Solid-state NMR and EPR study of fluorinated carbon nanofibers

Carbon nanofibers were fluorinated in two manners, in pure fluorine gas (direct fluorination) and with a fluorinating agent (TbF₄ during the so-called controlled fluorination). The resulting fluorinated nanofibers have been investigated by solid-state nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). This underlines that the fluorination mechanisms differ since a (CF)_n structural type is obtained, whatever the temperature, with the controlled reaction, whereas, during the direct process, a (C₂F)_n type is formed over a wide temperature range. Through a careful characterization of the products, i.e. density of dangling bonds (as internal paramagnetic centers), structural type (acting on molecular motion) and specific surface area (related to the amount of physisorbed O₂), the effect of atmospheric oxygen molecules on the spin-lattice nuclear relaxation has been underlined.     

Une preuve de la conjecture de Mahler-Manin

Sans résumé Oblatum 7-IV-1995     

Double entanglement and quantum cryptography

We propose a quantum transmission based on bi-photons, which are doubly-entangled both in polarisation and phase. This scheme finds a natural application in quantum cryptography, where we show that an eventual eavesdropper is bound to introduce a larger error on the quantum communication than for a single entangled bi-photon communication, when he steels the same information. Received 23 July 2001 / Received in final form 30 November 2001 Published online 24 September 2002     

Solid state NMR study of nanodiamond surface chemistry

Solid state NMR measurements using 13C, 1H and 19F nuclei (MAS, CP-MAS) underline the surface chemistry of nanodiamonds from different synthesis (detonation, high pressure high temperature and shock compression). The comparison of the spin-lattice relaxation times T1 and physicochemical characterization (spin densities of dangling bonds, specific surface area and Raman and infrared spectroscopies) for the various samples, as synthesized, chemically purified and fluorinated allows the nature and the location of the various groups, mainly C-OH, C-H and C-F to be investigated. C-OH groups are located only on the surface whereas C-H and dangling bonds seem to be distributed in the whole volume. Fluorination was studied as a chemical treatment for purification and change of the hydrophobicity through the conversion of the C-OH groups into covalent C-F bonds.     

MK801 attenuates secondary injury in a mouse experimental compression model of spinal cord trauma

Background  

Glutamergic excitotoxicity has been shown to play a deleterious role in the pathophysiology of spinal cord injury (SCI). The aim of this study was to investigate the neuroprotective effect of dizocilpine maleate, MK801 (2 mg/Kg, 30 min and 6 hours after injury) in a mice model of SCI. The spinal cord trauma was induced by the application of vascular clips to the dura via a four-level T5-T8 laminectomy.     

Crystal to crystal transformations and polymorphism in anionic hydrogen bonding networks stabilized by crown ether metal complexes

15-crown[5] or 18-crown[6] complexes of alkali, transition metal and ammonium cations together with polyprotic inorganic and organic anions have been used to construct crystalline molecular salts based on hydrogen bonded anionic networks. This new class of organic-inorganic complexes displays a variety of crystal-to-crystal transformations, mainly associated to the loss/uptake of water molecules and/or to the ionic reorganization accompanying phase transitions on varying the temperature. The dehydration and phase transition processes have been investigated by DSC, TGA and variable temperature X-ray powder diffraction. Most of the complexes described herein have been prepared by solid state mixing of the solid reactants.     

Dispersion spreading of biphotons in optical fibers and two-photon interference

We present the first observation of two-photon polarization interference structure in the second-order Glauber correlation function of two-photon light generated via type-II spontaneous parametric down-conversion. In order to obtain this result, two-photon light is transmitted through an optical fiber and the coincidence distribution is analyzed by means of the start-stop method. Beyond the experimental demonstration of an interesting effect in quantum optics, these results also have considerable relevance for quantum communications.     

Parametric solitons in two-dimensional lattices of purely nonlinear origin

We demonstrate spatial solitons via twin-beam second-harmonic generation in hexagonal lattices realized by poling lithium niobate planar waveguides. These simultons can be steered by acting on power, direction, and wavelength of the fundamental frequency input.     

Instrumental neutron activation analysis of peloids from main Cuban spas

Journal of Radioanalytical and Nuclear Chemistry - Peloids from some Cuban spas (San Diego, Elguea, Santa Lucía, Cajío and Colony) have been studied using Instrumental Neutron Activation...