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991.
Young-Tae Cho 《Journal of Mechanical Science and Technology》2002,16(2):192-202
In particle or short-fiber reinforced composites, cracking of the reinforcements is a significant damage mode because the
cracked reinforcements lose load carrying capacity. This paper deals with an incremental damage theory of particle or short-fiber
reinforced composites. The composite undergoing damage process contains intact and broken reinforcements in a matrix. To describe
the load carrying capacity of cracked reinforcement, the average stress of cracked ellipsoidal inhomogeneity in an infinite
body as proposed in the previous paper is introduced. An incremental constitutive relation on particle or short-fiber reinforced
composites including progressive cracking of the reinforcements is developed based on Eshelby’s (1957) equivalent inclusion
method and Mon and Tanaka’s (1973) mean field concept. Influence of the cracking damage on the stress-strain response of composites
is demonstrated. 相似文献
992.
TNF mediates lung leak, but not neutrophil accumulation, in lungs of rats given IL-1 intratracheally
BM Hybertson EK Jepson OJ Cho JH Clarke YM Lee JE Repine 《Canadian Metallurgical Quarterly》1997,155(6):1972-1976
Interleukin-1 (IL-1) is increased in lung lavages obtained from patients with acute respiratory distress syndrome, and administering IL-1 intratracheally to rats causes an acute, neutrophil-dependent, oxidative lung leak. We found that rats given IL-1 intratracheally had increased lung lavage fluid tumor necrosis factor (TNF) levels, and that rats treated with TNF binding protein (TNFbp) intravenously did not develop the increased lung leak that occurs after administration of IL-1 intratracheally. In contrast, rats given IL-1 intratracheally and TNFbp intravenously had the same elevations in lung lavage neutrophil accumulation and lung lavage cytokine-induced neutrophil chemoattractant levels as rats given IL-1 intratracheally. Our results show that TNFbp decreases neutrophil-mediated lung leak, but not lung neutrophil accumulation, after administration of IL-1 intratracheally in rats. 相似文献
993.
Mesophase pitches prepared by a heterogeneous nucleation method from various mixtures of coal tar-derived isotropic pitch
and petroleum-derived mesophase pitch (MP-P) were oxidatively stabilized, and the dependence of chemical reactivity and stabilization
rate on their chemical structure was investigated. The rate and amount of oxygen uptake of the mesophase pitch fibres, revealed
by thermogravimetry, increased under given conditions of oxidation with the amount of added MP-P, but the rate of stabilization
showed a reverse trend. The lower chemical reactivity of coal tar-derived mesophase pitch (MP-C) appears to induce a slower
rate of oxygen uptake, while the higher content of pyridine-insoluble fraction and higher aromaticity of MP-C may result in
a lesser content of oxygen being required for stabilization, as compared with MP-P. 相似文献
994.
Yamanaka K. Nagata Y. Nakano S. Koda T. Nishino H. Tsukahara Y. Cho H. Inaba M. Satoh A. 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》1995,42(3):381-386
We present principle and application of a novel noncontact velocity measurement of surface acoustic waves (SAW) on crystals and thin films using laser interference fringes scanned at the phase velocity of SAW. The scanning interference fringes (SIF) are produced by intersecting two laser beams with a frequency difference. The SAW velocity within the laser beam spot is measured as the ratio of observed SAW frequency and predetermined wave number of the SIF. The frequency measurement can be quite precise because of a large number of generated SAW carriers and amplitude enhancement effect. The SAW velocity measurement is free from the water loading effect accompanying the leaky SAW measurements. This principle was successfully applied to evaluate Si 3N4 and SiO2 films deposited on Si (001) surface 相似文献
995.
In the present study, fluid flow characteristics of a porous layer overlaid by a fluid layer were investigated through experiments.
The experimental results were analyzed in comparison with theoretical results of a porous medium bounded by impermeable walls.
With spheres, the slip coefficient was found to be 0.0107 for Poiseuille flow over a porous layer. As the permeability decreased,
the experimental results approached the values calculated by Darcy’s law and Forchheimer’s equation. In addition, the effects
of the presence of a fluid layer over a porous medium were examined in terms of the friction factor. The present experimental
data placed in the range of the Darcy to the non-Darcy region are shown to be in reasonable agreement with the proposed correlation. 相似文献
996.
997.
Dong Seong Oh Kwan Yuhl Cho Myong Joong Youn 《Power Electronics, IEEE Transactions on》1992,7(2):364-373
A current control technique for a voltage-fed PWM inverter is presented. The discretized state equation of an inverter and a load independent of operating conditions with the delayed input voltage feedback has been derived using the averaging concept. The discretized current controller is proposed to reduce the current error as fast as possible using the deadbeat control strategy and to stabilize the closed loop system asymptotically when the variations of load parameters are given in the predetermined stabilized region. This proposed control scheme is realized by the symmetrical uniform sampling method and is easily implemented using a microprocessor-based system. Computer simulation for the proposed controller has been carried out and the results show good static and dynamic performances 相似文献
998.
Ji J. Cho S.T. Zhang Y. Najafi K. Wise K.D. 《Electron Devices, IEEE Transactions on》1992,39(10):2260-2267
A multiplexed ultraminiature pressure sensor designed for use in a cardiovascular catheter is described. The sensor operates from only two loads, which are shared by two sensors per catheter. The sensing chip is 350 μm wide by 1.4 mm long by 100 μm thick. CMOS readout circuitry at the sensing site converts applied pressure to a frequency variation in the supply current, which is detected at the end of the catheter by a microprocessor-controlled interface. The nominal pressure sensitivity is 2 kHz/fF about a zero-pressure output frequency of 2.7 MHz. This on-site circuitry contains two reference capacitors which allow external compensation for nonlinearity and temperature sensitivity and has an idle-state power dissipation of less than 50 μW. With the transducer sealed at ambient pressure, the device can resolve pressure variations of about 3 mmHg, while vacuum-sealed devices do considerably better and should permit <2 mmHg resolution in practical systems 相似文献
999.
The source-drain series resistances of devices contacted by a local interconnection technology utilizing polysilicon strapped with selective CVD tungsten were measured and compared to predictions obtained using a theoretical model. Asymmetrical devices in which the local interconnections were intentionally misaligned to the gate were fabricated to study the effects of misalignment on device characteristics. Experiments indicate that the technology is quite forgiving to the misalignment between the gate and the local interconnection 相似文献
1000.
A new current control scheme with the reference voltage estimation for a voltage-fed pulsewidth modulated (PWM) inverter is presented. This scheme is simple and can provide smaller current error than predictive control with the same switching frequency when the load parameters are mismatched.<> 相似文献