First evaluation of the thermodynamic properties for spheres to elongated micelles transition of some propanediyl-alpha,omega-bis(dimethylalkylammonium bromide) surfactants in aqueous solution

The apparent and partial molar enthalpies, apparent molar volumes, and adiabatic compressibilities at 298 K of the aqueous solutions of the cationic gemini surfactants propanediyl-alpha,omega-bis(octyldimethylammonium bromide) (8-3-8) and propanediyl-alpha,omega-bis(dodecyldimethylammonium bromide) (12-3-12) have been measured as a function of concentration. The trends of the partial molar enthalpies versus concentration are the first well documented thermodynamic evidence of sphere to rod transition in the micellar phase, involving a detectable quantity of heat, and allow the determination of the change in enthalpy associated with this transition. The changes in enthalpies upon micellization and for the sphere to elongated micelles transition, DeltaH(s)(-->)(r), have been obtained from the experimental data by using a pseudo-phase transition approach: -1.5 kJ mol(-1) for 8-3-8 and -3.9 kJ mol(-1) for 12-3-12. No evidence of the above transition is found in the trends of volumetric properties versus m. The apparent adiabatic molar compressibilities for the compounds under investigation are also reported here for the first time: a negative group contribution for the methylene group is evaluated, when the surfactants are present in solution as a single molecule, reflecting its solvation structure. In the micellar phase, the -CH(2)- group contribution becomes positive. A value of 1.17 x 10(-3) cm(3) bar(-1) mol(-1) for the change in adiabatic molar compressibility upon micellization is obtained. The lower values of the methylene group contributions to the volumetric properties for the monomers support the hypothesis of partial association of the chains before the cmc.     

Cladding mode reorganization in high-refractive-index-coated long-period gratings: effects on the refractive-index sensitivity

We theoretically and experimentally investigated the reorganization of cladding modes in high-refractive-index- (HRI-) coated long-period gratings (LPGs), focusing on the influence of refractive-index sensitivity. When azimuthally symmetric nanoscale HRI coatings are deposited along LPG devices, a significant modification of the distribution of cladding modes occurs, depending on the layers' features (refractive index and thickness) and on the external refractive index. In particular, if these parameters are properly chosen, a transition between cladding modes and overlay modes occurs. Numerical and experimental effects of the mode transition on the sensitivity of the surrounding refractive index are described.     

Plume separation effect in pulsed laser ablation deposition

The results of a new geometrical configuration of pulsed laser ablation deposition technique that uses a hemi-cylindrical transparent plastic substrate are presented and discussed. With the new arrangement, two distinct components with different material compositions have been clearly observed. While the first component comprises atoms, ions and molecules and constitutes visible or the so-called luminous plume, the second component is formed of fragments, clusters and liquid droplets and is invisible to the naked eye. The latter component constitutes a major part of the ablated material. The luminous plume symmetry axis does not coincide with the mass distribution symmetry axis. In the case of Si ablation and 45° incident beam angle, the maximum deflection angle of the luminous plume reaches 30° with respect to the normal to the target surface, while the deflection angle of the second component is higher than 40°. The change in the target morphology and the dependence of the composition of the ablated material on local fluence, along with the hydrodynamic effects, is sought to explain this previously unexpected and unreported phenomenon. PACS 61.80.Ba; 47.35.+i; 52.38.Mf; 81.15.Fg     

Recycling asymmetric hydrogenation catalysts by their immobilisation onto ion-exchange resins

New systems based on cationic chiral phosphine-rhodium complexes anchored to a commercial cation-exchange gel-type resin showed high efficiency and easy recycling in the asymmetric hydrogenation of prochiral olefins.     

On spectral geometry of minimal parallel submanifolds

We consider the problem of characterizing some minimal submanifolds using the spectrum⁰Spec of the Laplace-Beltrami operator acting on fucntions. In particular we characterize then-dimensional compact minimal totally real parallel submanifolds immersed in the complex projective spaceCP ⁿ, 3≤n≤6, by their⁰Spec in the class of all compact totally real minimal submanifolds ofCP ⁿ. Moreover, we characterize the Clifford torus by its⁰Spec in the class of all compact minimal submanifolds of the Euclidean sphereS ⁿ⁺¹(1). Authors supported by funds of the University of Lecce and the M.U.R.S.T.     

The Ghirlanda-Guerra Identities

If the variance of a Gaussian spin-glass Hamiltonian grows like the volume the model fulfills the Ghirlanda-Guerra identities in terms of the normalized Hamiltonian covariance.     

Double XeCl laser with lateral UV preionization

We present a very compact and very reliable laser system formed of two discharge sections both with lateral UV preionization. The discharge electrodes are contained in a single vessel and form an oscillator-amplifier system. A single spark gap switches on both circuits. By applying a generalized self-filtering unstable resonator to the oscillator and injecting the laser beam into the single pass amplifier, an output beam of 105 mJ, with a brightness of 5.5×10¹³ W cm^–2Sr^–1 has been obtained. Moreover, by applying a pulse-forming network in one discharging circuit, the duration of the discharge breakdown has been increased and output laser pulses of 40 ns FWHM, and 80 ns base width duration (at 10% points) and of energy 100 mJ are obtained.