4,236 research outputs found
FLUKA Simulations of Pion Decay Gamma-radiation from Energetic Flare Ions
Gamma-ray continuum at > 10 MeV photon energy yields information on > 0.2 -
0.3 GeV/nucleon ions at the Sun. We use the general-purpose Monte Carlo code
FLUKA (FLUktuierende KAskade) to model the transport of ions injected into
thick and thin target sources, the nuclear processes that give rise to pions
and other secondaries and the escape of the resulting photons from the
atmosphere. We give examples of photon spectra calculated with a range of
different assumptions about the primary ion velocity distribution and the
source region. We show that FLUKA gives results for pion decay photon
emissivity in agreement with previous treatments. Through the directionality of
secondary products, as well as Compton scattering and pair production of
photons prior to escaping the Sun, the predicted spectrum depends significantly
on the viewing angle. Details of the photon spectrum in the 100 MeV range may
constrain the angular distribution of primary ions and the depths at which they
interact. We display a set of thick-target spectra produced making various
assumptions about the incident ion energy and angular distribution and the
viewing angle. If ions are very strongly beamed downward, or ion energies do
not extend much above 1 GeV/nucleon, the photon spectrum is highly insensitive
to details of the ion distribution. Under the simplest assumptions, flares
observed near disc centre should not display significant radiation above 1 GeV
photon energy. We give an example application to Fermi Large Area Telescope
data from the flare of 12 June 2010.Comment: 25 pages, 13 figures, to be published in Solar Physic
Association of radio polar cap brightening with bright patches and coronal holes
Radio-bright regions near the solar poles are frequently observed in Nobeyama
Radioheliograph (NoRH) maps at 17 GHz, and often in association with coronal
holes. However, the origin of these polar brightening has not been established
yet. We propose that small magnetic loops are the source of these bright
patches, and present modeling results that reproduce the main observational
characteristics of the polar brightening within coronal holes at 17 GHz. The
simulations were carried out by calculating the radio emission of the small
loops, with several temperature and density profiles, within a 2D coronal hole
atmospheric model. If located at high latitudes, the size of the simulated
bright patches are much smaller than the beam size and they present the
instrument beam size when observed. The larger bright patches can be generated
by a great number of small magnetic loops unresolved by the NoRH beam. Loop
models that reproduce bright patches contain denser and hotter plasma near the
upper chromosphere and lower corona. On the other hand, loops with increased
plasma density and temperature only in the corona do not contribute to the
emission at 17 GHz. This could explain the absence of a one-to-one association
between the 17 GHz bright patches and those observed in extreme ultraviolet.
Moreover, the emission arising from small magnetic loops located close to the
limb may merge with the usual limb brightening profile, increasing its
brightness temperature and width.Comment: 8 pages, 6 figures, 1 table. Accepted for publication in The
Astrophysical Journa
Special issue: Advances in Engineering Networks
[EN] This special issue of the International Journal of Production Management and Engineering is dedicated on the most recent and relevant research, theories and practices in Industrial Engineering and Operations Management presented at the 12th International Conference on Industrial Engineering and Industrial Management and XXII Congreso de IngenierĂa de OrganizaciĂłn - CIO18.De Castro, R.; Gimenez, G.; Mula, J.; Boza, A.; Cuenca, L.; GĂłmez-Gasquet, P.; Vicens-Salort, E. (2019). Special issue: Advances in Engineering Networks. International Journal of Production Management and Engineering. 7(NĂşmero Especial):63-64. https://doi.org/10.4995/ijpme.2019.11901SWORD63647NĂşmero Especia
LLAMA Millimeter and Submillimeter Observatory. Update on its Science Opportunities
The Large Latin American Millimeter Array (LLAMA for short) is a joint
scientific and technological undertaking of Argentina and Brazil whose goal is
to install and to operate an observing facility capable of performing
observations of the Universe at millimeter and sub-millimeter wavelengths. It
will consist of a 12m ALMA-like antenna with the addition of two Nasmyth
cabins. LLAMA is located at 4850m above sea level in the Puna Saltenia, in the
northwest region of Argentina. When completed, LLAMA will be equipped with six
ALMA receivers covering Bands 1, 2+3, 5, 6, 7, and 9, which will populate the
two Nasmyth cabins. We summarize here the main ideas related with the Science
that LLAMA could accomplish on different astronomical topics, gathered from the
experience of a group of international experts on each field.Comment: 11 pages, contributed paper to the workshop "Prospects for
low-frequency radio astronomy in South America", held in Buenos Aires, Nov
2022; to appear in the RevMexAA-S
ALMA Observations of the Sun in Cycle 4 and Beyond
