Fluorénacènes et fluorénaphènes synthèses dans la série des indéno-fluorènes,XVII. Dérivés méthylés du cis-fluorénacène,du trans-fluorénacène et du trans-fluorénaphène

By condensation of the chlorides of the three 9-oxo-fluorene-2-, -3-, and -4-carboxylic acids with 4-bromo-1,2-xylene on one side, and of the chlorides of o-bromobenzoic acid, 2-bromo-4-methyl-benzoic acid and 2-bromo-4,5-dimethyl-benzoic acid with fluorene, 2-methylfluorene and 3-methylfluorene on the other side, followed by direct or indirect cyclisation and by final reduction, several new methyl derivatives of the indenofluorenes I, II and IV are synthesized.     

Cluster formation, pressure and density measurements in a granular medium fluidized by vibrations

We report experimental results on the behavior of an ensemble of inelastically colliding particles, excited by a vibrated piston in a vertical cylinder. When the particle number is increased, we observe a transition from a regime where the particles have erratic motions (“granular gas”) to a collective behavior where all the particles bounce like a nearly solid body. In the gas-like regime, we measure the density of particles as a function of the altitude and the pressure as a function of the number N of particles. The atmosphere is found to be exponential far enough from the piston, and the “granular temperature”, T, dependence on the piston velocity, V, is of the form , where is a decreasing function of N. This may explain previous conflicting numerical results. Received 1 February 1999     

Ammonia RF-Plasma Treatment of Tubular ePTFE Vascular Prostheses

A cylindrically-configured plasma treatment system in Radio Frequency Glow Discharges fed with ammonia was used to modify the internal surface of ePTFE arterial prostheses. The effects of RF power, NH₃ pressure, and treatment time on the surface chemical composition were characterized by XPS. The effect of moving the prosthesis within the plasma on the homogeneity of the surface treatment was also investigated. XPS studies were conducted in order to investigate the evolution of the treated surface during storage in atmosphere or water. Results show that the treatment at 20 W, for 250 seconds and under an ammonia pressure of 300 mTorr yielded a good compromise between ablation and substitution phenomena on the surface. With this treatment, fluorine content was decreased, while up to 11.6% of the surface atoms were substituted by nitrogen. Atmospheric storage up to 80 days shows a remodeling and oxidation of the surface by introducing up to 14.5% of oxygen. Finally, immersion in water for up to 7 hours showed a rapid defluorination of the treated surface.     

Self-mixing laser Doppler velocimetry with a dual-polarization Yb:Er glass laser

Self-mixing laser Doppler velocimetry using a dual-polarization Yb:Er-doped phosphate glass laser is investigated. The two orthogonally polarized eigenstates emitted simultaneously by the laser oscillator are employed to perform a heterodyne detection, allowing a complete characterization of the lateral sidebands generated via the optical feedback around the beating peak. Two different experimental set-ups have been implemented: (i) direct feedback on one of the two modes or (ii) crosstalk between the two modes via a non-reciprocal Faraday element. The results are analysed and applications to velocity measurements are discussed. Finally, some considerations of the noise correlated in phase and in opposite phase on the two polarization states are also discussed. PACS 42.55.Xi; 42.60.Rn; 42.81.Pa     

Mesures physiques sur la torche electronique

Sans résumé     

Compact diode-pumped passively Q-switched tunable Er-Yb double-clad fiber laser

Efficient repetitive passive Q switching of a cladding-pumped Er-Yb fiber laser has been demonstrated by use of an external-cavity configuration containing a Co(2+): ZnS crystal as a saturable absorber. Energies of as much as 60muJ in pulses of durations as short as 3.5 ns (FWHM), corresponding to a peak power of >10kW, have been generated, and the maximum slope efficiency with respect to the absorbed pump power was 13%. Using a bulk diffraction grating in the Littrow configuration to provide wavelength-selective feedback, we tuned the passively Q -switched fiber laser over 31 nm from 1532 to 1563 nm. The prospects for further improvement in performance are discussed.     

Observation of depression solitary surface waves on a thin fluid layer

We report the observation of depression solitary surface waves on a layer of mercury when its depth is thin enough compared to the capillary length. These waves, as well as the well known elevation solitary waves, are studied with a new measurement technique using inductive sensors. The shape of the solitary waves, their amplitude-dependent velocity, and their damping rates by viscosity are found in good agreement with theoretical predictions.     

Impact of Peptide Micropatterning on Endothelial Cell Actin Remodeling for Cell Alignment under Shear Stress

HSVEC behavior under physiological shear stress in vitro is investigated on PET surfaces micropatterned with both RGDS and WQPPRARI peptides. This technique allows (i) creating geometries on surface to guide cell orientation under shear stress and (ii) controlling surface chemical composition in order to modulate cell behavior. Under shear stress, endothelial cells adhere on patterned PET surfaces and present a more rapid orientation in flow direction in comparison to cells cultured on homogeneous surfaces. Micropatterned surfaces presenting a large surface area ratio of RGDS/WQPPRARI peptides induce fibrillar adhesion, while surfaces presenting an equal RGDS/WQPPRARI peptides surface area ratio preferentially induce focal adhesion.

     

Near-field amplitude and phase measurements using heterodyne optical feedback on solid-state lasers

Heterodyne optical feedback on a solid-state laser is experimentally investigated as an efficient tool to characterize coherently near-field evanescent waves. A well-known topography of evanescent field is obtained via a total internal reflection of the light beam emitted by a class B Yb:Er glass laser. A subwavelength size optical fiber tip is scanned to locally probe the resulting evanescent wave in the near field. After a frequency shifting using a pair of acousto-optic modulators, the collected light is optically reinjected to excite the relaxation oscillations of the laser. The resulting dynamical response simultaneously allows very sensitive measurements of the amplitude and the phase of the evanescent wave. Extension of these preliminary results to near-field optical microscopy is suggested and discussed.