1,047 research outputs found
Using the Monte Carlo Markov Chain method to estimate contact parameter temperature dependence
No full textInternational audienceWide temperature range datasets on deposition mode ice nucleation have revealed a strong dependence of the contact parameter m on temperature. This dependence varies from linear to exponential, depending on the experiment and the temperature range. We have analyzed three datasets using a Monte Carlo Markov Chain (MCMC) method. The used method allows us to test and evaluate different functional forms for the temperature dependence of the contact parameter. This study (Määttänen and Douspis, 2014) provides a new framework, valid even for very small ice nucleus sizes, for analyzing heterogeneous nucleation datasets
Using the Monte Carlo Markov Chain method to estimate contact parameter temperature dependence
No full textInternational audienceWide temperature range datasets on deposition mode ice nucleation have revealed a strong dependence of the contact parameter m on temperature. This dependence varies from linear to exponential, depending on the experiment and the temperature range. We have analyzed three datasets using a Monte Carlo Markov Chain (MCMC) method. The used method allows us to test and evaluate different functional forms for the temperature dependence of the contact parameter. This study (Määttänen and Douspis, 2014) provides a new framework, valid even for very small ice nucleus sizes, for analyzing heterogeneous nucleation datasets
Mireille Blanchet-Douspis, L’influence de l’histoire contemporaine dans l’œuvre de Marguerite Yourcenar
No full textFrutto di una tesi di dottorato, lo studio di M. Blanchet-Douspis si propone di dimostrare che al di là di un palese interesse verso la storia classica, Marguerite Yourcenar fa delle sue opere una continua evocazione della storia contemporanea, dalla quale viene profondamente influenzata. Il confronto con i documenti storici dimostra che sia Les Mémoires d’Hadrien, sia L’Œuvre au noir, sia ancora Le Labyrinthe du monde rispecchiano fedelmente gli avvenimenti politici, le realtà sociali e il c..
Constraining the mass and redshift evolution of the hydrostatic mass bias using the gas mass fraction in galaxy clusters
No full textThe gas mass fraction in galaxy clusters is a convenient probe to use in cosmological studies, as it can help derive constraints on a range of cosmological parameters. This quantity is, however, subject to various effects from the baryonic physics inside galaxy clusters, which may bias the obtained cosmological constraints. Among different aspects of the baryonic physics at work, in this paper we focus on the impact of the hydrostatic equilibrium assumption. We analyzed the hydrostatic mass bias B, constraining a possible mass and redshift evolution for this quantity and its impact on the cosmological constraints. To that end, we considered cluster observations of the Planck-ESZ sample and evaluated the gas mass fraction using X-ray counterpart observations. We show a degeneracy between the redshift dependence of the bias and cosmological parameters. In particular we find evidence at 3.8I for a redshift dependence of the bias when assuming a Planck prior on Ωm. On the other hand, assuming a constant mass bias would lead to the extremely large value of ΩmA 0.860. We show, however, that our results are entirely dependent on the cluster sample under consideration. In particular, the mass and redshift trends that we find for the lowest mass-redshift and highest mass-redshift clusters of our sample are not compatible. In addition, we show that assuming self-similarity in our study can impact the results on the evolution of the bias, especially with regard to the mass evolution. Nevertheless, in all the analyses, we find a value for the amplitude of the bias that is consistent with BA 0.8, as expected from hydrodynamical simulations and local measurements. However, this result is still in tension with the low value of BA 0.6 derived from the combination of cosmic microwave background primary anisotropies with cluster number counts
Constraining the mass and redshift evolution of the hydrostatic mass bias using the gas mass fraction in galaxy clusters
No full textThe gas mass fraction in galaxy clusters is a quantity which can be used as a robust cosmological probe. It is however subject to various effects from the baryonic physics inside galaxy clusters, which may bias the obtained cosmological constraints. Among different aspects of the baryonic physics, in these proceedings we focus on the impact of the hydrostatic equilibrium assumption. From X-ray measurements of cluster gas fraction in the Planck-ESZ sample, we analyse the hydrostatic mass bias B, constraining a possible mass and redshift evolution of this quantity and its impact on the cosmological constraints. We show a degeneracy between the redshift dependence of the bias and cosmological parameters. In particular we find a 3.8σ evidence for a redshift dependence of the bias when assuming a Planck prior on Ωm. On the other hand, assuming a constant mass bias would lead to the extreme large value of Ωm > 0.860. We however show these results to be depending on the mass and redshift selections inside the main sample. Nevertheless, in all the analyses we find a value for the amplitude of the bias that is consistent with B ∼ 0.8, as expected from hydrodynamical simulations and local measurements, but still in tension with the low value of B ∼ 0.6 derived from the combination of cosmic microwave background primary anisotropies with cluster number counts. We also discuss cosmological constraints obtained from gas fraction data, combined with other probes like cluster number counts
Using the Monte Carlo Markov Chain method to estimate contact parameter temperature dependence: implications for Martian cloud modelling
