1,768 research outputs found
Masse des cristaux de glace et facteurs de réflectivité radar dans les systÚmes de nuages convectifs de moyenne échelle formés dans les Tropiques et la région de la mer Méditerranée
This study focuses on the variability of mass-diameter relationships (m(D)) and shape of ice hydrometeors in Mesoscale Convective Systems (MCS). It bases on data base which were recorded during four airborne measurement campaigns: (i) African monsoonâs MCS (continent; MT2010), (ii) Indian Oceanâs MCS (MT2011), (iii) Mediterraneanâs MCS (costs; HyMeX), (iv) North-Australian monsoonâs MCS (costs; HAIC-HIWC). m(D) of ice hydrometeors are derived from a combined analysis of particle images from 2D-array probes and associated reflectivity factors measured with a Doppler cloud radar on the same research aircraft. Usually, m(D) is formulated as a power law (with one pre-factor and one exponent) that need to be constrained from complementary information on hydrometeors. A theoretical study of numerous hydrometeor shapes simulated in 3D and arbitrarily projected on a 2D plan allowed to constrain the exponent ÎČ of the m(D) relationship from the exponent Ï of the surface-diameter S(D) relationship, which is likewise written as a power law. Since S(D) always can be determined for real data from 2D optical array probes or other particle imagers, the evolution of the m(D) exponent can be calculated. After that, the pre-factor α of m(D) is constrained from theoretical simulations of the radar reflectivity factor matching the measured reflectivity factor along the aircraft trajectory. Mean profiles of m(D) coefficients, particles size distributions and Condensed Water Content (CWC) are calculated in functions of the temperature, and are different for each type of MCS. For the four types of MCS, it is shown that the variability of m(D) coefficients is correlated with the variability of the temperature. Four types of m(D) parametrisations are calculated since the analysis of the variability of the m(D) coefficients. The significant benefit of using variable m(D) relations instead of a single m(D) relationship is demonstrated from the impact of all these m(D) relations on Z-CWC and Z-CWC-T fitted parametrisations.Cette thĂšse sâintĂ©resse Ă la variabilitĂ© de la relation mass-diamĂštre (m(D)) des hydromĂ©tĂ©ores en phase glace prĂ©sents dans les systĂšmes convectif de moyenne Ă©chelle (MCS). Elle sâappuie sur une base de donnĂ©es acquise pour 4 types de MCS diffĂ©rents durant 4 campagnes de mesure aĂ©roportĂ©e : (i) MCS de la mousson Africaine (Continent ; MT2010), (ii) MCS de lâocĂ©an Indien (MT2011), (iii) MCS de la MĂ©diterranĂ©e (cĂŽtes ; HyMeX), (iv) MCS de la mousson Nord-Australienne (cĂŽtes ; HAIC-HIWC). La relation m(D) est calculĂ©e Ă partir de lâanalyse combinĂ©e des images des hydromĂ©tĂ©ores enregistrĂ©es par les sondes optiques et les facteurs de rĂ©flectivitĂ© mesurĂ©s Ă lâaide dâun radar Doppler embarquĂ©s sur le mĂȘme avion de recherche. Il est dâusage que la relation m(D) des hydromĂ©tĂ©ores soit reprĂ©sentĂ©e par une loi puissance (avec un prĂ©-facteur et un exposant), qui doit ĂȘtre contrainte par des informations supplĂ©mentaires sur les hydromĂ©tĂ©ores. Une Ă©tude thĂ©orique sur les formes des hydromĂ©tĂ©ores Ă lâaide de simulations en 3 dimensions dans lesquelles les hydromĂ©tĂ©ores sont orientĂ©s alĂ©atoirement et projetĂ© sur un plan, permet de contraindre lâexposant ÎČ de la relation m(D) en fonction de lâexposant Ï de la relation surface-diamĂštre (S(D)). La relation S(D) est aussi reprĂ©sentĂ©e par une loi puissance, et elle peut-ĂȘtre calculĂ©e pour une population dâimages dâhydromĂ©tĂ©ores enregistrĂ©s par les sondes optiques. La variabilitĂ© de lâexposant est finalement calculĂ©e Ă partir de la variabilitĂ© de lâexposant Ï dĂ©duis des images des hydromĂ©tĂ©ores. Ensuite le prĂ©-facteur α est calculĂ© Ă partir de simulations des facteurs de rĂ©flectivitĂ©, de sorte que les facteurs de rĂ©flectivitĂ© simulĂ©s soient Ă©gaux aux facteurs de rĂ©flectivitĂ© mesurĂ©s par le radar nuage le long de la trajectoire de lâavion dans les MCS. Des profils moyens en fonction de la tempĂ©rature sont calculĂ©s pour les coefficients de la relation m(D), les distributions en tailles des hydromĂ©tĂ©ores et les contenus massiques de glace dans les MCS (CWC). Les profils moyens pour les quatre types de MCS sont diffĂ©rents les uns des autres. Pour les quatre types de MCS, il est montrĂ© que les variations des coefficients de la relation m(D) sont corrĂ©lĂ©es avec les variations de la tempĂ©rature. Four types de paramĂ©trisations de la relation m(D) sont calculĂ©es depuis lâanalyses des variations des coefficients de la relation m(D). Le bĂ©nĂ©fice apportĂ© par lâutilisation de relation m(D) non constante contrairement Ă lâutilisation de relation m(D) avec α et ÎČ constant, est dĂ©montrĂ© en Ă©tudiant lâimpact de toutes les paramĂ©trisations de la relation m(D) sur le calcul des relations Z-CWC et Z-CWC-T
