共查询到20条相似文献,搜索用时 375 毫秒
1.
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
2.
J.V. Jovanović S.B. Vrhovac Z.Lj. Petrović 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(3):335-342
Transport properties of ion swarms in presence of Resonant Charge Transfer (RCT) collisions are studied using Momentum Transfer
Theory (MTT). It was shown that, not surprisingly, RCT collisions may be represented as a special case of elastic scattering.
Using the developed MTT we tested a previously available anisotropic set of cross-sections for Ar+Ar
+ collisions by making the comparisons with the available data for the transverse diffusion coefficient. We also developed
an anisotropic set of Ne+Ne
+ integral cross-sections based on the available data for mobility, longitudinal and transverse diffusion. Anisotropic sets
of cross-sections are needed for Monte Carlo simulations of ion transport and plasma models.
Received 16 June 2002 / Received in final form 2nd August 2002 Published online 24 September 2002
RID="a"
ID="a"e-mail: vrhovac@phy.bg.ac.yu
RID="b"
ID="b"e-mail: zoran@phy.bg.ac.yu 相似文献
3.
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
4.
W. Christen U. Even 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):87-90
This contribution addresses the inelastic interaction of positively charged molecular cluster ions with a solid surface at
kinetic energies up to 30 eV/molecule. We report experimental results on the scattering of mass-selected, protonated methanol
cluster cations (CH3OH)nH+, n = 4-32, off a diamond-coated silicon surface. In particular we provide fragment size distributions of methanol cluster ions
following their impact on the target, as well as surface-induced neutralization probabilities of methanol cluster ions as
a function of the size and the kinetic energy of the parent clusters.
Received 30 November 2000 相似文献
5.
A model for scalar quarks and gluons that successfully gives rise to a ln s behavior in high-energy qq scattering and which contains a non-trivial three-gluon vertex is used to study collision theory with the following aspects:
i) A three-body interaction simulating QCD is present and ii) particle production and annihilation occur naturally. In this
paper, the collision term in the model is examined in detail in the quasiparticle approximation. The construction of cross-sections
in which self-energy terms are ordered according to a coupling constant expansion is undertaken. It is shown explicitly which
terms of second order are required to obtain the scattering amplitudes that are two body in nature. Additional ordering in
the number of colors shows that quark loop diagrams are suppressed and gluon production or scattering processes dominate.
It is also shown that a consistent calculation of the scattering graphs at the two-loop level also simultaneously yields terms
that renormalize one-loop level graphs. This can then be extended to arbitrary m↦n processes. We examine the constraint equation briefly, discussing the appearance of a width. The issue of pinch singularities
is also addressed, and examples of the elimination of such singularities in equilibrium are given explicitly.
Received: 7 November 2001 / Accepted: 12 June 2001 相似文献
6.
P.L. Christiansen Y.B. Gaididei F.G. Mertens S.F. Mingaleev 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(4):545-553
We investigate the properties of nonlinear excitations in different types of soliton carrying systems with long-range dispersive interactions. We show that length-scale competition in such systems, universally results in a multi-component structure of nonlinear excitations
which may lead to a new type of multistability: coexistence of different nonlinear excitations at the same value of the spectral parameter (i.e., velocity in the case of anharmonic lattices or frequency in nonlinear Schr?dinger models).
Received 31 August 2000 and Received in final form 14 December 2000 相似文献
7.
Lyotropic bicontinuous cubic phase single crystals investigated using high-resolved X-ray scattering
Single crystals of an Ia
d bicontinuous direct cubic phase formed by a non-ionic surfactant in water are investigated using high-resolved X-ray diffraction.
The shape of the Bragg peaks confirms the existence of a 3D long-range order inside the cubic phase. A weak diffuse scattered
intensity signal is measured very near the Bragg peaks. We attribute this signal to thermal diffuse scattering (TDS) and we
give an estimation of the contribution of elastic waves to this TDS.
Received 4 May 2000 相似文献
8.
The effect of fixed discrete colloidal charges in the primitive model is investigated for spherical macroions. Instead of
considering a central bare charge, as it is traditionally done, we distribute discrete charges randomly on the sphere. We use molecular dynamics simulations to study this effect on various properties such as
overcharging, counterion distribution and diffusion. In the vicinity of the colloid surface the electrostatic potential may
considerably differ from the one obtained with a central charge. In the strong Coulomb coupling, we showed that the colloidal
charge discretization qualitatively influences the counterion distribution and leads to a strong colloidal charge-counterion
pair association. However, we found that charge inversion still persists even if strong pair association is observed.
Received 30 June 2000 and Received in final form 28 November 2000 相似文献
9.
