共查询到20条相似文献,搜索用时 883 毫秒
1.
Bianchi Type-I magnetized bulk viscous fluid string dust cosmological model is investigated. To get a determinate model, we
have assumed the conditions σ ∝θ andζθ = constant where σ is the shear,θ the expansion in the model andζ the coefficient of bulk viscosity. The behaviour of the model in the presence and absence of magnetic field together with
physical and geometrical aspects of the model are also discussed. 相似文献
2.
Raj Bali Anirudh Pradhan Hassan Amirhashchi 《International Journal of Theoretical Physics》2008,47(10):2594-2604
A model of a cloud formed by massive strings is studied in the context of the usual general relativity. This model is used
as a source of Bianchi type VI
0 massive with magnetic field and bulk viscosity. To get a determinate model, we assume that the expansion (θ) in the model is proportional to the shear (σ) and also the fluid obeys the barotropic equation of state. The behaviour of the models from physical and geometrical aspects
in presence and absence of magnetic field and bulk viscosity is discussed. 相似文献
3.
F. Schümann S. Zavatarelli L. Gialanella U. Greife M. Junker D. Rogalla C. Rolfs F. Strieder H.P. Trautvetter 《The European Physical Journal A - Hadrons and Nuclei》1998,2(4):337-342
Abstact: The elastic scattering cross sections, σ (E,θ), for the systems He+Ta and He+W have been measured at θlab=165° and E
lab=76.1 keV to 3.988 MeV using targets with a thickness of a few atomic layers. The results are smaller than the results given
by the Rutherford scattering law, σR(E,θ), due to the effects of electron screening and can be described by σ(E,θ)/σR(E,θ)=(1+Ue/E)−1, where U
e is an atomic screening potential energy. The deduced average value, U
e=28 ± 3 keV, is consistent with the Moliére- and Lenz-Jensen-models as well as electron binding energies.
Received: 25 May 1998 相似文献
4.
F. N. Gygax P. Birrer B. Hitti E. Lippelt A. Schenck M. Weber 《Hyperfine Interactions》1991,64(1-4):489-495
μ
+ SR measurements have been performed in a single crystal indium sample between 12 K and 300 K with a stroboscopic μSR spectrometer.
The muonic Knight shiftK
μ and the muonic depolarization rate σ were obtained for various angles θ between the tetragonal crystallinec-axis and the direction of the external field. The isotropic part ofK
μ is only weakly temperature dependent and is consistent with the estimated Pauli spin susceptibility value. At a temperature
of 12 K the angular dependence ofM
2 (the second moment of the field distribution at the muon, obtained from the measured σ(θ) values) allows a clear determination
of the muon location — the symmetric tetrahedral site. The observed anisotropicK
μ cannot be explained by the dipoles at the In atoms responsible for the bulk magnetic susceptibility but probably originates
from an anisotropic Pauli spin susceptibility. 相似文献
5.
Raj Bali 《International Journal of Theoretical Physics》2009,48(2):476-486
Bianchi Type V magnetized string dust bulk viscous fluid cosmological model with variable magnetic permeability, is investigated.
The magnetic field is due to an electric current produced along x-axis. Thus the magnetic fields is in yz-plane and F
23 is the only non-vanishing component of electromagnetic field tensor F
ij
. To get the deterministic model in terms of cosmic time t, we have also assumed the condition ζ
θ=constant where ζ the coefficient of bulk viscosity and θ the expansion in the model. The behaviour of the model in presence and absence of magnetic field and bulk viscosity and singularities
in the model are also discussed.
相似文献
6.
Mahendra K. Verma 《Pramana》2003,61(3):577-594
Energy cascade rates and Kolmogorov’s constant for non-helical steady magnetohydrodynamic turbulence have been calculated
by solving the flux equations to the first order in perturbation. For zero cross helicity and space dimensiond = 3, magnetic energy cascades from large length-scales to small length-scales (forward cascade). In addition, there are energy
fluxes from large-scale magnetic field to small-scale velocity field, large-scale velocity field to small-scale magnetic field,
and large-scale velocity field to large-scale magnetic field. Kolmogorov’s constant for magnetohydrodynamics is approximately
equal to that for fluid turbulence (≈ 1.6) for Alfvén ratio 05 ≤r
A ≤ ∞. For higher space-dimensions, the energy fluxes are qualitatively similar, and Kolmogorov’s constant varies asd
1/3. For the normalized cross helicity σc →1, the cascade rates are proportional to (1 − σc)/(1 + σc , and the Kolmogorov’s constants vary significantly with σcc. 相似文献
7.
