5,964 research outputs found
Can type II Semi-local cosmic strings form?
We present the simplest possible model for a semi-local string defect in
which a U(1) gauged subgroup of an otherwise global SU(2) is broken to produce
local cosmic strings endowed with current-carrying properties. Restricting
attention to type II vortices for which the non current-carrying state is
unstable, we show that a condensate must form microscopically and
macroscopically evolve towards a chiral configuration. It has been suggested
that such configurations could potentially exist in a stable state, thereby
inducing large cosmological consequences based on equilibrium angular momentum
supported loop configurations (vortons). Here we show that the current itself
induces a macroscopic (longitudinal) instability: we conclude that type II
semi-local cosmic strings cannot form in a cosmological context.Comment: 11 pages, 5 figure
Single exposure 3D imaging of dusty plasma clusters
We have worked out the details of a single camera, single exposure method to
perform three-dimensional imaging of a finite particle cluster. The procedure
is based on the plenoptic imaging principle and utilizes a commercial Lytro
light field still camera. We demonstrate the capabilities of our technique on a
single layer particle cluster in a dusty plasma, where the camera is aligned
inclined at a small angle to the particle layer. The reconstruction of the
third coordinate (depth) is found to be accurate and even shadowing particles
can be identified.Comment: 6 pages, 7 figures. Submitted to Rev. Sci. Inst
Self-Consistent Projection Operator Theory for Quantum Many-Body Systems
We derive an exact equation of motion for the reduced density matrices of
individual subsystems of quantum many-body systems of any lattice dimension and
arbitrary system size. Our projection operator based theory yields a highly
efficient analytical and numerical approach. Besides its practical use it
provides a novel interpretation and systematic extension of mean-field
approaches and an adaption of open quantum systems theory to settings where a
dynamically evolving environment has to be taken into account. We show its high
accuracy for two significant classes of complex quantum many-body dynamics,
unitary evolutions of non-equilibrium states in closed and stationary states in
driven-dissipative systems.Comment: 13 pages, 4 figure
Factorization of 3-point static structure functions in 3D Yukawa liquids
In many-body systems the convolution approximation states that the 3-point
static structure function, , can
approximately be "factorized" in terms of the 2-point counterpart,
. We investigate the validity of this approximation in
3-dimensional strongly-coupled Yukawa liquids: the factorization is tested for
specific arrangements of the wave vectors and
, with molecular dynamics simulations. With the increase of the
coupling parameter we find a breakdown of factorization, of which a notable
example is the appearance of negative values of
, whereas the approximate factorized
form is restricted to positive values. These negative values -- based on the
quadratic Fluctuation-Dissipation Theorem -- imply that the quadratic part of
the density response of the system changes sign with wave number. Our
simulations that incorporate an external potential energy perturbation clearly
confirm this behavior
Model reduction of controlled Fokker--Planck and Liouville-von Neumann equations
Model reduction methods for bilinear control systems are compared by means of
practical examples of Liouville-von Neumann and Fokker--Planck type. Methods
based on balancing generalized system Gramians and on minimizing an H2-type
cost functional are considered. The focus is on the numerical implementation
and a thorough comparison of the methods. Structure and stability preservation
are investigated, and the competitiveness of the approaches is shown for
practically relevant, large-scale examples
Intensity distribution of non-linear scattering states
We investigate the interplay between coherent effects characteristic of the
propagation of linear waves, the non-linear effects due to interactions, and
the quantum manifestations of classical chaos due to geometrical confinement,
as they arise in the context of the transport of Bose-Einstein condensates. We
specifically show that, extending standard methods for non-interacting systems,
the body of the statistical distribution of intensities for scattering states
solving the Gross-Pitaevskii equation is very well described by a local
Gaussian ansatz with a position-dependent variance. We propose a semiclassical
approach based on interfering classical paths to fix the single parameter
describing the universal deviations from a global Gaussian distribution. Being
tail effects, rare events like rogue waves characteristic of non-linear field
equations do not affect our results.Comment: 18 pages, 7 figures, submitted to Proceedings MARIBOR 201
Marine Spatial Data Infrastructure in the Baltic
At its 15th Conference, the Baltic Sea Hydrographic Commission (BSHC) decided to establish a working group on marine spatial data infrastructure (MSDI) with the task of promoting MSDI in the Baltic Sea region. The working group’s focus is on national coordination of maritime information. Thus far, the group has conducted an in-depth survey of the participating countries’ respective approaches to coordinated access to maritime information. The study identifies areas where MSDI implementation is underway and where challenges can be foreseen
Financial integration, specialization and systemic risk
This paper studies the implications of cross-border financial integration for financial stability when banks' loan portfolios adjust endogenously. Banks can be subject to sectoral and aggregate domestic shocks. After integration they can share these risks in a complete interbank market. When banks have a comparative advantage in providing credit to certain industries, financial integration may induce banks to specialize in lending. An enhanced concentration in lending does not necessarily increase risk, because a well-functioning interbank market allows to achieve the necessary diversification. This greater need for risk sharing, though, increases the risk of cross-border contagion and the likelihood of widespread banking crises. However, even though integration increases the risk of contagion it improves welfare if it permits banks to realize specialization benefits. JEL Classification: D61, E44, G21.Financial integration, specialization, interbank market, financial contagion.
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