10,911 research outputs found
N-body Study of Anisotropic Membrane Inclusions: Membrane Mediated Interactions and Ordered Aggregation
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.Comment: 4 pages, 3 figs, LaTe
Dynamin recruitment by clathrin coats: a physical step?
Recent structural findings have shown that dynamin, a cytosol protein playing
a key-role in clathrin-mediated endocytosis, inserts partly within the lipid
bilayer and tends to self-assemble around lipid tubules. Taking into account
these observations, we make the hypothesis that individual membrane inserted
dynamins imprint a local cylindrical curvature to the membrane. This imprint
may give rise to long-range mechanical forces mediated by the elasticity of the
membrane. Calculating the resulting many-body interaction between a collection
of inserted dynamins and a membrane bud, we find a regime in which the dynamins
are elastically recruited by the bud to form a collar around its neck, which is
reminiscent of the actual process preempting vesicle scission. This physical
mechanism might therefore be implied in the recruitment of dynamins by clathrin
coats.Comment: 11 pages, 6 figures, to appear in C.R.A.S. ser II
Design aspects of a solar array drive for spot, with a high platform stability objective
A solar array drive mechanism (MEGS) for the SPOT platform, which is a prototype of a multimission platform, is described. High-resolution cameras and other optical instruments are carried by the platform, requiring excellent platform stability in order to obtain high-quality pictures. Therefore, a severe requirement for the MEGS is the low level of disturbing torques it may generate considering the 0.6 times 10 to the minus 3 power deg/sec stability required. The mechanical design aspects aiming at reducing the mean friction torque, and therefore its fluctuations, are described as well as the method of compensation of the motor imperfections. It was concluded, however, that this is not sufficient to reach the stability requirement
Nematic-Wetted Colloids in the Isotropic Phase: Pairwise Interaction, Biaxiality and Defects
We calculate the interaction between two spherical colloidal particles
embedded in the isotropic phase of a nematogenic liquid. The surface of the
particles induces wetting nematic coronas that mediate an elastic interaction.
In the weak wetting regime, we obtain exact results for the interaction energy
and the texture, showing that defects and biaxiality arise, although they are
not topologically required. We evidence rich behaviors, including the
possibility of reversible colloidal aggregation and dispersion. Complex
anisotropic self-assembled phases might be formed in dense suspensions.Comment: 4 pages, 6 figure
Determination of the interactions in confined macroscopic Wigner islands: theory and experiments
Macroscopic Wigner islands present an interesting complementary approach to
explore the properties of two-dimensional confined particles systems. In this
work, we characterize theoretically and experimentally the interaction between
their basic components, viz., conducting spheres lying on the bottom electrode
of a plane condenser. We show that the interaction energy can be approximately
described by a decaying exponential as well as by a modified Bessel function of
the second kind. In particular, this implies that the interactions in this
system, whose characteristics are easily controllable, are the same as those
between vortices in type-II superconductors.Comment: 8 pages, 8 figure
Bi-defects of Nematic Surfactant Bilayers
We consider the effects of the coupling between the orientational order of
the two monolayers in flat nematic bilayers. We show that the presence of a
topological defect on one bilayer generates a nontrivial orientational texture
on both monolayers. Therefore, one cannot consider isolated defects on one
monolayer, but rather associated pairs of defects on either monolayer, which we
call bi-defects. Bi-defects generally produce walls, such that the textures of
the two monolayers are identical outside the walls, and different in their
interior. We suggest some experimental conditions in which these structures
could be observed.Comment: RevTeX, 4 pages, 3 figure
Investigation of powered nacelles on a high aspect ratio NASA supercritical wing, phase 2
A modified wing with the long core separate flow nacelle and several E(3) nacelles was utilized. The effects of nacelle and pylon cant angles and nacelle longitudinal and vertical location were investigated over a Mach number range from 0.70 to 0.83. The results at the cruise condition 0.82 Mach number and 0.55 lift coefficient are presented
Long-range Ni/Mn structural order in epitaxial double perovskite La2NiMnO6 thin films
We report and compare the structural, magnetic, and optical properties of
ordered La2NiMnO6 thin films and its disordered LaNi0.5Mn0.5O3 counterpart. An
x-ray diffraction study reveals that the B-site Ni/Mn ordering induces
additional XRD reflections as the crystal symmetry is transformed from a
pseudocubic perovskite unit cell in the disordered phase to a monoclinic form
with larger lattice parameters for the ordered phase. Polarized Raman
spectroscopy studies reveal that the ordered samples are characterized by
additional phonon excitations that are absent in the disordered phase. The
appearance of these additional phonon excitations is interpreted as the
clearest signature of Brillouin zone folding as a result of the long-range
Ni/Mn ordering in La2NiMnO6. Both ordered and disordered materials display a
single ferromagnetic-to-paramagnetic transition. The ordered films display also
a saturation magnetization close to 4.8 mB/f.u. and a transition temperature
(FM-TC) around 270 K, while the disordered ones have only a 3.7 mB/f.u.
saturation magnetization and a FM-TC around 138 K. The differences in their
magnetic behaviours are understood based on the distinct local electronic
configurations of their Ni/Mn cations.Comment: 15 pages, 5 fig
Geothermal studies - Yellowstone National Park /test site 11/, Wyoming
Summary report of diamond drilling in thermal areas of Yellowstone National Park, and method for determining heat flow in thermal area
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