214 research outputs found
Making massive stars in the Galactic Centre via accretion onto low-mass stars within an accretion disc
The origin of the population of very massive stars observed within
pc of the supermassive black hole in the Galactic Centre is a mystery. Tidal
forces from the black hole would likely inhibit {\it in situ} star formation
whilst the youth of the massive stars would seem to exclude formation elsewhere
followed by transportation (somehow) into the Galactic centre. Here we consider
a third way to produce these massive stars from the lower-mass stars contained
in the nuclear stellar cluster which surrounds the supermassive black hole. A
passing gas cloud can be tidally shredded by the supermassive black hole
forming an accretion disc around the black hole. Stars embedded within this
accretion disc will accrete gas from the disc via Bondi-Hoyle accretion, where
the accretion rate onto a star, . This
super-exponential growth of accretion can lead to a steep increase in stellar
masses, reaching the required 40-50 M in some cases. The mass growth
rate depends sensitively on the stellar orbital eccentricities and their
inclinations. The evolution of the orbital inclinations and/or their
eccentricities as stars are trapped by the disc, and their orbits are
circularised, will increase the number of massive stars produced. Thus
accretion onto low-mass stars can lead to a top heavy stellar mass function in
the Galactic Centre and other galactic nuclei. The massive stars produced will
pollute the environment via supernova explosions and potentially produce
compact binaries whose mergers may be detectable by the LIGO-VIRGO
gravitational waves observatories.Comment: Accepted for publication in MNRA
Updated Composite Materials Handbook-17 (CMH-17) Volume 5 - Ceramic Matrix Composites
A wide range of issues must be addressed during the process of certifying CMC (ceramic matrix composite) components for use in commercial aircraft. The Composite Materials Handbook-17, Volume 5, Revision A on ceramic matrix composites has just been revised to help support FAA certification of CMCs for elevated temperature applications. The handbook supports the development and use of CMCs through publishing and maintaining proven, reliable engineering information and standards that have been thoroughly reviewed. Volume 5 contains detailed sections describing CMC materials/processing, design/analysis guidelines, testing procedures, and data analysis and acceptance. A review of the content of this latest revision will be presented along with a description of how CMH-17, Volume 5 could be used by companies applying for certification with the FAA (Federal Aviation Administration) and others in the future
Genomic characterization of Staphylococcus aureus at the swine-human interface
The epidemiology of S. aureus in swine held little interest until the ST398 lineage of MRSA was found to be prevalent in pigs and pig farmers in the Netherlands in 2004 (Voss et al. 2005). ST398 MRSA have since been detected in multiple livestock species and in many countries (EFSA, 2009; Smith and Pearson, 2011), while genetically distinct variants of ST398 S. aureus occur in some human populations independent of livestock reservoirs (Carrel et al., 2017). Furthermore, other genotypes of MRSA can occur in pigs, particularly ST9 MRSA in Asia, and ST5 MRSA in North America (Chuang and Huang, 2015; Frana et al. 2013). In the USA, methicillin susceptible variants of the ST398, ST9 and ST5 lineages are widespread in commercial swine, yet MRSA variants appear to occur at relatively low prevalence (Sun, et al., 2015). Despite common exposure to, and colonization of, swine workers by livestock associated S. aureus, significant clinical infections appear to be uncommon in occupationally exposed people. However, invasive and even fatal infections are reported at relatively low incidence in some countries, and medically compromised people appear to be at particular risk, even in the absence of animal contact (Larsen et al., 2017). There is evidence that ST398 MRSA of livestock origin are less transmissible among humans than MRSA of human origin. Also, genomic studies typically have indicated that livestock associated MRSA (both ST398 and ST5) lack most virulence factors that occur in human clinical isolates (Schijffelen et al. 2010; Price et al. 2012; Hau et al, 2015). However, to date there has been little genomic characterization of methicillin susceptible S. aureus (MSSA) that are prevalent in swine populations. The purpose of this study was to describe the occurrence of virulence factors and antibiotic resistance genes in S. aureus isolates from pigs and swine veterinarians in the USA
Hybrid configuration content of heavy S-wave mesons
We use the non-relativistic expansion of QCD (NRQCD) on the lattice to study
the lowest hybrid configuration contribution to the ground state of heavy
S-wave mesons. Using lowest-order lattice NRQCD to create the heavy-quark
propagators, we form a basis of ``unperturbed'' S-wave and hybrid states. We
then apply the lowest-order coupling of the quark spin and chromomagnetic field
at an intermediate time slice to create ``mixed'' correlators between the
S-wave and hybrid states. From the resulting amplitudes, we extract the
off-diagonal element of our two-state Hamiltonian. Diagonalizing this
Hamiltonian gives us the admixture of hybrid configuration within the meson
ground state. The present effort represents a continuation of previous work:
the analysis has been extended to include lattices of varying spacings, source
operators having better overlap with the ground states, and the pseudoscalar
(along with the vector) channel. Results are presented for bottomonium
(, ) using three different sets of quenched lattices. We
also show results for charmonium (, ) from one lattice set,
although we note that the non-relativistic approximation is not expected to be
very good in this case.Comment: 9 pages, 7 figures, version to appear in Phys Rev
Predictability of European winter 2019/20: Indian Ocean dipole impacts on the NAO
Northern Europe and the UK experienced an exceptionally warm and wet winter in 2019/20, driven by an anomalously positive North Atlantic Oscillation (NAO). This positive NAO was well forecast by several seasonal forecast systems, suggesting that this winter the NAO was highly predictable at seasonal lead times. A very strong positive Indian Ocean dipole (IOD) event was also observed at the start of winter. Here we use composite analysis and model experiments, to show that the IOD was a key driver of the observed positive NAO. Using model experiments that perturb the Indian Ocean initial conditions, two teleconnection pathways of the IOD to the north Atlantic emerge: a tropospheric teleconnection pathway via a Rossby wave train travelling from the Indian Ocean over the Pacific and Atlantic, and a stratospheric teleconnection pathway via the Aleutian region and the stratospheric polar vortex. These pathways are similar to those for the El Niño Southern Oscillation link to the north Atlantic which are already well documented. The anomalies in the north Atlantic jet stream location and strength, and the associated precipitation anomalies over the UK and northern Europe, as simulated by the model IOD experiments, show remarkable agreement with those forecast and observed
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Meteorological training for the digital age: A Blueprint for a new curriculum
Almost all professional meteorologists take part in meteorological training during their undergraduate or graduate study or professional job training in the public or private sector. Increased benefits can be accrued by employers and employees, if this training is based on the same underpinning skills and attributes, aimed to equip people entering meteorology for the wide range of future roles they might undertake.
