共查询到20条相似文献,搜索用时 828 毫秒
1.
Turşucu Ahmet 《辐射效应与固体损伤》2013,168(11-12):1037-1044
ABSTRACTGamma-ray albedo factors of rare-earth oxides were determined experimentally. The detection of albedo factors for selected materials includes albedo number, albedo energy and albedo dose calculations. 59.54 keV gamma rays of 5 Ci annular 241Am were used as a gamma source. Gamma rays were scattered by selected samples and collected by High Purity Germanium semiconductor detector. The albedo factors were plotted as a function of atomic number of target materials. 相似文献
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《Composite Interfaces》2013,20(1):17-39
The singular behaviour at the free edges of the fibre-matrix interface is analysed for the fibre push-out test geometry based on the boundary element method. The fibre push-out test has been extensively used to measure the fibre-matrix interfacial properties in polymer, ceramic and metal matrix composites. There are two free edges in the fibre push-out specimen: one is at the loaded fibre end and the other at the supported fibre end. The singular stresses can be expressed as a function of singular exponent and singular stress intensity. It is shown that the singular exponents obtained at both fibre ends are characteristic of composite constituent properties, such as Young's moduli of fibre and matrix, and does not vary with specimen dimensions. The singular exponents are real and identical for the shear and radial stress components at fibre ends where the wedge angles are the same. The singular stress intensities are also implicit in material properties, and vary with specimen dimensions, such as fibre to matrix radius ratio, fibre aspect ratio and support hole size. An interfacial failure criterion is proposed here based on the average stress concept to determine the critical singular stress intensities in mode I and mode II loads. 相似文献
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Sara Cruz?y?Cruz Oscar Rosas-Ortiz 《International Journal of Theoretical Physics》2011,50(7):2201-2210
The Schr?dinger equation for position-dependent mass singular oscillators is solved by means of the factorization method and
point transformations. These systems share their spectrum with the conventional singular oscillator. Ladder operators are
constructed to close the su(1,1) Lie algebra and the involved point transformations are shown to preserve the structure of the Barut-Girardello and Perelomov
coherent states. 相似文献
6.
Devinder Pal Ghai P. Senthilkumaran R.S. Sirohi 《Optics and Lasers in Engineering》2009,47(1):123-126
Single-slit diffraction of an optical beam carrying phase singularity is presented. Due to azimuthal phase dependence, the diffraction pattern of the singular beam differs from that of a plane wave. The fringes in the diffraction pattern of singular beam undergo continuous bending, while passing through the centre of the pattern and exhibit left to right or right to left shift, depending on the sign of the topological charge of singular beam. It is shown that diffraction of a singular beam through a slit can be used to determine magnitude and sign of its topological charge. 相似文献
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Colombeau's generalized functions are used to adapt the distributional approach to singular hypersurfaces in general relativity with signature change. Equations governing the dynamics of a singular hypersurface are derived and a specific non-vanishing form for the energy-momentum tensor of the singular hypersurface is obtained. It is shown that matching in the case of de Sitter space in the Lorentzian sector is possible along the boundary with minimum radius but leads to the vanishing of the energy-momentum tensor of the singular hypersurface. 相似文献
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L. I. Fedoseev I. V. Kuznetsov N. K. Polova A. A. Shvetsov 《International Journal of Infrared and Millimeter Waves》1982,3(6):917-927
Equipment and methods used for measuring the apparent temperature of snow cover in high mountains is described. The spectrum of dry snowpack emission in the wavelength region 0.85÷1.3 mm is obtained. The dependence of the apparent temperature of snow cover on the atmospheric optical depth is determined. It is shown that in the first approximation the snow cover emission is described by the Lambert law and the snow albedo is within 0.6÷0.67. 相似文献
9.
