Free surface effect on dune morphology and evolution

Our aim in this paper is to illustrate the importance of free water surface effects and sediment transport mode in the morphological evolution of sand dunes to upper stage plane beds. We have analyzed a large number of bed form data, 414 experiments from flumes and field, showing significantly different evolution of dune height and length in shallow (high Froude numbers) and in deep flows (low Froude numbers). In shallow flows, dune heights are observed to grow only in bed load dominant transport regime and start to decay for Suspension numbers greater than 1. Dunes in this case are not observed for Suspension number greater than 2.5. For low Froude numbers, dune heights continue to grow from bed load to suspended load dominant transport regime. Dunes in this case are not observed for Suspension number greater than 5. Furthermore, dunes in shallow flows reach significantly greater heights compared to dune heights in deep flows and dune lengths are generally larger in shallow flows

Probability Distributions of Particle Hop Distance and Travel Time Over Equilibrium Mobile Bedforms

The joint probability distribution of streamwise particle hop distance, lateral particle hop distance, and travel time constrains the relationships between topographic change and sediment transport at the granular scale. Previous studies have investigated the ensemble characteristics of particle motions over plane bed topography; however, it is unclear whether reported distributions remain valid when bedforms are present. Here, we present measurements of particle motion over bedform topography obtained in a laboratory flume and compare these to particle motions over plane bed topography with otherwise similar conditions. We find substantial differences in particle motion in the presence of bedforms that are relevant to macroscopic models of sediment transport. Most notably, bedforms increase the standard deviation of streamwise and lateral hop distances relative to the mean streamwise hop distance. This implies that bedforms increase the streamwise and lateral diffusion lengths and, equivalently, increase diffusive-like fluxes

Wohlfahrtspflegerische Leistungen von säkularen Migrantenorganisationen in Deutschland, unter Berücksichtigung der Leistungen für Geflüchtete

Der institutionalisierte Einbezug der Freien Wohlfahrtspflege in die staatliche Sozialpolitik ist nicht nur eine Besonderheit des politischen Systems in Deutschland, sondern wird auch als Erfolgsmodell begriffen. Die vorliegende Studie untersucht soziale Dienstleistungen, die von Migrantenorganisationen erbracht werden, hinsichtlich ihres Umfangs, ihrer Qualität und der Bedingungen der Angebotserbringung. The institutionalized inclusion of the Freie Wohlfahrtspflege in state social policy is not only a special feature of the political system in Germany, but is also seen as a model of success. This study examines social services provided by migrant organizations in terms of their scope, quality, and the conditions of provision

Sediment transport distribution along equilibrium sand dunes

Abstract The present study focuses on distribution of sediment transport along mobile dunes in equilibrium. To this end, using ACVP (Acoustic Concentration and Velocity Profiler), we have obtained simultaneous, co-located, high temporal-spatial resolution measurements of the multi-component flow velocity and suspended sediment concentration above dunes. In contrast to previous measurements of flow and sediment dynamics above dunes which are mostly carried out with more than one instrument, we are now able to address sediment fluxes directly for flow scales smaller than the separation distance between different instruments. In this paper, preliminary ACVP results are shown in terms of flow velocities, suspended sediment concentrations and suspended sediment fluxes along dune profiles

The impact of non-equilibrium flow on the structure of turbulence over river dunes

This piece of research expands our description of how rivers flow over dunes on a river bed. Most of the scientific communities' research to date has used unnaturally steady conditions to measure how water moves over dunes. Yet these flow conditions are not strictly true to the variety of conditions nature produces, most importantly during floods. This research is the first detailed description of a wide range of flow states over dunes, and changes our present understanding of the structure of flow over dunes in rivers. Consequently, the scientific community will be able to use this new information to better model and simulate how rivers work, how they flood, and how they transport sediment towards the worlds deltas

Criteria for determining the need for surgical treatment of tricuspid regurgitation during mitral valve replacement

