Selective epitaxial growth of graphene on SiC

We present an innovative method of selective epitaxial growth of few layers graphene (FLG) on a pre-patterned SiC substrate. The methods involves, successively, the sputtering of a thin AlN layer on top of a mono-crystalline SiC substrate and, then, patterning it with e-beam lithography (EBL) and wet etching. The sublimation of few atomic layers of Si from the SiC substrate occurs only through the selectively etched AlN layer. The presence of the Raman G-band at ~1582 cm-1 in the AlN-free areas is used to validate the concept, it gives absolute evidence of the selective FLG growth.Comment: comments: 3 pages, reference 3 replace

Video-assisted cardioscopy for removal of primary left ventricular myxoma.

Left ventricular myxoma is a rare benign cardiac tumor. Surgical excision is the treatment of choice and completeness of removal is mandatory to avoid late recurrence. A case is presented in which aortic transvalvular video-assisted cardioscopy was used to facilitate removal

Analysis of γ-rays induced chromosome aberrations : A fingerprint evaluation with a combination of pan-centromeric and pan-telomeric probes

Altres ajuts: This research received financial support from the Spanish "Consejo de Seguridad Nuclear" (SPR/04/4550)Purpose: To evaluate the types of induced chromosome aberrations after the exposure of peripheral blood to γ-rays by the simultaneous detection of all centromeres and telomeres; and to analyse the suitability of different radiation fingerprints for the assessment of radiation quality in cases of recent exposures. Material and methods: Peripheral blood samples were irradiated at 2, 4 and 6 Gy of γ-rays. Cytogenetic analysis was carried out by fluorescence in situ hybridization (FISH) technique with pan-centromeric and peptide nucleic acid (PNA)-telomeric DNA probes. Cells were analysed using a Cytovision® FISH workstation, chromosome aberrations and the length of the acentric fragments were recorded. Results: The total number of the incomplete chromosome elements was 276. The ratio between incomplete elements and multicentrics was 0.38. The number of acentrics was 1096, 71% were complete acentrics, 15% incomplete acentrics, and 14% interstitial fragments. The relative length of complete, incomplete and interstitial acentrics fragments were 2.70 ± 0.04, 1.91 ± 0.07, and 1.42 ± 0.04 respectively. The mean value of the F-ratio was 11.5 higher than the one, 5.5, previously obtained for α-particles. For the G-ratio there was no difference between γ-rays and α-particles, 2.8 and 2.8 respectively. The mean value of the H-ratio for γ-rays, 0.25, was lower than for α-particles 0.40. Conclusion: The results support that the percentage of incomplete chromosome aberrations depends on radiation type; low-linear energy transfer (LET) radiation would produces less incomplete aberrations than high-LET radiation. The F- and H-ratios seem to be good indicators of radiation quality, although a real estimation of the H-ratio is only possible using pan-telomeric probes

Contamination des milieux aquatiques Camarguais par les résidus de produits phyto sanitaires

Les auteurs font état des résultats qu’ils ont obtenu au terme de deux années de recherches sur la contamination des milieux aquatiques cam arguais par les résidus de produits phytosanitaires. En Camargue, les techniques culturales employées, notam ment en riziculture : irrigation intensive et extensive, lutte chimique contre les parasites, menacent de pollution l’ensemble des milieux aquatiques et plus particulièrement les étangs de la Réserve Naturelle Zoologique et Rotanique. Les polluants sont d’origine rhodanienne ou proviennent des traitements agricoles, herbicides et insecticides. L’étude concernant les herbicides est délicate à mener et les résultats obtenus jusqu’à présent sont trop fragmentaires pour pouvoir être interprétés. Des résultats plus complets concernant les insecticides montrent que la contamination de l’eau est encore très faible, mais que l’accumulation des résidus organochlorés aux différents échelons trophiques des biocœnoses présente un réel danger. Les pesticides les plus fréquemment rencontrés sont alpha HCH (d’origine rhodanienne), gamma HCH (d’origine rhodanienne et agricole). La présence à des doses décelables de DDT est moins courante. D’autres résidus ne sont soupçonnés dans l’eau que du fait de leur présence dans les tissus animaux (dieldrine). D’autres enfin ne sont décelés qu’en période de traitement des cultures (les organophosphorés et notamment le parathion), ou à la faveur de circonstances particulières (polychlorocamphane) . Les polychlorobiphényles présents dans le milieu posent un problème. Leur origine est probablement mixte (Rhône et spé cialités commerciales de pesticides agricoles où ils servent d’adjuvant). Ces organochlorés très stables sont accumulés à des taux relativement importants aussi bien dans les sédiments que dans les végétaux et les animaux aquatiques et présentent un réel danger pour la conservation des milieux naturels. La conciliation de l’agriculture et de la conservatoin de la nature en Camargue est subordonnée à deux conditions : le rejet au Rhône de toutes les eaux de drainage des cultures jusqu’à présent déversées dans le Vaccarès et la recherche de pratiques culturales moins polluantes que celles actuellement employées.Results are given of a two year study on the pollution by pesticide-residues of the aquatic environment in the Camargue. The agricultural techniques employed, notably in rice-growing (intensive and extensive irrigation, chemical control of pests) threaten the whole aquatic environment in the Camargue with pollution, particularly the lakes situated in the « Réserve Naturelie Zoologique et Botanique ». These pollutants originate from the Rhône river and from agricultural treatments using herbicides and insecticides. Herbicide studies have proved difficult to conduct and results obtained to date are too fragmentary to allow a clear interpretation. More detailed results on insecticides show that water pollu tion is still very low but that the accumulation of organo- chlorides at the different trophic levels of the ecosystem presents a real threat. The pesticides most frequently recorded are alpha HCH (BHC) (Rhone origin) and gamma HCH (Rhone and agricultural origin). Detectable doses of DDT are less frequently recorded. Other residues are only suspected in water because of their presence in animal tissues (dieldrin). Lastly, others are only revealed during the period when crops are treated (organophosphates and espe cially parathion) or as a result of very particular circumstances (polychlorocamphene) . The presence of polychlorobiphenyls in the environment raises a special problem. They probably have a mixed origin (Rhone and commercial types of agricultural pesticides where they serve as an adjuvant). These very stable organochlorides are accumulated at relatively high rates in sediments as well as in aquatic plants and animals, and present a real danger to the conservation of natural habitats. The conciliation of agriculture and nature conservation in the Camargue is dependent on two conditions : return into the Rhone of all run-off water from crops, at present discharged into the « Etang du Vaccarès », and research into cultural methods which produce less pollution than those in current use

