5,162 research outputs found
Temperature suppression of STM-induced desorption of hydrogen on Si(100) surfaces
The temperature dependence of hydrogen (H) desorption from Si(100)
H-terminated surfaces by a scanning tunneling microscope (STM) is reported for
negative sample bias. It is found that the STM induced H desorption rate ()
decreases several orders of magnitude when the substrate temperature is
increased from 300 K to 610 K. This is most noticeable at a bias voltage of -7
V where decreases by a factor of ~200 for a temperature change of 80 K,
whilst it only decreases by a factor of ~3 at -5 V upon the same temperature
change. The experimental data can be explained by desorption due to vibrational
heating by inelastic scattering via a hole resonance. This theory predicts a
weak suppression of desorption with increasing temperature due to a decreasing
vibrational lifetime, and a strong bias dependent suppression due to a
temperature dependent lifetime of the hole resonance.Comment: 5 pages, RevTeX, epsf files. Accepted for surface science letter
Characterization of Plum Procyanidins by Thiolytic Depolymerization
The phenolic compounds of ?Green Gage? (GG) plums (Prunus domestica L.), ?Rainha Cla?udia Verde?, from a ?protected designation of origin? (PDO), in Portugal, were quantified in both flesh and skin tissues of plums collected in two different orchards (GG-V and GG-C). Analyzes of phenolic compounds were also performed on another GG European plum obtained in France (GG-F) and two other French plums, ?Mirabelle? (M) and ?Golden Japan? (GJ). Thiolysis was used for the first time in the analysis of plum phenolic compounds. This methodology showed that the flesh and skin contain a large proportion of flavan-3-ols, which account, respectively, for 92 and 85% in GJ, 61 and 44% in GG-V, 62 and 48% in GG-C, 54 and 27% in M, and 45 and 37% in GG-F. Terminal units of procyanidins observed in plums are mainly (+)-catechin (54?77% of all terminal units in flesh and 57?81% in skin). The GJ plums showed a phenolic composition different from all of the others, with a lower content of chlorogenic acid isomers and the presence of A-type procyanidins as dimers and terminal residues of polymerized forms. The average degree of polymerization (DPn) of plum procyanidins was higher in the flesh (5?9 units) than in the skin (4?6 units). Procyanidin B7 was observed in the flesh of all GG plums and in the skin of the Portuguese ones. Principal component analysis of the phenolic composition of the flesh and skin of these plums obtained after thiolysis allowed their distinction according to the variety and origin, opening the possibility of the use of phenolic composition for variety/origin identification
Colloidal stability of tannins: astringency, wine tasting and beyond
Tannin-tannin and tannin-protein interactions in water-ethanol solvent
mixtures are studied in the context of red wine tasting. While tannin
self-aggregation is relevant for visual aspect of wine tasting (limpidity and
related colloidal phenomena), tannin affinities for salivary proline-rich
proteins is fundamental for a wide spectrum of organoleptic properties related
to astringency. Tannin-tannin interactions are analyzed in water-ethanol
wine-like solvents and the precipitation map is constructed for a typical grape
tannin. The interaction between tannins and human salivary proline-rich
proteins (PRP) are investigated in the framework of the shell model for
micellization, known for describing tannin-induced aggregation of beta-casein.
Tannin-assisted micellization and compaction of proteins observed by SAXS are
described quantitatively and discussed in the case of astringency
Beschrijving van het Instituut voor Doof-Stommen te Groningen: Ten geleide van eene systematisch gerangschikte lijst der werken en geschriften over doof-stommen en het onderwijs aan doof-stommen
Expédition de poisson vivant à un commissionaire chargé de la vente. Responsabilité des accidents postérieurs à la réception
Phenolic nature, occurrence and polymerization degree as marker of environmental adaptation in the edible halophyte Mesembryanthemum edule
AbstractMesembryanthemum edule is an edible medicinal halophyte traditionally used to treat several human diseases. In this study, particular importance was attached to the influence of environmental conditions on phenolic composition and antioxidant activities of two M. edule provenances from contrasting climatic regions (Djerba and Monastir sampled from arid and superior semi-arid bioclimatic stages, respectively). Shoot phenolic content was evaluated using colorimetric method and its composition was identified by HPLC analysis with or without thiolysis. Antioxidant activities were assessed by five in vitro antioxidant systems. Results showed that the two M. edule provenances were significantly different according to their antioxidant activity as well as their polyphenol profiles. Indeed, plants from Djerba (lack of rainfall and long light hour periods) exhibited stronger antioxidant activity together with higher phenolic content. For instance, Djerba provenance shoots showed much lower IC50 (4.8ÎŒgmlâ1) and EC50 (80ÎŒgmlâ1) values for DPPH and Fe-reducing tests, respectively. In addition, the superiority of this provenance (Djerba) was more marked as compared to positive controls (BHT, BHA, and VitC). HPLC identification revealed also an important difference between the two provenances on major flavonoid components. This difference was confirmed by the mean degrees of tannin polymerization (DPn) which was higher in Djerba plants. These data suggest that M. edule adaptation to environmental stresses proceeds through induced particular phenol quality and DPn for the improvement of their antioxidant capacities to protect plant tissues against oxidative stress
Consultation pluridisciplinaire spécialisée : activité physique adaptée et sclérose en plaques
Flux et crues singuliĂšres d'un petit cours d'eau andin ou les effets pervers de l'urbanisation
Sur un petit bassin de haute montagne (4000 m), situé dans les Andes à proximité de La Paz, la canalisation des "rios" en vue de gagner des terrains urbanisables, n'a guÚre modifié, en termes de bilan annuel, les régimes hydrologiques mais a eu des conséquences inattendues sur leur comportement en crue. Au delà d'un certain débit, bien inférieur au débit maximum décennal, apparaissent des vagues, parfois plus hautes que le canal, qui déferlent à prÚs de 10 m/s, endommageant sur leur passage ponts et parois de l'ouvrage, et provoquant d'importants débordements en zone urbaine. Plus en amont, dans le lit naturel, l'écoulement demeure stable. Plusieurs hypothÚses sont avancées pour expliquer ce phénomÚne. (Résumé d'auteur
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