128,255 research outputs found
Janus within Janus
We found a simple and interesting generalization of the non-supersymmetric
Janus solution in type IIB string theory. The Janus solution can be thought of
as a thick AdS_d-sliced domain wall in AdS_{d+1} space. It turns out that the
AdS_d-sliced domain wall can support its own AdS_{d-1}-sliced domain wall
within it. Indeed this pattern persists further until it reaches the
AdS_2-slice of the domain wall within self-similar AdS_{p (2<p\le d)}-sliced
domain walls. In other words the solution represents a sequence of little Janus
nested in the interface of the parent Janus according to a remarkably simple
``nesting'' rule. Via the AdS/CFT duality, the dual gauge theory description is
in general an interface CFT of higher codimensions.Comment: 15 pages, 6 figures, v2 references added. v3 eq.(3.33) correcte
JANUS: an FPGA-based System for High Performance Scientific Computing
This paper describes JANUS, a modular massively parallel and reconfigurable
FPGA-based computing system. Each JANUS module has a computational core and a
host. The computational core is a 4x4 array of FPGA-based processing elements
with nearest-neighbor data links. Processors are also directly connected to an
I/O node attached to the JANUS host, a conventional PC. JANUS is tailored for,
but not limited to, the requirements of a class of hard scientific applications
characterized by regular code structure, unconventional data manipulation
instructions and not too large data-base size. We discuss the architecture of
this configurable machine, and focus on its use on Monte Carlo simulations of
statistical mechanics. On this class of application JANUS achieves impressive
performances: in some cases one JANUS processing element outperfoms high-end
PCs by a factor ~ 1000. We also discuss the role of JANUS on other classes of
scientific applications.Comment: 11 pages, 6 figures. Improved version, largely rewritten, submitted
to Computing in Science & Engineerin
Note on Generalized Janus Configurations
We study several aspects of generalized Janus configuration, which includes a
theta term. We investigate the vacuum structure of the theory and find that
unlike the Janus configuration without theta term there is no nontrivial
vacuum. We also discuss BPS soliton configuration both by supersymmetry
analysis and from energy functional. The half BPS configurations could be
realized by introducing transverse (p,q)-strings in original brane
configuration corresponding to generalized Janus configuration. It turns out
the BPS soliton could be taken as modified dyon. We discuss the solution of
half BPS equations for the sharp interface case. Moreover we construct less
supersymmetric Janus configuration with theta term.Comment: 27 pages; References adde
Hydrodynamic simulations of self-phoretic microswimmers
A mesoscopic hydrodynamic model to simulate synthetic self-propelled Janus
particles which is thermophoretically or diffusiophoretically driven is here
developed. We first propose a model for a passive colloidal sphere which
reproduces the correct rotational dynamics together with strong phoretic
effect. This colloid solution model employs a multiparticle collision dynamics
description of the solvent, and combines potential interactions with the
solvent, with stick boundary conditions. Asymmetric and specific colloidal
surface is introduced to produce the properties of self-phoretic Janus
particles. A comparative study of Janus and microdimer phoretic swimmers is
performed in terms of their swimming velocities and induced flow behavior.
Self-phoretic microdimers display long range hydrodynamic interactions and can
be characterized as pullers or pushers. In contrast, Janus particles are
characterized by short range hydrodynamic interactions and behave as neutral
swimmers. Our model nicely mimics those recent experimental realization of the
self-phoretic Janus particles.Comment: 11pages, 12figures, 2table
Electrophoresis of Janus Particles: a Molecular Dynamics simulation study
In this work, we use Molecular Dynamics and Lattice-Boltzmann simulations to
study the properties of charged Janus particles in an electric field. We show
that for relatively small net charge and thick electrostatic diffuse layer
mobilities of Janus particles and uniformly charged colloids of the same net
charge are identical. However, for higher charges and thinner diffuse layers
Janus particles always show lower electrophoretic mobility. We also demonstrate
that Janus particles align with the electric field and the angular deviation
from the field's direction are related to their dipole moment. We show that the
latter is affected by the thickness of the electrostatic diffuse layer and
strongly correlates with the electrophoretic mobility.Comment: Accepted to JC
Molecular dynamics simulations of the rotational and translational diffusion of a Janus rod-shaped nanoparticle
The diffusion of a Janus rod-shaped nanoparticle in a dense Lennard-Jones
fluid is studied using molecular dynamics (MD) simulations. The Janus particle
is modeled as a rigid cylinder whose atoms on each half-side have different
interaction energies with fluid molecules, thus comprising wetting and
nonwetting surfaces. We found that both rotational and translational diffusion
coefficients are larger for Janus particles with higher wettability contrast,
and these values are bound between the two limiting cases of uniformly wetting
and nonwetting particles. It was also shown that values of the diffusion
coefficients for displacements parallel and perpendicular to the major axis of
a uniformly wetting particle agree well with analytical predictions despite a
finite slip at the particle surface present in MD simulations. It was further
demonstrated that diffusion of Janus particles is markedly different from that
of uniform particles; namely, Janus particles preferentially rotate and orient
their nonwetting sides along the displacement vector to reduce drag. This
correlation between translation and rotation is consistent with the previous
results on diffusive dynamics of a spherical Janus particle with two
hemispheres of different wettability.Comment: 27 pages, 9 figure
Conformal Janus on Euclidean Sphere
We interpret Janus as an interface in a conformal field theory and study its
properties. The Janus is created by an exactly marginal operator and we study
its effect on the interface conformal field theory on the Janus. We do this by
utilizing the AdS/CFT correspondence. We compute the interface free energy both
from leading correction to the Euclidean action in the dual gravity description
and from conformal perturbation theory in the conformal field theory. We find
that the two results agree each other and that the interface free energy scales
precisely as expected from the conformal invariance of the Janus interface.Comment: 37 pages, 5 figures, references added, section 2 and references
added, published versio
Critical adsorption of polyelectrolytes onto charged Janus nanospheres
Based on extensive Monte Carlo simulations and analytical considerations we
study the electrostatically driven adsorption of flexible polyelectrolyte
chains onto charged Janus nanospheres. These net-neutral colloids are composed
of two equally but oppositely charged hemispheres. The critical binding
conditions for polyelectrolyte chains are analysed as function of the radius of
the Janus particle and its surface charge density, as well as the salt
concentration in the ambient solution. Specifically for the adsorption of
finite-length polyelectrolyte chains onto Janus nanoparticles, we demonstrate
that the critical adsorption conditions drastically differ when the size of the
Janus particle or the screening length of the electrolyte are varied. We
compare the scaling laws obtained for the adsorption-desorption threshold to
the known results for uniformly charged spherical particles, observing
significant disparities. We also contrast the changes to the polyelectrolyte
chain conformations and the binding energy distributions close to the
adsorption-desorption transition for Janus nanoparticles to those for simple
spherical particles. Finally, we discuss experimentally relevant
physico-chemical systems for which our simulations results may become
important. In particular, we observe similar trends with polyelectrolyte
complexation with oppositely but heterogeneously charged proteins.Comment: 13 pages, 11 figures, RevTeX
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