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991.
T. J. Kim S. W. Lee B. K. Kang D. S. Kim A. S. Kim K. H. Shin M. K. Park Y. K. Sin 《Optical and Quantum Electronics》1995,27(5):465-471
High-quality and uniform bulk layers of (Al
x
Ga1–x
)0.5In0.5P (x=0–0.7) and AlGalnP/GainP quantum wells (QWs) are grown on 2°-off (100) GaAs substrates by low-pressure metal organic vapour phase epitaxy at a low growth rate of 0.3 nm s-1. The amount of lattice mismatch and the variation of PL peak energy of (Al0.5Ga0.5)0.5In0.5P on the 50-mm substrate are less than 6×10-4 and 2 meV, respectively. (Al0.5Ga0.5)0.5In0.5P/Ga0.5In0.5P SQWs show narrow PL spectra even from a 0.6 nm well measured at 20 K. The variation of PL peak energy from (Al0.5Ga0.5)0.5In0.5P/Ga0.5In0.5P MQWs is less than 10 meV. Also, as-cleaved AlGalnP/GalnP lasers fabricated by a three-step MOVPE show a pulsed threshold current of 82 mA at room temperature, output power of 12 mW, and the lasing wavelength at 668.2 nm. 相似文献
992.
It is shown that Lorentz harmonics provide a natural basis for the expansion and infrared regularization of a massless scalar field in two dimensions. The negative metric operators separate out simply. Each Lorentz component of the field is partially local. 相似文献
993.
994.
K. J. Lee D. Y. Moon O. O. Park Y. S. Kang 《Journal of Polymer Science.Polymer Physics》1992,30(7):707-716
Diffusion coefficients of ethylene glycol (EG) have been measured in poly(ethylene terephthlate) (PET) melts by a quartz-spring sorption apparatus. A simple mathematical model was developed to investigate the sorption behavior accompanied by chemical reactions of EG and PET at high temperatures. Diffusion coefficients are deduced from experimental data for an asymptotically thin sample in order to minimize the effects of reactions. The diffusion coefficient of EG is strongly dependent on the vapor pressure of EG and temperature but not on the molecular weight of PET in this experimental range (degree of polymerization 80–120). The diffusion coefficient of EG in PET melt at 265°C is 2.58 × 10?7 cm2/s at the limit of zero concentration of EG. The activation energy for diffusion is 38.4 kcal/gmol, and the heat of solution for sorption is ?44.9 kcal/gmol. The concentrations of the volatile materials resulting from reactions in PET-EG system were analyzed with gas chromatography. In addition, a fit of the current model to experimental data yields frequency factors for the polymerization reaction (k1) and the acetaldehyde formation reaction (k2) to be 5.84 × 108 cm3/mol ? min and 3.90 × 1011 min?1, respectively. 相似文献
995.
Eshelby showed that if an inclusion is of elliptic or ellipsoidal shape then for any uniform elastic loading the field inside the inclusion is uniform. He then conjectured that the converse is true, that is, that if the field inside an inclusion is uniform for all uniform loadings, then the inclusion is of elliptic or ellipsoidal shape. We call this the weak Eshelby conjecture. In this paper we prove this conjecture in three dimensions. In two dimensions, a stronger conjecture, which we call the strong Eshelby conjecture, has been proved: if the field inside an inclusion is uniform for a single uniform loading, then the inclusion is of elliptic shape. We give an alternative proof of Eshelby’s conjecture in two dimensions using a hodographic transformation. As a consequence of the weak Eshelby’s conjecture, we prove in two and three dimensions a conjecture of Pólya and Szegö on the isoperimetric inequalities for the polarization tensors (PTs). The Pólya–Szegö conjecture asserts that the inclusion whose electrical PT has the minimal trace takes the shape of a disk or a ball. 相似文献
996.
997.
998.
A computer program package is described for the evaluation of atomic local structure parameters from extended x-ray absorption fine-structure measurements. It was compiled for the IBM-PC microcomputer and use successfully in structure determination of many samples from different fields. It consists of twelve relatively independent modules; data-processing procedures are programmed in IBM FORTRAN and parts of the graphic procedures are written in IBM Advanced BASIC language. The whole process takes about 20 min. 相似文献
999.
In this paper, a kind of heat conduction problem subject to a moving boundary condition is studied, in which its equation has form of quasilinear parabolic e-quation with vaviable coefficients, under some assumptions, we have defined and provided existence of solution of this problem in domain Ω by singular perturbation methods, where Ω denotes the domain:{σ1(t)≤x≤ σ2(t), 0≤t相似文献
1000.
Bin Kang Cheng 《Physics letters. A》1984,100(9):490-494
We first show that the propagator of a charged particle in a time-dependent electromagnetic field, obtained by choosing the vector and scalar potentials to be in static symmetric gauge, is related to the propagator of a one-dimensional particle under a time-dependent perturbative force and with generalized memory. For the case of a constant magnetic field, the latter can then be evaluated exactly with the help of a gaussian integral. Our new results are in agreement with the well-known results of simpler cases. 相似文献