555 research outputs found
Barriers to prosthetic devices at a Tanzanian hospital
Background: Limb amputation, often from road trauma, is common in low-income countries. Providing prosthetic devices for amputees is challenging and limited research exists regarding barriers to prosthesis provision. This study aims to elucidate the Prosthesis Provision Pathway (PPP) and identify barriers of prosthesis accessibility at the Muhimbili Orthopaedic Institute (MOI) in Dar es Salaam, Tanzania.Patients and Methods: At MOI, 18 healthcare providers, who included 4 orthopaedic technicians, 4 physical therapists, 4 orthopaedic surgeons, 4 junior doctors, and 2 hospital administrators were interviewed and blinded. Responses from semi-structured interviews were transcribed and common themes were identified. A process map diagramming the prosthesis provision pathway was created to highlight barriers and potential areas of improvement.Results: Six main themes emerged from the interviews: the first is that the prosthetics are expensive both for patients and MOI. Second, there are misperceptions of how prosthesis cost will be distributed. Third, there is inefficient communication between providers. Fourth, improved surgical education is needed to improve amputation outcomes. Fifth, amputees face psychosocial stigma, but prosthetics are becoming more accepted. Lastly, healthcare providers understand that trauma is the most common aetiology for amputation.Conclusions: Potential solutions to solving the prosthetic shortage will involve making prostheses more affordable, integrating the orthopaedic prosthesis workshop earlier in the provision process, improving surgical education and communication between providers, and working to prevent road trauma.Keywords: Prosthesis, Amputee, Access, Barrier, Tanzani
Gauge-Invariant Initial Conditions and Early Time Perturbations in Quintessence Universes
We present a systematic treatment of the initial conditions and evolution of
cosmological perturbations in a universe containing photons, baryons,
neutrinos, cold dark matter, and a scalar quintessence field. By formulating
the evolution in terms of a differential equation involving a matrix acting on
a vector comprised of the perturbation variables, we can use the familiar
language of eigenvalues and eigenvectors. As the largest eigenvalue of the
evolution matrix is fourfold degenerate, it follows that there are four
dominant modes with non-diverging gravitational potential at early times,
corresponding to adiabatic, cold dark matter isocurvature, baryon isocurvature
and neutrino isocurvature perturbations. We conclude that quintessence does not
lead to an additional independent mode.Comment: Replaced with published version, 12 pages, 2 figure
Non-Commutative Inflation
We show how a radiation dominated universe subject to space-time quantization
may give rise to inflation as the radiation temperature exceeds the Planck
temperature. We consider dispersion relations with a maximal momentum (i.e. a
mimimum Compton wavelength, or quantum of space), noting that some of these
lead to a trans-Planckian branch where energy increases with decreasing
momenta. This feature translates into negative radiation pressure and, in
well-defined circumstances, into an inflationary equation of state. We thus
realize the inflationary scenario without the aid of an inflaton field. As the
radiation cools down below the Planck temperature, inflation gracefully exits
into a standard Big Bang universe, dispensing with a period of reheating.
Thermal fluctuations in the radiation bath will in this case generate curvature
fluctuations on cosmological scales whose amplitude and spectrum can be tuned
to agree with observations.Comment: 4 pages, 3 figure
Termination of the Phase of Quintessence by Gravitational Back-Reaction
We study the effects of gravitational back-reaction in models of
Quintessence. The effective energy-momentum tensor with which cosmological
fluctuations back-react on the background metric will in some cases lead to a
termination of the phase of acceleration. The fluctuations we make use of are
the perturbations in our present Universe. Their amplitude is normalized by
recent measurements of anisotropies in the cosmic microwave background, their
slope is taken to be either scale-invariant, or characterized by a slightly
blue tilt. In the latter case, we find that the back-reaction effect of
fluctuations whose present wavelength is smaller than the Hubble radius but
which are stretched beyond the Hubble radius by the accelerated expansion
during the era of Quintessence domination can become large. Since the
back-reaction effects of these modes oppose the acceleration, back-reaction
will lead to a truncation of the period of Quintessence domination. This result
impacts on the recent discussions of the potential incompatibility between
string theory and Quintessence.Comment: 7 pages a few clarifying comments adde
The Energy Density of "Wound" Fields in a Toroidal Universe
The observational limits on the present energy density of the Universe allow
for a component that redshifts like and can contribute significantly to
the total. We show that a possible origin for such a contribution is that the
universe has a toroidal topology with "wound" scalar fields around its cycles.Comment: 11 pages, 1figur
The distribution of transit durations for Kepler planet candidates and implications for their orbital eccentricities
