共查询到20条相似文献,搜索用时 94 毫秒
1.
Hassan Amirhashchi Anirudh Pradhan H. Zainuddin 《International Journal of Theoretical Physics》2011,50(11):3529-3543
We study the evolution of the dark energy parameter in a spatially homogeneous and isotropic FRW space-time filled with barotropic
fluid and dark energy by considering a time dependent deceleration parameter. Two cases are discussed when the dark energy
is minimally coupled to the perfect fluid as well as direct interaction with it. It is concluded that in both non-interacting
and interacting cases only open and flat universes cross the phantom region. We find that during the evolution of the universe,
the equation of state (EoS) for dark energy ω
D
changes from ω
D
>−1 to ω
D
<−1, which is consistent with recent observations. The cosmic jerk parameter in our derived models is also found to be in
good agreement with the recent data of astrophysical observations. 相似文献
2.
The temperature-induced frequency shifts (1/ω)(∂ω/∂T)
p
are calculated from the pressure induced frequency shifts (1/ω)(∂ω/∂P)
T
using the observed frequencies at various pressures for the Raman modes of II and III in phase II (P > P
C
) of s-triazine. The values of the mode Grüneisen parameters γ
T
(isobaric) and γ
T
(isothermal) of those Raman modes studied here, are determined through the Pippard relations in the spectroscopically modified
forms for this crystal. The temperature-induced and the pressure-induced frequency shifts are then used to predict the pressure
dependence of the isothermal compressibility, thermal expansion and the specific heat in phase II (P > P
C
) of s-triazine. 相似文献
3.
We study effects of cosmic fluids on finite-time future singularities in modified f (R, G)-gravity, where R and G are the Ricci scalar and the Gauss–Bonnet invariant, respectively. We consider the fluid equation of state in the general
form, ω = ω(ρ), and we suppose the existence of a bulk viscosity. We investigate quintessence region (ω > −1) and phantom region (ω < −1) and the possibility to change or avoid the singularities in f (R, G)-gravity. Finally, we study the inclusion of quantum effects in large curvature regime. 相似文献
4.
Jeong-Ryeol Choi 《Pramana》2005,65(2):165-176
We investigated quantum states with continuous spectrum for a general time-dependent oscillator using invariant operator and
unitary transformation methods together. The form of the transformed invariant operator by a unitary operator is the same
as the Hamiltonian of the simple harmonic oscillator:I’ = p2/2 +ω
2
q
2/2. The fact thatω
2 of the transformed invariant operator is constant enabled us to investigate the system separately for three cases, whereω
2 > 0,ω
2 < 0, andω
2 = 0. The eigenstates of the system are discrete forω
2 > 0. On the other hand, forω
2 <− 0, the eigenstates are continuous. The time-dependent oscillators whose spectra of the wave function are continuous are
not oscillatory. The wave function forω
2 < 0 is expressed in terms of the parabolic cylinder function. We applied our theory to the driven harmonic oscillator with
strongly pulsating mass. 相似文献
5.
A Gaussian whistler pulse is shown to cause ponderomotive acceleration of electrons in a plasma when the peak whistler amplitude
exceeds a threshold value and the whistler frequency is greater than half the cyclotron frequency, ω>ω
c
/2. The threshold amplitude decreases with the ratio of plasma frequency to electron cyclotron frequency, ω
p
/ω
c
. However, above the threshold amplitude, the acceleration energy decreases with ω
p
/ω
c
. The electrons gain velocities about twice the group velocity of the whistler. 相似文献
6.
L. Bartosch P. Kopietz 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(1):29-36
We consider the effect of Coulomb interactions on the average density of states (DOS) of disordered low-dimensional metals
for temperatures T and frequencies ω smaller than the inverse elastic life-time 1/τ. Using the fact that long-range Coulomb interactions in two dimensions (2d) generate ln2-singularities in the DOS ν(ω) but only ln-singularities in the conductivity σ(ω), we can re-sum the most singular contributions
to the average DOS via a simple gauge-transformation. If σ(ω) > 0, then a metallic Coulomb gapν(ω) ∝ |ω|/e
4 appears in the DOS at T = 0 for frequencies below a certain crossover frequency Ω
2 which depends on the value of the DC conductivity σ(0). Here, - e is the charge of the electron. Naively adopting the same procedure to calculate the DOS in quasi 1d metals, we find ν(ω) ∝ (|ω|/Ω
1)1/2exp(- Ω
1/|ω|) at T = 0, where Ω
1 is some interaction-dependent frequency scale. However, we argue that in quasi 1d the above gauge-transformation method is on less firm grounds than in 2d. We also discuss the behavior of the DOS at finite temperatures and give numerical results for the expected tunneling conductance
that can be compared with experiments.
Received 28 August 2001 / Received in final form 28 January 2002 Published online 9 July 2002 相似文献
7.
