1,526 research outputs found
Infrared divergence in QED at finite temperature
We consider various ways of treating the infrared divergence which appears in
the dynamically generated fermion mass, when the transverse part of the photon
propagator in N flavour at finite temperature is included in the
Matsubara formalism. This divergence is likely to be an artefact of taking into
account only the leading order term in the expansion when we
calculate the photon propagator and is handled here phenomenologically by means
of an infrared cutoff. Inserting both the longitudinal and the transverse part
of the photon propagator in the Schwinger-Dyson equation we find the dependence
of the dynamically generated fermion mass on the temperature and the cutoff
parameters. It turns out that consistency with certain statistical physics
arguments imposes conditions on the cutoff parameters. For parameters in the
allowed range of values we find that the ratio is approximately 6, consistently with previous calculations which
neglected the transverse photon contribution.Comment: 37 pages, 12 figures, typos corrected, references added, Introduction
rewritte
Randomised controlled trial of homoeopathy versus placebo in perennial allergic rhinitis with overview of four trial series
OBJECTIVE: To test the hypothesis that homoeopathy is a placebo by examining its effect in patients with allergic rhinitis and so contest the evidence from three previous trials in this series.
Design: Randomised, double blind, placebo controlled, parallel group, multicentre study.
SETTING: Four general practices and a hospital ear, nose, and throat outpatient department.
PARTICIPANTS: 51 patients with perennial allergic rhinitis. Intervention: Random assignment to an oral 30c homoeopathic preparation of principal inhalant allergen or to placebo.
MAIN OUTCOME MEASURES: Changes from baseline in nasal inspiratory peak flow and symptom visual analogue scale score over third and fourth weeks after randomisation.
RESULTS: Fifty patients completed the study. The homoeopathy group had a significant objective improvement in nasal airflow compared with the placebo group (mean difference 19.8 l/min, 95% confidence interval 10.4 to 29.1, P=0.0001). Both groups reported improvement in symptoms, with patients taking homoeopathy reporting more improvement in all but one of the centres, which had more patients with aggravations. On average no significant difference between the groups was seen on visual analogue scale scores. Initial aggravations of rhinitis symptoms were more common with homoeopathy than placebo (7 (30%) v 2 (7%), P=0.04). Addition of these results to those of three previous trials (n=253) showed a mean symptom reduction on visual analogue scores of 28% (10.9 mm) for homoeopathy compared with 3% (1.1 mm) for placebo (95% confidence interval 4.2 to 15.4, P=0.0007).
CONCLUSION: The objective results reinforce earlier evidence that homoeopathic dilutions differ from placebo
On dynamical mass generation in three dimensional supersymmetric U(1) gauge field theory
We investigate and contrast the non-perturbative infra red structure of N=1
and N=2 supersymmetric non-compact U(1) gauge field theory in three space-time
dimensions with N matter flavours. We study the Dyson-Schwinger equations in a
general gauge using superfield formalism; this ensures that supersymmetry is
kept manifest, though leads to spurious infra red divergences which we have to
avoid carefully. In the N=1 case the superfield formalism allows us to choose a
vertex which satisfies the U(1) Ward identity exactly, and we find the expected
critical behaviour in the wavefunction renormalization and strong evidence for
the existence of a gauge independent dynamically generated mass, but with no
evidence for a critical flavour number. We study the N=2 model by dimensional
reduction from four dimensional N=1 electrodynamics, and we refine the old
gauge dependence argument that there is no dynamical mass generation. We
recognize that the refinement only holds after dimensional reduction.Comment: 32 pages RevTeX; 3 axodraw figures include
Non-trivial Infrared Structure in (2+1)-dimensional Quantum Electrodynamics
We show that the gauge-fermion interaction in multiflavour
-dimensional quantum electrodynamics with a finite infrared cut-off is
responsible for non-fermi liquid behaviour in the infrared, in the sense of
leading to the existence of a non-trivial fixed point at zero momentum, as well
as to a significant slowing down of the running of the coupling at intermediate
scales as compared with previous analyses on the subject. Both these features
constitute deviations from fermi-liquid theory. Our discussion is based on the
