Integrated Numerical Modelling System for Extreme Wave Events at the Wave Hub Site

This paper examines an extreme wave event which occurred during a storm at the Wave Hub site in 2012. The extreme wave of 9.57 m height was identified from a time series of the heave data collected by an Oceanor Seawatch Mini II Buoy deployed at the site. An energy density spectrum was derived from this time series and then used to drive a physical model, which represents the extreme wave at 1:20 scale in Plymouth University’s new COAST Lab. The NewWave technique was used to define the input to the physical model. The experiment is reproduced in a numerical wave tank using the fully nonlinear CFD library OpenFOAM® and the wave generation toolbox waves2Foam. Results are evaluated, and issues regarding the predictions of a numerical model that is driven by the NewWave input signal are discussed. This study sets the basis for further research in coupling field data, physical modelling and numerical modelling in a more efficient and balanced way. This will lead to the new approach of composite modelling that will be implemented in future work

The speed of sequential asymptotic learning

In the classical herding literature, agents receive a private signal regarding a binary state of nature, and sequentially choose an action, after observing the actions of their predecessors. When the informativeness of private signals is unbounded, it is known that agents converge to the correct action and correct belief. We study how quickly convergence occurs, and show that it happens more slowly than it does when agents observe signals. However, we also show that the speed of learning from actions can be arbitrarily close to the speed of learning from signals. In particular, the expected time until the agents stop taking the wrong action can be either finite or infinite, depending on the private signal distribution. In the canonical case of Gaussian private signals we calculate the speed of convergence precisely, and show explicitly that, in this case, learning from actions is significantly slower than learning from signals

Evaluation of the infant at risk for neurodevelopmental disability

Background. Infants with neurodevelopmental abnormality need to start therapy early, and because of this they should be detected as soon as possible. Currently, no widely accepted method of early evaluation exists.Objectives_ To assess and compare, in terms of predicting neurodevelopmental outcome at 1 year of age: (i) a perinatal risk rating (PRR); (ii) the DubQwitz Neurological Assessment. (DNA); and (iii) the Infant Neuromotor Assessment (INA). Design and setting. A prospective neurodevelopmental followup study on graduates from the Groote Schuur Hospital (GSH) neonatal intensive care unit (NICU). Subjects. A cohort of 130 consecutive NICD graduates were selected according to high-risk criteria_Outcome measures. Each infant was examined at term gestational age on the DNAbefore discharge, and a PRR was allocated_ Study infants were seen again at 18 weeks of age when an INA was done, and at 1 year of age a Griffiths Developmental Assessment and full neurological examination was carried out.Results. All of the 130 infants assessed at term were seen at 18 weeks. Thereafter 5 were lost to follow-up and 2 died. The outcome for the remaining 123 is known.Conclusions. Prediction of a normal outcome at 1 year of age was 96% on the DNA and 98% for the PRR, but for an abnormal outcome they predicted only 56% and 42%, respectively. The INA done at 18 weeks predicted a normal outcome at 1 year in 99% of cases if 3 or less abnormal signs were present and an abnormal outcome in 82% of cases with 4 or more abnormal signs. Based on these findings a protocol for follow-up of these high-risk infants is suggested

Study of gas-sheared liquid film in horizontal rectangular duct using high-speed LIF technique: Three-dimensional wavy structure and its relation to liquid entrainment

© 2014 The Authors. The flow of a liquid film sheared by high velocity gas stream in a horizontal rectangular duct was investigated using a high-speed laser-induced fluorescence technique. Measurements of local film thickness were resolved in both longitudinal and transverse coordinates with high spatial and temporal resolution. It was found that the generation of fast and slow ripples by the disturbance waves was qualitatively the same as it was observed earlier in completely different conditions. The transverse size and curvature of the disturbance waves and ripples were measured. A relationship between the three-dimensional structure of ripples on top of disturbance waves and the two mechanisms of liquid entrainment, known as 'bag break-up' and 'ligament break-up', is proposed

Mathematically gifted and talented learners: Theory and practice

This is an Author's Accepted Manuscript of an article published in International Journal of Mathematical Education in Science and Technology, 40(2), 213-228, 2009, copyright Taylor & Francis, available online at: http://www.tandfonline.com/10.1080/00207390802566907.There is growing recognition of the special needs of mathematically gifted learners. This article reviews policy developments and current research and theory on giftedness in mathematics. It includes a discussion of the nature of mathematical ability as well as the factors that make up giftedness in mathematics. The article is set in the context of current developments in Mathematics Education and Gifted Education in the UK and their implications for Science and Technology. It argues that early identification and appropriate provision for younger mathematically promising pupils capitalizes on an intellectual resource which could provide future mathematicans as well as specialists in Science or Technology. Drawing on a Vygotskian framework, it is suggested that the mathematically gifted require appropriate cognitive challenges as well as attitudinally and motivationally enhancing experiences. In the second half of this article we report on an initiative in which we worked with teachers to identify mathematically gifted pupils and to provide effective enrichment support for them, in a number of London Local Authorities. A number of significant issues are raised relating to the identification of mathematical talent, enrichment provision for students and teachers’ professional development

