1,575 research outputs found
X-ray background and its correlation with the 21 cm signal
We use high resolution hydrodynamical simulations to study the contribution
to the X-ray background from high- energetic sources, such as X-ray
binaries, accreting nuclear black holes and shock heated interstellar medium.
Adopting the model discussed in Eide et al. (2018), we find that these X-ray
sources during the Epoch of Reionization (EoR) contribute less than a few
percent of the unresolved X-ray background. The same sources contribute to less
than 2\% of the measured angular power spectrum of the fluctuations of
the X-ray background. The outputs of radiative transfer simulations modeling
the EoR are used to evaluate the cross-correlations of X-ray background with
the 21~cm signal from neutral hydrogen. Such correlation could be used to
confirm the origin of the 21 cm signal, as well as give information on the
properties of the X-ray sources during the EoR. We find that the correlations
are positive during the early stages of reionization when most of the hydrogen
is neutral, while they become negative when the intergalactic medium gets
highly ionized, with the transition from positive to negative depending on both
the X-ray model and the scale under consideration. With {\tt SKA} as the
reference instrument for the 21~cm experiment, the predicted S/N for such
correlations is if the corresponding X-ray survey is only able to resolve
and remove X-ray sources with observed flux , while the cumulative S/N from to at
is if sources with observed flux are detected.Comment: 9 pages, 8 figure
Opening Reionization: Quantitative Morphology of the Epoch of Reionization and Its Connection to the Cosmic Density Field
We introduce a versatile and spatially resolved morphological
characterisation of binary fields, rooted in the opening transform of
mathematical morphology. We subsequently apply it to the thresholded ionization
field in simulations of cosmic reionization and study the morphology of ionized
regions. We find that an ionized volume element typically resides in an ionized
region with radius at the midpoint of reionization
() and follow the bubble size distribution even beyond the overlap
phase. We find that percolation of the fully ionized component sets in when 25%
of the universe is ionized and that the resulting infinite cluster incorporates
all ionized regions above . We also quantify the
clustering of ionized regions of varying radius with respect to matter and on
small scales detect the formation of superbubbles in the overlap phase. On
large scales we quantify the bias values of the centres of ionized and neutral
regions of different sizes and not only show that the largest ones at the
high-point of reionization can reach , but also that early small
ionized regions are positively correlated with matter and large neutral regions
and late small ionized regions are heavily anti-biased with respect to matter,
down to .Comment: 18 pages, 15 figure, as accepted for publication by MNRA
Cross-correlation between the 21-cm signal and [OIII] emitters during early cosmic reionization
We study statistics of the 21-cm signal from the epoch of reionization. We
propose to use [OIII] line emitting galaxies to cross-correlate with the 21-cm
signal from . To this aim, we employ simulations of reionization
obtained post-processing the high-resolution cosmological hydrodynamic
simulation Massive Black-II with the three-dimensional (3D) radiative transfer
code CRASH to follow the propagation of ionizing photons from a variety of
sources. We show that, during the early phases of reionization, the 21-cm
signal is positively correlated with the spatial distribution of the [OIII]
emitters on large scales . This positive correlation is
generated by the temperature-galaxy correlation and it is a few times larger
than when we assume that the heating is saturated. As the reionized regions
expand, the correlation changes its sign to negative from to 8. The
signals at this epoch can be detected by combining the Square Kilometre Array
(SKA) and a wide-field [OIII] emitter survey. We also calculate the cross-power
spectrum with a 3D [OIII] intensity field, aiming at exploiting future
intensity mapping observations. We conclude that high-redshift [OIII] line
emitters can be used to probe the reionization process when the intergalactic
medium is largely neutral.Comment: 7 pages, 5 figures, published in MNRA
Unlocking the Full Potential of Extragalactic Ly through Its Polarization Properties
Lyman- (Ly) is a powerful astrophysical probe. Not only is it
ubiquitous at high redshifts, it is also a resonant line, making Ly
photons scatter. This scattering process depends on the physical conditions of
the gas through which Ly propagates, and these conditions are imprinted
on observables such as the Ly spectrum and its surface brightness
profile. In this work, we focus on a less-used observable capable of probing
any scattering process: polarization. We implement the density matrix formalism
of polarization into the Monte Carlo radiative transfer code tlac. This allows
us to treat it as a quantum mechanical process where single photons develop and
lose polarization from scatterings in arbitrary gas geometries. We explore
static and expanding ellipsoids, biconical outflows, and clumpy multiphase
media. We find that photons become increasingly polarized as they scatter and
diffuse into the wings of the line profiles, making scattered Ly
polarized in general. The degree and orientation of Ly polarization
depends on the kinematics and distribution of the scattering HI gas. We find
that it generally probes spatial or velocity space asymmetries and aligns
itself tangentially to the emission source. We show that the mentioned
observables, when studied separately, can leave similar signatures for
different source models. We conclude by revealing how a joint analysis of the
Ly spectra, surface brightness profiles, and polarization can break
these degeneracies and help us extract unique physical information on galaxies
and their environments from their strongest, most prominent emission line.Comment: 26 pages, 12 figures. Figure 2 and 3 reordered, Figure 11 updated.
