384 research outputs found
Towards a Proof Theory of G\"odel Modal Logics
Analytic proof calculi are introduced for box and diamond fragments of basic
modal fuzzy logics that combine the Kripke semantics of modal logic K with the
many-valued semantics of G\"odel logic. The calculi are used to establish
completeness and complexity results for these fragments
Prospects for a Dark Matter annihilation signal towards the Sagittarius dwarf galaxy with ground based Cherenkov telescopes
Dwarf galaxies are widely believed to be among the best targets for indirect
dark matter searches using high-energy gamma rays; and indeed gamma-ray
emission from these objects has long been a subject of detailed study for
ground-based atmospheric Cherenkov telescopes. Here, we update current
exclusion limits obtained on the closest dwarf, the Sagittarius dwarf galaxy,
in light of recent realistic dark matter halo models. The constraints on the
velocity-weighted annihilation cross section of the dark matter particle are of
a few 10 cms in the TeV energy range for a 50 h exposure.
The limits are extrapolated to the sensitivities of future Cherenkov Telescope
Arrays. For 200 h of observation time, the sensitivity at 95% C.L. reaches
10 cms. Possible astrophysical backgrounds from gamma-ray
sources dissembled in Sagittarius dwarf are studied. It is shown that with
long-enough observation times, gamma-ray background from millisecond pulsars in
a globular cluster contained within Sagittarius dwarf may limit the sensitivity
to dark matter annihilations.Comment: 12 pages, 5 figures, 2 tables, accepted for publication in Ap
Affordability influences nutritional quality of seafood consumption among income and race/ethnicity groups in the United States
Background
The 2020 US Dietary Guidelines for Americans recommend that the US population consume more seafood. Most analyses of seafood consumption ignore heterogeneity in consumption patterns by species, nutritional content, production methods, and price, which have implications for applying recommendations.
Objectives
We assessed seafood intake among adults by socioeconomic and demographic groups, as well as the cost of seafood at retail to identify affordable and nutritious options.
Methods
NHANES 2011–2018 dietary data (n = 17,559 total, n = 3285 eating seafood) were used to assess adult (≥20 y) intake of seafood in relation to income and race/ethnicity. Multivariable linear regression assessed the association between seafood consumption and income, adjusted for age, sex, and race/ethnicity, and the association between nutrients and seafood price, using Nielsen 2017–2019 retail sales data, adjusted for sales volume.
Results
Low-income groups consume slightly less seafood than high-income groups [low income: mean 120.2 (95% CI: 103.5, 137.2) g/wk; high income: 141.8 (119.1, 164.1) g/wk] but substantially less seafood that is high in long-chain n–3 (ω-3) PUFAs [lower income: 21.3 (17.3, 25.5) g/wk; higher income: 46.8 (35.4, 57.8) g/wk]. Intake rates, species, and production method choices varied by race/ethnicity groups and within race/ethnicity groups by income. Retail seafood as a whole costs more than other protein foods (e.g., meat, poultry, eggs, beans), and fresh seafood high in n–3 PUFAs costs more (P < 0.002) than fresh seafood low in n–3 PUFAs. Retail seafood is available in a wide range of price points and product forms, and some lower-cost fish and shellfish were high in n–3 PUFAs, calcium, iron, selenium, and vitamins B-12 and D.
Conclusions
New insights into the relation between seafood affordability and consumption patterns among income and ethnicity groups suggest that specific policies and interventions may be needed to enhance the consumption of seafood by different groups.publishedVersio
Fermi-LAT Study of Gamma-ray Emission in the Direction of Supernova Remnant W49B
We present an analysis of the gamma-ray data obtained with the Large Area
Telescope (LAT) onboard the Fermi Gamma-ray Space Telescope in the direction of
SNR W49B (G43.3-0.2). A bright unresolved gamma-ray source detected at a
significance of 38 sigma is found to coincide with SNR W49B. The energy
spectrum in the 0.2-200 GeV range gradually steepens toward high energies. The
luminosity is estimated to be 1.5x10^{36} (D/8 kpc)^2 erg s^-1 in this energy
range. There is no indication that the gamma-ray emission comes from a pulsar.
