205 research outputs found
Effective interaction between star polymers
The distance-resolved effective interaction between two star polymers in a
good solvent is calculated by Molecular Dynamics computer simulations. The
results are compared with a pair potential proposed recently by Likos et al.
[Phys. Rev. Lett. 1998, 80, 4450] which is exponentially decaying for large
distances and crosses over, at the corona diameter of the star, to an ultrasoft
logarithmic repulsion for small distances. Excellent agreement is found in a
broad range of star arm numbers.Comment: final version as published, 9 pages + 5 ps-figure
Effective Electrostatic Interactions in Suspensions of Polyelectrolyte Brush-Coated Colloids
Effective electrostatic interactions between colloidal particles, coated with
polyelectrolyte brushes and suspended in an electrolyte solvent, are described
via linear response theory. The inner cores of the macroions are modeled as
hard spheres, the outer brushes as spherical shells of continuously distributed
charge, the microions (counterions and salt ions) as point charges, and the
solvent as a dielectric continuum. The multi-component mixture of macroions and
microions is formally mapped onto an equivalent one-component suspension by
integrating out from the partition function the microion degrees of freedom.
Applying second-order perturbation theory and a random phase approximation,
analytical expressions are derived for the effective pair interaction and a
one-body volume energy, which is a natural by-product of the one-component
reduction. The combination of an inner core and an outer shell, respectively
impenetrable and penetrable to microions, allows the interactions between
macroions to be tuned by varying the core diameter and brush thickness. In the
limiting cases of vanishing core diameter and vanishing shell thickness, the
interactions reduce to those derived previously for star polyelectrolytes and
charged colloids, respectively.Comment: 20 pages, 5 figures, Phys. Rev. E (in press
Fluid-fluid demixing transitions in colloid--polyelectrolyte star mixtures
We derive effective interaction potentials between hard, spherical colloidal
particles and star-branched polyelectrolytes of various functionalities and
smaller size than the colloids. The effective interactions are based on a
Derjaguin-like approximation, which is based on previously derived potentials
acting between polyelectrolyte stars and planar walls. On the basis of these
interactions we subsequently calculate the demixing binodals of the binary
colloid--polyelectrolyte star mixture, employing standard tools from
liquid-state theory. We find that the mixture is indeed unstable at moderately
high overall concentrations. The system becomes more unstable with respect to
demixing as the star functionality and the size ratio grow.Comment: 24 pages, 9 figures, submitted to Journal of Physics: Condensed
Matte
Dark matter signatures of black holes with Yukawa potential
This study uses a nonsingular Yukawa--modified potential to obtain a static
and spherically symmetric black hole solution with a cosmological constant.
Such Yukawa--like corrections are encoded in two parameters, and
, that modify Newton's law of gravity in large distances, and a
deformation parameter , which plays an essential role in short
distances. The most significant effect is encoded in , which modifies
the total black hole mass with an extra mass proportional to ,
mimicking the dark matter effects at large distances from the black hole. On
the other hand, the effect due to is small for astrophysical values.
We scrutinize the \textit{quasinormal} frequencies and shadows associated with
a spherically symmetric black hole and the thermodynamical behavior influenced
by the Yukawa potential. In particular, the thermodynamics of this black hole
displays a rich behavior, including possible phase transitions. We use the WKB
method to probe the \textit{quasinormal} modes of massless scalar,
electromagnetic, and gravitational field perturbations. In order to check the
influence of the parameters on the shadow radius, we consider astrophysical
data to determine their values, incorporating information on an optically thin
radiating and infalling gas surrounding a black hole to model the black hole
shadow image. In particular, we consider Sgr A* black hole as an example and we
find that its shadow radius changes by order of , meaning that the
shadow radius of a black hole with Yukawa potential practically gives rise to
the same result encountered in the Schwarzschild black hole. Also, in the
eikonal regime, using astrophysical data for Yukawa parameters, we show that
the value of the real part of the QNMs frequencies changes by .Comment: 24 pages in double column, 13 figures and 5 table
Accurate description of bulk and interfacial properties in colloid-polymer mixtures
Large-scale Monte Carlo simulations of a phase-separating colloid-polymer
mixture are performed and compared to recent experiments. The approach is based
on effective interaction potentials in which the central monomers of
self-avoiding polymer chains are used as effective coordinates. By
incorporating polymer nonideality together with soft colloid-polymer repulsion,
the predicted binodal is in excellent agreement with recent experiments. In
addition, the interfacial tension as well as the capillary length are in
quantitative agreement with experimental results obtained at a number of points
in the phase-coexistence region, without the use of any fit parametersComment: 4 pages, 4 figure
Constraining study of circular orbits and accretion disk around nonlinear electrodynamics black hole
The very latest observation of supermassive black hole (BH) by the
Event Horizon Telescope (EHT) provides the accretion onto BHs is an interesting
study in the theory of gravity. We study the geodesics structure and accretion
near a nonlinear electrodynamics BH in strong and weak field approximations.
These approximations provide the disc-like structure under the geodesic motion
and accretion around the BH. Near the equatorial plane, we provide some new
reasons to make circular orbits and accretion of test particles around the BH.
Then we investigate perturbations, the critical speed of the fluid and the mass
accretion rate of particles around the central object. The physical validity of
this study shows that the parameter and play an important role in
the circular orbits and the mass accretion rate in strong and weak field
approximations.Comment: 21 pages, 12 figure
Effective interactions between star polymers
We study numerically the effective pair potential between star polymers with
equal arm lengths and equal number of arms. The simulations were done for
the soft core Domb-Joyce model on the simple cubic lattice, to minimize
corrections to scaling and to allow for an unlimited number of arms. For the
sampling, we used the pruned-enriched Rosenbluth method (PERM). We find that
the potential is much less soft than claimed in previous papers, in particular
for . While we verify the logarithmic divergence of , with
being the distance between the two cores, predicted by Witten and Pincus, we
find for that the Mayer function is hardly distinguishable from that for
a Gaussian potential.Comment: 5 pages, 5 figure
Stability of a d-Dimensional Thin-Shell Wormhole Surrounded by Quintessence
We study the stability of different higher dimensional thin–shell wormholes (HDTSW) in general relativity with a cosmological constant. We show that a d-dimensional thin–shell wormhole surrounded by quintessence can have three different throat geometries: spherical, planar and hyperbolic. Unlike the spherical geometry, the planar and hyperbolic geometries allow different topologies that can be interpreted as higher-dimensional domain walls or branes connecting two universes. To construct these geometries, we use the cut-and-paste procedure by joining two identical vacuum space-time solutions. Properties such as the null energy condition and geodesics are also studied. A linear stability analysis around the static solutions is carried out, taking into account a more general HDTSW geometry than previous works, so it is possible to recover other well-known stability HDTSW conditions
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