5,865 research outputs found
On the injectivity of the circular Radon transform arising in thermoacoustic tomography
The circular Radon transform integrates a function over the set of all
spheres with a given set of centers. The problem of injectivity of this
transform (as well as inversion formulas, range descriptions, etc.) arises in
many fields from approximation theory to integral geometry, to inverse problems
for PDEs, and recently to newly developing types of tomography. The article
discusses known and provides new results that one can obtain by methods that
essentially involve only the finite speed of propagation and domain dependence
for the wave equation.Comment: To appear in Inverse Problem
"It's just horrible": a qualitative study of patients' and carers' experiences of bowel dysfunction in Multiple Sclerosis
Background:
Around 50% of people with multiple sclerosis (MS) experience neurogenic bowel dysfunction (constipation and / or faecal incontinence), reducing quality of life and increasing carer burden. No previous qualitative studies have explored the experiences of bowel problems in people with MS, or the views of their family carers.
Objective:
To understand 'what it is like' to live with bowel dysfunction and the impact this has on people with MS and carers.
Methods:
Using exploratory qualitative methods, 47 semi-structured interviews were conducted with participants recruited from specialist hospital clinics and community sources using purposive and chain-referral sampling. Data were analysed using a pragmatic inductive-deductive method.
Results:
Participants identified multiple psychological, physical and social impacts of bowel dysfunction. Health care professional support ranged from empathy and appropriate onward referral, to lack of interest or not referring to appropriate services. Participants want bowel issues to be discussed more openly, with clinicians instigating a discussion early after MS diagnosis and repeating enquiries regularly.
Conclusions:
Bowel dysfunction impacts on the lives of people with MS and their carers; their experience with care services is often unsatisfactory. Understanding patient and carer preferences about management of bowel dysfunction can inform clinical care and referral pathways
Multiple time scales in cataclysmic binaries. The low-field magnetic dwarf nova DO Draconis
We study the variability of the cataclysmic variable DO Dra, on time-scales
of between minutes and decades.
The characteristic decay time dt/dm=0.902(3) days/mag was estimated from our
3 nights of CCD R observations. The quiescent data show a photometric wave with
a cycle about 303(15)d. We analyzed the profile of the composite (or mean)
outburst. We discovered however, that a variety of different outburst heights
and durations had occurred, contrary to theoretical predictions. With
increasing maximum brightness, we find that the decay time also increases; this
is in contrast to the model predictions, which indicate that outbursts should
have a constant shape. This is interpreted as representing the presence of
outburst-to-outburst variability of the magnetospheric radius. A presence of a
number of missed weak narrow outbursts is predicted from this statistical
relationship. A new type of variability is detected, during 3 subsequent nights
in 2007: periodic (during one nightly run) oscillations with rapidly-decreasing
frequency from 86 to 47 cycles/day and a semi-amplitude increasing from 0.06 to
0. 10, during a monotonic brightness increase from 14. 27 to 14. 13. This
phenomenon was observed only during an unusually prolonged event of about 1 mag
brightening in 2007 (lasting till autumn), during which no (expected) outburst
was detected. We refer to this behaviour as to the transient periodic
oscillations (TPO). To study this new and interesting phenomenon, new regular
photometric and spectral (in a target of opportunity mode) observations are
required.Comment: 12pages, 8figures, accepted in Astronomy and Astrophysic
Techniques for assessing the performance of a landscape-based sediment source and transport model: sensitivity trials and physical methods
Widespread degradation of aquatic habitat and water quality has occurred since European settlement of Australia. Repairing this degradation is expensive and hence on-ground management needs to be carefully focussed. The Sediment River Network model, SedNet, used for the estimation of the sources and transport of sediment spatially and at catchment scales, potentially provides a useful tool to assist land managers in focusing this work. The complete model, whilst broadly applied has not been systematically tested to assess its accuracy or sensitivity to its various model components. The aim of this paper is to propose a framework for such testing. Results from the work will be used to prioritise data acquisition, and improve the structure and parameterisation of the model where necessary. The research is also particularly relevant for shifting application of the model from continental to catchment scales. The testing will comprise two components - sensitivity assessment and accuracy assessment. This paper provides a brief introduction to the SedNet model and a framework for assessing the model. Examples of sensitivity assessment and accuracy assessment are provided and discussed
A CFD based approach for determination of ammonia concentration profile and flux from poultry houses with natural ventilation
The understanding of concentration and emissions distribution of gases such as ammonia (NH3) in agricultural installations is of growing importance due to its effect on health and productivity of animals and workers. The objective of this study was to use validated Computational Fluid Dynamics (CFD) model as a tool to predict NH3 concentration distribution and mass fluxes in a non-insulated broiler chicken installation with natural ventilation, typically found in subtropical and tropical contries. Results from this study indicated that simulation with CFD can be used to predict NH3 concentration distribution and mass flux inside similar installations with incident winds from different directions of entrance at the lateral opening of the installation. The most direct application of the proposed mode would be to help improving the existing buildings and also to help in the conception of new ones, and may also apply the model to help in the development of NH3 emission inventories
Force-detected nuclear magnetic resonance: Recent advances and future challenges
We review recent efforts to detect small numbers of nuclear spins using
magnetic resonance force microscopy. Magnetic resonance force microscopy (MRFM)
is a scanning probe technique that relies on the mechanical measurement of the
weak magnetic force between a microscopic magnet and the magnetic moments in a
sample. Spurred by the recent progress in fabricating ultrasensitive force
detectors, MRFM has rapidly improved its capability over the last decade. Today
it boasts a spin sensitivity that surpasses conventional, inductive nuclear
magnetic resonance detectors by about eight orders of magnitude. In this review
we touch on the origins of this technique and focus on its recent application
to nanoscale nuclear spin ensembles, in particular on the imaging of nanoscale
objects with a three-dimensional (3D) spatial resolution better than 10 nm. We
consider the experimental advances driving this work and highlight the
underlying physical principles and limitations of the method. Finally, we
discuss the challenges that must be met in order to advance the technique
towards single nuclear spin sensitivity -- and perhaps -- to 3D microscopy of
molecules with atomic resolution.Comment: 15 pages & 11 figure
Background-Independence
Intuitively speaking, a classical field theory is background-independent if
the structure required to make sense of its equations is itself subject to
dynamical evolution, rather than being imposed ab initio. The aim of this paper
is to provide an explication of this intuitive notion. Background-independence
is not a not formal property of theories: the question whether a theory is
background-independent depends upon how the theory is interpreted. Under the
approach proposed here, a theory is fully background-independent relative to an
interpretation if each physical possibility corresponds to a distinct spacetime
geometry; and it falls short of full background-independence to the extent that
this condition fails.Comment: Forthcoming in General Relativity and Gravitatio
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Give What You Get: Capuchin Monkeys (Cebus apella) and 4-Year-Old Children Pay Forward Positive and Negative Outcomes to Conspecifics
The breadth of human generosity is unparalleled in the natural world, and much research has explored the mechanisms underlying and motivating human prosocial behavior. Recent work has focused on the spread of prosocial behavior within groups through paying-it-forward, a case of human prosociality in which a recipient of generosity pays a good deed forward to a third individual, rather than back to the original source of generosity. While research shows that human adults do indeed pay forward generosity, little is known about the origins of this behavior. Here, we show that both capuchin monkeys (Cebus apella) and 4-year-old children pay forward positive and negative outcomes in an identical testing paradigm. These results suggest that a cognitively simple mechanism present early in phylogeny and ontogeny leads to paying forward positive, as well as negative, outcomes
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