Dynamics of an HVDC system in the presence of unbalanced AC transmission line faults and a stabilization scheme

The introduction of an HVDC system into the trunk power supply system requires transmitting as much dc power as possible for improving the whole ac/dc system stability. The continued operation scheme of an HVDC system which makes it possible to operate even under very low commutation bus voltage is adopted to cope with such system requirement. Further stability improvement can be achieved by adding damping control which modulates converter active and/or reactive power. To take full advantage of these control effects, it is essential that the HVDC system can maintain stable operation during the ac system faults and reclosing. Particular attention should be given to a repetitive commutation failure following the unbalanced ac transmission line faults. This paper discusses first the cause of the repetitive commutation failure when supplied with unbalanced ac system voltage based on an experiment using the CRIEPI AC-DC Power System Simulator. Then a stabilization control scheme with an on-line extinction angle estimation is proposed and the effect is verified by digital simulation.     

Cosegregation of the new region on chromosome 3 with salt-induced hypertension in female F2 progeny from stroke-prone spontaneously hypertensive and Wistar-Kyoto rats

1. We investigated candidate loci for salt-sensitive high blood pressure (BP) in F2 progeny from crossing Wistar-Kyoto and stroke-prone spontaneously hypertensive rats. 2. In female F2 progeny, systolic and diastolic BP on the 12th day and the seventh month after salt loading was strongly linked with the D3Mgh12 and D3Mgh6 loci on chromosome 3, respectively. 3. These loci were linked with BP only in female F2 progeny, not in males. 4. These results indicate that hormonal factors may influence salt sensitivity, particularly with respect to gender differences.     

Evaluation of vibration in many positions by SOM

We propose a method of evaluating the vibration of motor-operated electric tools (MOETs) by using a self-organizing feature map (SOM). The vibration spectrum is used to evaluate the MOET vibration. These vibration spectra are derived from 18 vibration data obtained by measurements on three different positions of a MOET. The spectra are then sent to the SOM network for the calculations. The vibration spectra are classified by the SOM, and calculations give the Euclidean distance from the weight vector in order to develop a quantitative evaluation. A statistic analysis of the Euclidean distance allows a quantitative evaluation of a MOET with respect to vibration stress and other relevant parameters.This work was presented, in part, at the 9th International Symposium on Artificial Life and Robotics, Oita, Japan, January 28–30, 2004     

Environmental Problems Related to Refractories——Some Discussions Based on Historical Surveys mainly in Japan

1IntroductionThe significance of refractory-related environmen-tal problems are drawing a serious attention in the re-fractories industry and their markets worldwide.Thoserefractory-related problems,however,have been han-dled so far separately on a case-by-case basis.It willbe,therefore,of great help for future progress to havea bird’s-eye viewover these issues from historical andtechnological viewpoints.It has been the author’s attitude toward environ-mental problems that they should be dis…     

Heat Transfer & Thermal Stress Analysis of Plastic-Encapsulated ICs

Analytic approaches of thermal stress in plastic-encapslated ICs reliability have been studied using a simple, 2-dimensional model of the cross section of ICs by the finite-element method. To test the validity of the model, the actual stress within the silicon chip was measured using piezoresistive devices. The calculated stress in the silicon chip agreed with the experimental values. The stress distributions were changed by lead-frame properties. Package cracking, and delamination between the molding plastic and the lead-frame were qualitatively explained. We estimated the effect of the plastic properties on stress quantitatively. Furthermore, to test the validity of this model, the temperature change at the silicon chip was measured using the Vf temperature dependency of a diode. The calculated temperature change at the silicon chip agreed with the observed values. A very high temperature gradient was observed near the surface of the plastic immediately after solder dipping. The non-uniform temperature distributions produced different thermal stress distributions than those observed in the steady-state. This result indicated that rapid thermal shock could delaminate the plastic from the lead-frame. We believe that these results can guide the development of an optimum low-stress plastic.     

Optical Spectra of Synthetic Spinels in the System MgAl2O4–MgCr2O4

Unpolarized optical spectra were measured in the wavelength range 322–1666 nm by the diffuse reflection technique from spinel powders synthesized in the system MgAl₂O₄–MgCr₂O₄. The spectra were interpreted by the crystal-field theory on the basis of trigonally distorted spinel octahedra with D_3d symmetry. For chromium-rich solid solutions, including the MgCr₂O₄ end-member, results after peak fittings showed octahedral D_3d local symmetry around Cr³⁺ ions, identical to the crystallographic site symmetry. For chromium-poor solid solutions, however, octahedral C_3v local symmetry was suggested around Cr³⁺ ions, different from the D_3d crystallographically expected.     

