231 research outputs found
The transducin cascade is involved in the light-induced structural changes observed by neutron diffraction on retinal rod outer segments
No full textTime-resolved neutron diffraction on retinal rod outer segments are performed to reinvestigate the origin of the light-induced structural change observed by Saibil et al. (Saibil, H., M. Chabre, and D. L. Worcester, 1976, Nature (Lond.), 262:266–270). Photoactivating rhodopsin triggers in rods a cascade of GTP-dependent and transducin-mediated reactions controlling cyclic-GMP hydrolysis. Infrared light-scattering studies (Kühn, H., N. Bennett, M. Michel-Villaz, and M. Chabre, 1981, Proc. Natl. Acad. Sci. USA, 78:6873–6877; Vuong, T. M., M. Chabre, and L. Stryer, 1984, Nature (Lond.), 311:659–661) demonstrated the existence of structural changes that correspond to this cascade rather than to rhodopsin photoactivation. We thus look for neutron diffraction changes of similar origins. With 1-min time resolution, intensity changes are observed mainly for orders 2 and 4. The illumination and GTP dependence of these changes indicates an involvement of transducin. Without GTP, they are linear with the amount of photoexcited rhodopsin, saturate at 10% photolysis, and thus correlate well with the light-scattering "binding signal." With GTP, light sensitivity is higher and saturation occurs below 0.5% photolysis, as for the "dissociation signal" of light scattering. In both cases, lattice compressions of 0.2–0.3% are observed. With 4-s time resolution the intensity change with GTP present precedes the lattice compression. The fast intensity change is probably due to the displacement of transducin alpha-subunits away from the disc membrane and the slower lattice shrinkage to an osmotic readjustment of the rod
Kinetic analysis of the activation of transducin by photoexcited rhodopsin. Influence of the lateral diffusion of transducin and competition of guanosine diphosphate and guanosine triphosphate for the nucleotide site
No full textThe activation of transducin (T) by photoexcited rhodopsin (R*) is kinetically dissected within the framework of Michaelis-Menten enzymology, taking transducin as substrate of the enzyme R*. The light scattering "release" signal (Vuong, T.M., M. Chabre, and L. Stryer, 1984, Nature (Lond.). 311:659–661) was used to monitor the kinetics of transducin activation at 20 degrees C. In addition, the influence of nonuniform distributions of R* on these activation kinetics is also explored. Sinusoidal patterns of R* were created with interference fringes from two crossed laser beams. Two characteristic times were extracted from the Michaelis-Menten analysis: t(form), the diffusion-related time needed to form the enzyme-substrate R*-transducin is 0.25 +/- 0.1 ms, and T(cat), the time taken by R* to perform the chemistry of catalysis on transducin is 1.2 +/- 0.2 ms, in the absence of added guanosine diphosphate (GDP) and at saturating levels of guanosine triphosphate (GTP). With t(form) being but 20% of the total activation time t(form) + t(cat), transducin activation by R* is not limited by lateral diffusion. This is further borne out by the observation that uniform and sinusoidal patterns of R* elicited release signals of indistinguishable kinetics. When (GDP) = (GTP) = 500 microM, t(cat) is lengthened twofold. As the in vivo GDP and GTP levels are comparable, the exchange of nucleotides may well be the rate-limiting process
Fonds Francine Lancelot - Les sociétés de farandole en Provence et en Languedoc : Copie d'un Brevet de Prévôt de danse délivré à M. Bernard à Paris (verso)
No full textDépôt du fichier TIFF numérisé en 300 dpi.51cmx34cm. L'illustration est pratiquement invisible. En revanche, le nom du danseur, le lieu et la date de l'obtention du brevet, les signatures des membres du jury et les cachets sont assez clairement identifiables. Le verso indique que la copie a été réalisée par la société Castel-Chabre à Toulon
Fonds Francine Lancelot - Les sociétés de farandole en Provence et en Languedoc : Copie d'un Brevet de Prévôt de danse délivré à M. Bernard à Paris
No full textDépôt du fichier TIFF numérisé en 300 dpi.51cmx34cm. L'illustration est pratiquement invisible. En revanche, le nom du danseur, le lieu et la date de l'obtention du brevet, les signatures des membres du jury et les cachets sont assez clairement identifiables. Le verso indique que la copie a été réalisée par la société Castel-Chabre à Toulon
Éducation, internationalisation, mobilités et élites - Bibliographie générale
No full textÉducation, internationalisation, mobilités et élites - Bibliographie générale Magali Ballatore et Théotime Chabre Généralités Banos V., (2009) « Michel Lussault, De la lutte des classes à la lutte des places », Géographie et cultures, 72 |, 137-138. Beaud S., Pialoux M. (2003), Violences urbaines, violence sociale. Genèse des nouvelles classes dangereuses, Paris : Fayard, 426 p. Boutinet J‐P. (1998), L’Immaturité de la vie adulte, Paris : PUF, 267p. Brandi M.C., Segnana M.L. (2008..
