1,524 research outputs found
Polarization Properties of Extragalactic Radio Sources and Their Contribution to Microwave Polarization Fluctuations
We investigate the statistical properties of the polarized emission of
extragalactic radio sources and estimate their contribution to the power
spectrum of polarization fluctuations in the microwave region. The basic
ingredients of our analysis are the NVSS polarization data, the multifrequency
study of polarization properties of the B3-VLA sample (Mack et al. 2002) which
has allowed us to quantify Faraday depolarization effects, and the 15 GHz
survey by Taylor et al. (2001), which has provided strong constraints on the
high-frequency spectral indices of sources. The polarization degree of both
steep- and flat-spectrum at 1.4 GHz is found to be anti-correlated with the
flux density. The median polarization degree at 1.4 GHz of both steep- and
flat-spectrum sources brighter than mJy is . The data by Mack et al. (2002) indicate a substantial mean Faraday
depolarization at 1.4 GHz for steep spectrum sources, while the depolarization
is undetermined for most flat/inverted-spectrum sources. Exploiting this
complex of information we have estimated the power spectrum of polarization
fluctuations due to extragalactic radio sources at microwave frequencies. We
confirm that extragalactic sources are expected to be the main contaminant of
Cosmic Microwave Background (CMB) polarization maps on small angular scales. At
frequencies GHz the amplitude of their power spectrum is expected to be
comparable to that of the -mode of the CMB. At higher frequencies, however,
the CMB dominates.Comment: 10 pages, A&A in pres
The Quantum as an Emergent System
Double slit interference is explained with the aid of what we call
"21stcentury classical physics". We model a particle as an oscillator
("bouncer") in a thermal context, which is given by some assumed "zero-point"
field of the vacuum. In this way, the quantum is understood as an emergent
system, i.e., a steady-state system maintained by a constant throughput of
(vacuum) energy. To account for the particle's thermal environment, we
introduce a "path excitation field", which derives from the thermodynamics of
the zero-point vacuum and which represents all possible paths a particle can
take via thermal path fluctuations. The intensity distribution on a screen
behind a double slit is calculated, as well as the corresponding trajectories
and the probability density current. Further, particular features of the
relative phase are shown to be responsible for nonlocal effects not only in
ordinary quantum theory, but also in our classical approach.Comment: 24 pages, 2 figures, based on a talk given at "Emergent Quantum
Mechanics (Heinz von Foerster Conference 2011)",
http://www.univie.ac.at/hvf11/congress/EmerQuM.htm
Reproductive history differs by molecular subtypes of breast cancer among women aged ≤50 years in Scotland in 2009-16:A cross-sectional study
BACKGROUND: The aetiology of breast cancers diagnosed ≤ 50 years of age remains unclear. We aimed to compare reproductive risk factors between molecular subtypes of breast cancer, thereby suggesting possible aetiologic clues, using routinely collected cancer registry and maternity data in Scotland. METHODS: We conducted a cross-sectional study of 4108 women aged ≤ 50 years with primary breast cancer diagnosed between 2009 and 2016 linked to maternity data. Molecular subtypes of breast cancer were defined using immunohistochemistry (IHC) tumour markers, oestrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor-2 (HER2), and tumour grade. Age-adjusted polytomous logistic regression models were used to estimate odds ratios (OR) and 95% confidence intervals (CI) for the association of number of births, age at first birth and time since last birth with IHC-defined breast cancer subtypes. Luminal A-like was the reference compared to luminal B-like (HER2−), luminal B-like (HER2+), HER2-overexpressed and triple-negative breast cancer (TNBC). RESULTS: Mean (SD) for number of births, age at first birth and time since last birth was 1.4 (1.2) births, 27.2 (6.1) years and 11.0 (6.8) years, respectively. Luminal A-like was the most common subtype (40%), while HER2-overexpressed and TNBC represented 5% and 15% of cases, respectively. Larger numbers of births were recorded among women with HER2-overexpressed and TNBC compared with luminal A-like tumours (> 3 vs 0 births, OR 1.87, 95%CI 1.18–2.96; OR 1.44, 95%CI 1.07–1.94, respectively). Women with their most recent birth > 10 years compared to < 2 years were less likely to have TNBC tumours compared to luminal A-like (OR 0.63, 95%CI 0.41–0.97). We found limited evidence for differences by subtype with age at first birth. CONCLUSION: Number of births and time since last birth differed by molecular subtypes of breast cancer among women aged ≤ 50 years. Analyses using linked routine electronic medical records by molecularly defined tumour pathology data can be used to investigate the aetiology and prognosis of cancer
The SPHERE data center: a reference for high contrast imaging processing
The objective of the SPHERE Data Center is to optimize the scientific return
of SPHERE at the VLT, by providing optimized reduction procedures, services to
users and publicly available reduced data. This paper describes our motivation,
the implementation of the service (partners, infrastructure and developments),
services, description of the on-line data, and future developments. The SPHERE
Data Center is operational and has already provided reduced data with a good
reactivity to many observers. The first public reduced data have been made
available in 2017. The SPHERE Data Center is gathering a strong expertise on
SPHERE data and is in a very good position to propose new reduced data in the
future, as well as improved reduction procedures.Comment: SF2A proceeding
NGC 2579 and the carbon and oxygen abundance gradients beyond the solar circle
We present deep echelle spectrophotometry of the Galactic HII region NGC
2579. The data have been taken with the Very Large Telescope Ultraviolet-Visual
Echelle Spectrograph in the 3550--10400 \AA\ range. This object, which has been
largely neglected, shows however a rather high surface brightness, a high
ionization degree and is located at a galactocentric distance of 12.4 0.7
kpc. Therefore, NGC 2579 is an excellent probe for studying the behaviour of
the gas phase radial abundance gradients in the outer disc of the Milky Way. We
derive the physical conditions of the nebula using several emission
line-intensity ratios as well as the abundances of several ionic species from
the intensity of collisionally excited lines. We also determine the ionic
abundances of C, O and O -- and therefore the total O
abundance -- from faint pure recombination lines. The results for NGC 2579
permit to extend our previous determinations of the C, O and C/O gas phase
radial gradients of the inner Galactic disc (Esteban etal. 2005) to larger
galactocentric distances. We find that the chemical composition of NGC 2579 is
consistent with flatten gradients at its galactocentric distance. In addition,
we have built a tailored chemical evolution model that reproduces the observed
radial abundance gradients of O, C and N and other observational constraints.
