共查询到20条相似文献,搜索用时 46 毫秒
1.
T. Mercouris C.A. Nicolaides 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(2):241-248
By implementing a time-independent, nonperturbative many-electron, many-photon theory (MEMPT), cycle-averaged complex eigenvalues
were obtained for the He atom, whose real part gives the field-induced energy shift, Δ(ω
1, F
1;ω
2, F
2,ϕ), and the imaginary part is the multiphoton ionization rate, Γ(ω
1, F
1;ω
2, F
2,ϕ), where ω is the frequency, F is the field strength and ϕ is the phase difference. Through analysis and computation we show that, provided the intensities
are weak, the dependence of Γ(ω
1, F
1;ω
2, F
2,ϕ) on ϕ is simple. Specifically, for odd harmonics, Γ varies linearly with cos(ϕ) whilst for even harmonics it varies linearly
with cos(2ϕ). In addition, this dependence on ϕ holds for Δ(ω
1, F
1;ω
2, F
2,ϕ) as well. These relations may turn out to be applicable to other atomic systems as well, and to provide a definition of
the weak field regime in the dichromatic case. When the combination of (ω
1, F
1) and (ω
2, F
2) is such that higher powers of cos(ϕ) and cos(2ϕ) become important, these rules break down and we reach the strong field
regime. The herein reported results refer to Γ(ω
1, F
1;ω
2, F
2,ϕ) and Δ(ω
1, F
1;ω
2, F
2,ϕ) for He irradiated by a dichromatic ac-field consisting of the fundamental wavelength λ = 248 nm and its 2nd, 3rd and 4th
higher harmonics. The intensities are in the range 1.0×1012-3.5×1014 W/cm2, with the intensity of the harmonics being 1-2 orders of magnitude smaller. The calculations incorporated systematically
electronic structure and electron correlation effects in the discrete and in the continuous spectrum, for 1S, 1P, 1D, 1F, 1G, and 1H two-electron states of even and odd parity.
Received 9 July 2000 and Received in final form 2 November 2000 相似文献
2.
We compute the dynamical structure factor S(q,τ) of an elastic medium where force dipoles appear at random in space and in time, due to “micro-collapses” of the structure.
Various regimes are found, depending on the wave vector q and the collapse time θ. In an early time regime, the logarithm of the structure factor behaves as (qτ)3/2, as predicted in (L. Cipelletti et al., Phys. Rev Lett. 84, 2275 (2000)) using heuristic arguments. However, in an intermediate-time regime we rather obtain a (qτ)5/4 behaviour. Finally, the asymptotic long-time regime is found to behave as q
3/2τ. We also give a plausible scenario for aging, in terms of a strain-dependent energy barrier for micro-collapses. The relaxation
time is found to grow with the age tw, quasi-exponentially at first, and then as t
w
4/5 with logarithmic corrections.
Received 15 April 2002 相似文献
3.
We compute the dynamical structure factor S(q,τ) of an elastic medium where force dipoles appear at random in space and in time, due to “micro-collapses” of the structure.
Various regimes are found, depending on the wave vector q and the collapse time θ. In an early-time regime, the logarithm of the structure factor behaves as (qτ)3/2, as predicted in L. Cipelletti, S. Manley, R.C. Ball, D.A. Weitz, Phys. Rev. Lett. 84, 2275 (2000) using heuristic arguments. However, in an intermediate-time regime we rather obtain a (qτ)5/4 behaviour. Finally, the asymptotic long-time regime is found to behave as q
3/2τ. We also give a plausible scenario for aging, in terms of a strain-dependent energy barrier for micro-collapses. The relaxation
time is found to grow with the age t
w, quasi-exponentially at first, and then as t
w
4/5 with logarithmic corrections.
Received 23 July 2001 相似文献
4.
