282 research outputs found
Coping with ill-health: health care facility, chemist or medicinal plants? Health-seeking behaviour in a Kenyan wetland
Background: Sub-Saharan African wetlands, settlement areas to growing populations, expose their users to diseases as necessary health infrastructure remains underdeveloped.
Methods: Mixed methods were adopted to assess the health-seeking behaviour of different exposure groups (farmers, pastoralists, service sector workers) in a Kenyan wetland community. Based on a cross-sectional survey (nâ=â400), syndromic surveillance was linked to health-seeking event analysis. In-depth interviews with community members (nâ=â20) and experts (nâ=â8) enabled the integration of healthcare user and provider perspectives.
Results: Health-seeking behaviour in the wetland was determined by physical/infrastructural, natural/environmental, financial/socioeconomic and social/demographic factors, as well as human/cultural aspects such as traditional preferences rooted in health beliefs. Community members had different strategies of coping with ill-health and few symptoms remained untreated. Whether via a health care facility admission, the visit of a chemist, or the intake of pharmaceuticals or medicinal plants: treatment was usually applied either via a healthcare service provider or by the community members themselves. An undersupply of easy-to-reach healthcare options was detected, and healthcare services were not available and accessible to all. The widely-practiced self-treatment of symptoms, e.g. by use of local medicinal plants, mirrors both potential healthcare gaps and cultural preferences of wetland communities.
Conclusions: Integrated into an overall health-promoting wetland management approach, widely accepted (cultural) realities of health-seeking behaviours could complement health sector service provision and help ensure healthy lives and promote well-being for all in wetlands
Gravitational wave amplification of seed magnetic fields
We discuss how gravitational waves could amplify seed magnetic fields to
strengths capable of supporting the galactic dynamo. We consider the
interaction of a weak magnetic field with gravity wave distortions in almost
FRW cosmologies and find that the magnitude of the original field is amplified
proportionally to the wave induced shear anisotropy and, crucially,
proportionally to the square of the field's initial scale. The latter makes our
mechanism particularly efficient when operating on superhorizon sized magnetic
fields, like those produced during inflation. In that case, the achieved
amplification can easily boost magnetic strengths, which may still lie
relatively close to the galactic dynamo lower limits, well within the currently
accepted range.Comment: Revised version, to appear in Phys. Lett.
Cosmic magnetic fields from velocity perturbations in the early Universe
We show, using a covariant and gauge-invariant charged multifluid
perturbation scheme, that velocity perturbations of the matter-dominated dust
Friedmann-Lemaitre-Robertson-Walker (FLRW) model can lead to the generation of
cosmic magnetic fields. Moreover, using cosmic microwave background (CMB)
constraints, it is argued that these fields can reach strengths of between
10^{-28} and 10^{-29} G at the time the dynamo mechanism sets in, making them
plausible seed field candidates.Comment: 11 pages, 1 figure, IOP style, minor changes and typos correcte
Simple extension of the plane-wave final state in photoemission: Bringing understanding to the photon-energy dependence of two-dimensional materials
Angle-resolved photoemission spectroscopy (ARPES) is a method that measures orbital and band structure contrast through the momentum distribution of photoelectrons. Its simplest interpretation is obtained in the plane-wave approximation, according to which photoelectrons propagate freely to the detector. The photoelectron momentum distribution is then essentially given by the Fourier transform of the real-space orbital. While the plane-wave approximation is remarkably successful in describing the momentum distributions of aromatic compounds, it generally fails to capture kinetic-energy-dependent final-state interference and dichroism effects. Focusing our present study on quasi-freestanding monolayer graphene as the archetypical two-dimensional (2D) material, we observe an exemplary Ekin-dependent modulation of, and a redistribution of spectral weight within, its characteristic horseshoe signature around the KÂŻ and KÂŻâČ points: both effects indeed cannot be rationalized by the plane-wave final state. Our data are, however, in remarkable agreement with ab initio time-dependent density functional simulations of a freestanding graphene layer and can be explained by a simple extension of the plane-wave final state, permitting the two dipole-allowed partial waves emitted from the C 2pz orbitals to scatter in the potential of their immediate surroundings. Exploiting the absolute photon flux calibration of the Metrology Light Source, this scattered-wave approximation allows us to extract Ekin-dependent amplitudes and phases of both partial waves directly from photoemission data. The scattered-wave approximation thus represents a powerful yet intuitive refinement of the plane-wave final state in photoemission of 2D materials and beyond
