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1.
A review of commonly used analytical and empirical formulae for predicting sound diffracted by a thin screen 总被引:2,自引:0,他引:2
This paper reviews some useful analytical and empirical formulae that are used for the calculation of sound diffracted by a barrier. A brief historic overview of the study of spherical waves diffracted by a rigid half plane is presented also. The physical principles of sound diffraction by a thin plane are explained. The mathematical expressions are cast in a convenient form for ease of numerical implementation. Accurate analytical solutions are expressed in terms of standard mathematical functions that can be computed readily. Among the approximate solutions quoted, quite a few empirical formulations are adequate for most engineering purposes. The information presented in this paper should also be helpful for those who are interested in the study of sound diffracted by a barrier in a room or in a long industrial space. 相似文献
3.
Muhammad A. Mushref 《Central European Journal of Physics》2005,3(2):229-246
Scattering characteristics of two plane waves are investigated for a circular cylinder covered by a dielectric substance.
Fields are assumed to be transverse magnetic (TM) and represented in an exponential series form. The diffracted radiations
are found by applying the boundary conditions to the wave functions. The wave transformation method and the orthogonality
of the exponential functions are respectively employed to obtain an infinite series in the solution. Numerical results are
evaluated by reducing the infinite series to a finite number of terms and comparing estimates with the single plane wave scattering
situation. 相似文献
4.
Switching and Self-trapping Dynamics of Dark Solitons in a Two-Component Bose-Einstein Condensate
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Two coupled dark solitons are considered in a two-component Bose-Einstein condensate, and their dynamics are investigated by the variational approach based the renormalized integrals of motion. The stationary states as physical solutions to the describing equations are obtained, and the dynamic mechanism is demonstrated by performing a coordinate of a classical particle moving in an effective potential field. The switching and selftrapping dynamics of the coupled dark vector solitons are discussed by the evolution of the atom population transferring ratio. 相似文献
5.
本文理论研究了近红外波段硅基三角晶格光子晶体环形微腔的光场局域特性,通过将微腔在空间周期性排列组成耦合腔光波导,研究了多个导带区域内光束传输时的群速度,最大和最小值分别为0.0028c和0.00028c.将环形微腔在垂直于光传输方向上进行交错排列,通过改变相邻微腔之间的耦合区域,可以大幅降低多频段范围内光束在耦合腔波导中传输时群速度之间的差异,并提高部分频段的透过率数值.在不改变介质柱半径条件下,通过去掉三角晶格光子晶体中距中心介质柱距离分别为2a和√3a的六个介质柱构成了两种微腔,研究了两种微腔所支持的谐振波长之间的差异,在此基础上构造了两种耦合腔波导,进而将这两种耦合腔光波导与W1型输入/输出波导相连,最终实现了在多个不同频率范围内降低群速度的同时实现频段选择和频段分束功能,其导模群速度可降低到0.00047c. 相似文献
6.
K. -E. Hellwig 《International Journal of Theoretical Physics》1969,2(2):147-155
Effects are defined in this paper as observable changes in the state of a macrosystem, which are caused by interaction with a microsystem. These effects are the starting point of Ludwig's axiomatic foundation of quantum theory. In this theory the concept of commensurability is developed by considering effects which can be caused together, by one single microsystem. Such effects are called coexistent. It is shown that in ordinary quantum mechanics the formal definition of coexistence and the corresponding postulates given by Ludwig are consistent with the dynamics of interaction processes leading to effects.Part of a work supported by the Deutsche Forschungsgemeinschaft. 相似文献
7.
The ground states and pseudospin textures of rotating two-component Bose–Einstein condensates trapped in harmonic plus quartic potential
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The ground states of two-component miscible Bose–Einstein condensates(BECs) confined in a rotating annular trap are obtained by using the Thomas–Fermi(TF) approximation method.The ground state density distribution of the condensates experiences a transition from a disc shape to an annulus shape either when the angular frequency increases and the width and the center height of the trap are fixed,or when the width and the center height of the trap increase and the angular frequency is fixed.Meantime the numerical solutions of the ground states of the trapped two-component miscible BECs with the same condition are obtained by using imaginary-time propagation method.They are in good agreement with the solutions obtained by the TF approximation method.The ground states of the trapped two-component immiscible BECs are also given by using the imaginary-time propagation method.Furthermore,by introducing a normalized complex-valued spinor,three kinds of pseudospin textures of the BECs,i.e.,giant skyrmion,coaxial double-annulus skyrmion,and coaxial three-annulus skyrmion,are found. 相似文献
8.
