Supercollision cooling in undoped graphene

Carrier mobility in solids is generally limited by electron-impurity or electron-phonon scattering depending on the most frequently occurring event. Three body collisions between carriers and both phonons and impurities are rare; they are denoted supercollisions (SCs). Elusive in electronic transport they should emerge in relaxation processes as they allow for large energy transfers. As pointed out in Ref. \onlinecite{Song2012PRL}, this is the case in undoped graphene where the small Fermi surface drastically restricts the allowed phonon energy in ordinary collisions. Using electrical heating and sensitive noise thermometry we report on SC-cooling in diffusive monolayer graphene. At low carrier density and high phonon temperature the Joule power $P$ obeys a $P\propto T_e^3$ law as a function of electronic temperature $T_e$. It overrules the linear law expected for ordinary collisions which has recently been observed in resistivity measurements. The cubic law is characteristic of SCs and departs from the $T_e^4$ dependence recently reported for metallic graphene below the Bloch-Gr\"{u}neisen temperature. These supercollisions are important for applications of graphene in bolometry and photo-detection

Isolation and on-line identification of anti-oxidant compounds from three Baccharis species by HPLC-UV-MS/MS with post-column derivatisation

The aqueous extracts of aerial parts of Baccharis trimera (Less.) DC., B. crispa Spreng. and B. usterii Heering (Asteraceac) displayed significant radical scavenging activity in a diphenylpicrylhydrazole (DPPH)/TLC assay. In order to rapidly identify the active principles, the crude extracts were analysed by HPLC-UV, and an HPLC-micro-fractionation of the extract of R usterii was performed. Six quinic acids derivatives (1-6) were isolated from B. usterii by MPLC. The fractions were monitored by DPPH/TLC assay and a series of radical-scavenging quinic acid derivatives could be identified. The comparison of the HPLC profiles of the extracts of B. usterii, B. trimera and B. crispa was performed. In order to obtain complementary on-line structural information for all peaks of interest, HPLC-MS/MS together with HPLC-UV involving post-column addition of UV shift reagents was undertaken on the crude extract. The interpretation of these data permitted the on-line identification of known compounds, some of which are reported for the first time in this plant. Copyright (c) 2005 John Wiley & Sons, Ltd

Surface treatment by RF cold plasma on polyester fibres used in chemically bonded nonwovens and consequence on adhesion between fibre and binder.

Nonwovens (NW) are innovative textile materials and can be used in many fields including medical, hygiene, transport, civil engineering, etc.. They are sheet-like fabrics made up of fiber webs which are bonded either chem., mech. or thermally. Among all consolidation methods, chem.-bonded-NW are still widely used because of the extended range of binder flexibility, durability and the versatility of their final properties. The purpose of the present study is to investigate surface treatment by Radio Frequency (RF) cold plasma on polyester fibers in order to improve the adhesion mechanism with copolymer acrylic binders, the ultimate aim being to limit the amts. of chem. binder used for environmental and economical reasons. The phys. modifications on fiber surface are examd. using at. force microscopy (AFM), and the chem. modifications are discussed after surface anal. of fibers by XPS. The pull-out test was used to characterize the interfacial shear strength between fiber and matrix

Methylpyrrole Tropane Alkaloids from the Bark of Erythroxylum vacciniifolium

Nine new tropane alkaloids substituted by a methylpyrrole moiety were isolated from the bark of Erythroxylum vacciniifolium, a Brazilian endemic plant used in traditional medicine and locally known as catuaba. All compounds were elucidated as tropanediol or -triol alkaloids esterified by at least one 1-methyl-1H-pyrrole-2-carboxylic acid. One of the isolated compounds was identified as a tropane alkaloid N-oxide. Their structures were determined by high-resolution mass spectrometry and multidimensional NMR spectroscopy

Effect of spin finish on fiber/binder adhesion in chemically bonded nonwovens.

International audienceThe purpose of this study is to better understand the mechanisms governing the phenomena of fiber/matrix adhesion by controlling the fiber surface properties. This adhesion is evaluated by studying the micromech. and thermodynamical behavior of the fiber/matrix interface. The complexity of the interactions at the interface requires a global approach that takes into account the chem., morphol., and mechanics. The thermodynamical affinity between the binder and fibers is evaluated by the wetting behavior, whereas the mech. resistance of the fiber/matrix interface is characterized with the pull-out test. Three distinct approaches are used to classify the different systems according to the nature of the binder and the fiber surface. It is found that there is better adhesion when the spin finish is removed from the fibers, revealing the surface roughness on which the latex can mech. anchor

Electrochemical behaviour of austenitic stainless steel under tribological stresses and irradiation

International audienceAn experiment was developed to characterise the behaviour of 316 L stainless steel under the combined effects of corrosion, tribology, and irradiation. This original experiment shows that radiolysis, through the production of free radicals and H2O2, leads to an oxidising medium. The electrochemical behaviour of the material from the recorded polarisation curves and electrochemical impedance spectroscopy measurements indicates that the passive film under irradiation is a Cr oxi-hydroxide layer. The layer has more formative thickness under irradiation. When the irradiation is interrupted, the passive film is identical to that observed before irradiation. The repassivation is faster during irradiation and friction

On-line characterisation of apple polyphenols by liquid chromatography coupled with mass spectrometry and ultraviolet absorbance detection

Apple polyphenols were characterised by means of hyphenated techniques such as HPLC coupled to UV photodiode array detection (LC-DAD) and to mass spectrometry (LC-MS). LC-MS using atmospheric pressure ionisation (APCI) in the positive ion mode provided the molecular weight, the number of hydroxyl groups, the number of sugars and an idea about the substitution pattern of the polyphenols. LC-DAD with postcolumn addition of UV shift reagents afforded precise structural information about the position of the free hydroxyl groups in the polyphenolic nucleus. Five isorhamnetin glycosides, two hydroxyphloretin glycosides and quercetin were reported in apple peel for the first time. Postcolumn addition of UV shift reagents in LC-DAD analysis confirmed the presence of isorhamnetin glycosides and not the isomeric glycosides of rhamnetin. Moreover, isorhamnetin-3-O-rhamnoglucoside was identified unambiguously by comparison with a standard. These results are relevant not only from a chemotaxonomic point of view, but also in the control of authenticity of fruit derived products in order to detect fraudulent admixtures. (C) 2004 Elsevier B.V. All rights reserved