Analyses of extreme swell events on La RĂ©union Island from microseismic noise
International audienceOcean wave activity excites seismic waves that propagate through the solid earth, known as microseisms, which, once recorded on oceanic islands, can be used to analyze the swell. Here, we analyze the microseismic noise recorded in different period ranges by the permanent seismic station RER on La RĂ©union Island and by a temporary network of ten broad-band seismic stations deployed on the island to analyze extreme swell events. We perform a comparative analysis of cyclonic and austral swell events by analyzing the primary (PM, ⌠10 to 20 s period) and secondary (SM, ⌠3 to 10 s) microseisms, but also the long period secondary microseisms (LPSM, ⌠7 to 10 s), which may result from the interaction between incident ocean waves and the reflected waves off the coast. We compare the microseismic observations with buoy data when available and with predictions from numerical ocean wave models. We show that each cyclone is characterized by its own individual signature in the SM, which depends on its distance and intensity, but also on its dynamics and trajectory. Thus, the SM contains relevant information for cyclone detection and monitoring. Analyzing the PM and the LPSM, and comparing it to direct buoy observations and/or swell numerical models allows characterizing the local impact of the swell with the island in terms of amplitude, period, and sometimes, direction of propagation, making possible to use a seismic station as an ocean wave gauge. The microseisms, which link the atmosphere, the ocean and the solid Earth, can thus provide valuable observations on extreme swells, in addition to oceanic and meteorological data
Analytical and practical analysis of frictional-kinetic model for dense and dilute gas-solid flows
In granular flows, when the solid volume fraction is large, the dynamic behaviour of particles becomes controlled by frictional effects. Theoretically these effects can not be taken into account in an Eulerian approach, based on the kinetic theory of granular flows, because the inter-particle contact times are long. However, in the literature several empirical models have been proposed which introduce a frictional pressure and viscosity. In the paper, these models are first compared on a simple case of sheared dense granular flows in order to analyze the individual behavior of each model. Second, the models have been implemented in an Eulerian solver and numerical simulations have been performed of an experiment of bin discharge. The results show that for large diameter, the solid mass flow rate is well predicted, while it is systematically underestimated when the ratio between the injector diameter and the diameter of particles is small
Tide-induced microseismicity in the Mertz glacier grounding area, East Antarctica
International audienceThe deployment of a seismic network along the AdĂ©lie and George V coasts in East Antarctica during the period 2009â2012 provides the opportunity to monitor cryoseismic activity and to obtain new insights on the relationship between tidal cycles and coastal glacier dynamics. Here we focus on records from a seismometer located on a rocky outcrop in the vicinity of the grounding line of the 35 km broad Mertz glacier, a major outflow of this region. We detect numerous icequakes (50,000 events within 10 months and up to 100 events/h) and demonstrate their clear tidal modulation. We suggest that they result from ice friction and fracturing around the rocky peak and from the glacier flexure in response to the falling and rising tides at its grounding area. We propose that such icequake monitoring could be used as a climate proxy since grounding lines are subject to migrate with sea level changes
