2,161 research outputs found
Finding central decompositions of p-groups
Polynomial-time algorithms are given to find a central decomposition of
maximum size for a finite p-group of class 2 and for a nilpotent Lie ring of
class 2. The algorithms use Las Vegas probabilistic routines to compute the
structure of finite *-rings and also the Las Vegas C-MeatAxe. When p is small,
the probabilistic methods can be replaced by deterministic polynomial-time
algorithms.
The methods introduce new group isomorphism invariants including new
characteristic subgroups.Comment: 28 page
Measurement of zero degree single photon energy spectra for sqrt(s) = 7TeV proton-proton collisions at LHC
In early 2010, the Large Hadron Collider forward (LHCf) experiment measured
very forward neutral particle spectra in LHC proton-proton collisions. From a
limited data set taken under the best beam conditions (low beam-gas background
and low occurance of pile-up events), the single photon spectra at sqrt(s)=7TeV
and pseudo-rapidity (eta) ranges from 8.81 to 8.99 and from 10.94 to infinity
were obtained for the first time and are reported in this paper. The spectra
from two independent LHCf detectors are consistent with one another and serve
as a cross check of the data. The photon spectra are also compared with the
predictions of several hadron interaction models that are used extensively for
modeling ultra high energy cosmic ray showers. Despite conservative estimates
for the systematic errors, none of the models agree perfectly with the
measurements. A notable difference is found between the data and the DPMJET
3.04 and PYTHIA 8.145 hadron interaction models above 2TeV where the models
predict higher photon yield than the data. The QGSJET II-03 model predicts
overall lower photon yield than the data, especially above 2TeV in the rapidity
range 8.81<eta<8.99
Cosmic Rays at the highest energies
After a century of observations, we still do not know the origin of cosmic
rays. I will review the current state of cosmic ray observations at the highest
energies, and their implications for proposed acceleration models and secondary
astroparticle fluxes. Possible sources have narrowed down with the confirmation
of a GZK-like spectral feature. The anisotropy observed by the Pierre Auger
Observatory may signal the dawn of particle astronomy raising hopes for high
energy neutrino observations. However, composition related measurements point
to a different interpretation. A clear resolution of this mystery calls for
much larger statistics than the reach of current observatories.Comment: 8 pages, 4 figures, in the Proceedings of TAUP 201
SARS CoV-2 aggravates cellular metabolism mediated complications in COVID-19 infection.
Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), the primary causative organism in corona virus disease-19 (COVID-19) infections, is a novel member of the human coronavirus family which was first identified in Wuhan, China, towards the end of 2019. This letter reveals new vital missing links in our current understanding of the mechanisms that lead to cell death triggered by ferroptotic stress in COVID-19 infection. It further reveal the importance of homocysteine mediated trans-sulfuration pathway in COVID-19 infection. Hence, Vitamin B6, folic acid, and Vitamin B12 should be incorporated in the treatment regimen for SARS CoV-2 infections to suppress complications, as the virus mediates altered host cell metabolism
Observing Ultra High Energy Cosmic Particles from Space: SEUSO, the Super Extreme Universe Space Observatory Mission
The experimental search for ultra high energy cosmic messengers, from eV to beyond eV, at the very end of the known energy
spectrum, constitutes an extraordinary opportunity to explore a largely unknown
aspect of our universe. Key scientific goals are the identification of the
sources of ultra high energy particles, the measurement of their spectra and
the study of galactic and local intergalactic magnetic fields. Ultra high
energy particles might, also, carry evidence of unknown physics or of exotic
particles relics of the early universe. To meet this challenge a significant
increase in the integrated exposure is required. This implies a new class of
experiments with larger acceptances and good understanding of the systematic
uncertainties. Space based observatories can reach the instantaneous aperture
and the integrated exposure necessary to systematically explore the ultra high
energy universe. In this paper, after briefly summarising the science case of
the mission, we describe the scientific goals and requirements of the SEUSO
concept. We then introduce the SEUSO observational approach and describe the
main instrument and mission features. We conclude discussing the expected
performance of the mission
Study of Small-Scale Anisotropy of Ultrahigh Energy Cosmic Rays Observed in Stereo by HiRes
The High Resolution Fly's Eye (HiRes) experiment is an air fluorescence
detector which, operating in stereo mode, has a typical angular resolution of
0.6 degrees and is sensitive to cosmic rays with energies above 10^18 eV. HiRes
is thus an excellent instrument for the study of the arrival directions of
ultrahigh energy cosmic rays. We present the results of a search for
anisotropies in the distribution of arrival directions on small scales (<5
degrees) and at the highest energies (>10^19 eV). The search is based on data
recorded between 1999 December and 2004 January, with a total of 271 events
above 10^19 eV. No small-scale anisotropy is found, and the strongest
clustering found in the HiRes stereo data is consistent at the 52% level with
the null hypothesis of isotropically distributed arrival directions.Comment: 4 pages, 3 figures. Matches accepted ApJL versio
Highest Energy Cosmic Rays and results from the HiRes Experiment
The status of the field of ultrahigh energy cosmic rays is summarized, from
the point of view of the latest results of the High Resolution Fly's Eye
(HiRes) Experiment. HiRes results are presented, and compared with those of the
Akeno Giant Air Shower Array (AGASA), plus the Telescope Array and Pierre Auger
experiments. The HiRes measurements of the cosmic ray spectrum, and the
observation of the GZK cutoff are presented. HiRes results on composition,
searches for anisotropy, measurement of the proton-air total cross section, and
shapes of shower profiles are presented.Comment: 31 pages, 18 figures, submitted to Journal of Physics
Optical and thermal performance of bladed receivers
Bladed receivers use conventional receiver tube-banks rearranged into bladed/finned structures, and offer better light trapping, reduced radiative and convective losses, and reduced tube mass, based on the presented optical and thermal analysis. Optimising for optical performance, deep blades emerge. Considering thermal losses leads to shallower blades. Horizontal blades perform better, in both windy and no-wind conditions, than vertical blades, at the scales considered so far. Air curtains offer options to further reduce convective losses; high flux on blade-tips is still a concern
New constraints on Planck-scale Lorentz Violation in QED from the Crab Nebula
We set constraints on O(E/M) Lorentz Violation in QED in an effective field
theory framework. A major consequence of such assumptions is the modification
of the dispersion relations for electrons/positrons and photons, which in turn
can affect the electromagnetic output of astrophysical objects. We compare the
information provided by multiwavelength observations with a full and
self-consistent computation of the broad-band spectrum of the Crab Nebula. We
cast constraints of order 10^{-5} at 95% confidence level on the lepton Lorentz
Violation parameters.Comment: 23 pages, 9 figures. v2: added comments and references, matches
version accepted by JCA
Air fluorescence measurements in the spectral range 300-420 nm using a 28.5 GeV electron beam
Measurements are reported of the yield and spectrum of fluorescence, excited
by a 28.5 GeV electron beam, in air at a range of pressures of interest to
ultra-high energy cosmic ray detectors. The wavelength range was 300 - 420 nm.
System calibration has been performed using Rayleigh scattering of a nitrogen
laser beam. In atmospheric pressure dry air at 304 K the yield is 20.8 +/- 1.6
photons per MeV.Comment: 29 pages, 10 figures. Submitted to Astroparticle Physic
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