Manche (mer) | EPFL Graph Search

vignette|La Manche est classiquement divisée en trois grands secteurs : Manche occidentale, centrale et Manche orientale. La Manche (en anglais English Channel, en breton Mor Breizh, en normand Maunche, en cornique Mor Bretannek, en gallois Môr Udd, en néerlandais Het Kanaal) est une mer épicontinentale de l'océan Atlantique, située dans le nord-ouest de l'Europe et qui s'étend sur une superficie d'environ et sépare la France du Royaume-Uni ; longue d'environ , large de à son extrémité ouest, de à son extrémité est et profonde de en son point le plus profond avec une valeur moyenne de . L'extrémité orientale de la Manche constitue le pas de Calais, l'une des zones maritimes les plus fréquentées du globe. L'eau de cette zone est très turbide, tout en restant oxygénée. Le nom de la Manche Attestations anciennes D'anciennes dénominations sont attestées :

Mare Britannicum à l'époque romaine ;
Mare Gallicum à l'époque romaine ;
« mer du côté de la Gaule » à

New Analytical Methods for Size Fractionated, Quantitative, and Element Specific Analysis of Metallic Engineered Nanoparticles in Aerosols and Dispersions

Harald Hagendorfer

The application of engineered nanoparticles (ENP) increased almost exponentially during the last decade. Next to carbon based ENP, metal based ENP are the next most commonly employed. Utilization of such particles for medical applications, remediation of toxic substances, consumer products, new materials, and numerous other fields has been reported already. Despite their extraordinary success and implementation, concerns have been raised about possible negative effects in humans and the environment. Once released, ENP are easily distributed via the atmosphere and the aquatic environment where an exposure to organisms can occur. To understand ENP release, life cycle (fate), and exposure as well as to evaluate their toxicological mechanisms, appropriate, media-specific (aerosols and dispersions) analytical methods are required. First, the development of a new set-up to determine ENP in aerosols is presented. For this purpose online (SMPS) and offline (electrostatic sampling on TEM grids) aerosol particle measurement techniques were combined. The aim was to study the release and fate of metallic ENP from commercial available spray products. Method development and verification was performed employing a well characterized aqueous Ag-NP spray product. The investigations have shown that the method offers the possibility to determine size, and element -specific nanoparticle release. Furthermore information about particle morphology and quantity could be obtained. It was revealed, that the release of nanoparticles strongly depends on the type of spray. Pump sprays did not show to produce airborne ENP in the aerosol, whereas propellant gas sprays released nanoparticles in substantial quantities. The release of nanoparticles was correlated with the droplet size distributions generated from the different spray types. Following method development, the setup was applied to determine ENP release of commercial available sprays, indicated to contain ENP. The obtained data was useful to model the consumer exposure of ENP from such products. Second, a set-up to determine ENP in dispersions was developed. For this purpose an asymmetric flow field flow fractionation (A4F) apparatus was coupled to an UV/Vis, light scattering- and inductively coupled plasma mass spectrometric (ICPMS) detector, simultaneously. In the beginning, method development and systematic investigations of prospects and limitations was performed employing well-characterized Au nanoparticles (Au-NP). The investigation revealed that A4F is a versatile separation technique for metallic ENP. In contrast, size determination with the A4F system, derived from the retention times of nanoparticles in the chromatogram, was erroneous. Unspecific interaction of ENP with the A4F channel membrane led to retention time shifts resulting in biased size information. For this reason, online dynamic light scattering (DLS) was employed and it offered a reliable determination of nanoparticle dimensions. Determination of nanoparticle concentration also proved to be to be problematic. Unspecific loss of nanoparticles in the A4F separation channel led to insufficient recovery prevented direct quantification of nanoparticles. To overcome this problem an alternative method was employed. With ICPMS after ultracentrifugation, quantification of the ionic and particulate -fraction of metallic ENP dispersions was possible. Validation of the set-up was performed with certified Au-NP reference materials obtained from NIST and results showed excellent agreement. Combining both of these new methods provided a comprehensive understanding of the metallic ENP systems. After method development with well defined nanoparticle systems, the set-up was tested for its applicability to "real world" samples. First, the characterization of commercial available, polydisperse, commercial Ag nanoparticle (Ag-NP) products was performed. The new developed set-up allowed obtaining an element specific, mass, and number size distribution. Furthermore, Ag-NP concentrations as well as the toxicological relevant ionic Ag concentration could be determined. Figures of merit compared to transmission electron microscopy (TEM) and batch-DLS results were in good agreement and the new method was advantageous in terms of analysis time and reliability. Furthermore the possibility to characterize SiO2 coated Au nanoparticles (Au@SiO2) was investigated. These particles are employed for Shell-Isolated Nanoparticle Enhanced Raman Spectroscopy (SHINERS). It was shown that in terms of particle size characterization, the method provided excellent data. However, determination of Si concentrations to calculate the shell thickness of such particles was impeded by the poor A4F peak shape as well as the high Si background in ICPMS. In conclusion, both setups show great potential for the characterization of metallic ENP either in aerosols or dispersions, respectively.

