Modulational instability and wave amplification in finite water depth

The modulational instability of a uniform wave train to side band perturbations is one of the most plausible mechanisms for the generation of rogue waves in deep water. In a condition of finite water depth, however, the interaction with the sea floor generates a wave-induced current that subtracts energy from the wave field and consequently attenuates the instability mechanism. As a result, a plane wave remains stable under the influence of collinear side bands for relative depths <i>kh</i> &leq; 1.36 (where <i>k</i> is the wavenumber of the plane wave and <i>h</i> is the water depth), but it can still destabilise due to oblique perturbations. Using direct numerical simulations of the Euler equations, it is here demonstrated that oblique side bands are capable of triggering modulational instability and eventually leading to the formation of rogue waves also for <i>kh</i> &leq; 1.36. Results, nonetheless, indicate that modulational instability cannot sustain a substantial wave growth for <i>kh</i> < 0.8

Wave modelling - the state of the art

This paper is the product of the wave modelling community and it tries to make a picture of the present situation in this branch of science, exploring the previous and the most recent results and looking ahead towards the solution of the problems we presently face. Both theory and applications are considered. The many faces of the subject imply separate discussions. This is reflected into the single sections, seven of them, each dealing with a specific topic, the whole providing a broad and solid overview of the present state of the art. After an introduction framing the problem and the approach we followed, we deal in sequence with the following subjects: (Section) 2, generation by wind; 3, nonlinear interactions in deep water; 4, white-capping dissipation; 5, nonlinear interactions in shallow water; 6, dissipation at the sea bottom; 7, wave propagation; 8, numerics. The two final sections, 9 and 10, summarize the present situation from a general point of view and try to look at the future developments

Statistical Properties of mechanically generated surface gravity waves: a laboratory experiment in a three-dimensional wave basin

A wave basin experiment has been performed in the MARINTEK laboratories, in one of the largest existing three-dimensional wave tanks in the world. The aim of the experiment is to investigate the effects of directional energy distribution on the statistical properties of surface gravity waves. Different degrees of directionality have been considered, starting from long-crested waves up to directional distributions with a spread of ±30° at the spectral peak. Particular attention is given to the tails of the distribution function of the surface elevation, wave heights and wave crests. Comparison with a simplified model based on second-order theory is reported. The results show that for long-crested, steep and narrow-banded waves, the second-order theory underestimates the probability of occurrence of large waves. As directional effects are included, the departure from second-order theory becomes less accentuated and the surface elevation is characterized by weak deviations from Gaussian statistics

Impact assessment for the improved four boundary conditions (at bed, free-surface, land-boundary and offshore-boundary) on coastal hydrodynamics and particulate transport

The FIELD_AC project aims at providing an improved operational service for coastal areas and at generating added value for shelf and regional scale predictions. Coastal-zone oceanographic predictions seldom appraise the land discharge as a boundary condition. River fluxes are sometimes considered, but neglecting their 3D character, while the "distributed" continental run-off is not taken into consideration. Moreover, many coastal scale processes, particularly those relevant in geographically restricted domains (coast with harbors or river mouth areas), are not well parametrized in present simulations.Work package 3 dedicated to Boundary Fluxes aims to establish and use the best possible boundary conditions for coastal water quality modelling. On this scale, all boundaries become important. For the land boundary side the needed products are distributed and point wise run-off both quantitatively and qualitatively. For the offshore boundary condition, 3D current, water quality field, and wave spectra will be used. For the atmospheric boundary, products from local scale meteorological models (wind, atmospheric pressure and rainfall) are needed. For the seabed, boundary information on sediment composition, bedforms and bathymetry and bio-geo-chemical parameters is essential.This report addresses the impact assessment for improvements in the four boundary conditions (boundary fluxes from land, free-surface boundary condition, seabed boundary condition and open boundary fluxes) on coastal hydrodynamics and particulate transport. The description of the improved four boundary conditions is followed by examples of concrete impact assessment of the theory into the Catalan coast, Liverpool Bay, German Bight and Gulf of Venice

The impact of COVID-19 lockdown on the health and care of children and adolescents with a childhood-onset disability

[Resumen] Introducción. Durante el periodo inicial del confinamiento por la COVID-19 se tomaron una serie de medidas de restricción que modificaron el día a día de la población. En este estudio se buscó conocer el impacto de este periodo en la salud física y mental de niños y jóvenes con discapacidad originada en la infancia, y de sus familias, y describir los cambios que se produjeron en el acceso a la educación y a los servicios de salud. Material y métodos. Se realizó un estudio analítico observacional y transversal. Los datos se obtuvieron mediante una encuesta electrónica a través de una plataforma online realizada por la Academia Europea de Discapacidad Infantil. La encuesta incluyó preguntas sobre cuatro bloques temáticos: características sociodemográficas y de salud, impacto del confinamiento en la salud y bienestar, acceso a la educación y a los servicios de salud. Resultados. Se obtuvieron 145 respuestas. El 45,5% de los niños y jóvenes eran totalmente dependientes. Se percibió un impacto sobre su salud física (54,5%), mental (47,6%) y sobre ambas (32%), mayores niveles de estrés (68,3%) y problemas de sueño (41,4%), así como una sobrecarga muy elevada en el 84,8% de los progenitores, sobre todo en familias de niños con mayor nivel de dependencia (p < 0,001). El 55% de los niños y jóvenes no recibieron ningún tratamiento durante este periodo, ni siquiera remoto. Conclusiones. El confinamiento afectó en gran medida la salud física y mental, así como a los servicios recibidos por los niños y jóvenes con discapacidad y sus familias.[Abstract] Introduction. During the initial period of COVID-19 lockdown, restriction measures modified the day-to-day life of the population. This study sought to know the impact of this period on the physical and mental health of children and young people with disabilities originating in childhood, and their families, and to describe the changes that occurred in access to education and health services. Material and methods. An observational and cross-sectional analytical study was carried out. The data were obtained by means of an electronic survey through an online platform carried out by the European Academy of Childhood Disability. The survey included questions on four thematic blocks: sociodemographic and health characteristics, impact of lock down on health and well-being, and access to education and health services. Results. One hundred and forty-five responses were obtained. 45.5% of the children and young people were totally dependent. There was an impact on their physical (54.5%), mental health (47.6%) and both (32%), higher levels of stress (68.3%), and sleep problems (41.4%), as well as a high burden in 84.8% of parents, especially in families of children with a higher level of dependency (P = .00). 55% of children and young people did not receive any treatment during this period, not even remotely. Conclusions. COVID lock down period greatly affected physical and mental health, as well as the services for children and young people with disabilities and their families