一种改进的奇异值降噪阶次选取方法用于紫外光谱信号去噪的研究 总被引:1,自引:0,他引:1
光谱去噪是光谱检测的重要环节。针对光谱信号易受光谱仪热噪声、现场机械振动以及随机噪声等因素影响,而在线监测系统要求减少人为参数选择对去噪效果的影响,提出利用奇异值分解(SVD)理论对光谱信号去噪。提出一种改进的降噪阶次选取方法:指定奇异值差分谱最大峰值点θ1为所选阶次下界;利用奇异值、奇异值差分谱综合信息选取阶次上界θ2;将区间θ1~θ2定义为模糊区域,通过模糊C均值聚类求取隶属度,赋予模糊区域内奇异值相应的权重系数。用所提方法对不同信噪比下SO2紫外光谱信号去噪,将信噪比、均方根误差、波形相似系数、平滑度指标用于去噪效果的评价。去噪结果表明:所提方法完全基于数据驱动,具有较好的去噪效果,能够真实的恢复原始信号。 相似文献
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A numerical study is given on the spectral methods and the high order
WENO finite difference scheme for the solution of linear and nonlinear hyperbolic
partial differential equations with stationary and non-stationary singular sources.
The singular source term is represented by the $δ$-function. For the approximation
of the $δ$-function, the direct projection method is used that was proposed in [6].
The $δ$-function is constructed in a consistent way to the derivative operator. Nonlinear
sine-Gordon equation with a stationary singular source was solved with the
Chebyshev collocation method. The $δ$-function with the spectral method is highly
oscillatory but yields good results with small number of collocation points. The
results are compared with those computed by the second order finite difference
method. In modeling general hyperbolic equations with a non-stationary singular
source, however, the solution of the linear scalar wave equation with the non-stationary
singular source using the direct projection method yields non-physical
oscillations for both the spectral method and the WENO scheme. The numerical
artifacts arising when the non-stationary singular source term is considered on the
discrete grids are explained. 相似文献
11.
Jonathan F Schonfeld 《Annals of Physics》1980,126(1):123-134
The compact open four-dimensional manifold P2, with Euclidean metric, has recently attracted attention as an example of a spacetime in which fields of half-integral spin cannot be defined in the absence of additional structure (such as an electromagnetic background). In this note we identify the specific topological anomaly responsible for this phenomenon: P2 contains a class of two-dimensional spheres—“complex lines”— in small neighborhoods of each of which the two transverse degrees of freedom are forced to “twist” in a characteristic way. It is shown in detail how the twists force vierbeins—tetrads of orthonormal vector fields that play a central role in the theory of spinors—to have singularities on every complex line. As an aid to visualization we construct an example of a vierbein with, loosely speaking, the smallest possible set of singularities: It is ill-defined at every point of some one complex line and smooth everywhere else. The behavior of such a vierbein near any one of its singular points is characterized explicitly. The structure of the minimally singular vierbein is used to illuminate the observation of Hawking and Pope that in the presence of an appropriate electromagnetic background, fields of any spin can exist on P2 as long as their electric charges are correctly quantized, but that the charge values available to half-integral-spin fields differ from those available to integral-spin fields. 相似文献
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This paper studies the dynamics of dark optical solitons. The G′/G-expansion approach is utilized. The byproduct of this approach is the singular periodic solution of the governing nonlinear Schrödinger's equation for its corresponding parameter regime. The constraint conditions are also in place for the existence of dark solitons. 相似文献
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G. Weigt 《Annalen der Physik》1971,482(2):189-198
A marginal singular integral equation is solved numerically for a simple cutoff-model with additional singular short range forces using the Atkinson-Contogouris-method. Bassetto's and Paccanoni's parameterfree ?-meson calculation is investigated for cutoff Λ → ∞. 相似文献
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在卫星短波红外遥感二氧化碳的过程中, 表征地表特征的地表反照率是影响探测精度的重要参数之一. 针对温室气体二氧化碳高精度探测的需求, 本文研究了地表反照率对正演模拟光谱和反演近地面二氧化碳平均柱浓度XCO2的影响. 模拟计算结果显示, 地表反照率数值增大时, 观察的光谱强度也相应增大, 并且在O2-A波段造成的光谱差异比1.6 μm波段高出一个数量级, 即地表反照率在O2-A波段的影响比较大. 选取了两个不同地表类型的实际观测光谱, 仅改变O2-A波段和1.6 μm波段地表反照率数值, 得出草地点在O2-A波段地表反照率达到0.25的误差时, 会给XCO2的反演结果造成大于1%的相对误差, 而1.6 μm波段的地表反照率变化对XCO2的反演结果造成的误差可以忽略不计, 说明了地表反照率在反演XCO2过程中的重要性主要来自对O2-A波段的影响. 此研究表明了地表反照率在卫星遥感温室气体过程中的重要性, 为提高遥感探测二氧化碳的精度提供了重要的理论依据和指导. 相似文献
15.