9.
The strength distribution for an arbitrary excitation is given in terms of a double expansion, and its sum rules by single expansions, in polynomials defined by the initial and final energy spectra. In model spaces which are not too large, a rapid convergence, to within fluctuations, is assured by the action of a central limit theorem, as is shown in particular by considering the response of the system under infinitesimal deformations of the Hamiltonian. When larger spaces are decomposed into subspaces defined by a partitioning of the single-particle space a similar convergence results. At the same time, close contact is made with, and important corrections are found to, intuitive procedures which are often used for approximating strength distributions. The general features of the distribution are often easily understood in termsof a simple geometry made effective in the model space by the central limit theorem, and further features by exploiting the connection of this geometry to the unitary group of transformations in the single-particle space. Extensions are given for multipole strengths and sum rules, appropriate when the angular momenta (and isospins) are specified for the states involved in the transitions. Measures for the RMS fluctuations in the sum-rule quantities, and correlations between them, are given by combining the low-order-polynomial (statistically smoothed) strengths with an assumed Porter-Thomas distribution for the (high-order) strength fluctuations. 相似文献
10.
Influence of Concentration of Vanadium in Zinc Oxide on Structural and Optical Properties with Lower Concentration
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ZnO films doped with different vanadium concentrations are deposited onto glass substrates by dc reactive magnetron sputtering using a zinc target doped with vanadium. The vanadium concentrations are examined by energy dispersive spectroscopy (EDS) and the charge state of vanadium in ZnO thin films is characterized by x-ray photoelectron spectroscopy. The results of x-ray diffraction (XRD) show that all the films have a wurtzite structure and grow mainly in the c-axis orientation. The grain size and residual stress in the deposited films are estimated by fitting the XRD results. The optical properties of the films are studied by measuring the transmittance. The optical constants (refractive index and extinction coefficient) and the film thickness are obtained by fitting the transmittance. All the results are discussed in relation with the doping of the vanadium. 相似文献
11.
Hexagonally ordered arrays of magnetic FePt nanoparticles on Si substrates are prepared by a self assembly of diblock copolymer PS-b-P2VP in toluene, a dip coating process and finally plasma treatment. The as-treated FePt nanoparticles are covered by an oxide layer that can be removed by a 40 s Ar+ sputtering. The effects of the sequence of adding salts on the composition distribution are revealed by x-ray photoelectron spectroscopy measurements. No particle agglomeration is observed after 600℃annealing for the present ordered array of FePt nanoparticles, which exhibits advantages in patterning FePt nanoparticles by a micellar method. Moreover, magnetic properties of the annealed FePt nanoparticles at room temperature are investigated by a vibrating sample magnetometer. 相似文献
12.
Mechanoelectric effects caused by elastic deformation of glasses and marbles are studied in a neutral environment and with weak electric polarization of samples. It is found that the electric potentials that are produced by bending a sample are opposite in sign in compressed and stretched regions. The mechanoelectric effects increase or decrease depending on the direction of the electric field applied to the sample. It is concluded that the electric polarization and the polarization induced by mechanical deformation are of a common nature. Electromagnetic precursors of earthquakes are discussed. 相似文献
13.
低密度聚乙烯光引发交联机理——Ⅱ.BNB自旋捕捉ESR研究 总被引:6,自引:4,他引:2
在光引发剂二苯甲酮(BP)存在下,紫外光辐照低密度聚乙烯(LDPE)所形成的自由基中间体已被自旋捕捉剂2,4,6-三特丁基亚硝基苯(BNB)所捕捉,其自旋加合物自由基已为电子自旋共振(ESR)所特征。现已检测和鉴定到二种自旋加合物:一种是叔碳自由基;另一种是仲碳自由基。它们分别是由BP的激发三重态从LDPE链的支化点和亚甲基团上夺氢所形成的自由基中间体同自旋捕捉剂BNB反应生成的。上述的证据表明:LDPE的光引发交联点主要发生在叔碳和仲碳原子上,且H-型交联点占主导地位。 相似文献
14.
