270 research outputs found
Spectropolarimetric multi line analysis of stellar magnetic fields
In this paper we study the feasibility of inferring the magnetic field from
polarized multi-line spectra using two methods: The pseudo line approach and
The PCA-ZDI approach. We use multi-line techniques, meaning that all the lines
of a stellar spectrum contribute to obtain a polarization signature. The use of
multiple lines dramatically increases the signal to noise ratio of these
polarizations signatures. Using one technique, the pseudo-line approach, we
construct the pseudo-line as the mean profile of all the individual lines. The
other technique, the PCA-ZDI approach proposed recently by Semel et al. (2006)
for the detection of polarized signals, combines Principle Components Analysis
(PCA) and the Zeeman Do ppler Imaging technique (ZDI). This new method has a
main advantage: the polarized signature is extracted using cross correlations
between the stellar spectra nd functions containing the polarization properties
of each line. These functions are the principal components of a database of
synthetic spectra. The synthesis of the spectra of the database are obtained
using the radiative transfer equations in LTE. The profiles built with the
PCA-ZDI technique are denominated Multi-Zeeman-Signatures. The construction of
the pseudo line as well as the Multi-Zeeman-Signatures is a powerful tool in
the study of stellar and solar magnetic fields. The information of the physical
parameters that governs the line formation is contained in the final polarized
profiles. In particular, using inversion codes, we have shown that the magnetic
field vector can be properly inferred with both approaches despite the magnetic
field regime.Comment: Accepted for publication in Astronomy and Astrophysic
Headache, Delirium or Encephalitis?:A Case of Residual Mutism Secondary to Anti-NMDA Receptor Encephalitis
Encephalitis is a heterogeneous syndrome that is diagnosed through clinical assessment and the assistance of laboratory, neuroimaging and electroencephalographic workup. Over the past 10 years, autoimmune encephalitis has been more frequently recognized; however, most reports come from highly specialized hospital settings. Anti-N-methyl-D-aspartate receptor (NDMAR) encephalitis has been associated with paraneoplastic encephalitis syndromes and was first recognized in 2005. We present the case of a 34-year-old male patient who debuted clinically with a headache associated with neuropsychiatric symptoms (i.e., visual and auditory hallucinations, anxiety, aggressiveness) and memory deficits, progressing to autonomic dysfunction (i.e., tachycardia and hypertension), seizures, and stupor with catatonic features. Initially, infectious, metabolic, and toxicological etiologies were excluded; followed by the assessment of immunological and paraneoplastic etiologies, yielding positive IgG levels for anti-NMDAR antibodies. The patient was treated successfully with systemic steroid therapy and therapeutic plasmapheresis, while mutism was the only sequela. Although large case series reporting on paraneoplastic and autoimmune anti-NMDAR encephalitis have been reported in the literature in recent years, this case is of particular importance due to the stepwise differential diagnosis and treatment management procedure that was used in a regional but not highly specialized hospital setting
VAMOS: a Pathfinder for the HAWC Gamma-Ray Observatory
VAMOS was a prototype detector built in 2011 at an altitude of 4100m a.s.l.
in the state of Puebla, Mexico. The aim of VAMOS was to finalize the design,
construction techniques and data acquisition system of the HAWC observatory.
HAWC is an air-shower array currently under construction at the same site of
VAMOS with the purpose to study the TeV sky. The VAMOS setup included six water
Cherenkov detectors and two different data acquisition systems. It was in
operation between October 2011 and May 2012 with an average live time of 30%.
Besides the scientific verification purposes, the eight months of data were
used to obtain the results presented in this paper: the detector response to
the Forbush decrease of March 2012, and the analysis of possible emission, at
energies above 30 GeV, for long gamma-ray bursts GRB111016B and GRB120328B.Comment: Accepted for pubblication in Astroparticle Physics Journal (20 pages,
10 figures). Corresponding authors: A.Marinelli and D.Zaboro
Effects of an exercise program on hepatic metabolism, hepatic fat, and cardiovascular health in overweight/obese adolescents from Bogotá, Colombia (the HEPAFIT study): study protocol for a randomized controlled trial
Background: A considerable proportion of contemporary youth have a high risk of obesity-related disorders such
as cardiovascular disease, metabolic syndrome, or non-alcoholic fatty liver disease (NAFLD). Although there is consistent
evidence for the positive effects of physical activity on several health aspects, most adolescents in Colombia are
sedentary. It is, therefore, important to implement strategies that generate changes in lifestyle. The HEPAFIT study
aims to examine whether a 6-month exercise program has benefits for hepatic fat content and cardiovascular health
outcomes among overweight/obese adolescents from Bogotá, Colombia.
