A generalised equivalent storm model for long-term statistics of ocean waves

This is the final version of the article. Available from Elsevier via the DOI in this record.To calculate the return periods of individual wave or crest heights, the long-term distribution of sea states must be combined with the short-term distribution of individual wave or crest heights conditional on sea state. This is normally achieved using an equivalent storm model to parameterise the distribution of the maximum wave or crest height in a storm. A new equivalent storm model is introduced that generalises the approach of Tromans and Vanderschuren (1995). The generalised equivalent storm (GES) method is significantly simpler than equivalent storm methods that model the temporal evolution of the significant wave height in a storm. The GES method is applied to long time series of wave buoy measurements for deep and shallow water sites and demonstrated to be more accurate than existing methods at representing the statistical characteristics of measured storms. Return periods of crest heights from the GES method are shown to be more robust to uncertainties in the fitted models of the equivalent storm parameters than estimates from temporal evolution methods such as the equivalent triangular storm and equivalent power storm model.This work was partly funded through EPSRC grant EP/R007519/1

Towards gravitationally assisted negative refraction of light by vacuum

Propagation of electromagnetic plane waves in some directions in gravitationally affected vacuum over limited ranges of spacetime can be such that the phase velocity vector casts a negative projection on the time-averaged Poynting vector. This conclusion suggests, inter alia, gravitationally assisted negative refraction by vacuum.Comment: 6 page

The prevalence of femoroacetabular impingement anatomy in Division 1 aquatic athletes who tread water

Abstract Femoroacetabular impingement (FAI) is a disorder that causes hip pain and disability in young patients, particularly athletes. Increased stress on the hip during development has been associated with increased risk of cam morphology. The specific forces involved are unclear, but may be due to continued rotational motion, like the eggbeater kick. The goal of this prospective cohort study was to use magnetic resonance imaging (MRI) to identify the prevalence of FAI anatomy in athletes who tread water and compare it to the literature on other sports. With university IRB approval, 20 Division 1 water polo players and synchronized swimmers (15 female, 5 male), ages 18–23 years (mean age 20.7 ± 1.4), completed the 33-item International Hip Outcome Tool and underwent non-contrast MRI scans of both hips using a 3 Tesla scanner. Recruitment was based on sport, with both symptomatic and asymptomatic individuals included. Cam and pincer morphology were identified. The Wilcoxon Signed-Rank/Rank Sum tests were used to assess outcomes. Seventy per cent (14/20) of subjects reported pain in their hips yet only 15% (3/20) sought clinical evaluation. Cam morphology was present in 67.5% (27/40) of hips, while 22.5% (9/40) demonstrated pincer morphology. The prevalence of cam morphology in water polo players and synchronized swimmers is greater than that reported for the general population and at a similar level as some other sports. From a clinical perspective, acknowledgment of the high prevalence of cam morphology in water polo players and synchronized swimmers should be considered when these athletes present with hip pain

Surface disinfection challenges for Candida auris: an in-vitro study

The emerging pathogenic multidrug-resistant yeast Candida auris is an important source of healthcare-associated infections and of growing global clinical concern. The ability of this organism to survive on surfaces and withstand environmental stressors creates a challenge for eradicating it from hospitals. A panel of C. auris clinical isolates was evaluated on different surface environments against the standard disinfectant sodium hypochlorite and high-level disinfectant peracetic acid. C. auris was shown to selectively tolerate clinically relevant concentrations of sodium hypochlorite and peracetic acid in a surface-dependent manner, which may explain its ability to successfully persist within the hospital environment

Breathers in the weakly coupled topological discrete sine-Gordon system

Existence of breather (spatially localized, time periodic, oscillatory) solutions of the topological discrete sine-Gordon (TDSG) system, in the regime of weak coupling, is proved. The novelty of this result is that, unlike the systems previously considered in studies of discrete breathers, the TDSG system does not decouple into independent oscillator units in the weak coupling limit. The results of a systematic numerical study of these breathers are presented, including breather initial profiles and a portrait of their domain of existence in the frequency-coupling parameter space. It is found that the breathers are uniformly qualitatively different from those found in conventional spatially discrete systems.Comment: 19 pages, 4 figures. Section 4 (numerical analysis) completely rewritte

Comparison of analytical and numerical solutions for wave interaction with a vertical porous barrier

This is the final version. Available on open access from Elsevier via the DOI in this record.Analytical solutions for wave interaction with a vertical porous barrier are presented. The analytical solutions are derived using two different methods for taking the depth-average of the pressure drop across the porous barrier. Both solutions assume that the evanescent modes in the wave field can be neglected. The results from the analytical models are compared to results from an iterative boundary element method (BEM) model. The BEM model shows that neglecting evanescent modes is a reasonable assumption for long waves, but that for short waves the velocity through the porous wall from the evanescent modes can be up to 25% of the velocity from the progressive modes at the free surface. However, the effect of neglecting the evanescent modes has only a small effect on the depth-averaged velocity through porous wall and the analytical models derived using depth-averaged assumptions are shown to give good agreement with the BEM model for the reflection coefficient, horizontal force and overturning moment on the porous barrier. The analytical models are used to investigate the effects of the drag and inertia coefficients of the porous barrier on the behaviour of the solution. It is shown that for fixed values of the drag coefficient, wave frequency and amplitude, the solutions for the reflection coefficient lie on approximately semicircular arcs on the complex plane, with the position on the arc determined by the inertial coefficient. This places bounds on the size of the phase change in the reflected and transmitted wave which are possible. The analytical models are also used to derive the asymptotic behaviour of the solution in long and short waves. The implications of the results for more general cases of wave interaction with porous structures are discussed.Engineering and Physical Sciences Research Council (EPSRC