共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
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
RID="a"
ID="a"e-mail: bivas@issp.bas.bg 相似文献
3.
Equilibrium phase coexistence between two chemical species implies the equality of the chemical potentials and of the osmotic
pressures. We study this problem on a deformable membrane when one type of the molecules serves as anchor for polymeric chains
immersed in the surrounding medium (considered as a good solvent). We derive the general conditions for phase coexistence
when both the curvature of the membrane and the density field of the anchor molecule are free to adjust themselves. We show
that curvature favors phase segregation. Our model predicts that membranes decorated with polymeric chains exhibit new shape
bifurcations without equivalent in fixed density systems.
Received: 26 November 2002 / Accepted: 2 April 2003 / Published online: 12 May 2003
RID="a"
ID="a"e-mail: nicolas@drfmc.ceng.cea.fr
RID="b"
ID="b"e-mail: bfourcade@cea.fr 相似文献
4.
The adhesion of fluid vesicles at chemically structured substrates is studied theoretically via Monte Carlo simulations. The
substrate surface is planar and repels the vesicle membrane apart from a single surface domain γ , which strongly attracts
this membrane. If the vesicle is larger than the attractive γ domain, the spreading of the vesicle onto the substrate is restricted
by the size of this surface domain. Once the contact line of the adhering vesicle has reached the boundaries of the γ domain,
further deflation of the vesicle leads to a regime of low membrane tension with pronounced shape fluctuations, which are now
governed by the bending rigidity. For a circular γ domain and a small bending rigidity, the membrane oscillates strongly around
an average spherical cap shape. If such a vesicle is deflated, the contact area increases or decreases with increasing osmotic
pressure, depending on the relative size of the vesicle and the circular γ domain. The lateral localization of the vesicle's
center of mass by such a domain is optimal for a certain domain radius, which is found to be rather independent of adhesion
strength and bending rigidity. For vesicles adhering to stripe-shaped surface domains, the width of the contact area perpendicular
to the stripe varies nonmonotonically with the adhesion strength. 相似文献
5.
We present a model of bi-phasic vesicles in the limit of large surface tension. In this regime, the vesicle is completely
stretched and well described by two spherical caps with a fold, which concentrates the membrane stress. The conservation laws
and geometric constraints restrict the space of possible shapes to a pair of solutions labeled by a parameter
given by line tension/pressure. For a given value of
, the two solutions differ by the length of the interface between domains. For a critical value,
, the two vesicle shapes become identical and no connected solution exists above this critical value. This model sheds new
light on two proposed mechanisms (osmotic shocks and molecule absorption) to explain the budding and the fission in recent
experiments. 相似文献
6.
Perino-Gallice L Fragneto G Mennicke U Salditt T Rieutord F 《The European physical journal. E, Soft matter》2002,8(3):275-282
Thin multilamellar assemblies of neutral lipid bilayers deposited on silicon substrates are shown to be unstable upon hydration.
We analyze the stability of these systems taking into account a reduction of the fluctuation-related components of the bilayer
interaction potential. The sizes of the patterns observed are consistent with a spinodal dewetting process.
Received 27 November 2001 相似文献
7.
R. Capovilla C. Chryssomalakos J. Guven 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,29(2):163-166
We examine the equilibria of a rigid loop in the plane, characterized by an energy functional quadratic in the curvature,
subject to the constraints of fixed length and fixed enclosed area. Whereas the only non self-intersecting equilibrium corresponding
to the fixed length constraint is the circle, the area constraint gives rise to distinct equilibria labeled by an integer.
These configurations exhibit self-intersections and bifurcations as the area is reduced. In addition, not only can the Euler-Lagrange
equation be integrated to provide a quadrature for the curvature but the embedding itself can be expressed as a local function
of the curvature. Perturbations connecting equilibria are shown to satisfy a first order ODE which is readily solved. Analytical
expressions for the energy as a function of the area are obtained in the limiting regimes.