‘In these times, during the rise in the popularity of institutional repositories, the Society does not forbid authors from depositing their work in such repositories. However, the AAS regards the deposit of scholarly work in such repositories to be a decision of the individual scholar, as long as the individual's actions respect the diligence of the journals and their reviewers.’ Original article can be found at : http://iopscience.iop.org/ Copyright American Astronomical SocietyDoppler planet searches have discovered that giant planets follow orbits with a wide range of orbital eccentricities, revolutionizing theories of planet formation. The discovery of hundreds of exoplanet candidates by NASA's Kepler mission enables astronomers to characterize the eccentricity distribution of small exoplanets. Measuring the eccentricity of individual planets is only practical in favorable cases that are amenable to complementary techniques (e.g., radial velocities, transit timing variations, occultation photometry). Yet even in the absence of individual eccentricities, it is possible to study the distribution of eccentricities based on the distribution of transit durations (relative to the maximum transit duration for a circular orbit). We analyze the transit duration distribution of Kepler planet candidates. We find that for host stars with T > 5100 K we cannot invert this to infer the eccentricity distribution at this time due to uncertainties and possible systematics in the host star densities. With this limitation in mind, we compare the observed transit duration distribution with models to rule out extreme distributions. If we assume a Rayleigh eccentricity distribution for Kepler planet candidates, then we find best fits with a mean eccentricity of 0.1-0.25 for host stars with T ≤ 5100 K. We compare the transit duration distribution for different subsets of Kepler planet candidates and discuss tentative trends with planetary radius and multiplicity. High-precision spectroscopic follow-up observations for a large sample of host stars will be required to confirm which trends are real and which are the results of systematic errors in stellar radii. Finally, we identify planet candidates that must be eccentric or have a significantly underestimated stellar radius.Peer reviewedFinal Accepted Versio
Asymptotic behavior of w in general quintom model
For the quintom models with arbitrary potential , the
asymptotic value of equation of state parameter w is obtained by a new method.
In this method, w of stable attractors are calculated by using the ratio (d ln
V)/(d ln a) in asymptotic region. All the known results, have been obtained by
other methods, are reproduced by this method as specific examples.Comment: 8 pages, one example is added, accepted for publication in Gen. Rel.
Gra
Inducing the cosmological constant from five-dimensional Weyl space
We investigate the possibility of inducing the cosmological constant from
extra dimensions by embedding our four-dimensional Riemannian space-time into a
five-dimensional Weyl integrable space. Following approach of the induced
matter theory we show that when we go down from five to four dimensions, the
Weyl field may contribute both to the induced energy-tensor as well as to the
cosmological constant, or more generally, it may generate a time-dependent
cosmological parameter. As an application, we construct a simple cosmological
model which has some interesting properties.Comment: 7 page
Constraining the dark energy with galaxy clusters X-ray data
The equation of state characterizing the dark energy component is constrained
by combining Chandra observations of the X-ray luminosity of galaxy clusters
with independent measurements of the baryonic matter density and the latest
measurements of the Hubble parameter as given by the HST key project. By
assuming a spatially flat scenario driven by a "quintessence" component with an
equation of state we place the following limits on the
cosmological parameters and : (i) and (1) if the
equation of state of the dark energy is restricted to the interval (\emph{usual} quintessence) and (ii) and
() if violates the null energy condition and assume values (\emph{extended} quintessence or ``phantom'' energy). These results are in
good agreement with independent studies based on supernovae observations,
large-scale structure and the anisotropies of the cosmic background radiation.Comment: 6 pages, 4 figures, LaTe
Ultracold molecules for quantum simulation: rotational coherence in CaF and RbCs
Polar molecules offer a new platform for quantum simulation of systems with long-range interactions, based on the electrostatic interaction between their electric dipole moments. Here, we report the development of coherent quantum state control using microwave fields in CaF and RbCs molecules, a crucial ingredient for many quantum simulation applications. We perform Ramsey interferometry measurements with fringe spacings of and investigate the dephasing time of a superposition of and rotational states when the molecules are confined. For both molecules, we show that a judicious choice of molecular hyperfine states minimises the impact of spatially varying transition-frequency shifts across the trap. For magnetically trapped CaF we use a magnetically insensitive transition and observe a coherence time of 0.61(3)~ms. For optically trapped RbCs we exploit an avoided crossing in the AC Stark shifts and observe a maximum coherence time of 0.75(6)~ms
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