1,897 research outputs found
The secular acceleration of the moon determined from Lunar Laser Ranging data
No full textLunar Laser Ranging data covering the interval from August 1969 to December 1987 were used to determine the seculer acceleration in the mean longitude of the Moon (n). In our analysis, the DE200/LE200 planets and lunar ephemerides were adopted for calculating the theoretical distance between the observing station and reflector. The method of stepwise regression was used in the processing of the data and the value of -25 ''.4 +/- 0 ''.1/cy(2) was obtained by a weighted least squares fit
High strain rate superplasticity in powder metallurgy aluminium alloy 6061+20 vol.-%SiCp composite with relatively large particle size
No full textThe possibility of high strain rate superplasticity (HSRS) was examined over a wide range of temperatures in a powder metallurgy aluminium alloy 6061/SiCp composite with a relatively large SiC particle size of similar to 8 mu m. A maximum tensile elongation of 350% was obtained at 600 degrees C and 10(-2) s(-1). Tensile elongations over 200% were obtained in a narrow temperature range between 590 and 610 degrees C at high strain rates of 10-2 and 10(-1) s(-1). The current testing temperature range could be divided into two regions depending on the rate-controlling deformation mechanism. Region I is in the lower temperature range from 430 to 490 degrees C, where lattice diffusion controlled dislocation climb creep (n = 5) is the rate-controlling deformation process, and region II is in the higher temperature range from 520 to 610 degrees C, where lattice diffusion controlled grain boundary sliding controls the plastic flow. An abnormally large increase in activation energy was noted at temperatures above 590 degrees C, where large tensile elongations over 200% were obtained at high strain rates. This increase in activation energy and high tensile ductility may be explained in terms of presence of a liquid phase created by partial melting, but such evidence could not be provided by the current differential scanning calorimetry (DSC) test. This may be because the DSC is not sensitive enough to detect the small amount of liquid phase. MST/4499
A new PWM-controlled quasi-resonant converter for a high efficiency PDP sustaining power module
No full textA new pulsewidth modulation (PWM)-controlled quasi-resonant converter for a high-efficiency plasma display panel (PDP) sustaining power module is proposed in this paper. The load regulation of the proposed converter can be achieved by controlling the ripple of the resonant voltage across the primary resonant capacitor with a bidirectional auxiliary circuit, while the main switches are operating at a fixed duty ratio and fixed switching frequency. Hence, the waveforms of the currents can be expected to be optimized from the view-point of conduction loss. Furthermore, the proposed converter has good zero-voltage switching (ZVS) capability, simple control circuits, no high-voltage ringing problem of rectifier diodes, no dc offset of the magnetizing current and low-voltage stresses of power switches. Thus, the proposed converter shows higher efficiency than that of a half-bridge LLC resonant converter under light load condition. Although it shows the lower efficiency at heavy load, because of the increased power loss in auxiliary circuit, it still shows the high efficiency around 94%. In this paper, operational principles, features of the proposed converter, and analysis and design considerations are presented. Experimental results demonstrate that the output voltage can be controlled well by the auxiliary circuit using the PWM method
Selective hydrogenation of 1,3-butadiene on TiO2-modified Pd/SiO2 catalysts
No full textThe properties of Pd/SiO2 catalysts modified with titanium oxide were examined by determining their activity with respect to the partial hydrogenation of 1,3-butadiene included in an excess amount of butenes and by characterizing their surfaces using infrared (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), H-2 chemisorption, and temperature-programmed desorption (TPD). The TiO2-modified catalysts had an improved selectivity for the conversion of 1,3-butadiene to 1-butene, particularly when the catalysts were reduced at high temperatures, e.g., 500 degreesC. IR and chemisorption results suggest that, when the catalyst is reduced at 500 degreesC, the Pd surface is decorated with partially-reduced TiOx similar to the case of TiO2-supported catalysts, which show strong metal-support interaction (SMSI). XPS and TPD results indicate that the I'd surface is also modified electronically, in that the charge is transferred from the Ti species to Pd and the adsorption of I-butene to the Pd surface becomes weaker. It can be concluded that the strong interaction between the Pd surface and partially reduced TiO2 is responsible for the improved selectivity of the catalyst for the conversion of 1,3-butadiene to 1-butene. (C) 2002 Elsevier Science B.V. All rights reserved
