2,548 research outputs found
On Small Beams with Large Topological Charge II: Photons, Electrons and Gravitational Waves
Beams of light with a large topological charge significantly change their
spatial structure when they are focused strongly. Physically, it can be
explained by an emerging electromagnetic field component in the direction of
propagation, which is neglected in the simplified scalar wave picture in
optics. Here we ask: Is this a specific photonic behavior, or can similar
phenomena also be predicted for other species of particles? We show that the
same modification of the spatial structure exists for relativistic electrons as
well as for focused gravitational waves. However, this is for different
physical reasons: For electrons, which are described by the Dirac equation, the
spatial structure changes due to a Spin-Orbit coupling in the relativistic
regime. In gravitational waves described with linearized general relativity,
the curvature of space-time between the transverse and propagation direction
leads to the modification of the spatial structure. Thus, this universal
phenomenon exists for both massive and massless elementary particles with Spin
1/2, 1 and 2. It would be very interesting whether other types of particles
such as composite systems (neutrons or C) or neutrinos show a similar
behaviour and how this phenomenon can be explained in a unified physical way.Comment: 8 pages, 3 figure
Young's experiment and the finiteness of information
Young's experiment is the quintessential quantum experiment. It is argued
here that quantum interference is a consequence of the finiteness of
information. The observer has the choice whether that information manifests
itself as path information or in the interference pattern or in both partially
to the extent defined by the finiteness of information.Comment: 5 pages, 3 figures, typos remove
Rethinking affordance
n/a – Critical survey essay retheorising the concept of 'affordance' in digital media context. Lead article in a special issue on the topic, co-edited by the authors for the journal Media Theory
Maximal violation of Clauser-Horne-Shimony-Holt inequality for four-level systems
Clauser-Horne-Shimony-Holt inequality for bipartite systems of 4-dimension is
studied in detail by employing the unbiased eight-port beam splitters
measurements. The uniform formulae for the maximum and minimum values of this
inequality for such measurements are obtained. Based on these formulae, we show
that an optimal non-maximally entangled state is about 6% more resistant to
noise than the maximally entangled one. We also give the optimal state and the
optimal angles which are important for experimental realization.Comment: 7 pages, three table
Maximum Likelihood Methods for Inverse Learning of Optimal Controllers
This paper presents a framework for inverse learning of objective functions
for constrained optimal control problems, which is based on the
Karush-Kuhn-Tucker (KKT) conditions. We discuss three variants corresponding to
different model assumptions and computational complexities. The first method
uses a convex relaxation of the KKT conditions and serves as the benchmark. The
main contribution of this paper is the proposition of two learning methods that
combine the KKT conditions with maximum likelihood estimation. The key benefit
of this combination is the systematic treatment of constraints for learning
from noisy data with a branch-and-bound algorithm using likelihood arguments.
This paper discusses theoretic properties of the learning methods and presents
simulation results that highlight the advantages of using the maximum
likelihood formulation for learning objective functions.Comment: 21st IFAC World Congres
Age and metallicity gradients in fossil ellipticals
Fossil galaxy groups are speculated to be old and highly evolved systems of
galaxies that formed early in the universe and had enough time to deplete their
galaxies through successive mergers of member galaxies, building up one
massive central elliptical, but retaining the group X-ray halo. Considering
that fossils are the remnants of mergers in ordinary groups, the merger history
of the progenitor group is expected to be imprinted in the fossil central
galaxy (FCG). We present for the first time radial gradients of single-stellar
population (SSP) ages and metallicites in a sample of FCGs to constrain their
formation scenario. Our sample comprises some of the most massive galaxies in
the universe exhibiting an average central velocity dispersion of
km s. Metallicity gradients are throughout negative
with comparatively flat slopes of while
age gradients are found to be insignificant ().
All FCGs lie on the fundamental plane, suggesting that they are virialised
systems. We find that gradient strengths and central metallicities are similar
to those found in cluster ellipticals of similar mass. The comparatively flat
metallicity gradients with respect to those predicted by monolithic collapse
() suggest that fossils are indeed the result of multiple
major mergers. Hence we conclude that fossils are not 'failed groups' that
formed with a top heavy luminosity function. The low scatter of gradient slopes
suggests a similar merging history for all galaxies in our sample.Comment: 14 pages, 12 Figures, accepted for publication in A&
- …