We find that a levelling out of the star formation efficiency about and beyond
the isophotal radius can explain the flattening of chemical gradients observed
in the outer Galactic disc.Comment: 10 pages, 5 figures. Accepted for publication in Monthly Notices of
the Royal Astronomical Societ
Operacionalização de uma planta de pirólise rápida de biomassa com reator de leito fluidizado.
Neste trabalho são discutidos os principais problemas encontrados durante a operação da planta piloto de pirólise rápida de biomassa, pertencente à Universidade Estadual de Campinas- Unicamp, Brasil. Essa planta foi ajustada para a produção de bio-óleo, a partir de resíduos de biomassa de pequeno tamanho. Durante os testes, os principais problemas identificados foram: escoamento de vapores da pirólise pelo sistema de alimentação de biomassa; travamento da rosca de alimentação de biomassa; segregação da biomassa no leito; sinterização do material inerte; acúmulo de biomassa e de carvão vegetal dentro do reator; dificuldade para o aquecimento do inerte e baixa eficiência de recuperação de bio-óleo. Os resultados dos testes exploratórios permitiram definir condições operacionais para possibilitar o trabalho estável do reator, aumentar o conhecimento sobre os fenômenos que ocorrem durante a pirólise rápida em leito fluidizado, além do estabelecimento de faixas operacionais para vários fatores independentes, visando a futuros trabalhos de otimização experimental
Connection Between Type A and E Factorizations and Construction of Satellite Algebras
Recently, we introduced a new class of symmetry algebras, called satellite
algebras, which connect with one another wavefunctions belonging to different
potentials of a given family, and corresponding to different energy
eigenvalues. Here the role of the factorization method in the construction of
such algebras is investigated. A general procedure for determining an so(2,2)
or so(2,1) satellite algebra for all the Hamiltonians that admit a type E
factorization is proposed. Such a procedure is based on the known relationship
between type A and E factorizations, combined with an algebraization similar to
that used in the construction of potential algebras. It is illustrated with the
examples of the generalized Morse potential, the Rosen-Morse potential, the
Kepler problem in a space of constant negative curvature, and, in each case,
the conserved quantity is identified. It should be stressed that the method
proposed is fairly general since the other factorization types may be
considered as limiting cases of type A or E factorizations.Comment: 20 pages, LaTeX, no figure, to be published in J. Phys.
The gravitational mass of Proxima Centauri measured with SPHERE from a microlensing event
Proxima Centauri, our closest stellar neighbour, is a low-mass M5 dwarf
orbiting in a triple system. An Earth-mass planet with an 11 day period has
been discovered around this star. The star's mass has been estimated only
indirectly using a mass-luminosity relation, meaning that large uncertainties
affect our knowledge of its properties. To refine the mass estimate, an
independent method has been proposed: gravitational microlensing. By taking
advantage of the close passage of Proxima Cen in front of two background stars,
it is possible to measure the astrometric shift caused by the microlensing
effect due to these close encounters and estimate the gravitational mass of the
lens (Proxima Cen). Microlensing events occurred in 2014 and 2016 with impact
parameters, the closest approach of Proxima Cen to the background star, of
1\farcs6 0\farcs1 and 0\farcs5 0\farcs1, respectively. Accurate
measurements of the positions of the background stars during the last two years
have been obtained with HST/WFC3, and with VLT/SPHERE from the ground. The
SPHERE campaign started on March 2015, and continued for more than two years,
covering 9 epochs. The parameters of Proxima Centauri's motion on the sky,
along with the pixel scale, true North, and centering of the instrument
detector were readjusted for each epoch using the background stars visible in
the IRDIS field of view. The experiment has been successful and the astrometric
shift caused by the microlensing effect has been measured for the second event
in 2016. We used this measurement to derive a mass of
0.150 (an error of 40\%) \MSun for Proxima
Centauri acting as a lens. This is the first and the only currently possible
measurement of the gravitational mass of Proxima Centauri.Comment: 10 pages, 6 figures, accepted by MNRA
Eliminating Error in the Chemical Abundance Scale for Extragalactic HII Regions
In an attempt to remove the systematic errors which have plagued the
calibration of the HII region abundance sequence, we have theoretically modeled
the extragalactic HII region sequence. We then used the theoretical spectra so
generated in a double blind experiment to recover the chemical abundances using
both the classical electron temperature + ionization correction factor
technique, and the technique which depends on the use of strong emission lines
(SELs) in the nebular spectrum to estimate the abundance of oxygen. We find a
number of systematic trends, and we provide correction formulae which should
remove systematic errors in the electron temperature + ionization correction
factor technique. We also provide a critical evaluation of the various
semi-empirical SEL techniques. Finally, we offer a scheme which should help to
eliminate systematic errors in the SEL-derived chemical abundance scale for
extragalactic HII regions.Comment: 24 pages, 9 Tables, 13 figures, accepted for publication in MNRAS.
Updated considering minor changes during the final edition process and some
few missing reference
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