High temperature oxidation of Zr- and Hf-carbides: Influence of matrix and sintering additive

Ultra-high temperature ceramics having melting points above 3500 K and high thermal conductivities are envisaged as future receivers of concentrating solar power plants. The high pressure and solar temperature reactor (Réacteur Hautes Pression et Température Solaire, REHPTS) implemented at the focus of the Odeillo 5 kW solar furnace was used to investigate the oxidation of three refractory carbides containing different sintering additives (HfC/MoSi₂, ZrC/MoSi₂, ZrC/TaSi₂) that could be considered as promising candidates. The concentration of the additive, TaSi₂ or MoSi₂, was 20 vol%. Each kind of sample was oxidized in air for 20 min at 1800, 2000 and 2200 K. Experiments were filmed using a video camera and the gaseous phases were analyzed in situ by mass spectrometry. Various post-test characterizations have shown that the nature of the carbide and additive strongly affects the composition of the oxide layer and therefore the high-temperature behaviour.     

Single-molecule dynamics in a self-assembled 2D molecular sieve

A two-dimensional molecular sieve has been realized. It consists of a host matrix of molecularly engineered building blocks self-assembled at the liquid-solid interface. The simultaneous size- and shape-dependent dynamics of different guest molecules is observed in situ, in real time with submolecular resolution using a scanning tunneling microscope both at the liquid-solid interface and under vacuum. The temperature-dependent dynamics reveals that the diffusion proceeds through thermally activated channeling between single-molecule surface cavities.     

Tunable acousto-optic spectral imager for atmospheric composition measurements in the visible spectral domain

We describe a new spectral imaging instrument using a TeO₂ acousto-optical tunable filter (AOTF) operating in the visible domain (450-900?nm). It allows for fast (～1 second), monochromatic (FWHM ranges from 0.6?nm at 450?nm to 3.5?nm at 800?nm) picture acquisition with good spatial resolution. This instrument was designed as a breadboard of the visible channel of a new satellite-borne atmospheric limb spectral imager, named the Atmospheric Limb Tracker for the Investigation of the Upcoming Stratosphere (ALTIUS), that is currently being developed. We tested its remote sensing capabilities by observing the dense, turbulent plume exhausted by a waste incinerator stack at two wavelengths sensitive to NO₂. An average value of 6.0±0.4×10¹⁷ molecules?cm^-2 has been obtained for the NO₂ slant column density within the plume, close to the stack outlet. Although this result was obtained with a rather low accuracy, it demonstrates the potential of spectral imaging by using AOTFs in remote sensing.     

Microstructure and texture of copper/niobium composites processed by ECAE

The structure refinement is a challenge for conductors used for the winding of resistive coils producing non-destructive pulsed magnetic fields over 80T. These nanocomposite conductors composed of a conducting multiscale Cu matrix embedding Nb reinforcing nanofilaments are usually manufactured by using a Severe Plastic Deformation (SPD) process based on hot extrusion, accumulative cold drawing and bundling (ADB) steps [Thilly et al. Philos Mag A 82:925, 2002]. Equal-channel angular extrusion (ECAE) is investigated here as an alternative route since it may provide faster refinement to obtain the ultrafine structure needed for optimized electrical and mechanical properties of the conductors. Therefore, copper-niobium specimens obtained by hot extrusion were processed by ECAE at room temperature. The specific die of the ECAE tool used here is constituted by a round channel with three angles corresponding to a total equivalent strain of about 2.5. Deformed samples were examined by optical microscopy and characterized by hardness profiles and x-ray diffraction (texture pole figures). After one ECAE-pass, the shape of the samples is modified but no trace of damage appeared at the Cu-Nb interfaces. An increase of the hardness values localized in the copper matrix is revealed whereas the hardness of the niobium remains unchanged. Prior to ECAE, the hot extrusion process induced a fibre texture for both copper and niobium. Two fibre texture components were observed for copper: <111> and <200>. A single <110> fibre texture component is evidenced for the niobium. After ECAE a significant variation of the texture is observed in relation with the strong shear induced by this process.     

Wundt's laboratory at Leipzig in 1891.

This article describes W. Wundt's laboratory at Leipzig in 1891 as viewed by a Belgian psychologist, J. J. Van Biervliet (1859-1945). Although few French-speaking psychologists worked in Wundt's laboratory, several of those who did reports wrote on how students were trained there. Van Biervliet decided to visit Wundt's laboratory at Leipzig in order to strengthen the foundation of his own laboratory at the University of Ghent and to become familiar with Wundt's experimental techniques. A translation of J. J. Van Biervliet's (1892) article "Experimental Psychology. Wundt's Institute at Leipzig" is presented here as one of the first and most complete articles in French describing the functioning of Wundt's laboratory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Early Experience and Postembryonic Maturation of Body Patterns in Cuttlefish (Sepia officinalis).

This study investigates effects of the environment on the maturation of body patterns in cuttlefish (Sepia officinalis). Cuttlefish were reared either individually on a uniform background, which the authors have termed uniform-solitary conditions (Group A), or grouped on variegated backgrounds, which the authors have termed varied-social conditions (Group B). At Days 1, 15, 30, and 60, juveniles were placed individually in perceptually different testing conditions, either on small, variegated stones or on a uniform pale gray background. During development in both testing conditions, juveniles from Group B concealed themselves differently from those from Group A. Thus, it appears that the response to the background is subject to individual experience. Some hypotheses are discussed relating to the effect of early experience on the maturation of body patterns. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Elastically driven morphology of coherent trigonal precipitates inside a close-packed hexagonal matrix

The influence of a crystallographic symmetry break on the morphology of precipitates during the coherent precipitation of a trigonal phase in a close-packed hexagonal matrix is analyzed. It is pointed out that in spite of the isotropy of the stress-free strain of the precipitate in the basal plane, the existence of an extra elastic constant in the precipitate (associated to the loss of symmetry) induces a morphological evolution from a shape having a symmetry of revolution around the threefold axis to a needle-like one oriented along the compact directions in the basal plane. These general considerations are applied to the case of zirconium hydrides, the crystallography of which has recently been identified to be coherent with that of the αZr matrix.     

Variable‐Wavelength Quick Scanning Nanofocused X‐Ray Microscopy for In Situ Strain and Tilt Mapping

Compression of micropillars is followed in situ by a quick nanofocused X‐ray scanning microscopy technique combined with 3D reciprocal space mapping. Compared to other attempts using X‐ray nanobeams, it avoids any motion or vibration that would lead to a destruction of the sample. The technique consists of scanning both the energy of the incident nanofocused X‐ray beam and the in‐plane translations of the focusing optics along the X‐ray beam. Here, the approach by imaging the strain and lattice orientation of Si micropillars and their pedestals during in situ compression is demonstrated. Varying the energy of the incident beam instead of rocking the sample and mapping the focusing optics instead of moving the sample supplies a vibration‐free measurement of the reciprocal space maps without removal of the mechanical load. The maps of strain and lattice orientation are in good agreement with the ones recorded by ordinary rocking‐curve scans. Variable‐wavelength quick scanning X‐ray microscopy opens the route for in situ strain and tilt mapping toward more diverse and complex materials environments, especially where sample manipulation is difficult.