3,868 research outputs found
Cosmic-ray acceleration and gamma-ray signals from radio supernovae
In this work the efficiency of particle acceleration at the forward shock
right after the SN outburst for the particular case of the well-known SN 1993J
is analyzed. Plasma instabilities driven by the energetic particles accelerated
at the shock front grow over intraday timescales and drive a fast amplification
of the magnetic field at the shock, that can explain the magnetic field
strengths deduced from the radio monitoring of the source. The maximum particle
energy is found to reach 1-10 PeV depending on the instability dominating the
amplification process. We derive the time dependent particle spectra and the
associated hadronic signatures of secondary particles arising from proton
proton interactions. We find that the Cherenkov Telescope Array (CTA) should
easily detect objects like SN 1993J in particular above 1 TeV, while current
generation of Cherenkov telescopes such as H.E.S.S. could only marginally
detect such events. The gamma-ray signal is found to be heavily absorbed by
pair production process during the first week after the outburst. We predict a
low neutrino flux above 10 TeV, implying a detectability horizon with a
KM3NeT-type telescope of 1 Mpc only. We finally discuss the essential
parameters that control the particle acceleration and gamma-ray emission in
other type of SNe.Comment: 7 pages, 3 figures (Note: conflict of .sty file version explains the
problems with journal title and the abstract, apologies for any
inconvenience). Appears as Nuclear Physics B Proceedings Supplement 2014
Proceedings of the workshop "Cosmic Ray Origin beyond the standard models",
San Vito (2014), ed. by O.Tibolla, L. Drur
Inflationary spectra and violations of Bell inequalities
In spite of the macroscopic character of the primordial fluctuations, the
standard inflationary distribution (that obtained using linear mode equations)
exhibits inherently quantum properties, that is, properties which cannot be
mimicked by any stochastic distribution. This is demonstrated by a Gedanken
experiment for which certain Bell inequalities are violated. These violations
are {\it in principle} measurable because, unlike for Hawking radiation from
black holes, in inflationary cosmology we can have access to both members of
correlated pairs of modes delivered in the same state. We then compute the
effect of decoherence and show that the violations persist provided the
decoherence level (and thus the entropy) lies below a certain non-vanishing
threshold. Moreover, there exists a higher threshold above which no violation
of any Bell inequality can occur. In this regime, the distributions are
``separable'' and can be interpreted as stochastic ensembles of fluctuations.
Unfortunately, the precision which is required to have access to the quantum
properties is so high that, {\it in practice}, an observational verification
seems excluded.Comment: 5 pages, 1 figure; new presentation and extended discussio
Strains Induced by Point Defects in Graphene on a Metal
Strains strongly affect the properties of low-dimensional materials, such as
graphene. By combining in situ, in operando, reflection high energy electron
diffraction experiments with first-principles calculations, we show that large
strains, above 2%, are present in graphene during its growth by chemical vapor
deposition on Ir(111) and when it is subjected to oxygen etching and ion
bombardment. Our results unravel the microscopic relationship between point
defects and strains in epitaxial graphene and suggest new avenues for graphene
nanostructuring and engineering its properties through introduction of defects
and intercalation of atoms and molecules between graphene and its metal
substrate
Universal design for website authentication:views and experiences of senior citizens
Using digital devices and online products and services requires users to regularly authenticate themselves. Given that the vast majority of websites use passwords to authenticate users, this study focuses on the accessibility and inclusivity of this mechanism, using Universal Design Principles as a lens. Collecting and analysing autobiographical narrative data from 50 respondents, we use a qualitative approach to explore the views and experiences of senior citizens across various phases of website authentication. Our analysis uncovers barriers and challenges, leading to several undesirable consequences, when authentication is not accessible and inclusive. Our findings also show how users, many of whom have cognitive and other age-related infirmities which are seldom accommodated in authentication design, try to cope with these issues. Our findings show how authentication may fail to align with the principles of universal design and highlight considerations in making authentication more accessible and inclusive for all users
Evolution of the mass, size, and star formation rate in high-redshift merging galaxies MIRAGE - A new sample of simulations with detailed stellar feedback
We aim at addressing the questions related to galaxy mass assembly through
major and minor wet merging processes in the redshift range 1<z<2. A consequent
fraction of Milky Way like galaxies are thought to have undergone an unstable
clumpy phase at this early stage. Using the adaptive mesh refinement code
RAMSES, with a recent physically-motivated implementation of stellar feedback,
we build the Merging and Isolated high-Redshift Adaptive mesh refinement
Galaxies (MIRAGE) sample. It is composed of 20 mergers and 3 isolated idealized
disks simulations with global physical properties in accordance with the 1<z<2
mass complete sample MASSIV. The numerical hydrodynamical resolution reaches 7
parsecs in the smallest Eulerian cells. Our simulations include: star
formation, metal line cooling, metallicity advection, and a recent
implementation of stellar feedback which encompasses OB-type stars radiative
pressure, photo-ionization heating, and supernovae. The initial conditions are
set to match the z~2 observations, thanks to a new public code DICE. The
numerical resolution allows us to follow the formation and evolution of giant
clumps formed in-situ from Jeans instabilities triggered by high initial gas
fraction. The star formation history of isolated disks shows stochastic star
formation rate, which proceeds from the complex behavior of the giant clumps.
Our minor and major gas-rich merger simulations do not trigger starbursts,
suggesting a saturation of the star formation in a turbulent and clumpy
interstellar medium fed by substantial accretion from the circum-galactic
medium. Our simulations are close to the normal regime of the disk-like star
formation on a Schmidt-Kennicutt diagram. The mass-size relation and its rate
of evolution matches observations, suggesting that the inside-out growth
mechanisms of the stellar disk do not necessarily require to be achieved
through a cold accretion.Comment: 18 pages, 12 figures. Accepted in A&
Des systemes simplifies aux combustibles modeles etude in situ du frittage d'oxydes d'actinides et de lanthanides
International audienceresume JSM 201
The Stabilized Poincare-Heisenberg algebra: a Clifford algebra viewpoint
The stabilized Poincare-Heisenberg algebra (SPHA) is the Lie algebra of
quantum relativistic kinematics generated by fifteen generators. It is obtained
from imposing stability conditions after attempting to combine the Lie algebras
of quantum mechanics and relativity which by themselves are stable, however not
when combined. In this paper we show how the sixteen dimensional Clifford
algebra CL(1,3) can be used to generate the SPHA. The Clifford algebra path to
the SPHA avoids the traditional stability considerations, relying instead on
the fact that CL(1,3) is a semi-simple algebra and therefore stable. It is
therefore conceptually easier and more straightforward to work with a Clifford
algebra. The Clifford algebra path suggests the next evolutionary step toward a
theory of physics at the interface of GR and QM might be to depart from working
in space-time and instead to work in space-time-momentum.Comment: 14 page
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