Accepted for publication in Ap
The NOMA track module on nutrition, human rights and governance: Part 2. A transnational curriculum using a human rights-based approach to foster key competencies in nutrition professionals
Background. In response to the challenge of the global health needs of the 21st century, four academic institutions in Norway, South Africa and Uganda,each offering a Master’s degree in nutrition, collaboratively developed the NOrwegian MAsters (NOMA) track module on nutrition, human rights andgovernance, integrating a human rights-based approach into graduate education in nutrition.Objective. To capture students’ perceptions about the NOMA track module, focusing on the development of key competencies.Methods. Employing a qualitative approach, 20 (91% response rate) in-depth telephonic interviews were conducted with participating students, voicerecorded and transcribed. Through an inductive process, emerging themes were used to compile a code list for content analysis of the transcribed text. Relevant themes were reported according to the professionals’ roles described by the CanMEDS competency framework.Results. Participation in the module enhanced key competencies in the students, e.g. communication skills and the adoption of a holistic approach tointeraction with people or communities. Their role as collaborator was enhanced by their learning to embrace diversity and cultural differences and similarities. Students had to adapt to different cultures and educational systems. They were inspired to contribute in diverse contexts and act as agents for change in the organisations in which they may work or act as leaders or co-ordinators during interaction with community groups and policy makers. Higher education institutions offering transnational modules should support lecturers to manage the inherent diversity in the classroom as a way of enhancing student performance.Conclusion. The development of future transprofessional modules will benefit from the inclusion of desirable key competencies as part of the moduleoutcomes by following a competency by design process
Large-scale simulations of H and He reionization and heating driven by stars and more energetic sources
We present simulations of cosmic reionization and reheating from z = 18 to z = 5, investigating the role of stars (emitting soft UV-photons), nuclear black holes (BHs, with power-law spectra), X-ray binaries (XRBs, with hard X-ray dominated spectra), and the supernova-associated thermal bremsstrahlung of the diffuse interstellar medium (ISM, with soft X-ray spectra). We post-process the hydrodynamical simulation MassiveBlack-II (MBII) with multifrequency ionizing radiative transfer. The source properties are directly derived from the physical environment of MBII, and our only real free parameter is the ionizing escape fraction fesc. We find that, among the models explored here, the one with an escape fraction that decreases with decreasing redshift yields results most in line with observations, such as of the neutral hydrogen fraction and the Thomson scattering optical depth. Stars are the main driver of hydrogen reionization and consequently of the thermal history of the intergalactic medium (IGM). We obtain = 0.99998 at z = 6 for all source types, with volume-averaged temperatures < T > ∼ 20 000 K. BHs are rare and negligible to hydrogen reionization, but conversely they are the only sources that can fully ionize helium, increasing local temperatures by ∼104 K. The thermal and ionization state of the neutral and lowly ionized hydrogen differs significantly with different source combinations, with ISM and (to a lesser extent) XRBs, playing a significant role and, as a consequence, determining the transition from absorption to emission of the 21-cm signal from neutral hydrogen
New Pulsating White Dwarfs in Cataclysmic Variables
The number of discovered non-radially pulsating white dwarfs (WDs) in
cataclysmic variables (CVs) is increasing rapidly by the aid of the Sloan
Digital Sky Survey (SDSS). We performed photometric observations of two
additional objects, SDSS J133941.11+484727.5 (SDSS 1339), independently
discovered as a pulsator by Gansicke et al., and SDSS J151413.72+454911.9,
which we identified as a CV/ZZ Ceti hybrid. In this Letter we present the
results of the remote observations of these targets performed with the Nordic
Optical Telescope (NOT) during the Nordic-Baltic Research School at Moletai
Observatory, and follow-up observations executed by NOT in service mode. We
also present 3 candidates we found to be non-pulsating. The results of our
observations show that the main pulsation frequencies agree with those found in
previous CV/ZZ Ceti hybrids, but specifically for SDSS 1339 the principal
