260 research outputs found
A New Local Temperature Distribution Function for X-ray Clusters: Cosmological Applications
(abridged) We present a new determination of the local temperature function
of X-ray clusters. We use a new sample comprising fifty clusters for which
temperature information is now available, making it the largest complete sample
of its kind. It is therefore expected to significantly improve the estimation
of the temperature distribution function of moderately hot clusters. We find
that the resulting temperature function is higher than previous estimations,
but agrees well with the temperature distribution function inferred from the
BCS and RASS luminosity function. We have used this sample to constrain the
amplitude of the matter fluctuations on cluster's scale of
Mpc, assuming a mass-temperature relation based
on recent numerical simulations. We find for an
model. Our sample provides an ideal reference at to
use in the application of the cosmological test based on the evolution of X-ray
cluster abundance (Oukbir & Blanchard 1992, 1997). Using Henry's sample, we
find that the abundance of clusters at is significantly smaller, by
a factor larger than 2, which shows that the EMSS sample provides strong
evidence for evolution of the cluster abundance. A likelihood analysis leads to
a rather high value of the mean density parameter of the universe: (open case) and (flat case), which is
consistent with a previous, independent estimation based on the full EMSS
sample by Sadat et al.(1998). Some systematic uncertainties which could alter
this result are briefly discussed.Comment: 31 pages, 12 figures, mathches the version published in Astronomy and
Astrophysic
An Approximation to the Likelihood Function for Band-Power Estimates of CMB Anisotropies
Band-power estimates of cosmic microwave background fluctuations are now
routinely used to place constraints on cosmological parameters. For this to be
done in a rigorous fashion, the full likelihood function of band-power
estimates must be employed. Even for Gaussian theories, this likelihood
function is not itself Gaussian, for the simple reason that band-powers measure
the {\em variance} of the random sky fluctuations. In the context of Gaussian
sky fluctuations, we use an ideal situation to motivate a general form for the
full likelihood function from a given experiment. This form contains only two
free parameters, which can be determined if the 68% and 95% confidence
intervals of the true likelihood function are known. The ansatz works
remarkably well when compared to the complete likelihood function for a number
of experiments. For application of this kind of approach, we suggest that in
the future both 68% and 95% (and perhaps also the 99.7%) confidence intervals
be given when reporting experimental results.Comment: Published versio
Heat transfer and thermo-mechanical stresses in a gravity casting die - Influence of process parameters
International audienceThe paper is concerned with thermal measurements in a gravity casting die of simple geometry. A inverse method, based on the Laplace Transform of the heat conduction equation, is used to determine the heat flux exchanged between the die and the aluminium product. This estimation is compared to the flux that can be determined from temperature difference between two thermocouples. A ratio between 1.5 and 2 is reported. In a specific experiment, both estimated heat flux are compared with the heat exchanged with an ice cylinder. This validates the measurements and the inverse method as far as order of magnitude is concerned. Thermal measurements are used to evaluate the thermal stresses in the mould. using a simple analytical formulation. The influence of two process parameters, the initial temperature of the die and the coating on the moulding surface, is studied. Basically the more conductive the coating and the lower the initial temperature of the die, the higher the heat transfer and the higher the thermal stresses. Less obvious is the influence of ageing for the graphite based coating. A phenomenon is observed from the heat flux vs. time curves, that can be related to recalescence. It is discussed in terms of reactivity of the coating, heterogeneous nucleation on the coating and supercooling of the melt
Bias in Matter Power Spectra ?
