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1.
The effect of rigid inclusions on the phase behavior of a film containing a mixture of lipid molecules is investigated. In
the proposed model, the inclusion-induced deformation of the film, and the resulting energy cost are strongly dependent upon
the spontaneous curvature of the mixed film. The spontaneous curvature is in turn strongly influenced by the composition of
film. This coupling between the film composition and the energy per inclusion leads to a lateral modulation of the composition,
which follows the local curvature of the membrane. In particular, it is shown that inclusions may induce a global phase separation
in a film which would otherwise be homogeneously mixed. The mixed film is then composed of patches of different average composition,
separated by the inclusions. This process may be of relevance to explain some aspects of lipid-protein association in biological
membranes.
Received 8 April 1999 and Received in final form 4 October 1999 相似文献
2.
P.G. Dommersnes J.-B. Fournier 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(1):9-12
We study the collective behavior of inclusions inducing local anisotropic curvatures in a flexible fluid membrane. The N-body interaction energy for general anisotropic inclusions is calculated explicitly, including multi-body interactions. Long-range
attractive interactions between inclusions are found to be sufficiently strong to induce aggregation. Monte Carlo simulations
show a transition from compact clusters to aggregation on lines or circles. These results might be relevant to proteins in
biological membranes or colloidal particles bound to surfactant membranes.
Received 30 July 1999 and Received in final form 8 September 1999 相似文献
3.
Two direct methods to calculate fluctuation forces between rigid objects embedded in fluid membranes
The fluctuation-induced attractive interaction of rigid flat objects embedded in a fluid membrane is calculated for a pair
of parallel strips and a pair of equal circular disks. Assuming flat boundary conditions, we derive the interaction from the
entropy of the suppressed boundary angle fluctuation modes. Each mode entropy is computed in two ways: from the boundary angles
themselves and from the mean-curvature mode functions. A formula for the entropy loss of suppressing one or more mean-curvature
modes is developed and applied. For the pair of disks we recover the result of Goulian et al. and Golestanian et al. in a direct manner, avoiding any mappings by Hubbard-Stratonovitch transformations. The mode-by-mode agreement of the two
computed entropies in both systems confirms an earlier claim that mean curvature is the natural measure of integration for
fluid membranes.
Received 15 December 2000 相似文献
4.
J. -B. Fournier 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(2):261-272
A phenomenological Landau elasticity for the shape, dilation, and lipid-tilt of bilayer membranes is developed. The shape
mode couples with the sum of the monolayers' tilt, while the dilation mode couples with the difference of the monolayers'
tilts. Interactions among membrane inclusions within regular arrays are discussed. Inclusions modifying the membrane thickness
and/or inducing a tilt-difference due to their convex or concave shape yield a dilation-induced attraction and a tilt-difference-induced
repulsion. The resulting interaction can stabilize 2D crystal phases, with the possible coexistence of different lattice spacings when the dilation-tilt-difference coupling is
large. Inclusions favoring crystals are those with either a long-convex or a short-concave hydrophobic core. Inclusions inducing
a local membrane curvature due to their conical shape repel one another. At short inclusions separations, a tilt comparable
with the inclusion's cone angle develops: it relaxes the membrane curvature and reduces the repulsion. At large separations
the tilt vanishes, whatever the value of the shape-tilt coupling.
Received 23 October 1998 and Received in final form 12 January 1999 相似文献
5.
M.J. Bowick A. Cacciuto G. Thorleifsson A. Travesset 《The European physical journal. E, Soft matter》2001,5(2):149-160
We present an analysis of extensive large-scale Monte Carlo simulations of self-avoiding fixed-connectivity membranes for sizes (number of faces) ranging from 512 to 17672 (triangular) plaquettes. Self-avoidance is implemented via
impenetrable plaquettes. We simulate the impenetrable plaquette model in both three and four bulk dimensions. In both cases we find the
membrane to be flat for all temperatures: the size exponent in three dimensions is ν = 0.95(5) (Hausdorff dimension d
H = 2.1(1)). The single flat phase appears, furthermore, to be equivalent to the large bending rigidity phase of non-self-avoiding fixed-connectivity membranes --the roughness exponent in three dimensions is ξ = 0.63(4). This suggests that there is a unique
universality class for flat fixed-connectivity membranes without attractive interactions. Finally, we address some theoretical
and experimental implications of our work.
