共查询到20条相似文献,搜索用时 609 毫秒
1.
R.A. Radhi 《The European Physical Journal A - Hadrons and Nuclei》2003,16(3):387-392
Electron scattering Coulomb form factors for the single-particle quadrupole transitions in p-shell and sd-shell nuclei have been studied. Core polarization effects are included through a microscopic theory that includes excitations
from the core orbits up to higher orbits with 2ω excitations. The modified surface delta interaction is adopted as a residual
interaction. The results are discussed for the ( 1p
1/2
-1↦1p
3/2
-1) proton transition in 15N, ( 1d
5/2↦2s
1/2) neutron transition in 17O and ( 1d
3/2
-1↦2s
1/2
-1) proton transition in 39K. The inclusion of core polarization effects modifies the form factors markedly and describes the experimental data very
well in both the absolute strength and the momentum transfer dependence.
Received: 18 April 2002 / Accepted: 1 July 2002 / Published online: 6 March 2003
RID="a"
ID="a"e-mail: baguniv@uruklink.net
Communicated by A. Molinari 相似文献
2.
D. Merten U. Löring K. Kretzschmar B. Metsch H.-R. Petry 《The European Physical Journal A - Hadrons and Nuclei》2002,14(4):477-489
We compute electroweak form factors of the nucleon and photon transition form factors of non-strange baryon resonances up
to the third resonance region in a model with instanton-induced interaction. The calculation is based on the Bethe-Salpeter
equation for three light constituent quarks and is fully relativistic (U. L?ring et al., Eur. Phys. J. A 10, 309 (2001)). Static nucleon properties and photon resonance couplings are in good agreement with experiment and the Q2 behaviour of the experimentally known form factors up to large momentum transfer is accounted for.
Received: 4 April 2002 / Accepted: 2 May 2002 相似文献
3.
Y.B. DongOn leave from Institute of High Energy Physics Academia Sinica Beijing P. R. China--> A. Faessler K. Shimizu 《The European Physical Journal A - Hadrons and Nuclei》1999,6(2):203-210
Electromagnetic form factors of protons and neutrons are investigated based on a relativistic quark model with the inclusion
of a pion cloud. Pseudo-scalar π-quark interaction is employed to study the coupling between the nucleon and the π. The results
show the important role of the pion cloud for the neutron charge form factor. Moreover, our numerical analysis indicates a
difference between the relativistic and the nonrelativistic treatments.
Received: 10 March 1999 / Revised version: 14 June 1999 相似文献
4.
5.
E. Del Gado L. de Arcangelis A. Coniglio 《The European physical journal. E, Soft matter》2000,2(4):359-365
Within a recently introduced model based on the bond-fluctuation dynamics, we study the viscoelastic behaviour of a polymer
solution at the gelation threshold. We here present the results of the numerical simulation of the model on a cubic lattice:
the percolation transition, the diffusion properties and the time autocorrelation functions have been studied. From both the
diffusion coefficients and the relaxation times critical behaviour a critical exponent k for the viscosity coefficient has been extracted: the two results are comparable within the errors giving , in close agreement with the Rouse model prediction and with some experimental results. In the critical region below the
transition threshold the time autocorrelation functions show a long-time tail which is well fitted by a stretched exponential
decay.
Received 20 December 1999 and Received in final form 18 February 2000 相似文献
6.
Reiter G 《The European physical journal. E, Soft matter》2002,8(2):251-255
I present some tentative ideas on the possibility of plastic deformation which might be relevant in ultra-thin polymer films
at temperatures close but below the glass transition temperature. Several possible sources for sufficiently strong forces
are discussed. The relevance of such forces in experiments aiming at determining thin-film properties like the glass transition
temperature, thermal expansion or surface morphology is discussed.
Received 19 September 2001 and Received in final form 5 December 2001 相似文献
7.
