2,928 research outputs found
CPT symmetry and antimatter gravity in general relativity
The gravitational behavior of antimatter is still unknown. While we may be
confident that antimatter is self-attractive, the interaction between matter
and antimatter might be either attractive or repulsive. We investigate this
issue on theoretical grounds. Starting from the CPT invariance of physical
laws, we transform matter into antimatter in the equations of both
electrodynamics and gravitation. In the former case, the result is the
well-known change of sign of the electric charge. In the latter, we find that
the gravitational interaction between matter and antimatter is a mutual
repulsion, i.e. antigravity appears as a prediction of general relativity when
CPT is applied. This result supports cosmological models attempting to explain
the Universe accelerated expansion in terms of a matter-antimatter repulsive
interaction.Comment: 6 pages, to be published in EPL (http://epljournal.edpsciences.org/
Children with complex support needs in healthcare settings for prolonged periods: their numbers, characteristics and experiences
This report details the findings of research conducted in England and Scotland to identify how many children with complex support needs are spending longer than one month in healthcare settings in Scotland and England, how and why they are in hospital, why they have not been discharged home or to appropriate alternative community-based facilities, and how well the hospital or healthcare setting is meeting their emotional, social and educational needs. It finds that many of these children could and should be discharged but are not, for a variety of reasons: primarily the lack of appropriate resources in the community and poor discharge planning processes, coupled with the inability of their families to manage their care and supervision without intensive support. Hospitals and healthcare settings in many cases are not meeting their needs and these children are being denied the protection offered by UK legislation governing children's rights and welfare
Resilience in Children and Young People with Disabilities: A Systematic Review with Embedded Primary Research
Combined ultraviolet studies of astronomical sources
Ultraviolet studies of astronomical sources are discussed. Some studies utilized IVE data. Non-radiative shock at the edge of the Cygnses Loop, stellar flares, local interestellar medium, hot galaxies, stellar mass ejection, contact binaries, double quasars, and stellar chromosphere and coronae are discussed
In and out of Madagascar : dispersal to peripheral islands, insular speciation and diversification of Indian Ocean daisy trees (Psiadia, Asteraceae)
This study was supported by the European Union’s HOTSPOTS Training Network (MEST-2005-020561)Madagascar is surrounded by archipelagos varying widely in origin, age and structure. Although small and geologically young, these archipelagos have accumulated disproportionate numbers of unique lineages in comparison to Madagascar, highlighting the role of waif-dispersal and rapid in situ diversification processes in generating endemic biodiversity. We reconstruct the evolutionary and biogeographical history of the genus Psiadia (Asteraceae), a plant genus with near equal numbers of species in Madagascar and surrounding islands. Analyzing patterns and processes of diversification, we explain species accumulation on peripheral islands and aim to offer new insights on the origin and potential causes for diversification in the Madagascar and Indian Ocean Islands biodiversity hotspot. Our results provide support for an African origin of the group, with strong support for non-monophyly. Colonization of the Mascarenes took place by two evolutionary distinct lineages from Madagascar, via two independent dispersal events, each unique for their spatial and temporal properties. Significant shifts in diversification rate followed regional expansion, resulting in co-occurring and phenotypically convergent species on high-elevation volcanic slopes. Like other endemic island lineages, Psiadia have been highly successful in dispersing to and radiating on isolated oceanic islands, typified by high habitat diversity and dynamic ecosystems fuelled by continued geological activity. Results stress the important biogeographical role for Rodrigues in serving as an outlying stepping stone from which regional colonization took place. We discuss how isolated volcanic islands contribute to regional diversity by generating substantial numbers of endemic species on short temporal scales. Factors pertaining to the mode and tempo of archipelago formation and its geographical isolation strongly govern evolutionary pathways available for species diversification, and the potential for successful diversification of dispersed lineages, therefore, appears highly dependent on the timing of arrival, as habitat and resource properties change dramatically over the course of oceanic island evolution.Publisher PDFPeer reviewe
Tobacco: harm-reduction approaches to smoking Review 4: Barriers and facilitators to implementing tobacco harm reduction approaches; including user and provider perspectives.
Exploring social patterns of participation in university-entrance level mathematics in England
In recent years in England there has been considerable attention given to a range of apparent crises in mathematics education, one of which has been the long term decline of participation in university-entrance level (Advanced or A) mathematics. Given the negative impact upon mathematics participation of Curriculum 2000, together with the government’s emphasis on Science Technology Engineering and Mathematics (STEM) subjects, the political intent to increase participation in Advanced level mathematics is clear. This paper uses the National Pupil Database (NPD) to develop a descriptive statistical account of how completion of Advanced level mathematics varies along the social axes of SES, ethnicity and gender. The process of working with the NPD is discussed in some depth in order to clarify the processes involved in this type of quantitative analysis and to illustrate how this analysis can be used to raise questions about who is doing what mathematics in the post-16 age-range
Carbon monoxide in the solar atmosphere I. Numerical method and two-dimensional models
The radiation hydrodynamic code CO5BOLD has been supplemented with the
time-dependent treatment of chemical reaction networks. Advection of particle
densities due to the hydrodynamic flow field is also included. The radiative
transfer is treated frequency-independently, i.e. grey, so far. The upgraded
code has been applied to two-dimensional simulations of carbon monoxide (CO) in
the non-magnetic solar photosphere and low chromosphere. For this purpose a
reaction network has been constructed, taking into account the reactions which
are most important for the formation and dissociation of CO under the physical
conditions of the solar atmosphere. The network has been strongly reduced to 27
reactions, involving the chemical species H, H2, C, O, CO, CH, OH, and a
representative metal. The resulting CO number density is highest in the cool
regions of the reversed granulation pattern at mid-photospheric heights and
decreases strongly above. There, the CO abundance stays close to a value of 8.3
on the usual logarithmic abundance scale with [H]=12 but is reduced in hot
shock waves which are a ubiquitous phenomenon of the model atmosphere. For
comparison, the corresponding equilibrium densities have been calculated, based
on the reaction network but also under assumption of instantaneous chemical
equilibrium by applying the Rybicki & Hummer (RH) code by Uitenbroek (2001).
Owing to the short chemical timescales, the assumption holds for a large
fraction of the atmosphere, in particular the photosphere. In contrast, the CO
number density deviates strongly from the corresponding equilibrium value in
the vicinity of chromospheric shock waves. Simulations with altered reaction
network clearly show that the formation channel via hydroxide (OH) is the most
important one under the conditions of the solar atmosphere.Comment: 15 pages, 6 figures, final version will contain online materia
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