No full textInternational audienceIn the last years several datasets on deposition mode ice nucleation in Martian conditions have showed that the effectiveness of mineral dust as a condensation nucleus decreases with temperature (Iraci et al., 2010; Phebus et al., 2011; Trainer et al., 2009). Previously, nucleation modelling in Martian conditions used only constant values of this so-called contact parameter, provided by the few studies previously published on the topic. The new studies paved the way for possibly more realistic way of predicting ice crystal formation in the Martian environment. However, the caveat of these studies (Iraci et al., 2010; Phebus et al., 2011) was the limited temperature range that inhibits using the provided (linear) equations for the contact parameter temperature dependence in all conditions of cloud formation on Mars. One wide temperature range deposition mode nucleation dataset exists (Trainer et al., 2009), but the used substrate was silicon, which cannot imitate realistically the most abundant ice nucleus on Mars, mineral dust. Nevertheless, this dataset revealed, thanks to measurements spanning from 150 to 240 K, that the behaviour of the contact parameter as a function of temperature was exponential rather than linear as suggested by previous work. We have tried to combine the previous findings to provide realistic and practical formulae for application in nucleation and atmospheric models. We have analysed the three cited datasets using a Monte Carlo Markov Chain (MCMC) method. The used method allows us to test and evaluate different functional forms for the temperature dependence of the contact parameter. We perform a data inversion by finding the best fit to the measured data simultaneously at all points for different functional forms of the temperature dependence of the contact angle m(T). The method uses a full nucleation model (Määttänen et al., 2005; Vehkamäki et al., 2007) to calculate the observables at each data point. We suggest one new and test several m(T) dependencies. Two of these may be used to avoid unphysical behaviour (m > 1) when m(T) is implemented in heterogeneous nucleation and cloud models. However, more measurements are required to fully constrain the m(T) dependencies. We show the importance of large temperature range datasets for constraining the asymptotic behaviour of m(T), and we call for more experiments in a large temperature range with well-defined particle sizes or size distributions, for different IN types and nucleating vapours. This study (Määttänen and Douspis, 2014) provides a new framework for analysing heterogeneous nucleation datasets. The results provide, within limits of available datasets, well-behaving m(T) formulations for nucleation and cloud modelling. Iraci, L. T., et al. (2010). Icarus 210, 985-991. Määttänen, A., et al. (2005). J. Geophys. Res. 110, E02002. Määttänen, A. and Douspis, M. (2014). GeoResJ 3-4 , 46-55. Phebus, B. D., et al. (2011). J. Geophys. Res. 116, 4009. Trainer, M. G., et al. (2009). J. Phys. Chem C 113 , 2036-2040. Vehkamäki, H., et al. (2007). Atmos. Chem. Phys. 7, 309-313
Cosmology from cosmic microwave background and galaxy clusters
No full textWe present the results of analysis of constraints on cosmological parameters
from cosmic microwave background (CMB) alone and in combination with
the galaxy cluster baryon fraction assuming inflation-generated adiabatic
scalar fluctuations. The CMB constraints are obtained using our likelihood
approximation method (Bartlett et al. 2000; Douspis et al. 2001).
In the present analysis we use the new data coming from MAXIMA and
BOOMERanG balloon-borne experiments and the first results of the DASI
interferometer together with the COBE/DMR data. The quality of these
independent data sets implies that the are rather well
known, and allow reliable constraints. We found that the constraints
in the plane are very tightened, favouring a flat
Universe, that the index of the primordial fluctuations is very
close to one, that the primordial baryon density is now in good
agreement with primordial nucleosynthesis. Nevertheless degeneracies
between several parameters still exist, and for instance the
constraint on the cosmological constant or the Hubble constant are
very weak, preferred values being low. A way to break these
degeneracies is to "cross-constrain" the parameters by combining them
with constraints from other independent data. We use the baryon
fraction determination from X-ray clusters of galaxies as an
additional constraint and show that the combined analysis leads to
strong constraints on all cosmological parameters. Using a high baryon
fraction (∼15% for ) we found a rather low Hubble
constant, values around 80 km s-1/Mpc being ruled out. Using a recent
and low baryon fraction estimation (∼10% for ) we found a
preferred model with a low Hubble constant and a high density content
(), an Einstein-de Sitter model being only weakly ruled
out
“Homme obscur” : un roman "autre" dans l'oeuvre de M. Yourcenar?
No full textDans son roman Un homme obscur, Marguerite Yourcenar paraît renier les valeurs de la culture antique et du livre, qu’elle avait révérées jusque-là ; en effet, le personnage principal, Nathanaël, semble fort bien se passer des livres et son jugement n’en est pas moins extrêmement juste et pertinent. Peut-on vraiment parler de reniement de la part de la romancière ? La lecture attentive et l’étude d’Un homme obscur font apparaître de multiples références aux grands romans de la littérature française et cette œuvre de Marguerite Yourcenar - originale et inattendue certes - n’est pas radicalement différente des précédentes
Evidence for new physics from clusters ?
No full textNew version including changes and typos corrected, accepted for publication in A&AThe abundance of local clusters is a traditional way to derive the amplitude of matter fluctuations. In the present work, by assuming that the observed baryon content of clusters is representative of the universe, we show that the mass temperature relation (M-T) can be specified for any cosmological model. This approach allows one to remove most of the uncertainty coming from M-T relation, and to provide an estimation of sigma_8 whose uncertainty is essentially statistical. The values we obtain are fortuitously almost independent of the matter density of the Universe (sigma_8 ~ 0.6-0.63) with an accuracy better than 5%. Quite remarkably, the amplitude of matter fluctuations can be also tightly constrained to similar accuracy from existing CMB measurements alone. However, the amplitude inferred in this way in a concordance model (Lambda-CDM) is significantly larger than the value derived from the above method based on X-ray clusters. Such a discrepancy would almost disappear if the actual optical thickness of the Universe was 0 but could also be alleviated from more exotic solutions: the existence of a new dark component in the Universe as massive neutrinos. However, recent other indications of sigma_8 favor a high normalization. In this case, the assumption that the baryonic content observed in clusters actually reflects the primordial value has to be relaxed : either there exists a large baryonic dark component in the Universe or baryons in clusters have undergone a large depletion during the formation of these structures. We concluded that the baryon fraction in clusters is not representative and therefore that an essential piece of the physics of baryons in clusters is missing in standard structure formation scenario
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