M. Baiesi E. Carlon E. Orlandini A.L. Stella 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):129-134
Recently Garel, Monthus and Orland [Europhys. Lett. 55, 132 (2001)] considered a model of DNA denaturation in which excluded volume effects within each strand are neglected, while
mutual avoidance is included. Using an approximate scheme they found a first order denaturation. We show that a first order
transition for this model follows from exact results for the statistics of two mutually avoiding random walks, whose reunion
exponent is c > 2, both in two and three dimensions. Analytical estimates of c due to the interactions with other denaturated loops, as well as numerical calculations, indicate that the transition is
even sharper than in models where excluded volume effects are fully incorporated. The probability distribution of distances
between homologous base pairs decays as a power law at the transition.
Received 8 July 2002 / Received in final form 25 July 2002 Published online 17 September 2002 相似文献
8.
D. Starešinić A. Kiš K. Biljaković B. Emerling J. W. Brill J. Souletie H. Berger F. Lévy 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(1):71-77
Specific heats of the charge-density-wave compounds o-TaS3 and (TaSe4)2I have been measured over the wide temperature interval 10 K-300 K. Both systems exhibit strong non-Debye behavior. Very weak
and broad anomalies are observed at the Peierls transition temperatures. For o-TaS3, the change in the curvature of the specific heat occurs at temperature of 40 K where glass transition has been deduced from
dielectric measurements, and an extended scaling analysis suggests that the glass transition is associated with a dynamical
cross over in length scales. We briefly discuss the characteristics and physical origins of the anomalies at both the Peierls
and glass transitions.
Received 5 April 2002 / Received in final form 28 June 2002 Published online 17 September 2002 相似文献
9.
R.A. Radhi 《The European Physical Journal A - Hadrons and Nuclei》2003,16(3):381-385
Coulomb form factors of C4 transitions in even-even N = Z sd-shell nuclei ( 20Ne, 24Mg, 28Si and 32S) are discussed taking into account higher-energy configurations outside the sd-shell model space which are called core polarization effects. Higher configurations are taken into account through a microscopic
theory, which allows particle-hole excitations from the 1s and 1p shells core orbits and also from the 2s1d-shell orbits to the higher allowed orbits with excitations up to 4 ω. The effect of core polarization is found essential
in both the transition strengths and momentum transfer dependence of form factors, and gives a remarkably good agreement with
the measured data with no adjustable parameters. The calculations are based on the Wildenthal interaction for the sd-shell model space and on the modified surface delta interaction (MSDI) for the core polarization effects.
Received: 24 January 2002 / Accepted: 29 July 2002 / Published online: 6 March 2003
RID="a"
ID="a"e-mail: baguniv@uruklink.net
Communicated by P. Schuck 相似文献
10.
L. Pareti M. Solzi F. Albertini A. Paoluzi 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):303-307
We have studied the isothermal entropy change around a first-order structural transformation and in correspondence to the
second-order Curie transition in the ferromagnetic Heusler alloy Ni2.15Mn0.85Ga. The results have been compared with those obtained for the composition Ni2.19Mn0.81Ga, in which the martensitic structural transformation and the magnetic transition occur simultaneously. With a magnetic field
span from 0 to 1.6 T, the magnetic entropy change reaches the value of 20 J/kg K when transitions are co-occurring, while
5 J/kg K is found when the only structural transition occurs.
Received 27 September 2002 / Received in final form 17 February 2003 Published online 11 April 2003
RID="a"
ID="a"e-mail: solzi@fis.unipr.it 相似文献
11.
N. Bouarissa 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(2):153-158
Dependencies of electronic structure and lattice properties of InN with zinc-blende structure on hydrostatic pressure are
presented based on band structures computed using the empirical pseudopotential method. The pressure behavior of the pseudopotential
form factors have been analyzed. The effect of pressure on the density of states has been examined. Trends in bonding and
ionicity under pressure are also discussed. Our results show as well that the absolute value of the Fourier transform of the
valence charge density might be useful in the prediction of the phase transition in zinc-blende materials.