Hassan Amirhashchi Hishamuddin Zainuddin 《International Journal of Theoretical Physics》2010,49(11):2815-2828
The present study deals with Bianchi type III string cosmological models with magnetic field. The magnetic field is assumed
to be along z direction. Therefore F
12 is only the non-vanishing component of electromagnetic field tensor F
ij
. The expansion (θ) in the model is assumed to be proportional to the shear (σ). To get determinate solution in term of cosmic time, we have solved the fields equations in two cases (i) Reddy and (ii)
Nambu string. The physical and geometrical behaviour of these models is discussed. 相似文献
8.
Raj Bali 《International Journal of Theoretical Physics》1986,25(7):755-761
The object of this paper is to investigate the behavior of the magnetic field in a cosmological model for perfect fluid distribution. The magnetic field is due to an electric current produced along thex axis. It is assumed that expansion () in the model is proportional to
1
1
, the eigenvalue of the shear tensor
i
j
. The behavior of the model when the magnetic field tends to zero and other physical properties are also discussed. 相似文献
9.
The dependences of the electrical resistivity ρ and the Hall coefficient R on the magnetic field have been measured for single-crystal samples of the n-Bi0.93Sb0.07 semiconductor alloys with electron concentrations in the range 1 × 1016 cm−3 < n < 2 × 1018 cm−3. It has been found that the measured dependences exhibit Shubnikov-de Haas quantum oscillations. The magnetic fields corresponding
to the maxima of the quantum oscillations of the electrical resistivity are in good agreement with the calculated values of
the magnetic fields in which the Landau quantum level with the number N intersects the Fermi level. The quantum oscillations of the Hall coefficient with small numbers are characterized by a significant
spin splitting. In a magnetic field directed along the trigonal axis, the quantum oscillations of the resistivity ρ and the
Hall coefficient R are associated with electrons of the three-valley semiconductor and are in phase with the magnetic field. In the case of
a magnetic field directed parallel to the binary axis, the quantum oscillations associated both with electrons of the secondary
ellipsoids in weaker magnetic fields and with electrons of the main ellipsoid in strong magnetic fields (after the overflow
of electrons from the secondary ellipsoids to the main ellipsoid) are also in phase. In magnetic fields of the quantum limit
ħω
c
/2 ≥ E
F, the electrical conductivity increases with an increase in the magnetic field: σ22(H) ∼ H
k
. A theoretical evaluation of the exponent in this expression for a nonparabolic semiconductor leads to values of k close to the experimental values in the range 4 ≤ k ≤ 4.6, which were obtained for samples of the semiconductor alloys with different electron concentrations. A further increase
in the magnetic field results in a decrease of the exponent k and in the transition to the inequality σ22(H) ≤ σ21(H). 相似文献
10.
M. Weis P. Bartsch D. Baumann J. Bermuth A. M. Bernstein K. Bohinc R. Böhm M. Ding M. O. Distler I. Ewald J. M. Friedrich J. Friedrich M. Kahrau M. Kohl K. W. Krygier A. Liesenfeld H. Merkel P. Merle U. Müller R. Neuhausen M. M. Pavan Th. Pospischil M. Potokar G. Rosner H. Schmieden M. Seimetz S. Širca A. Wagner Th. Walcher 《The European Physical Journal A - Hadrons and Nuclei》2008,38(1):27-33
The differential cross-sections σ0 = σT + εσL , σLT , and σTT of electroproduction from the proton were measured from threshold up to an additional center-of-mass energy of 40MeV, at a value
of the photon four-momentum transfer of Q
2 = 0.05 GeV2/c2 and a center-of-mass angle of θ = 90° . By an additional out-of-plane measurement with polarized electrons σLT' was determined. This showed for the first time the presence of an imaginary part of the s -wave above the threshold, which is usually interpreted as a unitary cusp. The predictions of the Heavy Baryon Chiral Perturbation Theory
(HBChPT) are in disagreement with these data. On the other hand, the data are somewhat better predicted by the MAID phenomenological
model and are in good agreement with the dynamical model DMT. 相似文献
11.
We investigate the behavior of a magnetic field in a viscous fluid cosmological model where the expansion in the model is proportional to
1
1
, the component of shear tensor
i
j
, which leads to A=(Bc)n. We also assume that the shear viscosity is proportional to the rate of expansion in the model. The behavior of the model in the absence of a magnetic field and viscosity is discussed as are some other physical and geometrical aspects. 相似文献
12.
