共查询到20条相似文献,搜索用时 31 毫秒
1.
Entrance channel potentials in nucleus-nucleus collisions, relevant for the synthesis of superheavy elements, are systematically
studied within a semi-microscopic approach, where microscopic nuclear densities of the colliding spherical or deformed nuclei
are used in semi-classical expressions of the energy-density functional. From experimental data on fusion windows evidence
is found that the existence of pockets in the entrance channel potentials is crucial for fusion. Criteria for the choice of
the best collision systems for the synthesis of superheavy elements are discussed.
Received: 14 May 2002 / Accepted: 6 June 2002 / Published online: 26 November 2002
RID="a"
ID="a"e-mail: v.denisov@gsi.de, denisov@kinr.kiev.ua
RID="b"
ID="b"e-mail: w.nrnbrg@gsi.de
Communicated by P. Schuck 相似文献
2.
P. Hillion 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):527-532
A particular transformation of coordinates, associated with superluminal X-pulses, leaves the wave equation invariant and
changes focus wave modes into superluminal focus wave pulses. Rather simple and manageable expressions for TM electromagnetic
waves allow the investigation of these new localized solutions of Maxwell's equations.
Received 11 June 2002 / Received in final form 27 August 2002 Published online 31 December 2002 相似文献
3.
B. Castaing 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(3):357-358
Usual turbulence experiments, based on the Taylor hypothesis, differ from true Eulerian measurements. This is the origin of
the apparent discrepancy between a recent two point correlation analysis and the multiplicative cascade picture. Indeed, both
Eulerian and Lagrangian observations perfectly agree with this picture.
Received 19 June 2002 / Received in final form 29 July 2002 Published online 14 October 2002
RID="a"
ID="a"e-mail: bcastain@ens-lyon.fr 相似文献
4.
The compaction of granular packings or soils is a collective process which for higher densities becomes increasingly slower
reaching glassy behaviour. We present a study of this problem from various points of view, in particular we will represent
the evolving force network that percolates through the system by an inverse fiber rupture model.
Received 15 March 2002 and Received in final form 29 July 2002 相似文献
5.
A. Namazi N. Eissfeldt P. Wagner A. Schadschneider 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):559-570
The Krauss-model is a stochastic model for traffic flow which is continuous in space. For periodic boundary conditions it
is well understood and known to display a non-unique flow-density relation (fundamental diagram) for certain densities. In
many applications, however, the behaviour under open boundary conditions plays a crucial role. In contrast to all models investigated
so far, the high flow states of the Krauss-model are not metastable, but also stable. Nevertheless we find that the current
in open systems obeys an extremal principle introduced for the case of simpler discrete models. The phase diagram of the open
system will be completely determined by the fundamental diagram of the periodic system through this principle. In order to
allow the investigation of the whole state space of the Krauss-model, appropriate strategies for the injection of cars into
the system are needed. Two methods solving this problem are discussed and the boundary-induced phase transitions for both
methods are studied. We also suggest a supplementary rule for the extremal principle to account for cases where not all the
possible bulk states are generated by the chosen boundary conditions.
Received 16 September 2002 / Received in final form 4 November 2002 Published online 31 December 2002 相似文献
6.
V.D. Natsik Y.I. Nazarenko 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):285-289
The problem of crowdion motion is formulated and analyzed as a dynamical problem of a three-dimensional crystal lattice formed
by atoms of several kinds, which interact with each other by means of short-range pair potentials. It is explained that in
order for the the crowdion excitations of the close-packed atomic rows to be distinguishable against the background of small
dynamic deformations of the crystal as a whole, the microscopic parameters of the crystal structure must meet certain stated
requirements. The equation of motion of a crowdion in an arbitrary elastic strain field of the crystal is derived in the Lagrangian
formalism. Expressions are obtained which relate the effective mass and the rest energy of a crowdion with the geometric and
force parameters of the crystal lattice.
Received 4 October 2001 / Received in final form 27 February 2002 Published online 2 October 2002
RID="a"
ID="a"e-mail: nazarenko@ksame.kharkov.ua 相似文献
7.
We consider a spatially periodic inviscid random forced Burgers equation in arbitrary dimension and the random time-dependent
Lagrangian system related to it. We construct a unique stationary distribution for ``viscosity' solutions of the Burgers
equation. We also show that with probability 1 there exists a unique minimizing trajectory for the random Lagrangian system
which generates a non-trivial ergodic invariant measure for the non-random skew-product extension of the Lagrangian system.
Received: 25 March 2002 / Accepted: 30 July 2002 Published online: 22 November 2002 相似文献
8.