Summary Within the generalized equilibrium statistics recently introduced by Tsallis (p
n
∝[1−β(q−-1)
εn
]1/(q−)), we calculate the thermal dependence of the specific heat corresponding to a harmonic-oscillator-like spectrum, namely ε
n
ω(n−α) (∀ω>0,n=0,1,2,...). The influences ofq and α are exhibited. Physically inaccessible and/or thermally frozen gaps are obtained in the low-temperature region, and,
forq>1, oscillations are observed in the high-temperature region. The specific heat of the two-level system is also shown. 相似文献
8.
W. A. Majewski 《Letters in Mathematical Physics》1982,6(6):437-440
Let ℳ be a von Neumann algebra with a cyclic and separating vector Ω and let ω(·) denote the corresponding vector state, i.e.,
ω(A)=(Ω, AΩ) A ∈ ℳ. We have proved that a positive semigroup τ on ℳ can induce the dynamical semigroup in the GNS representation associated
with ω if the state ω is a τ-invariant one. Some applications are given. 相似文献
9.
L. M. Chasman 《Communications in Mathematical Physics》2011,303(2):421-449
We establish an isoperimetric inequality for the fundamental tone (first nonzero eigenvalue) of the free plate of a given
area, proving the ball is maximal. Given τ > 0, the free plate eigenvalues ω and eigenfunctions u are determined by the equation ΔΔu − τΔu = ωu together with certain natural boundary conditions. The boundary conditions are complicated but arise naturally from the plate
Rayleigh quotient, which contains a Hessian squared term |D
2
u|2. 相似文献
10.
An analytical expression I(ω) is obtained for a normalized function of the shape of an idealized nuclear quandrupole resonance
nutation line of a powdered sample for spins I=3/2 (η≠0). Calculations are made of the initial moments <ωn> of the nutation spectrum of the powder in the form of functions of ω0=γB1 and the asymmetry parameter η of the electric field gradient tensor. A method is proposed for determining the spectral parameters
η and eQqzz from the experimentally measured values of <ω>, <ω2>, <ω4>, and ω1/2 of the nuclear quadrupole resonance nutation spectrum of the powder.
State University, Kaliningrad. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 3–8, July, 1997. 相似文献
11.
The mechanism governing the shaping of the echo response in a monodomain order-disorder ferroelectric crystal to excitation
by two pulses of a microwave electric field at the frequencies ω and 2ω [(ω, 2ω) echo] and at the frequency ω [(ω, ω) echo] is described in the framework of the pseudospin formalism (S=1/2). The parameters of the echo response are calculated, and the results obtained are in good qualitative agreement with
experiment.
Fiz. Tverd. Tela (St. Petersburg) 39, 697–703 (April 1997) 相似文献
12.
A. V. Luchinsky 《Physics of Atomic Nuclei》2007,70(1):53-55
The leading twist contribution to χ
c0,2 → ωω decays in the color-singlet approximation is considered. It is shown that the prediction for Br(χ
c0 → ωω) is in good agreement with the experimental data, while Br(χ
c2 → ωω) differs from the experiment significantly.
The text was submitted by the author in English. 相似文献
13.
The microwave photoresistance of a double GaAs quantum well with two occupied size-quantization sub-bands E
1 and E
2 has been studied at the temperatures T = 1.6–4.2 K in the magnetic fields B < 0.5 T. The microwave photoresistance of such a system has been found to have a maximum amplitude when the maximum of the
magneto-intersubband oscillations with the number k = (E
2 − E
1)ℏωc coincides with the maximum or minimum of the ω/ωc oscillations, where ω is the microwave frequency and ωc is the cyclotron frequency. It has been shown that the resonance photoresistance that appears in the kth maximum of the magneto-intersubband oscillations is determined by the condition ℏω/(E
2 − E
1) = (j ± 0.2)/k, where k and j are positive integers. 相似文献
14.
The Bardeen-Cooper-Schrieffer (BCS) gap equation is solved analytically in one, two and three dimensions, for temperatures
close to zero andT
c. We work in the weak coupling limit, but allow the interaction widthν≡ħω
m/E
F to lie in the interval (0, ∞) Here,ħω
m is the maximum energy of a force-mediating boson, andE
F denotes the Fermi energy. We obtain expressions forT
c and ΔC, the jump in the electronic specific heat acrossT=T
c, in the limitsν≪1 (the usual phonon pairing) andν>1 (non-phononic pairing). This enables us to see howT
c scales with the mediating boson cut off. Our results predict a larger jump in the specific heat for the caseν>1, compared toν≪1. We also briefly touch upon the role of a van Hove singularity in the density of states. 相似文献
15.
The role of low density upflowing field-aligned electron beams (FEBs) on the growth rate of the electron cyclotron waves at
the frequencies ω
r < Ωe, propagating downward in the direction of the Earth’s magnetic field, has been analysed in the auroral region at ω
e/Ωe < 1 where ω
e is the plasma frequency and Ωe is the gyrofrequency. The FEBs with low to high energy (E
b) but with low temperature (T
‖b) have no effect on these waves. The FEBs with E
b < 1 keV and T
‖b (> 1.5 keV) have been found to have significant effect on the growth rate. Analysis has revealed that it is mainly the T
‖b which inhibits the growth rate (magnitude) and the range of frequency (bandwidth) of the instability mainly in the higher
frequency spectrum. The inhibition in the growth rate and bandwidth increases with increase in T
‖b. The FEBs with less E
b (giving drift velocity) reduce growth rate more than the beams with larger E
b. The inhibition of growth rate increases with the increase in the ratio ω
e/Ωe indicating that the beams are more effective at higher altitudes.
