173 research outputs found
Minimal access surgery compared with medical management for gastro-oesophageal reflux disease : five year follow-up of a randomised controlled trial (REFLUX)
Peer reviewedPublisher PD
Clinical and economic evaluation of laparoscopic surgery compared with medical management for gastro-oesophageal reflux disease : 5-year follow-up of multicentre randomised trial (the REFLUX trial)
Peer reviewedPublisher PD
The Stokes Phenomenon and Schwinger Vacuum Pair Production in Time-Dependent Laser Pulses
Particle production due to external fields (electric, chromo-electric or
gravitational) requires evolving an initial state through an interaction with a
time-dependent background, with the rate being computed from a Bogoliubov
transformation between the in and out vacua. When the background fields have
temporal profiles with sub-structure, a semiclassical analysis of this problem
confronts the full subtlety of the Stokes phenomenon: WKB solutions are only
local, while the production rate requires global information. Incorporating the
Stokes phenomenon, we give a simple quantitative explanation of the recently
computed [Phys. Rev. Lett. 102, 150404 (2009)] oscillatory momentum spectrum of
e+e- pairs produced from vacuum subjected to a time-dependent electric field
with sub-cycle laser pulse structure. This approach also explains naturally why
for spinor and scalar QED these oscillations are out of phase.Comment: 5 pages, 4 figs.; v2 sign typo corrected, version to appear in PR
Complex WKB Analysis of a PT Symmetric Eigenvalue Problem
The spectra of a particular class of PT symmetric eigenvalue problems has
previously been studied, and found to have an extremely rich structure. In this
paper we present an explanation for these spectral properties in terms of
quantisation conditions obtained from the complex WKB method. In particular, we
consider the relation of the quantisation conditions to the reality and
positivity properties of the eigenvalues. The methods are also used to examine
further the pattern of eigenvalue degeneracies observed by Dorey et al. in
[1,2].Comment: 22 pages, 13 figures. Added references, minor revision
Study of a class of non-polynomial oscillator potentials
We develop a variational method to obtain accurate bounds for the
eigenenergies of H = -Delta + V in arbitrary dimensions N>1, where V(r) is the
nonpolynomial oscillator potential V(r) = r^2 + lambda r^2/(1+gr^2), lambda in
(-infinity,\infinity), g>0. The variational bounds are compared with results
previously obtained in the literature. An infinite set of exact solutions is
also obtained and used as a source of comparison eigenvalues.Comment: 16 page
Cosmological particle production and the precision of the WKB approximation
Particle production by slow-changing gravitational fields is usually
described using quantum field theory in curved spacetime. Calculations require
a definition of the vacuum state, which can be given using the adiabatic (WKB)
approximation. I investigate the best attainable precision of the resulting
approximate definition of the particle number. The standard WKB ansatz yields a
divergent asymptotic series in the adiabatic parameter. I derive a novel
formula for the optimal number of terms in that series and demonstrate that the
error of the optimally truncated WKB series is exponentially small. This
precision is still insufficient to describe particle production from vacuum,
which is typically also exponentially small. An adequately precise
approximation can be found by improving the WKB ansatz through perturbation
theory. I show quantitatively that the fundamentally unavoidable imprecision in
the definition of particle number in a time-dependent background is equal to
the particle production expected to occur during that epoch. The results are
illustrated by analytic and numerical examples.Comment: 14 pages, RevTeX, 5 figures; minor changes, a clarification in Sec.