While there is a great deal of excellent, innovative practice in our community, the time is now right to look again at the nature of the meteorological curriculum. Meteorology faces significant challenges in the 21st century to deal with the twin challenges of increases in the number and severity of extreme weather events and the increased complexity of forecasts demanded by end-users.
Here, a blueprint which describes a number of key principles which should be used to design, evaluate and enhance curricula for students entering our field in the next 10 years is proposed. The blueprint does not discuss in detail the core mathematical and physical principles which underlie any high quality training in meteorology but rather focuses on the key skills and attributes needed to make the next-generation of meteorologists innovative and effective which include:
• Meteorological competencies,
• Personal and inter-personal attributes,
• Core skills as a scientist and
• Ethical and professional interaction with broader society.
The blueprint is intended to encourage debate about how we equip new meteorologists for the digital age. We plan to use these principles to review and enhance our own curricula in the near future
The impact of training non-physician clinicians in Malawi on maternal and perinatal mortality : a cluster randomised controlled evaluation of the enhancing training and appropriate technologies for mothers and babies in Africa (ETATMBA) project
Background:
Maternal mortality in much of sub-Saharan Africa is very high whereas there has been a steady decline in over the past 60 years in Europe. Perinatal mortality is 12 times higher than maternal mortality accounting for about 7 million neonatal deaths; many of these in sub-Saharan countries. Many of these deaths are preventable. Countries, like Malawi, do not have the resources nor highly trained medical specialists using complex technologies within their healthcare system. Much of the burden falls on healthcare staff other than doctors including non-physician clinicians (NPCs) such as clinical officers, midwives and community health-workers. The aim of this trial is to evaluate a project which is training NPCs as advanced leaders by providing them with skills and knowledge in advanced neonatal and obstetric care. Training that will hopefully be cascaded to their colleagues (other NPCs, midwives, nurses).
Methods/design:
This is a cluster randomised controlled trial with the unit of randomisation being the 14 districts of central and northern Malawi (one large district was divided into two giving an overall total of 15). Eight districts will be randomly allocated the intervention. Within these eight districts 50 NPCs will be selected and will be enrolled on the training programme (the intervention). Primary outcome will be maternal and perinatal (defined as until discharge from health facility) mortality. Data will be harvested from all facilities in both intervention and control districts for the lifetime of the project (3–4 years) and comparisons made. In addition a process evaluation using both quantitative and qualitative (e.g. interviews) will be undertaken to evaluate the intervention implementation.
Discussion:
Education and training of NPCs is a key to improving healthcare for mothers and babies in countries like Malawi. Some of the challenges faced are discussed as are the potential limitations. It is hoped that the findings from this trial will lead to a sustainable improvement in healthcare and workforce development and training.
Trial registration:
ISRCTN6329415
AtlantOS Deliverable 6.2: Roadmap for emerging networks
Whilst the AtlantOS project is directed towards bringing together the existing, but
currently disparate observing programmes in the Atlantic Ocean, there are still some
gaps in terms of requirements for addressing the collection and curation of data
around the Essential Ocean Variables. This deliverable will identify gaps and
emerging observing networks. Here we use the term emerging network to classify
science areas that are starting to gain importance with respect to EOV’s and their
measurement and curation, or are existing small scale programmes or communities
that might become more important in the future if we can find means of enhancing
the collaboration among investigators/groups, increasing resources to the area or
using new technological developments.
In the AtlantOS project we have identified a number of areas in which there are gaps
in our knowledge and where opportunities exist to enhance current small-scale
networks.
The scope of this document is to assess these networks, based on where we are
now and where the networks could be in three and ten years’ time, respectively. An
assessment of the state of the existing networks is useful to identify the level of
international organisation and potential for further development in the future. We
identify opportunities where synergies are possible with more established global
projects, and where small levels of investment in resource and time for governance
and coordination can productively and realistically develop the networks. We also
identify if there are ways to develop coordinated approaches to metrology technology
development.
For this analysis, the networks have been allocated to one of the three groups
outlined below
Roadmap for emerging networks
Assessment of networks and gap analysis that highlights opportunities for development over three and ten year timescale
Open Data and Digital Morphology
Over the past two decades, the development of methods for visualizing and analysing specimens digitally, in three and even four dimensions, has transformed the study of living and fossil organisms. However, the initial promise that the widespread application of such methods would facilitate access to the underlying digital data has not been fully achieved. The underlying datasets for many published studies are not readily or freely available, introducing a barrier to verification and reproducibility, and the reuse of data. There is no current agreement or policy on the amount and type of data that should be made available alongside studies that use, and in some cases are wholly reliant on, digital morphology. Here, we propose a set of recommendations for minimum standards and additional best practice for three-dimensional digital data publication, and review the issues around data storage, management and accessibility
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