共查询到20条相似文献,搜索用时 62 毫秒
1.
T. Russ R. Brenn F. Abel F. Boué M. Geoghegan 《The European physical journal. E, Soft matter》2001,4(4):419-433
We have used helium-3 nuclear reaction analysis to measure the interdiffusion of linear polystyrene into a film of crosslinked
polystyrene and the intradiffusion of polystyrene in polystyrene networks. The interdiffusion is compared with that predicted
from the Kramer-Sillescu theory, and is found to be considerably faster. This is attributed to the relaxation of inhomogeneities
in the network. The molecular weight and crosslinking dependence of the intradiffusion coefficients of free polystyrene chains
trapped inside networks is discussed in terms of the simple tube model and provides reasonably good agreement with that predicted
from reptation theory.
Received 2 August 2000 and Received in final form 6 November 2000 相似文献
2.
S. F. Ban L. S. Geng W. H. Long J. Meng J. Peng J. M. Yao S. Q. Zhang S. G. Zhou 《The European physical journal. Special topics》2007,150(1):139-144
The recent progress of the relativistic many-body approach
by the group at Peking University will be reviewed. In particular,
axially deformed relativistic Hartree-Bogoliubov approach in
Woods-Saxon basis aiming at halo nucleus, time-odd triaxial RMF
approach, the adiabatic and configuration-fixed constrained triaxial
RMF approaches, a Reflection ASymmetric RMF (RAS-RMF) approach, and
a new relativistic Hartree-Fock (RHF) approach with
density-dependent σ,ω,ρ and π meson-nucleon
couplings for finite nuclei and nuclear matter, will be highlighted. 相似文献
3.
Hutchings LR Richards RW Thompson RL Bucknall DG 《The European physical journal. E, Soft matter》2002,8(2):121-128
High-molecular-weight heterotelechelic deuteriopolystyrene, NDPSF, possessing an amine functional group at one end of the
chain and a fluorocarbon group at the other was tethered to a silicon substrate by its amine functional group. These layers
were coated with an unfunctionalised polystyrene matrix, HPS, such that the total film thickness covered a range from 2.2
to 9 times the radius of gyration of NDPSF. The detailed distribution of the polymers after annealing for times much greater
than the reptation period of either of the components, was obtained using neutron reflectometry. No evidence for bridging
of the two interfaces was found for the thicker films, but the finite concentration of the NDPSF polymer observed for the
thinnest films may be due to bridging since the energy gain of the fluorocarbon end is just greater than the loss due to configurational
entropy losses. A linear increase in the ellipsometric thickness of the excess of NDPSF at the substrate was discovered and
we attribute this to the NDPSF slowly being leached out of the layer initially at the substrate followed by diffusion into
the bulk of the film. The concentration profiles obtained are consistent with hindered relaxation of the large NDPSF molecules,
when they are tethered at the substrate or at the vacuum surface.
Received 21 August 2001 and Received in final form 7 January 2002 相似文献
4.
Economic small-world behavior in weighted networks 总被引:25,自引:0,他引:25
V. Latora M. Marchiori 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(2):249-263
The small-world phenomenon has been already the subject of a huge variety of papers, showing its appeareance in a variety
of systems. However, some big holes still remain to be filled, as the commonly adopted mathematical formulation is valid only
for topological networks. In this paper we propose a generalization of the theory of small worlds based on two leading concepts,
efficiency and cost, and valid also for weighted networks. Efficiency measures how well information propagates over the network,
and cost measures how expensive it is to build a network. The combination of these factors leads us to introduce the concept
of economic small worlds, that formalizes the idea of networks that are “cheap” to build, and nevertheless efficient in propagating information, both
at global and local scale. In this way we provide an adequate tool to quantitatively analyze the behaviour of complex networks
in the real world. Various complex systems are studied, ranging from the realm of neural networks, to social sciences, to
communication and transportation networks. In each case, economic small worlds are found. Moreover, using the economic small-world
framework, the construction principles of these networks can be quantitatively analyzed and compared, giving good insights
on how efficiency and economy principles combine up to shape all these systems.
Received 6 November 2002 / Received in final form 24 January 2003 Published online 1st April 2003
RID="a"
ID="a"e-mail: latora@ct.infn.it 相似文献
5.
