共查询到20条相似文献,搜索用时 31 毫秒
1.
M. Ouarch M. Benhamou M. Chahid H. Kaidi 《The European physical journal. E, Soft matter》2009,29(3):319-327
We consider bilayer biomembranes or surfactants made of two chemically incompatible amphiphile molecules, which may laterally
or transversely phase separate into macrodomains, upon variation of some suitable parameter (temperature, lateral pressure,
etc.). The purpose is an extensive study of the dynamics of both lateral and transverse phase separations, when the bilayer
is suddenly cooled down from a high initial temperature towards a final one very close to the spinodal point. The critical
dynamics are investigated through the partial dynamic structure factors of different species. Using a two-order parameter
field theory, where the two fields are the composition fluctuations of one component in the leaflets of the bilayer, combined
with an extended van Hove approach that is based on two coupled Langevin equations (with noise), we exactly compute these dynamic structure factors. We first find that the dynamics is governed by two time scales. The longest one,
, can be related to the thermal correlation length,
| T - T
c|-1/2 , by
, with the dynamic critical exponent z = 4 , where is an atomic length scale, T the absolute temperature, and Tc its critical value. The characteristic time can be interpreted as the time required for the formation of the final macrophase domains. The second time scale is rather
shorter, and can be viewed as the short time during which the unlike phospholipids execute local motion. Second, we demonstrate
that the dynamic structure factors obey exact scaling laws, and depend on three lengths, namely the wavelength q-1 (q is the wave vector modulus), the correlation length , and a length scale R(t)
t
1/z (z = 4representing the size of macrophase domains at time t . Of course, the two lengths and R(t) coincide at the final time at which the bilayer reaches its final equilibrium state. Finally, the present work must be considered as a natural extension
of our previously published one dealing with the study of lateral and transverse phase separations from a static point of
view. 相似文献
2.
M. K. Kirejczyk 《The European Physical Journal A - Hadrons and Nuclei》2009,41(2):141-143
The -variable, a measure of statistical correlation of particle momenta, introduced by Mrówczyński and Gaździcki, has been calculated
for the events simulated with a simple thermal toy model. It is shown that mixing two thermal sources of unequal temperature
can result in negative values of . 相似文献
3.
After deriving the projected stress tensor in cylindrical geometry for a fluid membrane described by the Helfrich Hamiltonian,
we calculate the average force f exerted by a thermally fluctuating nanotubule of radius R , and its standard deviation
f . We obtain f and
f in terms of the internal membrane tension , the bending rigidity , the temperature k
B
T and a molecular cutoff . We find for f a shift ∼ 1/ with respect to the mean field behavior ∼ . We obtain (
f )2 ∼ R ln(R/b) where b is a molecular length,
f being typically small compared to f . Taking into account the difference between the internal tension and the actual mechanical tension applied to the membrane from which the tubule is drawn, we discuss the amplitude of the fluctuation-induced corrections to
the average force. Our results, obtained in the harmonic approximation, hold for tubules with aspect ratio not larger than
200 , of radius significantly smaller than 100nm, that are connected to a large membrane reservoir, e.g., a giant vesicle. 相似文献
4.
Microwave propagation parameters in magnetic fluids 总被引:1,自引:0,他引:1
P. C. Fannin I. Malaescu C. N. Marin N. Stefu 《The European physical journal. E, Soft matter》2009,29(3):299-303
Complex dielectric permittivity and complex magnetic permeability measurements of two magnetic fluids (as microwave propagation
media), in the approximate range 0.2-5GHz were performed. The two samples consisted of magnetite nanoparticles, dispersed
in kerosene and in water, respectively. Based on the dielectric and magnetic measurements, the frequency (f ) dependence of the attenuation parameter, , the phase constant, , the propagation constant, , the intrinsic impedance, Zm, the refractive index, n , the reflection coefficient, R , the wavelength, and the skin depth, , of the investigated samples were determined. 相似文献
5.
We study the thermophoretic coefficient DT of a charged colloid. The non-uniform electrolyte is characterized in terms of densities and diffusion currents of mobile
ions. The hydrodynamic treatment in the vicinity of a solute particle relies on the Hückel approximation, which is valid for
particles smaller than the Debye length, a ≪ . To leading order in the parameter a/ , we find that the coefficient DT consists of two contributions, a dielectrophoretic term proportional to the permittivity derivative d/dT , and a Seebeck term, i.e., the macroscopic electric field induced by the thermal gradient in the electrolyte solution. Depending on the particle valency,
these terms may take opposite signs, and their temperature dependence may result in a change of sign of thermophoresis, as
observed in several recent experiments. 相似文献
6.