Received 25 May 2001 and Received in final form 16 January 2002 相似文献
12.
Yun Chang Shin Bong Soo Han Myung Ki Cheoun K.S. Kim Il-Tong Cheon 《The European Physical Journal A - Hadrons and Nuclei》2000,9(2):269-276
A SU(2) effective Lagrangian is extended to a SU
L(3) ⊗SU
R(3) by including the vector and axial vector meson. With this effective Lagrangian, electromagnetic form factors of charged
pion and kaon are calculated in both time- and space-like regions. The pseudoscalar meson loops are taken into account. Good
agreement with experimental data is obtained for those form factors and charged pseudoscalar meson radii. Decay widths of
ρ→ππ and φ→K
+
K
- are also calculated and shown to agree with experimental data very well.
Received: 20 December 1999 / Accepted: 12 October 2000 相似文献
13.
M.A. Ivanov P. Santorelli N. Tancredi 《The European Physical Journal A - Hadrons and Nuclei》2000,9(1):109-114
The form factors of the weak currents, which appear in the semileptonic decays of the heavy pseudoscalar mesons are calculated
within the quark confinement model by taking into account, for the first time, the structure of heavy-meson vertex and the
finite quark mass contribution in the heavy-quark propagators. The results are in quite good agreement with the experimental
data.
Received: 9 June 2000 / Accepted: 15 August 2000 相似文献
14.
J.M. Polson I. Vattulainen H. Zhu M.J. Zuckermann 《The European physical journal. E, Soft matter》2001,5(4):485-497
We employ off-lattice Monte Carlo simulations to study lateral diffusion in lipid-sterol bilayers using a two-dimensional
model system which has been designed to simulate the experimental phase diagrams of both lipid-cholesterol and lipid-lanosterol
systems. We focus on the effects of varying sterol concentration and temperature on the tracer diffusion coefficient, D, which characterizes the lateral motion of single tagged lipids in a bilayer. Generally, we find that increasing the cholesterol
concentration suppresses D due to an increased conformational ordering of lipid chains. We argue that this effect competes with an increase in the average
free area per lipid, which favours an increase in D. At temperatures close to the main transition temperature, the competition between the two effects leads to intriguing behavior
of D. Overall, the model results are in excellent qualitative agreement with available experimental results for lipid-cholesterol
mixtures. Additional studies of a model lipid-lanosterol system, for which experimental diffusion results are not available,
predict that the presence of lanosterol has a smaller effect than cholesterol on reducing D relative to the pure lipid system. We conclude that the molecular model employed contains the essential features required
to describe many of the qualitative features of the lateral diffusion behavior in lipid-sterol systems.
Received 24 November 2000 and Received in final form 30 April 2001 相似文献
15.
Q.S. Hu H. Zheng 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):255-262
A new perturbation approach is developed for single- and many-electron Holstein model in one-, two-, and three-dimension.
The results show that this approach has a good agreement with the Migdal theory in the adiabatic regime when the coupling
is moderate (λ < 1), but with the Lang-Firsov theory in the antiadiabatic regime ( ω/W≫ 1). In the intermediate region, our approach can describe the transition from a large-polaron Fermi-liquid to the small-polaron,
and this transition may be discontinuous in adiabatic regime, which means a phase transition appears in many-electron system.
In single-electron case, we eliminate the abrupt transition using the degenerate perturbation theory, and the calculated ground
state energy and effective mass are successfully compared with those of previous authors. Besides, the method has the advantage
of requiring little computational effort.
Received 27 December 2001 / Received in final form 8 April 2002 Published online 31 July 2002 相似文献
16.
