1,187 research outputs found
Design and optimization of electrochemical microreactors for continuous electrosynthesis
The study focuses on the design and construction, as well as the theoretical and experimental optimization of electrochemical filter press microreactors for the electrosynthesis of molecules with a high added value. The main characteristics of these devices are firstly a high-specific electrochemical area to increase conversion and selectivity, and secondly the shape and size of themicrochannels designed for a uniform residence time distribution of the fluid. A heat exchanger is integrated into the microstructured electrode to rapidly remove (or supply) the heat required in exo- or endothermic reactions. The microreactors designed are used to perform-specific electrosynthesis reactions such as thermodynamically unfavorable reactions (continuous NADH regeneration), or reactions with high enthalpy changes
Microscopic work function anisotropy and surface chemistry of 316L stainless steel using photoelectron emission microscopy
International audienceWe have studied the variation in the work function of the surface of sputtered cleaned 316L stainless steel with only a very thin residual oxide surface layer as a function of grain orientation using X-ray photo-electron emission microscopy (XPEEM) and Electron Backscattering Diffraction. The grains are mainly oriented [1 1 1] and [1 0 1]. Four distinct work function values spanning a 150 meV energy window are measured. Grains oriented [1 1 1] have a higher work function than those oriented [1 0 1]. From core level XPEEM we deduce that all grain surfaces are Cr enriched and Ni depleted whereas the Cr/Fe ratio is similar for all grains. The [1 1 1] oriented grains show evidence for a Cr 2 O 3 surface oxide and a higher concentration of defective oxygen sites
Black Hole Relics in String Gravity: Last Stages of Hawking Evaporation
One of the most intriguing problem of modern physics is the question of the
endpoint of black hole evaporation. Based on Einstein-dilaton-Gauss-Bonnet four
dimensional string gravity model we show that black holes do not disappear and
that the end of the evaporation process leaves some relic. The possibility of
experimental detection of the remnant black holes is investigated. If they
really exist, such objects could be a considerable part of the non baryonic
dark matter in our Universe.Comment: 15 pages, accepted to Class. Quant. Gra
Synchrotron X-ray diffraction experiments with a prototype hybrid pixel detector
International audienceA prototype X-ray pixel area detector (XPAD3.1) has been used for X-ray diffraction experiments with synchrotron radiation. The characteristics of this detector are very attractive in terms of fast readout time, high dynamic range and high signal-to-noise ratio. The prototype XPAD3.1 enabled various diffraction experiments to be performed at different energies, sample-to-detector distances and detector angles with respect to the direct beam, yet it was necessary to perform corrections on the diffraction images according to the type of experiment. This paper is focused on calibration and correction procedures to obtain high-quality scientific results specifically developed in the context of three different experiments, namely mechanical characterization of nanostructured multilayers, elastic-plastic deformation of duplex steel and growth of carbon nanotubes
Charge-Density-Waves Tuned by Crystal Symmetry
The electronic orders appearing in condensed matter systems are originating
from the precise arrangement of atoms constituting the crystal as well as their
nature. This teneous relationship can lead to highly different phases in
condensed matter, and drive electronic phase transitions. Here, we show that a
very slight deformation of the crystal structure of TbTe can have a
dramatic influence on the electronic order that is stabilized. In particular,
we show that the Charge Density Wave (CDW) developping along the axis
in the pristine state, switches to an orientation along when the
naturally orthorhombic system is turned into a tetragonal system. This is
achieved by performing true biaxial mechanical deformation of a TbTe sample
from 250K to 375K, and by measuring both structural and electronic parameters
with x-ray diffraction and transport measurements. We show that this switching
transition is driven by the tetragonality parameter , and that the
transition occurs for , with a coexistence region for . The CDW transition temperature is found to have a linear
dependence with , with no saturation in the deformed states investigated
here, while the gap saturates out of the coexistence region. The linear
dependence of is accounted for within a tight-binding model. Our results
question the relationship between the gap and in RTe systems. More
generally, our method of applying true biaxial deformation at cryogenic
temperatures can be applied to many systems displaying electronic phase
transitions, and opens a new route towards the study of coexisting or competing
electronic orders in condensed matter
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