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91.
基于大气信道内的空间激光通信演示验证实验,对系统光斑跟踪精度的影响因素进行了分析,研究了大气湍流对光斑跟踪精度的影响,建立了光斑质心检测模型,设计了一套信标光光斑粗精复合跟踪系统.搭建了室内测试实验系统,完成了大气湍流对光斑跟踪精度影响的测量,结果表明在中弱湍流时,跟踪精度随湍流增大有近似线性关系,系统整体跟踪精度在5~15μrad之间,可较好地完成光斑跟踪功能.在野外环境开展的飞机-飞机激光通信演示实验中,对伺服系统的跟踪性能及跟踪精度进行实际测量,整体跟踪精度不大于15μrad,与室内实验测试系统基本一致. 相似文献
92.
Excitation functions for the production of68Ga,67Ga,66Ga,65Ga +65Zn and61Cu fromα-induced reactions in natural copper have been measured in the energy range ≈ 10–40 MeV using the stacked foil technique.
A stack of nine copper foils was irradiated by a 40 MeVα-beam. Theγ-rays emitted from the irradiated samples were recorded. Excitation functions have also been calculated theoretically using
a statistical model with and without the inclusion of pre-equilibrium emission of particles. Pre-equilibrium component simulated
by exciton model shows that the inclusion of pre-equilibrium emission gives better agreement between experimental and theoretical
excitation functions. Pre-equilibrium fraction depends on the incident energy and the target mass number. 相似文献
93.
Crossed Modules and Quantum Groups in Braided Categories 总被引:2,自引:0,他引:2
Yu. N. Bespalov 《Applied Categorical Structures》1997,5(2):155-204
Let A be a Hopf algebra in a braided category
. Crossed modules over A are introduced and studied as objects with both module and comodule structures satisfying a compatibility condition. The category
of crossed modules is braided and is a concrete realization of a known general construction of a double or center of a monoidal category. For a quantum braided group
the corresponding braided category of modules
is identified with a full subcategory in
. The connection with cross products is discussed and a suitable cross product in the class of quantum braided groups is built. Majid–Radford theorem, which gives equivalent conditions for an ordinary Hopf algebra to be such a cross product, is generalized to the braided category. Majid's bosonization theorem is also generalized. 相似文献
94.
本文基于Reddy高阶剪切变形板理论导出Karman型非线性大挠度方程并用于层合板热后屈曲分析.分析中计及板初始几何缺陷和热效应.给出了四边简支.对称正交铺设层合板在均匀或非均匀抛物型热分布作用下的后屈曲分析.采用摄动-Galerkin混合法确定板的热屈曲载荷与热后屈曲平衡路径.同时讨论了横向剪切变形,板长宽比,铺层数以及初始几何缺陷等各种参数变化的影响. 相似文献
95.
B. Manz P. S. Chow L. F. Gladden 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1999,136(2):226
A modified version of the echo-planar imaging technique incorporating a Carr–Purcell train of 180° rf pulses (PEPI) has been implemented on a standard spectrometer. It is demonstrated that artifacts in the image due to cumulative errors in the rf field can be reduced by replacing each 180° pulse by a composite sequence of three rf pulses. Artifact-free 3D images at 94 μm voxel resolution are obtained within 15 min. This technique has been applied to study the drying process in an initially water-saturated model porous medium with characteristicT*2of order 700 μs. 相似文献
96.
O. Ciftja 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,13(4):671-677
The experimentally observed filling factors of the fractional quantum Hall effect can be described in terms of the composite
fermion wave function of the Jastrow-Slater form [0pt] fully projected into the lowest Landau level. The Slater determinant of the above composite fermion wave function represents
the filled Landau levels of composite fermions evaluated at the corresponding reduced magnetic field. For a system of fermions
studied in the thermodynamic limit, we prove that in the even-denominator-filled state limit (when the number of filled Landau
levels of composite fermions becomes infinite), the above composite fermion wave function exactly transforms into the Rezayi-Read
Fermi-sea-like wave function [0pt] constructed by attaching 2m flux quanta to the Slater determinant of two-dimensional free fermions at the density corresponding to that filling. We study
the composite fermion wave function and its evolution into the Fermi-sea-like wave function for a range of filling factors
very close to the even-denominator-filled state.
Received 19 March 1999 相似文献
97.