An economic and energy analysis on bio-hydrogen fuel using a gasification process

Recently, in Japan, recycling technologies have been developed using waste biomass material. Waste biomass is traded in the waste materials market between users and a third-party, who receives a fee for processing them. This study is an environmental and economic analysis of a biomass energy system, which can produce hydrogen fuel for fuel cells (purity of 99.99%) as an example of an environmental business model. The experimental apparatus was made based on the moving-bed gasifier by the German company, DM2 Inc., and the hydrogen gas yield was measured. Finally, the economic viability of the future hydrogen business was estimated.The experimental results obtained gave the gas concentration of 57.5% in a Steam/Carbon ratio of 1.40 at 900 °C.Assuming the plant scale of 10 t/d, the production amount of hydrogen gas would be 21.3 kg/h. Based on the law concerning waste processing in Japan, a sizeable amount of waste biomass could be expected. Therefore, if the processing fee which is paid to the group (contractor) ranges between 5.0 and 10.0 $/t, and if the whole investment cost is 6 million dollars and the depreciation period is 15 years, the bio-hydrogen production cost using the experimental data would be 5.75–7.86 $/kg-H₂ without receiving related subsidies. In a one-third grant proportion, the cost would become 4.60–6.72 $/kg-H₂.     

Low-Temperature Synthesis of NaNbO3 Nanopowders and their Thin Films from a Novel Carbon-Free Precursor

We have demonstrated a synthetic procedure for nano-sized NaNbO₃ powder and its thin films using a carbon-free precursor prepared by the reaction of H₂O₂ with sodium and niobium alkoxides. A combination of X-ray powder diffraction, Raman spectra, and thermal gravity and differential thermal analysis, carbon analysis, fourier transform infrared spectra, transmission electron microscopy, and atomic force microscopy was used to characterize the resulting materials and precursor compounds. Results show that this procedure demonstrates the major advantages of low-temperature synthesis (∼400°C) and low weight loss during transformation into NaNbO₃ because of its carbon-free nature, which also provides the option of preparing nano-sized particles and dense, crack-free NaNbO₃ thin films.     

Arterial oxygenation and shunt fraction during one-lung ventilation: a comparison of isoflurane and sevoflurane

The aim of this study was to evaluate the effect of isoflurane and sevoflurane on oxygenation and shunt fraction during one-lung ventilation (OLV). Twenty patients undergoing lobectomy for lung cancer and scheduled for long-term OLV were enrolled in this study. Patients were allocated to treatment with either isoflurane or sevoflurane. Arterial oxygenation, shunt fraction, and hemodynamics were evaluated at the end of two-lung ventilation; 20 min after the initiation of OLV; 20 min after the application of 4-cm positive end-expiratory pressure (PEEP) to the dependent lung; 20 min after 8-cm PEEP; and 20 min after the conversion from OLV to two-lung ventilation. There was no significant difference between isoflurane and sevoflurane with regard to oxygenation, shunt fraction, or hemodynamics during OLV. PaO2 values after the application of 4-cm PEEP increased from 131.1 +/- 11.8 mm Hg to 190.6 +/- 22.9 mm Hg in the isoflurane group (P < 0.05) and from 127.2 +/- 14.3 mm Hg to 192.4 +/- 26.9 mm Hg in the sevoflurane group (P < 0.05). The selection of either isoflurane or sevoflurane for OLV was made without regard to arterial oxygenation and shunt fraction. PEEP application to the dependent lung is useful for improving oxygenation during OLV, but 8-cm PEEP had no added effect compared with 4-cm PEEP. Implications: We compared the effects of isoflurane and sevoflurane on oxygenation, hemodynamics, and shunt fraction during one-lung ventilation in 20 patients undergoing scheduled lobectomy for lung cancer. There was no significant difference between isoflurane and sevoflurane with regard to oxygenation, shunt fraction, and hemodynamics during one-lung ventilation. The application of 4-cm positive end-expiratory pressure increased the partial pressure of arterial oxygen during one-lung ventilation.     

Reactive wetting of SiO<Subscript>2</Subscript> substrates by molten Al

The reactive wetting behavior of SiO₂ substrates by molten Al was investigated at temperatures between 800 °C to 1250 °C in a purified Ar-3 pct H₂ atmosphere of about 0.11 MPa using an improved sessile drop method. The time dependence of the changes in contact angle and droplet geometry was monitored and the wetting kinetics was identified. The initial equilibrium or quasi-equilibrium contact angles are generally larger than 90 deg and do not significantly vary with temperature. The subsequent remarkable decrease in the contact angle mainly results from the progressive decrease in the droplet volume rather than the advance of the solid-liquid interfacial front. The significant effect of temperature on the wetting kinetics is essentially related to its effect on the reaction and molten Al penetration progress. For systems with a considerable decrease in the droplet volume during reactive wetting, a criterion for evaluation of the true wetting improvement was proposed.