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151.
A. A. Berezhnoy F. L. Vladimirov I. Yu. Grodetskii Yu. L. Korzinin V. I. Sukhanov 《Optics and Spectroscopy》2002,93(5):777-780
The possibility of usage of the spontaneous electrooptical (EO) effect in strontium barium niobate (SBN) crystals for the creation of controlled electroholographic elements is studied. It is found that unipolar EO properties of these crystals with respect to switching their spontaneous polarization make it possible to devise field-controlled holographic elements with reversible energy-independent memory for spatial position of an optical beam. 相似文献
152.
153.
L. Pillier C. Moreau X. Mercier J.F. Pauwels P. Desgroux 《Applied physics. B, Lasers and optics》2002,74(4-5):427-434
Cavity ring-down spectroscopy (CRDS) is used to measure the NO mole fraction formed in the burnt gases of low-pressure premixed
flames. It is shown that the line-of-sight absorption is greatly increased by the contribution of the NO molecules surrounding
the burner. This contribution has been quantified by developing a mathematical procedure taking into account the spatial and
spectral features of the CRDS measurement. Calculations have been undertaken in the general case of a stable species not consumed
in the flame. The most sensitive parameter is the temperature both in the flame and outside the flame. Simulations allow the
selection of the best spectroscopic transitions for a given flame (i.e. a given temperature profile), ensuring the weakest
influence of the inaccuracy affecting the temperature determination. High quantum states belonging to the A–X (0–1) band of
NO have been found to be the most valuable and have led to a NO mole fraction determination with an accuracy of ±13%. NO absorption
in the flame was completely masked using the A–X (0–0) band. Finally, the prompt-NO mole fraction formed in a methane/air
flame stabilized at 33 Torr is obtained by combining CRDS and laser induced fluorescence techniques.
Received: 12 October / Revised version: 1 February 2002 / Published online: 14 March 2002 相似文献
154.
The generalized canonical model obtained from extended state-space averaging is used as a design tool for the evaluation of the buck converter dynamics in different switching schemes. Designs are given at a specified constant conversion ratio and load for the pulse width modulated, zero current, zero voltage, and nonlinear resonant switch full- and half-wave converters. The small signal equivalent circuit model is discussed, and the feedback effects introduced by resonant switching on line and control transfer functions are evaluated. The small signal transfer functions of half-wave converters are heavily load-current dependent, and exhibit significant damping at light loads, which can result in two real poles in the converter response instead of a complex conjugate pair. This damping effect is evaluated over the entire normalized load current range for the linear and nonlinear zero-current switching converters. Simple approximate expressions are given for the real poles. Experimental verification of the half-wave analysis is presented, and the effects of converter efficiency on model accuracy are discussed 相似文献
155.
The liquid chromatographic analysis of drugs in urine through direct injection without any sample pretreatment was extended to micellar chromatography with nonionic surfactants, the Pinkerton ISRP column and the shielded hydrophobic phase (Hisep) column. The feasibility of using each was demonstrated through the determination of the diuretic, hydrochlorothiazide, in urine. Good separation, recovery, precision and linearity, and adequate limits of detection were obtained for this analysis with all three techniques. The advantages and limitations of the mobile phase approach of micellar chromatography and the two stationary phase approaches are discussed for the direct injection of urine as well as other biological fluids. 相似文献
156.
V. Vittoria R. Russo F. De Candia P. L. Magagnini B. Bresci 《Journal of Polymer Science.Polymer Physics》1991,29(9):1163-1168
The transport properties of a side-chain liquid-crystalline polymer forming a smectic A phase have been investigated using dichloromethane as a permeant. Samples differing in the isotropization enthaoly were analyzed. A. Correlation between this thermal parameter and sorption has been found, while the diffusion coefficient is substantially the same in all samples. The results obtained can be explained in terms of a biphasis model in which a disordered permeable phase is present within the liquid-crystalline phase, which is impermeable to the diffusant molecules. 相似文献
157.
The gain recovery time of 1.55-μm bulk semiconductor optical amplifiers (SOA's) with lengths from 500 to 1500 μm has been measured with a continuous-wave (CW) probe in the time domain. It is shown to decrease with increasing length down to 60 ps for the longest SOA. This behavior is theoretically explained. A lower limit for the recovery time is observed and explained 相似文献
158.
Streit D.C. Oki A.K. Umemoto D.K. Velebir J.R. Stolt K.S. Yamada F.M. Saito Y. Hafizi M.E. Bui S. Tran L.T. 《Electron Device Letters, IEEE》1991,12(9):471-473
The authors have developed a modified MBE growth process to produce high-gain n-p-n GaAs-AlGaAs heterojunction bipolar transistors (HBTs) with a mean time to failure (MTTF) of 1.5×108 h at 125°C. Beryllium incorporation and diffusion are controlled through a combination of reduced substrate temperature and increased As/Ga flux ratio during MBE growth, resulting in extremely stable HBT profiles. The authors also demonstrate graded InGaAs surface layers with nonalloyed refractory metal contacts that significantly improve ohmic reliability compared to alloyed AuGe contacts. The ability to produce robust HBTs by MBE is critically important to this technology 相似文献
159.
P. Cifra F. E. Karasz W. J. Macknight 《Journal of Polymer Science.Polymer Physics》1991,29(11):1389-1395
Local ordering in miscible binary polymer blends with strong attractive interactions between the two types of chains was investigated by computer simulation of allowable conformations on an incompressible cubic lattice. A tendency toward maximum ordering (in which chains pack in alternate parallel rows) is shown by the calculation of pair correlations and in “snapshots” of the mixtures. A specific directional interaction is not necessarily required for ordering. A comparison of these results with those recently obtained using mean-field theory is presented. The heat capacity of mixing was also calculated and found to be positive, with a value close to that reported experimentally. 相似文献
160.
Spectroscopic determinations of the concentrations associated with the onset of intermolecular interaction in solutions of poly(ethylene terephthalate) (PET) are described. The intersegment forces perturb the electronic spectra and induce ground-state aggregation. These phenomena become observable at different chain densities, reflecting the influence of concentration on the coil dimensions, as well as the dynamical nature of the interactions. An estimate of the equilibrium constant for PET dimer formation in hexafluoroisopropanol is reported. 相似文献