245 research outputs found
Measurement of the Radius of Neutron Stars with High S/N Quiescent Low-mass X-ray Binaries in Globular Clusters
This paper presents the measurement of the neutron star (NS) radius using the
thermal spectra from quiescent low-mass X-ray binaries (qLMXBs) inside globular
clusters (GCs). Recent observations of NSs have presented evidence that cold
ultra dense matter -- present in the core of NSs -- is best described by
"normal matter" equations of state (EoSs). Such EoSs predict that the radii of
NSs, Rns, are quasi-constant (within measurement errors, of ~10%) for
astrophysically relevant masses (Mns > 0.5 Msun). The present work adopts this
theoretical prediction as an assumption, and uses it to constrain a single Rns
value from five qLMXB targets with available high signal-to-noise X-ray
spectroscopic data. Employing a Markov-Chain Monte-Carlo approach, we produce
the marginalized posterior distribution for Rns, constrained to be the same
value for all five NSs in the sample. An effort was made to include all
quantifiable sources of uncertainty into the uncertainty of the quoted radius
measurement. These include the uncertainties in the distances to the GCs, the
uncertainties due to the Galactic absorption in the direction of the GCs, and
the possibility of a hard power-law spectral component for count excesses at
high photon energy, which are observed in some qLMXBs in the Galactic plane.
Using conservative assumptions,we found that the radius, common to the five
qLMXBs and constant for a wide range of masses, lies in the low range of
possible NS radii, Rns=9.1(+1.3)(-1.5) km (90%-confidence). Such a value is
consistent with low-res equations of state. We compare this result with
previous radius measurements of NSs from various analyses of different types of
systems. In addition, we compare the spectral analyses of individual qLMXBs to
previous works.Comment: Accepted to Apj. 31 pages, 17 figures, 8 table
Evolution of Exoplanets and their Parent Stars
Studying exoplanets with their parent stars is crucial to understand their
population, formation and history. We review some of the key questions
regarding their evolution with particular emphasis on giant gaseous exoplanets
orbiting close to solar-type stars. For masses above that of Saturn, transiting
exoplanets have large radii indicative of the presence of a massive
hydrogen-helium envelope. Theoretical models show that this envelope
progressively cools and contracts with a rate of energy loss inversely
proportional to the planetary age. The combined measurement of planetary mass,
radius and a constraint on the (stellar) age enables a global determination of
the amount of heavy elements present in the planet interior. The comparison
with stellar metallicity shows a correlation between the two, indicating that
accretion played a crucial role in the formation of planets. The dynamical
evolution of exoplanets also depends on the properties of the central star. We
show that the lack of massive giant planets and brown dwarfs in close orbit
around G-dwarfs and their presence around F-dwarfs are probably tied to the
different properties of dissipation in the stellar interiors. Both the
evolution and the composition of stars and planets are intimately linked.Comment: appears in The age of stars - 23rd Evry Schatzman School on Stellar
Astrophysics, Roscoff : France (2013
Conception et validation d'une matrice 2D de détecteurs à fibres scintillantes plastiques pour la dosimétrie en radiothérapie externe
Cette thĂšse porte sur le dĂ©veloppement et la caractĂ©risation dâune matrice 2D de dĂ©tecteurs Ă fibres scintillantes plastiques pour la dosimĂ©trie des faisceaux de photons dâĂ©nergie mĂ©gavoltage utilisĂ©s en radiothĂ©rapie. Les propriĂ©tĂ©s visĂ©es lors de la conception du dĂ©tecteur matriciel furent la justesse, lâĂ©quivalence Ă lâeau, une bonne rĂ©solution spatiale, un nombre Ă©levĂ© de dĂ©tecteurs, et une lecture Ă haute frĂ©quence des doses dĂ©posĂ©es. La premiĂšre partie de cette thĂšse fut consacrĂ©e Ă amĂ©liorer la justesse de la mĂ©thode spectrale utilisĂ©e pour corriger lâeffet Cerenkov. Deux procĂ©dures aptes Ă extraire de façon juste les coefficients dâĂ©talonnage ont Ă©tĂ© dĂ©veloppĂ©es. Les rĂ©sultats ont montrĂ© que cette mĂ©thode peut corriger lâeffet Cerenkov avec une justesse de 1%. La seconde partie de cette thĂšse fut consacrĂ©e Ă la conception, la rĂ©alisation et la validation dâun dĂ©tecteur matriciel composĂ© de 781 dosimĂštres insĂ©rĂ©s dans un fantĂŽme eau-Ă©quivalent. Un systĂšme optique a aussi Ă©tĂ© dĂ©veloppĂ©. Il fut dĂ©terminĂ© quâen moyenne, lâĂ©cart-type des mesures est infĂ©rieure Ă 1 % pour les doses supĂ©rieures Ă 6.3 cGy. Il fut aussi dĂ©montrĂ© que les distributions de dose ne sont pas perturbĂ©es (Ă +/- 1.1 %) par la prĂ©sence des dosimĂštres Ă lâintĂ©rieur du fantĂŽme. La caractĂ©risation de la dĂ©pendance angulaire a rĂ©vĂ©lĂ©e que les incidences des faisceaux ont peu dâimpact sur la justesse des mesures. Le dĂ©tecteur matriciel a aussi Ă©tĂ© validĂ© dans le contexte de la radiothĂ©rapie Ă intensitĂ© modulĂ©e (IMRT). Onze plans de traitement ont Ă©tĂ© mesurĂ©s et les rĂ©sultats ont montrĂ© dâexcellents accords avec les doses calculĂ©es Ă lâaide dâalgorithmes convolution-superposition ou mesurĂ©es avec des films radiochromiques. La sensibilitĂ© et la spĂ©cificitĂ© du