M. Ya. Amusia R. Krivec E. Z. Liverts V. B. Mandelzweig 《Journal of Experimental and Theoretical Physics》2006,102(4):556-561
We discuss the results of the calculation of the photoionization with deexcitation of excited He and helium-like ions Li+ and B3+ at high but nonrelativistic photon energies θ. Several lower 1
S and 3
S states are considered. We present and analyze the ratios R
d
+
* of the cross sections of photoionization with deexcitation, σ
(d)
+
*(θ), and of the photoionization with excitation, σ+*(θ). The dependence of R
d
+
* on the excitation of the target object and the charge of its nucleus is presented. In addition to theoretical interest,
the results obtained can be verified using long-lived excited states such as 23
S of He.
The text was submitted by authors in English. 相似文献
13.
I. L. Drichko I. Yu. Smirnov A. V. Suslov O. A. Mironov D. R. Leadley 《Journal of Experimental and Theoretical Physics》2010,111(3):495-502
Magnetoresistivity ρ
xx
and ρ
xy
and the acoustoelectronic effects are measured in p-Si/SiGe/Si with an impurity concentration p = 1.99 × 1011 cm−2 in the temperature range 0.3–2.0 K and an tilted magnetic field up to 18 T. The dependence of the effective g factor on the angle of magnetic field tilt θ to the normal to the plane of a two-dimensional p-Si/SiGe/Si channel is determined. A first-order ferromagnet-paramagnet phase transition is observed in the magnetic fields
corresponding to a filling factor ν = 2 at θ ≈ 59°–60°. 相似文献
14.
Influence of the reagent vibration on the stereo-dynamics of the reactions D- + H2 and H- + D2
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Employing the quasi-classical trajectory method and the potential energy surface of Panda and Sathyamurhy [Panda A N and Sathyamurthy N 2004 J. Chem. Phys. 121 9343], the effect of the reagent vibration on vector correlation of the ion-molecule reactions D- + H2 and H- + D2 is studied at a collision energy of 35.7 kcal/mol. Four generalized polarization-dependent differential cross sections (2π/σ)(dσ00/dωt),(2π/σ)(dσ20/dωt),(2π/σ)(dσ22/dωt), and (2π/σ)(dσ20/dωt) are presented in the centre-of-mass reference frame, separately. At the same time, the effects on the product angular distributions P(θr), P(φr) and P(θr,φr) of the title reactions are also analysed. The calculated results show that the scattering tendencies of the product HD, the alignment and the orientation of j' sensitively depend on reagent molecule vibration. 相似文献
15.
We show that, in the presence of a scalar field the range of the value of external field parameters a and b, at which corresponding Hamiltonian operator is hermitian, essentially wider than in its absence. It allows us to study precisely
the question on stability of QED vacuum in the presence of a strong electric field of a point charge Z|e| and external scalar Coulomb field with respect to electron-positron pair production. Also, we consider the scattering of
Dirac particle by the specified fields in 3+1 dimensions. The phase shift and wave functions are obtained exactly. We calculate
the scattering amplitude in a quasi-classical approximation as a partial wave series. By means of figures obtained for the
cross section σ(θ) in general and special cases, such as a≠b and a=b, we find that σ(θ) is not exactly symmetric about θ=π. 相似文献
16.
Three-body interaction plays an important role in many-body physics, and quantum computer is efficient in simulating many-body
interactions. We have experimentally demonstrated the general three-body interactions in a three-qubit nuclear magnetic resonance
ensemble quantum computer. Using a nuclear magnetic resonance computer we implemented general forms of three-body interactions
including σ
x
1
σ
z
2
σ
x
3 and σ
x
1
σ
z
2
σ
y
3 The results show good agreement between theory and experiment. We have also given a concise and practical formula for a general
n-body interaction in terms of one-and two-body interactions.
Supported by the National Natural Science Foundation of China (Grant Nos. 10374010 and 10325521) and the National Basic Research
Program of China (Grant No. 2006CB921106) 相似文献
17.