period differs slightly between individual observations and also from the
recent independent observation by Gansicke et al. Analysis of SDSS colour data
for the small sample of pulsating and non-pulsating CV/ZZ Ceti hybrids found so
far, seems to indicate that the r-i colour could be a good marker for the
instability strip of this class of pulsating WDs.Comment: 5 pages, 6 figures, 2 tables, accepted for publication in MNRAS
Letter
A CRASH simulation of the contribution of binary stars to the epoch of reionization
We use a set of 3D radiative transfer simulations to study the effect that a
large fraction of binary stars in galaxies during the epoch of reionization has
on the physical properties of the intergalactic medium (i.e. the gas
temperature and the ionization state of hydrogen and helium), on the topology
of the ionized bubbles and on the 21 cm power spectra. Consistently to previous
literature, we find that the inclusion of binary stars can speed up the
reionization process of HI and HeI, while HeII reionization is still dominated
by more energetic sources, especially accreting black holes. The earlier
ionization attained with binary stars allows for more time for cooling and
recombination, so that gas fully ionized by binary stars is typically colder
than that ionized by single stars at any given redshift. With the same volume
averaged ionization fraction, the inclusion of binary stars results in fewer
small ionized bubbles and more large ones, with visible effects also on the
large scales of the 21 cm power spectrum.Comment: 14 pages, 11 figures, MNRAS accepte
Marine n-3 fatty acid consumption in a Norwegian renal transplant cohort:Comparison of a food frequency questionnaire with plasma phospholipid marine n-3 levels
BackgroundHigh levels of plasma marine n-3 fatty acids (n-3FAs) are associated with improved patient and graft survival in renal transplant recipients (RTRs). The aim of this study was to evaluate the utility of a new food frequency questionnaire (FFQ) to estimate marine n-3FA consumption in future epidemiological research.MethodsWe developed an FFQ with a simple design of 10 questions to assess intake of marine sources of n-3FAs. RTRs included in the recent ORENTRA trial (n = 132) completed the study FFQ at the baseline visit eight weeks after engraftment and at the end of study visit one year post-transplant. We measured the reference biomarker plasma phospholipid (PL) marine n-3FA levels by gas chromatography at the same time points to evaluate association and degree of agreement between FFQ based marine n-3FA consumption estimates and the biomarker.ResultsThe median plasma PL marine n-3FA level was 6.0 weight percentage (wt)% (interquartile range [IQR] 4.7 to 7.3) at baseline and 6.3 wt% (IQR 4.8 to 7.4) at end of study. Median FFQ based marine n-3FA consumption estimates were 22.8 g/month (IQR 13.0 to 34.0) at baseline and 20.3 g/month (IQR 14.5 to 32.3) at end of study. FFQ based marine n-3FA consumption estimates showed a moderate correlation with plasma PL marine n-3FA levels at baseline (Spearman's correlation coefficient rs = 0.43, pConclusionsMarine n-3FA consumption estimates based on the FFQ showed a moderate correlation with the reference biomarker plasma PL marine n-3FA levels. The FFQ might be useful in epidemiological studies where resources are limited
Indigenous knowledge of rural communities in Malawi on socio-economic use, propagation, biology, biodiversity and ecology of Uapaca kirkiana Muell. Arg
Uapaca kirkiana Muell Arg. is one of the most popular indigenous fruit trees in the Miombo woodlands of southern Africa. An investigation into existing indigenous knowledge and socio- economic use ofthis fruit tree was conducted in Malawi. The survey revealed that U. kirkiana fruits contribute considerably to livelihood as a food supplement and for income generation among local communities.However, U. kirkiana trees are not widely cultivated due to lack of improved planting materials and difficulties in establishment outside their natural habitats. The results from the survey indicate thatfruits are the main non-timber products that contribute to demand for domestication and the attributes preferred by the rural communities for improvement are mainly related to fruit taste and yield. Poormanagement and anthropogenic activities have resulted in the destruction of forest reserves and the local people do not have maximum stewardship of U. kirkiana trees in the forest reserve. Theindigenous knowledge on U. kirkiana trees provides a valuable basis for domestication, propagation and improvement of fruit and tree attributes, and management issues on both co-managed and government forest reserve
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