Methods/design: Altogether, 100 hundred overweight/obese, sedentary adolescents (aged 11–17 years) attending two
public schools in Bogotá, Colombia, will be included in a parallel-group randomized controlled trial. Adolescents will be
randomly assigned to an intervention group following one of four curricula: (1) the standard physical education
curriculum (60 min per week of physical activity, n = 25) at low-to-moderate intensity; (2) a high-intensity physical
education curriculum (HIPE, n = 25), consisting of endurance and resistance games and non-competitive activities,
such as running, gymkhanas, lifting, pushing, wrestling, or hauling, for 60-min sessions, three times per week, with
an energy expenditure goal of 300 to 500 kcal/session at 75–85% maximum heart rate (HRmax); (3) a low-to-moderate
intensity physical education curriculum (LIPE, n = 25) consisting of endurance and resistance games and non-competitive
activities (e.g., chasing, sprinting, dribbling, or hopping) for 60-min sessions, three times per week with an energy
expenditure goal of 300 kcal/session at 55–75% HRmax; and (4) a combined HIPE and LIPE curriculum (n = 25).
The HIPE, LIPE, and combined interventions were performed in addition to the standard physical education curriculum.
The primary outcome for effectiveness is liver fat content, as measured by the controlled attenuation parameter 1
week after the end of the intervention program.
Discussion: The translational focus may be suitable for collecting new information in a school setting on the
possible effects of physical activity interventions to reduce liver fat content and to improve metabolic profiles
and the cardiometabolic health of overweight/obese adolescents. This may lead to the more efficient use of
school physical education resources.The HEPAFIT study was carried out with the financial support of Instituto
Colombiano para el Desarrollo de la Ciencia y la Tecnología “Francisco José
de Caldas” COLCIENCIAS (code 59700 and no 122277757900). Katherine
González-Ruíz receive a scholarship from Universidad del Rosario, Colombia,
Escuela de Medicina y Ciencias de la Salud, to do a Doctorate. This article
presents independent research commissioned by COLCIENCIAS under its
Program Grants for Applied Research funding scheme (Convocatoria 777–2017)
"Invisible burials" and fragmentation practices in Iron Age Europe:Excavations at the Monte Bernorio Necropolis (Northern Spain)
The scarcity of burial remains in large parts of Iron Age Europe, particularly in the Atlantic regions, has often led scholars to discuss the apparent “invisibility” of graves. This paper presents the results from several excavation campaigns at Monte Bernorio, one of the most important sites of the 1st millennium b.c. on the Iberian Peninsula. The fieldwork and post-excavation work carried out in the area of the necropolis have identified numerous burial pits, with complex ritual activities characterized by fragmentation and the practice of the pars pro toto. In addition, evidence for later rituals in some of the graves can be linked to ancestor worship. The results provide important insights into funerary practices in Late Iron Age Europe, leading us to rethink the very meaning of cemeteries in the study area and beyond.- Burial Traditions in Iron Age Europe - The Monte Bernorio Archaeological Zone - The 2007–2008 Necropolis Excavations - The 2015–2016 Necropolis Excavations - Post-Excavation Work and Interpretation: The Faunal and Human Remains - Structure and Chronology of Monte Bernorio Area 7 - Destruction of the Body, Commemoration in the Absence of a Corpse, and Visibility of the Mortuary Rite
Observation of the Crab Nebula with the HAWC Gamma-Ray Observatory
The Crab Nebula is the brightest TeV gamma-ray source in the sky and has been
used for the past 25 years as a reference source in TeV astronomy, for
calibration and verification of new TeV instruments. The High Altitude Water
Cherenkov Observatory (HAWC), completed in early 2015, has been used to observe
the Crab Nebula at high significance across nearly the full spectrum of
energies to which HAWC is sensitive. HAWC is unique for its wide field-of-view,
nearly 2 sr at any instant, and its high-energy reach, up to 100 TeV. HAWC's
sensitivity improves with the gamma-ray energy. Above 1 TeV the
sensitivity is driven by the best background rejection and angular resolution
ever achieved for a wide-field ground array.