<p>Abstract</p> <p>Background</p> <p>Tricuspid regurgitation (TR) is common in patients with mitral valve disease; however, there are no straightforward, rapidly determinably criteria available for deciding whether TR repair should be performed during mitral valve replacement. The aim of our retrospective study was to identify a simple and fast criterion for determining whether TR repair should be performed in patients undergoing mitral valve replacement.</p> <p>Methods</p> <p>We reviewed the records of patients who underwent mitral valve replacement with or without (control) TR repair (DeVega or Kay procedure) from January 2005 to December 2008. Preoperative and 2-year postoperative echocardiographic measurements included right ventricular and atrial diameter, interventricular septum size, TR severity, ejection fraction, and pulmonary artery pressure.</p> <p>Results</p> <p>A total of 89 patients were included (control, n = 50; DeVega, n = 27; Kay, n = 12). Demographic and clinical characteristics were similar between groups. Cardiac variables were similar between the DeVega and Kay groups. Right atrium and ventricular diameter and ejection fraction were significantly decreased postoperatively both in the control and operation (DeVega + Kay) group (<it>P </it>< 0.05). Pulmonary artery pressure was significantly decreased postoperatively in-operation groups (<it>P </it>< 0.05). Our findings indicate that surgical intervention for TR should be considered during mitral valve replacement if any of the following preoperative criteria are met: right atrial transverse diameter > 57 mm; right ventricular end-diastolic diameter > 55 mm; pulmonary artery pressure > 58 mmHg.</p> <p>Conclusions</p> <p>Our findings suggest echocardiography may be used as a rapid and simple means of determining which patients require TR repair during mitral valve replacement.</p

Supporting Information for the publication: The influence of slipface angle on dune growth

Dune characteristics as calculated with the bedform tracking tool. Data contains dune characteristics (dune height, length and slipface angles) during dune growth from an initial flatbed in a laboratory flume. Explanation of variables in columns from left to right: 1: Time relative to dune equilibrium time ((T/Te) in (s/s)) 2: Dune height relative to equilibrium dune heigth ((H/He) in (m/m)) 3: Dune length relative to equilibrium dune length (L/Le in (m/m)) 4: Dune steepness (height over length) ((H/L) in (m/m)). 5: Dune slipface angles (in degrees). Experiments were conducted in a tilting flume with recirculation facilities for both water and sediment in the Kraijenhoff van de Leur laboratory for Water and Sediment dynamics, Wageningen University & Research. The flume measures 1.20 m x 0.50 m x 14.4 m internally (width x height x length). A 15 cm thick layer of uniformly distributed, light-weight polystyrene particles was installed at the flume bed with a density of p_s=1055 kg m^(-3). Dune slipface angles are the steepest part of a dune leeside. Dune slipface angles are calculated with the bedform tracking tool using MATLAB. Methods, materials and software: Experiments were conducted in a tilting flume with recirculation facilities for both water and sediment in the Kraijenhoff van de Leur laboratory for Water and Sediment dynamics, Wageningen University & Research. The flume measures 1.20 m x 0.50 m x 14.4 m internally (width x height x length). A 15 cm thick layer of uniformly distributed, light-weight polystyrene particles was installed at the flume bed with a density of p_s=1055 kg m^(-3). Dune slipface angles are the steepest part of a dune leeside. Dune slipface angles are calculated with the bedform tracking tool using MATLAB

Morphodynamics of river dunes: suspended sediment transport along mobile dunes and dune development towards upper stage plane bed

Dunes are the most common bedforms present in nearly all fluvial channels. Because of their dimensions, dunes are of central importance in predicting flow roughness and water levels. During floods in several rivers, dunes are observed to undergo an unstable transition regime after which they are washed out in what is called the upper stage plane bed. This morphological evolution of dunes to upper stage plane bed is the strongest bedform adjustment during time-varying flows and is associated with a significant change in hydraulic roughness and water levels. This thesis aims to obtain a better understanding and quantitative data of the flow and sediment transport mechanisms controlling the dune morphology and dune transition to upper stage plane beds