7,969 research outputs found
Many-Body Corrections to Charged-Current Neutrino Absorption Rates in Nuclear Matter
Including nucleon--nucleon correlations due to both Fermi statistics and
nuclear forces, we have developed a general formalism for calculating the
charged--current neutrino--nucleon absorption rates in nuclear matter. We find
that at one half nuclear density many--body effects alone suppress the rates by
a factor of two and that the suppression factors increase to 5 at
g cm. The associated increase in the neutrino--matter
mean--free--paths parallels that found for neutral--current interactions and
opens up interesting possibilities in the context of the delayed supernova
mechanism and protoneutron star cooling.Comment: 11 pages, APS REVTeX format, 1 PostScript figure, uuencoded
compressed, and tarred, submitted to Physical Review Letter
A Framework to Manage the Complex Organisation of Collaborating: Its Application to Autonomous Systems
In this paper we present an analysis of the complexities of large group
collaboration and its application to develop detailed requirements for
collaboration schema for Autonomous Systems (AS). These requirements flow from
our development of a framework for collaboration that provides a basis for
designing, supporting and managing complex collaborative systems that can be
applied and tested in various real world settings. We present the concepts of
"collaborative flow" and "working as one" as descriptive expressions of what
good collaborative teamwork can be in such scenarios. The paper considers the
application of the framework within different scenarios and discuses the
utility of the framework in modelling and supporting collaboration in complex
organisational structures
Social networks, social capital and end-of-life care for people with dementia: a realist review
OBJECTIVES (1) To develop an understanding of how social
capital may be conceptualised within the context of endof-life care and how it can influence outcomes for people
with dementia and their families with specific reference
to the context and mechanisms that explain observed
outcomes. (2) To produce guidance for healthcare systems
and researchers to better structure and design a public
health approach to end-of-life care for people with
dementia.
DESIGN A realist review.
Data sources MEDLINE, EMBASE, CINAHL and grey
literature.
ANALYSIS We conceptualised social capital as a complex
intervention and, in order to understand how change is
generated, used realist evaluation methods to create
different configurations of context, mechanism and
outcomes. We conducted an iterative search focusing
on social capital, social networks and end-of-life care in
dementia. All study designs and outcomes were screened
and analysed to elicit explanations for a range of outcomes
identified. Explanations were consolidated into an
overarching programme theory that drew on substantive
theory from the social sciences and a public health
approach to palliative care.
RESULTS We identified 118 articles from 16 countries
ranging from 1992 to 2018. A total of 40 contextmechanism-outcome configurations help explain how
social capital may influence end-of-life care for people
with dementia. Such influence was identified within five
key areas. These included: (1) socially orientating a person
with dementia following diagnosis; (2) transitions in the
physical environment of care; (3) how the caregiving
experience is viewed by those directly involved with it; (4)
transition of a person with dementia into the fourth age;
(5) the decision making processes underpinning such
processes.
CONCLUSION This review contributes to the dispassionate
understanding of how complex systems such as
community and social capital might be viewed as a tool to
improve end-of-life care for people with dementia.
PROSPERO REGISTRATION NUMBER CRD42018084524
A Self-Consistent Approach to Neutral-Current Processes in Supernova Cores
The problem of neutral-current processes (neutrino scattering, pair emission,
pair absorption, axion emission, \etc) in a nuclear medium can be separated
into an expression representing the phase space of the weakly interacting
probe, and a set of dynamic structure functions of the medium. For a
non-relativistic medium we reduce the description to two structure functions
S_A(\o) and S_V(\o) of the energy transfer, representing the axial-vector
and vector interactions. is well determined by the single-nucleon
approximation while may be dominated by multiply interacting nucleons.