S.T. Hyde S. Ramsden 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,31(2):273-284
We demonstrate the usefulness of two-dimensional hyperbolic geometry as a tool to generate three-dimensional Euclidean (E3) networks. The technique involves projection of edges of tilings of the hyperbolic plane (H2) onto three-periodic minimal surfaces, embedded in E3. Given the extraordinary wealth of symmetries commensurate with H2, we can generate networks in E3 that are difficult to construct otherwise. In particular, we form four-, five- and seven-connected (E3) nets containing three- and five-rings, viz. (3, 7), (5, 4) and (5, 5) tilings in H2.
Received 14 January 2002 / Received in final form 12 August 2002 Published online 4 February 2003
RID="a"
ID="a"e-mail: stephen.hyde@anu.edu.au 相似文献
6.
Epidemic outbreaks in complex heterogeneous networks 总被引:23,自引:0,他引:23
Y. Moreno R. Pastor-Satorras A. Vespignani 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(4):521-529
We present a detailed analytical and numerical study for the spreading of infections with acquired immunity in complex population
networks. We show that the large connectivity fluctuations usually found in these networks strengthen considerably the incidence
of epidemic outbreaks. Scale-free networks, which are characterized by diverging connectivity fluctuations in the limit of
a very large number of nodes, exhibit the lack of an epidemic threshold and always show a finite fraction of infected individuals.
This particular weakness, observed also in models without immunity, defines a new epidemiological framework characterized
by a highly heterogeneous response of the system to the introduction of infected individuals with different connectivity.
The understanding of epidemics in complex networks might deliver new insights in the spread of information and diseases in
biological and technological networks that often appear to be characterized by complex heterogeneous architectures.
Received 20 September 2001 and Received in final form 4 February 2002 相似文献
7.
S. Mangenot E. Raspaud C. Tribet L. Belloni F. Livolant 《The European physical journal. E, Soft matter》2002,7(3):221-231
Interactions between isolated nucleosome core particles are studied as a function of the monovalent salt concentration by
osmometry and by electrophoretic mobility measurements. The data are compared to the measurements performed on the protein-free
DNA fragments and also analysed using the conventional theoretical approach. At low salt, an electrostatic screening effect
accounts for the variation of the second virial coefficient whereas the simple hard-core contribution becomes predominant
at high salt. In the intermediate range, an attraction occurs. In the light of previous results (Mangenot et al. Biophys. J. 82, 345 (2002)), we show that the flexible basic proteic tails are responsible for this attraction. A tail-bridging effect is
discussed.
Received 4 October 2001 相似文献
8.
The configuration-dependent cranked Nilsson-Strutinsky approach has been employed to study the properties and band structures
at high spin in the Z = N odd-odd nuclei 46V and 50Mn. The observed bands are explained and terminating states are confirmed by the calculations. The calculated and observed
bands are in good agreement without normalization, especially for terminating states. Possible bands with rotation around
the intermediate axis and the effect of γ-deformation on the total energy of several interesting configurations are discussed.
Received: 2 April 2002 / Accepted: 27 January 2003 / Published online: 15 April 2003 相似文献
9.
G.J. Rodgers K. Darby-Dowman 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,23(2):267-271
We study a number of properties of a simple random growing directed network which can be used to model real directed networks
such as the world-wide web and call graphs. We confirm numerically that the distributions of in- and out-degree are consistent
with a power law, in agreement with previous analytical results and with empirical measurements from real graphs. We study
the distribution and mean of the minimum path length, the high degree nodes, the appearance and size of the giant component
and the topology of the nodes outside the giant component. These properties are compared with empirical studies of the world-wide
web.
Received 15 June 2001 and Received in final form 12 July 2001 相似文献
10.
Y. Kafri D. Mukamel L. Peliti 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(1):135-146
Existing experimental studies of the thermal denaturation of DNA yield sharp steps in the melting curve suggesting that the
melting transition is first order. This transition has been theoretically studied since the early sixties, mostly within an
approach in which the microscopic configurations of a DNA molecule consist of an alternating sequence of non-interacting bound
segments and denaturated loops. Studies of these models neglect the repulsive, self-avoiding, interaction between different
loops and segments and have invariably yielded continuous denaturation transitions. In the present study we take into account
in an approximate way the excluded-volume interaction between denaturated loops and the rest of the chain. This is done by
exploiting recent results on scaling properties of polymer networks of arbitrary topology. We also ignore the heterogeneity
of the polymer. We obtain a first-order melting transition in d = 2 dimensions and above, consistent with the experimental results. We also consider within our approach the unzipping transition,
which takes place when the two DNA strands are pulled apart by an external force acting on one end. We find that the under
equilibrium condition the unzipping transition is also first order. Although the denaturation and unzipping transitions are
thermodynamically first order, they do exhibit critical fluctuations in some of their properties. For instance, the loop size
distribution decays algebraically at the transition and the length of the denaturated end segment diverges as the transition
is approached. We evaluate these critical properties within our approach.
