共查询到20条相似文献,搜索用时 15 毫秒
1.
S. Ispolatov P.L. Krapivsky S. Redner 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(2):267-276
A model for the evolution of the wealth distribution in an economically interacting population is introduced, in which a specified
amount of assets are exchanged between two individuals when they interact. The resulting wealth distributions are determined
for a variety of exchange rules. For “random” exchange, either individual is equally likely to gain in a trade, while “greedy”
exchange, the richer individual gains. When the amount of asset traded is fixed, random exchange leads to a Gaussian wealth
distribution, while greedy exchange gives a Fermi-like scaled wealth distribution in the long-time limit. Multiplicative processes
are also investigated, where the amount of asset exchanged is a finite fraction of the wealth of one of the traders. For random
multiplicative exchange, a steady state occurs, while in greedy multiplicative exchange a continuously evolving power law
wealth distribution arises.
Received: 13 August 1997 / Revised: 31 December 1997 / Accepted: 26
January 1998 相似文献
2.
J. Bachteler H.-R. Trebin 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):299-306
The elastic theory of quasicrystals considers, in addition to the “normal” displacement field, three “phason” degrees of freedom.
We present an approximative solution for the elastic Green's function of icosahedral quasicrystals, assuming that the coupling
between the phonons and phasons is small.
Received: 18 December 1997 / Accepted: 6 March 1998 相似文献
3.
F. Ricoul M. Dubois T. Zemb D. Plusquellec 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(3):333-340
By use of a mean-field approach the spin-wave dispersion of the Cu degrees of freedom in the undoped high-T C material Nd2CuO4is investigated. The experimentally observed sharp decrease of the Cu spin-wave gap with increasing temperature in the range
is explained by a paramagnetic-like susceptibility of the Nd spins which couple to the Cu subsystem. The degeneracy of the
“in-plane” and “out-of-plane” polarized Cu spin-wave branches is shown to be lifted by the uniaxial anisotropy of the Cu-Cu
nearest-neighbor interaction.
Received: 13 August 1997 / Revised: 4 December 1997 / Accepted: 11 December 1997 相似文献
4.
K. Urayama S. Kohjiya 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,2(1):75-78
The stress-elongation relations at large deformations for the polymer network chains with randomcoiled and supercoiled conformations are investigated
using the polysiloxane networks with high elongations at break far over 10. Supercoil is the conformation of network chains
in deswollen polymer networks which are made by removing solvent from the networks crosslinked in solutions at low polymer
concentrations. The validity of the scaling concept of Pincus blob for the mechanical response of a polymer chain is experimentally
confirmed for the network composed of randomcoiled chains. The analysis of the stress- relations for the deswollen networks comprised of supercoiled chains on the basis of the Pincus blob concept suggests that
supercoil is a much more contracted conformation relative to randomcoil.
Received: 25 August 1997 / Received in final form: 13 October 1997 / Accepted: 22 January 1998 相似文献
5.
X. Waintal J.-L. Pichard 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(1):117-121
For N interacting particles in a one dimensional random potential, we study the structure of the corresponding network in Hilbert
space. The states without interaction play the role of the “sites”. The hopping terms are induced by the interaction. When
the one body states are localized, we numerically find that the set of directly connected “sites” is multifractal. For the
case of two interacting particles, the fractal dimension associated to the second moment of the hopping term is shown to characterize
the Golden rule decay of the non interacting states and the enhancement factor of the localization length.
Received: 17 April 1998 / Accepted: 14 May 1998 相似文献
6.
7.
F. Thalmann 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):497-505
A one dimensional trap model for a thermally activated classical particle is introduced to simulate driven dynamics in presence
of “ageing” effects. The depth of each trap increases with the time elapsed since the particle has fallen into it. The consequences
of this dynamical pinning are studied, and velocity-force characteristics are numerically obtained. A special attention is
paid to the situation where the particle is pulled with a spring to ensure a finite average velocity. In the low velocity
regime, the presence of a broad distribution of trapping times leads to suppression of linear response, replaced by a threshold
or by sublinear dynamics. A regime of strong fluctuations is obtained when the particle is driven at intermediate velocities.
Received: 12 December 1997 / Accepted: 25 February 1998 相似文献
8.
G.S. Neugschwandtner R. Schwödiauer S. Bauer-Gogonea S. Bauer 《Applied Physics A: Materials Science & Processing》2000,70(1):1-4
Large piezoelectric d33 coefficients around 600 pC/N are found in corona-charged non-uniform electrets consisting of elastically “soft” (microporous
polytetrafluoroethylene PTFE) and “stiff” (perfluorinated cyclobutene PFCB) polymer layers. The piezoelectric activity of
the two-layer fluoropolymer stack exceeds the d33 coefficient of the ferroelectric ceramic lead zirconate titanate (PZT) by more than a factor of two and that of the ferroelectric
polymer polyvinylidene fluoride (PVDF) by a factor of 20. Soft piezoelectric materials may become interesting for a large
number of sensor and transducer applications, in areas such as security systems, medical diagnostics, and nondestructive testing.
Accepted: 9 November 1999 / Published online: 3 December 1999 相似文献
9.
