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991.
Yu. I. Kadashevich 《Strength of Materials》1991,23(5):552-555
The significance of the concepts of thermodynamic time and microstress tensor introduced by A. A. Vakulenko for development of the theory of viscoplasticity is analyzed.Translated from Problemy Prochnosti, No. 5, pp. 56–58, May, 1991. 相似文献
992.
993.
994.
Polyurethanes were prepared from pure 4,4′-diphenylmethane diisocyanate (MDI), 1,4-butane diol (BDO) or 1,2-ethane diol (EDO) and α,ω-hydroxyl poly(propylene oxide) (PPO) by reaction injection moulding (RIM). Hard segment (MDI + BDO or EDO) level was 45–50 wt%. The PPO had about 20% ethylene oxide copolymerized in at the chain ends to provide 80% primary OH end groups. Mn was varied from 2000 to 4000. Dibutyl tin dilaurate catalyst and mould temperature were varied. Dynamic mechanical, wide-angle X-ray, differential scanning calorimeter, molecular weight and tensile elongation measurements were made on the RIM polyurethanes. At low reaction rates (low catalyst or temperature) highly crystalline, well phase separated but low molecular weight polymers were produced. At high catalyst or temperature levels more poorly phase separated but high molecular weight, tough polymers resulted. Higher Mn PPO gave better phase separation and EDO gave higher melting temperatures. Preventing hard segment crystallinity by substituting asymmetric MDI or glycols resulted in phase compatibility. 相似文献
995.
A. G. Kalandarishvili V. A. Kuchukhidze Sh. Sh. Shartava S. S. Chkadua 《Atomic Energy》1989,66(1):27-29
Translated from Atomnaya Énergiya, Vol. 66, No. 1., pp. 22–24, January, 1989. 相似文献
996.
997.
V. A. Tsykanov A. A. Maershin A. A. Petukhov O. V. Skiba P. T. Porodnov G. I. Gadzhiev I. S. Golubenko E. P. Klochkov A. A. Teikovtsev V. K. Shamardin 《Atomic Energy》1989,66(5):329-333
Translated from Atomnaya Énergiya, Vol. 66, No. 5, pp. 299–302, May 1989. 相似文献
998.
Bowers J. Chipaloski A. Boodaghians S. Carlin J. 《Lightwave Technology, Journal of》1987,5(12):1733-1741
We demonstrate here the use of high-speed semiconductor lasers and detectors with low loss optical fiber for the transmission of the 500-MHz C-band microwave signal spectrum to and from a satellite antenna. The optical system has low attenuation and large band, width, so the microwave signals can be transmitted directly at the microwave frequency (4 or 6 GHz) over 20 km of fiber without regeneration or qualization. The optical system introduces ≈ 1 dB or less of degradation for both low spectral density QPSK signals and high spectral density FM video signals present in typical satellite transmission systems. For the video signals, the signal to noise after AM conversion was reduced from 56 to 55 dB. The microwave drive level to the laser must be significantly larger (typically > -10 dBm) than the intensity noise of the laser, yet small enough (typically < 10 dBm) to reduce the intermodulation distortion signals to an acceptable level. The laser bias current must be several times threshold so that the resonance frequency is beyond the frequency band of interest (4-6 GHz in this case). A flat modulation response is then obtained, and the intensity noise and intermodulation levels are low. 相似文献
999.
V. Ya. Malikov P. E. Stadnik O. Ts. Sidletskiy L. N. Lisetskiy S. V. Budakovskiy N. Z. Galunov 《Instruments and Experimental Techniques》2002,45(4):576-578
The device developed allows one to measure the dielectric characteristics of solid substances and their melts at frequencies of 20–20000 Hz and in a wide temperature range of 20–250°C. The measured temperature dependencies of the dielectric permittivities of several molecular and liquid crystals (stilbene, diphenyl, naphthalene, cholesterylpelargonate, and 8OCB) are presented. 相似文献
1000.
Ferrari A. Ghislotti G. Balsamo S. Spano V. Trezzi F. 《Lightwave Technology, Journal of》2002,20(3):515-518
The behavior of fiber Bragg grating (FBG)-stabilized 980-nm pump lasers is experimentally and theoretically investigated. The subkilohertz noise in the emitted power is related to the coexistence and oscillation between coherence collapsed state and narrow linewidth single-mode (SM) operation. These findings are theoretically discussed by using a multimode time-domain model that accounts for spatial harmonics and includes nonlinear gain. One additional result is an indication that kinks in the L-I curve can be explained by nonlinear mode competition 相似文献