595 research outputs found
Synthesis of Tetrathiafulvalene-Containing Zirconium (IV) Pincers and Metallocavitands for Hosting Fullerenes
The synthesis and spectroscopic characterization of zirconium(IV) dicarboxylate 1 and metallocavitand 2 are described. Encapsulation studies of fullerenes C60 and C70 were performed using UVâVis spectroscopy in chlorobenzene, toluene, benzene, carbon disulfide and in a mixture of toluene/dichloromethane. UVâVis titrations have shown that the binding abilities of the hosts toward fullerene C70 are considerably higher than those obtained for fullerene C60
Le traitement de l'incertitude en gestion de crise : mise en place d'une veille stratégique du territoire
National audienceThe catastrophic events of these last years such as the catastrophe of AZF in 2001 or the various terrorist attacks made evolve the concept of risk by integrating dimensions of crisis and threat. The damages which result from this do not limit to a delimited zone but impact the whole society. The crisis organizations are destabilized by the unusual feature of these situations. The managers must anticipate these situations as soon as possible; react efficiently and in a fast way in order to avoid the consequences of the crisis. However, the decision makers need a fast, clear and structured expertise allowing reducing uncertainties related to the situation. The objective of this project is to present, after a state of the art on the crises, a methodology of decision-making aid to help the Prefects through a potential of crisis usable in vigilance and during the emergency phase.Les évÚnements catastrophiques de ces derniÚres années tels que la catastrophe d'AZF en 2001 ou les différents attentats terroristes ont fait évoluer le concept de risque en lui intégrant les dimensions de crise et de menace. Les dommages qui en découlent ne se limitent pas à une zone délimitée mais impactent la société dans son ensemble. Les organisations gestionnaires des crises sont déstabilisées en raison du caractÚre inhabituel de ces situations. Les gestionnaires se doivent d'anticiper au plus tÎt ces situations, de réagir efficacement et de maniÚre rapide afin d'éviter une crise. Or, les décideurs ont besoin d'une expertise rapide, claire et structurée permettant de réduire les incertitudes liées à la situation. L'objectif de ce projet est de présenter, aprÚs un état de l'art sur les situations de crise, une méthodologie d'aide à la décision permettant d'apporter de la lisibilité aux préfets à travers l'établissement d'un potentiel de crise utilisable en veille et pendant la phase d'urgence
Zirconium(IV) metallocavitands as blue-emitting materials
A series of zirconium-carboxylate metallocavitands with the general formula [(CpZr)3(ÎŒ-Îș2,OâČ,OâłCR)3(ÎŒ3-O)(ÎŒ2-OH)3]Cl (Cp = cyclopentadienyl; R = C5H4N (5), C6H7N (6), C18H14N (7), and C18H12N (8)) were synthesized in moderate to high yields (40â83%) by reacting the corresponding carboxylic acids 1â4 with Cp2ZrCl2 in a self-assembly procedure at room temperature. The metallocavitands were characterized using 1H and 13C NMR spectroscopy and by single-crystal X-ray diffraction. Complexes 7 and 8 exhibit efficient photoluminescence properties in solution. The photoluminescence peak of 7 was observed at 464 nm and that of 8 at 422 nm with respective quantum yields in solution of 87 and 65%
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
ETUDE DES SĂDIMENTS COTIERS DU CAP CORSE: RECONSTRUCTION PALĂOENVIRONNEMENTALE ET SUIVI DE LA CONTAMINATION EN ĂLĂMENTS TRACES MĂTALLIQUES AU COURS DE LA PĂRIODE HISTORIQUE
Les sĂ©diments sont dâexcellentes archives de la contamination de notre environnement. Depuis lâAntiquitĂ©, les activitĂ©s humaines gĂ©nĂšrent des aĂ©rosols anthropiques enrichis en mĂ©taux lourds (e.g. Pb, Zn, Cu, Cd, Hg) ou associĂ©s (As, Sb). Ces polluants mĂ©talliques se mĂ©langent aux aĂ©rosols naturels (altĂ©ration des roches) et leurs retombĂ©es sont incorporĂ©es dans les sols et les sĂ©diments oĂč ils sont prĂ©servĂ©s (Boyd, 2004). Sur des sĂ©diments datĂ©s, une approche gĂ©ochimique permet de quantifier lâapport anthropique en Ă©lĂ©ments mĂ©talliques par rapport aux sources naturelles et de reconstituer lâhistorique de la pollution.
Les cĂŽtes mĂ©diterranĂ©ennes sont caractĂ©risĂ©es par dâintenses Ă©changes commerciaux, et ce depuis lâAntiquitĂ©. Nous proposons une reconstruction palĂ©oenvironnementale ainsi quâun suivi de la contamination anthropique au cours de la pĂ©riode historique pour diffĂ©rents sites du Cap Corse (France ; Figure 1). Cette rĂ©gion de MĂ©diterranĂ©e se caractĂ©rise par une riche activitĂ© Ă©conomique au cours de la pĂ©riode historique. Depuis le VIĂšme siĂšcle, la Corse a Ă©tĂ© colonisĂ©e successivement par les Grecs, les Carthaginois, les Etrusques puis par les Romains. En milieu continental, des tĂ©moins archĂ©ologiques (sĂ©pulture, oppidum, chapelle) attestent dâune occupation de cette zone sur une pĂ©riode assez longue. Cependant de nombreuses interrogations subsistent quant Ă lâimportance des Ă©tablissements, leurs pĂ©riodes dâoccupation, leurs activitĂ©s Ă©conomiques et leurs rapports commerciaux avec les autres citĂ©s du Cap Corse et des cĂŽtes mĂ©diterranĂ©ennes (de La BriĂšre, 2010).
