排序方式: 共有105条查询结果,搜索用时 15 毫秒
31.
Y.C. Shin M.K. Cheoun K.S. Kim T.K. Choi 《The European Physical Journal A - Hadrons and Nuclei》2002,14(1):87-93
A role of the axial-vector mesons, such as K1 and a1, on the emitted-photon spectrum in hot hadronic matter is studied through the channels πρ→a
1→πγ and Kρ→K
1→Kγ. Both channels could be dominant over the region lower than E
γ∼ 0.5 GeV, while the role of the K1 meson is diminished in the higher E
γ region. This study is carried out with an SU
L(3) ⊗SU
R(3) effective chiral Lagrangian which includes vector and axial-vector mesons systematically and explains well their hadronic
and radiative decays simultaneously.
Received: 8 August 2001 / Accepted: 4 February 2002 相似文献
32.
We report on the X-ray Bragg diffraction analysis of periodic surface gratings on (100) GaAs crystals. We show that the X-ray Bragg diffraction is a very powerful method to investigate ultrafine surface gratings and allow us to determine not only the grating period but, in particular, the width of the grooves and to characterize the quality of the sidewalls, which is not easily possible with optical methods. The X-ray diffraction on surface crystal gratings is analogue to the Fraunhofer diffraction of multiple slits or reflection gratings. 相似文献
33.
L.F. Chibotaru A. Ceulemans G. Teniers V. Bruyndoncx V.V. Moshchalkov 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):341-346
An approach to the Ginzburg-Landau problem of superconducting polygons is developed, based on the exact fulfillment of superconducting
boundary conditions along the boundary of the sample. To this end an analytical gauge transformation for the vector potential
A is found which gives A
n = 0 for the normal component along the boundary line of an arbitrary regular polygon. The use of the new gauge reduces the
Ginzburg-Landau problem of superconducting polygons in external magnetic fields to an eigenvalue problem in a basis set of
functions obeying Neumann boundary conditions. The advantages of this approach, especially for low magnetic fields, are illustrated
and novel vortex patterns are obtained which can be probed experimentally.
Received 28 February 2002 and Received in final form 12 April 2002 Published online 6 June 2002 相似文献
34.
D. Bensimon R. Zeyher 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,59(2):141-150
Phase fluctuations of a d-wave superconducting order parameter are
theoretically studied in the context of high-Tc cuprates. We consider
an extended t-J model describing electrons in a layer which also contains
long-range Coulomb interactions. The constraint of having at most singly
occupied sites is enforced by an additional Hubbard term. The Heisenberg interaction is decoupled by a d-wave order parameter
in the particle-particle channel. Assuming first that the equilibrium state has long-range phase order, the effective action
is derived perturbatively for small fluctuations within a path integral formalism, in the presence of the
Coulomb and Hubbard interaction terms. In a second step, a more general
derivation of
is performed in terms of a gradient
expansion which only assumes that the gradients of the order parameter are
small whereas the value of the phase may be large. We show that in the
phase-only approximation the resulting
reduces in
leading order in the field gradients to the perturbative one which thus allows to treat also the case without long-range phase
order or vortices. Our result generalizes previous
expressions for
to the case of interacting electrons,
is explicitly gauge invariant, and avoids problematic singular
gauge transformations. 相似文献
35.
The collective flow of positive charged kaons in heavy ion reactions at SIS energy is investigated within the frame of covariant kann dynamics. The theoretical results calculated by using quantum molecular dynamics show that the rapidity distribution of K^+ mesons is more sensitive to the nuclear equation of state than the differential directed flow. The contribution of various K^+ production reaction channels to the rapidity distribution of the K^+ is also analysed in detail. The results indicate that the rapidity distribution of K^+ mesons is mainly from the contribution of the N-△ and N-N channel. This means that the delta resonance state plays a predominantly important role for the K^+ subthreshold production. 相似文献
36.
《The European Physical Journal A - Hadrons and Nuclei》2009,40(1):45-59
We present the results of a study of charged-pion production in 12C + 12C collisions at incident beam energies of 1A GeV and 2A GeV using the HADES spectrometer at GSI. The main emphasis of the
HADES program is on the dielectron signal from the early phase of the collision. Here, however, we discuss the data with respect
to the emission of charged hadrons, specifically the production of mesons, which are related to neutral pions representing a dominant contribution to the dielectron yield. We have performed
the first large-angular-range measurement of the distribution of mesons for the 12C + 12C collision system covering a fairly large rapidity interval. The pion yields, transverse-mass and angular distributions are
compared with calculations done within a transport model, as well as with existing data from other experiments. The anisotropy
of pion production is systematically analyzed. 相似文献
37.
A superconductor with 4-fermion attraction, considered by Maćkowiak and Tarasewicz is modified by adding to the Hamiltonian
a long-range magnetic interaction V between conduction fermions and localized distinguishable spin 1/2 magnetic impurities. V has the form of a reduced s-d interaction. An upper and lower bound to the system’s free energy density f(H, β) is derived and the two bounds are shown to coalesce in the thermodynamic limit. The resulting mean-field equations for the
gap Δ and a parameter y, characterizing the impurity subsystem are solved and the solution minimizing f is found for various values of magnetic coupling constant g and impurity concentration. The phase diagrams of the system are depicted with five distinct phases: the normal phase, unperturbed
superconducting phase, perturbed superconducting phase with nonzero gap in the excitation spectrum, perturbed gapless superconducting
phase and impurity phase with completely suppressed superconductivity. 相似文献
38.
Y. Nakajima T. Shibauchi H. Shishido K. Behnia M. Hedo T. Matsumoto Y. Onuki Y. Matsuda 《Journal of Physics and Chemistry of Solids》2008,69(12):3261-3264
We observe several non-Fermi liquid behaviors in the normal-state transport properties of CeMIn5 (M: Rh and Co) under pressure at low temperatures: (1) The dc-resistivity shows T-linear dependence, ρxx∝T. (2) The magnitude of Hall coefficient |RH| increases rapidly with decreasing temperature, and reaches a value much larger than |1/ne| at low temperatures. (3) The magnetoresistance displays T- and H-dependence that strongly violate Kohler's rule, and is well scaled by the tangent of the Hall angle, . These non-Fermi liquid properties in the electron transport are remarkably pronounced when the AF fluctuations are enhanced in the vicinity of the quantum critical point. Since all of these salient features have been also reported for high-Tc cuprates, we infer that the non-Fermi liquid transport properties capture universal features of strongly correlated electron systems in the presence of strong antiferromagnetic fluctuations. 相似文献
39.
Based on a relativistic hydrodynamic model describing the evolution of the chemically equilibrating quark-gluon plasma system with finite baryon density in a 3+1-dimensional spacetime, we compute photons from the quark phase, hadronic phase and initial non-thermal contributions. It is found that due to the effects of the initial quark chemical potential, chemical equilibration and rapid expansion of the system, the photon yield of the quark-gluon plasma is strongly suppressed, and photons from hadronic matter and initial non-thermal contributions almost reproduce experimental data. 相似文献
40.
The early parton momentum distribution is extracted by using the STAR collaboration data of ridge particles associated with a near-side jet in centred AuAu collisions at √SNN = 200 GeV. The ridge particles are identified as medium partons kicked by the jet near the surface and they carry direct information on the parton momentum distribution at the moment of jet-patton collisions. The extracted patton momentum distribution has a thermallike transverse momentum distribution but a rapidity plateau structure with a relatively fiat rapidity distribution at mid-rapidities with sharp kinematic boundaries at large rapidities that depend on the transverse momentum. 相似文献