7,325 research outputs found
Syringomyelia: A review of the biomechanics
Syringomyelia is a neurological disorder caused by the development of one or more macroscopic fluid-filled cavities in the spinal cord. While the aetiology remains uncertain, hydrodynamics appear to play a role. This has led to the involvement of engineers, who have modelled the system in silico and on the bench. In the process, hypotheses from the neurosurgical literature have been tested, and others generated, while aspects of the system mechanics have been clarified. The spinal cord is surrounded by cerebrospinal fluid (CSF) which is subject both to the periodic excitation of CSF expelled from the head with each heartbeat, and to intermittent larger transients from cough, sneeze, etc., via vertebral veins. The resulting pulsatile flow and pressure wave propagation, and their possible effects on cord cavities and cord stresses, have been elucidated. These engineering contributions are here reviewed for the first time
Dynamical approach to chains of scatterers
Linear chains of quantum scatterers are studied in the process of
lengthening, which is treated and analysed as a discrete dynamical system
defined over the manifold of scattering matrices. Elementary properties of such
dynamics relate the transport through the chain to the spectral properties of
individual scatterers. For a single-scattering channel case some new light is
shed on known transport properties of disordered and noisy chains, whereas
translationally invariant case can be studied analytically in terms of a simple
deterministic dynamical map. The many-channel case was studied numerically by
examining the statistical properties of scatterers that correspond to a certain
type of transport of the chain i.e. ballistic or (partially) localised.Comment: 16 pages, 7 figure
Computer simulation of syringomyelia in dogs
Syringomyelia is a pathological condition in which fluid-filled cavities (syringes) form and expand in the spinal cord. Syringomyelia is often linked with obstruction of the craniocervical junction and a Chiari malformation, which is similar in both humans and animals. Some brachycephalic toy breed dogs such as Cavalier King Charles Spaniels (CKCS) are particularly predisposed. The exact mechanism of the formation of syringomyelia is undetermined and consequently with the lack of clinical explanation, engineers and mathematicians have resorted to computer models to identify possible physical mechanisms that can lead to syringes. We developed a computer model of the spinal cavity of a CKCS suffering from a large syrinx. The model was excited at the cranial end to simulate the movement of the cerebrospinal fluid (CSF) and the spinal cord due to the shift of blood volume in the cranium related to the cardiac cycle. To simulate the normal condition, the movement was prescribed to the CSF. To simulate the pathological condition, the movement of CSF was blocked
What happens before, during and after crisis for someone with dementia living at home: a systematic review
Background People living with dementia often experience crisis. Home treatment of crisis is an alternative to hospital admission that can have better outcomes. This systematic review is about people with dementia living at home and in crisis. It identifies modifiable factors in the crisis process that may facilitate crisis resolution. Methods The protocol is registered on PROSPERO. A systematic search of MEDLINE, EMBASE, CINAHL, AHMED, PsycINFO, Cochrane Library and references of retrieved publications, identified empirical research in English language and date range January 2000 to February 2019. Two researchers independently screened abstracts, selected publications and extracted data using a framework based on published guidelines. This is a report of the analysis and narrative synthesis. Results The search identified 2755 titles and abstracts, 76 were selected for full-text examination and 13 agreed for inclusion. The included studies evidence that: for a person with dementia, crisis is a process that begins with a problem judged to put them or others at risk of harm. It leads to decision and action to treat this risk, thus resolve the crisis. Such crisis can be predicted or unpredicted and progress quickly or slowly. Medical treatment, community resources and psychosocial support of personal resources, decision making, relationships and social networks, are all modifiable factors that can treat the risk of harm during crisis. Carers’ and professionals’ knowledge and skills in dementia care are likely to play a key role in crisis resolution in the home. Conclusion There has been limited investigation of the process and management of crisis at home for people living with dementia. The results of this review provide a foundation for future research. There is no consensus on critical components of home treatment to facilitate crisis resolution. However, education in dementia care for carers and professionals is likely to prove essential to successful home treatment
Resonant two-magnon Raman scattering in parent compounds of high-T superconductors.
We propose a theory of two-magnon Raman scattering from the insulating parent
compounds of high-T superconductors, which contains information not only on
magnetism, but also on the electronic properties in these materials. We use
spin density wave formalism for the Hubbard model, and study diagrammatically
the profile of the two-magnon scattering and its intensity dependence on the
incoming photon frequency both for and in the
resonant regime, in which the energy of the incident photon is close to the gap
between conduction and valence bands. In the nonresonant case, we identify the
diagrams which contribute to the conventional Loudon-Fleury Hamiltonian. In the
resonant regime, where most of the experiments have been done, we find that the
dominant contribution to Raman intensity comes from a different diagram, one
which allows for a simultaneous vanishing of all three of its denominators
(i.e., a triple resonance). We study this diagram in detail and show that the
triple resonance, combined with the spin-density-wave dispersion relation for
the carriers, explains the unusual features found in the two-magnon profile and
in the two-magnon peak intensity dependence on the incoming photon frequency.
