Azimuthal Asymmetry of Prompt Photons in Nuclear Collisions

The azimuthal elliptic asymmetry v2 observed in heavy ion collisions, is usually associated with properties of the medium created in the final state. We compute the azimuthal asymmetry which is due to multiple interactions of partons at the initial stage of nuclear collisions, and which is also present in $pA$ collisions. In our approach the main source of azimuthal asymmetry is the combination of parton multiple interactions with the steep variation of the nuclear density at the edge of nuclei. We apply the light-cone dipole formalism to compute the azimuthal asymmetry of prompt photons yield from parton-nucleus, proton-nucleus and nucleus-nucleus collisions at the RHIC energy.Comment: 13 pages, 4 figures, Eq.(4) corrected, figures and references updated. The version to appear in Nucl. Phys.

Perturbation theories for the S=1/2 spin ladder with four-spin ring exchange

The isotropic S=1/2 antiferromagnetic spin ladder with additional four-spin ring exchange is studied perturbatively in the strong coupling regime with the help of cluster expansion technique, and by means of bosonization in the weak coupling limit. It is found that a sufficiently large strength of ring exchange leads to a second-order phase transition, and the shape of the boundary in the vicinity of the known exact transition point is obtained. The critical exponent for the gap is found to be $\eta\simeq1$, in agreement both with exact results available for the dimer line and with the bosonization analysis. The phase emerging for high values of the ring exchange is argued to be gapped and spontaneously dimerized. The results for the transition line from strong coupling and from weak coupling match with each other naturally.Comment: 8 pages, 4 figures, some minor changes in text and reference

Enhancement of Hydroxyapatite Dissolution through Krypton Ion Irradiation

International audienceHydroxyapatite (HA) synthesized by a wet chemical route was subjected to heavy ion irradiation, using 4 MeV Krypton ions (Kr 17+) with ion fluence ranging from 1×10 13 to 1×10 15 ions/cm 2. Glancing incidence X-ray diffraction (GIXRD) results confirmed the phase purity of irradiated HA with a moderate contraction in lattice parameters, and further indicated irradiation-induced structural disorder, evident by a broadening of diffraction peaks. High-resolution transmission electron microscopy (HRTEM) observations indicated that the applied Kr irradiation induced significant damage in the hydroxyapatite lattice. Specifically, cavities were observed with their diameter and density varying with irradiation fluences while a radiation-induced crystalline-to-amorphous transition with increasing ion dose was identified. Raman and X-ray photoelectron spectroscopy (XPS) analysis further indicated the presence of irradiation-induced defects. Compositional analysis of pristine and irradiated materials following immersion in Tris (pH 7.4, 37℃) buffer showed that dissolution in vitro was enhanced by irradiation, reaching a peak for 0.1dpa. We examined the effects of irradiation on the early stages of the mouse osteoblast-like cells (MC3T3-E) response. A cell counting kit-8 assay (CCK-8 test) was carried out to investigate the cytotoxicity of samples, and viable cells can be observed on the irradiated materials.L'hydroxyapatite (HA) synthétisée par voie chimique a été soumise à une irradiation ionique lourde, en utilisant des ions Krypton 4 MeV (Kr 17+) avec une fluence ionique allant de 1 × 10 13 à 1 × 10 15 ions / cm 2. Incidence du regard X- Les résultats de la diffraction des rayons (GIXRD) ont confirmé la pureté de phase de l'AH irradié avec une contraction modérée des paramètres du réseau et ont en outre indiqué un trouble structurel induit par l'irradiation, évident par un élargissement des pics de diffraction. Des observations en microscopie électronique à transmission à haute résolution (HRTEM) ont indiqué que l'irradiation au Kr appliquée a induit des dommages importants dans le réseau d'hydroxyapatite. Plus précisément, des cavités ont été observées avec leur diamètre et leur densité variant avec les fluences d'irradiation tandis qu'une transition cristalline-amorphe induite par le rayonnement avec une dose ionique croissante a été identifiée. L'analyse par spectroscopie photoélectronique Raman et X (XPS) a en outre indiqué la présence de défauts induits par l'irradiation. L'analyse de la composition des matériaux vierges et irradiés après immersion dans du tampon Tris (pH 7,4, 37 ℃) a montré que la dissolution in vitro était améliorée par irradiation, atteignant un pic de 0,1 dpa. Nous avons examiné les effets de l'irradiation sur les premiers stades de la réponse des cellules de type ostéoblaste de souris (MC3T3-E). Un test de comptage de cellules kit 8 (test CCK-8) a été réalisé pour étudier la cytotoxicité des échantillons, et des cellules viables peuvent être observées sur les matériaux irradiés

