158 research outputs found
Lateral phase separation of confined membranes
We consider membranes interacting via short, intermediate and long stickers.
The effects of the intermediate stickers on the lateral phase separation of the
membranes are studied via mean-field approximation. The critical potential
depth of the stickers increases in the presence of the intermediate sticker.
The lateral phase separation of the membrane thus suppressed by the
intermediate stickers. Considering membranes interacting with short and long
stickers, the effect of confinement on the phase behavior of the membranes is
also investigated analytically
Effective free energy for pinned membranes
We consider membranes adhered through specific receptor-ligand bonds. Thermal
undulations of the membrane induce effective interactions between adhesion
sites. We derive an upper bound to the free energy that is independent of
interaction details. To lowest order in a systematic expansion we obtain
two-body interactions which allow to map the free energy onto a lattice gas
with constant density. The induced interactions alone are not strong enough to
lead to a condensation of individual adhesion sites. A measure of the thermal
roughness is shown to depend on the inverse square root of the density of
adhesion sites, which is in good agreement with previous computer simulations.Comment: to appear as a Rapid Communication in Phys. Rev.
An Effective Membrane Model of the Immunological Synapse
The immunological synapse is a patterned collection of different types of
receptors and ligands that forms in the intercellular junction between T Cells
and antigen presenting cells (APCs) during recognition. The synapse is
implicated in information transfer between cells, and is characterized by
different spatial patterns of receptors at different stages in the life cycle
of T cells. We obtain a minimalist model that captures this experimentally
observed phenomenology. A functional RG analysis provides further insights.Comment: 6 pages, 3 figures, submitted for publicatio
Phi-values in protein folding kinetics have energetic and structural components
Phi-values are experimental measures of how the kinetics of protein folding
is changed by single-site mutations. Phi-values measure energetic quantities,
but are often interpreted in terms of the structures of the transition state
ensemble. Here we describe a simple analytical model of the folding kinetics in
terms of the formation of protein substructures. The model shows that
Phi-values have both structural and energetic components. In addition, it
provides a natural and general interpretation of "nonclassical" Phi-values
(i.e., less than zero, or greater than one). The model reproduces the
Phi-values for 20 single-residue mutations in the alpha-helix of the protein
CI2, including several nonclassical Phi-values, in good agreement with
experiments.Comment: 15 pages, 3 figures, 1 tabl
Stable patterns of membrane domains at corrugated substrates
Multi-component membranes such as ternary mixtures of lipids and cholesterol
can exhibit coexistence regions between two liquid phases. When such membranes
adhere to a corrugated substrate, the phase separation process strongly depends
on the interplay between substrate topography, bending rigidities, and line
tension of the membrane domains as we show theoretically via energy
minimization and Monte Carlo simulations. For sufficiently large bending
rigidity contrast between the two membrane phases, the corrugated substrate
truncates the phase separation process and leads to a stable pattern of
membrane domains. Our theory is consistent with recent experimental
observations and provides a possible control mechanism for domain patterns in
biological membranes.Comment: to appear in Physical Review Letter
Dynamic phase separation of fluid membranes with rigid inclusions
Membrane shape fluctuations induce attractive interactions between rigid
inclusions. Previous analytical studies showed that the fluctuation-induced
pair interactions are rather small compared to thermal energies, but also that
multi-body interactions cannot be neglected. In this article, it is shown
numerically that shape fluctuations indeed lead to the dynamic separation of
the membrane into phases with different inclusion concentrations. The tendency
of lateral phase separation strongly increases with the inclusion size. Large
inclusions aggregate at very small inclusion concentrations and for relatively
small values of the inclusions' elastic modulus.Comment: 6 pages, 6 figure
Characterization of a Combined CARS and Interferometric Rayleigh Scattering System
This paper describes the characterization of a combined Coherent anti-Stokes Raman Spectroscopy and Interferometric Rayleigh Scattering (CARS-IRS) system by reporting the accuracy and precision of the measurements of temperature, species mole fraction of N2, O2, and H2, and two-components of velocity. A near-adiabatic H2-air Hencken burner flame was used to provide known properties for measurements made with the system. The measurement system is also demonstrated in a small-scale Mach 1.6 H2-air combustion-heated supersonic jet with a co-flow of H2. The system is found to have a precision that is sufficient to resolve fluctuations of flow properties in the mixing layer of the jet
Mobile CARS - IRS Instrument for Simultaneous Spectroscopic Measurement of Multiple Properties in Gaseous Flows
This paper describes a measurement system based on the dual-pump coherent anti-Stokes Raman spectroscopy (CARS) and interferometric Rayleigh scattering (IRS) methods. The IRS measurement is performed simultaneously with the CARS measurement using a common green laser beam as a narrow-band light source. The mobile CARS-IRS instrument is designed for the use both in laboratories as well as in ground-based combustion test facilities. Furthermore, it is designed to be easily transported between laboratory and test facility. It performs single-point spatially and temporally resolved simultaneous measurements of temperature, species mole fraction of N2, O2, and H2, and two-components of velocity. A mobile laser system can be placed inside or outside the test facility, while a beam receiving and monitoring system is placed near the measurement location. Measurements in a laboratory small-scale Mach 1.6 H2-air combustion-heated supersonic jet were performed to test the capability of the system. Final setup and pretests of a larger scale reacting jet are ongoing at NASA Langley Research Center s Direct Connect Supersonic Combustor Test Facility (DCSCTF)
Impermeability effects in three-dimensional vesicles
We analyse the effects that the impermeability constraint induces on the
equilibrium shapes of a three-dimensional vesicle hosting a rigid inclusion. A
given alteration of the inclusion and/or vesicle parameters leads to shape
modifications of different orders of magnitude, when applied to permeable or
impermeable vesicles. Moreover, the enclosed-volume constraint wrecks the
uniqueness of stationary equilibrium shapes, and gives rise to pear-shaped or
stomatocyte-like vesicles.Comment: 16 pages, 7 figure
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