leading- resummed solution for the wave-function renormalization of the
Schwinger-Dyson equations . The present work completes and confirms the
expectations of an earlier work by two of the authors (I.J.R.A. and N.E.M.) on
the non-trivial infrared structure of the theory.Comment: 10 pages (LaTex), 5 figures (Postscript
\u3ci\u3e On the flora of the Kuram Valley &c., Afghanistan\u3c/i\u3e
The collection of plants was made during the summer of 1879 in Afghanistan territory, along the left bank of he Kuram river from Thal to Pewar kotal. It consists of 15,000 specimens, belonging to 950 species
Dynamical Mass Generation in a Finite-Temperature Abelian Gauge Theory
We write down the gap equation for the fermion self-energy in a
finite-temperature abelian gauge theory in three dimensions. The instantaneous
approximation is relaxed, momentum-dependent fermion and photon self-energies
are considered, and the corresponding Schwinger-Dyson equation is solved
numerically. The relation between the zero-momentum and zero-temperature
fermion self-energy and the critical temperature T_c, above which there is no
dynamical mass generation, is then studied. We also investigate the effect
which the number of fermion flavours N_f has on the results, and we give the
phase diagram of the theory with respect to T and N_f.Comment: 20 LaTeX pages, 4 postscript figures in a single file, version to
appear in Physical Review
Finiteness properties of cubulated groups
We give a generalized and self-contained account of Haglund-Paulin's
wallspaces and Sageev's construction of the CAT(0) cube complex dual to a
wallspace. We examine criteria on a wallspace leading to finiteness properties
of its dual cube complex. Our discussion is aimed at readers wishing to apply
these methods to produce actions of groups on cube complexes and understand
their nature. We develop the wallspace ideas in a level of generality that
facilitates their application.
Our main result describes the structure of dual cube complexes arising from
relatively hyperbolic groups. Let H_1,...,H_s be relatively quasiconvex
codimension-1 subgroups of a group G that is hyperbolic relative to
P_1,...,P_r. We prove that G acts relatively cocompactly on the associated dual
CAT(0) cube complex C. This generalizes Sageev's result that C is cocompact
when G is hyperbolic. When P_1,...,P_r are abelian, we show that the dual
CAT(0) cube complex C has a G-cocompact CAT(0) truncation.Comment: 58 pages, 12 figures. Version 3: Revisions and slightly improved
results in Sections 7 and 8. Several theorem numbers have changed from the
previous versio
Measuring visual cortical oxygenation in diabetes using functional near-infrared spectroscopy
Aims: Diabetes mellitus affects about 6% of the world’s population, and the chronic complications of the disease may result in macro- and micro-vascular changes. The purpose of the current study was to shed light on visual cortical oxygenation in diabetic individuals. We then aimed to compare the haemodynamic response (HDR) to visual stimulation with glycaemic control, given the likelihood of diabetic individuals suffering from such macro- and micro-vascular insult.
Methodology: Thirty participants took part in this explorative study, fifteen of whom had diabetes and fifteen of whom were non-diabetic controls. The HDR, measured as concentrations of oxyhaemoglobin [HbO] and deoxyhaemoglobin [HbR], to visual stimulation was recorded over the primary visual cortex (V1) using a dual-channel oximeter. The stimulus comprised a pattern-reversal checkerboard presented in a block design. Participants’ mean glycated haemoglobin (HbA1c) level (±SD) was 7.2±0.6% in the diabetic group and 5.5±0.4% in the non-diabetic group. Raw haemodynamic data were normalised to baseline, and the last 15 s of data from each ‘stimulus on’ and ‘stimulus off’ condition were averaged over seven duty cycles for each participant.
Results: There were statistically significant differences in ∆[HbO] and ∆[HbR] to visual stimulation between diabetic and non-diabetic groups (p<0.05). In the diabetic group, individuals with type 1 diabetes displayed an increased [HbO] (p<0.01) and decreased [HbR] (p<0.05) compared to their type 2 counterparts. There was also a linear relationship between both ∆[HbO] and ∆[HbR] as a function of HbA1c level (p<0.0005).
Conclusions: Our findings suggest that fNIRS can be used as a quantitative measure of cortical oxygenation in diabetes. Diabetic individuals have a larger HDR to visual stimulation compared to non-diabetic individuals. This increase in ∆[HbO] and decrease in ∆[HbR] appears to be correlated with HbA1c level
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