Coherent and turbulent processes in the bistable regime around a tandem of cylinders including reattached flow dynamics by means of high-speed PIV

The turbulent flow around two cylinders in tandem at the sub-critical Reynolds number range of order of 105 and pitch to diameter ratio of 3.7 is investigated by using time-resolved Particle Image Velocimetry (TRPIV) of 1 kHz and 8 kHz. The bi-stable flow regimes including a flow pattern I with a strong vortex shedding past the upstream and the downstream cylinder, as well as a flow pattern II corresponding to a weak alternating vortex shedding with reattachment past the upstream cylinder are investigated. The structure of this “reattachment regime” has been analyzed in association with the vortex dynamics past the downstream cylinder, by means of POD and phase-average decomposition. These elements allowed interconnection among all the measured PIV planes and hence analysis of the reattachment structure and the flow dynamics past both cylinders. The results highlight fundamental differences of the flow structure and dynamics around each cylinder and provide the ‘gap’ flow nature between the cylinders. Thanks to a high-speed camera of 8 kHz, the shear-layer vortices tracking has been possible downstream of the separation point and the quantification of their shedding frequency at the present high Reynolds number range has been achieved. This issue is important regarding fluid instabilities involved in the fluid–structure interaction of cylinder arrays in nuclear reactor systems, as well as acoustic noise generated from the tandem cylinders of a landing gear in aeronautics

Evaluation of time profile reconstruction from complex two-color microarray designs

<p>Abstract</p> <p>Background</p> <p>As an alternative to the frequently used "reference design" for two-channel microarrays, other designs have been proposed. These designs have been shown to be more profitable from a theoretical point of view (more replicates of the conditions of interest for the same number of arrays). However, the interpretation of the measurements is less straightforward and a reconstruction method is needed to convert the observed ratios into the genuine profile of interest (e.g. a time profile). The potential advantages of using these alternative designs thus largely depend on the success of the profile reconstruction. Therefore, we compared to what extent different linear models agree with each other in reconstructing expression ratios and corresponding time profiles from a complex design.</p> <p>Results</p> <p>On average the correlation between the estimated ratios was high, and all methods agreed with each other in predicting the same profile, especially for genes of which the expression profile showed a large variance across the different time points. Assessing the similarity in profile shape, it appears that, the more similar the underlying principles of the methods (model and input data), the more similar their results. Methods with a dye effect seemed more robust against array failure. The influence of a different normalization was not drastic and independent of the method used.</p> <p>Conclusion</p> <p>Including a dye effect such as in the methods lmbr_dye, anovaFix and anovaMix compensates for residual dye related inconsistencies in the data and renders the results more robust against array failure. Including random effects requires more parameters to be estimated and is only advised when a design is used with a sufficient number of replicates. Because of this, we believe lmbr_dye, anovaFix and anovaMix are most appropriate for practical use.</p

Marine observations with a harmonic single-beam echo-sounder

International audienceTo characterise the seabed or water-column targets with acoustics, it is common to use multiple frequencies and therefore several sonar transducers or echo-sounders. The single beam echo-sounder we present here is able, thanks to non-linearity of the sea water, to generate more than three harmonics above its fundamental transmitted frequency, in effect producing four distinct frequencies with a single echo-sounder. In addition, all transmitted signals are perfectly in phase because they are carried by the same pulse, which has obvious benefits for further processing of the echoes. In this presentation, after a short review of the entire system, its application to seabed characterisation using the reflectivity level (acoustic backscattering strength from the seafloor) will be exposed. Further developments of plans to use this echo-sounder for fishery acoustics will then be highlighted, based on datasets acquired in the Bay of Brest (France). (Project funded by ANR and DGA / ANR-14-ASTR-0022-00)

Metrology of the Acoustic Seafloor Response:How to accurately estimate backscatter and its intrinsic uncertainty using single-beam echosounder

Its measurements have been widely extended in hydrography using predominantly bathymetric echosounders, and they are used in diverse applications such as habitat mapping, seabed characterisation or classification. In recent decades, numerous theoretical models have also been developed to study its link with physical or heuristic bottom parameters. While analysing how these three domains (measurement, application, and theory) deal with the seafloor acoustic response, it appeared that the nature itself of the seafloor acoustic response is equivocal.The work presented here proposes a relationship between the three uses of the seafloor acoustic response. Based on statistical and physical hypotheses, a metrological method is established, connecting seafloor response measurements, applications and theory. In particular, the deterministic backscatter parameter derived theoretically is usefully linked to the stochastic nature observed in practice during backscatter measurements. This yieldsa method for accurately estimating backscatter values from bathymetric echosounder data: the best choice of backscatter estimator is justified based on analytical calculations, and ways to represent its uncertainties are proposed. Theoretical hypotheses are validated using real data from handmade single-beam echosounders tested at ENSTA Bretagne (France) and at the University of Bath (UK). After application of the method to survey data, its benefits, limits, and future implementation are discussed

