3 research outputs found
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
obeys a law as a function of electronic temperature .
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 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
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