This document was created by the Solar Simulations for the Atacama Large
Millimeter Observatory Network (SSALMON) in preparation of the first regular
observations of the Sun with the Atacama Large Millimeter/submillimeter Array
(ALMA), which are anticipated to start in ALMA Cycle 4 in October 2016. The
science cases presented here demonstrate that a large number of scientifically
highly interesting observations could be made already with the still limited
solar observing modes foreseen for Cycle 4 and that ALMA has the potential to
make important contributions to answering long-standing scientific questions in
solar physics. With the proposal deadline for ALMA Cycle 4 in April 2016 and
the Commissioning and Science Verification campaign in December 2015 in sight,
several of the SSALMON Expert Teams composed strategic documents in which they
outlined potential solar observations that could be feasible given the
anticipated technical capabilities in Cycle 4. These documents have been
combined and supplemented with an analysis, resulting in recommendations for
solar observing with ALMA in Cycle 4. In addition, the detailed science cases
also demonstrate the scientific priorities of the solar physics community and
which capabilities are wanted for the next observing cycles. The work on this
White Paper effort was coordinated in close cooperation with the two
international solar ALMA development studies led by T. Bastian (NRAO, USA) and
R. Brajsa, (ESO). This document will be further updated until the beginning of
Cycle 4 in October 2016. In particular, we plan to adjust the technical
capabilities of the solar observing modes once finally decided and to further
demonstrate the feasibility and scientific potential of the included science
cases by means of numerical simulations of the solar atmosphere and
corresponding simulated ALMA observations.Comment: SSALMON White Paper with focus on potential solar science with ALMA
in Cycle 4; 54 pages. Version 1.2, March 29th, 2016 (updated technical
capabilities and observing plans
Gaia Early Data Release 3: Summary of the contents and survey properties
Context. We present the early installment of the third Gaia data release, Gaia EDR3, consisting of astrometry and photometry for 1.8 billion sources brighter than magnitude 21, complemented with the list of radial velocities from Gaia DR2. Aims. A summary of the contents of Gaia EDR3 is presented, accompanied by a discussion on the differences with respect to Gaia DR2 and an overview of the main limitations which are present in the survey. Recommendations are made on the responsible use of Gaia EDR3 results. Methods. The raw data collected with the Gaia instruments during the first 34 months of the mission have been processed by the Gaia Data Processing and Analysis Consortium and turned into this early third data release, which represents a major advance with respect to Gaia DR2 in terms of astrometric and photometric precision, accuracy, and homogeneity. Results. Gaia EDR3 contains celestial positions and the apparent brightness in G for approximately 1.8 billion sources. For 1.5 billion of those sources, parallaxes, proper motions, and the (GBP â GRP) colour are also available. The passbands for G, GBP, and GRP are provided as part of the release. For ease of use, the 7 million radial velocities from Gaia DR2 are included in this release, after the removal of a small number of spurious values. New radial velocities will appear as part of Gaia DR3. Finally, Gaia EDR3 represents an updated materialisation of the celestial reference frame (CRF) in the optical, the Gaia-CRF3, which is based solely on extragalactic sources. The creation of the source list for Gaia EDR3 includes enhancements that make it more robust with respect to high proper motion stars, and the disturbing effects of spurious and partially resolved sources. The source list is largely the same as that for Gaia DR2, but it does feature new sources and there are some notable changes. The source list will not change for Gaia DR3. Conclusions. Gaia EDR3 represents a significant advance over Gaia DR2, with parallax precisions increased by 30 per cent, proper motion precisions increased by a factor of 2, and the systematic errors in the astrometry suppressed by 30-40% for the parallaxes and by a factor ~2.5 for the proper motions. The photometry also features increased precision, but above all much better homogeneity across colour, magnitude, and celestial position. A single passband for G, GBP, and GRP is valid over the entire magnitude and colour range, with no systematics above the 1% leve
Multi-particle azimuthal correlations in p-Pb and Pb-Pb collisions at the CERN Large Hadron Collider
Measurements of multi-particle azimuthal correlations (cumulants) for charged
particles in p-Pb and Pb-Pb collisions are presented. They help address the
question of whether there is evidence for global, flow-like, azimuthal
correlations in the p-Pb system. Comparisons are made to measurements from the
larger Pb-Pb system, where such evidence is established. In particular, the
second harmonic two-particle cumulants are found to decrease with multiplicity,
characteristic of a dominance of few-particle correlations in p-Pb collisions.
