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61.
Horng-Shyang Chen Shun-Lee Liu C. C. Yang Yean-Woei Kiang 《Optics Communications》2003,220(4-6):383-388
We report the reduced waveguiding efficiency for the signals around 1560 nm as the injection current of an GaAs/AlGaAs multiple quantum well laser diode (lasing wavelength at 840 nm) with a ridge-loading waveguide configuration increased. This reduction trend stopped when the injection current reached the threshold condition of the laser diode. The decreased waveguide transmission and the more expanded mode profile indicated the variation of the effective refractive index gradient in the lateral dimension with injection current. This variation was due to the refractive index decrease with increasing carrier density even below band gap. A slab waveguide model was used to simulate the lateral mode profile variation with injection current. The refractive index differences between the guiding layer and claddings in the slab waveguide model provided estimates of refractive index contrasts of the laser diode at a concerned wavelength under various injection conditions. 相似文献
62.
Yen-Shung TSAI 《中国科学A辑(英文版)》2007,50(7):1026-1034
By means of further investigation of solid codes,the problem“Is every fd-domain uni- formly dense”proposed by Yuqi Guo,C.M.Reis and G.Thierrin in 1988 is solved in this paper. 相似文献
63.
S. D. Gunapala S. V. Bandara J. K. Liu S. B. Rafol J. M. Mumolo C. A. Shott R. Jones J. Woolaway II J. M. Fastenau A. K. Liu M. Jhabvala K. K. Choi 《Infrared Physics & Technology》2003,44(5-6):411-425
A 9 μm cutoff 640 × 512 pixel hand-held quantum well infrared photodetector (QWIP) camera has been demonstrated with excellent imagery. A noise equivalent differential temperature (NEDT) of 10.6 mK is expected at a 65 K operating temperature with f/2 optics at a 300 K background. This focal plane array has shown background limited performance at a 72 K operating temperature with the same optics and background conditions. In this paper, we discuss the development of this very sensitive long-wavelength infrared camera based on a GaAs/AlGaAs QWIP focal plane array and its performance in quantum efficiency, NEDT, uniformity, and operability. In the second section of this paper, we discuss the first demonstration of a monolithic spatially separated four-band 640 × 512 pixel QWIP focal plane array and its performance. The four spectral bands cover 4–5.5, 8.5–10, 10–12, and 13.5–15 μm spectral regions with 640 × 128 pixels in each band. In the last section, we discuss the array performance of a 640 × 512 pixel broad-band (10–16 μm full-width at half-maximum) QWIP focal plane. 相似文献
64.
Hua Jin Zhuangqi Hu Qingmin Liu Yunlong Ge Changxu Shi 《Applied Physics A: Materials Science & Processing》1992,54(5):399-403
A crystallization study has been carried out for rapidly solidified Bi2Pb0.5Sr2Ca4Cu5Ox glass. Glass transition temperature T
g, crystallized superconducting phases and microstructural changes were measured and analysed by differential thermal analysis (DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The crystallization mechanism of the three superconducting phases — (2201) 20 K phase, (2212) 80 K phase, and (2223) 110 K phase — has been discussed, and a time-temperature-transformation diagram for the glass has been constructed. 相似文献
65.
66.
Jiuqiang Liu 《Journal of Graph Theory》1994,18(2):195-204
A maximal independent set of a graph G is an independent set that is not contained properly in any other independent set of G. Let i(G) denote the number of maximal independent sets of G. Here, we prove two conjectures, suggested by P. Erdös, that the maximum number of maximal independent sets among all graphs of order n in a family Φ is o(3n/3) if Φ is either a family of connected graphs such that the largest value of maximum degrees among all graphs of order n in Φ is o(n) or a family of graphs such that the approaches infinity as n → ∞. 相似文献
67.
68.
给出了一种新的二进小波1/f过程模型,从理论上证明了一类谱指数为H的近似1/f过程可通过一簇平稳随机过程产生.由于所提方法利用了1/f过程小波系数的相关性,因而有效地减少了合成1/f过程的谱误差.数值实验结果表明,新模型很好地改进了已有模型. 相似文献
69.
Lei Liu 《Journal of Mathematical Analysis and Applications》2007,328(2):1484-1486
In this note, we generalize the inequality about the trace of positive semidefinite matrix trk(AB)?k(trA)k(trB) to Hilbert space, and obtain a relevant inequality about positive trace class operator. 相似文献
70.
Ke Sha Dongshuang Li Yapeng Li Xiaotian Liu Shuwei Wang Jingqi Guan Jingyuan Wang 《Journal of polymer science. Part A, Polymer chemistry》2007,45(22):5037-5049
Amphiphilic diblock copolymer polycaprolactone‐block‐poly(glycidyl methacrylate) (PCL‐b‐PGMA) was synthesized via enzymatic ring‐opening polymerization (eROP) and atom transfer radical polymerization (ATRP). Methanol first initiated eROP of ?‐caprolactone (?‐CL) in the presence of biocatalyst Novozyme‐435 under anhydrous conditions. The resulting monohydroxyl‐terminated polycaprolactone (PCL–OH) was subsequently converted to a bromine‐ended macroinitiator (PCL–Br) for ATRP by esterification with α‐bromopropionyl bromide. PCL‐b‐PGMA diblock copolymers were synthesized in a subsequent ATRP of glycidyl methacrylate (GMA). A kinetic analysis of ATRP indicated a living/controlled radical process. The macromolecular structures were characterized for PCL–OH, PCL–Br, and the block copolymers by means of nuclear magnetic resonance, gel permeation chromatography, and infrared spectroscopy. Differential scanning calorimetry and wide‐angle X‐ray diffraction analyses indicated that the copolymer composition (?‐CL/GMA) had a great influence on the thermal properties. The well‐defined, amphiphilic diblock copolymer PCL‐b‐PGMA self‐assembled into nanoscale micelles in aqueous solutions, as investigated by dynamic light scattering and transmission electron microscopy. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5037–5049, 2007 相似文献