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881.
F. Grisch P. Bouchardy M. Péalat B. Chanetz T. Pot M. C. Coët 《Applied physics. B, Lasers and optics》1993,56(1):14-20
Rotational temperature and nitrogen number density are measured in the shock wave/boundary layer interaction region in the vicinity of a two-dimensional compression corner disposed in a low pressure, 55 K, Mach 10 hypersonic air flow. Spatially-resolved data are recorded using a nonlinear optical technique named dual-line coherent anti-Stokes Raman scattering (DLCARS). Averaged temperature and density profiles are compared with those predicted by a Navier-Stokes solver. Good agreement is found. 相似文献
882.
An experiment to determine the effect of gate electrode resistivity on circuit speed gave unexpected results: circuits with the lowest sheet resistance had the poorest circuit speed. Explanation of this behaviour required development of a new high-frequency method of measuring the impedance of the gate electrode. This method revealed that the circuits with a composite gate electrode had been formed with a partial discontinuity. The measurement technique is described, and the evidence of the discontinuity is shown. The effect of the discontinuity on device and circuit speed is demonstrated 相似文献
883.
Electric fields of the anions, cations and neutral forms of 2-aminopurine and 6-thioguanine have been mapped. Certain important
features of the maps are similar to those found earlier in the neutral and ionic forms of adenine and guanine. The computed
electric field patterns satisfactorily explain reactive sites and biological activity of the molecules. 相似文献
884.
P. C. Chen 《中国化学会会志》1995,42(5):755-760
Three ab initio calculations (HF/6-3IG, HF/6-3IG*, and HF/6-3IG**) on 2,4,6-trinitrotoluene were made, The results compare well with xray data, except dihedral angles of NO2 relative to the plane of the benzene ring. The deviations are attributed to packing forces and steric effects in the crystal. The most stable structure was a torsional angle 10° of the methyl top with the benzene ring, unlike toluene. The rotational barriers of the methyl top and the 4-nitro group are small. Hydrogen bonding, dipole moments and total atomic charges arc calculated. 相似文献
885.
Dependence of ion-pair induced self-pulsing in Er-doped fiber lasers on emission to absorption ratio 总被引:1,自引:0,他引:1
Ming Ding P.K. Cheo 《Photonics Technology Letters, IEEE》1996,8(12):1627-1629
We show theoretically that the ion-pair induced self-pulsing in Er-doped fiber lasers depends largely on the ratio of emission to absorption cross sections, and can be significantly suppressed as this ratio is increased. Our experimental results agree qualitatively with this prediction. This result is important for stabilizing Er-doped fiber lasers where short-cavities and high-gain fibers are required. 相似文献
886.
A. A. Vertiy S. P. Gavrilov S. Aydinlik S. Samedov 《Journal of Infrared, Millimeter and Terahertz Waves》1996,17(10):1613-1637
In millimeter wave lengths region semiconductor generators, amplifiers, mixers and other solid state UHF devices find a wide application. In our work, we suggested to use aCircular Through-Shaped Resonator for obtaining power combination using active elements at frequency region Δf≈20–40 GHz. The resonator is formed by two plane aluminum reflectors. The first reflector has a circular groove. The second reflector has coupling elements. The first and the second reflectors are considered as a ring groove shaped waveguide. A resonator spectrum was calculated and analyzed in the frequency range Δf ≈20–40 GHz. It is showed that, in the given frequency range the resonator spectrum has a complicated structure and is formed by a series of spectrum lines; a frequency range between the series increases with the frequency increasing. We studied on transmission coefficient of the resonator, frequency shifts of spectrum lines when inserting a thin (t/λ≈0.003) dielectric substrates into the resonator, and also attenuation constants of waves propagating in circular groove (due to losses in metal). 相似文献
887.
A number of biphenyl, terphenyl analogues and ethynes which contain a pyrazine ring have been made and their liquid crystal transition temperatures, together with examples of birefringence measurements, are reported. All the 2,5-disubstituted pyrazine systems are liquid crystalline showing high birefringence values for the biphenyl and terphenyl analogues, whereas the 1,5-disubstituted systems are not liquid crystalline. The pyrazine ethyne systems exhibit very high birefringence values. X-ray diffraction has been used to identify the liquid crystal phases of 2-n-nonyloxy-5-(4'-propylbiphenyl-4-yl)pyrazine. 相似文献
888.
M. R. Islam R. V. Chelakaea J. G. Neff K. G. Fertitta P. A. Grudowski A. L. Holmes F. J. Ciuba R. D. Dupuis J. E. Fouquet 《Journal of Electronic Materials》1995,24(6):787-792
AlGaAs double heterostructures are grown by low-pressure metalorganic chemical vapor deposition to evaluate the level of oxygen
contamination in different trimethylaluminum sources. Effects of arsine purifiers, misoriented substrates, atmospheric exposure
of the growth chamber, and possible phosphorus contamination are also studied. Extensive characterization is performed on
these films by a variety of methods, including high-resolution x-ray diffraction, photoluminescence (PL), time-resolved photoluminescence,
and secondary-ion mass spectrometry. The PL intensities for structures grown with the low-alkoxide grade are reproducibly
much greater than those grown with the regular-grade TMA1. The use of AsH3 purification improves the PL intensity. 相似文献
889.
Rothman M.A. Shieh C.L. Negri A.J. Thompson J.A. Armiento C.A. Holmstrom R.P. Kaur J. 《Photonics Technology Letters, IEEE》1993,5(2):169-171
An InGaAsP/InP laser monolithically integrated with a rear facet monitor and a fiber V-groove has been demonstrated for the first time. The integrated device incorporates an etched-facet laser fabricated using an in situ, multistep, reactive ion etch process. The integrated V-groove, which is etched directly into the InP substrate, is designed to enable passive alignment of an optical fiber to the active region of the laser. Passive coupling efficiencies of 18% and 8% have been obtained using cleaved multimode and single mode fibers, respectively. Responsivities of the rear facet monitor were as high as 0.49 A/W 相似文献
890.
Emulsions of perfluorotributylamine (FTBA) and perflubron were evaluated for their utility in 19F echo planar imaging. Fluorine images of the emulsions were obtained in a phantom and two mice that had been predosed. Both agents, but particularly perflubron, show potential for fluorine echo planar studies because of the long spin-spin relaxation times of the CF3 resonances. High resolution thin slice images obtained in as little as 26.6 ms are presented. 相似文献