Des carottes de 1 m Ă 1,5 m ont Ă©tĂ© prĂ©levĂ©es Ă la tariĂšre dans diffĂ©rents sites du Cap Corse. Les concentrations en Ă©lĂ©ments majeurs et en Ă©lĂ©ments traces mĂ©talliques ont Ă©tĂ© mesurĂ©es par spectromĂ©trie de masse (ICP-MS), activation neutronique (INAA) et par XRF core scanner. Les datations 14C rĂ©alisĂ©es sur des macrorestes de matiĂšres vĂ©gĂ©tales et charbons montrent que ces carottes couvrent toute la pĂ©riode historique, Ă lâexception de celle prĂ©levĂ©e Ă MĂ©ria qui ne couvre quâenviron 300 ans. Cette carotte a Ă©galement la particularitĂ© de contenir dâimportantes concentrations en mĂ©taux lourds tels que le Sb (2000 ppm) et lâAs (300 ppm). Cette contamination est dâorigine locale et liĂ©e Ă la prĂ©sence dâune ancienne mine dâantimoine Ă 2 km en amont de MĂ©ria. Afin dâobtenir un enregistrement sur les 2000 derniĂšres annĂ©es, un carottage plus long sera rĂ©alisĂ© lors dâune nouvelle campagne de terrain. Dâautres carottages seront Ă©galement rĂ©alisĂ©s entre la mine et la cĂŽte actuelle afin dâobserver la variation spatiale dans le but de quantifier lâimpact environnemental des activitĂ©s humaines locales et rĂ©gionales
Tenure, Experience, Human Capital and Wages:A Tractable Equilibrium Search Model of Wage Dynamics
We develop and estimate an equilibrium job search model of worker careers, allowing for human capital accumulation, employer heterogeneity and individual-level shocks. Wage growth is decomposed into contributions of human capital and job search, within and between jobs. Human capital accumulation is largest for highly educated workers. The contribution from job search to wage growth, both within- and between-job, declines over the first ten years of a career â the âjob-shoppingâ phase of a working life â after which workers settle into high-quality jobs using outside offers to generate gradual wage increases, thus reaping the benefits from competition between employers
DHWM: A Scheme for Managing Watermarking Keys in the Aquarelle Multimedia Distributed System
International audienceThis paper presents secure architecture and protocols for managing Intellectual Property Rights in distributed content databases in a close environment. The implementation of this architecture is cur- rently being realized in the European project AQUARELLE. Registered users will access on the Internet to high value content through secure servers. The main interest of this paper is protocols and architecture de- veloped for using watermarking technologies, with a clever and efficient key management based on the Diffie-Hellman (DH) protocol and Trusted Third Parties (TTP). This paper presents a short survey of watermarking technologies. Next Aquarelle background is specified, along with the chosen watermarking algorithm, which is convenient for the project. Next the DHWM key exchange is presented, based on the simple idea that watermarking and verification can be separated. This scheme uses the Diffie-Hellman key- exchange protocol. Next some hints on the implementation of the scheme and on its correctness are given
Synthesis of carboxylate Cp*Zr(IV) species : towards the formation of novel metallocavitands
With the intent of generating metallocavitands isostructural to species [(CpZr)3(ÎŒ(3)-O)(ÎŒ(2)-OH)3(ÎșO,O,ÎŒ(2)-O2C(R))3](+), the reaction of Cp*2ZrCl2 and Cp*ZrCl3 with phenylcarboxylic acids was carried out. Depending on the reaction conditions, five new complexes were obtained, which consisted of Cp*2ZrCl(Îș(2)-OOCPh) (1), (Cp*ZrCl(Îș(2)-OOCPh))2(ÎŒ-Îș(2)-OOCPh)2 (2), [(Cp*Zr(Îș(2)-OOCPh))2(ÎŒ-Îș(2)-OOCPh)2(ÎŒ(2)-OH)2]·Et2O (3·Et2O), [[Cp*ZrCl2](ÎŒ-Cl)(ÎŒ-OH)(ÎŒ-O2CC6H5)[Cp*Zr]]2(ÎŒ-O2CC6H5)2 (4), and [Cp*ZrCl4][(Cp*Zr)3(Îș2-OOC(C6H4Br)3(ÎŒ3-O)(ÎŒ2-Cl)2(ÎŒ2-OH)] [5](+)[Cp*ZrCl4](-). The structural characterization of the five complexes was carried out. Species 3·Et2O exhibits host-guest properties where the diethyl ether molecule is included in a cavity formed by two carboxylate moieties. The secondary interactions between the cavity and the diethyl ether molecule affect the structural parameters of the complex, as demonstrated be the comparison of the density functional theory models for 3 and 3·Et2O. Species 5 was shown to be isostructural to the [(CpZr)3(ÎŒ(3)-O)(ÎŒ(2)-OH)3(ÎșO,O,ÎŒ(2)-O2C(R))3](+) metallocavitands
Synthesis of 3,6-Divinyl-1,2,4,5-Tetrazine, the First Member of the Elusive Vinyltetrazine Family
International audienceThe synthesis of the first vinyltetrazine derivative is Âdescribed. 3,6-Divinyl-1,2,4,5-tetrazine was obtained following a methodology involving cyclization from an imidate and use of 2-phenylsulfonylethyl groups as masked vinyl entities. The first properties of this unique compound are reported
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