高自由度体系微振动本征模式的求解方法 总被引:1,自引:1,他引:0
介绍两种求解高自由度体系微振动本征模式的方法.第一种方法:利用对称性经过物理分析寻找本征模式;第二种方法:利用对称性降低体系的自由度,然后用求解本征模式的一般方法解之. 相似文献
15.
Time evolution of the relative density of speakers of an endangered language, Aromanian, which is spoken by a bilingual community in North-Western Greece, is approached theoretically by means of a two-state model and a three-state model. The same prestige and volatility parameters are used in these two models. Furthermore, a culture parameter and a second exponent are introduced in the three-state model. The parameters of each model are fitted to the current status of Aromanian, on the basis of field evidence collected by us, and the first findings about the risk of the language’s extinction are presented. 相似文献
16.
S. R. Seshadri 《Applied physics. B, Lasers and optics》1977,14(1):35-42
The characteristics of surface waves (i) in a passive medium supported by a passive surface with reactance modulation and
an active surface with the modulation of either the reactance or the negative resistance, and (ii) in an active medium supported
by a passive surface with a reactance modulation are investigated with emphasis on the band regions. The periodic variation
is sinusoidal and is in the propagation direction. For a passive medium terminated by a passive surface with a reactance modulation,
there are stop bands in frequency for the surface waves and the structure of the first two stop bands is analyzed. For a passive
medium terminated by an active surface and for an active medium terminated by a reactance-modulated passive surface, the characteristics
of the absolute instabilities occurring in the first-order band are examined. The nature of the convective instability taking
place in the second-order band for an active medium terminated by a reactance-modulated surface is discussed. Analytical expressions
for the frequency shift of the second-order band are deduced. The Floquet theory is used to obtain the exact dispersion relation
in the form of a continued fraction which is analyzed by singular expansions. 相似文献
17.
Surface wave motions generated by a time-harmonic point load applied at the surface of an isotropic linearly elastic half-space are conventionally solved by the use of integral transform techniques. The inverse transforms, are often complicated and will not always yield closed-form solutions. In this paper expressions for the displacements for surface wave motions radiated from point-load excitation are determined in a simple manner by the use of the elastodynamic reciprocity theorem. It is shown that the radiated amplitudes of the surface displacements obtained by the reciprocity approach are identical to the corresponding results obtained by the use of Hankel transform and by Lamb in his classical paper. 相似文献
18.
K. Ogawa J. Allam N. De B. Baynes J. R. A. Cleaver T. Mishima I. Ohbu 《Optical and Quantum Electronics》1996,28(7):907-917
In-plane-gate field-effect transistors are probed by femtosecond electrooptic sampling. Ultrafast response of the transistors is dominated by a displacement current induced by parasitic gate-drain capacitance. Intrinsic and parasitic gate-drain capacitances of various transistor structures are obtained from displacement-current characteristics and are in quantitative agreement with the calculation of planar capacitances. Intrinsic gate-drain capacitances are in the order of 100 aF, while parasitic gate-drain capacitances are between 1.7 and 4.8 fF, more than ten times that of intrinsic gate-drain capacitances. Reduction in parasitic capacitance by a factor of two is achieved by means of grounded shields and is confirmed by calculation. The grounded-shields screen parasitic electric fields and transform parasitic coupling into a part of the waveguide coupling. This reduction in parasitic capacitance is the first demonstration that the parasitic field effect is controlled artificially by nanometre-scale device technology. 相似文献
19.
K. G. Grigorov D. Bouchier G. I. Grigorov J-L Vignes J-P Langeron 《Applied Physics A: Materials Science & Processing》1994,58(6):619-622
Analytical expressions for estimating the energy dissipation and the film constituent concentration profiles in films grown by Ion-Assisted Physical Vapour Deposition (IA PVD) are given. Two cases of IA PVD are considered: ion-assistance performed by inert-gas ions as well as by ions of a film constituent. As an example of application, concentration and damage depth profiles in h-BN films grown by IA PVD are calculated and a comparison is made with results obtained by computer simulation. 相似文献
20.
Closed series solution of electromagnetic scattering by an eccentric coated cylinder is achieved in matrix form. Diffracted field patterns are examined for an incident plane transverse magnetic (TM) wave. The solution is found by the classical separation of variables technique and the translational addition theorems. Wave transformation and orthogonality of the complex exponentials are employed to produce an infinite series. Numerical results are then shown by shortening the infinite series to a limited number of terms. Solutions are discussed for a dielectric or a metamaterial coating. 相似文献