NO2 disproportionation for the IR characterisation of basic zeolites

NO2 disproportionation on alkaline zeolites is used to generate nitrosonium (NO+) and nitrate ions on the surface, and the infrared vibrations observed are very sensitive to the cation chemical hardness and to the basicity of zeolitic oxygen atoms.     

Complex gold nanostructures derived by templating from diatom frustules

Diatom frustules have been used for the first time as templates for the fabrication of gold nanostructures; high-precision replicas featuring complex three-dimensional gold nanostructures from the nano- to the microscale were achieved.     

Quantum cryptography protocols robust against photon number splitting attacks for weak laser pulse implementations

We introduce a new class of quantum key distribution protocols, tailored to be robust against photon number splitting (PNS) attacks. We study one of these protocols, which differs from the original protocol by Bennett and Brassard (BB84) only in the classical sifting procedure. This protocol is provably better than BB84 against PNS attacks at zero error.     

Direct femtosecond laser writing of waveguides in As2S3 thin films

Single-channel waveguides and Y couplers were fabricated in chalcogenide thin films by use of femtosecond laser pulses from a 25-MHz repetition rate Ti:sapphire laser. Refractive-index differentials (delta n > 10(-2)) were measured through interferometric microscopy and are higher than the typical values reported for oxide glasses. The dependence of the index differential on the peak intensity reveals the nonlinear nature of the photosensitivity in arsenic trisulfide below its bandgap energy, and the refractive-index change is correlated to the photoinduced structural changes inferred by Raman spectroscopy data. A free-electron model to predict the parametric dependence of delta n is proposed.     

Medium-spin excitations of the neutron-rich 84Se isotope: Possible decrease in energy of the N = 50 neutron-core excitation

The ⁸⁴Se nucleus has been produced as fission fragment in the fusion reaction ¹⁸O + ²⁰⁸Pb at 85MeV bombarding energy and studied with the Euroball IV array. Medium-spin states of this neutron-rich isotope have been identified for the first time. Its level scheme has been obtained up to 4.9MeV excitation energy and spin I 7. Its structure is interpreted by analogy with those of the stable heavier isotones. The evolution of the energy of the N = 50 neutron-core excitation is discussed as a function of the proton number.     

First identification of excited states in the T_z\! = \!1/2 nucleus 93 Pd

The first experimental information about excited states in the N = Z + 1 nucleus ⁹³Pd is presented. The experiment was performed using a 205 MeV ⁵⁸Ni beam from the Vivitron accelerator at IReS, Strasbourg, impinging on a bismuth-backed ⁴⁰Ca target. Gamma-rays, neutrons and charged particles emitted in the reactions were detected using the Ge detector array Euroball, the Neutron Wall liquid-scintillator array and the Euclides Si charged-particle detector system. The experimental level scheme is compared with the results of new shell model calculations which predict a coupling scheme with aligned neutron-proton pairs to greatly influence the level structure of nuclei at low excitation energies.Received: 28 October 2003, Revised: 4 December 2003, Published online: 26 January 2004PACS: 21.10.Hw Spin, parity, and isobaric spin - 23.20.Lv transitions and level energies - 27.60. + j - 21.60.Cs Shell model     

Molecular dynamics simulations of a silver atom in water: evidence for a dipolar excitonic state

The properties of a silver atom in bulk water were studied for the first time by molecular dynamics simulations using two complementary mixed quantum-classical approaches. The first one consists of treating by quantum mechanics one electron only, which interacts with a classical silver cation and solvent through one-electron pseudopotentials. The second one is Car-Parrinello molecular dynamics that treats all the valence electrons quantum-mechanically. Very good agreement is obtained between these two methods, and the calculated absorption spectrum of the solvated silver atom agrees very well with experimental data. Both simulations reveal that the silver atom is in the critical region for the appearance of a dipolar excitonic state and exhibits a dipole moment of approximately 2 D with large fluctuations of +/-1 D. The structure of the solvation shell is also analyzed.     

Connection between Adam-Gibbs theory and spatially heterogeneous dynamics

We investigate the spatially heterogeneous dynamics in the extended simple point charge model of water using molecular dynamics simulations. We relate the average mass n* of mobile particle clusters to the diffusion constant and the configurational entropy. Hence, n* can be interpreted as the mass of the "cooperatively rearranging regions" that form the basis of the Adam-Gibbs theory of the dynamics of supercooled liquids. We also examine the time and temperature dependence of these transient clusters.     

Photosensitivity of As2S3 chalcogenide thin films at 1.5 microm

Chalcogenide glasses are promising candidates for all-optical switching and various nonlinear applications. However, we show that As2S3 thin films are photosensitive at wavelengths in the 1.5-microm telecommunication window. This sensitivity is evidenced by the formation of self-written waveguides in slabs, where channels as narrow as 1 microm are created. We also show the detrimental effects of such photosensitivity in ridge waveguides. This photosensitivity seems to occur only in thin-film form and not in bulk samples or fibers.     

Performance parameters for detection in low-flux coherent images

We analyze the optimization of low-flux coherent active imagery systems for target detection. We demonstrate that, unlike the Fisher ratio, the Bhattacharyya distance is an efficient figure of merit when one uses detection algorithms based on the generalized likelihood ratio test for realistic situations when the target and the background mean values are unknown. For example, we show that detection capabilities can be better if the pulse energy is divided into four shots, whereas using more than ten shots does not significantly improve the results.