J. Kovac 《Physica A》1977,86(1):1-24
The theory of non-equilibrium thermodynamics is applied to a multi-component system containing an interface using a method developed by Bedeaux, Albano, and Mazur. A singular mass density is allowed at the interface as well as singular densities of energy and entropy. All currents are also allowed to be singular at the interface. The conservation laws and the Gibbs relation for the entropy are used to derive the entropy production at the surface. Linear laws relating the fluxes and thermodynamic forces are presented. The theory is then applied to a two component system where one of the phases is a liquid and the other a low density gas and the boundary conditions at the free surface of the liquid derived. The boundary conditions include the conditions used by Levich in his theory of the damping of waves by surface-active substances, but include other effects as well. 相似文献
16.
Sengupta AM Mitra PP 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(3):3389-3392
The singular value decomposition is a matrix decomposition technique widely used in the analysis of multivariate data, such as complex space-time images obtained in both physical and biological systems. In this paper, we examine the distribution of singular values of low-rank matrices corrupted by additive noise. Past studies have been limited to uniform uncorrelated noise. Using diagrammatic and saddle point integration techniques, we extend these results to heterogeneous and correlated noise sources. We also provide perturbative estimates of error bars on the reconstructed low-rank matrix obtained by truncating a singular value decomposition. 相似文献
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The application of non-equilibrium thermodynamics to a system consisting of two bulk phases and their interface is extended to include electromagnetic effects. The interface is assumed to carry singular mass, energy, and entropy densities as well as singular electric charge, electric current, polarization and magnetization. Electric and magnetic fields are allowed to be discontinuous across the interface, but not singular.Maxwell's equations are used to derive relationships among electromagnetic quantities on the surface and boundary conditions for the bulk phases. An expression for the surface entropy production including electromagnetic effects is obtained, and the resulting linear laws relating thermodynamic forces and fluxes are investigated. 相似文献
18.
This paper presents a robust phase space reconstruction method based on singular value decomposition technique and its applications to large rotating machine and gear system condition monitoring and fault diagnosis. The singular value decomposition is used to determine the effective embedding space and to reduce the noise level of a measured vibration signal. Following the singular value decomposition, a pseudo-phase portrait can be obtained in the effective embedding space. This pseudo-phase portrait is then used to extract qualitative features of machine faults. Experience has shown that when one compares the pseudo-phase portraits obtained under different machine conditions, it is often possible to detect major differences due to different dynamic and kinematic mechanisms. In the case of gear system condition monitoring, correlation dimension has been introduced to evaluate these differences in order to obtain more accurate and reliable diagnosis. The pseudo-phase portrait is conceptually simple and has been found to be sensitive to some fault types. It is promising therefore that such pseudo-phase portraits can be used to realize real-time, online computer-aided diagnosis of machine faults. 相似文献
19.
利用时域奇异值分解(SVD)技术对并行时域有限差分(FDTD)方法计算得到的分布式负载平行板有界波电磁脉冲(EMP)模拟器内的场进行模式分析,给出有、无效应物时模拟器内场的3个主要模式(即TEM,TM1和TM2模)奇异值的变化及该奇异值随效应物的位置及高度的变化规律。研究结果表明:电磁波在模拟器中传播时,其主模TEM模的高频分量在衰减;效应物越靠近源时测试点场的3个主要模式所对应的奇异值变化越大;且当效应物的高度与所在位置处两极板距离之比小于等于60%时,效应物附近位置处场的TEM模对应的奇异值会出现两个极大值点,两点的水平间距与效应物的水平尺寸相当。 相似文献