429 research outputs found
Multiwavelength Raman spectroscopy analysis of a large sampling of disordered carbons extracted from the Tore Supra tokamak
Disordered carbon often exhibit a complex Raman spectrum, with four to six
components. Here, a large variety of disordered carbons, forming a collection
of samples with a great variety of structures, are analysed using
multi-wavelength Raman microscopy (325.0, 514.5, 785.0 nm). They allow us to
extend Raman behaviour known for nano-crystalline graphite to amorphous
carbons, (dependence with the excitation wavelength) and other known for
amorphous carbons to nano-crystalline graphite, (differentiation of the
smallest cluster size probed using different excitation wavelengths).
Experimental spectra were compared to simulated spectra, built using known
laws, to evidence a new source of broadening
Persistence of viable but non-culturable bacteria during the production and distribution of drinking water
The direct measurement of in situ respiring bacteria using 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) shows that, especially for Gram-negative bacteria, large numbers of viable but non-culturable (VBNC) bacteria are present in finished water from a conventional water treatment plant, and the regrowth of bacteria along distribution networks can be seen rapidly by using this very sensitive technique. The level of bacterial inactivation with chlorine is much less important than has been previously supposed (based on experiments with non-injured laboratory strains of bacteria and classical culture techniques). Threshold values of VBNC bacteria leaving water treatment plants or regrowing along distribution systems have to be determined for better control of coliform regrowth and health- risks associated with the consumption of drinking water
Thermal stability and long term hydrogen/deuterium release from soft to hard amorphous carbon layers analyzed using in-situ Raman spectroscopy. Comparison with Tore Supra deposits
The thermal stability of 200 nm thick plasma enhanced chemical vapor
deposited a-C:H and a-C:D layers ranging from soft to hard layers has been
studied and compared to that of deposits collected on the Tore Supra tokamak
plasma facing components by means of in-situ Raman spectroscopy. Linear ramp
heating and long term isotherms (from several minutes to 21 days) have been
performed and correlations between spectrometric parameters have been found.
The information obtained on the sp 2 clustering has been investigated by
comparing the G band shift and the 514 nm photon absorption evolution due to
the thermal treatment of the layer. The effects of isotopic substitution have
also been investigated.Comment: appears in Thin Solid Films, Elsevier, 201
Comparison between carbon dust produced in laboratory plasmas and in Tore Supra
12th International Congress on Plasma Physics, 25-29 October 2004, Nice (France)Laboratory experiments are proposed to understand the growth mechanisms of spherical carbonaceous dust observed in Tokamaks with inside wall elements in graphite materials. The sputtering process is used to form continuous carbon vapours. Their cooling in the plasmas gives rise to carbon clusters which size goes increasing with time. In the nanometer scale range, the obtained primary particles are spherical. They can also agglomerate in the plasma likely by coulomb attraction and form spherical aggregates of higher size. A comparison between the carbon structure of these dust grains and of some dust samples collected on the toroïdal pumped limiter surface of Tore Supra is also proposed. The differences are discussed
Correlated Microscopic Observations of Arterial Responses to Intravascular Stenting
Percutaneous catheter implantation of intravascular stent prostheses has emerged as a novel clinical adjunct to balloon angioplasty in the treatment of obstructive atherosclerotic vascular disease. We have examined the cellular and subcellular responses to stenting in the coronary arteries of the dog and pig (both normal and atherosclerotic), and in the iliac arteries and aorta of the atherosclerotic rabbit, using scanning electron, transmission electron, and light microscopies. Stenting in these models resulted in a thrombotic reaction ranging from mild to severe, depending on species and antithrombotic therapy. Subsequent organization of thrombotic material with hyperplasia of smooth muscle and inflammatory cells, luminal recovering with endothelial or pseudoendothelial cells, and atrophy of the tunica media led to incorporation of the prosthesis into the arterial wall. Endothelial or pseudoendothelial cells were observed adherent to the prosthesis as early as one day after placement, and regeneration of a confluent periluminal cell layer occurred within 2 to 4 weeks. Persistent ultrastructural abnormalities of the periluminal cell layer were seen as late as 2 years after stenting, but the intimal hyperplastic response appeared limited
Raman spectroscopy investigation of the H content of heated hard amorphous carbon layers
We revisit here how Raman spectroscopy can be used to estimate the H content
in hard hydrogenated amorphous carbon layers. The H content was varied from 2
at.% to 30 at.%, using heat treatments of a a-C:H, from room temperature to
1300 K and was determined independently using ion beam analysis. We examine the
correlation of various Raman parameters and the consistency of their thermal
evolution with thermo-desorption results. We identify a weak band at 860 cm-1
attributed to H bonded to C(sp2). We show that the HD/HG parameter (Height
ratio between the D and G bands) is quasi-linear in the full range of H content
and can thus be used to estimate the H content. Conversely, we show that the
m/HG parameter (ratio between the photoluminescence background, m, and the
height of the G band), often used to estimate the H content, should be used
with care, first because it is sensitive to various photoluminescence quenching
processes and second because it is not sensitive to H bonded to C(sp2)
Raman micro-spectroscopy as a tool to measure the absorption coefficient and the erosion rate of hydrogenated amorphous carbon films heat-treated under hydrogen bombardment
We present a fast and simple way to determine the erosion rate and absorption
coefficient of hydrogenated amorphous carbon films exposed to a hydrogen atomic
source based on ex-situ Raman micro-spectroscopy. Results are compared to
ellipsometry measurement. The method is applied to films eroded at different
temperatures. A maximum of the erosion rate is found at ~ 450 {\degree}C in
agreement with previous results. This technique is suitable for future
quantitative studies on the erosion of thin carbonaceous films, especially of
interest for plasma wall interactions occurring in thermonuclear fusion
devices
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