M. Hiane J. Ebothé 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,22(4):485-495
We show that the electrodeposition of Ni-Zn alloys at the lowest growth velocities, v < 0.5μm/s, exclusively proceeds from an abnormal co-deposition phenomenon. The growth process in this v region greatly depends on the initial [Co2+] concentration of the film deposition bath. A theoretical approach of this process including the role of the saturation surface
roughness of the alloy, , leads to an estimation of the transport properties of the ad-atoms involved during the deposit formation. Their surface
diffusion coefficient varying between 1.76×10-10 and 2.40×10-8 cm-2/s exhibits a minimal value, D
s = 2.10×10-10 cm-2/s located between v = 0.17 and 0.35μm/s. The spatial scaling analysis of the local roughness, σ, examined according to the power-law σ≈L
α reveals that the resulting roughness exponents concurs with the Kardar-Parisi-Zhang dynamics including the restricted surface
diffusion. Two main v regions leads to different fractal textural features of the alloy film surface. Below 0.10 μm/s, the roughness exponent obtained
is α≈ 0.6, depicting a limited ad-atom mobility. Over v = 0.30μm/s, this exponent stabilises at α≈ 0.82, indicating an increase of the surface diffusion.
Received 16 August 2000 and Received in final form 20 June 2001 相似文献
5.
We introduce the model of inelastic hard spheres with random restitution coefficient α, in order to account for the fact that,
in a vertically shaken granular system interacting elastically with the vibrating boundary, the energy injected vertically
is transferred to the horizontal degrees of freedom through collisions only, which leads to heating through collisions, i.e. to inelastic horizontal collisions with an effective restitution coefficient that can be larger than 1. This allows the system
to reach a non-equilibrium steady state, where we focus, in particular, on the single-particle velocity distribution f (v) in the horizontal plane, and on its deviation from a Maxwellian. Molecular Dynamics simulations and Direct Simulation Monte
Carlo (DSMC) show that, depending on the distribution of α, different shapes of f (v) can be obtained, with very different high-energy tails. Moreover, the fourth cumulant of the velocity distribution quantifying
the deviations from Gaussian statistics is obtained analytically from the Boltzmann equation and successfully tested against
the simulations.
Received 24 November 2000 and Received in final form 8 February 2001 相似文献
6.
J. Horbach W. Kob K. Binder 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(4):531-543
We present the results of extensive molecular dynamics computer simulations in which the high frequency dynamics of silica,
i.e. for frequencies ν > 0.5 THz, is investigated in the viscous liquid state as well as in the glass state. We characterize the
properties of high frequency sound modes by analyzing J
l(q,ν) and J
t(q,ν), the longitudinal and transverse current correlation function, respectively. For wave-vectors q > 0.4 ?-1 the spectra are sitting on top of a flat background. The dynamic structure factor S(q,ν) exhibits for q > 0.23 ?-1 a boson peak which is located nearly independent of q around 1.7 THz and for which the intensity scales approximately linearly with temperature. We show that the low frequency
part of the boson peak is mainly due to the elastic scattering of transverse acoustic modes with frequencies around 1 THz.
The strength of this scattering depends on q and is largest around q = 1.7 ?-1, the location of the first sharp diffraction peak in the static structure factor. By studying S(q,ν) for different system sizes we show that strong finite size effects are present in the low frequency part of the boson
peak in that for small systems part of its intensity is missing. We discuss the consequences of these finite size effects
for the structural relaxation.
Received 27 June 2000 and Received in final form 9 January 2001 相似文献
7.
J. Dunkel W. Ebeling U. Erdmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,24(4):511-524
We investigate the stochastic dynamics of an one-dimensional ring with N self-driven Brownian particles. In this model neighboring particles interact via conservative Morse potentials. The influence of the surrounding heat bath is modeled by Langevin-forces (white noise) and
a constant viscous friction coefficient γ. The Brownian particles are provided with internal energy depots which may lead to active motions of the particles. The depots
are realized by an additional nonlinearly velocity-dependent friction coefficient γ
1(v) in the equations of motions. In the first part of the paper we study the partition functions of time averages and thermodynamical
quantities (e.g. pressure) characterizing the stationary physical system. Numerically calculated non-equilibrium phase diagrams are represented.
The last part is dedicated to transport phenomena by including a homogeneous external force field that breaks the symmetry
of the model. Here we find enhanced mobility of the particles at low temperatures.
Received 21 July 2001 相似文献
8.