G. N. Kichigin 《Journal of Experimental and Theoretical Physics》2009,109(3):408-416
We consider the problem of cosmic-ray generation through the surfing acceleration of charged particles in relativistic magnetosonic
shock waves (the branch of fast magnetic sound) propagating in magnetized space plasmas. The dependence of the particle surfing
acceleration efficiency on the angle θ
Bn
between the normal to the shock front plane and the magnetic field vector in the plasma upstream of the shock is analyzed
in detail. We show that for angles satisfying the condition χ = βΓ tan θ
Bn
⩾ 1, where β = U/c, Γ = (1 − β)2
−1/2, U is the shock velocity, and c is the speed of light, the particles can theoretically be accelerated through surfing for an unlimited time and can gain
an unlimited energy. For angles satisfying the condition χ < 1, the kinetic energy ℰ of the particles is limited by ℰ = 2mc
2χ2/(1 − χ2) (m is the particle rest mass). Our main conclusion is that the generation of cosmic rays through the surfing acceleration of
particles in the front of a relativistic shock wave for Γ ≫ 1 is also efficient when the angle θ
Bn
is very small, i.e., it differs significantly from a right angle. Estimates for the energies of particles accelerated through
surfing in relativistic jets are provided. 相似文献
18.
Yong-Chang Huang Xi-Guo Lee Liu-Ji Li 《International Journal of Theoretical Physics》2007,46(2):221-236
We give a general SU(2)
L
× SU(2)
R
× U(1)
EM
sigma model with external sources, dynamical breaking and spontaneous vacuum symmetry breaking, and present the general formulation
of the model. It is found that σ and π0 without electric charges have electromagnetic interaction effects coming from their internal structures. A general Lorentz
transformation relative to external sources is derived, using the general Lorentz transformation and the four-dimensional current of nuclear matter of the ground state
with J
gauge = 0, we give the four-dimensional general relations between the different currents of nuclear matter systems with J
gauge≠ 0 and those with J
gauge = 0. The relation of the density’s coupling with external magnetic field is derived, which conforms well to dense nuclear
matter in a strong magnetic field. We show different condensed effects in strong interaction about fermions and antifermions,
and give the concrete scalar and pseudoscalar condensed expressions of σ0 and π0 bosons. About different dynamical breaking and spontaneous vacuum symmetry breaking, the concrete expressions of different
mass spectra are obtained in field theory. This paper acquires the running spontaneous vacuum breaking value σ′0, and obtains the spontaneous vacuum breaking in terms of the running σ′0, which make nucleon, σ and π particles gain effective masses. We achieve both the effect of external sources and nonvanishing
value of the condensed scalar and pseudoscalar paticles. It is deduced that the masses of nucleons, σ and π generally depend
on different external sources.
PACA numbers: 24.10.-i, 11.30.Qc 相似文献
19.
E. Lippelt P. Birrer F. N. Gygax B. Hitti A. Schenck M. Weber 《Hyperfine Interactions》1991,64(1-4):477-487
The angular dependence of the muon Knight shift,K
μ, and the muon relaxation rate in Bi at 11 K were measured in external magnetic fields up to 1 T. BothK
μ and the second moment,M
2, are field dependent and involveP
4
0(cos θ) andP
4
3(cos θ) terms in the angular dependence. The Knight shift behaviour is discussed in terms of the dipole-dipole interaction
and the de Haas-van Alphen effect, a consistent interpretation was not achieved in either case. The field dependence ofM
2 is in complete contrast to the second moment calculations and points to a field dependent redistribution of the charge distribution
around the interstitial site. 相似文献
20.
E.T. Seppälä M.J. Alava 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):407-424
We study the effect of an external field on (1 + 1) and (2 + 1) dimensional elastic manifolds, at zero temperature and with
random bond disorder. Due to the glassy energy landscape the configuration of a manifold changes often in abrupt, “first order”-type
of large jumps when the field is applied. First the scaling behavior of the energy gap between the global energy minimum and
the next lowest minimum of the manifold is considered, by employing exact ground state calculations and an extreme statistics
argument. The scaling has a logarithmic prefactor originating from the number of the minima in the landscape, and reads ΔE
1∼L
θ[ln(L
z
L
- ζ)]-1/2, where ζ is the roughness exponent and θ is the energy fluctuation exponent of the manifold, L is the linear size of the manifold, and Lz is the system height. The gap scaling is extended to the case of a finite external field and yields for the susceptibility
of the manifolds ∼L
2D + 1 - θ[(1 - ζ)ln(L)]1/2. We also present a mean field argument for the finite size scaling of the first jump field, h
1∼L
d - θ. The implications to wetting in random systems, to finite-temperature behavior and the relation to Kardar-Parisi-Zhang non-equilibrium
surface growth are discussed.
Received December 2000 and Received in final form April 2001 相似文献