M. Pleimling W. Selke 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(3):385-391
The effect of imperfections on surface critical properties is studied for Ising models with nearest-neighbour ferromagnetic
couplings on simple cubic lattices. In particular, results of Monte Carlo simulations for flat, perfect surfaces are compared
to those for flat surfaces with random, “weak” or “strong”, interactions between neighbouring spins in the surface layer,
and for surfaces with steps of monoatomic height. Surface critical exponents at the ordinary transition, in particular ,are found to be robust against these perturbations.
Received: 7 October 1997 / Accepted: 19 November 1997 相似文献
10.
Aaron Sellinger Elodie Leveugle James M. Fitz-Gerald Leonid V. Zhigilei 《Applied Physics A: Materials Science & Processing》2008,92(4):821-829
Coarse-grained molecular dynamics simulations are applied to investigate the origins of the surface features observed in films
deposited by the Matrix-Assisted Pulsed Laser Evaporation (MAPLE) technique. The formation of transient balloon-like structures
with a polymer-rich surface layer enclosing matrix vapor, observed in earlier simulations of slow heating of polymer-matrix
droplets, has been explored in this work at higher rates of thermal energy deposition. Tensile stresses generated in the regime
of partial stress confinement are found to induce an internal boiling in the overheated droplets and associated generation
of “molecular balloons” at thermal energy densities at which no homogeneous boiling takes place without the assistance of
tensile stresses. Simulations of the dynamic processes occurring upon the collision of a polymer-matrix droplet with a substrate
provide the molecular-level pictures of the droplet impact phenomenon and reveal the connections between the droplet landing
velocity and the shapes of the polymer features observed in scanning electron microscopy images of films deposited in MAPLE
experiments. The distinct types of surface features observed in MAPLE experiments, namely, wrinkled “deflated balloons,” localized
arrangements of interconnected polymer filaments, and elongated “nanofibers,” are shown to emerge from different scenarios
of droplet landing and/or disintegration observed in the simulations. 相似文献
11.
A.K. Kolezhuk H.-J. Mikeska 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(3):543-550
We study the “mixed spin” isotropic ladder system having S=1 spins on one leg and S=1/2 spins on the other, with general-type exchange interactions between spins on neighboring rungs. A set of model Hamiltonians
with exact ground states in the form of a certain matrix product wave function is obtained. We show that sufficiently strong
frustration can lead to exotic singlet ground states with infinite (exponential) degeneracy. We also list a couple of rather
simple models with nontrivial ground states, including a model with only bilinear exchange.
Received: 2 December 1997 / Accepted: 28 January 1998 相似文献
12.
Higgins AM Sferrazza M Jones RA Jukes PC Sharp JS Dryden LE Webster J 《The European physical journal. E, Soft matter》2002,8(2):137-143
We investigate the dynamics of spinodal dewetting in liquid-liquid polymer systems. Dewetting of poly(methyl-methacrylate)
(PMMA) thin films on polystyrene (PS) “substrates” is followed in situ using neutron reflectivity. By following the development of roughness at the PS/PMMA interface and the PMMA surface we extract
characteristic growth times for the dewetting process. These characteristic growth times are measured as a function of the
molecular weight of the two polymers. By also carrying out experiments in the regime where the dynamics are independent of
the PS molecular weight, we are able to use dewetting to probe the scaling of the PMMA thin film viscosity with temperature
and molecular weight. We find that this scaling reflects bulk behaviour. However, absolute values are low compared to bulk
viscosities, which we suggest may be due in part to slippage at the polymer/polymer interface.
Received 25 June 2001 and Received in final form 5 December 2001 相似文献
13.
D. Stauffer M. Sahimi 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,57(2):147-152
Models that provide insight into how extreme positions regarding any social phenomenon may spread in a society or at the global
scale are of great current interest. A realistic model must account for the fact that globalization, internet, and other means
of mass communications have given rise to scale-free networks of interactions between people. We propose a novel model which
takes into account the nature of the interactions network, and provides some key insights into this phenomenon. These include,
(1) the existence of a
fundamental difference between a hierarchical network whereby people are influenced by those that are higher in the hierarchy
but not by those below them, and a symmetrical network where person-on-person influence works mutually, and (2) that a few
“fanatics” can influence a large fraction of the population either temporarily (in the hierarchical networks) or permanently
(in symmetrical networks). Even if the “fanatics” disappear, the population may still remain susceptible to the positions
originally advocated by them. The
model is, however, general and applicable to any phenomenon for which there is a degree of enthusiasm or susceptibility to
in the population. 相似文献
14.
E. Estrada 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(4):563-574
We study the property of certain complex networks of being both sparse and
highly connected, which is known as “good expansion” (GE). A network has
GE properties if every subset S of nodes (up to 50% of the nodes) has a
neighborhood that is larger than some “expansion factor” φ
multiplied by the number of nodes in S. Using a graph spectral method we
introduce here a new parameter measuring the good expansion character of a
network. By means of this parameter we are able to classify 51 real-world
complex networks — technological, biological, informational, biological and
social — as GENs or non-GENs. Combining GE properties and node degree
distribution (DD) we classify these complex networks in four different
groups, which have different resilience to intentional attacks against their
nodes. The simultaneous existence of GE properties and uniform degree
distribution contribute significantly to the robustness in complex networks.