Assuming that the SNR shell is the site of gamma-ray production, the observed
spectrum can be explained either by the decay of neutral pi mesons produced
through the proton-proton collisions or by electron bremsstrahlung. The
calculated energy density of relativistic particles responsible for the LAT
flux is estimated to be remarkably large, U_{e,p}>10^4 eV cm^-3, for either
gamma-ray production mechanism.Comment: 9 pages, 10 figure
Fermi observations of high-energy gamma-ray emission from GRB 090217A
The Fermi observatory is advancing our knowledge of Gamma-Ray Bursts (GRBs)
through pioneering observations at high energies, covering more than 7 decades
in energy with the two on-board detectors, the Large Area Telescope (LAT) and
the Gamma-ray Burst Monitor (GBM). Here we report on the observation of the
long GRB 090217A which triggered the GBM and has been detected by the LAT with
a significance greater than 9 sigma. We present the GBM and LAT observations
and on-ground analyses, including the time-resolved spectra and the study of
the temporal profile from 8 keV up to 1 GeV. All spectra are well reproduced by
a Band model. We compare these observations to the first two LAT-detected, long
bursts GRB 080825C and GRB 080916C. These bursts were found to have
time-dependent spectra and exhibited a delayed onset of the high-energy
emission, which are not observed in the case of GRB 090217A. We discuss some
theoretical implications for the high-energy emission of GRBs.Comment: 17 pages, 4 figures. Contact Authors: Fred, Piron; Sara, Cutini;
Andreas, von Kienli
GeV Gamma-ray Flux Upper Limits from Clusters of Galaxies
The detection of diffuse radio emission associated with clusters of galaxies
indicates populations of relativistic leptons infusing the intracluster medium.
Those electrons and positrons are either injected into and accelerated directly
in the intracluster medium, or produced as secondary pairs by cosmic-ray ions
scattering on ambient protons. Radiation mechanisms involving the energetic
leptons together with decay of neutral pions produced by hadronic interactions
have the potential to produce abundant GeV photons. Here, we report on the
search for GeV emission from clusters of galaxies using data collected by the
Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (Fermi) from
August 2008 to February 2010. Thirty-three galaxy clusters have been selected
according to their proximity and high mass, X-ray flux and temperature, and
indications of non-thermal activity for this study. We report upper limits on
the photon flux in the range 0.2-100 GeV towards a sample of observed clusters
(typical values 1-5 x 10^-9 ph cm^-2 s^-1) considering both point-like and
spatially resolved models for the high-energy emission, and discuss how these
results constrain the characteristics of energetic leptons and hadrons, and
magnetic fields in the intracluster medium. The volume-averaged
relativistic-hadron-to-thermal energy density ratio is found to be < 5-10% in
several clusters.Comment: 9 pages, 3 tables, 1 figure, accepted for publication in ApJ Letter
Gamma-ray flares from the Crab Nebula
A young and energetic pulsar powers the well-known Crab Nebula. Here we
describe two separate gamma-ray (photon energy >100 MeV) flares from this
source detected by the Large Area Telescope on board the Fermi Gamma-ray Space
Telescope. The first flare occurred in February 2009 and lasted approximately
16 days. The second flare was detected in September 2010 and lasted
approximately 4 days. During these outbursts the gamma-ray flux from the nebula
increased by factors of four and six, respectively. The brevity of the flares
implies that the gamma rays were emitted via synchrotron radiation from PeV
(10^15 eV) electrons in a region smaller than 1.4 10^-2 pc. These are the
highest energy particles that can be associated with a discrete astronomical
source, and they pose challenges to particle acceleration theory.Comment: Contact authors: Rolf Buehler,[email protected]; Stefan
Funk,[email protected]; Roger Blandford,rdb3@stanford ; 16 pages,2
figure
Constraints on dark matter models from a Fermi LAT search for high-energy cosmic-ray electrons from the Sun
During its first year of data taking, the Large Area Telescope (LAT) onboard
the Fermi Gamma-Ray Space Telescope has collected a large sample of high-energy
cosmic-ray electrons and positrons (CREs). We present the results of a
directional analysis of the CRE events, in which we searched for a flux excess
correlated with the direction of the Sun. Two different and complementary
analysis approaches were implemented, and neither yielded evidence of a
significant CRE flux excess from the Sun. We derive upper limits on the CRE
flux from the Sun's direction, and use these bounds to constrain two classes of
dark matter models which predict a solar CRE flux: (1) models in which dark
matter annihilates to CREs via a light intermediate state, and (2) inelastic
dark matter models in which dark matter annihilates to CREs.Comment: 18 pages, 8 figures, accepted for publication in Physical Review D -
contact authors: Francesco Loparco ([email protected]), M. Nicola Mazziotta
([email protected]) and Jennifer Siegal-Gaskins ([email protected]
Searches for Cosmic-Ray Electron Anisotropies with the Fermi Large Area Telescope
The Large Area Telescope on board the \textit{Fermi} satellite
(\textit{Fermi}-LAT) detected more than 1.6 million cosmic-ray
electrons/positrons with energies above 60 GeV during its first year of
operation. The arrival directions of these events were searched for
anisotropies of angular scale extending from 10 up to
90, and of minimum energy extending from 60 GeV up to 480 GeV. Two
independent techniques were used to search for anisotropies, both resulting in
null results. Upper limits on the degree of the anisotropy were set that
depended on the analyzed energy range and on the anisotropy's angular scale.
The upper limits for a dipole anisotropy ranged from to .Comment: 16 pages, 10 figures, accepted for publication in Physical Review D -
contact authors: M.N. Mazziotta and V. Vasileio
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