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1.
A. Villesuzanne C. Elissalde M. Pouchard J. Ravez 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(3):307-312
We consider the interaction of an homogeneous polyelectrolyte with an obstacle during electrophoretic drift. We explicitly
take into account the hydrodynamic interactions generated by this mechanical trapping, and we evaluate their influence on
the unhooking process. Important qualitative effects are pointed out in low and moderate field regimes. However, numerical
simulations indicate that, in strong field, the existing simpler local force models, which neglect these hydrodynamic interactions,
are quantitatively acceptable.
Received: 18 March 1998 / Received in final form and accepted: 20 May 1998 相似文献
2.
K. Suematsu 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(1):93-100
We develop a new theory of gelation which takes into account (i) delay of the gel point and (ii) change of functionality due
to ring formation. We show that the problem of finding the gel point in real polymer solutions reduces to the problem of calculating
the total ring concentration and the extent of reaction of intermolecular reaction at the gel point. In this paper, we solve
a special case of this problem, on the basis of the independence assumption between intermolecular reaction and cyclization
which takes into account only (i) the delay of the gel point: making use of the asymptotic equality of the total ring concentration,
we acquire an approximate solution for the gel point Dc as a function of the inverse concentration , the relative frequency of cyclization and dimension d. Applying the observed values of in linear polyesters, the theoretical result reproduces well the Wile and the Gordon-Scantlebury observations, showing the
existence of a critical dilution beyond which gelation can not occur, and an asymptote . As the classical gel point is approached, the present theory reduces to the linear equation, which makes one-to-one correspondence
with the real slope , suggesting the inequality which is just what polymer chemists have quested for so far, with the physical meaning having remained unknown.
Receveid: 30 December 1997 / Revised: 28 May 1998 / Accepted: 12 June 1998 相似文献
3.
The density of the elastic energy of a deformed membrane in a liquid state is calculated. The thermodynamic equilibrium of
its different parts is taken into account. The shape equation of a closed membrane is deduced. The quantity which keeps its
value, when the variations of the energy of the system are calculated, is not the area of the deformed membrane, but its area
in the flat tension free state. Because of this, additional terms appear in the second variation around the stable state.
The case of a lipid bilayer and its fluctuations is examined for both free and blocked exchange of molecules between the monolayers,
comprising the bilayer.
Received 4 February 2002 / Received in final form 15 April 2002 Published online 2 October 2002
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ID="a"e-mail: bivas@issp.bas.bg 相似文献
4.
5.
V. Lesturgeon D. Durand T. Nicolai 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(1):83-91
Free radical co-polymerization of methyl methacrylate (MMA) and ethyl glycol dimethyl methacrylate (EGDMA) in solution leads
to the formation of polydisperse branched PMMA which grows in size until the system gels. The structure and the size distribution
of the PMMA aggregates were characterized at infinite dilution using static and dynamic light scattering and size exclusion
chromatography (SEC). The reaction extent was measured using SEC and Raman spectroscopy. The results show that the structure
and size distribution of PMMA aggregates formed close to the gel point are compatible with those of percolating clusters.
The structure factor of semi-dilute solutions of PMMA aggregates is the same as that of dilute solutions at distance scales
much smaller than the correlation length of the concentration fluctuations (). However, the cut-off function of the pair correlation function at for semi-dilute solutions is more gradual than the cut-off function at for dilute solutions.
Received 11 May 1998 and Received in final form 22 October 1998 相似文献
6.
7.
P.I.C. Teixeira E.M. Terentjev 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(2):237-245
We propose a microscopic model of a chiral polymer chain with permanent transverse dipoles interacting with an external electric
field. Its behaviour has been investigated by computer simulation in the limit of weak chirality. Large-scale (tertiary) helical
winding induced along the field direction has been found above a threshold field Ec, and the helix parameters have been calculated as functions of the field strength. Below Ec there is no coherent helical structure of the chain conformation. We find a characteristic scaling of the threshold and the
winding radius a with the chain bending modulus , and .
Received: 15 November 1997 / Accepted: 16 February 1998 相似文献
8.
