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Inner plasma structure of the low-latitude reconnection layer
No full textWe report a clear transition through a reconnection layer at the low-latitude magnetopause which shows a complete traversal across all reconnected field lines during northwestward interplanetary magnetic field (IMF) conditions. The associated plasma populations confirm details of the electron and ion mixing and the time history and acceleration through the current layer. This case has low magnetic shear with a strong guide field and the reconnection layer contains a single density depletion layer on the magnetosheath side which we suggest results from nearly field-aligned magnetosheath flows. Within the reconnection boundary layer, there are two plasma boundaries, close to the inferred separatrices on the magnetosphere and magnetosheath sides (Ssp and Ssh) and two boundaries associated with the Alfvén waves (or Rotational Discontinuities, RDsp and RDsh). The data are consistent with these being launched from the reconnection site and the plasma distributions are well ordered and suggestive of the time elapsed since reconnection of the field lines observed. In each sub-layer between the boundaries the plasma distribution is different and is centered around the current sheet, responsible for magnetosheath acceleration. We show evidence for a velocity dispersion effect in the electron anisotropy that is consistent with the time elapsed since reconnection. In addition, new evidence is presented for the occurrence of partial reflection of magnetosheath electrons at the magnetopause current layer
Suppression of turbulent diffusion on the water surface by viscoelastic nano layer
No full textWe study effects of thin (10 nm) layers of adsorbed proteins on the water surface hydrodynamics. We show that extremely small concentrations of protein (less than 1 ppm) form strong viscoelastic layer at the water-air interface. This layer greatly reduces single particle dispersion on the surface perturbed by Faraday waves and turns disordered surface waves into a square stationary oscillating crystal. The viscoelastic film is destroyed by minute addition of surfactant which leads to the recovery of the horizontal mobility of fluid particles and the restoration of the Faraday wave driven turbulence
Mechanics of inhomogeneous turbulence and interfacial layers
No full textThe mechanics of inhomogeneous turbulence in and adjacent to interfacial layers bounding turbulent and non-turbulent regions are analysed. Different mechanisms are identified according to the straining by the turbulent eddies in relation to the strength of the mean shear adjacent to, or across, the interfacial layer. How the turbulence is initiated and the topology of the region of turbulence are also significant factors. Specifically the cases of a layer of turbulence bounded on one, or two, sides by a uniform and/or shearing flow, and a circular region of a rotating turbulent vortex are considered and discussed.
The entrainment processes at fluctuating interfaces occur both at the outer edges of turbulent shear layers, with and without free-stream turbulence (e.g. jets, wakes and boundary layers), at internal boundaries such as those at the outside of the non-turbulent core of swirling flows (e.g. the ‘eye-wall’ of a hurricane) or at the top of the viscous sublayer and roughness elements in turbulent boundary layers. Conditionally sampled data enables these concepts to be tested. These concepts lead to physically based estimates for critical modelling parameters such as eddy viscosity near interfaces, entrainment rates, maximum velocity and displacement heights
Turbulence statistics of turbulent boundary layer flow following injection of drag-reducing surfactant solution
No full textTo investigate streamwise variations of turbulence statistics in the wide range of the drag reduction ratio for the zero-pressure-gradient turbulent boundary layer flow due to the injection of drag-reducing nonionic surfactant solutions, we performed the laser-Doppler velocimetry (LDV) measurement at a new experimental apparatus with the larger size than previous one. The drag reduction ratio up to 76% could be obtained, at which the mean velocity in wall-units was beyond the Virk's ultimate for polymer solutions
A cross-layer approach to enhance QoS for multimedia applications over satellite
No full textThe need for on-demand QoS support for communications over satellite is of primary importance for distributed multimedia applications. This is particularly true for the return link which is often a bottleneck due to the large set of end-users accessing a very limited uplink resource. Facing this need, Demand Assignment Multiple Access (DAMA) is a classical technique that allows satellite operators to offer various types of services, while managing the resources of the satellite system efficiently. Tackling the quality degradation and delay accumulation issues that can result from the use of these techniques, this paper proposes an instantiation of the Application Layer Framing (ALF) approach, using a cross-layer interpreter(xQoS-Interpreter). The information provided by this interpreter is used to manage the resource provided to a terminal by the satellite system in order to improve the quality of multimedia presentations from the end users point of view. Several experiments are carried out for different loads on the return link. Their impact on QoS is measured through different application as well as network level metrics
Effects of a fence on pollutant dispersion in a boundary layer exposed to a rural-to-urban transition
