179 research outputs found
Off-axis MeV and very-high-energy gamma-ray emissions from structured gamma-ray burst jets
Very-high-energy (VHE) photons around TeV energies from a gamma-ray burst
(GRB) jet will play an essential role in the multi-messenger era, with a fair
fraction of the events being observed off-axis to the jet. We show that
different energy photons (MeV and TeV photons in particular) arrive from
different emission zones for off-axis observers even if the emission radius is
the same. The location of the emission region depends on the jet structure of
the surface brightness, and the structures are generally different at different
energies, mainly due to the attenuation of VHE photons by electron-positron
pair creation. This off-axis zone-shift effect does not justify the usual
one-zone approximation and also produces a time-delay of VHE photons comparable
to the GRB duration, which is crucial for future VHE observations, such as by
the Cherenkov Telescope Array.Comment: 7 pages, 5 figures, submitted to MNRA
Low-temperature tension properties of glass-epoxy composite materials
Predmet i cilj ispitivanja prikazanih u ovom radu predstavlja određivanje zatezne čvrstoće (Rm) i modula elastičnosti (EJ staklo-epoksi kompozitnih materijala ispitivanjem na zatezanje na dve različite temperature (t=20°S i t=-50°S). Ispitivanja su izvedena prema standardu na staklo-epoksi kompozitnom materijalu različitih struktura (dve specifične težine ojačanja 210 g/m2H 550 g/m2) i orijentacija ojačanja (0°/90° i ±45°). Doprinos predstavlja i mikromehanička analiza na prelomnim površinama izvedena na stereo i elektronskom mikroskopu kojom se došlo do stvarnih modela nastanka i razvoja oštećenja pri izvedenim ispitivanjima.The aim of this paper was to present the determination of tensile strength Rm and modulus of elasticity Et of glass-epoxy composites at two different temperatures (at room temperature t=20°C, and at t =-50°C). Standard mechanical testing was carried out on glass woven-epoxy composite material with different structures (two specific weights of reinforcement, 210 g/m2 and 550 g/m2) and orientations (0°/90° and ±45°). Micromechanical analysis of failure was performed on a stereo microscope and SEM in order to determine real models and mechanisms of crack
Failure analysis of the mobile elevating work platform
This paper presents an investigation of the accident which occurred during startup of the extending structure from the transport position. In order to clarify the causes of crack occurrence along almost the entire surface of the lever cross-section, the authors performed visual, experimental (chemical composition, tensile properties, microhardness) as well as metallographic examinations. Stress states in the critical zone are defined by applying the finite element method (FEM). Based on the investigation results it was concluded that the lever breakdown is predominantly caused by both the 'operating-in' defect (the malfunction of the limit switch) and the 'manufacturing-in' defect (poor weld quality). The investigation results presented in this paper are important because same or similar problems could arise in supporting structures of various types of transportation, construction and mining machines
emoji2vec: Learning Emoji Representations from their Description
Many current natural language processing applications for social media rely on representation learning and utilize pre-trained word embeddings. There currently exist several publicly-available, pre-trained sets of word embeddings, but they contain few or no emoji representations even as emoji usage in social media has increased. In this paper we release emoji2vec, pre-trained embeddings for all Unicode emoji which are learned from their description in the Unicode emoji standard. The resulting emoji embeddings can be readily used in downstream social natural language processing applications alongside word2vec. We demonstrate, for the downstream task of sentiment analysis, that emoji embeddings learned from short descriptions outperforms a skip-gram model trained on a large collection of tweets, while avoiding the need for contexts in which emoji need to appear frequently in order to estimate a representation
Probing extreme environments with the Cherenkov Telescope Array
The physics of the non-thermal Universe provides information on the
acceleration mechanisms in extreme environments, such as black holes and
relativistic jets, neutron stars, supernovae or clusters of galaxies. In the
presence of magnetic fields, particles can be accelerated towards relativistic
energies. As a consequence, radiation along the entire electromagnetic spectrum
can be observed, and extreme environments are also the most likely sources of
multi-messenger emission. The most energetic part of the electromagnetic
spectrum corresponds to the very-high-energy (VHE, E>100 GeV) gamma-ray regime,
which can be extensively studied with ground based Imaging Atmospheric
Cherenkov Telescopes (IACTs). The results obtained by the current generation of
IACTs, such as H.E.S.S., MAGIC, and VERITAS, demonstrate the crucial importance
of the VHE band in understanding the non-thermal emission of extreme
environments in our Universe. In some objects, the energy output in gamma rays
can even outshine the rest of the broadband spectrum. The Cherenkov Telescope
Array (CTA) is the next generation of IACTs, which, with cutting edge
technology and a strategic configuration of ~100 telescopes distributed in two
observing sites, in the northern and southern hemispheres, will reach better
sensitivity, angular and energy resolution, and broader energy coverage than
currently operational IACTs. With CTA we can probe the most extreme
environments and considerably boost our knowledge of the non-thermal Universe.Comment: Submitted as input to ASTRONET Science Vision and Infrastructure
roadmap on behalf of the CTA consortiu
EuCAPT White Paper: Opportunities and Challenges for Theoretical Astroparticle Physics in the Next Decade
Astroparticle physics is undergoing a profound transformation, due to a
series of extraordinary new results, such as the discovery of high-energy
cosmic neutrinos with IceCube, the direct detection of gravitational waves with
LIGO and Virgo, and many others. This white paper is the result of a
collaborative effort that involved hundreds of theoretical astroparticle
physicists and cosmologists, under the coordination of the European Consortium
for Astroparticle Theory (EuCAPT). Addressed to the whole astroparticle physics
community, it explores upcoming theoretical opportunities and challenges for
our field of research, with particular emphasis on the possible synergies among
different subfields, and the prospects for solving the most fundamental open
questions with multi-messenger observations.Comment: White paper of the European Consortium for Astroparticle Theory
(EuCAPT). 135 authors, 400 endorsers, 133 pages, 1382 reference
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