II
Unsupervised Classifiers, Mutual Information and 'Phantom Targets'
We derive criteria for training adaptive classifier networks to perform unsupervised
data analysis. The first criterion turns a simple Gaussian classifier
into a simple Gaussian mixture analyser. The second criterion, which is
much more generally applicable, is based on mutual information. It simplifies
to an intuitively reasonable difference between two entropy functions,
one encouraging 'decisiveness,' the other 'fairness' to the alternative interpretations
of the input. This 'firm but fair' criterion can be applied
to any network that produces probability-type outputs, but it does not
necessarily lead to useful behavior
Kelvin mode of a vortex in a nonuniform Bose-Einstein condensate
In a uniform fluid, a quantized vortex line with circulation h/M can support
long-wavelength helical traveling waves proportional to e^{i(kz-\omega_k t)}
with the well-known Kelvin dispersion relation \omega_k \approx (\hbar k^2/2M)
\ln(1/|k|\xi), where \xi is the vortex-core radius. This result is extended to
include the effect of a nonuniform harmonic trap potential, using a quantum
generalization of the Biot-Savart law that determines the local velocity V of
each element of the vortex line. The normal-mode eigenfunctions form an
orthogonal Sturm-Liouville set. Although the line's curvature dominates the
dynamics, the transverse and axial trapping potential also affect the normal
modes of a straight vortex on the symmetry axis of an axisymmetric Thomas-Fermi
condensate. The leading effect of the nonuniform condensate density is to
increase the amplitude along the axis away from the trap center. Near the ends,
however, a boundary layer forms to satisfy the natural Sturm-Liouville boundary
conditions. For a given applied frequency, the next-order correction
renormalizes the local wavenumber k(z) upward near the trap center, and k(z)
then increases still more toward the ends.Comment: 9 pages, 1 figur
Minimal access surgery compared with medical management for chronic gastro-oesophageal reflux disease : UK collaborative randomised trial
ABSTRACT
Objective To determine the relative benefits and risks of laparoscopic fundoplication surgery as an alternative to long term drug treatment for chronic gastro-oesophageal reflux disease (GORD). Design Multicentre, pragmatic randomised trial (with parallel preference groups). Setting 21 hospitals in the United Kingdom.
Participants 357 randomised participants (178 surgical,179 medical) and 453 preference participants (261, 192); mean age 46; 66% men. All participants had documented evidence of GORD and symptoms for >12 months. Intervention The type of laparoscopic fundoplication used was left to the discretion of the surgeon. Those allocated to medical treatment had their treatment reviewed and adjusted as necessary by a local gastroenterologist, and subsequent clinical management was at the discretion of the clinician responsible for care. Main outcome measures The disease specific REFLUX quality of life score (primary outcome), SF-36, EQ-5D, and medication use, measured at time points equivalent to three and 12 months after surgery, and surgical complications. Main results Randomised participants had received drugs for GORD for median of 32 months before trial entry. Baseline REFLUX scores were 63.6 (SD 24.1) and 66.8 (SD 24.5) in the surgical and medical randomised groups, respectively. Of those randomised to surgery, 111 (62%) actually had total or partial fundoplication. Surgical complications were uncommon with a conversion rate of 0.6% and no mortality. By 12 months, 38% (59/154) randomised to surgery (14% (14/104) among those who had fundoplication) were taking reflux medication versus 90% (147/164) randomised medical management. The REFLUX score favoured the randomised surgical group (14.0, 95% confidence interval 9.6 to 18.4; P<0.001). Differences of a third to half of 1 SD in other health status measures also favoured the randomised surgical group. Baseline scores in the preference for surgery group were the worst; by 12 months these were better than in the preference for medical treatment group. Conclusion At least up to 12 months after surgery, laparoscopic fundoplication significantly increased measures of health status in patients with GORD. Trial registration ISRCTN15517081This study was funded by the NIHR Health Technology Assessment Programme (as part of project no. 97/10/99) and the full
project report is published in Health Technology Assessment 2008;12:1/181. The Health Services Research Unit is funded by the Chief Scientist Office of the Scottish Government Health Directorates.Peer reviewe
Res Medica, Winter 1965-66, Volume V, Number 1
TABLE OF CONTENTSSELF POISONING - A STUDY IN EDINBURGH: Neil KesselON THE MODE IN WHISLT EXTERNAL APPLICATIONS ACT ON INTERNAL PARTS: Joseph Lister WAYSIDE HOUSES OF ILL-REPUTE —DIVERTICULAR DISEASE OF THE COLON: T. W. BalfourANAESTHESIA IN PATIENTS WITH CARDIAC OR RESPIRATORY DISEASE: J. D. Robertson. M.D., F.R.C.P., F.R.C.S.E., F.F.A.R.C.S., D.A.PRE-ECLAMPTIC TOXAEMIA OF PREGNANCY: R. C. Heading, B.Sc.THE SOCIETYRES MEDICABOOK REVIEW
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