R. Capovilla C. Chryssomalakos J. Guven 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):163-166
We examine the equilibria of a rigid loop in the plane, characterized by an energy functional quadratic in the curvature,
subject to the constraints of fixed length and fixed enclosed area. Whereas the only non self-intersecting equilibrium corresponding
to the fixed length constraint is the circle, the area constraint gives rise to distinct equilibria labeled by an integer.
These configurations exhibit self-intersections and bifurcations as the area is reduced. In addition, not only can the Euler-Lagrange
equation be integrated to provide a quadrature for the curvature but the embedding itself can be expressed as a local function
of the curvature. Perturbations connecting equilibria are shown to satisfy a first order ODE which is readily solved. Analytical
expressions for the energy as a function of the area are obtained in the limiting regimes.
Received 18 October 2001 / Received in final form 31 May 2002 Published online 2 October 2002
RID="a"
ID="a"e-mail: capo@fis.cinvestav.mx
RID="b"
ID="b"e-mail: chryss@nuclecu.unam.mx
RID="c"
ID="c"e-mail: jemal@nuclecu.unam.mx 相似文献
9.
G. Vilasi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(2):207-210
Melnikov-method-based theoretical results are demonstrated concerning the relative effectiveness of any two weak excitations in suppressing homoclinic/heteroclinic chaos of a relevant class of dissipative, low-dimensional and
non-autonomous systems for the main resonance between the chaos-inducing and chaos-suppressing excitations. General analytical
expressions are derived from the analysis of generic Melnikov functions providing the boundaries of the regions as well as
the enclosed area in the amplitude/initial phase plane of the chaos-suppressing excitation where homoclinic/heteroclinic chaos
is inhibited. The relevance of the theoretical results on chaotic attractor elimination is confirmed by means of Lyapunov
exponent calculations for a two-well Duffing oscillator.
Received 21 May 2002 / Received in final form 13 September 2002 Published online 29 November 2002 相似文献
10.
M.P. Machado P. Piquini R. Mota 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(1):91-93
The geometric structures, energetics and electronic properties of the recently discovered BN nanocones are investigated using
first-principles calculations based on the density-functional theory. We have proposed one particular structure for BN nanocones
associated with the 240° disclination, derived by the extraction of four 60° segments, presenting as characteristic four pentagons at the apex and termination in two atoms. The cones are simulated by
three clusters containing 58 B plus N atoms and additional 12 H atoms to saturate the dangling bonds at the edge. The most
stable configuration is obtained when the two terminating atoms are one B and one N. For the cases where the two terminating
atoms are of the same kind, the tip with B atoms is determined to have lower binding energy than with N atoms. The local densities
of states of these BN nanocones are investigated and sharp states are found in the regions close (below and above) to the
Fermi energy.
Received 14 October 2002 / Received in final form 6 December 2002 Published online 11 February 2003
RID="a"
ID="a"e-mail: ppiquini@smail.ufsm.br 相似文献
11.
L. Colletti F. Pederiva E. Lipparini C.J. Umrigar 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):385-392
We use diffusion Monte Carlo to study the ground state, the low-lying excitation spectrum and the spin densities of circular
quantum dots with parabolic radial potentials containing N = 16 and N = 24 electrons, each having four open-shell electrons and compare the results to those obtained from Hartree-Fock (HF) and
density functional local spin density approximation (LSDA) calculations. We find that Hund's first rule is obeyed in both
cases and that neither HF nor LSDA correctly predict the ordering of the energy levels.
Received 20 November 2001 and Received in final form 20 February 2002 Published online 6 June 2002 相似文献
12.
Using perturbation analysis to solve the rate equations of semiconductor lasers, the analytical expressions for the evolution
of the carrier and photon densities have been derived when the laser is switched from one oscillation mode (or wavelength)
to another. The solutions show that the deviations of the carrier and photon densities are damped and oscillatory. The decay
rate of these deviations depends not only on the carrier lifetime, but also on the photon lifetime, which is different from
that of an ordinary diode laser experiencing switch-on processes.
Received: 5 December 2000 / Revised version: 5 March 2001 / Published online: 7 June 2001 相似文献
13.
A construction procedure is derived to obtain expressions for Hamiltonian densities which characterize the bi-Hamiltonian structure of the equations in the KdV hierarchy. All results are obtained by Hamiltonizing the appropriate Lagrangian densities recently found by us. The method is seento work for both real and complex fields. 相似文献
14.
An approach is proposed to calculate Generalized Parton Distributions (GPDs) in a Constituent Quark Model (CQM) scenario.
