Improving HTc Josephson Junctions (HTc JJ) by annealing: the role of vacancy-interstitial annihilation

We have studied the annealing effect in transport properties of High temperature Josephson Junctions (HTc JJ) made by ion irradiation. Low temperature annealing (80 degrees Celsius) increases the JJ transition temperature (TJ) and the Ic.Rn product, where Ic is the critical current and Rn the normal resistance. We found that the spread in JJ characteristics can be lowered by sufficient long annealing times. Using random walk numerical simulations, we showed that the characteristic annealing time and the evolution of the spread in JJ characteristics can be explained by a vacancy-interstitial annihilation process rather than by an oxygen diffusion one.Comment: 7 pages and 3 figures submitted to Applied Physics Letter

Understanding Traditional Anti-Seismic Strategies Beyond Their Disappearance and Distortions: Yazd Qajar Architecture Case Study

Understanding traditional seismic strategies is necessary to conduct appropriate restoration of historic buildings and city centers located in earthquake-prone areas. But, the fast disappearance of vernacular built heritage and of the associated popular knowledge and know-how, along with the spread of inappropriate maintenance works, make it very difficult. To overcome these obstacles, it is suggested to broaden the scope of observations by including both larger geographical areas and elements that do not appear as seismic features at first consideration. This paper illustrates the relevance and the limits of this approach by applying it to the case study of Yazd historic city center. Yazd is located in a moderate seismic area and is famous for its well-preserved historic city center, with a high number of Qajar adobe buildings in various conditions. The authors combined literature review, direct observation of numerous buildings and a deeper study of four Qajar houses to conduct the first part of their research. The data collected mainly relates to the geometrical features, the materials used and the interconnections between elements at different scales. Their analyses led to the elaboration of several assumptions on the seismic behaviour of the studied adobe buildings and vaults and on the distortions some features may have suffered. To validate these assumptions, two methodologies were used. Both are illustrated in this paper through the study of the insertion of baked bricks in adobe vaults. The first one is based on observation campaigns on damaged houses. The second one is based on experimental works, with tests conducted on the shear strengths of masonry made with mud mortars and adobes or baked bricks to better understand how builders benefited from mixing these materials in an adobe vault. Finally, the authors discuss the limits of the method and the extent to which restoration projects can benefit from it

ISOCAM view of the starburst galaxies M82, NGC253, and NGC1808

We present results of mid-infrared 5.0-16.5 micron spectrophotometric imaging of the starburst galaxies M82, NGC253, and NGC1808 from the ISOCAM instrument on board the Infrared Space Observatory. The mid-infrared spectra of the three galaxies are very similar in terms of features present. The > 11 micron continuum attributed to very small dust grains (VSGs) exhibits a large spread in intensity relative to the short-wavelength emission. We find that the 15 micron dust continuum flux density correlates well with the fine-structure [ArII] 6.99 micron line flux and thus provides a good quantitative indicator of the level of star formation activity. By contrast, the 5-11 micron region dominated by emission from polycyclic aromatic hydrocarbons (PAHs) has a nearly invariant shape. Variations in the relative intensities of the PAH features are nevertheless observed, at the 20%-100% level. We illustrate extinction effects on the shape of the mid-infrared spectrum of obscured starbursts, emphasizing the differences depending on the applicable extinction law and the consequences for the interpretation of PAH ratios and extinction estimates. The relative spatial distributions of the PAH, VSG, and [ArII] 6.99 micron emission between the three galaxies exhibit remarkable differences. The < 1 kpc size of the mid-infrared source is much smaller than the optical extent of our sample galaxies and 70%-100% of the IRAS 12 micron flux is recovered within the ISOCAM < 1.5 arcmin squared field of view, indicating that the nuclear starburst dominates the total mid-infrared emission while diffuse light from quiescent disk star formation contributes little.Comment: 25 pages, 12 figures, accepted for publication in Astronomy and Astrophysics; Figs. 3, 4, 5, 6, 7, 9, 10, 12 appear after Sect.

On the contact law of open-cell poro-granular materials

International audienceThe contact stiffness between a poro-elastic spherical grain, made out of an open-cell foam, and a plane is studied with the aim of determining the contact law, and in particular verifying if the Hertz interaction potential, originally derived in the frame of continuum mechanics, holds. The contact law is studied experimentally by compressing a half-sphere of melamine foam into a rigid flat surface, and numerically by mean of a finite element model where the porous half-sphere is modeled by irregular tetrakaidecahedral cells. Both approaches reveal two regimes, at low and at high deformations in respect to the size of the cells. Above a cutoff value of the indentation, larger than the ligament length, a Hertzian interaction is observed. The latter is reliably described in terms of the radii of curvature of the contacting bodies and the effective elasticity of the foam structure. Below the cutoff, at the microscale, a more complex trend emerges because of the discrete nature of the foam and in particular the small number of ligaments in contact with the plane, which is function of the sphere radius at the macroscale and the cells shape at the mesoscale. Such microscopic features are akin to a surface roughness between continuous materials. These findings have practical implications to accurately describe the mechanical response of poro-granular media, used for instance in sound and vibration insulation

Stable isotope analysis of carnivores from the Turkana Basin, Kenya: Evidence for temporally-mixed fossil assemblages

 Stable isotope palaeoecology of fossil mammals is a key research tool for understanding the environmental context of hominin evolution in the Plio-Pleistocene of Africa. Well studied mammal groups include bovids, suids, equids, proboscideans and primates, but to date there has been no in-depth study of modern and fossil carnivores. Here we produce an Africa-wide oxygen and carbon enamel isotope dataset for modern carnivores and compare it with fossil carnivore data sampled from the Plio-Pleistocene Omo Group of the Turkana Basin, Kenya. Comparison of modern carnivore carbon isotopes with satellite images of land cover indicates that carnivore δ13C is related to the proportion of woody cover in the local environment. Modern carnivore oxygen isotopes are strongly influenced by the δ18O of meteoric water, through drinking from standing water and through prey body fluids. Carbon isotope data from fossil carnivores shows close agreement with palaeovegetation reconstructions from δ13C of palaeosol carbonates from the same geological Members, and a similar long-term trend in δ13C values through time (4 Ma to 1 Ma), reflecting a gradual increase in the proportion of C4 grasses in the Turkana Basin. This increase in the δ13C of large carnivores is consistent with the evidence from other mammalian groups for an increase in the proportion of grazers compared to browsers and mixed feeders during this time interval. Two distinct trends within oxygen versus carbon isotope space indicates that the fossil carnivores lived during two distinct climatic regimes – one in which palaeo-lake Turkana was freshwater, and one in which the lake resembled its modern-day hyperalkaline state. These two climatic states most likely represent the end-members of precessionally-driven rainfall extremes over the Ethiopian Highlands. This indicates that each studied faunal assemblage from the Omo Group is a time- and climate-averaged palimpsest; this has significant implications for the interpretation of environmental signals and community palaeoecology derived from Turkana Basin fossil mammals, including early hominins.