相似文献
16.
O. S. Barišić S. Barišić 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,54(1):1-9
The translationally invariant diagrammatic quantum perturbation theory (TPT) is applied to the polaron problem on the 1D lattice,
modeled through the Holstein Hamiltonian with the phonon frequency ω0, the electron hopping t and the electron-phonon coupling constant g. The self-energy diagrams of the fourth-order in g are
calculated exactly for an intermittently added electron, in addition to the previously known second-order term. The corresponding
quadratic and quartic corrections to the polaron ground state energy become comparable at t/ω0>1 for g/ω0∼(t/ω0) 1/4 when the electron self-trapping and translation become adiabatic. The corresponding non adiabatic/adiabatic crossover occurs
while the polaron width is large, i.e. the lattice coarsening negligible. This result is extended to the range (t/ω0)1/2>g/ω0>(t/ω0)1/4>1 by considering the scaling properties of the high-order self-energy diagrams. It is shown that the polaron ground state
energy, its width and the effective mass agree with the results found traditionally from the broken symmetry side, kinematic
corrections included. The Landau self-trapping of the electron in the classic self-consistent, localized displacement potential,
the restoration of the translational symmetry by the classic translational Goldstone mode and the quantization of the polaronic
translational coordinate are thus all encompassed by a quantum theory which is translationally invariant from the outset.
This represents the first example, open to various generalizations, of the capability of TPT to hold through the adiabatic
symmetry breaking crossover. Plausible arguments are also given that TPT can describe the g/ω0>(t/ω0)1/2 regime of the small polaron with adiabatic or non-adiabatic translation, i.e., that TPT can cover the whole g/ω0, t/ω0 parameter space of the Holstein Hamiltonian. 相似文献
17.
Anil Kumar Yadav Farook Rahaman Saibal Ray 《International Journal of Theoretical Physics》2011,50(3):871-881
The dark energy models with variable equation of state parameter ω are investigated by using law of variation of Hubble’s parameter that yields the constant value of deceleration parameter.
Here the equation of state parameter ω is found to be time dependent and its existing range for this model is consistent with the recent observations of SN Ia data,
SN Ia data (with CMBR anisotropy) and galaxy clustering statistics. The physical significance of the dark energy models have
also been discussed. 相似文献
18.
G.I. Lykasov W. Cassing A. Sibirtsev M.V. Rzjanin 《The European Physical Journal A - Hadrons and Nuclei》1999,6(1):71-81
We calculate the elastic and inelastic ωN→ωN, →πN, →ρN, →ρπN, →ππN, →σN reactions within a boson exchange approximation where the ωρπ coupling constant and form factor are fixed by the reaction
πN→ωN in comparison to the experimental data. We find rather large ωN cross sections at low relative momenta of the ω-meson which
leads to a substantial broadening of the ω-meson width in nuclear matter. The implications of the ωN final state interactions are studied for ω production in 12C +12C, 40Ca +40Ca and 58Ni +58Ni reactions at about 2 · A GeV within the HSD transport approach; the drastic changes of the transverse mass spectra relative
to a general m
T-scaling (for π0 and η mesons) might be controlled experimentally by the TAPS Collaboration.
Received: 28 April 1999 / Revised version: 7 June 1999 相似文献
19.
Zhenbao Feng Haiquan Hu Shouxin Cui Wenjun Wang Canyun Lu 《Central European Journal of Physics》2009,7(4):786-790
The electronic and optical properties of InAs in core-level spectra are calculated using the full-potential linearized augmented
plane wave plus local orbitials (FP-LAPW +lo) method. The real and imaginary parts of the dielectric function ε(ω), the optical absorption coefficient I(ω), the reflectivity R(ω), the refractive index n(ω), and the extinction coefficient k(ω)are calculated. All these values are in good agreement with the experimental data. The effect of spin-orbit coupling on optical
properties is also investigated and found to be quite small.
相似文献
20.
V. N. Gridnev 《JETP Letters》1999,69(7):546-550
It is shown that the contribution of low-frequency excitations with characteristic energy ℏω
l to T-odd (nonreciprocal) optical effects, including spatial dispersion effects, at optical frequencies ω≫ω
l can be calculated in the zeroth-order approximation with respect to the parameter ω
l/ω. This greatly simplifies their analysis. Some of these effects are found to be frequency independent in the spectral regions
where the refractive index n(ω)≈ const. It is shown that frequency-independent Faraday rotation can be observed in media with zero magnetization, including
in media with zero microscopic magnetic moment density.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 7, 510–513 (10 April 1999) 相似文献