Received 21 August 2001 and Received in final form 26 January 2002 相似文献
11.
V.A. Kholodnyi 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(2):229-238
Although symmetries play a major role in physics, their use in finance is relatively new and, to the best of our knowledge,
can be traced to 1995 when Kholodnyi introduced the beliefs-preferences gauge symmetry. One of the main outcomes of the beliefs-preferences
gauge symmetry is that it allows for the valuation and dynamic replication of contingent claims in a general market environment,
that is, in the case of a general, not necessarily diffusion Markov process for the prices of underlying securities. This
valuation and dynamic replication is based on the novel ideas of symmetry in contrast to the standard approach which uses
stochastic analysis. The practical applications of the beliefs-preferences gauge symmetry range from the detection of a new
type of true arbitrage to the beliefs-preferences-independent valuation and dynamic replication of contingent claims in a
general market environment.
Received 31 December 2001 相似文献
12.
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
13.
D. T. Khoa 《The European physical journal. Special topics》2007,150(1):31-34
DWBA analysis of the inelastic 30-40S(p,p') and
18-22O(p,p') scattering data measured in the inverse kinematics has been
performed to determine the isoscalar (δ0) and isovector (δ1)
deformation lengths of the 2+1 excitations in the Sulfur and Oxygen isotopes
using a compact folding approach. A systematic N-dependence of δ0 and
δ1 has been established which shows a link between δ1 and the
neutron-shell closure. Strong isovector deformations were found in several
cases, e.g., the 2+1 state in 20O where δ1 is nearly three
times larger than δ0. These results confirm the relation
δ1>δ0 anticipated from the core polarization by the valence
neutrons in the open-shell (neutron rich) nuclei. The effect of neutron shell
closure at N=14 or 16 has been discussed based on the folding model analysis
of the inelastic 22O+p scattering data at 46.6 MeV/u measured recently at
GANIL. 相似文献
14.
D. O. Odero 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(1):3-8
The time-dependent treatment of positron-hydrogen scattering for a zero total angular momentum has been presented. The initial
wavefunction of the positron-hydrogen scattering system has been expanded in terms of three dimensional dynamical wave functions
to include all higher angular momenta by solving a set of three coupled differential equations. This wavefunction is then
time evolved using Taylor series expansion of the evolution operator. The excitation probabilities are monitored as the wavefunction
propagates until there is no more change in the probabilities. The positron impact excitation cross-sections extracted from
the final wavefunction are compared with the available results of converged close coupling approach.
Received 23 July 2001 and Received in final form 25 November 2001 相似文献
15.
L.F. Chibotaru A. Ceulemans G. Teniers V. Bruyndoncx V.V. Moshchalkov 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,27(3):341-346
An approach to the Ginzburg-Landau problem of superconducting polygons is developed, based on the exact fulfillment of superconducting
boundary conditions along the boundary of the sample. To this end an analytical gauge transformation for the vector potential
A is found which gives A
n = 0 for the normal component along the boundary line of an arbitrary regular polygon. The use of the new gauge reduces the
Ginzburg-Landau problem of superconducting polygons in external magnetic fields to an eigenvalue problem in a basis set of
functions obeying Neumann boundary conditions. The advantages of this approach, especially for low magnetic fields, are illustrated
and novel vortex patterns are obtained which can be probed experimentally.
Received 28 February 2002 and Received in final form 12 April 2002 Published online 6 June 2002 相似文献
16.
D. Stauffer A. Aharony L. da Fontoura Costa J. Adler 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):395-399
Neural networks are supposed to recognise blurred images (or patterns) of N pixels (bits) each. Application of the network to an initial blurred version of one of P pre-assigned patterns should converge to the correct pattern. In the “standard" Hopfield model, the N “neurons” are connected to each other via N2 bonds which contain the information on the stored patterns. Thus computer time and memory in general grow with N2. The Hebb rule assigns synaptic coupling strengths proportional to the overlap of the stored patterns at the two coupled
neurons. Here we simulate the Hopfield model on the Barabási-Albert scale-free network, in which each newly added neuron is
connected to only m other neurons, and at the end the number of neurons with q neighbours decays as 1/q
3. Although the quality of retrieval decreases for small m, we find good associative memory for 1 ≪ m ≪ N. Hence, these networks gain a factor N/m ≫ 1 in the computer memory and time.