Received 23 June 2000 and Received in final form 25 October 2000 相似文献
6.
Motivated by numerous X-ray scattering studies of lamellar phases with membrane proteins, amphiphilic peptides, polymers,
or other inclusions, we have determined the modifications of the classical Caillé law for a smectic phase as a function of
the nature and concentration of inclusions added to it. Besides a fundamental interest on the behavior of fluctuating systems
with inclusions, a precise characterization of the action of a given protein on a lipid membrane (anchoring, swelling, stiffening
...) is of direct biological interest and could be probed by way of X-ray measurements. As a first step we consider three
different couplings involving local pinching (or swelling), stiffening or curvature of the membrane. In the first two cases
we predict that independent inclusions induce a simple renormalization of the bending and compression moduli of the smectic
phase. The X-ray experiments may also be used to probe correlations between inclusions. Finally we show that asymmetric coupling
(such as a local curvature of the membrane) results in a modification of the usual Caillé law.
Received 10 March 2000 and Received in final form 30 August 2000 相似文献
7.
8.
We develop an exact method to calculate thermal Casimir forces between inclusions of arbitrary shapes and separation, embedded in a fluid membrane whose fluctuations are governed by the combined action of surface tension, bending modulus, and Gaussian rigidity. Each object's shape and mechanical properties enter only through a characteristic matrix, a static analog of the scattering matrix. We calculate the Casimir interaction between two elastic disks embedded in a membrane. In particular, we find that at short separations the interaction is strong and independent of surface tension. 相似文献
9.
R. Holzlöhner M. Schoen 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(3):413-419
The fluctuation-induced interaction between two rod-like, rigid inclusions in a fluid vesicle is studied by means of canonical
ensemble Monte-Carlo simulations. The vesicle membrane is represented by a triangulated network of hard spheres. Five rigidly
connected hard spheres form rod-like inclusions that can leap between sites of the triangular network. Their effective interaction
potential is computed as a function of mutual distance and angle of the inclusions. On account of the hard-core potential
among these, the nature of the potential is purely entropic. Special precaution is taken to reduce lattice artifacts and the
influence of finite-size effects due to the spherical geometry. Our results show that the effective potential is attractive
and short-range compared with the rod length L. Its well depth is of the order of , where is the bending modulus.
Received 5 February 1999 and Received in final form 14 May 1999 相似文献
10.
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
11.
J. Prost J.-B. Manneville R. Bruinsma 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(4):465-480
Membranes in thermal equilibrium are well known to exhibit Brownian motion type shape fluctuations. Membranes containing active
force centers -- such as chemically active membrane proteins -- suffer additional non-equilibrium shape fluctuations due to
the activity of these force centers. We demonstrate, using scaling arguments, that non-equilibrium shape fluctuations are
in general greatly amplified by the presence of a nearby wall or membrane due to the absence of a fluctuation-dissipation
theorem. For adhesive membranes, this fluctuation magnification effect may facilitate the establishment of bonding. For non-adhesive
membranes, fluctuation magnification produces a long-range repulsive pressure which can exceed the well known Helfrich repulsion
due to purely thermal fluctuations.
Received: 1 September 1997 / Accepted: 3 December 1997 相似文献
12.
Adhesion between membranes is studied using a phenomenological model, where the inter-membrane distance is coupled to the
concentration of sticker molecules on the membranes. The model applies to both adhesion of two flexible membranes and to adhesion
of one flexible membrane onto a second membrane supported on a solid substrate. We mainly consider the case where the sticker
molecules form bridges and adhere directly to both membranes. The calculated mean-field phase diagrams show an upward shift
of the transition temperature indicating that the lateral phase separation in the membrane is enhanced due to the coupling effect. Hence the possibility of adhesion-induced lateral phase separation is predicted. For a particular
choice of the parameters, the model exhibits a tricritical behavior. We also discuss the non-monotonous shape of the inter-membrane
distance occurring when the lateral phase separation takes place. The inter-membrane distance relaxes to the bulk values with
two symmetric overshoots. Adhesion mediated by other types of stickers is also considered.