R.R. Netz H. Orland 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,8(1):81-98
Variational methods are applied to a single polyelectrolyte chain. The polymer is modeled as a Gaussian chain with screened
electrostatic repulsion between all monomers. As a variational Hamiltonian, the most general Gaussian kernel, including the
possibility of a classical or mean polymer path, is employed. The resulting self-consistent equations are systematically solved
both for large and small monomer-monomer separations along the chain. In the absence of screening, the polymer is stretched
on average. It is described by a straight classical path with Gaussian fluctuations around it. If the electrostatic repulsion
is screened, the polymer is isotropically swollen for large separations, and for small separations the polymer correlation
function is calculated as an analytic expansion in terms of the monomer-monomer separation along the chain. The electrostatic
persistence length and the electrostatic blobsize are inferred from the crossover between distinct scaling ranges. We perform
a global analysis of the scaling behavior as a function of the screening length and electrostatic interaction strength , where is the Bjerrum length and A is the distance of charges along the polymer chain. We find three different scaling regimes. i) A Gaussian-persistent regime with Gaussian behavior at small, persistent behavior at intermediate, and isotropically swollen behavior at large length
scales. This regime occurs for weakly charged polymers and only for intermediate values of the screening length. The electrostatic
persistence length is defined as the crossover length between the persistent and the asymptotically swollen behavior and is given by and thus disagrees with previous (restricted) variational treatments which predict a linear dependence on the screening length
.ii) A Gaussian regime with Gaussian behavior at small and isotropically swollen behavior at large length scales. This regime occurs for weakly
charged polymers and/or strong screening, and the electrostatic repulsion between monomers only leads to subfluent corrections
to Gaussian scaling at small separations. The concept of a persistence length is without meaning in this regime. iii) A persistent regime , where the chain resembles a stretched rod on intermediate and small scales. Here the persistence length is given by the
original Odijk prediction, , if the overstretching of the chain is avoided. We also investigate the effects of a finite polymer length and of an additional
excluded-volume interaction, which modify the resultant scaling behavior. Applications to experiments and computer simulations
are discussed.
Received 24 December 1997 相似文献
9.
Schiessel H 《The European physical journal. E, Soft matter》2006,19(3):251-262
Roughly three quarters of eucaryotic DNA are tightly wrapped onto protein cylinders organized in so-called nucleosomes. Despite
this fact, the wrapped DNA cannot be inert since DNA is at the heart of many crucial life processes. We focus here on physical
mechanisms that might allow nucleosomes to perform a great deal of such processes, specifically 1) on unwrapping fluctuations
that give DNA-binding proteins access to the wrapped DNA portions without disrupting the nucleosome as a whole, 2) on corkscrew
sliding along DNA and some implications and on 3) tail-bridging-induced attraction between nucleosomes as a means of controlling
higher-order folding. 相似文献
10.
V. Yamakov A. Milchev G.M. Foo R.B. Pandey D. Stauffer 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):659-667
A coarse-grained off-lattice bead-spring model is used to reveal the complex dynamics of a polymer chain in a quenched porous
medium in the presence of an external field B. The behavior of the mean square displacement (MSD) of the center chain bead and that of the center of mass of the chain
as a function of time is studied at different values of the barrier concentration C, the field strength B and the chain length N. In a field, important information on the way in which chains move between obstacles and overcome them is gained from the
MSD vs. time analysis in the directions parallel and perpendicular to the flow. Instead of a steady approach to uniform drift-like
motion at low C, for sufficiently strong field B we observe logarithmic oscillations in the effective exponents describing the time dependence of the MSD along and perpendicular to field. A common nature of
this phenomenon with oscillatory behavior, observed earlier for biased diffusion of tracers on random lattices, is suggested.
Received 7 August 1998 相似文献
11.
12.
Schiessel H 《The European physical journal. E, Soft matter》2006,19(3):291-292
In this comment on the contribution of A. Lesne and J.-M. Victor I provide some additional ideas on the hypothesis that higher-order
chromatin structures stamp their marks on their small subunits. 相似文献
13.
J.F. Sadoc N. Rivier 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(2):309-318
Helices and dense packing of spherical objects are two closely related problems. For instance, the Boerdijk-Coxeter helix,
which is obtained as a linear packing of regular tetrahedra, is a very efficient solution to some close-packing problems.
The shapes of biological helices result from various kinds of interaction forces, including steric repulsion. Thus, the search
for a maximum density can lead to structures related to the Boerdijk-Coxeter helix. Examples are presented for the -helix structure in proteins and for the structure of the protein collagen, but there are other examples of helical packings
at different scales in biology. Models based on packing efficiency related to the Boerdijk-Coxeter helix, explain, mainly
from topological arguments, why the number of amino acids per turn is close to 3.6 in -helices and 2.7 in collagen.
Received 26 November 1998 and Received in final form 12 April 1999 相似文献
14.
The lifetime of the soliton in the improved Davydov model at the biological temperature 300 K for protein molecules 总被引:7,自引:0,他引:7
Pang Xiao-feng 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(2):297-316
We study the effects of quantum fluctuations and thermal perturbations on the lifetime of the soliton in the improved Davydov
model proposed by us with two-quanta and with an added interaction. By using quantum perturbation theory, we compute the soliton
lifetime for a wide ranges of parameter values relevant for protein molecules. The lifetime of the new soliton at the biological
temperature 300 K is of the order of 10-10 second or τ/τ≥ 500 for parameters appropriate to α-helical protein molecules. This shows clearly that the new soliton in the improved model
is a viable mechanism for the bio-energy transport in the α-helix region of proteins.