Study of bubbles entrapped into a gas-sheared liquid film

The surface of a thick liquid film under strong gas shear is covered by large-scale disturbance waves and small-scale ripples. Disruption of these ripples on top of disturbance waves by the gas stream leads to the creation of droplets that are entrained into the gas core and may deposit back onto the film surface. In addition, gas may be entrapped by the liquid film in the form of bubbles of various sizes. In this work, the study of gas bubble creation was performed in a horizontal rectangular duct using the brightness- based laser-induced fluorescence technique. With this technique, the instantaneous height of the liquid film was measured with a 40 μm spatial resolution over a 51 mm by 20 mm area at speeds of 10 kHz. The entrapped bubbles and entrained/depositing droplets are detectable in the data and can thus be studied simultaneously with the waves on the film surface. Several scenarios of bubble entrapment and collapse were identified and discussed. The dynamics of entrapped bubbles was studied quantitatively using an automatic processing algorithm, confirming and elucidating the results of qualitative observations. The effect of the flow parameters on the bubbles concentration, velocity and size distributions was studied separately for the bubbles inside the disturbance waves and inside the thin base film between the dis- turbance waves. It was shown that the bubbles are mostly created due to oblique impacts of droplets at the base film and are accumulated by the disturbance waves. A small number of bubbles of larger size are created in front of disturbance waves and remain inside the disturbance waves. The velocity of the bubbles is affected by the velocity of the surrounding liquid. Using the bubbles as tracers, a profile of longitudinal liquid velocity was constructed and a noticeable increase of wall shear under the rear slopes of disturbance waves was found

Analysis and comparison of nonlinear tree height prediction strategies for Douglas-fir forests

Using an extensive Douglas-fir data set from southwest Oregon, we examined the (1) performance and suitability of selected prediction strategies, (2) contribution of relative position and stand-density measures in improving tree height (h) prediction values, and (3) effect of different subsampling designs to fill in missing h values in a new stand using a regional nonlinear model. Nonlinear mixed-effects models (NMEM) substantially improved the accuracy and precision of height prediction over the conventional nonlinear fixed-effects model (NFEM) that assumes the observations are independent, particularly when a few trees are subsampled for height. The predictive performance of a correction factor on a NFEM with relative position and stand-density measures was comparable to that of a NMEM when four or more trees were subsampled for height. When two or more heights were randomly subsampled, the NMEM efficiently explained the differences in the height–diameter relationship because of the variations in relative position of trees and stand density without having to incorporate them into the model. When only one height was subsampled, selecting the largest diameter tree in the stand would result in a lower predicted root mean square error (RMSE) than randomly selecting the height, regardless of the model form or fitting strategy used.A` l’aide d’une banque de donne´es exhaustive sur le sapin Douglas du sud-ouest de l’Oregon, nous avons examine ´ (1) la performance et la pertinence des strate´gies de pre´diction se´lectionne´es, (2) la contribution de la position relative de l’arbre et de la densite´ du peuplement pour ame´liorer la pre´diction de la hauteur des arbres et (3) l’effet de diffe´rents dispositifs d’e´chantillonnage pour imputer la hauteur manquante dans un nouveau peuplement a` l’aide d’un mode`le non line´aire re´gional. Les mode`les non line´aires a` effets mixtes (MNLEM) ame´liorent substantiellement l’exactitude et la pre´cision des pre´dictions de la hauteur comparativement au mode`le non line´aire a` effets fixes conventionnel (MNLEF). Ce dernier suppose que les observations sont inde´pendantes, particulie`rement lorsque peu d’arbres sont e´chantillonne´s pour e´valuer la hauteur. La performance pre´dictive d’un facteur de correction pour le MNLEF base´ sur la mesure de la position relative de l’arbre et de la densite´ du peuplement est comparable a` celle du MNLEM lorsque quatre arbres ou plus sont e´chantillonne´s pour e´valuer la hauteur. Lorsque deux hauteurs ou plus sont e´chantillonne´es ale´atoirement, le MNLEM explique efficacement les diffe´rences dans la relation hauteur-diame`tre dues aux variations de la position relative des arbres et de la densite´ sans avoir a` les incorporer formellement dans le mode`le. Lorsqu’une seule hauteur est e´chantillonne´e, le choix du plus gros arbre dans le peuplement pourrait entraıˆner une erreur de pre´diction plus faible que lorsque la hauteur est se´lectionne´e au hasard, peu importe la forme du mode`le ou la strate´gie d’ajustement utilise´e

Comparison of disturbance wave parameters with flow orientation in vertical annular gas-liquid flows in a small pipe

The interfacial wave structure of the liquid film in both upward and downward annular gas-liquid flows in an 11.7 mm pipe were investigated using the Brightness Based Laser Induced Fluorescence technique (BBLIF). Film thickness measurements were carried out with high spatial and temporal resolution between 330 and 430 mm from the inlet, where the properties of disturbance waves are almost stabilised. Using a tracking algorithm to detect disturbance waves, a full characterisation in terms of their velocity, frequency, longitudinal size and spacing was carried out. Direct comparison between both flow orientations while testing the same flow conditions shows that although the flow orientation does not affect the velocity of disturbance waves, the fraction of film surface occupied by the disturbance waves is smaller in upwards flow. Thus, more liquid travels in the base film in upwards flow, which is consistent with the base film thickness measurements. These observations, together with qualitatively different behaviour of ripple wave velocity in upwards and downwards flows, studied using 2D Fourier analysis, indicate that the role of gravity is much more important on the base film than on disturbance waves. This supposedly occurs due to a local decrease in the interfacial shear stress on the base film surface because of the resistance of the disturbance waves to the gas stream in upward flow