Étude des réactions de protons de 400 MeV sur des noyaux de masse moyenne par une experience de coïncidences proton-gamma

A p-γ coincidence experiment has been performed with 400 MeV protons on medium nuclei. The angular and momentum analysis of the scattered protons demonstrates a nucleon primary quasi-free process. No indication of knockout reactions on clusters has been seen. The residual nuclei which have been identified from γ-ray spectra are mainly produced by evaporation processes. Intranuclear cascades followed by evaporation are sufficient to describe the multinucleon removal but residual nuclei near the target nucleus are sensitive to the nuclear structure.     

Two-dimensional time-resolved direct imaging through thick biological tissues: a new step toward noninvasive medical imaging

We report an original two-dimensional time-resolved direct imaging method for transillumination optical tomography that combines the time-gating and forward phase-conjugation properties of type II degenerate parametric amplification. An object with subcentimeter resolution embedded in 4-cm-thick chicken breast tissue was imaged with a signal-to-noise ratio of 2.     

Direct experimental characterization of the Bose-Einstein distribution of spatial fluctuations of spontaneous parametric down-conversion

We present, to the best of our knowledge, the first experimental demonstration by direct detection of the Bose-Einstein photon-number distribution of highly spatially multi-mode but temporally single mode spontaneous parametric down-conversion.Received: 20 November 2003, Published online: 6 January 2004PACS: 42.50.-p Quantum optics - 42.50.Ar Photon statistics and coherence theory - 42.65.-k Nonlinear optics - 42.65.Lm Parametric down conversion and production of entangled photons     

Phase sensitive parametric amplification of optical vortex beams

Optical vortex beams with different topological charges are amplified in a travelling wave phase sensitive parametric interaction. Amplified beams observed either in the near field or in the far field domains exhibit patterns that depend on the relative phase between the pump and the vortex beams. Experimental results are compatible with the conservation of orbital angular momentum of the input beam whatever phase matching conditions.     

Study of some rare decays of the K+ meson

In a search for very rare decays of the K⁺ meson we observed the K⁺→μ⁺νe⁺e^? and K⁺→e⁺ν e⁺e^? modes with branching ratios of (10±3) ×10^?7 and (2⁺²_?2)×10^?7 respectively. We also put new limits on a decay allowed by the alternate scheme of lepton conservation K⁺→π^?μ⁺e⁺, on a decay with double charged weak current K⁺→π^? e⁺e⁺ and on other forbidden decays K⁺→μ^?νe⁺e⁺ and K⁺→π⁺μ^±e^±.     

Gain in phase sensitive parametric image amplification

We report an experiment of type 2 parametric image amplification in a phase sensitive configuration. In the spatial frequency domain, the parametric gain corresponds to amplification or deamplification, depending on the relative phase of the input image with respect to the pump wave and on the spatial frequencies of the input image.     

Crystalline structure of poly(methyl-n-propylsilane)

The thermal behavior and physical structure of atactic poly(methyl-n-propylsilane) (PMPrS) have been investigated by complementary techniques. Temperature-dependent wide-angle X-ray scattering as well as thermal analysis clearly indicate that atactic PMPrS crystallizes below 40°C in a monoclinic lattice with PMPrS adopting an all-trans planar zigzag conformation. Above 40°C, the polymer is in the isotropic amorphous state. A restricted analysis of the structure factors of PMPrS has been performed, indicating that the zigzag planes most probably lie in (1 10) planes. The chains pack with little interpenetration, and the crystals may be considered as bundles of long, closely packed prisms. The restricted interlocking of neighboring chains results, in turn, in a poor register of the chains along the c-axis. Moreover, transmission electron microscopy reveals that the crystallized polymer adopts a lamellar microstructure, with parallel lamellae tending to form tight bundles. Both electron microscopy and small-angle X-ray scattering indicate crystal thicknesses of about 60 Å. Finally, PMPrS was found to crystallize with a nucleation-controlled type of kinetics. Avrami exponents were calculated as n ≈ 1, suggesting a fibrillar growth geometry compatible with the absence of spherulitic superstructure. A double-melting behavior is also observed for PMPrS. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1533–1543, 1997     

29Si nuclear magnetic resonance of poly(methylphenyl)silane

A Cl-terminated poly(methylphenyl)silane is synthesized and analyzed by ²⁹Si-NMR spectroscopy. Assignments are proposed for the different peaks observed. A modification of the chemical shifts of the peaks relative to the main chain atoms is observed upon heating. From these experimental results and computational calculations on model compounds, the assignments of the three main peaks to configurationally different Si atoms are confirmed. © 1996 John Wiley & Sons, Inc.     

Contribution to poly(m-xylylene adipamide) characterization: Hydrolysis,condensation, and oxidation in the melt

PAmXD,6 [poly(m-xylylene adipamide)] was processed using a Brabender plastograph at 30 rpm and at 265 ± 5°C. The evolution of the M_n versus mixing time determined from solution viscosity and chain end concentrations measurements shows that PAmXD,6 undergoes hydrolysis or condensation reactions depending on its initial molecular mass. Lower masses undergo condensation while higher masses undergo hydrolysis. The determination of water concentration in the melt during mixing time confirmed that this behavior is related to an equilibrium constant which was estimated at 500 ± 100. For a mixing period shorter than 20 min, a good correspondence was observed between M_n values determined either by chain end concentrations or by solution viscosity. However, for a mixing period longer than 20 min, discrepancy between M_n values using both methods witnesses the probable appearance of oxidative degradation of PAmXD,6. Mechanisms adapted from the established oxidation reactions of PA6 and PA6,6 are proposed to justify the PAmXD,6 behavior. Those reactions could explain the slight yellowing of PAmXD,6 during its processing. It was also shown that the PAmXD,6 Brabender plastograph mixing torque (30 rpm, 265 ± 5°C) is linearly related to M_n in a log/log diagram. © 1996 John Wiley & Sons, Inc.     

End‐capping of polystyrene by aliphatic primary amine by derivatization of precursor hydroxyl end group

A new and very efficient route for the synthesis of aliphatic primary amine terminated polystyrene (PS) is reported. In contrast to most known methods, only traditional commercially available reagents are used. PS is synthesized by anionic polymerization with a lithium counter ion and the living chains are end‐capped by a hydroxyl group upon addition of ethylene oxide followed by protonation. The ω‐hydroxyl end group is tosylated and the tosylate is then reacted with sodium azide. The azide terminal group is finally reduced into primary amine. The different steps of functionalization have been fully characterized by SEC, ToF‐SIMS, FTIR, and ¹H NMR. The amine content (= 98%) has been determined by acid‐base titration with perchloric acid. It clearly shows the efficiency of the synthetic method reported in this article although it is a multistep method. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1618–1629, 2000