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1.
Maslov’s method is applied to derive high frequency field expressions for the wave reflected by a three dimensional Gregorian system when the plane wave is incident. Expression is relatively simple and is valid in the caustic region. Geometrical optics approximation generally used to study high frequency field, fails in the vicinity of a caustic. Maslov’s method is a systematic procedure for predicting the field in the caustic region combining the simplicity of ray and generality of the transform method. Field distributions around the caustic region are calculated and the results are compared with obtained using current distribution method. Agreement among them is fairly good. 相似文献
2.
Balance equations are derived from Enskog’s kinetic equation for a two-dimensional system of hard disks using Grad’s moment
expansion method. This set of equations constitute an extended hydrodynamics for moderately dense bi-dimensional fluids. The
set of independent hydrodynamic fields in the present formulations are: density, velocity, temperature and also—following Grad’s original idea—the symmetric and traceless pressure tensor p
ij
and the heat flux vector q
k
. An approximation scheme similar in spirit to one made by Grad in his original work is made. Once the hydrodynamics is derived
it is used to discuss the nature of a simple one-dimensional heat conduction problem. It is shown that, not too far from equilibrium,
the nonequilibrium pressure in this case only depends on the density, temperature and heat flux vector.
PACS: 51.10.+y, 05.20.Jj, 44.10.+i, 05.70.Ln 相似文献
3.
Christo I. Christov 《Foundations of Physics》2006,36(11):1701-1717
Maxwell accounted for the apparent elastic behavior of the electromagnetic field by augmenting Ampere’s law with the so-called displacement current, in much the same way that he treated the viscoelasticity of gases. Maxwell’s original constitutive relations for both electrodynamics and fluid dynamics were not material invariant. In the theory of viscoelastic fluids, the situation was later corrected by Oldroyd, who introduced the upper-convective derivative. Assuming that the electromagnetic field should follow the general requirements for a material field, we show that if the upper convected derivative is used in place of the partial time derivative in the displacement current term, Maxwell’s electrodynamics becomes material invariant. Note, that the material invariance of Faraday’s law is automatically established if the Lorentz force is admitted as an integral part of the model. The new formulation ensures that the equation for conservation of charge is also material invariant in vacuo. The viscoelastic medium whose apparent manifestation are the known phenomena of electrodynamics is called here the metacontinuum. 相似文献
4.
K L Sebastian 《Pramana》1978,10(4):341-348
As an improvement over the Hartree-Fock approximation, we investigate a Green’s Function method—theΣ perturbation method—for molecular calculations. The method is applied to hydrogen molecule and to theπ-electron system of ethylene under PPP approximation. When the algebraic approximation is used, the energy obtained is better
than that of the HF approach, but is not as good as that of the configuration-interaction method. The main advantage of this
procedure is that it is devoid of the most serious defect of HF method, viz. incorrect dissociation limits. 相似文献
5.
We present the main aspects of Weber’s electrodynamics and of Maxwell’s equations. We discuss Maxwell’s point of view related
to Weber’s electrodynamics. We compare Weber’s force with Lorentz’s force. We analyse the relation between Weber’s law and
Maxwell’s equations. Finally, we discuss some experiments performed and proposed with which we can distinguish Weber’s force
from Lorentz’s one. 相似文献
6.
7.
Hong Yuan 《中国科学G辑(英文版)》2008,51(6):678-686
Based on the dynamic equations of nonlinear large deflection of axisymmetric shallow shells of revolution, the nonlinear free
vibration and forced vibration of a corrugated shallow shell under concentrated load acting at the center have been investigated.
The nonlinear partial differential equations of shallow shell were reduced to the nonlinear integral-differential equations
by using the method of Green’s function. To solve the integral-differential equations, the expansion method was used to obtain
Green’s function. Then the integral-differential equations were reduced to the form with a degenerate core by expanding Green’s
function as a series of characteristic function. Therefore, the integral-differential equations became nonlinear ordinary
differential equations with regard to time. The amplitude-frequency relation, with respect to the natural frequency of the
lowest order and the amplitude-frequency response under harmonic force, were obtained by considering single mode vibration.
As a numerical example, nonlinear free and forced vibration phenomena of shallow spherical shells with sinusoidal corrugation
were studied. The obtained solutions are available for reference to the design of corrugated shells. 相似文献
8.
9.
In this paper, a spatially homogeneous and anisotropic Bianchi type-I space-time filled with perfect fluid is investigated
within the framework of a scalar-tensor theory proposed by Saez and Ballester. Two different physically viable models of the
universe are obtained by using a special law of variation for Hubble’s parameter that yields a constant value of deceleration
parameter. One of the models is found to generalize a model recently investigated by Reddy et al. (Astrophys. Space Sci. 306:171,
2006). The Einstein’s field equations are solved exactly and the solutions are found to be consistent with the recent observations
of type Ia supernovae. A detailed study of physical and kinematical properties of the models is carried out. 相似文献
10.
Jagmeet Singh 《Pramana》1999,53(5):807-813
Biswas and Soni [4] have surmised a semiclassical formula for Berry’s phase in terms of a generating function. We derive this
formula apart from showing that it is not true in general and investigate its domain of validity. We also derive transformation
formulae for Berry’s phase (Hannay’s angle) under general canonical transformations. A simpler proof for total angle invariance
than hitherto available, is given. 相似文献
11.
K S Virbhadra 《Pramana》1993,40(4):273-275
An exact solution of Einstein’s equations is interpreted as describing the gravitational field of a tachyon in a de Sitter
universe. Switching off the cosmological constant yields the gravitational field of a tachyon in flat spacetime background. 相似文献
12.
