412 research outputs found
Investigating the flyby scenario for the HD 141569 system
HD 141569, a triple star system, has been intensively observed and studied
for its massive debris disk. It was rather regarded as a gravitationally bound
triple system but recent measurements of the HD 141569A radial velocity seem to
invalidate this hypothesis. The flyby scenario has therefore to be investigated
to test its compatibility with the observations. We present a study of the
flyby scenario for the HD141569 system, by considering 3 variants: a sole
flyby, a flyby associated with one planet and a flyby with two planets. We use
analytical calculations and perform N-body numerical simulations of the flyby
encounter. The binary orbit is found to be almost fixed by the observational
constraint on a edge-on plane with respect to the observers. If the binary has
had an influence on the disk structure, it should have a passing time at the
periapsis between 5000 and 8000 years ago and a distance at periapsis between
600 and 900 AU. The best scenario for reproducing the disk morphology is a
flyby with only 1 planet. For a 2 Mj (resp. 8 Mj) planet, its eccentricity must
be around 0.2 (resp. below 0.1). In the two cases, its apoapsis is about 130
AU. Although the global disk shape is reasonably well reproduced, some features
cannot be explain by the present model and the likehood of the flyby event
remains an issue. Dynamically speaking, HD 141569 is still a puzzling system
Thermochemistry of iron manganese oxide spinels
Oxide melt solution calorimetry has been performed on iron manganese oxide spinels prepared at high temperature. The enthalpy of formation of (MnxFe1āx)3O4 at 298 K from the oxides, tetragonal Mn3O4 (hausmannite) and cubic Fe3O4 (magnetite), is negative from x=0 to x=0.67 and becomes slightly positive for 0.670.6) spinels of intermediate compositions. The enthalpies of formation are discussed in terms of three factors: oxidationāreduction relative to the end-members, cation distribution, and tetragonality. A combination of measured enthalpies and Gibbs free energies of formation in the literature provides entropies of mixing. ĪSmix, consistent with a cation distribution in which all
trivalent manganese is octahedral and all other ions are randomly distributed for x>0.5, but the entropy of mixing appears to be smaller than these predicted values for x<0.4
The environmental Kuznets curve for deforestation: a threatened theory? A meta-analysis
Although widely studied, deforestation remains a topical and typical issue. The relationship between economic development and deforestation is still at stake. This paper presents a meta-analysis of Environmental Kuznets Curve (EKC) studies for deforestation. Using 71 studies, offering 631 estimations, we shed light on why EKC results differ. We investigate the incidence of choices made by authors (econometric strategy, deforestation measure, temporal coverage, geographical area, measure of economic development...) on the probability of finding an EKC. After a phase of work corroborating the EKC, we find a turning point after the year 2001. Building on our results, we conclude that the EKC story will not fade until theoretical alternatives will be provided
Bivariate lifetime distributions
A thorough investigation of a bivariate Gompertz hazard function for failure time (x,y) and its joint survival distribution
Uniqueness results for an ODE related to a generalized Ginzburg-Landau model for liquid crystals
We study a singular nonlinear ordinary differential equation on intervals {[}0, R) with R <= +infinity, motivated by the Ginzburg-Landau models in superconductivity and Landau-de Gennes models in liquid crystals. We prove existence and uniqueness of positive solutions under general assumptions on the nonlinearity. Further uniqueness results for sign-changing solutions are obtained for a physically relevant class of nonlinearities. Moreover, we prove a number of fine qualitative properties of the solution that are important for the study of energetic stability
QUALITE PERCĢ§UE ET SATISFACTION DES CLIENTS BUSINESS-TO-CONSUMER DE LA TELEPHONIE MOBILE EN CONTEXTE CAMEROUNAIS
Cet article sāinscrit dans le cadre de lāameĢlioration permanente de la satisfaction de la clienteĢle business-to-consumer, particulieĢrement dans le secteur de la teĢleĢphonie mobile. Son objet a eĢteĢ de mettre en exergue le roĢle modeĢrateur du traitement des reĢclamations dans la relation entre la qualiteĢ percĢ§ue et la satisfaction des clients business-to-consumer des services de teĢleĢphonie mobile en contexte camerounais. Une recherche documentaire nous a permis de cerner lāapproche conceptuelle. Dans lāapproche meĢthodologique, une enqueĢte par sondage nous a permis de collecter les donneĢes aĢ partir dāun questionnaire administreĢ aupreĢs dāun eĢchantillon de convenance constitueĢ de 399 personnes issues de lāensemble des abonneĢs aĢ la teĢleĢphonie mobile au Cameroun. Le traitement et lāanalyse de ces donneĢes se sont effectueĢs aĢ lāaide du logiciel SPSS et AMOS. Nous avons utiliseĢ le modeĢle dāeĢquations structurelles pour le test des hypotheĢses. Les principaux reĢsultats obtenus montrent que (i) les clients b- to-c de la teĢleĢphonie mobile ne sont satisfaits de la qualiteĢ de service offert par les opeĢrateurs de teĢleĢphonie mobile et (ii) que le traitement des reĢclamations influence (modeĢrateur) dans la relation entre la qualiteĢ percĢ§ue et la satisfaction globale des clients b-to-c de la teĢleĢphonie mobile en contexte camerounais
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Condensed tannin changes along the digestive tract in lambs fed with sainfoin pellets or hazelnut skins
The variable anthelmintic efficacy of condensed tannins (CT) against gastrointestinal nematodes may depend on CT concentration, composition, or fate along the digestive tract. We analyzed CT concentration and composition by acetoneāHClābutanol and thiolysis coupled to HPLC-MS in digesta and feces of lambs. Lambs had been infected with Haemonchus contortus and Trichostrongylus colubriformis and received sainfoin pellets and hazelnut skins of contrasting prodelphinidin/procyanidin ratios. The digesta and feces had lower CT concentrations than the original feeds but similar concentration patterns across the digestive compartments. The changes in assayable CT concentrations between rumen, abomasum, and small intestine may be due to complex formation between CT and other dietary components. However, the large CT disappearance (61ā85%) from feed to feces could also indicate that CT may have been structurally modified, degraded, or absorbed during digestion. Interestingly, there were no changes in the structural features of assayable CT in the digesta
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