A new phase-shifted full-bridge converter with voltage-doubler-type rectifier for high-efficiency PDP sustaining power module
No full textA new phase-shifted full-bridge converter with a voltage-doubler-type rectifier for a high-efficiency power-sustaining module of a plasma display panel is proposed in this paper. The proposed converter employs a voltage-doubler rectifier without an output inductor. Since it does not have an output inductor, the voltage stresses of the rectifier diodes can be clamped at the output voltage level. Thus, since no dissipative resistor-capacitor snubber for rectifier diodes is needed, high-efficiency low-noise output voltage can be realized. Due to the elimination of the large output inductor, it features simpler structure, lower cost, smaller mass, and lighter weight. Furthermore, the proposed converter has wide zero-voltage-switching ranges of lagging leg switches with low current stresses of the primary power switches by using the magnetizing current. In addition, the resonance between the leakage inductor of the transformer and the rectifier capacitors can reduce the current stresses of the rectifier diodes and conduction losses. In this paper, the operational principles, analysis, design considerations, and experimental results are presented
A new PWM-controlled quasi-resonant converter for a high efficiency PDP sustaining power module
No full textA new PWM-controlled quasi-resonant converter for a high efficiency PDP sustaining power module is proposed in this paper. The load regulation of the proposed converter can be achieved by controlling the ripple of the resonant voltage across the resonant capacitor with a bi-directional auxiliary circuit, while the main switches are operating at a fixed duty ratio and fixed switching frequency. Hence, the waveforms of the currents can be expected to be optimized from the view-point of conduction loss. Furthermore, the proposed converter has good ZVS capability, simple control circuits, no high voltage ringing problem of rectifier diodes, no DC offset of the magnetizing current and low voltage stresses of power switches. In this paper, operational principles, features of the proposed converter, and analysis and design considerations are presented. Experimental results demonstrate that the output voltage can be controlled well by the auxiliary circuit using the PWM method
Ashburn Anstalt v WJ Arnold & Co. Ltd [1989] Ch 1, Court of Appeal
No full textEssential Cases: Land Law provides a bridge between course textbooks and key case judgments. This case document summarizes the facts and decision in Ashburn Anstalt v WJ Arnold & Co. Ltd [1989] Ch 1, Court of Appeal. The document also includes supporting commentary from author Aruna Nair.</p
A Subband Adaptive Filtering Algorithm Employing Dynamic Selection of Subband Filters
No full textWe present a novel normalized subband adaptive filter (NSAF) which dynamically selects subband filters in order to reduce computational complexity while maintaining convergence performance of conventional NSAF. The selection operation is performed to achieve the largest decrease between the successive mean square deviations at every iteration. As a result, an efficient and competent NSAF algorithm is derived. The experimental results show that the proposed NSAF algorithm gains an advantage over the conventional NSAF in that it leads to a similar convergence performance with a substantial saving of overall computational burden.X1117sciescopu
Voltage-Source-Integrated Driving Waveform Amplifier With Energy Recovery Capability for Plasma Display Panel
No full textThis paper proposes a voltage-source-integrated driving waveform amplifier with energy recovery capability for plasma display panel (PDP). Different from conventional driving circuits having multiple voltage sources and power switches, the proposed circuit can generate various driving waveforms of PDP by using just the sustaining voltage source and fewer devices. Moreover, the proposed circuit can recover the reactive energy of the panel regardless of the slope of the driving waveform, which improves the power efficiency. Since the proposed circuit has the degrees of freedom in programming the waveforms, it also can compensate the driving waveforms to guarantee stable and uniform light emission of the PDP according to the operating temperature and variation of discharge characteristics of the PDP. Therefore, the proposed circuit may help bring the circuit cost down and enhance the reliability of the PDP
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