F. Arias de Saavedra E. Buendıa F.J. Gálvez A. Sarsa 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(2):201-206
A generalized Hylleraas-type basis set with three nonlinear parameters is proposed to study three-body systems interacting
via coulomb forces within the framework of non-relativistic quantum mechanics. This basis set improves the rate of convergence
with respect to previous ones, specially for non-symmetric systems and excited states of two electron atoms. Accurate binding
energies and other properties for S-states of helium-like ions, muonic molecules and the positronium negative ion are reported.
Received 21 July 2000 and Received in final form 4 October 2000 相似文献
10.
We have investigated the algebraic structure of the Fokker-Planck equation with a variable diffusion coefficient and a time-dependent
mean-reverting force. Such a model could be useful to study the general problem of a Brownian walker with a space-dependent
diffusion coefficient. We also show that this model is related to the Fokker-Planck equation with a constant diffusion coefficient
and a time-dependent anharmonic potential of the form V(x, t) = ?a(t)x
2 + b ln x, which has been widely applied to model different physical and biological phenomena, e.g. the study of neuron models and stochastic resonance in monostable nonlinear oscillators. Using the Lie algebraic approach
we have derived the exact diffusion propagators for the Fokker-Planck equations associated with different boundary conditions,
namely (i) the case of a single absorbing barrier, and (ii) the case of two absorbing barriers. These exact diffusion propagators
enable us to study the time evolution of the corresponding stochastic systems.
Received 23 October 2001 and Received in final form 24 December 2001 相似文献
11.
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
12.
E. Mezzetti A. Chiodoni R. Gerbaldo G. Ghigo L. Gozzelino B. Minetti C. Camerlingo C. Giannini 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):357-362
This paper reports on the striking correlation between nanosize mosaic domain walls in YBCO films and 1D rows of parallel
Josephson junctions, determining the J
c
vs.B curves. From X-ray data analysis, it results that the average “hidden" domain wall, faceted at a nanometric scale, is almost
mimicking the Josephson Junction (JJ) 1D array. The assumption that the JJs and the domain-wall arrays are coincident, enables
to find out the particular scaling field, making the J
c
vs.B curves independent of temperature. This scaling field can be interpreted in terms of the Josephson nature of the transport
current across these particular patterns in the intermediate temperature range. By means of our model it is also possible
to calculate two asymptotic behaviors of the pinning force as a function of field, for low and high fields, respectively.
These behaviors are punctually repeated by the experimental results in the same asymptotic limit, so that two corresponding
vortex regimes are clearly pointed out. All results can be interpreted by concluding that in the intermediate temperature
range, the strong pinning observed in high quality YBCO films is due to the Josephson Junctions average patterns. These patterns
are the counterpart related to the transport mechanisms of “hidden" structural nano-domains.
Received 16 October 2000 and Received in final form 28 November 2000 相似文献
13.
T. Schaub J. Delahaye C. Berger H. Guyot R. Belkhou A. Taleb-Ibrahimi Y. Calvayrac 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(2):183-188
High resolution photoemission measurements performed at low temperatures on a single-grained sample of the AlPdMn icosahedral
phase show that the density of states N(E) strongly depends on the nature of the surface. For an ordered quasicrystalline surface, prepared by Ar etching and ultra
high vacuum annealing, a dip feature is observed in N(E) near the Fermi level, which energy dependence can be analyzed with a simple square-root power law. By contrast, N(E) varies only little with energy both for a disordered surface and a crystalline surface of the same sample. A sharp Fermi
edge is then clearly observed. This shows that the metallic character of the surface of a quasicrystal is strongly reduced
when the surface presents a quasicrystalline ordering.
Received 19 February 2000 and Received in final form 6 November 2000 相似文献
14.
It has been shown over the last few years that the dynamics close to the glass transition is strongly heterogeneous, both
by measuring the diffusion coefficient of tagged particles or by NMR studies. Recent experiments have also demonstrated that
the glass transition temperature of thin polymer films can be shifted as compared to the same polymer in the bulk. We propose
here first a thermodynamical model for van der Waals liquids, which accounts for experimental results regarding the bulk modulus
of polymer melts and the evolution of the density with temperature. This model allows us to describe the density fluctuations
in such van der Waals liquids. Then, by considering the thermally induced density fluctuations in the bulk, we propose that
the 3D glass transition is controlled by the percolation of small domains of slow dynamics, which allows to explain the heterogeneous
dynamics close to T
g. We show then that these domains percolate at a lower temperature in the quasi-2D case of thin suspended polymer films and
we calculate the corresponding glass transition temperature reduction, in quantitative agreement with experimental results
of Jones and co-workers. In the case of strongly adsorbed films, we show that the strong adsorption amounts to enhance the
slow domains percolation. This effect leads to 1) a broadening of the glass transition and 2) an increase of T
g in quantitative agreement with experimental results. For both strongly and weakly adsorbed films, the shift in T
g is given by a power law, the exponent being the inverse of that of the correlation length of 3D percolation.