Spatially Offset Raman Spectroscopic (SORS) Analysis of Wine Alcoholic Fermentation: A Preliminary Study

Spatially offset Raman spectroscopy (SORS) is a non-invasive analytical technique that allows the analysis of samples through a container. This makes it an effective tool for studying food and beverage products, as it can measure the sample without being affected by the packaging or the container. In this study, a portable SORS equipment was used for the first time to analyse the alcoholic fermentation process of white wine. Different sample measurement arrangements were tested in order to determine the most effective method for monitoring the fermentation process and predicting key oenological parameters. The best results were obtained when the sample was directly measured through the glass container in which the fermentation was occurring. This allowed for the accurate monitoring of the process and the prediction of density and pH with a root mean square error of cross-validation (RMSECV) of 0.0029 g·L−1 and 0.04, respectively, and R2 values of 0.993 and 0.961 for density and pH, respectively. Additionally, the sources of variability depending on the measurement arrangements were studied using ANOVA-Simultaneous Component Analysis (ASCA)

Early stage formation of graphene on the C-face of 6H-SiC

An investigation of the early stage formation of graphene on the C-face of 6H-SiC is presented. We show that the sublimation of few atomic layers of Si out of the SiC substrate is not homogeneous. In good agreement with the results of theoretical calculations it starts from defective sites, mainly dislocations that define nearly circular flakes, which have a pyramidal, volcano-like, shape with a center chimney where the original defect was located. At higher temperatures, complete conversion occurs but, again, it is not homogeneous. Within the sample surface the intensity of the Raman G and 2D bands, evidences non-homogeneous thickness.Comment: 12 pages, 3 figure

Nuclear recoil measurements in Superheated Superconducting Granule detectors

The response of Superheated Superconducting Granule (SSG) devices to nuclear recoils has been explored by irradiating SSG detectors with a 70Me$\!$V neutron beam. In the past we have tested Al SSG and more recently, measurements have been performed with Sn and Zn detectors. The aim of the experiments was to test the sensitivity of SSG detectors to recoil energies down to a few ke$\!$V. In this paper, the preliminary results of the neutron irradiation of a SSG detector made of Sn granules 15-20$\mu$m in diameter will be discussed. For the first time, recoil energy thresholds of $\sim$1ke$\!$V have been measured.Comment: 7pages in Latex format, Preprint Bu-He 93/6 (University of Berne, Switzerland), four figures available upon request via [email protected] or [email protected]

Investigation of Long Monolayer Graphene Ribbons grown on Graphite Capped 6H-SiC (000-1)

We present an investigation of large, isolated, graphene ribbons grown on the C-face of on-axis semi-insulating 6H-SiC wafers. Using a graphite cap to cover the SiC sample, we modify the desorption of the Si species during the Si sublimation process. This results in a better control of the growth kinetics, yielding very long (about 300 microns long, 5 microns wide), homogeneous monolayer graphene ribbons. These ribbons fully occupy unusually large terraces on the step bunched SiC surface, as shown by AFM, optical microscopy and SEM. Raman spectrometry indicates that the thermal stress has been partially relaxed by wrinkles formation, visible in AFM images. In addition, we show that despite the low optical absorption of graphene, optical differential transmission can be successfully used to prove the monolayer character of the ribbons

High-Energy gamma-ray Astronomy and String Theory

There have been observations, first from the MAGIC Telescope (July 2005) and quite recently (September 2008) from the FERMI Satellite Telescope, on non-simultaneous arrival of high-energy photons from distant celestial sources. In each case, the highest energy photons were delayed, as compared to their lower-energy counterparts. Although the astrophysics at the source of these energetic photons is still not understood, and such non simultaneous arrival might be due to non simultaneous emission as a result of conventional physics effects, nevertheless, rather surprisingly, the observed time delays can also fit excellently some scenarios in quantum gravity, predicting Lorentz violating space-time "foam" backgrounds with a non-trivial subluminal vacuum refractive index suppressed linearly by a quantum gravity scale of the order of the reduced Planck mass. In this pedagogical talk, I discuss the MAGIC and FERMI findings in this context and I argue on a theoretical model of space-time foam in string/brane theory that can accommodate the findings of those experiments in agreement with all other stringent tests of Lorentz invariance. However, I stress the current ambiguities/uncertainties on the source mechanisms, which need to be resolved first before definite conclusions are reached regarding quantum gravity foam scenarios.Comment: 34 pages latex, 12 eps figures incorporated, uses special macros. Based on invited plenary talk at DICE 2008 Conference (Castiglioncello, Italy), September 22-26 200