dĂ©tecteur matriciel aux erreurs de position dâune lame et dâun banc de lame dâun collimateur multi-lames (MLC) ont Ă©tĂ© dĂ©terminĂ©es en appliquant la thĂ©orie de dĂ©tection du signal. Cette Ă©tude conclut que les dosimĂštres Ă fibres scintillantes plastiques pourraient permettre dâamĂ©liorer la qualitĂ© de la dosimĂ©trie en IMRT, en raison de leurs avantages par rapport aux autres dosimĂštres, tels que lâĂ©quivalence Ă lâeau, une haute rĂ©solution spatiale, la lecture Ă haute frĂ©quence, et une trĂšs faible dĂ©pendance angulaire.This thesis deals with the development and characterization of a 2D array of plastic scintillation detectors for the dosimetry of megavoltage energy photon beams used in radiation therapy. The characteristics sought with the detector array are accuracy, water-equivalence, a good spatial resolution, a large number of detectors and a high frequency readout of the doses deposited. The first part of this thesis is devoted to the improvement of the accuracy of the spectral method used to correct the Cerenkov effect. A study has determined the optimal attenuation characteristics for the optical fibers and two procedures able to accurately extract the calibration coefficients were developed. Measurements performed in various situations showed that this method can correct the Cerenkov effect with an accuracy of 1 %. The second part of this thesis relates to the design, realization and validation of a detector array consisting of 781 plastic scintillation detectors inserted vertically into a plane of a water-equivalent phantom. An novel optical system was also designed. It was determined that, on average, the standard deviation of measurements is smaller than 1 % for doses deposited greater than 6.3 cGy. It was also demonstrated that the dose distributions are not perturbed (within +/- 1.1 %) by the presence of the detectors inside the phantom. The characterization of the angular dependence showed that the incidences of radiation beams have very little effect on the accuracy of measurements. The detector array was also validated in the context of intensity-modulated radiation therapy (IMRT). Eleven treatment plans were measured and the results showed excellent agreements with dose distributions calculated with convolution-superposition algorithms or measured with radiochromic films. The sensitivity and specificity of the detector array to position errors of one leaf and one leaf bank of a multileaf collimator (MLC) were also determined by applying the principles of signal detection theory. The study concluded that plastic scintillation detectors could allow improving the quality of dosimetry in IMRT, due to their advantages compared to other dosimeters, such as water-equivalence, high frequency readout, high spatial resolution and a very low angular dependence
La réussite criminelle des participants à la fraude financiÚre en ligne
Le carding est un pheÌnomeÌne cybercriminel de par lequel des cyberdeÌlinquants (appeleÌs carders) vont compromettre et utiliser frauduleusement des donneÌes financieÌres et bancaires. De nombreuses entiteÌs priveÌes ou publiques ont mis en eÌvidence l'importance des pertes moneÌtaires occasionneÌes par ce nouveau type de criminaliteÌ. D'un point de vu criminologique, peu de recherches acadeÌmiques se sont pencheÌes sur l'ampleur de ce pheÌnomeÌne et plus particulieÌrement sur la reÌussite criminelle des carders.
Pour combler ce manque de connaissances, ce projet de recherche a pour objectif de comprendre la reÌussite criminelle des carders en observant l'impact de leurs caracteÌristiques personnelles et sociales sur leurs revenus criminels. Les diffeÌrentes variables mobiliseÌes relatent entre autres les activiteÌs marchandes ou encore les caracteÌristiques sociodeÌmographiques des carders interrogeÌs. Pour ce faire, un sondage en ligneÌ, heÌbergeÌ sur Tor, a eÌteÌ meneÌ. Au total, 49 sondages complets ont eÌteÌ collecteÌs pour eÌtre analyseÌs.
En s'attelant aÌ deÌcrire les caracteÌristiques personnelles et sociales des carders, ce travail a eÌteÌ en mesure de mettre aÌ jour les connaissances preÌalablement acquises sur les carders et de reÌpondre aÌ des manques de consensus sur certains pans des activiteÌs de ces cyberdeÌlinquants. L'ensemble des reÌsultats reÌveÌlent que peu de carders affichent une reÌussite criminelle eÌleveÌe et qu'une minoriteÌ d'entre eux gagnent de forts revenus. La reÌussite crimnelle des carders s'explique par le fait de disposer de compeÌtences speÌcialiseÌes, de beÌneÌficier d'une bonne expeÌrience, d'utiliser des forums de discussion en ligne ou encore d'occuper des roÌles centraux sur les lieux de convergence virtuels. Outre le fait d'apporter des reÌponses quant aÌ ces preÌdicteurs sur la reÌussite criminelle des carders, ce projet de recherche permet de constater les apports et les faiblesses de l'utilisation d'un sondage pour collecter des donneÌes dans une eÌcosysteÌme cybercriminel.Carding is a criminal phenomenon which consists of compromising financial data in order to do fraudulent transactions. Several private and public parties highlighted the size of the loss caused by this new form of criminality. From the criminological angle, little research is available in the size and scope of the phenomenon, particularly on the criminal achievement of this kind of online offenders (called carders).
