678 research outputs found
Monte Carlo Study of the Inflation-Deflation Transition in a Fluid Membrane
We study the conformation and scaling properties of a self-avoiding fluid
membrane, subject to an osmotic pressure , by means of Monte Carlo
simulations. Using finite size scaling methods in combination with a histogram
reweighting techniques we find that the surface undergoes an abrupt
conformational transition at a critical pressure , from low pressure
deflated configurations with a branched polymer characteristics to a high
pressure inflated phase, in agreement with previous findings
\cite{gompper,baum}. The transition pressure scales with the system
size as , with . Below
the enclosed volume scales as , in accordance with the
self-avoiding branched polymer structure, and for our data
are consistent with the finite size scaling form ,
where .
Also the finite size scaling behavior of the radii of gyration and the
compressibility moduli are obtained. Some of the observed exponents and the
mechanism behind the conformational collapse are interpreted in terms of a
Flory theory.Comment: 20 pages + postscript-file, Latex + Postscript, IFA Report No. 94/1
A note on the Lee-Yang singularity coupled to 2d quantum gravity
We show how to obtain the critical exponent of magnetization in the Lee-Yang
edge singularity model coupled to two-dimensional quantum gravity
Membrane mediated aggregation of curvature inducing nematogens and membrane tubulation
The shapes of cell membranes are largely regulated by membrane associated,
curvature active, proteins. We use a numerical model of the membrane with
elongated membrane inclusions, recently developed by us, which posses
spontaneous directional curvatures that could be different along and
perpendicular to its long axis. We show that, due to membrane mediated
interactions these curvature inducing membrane nematogens can oligomerize
spontaneously, even at low concentrations, and change the local shape of the
membrane. We demonstrate that for a large group of such inclusions, where the
two spontaneous curvatures have equal sign, the tubular conformation and
sometime the sheet conformation of the membrane are the common equilibrium
shapes. We elucidate the factors necessary for the formation of these {\it
protein lattices}. Furthermore, the elastic properties of the tubes, like their
compressional stiffness and persistence length are calculated. Finally, we
discuss the possible role of nematic disclination in capping and branching of
the tubular membranes.Comment: 15pages, 8 figure
Creasing of flexible membranes at vanishing tension
The properties of freestanding tensionless interfaces and membranes at low bending rigidity κ are dominated by strong fluctuations and self-avoidance and are thus outside the range of standard perturbative analysis. We analyze this regime by a simple discretized, self-avoiding membrane model on a frame subject to periodic boundary conditions by use of Monte Carlo simulation and dynamically triangulated surface techniques. We find that at low bending rigidities, the membrane properties fall into three regimes: Below the collapse transition κBP it is subject to branched polymer instability where the framed surface is not defined, in a range below a threshold rigidity κc the conformational correlation function are characterized by power-law behavior with a continuously varying exponent α, 2<α≤4 and above κc, α=4 characteristic for linearized bending excitations. Response functions specific heat and area compressibility display pronounced peaks close to κc. The results may be important for the description of soft interface systems, such as microemulsions and membranes with in-plane cooperative phenomena
Computational Approaches to Explore Bacterial Toxin Entry into the Host Cell
Many bacteria secrete toxic protein complexes that modify and disrupt essential processes in the infected cell that can lead to cell death. To conduct their action, these toxins often need to cross the cell membrane and reach a specific substrate inside the cell. The investigation of these protein complexes is essential not only for understanding their biological functions but also for the rational design of targeted drug delivery vehicles that must navigate across the cell membrane to deliver their therapeutic payload. Despite the immense advances in experimental techniques, the investigations of the toxin entry mechanism have remained challenging. Computer simulations are robust complementary tools that allow for the exploration of biological processes in exceptional detail. In this review, we first highlight the strength of computational methods, with a special focus on all-atom molecular dynamics, coarse-grained, and mesoscopic models, for exploring different stages of the toxin protein entry mechanism. We then summarize recent developments that are significantly advancing our understanding, notably of the glycolipid–lectin (GL-Lect) endocytosis of bacterial Shiga and cholera toxins. The methods discussed here are also applicable to the design of membrane-penetrating nanoparticles and the study of the phenomenon of protein phase separation at the surface of the membrane. Finally, we discuss other likely routes for future development
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