Received 7 January 1999 and Received in final form 16 August 2000 相似文献
15.
We present here a neutron reflectivity study of the influence of an alternative electric field on a supported phospholipid
double bilayer. We report for the first time a reproducible increase of the fluctuation amplitude leading to the complete
unbinding of the floating bilayer. Results are in good agreement with a semi-quantitative interpretation in terms of negative
electrostatic surface tension. 相似文献
16.
C.W. Maier A. Behrisch A. Kloboucek D.A. Simson R. Merkel 《The European physical journal. E, Soft matter》2001,6(4):273-276
We studied biomembrane adhesion using the micropipet aspiration technique. Adhesion was caused by contact site A, a laterally
mobile and highly specific cell adhesion molecule from Dictyostelium discoideum, reconstituted in lipid vesicles of DOPC (L-α-dioleoylphosphatidylcholine) with an addition of 5 mol % DOPE-PEG2000 (1,2-diacyl-sn-glycero-3-phosphatidylethanolamine-N-[poly(ethyleneglycol) 2000]). The “fuzzy” membrane mimics the cellular
plasma membrane including the glycocalyx. We found adhesion and subsequent receptor migration into the contact zone. Using
membrane tension jumps to probe the equation of state of the two-dimensional “gas” of bound receptor pairs within the contact
zone, we found strong, attractive lateral interactions.
Received 16 February 2001 相似文献
17.
W. Michalke S. Kreitmeier 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,4(4):469-473
The diffusion Quantum-Monte-Carlo method of solving the Schr?dinger equation is applied to the vibrational ground state of
a polyethylene molecule. The results for the ground state energy show good agreement with normal mode analysis. In addition
to stretching, bending and torsional interaction van-der-Waals interaction is applied to a single chain showing a decrease
of the energy of 5%. The decrease for a polyethylene system of 5 chains with 10 atoms per molecule at the positions of a unit
cell is determined to be 4.8% per molecule. Finally first steps towards simulating excited states were performed.
Received: 9 February 1998 / Revised: 2 April 1998 / Accepted: 23 April 1998 相似文献
18.
J. Nissen S. Gritsch G. Wiegand J.O. Rädler 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,10(2):335-344
We report on the wetting behavior of phospholipid membranes on solid surfaces immersed in aqueous solution. Using fluorescence
microscopy, the spreading velocity of fluid bilayers advancing from a lipid source is investigated. The kinetic spreading
coefficient was measured as a function of temperature for pure DMPC membranes and as a function of charge density and cholesterol
content for binary membranes. A theoretical model for the membrane flow is presented, which takes into account the liquid
crystalline bilayer architecture of the lipid membrane. The spreading power results from the membrane-solid VdW interaction
and is dissipated in hydrodynamic shear flow as well as by inter-monolayer friction within the bilayer. The frictional drag
causes a dynamic tension gradient in the spreading membrane, which is manifested by a single exponential decay of the fluorescence
intensity profile along the spreading direction. Obstacles are shown to act as pinning centers deforming the advancing line
interface. However, no depinning was observed, since the centers are circumflown without abrupt relaxation.
Received 6 November 1998 相似文献
19.
P. Dommersnes S. Straumsnes E.G. Flekkøy T. Nicolai S. Roux 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(4):669-677
We study the hydrodynamic properties of polymers and more generally self-similar structures using a new recursion model. The
hydrodynamic interaction between monomers is modeled by the standard Green's function of Stokes flow in which an ultrametric
distance is substituted for the usual Euclidean distance. This leads to a model where the long-range hydrodynamic interactions
and the long-range correlations of the polymer conformation can both be accounted for and yet allow for analytical solutions.
We explore the asymptotic as well as the finite size corrections to the scaling behavior with this model. In order to compare
the results of the present scheme with more conventional techniques a generalized version of the existing mean field results
by Kirkwood and Riseman for the hydrodynamic drag is introduced.
Received 26 August 1998 and Received in final form 7 December 1998 相似文献
20.
J. Jimenez R. Rajagopalan 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(2):237-243
We introduce a new simulation method, which we call the contact-distribution method, for the determination of the Helmholtz potential for polymer/colloid systems from lattice Monte-Carlo simulations. This
method allows one to obtain forces between finite or semi-infinite objects of any arbitrary shape and dimensions in the presence
of polymer chains in solution or physisorbed or chemisorbed at interfaces. We illustrate the application of the method using
two examples: (i) the interaction between the tip of an atomic force microscope (AFM) and a single, end-grafted polymer chain
and (ii) the interaction between an AFM tip and a polymer brush. Numerical results for the first two cases illustrate how
the method can be used to confirm and extend scaling laws for forces and Helmholtz potentials, to examine the effects of the
shapes and sizes of the objects and to examine conformational transitions in the polymer chains.
Received: 15 May 1998 / Revised: 11 June 1998 / Accepted: 12 June 1998 相似文献