312 research outputs found
Vacuum polarization on the spinning circle
Vacuum polarization of a massive scalar field in the background of a
two-dimensional version of a spinning cosmic string is investigated. It is
shown that when the `radius of the universe' is such that spacetime is globally
hyperbolic the vacuum fluctuations are well behaved, diverging though on the
`chronology horizon'. Naive use of the formulae when spacetime is nonglobally
hyperbolic leads to unphysical results. It is also pointed out that the set of
normal modes used previously in the literature to address the problem gives
rise to two-point functions which do not have a Hadamard form, and therefore
are not physically acceptable. Such normal modes correspond to a locally (but
not globally) Minkowski time, which appears to be at first sight a natural
choice of time to implement quantization.Comment: 3 pages, no figures, REVTeX4, published versio
Euclidean thermal spinor Green's function in the spacetime of a straight cosmic string
Within the framework of the quantum field theory at finite temperature on a
conical space, we determine the Euclidean thermal spinor Green's function for a
massless spinor field. We then calculate the thermal average of the
energy-momentum tensor of a thermal bath of massless fermions. In the
high-temperature limit, we find that the straight cosmic string does not
perturb the thermal bathComment: 11 pages, latex, no figure
Non-relativistic quantum systems on topological defects space-times
We study the behavior of non-relativistic quantum particles interacting with
different potentials in the space-times generated by a cosmic string and a
global monopole. We find the energy spectra in the presence of these
topological defects and show how they differ from their free space-time values.Comment: 17 pages, LATEX fil
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Are there valid proxy measures of clinical behaviour?
Background: Accurate measures of health professionals' clinical practice are critically important to guide health policy decisions, as well as for professional self-evaluation and for research-based investigation of clinical practice and process of care. It is often not feasible or ethical to measure behaviour through direct observation, and rigorous behavioural measures are difficult and costly to use. The aim of this review was to identify the current evidence relating to the relationships between proxy measures and direct measures of clinical behaviour. In particular, the accuracy of medical record review, clinician self-reported and patient-reported behaviour was assessed relative to directly observed behaviour.
Methods: We searched: PsycINFO; MEDLINE; EMBASE; CINAHL; Cochrane Central Register of Controlled Trials; science/social science citation index; Current contents (social & behavioural med/clinical med); ISI conference proceedings; and Index to Theses. Inclusion criteria: empirical, quantitative studies; and examining clinical behaviours. An independent, direct measure of behaviour (by standardised patient, other trained observer or by video/audio recording) was considered the 'gold standard' for comparison. Proxy measures of behaviour included: retrospective self-report; patient-report; or chart-review. All titles, abstracts, and full text articles retrieved by electronic searching were screened for inclusion and abstracted independently by two reviewers. Disagreements were resolved by discussion with a third reviewer where necessary.
Results: Fifteen reports originating from 11 studies met the inclusion criteria. The method of direct measurement was by standardised patient in six reports, trained observer in three reports, and audio/video recording in six reports. Multiple proxy measures of behaviour were compared in five of 15 reports. Only four of 15 reports used appropriate statistical methods to compare measures. Some direct measures failed to meet our validity criteria. The accuracy of patient report and chart review as proxy measures varied considerably across a wide range of clinical actions. The evidence for clinician self-report was inconclusive.
Conclusion: Valid measures of clinical behaviour are of fundamental importance to accurately identify gaps in care delivery, improve quality of care, and ultimately to improve patient care. However, the evidence base for three commonly used proxy measures of clinicians' behaviour is very limited. Further research is needed to better establish the methods of development, application, and analysis for a range of both direct and proxy measures of behaviour
SO(10) Cosmic Strings and Baryon Number Violation
SO(10) cosmic strings formed during the phase transition Spin(10)
SU(5) are studied. Two types of strings ---
one effectively Abelian and one non-Abelian --- are constructed and the string
solutions are calculated numerically. The non-Abelian string can catalyze
baryon number violation via the ``twisting'' of the scalar field which causes
mixing of leptons and quarks in the fermion multiplet. The non-Abelian string
is also found to have the lower energy possibly for the entire range of the
parameters in the theory. Scattering of fermions in the fields of the strings
is analyzed, and the baryon number violation cross section is calculated. The
role of the self-adjoint parameters is discussed and the values are computed.Comment: LaTex (RevTex), 36 pages, 6 figures (available upon request),
MIT-CTP#215
Path integrals on a flux cone
This paper considers the Schroedinger propagator on a cone with the conical
singularity carrying magnetic flux (``flux cone''). Starting from the operator
formalism and then combining techniques of path integration in polar
coordinates and in spaces with constraints, the propagator and its path
integral representation are derived. "Quantum correction" in the Lagrangian
appears naturally and no a priori assumption is made about connectivity of the
configuration space.Comment: LaTeX file, 9 page
Aspects of classical and quantum motion on a flux cone
Motion of a non-relativistic particle on a cone with a magnetic flux running
through the cone axis (a ``flux cone'') is studied. It is expressed as the
motion of a particle moving on the Euclidean plane under the action of a
velocity-dependent force. Probability fluid (``quantum flow'') associated with
a particular stationary state is studied close to the singularity,
demonstrating non trivial Aharonov-Bohm effects. For example, it is shown that
near the singularity quantum flow departs from classical flow. In the context
of the hydrodynamical approach to quantum mechanics, quantum potential due to
the conical singularity is determined and the way it affects quantum flow is
analysed. It is shown that the winding number of classical orbits plays a role
in the description of the quantum flow. Connectivity of the configuration space
is also discussed.Comment: LaTeX file, 21 pages, 8 figure
Self-Forces on Electric and Magnetic Linear Sources in the Space-Time of a Cosmic String
In this paper we calculate the magnetic and electric self-forces, induced by
the conical structure of a cosmic string space-time, on a long straight wire
which presents either a constant current or a linear charge density. We also
show how these self-forces are related by a Lorentz tranformation and, in this
way, explain what two different inertial observers detect in their respective
frames.Comment: 10 pages, LaTeX, to be published in Phys. Rev. D
Time-Dependent Open String Solutions in 2+1 Dimensional Gravity
We find general, time-dependent solutions produced by open string sources
carrying no momentum flow in 2+1 dimensional gravity. The local Poincar\'e
group elements associated with these solutions and the coordinate
transformations that transform these solutions into Minkowski metric are
obtained. We also find the relation between these solutions and the planar wall
solutions in 3+1 dimensions.Comment: CU-TP-619, 18 pages. (minor changes
Proper incorporation of self-adjoint extension method to Green's function formalism : one-dimensional -function potential case
One-dimensional -function potential is discussed in the framework
of Green's function formalism without invoking perturbation expansion. It is
shown that the energy-dependent Green's function for this case is crucially
dependent on the boundary conditions which are provided by self-adjoint
extension method. The most general Green's function which contains four real
self-adjoint extension parameters is constructed. Also the relation between the
bare coupling constant and self-adjoint extension parameter is derived.Comment: LATEX, 13 page
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