21,559 research outputs found
Attractive forces between anisotropic inclusions in the membrane of a vesicle
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
\kappa/10, where \kappa is the bending modulus.Comment: 7 pages, 5 eps + 3 latex figures. REVTeX. Submitted to Eur. Phys. J.
Identifying Proteins of High Designability via Surface-Exposure Patterns
Using an off-lattice model, we fully enumerate folded conformations of
polypeptide chains of up to N = 19 monomers. Structures are found to differ
markedly in designability, defined as the number of sequences with that
structure as a unique lowest-energy conformation. We find that designability is
closely correlated with the pattern of surface exposure of the folded
structure. For longer chains, complete enumeration of structures is
impractical. Instead, structures can be randomly sampled, and relative
designability estimated either from designability within the random sample, or
directly from surface-exposure pattern. We compare the surface-exposure
patterns of those structures identified as highly designable to the patterns of
naturally occurring proteins.Comment: 17 pages, 12 figure
The Mass Function and Average Mass Loss Rate of Dark Matter Subhaloes
We present a simple, semi-analytical model to compute the mass functions of
dark matter subhaloes. The masses of subhaloes at their time of accretion are
obtained from a standard merger tree. During the subsequent evolution, the
subhaloes experience mass loss due to the combined effect of dynamical
friction, tidal stripping, and tidal heating. Rather than integrating these
effects along individual subhalo orbits, we consider the average mass loss
rate, where the average is taken over all possible orbital configurations. This
allows us to write the average mass loss rate as a simple function that depends
only on redshift and on the instantaneous mass ratio of subhalo and parent
halo. After calibrating the model by matching the subhalo mass function (SHMF)
of cluster-sized dark matter haloes obtained from numerical simulations, we
investigate the predicted mass and redshift dependence of the SHMF.We find
that, contrary to previous claims, the subhalo mass function is not universal.
Instead, both the slope and the normalization depend on the ratio of the parent
halo mass, M, and the characteristic non-linear mass M*. This simply reflects a
halo formation time dependence; more massive parent haloes form later, thus
allowing less time for mass loss to operate. We analyze the halo-to-halo
scatter, and show that the subhalo mass fraction of individual haloes depends
most strongly on their accretion history in the last Gyr. Finally we provide a
simple fitting function for the average SHMF of a parent halo of any mass at
any redshift and for any cosmology, and briefly discuss several implications of
our findings.Comment: Replaced to match version accepted for publication in MNRAS. Small
section added that discusses higher-order moments of subhalo occupation
distribution (including a new figure). Otherwise, few small change
On homogeneous statistical distributions exoplanets for their dynamic parameters
Correct distributions of extrasolar systems for their orbital parameters
(semi-major axes, period, eccentricity) and physical characteristics (mass,
spectral type of parent star) are received. Orbital resonances in extrasolar
systems are considered. It is shown, that the account of more thin effects,
including with use of wavelet methods, in obviously incorrectly reduced
distributions it is not justified, to what the homogeneous statistical
distributions for dynamic parameters of exoplanets, received in the present
work, testify.Comment: 9 pages, 15 figures; International Conference "100 years since
Tunguska phenomenon: Past, present and future", (June 26-28, 2008. Russia,
Moscow), Lomonosov readings 2009 (Moscow State University
Color enhancement of landsat agricultural imagery: JPL LACIE image processing support task
Color enhancement techniques were applied to LACIE LANDSAT segments to determine if such enhancement can assist analysis in crop identification. The procedure involved increasing the color range by removing correlation between components. First, a principal component transformation was performed, followed by contrast enhancement to equalize component variances, followed by an inverse transformation to restore familiar color relationships. Filtering was applied to lower order components to reduce color speckle in the enhanced products. Use of single acquisition and multiple acquisition statistics to control the enhancement were compared, and the effects of normalization investigated. Evaluation is left to LACIE personnel
Elementary preamble to a theory of granular gases
Granular materials partake almost dramatically at times of the properties of
solids and, under different circumstances, of some properties of gases. Here,
within the mechanics of mass points, an elementary analysis, involving
predominantly velocities rather than places, is shown to lead to a global
equation concerning the shuffling motions (in addition to continuity and
Cauchy's equations); it involves a stirring tensor and rules the evolution of a
Reynolds' tensor.Comment: 17 page
Method for Computing Short-Range Forces between Solid-Liquid Interfaces Driving Grain Boundary Premelting
We present a molecular dynamics based method for computing accurately
short-range structural forces resulting from the overlap of spatially diffuse
solid-liquid interfaces at wetted grain boundaries close to the melting point.
The method is based on monitoring the fluctuations of the liquid layer width at
different temperatures to extract the excess interfacial free-energy as a
function of this width. The method is illustrated for a high energy Sigma 9
twist boundary in pure Ni. The short-range repulsion driving premelting is
found to be dominant in comparison to long-range dispersion and entropic forces
and consistent with previous experimental findings that nanometer-scale layer
widths may only be observed very close to the melting point.Comment: 5 pages, four figure
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