Shao-Long Chen Xiao-Gang He Xue-Peng Hu Yi Liao 《The European Physical Journal C - Particles and Fields》2009,60(2):317-321
An unparticle
with scaling dimension
has peculiar thermal properties due to its unique phase space structure. We find that the equation of state parameter
, the ratio of pressure to energy density, is given by
providing a new form of energy in our universe. In an expanding universe, the unparticle energy density
evolves dramatically differently from that for photons. For
, even if
at a high decoupling temperature T
D is very small, it is possible to have a large relic density
at present photon temperature T
γ
0, large enough to play the role of dark matter. We calculate T
D and
using photon–unparticle interactions for illustration. 相似文献
7.
M. W. Matsen J. U. Kim A. E. Likhtman 《The European physical journal. E, Soft matter》2009,29(1):107-115
This paper addresses the statistical mechanics of ideal polymer chains next to a hard wall. The principal quantity of interest,
from which all monomer densities can be calculated, is the partition function, G
N(z) , for a chain of N discrete monomers with one end fixed a distance z from the wall. It is well accepted that in the limit of infinite N , G
N(z) satisfies the diffusion equation with the Dirichlet boundary condition, G
N(0) = 0 , unless the wall possesses a sufficient attraction, in which case the Robin boundary condition, G
N(0) = -
G
N
′(0) , applies with a positive coefficient, . Here we investigate the leading N
-1/2 correction,
G
N(z) . Prior to the adsorption threshold,
G
N(z) is found to involve two distinct parts: a Gaussian correction (for z
aN
1/2 with a model-dependent amplitude, A , and a proximal-layer correction (for z
a described by a model-dependent function, B(z) . 相似文献
8.
The effect of confinement in the segmental relaxation of polymers is considered. On the basis of a thermodynamic model we
discuss the emerging relevance of the fast degrees of freedom in stimulating the much slower segmental relaxation, as an effect
of the constraints at the walls of the amorphous regions. In the case that confinement is due to the presence of crystalline
domains, a quasi-Poissonian distribution of local constraining conditions is derived as a result of thermodynamic equilibrium.
This implies that the average free-energy barrier
F for conformational rearrangement is of the same order of the dispersion of the barrier heights, (
F) , around
F . As an example, we apply the results to the analysis of the -relaxation as observed by dielectric broad-band spectroscopy in semicrystalline poly(ethylene terephthalate) cold-crystallized
from either an isotropic or an oriented glass. It is found that in the latter case the regions of cooperative rearrangement
are significantly larger than in the former. 相似文献
9.
E. Akkermans 《The European physical journal. E, Soft matter》2009,28(2):199-204
The storage and transmission of information is well defined using the notions of entropy, mutual information and channel capacity
as formalized by Shannon. These quantities are calculated for a quantum mesoscopic system in terms of scattering parameters.
For a one-dimensional system, the mutual information is related to the thermal conductance. This relation allows to show that
for an incident signal of power P, the channel capacity C has a universal upper bound given by C
independent of quantum statistics. A general framework is proposed which makes use of a natural underlying symplectic structure,
to relate the entropy of a quantum mesoscopic system to the scattering matrix. 相似文献
10.
Nikolay M. Nikolov Karl-Henning Rehren Ivan Todorov 《Communications in Mathematical Physics》2008,279(1):225-250
The twist two contribution in the operator product expansion of for a pair of globally conformal invariant, scalar fields of equal scaling dimension d in four space–time dimensions is a field V
1 (x1, x2) which is harmonic in both variables. It is demonstrated that the Huygens bilocality of V
1 can be equivalently characterized by a “single–pole property” concerning the pole structure of the (rational) correlation
functions involving the product . This property is established for the dimension d = 2 of . As an application we prove that any system of GCI scalar fields of conformal dimension 2 (in four space–time dimensions)
can be presented as a (possibly infinite) superposition of products of free massless fields. 相似文献
11.