Tatsuo Nakagawa Satoshi Fukura Munenori Nakai Kazumasa Sugiyama Ryohei Kokawa Hiroyuki Kagi 《Optical Review》2006,13(4):269-275
We constructed a scanning near-field optical microscope (SNOM) on a commercially available atomic force microscopy (AFM) apparatus
(SPM-9500J2; Shimadzu Corp.) to measure the stress distribution in ceramic composite materials. Features of our SNOM system
are: (1) a compact SNOM head substituted for the original AFM head; (2) a wide scanning range (125 × 125 μm2) inherited from the original scanner; (3) use of conventional shear-force regulation; (4) an optical system for the illumination-collection
(I-C) mode; (5) excitation by a 488 nm line of an Ar-ion laser, and (6) light detection by photon counting or a polychromator
equipped with an electronically cooled charge coupled device (CCD). This SNOM system was used to measure the surface structure
and stress distribution of an Al2O3/ZrO2 eutectic composite. We simultaneously measured topographic images and fluorescence spectra of an Al2O3/ZrO2 eutectic composite. We estimated its peak intensity, peak position, and peak width from the fluorescence spectrum during
scanning, which respectively correspond to the abundance of Al2O3, stress in the grain, and the anisotropy of that stress. Mapping images showed that the stress and its anisotropy were weaker
in the center of the Al2O3 grain than its boundary between Al2O3 and ZrO2. That observation suggests that Al2O3 underwent intense anisotropic stress induced by volume expansion in the phase transition of ZrO2 from the cubic phase to the monoclinic phase during preparation. 相似文献
98.
Ni + Mo + Si composite coatings were prepared by co-deposition of nickel with molybdenum and silicon powders from a nickel solution in which Mo and Si particles were suspended by stirring. The layers have been deposited on a carbon steel substrate (St3S) under galvanostatic conditions. The content of Si in deposited layers was about 2-5 wt.% depending on deposition current density and the value of electric charge. For comparison Ni + Mo composite coatings were obtained under analogous current conditions. Composite coatings of enhanced Si content (15 wt.%) were deposited from an electrolyte in which 40 g/dm3 of Si covered with electroless plated nickel was dispersed. Deposition current density was equal 0.1 A/cm2 and the value of electric charge Q = 500 C/cm2. The thickness of the coatings was about 100-300 μm depending on their kind, electric charge and the deposition current density. Surface and cross-section morphology were investigated by scanning electron microscope (SEM). All deposited coatings are characterized by great, developed surface area. No internal stresses causing their cracking were observed. Chemical composition of the layers was determined by X-ray fluorescence spectroscopy (XRF) method and quantitative X-ray analysis (QXRD). It was stated, that the content of molybdenum and silicon in Ni + Mo + Si coatings depends on deposition current density and the amount of the powder in bath. The results of structural investigation of the obtained layers by the X-ray diffraction (XRD) method show, that they consist in crystalline Mo or Mo and Si phases built into Ni matrix. Moreover, Ni + Mo + Si composite coatings were modified by thermal treatment. It has been found that the thermal treatment of Ni + Mo + Si composite coatings caused that the new phases (NiSi, Mo2Ni3Si and Ni6Mo6C1.06) were obtained. 相似文献
99.
Jin Hu Gang Liu Jixiu Zhang Lingchao Kong Weidong Fei 《Applied Surface Science》2006,253(5):2792-2795
The microstructure of a laser treated Al18B4O33w/2024Al composite has been investigated using transmission electron microscope (TEM), low-angle (glancing angle) X-ray diffraction (XRD) techniques. Various surface microstructures were observed in the laser treated composite. The Al18B4O33 whisker on the surface of the composite was decomposed during laser surface melting, various decomposition products were studied in the laser treated composite. Eutectic phases and the precipitation in the matrix of the composite with laser-treated were observed. The main phases detected in the molten zone were aluminum and decomposition products Al2O3. The effect of laser treatment on the hardness of the composite was also examined. A surface hardness of 400 Hv was noted. 相似文献
100.
Xiangming He Weihua Pu Jianguo Ren Li Wang Jiulin Wang Changyin Jiang Chunrong Wan 《Ionics》2008,14(4):335-337
The charge/discharge characteristics of the sulfur composite cathodes were investigated at different temperatures and different
current densities. The composite presented the discharge capacities of 854 and 632 mAh g−1 at 60 and −20 °C, respectively, while it had the discharge capacities of 792 mAh g−1 at 25 °C. The composite presented the discharge capacities of 792 and 604 mAh g−1 at 55.6 and 667 mA g−1, respectively, at room temperature. The results showed that the sulfur composite cathodes presented good charge/discharge
characteristics between 60 and −20 °C and at a high c-rate up to 667 mA g−1. 相似文献