These features appear solely in 14% of the 51 real-world networks studied
here. At the other extreme we find that ∼40% of all networks are
very vulnerable to targeted attacks. They lack GE properties, display skewed
DD — exponential or power-law — and their topologies are changed more
dramatically by targeted attacks directed at bottlenecks than by the removal
of network hubs. 相似文献
15.
T. Schenkel A.V. Barnes A.V. Hamza D.H. Schneider 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(3):297-302
Cluster ion emission from a variety of surfaces upon impact of highly charged ions is investigated by time-of-flight secondary
ion mass spectrometry. The yield of cluster ions as a function of cluster size for and surface follow a power law decline with exponent approaching the -2 limit of the ”equilibrium” and ”shock wave” cluster emission
models. While the decline of the cluster ion emission with cluster size is an exponential decay for highly oriented pyrolytic
graphite upon impact, the decline is more gradual than for impact, such that at the relative cluster yield is 1000 times higher.
Received: 22 April 1997 / Revised: 29 December 1997 / Accepted: 19 January 1998 相似文献
16.
S. L?mmer R. Donner D. Helbing 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(3):341-347
The relevant dynamics of a queueing process can be anticipated by taking
future arrivals into account. If the transport from one queue to another is associated
with transportation delays, as it is typical for traffic or productions networks, future
arrivals to a queue are known over some time horizon and, thus, can be used for an
anticipative control of the corresponding flows.
A queue is controlled by switching its outflow between “on” and “off” similar to
green and red traffic lights, where switching to “on” requires a non-zero setup time.
Due to the presence of both continuous and discrete state variables, the queueing process
is described as a hybrid dynamical system. From this formulation, we derive one
observable of fundamental importance: the green time required to clear the queue. This
quantity allows to detect switching time points for serving platoons without delay, i.e.,
in a “green wave” manner. Moreover, we quantify the cost of delaying the start of a
service period or its termination in terms of additional waiting time. Our findings may
serve as a basis for strategic control decisions. 相似文献
17.
F. Despa R.S. Berry 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):261-264
We explore the way free particles produced by dissociating “particle-hole pairs” on a surface-melted cluster can be transferred
to a second, nearby surface-melted cluster. This mass transport is based on an inter-cluster direct transfer mechanism of
the particles. We found that in this particular case one cluster may grow at the expense of another, obeying a temporal power
law with the exponent 1/2 for the average radius (R∼t
1/2). The change from the expected universal power law (R∼t
1/3) is a consequence of the proximity relation between these two clusters which lead to enhance the effective transport rates.
Received 4 December 2000 相似文献
18.
M. Combescot M.-A. Dupertuis 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(3):459-464
We show that the carrier “antibinding” observed recently in
semiconductor quantum dots, i.e., the fact that the ground state
energy of two electron-hole pairs goes above twice the ground-state
energy of one pair, can entirely be assigned to a charge separation
effect, whatever its origin. In the absence of external electric field, this charge
separation comes from different “spreading-out” of the electron and
hole wavefunctions linked to the finite height of the barriers. When
the dot size shrinks, the two-pair energy always stays below when the
barriers are infinite. On the opposite, because barriers are less
efficient for small dots, the energy of two-pairs in a dot with
finite barriers, ends by behaving like the one in bulk, i.e., by
going above twice the one-pair energy when the pairs get too close.
For a full understanding of this “antibinding” effect, we have also
reconsidered the case of one pair plus one carrier. We find that,
while the carriers just have to spread out of the dot differently for
the “antibinding” of two-pairs to appear, this “antibinding” for
one pair plus one carrier only appears if this carrier is the one
which spreads out the less. In addition a remarkable sum rule exists
between the “binding energies” of two pairs and of one pair plus one carrier. 相似文献
19.
Y.O. Popov A.N. Semenov 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(2):245-256
Nematic ordering in anisotropic non-Gaussian elastomers is considered theoretically using mean field approximation. We focus on the effect of anisotropy during network
cross-linking on the system elasticity and, in particular, on the so-called soft deformation mode. As the main result, we
calculate the dependence of the elastomer free energy on the angle between the axis of “frozen” anisotropy and the nematic
director. The dependence of the isotropic-nematic transition point on the orientational field acting on the monomers during
the cross-linking process is also calculated.
Received: 5 November 1997 / Revised and Accepted: 29 June 1998 相似文献
20.
H.P. Breuer B. Kappler F. Petruccione 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(1):9-13
A fast simulation algorithm for the calculation of multitime correlation functions of open quantum systems is presented. It
is demonstrated that any stochastic process which “unravels” the quantum Master equation can be used for the calculation of
matrix elements of reduced Heisenberg picture operators, and thus for the calculation of multitime correlation functions,
by extending the stochastic process to a doubled Hilbert space. The numerical performance of the stochastic simulation algorithm
is investigated by means of a standard example.
Received: 30 May 1997 / Revised: 4 November 1997 / Accepted: 7 November 1997 相似文献