4,805 research outputs found
Kinetic energy functional for Fermi vapors in spherical harmonic confinement
Two equations are constructed which reflect, for fermions moving
independently in a spherical harmonic potential, a differential virial theorem
and a relation between the turning points of kinetic energy and particle
densities. These equations are used to derive a differential equation for the
particle density and a non-local kinetic energy functional.Comment: 8 pages, 2 figure
Low energy proton bidirectional anisotropies and their relation to transient interplanetary magnetic structures: ISEE-3 observations
It is known that the interplanetary medium in the period approaching solar maximum is characterized by an enhancement in the occurrence of transient solar wind streams and shocks and that such systems are often associated with looplike magnetic structures or clouds. There is observational evidence that bidirectional, field aligned flows of low energy particles could be a signature of such looplike structures, although detailed models for the magnetic field configuration and injection mechanisms do not exist at the current time. Preliminary results of a survey of low energy proton bidirectional anisotropies measured on ISEE-3 in the interplanetary medium between August 1978 and May 1982, together with magnetic field data from the same spacecraft are presented
Discrete Routh Reduction
This paper develops the theory of abelian Routh reduction for discrete
mechanical systems and applies it to the variational integration of mechanical
systems with abelian symmetry. The reduction of variational Runge-Kutta
discretizations is considered, as well as the extent to which symmetry
reduction and discretization commute. These reduced methods allow the direct
simulation of dynamical features such as relative equilibria and relative
periodic orbits that can be obscured or difficult to identify in the unreduced
dynamics. The methods are demonstrated for the dynamics of an Earth orbiting
satellite with a non-spherical correction, as well as the double
spherical pendulum. The problem is interesting because in the unreduced
picture, geometric phases inherent in the model and those due to numerical
discretization can be hard to distinguish, but this issue does not appear in
the reduced algorithm, where one can directly observe interesting dynamical
structures in the reduced phase space (the cotangent bundle of shape space), in
which the geometric phases have been removed. The main feature of the double
spherical pendulum example is that it has a nontrivial magnetic term in its
reduced symplectic form. Our method is still efficient as it can directly
handle the essential non-canonical nature of the symplectic structure. In
contrast, a traditional symplectic method for canonical systems could require
repeated coordinate changes if one is evoking Darboux' theorem to transform the
symplectic structure into canonical form, thereby incurring additional
computational cost. Our method allows one to design reduced symplectic
integrators in a natural way, despite the noncanonical nature of the symplectic
structure.Comment: 24 pages, 7 figures, numerous minor improvements, references added,
fixed typo
Mapping of serotype-specific, immunodominant epitopes in the NS-4 region of hepatitis C virus (HCV):use of type-specific peptides to serologically differentiate infections with HCV types 1, 2, and 3
The effect of sequence variability between different types of hepatitis C virus (HCV) on the antigenicity of the NS-4 protein was investigated by epitope mapping and by enzyme-linked immunosorbent assay with branched oligopeptides. Epitope mapping of the region between amino acid residues 1679 and 1768 in the HCV polyprotein revealed two major antigenic regions (1961 to 1708 and 1710 to 1728) that were recognized by antibody elicited upon natural infection of HCV. The antigenic regions were highly variable between variants of HCV, with only 50 to 60% amino acid sequence similarity between types 1, 2, and 3. Although limited serological cross-reactivity between HCV types was detected between peptides, particularly in the first antigenic region of NS-4, type-specific reactivity formed the principal component of the natural humoral immune response to NS-4. Type-specific antibody to particular HCV types was detected in 89% of the samples from anti-HCV-positive blood donors and correlated almost exactly with genotypic analysis of HCV sequences amplified from the samples by polymerase chain reaction. Whereas almost all blood donors appeared to be infected with a single virus type (97%), a higher proportion of samples (40%) from hemophiliacs infected from transfusion of non-heat-inactivated clotting factor contained antibody to two or even all three HCV types, providing evidence that long-term exposure may lead to multiple infection with different variants of HCV
Thoracic respiratory motion estimation from MRI using a statistical model and a 2-D image navigator
Sustainability in quality improvement (SusQI): a case-study in undergraduate medical education
Background There is a pressing need for more sustainable healthcare. UK medical graduates are required to apply social, economic, and environmental principles of sustainability to their practice. The Centre for Sustainable Healthcare has developed a sustainability in quality improvement (SusQI) framework and educator’s toolkit to address these challenges. We aimed to develop and evaluate SusQI teaching using this toolkit at Bristol Medical School. Methods We facilitated a SusQI workshop for all third-year Bristol Medical School students. We used mixed methods including questionnaires, exit interviews and follow-up focus groups to evaluate the outcomes and processes of learning. Results Students reported: improvements in knowledge, confidence, and attitudes in both sustainable healthcare and quality improvement; increased self-rated likelihood to engage in SusQI projects; and willingness to change practices to reduce environmental impact in their healthcare roles. Factors for successful teaching included: interactivity; collaboration and participation; and real-life, relevant and tangible examples of projects delivered by credible role models. Conclusions Students reported that SusQI education supported by the toolkit was effective at building knowledge and skills, and reframed their thinking on sustainability in quality improvement. Combining the two topics provided enhanced motivation for and engagement in both. Further research is needed on the clinical impacts of SusQI learning