Unless the shape of S_A(\o) changes dramatically at high densities,
scattering processes always dominate over pair processes for neutrino transport
or the emission of right-handed states. Because the emission of right-handed
neutrinos and axions is controlled by the same medium response functions, a
consistent constraint on their properties from consideration of supernova
cooling should use the same structure functions for both neutrino transport and
exotic cooling mechanisms.Comment: 33 pages, Te
Response of selected plant and insect species to simulated solid rocket exhaust mixtures and to exhaust components from solid rocket fuels
The effects of solid rocket fuel (SRF) exhaust on selected plant and and insect species in the Merritt Island, Florida area was investigated in order to determine if the exhaust clouds generated by shuttle launches would adversely affect the native, plants of the Merritt Island Wildlife Refuge, the citrus production, or the beekeeping industry of the island. Conditions were simulated in greenhouse exposure chambers and field chambers constructed to model the ideal continuous stirred tank reactor. A plant exposure system was developed for dispensing and monitoring the two major chemicals in SRF exhaust, HCl and Al203, and for dispensing and monitoring SRF exhaust (controlled fuel burns). Plants native to Merritt Island, Florida were grown and used as test species. Dose-response relationships were determined for short term exposure of selected plant species to HCl, Al203, and mixtures of the two to SRF exhaust
Variable Stars in the Globular Cluster M5. Application of the Image Subtraction Method
We present -band light curves of 61 variables from the core of the
globular cluster M5 obtained using a newly developed image subtraction method
(ISM). Four of these variables were previously unknown. Only 26 variables were
found in the same field using photometry obtained with DoPHOT software. Fourier
parameters of the ISM light curves have relative errors up to 20 times smaller
than parameters measured from DoPHOT photometry. We conclude that the new
method is very promising for searching for variable stars in the cores of the
globular clusters and gives very accurate relative photometry with quality
comparable to photometry obtained by HST. We also show that the variable V104
is not an eclipsing star as has been suggested, but is an RRc star showing
non-radial pulsations.Comment: submitted to MNRAS, 9 pages, 4 figure
Exotic bulk viscosity and its influence on neutron star r-modes
We investigate the effect of exotic matter in particular, hyperon matter on
neutron star properties such as equation of state (EoS), mass-radius
relationship and bulk viscosity. Here we construct equations of state within
the framework of a relativistic field theoretical model. As hyperons are
produced abundantly in dense matter, hyperon-hyperon interaction becomes
important and is included in this model. Hyperon-hyperon interaction gives rise
to a softer EoS which results in a smaller maximum mass neutron star compared
with the case without the interaction. Next we compute the coefficient of bulk
viscosity and the corresponding damping time scale due to the non-leptonic weak
process including hyperons. Further, we investigate the role of the
bulk viscosity on gravitational radiation driven r-mode instability in a
neutron star of given mass and temperature and find that the instability is
effectively suppressed.Comment: 5 pages, 3 figure, presented in the Conference on Isolated Neutron
Stars: From the Interior to The Surface, London, UK, 24-28 April, 2006;
revised and final version to appear in Astrophys. Space Sc
Nucleon Spin Fluctuations and the Supernova Emission of Neutrinos and Axions
In the hot and dense medium of a supernova (SN) core, the nucleon spins
fluctuate so fast that the axial-vector neutrino opacity and the axion
emissivity are expected to be significantly modified. Axions with
m_a\alt10^{-2}\,{\rm eV} are not excluded by SN~1987A. A substantial transfer
of energy in neutrino-nucleon () collisions is enabled which may alter
the spectra of SN neutrinos relative to calculations where energy-conserving
collisions had been assumed near the neutrinosphere.Comment: 8 pages. REVTeX. 2 postscript figures, can be included with epsf.
Small modifications of the text, a new "Note Added", and three new
references. To be published in Phys. Rev. Let
Second-order rotational effects on the r-modes of neutron stars
Techniques are developed here for evaluating the r-modes of rotating neutron
stars through second order in the angular velocity of the star. Second-order
corrections to the frequencies and eigenfunctions for these modes are evaluated
for neutron star models. The second-order eigenfunctions for these modes are
determined here by solving an unusual inhomogeneous hyperbolic boundary-value
problem. The numerical techniques developed to solve this unusual problem are
somewhat non-standard and may well be of interest beyond the particular
application here. The bulk-viscosity coupling to the r-modes, which appears
first at second order, is evaluated. The bulk-viscosity timescales are found
here to be longer than previous estimates for normal neutron stars, but shorter
than previous estimates for strange stars. These new timescales do not
substantially affect the current picture of the gravitational radiation driven
instability of the r-modes either for neutron stars or for strange stars.Comment: 13 pages, 5 figures, revte
How to identify a Strange Star
Contrary to young neutron stars, young strange stars are not subject to the
r-mode instability which slows rapidly rotating, hot neutron stars to rotation
periods near 10 ms via gravitational wave emission. Young millisecond pulsars
are therefore likely to be strange stars rather than neutron stars, or at least
to contain significant quantities of quark matter in the interior.Comment: 4 pages, 1 figur
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