Calibration of the mixing-length theory for convective white dwarf envelopes
A calibration of the mixing-length parameter in the local mixing-length theory (MLT) is presented for the lower part of the convection zone in pure-hydrogen-atmosphere white dwarfs. The parameterization is performed from a comparison of three-dimensional (3D) CO5BOLD simulations with a grid of one-dimensional (1D) envelopes with a varying mixing-length parameter. In many instances, the 3D simulations are restricted to the upper part of the convection zone. The hydrodynamical calculations suggest, in those cases, that the entropy of the upflows does not change significantly from the bottom of the convection zone to regions immediately below the photosphere. We rely on this asymptotic entropy value, characteristic of the deep and adiabatically stratified layers, to calibrate 1D envelopes. The calibration encompasses the convective hydrogen-line (DA) white dwarfs in the effective temperature range 6000 †T eff (K) â€15, 000 and the surface gravity range 7.0 †log g †9.0. It is established that the local MLT is unable to reproduce simultaneously the thermodynamical, flux, and dynamical properties of the 3D simulations. We therefore propose three different parameterizations for these quantities. The resulting calibration can be applied to structure and envelope calculations, in particular for pulsation, chemical diffusion, and convective mixing studies. On the other hand, convection has no effect on the white dwarf cooling rates until there is a convective coupling with the degenerate core below T eff ~ 5000 K. In this regime, the 1D structures are insensitive to the MLT parameterization and converge to the mean 3D results, hence they remain fully appropriate for age determinations
Artificial insemination in felids
Artificial insemination in the domestic cat and in wild felids has several indications. In the cat, it may
replace natural reproduction when matings are unsuccessful or difficult, and it may help to perform
geographical exchanges of semen and therefore enhance genetic improvement. In wild felids, it plays
a complementary role inside conservation programs. However, its use is complex. First, oestrus and
ovulation have to be induced. This is most often obtained using gonadotrophins, which unfortunately
may induce undesirable effects, like ovarian hyperstimulation. In males, the semen is generally collected
by electro-ejaculation. It may be frozen. However, teratospermia, which is the production of
numerous spermatozoa showing morphological abnormalities, is a specific problem affecting felids.
Intrauterine inseminations give better results. For a long period, laparoscopy was recommended in
felids to perform intrauterine inseminations. Recently, new techniques consisting of catheterizing the
cervix through a vaginal access have been developed in the cat as in some wild felids species. Altogether,
the rate of success of artificial insemination in felids remains moderate.L'insémination artificielle
chez le chat domestique et les félidés sauvages répond à plusieurs indications. Chez le
chat, elle peut notamment permettre d'aider la reproduction lorsque l'accouplement ne se
produit pas ou difficilement et de favoriser les échanges géographiques de semence et donc
un brassage et une meilleure sélection génétiques. Chez les félins sauvages, elle joue un
rÎle complémentaire au sein des programmes de conservation. Son utilisation est cependant
complexe. L'oestrus et l'ovulation sont le plus souvent induits par l'emploi de
gonadotropines qui possÚdent cependant des effets indésirables, notamment un risque
d'hyperstimulation ovarienne. La semence des mùles est généralement récoltée par
Ă©lectro-Ă©jaculation. Elle peut ĂȘtre congelĂ©e. NĂ©anmoins, un problĂšme spĂ©cifique aux fĂ©lins
tient à la tératospermie, c'est-à -dire la production de nombreux spermatozoïdes porteurs
d'anomalies morphologiques. L'insémination artificielle donne de meilleurs résultats lorsque
la semence est déposée par voie intra-utérine. Pendant longtemps, la laparoscopie a été la
technique de référence, mais récemment, des techniques de cathétérisme du col utérin par
voie vaginale ont été mises au point, aussi bien chez le chat que chez certains félidés
sauvages. Les résultats de l'insémination artificielle chez les félidés restent moyens
(souvent moins de 50 % de gestations obtenues)
Caractérisation expérimentale de la dispersion d'un pseudo-polluant d'usinage