Diamagnetic Anisotropy of Proteins and Magnetic Orientation of Biological Membranes and Protein Assemblies
No full textFrom the photons to the neuronal signals: visual transduction and related biological problems
No full textFree Flight Physiology: Paragliding and the Study of Extreme Altitude.
No full textThis is the author accepted manuscript. The final version is available from Mary Ann Liebert via the DOI in this record.Aims
We sought to describe the physiological demands and the impact of environmental stressors of paragliding, a popular and evolving form of free flight, at moderate and extreme altitudes.
We recorded oxygen consumption (VO2), heart rate (HR), respiratory frequency (fR), tidal volume (VT), oxygen saturation, accelerometry (G) and altitude in eight male pilots: 9.3 hours of flight at moderate altitudes (to 3,073 m, n=4), 19.3 hours at extreme altitude (to 7,458 m, n=2) and during high-G manoeuvers (n=2). We also analysed heart rate data from 17 male pilots (138 hours).
Results
Overall energy expenditure at moderate altitude was low (1.7 (0.6) metabolic equivalents) but physiological parameters were notably higher during take-off (p < 0.05). Pilots transiently reached ~7 G during manoeuvres. Mean HR at extreme altitude (112 (14) bpm) were elevated compared to moderate altitude (98 (15) bpm, p = 0.048). While VT were similar (p = 0.958), elevation in fR at extreme compared to moderate altitude approached significance (p = 0.058).
Conclusions
Physical exertion in paragliding appears low, so any subjective fatigue felt by pilots is likely to be cognitive or environmental. Future research should focus on reducing mental workload, enhancing cognitive function and improving environmental protection.Equipment for the study was provided by the University of Portsmouth Department of Sports Science, the University of Exeter Link Fund Award and Research QR uplift fund. We gratefully acknowledge the assistance of Dr Juliana Pugmire (University of Glasgow) for review of the manuscript and advice regarding statistical analysis; Professor Adrian Thomas, Professor Sue Ward, Dr Pete Hodkinson, Dr Bonnie Posselt, Dr Tom Yeoman, Dr Ellie Heath; The Free Flight Physiology Project; CASE Medicine; Escape Paragliding, Ozone Chabre Open, SEARCH Projects, Flyeo, Flymaster Avionics and all the pilots who kindly volunteered to take part
Proton Intercalation in γ-MnO<sub>2</sub> from Ramsdellite to Groutite Through Groutellite
No full textAbstractThis paper presents an investigation of electrochemical proton intercalation in two chemically prepared MDs containing low amounts of structural defects and in a natural MD containing 89%of highly crystalline ramsdellite. XRD examination of equilibrated partly reduced synthetic samples confirms the formation of groutite as a final reduction product and, before mid-reduction, suggests the formation of a solid solution between ramsdellite and groutellite H0.5MnO2. In contrast, electrochemical spectroscopy hint at a two-phase process with an equilibrium potential at –60 m V vs Hg/HgO. The implication of the structural defects on these observations are discussed.</jats:p
Anomalie du spectre β de 32P
No full textThe β spectrum of 32P has been measured, using an intermediate image spectrometer. The shape factor is nearly linear, decreasing by 8 % between 250 and 1 600 keV. If the transition is considered as l-forbidden, a V-1,21 A interaction seems sufficient to interpret the data. An important contribution from the pseudoscalar interaction is dubious. No conclusion can be drawn concerning the conserved vector current theory. As a test of the spectrometer, we have measured the β spectrum of 24Na, and found the allowed shape within 0.5 % between 300 and 1 300 keV.Le spectre β de 32P a été mesuré au moyen d'un spectromètre à image intermédiaire. Le facteur de correction décroît à peu près linéairement de 8 % entre 250 et 1 600 keV. En considérant la transition comme l-interdite, on peut interpréter ce résultat au moyen d'une interaction V-1,21 A. La présence d'une interaction pseudoscalaire importante est douteuse. Aucune conclusion ne peut être tirée sur la validité de la théorie du courant vectoriel conservé. Comme test du spectromètre, nous avons étudié le spectre β de 24Na et trouvé la forme permise à 0,5 % entre 300 keV et 1 300 keV
- …