We review the constraints given by the linear matter power spectra data on
cosmological and bias parameters, comparing the data from the PSCz survey
(Hamilton et al., 2000) and from the matter power spectrum infered by the study
of Lyman alpha spectra at z=2.72 (Croft et al., 2000). We consider
flat-- cosmologies, allowing , and to vary, and we
also let the two ratio factors and () vary independently. Using a simple
minimisation technique, we find confidence intervals on our parameters for each
dataset and for a combined analysis. Letting the 5 parameters vary freely gives
almost no constraints on cosmology, but requirement of a universal ratio for
both datasets implies unacceptably low values of and . Adding
some reasonable priors on the cosmological parameters demonstrates that the
power derived by the PSCz survey is higher by a factor compared to
the power from the Lyman forest survey.Comment: Accepted in A&
Géologie et caractérisation pétrographique et géochimique des minéralisations Cu-Au-Mo de « Type Opémiska » de Chapais (Qc, Canada)
Les minĂ©ralisations de « type OpĂ©miska » sont localisĂ©es dans la partie nord-est de la ceinture de roche verte archĂ©ennes de la Sous-province de lâAbitibi, Ă proximitĂ© de la ville de Chapais. Elles sont encaissĂ©es au sein dâun rĂ©seau de fractures localisĂ©es dans le nez de plis du Filon-couche de Ventures appartenant Ă la Suite intrusive de Cummings (~2716 Ma). Ces minĂ©ralisations reprĂ©sentent une catĂ©gorie de gisement Cu-Au filonien atypique et caractĂ©ristique du camp de Chibougamau-Chapais. Ces minĂ©ralisations ont historiquement reprĂ©sentĂ© une part trĂšs importante de la mĂ©tallogĂ©nie et de lâĂ©conomie rĂ©gionale. Avec une production de plus de 475 000 tonnes de Cu Ă partir des mines Springer et Perry, elles Ă©quivalent Ă elles seules Ă plus de la moitiĂ© de la production en Cu du camp minier de Chibougamau (~737 000 tonnes Cu). La formation de ces veines riches en Cu, Au, Ag est nĂ©anmoins restĂ©e Ă©nigmatique en raison de son caractĂšre assez unique en Abitibi. Le nouvel intĂ©rĂȘt pour ce camp minier depuis les annĂ©es 2000 et les projets de rĂ©ouverture des anciennes mines ont motivĂ© la nĂ©cessitĂ© dâamĂ©liorer la comprĂ©hension de ce type de gisement « inclassable ». LâĂ©tude pĂ©trologique et gĂ©ochimique Ă la mine Springer, a mis en Ă©vidence 2 types de minĂ©ralisations. Le premier type correspond aux veines de quartz-sulfures qui ont constituĂ©es le minerai principal. Elles reprĂ©sentent un type de minĂ©ralisation Cu-Au-Mo avec une paragĂ©nĂšse principale Ă chalcopyrite, pyrite, magnĂ©tite et molybdĂ©nite, et une association Cu, Au, Ag, Bi, Mo. Elles sâaccompagnent dâune altĂ©ration sodique-potassique proximale Ă biotite, stilpnomĂ©lane, feldspaths Na-K et propyllitique distale Ă chlorite-Ă©pidote. Les signatures en Ă©lĂ©ments traces des pyrites de Springer, Perry et de lâindice Chibougamau-Copper prĂ©sentent des associations Ă Se, Te, Bi, Cu, Co, Ag comparables aux minĂ©ralisations magmatiques-hydrothermales, ainsi quâĂ celles des veines Cu-Au filoniens et porphyriques du Camp minier du lac DorĂ©. Les magnĂ©tites hydrothermales montrent Ă©galement des signatures en Ă©lĂ©ments traces similaires Ă celles des systĂšmes magmatiques-hydrothermaux et ont permis dâestimer une tempĂ©rature de formation de lâordre de 200 â 300°C. Le second type de minĂ©ralisation est reprĂ©sentĂ© par des veines de quartz-carbonate en cisaillement orientĂ©es 300 â 330° qui recoupe les veines Cu-Au-Mo. Elles se caractĂ©risent par une paragĂ©nĂšse Ă arsĂ©nopyrite-pyrite±sphalĂ©rite±galĂšne±sulfosels, une association Au, As, Zn, Pb, Bi, Sb et une altĂ©ration Ă chlorite-sĂ©ricite-carbonate. La signature de ces pyrites est marquĂ©e par des enrichissements en Au, As, Sb, Bi et de trĂšs faibles concentrations en Se, Te par rapport aux veines Cu-Au-Mo. Ces caractĂ©ristiques sont comparables aux signatures observĂ©es dans les minĂ©ralisations dâor orogĂ©nique des mines Cooke et Norbeau. LâinterprĂ©tation des donnĂ©es obtenues dans cette Ă©tude et lâintĂ©gration des travaux antĂ©rieurs ont permis de conclure que les veines de « type OpĂ©miska » de Springer et Perry appartiennent Ă un large systĂšme Cu-Au-Mo magmatique-hydrothermal. Sa mise en place serait contemporaine Ă lâactivitĂ© magmatique de la pĂ©riode synvolcanique. Les minĂ©ralisations Au-As sont plus tardives et formĂ©es durant la pĂ©riode syntectonique, probablement par un processus similaire aux veines dâor orogĂ©nique. Cet Ă©vĂ©nement a contribuĂ© Ă enrichir en Au le systĂšme prĂ©coce, ce qui a des implications majeures pour lâexploration du secteur
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