable phase agreed with that of the low yttrium region.     

Cytochrome P450-Dependent Metabolism of Vitamin E Isoforms is a Critical Determinant of Their Tissue Concentrations in Rats

The aim of this study was to clarify the contribution of cytochrome P450 (CYP)-dependent metabolism of vitamin E isoforms to their tissue concentrations. We studied the effect of ketoconazole, a potent inhibitor of CYP-dependent vitamin E metabolism in cultured cells, on vitamin E concentration in rats. Vitamin E-deficient rats fed a vitamin E-free diet for 4 weeks were administered by oral gavage a vitamin E-free emulsion, an emulsion containing α-tocopherol, γ-tocopherol or a tocotrienol mixture with or without ketoconazole. α-Tocopherol was detected in the serum and various tissues of the vitamin E-deficient rats, but γ-tocopherol, α- and γ-tocotrienol were not detected. Ketoconazole decreased urinary excretion of 2,5,7,8-tetramethyl-2(2′-carboxyethyl)-6-hydroxychroman after α-tocopherol or a tocotrienol mixture administration, and that of 2,7,8-trimethyl-2(2′-carboxyethyl)-6-hydroxychroman (γ-CEHC) after γ-tocopherol or a tocotrienol mixture administration. The γ-tocopherol, α- and γ-tocotrienol concentrations in the serum and various tissues at 24 h after their administration were elevated by ketoconazole, while the α-tocopherol concentration was not affected. The γ-tocopherol or γ-tocotrienol concentration in the jejunum at 3 h after each administration was also elevated by ketoconazole. In addition, significant amount of γ-CEHC was in the jejunum at 3 h after γ-tocopherol or γ-tocotrienol administration, and ketoconazole inhibited γ-tocopherol metabolism to γ-CEHC in the jejunum. These results showed that CYP-dependent metabolism of γ-tocopherol and tocotrienol is a critical determinant of their concentrations in the serum and tissues. The data also suggest that some amount of dietary vitamin E isoform is metabolized by a CYP-mediated pathway in the intestine during absorption.     

Phenolic compounds from sugarcane molasses possessing antibacterial activity against cariogenic bacteria

During the course of our research into the use of cane by-products from sugar manufacturing, we have studied the isolation and structural determination of bioactive compounds present in sugarcane molasses. In this study, dehydrodiconiferylalcohol-9'-O-beta-D-glucopyranoside (1) and isoorientin-7, 3'-O-dimethyl ether (2) were isolated as antibacterial active compounds against cariogenic bacteria. Their structures were elucidated by (1)H-NMR, (13)C-NMR and ESI-MS. The activities of these isolated compounds against Streptococcus mutans and Streptococcus sobrinus were assessed by a minimum inhibitory concentration (MIC) test. The MICs of compounds 1 and 2 against both S. mutans and S. sobrinus were >4 mg/mL and 4 mg/mL, respectively.     

Evaluation of noninvasive approach for monitoring PCB pollution of seabirds using preen gland oil

Oil secreted from the preen gland (located at the base of the tail feathers) of seabirds can be collected from live birds. We determined PCB concentrations and profiles in the preen gland oil and corresponding abdominal adipose tissue collected from 30 seabirds (2 orders, 3 families, 10 genera, 13 species) to examine the utility of the oil as a monitoring medium. Samples were collected from seabirds that had died in traffic accidents or had become caught unintentionally in experimental drift nets and long-lines in the North Pacific Ocean. Significant concentrations of PCBs were detected in all oil samples, with a concentration range of 9-4834 ng/g-lipid and a geometric mean of 404 ng/ g-lipid. PCBs in the oil had more lower-chlorinated congeners than those in corresponding abdominal adipose, suggesting that they had less opportunity to undergo metabolism before they were secreted from the gland. We observed a weak but significant correlation between the PCB concentrations in the oil and abdominal adipose tissue (R2 = 0.19, P < 0.05). Correcting for the metabolic loss of PCBs on the basis of congener profiles improved the correlation (R2 = 0.48, P < 0.001), implying that congener-specific determination of PCBs in the preen gland oil enables us to estimate PCB concentrations in the abdominal adipose within 1 order of magnitude difference. The differences in PCB concentrations among the 13 species are discussed in terms of dietary behavior, habitat, and migration.