1,176 research outputs found
Transport of a colloidal particle driven across a temporally oscillating optical potential energy landscape
A colloidal particle is driven across a temporally oscillating one-dimensional optical potential energy landscape and its particle motion is analysed. Different modes of dynamic mode locking are observed and are confirmed with the use of phase portraits. The effect of the oscillation frequency on the mode locked step width is addressed and the results are discussed in light of a high-frequency theory and compared to simulations. Furthermore, the influence of the coupling between the particle and the optical landscape on mode locking is probed by increasing the maximum depth of the optical landscape. Stronger coupling is seen to increase the width of mode locked steps. Finally, transport across the temporally oscillating landscape is studied by measuring the effective diffusion coefficient of a mobile particle, which is seen to be highly sensitive to the driving velocity and mode locking
Oscillatory behavior of the in-medium interparticle potential in hot gauge system with scalar bound states
We investigate the in-medium interparticle potential of hot gauge system with
bound states by employing the QED and scalar QED coupling. At finite
temperature an oscillatory behavior of the potential has been found as well as
its variation in terms of different free parameters. We expect the competition
among the parameters will lead to an appropriate interparticle potential which
could be extended to discuss the fluid properties of QGP with scalar bound
states
Self-assembly and crystallisation of indented colloids at a planar wall
We report experimental and simulation studies of the structure of a monolayer
of indented ("lock and key") colloids, on a planar surface. On adding a
non-absorbing polymer with prescribed radius and volume fraction, depletion
interactions are induced between the colloids, with controlled range and
strength. For spherical particles, this leads to crystallisation, but the
indented colloids crystallise less easily than spheres, in both simulation and
experiment. Nevertheless, simulations show that indented colloids do form
plastic (rotator) crystals. We discuss the conditions under which this occurs,
and the possibilities of lower-symmetry crystal states. We also comment on the
kinetic accessibility of these states.Comment: 8 pages, 8 figure
Localization dynamics of fluids in random confinement
The dynamics of two-dimensional fluids confined within a random matrix of
obstacles is investigated using both colloidal model experiments and molecular
dynamics simulations. By varying fluid and matrix area fractions in the
experiment, we find delocalized tracer particle dynamics at small matrix area
fractions and localized motion of the tracers at high matrix area fractions. In
the delocalized region, the dynamics is subdiffusive at intermediate times, and
diffusive at long times, while in the localized regime, trapping in finite
pockets of the matrix is observed. These observations are found to agree with
the simulation of an ideal gas confined in a weakly correlated matrix. Our
results show that Lorentz gas systems with soft interactions are exhibiting a
smoothening of the critical dynamics and consequently a rounded
delocalization-to-localization transition.Comment: 5 pages, 3 figure
Real-time Chern-Simons term for hypermagnetic fields
If non-vanishing chemical potentials are assigned to chiral fermions, then a
Chern-Simons term is induced for the corresponding gauge fields. In thermal
equilibrium anomalous processes adjust the chemical potentials such that the
coefficient of the Chern-Simons term vanishes, but it has been argued that
there are non-equilibrium epochs in cosmology where this is not the case and
that, consequently, certain fermionic number densities and large-scale
(hypermagnetic) field strengths get coupled to each other. We generalise the
Chern-Simons term to a real-time situation relevant for dynamical
considerations, by deriving the anomalous Hard Thermal Loop effective action
for the hypermagnetic fields, write down the corresponding equations of motion,
and discuss some exponentially growing solutions thereof.Comment: 13 page
Degenerate distributions in complex Langevin dynamics: one-dimensional QCD at finite chemical potential
We demonstrate analytically that complex Langevin dynamics can solve the sign
problem in one-dimensional QCD in the thermodynamic limit. In particular, it is
shown that the contributions from the complex and highly oscillating spectral
density of the Dirac operator to the chiral condensate are taken into account
correctly. We find an infinite number of classical fixed points of the Langevin
flow in the thermodynamic limit. The correct solution originates from a
continuum of degenerate distributions in the complexified space.Comment: 20 pages, several eps figures, minor comments added, to appear in
JHE
Convergence of simulated annealing by the generalized transition probability
We prove weak ergodicity of the inhomogeneous Markov process generated by the
generalized transition probability of Tsallis and Stariolo under power-law
decay of the temperature. We thus have a mathematical foundation to conjecture
convergence of simulated annealing processes with the generalized transition
probability to the minimum of the cost function. An explicitly solvable example
in one dimension is analyzed in which the generalized transition probability
leads to a fast convergence of the cost function to the optimal value. We also
investigate how far our arguments depend upon the specific form of the
generalized transition probability proposed by Tsallis and Stariolo. It is
shown that a few requirements on analyticity of the transition probability are
sufficient to assure fast convergence in the case of the solvable model in one
dimension.Comment: 11 page
Model-free measurement of the pair potential in colloidal fluids using optical microscopy
We report a straightforward, model-free approach for measuring pair
potentials from particle-coordinate data, based on enforcing consistency
between the pair distribution function measured separately by the
distance-histogram and test-particle insertion routes. We demonstrate the
method's accuracy and versatility in simulations of simple fluids, before
applying it to an experimental system composed of superparamagnetic colloidal
particles. The method will enable experimental investigations into many-body
interactions and allow for effective coarse-graining of interactions from
simulations.Comment: 8 pages, 3 figures including supplemental materia
Spin Screening and Antiscreening in a Ferromagnet/Superconductor Heterojunction
We present a theoretical study of spin screening effects in a
ferromagnet/superconductor (F/S) heterojunction. It is shown that the magnetic
moment of the ferromagnet is screened or antiscreened, depending on the
polarization of the electrons at the Fermi level. If the polarization is
determined by the electrons of the majority (minority) spin band then the
magnetic moment of the ferromagnet is screened (antiscreened) by the electrons
in the superconductor. We propose experiments that may confirm our theory: for
ferromagnetic alloys with certain concentration of Fe or Ni ions there will be
screening or antiscreening respectively. Different configurations for the
density of states are also discussed.Comment: 5 pages; 4 figures. to be published in Phys. Rev,
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