Received 18 October 2001 / Received in final form 31 May 2002 Published online 2 October 2002
RID="a"
ID="a"e-mail: capo@fis.cinvestav.mx
RID="b"
ID="b"e-mail: chryss@nuclecu.unam.mx
RID="c"
ID="c"e-mail: jemal@nuclecu.unam.mx 相似文献
8.
9.
We studied the formation of actin scaffolds in giant vesicles of dimyristoylphosphatidylcholine (DMPC). Polymerization of
actin was induced at low ionic strength through ionophore-mediated influx of Mg2+ (2 mM). The spatial organization of the filamentous actin was visualized by confocal and epifluorescence microscopy as a
function of the filaments length and membrane composition, by including various amounts of cholesterol or lipids with neutral
and positively charged polyethyleneglycol headgroups (PEG lipopolymers). In vesicles of pure DMPC, the newly polymerized actin
adsorbs to the membrane and forms a thin shell. In the presence of 2.5 mol% lipopolymers or of cholesterol at a molar fraction
x = 0.37, formation of a thin adsorbed film is impeded. A fuzzy cortex is predominantly formed in vesicles of diameter d smaller than the filament persistence length ( d ⩽ 15μm) while for larger vesicles a homogeneous network formation is favoured in the bulk of the vesicle. The fuzzy-cortex
formation is interpreted as a consequence of the reduction of the bending energy if the actin filaments accumulate close to
the vesicle wall.
Received: 17 January 2002 / Accepted: 21 March 2003 / Published online: 24 April 2003
RID="a"
ID="a"e-mail: Laurent_Limozin@ph.tum.de 相似文献
10.
Chécot F Lecommandoux S Klok HA Gnanou Y 《The European physical journal. E, Soft matter》2003,10(1):25-35
This paper discusses the self-assembly of block copolymers into vesicular morphology. After a brief state of art of the field,
a system based on an amphiphilic poly(butadiene)-b-poly(-L-glutamic acid) (PB-b-PGA) diblock copolymer in aqueous solution is discussed in detail. The aggregation behavior of this block copolymer has been
investigated by means of fluorescence spectroscopy, dynamic (DLS) and static (SLS) light scattering as well as transmission
electron microscopy (TEM). The diblock copolymer was found to form well-defined vesicles in water. The size of these so-called
polymersomes or peptosomes could be reversibly manipulated as a function of both pH and ion strength. Depending on the pH
of the aqueous solution, the hydrodynamic radii of these vesicles were found to vary from 100 nm to 150 nm. By cross-linking
the 1,2-vinyl double bonds present in the polybutadiene block, the ability to transform a transient supramolecular self-organized
aggregate into a permanent “shape-persistent stimuli-responsive nanoparticle” has been demonstrated.
Received 25 June 2002 and Received in final form 22 October 2002 Published online: 11 March 2003 相似文献
11.
Inclusions embedded in lipid membranes undergo a mediated force, due to the tendency of the membrane to relax its excess of
elastic energy. In this paper we determine the exact shape of a two-dimensional vesicle hosting two different inclusions,
and we analyse how the inclusion conformation influences the mediated interaction. We find non-trivial equilibrium configurations
for the inclusions along the hosting membrane, and we derive the complete phase diagram of the mediated interaction. In particular,
we find a non-vanishing mediated force even when the distance between the inclusions is much greater than their size. Our
model can be applied to describe the mediated interactions of parallel, elongated inclusions embedded in three-dimensional
membranes.
Received 22 October 2001 and Received in final form 8 March 2002 相似文献
12.
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
13.
T. Salditt C. Li A. Spaar U. Mennicke 《The European physical journal. E, Soft matter》2002,7(2):105-116
We have investigated the structure of solid-supported, multilamellar membranes by X-ray reflectivity. The density profile
is obtained by fitting the full q-range to a model using the bilayer Fourier coefficients as fitting parameters. The effect of hydration and the substrate
boundary condition are discussed in view of the well-known Landau-Peierls effect and its implications for structure determination.
The resulting bilayer density profile agrees remarkably well with previously published data of a molecular dynamics (MD) simulation
for 1,2-oleoyl-palmitoyl-sn-glycero-3-phosphocholine (OPPC).