S. T. T. Ollila K. F. Luo T. Ala-Nissila S. -C. Ying 《The European physical journal. E, Soft matter》2009,28(4):385-393
Using Langevin dynamics simulations, we investigate the translocation dynamics of an externally driven polymer chain through
a nanopore, where a pulling force F is exerted on the first monomer whilst there is an opposing force F
E < F within the pore. Such a double-force arrangement has been proposed recently to allow better dynamical control of the translocation
process in order to sequence biopolymers. We find that in the double-force arrangement translocation becomes slower as compared
to the case under a single monomer pulling force of magnitude F - F
E , but scaling of the translocation time as a function of the chain length ∼ N
2 does not change. The waiting time (m) for monomer m to exit the pore is found to be a monotonically increasing function of the bead number almost until m
N , which indicates relatively well-defined slowing down and control of the chain velocity during translocation. We also study
the waiting time distributions for the beads in the chain, and characterize in detail fluctuations in the bead positions and
their transverse position coordinates during translocation. These data should be useful in estimating position-dependent sequencing
errors in double-force experiments. 相似文献
12.
M. Gross M. Lesaffre F. Ramaz P. Delaye G. Roosen A. C. Boccara 《The European physical journal. E, Soft matter》2009,28(2):173-182
When -lactoglobulin in low p H aqueous solutions is exposed to high temperature for extended time, spherulites composed of amyloid fibrils of the -lactoglobulin protein form. Many of these spherulites have fibrils that radiate out from a centre and, under crossed polarisers,
exhibit a symmetric Maltese Cross structure. However, a significant fraction (50 of the 101 observed spherulites) of -lactoglobulin spherulites formed under these conditions demonstrate various forms of irregularity in apparent structure.
The irregularities of spherulites structures were qualitatively investigated by comparing optical microscopy images observed
under crossed polarisers to computationally produced images of various internal structures. In this way, inner spherulite
structures are inferred from microscopy images. Modelled structures that were found to produce computed images similar to
some of the experimentally viewed images include fibrils curving as they radiate from a single nucleation point; multiple
spherulites nucleating in close proximity to one another; and fibrils curving in opposite directions above and below a single
nucleation point. 相似文献
13.
J. J. Liétor-Santos C. Kim P. J. Lu A. Fernández-Nieves D. A. Weitz 《The European physical journal. E, Soft matter》2009,28(2):159-164
We study the compression of depletion gels under the influence of a gravitational stress by monitoring the time evolution
of the gel interface and the local volume fraction, , inside the gel. We find is not constant throughout the gel. Instead, there is a volume fraction gradient that develops and grows along the gel height
as the compression process proceeds. Our results are correctly described by a non-linear poroelastic model that explicitly
incorporates the -dependence of the gravitational, elastic and viscous stresses acting on the gel. 相似文献
14.
Zhi-Gang Wang 《The European Physical Journal C - Particles and Fields》2009,61(2):321-329
We calculate the masses and the pole residues of the
heavy baryons Ω
c
0(css) and Ω
b
−(bss) with the QCD sum rules. The numerical values
GeV (or
GeV) and
GeV (or
GeV) are in good agreement with the experimental data. 相似文献
15.
S. Abd El-Samad R. Bilger K. -Th. Brinkmann H. Clement M. Dietrich E. Doroshkevich S. Dshemuchadse K. Ehrhardt A. Erhardt W. Eyrich A. Filippi H. Freiesleben M. Fritsch R. Geyer A. Gillitzer J. Hauffe D. Hesselbarth R. Jaekel B. Jakob L. Karsch K. Kilian J. Kress E. Kuhlmann S. Marcello S. Marwinski R. Meier K. M?ller H. P. Morsch L. Naumann J. Ritman E. Roderburg P. Sch?nmeier M. Schulte-Wissermann W. Schroeder F. Stinzing G. Y. Sun J. W?chter G. J. Wagner M. Wagner U. Weidlich A. Wilms S. Wirth G. Zhang P. Zupranski 《The European Physical Journal A - Hadrons and Nuclei》2009,39(3):281-289
The single-pion production reactions pp
d
, pp
np
and pp
pp
were measured at a beam momentum of 0.95GeV/c ( T
p
400 MeV) using the short version of the COSY-TOF spectrometer. The central calorimeter provided particle identification,
energy determination and neutron detection in addition to time-of-flight and angle measurements from other detector parts.
Thus all pion production channels were recorded with 1-4 overconstraints. The main emphasis is put on the presentation and
discussion of the np
channel, since the results on the other channels have already been published previously. The total and differential cross-sections
obtained are compared to theoretical calculations. In contrast to the pp
channel we observe in the np
channel a strong influence of the excitation. In particular, the pion angular distribution exhibits a (3 cos2
+ 1) -dependence, typical for a pure s -channel excitation and identical to that observed in the d
channel. Since the latter is understood by a s -channel resonance in the 1
D
2
pn partial wave, we discuss an analogous scenario for the pn
channel. 相似文献
16.