Integrated monitoring of nature restoration along ecotones, the example of the Yser Estuary

Within the framework of LIFE, one of the larger nature restoration projects in Flanders was realized on the right bank of the estuarine part of the Yser. General aim of the initiative was to restore or create beach-dune-salt marsh ecotones with salt-fresh, dynamic-stable, wet-dry and mud-sand ecotones. In order to reach this goal, several large buildings and roads were broken down, an entire tidal dock was restructured and some 500,000m³ of dredging material was removed to restore or create intertidal and coastal dune habitats and their connecting ecotones. Measures were taken to avoid abrupt topographical transitions along potential ecological gradients. It was decided to begin monitoring (2001-2004) from the very start of the restoration process (1999-2003). Monitoring was multidisciplinary and realized in a partnership between several scientific institutes (Ghent University, Catholic University of Louvain, Royal Belgian Institute of Natural Sciences and Institute of Nature Conservation with facility support of VLIZ). Monitoring included the most relevant abiotic conditions such as sedimentation and erosion, topography and ground water fluctuations, and biological response variables, i.e. flora and vegetation, terrestrial arthropods, benthic macrofauna and birds. It was decided to include two monitoring levels, an area-covering monitoring of the entire nature reserve (ca. 128ha) and a detailed monitoring of changes along transects perpendicular to the main ecological gradients. In this paper we present some results of the first three years of monitoring

Hypothermic Machine Perfusion in Liver Transplantation - A Randomized Trial

BACKGROUND Transplantation of livers obtained from donors after circulatory death is associated with an increased risk of nonanastomotic biliary strictures. Hypothermic oxygenated machine perfusion of livers may reduce the incidence of biliary complications, but data from prospective, controlled studies are limited. METHODS In this multicenter, controlled trial, we randomly assigned patients who were undergoing transplantation of a liver obtained from a donor after circulatory death to receive that liver either after hypothermic oxygenated machine perfusion (machine-perfusion group) or after conventional static cold storage alone (control group). The primary end point was the incidence of nonanastomotic biliary strictures within 6 months after transplantation. Secondary end points included other graft-related and general complications. RESULTS A total of 160 patients were enrolled, of whom 78 received a machine-perfused liver and 78 received a liver after static cold storage only (4 patients did not receive a liver in this trial). Nonanastomotic biliary strictures occurred in 6% of the patients in the machine-perfusion group and in 18% of those in the control group (risk ratio, 0.36; 95% confidence interval [CI], 0.14 to 0.94; P=0.03). Postreperfusion syndrome occurred in 12% of the recipients of a machine-perfused liver and in 27% of those in the control group (risk ratio, 0.43; 95% CI, 0.20 to 0.91). Early allograft dysfunction occurred in 26% of the machine-perfused livers, as compared with 40% of control livers (risk ratio, 0.61; 95% CI, 0.39 to 0.96). The cumulative number of treatments for nonanastomotic biliary strictures was lower by a factor of almost 4 after machine perfusion, as compared with control. The incidence of adverse events was similar in the two groups. CONCLUSIONS Hypothermic oxygenated machine perfusion led to a lower risk of nonanastomotic biliary strictures following the transplantation of livers obtained from donors after circulatory death than conventional static cold storage

Ecophysiology of Aspergillus Section Nigri Species Potential Ochratoxin A Producers

After aflatoxins, ochratoxin A (OTA) is the most studied mycotoxin due to the toxicological significance in human and animal diets. OTA presence has been extensively reported worldwide in the last decade in several agricultural products. The main OTA producer in tropical and temperate climates is Aspergillus carbonarius followed by species belonging to A. niger aggregate. Currently, many scientists worldwide have studied the influence of water activity and temperature for growth and biosynthesis of OTA by these species on synthetic media. This article reviews ecophysiological studies of Aspergillus section Nigri strains on synthetic media and natural substrates. The results of these investigations suggest that significant amounts of OTA can be produced in only five days and that the use of different storage practices, such as aW and temperature levels below 0.930 and 15 °C, respectively, allow controlling fungal contamination and minimizing the OTA production in several products as peanuts, corn, dried grapes and derived products for human consumption