Sustainability in Quality Improvement (SusQI): challenges and strategies for translating undergraduate learning into clinical practice
Background The healthcare sector is a major contributor to climate change and there are international calls to mitigate environmental degradation through more sustainable forms of clinical care. The UK healthcare sector has committed to net zero carbon by 2040 and sustainable healthcare is a nationally mandated outcome for all UK graduating doctors who must demonstrate their ability to address social, economic and environmental challenges. Bristol Medical School piloted successful Sustainability in Quality Improvement (SusQI) workshop, but identified challenges translating classroom learning into clinical practice. This paper aims to identify and address those challenges. Methods We conducted five focus groups that identified and iteratively explored barriers and facilitators to practice among medical students, comparing a range of experiences to generate a conceptual framework. We then combined our findings with behaviour change theory to generate educational recommendations. Results Students that applied their learning to the clinical workplace were internally motivated and self-determined but needed time and opportunity to complete projects. Other students were cautious of disrupting established hierarchies and practices or frustrated by institutional inertia. These barriers impacted on their confidence in suggesting or achieving change. A minority saw sustainable healthcare as beyond their professional role. Conclusions We present a series of theoretically informed recommendations. These include wider curricular engagement with concepts of sustainable clinical practice; supportive workplace enablement strategies such as workplace champions and co-creation of improvement goals; and time and headspace for students to engage through structured opportunities for credit-bearing project work
Covariant gauge fixing and Kuchar decomposition
The symplectic geometry of a broad class of generally covariant models is
studied. The class is restricted so that the gauge group of the models
coincides with the Bergmann-Komar group and the analysis can focus on the
general covariance. A geometrical definition of gauge fixing at the constraint
manifold is given; it is equivalent to a definition of a background (spacetime)
manifold for each topological sector of a model. Every gauge fixing defines a
decomposition of the constraint manifold into the physical phase space and the
space of embeddings of the Cauchy manifold into the background manifold (Kuchar
decomposition). Extensions of every gauge fixing and the associated Kuchar
decomposition to a neighbourhood of the constraint manifold are shown to exist.Comment: Revtex, 35 pages, no figure
Doppler images and the underlying dynamo. The case of AF Leporis
The (Zeeman-)Doppler imaging studies of solar-type stars very often reveal
large high-latitude spots. This also includes F stars that possess relatively
shallow convection zones, indicating that the dynamo operating in these stars
differs from the solar dynamo. We aim to determine whether mean-field dynamo
models of late-F type dwarf stars can reproduce the surface features recovered
in Doppler maps. In particular, we wish to test whether the models can
reproduce the high-latitude spots observed on some F dwarfs. The photometric
inversions and the surface temperature maps of AF Lep were obtained using the
Occamian-approach inversion technique. Low signal-to-noise spectroscopic data
were improved by applying the least-squares deconvolution method. The locations
of strong magnetic flux in the stellar tachocline as well as the surface fields
obtained from mean-field dynamo solutions were compared with the observed
surface temperature maps. The photometric record of AF Lep reveals both long-
and short-term variability. However, the current data set is too short for
cycle-length estimates. From the photometry, we have determined the rotation
period of the star to be 0.9660+-0.0023 days. The surface temperature maps show
a dominant, but evolving, high-latitude (around +65 degrees) spot. Detailed
study of the photometry reveals that sometimes the spot coverage varies only
marginally over a long time, and at other times it varies rapidly. Of a suite
of dynamo models, the model with a radiative interior rotating as fast as the
convection zone at the equator delivered the highest compatibility with the
obtained Doppler images.Comment: accepted for publication in Astronomy & Astrophysic
On the Nature of Singularities in Plane Symmetric Scalar Field Cosmologies
The nature of the initial singularity in spatially compact plane symmetric
scalar field cosmologies is investigated. It is shown that this singularity is
crushing and velocity dominated and that the Kretschmann scalar diverges
uniformly as it is approached. The last fact means in particular that a maximal
globally hyperbolic spacetime in this class cannot be extended towards the past
through a Cauchy horizon. A subclass of these spacetimes is identified for
which the singularity is isotropic.Comment: 7 pages, MPA-AR-94-
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