We study mode-locking in disordered media as a boundary-value problem. Focusing on the simplest class of mode-locking models
that consists of a single driven overdamped degree-of-freedom, we develop an analytical method to obtain the shape of the
Arnol’d tongues in the regime of low AC-driving amplitude or high AC-driving frequency. The method is exact for a scalloped
pinning potential and easily adapted to other pinning potentials. It is complementary to the analysis based on the well-known
Shapiro’s argument that holds in the perturbative regime of large driving amplitudes or low driving frequency where the effect
of pinning is weak. 相似文献
13.
The reflection and transmission amplitudes are defined from the asymptotic form of the solution of Dirac equation of a charged
fermion in the presence of uniform time independent external electromagnetic field (E, H). Schwinger’s effective lagrangian is derived from the reflection and transmission amplitudes. It is found that both the
real and imaginary parts of the effective lagrangian agree with Schwinger’s expressions derived from the elegant method of
proper time formalism. 相似文献
14.
Considering external electric field as well as third- and fourth-order phonon anharmonic interaction terms in the pseudospin-lattice
coupled mode (PLCM) model Hamiltonian for KDP-type ferroelectrics, expressions for field-dependent shift, width, renormalized
soft mode frequency, Curie temperature, dielectric constant and dielectric loss are evaluated. For the calculation, method
of statistical double-time temperature-dependent Green’s function has been used. By fitting model values of physical quantities,
temperature and electric field dependences of soft mode frequency, dielectric constant and loss have been calculated which
compare well with experimental results of Baumgartner [8] and Choi and Lockwood [9]. Both dielectric constant and loss decrease
with electric field. 相似文献
15.
Louis Sica 《Foundations of Physics Letters》2002,15(5):473-486
Proofs of Bell’s theorem and the data analysis used to show its violation have commonly assumed a spatially stationary underlying
process. However, it has been shown recently that the appropriate Bell’s inequality holds identically for cross correlations
of three or four lists of ±l’s, independently of statistical assumptions. When data consistent with its derivation are analyzed
without imposition of the stationarity assumption, the resulting correlations satisfy the Bell inequality. 相似文献
16.
Travis Norsen 《Foundations of Physics》2009,39(3):273-294
J.S. Bell believed that his famous theorem entailed a deep and troubling conflict between the empirically verified predictions
of quantum theory and the notion of local causality that is motivated by relativity theory. Yet many physicists continue to
accept, usually on the reports of textbook writers and other commentators, that Bell’s own view was wrong, and that, in fact,
the theorem only brings out a conflict with determinism or the hidden-variables program or realism or some other such principle
that (unlike local causality), allegedly, nobody should have believed anyway. Moreover, typically such beliefs arise without
the person in question even being aware that the view they are accepting differs so radically from Bell’s own. Here we try
to shed some light on the situation by focusing on the concept of local causality that is the heart of Bell’s theorem, and,
in particular, by contrasting Bell’s own understanding with the analysis of Jon Jarrett which has been the most influential
source, in recent decades, for the kinds of claims mentioned previously. We point out a crucial difference between Jarrett’s
and Bell’s own understanding of Bell’s formulation of local causality, which turns out to be the basis for the erroneous claim,
made by Jarrett and many others, that Bell misunderstood the implications of his own theorem. 相似文献
17.
A study of ultrasonic velocities and internal friction has been carried out in Pb-Bi alloys in the concentration range of
0 to 49.5 atomic % Bi using the composite oscillator technique. From the velocity and density data a set of elastic constants
namely, Young’s modulus, rigidity modulus, bulk modulus and Poisson’s ratio are estimated. The results are interpreted in
terms of the phase changes occurring in the alloy system. Internal friction is found to be more sensitive than the elastic
constants to the phase changes. 相似文献
18.
The Green function for a Dirac particle subject to a plane wave field is constructed according to the path integral approach
and the Barut’s electron model. Then it is exactly determined after having fixed a matrix U chosen so that the equations of motion are those of a free particle, and by using the properties of the plane wave and also
with some shifts.
相似文献
19.
Using recent results for the surface current density on cylindrical surfaces of arbitrary cross-section producing uniform
interior magnetic field and an assumed set of flux-fronts, solutions of Bean’s critical state model for cylindrical samples
with non-elliptic cross-section are presented. Magnetization hysteresis loops for two cross-sections with different aspect ratios are obtained.
A comparison with some exact results shows the limitations of this approach. 相似文献
20.
Wei Shao Bing-Zhong Wang Huilai Liu 《International Journal of Infrared and Millimeter Waves》2006,27(9):1217-1225
In this paper, the application of the order-marching time-domain (OMTD) method to the solution of the cutoff frequencies of
TE and TM modes in millimeter-wave waveguides is described. Starting from Maxwell’s two-dimensional (2-D) differential equations
for TE or TM case, the OMTD method uses the orthonormality of weighted Laguerre polynomials and Galerkin’s testing procedure
to eliminate the temporal variables and results in an order-marching scheme. To verify it’s accuracy and efficiency, the numerical
results for millimeter-wave guided systems are compared with those of finite-difference time-domain (FDTD) method and analytical
solutions. The OMTD method improves computational efficiency notably, especially for fine grid division problems restricted
by stability constraints in the FDTD method.
This work was supported by the National Natural Science Foundation of China (No. 60371008) and the CRT Program of UESTC. 相似文献