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961.
Summary We present an approximation method of a space-homogeneous transport equation which we prove is convergent. The method is very promising for numerical computation. Comparison of a numerical computation with an exact solution is given for the Master equation. 相似文献
962.
A laser diode directly end-pumped, passively Q-switched Nd:YVO4/Cr:YAG laser is presented in this paper. With 600 mW incident pump laser, Q-switched 1064 nm laser with an average power of 138 mW, pulse width of 19.8 ns, repetition rate of 170.1 kHz and peak power of 40.96 W is obtained. When a KTP crystal was inserted into the cavity, Q-switched 532 nm laser with an average power of 56 mW, pulse width of 28.4 ns, repetition rate of 118.2 kHz and peak power of 16.7 W is obtained at last. 相似文献
963.
Keiko Kanamori Brian D. Ross 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,153(2):193
[5-13C,15N]Glutamine, with 1J(13C–15N) of 16 Hz, was observed in vivo in the brain of spontaneously breathing rats by 13C MRS at 4.7 T. The brain [5-13C]glutamine peak consisted of the doublet from [5-13C,15N]glutamine and the center [5-13C,14N]glutamine peak, resulting in an apparent triplet with a separation of 8 Hz. The time course of formation of brain [5-13C,15N]glutamine was monitored in vivo with a time resolution of 20–35 min. This [5-13C,15N]glutamine was formed by glial uptake of released neurotransmitter [5-13C]glutamate and its reaction with 15NH3 catalyzed by the glia-specific glutamine synthetase. The neurotransmitter glutamate C5 was selectively13C-enriched by intravenous [2,5-13C]glucose infusion to 13C-label whole-brain glutamate C5, followed by [12C]glucose infusion to chase 13C from the small and rapidly turning-over glial glutamate pool, leaving 13C mainly in the neurotransmitter [5-13C]glutamate pool, which is sequestered in vesicles until release. Hence, the observed [5-13C,15N]glutamine arises from a coupling between 13C of neuronal origin and 15N of glial origin. Measurement of the rate of brain [5-13C,15N]glutamine formation provides a novel noninvasive method of studying the kinetics of neurotransmitter uptake into glia in vivo, a process that is crucial for protecting the brain from glutamate excitotoxicity. 相似文献
964.
Emanuela Locci Yves Dehouck Mariano Casu Giuseppe Saba Adolfo Lai Michel Luhmer Jacques Reisse Kristin Bartik 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2001,150(2):167
The interaction of xenon with different proteins in aqueous solution is investigated by 129Xe NMR spectroscopy. Chemical shifts are measured in horse metmyoglobin, hen egg white lysozyme, and horse cytochrome c solutions as a function of xenon concentration. In these systems, xenon is in fast exchange between all possible environments. The results suggest that nonspecific interactions exist between xenon and the protein exteriors and the data are analyzed in term of parameters which characterize the protein surfaces. The experimental data for horse metmyoglobin are interpreted using a model in which xenon forms a 1:1 complex with the protein and the chemical shift of the complexed xenon is reported (Locci et al., Keystone Symposia “Frontiers of NMR in Molecular Biology VI”, Jan. 9–15, 1999, Breckenridge, CO, Abstract E216, p. 53; Locci et al., XeMAT 2000 “Optical Polarization and Xenon NMR of Materials”, June 28–30, 2000, Sestri Levante, Italy, p. 46). 相似文献
965.
The accurate measurement of small spin–spin coupling constants in macromolecules dissolved in a liquid crystalline phase is important in the context of molecular structure investigation by modern liquid state NMR. A new spin-state-selection filter, DIPSAP, is presented with significantly reduced sensitivity to J-mismatch of the filter delays compared to previously proposed pulse sequences. DIPSAP presents an attractive new approach for the accurate measurement of small spin–spin coupling constants in molecules dissolved in anisotropic solution. Application to the measurement of 15N–13C′ and 1HN–13C′ coupling constants in the peptide planes of 13C, 15N labeled proteins demonstrates the high accuracy obtained by a DIPSAP-based experiment. 相似文献
966.
