Soliton formation from a pulse passing the zero-dispersion point in a nonlinear Schr\"odinger equation

We consider in detail the self-trapping of a soliton from a wave pulse that passes from a defocussing region into a focussing one in a spatially inhomogeneous nonlinear waveguide, described by a nonlinear Schrodinger equation in which the dispersion coefficient changes its sign from normal to anomalous. The model has direct applications to dispersion-decreasing nonlinear optical fibers, and to natural waveguides for internal waves in the ocean. It is found that, depending on the (conserved) energy and (nonconserved) mass of the initial pulse, four qualitatively different outcomes of the pulse transformation are possible: decay into radiation; self-trapping into a single soliton; formation of a breather; and formation of a pair of counterpropagating solitons. A corresponding chart is drawn on a parametric plane, which demonstrates some unexpected features. In particular, it is found that any kind of soliton(s) (including the breather and counterpropagating pair) eventually decays into pure radiation with the increase of the energy, the initial mass being kept constant. It is also noteworthy that a virtually direct transition from a single soliton into a pair of symmetric counterpropagating ones seems possible. An explanation for these features is proposed. In two cases when analytical approximations apply, viz., a simple perturbation theory for broad initial pulses, or the variational approximation for narrow ones, comparison with the direct simulations shows reasonable agreement.Comment: 18 pages, 10 figures, 1 table. Phys. Rev. E, in pres

THE USE OF MOTION ANALYSIS AS A COACHING AID TO IMPROVE THE INDIVIDUAL TECHNIQUE IN SPRINT HURDLES

Biomechanical data are oflen presented as a group average, which may not always help individual athletes to improve their own performance. The purpose of this study was to analyse techniques in sprint hurdles within the athlete and find critical individual aspects, which influence performance. The hurdle clearance of three athletes (eight trials each) were videotaped with four video camera recorders and analysed three-dimensionally. There were several statistically significant correlations between the critical overall horizontal velocity and other variables, especially for one athlete. Such trends in individual performance presented ideas to coaches, athletes and also to researchers, regarding what happened in less successful runs and which technical points were worth individual attention in training

VARIATION IN MOTION ANALYSIS OF SPRINT HURDLES: PART 1CO-ORDINATE DEVIATION IN 3-DIMENSIONAL RECONSTRUCTION

INTRODUCTION. An understanding of the different variation sources in experimental sport research is fundamental to technical analysis (Yeadon, 1994). Individual variable level variation in the event of sprint hurdles was presented by Salo el al. (1995). The aim of this study was to investigate the variation al the digitised co-ordinate level. METHODS Hurdle c1earances were videotaped with two genlocked cameras (50 Hz, at a 90 degree angle from the hurdle symmetrically on both sides of the lane). Two randomly selected trials (female and male) were digitised eight times by the same operator using APAS. The separate raw co-ordinates (u, v) of both camera views and the raw 30 co-ordinates (after OLT) 01 all digitised trials were transformed to Excel software. Standard deviation (SO) for the all 18 body landmarks were calculated separately for every single analysed field. The lowest SO of each condition and each co-ordinate direction (including diagonal combination) was selected as a base unit. All other SOs were standardised to these base units. RESULTS The mean SO of each landmark over all digitised fjelds in u-and v-directions ranged fram 2.3 to 8.7 (female) and from 2.6 to 7.1 (male) relative SO units. This variation resulted in SO of 0.017, 0.009, 0.016 and 0.025 m in X-, y-, z-and diagonal directions, respectively, for the female athlete as a maxirna mean of an individual landmark in the 30 re-construction. The respective SO values for the male trial were 0.017, 0.012, 0.018 and 0.027m. The maximum variation of an individual landmark in a single field of one view was 22.5 SO-units (female) and 30.0 SO-units (male). However, most of the landmarks had less than 4 SO-units variation in most of the analysed fields. DISCUSSION The lowest SO was selected for the base unit, as this presented the most accurate situation which an operator was able to reach in repeated digitising. Generally at an average level, the variation of raw 3D coordinates can be considered acceptable. However, there were c1early problematic situations, when landmarks gained up to 30 times more variation in a single field than the best situation. The influence of this huge variation on variables depends upon whether it appears at a critical moment. In this study, the largest variation occurred in an air phase around the highest point of the flight path. For the male athlete, the trailleg and the ipsilateral arm were obstructed by the trunk for the other camera view. This had only a slight eHect on the maximum height of the centre of mass (GM) (SO= 0.01 m). However, the distance of the GM peak to the hurdle varied significantly (SO= 0.11 m). Oue to lower trail leg path Ihe same problem did not occur for the female athlete (SO= 0.00 and 0.01 m, respectively). Based on this study, it is elear that large variation occurs in manual digitising at the co-ordinate level and this variation can have critica! and important effects for variable values. REFERENCES Salo, A., Grimshaw, P.N. & Viitasalo, J.T. (1995). The repeatabIlity of motion analysis and the reproducibility of athletes in sprint hurdles. In: XlIIISBS Symposium. Abstracts. Thunder Bay, Ontario, Canada. Yeadon, M.A., & Ghallis, J.H. (1994). The future of pertormance-related sports biomechanics research. Journal 01 Sports Sciences, 12, 3-32