Received 1 October 2001 and Received in final form 21 December 2001 相似文献
14.
B. Božič V. Heinrich S. Svetina B. Žekš 《The European physical journal. E, Soft matter》2001,6(1):91-98
Shapes of nearly cylindrical sections of axisymmetric phospholipid membranes are studied theoretically. Describing the shape
of such sections by their deviation from a reference cylinder, the well-established shape equation for axisymmetric bilayer
membranes is expanded in terms of this deviation, and it is then solved analytically. The phase diagram shows the resulting
stationary shapes as functions of system parameters and external conditions, i.e., the pressure difference across the membrane, the membrane tension, the difference between the tensions of the two monolayers,
and the axial force acting on the vesicle. The accuracy of the approximate analytical solution is demonstrated by comparison
with numerical results. The obtained analytical solution allows to extend the analysis to include shapes where numerical methods
have failed.
Received 27 September 2000 and Received in final form 26 March 2001 相似文献
15.
In search for the optimal strategy in population dynamics 总被引:1,自引:0,他引:1
K. Sznajd-Weron M. Wolański 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,25(2):253-259
A unification of recently proposed models describing population dynamics is presented. We study the effect of different factors,
like environmental conditions, concentration of individuals in a given area and migration strategies, on population dynamics.
Moreover, we show that a population occupying a smaller area is more susceptible to extinction, which is a well known biological
fact. We solve the model using Monte Carlo simulations and the mean-field approach. Constructing flow diagrams we find the
optimal strategy in population dynamics.
Received 10 June 2001 and Received in final form 22 November 2001 相似文献
16.
Mader MA Ez-Zahraouy H Misbah C Podgorski T 《The European physical journal. E, Soft matter》2007,22(4):275-280
A simple 2D model of deformable vesicles tumbling in a shear under flow is introduced in order to
account for the main qualitative features observed experimentally as shear rates are increased.
The simplicity of the model allows for a full analytical
tractability while retaining the essential physical ingredients. The model reveals that the main axes of the vesicle
undergo oscillations which are coupled to the vesicle orientation in
the flow. The model reproduces and sheds light on the main novel features reported in
recent experiments [M. Mader et al., Eur. Phys. J. E. 19, 389
(2006)], namely that both coefficients A and B that enter the
Keller-Skalak equation, dψ/dt = A+Bcos(2 ψ) (ψ is
the vesicle orientation angle in the shear flow), undergo a collapse
upon increasing shear rate. 相似文献
17.
Weikl TR Andelman D Komura S Lipowsky R 《The European physical journal. E, Soft matter》2002,8(1):59-66
Biomimetic membranes in contact with a planar substrate or a second membrane are studied theoretically. The membranes contain
specific adhesion molecules (stickers) which are attracted by the second surface. In the absence of stickers, the trans-interaction
between the membrane and the second surface is assumed to be repulsive at short separations. It is shown that the interplay
of specific attractive and generic repulsive interactions can lead to the formation of a potential barrier. This barrier induces
a line tension between bound and unbound membrane segments which results in lateral phase separation during adhesion. The
mechanism for adhesion-induced phase separation is rather general, as is demonstrated by considering two distinct cases involving:
i) stickers with a linear attractive potential, and ii) stickers with a short-ranged square-well potential. In both cases,
membrane fluctuations reduce the potential barrier and, therefore, decrease the tendency of phase separation.
Received 24 January 2002 and Received in final form 24 April 2002 相似文献
18.
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
19.
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
20.
Recent experiments have demonstrated that the dynamics in liquids close to the glass transition temperature is strongly heterogeneous.
The characteristic size of these heterogeneities has been measured to be a few nanometers at T
g. We extend here a recent model for describing the heterogeneous nature of the dynamics which allows both to derive this length
scale and the right orders of magnitude of the heterogeneities of the dynamics close to the glass transition. Our model allows
then to interpret quantitatively small probes diffusion experiments.
Received 29 March 2002 and Received in final form 11 November 2002
RID="a"
ID="a"e-mail: long@lps.u-psud.fr 相似文献