32,288 research outputs found
Relating monomer to centre-of-mass distribution functions in polymer solutions
A relationship between the measurable monomer-monomer structure factor, and
the centre-of-mass (CM) structure factor of dilute or semi-dilute polymer
solutions is derived from Ornstein-Zernike relations within the ``polymer
reference interaction site model'' (PRISM) formalism, by considering the CM of
each polymer as an auxiliary site and neglecting direct correlations between
the latter and the CM and monomers of neighbouring polymers. The predictions
agree well with Monte Carlo data for self-avoiding walk polymers, and are
considerably more accurate than the predictions of simple factorization
approximations.Comment: uses eps.cls, v2 is close to final published versio
Glass transition in fullerenes: mode-coupling theory predictions
We report idealized mode-coupling theory results for the glass transition of
ensembles of model fullerenes interacting via phenomenological two-body
potentials. Transition lines are found for C60, C70 and C96 in the
temperature-density plane. We argue that the observed glass-transition behavior
is indicative of kinetic arrest that is strongly driven by the inter-particle
attraction in addition to excluded-volume repulsion. In this respect, these
systems differ from most standard glass-forming liquids. They feature arrest
that occurs at lower densities and that is stronger than would be expected for
repulsion-dominated hard-sphere-like or Lennard-Jones-like systems. The
influence of attraction increases with increasing the number of carbon atoms
per molecule. However, unrealistically large fullerenes would be needed to
yield behavior reminiscent of recently investigated model colloids with strong
short-ranged attraction (glass-glass transitions and logarithmic decay of
time-correlation functions).Comment: 10 pages, 5 figure
The application of the global isomorphism to the study of liquid-vapor equilibrium in two and three dimensional Lenard-Jones fluids
We analyze the interrelation between the coexistence curve of the
Lennard-Jones fluid and the Ising model in two and three dimensions within the
global isomorphism approach proposed earlier [V. L. Kulinskii, J. Phys. Chem. B
\textbf{114} 2852 (2010)]. In case of two dimensions we use the exact Onsager
result to construct the binodal of the corresponding Lennard-Jones fluid and
compare it with the results of the simulations. In the three dimensional case
we use available numerical results for the Ising model for the corresponding
mapping. The possibility to observe the singularity of the binodal diameter is
discussed.Comment: 9 pages, 2 figure
Structure Functions and Pair Correlations of the Quark-Gluon Plasma
Recent experiments at RHIC and theoretical considerations indicate that the
quark-gluon plasma, present in the fireball of relativistic heavy-ion
collisions, might be in a liquid phase. The liquid state can be identified by
characteristic correlation and structure functions. Here definitions of the
structure functions and pair correlations of the quark-gluon plasma are
presented as well as perturbative results. These definitions might be useful
for verifying the quark-gluon-plasma liquid in QCD lattice calculations.Comment: 9 pages, 1 figure, revised version (new remark on the coupling
parameter on page 2), to be published in Phys. Rev.
Fundamental Gates for a Strongly Correlated Two-Electron Quantum Ring
We demonstrate that conditional as well as unconditional basic operations
which are prerequisite for universal quantum gates can be performed with almost
100% fidelity within a strongly interacting two-electron quantum ring. Both
sets of operations are based on a quantum control algorithm that optimizes a
driving electromagnetic pulse for a given quantum gate. The demonstrated
transitions occur on a time scale much shorter than typical decoherence times
of the system.Comment: 4 pages, 4 figures, copyright 2010 The American Physical Societ
A multi-blob representation of semi-dilute polymer solutions
A coarse-grained multi-blob description of polymer solutions is presented,
based on soft, transferable effective interactions between bonded and
non-bonded blobs. The number of blobs is chosen such that the blob density does
not exceed their overlap threshold, allowing polymer concentrations to be
explored deep into the semi-dilute regime. This quantitative multi-blob
description is shown to preserve known scaling laws of polymer solutions and
provides accurate estimates of amplitudes, while leading to orders of magnitude
increase of simulation efficiency and allowing analytic calculations of
structural and thermodynamic properties.Comment: 4 pages, 4 figure
Coarse-graining diblock copolymer solutions: a macromolecular version of the Widom-Rowlinson model
We propose a systematic coarse-grained representation of block copolymers,
whereby each block is reduced to a single ``soft blob'' and effective intra- as
well as intermolecular interactions act between centres of mass of the blocks.
The coarse-graining approach is applied to simple athermal lattice models of
symmetric AB diblock copolymers, in particular to a Widom-Rowlinson-like model
where blocks of the same species behave as ideal polymers (i.e. freely
interpenetrate), while blocks of opposite species are mutually avoiding walks.
This incompatibility drives microphase separation for copolymer solutions in
the semi-dilute regime. An appropriate, consistent inversion procedure is used
to extract effective inter- and intramolecular potentials from Monte Carlo
results for the pair distribution functions of the block centres of mass in the
infinite dilution limit.Comment: To be published in mol.phys(2005
A simple analytical model for dark matter halo structure and adiabatic contraction
A simple analytical model for describing inner parts of dark matter halo is
considered. It is assumed that dark matter density is power-law. The model
deals with dark matter distribution function in phase space of adiabatic
invariants (radial action and angular momentum). Two variants are considered
for the angular part of the distribution function: narrow and broad
distribution. The model allows to describe explicitly the process of adiabatic
contraction of halo due to change of gravitational potential caused by
condensation of baryonic matter in the centre. The modification of dark matter
density in the centre is calculated, and is it shown that the standard
algorithm of adiabatic contraction calculation overestimates the compressed
halo density, especially in the case of strong radial anisotropy.Comment: 5 pages, 3 figures. v3 - major improvements, another halo model
introduced, discussion extende
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