C. Yannouleas U. Landman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):373-380
We show that the spin-and-space unrestricted Hartree-Fock method, in conjunction with the companion step of the restoration
of spin and space symmetries via Projection Techniques (when such symmetries are broken), is able to describe the full range of couplings in two-dimensional
double quantum dots, from the strong-coupling regime exhibiting delocalized molecular orbitals to the weak-coupling and dissociation
regimes associated with a Generalized Valence Bond combination of atomic-type orbitals localized on the individual dots. The
weak-coupling regime is always accompanied by an antiferromagnetic ordering of the spins of the individual dots. The cases
of dihydrogen (H2, 2e) and dilithium (Li2, 6e) quantum dot molecules are discussed in detail.
Received 19 December 2000 相似文献
9.
S. Mossa E. La Nave F. Sciortino P. Tartaglia 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(3):351-355
The equation of state for a liquid in equilibrium, written in the potential energy landscape formalism, is generalized to
describe out-of-equilibrium conditions. The hypothesis that during aging the system explores basins associated to equilibrium
configurations is the key ingredient in the derivation. Theoretical predictions are successfully compared with data from molecular
dynamics simulations of different aging processes, such as temperature and pressure jumps.
Received 7 August 2002 / Received in final form 8 October 2002
Published online 19 December 2002
RID="a"
ID="a"Present address: Laboratoire de Physique Théorique des Liquides, Université Pierre et Marie Curie, 4 place Jussieu, Paris 75005, France e-mail:
mossa@lptl.jussieu.fr 相似文献
10.
P. Stein N. Aßfalg H. Finkelmann P. Martinoty 《The European physical journal. E, Soft matter》2001,4(3):255-262
We investigate the behavior of the complex shear modulus of a series of elastomers including mono-domain and poly-domain liquid
crystal samples, and a non-mesomorphic sample. We find that the dynamics of the glass transition are strongly modified by
the nematic order. This result explains why the truly elastic response of liquid crystal elastomers can only be observed in
the isotropic phase at very high temperatures and at very low frequencies. Between the elastic regime and the glassy state,
the elastomers have a visco-elastic regime, which is characterized by a Rouse-like behavior for mono-domain and poly-domain
samples, and by a Zimm-like behavior for the non-mesomorphic sample. We also show that the mono-domain sample exhibits marked
anisotropy of the shear-modulus G
′. This anisotropy, which is observed for the first time, is a function of frequency and is inverted between low and high frequencies,
due to relaxation effects of the orientational order.
Received 28 January 2000 and Received in final form 16 October 2000 相似文献
11.
Verneuil E Clain J Buguin A Brochard-Wyart F 《The European physical journal. E, Soft matter》2003,10(4):345-353
A soft bead (radius R
b) is pressed with a force F against a hydrophobic glass plate through a water drop (“wet” JKR set-up). We observe with a fast camera the growth of the
contact zone bridging the rubber bead to the glass. Depending on the approach velocity V, two regimes are observed : i) at large V a liquid film is squeezed at the interface and dewets by nucleation and growth of a dry contact; ii) at low velocities, the
bead remains nearly spherical. As it comes into contact, the rubber bead spreads on the glass with a characteristic time (in
the range of one millisecond) τ ≈ ηR
b
2/F, where η is the liquid viscosity. The laws of spreading are interpreted by a balance of global mechanical and viscous forces.
Received: 22 December 2002 / Accepted: 24 March 2003 / Published online: 29 April 2003
RID="a"
ID="a"e-mail: brochard@curie.fr 相似文献
12.
A. Latz M. Letz 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):323-343
The theory of light scattering for a system of linear molecules with anisotropic polarizabilities is considered. As a starting
point for our theory, we express the result of a scattering experiment in VV and VH symmetry as dynamic correlation functions
of tensorial densities ρ
lm(q) with l = 0 and l = 2. l, m denote indices of spherical harmonics. To account for all observed hydrodynamic singularities, a generalization of the theory
of Schilling and Scheidsteger [1] for these correlation functions is presented, which is capable to describe the light scattering
experiments from the liquid regime to the glassy state. As a microscopic theory it fulfills all sum rules contrary to previous
phenomenological theories. We emphasize the importance of the helicity index m for the microscopic theory by showing, that only the existence of m = 1 components lead to the well known Rytov dip in liquids and to the appearance of transversal sound waves in VH symmetry
in the deeply supercooled liquid and the glass. Exact expressions for the phenomenological frequency dependent rotation translation
coupling coefficients of previous theories are derived.