However, when a gap is placed to suppress such correlations,
the two-particle cumulants begin to rise at high-multiplicity, indicating the
presence of global azimuthal correlations. The Pb-Pb values are higher than the
p-Pb values at similar multiplicities. In both systems, the second harmonic
four-particle cumulants exhibit a transition from positive to negative values
when the multiplicity increases. The negative values allow for a measurement of
to be made, which is found to be higher in Pb-Pb collisions at
similar multiplicities. The second harmonic six-particle cumulants are also
found to be higher in Pb-Pb collisions. In Pb-Pb collisions, we generally find
which is indicative of a Bessel-Gaussian
function for the distribution. For very high-multiplicity Pb-Pb
collisions, we observe that the four- and six-particle cumulants become
consistent with 0. Finally, third harmonic two-particle cumulants in p-Pb and
Pb-Pb are measured. These are found to be similar for overlapping
multiplicities, when a gap is placed.Comment: 25 pages, 11 captioned figures, 3 tables, authors from page 20,
published version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/87
Multiplicity dependence of jet-like two-particle correlations in p-Pb collisions at = 5.02 TeV
Two-particle angular correlations between unidentified charged trigger and
associated particles are measured by the ALICE detector in p-Pb collisions at a
nucleon-nucleon centre-of-mass energy of 5.02 TeV. The transverse-momentum
range 0.7 5.0 GeV/ is examined,
to include correlations induced by jets originating from low
momen\-tum-transfer scatterings (minijets). The correlations expressed as
associated yield per trigger particle are obtained in the pseudorapidity range
. The near-side long-range pseudorapidity correlations observed in
high-multiplicity p-Pb collisions are subtracted from both near-side
short-range and away-side correlations in order to remove the non-jet-like
components. The yields in the jet-like peaks are found to be invariant with
event multiplicity with the exception of events with low multiplicity. This
invariance is consistent with the particles being produced via the incoherent
fragmentation of multiple parton--parton scatterings, while the yield related
to the previously observed ridge structures is not jet-related. The number of
uncorrelated sources of particle production is found to increase linearly with
multiplicity, suggesting no saturation of the number of multi-parton
interactions even in the highest multiplicity p-Pb collisions. Further, the
number scales in the intermediate multiplicity region with the number of binary
nucleon-nucleon collisions estimated with a Glauber Monte-Carlo simulation.Comment: 23 pages, 6 captioned figures, 1 table, authors from page 17,
published version, figures at
http://aliceinfo.cern.ch/ArtSubmission/node/161
Single hadron response measurement and calorimeter jet energy scale uncertainty with the ATLAS detector at the LHC
The uncertainty on the calorimeter energy response to jets of particles is
derived for the ATLAS experiment at the Large Hadron Collider (LHC). First, the
calorimeter response to single isolated charged hadrons is measured and
compared to the Monte Carlo simulation using proton-proton collisions at
centre-of-mass energies of sqrt(s) = 900 GeV and 7 TeV collected during 2009
and 2010. Then, using the decay of K_s and Lambda particles, the calorimeter
response to specific types of particles (positively and negatively charged
pions, protons, and anti-protons) is measured and compared to the Monte Carlo
predictions. Finally, the jet energy scale uncertainty is determined by
propagating the response uncertainty for single charged and neutral particles
to jets. The response uncertainty is 2-5% for central isolated hadrons and 1-3%
for the final calorimeter jet energy scale.Comment: 24 pages plus author list (36 pages total), 23 figures, 1 table,
submitted to European Physical Journal
Standalone vertex ďŹnding in the ATLAS muon spectrometer
A dedicated reconstruction algorithm to find decay vertices in the ATLAS muon spectrometer is presented. The algorithm searches the region just upstream of or inside the muon spectrometer volume for multi-particle vertices that originate from the decay of particles with long decay paths. The performance of the algorithm is evaluated using both a sample of simulated Higgs boson events, in which the Higgs boson decays to long-lived neutral particles that in turn decay to bbar b final states, and pp collision data at âs = 7 TeV collected with the ATLAS detector at the LHC during 2011
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