Y. Chushak L.S. Bartell 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):43-46
A set of molten gold clusters, each with 1157 gold atoms, was studied by molecular dynamics simulations as the clusters underwent
freezing at three different temperatures. Most of the clusters attained an icosahedral structure upon freezing, a structure
found to be stable to mild annealing. Other structures observed were imperfect truncated decahedral, truncated octahedral
and hexagonal close packed structures. The role of kinetics in the process of cluster solidification is discussed.
Received 6 November 2000 相似文献
967.
A.G. Kofman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(2):153-165
The electromagnetically induced transparency (EIT) with a (near-)resonant chaotic (amplitude-phase fluctuating, Gaussian-Markovian)
coupling field is studied theoretically. The Fourier transform of the steady-state EIT spectrum, which determines a nonstationary
probe absorption, is also considered. This quantity equals the average diagonal element of the (reduced) evolution operator
of the coupled transition (the evolution function). The exact solution in the form of a continued fraction is obtained and
used to perform numerical calculations. Moreover, a number of approximate analytical results are obtained, which, together
with the results of previous publications, describe the EIT and the evolution function in all possible regimes. In particular,
in the constructive-interference case the EIT increases with the coupling-field bandwidth ν at sufficiently small ν. For a strong field, the maximum of the transparency as a function
of ν is less than that for a monochromatic field of the same average intensity. In contrast, for a weak field, there is a
range of ν values, where the field fluctuations do not affect the EIT. The latter result is shown to hold for a broad class of stochastic fields.
Received 31 December 2000 and Received in final form 14 May 2001 相似文献
968.
激光雷达研制及其探测大气气溶胶的实验研究 总被引:5,自引:2,他引:5
作为一种激光探测大气气溶胶特征的新技术,采用分子滤波技术的高光变分辨率激光雷达在国际上得到了发展,给出了对这种YAG激光雷达系统的理论分析并建立了实验装置,其接收望远镜孔径为300mm,YAG激光脉冲能量为150mJ。通过数值模拟与初步测量估计了激光雷达性能,测量了大气回向散射信号,测量结果表明实结果与理论分析一致。 相似文献
969.
Applying single- and double-pulse excitation at 800 nm, the kinetics of the upconversion fluorescence in the green, as well
as the upconversion laser at 543 nm was studied. No significant delay between the pumping pulse and the laser emission was
found. In the erbium doped (1000 ppm) optical fiber, the mechanism responsible for the upconversion is purely of the excited
state absorption (ESA) type. The double-pulse technique enables also a determination of the lifetime of the intermediate metastable
state 4
I
11/2 (7±0.3 ms). Some other basic properties of the upconverted fluorescence and of the laser itself (fluorescence spectrum, optical
gain, laser threshold) are also described.
Received: 11 December 2000 / Revised version: 18 February 2001 / Published online: 18 July 2001 相似文献
970.
(001)-oriented strontium bismuth tantalate thin films have been grown on Pt/TiO2/SiO2/Si (100) substrates by pulsed laser deposition. The room-temperature current–electric field dependence of the films has been
investigated, which revealed a space-charge-limited conduction mechanism. The microstructures of grain boundaries and structural
defects in these films were also examined by transmission electron microscopy and high-resolution transmission electron microscopy,
respectively. The grains of the films deposited at 550 °C exhibited polyhedral morphologies, and the average grain size was
about 50 nm in length and 35 nm in width. At a small misorientation angle (8.2°) tilt boundary, a regular array of edge dislocations
with about 3-nm periodic distance was observed, and localized strain contrast near the dislocation cores was also observed.
The Burgers vector b of the edge dislocation was determined to be [110]. At a high misorientation angle (39.0°) tilt grain boundary lattice strain contrast associated with the distortion of
lattice planes was observed, and the mismatching lattice images occurred at about 2 nm along the boundary. The relationship
between microstructural defects at grain boundaries and leakage currents of these films is also discussed.
Received: 8 September 2000 / Accepted: 18 December 2000 / Published online: 28 February 2001 相似文献