EPFL2011

An experimental study on main flow, secondary flow and turbulence in open-channel bends with emphasis on their interaction with the outer-bank geometry

Alexandre José Pessanha De Oliveira Caimoto Duarte

This research focus on the influence of bank inclination and roughness on the near-bank flow patterns which is relevant for bank protection, bank erosion and design of stable river configuration. Foregoing studies have been carried out mostly in rectangular channels which are far from being representative of natural conditions. In straight-channel flows large scale vortical structures, such as secondary currents or circulation cells of Prandtl's second kind, play a fundamental role. In curved flows mainly two circulation cells are generated, the center-region cell and the outer-bank cell. The outer-bank cell has a fundamental role in protecting the outer-bank by constraining the center-region cell and thereby decreasing the downstream velocity and turbulence. It is still not clear how the secondary circulation cells interact with varying channel shape and wetted perimeter roughness distribution in straight as in curved flows. This work is a part of a joint research program. The project other three partners are: Delft University of Technology (TUD), WL | Delft Hydraulics (WL) and the Leibniz Institute of Freshwater Ecology and Inland Fisheries (IGB). The main goal is to improve the understanding of flow underlying mechanisms and to improve existing hydrodynamic and morphodynamic tools. Despite the broader program where this research project is inserted, it is also self-contained. This research project is situated in the discipline of fluid dynamics applied to open-channel flows in the topic of dynamics of the mean-flow field and the turbulence in straight and curved channels. The two main goals are: i) To investigate, systematically in laboratory controlled conditions the influence of the outer bank inclination and roughness on the patterns of main flow, secondary flow, turbulence and outer-bank shear stress in straight and curved flows; ii) To give insight in the flow mechanisms responsible for the observed patterns. The channel width of B = 1.3 m, water depth of H = 0.16 m and a bulk velocity of U = 0.43 m/s were kept constant. The bank inclination was varied between 90°, 45° and 30° whereas the bank roughness was varied between smooth PVC, sand (d = 0.002 m) and d = 0.03 m materials (simulating riprap). The measurements were performed using the Acoustic Doppler Velocimetry Profiler (ADVP). The ADVP is fundamental for the accomplishment of these goals due to its accuracy and profiler capabilities. Straight channel results reveal that rectangular and trapezoidal channels have different flow patterns. The trapezoidal channels have less circulation cells than rectangular channels and a bed shear stress distribution with fewer oscillations. In trapezoidal channels the bed shear stress is higher than the cross-section averaged shear stress regardless the bank/bed roughness ratio. The bank shear stress value increases with outer-bank roughness. The experimental measurements were compared with methods of estimating mean and maximum bed and bank shear stresses, Chow (1959) and Knight et al. (1994). Chow (1959) wetted perimeter shear stress distribution is in agreement with the experiments for the trapezoidal channel experiments with homogeneous roughness distribution whereas for heterogeneous roughness distribution no agreement is verified. Knight (1994) estimations are in good agreement with measurements suggesting its applicability as engineering expedite process. In the curved flow experiments focus is given to the outer-bank roughness and inclination effect on the outer-bank flow region mainly on the outer-bank cell. Curved channel flow results reveal that the outer-bank roughness and inclination has a strong effect on the outer-bank cell, and as consequence, on the center-region cell and downstream velocity evolution along the bend. In all experiments the outer-bank cell constrains the outward limit of the center-region cell regardless its size or strength. In curved flows with rectangular channel, the outer-bank cell size increases with increasing outer-bank roughness and so further protect the bed close to the outer-bank. In curved flows with trapezoidal channel, the outer-bank cell is located over the outer-bank toe close to the free-surface even for low-bank inclination, however, the outer-bank basal zone is more exposed to higher shear stresses. In curved flows with trapezoidal channel, low outer-bank angle and varying bank roughness, the outer-bank cell does not increase with increasing outer-bank roughness. The mechanisms underlying the outer-bank cell are disclosed by analyzing the downstream vorticity equation main terms. The centrifugal term and the cross-stream shear term favor the outer-bank cell rotation sense but cross-stream turbulent anisotropy

EPFL2008

Secondary Currents and Corresponding Surface Velocity Patterns in a Turbulent Open-Channel Flow over a Rough Bed

Ismail Albayrak, Ulrich Lemmin

River and open-channel flows present complex three-dimensional (3D) structures in the water column and on the surface as a result of the existence of secondary currents driven by either centrifugal force or turbulence. This paper experimentally investigates secondary currents in a straight, turbulent, rough-bed open-channel flow; the effect of different channel width to flow depth ratios (12.25, 15, and 20) on secondary currents; and surface boils associated with secondary currents at moderate Reynolds numbers. Nearly instantaneous profiles of three components of flow velocity and turbulence characteristics in the water column were measured by using an acoustic Doppler velocity profiler (ADVP). Simultaneously, large-scale particle image velocimetry was used to measure the water surface velocities and turbulence structures. Mean velocity patterns in the water undulate across the channel, indicating the presence of secondary currents in the long-term average flow structure. Secondary currents affect the distribution of bed shear stress, Reynolds stress, and turbulence intensities across the channel. The aspect ratio determines the number of secondary cells in the water column. A mean multiband undulating surface velocity pattern in the transverse direction correlates with the secondary cell distribution in the water column below. The instantaneous position of the upwelling and downwelling regions on the surface may deviate from their long-term mean position, indicating a meandering of the surface pattern. Vortex structures are detected from instantaneous surface velocity maps, and vortex boil lines are identified. Boil vortices mainly occur in upwelling areas with high vorticity. The simultaneous detailed velocity measurements in the water column and on the free surface have shown a good agreement between the secondary cell patterns obtained by the two methods. DOI: 10.1061/(ASCE)HY.1943-7900.0000438. (C) 2011 American Society of Civil Engineers.

2011