Received 3 July 2000 and Received in final form 7 November 2000 相似文献
13.
G. Savona D.V. Livanov A.A. Varlamov 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(4):415-420
We study the fluctuation-induced magnetotransport of a two-dimensional superconductor in the quasiballistic regime, where
ξ
GL(T) ≪ ℓ (ℓ is the electron mean free path and ξ
GL(T) is the Ginzburg-Landau coherence length). The magnetoconductivity is evaluated in the nonlocal fluctuation regime thereby
extending the existing theory valid in the local limit. We show that the Maki-Thompson (MT) and density-of-states (DOS) contributions
strongly compensate each other and their sum is negligible in comparison with the Aslamazov-Larkin (AL) term. The hierarchy
of the fluctuation contributions to the magnetoconductivity in the high-field limit is also qualitatively discussed.
Received 10 July 2002 / Received in final form 21 November 2002 Published online 7 May 2003 相似文献
14.
Alessandro Torcini Paolo Politi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(4):519-529
Surface growth models may give rise to instabilities with mound formation whose typical linear size L increases with time (coarsening process). In one dimensional systems coarsening is generally driven by an attractive interaction
between domain walls or kinks. This picture applies to growth models for which the largest surface slope remains constant
in time (corresponding to model B of dynamics): coarsening is known to be logarithmic in the absence of noise ( L(t) ∼ ln t) and to follow a power law ( L(t) ∼t
1/3) when noise is present. If the surface slope increases indefinitely, the deterministic equation looks like a modified Cahn-Hilliard
equation: here we study the late stages of coarsening through a linear stability analysis of the stationary periodic configurations
and through a direct numerical integration. Analytical and numerical results agree with regard to the conclusion that steepening
of mounds makes deterministic coarsening faster : if α is the exponent describing the steepening of the maximal slope M of mounds ( M
α∼L) we find that L(t) ∼t
n: n is equal to for 1≤α≤2 and it decreases from to for α≥2, according to n = α/(5α - 2). On the other side, the numerical solution of the corresponding stochastic equation clearly shows that in the
presence of shot noise steepening of mounds makes coarsening slower than in model B: L(t) ∼t
1/4, irrespectively of α. Finally, the presence of a symmetry breaking term is shown not to modify the coarsening law of model
α = 1, both in the absence and in the presence of noise.
Received 28 September 2001 and Received in final form 21 November 2001 相似文献
15.
J.-Ph. Bouchaud P. Doussineau T. de Lacerda-Arôso A. Levelut 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(3):335-340
We characterize in details the aging properties of the ferroelectric phase of KTa1-xNbx O3 (KTN), where both rejuvenation and (partial) memory are observed. In particular, we carefully examine the frequency dependence
of several quantities that characterize aging, rejuvenation and memory. We find a marked subaging behaviour, with an a.c.
dielectric susceptiblity scaling as ω, where t
w is the waiting time. We suggest an interpretation in terms of pinned domain walls, much along the lines proposed for aging
in a disordered ferromagnet, where both domain wall reconformations and overall (cumulative) domain growth are needed to rationalize the experimental findings.
Received 10 November 2000 and Received in final form 20 February 2001 相似文献
16.
The double differential dilepton spectrum d/(d
2
d
⊥
2) at fixed transverse mass M
⊥ allows a direct access to the vector meson spectral functions. Within a fireball model the sensitivity of d/(d
2
d
⊥
2) against variations of both the in-medium properties of mesons and the dynamics of the fireball is investigated. In contrast
to the integrated invariant-mass spectrum d/d
2, in the spectrum d/(d
2
d
⊥
2) with fixed M
⊥ the ω signal is clearly seen as bump riding on the ρ background even in case of strong in-medium modifications.[3mm]
Received: 16 November 2000 / Accepted: 16 January 2001 相似文献
17.