Stable embedded solitons

Stable embedded solitons are discovered in the generalized third-order nonlinear Schroedinger equation. When this equation can be reduced to a perturbed complex modified KdV equation, we developed a soliton perturbation theory which shows that a continuous family of sech-shaped embedded solitons exist and are nonlinearly stable. These analytical results are confirmed by our numerical simulations. These results establish that, contrary to previous beliefs, embedded solitons can be robust despite being in resonance with the linear spectrum.Comment: 2 figures. To appear in Phys. Rev. Let

Using the theory of planned behaviour as a process evaluation tool in randomised trials of knowledge translation strategies : A case study from UK primary care

Peer reviewedPublisher PD

Impact of CONSORT extension for cluster randomised trials on quality of reporting and study methodology : review of random sample of 300 trials, 2000-8

Peer reviewedPublisher PD

The impact of Cochrane Systematic Reviews : a mixed method evaluation of outputs from Cochrane Review Groups supported by the UK National Institute for Health Research

© 2014 Bunn et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.Background: There has been a growing emphasis on evidence-informed decision making in health care. Systematic reviews, such as those produced by the Cochrane Collaboration, have been a key component of this movement. The UK National Institute for Health Research (NIHR) Systematic Review Programme currently supports 20 Cochrane Review Groups (CRGs). The aim of this study was to identify the impacts of Cochrane reviews published by NIHR funded CRGs during the years 2007-11. Methods: We sent questionnaires to CRGs and review authors, interviewed guideline developers and used bibliometrics and documentary review to get an overview of CRG impact and to evaluate the impact of a sample of 60 Cochrane reviews. We used a framework with four categories (knowledge production, research targeting, informing policy development, and impact on practice/services). Results: A total of 1502 new and updated reviews were produced by the 20 NIHR funded CRGs between 2007-11. The clearest impacts were on policy with a total of 483 systematic reviews cited in 247 sets of guidance; 62 were international, 175 national (87 from the UK) and 10 local. Review authors and CRGs provided some examples of impact on practice or services, for example safer use of medication, the identification of new effective drugs or treatments and potential economic benefits through the reduction in the use of unproven or unnecessary procedures. However, such impacts are difficult to objectively document and the majority of reviewers were unsure if their review had produced specific impacts. Qualitative data suggested that Cochrane reviews often play an instrumental role in informing guidance although a poor fit with guideline scope or methods, reviews being out of date and a lack of communication between CRGs and guideline developers were barriers to their use. Conclusions: Health and economic impacts of research are generally difficult to measure. We found that to be the case with this evaluation. Impacts on knowledge production and clinical guidance were easier to identify and substantiate than those on clinical practice. Questions remain about how we define and measure impact and more work is needed to develop suitable methods for impact analysis.Peer reviewe

Noise induced oscillations in non-equilibrium steady state systems

We consider effect of stochastic sources upon self-organization process being initiated with creation of the limit cycle. General expressions obtained are applied to the stochastic Lorenz system to show that departure from equilibrium steady state can destroy the limit cycle at certain relation between characteristic scales of temporal variation of principle variables. Noise induced resonance related to the limit cycle is found to appear if the fastest variations displays a principle variable, which is coupled with two different degrees of freedom or more.Comment: 11 pages, 4 figures. Submitted to Physica Script

Nonlinear interfacial waves in a constant-vorticity planar flow over variable depth

Exact Lagrangian in compact form is derived for planar internal waves in a two-fluid system with a relatively small density jump (the Boussinesq limit taking place in real oceanic conditions), in the presence of a background shear current of constant vorticity, and over arbitrary bottom profile. Long-wave asymptotic approximations of higher orders are derived from the exact Hamiltonian functional in a remarkably simple way, for two different parametrizations of the interface shape.Comment: revtex, 4.5 pages, minor corrections, summary added, accepted to JETP Letter