C.P. Sun X.F. Liu D.L. Zhou S.X. Yu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(1):85-92
To account for the phenomenon of quantum decoherence of a macroscopic object, such as the localization and disappearance of
interference, we invoke the adiabatic quantum entanglement between its collective states (such as that of the center-of-mass
(CM)) and its inner states based on our recent investigation. Under the adiabatic limit where motion of the CM does not excite
the transition of inner states, it is shown that the wave function of the macroscopic object can be written as an entangled
state with correlation between adiabatic inner states and quasi-classical motion configurations of the CM. Since the adiabatic
inner states are factorized with respect to each component of the macroscopic object, this adiabatic separation can induce
the quantum decoherence. This observation thus provides us with a possible solution to the Schr?dinger cat paradox.
Received 24 October 2000 and Received in final form 8 March 2001 相似文献
17.
Depletion interaction in a suspension of rodlike colloids with added non-adsorbing polymer coils is theoretically studied.
We calculate an overlap volume of depletion zone between two rodlike colloids, based on the second virial approximation. We
examine nematic-isotropic phase transition (NIT) and two-phase coexistence between an isotropic and a nematic phase at low
polymer concentrations. We find that the depletion interaction is dependent on the orientational order parameter of rodlike
colloids and leads to a decrease in the NIT concentration on the addition of polymer. The coexistence curves have a leaning-chimney
shape and are shifted to lower rod concentrations on increasing the polymer concentration.
Received 23 May 2001 and Received in final form 18 July 2001 相似文献
18.
R.J. Tarento P. Joyes J. van de Walle 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(3):355-360
The present study focuses on electronic correlation effects on magnetic energy, the spin-spin correlation function of an octahedron
cluster in the (3↑, 3 ↓) electronic configuration threaded by a magnetic field. Some other spin configurations are also discussed
and various field directions are considered. An accurate diagonalisation technique has been used to solve the Hubbard Hamiltonian.
A result is analysed on a linear energy stabilisation at low magnetic flux. Moreover, two types of antiferromagnetic transition
versus the flux occurring for a correlation term larger than a critical one have been observed, i.e. the likelihood of a charge excitation before the antiferromagnetic transition. Finally, a comparison between the results
obtained from the exact diagonalisation and the Gutzwiller method has been carried out, leading to a suggested modification
of the Gutzwiller approach in order to improve it.
Received 23 June 1999 and Received in final form 28 July 2000 相似文献
19.
In treating the relativistic 3-quark problem, a dressed-quark propagator parameterization is used which is compatible with
recent lattice data and pion observables. Furthermore 2-quark correlations are modeled as a series of quark loops in the scalar
and axialvector channel. The resulting reduced Faddeev equations are solved for nucleon and delta. Nucleon electromagnetic
form factors are calculated in a fully covariant and gauge-invariant scheme. Whereas the proton electric form factor G
E and the nucleon magnetic moments are described correctly, the neutron electric form factor and the ratio G
E/G
M for the proton appear to be quenched. The influence of vector mesons on the form factors is investigated which amounts to
a 25% modification of the electromagnetic proton radii within this framework.
Received: 16 April 2002 / Accepted: 29 August 2002 / Published online: 17 January 2003
RID="a"
ID="a"Supported by a Feodor-Lynen fellowship of the Alexander-von-Humboldt foundation and the Australian Research Council.
RID="b"
ID="b"Address after April 30: MPI für Metallforschung, Heisenbergstr. 1, 70569 Stuttgart, Germany.
RID="c"
ID="c"e-mail: Reinhard.Alkofer@uni-tuebingen.de
Communicated by A. Sch?fer 相似文献
20.
P.K. Mukherjee H. Pleiner H.R. Brand 《The European physical journal. E, Soft matter》2001,4(3):293-297
A simple Landau-type free energy function is presented to describe the smectic-A-isotropic phase transition. Varying the coupling
between orientational and positional order parameters, a smectic-A-isotropic or a nematic-isotropic phase transition occurs.
Within this model the smectic-A-isotropic phase transition is found to be always more strongly first order than the nematic-isotropic
phase transition. The theoretical results are found to be in good agreement with all published experimental results.
Received 27 June 2000 相似文献