M. Holthaus S. Stenholm 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(3):451-467
We discuss the dynamics of two weakly coupled Bose-Einstein condensates in a double-well potential, contrasting the mean-field
picture to the exact N-particle evolution. On the mean-field level, a self-trapping transition occurs when the scaled interaction strength exceeds
a critical value; this transition essentially persists in small condensates comprising about 1000 atoms. When the double-well
is modulated periodically in time, Floquet-type solutions to the nonlinear Schr?dinger equation take over the role of the
stationary mean-field states. These nonlinear Floquet states can be classified as “unbalanced” or “balanced”, depending on
whether or not they entail long-time confinement of most particles to one well. Since the emergence of unbalanced Floquet
states depends on the amplitude and frequency of the modulating force, we predict that the onset of self-trapping can efficiently
be controlled by varying these parameters. This prediction is verified numerically by both mean-field and N-particle calculations.
Received 5 November 2000 and Received in final form 16 February 2001 相似文献
18.
H. Gayvallet J.-C. Géminard 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(3):369-375
We have studied the temperature dependent resistivity ρ(
T
) of La2-xSrxCuO4 epitaxial thin films in the doping range 0.045 ⩽
x
⩽ 0.25 in pulsed magnetic fields up to 50 T. The zero-field resistivity ρ(
T
) of these samples in the pseudogap regime, can be scaled onto one single universal curve in a broad temperature range by using
a linear transformation of both temperature and resistivity. The high field data ρ(
T
) reveal a metal to insulator transition (MIT) at low temperatures, well into the overdoped regime. For samples having k
F
l
< 1, with kF the Fermi wave vector and l the mean free path, this low temperature insulating behavior of the resistivity is described by the variable range hopping
conductivity (VRH). For samples with k
F
l
> 1, the divergence follows ρ(
T
) ∼
ln
(1/
T
) or a power law, depending upon the Sr-content. We further found that the residual conductivity at the minimum in ρ(
T
), appearing due to the MIT, follows a linear behavior with respect to the Sr-content. It is argued that the unusual MIT in
compounds with k
F
l
> 1, is most probably associated with the pseudogap and the behavior of charge stripes at low temperatures.
Received 4 January 2002 / Received in final form 7 May 2002 Published online 14 October 2002
RID="a"
ID="a"e-mail: liesbet.weckhuysen@fys.kuleuven.ac.be 相似文献
19.
R. Metzler 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):249-258
A generalised random walk scheme for random walks in an arbitrary external potential field is investigated. From this concept
which accounts for the symmetry breaking of homogeneity through the external field, a generalised master equation is constructed.
For long-tailed transfer distance or waiting time distributions we show that this generalised master equation is the genesis
of apparently different fractional Fokker-Planck equations discussed in literature. On this basis, we introduce a generalisation
of the Kramers-Moyal expansion for broad jump length distributions that combines multiples of both ordinary and fractional
spatial derivatives. However, it is shown that the nature of the drift term is not changed through the existence of anomalous
transport statistics, and thus to first order, an external potential Φ(x) feeds back on the probability density function W through the classical term ∝/
x
(x)W(x, t), i.e., even for Lévy flights, there exists a linear infinitesimal generator that accounts for the response to an external field.
Received 30 June 2000 and Received in final form 12 November 2000 相似文献
20.
We consider a low-density assembly of spherical colloids, such that each is clothed by L end-grafted chemically incompatible polymer chains either of types A or B. These are assumed to be dissolved in a good common solvent. We assume that colloids are of small size to be considered as
star-polymers. Two adjacent star-polymers A and B interact through a force F originating from both excluded-volume effects and chemical mismatch between unlike monomers. Using a method developed by
Witten and Pincus (Macromolecules 19, 2509 (1986)) in the context of star-polymers of the same chemical nature, we determine exactly the force F as a function of the center-to-center distance h. We find that this force is the sum of two contributions F
e and F
s. The former, that results from the excluded volume, decays as F
e∼A
L
h
-1, with the L -dependent universal amplitude A
L∼L
3/2. While the second, which comes from the chemical mismatch, decays more slowly as F
s∼χB
L
h
-1 - τ, where τ is a critical exponent whose value is found to be τ 0.40, and χ is the standard Flory interaction parameter. We find that the corresponding L-dependent universal amplitude is B
L∼L
3 + τ
/2. Theses forces are comparable near the cores of two adjacent star-polymers, i.e. for h∼h
c∼a
(a is the monomer size). Finally, for two star-polymers of the same chemical nature (A or B), the force F that simply results from excluded-volume effects coincides exactly with F
e, and then the known result is recovered.
Received 2 October 2000 and Received in final form 24 January 2001 相似文献