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961.
The characteristics of supercontinuum produced by high-intensity femtosecond pulses were investigated under different interaction
lengths, various pump intensities, different pump wavelengths at the fundamental 800 nm and its second-harmonic 400 nm. High
transfer-efficiency supercontinuum with flat-top in liquid media was produced. As the main nonlinear mechanisms, the effects
of self-phase modulation (SPM) and four-photon parametric emission were also investigated.
Project supported by Hong Kong Research Grant Council Project HKUST 633/94P, the China National Climbing Plan, and the Laboratory
of Optoelectronics and Information Engineering, the State Education Commission. 相似文献
962.
It is found by Mo¨ssbauer measurements on M0.025Fe0.975S (M=Sc, Ti, V, Cr, Mn, Co, Ni, Cu) that the 3d-transition metal impurities profoundly affect both the crystallographic and spin rotation transitions of iron sulfide.It is noteworthy that both V0.025Fe0.975S and Co0.025Fe0.975S have Morin transition temperatures TM which are distinctly different from that of FeS; furthermore, the directions of changes of TM are opposite for V0.025Fe0.975S and Co0.025Fe0.975S.A vanadium impurity of 2.5% of the metal atoms in the iron sulfide makes the crystallographic transition take place rapidly in a narrow temperature region of about 15 K, while the α transition in FeS takes place over a wide temperature range of about 200 K.It is also found that the α transition for V0.025Fe0.975S has a hysteresis width of 5 K. 相似文献
963.
Hyeong Soo Chang 《Journal of Mathematical Analysis and Applications》2003,286(2):636-651
We consider an approximation scheme for solving Markov decision processes (MDPs) with countable state space, finite action space, and bounded rewards that uses an approximate solution of a fixed finite-horizon sub-MDP of a given infinite-horizon MDP to create a stationary policy, which we call “approximate receding horizon control.” We first analyze the performance of the approximate receding horizon control for infinite-horizon average reward under an ergodicity assumption, which also generalizes the result obtained by White (J. Oper. Res. Soc. 33 (1982) 253-259). We then study two examples of the approximate receding horizon control via lower bounds to the exact solution to the sub-MDP. The first control policy is based on a finite-horizon approximation of Howard's policy improvement of a single policy and the second policy is based on a generalization of the single policy improvement for multiple policies. Along the study, we also provide a simple alternative proof on the policy improvement for countable state space. We finally discuss practical implementations of these schemes via simulation. 相似文献
964.
Reflection high-energy electron diffraction, atomic force microscopy, transmission electron microscopy, and double-crystal X-ray curves showed that high-quality InAs quantum dot (QD) arrays inserted into GaAs barriers were embedded in an Al0.3Ga0.7As/GaAs heterostructure. The temperature-dependent photoluminescence (PL) spectra of the InAs/GaAs QDs showed that the exciton peak corresponding interband transition from the ground electronic subband to the ground heavy-hole subband (E1-HH1) was dominantly observed and that the peak position and the full width at half maximum corresponding to the interband transitions of the PL spectrum were dependent on the temperature. The activation energy of the electrons confined in the InAs/GaAs QDs was 115 meV. The electronic subband energy and the energy wave function of the Al0.3Ga0.7As/GaAs heterostructures were calculated by using a self-consistent method. The electronic subband energies in the InAs/GaAs QDs were calculated by using a three-dimensional spatial plane wave method, and the value of the calculated (E1-HH1) transition in the InAs/GaAs QDs was in reasonable agreement with that obtained from the PL measurement. 相似文献
965.
Exact analytical expressions for the dispersion relation of one-dimensional chiral photonic crystals
We consider one-dimensional photonic crystals made of alternating layers of two kinds of isotropic chiral media. The two layers are characterized by the dielectric permittivities ε1 and ε2, the magnetic permeabilities μ1 and μ2, the chirality parameters γ1 and γ2 and the thicknesses d1 and d2. By diagonalizing an 8 × 8 matrix derived from the two coupled wave equations satisfied by our system, we obtain exact analytical expressions for the dispersion relation for plane electromagnetic waves propagating at an arbitrary angle with respect to the layers. We present a detailed analysis of our dispersion relation and explore the evolution of the photonic band structure as the frequency, the chirality parameter and the incident angle vary, with a special emphasis on the generation of the cross- and co-polarization bandgaps. 相似文献
966.
Correction of a coherent image during KrF excimer laser ablation using a mask projection 总被引:1,自引:1,他引:0
Dong Sig Shin Jae Hoon Lee Jeong Suh To Hoon Kim 《Optics and Lasers in Engineering》2006,44(6):615-622
Using masks for laser ablation has proven useful in the fabrication of prototypes for the manufacturing of micro-fluidic devices. In this work, an excimer laser was used to engrave microscopic channels on the surface of polyethylene terephthalate (PET), which showed a high absorption ratio for an excimer laser beam with a wavelength of 248 nm. When 50 μm wide rectangular microscopic channels were made using a 500×500 μm square mask and a magnification ratio of 1/10, ditch-shaped defects were found at both corners. The calculation of the laser beam intensity showed that a coherent image in the PET specimen caused the defects. An analysis based on the Fourier diffraction theory enabled the prediction of a coherent shape at the image plane, as well as a diffracted beam between the mask and the image plane. The analysis also showed that the diameter of the aperture was a predominant factor toward the elimination of ditch-shaped defects in the rectangular microscopic channels on the PET produced by an excimer laser ablation. 相似文献
967.
Kyun Young Park Jae Gil Choi Kiwhan Sung Yunsoo Kim 《Journal of nanoparticle research》2006,8(6):1075-1081
A solid-precursor vaporizer for laboratory-scale aerosol reactors has been developed and successfully tested on the synthesis of magnesium aluminate (MgAl2O4) nanoparticles by thermal decomposition of magnesium aluminum tert-butoxide (Mg[Al(OtBu)4]2), a single-source precursor, in a furnace aerosol reactor. The reactor temperature was varied from 600 to 1000°C with the precursor concentration at 6.4 × 10−6 mol/l. The atomic ratio of Al to Mg of produced particles was determined by XPS to be 2:1 and the primary particle size ranged from 28 to 55 nm. As-produced particles were all amorphous, but the particles further heated to 1000°C exhibited crystalline MgAl2O4 structures. 相似文献
968.
969.
970.
Cu(ClO4)2·6H2O has been found to be an efficient catalyst for cyanosilylation reaction of aldehydes in THF at room temperature with low catalytic loading (1.0 mol%) in short reaction time (mostly within 10 min). Copyright © 2008 John Wiley & Sons, Ltd. 相似文献