Received 12 January 2000 and Received in final form 15 May 2000 相似文献
13.
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
14.
In this paper, we discuss the equilibrium phases and collapse transitions of a lyotropic nematic gel immersed in an isotropic
solvent. A nematic gel consists of a cross-linked polymer network with rod-like molecules embedded in it. Upon decreasing
the quality of the solvent, we find that a lyotropic nematic gel undergoes a discontinuous volume change accompanied by an
isotropic-nematic transition. We also present phase diagrams that these systems may exhibit. In particular, we show that coexistence
of two isotropic phases, of two nematic phases, or of an isotropic and a nematic phase can occur.
Received 15 February 2002 and Received in final form 14 June 2002 相似文献
15.
Effect of thermal undulations on the bending elasticity and spontaneous curvature of fluid membranes
We amplify previous arguments why mean curvature should be used as measure of integration in calculating the effective bending
rigidity of fluid membranes subjected to a weak background curvature. The stiffening of the membrane by its fluctuations,
recently derived for spherical shapes, is recovered for cylindrical curvature. Employing curvilinear coordinates, we then
discuss stiffening for arbitrary shapes, confirm that the elastic modulus of Gaussian curvature is not renormalized in the
presence of fluctuations, and show for the first time that any spontaneous curvature also remains unchanged.
Received 19 April 1999 and in Received in final form 7 January 2000 相似文献
16.
Self-consistent calculation of electrostatic force for two kinds of mesoscopic surface structures 总被引:1,自引:0,他引:1
Z.-Y. Li B.-Y. Gu G.-Z. Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,6(1):123-131
The scanning electrostatic force microscopy (SEFM) can acquire information of surface structures in a non-contact way. We
calculate the electrostatic force between the charged tip and polarized surface structure in SEFM in the framework of self-consistent
integral equation formalism (SCIEF), incorporating the image method to treat the electrostatic coupling of substrate and tip.
We consider two kinds of surface structures, one is the topographic structure on the surface, the other is the dielectric
structure embedded in the substrate. The force pattern of the topographic structure shows a protrusion around the surface
structure. However, the force pattern displays a hollow around an embedded structure with a dielectric constant less than
that of substrate medium. For an embedded structure with a larger dielectric constant, the force pattern exhibits a protrusion,
and the force signal is much weaker than that of the topographic structure. Therefore, it is expected that one may identify
these surface structures from the pure electrostatic force information in SEFM. The force signal of the densely arranged dielectric
pads is simply the superposition of force signal of each pad individually, the interference effect of electric field is not
remarkable.
Received: 26 March 1998 / Accepted: 9 June 1998 相似文献
17.
18.
19.
K.J. Wiese 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,1(3):273-276
The dynamical scaling properties of selfavoiding polymerized membranes with internal dimension D embedded into d dimensions are studied including hydrodynamical interactions. It is shown that the theory is renormalizable to all orders
in perturbation theory and that the dynamical scaling exponent z is given by z=d. The crossover to the region, where the membrane is crumpled swollen but the hydrodynamic interaction irrelevant is discussed.
The results apply as well to polymers (D=1) as to membranes (D=2).
Received: 5 September 1997 / Accepted: 17 November 1997 相似文献
20.
Chaotic solitons in Sine-Gordon system 总被引:2,自引:0,他引:2
Wenhua Hai Zelan Zhang Jianshu Fang 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(1):103-107
We extend the constant-variation method to the case of partial differential equations. Applying the method to periodically
perturbed Sine-Gordon system, we find some novel solitons, which are embedded in a chaotic attractor and possess controllable
velocity of motion. Taking periodically driven long Josephson junction as an example the corresponding chaotic region in parameter
space and chaotic orbit are obtained analytically and numerically.
Received 25 December 2000 相似文献