Received 12 January 2003 Published online 11 April 2003
RID="a"
ID="a"e-mail: stauffer@thp.uni-koeln.de 相似文献
17.
V.I. Yukalov 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(4):609-617
A novel approach to analyzing time series generated by complex systems, such as markets, is presented. The basic idea of the
approach is the Law of Self-Similar Evolution, according to which any complex system develops self-similarly. There always exist some internal laws governing the evolution
of a system, say of a market, so that each of such systems possesses its own character regulating its behaviour. The problem
is how to discover these hidden internal laws defining the system character. This problem can be solved by employing the self-similar approximation theory, which supplies the mathematical foundation for the law of self-similar evolution. In this report, the theoretical basis
of the new approach to analyzing time series is formulated, with an accurate explanation of its principal points.
Received 15 August 2000 相似文献
18.
E. Ben-Naim P.L. Krapivsky 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):239-243
We study an elementary two-player card game where in each round players compare cards and the holder of the card with the
smaller value wins. Using the rate equations approach, we treat the stochastic version of the game in which cards are drawn
randomly. We obtain an exact solution for arbitrary initial conditions. In general, the game approaches a steady state where
the card value densities of the two players are proportional to each other. The leading small value behavior of the initial
densities determines the corresponding proportionality constant, while the next correction governs the asymptotic time dependence.
The relaxation toward the steady state exhibits a rich behavior, e.g., it may be algebraically slow or exponentially fast. Moreover, in ruin situations where one player eventually wins all cards,
the game may even end in a finite time.
Received 24 August 2001 and Received in final form 12 November 2001 相似文献
19.
The elastic anisotropy of nematic elastomers 总被引:2,自引:0,他引:2
We examine the robustness of order in nematic elastomers under mechanical strains imposed along and perpendicularly to the
director when director rotation is prohibited. In contrast to electric and magnetic fields applied to conventional nematics,
mechanical fields are shown theoretically and experimentally to greatly affect the degree of nematic order and related quantities.
Unlike in liquid nematics, one can impose fields perpendicular to the director, thereby inducing biaxial order which should
be susceptible to experimental detection. Nematic elastomers with unchanging director and degree of order should theoretically
have the same elastic moduli for longitudinal and transverse extensions. This is violated when nematic order is permitted
to relax in response to strains. Near the transition we predict the longitudinal modulus to be smaller than the transverse
modulus; at lower temperatures the converse is true, with a crossover a few degrees below the transition. The differences
are ascribed to the different temperature dependence of the stiffness of uniaxial and biaxial order. We synthesised side chain
single-crystal nematic polymer networks, performed DSC, X-ray, birefringence, and thermo-mechanical characterisations, and
then obtained linear moduli from stress-strain measurements.
Received 29 September 2000 相似文献
20.
Mattioni L Wittmer JP Baschnagel J Barrat JL Luijten E 《The European physical journal. E, Soft matter》2003,10(4):369-385
Correlations in the motion of reptating polymers in a melt are investigated by means of Monte Carlo simulations of the three-dimensional
slithering-snake version of the bond-fluctuation model. Surprisingly, the slithering-snake dynamics becomes inconsistent with
classical reptation predictions at high chain overlap (created either by chain length N or by the volume fraction φ of occupied lattice sites), where the relaxation times increase much faster than expected. This
is due to the anomalous curvilinear diffusion in a finite time window whose upper bound (N) is set by the density of chain ends φ/N. Density fluctuations created by passing chain ends allow a reference polymer to break out of the local cage of immobile
obstacles created by neighboring chains. The dynamics of dense solutions of “snakes” at t ≪ is identical to that of a benchmark system where all chains but one are frozen. We demonstrate that the subdiffusive dynamical
regime is caused by the slow creeping of a chain out of its correlation hole. Our results are in good qualitative agreement
with the activated-reptation scheme proposed recently by Semenov and Rubinstein (Eur. Phys. J. B, 1 (1998) 87). Additionally, we briefly comment on the relevance of local relaxation pathways within a slithering-snake scheme.
Our preliminary results suggest that a judicious choice of the ratio of local to slithering-snake moves is crucial to equilibrate
a melt of long chains efficiently.
Received: 18 December 2002 / Accepted: 3 April 2003 / Published online: 12 May 2003
RID="a"
ID="a"e-mail: jwittmer@dpm.univ-lyon1.fr
RID="b"
ID="b"Current address: University of Illinois at Urbana-Champaign. 相似文献