Gauhar Abbas B. Ananthanarayan 《The European Physical Journal A - Hadrons and Nuclei》2009,41(1):7-11
We obtain stringent bounds in the 〈r
2
-c plane where these are the scalar radius and the curvature parameters of the scalar K
form factor, respectively, using analyticity and dispersion relation constraints, the knowledge of the form factor from the
well-known Callan-Treiman point , as well as at , which we call the second Callan-Treiman point. The central values of these parameters from a recent determination are accomodated
in the allowed region provided the higher loop corrections to the value of the form factor at the second Callan-Treiman point
reduce the one-loop result by about 3% with . Such a variation in magnitude at the second Callan-Treiman point yields 0.12 fm2
〈r
2
0.21 fm2and 0.56 GeV-4
c
1.47 GeV-4and a strong correlation between them. A smaller value of shifts both bounds to lower values. 相似文献
17.
Benhamou M Himmi M Benzouine F Bettachy A Derouiche A 《The European physical journal. E, Soft matter》2004,13(4):353-358
We re-examine here the computation of the effective force between two star-polymers of respective numbers of branches f1 and f2, immersed in a common
-solvent. Such a force originates essentially from the repulsive three-body interactions. To achieve this, we take advantage of some established results using renormalization theory for three-dimensional star-polymers, or conformal invariance for two-dimensional ones. We first show that, in dimension d = 3, the force,
, decreases with the center-to-center distance r as
, with the exact universal amplitude
. Second, in dimension d = 2, we find that the force decays more slowly as
, with the exact universal amplitude
. For high distances compared to the gyration radius,
, of a single polymer chain at the
-point, an exponential decay of the force is expected.Received: 3 February 2004, Published online: 24 May 2004PACS:
61.25.Hq Macromolecular and polymer solutions; polymer melts; swelling - 05.20.-y Classical statistical mechanics 相似文献
18.
M. V. Polyakov K. M. Semenov-Tian-Shansky 《The European Physical Journal A - Hadrons and Nuclei》2009,40(2):181-198
We establish a link between the dual parametrization of GPDs and a popular parametrization based on the double distribution
Ansatz, which is in prevalent use in phenomenological applications. We compute several first forward-like functions that express
the double distribution Ansatz for GPDs in the framework of the dual parametrization and show that these forward-like functions
make the dominant contribution into the GPD quintessence function. We also argue that the forward-like functions with
1 contribute to the leading singular small-xBj behavior of the imaginary part of DVCS amplitude. This makes the small-xBj behavior of independent of the asymptotic behavior of PDFs. Assuming analyticity of Mellin moments of GPDs in the Mellin space we are
able to fix the value of the D -form factor in terms of the GPD quintessence function N(x, t) and the forward-like function Q
0(x, t) . 相似文献
19.
A. Majethiya B. Patel P. C. Vinodkumar 《The European Physical Journal A - Hadrons and Nuclei》2008,38(3):307-315
Properties of single heavy flavor baryons in a non-relativistic potential model with colour Coulomb plus a power law confinement
potential have been studied using a simple variational method. The ground-state masses of single heavy baryons and the mass
difference between the J
P =
+ and J
P =
+ states are computed using a spin-dependent two-body potential. Using the spin-flavour structure of the constituting quarks
and by defining an effective confined mass of the constituent quarks within the baryons, the magnetic moments are computed.
The masses and magnetic moments of the single heavy baryons are found to be in accordance with the existing experimental values
and with other theoretical predictions. It is found that an additional attractive interaction of the order of -200 MeV is
required for the antisymmetric states of (Q
c, b) . It is also found that the spin-hyperfine interaction parameters play a decisive role in hadron spectroscopy. 相似文献
20.
We discuss one of the most prominent features of the very recent preliminary elliptic flow data of J/ψ-mesons from the PHENIX Collaboration (PHENIX Collaboration (C. Silvestre), arXiv:0806.0475 [nucl-ex]). Even within the
rather large error bars of the measured data a negative elliptic flow parameter (v2) for J/ψ in the range of p
T = 0.5-2.5 GeV/c is visible. We argue that this negative elliptic flow at intermediate pT is a clear and qualitative signature for the collectivity of charm quarks produced in nucleus-nucleus reactions at RHIC.
Within a parton recombination approach we show that a negative elliptic flow puts a lower limit on the collective transverse
velocity of heavy quarks. The numerical value of the transverse flow velocity for charm quarks that is necessary to reproduce the data is (charm) ∼ 0.55-0.6c and therefore compatible with the flow of light quarks. 相似文献