We present a time-integrated analysis of the Crab using 507 live days of HAWC
data from 2014 November to 2016 June. The spectrum of the Crab is fit to a
function of the form . The data is well-fit with values of
, , and
log when
is fixed at 7 TeV and the fit applies between 1 and 37 TeV. Study of the
systematic errors in this HAWC measurement is discussed and estimated to be
50\% in the photon flux between 1 and 37 TeV.
Confirmation of the Crab flux serves to establish the HAWC instrument's
sensitivity for surveys of the sky. The HAWC survey will exceed sensitivity of
current-generation observatories and open a new view of 2/3 of the sky above 10
TeV.Comment: Submitted 2017/01/06 to the Astrophysical Journa
Search for very-high-energy emission from Gamma-ray Bursts using the first 18 months of data from the HAWC Gamma-ray Observatory
The High Altitude Water Cherenkov (HAWC) Gamma-ray Observatory is an
extensive air shower detector operating in central Mexico, which has recently
completed its first two years of full operations. If for a burst like GRB
130427A at a redshift of 0.34 and a high-energy component following a power law
with index -1.66, the high-energy component is extended to higher energies with
no cut-off other than from extragalactic background light attenuation, HAWC
would observe gamma rays with a peak energy of 300 GeV. This paper
reports the results of HAWC observations of 64 gamma-ray bursts (GRBs) detected
by and , including three GRBs that were also
detected by the Large Area Telescope (-LAT). An ON/OFF analysis
method is employed, searching on the time scale given by the observed light
curve at keV-MeV energies and also on extended time scales. For all GRBs and
time scales, no statistically significant excess of counts is found and upper
limits on the number of gamma rays and the gamma-ray flux are calculated. GRB
170206A, the third brightest short GRB detected by the Gamma-ray Burst Monitor
on board the satellite (-GBM) and also
detected by the LAT, occurred very close to zenith. The LAT measurements can
neither exclude the presence of a synchrotron self-Compton (SSC) component nor
constrain its spectrum. Instead, the HAWC upper limits constrain the expected
cut-off in an additional high-energy component to be less than
for reasonable assumptions about the energetics and redshift of the burst.Comment: 19 pages, 6 figures, published in Ap
All-particle cosmic ray energy spectrum measured by the HAWC experiment from 10 to 500 TeV
We report on the measurement of the all-particle cosmic ray energy spectrum
with the High Altitude Water Cherenkov (HAWC) Observatory in the energy range
10 to 500 TeV. HAWC is a ground based air-shower array deployed on the slopes
of Volcan Sierra Negra in the state of Puebla, Mexico, and is sensitive to
gamma rays and cosmic rays at TeV energies. The data used in this work were
taken from 234 days between June 2016 to February 2017. The primary cosmic-ray
energy is determined with a maximum likelihood approach using the particle
density as a function of distance to the shower core. Introducing quality cuts
to isolate events with shower cores landing on the array, the reconstructed
energy distribution is unfolded iteratively. The measured all-particle spectrum
is consistent with a broken power law with an index of prior to
a break at ) TeV, followed by an index of . The
spectrum also respresents a single measurement that spans the energy range
between direct detection and ground based experiments. As a verification of the
detector response, the energy scale and angular resolution are validated by
observation of the cosmic ray Moon shadow's dependence on energy.Comment: 16 pages, 11 figures, 4 tables, submission to Physical Review
Extended gamma-ray sources around pulsars constrain the origin of the positron flux at Earth
The unexpectedly high flux of cosmic ray positrons detected at Earth may
originate from nearby astrophysical sources, dark matter, or unknown processes
of cosmic-ray secondary production. We report the detection, using the
HighAltitude Water Cherenkov Observatory (HAWC), of extended tera-electron volt
gamma-ray emission coincident with the locations of two nearby middle-aged
pulsars (Geminga and PSR B0656+14). The HAWC observations demonstrate that
these pulsars are indeed local sources of accelerated leptons, but the measured
tera-electron volt emission profile constrains the diffusion of particles away
from these sources to be much slower than previously assumed. We demonstrate
that the leptons emitted by these objects are therefore unlikely to be the
origin of the excess positrons, which may have a more exotic origin.Comment: 16 pages (including supplementary material), 5 figure
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