These off-diagonal distributions are obtained from momentum space wave functions to be evaluated in a given non-relativistic
or relativized CQM. The general relations linking the twist-two GPDs to the form factors and to the leading-twist quark densities
are consistently recovered from our expressions. Results for the leading twist, unpolarized GPD, H, in a simple harmonic-oscillator model, as well as in the Isgur and Karl model, are shown to have the general behavior found
in previous estimates. NLO evolution of the obtained distributions, from the low-momentum scale of the model up to the experimental
one, is also shown. Further applications of the proposed formalism are addressed.
Received: 31 January 2002 / Accepted: 25 November 2002 / Published online: 18 March 2003
RID="a"
ID="a"e-mail: sergio.scopetta@pg.infn.it
RID="b"
ID="b"e-mail: vicente.vento@uv.es
Communicated by A. Sch?fer 相似文献
15.
E. Leboucher-Dalimier E. Oks E. Dufour P. Angelo P. Sauvan R. Schott A. Poquerusse 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):269-274
We present an advanced theory of charge-exchange-caused dips (also called X-dips) in spectral lines from laser-produced plasmas.
We compare predictions of this advanced theory with our previously published experimental results where, in the process of
a laser irradiation of targets made out of aluminum carbide, we observed two X-dips in the L
γ line of Al XIII perturbed by fully stripped carbon. We show that our advanced theory is in excellent agreement with our experimental
results. From the practical point of view, our results open up a way to experimentally produce not-yet-available fundamental
data on charge exchange between multicharged ions, virtually inaccessible by other experimental methods. From the theoretical
viewpoint, the results are important because the X-dips are the only one signature of charge exchange in profiles of spectral
lines emitted by plasmas and they are the only one quasimolecular phenomenon that could be observed at relatively “low” densities
of laser-produced plasmas.
Received 25 March 2002 Published online 19 July 2002 相似文献
16.
S. Mancini D. Vitali V. Giovannetti P. Tombesi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):417-422
We show that the optomechanical coupling between an optical cavity mode and two movable cavity mirrors is able to entangle
two different macroscopic oscillation modes of the mirrors. This continuous variable entanglement is maintained by the light
bouncing between the mirrors and is robust against thermal noise. In fact, it could be experimentally demonstrated using present
technology.
Received 2 September 2002 / Received in final form 10 October 2002 Published online 7 January 2003 相似文献
17.
E. Santos 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):423-431
Several examples of photon entanglement are studied in the Q representation of quantum optics. In particular, the entangled states produced in parametric downconversion are studied in
detail, and we determine the conditions for the violation of Bell's inequality. Our approach shows that photon entanglement
is related to the existence of correlations between the quantum fluctuations of the electromagnetic field associated to different
modes.
Received 10 August 2002 / Received in final form 7 November 2002 Published online 4 February 2003 相似文献
18.
We examine the unitarity issue in the recently proposed time-ordered perturbation theory on noncommutative (NC) spacetime.
We show that unitarity is preserved as long as the interaction Lagrangian is explicitly hermitian. We explain why it makes
sense to distinguish the hermiticity of the Lagrangian from that of the action in perturbative NC field theory and how this
requirement fits in this framework.
Received: 25 June 2002 / Published online: 30 August 2002
RID="a"
ID="a" e-mail: liaoy@itp.uni-leipzig.de
RID="b"
ID="b" e-mail: sibold@itp.uni-leipzig.de 相似文献
19.
I. Josopait L. Dobrek L. Santos A. Sanpera M. Lewenstein 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(3):385-391
The atom optics of Bose-Einstein condensates containing a vortex of circulation one is discussed. We first analyze in detail
the reflection of such a condensate falling on an atomic mirror. In a second part, we consider a rotating condensate in the
case of attractive interactions. We show that for sufficiently large nonlinearity the rotational symmetry of the rotating
condensate is broken.
Received 16 September 2002 / Received in final form 17 November 2002 Published online 11 February 2003 相似文献
20.
The modeling of the elastic properties of disordered or nanoscale solids requires the foundations of the theory of elasticity
to be revisited, as one explores scales at which this theory may no longer hold. The only cases for which microscopically
based derivations of elasticity are documented are (nearly) uniformly strained lattices. A microscopic approach to elasticity
is proposed. As a first step, microscopically exact expressions for the displacement, strain and stress fields are derived.
Conditions under which linear elastic constitutive relations hold are studied theoretically and numerically. It turns out
that standard continuum elasticity is not self-evident, and applies only above certain spatial scales, which depend on details
of the considered system and boundary conditions. Possible relevance to granular materials is briefly discussed.
Received 18 March 2002 and Received in final form 29 May 2002 相似文献