Dans le cadre du développement d'une méthode numérique de conception des captages de polluants sur machines d'usinage, un banc d'essai recréant une situation similaire à une opération de meulage est utilisé. Le jet de polluant particulaire obtenu est caractérisé par la vélocimétrie par suivi de particules (PTV) afin d'obtenir des données d'entrée et de validation pour les simulations numériques. Ensuite, le traçage gazeux par SF6 est utilisé pour mesurer la concentration des plus fines particules. Nous présentons ici ces résultats expérimentaux, ainsi que le banc d'essai réalisé
USE OF SUB-CUTANEOUS IMPLANTS CONTAINING GNRH AGONISTS FOR THE CONTROL OF REPRODUCTION IN DOMESTIC CARNIVORES
The recent commercialisation in Europe of sub-cutaneous implants containing an agonist of the hypothalamic
hormone GnRH, called deslorelin, has been done in the purpose of offering a chemical alternative
to surgical castration in the adult male dog. The efficacy of these implants in this indication
is real. They have an action on the endocrine function ( spectacular diminution of testosteronemia),
on the exocrine function (alteration of sperm quality and infertility) and on the clinical evolution (
diminution of the size of the testis). The availability of these implants also gave rise to numerous other
indications in the canine and feline species. Many recent publications, or even unpublished studies
still going on, seem to show an interest in the improvement of unpleasant behavior potentially linked
with testosterone in the male, but also to prevent fertility in the adult male cat and to prevent oestrus
in the bitch or in the queen. Implantation of pre-pubertal animals to postpone puberty seems successful.
In the adult bitch, induction of a fertile oestrus post-implantation is even possible, which bears
a zootechnical interest. However, secondary effects, duration of action and further fertility after implantation
are not well known at the moment and need to be further studiedLa mise rĂ©cente sur le marchĂ© europĂ©en dâimplants sous-cutanĂ©s contenant un agoniste de lâhormone
hypothalamique GnRH, la desloréline, offre une alternative chimique à la castration chirurgicale du
chien mùle adulte. Ces implants agissent sur la fonction endocrine (effondrement de la testostéronémie),
sur la fonction exocrine (altération de la qualité du sperme et infertilité) et permettent un
suivi de lâĂ©volution clinique (diminution de la taille des testicules). Leur disponibilitĂ© a Ă©galement ouvert
la voie Ă de multiples autres indications dans les espĂšces canines et fĂ©lines. Ils prĂ©senteraient un intĂ©rĂȘt
pour amĂ©liorer certains comportements gĂȘnants du mĂąle, potentiellement liĂ©s Ă la testostĂ©rone,
pour bloquer la fertilitĂ© du chat mĂąle et Ă©viter lâapparition de lâoestrus chez la chienne ou la chatte.
Lâimplantation dâanimaux prĂ©-pubĂšres dans le but de retarder la pubertĂ© semble efficace. Chez la
chienne adulte, lâinduction dâun oestrus induit post-implantation est mĂȘme possible, ce qui prĂ©sente
un intĂ©rĂȘt zootechnique. Toutefois, les effets secondaires potentiels, la durĂ©e dâaction et la reprise
de la fertilitĂ© aprĂšs implantation ne sont pas encore bien connus et doivent ĂȘtre davantage Ă©tudiĂ©
Eulerian modelling of the powder discharge of a silo: Attempting to shed some light on the origin of jet expansion
Powder discharging from a silo provokes an emission of dust. To understand and prevent this source of danger,3D simulations of a silo dischargewere performed using an Euler-Euler approach. The impact of the coupling between the flow inside the silo and the granular jet in free-fall is analyzed. Results show that the solid mass flow rate is correctly predicted and that gas back-flowing at the hopper exhaust appears responsible for the formation of a fluctuating and radially expanding jet. However, the radial expansion of the free-falling jet is underestimated. Stochastic fluctuations of the particles velocity at the hopper exhaust are introduced to evaluate their effect on
the downstream development of the free-falling jet. These fluctuations are found capable of generating a development of the jet similar to that observed experimentally. This suggests that the granular flow conditions at the hopper exhaust are responsible for the further dispersion of powder
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