20,322 research outputs found
Extremal maps of the universal hyperbolic solenoid
We show that the set of points in the Teichmuller space of the universal
hyperbolic solenoid which do not have a Teichmuller extremal representative is
generic (that is, its complement is the set of the first kind in the sense of
Baire). This is in sharp contrast with the Teichmuller space of a Riemann
surface where at least an open, dense subset has Teichmuller extremal
representatives. In addition, we provide a sufficient criteria for the
existence of Teichmuller extremal representatives in the given homotopy class.
These results indicate that there is an interesting theory of extremal (and
uniquely extremal) quasiconformal mappings on hyperbolic solenoids.Comment: LaTeX, 15 page
Convex regions in the plane and their domes
We make a detailed study of the relation of a euclidean convex region to . The dome is the relative boundary, in the upper halfspace model of hyperbolic space, of the hyperbolic convex hull of the complement of . The first result is to prove that the nearest point retraction is 2-quasiconformal. The second is to establish precise estimates of the distortion of near
Cost-effectiveness of treatments for superficial venous refluxin patients with chronic venous ulceration.
Background Venous leg ulcers impair quality of life significantly, with substantial costs to health services. The aim of this study was to estimate the cost‐effectiveness of interventional procedures alongside compression therapy versus compression therapy alone for the treatment of chronic venous leg ulceration. Methods A Markov decision analytical model was developed. The main outcome measures were quality‐adjusted life‐years (QALYs) and lifetime costs per patient, from the perspective of the UK National Health Service at 2015 prices. Resource use included the initial procedures, compression therapy, primary care and outpatient consultations. The interventional procedures included superficial venous surgery, endothermal ablation and ultrasound‐guided foam sclerotherapy (UGFS). The study population was patients with a chronic venous ulcer who were eligible for either compression therapy or an interventional procedure. Data were obtained from systematic review and meta‐analysis of RCTs. Results Surgery gained 0·112 (95 per cent c.i. −0·011 to 0·213) QALYs compared with compression therapy alone, with a difference in lifetime costs of €−1330 (−3570 to 1262). Given the expected savings in community care, the procedure would pay for itself within 4 years. There was insufficient evidence regarding endothermal ablation and UGFS to draw conclusions. Discussion This modelling study found surgery to be more effective and less costly than compression therapy alone. Further RCT evidence is required for both endothermal ablation and UGFS
Pseudo-Riemannian geodesic foliations by circles
We investigate under which assumptions an orientable pseudo-Riemannian
geodesic foliations by circles is generated by an -action. We construct
examples showing that, contrary to the Riemannian case, it is not always true.
However, we prove that such an action always exists when the foliation does not
contain lightlike leaves, i.e. a pseudo-Riemannian Wadsley's Theorem. As an
application, we show that every Lorentzian surface all of whose
spacelike/timelike geodesics are closed, is finitely covered by .
It follows that every Lorentzian surface contains a non-closed geodesic.Comment: 14 page
Photovoltaic effect in ferroelectric ceramics
The ceramic structure was simulated in a form that is more tractable to correlation between experiment and theory. Single crystals (of barium titanate) were fabricated in a simple corrugated structure in which the pedestals of the corrugation simulated the grain while the intervening cuts could be filled with materials simulating the grain boundaries. The observed photovoltages were extremely small (100 mv)
Ferrite post in a rectangular wave guide
A thin circular ferrite post magnetized lengthwise is placed in a rectangular wave guide with its axis normal to the direction of propagation of the incident waves. The polarization is such that the electric vector is parallel to the post. The reflected and transmitted waves are calculated both with respect to their intensities and phases. The results are also applied to find the influence of a thin ferrite post upon the resonant frequency of a rectangular cavity
On Epstein's trajectory model of non-relativistic quantum mechanics
In 1952 Bohm presented a theory about non-relativistic point-particles moving
along deterministic trajectories and showed how it reproduces the predictions
of standard quantum theory. This theory was actually presented before by de
Broglie in 1926, but Bohm's particular formulation of the theory inspired
Epstein to come up with a different trajectory model. The aim of this paper is
to examine the empirical predictions of this model. It is found that the
trajectories in this model are in general very different from those in the de
Broglie-Bohm theory. In certain cases they even seem bizarre and rather
unphysical. Nevertheless, it is argued that the model seems to reproduce the
predictions of standard quantum theory (just as the de Broglie-Bohm theory).Comment: 12 pages, no figures, LaTex; v2 minor improvement
- …