Étude comparative et validation de modèles prédictifs de résistance thermique de contact dans le cas solide-liquide avec prise en compte de la tension superficielle

La plupart des modèles prédictifs de résistance thermique de contact portent sur les contacts solides-solides. La nature des contacts (glissant ou statique), la complexité de la description des rugosités de surface ou les niveaux de pressions de contact mises en jeu, ont conduit au développement d'un nombre important de modèles prédictifs. Cependant, ceux portant sur l’étude des contacts solides-liquides sont très rares bien que l’étude des transferts thermiques dans ce type de contacts soit d’un intérêt majeur dans de nombreuses applications: contact polymère fondu et surface métallique au cours de la mise en forme de composites, contact bitume liquide et granulat au cours de la fabrication d'enrobé bitumineux, contact solide-solide avec matériau d'interface en microélectronique. Toutefois, ces modèles nécessitent la prise en compte de propriétés adhésives des liquides sur les surfaces solides contribuant à modifier les résistances de contacts. La validation de ces modèles prédictifs nécessite des tests sur un grand nombre de matériaux de textures et de caractéristiques chimiques de surface différentes (tension superficielle, angle de contact). Dans cette étude nous présentons et comparons deux modèles prédictifs de résistance thermique de contact récemment mis au point pour les contacts solides-liquides et mettant en évidence l'influence des caractéristiques chimiques de surface ainsi que la structure topographique de l'interface solide-liquide. Ces modèles ont été confrontés à des résultats expérimentaux obtenus par mesure de résistance de contact entre un granulat très rugueux et du bitume liquide pour différentes températures de contact et pour une pression de contact modérée correspondant aux conditions d’élaboration de nouveaux procédés d'enrobés bitumineux économes en énergie. Les résultats obtenus montrent un bon accord entre les prédictions et les résultats expérimentaux obtenus

Direct mass measurements of 19B, 22C, 29F, 31Ne, 34Na and other light exotic nuclei

We report on direct time-of-flight based mass measurements of 16 light neutron-rich nuclei. These include the first determination of the masses of the Borromean drip-line nuclei $^{19}$B, $^{22}$C and $^{29}$F as well as that of $^{34}$Na. In addition, the most precise determinations to date for $^{23}$N and $^{31}$Ne are reported. Coupled with recent interaction cross-section measurements, the present results support the occurrence of a two-neutron halo in $^{22}$C, with a dominant $\nu2s_{1/2}^2$ configuration, and a single-neutron halo in $^{31}$Ne with the valence neutron occupying predominantly the 2$p_{3/2}$ orbital. Despite a very low two-neutron separation energy the development of a halo in $^{19}$B is hindered by the 1$d_{5/2}^2$ character of the valence neutrons.Comment: 5 page

Structure of unbound neutron-rich 9^{9}He studied using single-neutron transfer

The 8He(d,p) reaction was studied in inverse kinematics at 15.4A MeV using the MUST2 Si-CsI array in order to shed light on the level structure of 9He. The well known 16O(d,p)17O reaction, performed here in reverse kinematics, was used as a test to validate the experimental methods. The 9He missing mass spectrum was deduced from the kinetic energies and emission angles of the recoiling protons. Several structures were observed above the neutron-emission threshold and the angular distributions were used to deduce the multipolarity of the transitions. This work confirms that the ground state of 9He is located very close to the neutron threshold of 8He and supports the occurrence of parity inversion in 9He.Comment: Exp\'erience GANIL/SPIRAL1/MUST

Lifetime measurements in 63^{63}Co and 65^{65}Co

Lifetimes of the $9/2^-_1$ and $3/2^-_1$ states in $^{63}$Co and the $9/2^-_1$ state in $^{65}$Co were measured using the recoil distance Doppler shift and the differential decay curve methods. The nuclei were populated by multi-nucleon transfer reactions in inverse kinematics. Gamma rays were measured with the EXOGAM Ge array and the recoiling fragments were fully identified using the large-acceptance VAMOS spectrometer. The E2 transition probabilities from the $3/2^-_1$ and $9/2^-_1$ states to the $7/2^-$ ground state could be extracted in $^{63}$Co as well as an upper limit for the $9/2^-_1\rightarrow7/2^-_1$ $B$(E2) value in $^{65}$Co. The experimental results were compared to large-scale shell-model calculations in the $pf$ and $pfg_{9/2}$ model spaces, allowing to draw conclusions on the single-particle or collective nature of the various states.Comment: 8 pages, 8 figures, 1 table, accepted for publication in Physical Review

