13,945 research outputs found
On amenability and co-amenability of algebraic quantum groups and their corepresentations
We introduce and study several amenability properties for unitary
corepresentations and *-representations of algebraic quantum groups, which may
be used to characterize amenability or co-amenability of such groups. As a
background for this study, we also investigate the involved tensor
C*-categories.Comment: 46 pages, (some misprints corrected, a couple of remarks and a new
reference added
Experimental study of the microwave emission from electrons in air
We searched for the emission of microwave radiation in the Ku band generated
by a 95 keV electron beam in air. We unequivocally detected the radiation, and
measured its yield and angular dependence. Both the emitted power and its
angular pattern are well described by a model, where microwave photons are
generated via bremsstrahlung in the free-electron atomic-nucleus collisions,
during the slowdown of the electrons. As a consequence, the radiation is not
isotropic but peaked in the forward direction. The emission yield scales
proportionally with the number of electrons. This contrasts a previous claim
that the yield scales with the number squared, due to coherence. With a Monte
Carlo simulation we extrapolate our results to the Ultra High Energy Cosmic Ray
energy range.Comment: 5 pages, 4 figures. Accepted for publication in Phys.Rev.
Superselection Theory for Subsystems
An inclusion of observable nets satisfying duality induces an inclusion of
canonical field nets. Any Bose net intermediate between the observable net and
the field net and satisfying duality is the fixed-point net of the field net
under a compact group. This compact group is its canonical gauge group if the
occurrence of sectors with infinite statistics can be ruled out for the
observable net and its vacuum Hilbert space is separable.Comment: 28 pages, LaTe
Measurement of scaling laws for shock waves in thermal nonlocal media
We are able to detect the details of spatial optical collisionless
wave-breaking through the high aperture imaging of a beam suffering shock in a
fluorescent nonlinear nonlocal thermal medium. This allows us to directly
measure how nonlocality and nonlinearity affect the point of shock formation
and compare results with numerical simulations.Comment: 4 pages, 4 figure
Identifying Emotions in Social Media: Comparison of Word-emotion lexica
In recent years, emotions expressed in social media messages have become a vivid research topic due to their influence on the spread of misinformation and online radicalization over online social networks. Thus, it is important to correctly identify emotions in order to make inferences from social media messages. In this paper, we report on the performance of three publicly available word-emotion lexicons (NRC, DepecheMood, EmoSenticNet) over a set of Facebook and Twitter messages. To this end, we designed and implemented an algorithm that applies natural language processing (NLP) techniques along with a number of heuristics that reflect the way humans naturally assess emotions in written texts. In order to evaluate the appropriateness of the obtained emotion scores, we conducted a questionnaire-based survey with human raters. Our results show that there are noticeable differences between the performance of the lexicons as well as with respect to emotion scores the human raters provided in our surve
Shock waves in thermal lensing
We review experimental investigation on spatial shock waves formed by the
self-defocusing action of a laser beam propagation in a disordered thermal
nonlinear media.Comment: 9 pages, 12 figure
Beam Instabilities in the Scale Free Regime
The instabilities arising in a one-dimensional beam sustained by the
diffusive photorefractive nonlinearity in out-of-equilibrium ferroelectrics are
theoretically and numerically investigated. In the "scale-free model", in
striking contrast with the well-known spatial modulational instability, two
different beam instabilities dominate: a defocusing and a fragmenting process.
Both are independent of the beam power and are not associated to any specific
periodic pattern.Comment: 4 pages, 3 figure
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