No full textSimultaneous particle-image velocimetry and laser-induced fluorescence combined with large-eddy simulations are used to investigate the flow and pollutant dispersion behaviour in a rural-to-urban roughness transition. The urban roughness is characterized by an array of cubical obstacles in an aligned arrangement. A plane fence is added one obstacle height h upstream of the urban roughness elements, with three different fence heights considered. A smooth-wall turbulent boundary layer with a depth of 10h is used as the approaching flow, and a passive tracer is released from a uniform line source 1h upstream of the fence. A shear layer is formed at the top of the fence, which increases in strength for the higher fence cases, resulting in a deeper internal boundary layer (IBL). It is found that the mean flow for the rural-to-urban transition can be described by means of a mixing-length model provided that the transitional effects are accounted for. The mixing-length formulation for sparse urban canopies, as found in the literature, is extended to take into account the blockage effect in dense canopies. Additionally, the average mean concentration field is found to scale with the IBL depth and the bulk velocity in the IBL.Fluid MechanicsAtmospheric PhysicsAtmospheric Remote Sensin
Turbulent dispersion in cloud-topped boundary layers
No full textCompared to dry boundary layers, dispersion in cloud-topped boundary layers has received less attention. In this LES based numerical study we investigate the dispersion of a passive tracer in the form of Lagrangian particles for four kinds of atmospheric boundary layers: 1) a dry convective boundary layer (for reference), 2) a "smoke" cloud boundary layer in which the turbulence is driven by radiative cooling, 3) a stratocumulus topped boundary layer and 4) a shallow cumulus topped boundary layer. We show that the dispersion characteristics of the smoke cloud boundary layer as well as the stratocumulus situation can be well understood by borrowing concepts from previous studies of dispersion in the dry convective boundary layer. A general result is that the presence of clouds enhances mixing and dispersion – a notion that is not always reflected well in traditional parameterization models, in which clouds usually suppress dispersion by diminishing solar irradiance. The dispersion characteristics of a cumulus cloud layer turn out to be markedly different from the other three cases and the results can not be explained by only considering the well-known top-hat velocity distribution. To understand the surprising characteristics in the shallow cumulus layer, this case has been examined in more detail by 1) determining the velocity distribution conditioned on the distance to the nearest cloud and 2) accounting for the wavelike behaviour associated with the stratified dry environment.Infrastructures, Systems and ServicesTechnology, Policy and Managemen
Mesoscale surface analyses of the ERICA IOP-2 cyclone
No full textThe mesoscale structure of an explosively deepening open-ocean cyclone, the Intensive Observation Period (IOP) 2 of the Experiment on Rapidly Intensifying Cyclones over the Atlantic (ERICA) which occurred 13-14 December 1988, was studied. Aircraft, buoy and ship observations were plotted in 3 h blocks, and detailed hand-analyses of surface pressure and temperature, as well as frontal and cyclone structure, were prepared. The analyses were then converted to a 20 km grid using a Cressman analysis scheme, and the gridded fields passed to a Brown-Liu planetary boundary layer (PBL) model to calculate surface latent and sensible heat fluxes. The results of the mesoscale surface analysis showed that the regions east and northeast of the low featured less warm thermal advection than expected for a typical maritime cyclone and a low- level easterly flow that had a 5-10 C thermal disequilibrium between the sea surface and the overlying air. This caused substantial positive heat fluxes east of the low throughout the 12 h prior to and during rapid deepening. This pattern of surface interaction is substantially different from other cyclones and suggests that surface processes contributed significantly to the cyclogenesis.Approved for public release; distribution is unlimited.Lieutenant Commander, United States Navyhttp://archive.org/details/mesoscalesurface109452762
A genetic variation map for chicken with 2.8 million single-nucleotide polymorphisms
No full textWe describe a genetic variation map for the chicken genome containing 2.8 million single-nucleotide polymorphisms (SNPs). This map is based on a comparison of the sequences of three domestic chicken breeds (a broiler, a layer and a Chinese silkie) with that of their wild ancestor, red jungle fowl. Subsequent experiments indicate that at least 90% of the variant sites are true SNPs, and at least 70% are common SNPs that segregate in many domestic breeds. Mean nucleotide diversity is about five SNPs per kilobase for almost every possible comparison between red jungle fowl and domestic lines, between two different domestic lines, and within domestic lines--in contrast to the notion that domestic animals are highly inbred relative to their wild ancestors. In fact, most of the SNPs originated before domestication, and there is little evidence of selective sweeps for adaptive alleles on length scales greater than 100 kilobases
The Effect of Ambient Ageing on the Corrosion Protective Properties of a Lithium-Based Conversion Layer
No full textThe influence of ageing under ambient conditions on the corrosion protective behaviour of a lithium-based conversion layer on AA2024-T3 is studied in this work. Conversion layers aged at ambient conditions for relatively short times (0 h and 4 h), show an initial high degree of corrosion inhibition but a much lower protectiveness after the inhibition stage terminates. Conversion layers with relatively long ageing times (24 h and 72 h) show a rather stable corrosion resistance which is higher than that of short-time aged samples. It is hypothesized that the freshly-formed conversion layer has trapped a certain amount of lithium ions and water molecules, leading to ongoing and heterogeneous growth of the conversion layer with time under ambient indoor conditions. Moreover, conversion layers with short ageing times show early-stage active corrosion protection by lithium-ion release.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Team Arjan MolTeam Yaiza Gonzalez GarciaTeam Peyman Taher
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