To fill this gap, this research project is aimed at understand the criminal achievement of carders by observing the impact of their personal and social characteristics on their criminal income. Theses variables relate among others to their market activities or their sociodemographic. To do so, an online survey, hosted on Tor, was conducted. A total of 49 completed surveys were collected to do our analysis.
By describing these personal and social characteristics, this work has been able to update our knowledge about carders and to address gaps about certain part of what we known about carding. Overall, the results shown that few carders can claim a good criminal achievement and that a minority of them can earn large amounts of money. Experience, speciliazed skills, the use of online forums or play the role of broker explained the criminal achievement among carders.Apart from the fact that our study brings some answers about those predictors, this project highlights the strengths and weaknesses of using an online survey to collect data from a criminal ecosystem
Extracting the hydrodynamic resistance of droplets from their behavior in microchannel networks
The overall traffic of droplets in a network of microfluidic channels is
strongly influenced by the liquid properties of the moving droplets. In
particular, the effective hydrodynamic resistance of individual droplets plays
a key role in their global behavior. We here propose two simple and low-cost
experimental methods for measuring this parameter by analyzing the dynamics of
a regular sequence of droplets injected into an "asymmetric loop" network. The
choice of a droplet taking either route through the loop is influenced by the
presence of previous droplets which modulate the hydrodynamic resistance of the
branches they are sitting in. We propose to extract the effective resistance of
a droplet from easily observable time series, namely from the choices the
droplets make at junctions and from the inter-droplet distances. This becomes
possible when utilizing a recently proposed theoretical model, based on a
number of simplifying assumptions. We here present several sets of measurements
of the hydrodynamic resistance of droplets, expressed in terms of a "resistance
length". The aim is twofold, (1) to reveal its dependence on a number of
parameters, such as the viscosity, the volume of droplets, their velocity as
well as the spacing between them. At the same time (2), by using a standard
measurement technique, we compare the limitations of the proposed methods. As
an important result of this comparison we obtain the range of validity of the
simplifying assumptions made in the theoretical model.Comment: 11 pages, 11 figure
Les relations entre épargne salariale et rémunérations : une analyse des stratégies et de la cohérence des pratiques
Cette communication s'inscrit dans la lignĂ©e des travaux qui Ă©tudient le lien entre partage des profits et niveau des salaires. Si les travaux antĂ©rieurs se sont largement focalisĂ©s sur les enjeux de l'intĂ©ressement, il paraĂźt intĂ©ressant de considĂ©rer, au travers du cas français, la diversitĂ© des dispositifs d'Ă©pargne salariale (ES), en particulier le Plan d'Ă©pargne et les pratiques d'abondement et de versements volontaires des salariĂ©s. En croisant les donnĂ©es de l'enquĂȘte REPONSE menĂ©e par la DARES en 2004 et de l'enquĂȘte PIPA de 2005 portant sur les pratiques d'ES des entreprises françaises, nous avons, sur un Ă©chantillon final de 1143 entreprises, construit une typologie originale fondĂ©e sur le caractĂšre volontaire et l'intensitĂ© des politiques d'ES menĂ©es par les entreprises. L'objectif Ă©tait ensuite, Ă l'aide de modĂšles de rĂ©gression, de chercher la cohĂ©rence entre l'intensitĂ© des politiques d'ES et les pratiques salariales par ailleurs, en considĂ©rant non seulement les caractĂ©ristiques de niveau et de dispersion des salaires mais aussi les modalitĂ©s de rĂ©munĂ©ration. Nos rĂ©sultats valident la thĂšse selon laquelle les pratiques d'ES plus intenses auraient plutĂŽt tendance Ă ĂȘtre associĂ©es Ă un niveau de salaire plus Ă©levĂ© et mettent en Ă©vidence l'intĂ©gration de la politique d'ES dans une stratĂ©gie de rĂ©munĂ©ration globale cohĂ©rente, en lien avec les pratiques d'augmentations et de primes aux performances collectives ou individuelles
Kepler-424 b: A "lonely" hot Jupiter that found a companion
Peer reviewedFinal Accepted Versio
EyeSchool: an educational assistive technology for people with disabilities - Passing from single actors to multiple-actor environment
International audienceSince 2005, public policy in France has strongly been encouraging young people with disabilities inclusion within the regular school system. This has found a direct application through technical innovation, intended to help students being more independent within their learning activities. In this context, the purpose of this paper is to underline the manner in which using assistive information and communication technologies may improve the inclusive education for people with disabilities. The case study we present underlines the complexity of the social world into which the use of a precise assistive tool takes it place
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