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91.
92.
Mohapatra D Nakao M Nishida S Abe K Abe K Adachi I Aihara H Anipko D Arinstein K Asano Y Aulchenko V Aushev T Bahinipati S Bakich AM Balagura V Barbero M Bedny I Bitenc U Bizjak I Blyth S Bondar A Bozek A Bracko M Browder TE Chao Y Chen A Chen KF Chen WT Cheon BG Chistov R Choi Y Chuvikov A Cole S Dalseno J Danilov M Dash M Dragic J Drutskoy A Eidelman S Epifanov D Fratina S Gabyshev N Gershon T Gokhroo G Golob B Gorisek A Ha HC Haba J Hara T Hastings NC Hayasaka K Hayashii H Hazumi M Hinz L 《Physical review letters》2006,96(22):221601
We report the observation of the flavor-changing neutral current process b-->dgamma using a sample of 386 x 106 B meson pairs accumulated by the Belle detector at the KEKB e+e- collider. We measure branching fractions for the exclusive modes B--->rho-gamma, B0rho0gamma, and B0omegagamma. Assuming that these three modes are related by isospin, we find B(B-->(rho,gamma)gamma)=[Formula: See Text] with a significance of 5.1sigma. This result is used to determine the ratio of Cabibbo-Kobayashi-Maskawa matrix elements /Vtd/Vts/ to be [Formula: See Text]. 相似文献
93.
Symmetry considerations yield the general form, up to second order
terms, for the deformation elastic energy of a nematic monolayer,
composed by symmetric achiral molecules, on a rigid planar
substrate. The deformation energy contains an elastic contribution
linear in the deformation tensor, whose elements are the spatial
derivatives of the average molecular orientation. This linear
Lifshitz-invariant-like term can be responsible for a ground state
of the nematic monolayer periodically deformed if the relevant
elastic constant is stiffer than a critical value. The wave-length
of the modulation diverges at the transition threshold. We show
that only large variations of the tilt angle form stable states.
The effect of a destabilizing electric or magnetic field on the
layer is to induce (i) the transition towards the tilt-modulated
phase, while (ii) for higher enough values of the field the
modulation is destroyed. 相似文献
94.
Ludivine Lebedel Ana Ard Amlie Martin Jrme Dsir Agns Mingot Marialuisa Aufiero Nuria AiguabellaFont Ryan Gilmour Jesus Jimnez‐Barbero Yves Blriot Sbastien Thibaudeau 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(39):13896-13900
An expansive NMR‐based structural analysis of elusive glycosyl cations derived from natural and non‐natural monosaccharides in superacids is disclosed. For the first time, it has been possible to explore the consequence of deoxygenation and halogen substitution at the C2 position in a series of 2‐halogenoglucosyl, galactosyl, and mannosyl donors in the condensed phase. These cationic intermediates were characterized using low‐temperature in situ NMR experiments supported by DFT calculations. The 2‐bromo derivatives display intramolecular stabilization of the glycosyl cations. Introducing a strongly electron‐withdrawing fluorine atom at C2 exerts considerable influence on the oxocarbenium ion reactivity. In a superacid, these oxocarbenium ions are quenched by weakly coordinating SbF6? anions, thereby demonstrating their highly electrophilic character and their propensity to interact with poor nucleophiles. 相似文献
95.
96.
Ali Liazid Gerardo F. Barbero Miguel Palma Jamal Brigui Carmelo G. Barroso 《Chromatographia》2010,72(5-6):417-424
The development of a rapid, reliable and reproducible LC method for the determination and quantification of 13 polyphenols (gallic acid, protocatechuic aldehyde, gentisic acid, catechin, vanillinic acid, caffeic acid, vanillin, epicatechin, syringaldehyde, p-coumaric acid, ferulic acid, sinapic acid and resveratrol) in grapes and derived products is reported. The polyphenols were separated in less than 8 min. Employed was an RP-18e (100 mm × 4.6 mm) monolithic type column. A gradient method with the following solvents was utilised for the chromatographic separation: A: 90% water, 2% acetic acid in methanol, and B: 90% methanol, 2% acetic acid in water. Two detectors in series were employed: a UV–Vis detector and a fluorescence excitation/emission detector. Influence of temperature (15–40 °C) and solvent flow rate (2–5 mL min?1) on the separation were studied, and 25 °C and 2.5 mL min?1 were found to be the optimum conditions. The relative standard deviations of the resulting peak areas, for both intra- and inter- experiments, were less than 2.4 and 2.6%, respectively. Finally, the developed method has been utilised for the quantification of the polyphenols in real samples. 相似文献
97.
Baena-Moncada Angélica María Coneo-Rodríguez Rusbel La Rosa-Toro Adolfo Pastor Elena Barbero Cesar Planes Gabriel Ángel 《Journal of Solid State Electrochemistry》2019,23(9):2683-2693
Journal of Solid State Electrochemistry - A new family of PtFe catalysts supported on hierarchical porous carbon (HPC), with different porous sizes, was developed and tested as cathodes in oxygen... 相似文献
98.
99.
A. L. Alexe-Ionescu R. Barberi G. Barbero J. J. Bonvent M. Giocondo 《Applied Physics A: Materials Science & Processing》1995,61(4):425-430
The orientation induced by a Langmuir-Blodgett film on a Nematic Liquid Crystal (NLC) is theoretically analyzed. We show that the effective surface energy is due to different contributions connected with steric and van der Waals interactions between the nematic and the solid substrate. The analysis shows that the Langmuir-Blodgett film orientation depends on the surface density of the molecules. The initial homeotropic orientation may become unstable giving rise to a tilted film. The average orientation of the nematic molecules is also analyzed. We show that, in the event in which the steric interaction Nematic-Langmuir-Blodgett film is very large with respect to the dispersion interaction Nematic-Substrate, the nematic orientation coincides with the one of the film. On the contrary, when the two interactions are comparable, the orientation of the two media may differ. In particular, we analyze how the stable orientation depends on the surface molecular density of the film. 相似文献
100.
Silylcupration of allene using phenyldimethylsilylcopper 1 followed by BF3-mediated reaction with alpha,beta-unsaturated nitriles at -40 degrees C affords allylsilane-vinylsilane-containing ketones resulting from consecutive addition (1,2 and 1,4) of the intermediate allyl- and vinylcopper species formed in the silylcupration of allene. 相似文献