Received 21 March 2000 and Received in final form 4 December 2000 相似文献
15.
The general formalism for polarization observables in elastic electron deuteron scattering is extended to incorporate parity-
and time-reversal-violating contributions. Parity-violating effects arise from the interference of γ and Z exchange as well as from the hadronic sector via a small parity-violating component in the deuteron. In addition we have
allowed for time-reversal-invariance-violating contributions in the hadronic sector. Formal expressions for the additional
structure functions are derived, and their decomposition into the various multipole contributions are given explicitly.
Received: 19 December 2000 / Accepted: 14 February 2001 相似文献
16.
V.Yu. Irkhin M.I. Katsnelson 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,30(4):481-486
Peculiarities of transport properties of three- and two-dimensional half-metallic ferromagnets are investigated, which are
connected with the absence of spin-flip scattering processes. The temperature and magnetic field dependences of resistivity
in various regimes are calculated. The resistivity is proportional to T
9/2 for T < T
* and to T
7/2 for T > T
*, T* being the crossover temperature for longitudinal scattering processes. The latter scale plays also an important role in magnetoresistance.
The contribution of non-quasiparticle (incoherent) states to the transport properties is discussed. It is shown that they
can dominate in the temperature dependence of the impurity-induced resistivity and in the tunnel junction conductivity.
Received 16 September 2002 / Received in final form 6 November 2002 Published online 31 December 2002 相似文献
17.
J. Schulenburg J.S. Flynn D.D. Betts J. Richter 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(2):191-204
In this paper finite bcc lattices are defined by a triple of vectors in two different ways - upper triangular lattice form
and compact form. In Appendix A are lists of some 260 distinct and useful bcc lattices of 9 to 32 vertices. The energy and
magnetization of the S = 1/2 XY ferromagnet have been computed on these bcc lattices in the lowest states for S
z = 0, 1/2, 1 and 3/2. These data are studied statistically to fit the first three terms of the appropriate finite lattice
scaling equations. Our estimates of the T = 0 energy and magnetization agree very well with spin wave and series expansion estimates.
Received 1st August 2000 and Received in final form 22 December 2000 相似文献
18.
G.K. Paramonov H. Naundorf O. Kühn 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(2):205-215
The laser driven dynamics of the OH(D) stretching vibration in phthalic acid monomethylester is investigated. The combination
of a 55-dimensional all-Cartesian reaction surface Hamiltonian and the time-dependent self-consistent field approach is shown
to provide a microscopic picture of intramolecular vibrational energy redistribution taking place upon interaction with an
external laser field. Choosing suitable zeroth-order vibrational states and combinations thereof a quasi-periodic in-phase and out-of-phase oscillatory behavior is observed manifesting energy flow on different time scales. The fingerprints of this behavior in transient
absorption spectroscopy are also discussed.
Received 24 August 2000 and Received in final form 11 October 2000 相似文献
19.
Ş. Erkoç H. Kökten Z. Güvenç 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(3):361-365
The fragmentation of water clusters, [(H
2
O)n;n = 2-8], have been investigated by using molecular-dynamics simulation method. In the simulations a polarizable-dissociable
potential energy function for water has been used. Particular attention has bee paid to investigate the effect of structural
properties and cluster size on the fragmentation.
Received 27 April 2000 and Received in final form 6 October 2000 相似文献
20.
The sodium salt of polyacrylic acid (NaPA) precipitates in the presence of Ca2+-ions. This phase behaviour can be represented by a phase diagram where the critical NaPA concentration is plotted versus the critical Ca2+ concentration resulting in a straight line as a phase boundary. The location of this phase boundary is influenced by the
presence of an inert monovalent salt like NaCl. The present contribution focuses on the coil dimensions of NaPA chains in
dilute aqueous solution corresponding to the one phase region of such a phase diagram. A variety of parameters with which
the size and shape of the polyelectrolyte chains can be modulated are revealed. Approaching the phase boundary by decreasing
the NaPA concentration at a constant Ca2+ content leads to a collapse of the NaPA chains. Combined static and dynamic light scattering suggests a compact spherical
shape as the final state of this transition, both in 0.1 M NaCl and in 0.01 M NaCl. In the lower NaCl concentration, indication
is presented for the existence of a cigar or pearl necklace like intermediate. Most strikingly, the collapsed chains can be
reexpanded by increasing the concentration of inert NaCl at constant content of NaPA and Ca2+. Clearly, excessive Na+-ions displace the Ca2+-ions from the NaPA chains.
Received 18 July 2000 and Received in final form 24 August 2000 相似文献