In particular, our theory predicts a maximum of the two-magnon peak intensity
right at the upper edge of the features in the optical data, which has been one
of the key experimental puzzles.Comment: Revtex, 12 postscript figures (uuencoded
Two-Loop Renormalization Group Equations for Soft Supersymmetry-Breaking Couplings
We compute the two-loop renormalization group equations for all soft
supersymmetry-breaking couplings in a general softly broken N=1 supersymmetric
model. We also specialize these results to the Minimal Supersymmetric Standard
Model.Comment: 26 pages. [v4: Signs of equations (4.2) and (4.3) are fixed.
Rotor equivalent wind speed for power curve measurement – comparative exercise for IEA Wind Annex 32
Kepler-20: A Sun-like Star with Three Sub-Neptune Exoplanets and Two Earth-size Candidates
We present the discovery of the Kepler-20 planetary system, which we
initially identified through the detection of five distinct periodic transit
signals in the Kepler light curve of the host star 2MASSJ19104752+4220194. We
find a stellar effective temperature Teff=5455+-100K, a metallicity of
[Fe/H]=0.01+-0.04, and a surface gravity of log(g)=4.4+-0.1. Combined with an
estimate of the stellar density from the transit light curves we deduce a
stellar mass of Mstar=0.912+-0.034 Msun and a stellar radius of
Rstar=0.944^{+0.060}_{-0.095} Rsun. For three of the transit signals, our
results strongly disfavor the possibility that these result from astrophysical
false positives. We conclude that the planetary scenario is more likely than
that of an astrophysical false positive by a factor of 2e5 (Kepler-20b), 1e5
(Kepler-20c), and 1.1e3 (Kepler-20d), sufficient to validate these objects as
planetary companions. For Kepler-20c and Kepler-20d, the blend scenario is
independently disfavored by the achromaticity of the transit: From Spitzer data
gathered at 4.5um, we infer a ratio of the planetary to stellar radii of
0.075+-0.015 (Kepler-20c) and 0.065+-0.011 (Kepler-20d), consistent with each
of the depths measured in the Kepler optical bandpass. We determine the orbital
periods and physical radii of the three confirmed planets to be 3.70d and
1.91^{+0.12}_{-0.21} Rearth for Kepler-20b, 10.85 d and 3.07^{+0.20}_{-0.31}
Rearth for Kepelr-20c, and 77.61 d and 2.75^{+0.17}_{-0.30} Rearth for
Kepler-20d. From multi-epoch radial velocities, we determine the masses of
Kepler-20b and Kepler-20c to be 8.7\+-2.2 Mearth and 16.1+-3.5 Mearth,
respectively, and we place an upper limit on the mass of Kepler-20d of 20.1
Mearth (2 sigma).Comment: accepted by ApJ, 58 pages, 12 figures revised Jan 2012 to correct
table 2 and clarify planet parameter extractio
Crisis care for children and young people with mental health problems: national mapping, models of delivery, sustainability and experience (CAMH-Crisis2). A study protocol
Background
One in six five 16-year-olds have a probable mental health difficulty. Of these, almost half of older teenagers and a quarter of 11–16-year-olds report having self-harmed or attempted suicide. Currently, there is little research into mental health crisis services for young people, with little understanding of what services exist, who uses them, or what works best.
Question
‘How are mental health crisis responses for children and young people up to the age of 25 sustained, experienced and integrated within their local systems of services’?
Objectives
To describe National Health Service (NHS), local authority, education and third sector approaches to the implementation and organisation of crisis care for children and young people across England and Wales.
To identify eight contrasting case studies in which to evaluate how crisis services have developed and are currently organised, sustained, experienced and integrated within the context of their local systems of services.
To compare and contrast these services in the context of the available international evidence, drawing out and disseminating clear implications for the design and delivery of future crisis responses for children and young people and their families.
Methods
A sequential mixed methods approach, underpinned by normalisation process theory will be employed. A survey will create a detailed record of how crisis responses across England and Wales are organised, implemented and used. Subsequently, eight contrasting services in relation to geographic and socioeconomic setting, populations served, and service configuration will be identified as case studies. Interviews will be conducted with children, young people and parents/carers who have used the service, as well as commissioners, managers and practitioners. Operational policies and service usage data will also be examined. Analysis of how each service is provided, experienced, implemented and sustained will be conducted both inductively and deductively, reflecting normalisation process theory construct
A linear RFQ ion trap for the Enriched Xenon Observatory
The design, construction, and performance of a linear radio-frequency ion
trap (RFQ) intended for use in the Enriched Xenon Observatory (EXO) are
described. EXO aims to detect the neutrinoless double-beta decay of Xe
to Ba. To suppress possible backgrounds EXO will complement the
measurement of decay energy and, to some extent, topology of candidate events
in a Xe filled detector with the identification of the daughter nucleus
(Ba). The ion trap described here is capable of accepting, cooling, and
confining individual Ba ions extracted from the site of the candidate
double-beta decay event. A single trapped ion can then be identified, with a
large signal-to-noise ratio, via laser spectroscopy.Comment: 18 pages, pdflatex, submitted to NIM
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