918 research outputs found
Combining Molecular Dynamics with Lattice-Boltzmann: A Hybrid Method for the Simulation of (Charged) Colloidal Systems
We present a hybrid method for the simulation of colloidal systems, that
combines molecular dynamics (MD) with the Lattice-Boltzmann (LB) scheme. The LB
method is used as a model for the solvent in order to take into account the
hydrodynamic mass and momentum transport through the solvent. The colloidal
particles are propagated via MD and they are coupled to the LB fluid by viscous
forces. With respect to the LB fluid, the colloids are represented by uniformly
distributed points on a sphere. Each such point (with a velocity V(r) at any
off-lattice position r is interacting with the neighboring eight LB nodes by a
frictional force F=\xi_0(V(r)-u(r)) with \xi_0 being a friction force and u(r)
being the velocity of the fluid at the position r. Thermal fluctuations are
introduced in the framework of fluctuating hydrodynamics. This coupling scheme
has been proposed recently for polymer systems by Ahlrichs and D"unweg [J.
Chem. Phys. 111, 8225 (1999)]. We investigate several properties of a single
colloidal particle in a LB fluid, namely the effective Stokes friction and long
time tails in the autocorrelation functions for the translational and
rotational velocity. Moreover, a charged colloidal system is considered
consisting of a macroion, counterions and coions that are coupled to a LB
fluid. We study the behavior of the ions in a constant electric field. In
particular, an estimate of the effective charge of the macroion is yielded from
the number of counterions that move with the macroion in the direction of the
electric field.Comment: 37 pages, 12 figure
Second surface: multi-user spatial collaboration system based on augmented reality
An environment for creative collaboration is significant for enhancing human communication and expressive activities, and many researchers have explored different collaborative spatial interaction technologies. However, most of these systems require special equipment and cannot adapt to everyday environment. We introduce Second Surface, a novel multi-user Augmented reality system that fosters a real-time interaction for user-generated contents on top of the physical environment. This interaction takes place in the physical surroundings of everyday objects such as trees or houses. Our system allows users to place three dimensional drawings, texts, and photos relative to such objects and share this expression with any other person who uses the same software at the same spot. Second Surface explores a vision that integrates collaborative virtual spaces into the physical space. Our system can provide an alternate reality that generates a playful and natural interaction in an everyday setup
On reducing the Heun equation to the hypergeometric equation
The reductions of the Heun equation to the hypergeometric equation by
polynomial transformations of its independent variable are enumerated and
classified. Heun-to-hypergeometric reductions are similar to classical
hypergeometric identities, but the conditions for the existence of a reduction
involve features of the Heun equation that the hypergeometric equation does not
possess; namely, its cross-ratio and accessory parameters. The reductions
include quadratic and cubic transformations, which may be performed only if the
singular points of the Heun equation form a harmonic or an equianharmonic
quadruple, respectively; and several higher-degree transformations. This result
corrects and extends a theorem in a previous paper, which found only the
quadratic transformations. [See K. Kuiken, "Heun's equation and the
hypergeometric equation", SIAM Journal on Mathematical Analysis 10:3 (1979),
655-657.]Comment: 36 pages, a few additional misprints correcte
Synchronization of chaotic networks with time-delayed couplings: An analytic study
Networks of nonlinear units with time-delayed couplings can synchronize to a
common chaotic trajectory. Although the delay time may be very large, the units
can synchronize completely without time shift. For networks of coupled
Bernoulli maps, analytic results are derived for the stability of the chaotic
synchronization manifold. For a single delay time, chaos synchronization is
related to the spectral gap of the coupling matrix. For networks with multiple
delay times, analytic results are obtained from the theory of polynomials.
Finally, the analytic results are compared with networks of iterated tent maps
and Lang-Kobayashi equations which imitate the behaviour of networks of
semiconductor lasers
Three-dimensional magnetic flux-closure patterns in mesoscopic Fe islands
We have investigated three-dimensional magnetization structures in numerous
mesoscopic Fe/Mo(110) islands by means of x-ray magnetic circular dichroism
combined with photoemission electron microscopy (XMCD-PEEM). The particles are
epitaxial islands with an elongated hexagonal shape with length of up to 2.5
micrometer and thickness of up to 250 nm. The XMCD-PEEM studies reveal
asymmetric magnetization distributions at the surface of these particles.
Micromagnetic simulations are in excellent agreement with the observed magnetic
structures and provide information on the internal structure of the
magnetization which is not accessible in the experiment. It is shown that the
magnetization is influenced mostly by the particle size and thickness rather
than by the details of its shape. Hence, these hexagonal samples can be
regarded as model systems for the study of the magnetization in thick,
mesoscopic ferromagnets.Comment: 12 pages, 11 figure
Tuning the domain wall orientation in thin magnetic strips by induced anisotropy
We report on a method to tune the orientation of in-plane magnetic domains
and domain walls in thin ferromagnetic strips by manipulating the magnetic
anisotropy. Uniaxial in-plane anisotropy is induced in a controlled way by
oblique evaporation of magnetic thin strips. A direct correlation between the
magnetization direction and the domain wall orientation is found experimentally
and confirmed by micromagnetic simulations. The domain walls in the strips are
always oriented along the oblique evaporation-induced easy axis, in spite of
the shape anisotropy. The controlled manipulation of domain wall orientations
could open new possibilities for novel devices based on domain-wall
propagation
Separability of the massive Dirac's equation in 5-dimensional Myers-Perry black hole geometry and its relation to a rank-three Killing-Yano tensor
The Dirac equation for the electron around a five-dimensional rotating black
hole with two different angular momenta is separated into purely radial and
purely angular equations. The general solution is expressed as a superposition
of solutions derived from these two decoupled ordinary differential equations.
By separating variables for the massive Klein-Gordon equation in the same
space-time background, I derive a simple and elegant form for the
Stackel-Killing tensor, which can be easily written as the square of a
rank-three Killing-Yano tensor. I have also explicitly constructed a symmetry
operator that commutes with the scalar Laplacian by using the Stackel-Killing
tensor, and the one with the Dirac operator by the Killing-Yano tensor admitted
by the five-dimensional Myers-Perry metric, respectively.Comment: 15 pages, no figure, revtex4.cls. Typos removed. PRD published
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