Comparison of methods employed to extract information contained in seafloor backscatter

International audienceSeabed maps are based on quantities extracted from measurements of the seafloor‘s acoustic response by sonar systems such as single-beam echo-sounders (SBES), multibeam echo-sounders (MBES) or sidescan sonars (SSS). In this paper, a comparison of various strategies to estimate the backscattering strength (BS) from recorded time-series, i.e. seabed echoes extracted from pings, is presented. The work hypotheses are based on processed data from a SBES designed to be tilted mechanically. Ideal survey conditions are taken into account and the seafloor is supposed to be rough so that BS is assumed to be equivalent to the Rayleigh probability density function parameter. Classical methods such as averaging corrected (sonar equation) backscattered single values over a set of pings to estimate BS are compared to other methods exploiting several time-samples being part of pings. Simulated data is considered to estimate BS in different situations (several estimators, natural/squared values, number of samples and pings). The best estimator to reach a 0.1dB uncertainty is proposed, and a formula governing the number of time-samples and pings needed to reach an accurate BS estimation according to the measurement conditions is derived

Metrology of the Acoustic Seafloor Response:How to accurately estimate backscatter and its intrinsic uncertainty using single-beam echosounder

Its measurements have been widely extended in hydrography using predominantly bathymetric echosounders, and they are used in diverse applications such as habitat mapping, seabed characterisation or classification. In recent decades, numerous theoretical models have also been developed to study its link with physical or heuristic bottom parameters. While analysing how these three domains (measurement, application, and theory) deal with the seafloor acoustic response, it appeared that the nature itself of the seafloor acoustic response is equivocal.The work presented here proposes a relationship between the three uses of the seafloor acoustic response. Based on statistical and physical hypotheses, a metrological method is established, connecting seafloor response measurements, applications and theory. In particular, the deterministic backscatter parameter derived theoretically is usefully linked to the stochastic nature observed in practice during backscatter measurements. This yieldsa method for accurately estimating backscatter values from bathymetric echosounder data: the best choice of backscatter estimator is justified based on analytical calculations, and ways to represent its uncertainties are proposed. Theoretical hypotheses are validated using real data from handmade single-beam echosounders tested at ENSTA Bretagne (France) and at the University of Bath (UK). After application of the method to survey data, its benefits, limits, and future implementation are discussed

Bipédie du babouin olive (Papio anubis) : étude de la cinématique articulaire du membre inférieur au cours de l’ontogenèse

La bipédie habituelle représente un marqueur morpho- logique, fonctionnel et comportemental de la lignée humaine. Tous les primates non-humains (PNHs) pratiquent la bipédie spontanément, cependant son utilisation reste occasionnelle chez ces espèces. L’étude de la bipédie dans un cadre comparatif est donc primordiale pour comprendre notre évolution. Des études ont révélé que la fréquence d’utilisation de la bipédie semble plus importante chez les jeunes. Le sujet abordé ici est de savoir si u..

Environmental characterisation of retification process by-products (liquid and gaseous wastes)

6th International Symposium “Environment and Wood Preservation” Cannes-Mandelieu, France 7-8 February 2005 14 pagesIn order to reduce environmental risks during the service life of the treated wood and to find new alternative developments on the durability of wood, some research and technology development have been made on thermal treatment. The retification process is one of these processes. The retification process induces chemical modification of the lignin and cellulosic components and modifies the intrinsic properties of wood : efficient increases the durability against fungi and insects, increases of the dimensional stability, decrease of the mechanical properties. The interest of this process is to reduce the environmental impact during the service life. In order to confirm the high interest of this process for the reduction of the environmental impact, an environmental characterisation of wastes on pilot plant have been carried out. Chemical analysis on gaseous and liquid effluents have been performed. An energetic assessment has been realised. The results indicate the high interest of this process in terms of possible biodegradable wastes and chemical valorisation interest, interest on energetic consumption in comparison with other wood processing treatment, interest on using retification treated wood in flooring according to indoor air quality requirements