Aperçu nanostructural du comportement en dissolution de l'hydroxyapatite dopée au Sr

International audienceIn this study, high-resolution transmission electron microscopy (HRTEM) was employed to characterize the nanostructure of strontium-substituted hydroxyapatite (Sr-HA) and its evolution following in vitro immersion in physiological solutions. HRTEM images showed that the substitution of Sr induced local distortions in the hydroxyapatite (HA) lattice: minor levels of edge dislocations were detected at low doping contents of Sr ions (1 at %); when the Sr content exceeded 10 at%, the density of grain boundaries increased notably and triple junctions were clearly observed. The dissolution of undoped HA was initiated at crystallite surfaces, whereas the dissolution of Sr-HA started around grain boundaries. Acicular nanocrystal reprecipitation was observed on grain surfaces immersed in simulated body fluid (SBF), while not in dilute hydrochloric acid (HCl). These findings suggest appropriate levels of Sr incorporation can introduce imperfections in the crystal structure of apatite and thus enhance its dissolution rate towards enhanced physicochemical performance in biomedical applicationshttps://doi.org/10.1016/j.jeurceramsoc.2018.07.056Dans cette étude, la microscopie électronique à transmission à haute résolution (HRTEM) a été utilisée pour caractériser la nanostructure de l'hydroxyapatite substituée au strontium (Sr-HA) et son évolution après immersion in vitro dans des solutions physiologiques. Les images HRTEM ont montré que la substitution des distorsions locales induites par le Sr dans le réseau d'hydroxyapatite (HA): des niveaux mineurs de dislocations de bords ont été détectés à de faibles teneurs en dopage d'ions Sr (1 at%); lorsque la teneur en Sr dépassait 10% at%, la densité des joints de grains augmentait de manière notable et des triple jonctions étaient clairement observées. La dissolution de l'HA non dopée a été initiée au niveau des surfaces de cristallites, alors que la dissolution de Sr-HA a commencé autour des joints de grains. Une reprécipitation aciculaire de nanocristaux a été observée sur des surfaces de grains immergées dans un fluide corporel simulé (SBF), mais non dans de l'acide chlorhydrique dilué (HCl). Ces découvertes suggèrent que des niveaux appropriés d’incorporation de Sr peuvent introduire des imperfections dans la structure cristalline de l’apatite et ainsi augmenter sa vitesse de dissolution afin d’améliorer les performances physicochimiques dans les applications biomédicales.https://doi.org/10.1016/j.jeurceramsoc.2018.07.05

Influence of temperature gradients on tunnel junction thermometry below 1 K: cooling and electron-phonon coupling

We have studied thermal gradients in thin Cu and AlMn wires, both experimentally and theoretically. In the experiments, the wires were Joule heated non-uniformly at sub-Kelvin temperatures, and the resulting temperature gradients were measured using normal metal-insulator-superconducting tunnel junctions. The data clearly shows that even in reasonably well conducting thin wires with a short ($\sim 10 \mu$m) non-heated portion, significant temperature differences can form. In most cases, the measurements agree well with a model which includes electron-phonon interaction and electronic thermal conductivity by the Wiedemann-Franz law.Comment: J. Low Temp. Phys. in pres

Outskirts of Distant Galaxies In Absorption

QSO absorption spectroscopy provides a sensitive probe of both the neutral medium and diffuse ionized gas in the distant Universe. It extends 21cm maps of gaseous structures around low-redshift galaxies both to lower gas column densities and to higher redshifts. Combining galaxy surveys with absorption-line observations of gas around galaxies enables comprehensive studies of baryon cycles in galaxy outskirts over cosmic time. This Chapter presents a review of the empirical understanding of the cosmic neutral gas reservoir from studies of damped Lya absorbers (DLAs). It describes the constraints on the star formation relation and chemical enrichment history in the outskirts of distant galaxies from DLA studies. A brief discussion of available constraints on the ionized circumgalactic gas from studies of lower column density Lya absorbers and associated ionic absorption transitions is presented at the end.Comment: 45 pages, 7 figures, invited review, Book chapter in "Outskirts of Galaxies", Eds. J. H. Knapen, J. C. Lee and A. Gil de Paz, Astrophysics and Space Science Library, Springer, in pres