On the origin of X-shaped radio galaxies
After a brief, critical review of the leading explanations proposed for the
small but important subset of radio galaxies showing an X-shaped morphology
(XRGs) we propose a generalized model, based on the jet-shell interaction and
spin-flip hypotheses. The most popular scenarios for this intriguing phenomenon
invoke either hydrodynamical backflows and over-pressured cocoons or rapid jet
reorientations, presumably from the spin-flips of central engines following the
mergers of pairs of galaxies, each of which contains a supermassive black hole
(SMBH). We confront these models with a number of key observations and thus
argue that none of the models is capable of explaining the entire range of
salient observational properties of XRGs, although some of the arguments raised
in the literature against the spin-flip scenario are probably not tenable. We
then propose here a new scenario which also involves galactic mergers but would
allow the spin of the central engine to maintain its direction. Motivated by
the detailed multi-band observations of the nearest radio galaxy, Centaurus A,
this new model emphasizes the role of interactions between the jets and the
shells of stars and gas that form and rotate around the merged galaxy and can
cause temporary deflections of the jets, occasionally giving rise to an
X-shaped radio structure. Although each of the models is likely to be relevant
to a subset of XRGs, the bulk of the evidence indicates that most of them are
best explained by the jet-shell interaction or spin-flip hypotheses.Comment: 19 pages, major revision including two Appendices and a Table,
accepted in Research in Astronomy and Astrophysic
Flat-spectrum symmetric objects with ~1 kpc sizes I. The candidates
In order to understand the origin and evolution of radio galaxies, searches
for the youngest such sources have been conducted. Compact-medium symmetric
objects (CSO-MSOs) are thought to be the earliest stages of radio sources, with
possible ages of <10^3 yrs for CSOs (<1 kpc in size) and 10^4-10^5 yrs for MSOs
(1-15 kpc). From a literature selection in heterogeneous surveys, we have
established a sample of 37 confirmed CSOs. In addition, we only found three
confirmed flat-spectrum MSOs in the literature.
The typical CSO resides on a z<0.5 galaxy, has a flat radio spectrum
(a_thin<0.5; S_v proportional to v^-a), is <0.3 kpc in size, has an arm length
ratio <2, and well-aligned (theta<20 deg) opposite lobes with a flux density
ratio <10. In order to populate the 0.3-1 kpc size range (large CSOs) and also
in order to find more flat-spectrum MSOs, we have built a sample of 157 radio
sources with a_{1.40}^{4.85}<0.5 that were resolved with the VLA-A 8.4 GHz. As
first results, we have 'rediscovered' nine of the known CSO/MSOs while
identifying two new ~14 kpc MSOs and two candidate CSO/MSOs (which only lack
redshifts for final classification). We were able to reject 61 of the remaining
144 objects from literature information alone. In the series of papers that
starts with this one we plan to classify the remaining 83 CSO/MSO candidates
(thanks to radio and optical observations) as well as characterize the physical
properties of the (likely) many 0.3-15 kpc flat-spectrum CSO/MSOs to be found.Comment: 19 pages, 14 figures, 6 tables (note that Table 2, in landscape
format, has a separate file); accepted by MNRA
Theoretical tools for CMB physics
This review presents, in a self-consistent manner, those analytical tools
that are relevant for the analysis of the physics of CMB anisotropies generated
in different theoretical models of the early Universe. After introducing the
physical foundations of the Sachs-Wolfe effect, the origin and evolution of the
scalar, tensor and vector modes of the geometry is treated in both
gauge-invariant and gauge-dependent descriptions. Some of the recent progresses
in the theory of cosmological perturbations are scrutinized with particular
attention to their implications for the adiabatic and isocurvature paradigms,
whose description is reviewed both within conventional fluid approaches and
within the the Einstein-Boltzmann treatment. Open problems and theoretical
challenges for a unified theory of the early Universe are outlined in light of
their implications for the generation of large-scale anisotropies in the CMB
sky and in light of the generation of stochastic backgrounds of relic gravitons
between few Hz and the GHz.Comment: 147 pages, 6 figures; minor corrected typo
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