Synthesis of Specimen Preparation and Curing Processes for Cold Recycled Asphalt Mixes

The process of cold recycling (CR) is becoming method of choice for pavement rehabilitation due to significantly added environmental and economic benefits. Understanding and standardization of specimen preparation and curing processes are critical to replicate field conditions in lab. This paper presents an extensive synthesis of various specimen preparation and curing processes for cold recycled asphalt mixes. Topics synthesized include RAP, emulsion/bitumen and aggregate preparation, mixing processes, pre- and post- compaction curing, compaction and mechanical testing. This paper was developed through efforts of cold recycling task group (TG6) of RILEM Technical Committee on Testing and Characterization of Sustainable Innovative Bituminous Materials and Systems (TC-SIB)

Spectroscopy of 28^{28}Na: shell evolution toward the drip line

Excited states in $^{28}$Na have been studied using the $\beta$-decay of implanted $^{28}$Ne ions at GANIL/LISE as well as the in-beam $\gamma$-ray spectroscopy at the NSCL/S800 facility. New states of positive (J$^{\pi}$=3,4$^+$) and negative (J$^{\pi}$=1-5$^-$) parity are proposed. The former arise from the coupling between 0d$\_{5/2}$ protons and a 0d$\_{3/2}$ neutron, while the latter are due to couplings with 1p$\_{3/2}$ or 0f$\_{7/2}$ neutrons. While the relative energies between the J$^{\pi}$=1-4$^+$ states are well reproduced with the USDA interaction in the N=17 isotones, a progressive shift in the ground state binding energy (by about 500 keV) is observed between $^{26}$F and $^{30}$Al. This points to a possible change in the proton-neutron 0d$\_{5/2}$-0d$\_{3/2}$ effective interaction when moving from stability to the drip line. The presence of J$^{\pi}$=1-4$^-$ negative parity states around 1.5 MeV as well as of a candidate for a J$^{\pi}$=5$^-$ state around 2.5 MeV give further support to the collapse of the N=20 gap and to the inversion between the 0f$\_{7/2}$ and 1p$\_{3/2}$ levels below Z=12. These features are discussed in the framework of Shell Model and EDF calculations, leading to predicted negative parity states in the low energy spectra of the $^{26}$F and $^{25}$O nuclei.Comment: Exp\'erience GANIL/LISE et NSCL/S80

Search for a long lived component in the reaction U+U near the Coulomb barrier

Expérience GANILInternational audienceWe performed an experiment to search for a signature of a long living component in the collision of $^{238}$U + $^{238}$U between 6.09 and 7.35A MeV. The experiment was performed at GANIL using the spectrometer VAMOS, tuned for observing reactions with kinematics similar to fusion-fission events. Theoretical calculations indicate that if a long living component would exist for this reaction, the most probable fission channel of such a giant system would be via the emissionof quasi-lead nuclei. We detected events of such a category in the focal plane of VAMOS. These events present an excitation function growing as a function of the bombarding energy

Resonances of 6He via the 8He(p,t)6He reaction

CERN-Proceedings-2010-001 available at http://www.fluka.org/Varenna2009/procmat.htmInternational audienceWe investigated the low-lying spectroscopy of 6He via the 2-neutron transfer reaction induced by the 8He SPIRAL beam at 15.4 A.MeV on a proton-rich target. The light charged recoil particles produced by the direct reactions were measured using theMUST2 Si-strip telescope array. Two new resonances were observed above the known 2+ state in 6He, and the angular momentum transfer was deduced through the analysis of the angular distributions. Results are discussed in comparison with the recent calculations of various nuclear structure theories which include the coupling to the continuum technique and to the ones which give an understanding of the cluster correlations in the light weakly-bound nuclei