Synthesis and characterization of stabilized subnanometric cobalt metal particles

Subnanometric cobalt metallic particles, with an average size of 0.8 nm and an estimated number of 50 atoms, have been stabilized in the confined spaces within the nanopores of crystalline molecular sieves. Remarkably, these clusters show a rapid vanishing of the magnetization as the temperature is increased from 10 to 20 K because of the ferromagnetic-paramagnetic transition together with thermal fluctuations of the remaining moment. This dramatic reduction of the transition temperature is due to strong finite size effects. Such behavior, predicted for very small metallic particles, was never observed before due to the inherent difficulty in achieving subnanometric stable metallic particles.     

Settling motion of interacting solid particles in the vicinity of a plane solid boundary

The sedimentation of $N?1$ small arbitrarily-shaped solid bodies near a solid plane is addressed by discarding inertial effects and using 6N boundary-integral equations. Numerical results for 2 or 3 identical spheres reveal that combined wall–particle and particle–particle interactions deeply depend on the cluster's geometry and distance to the wall and may even cancel for a sphere which then moves as it were isolated. To cite this article: A. Sellier, C. R. Mecanique 333 (2005).     

Estimation spatio-temporelle d'un modèle de système de particules

Let X be a discrete time contact process (CP) on ${\mathbb{Z}}^2$ as defined by Durrett and Levin (1994). We study the estimation of the model based on space–time evolution of X, that is, $T+1$ successive observations of X on a finite subset S of sites. We consider the maximum marginal pseudo-likelihood (MPL) estimator and show that, when $T\to \infty$, this estimator is consistent and asymptotically normal for a non vanishing supercritical CP. To cite this article: X. Guyon, B. Pumo, C. R. Acad. Sci. Paris, Ser. I 340 (2005).     

Hybrid phase at the quantum melting of the Wigner crystal

We study the quantum melting of the two-dimensional Wigner crystal using a fixed node quantum Monte Carlo approach. In addition to the two already known phases (Fermi liquid at large density and Wigner crystal at low density), we find a third stable phase at intermediate values of the density. The third phase has hybrid behaviors in between a liquid and a solid. This hybrid phase has the nodal structure of a Slater determinant constructed out of the bands of a triangular lattice.     

Complete-angle projection diffuse optical tomography by use of early photons

We present the first, to our knowledge, experimental images of complex-shaped phantoms embedded in diffuse media by use of optical tomography. Imaging is based on a complete-angle projection tomographic technique that utilizes transmitted early photons. Results are contrasted with measurements obtained at later gates as well as pseudocontinuous-wave data. The scanning system developed employs noncontact illumination and detection technologies that allow for high spatial sampling of transmitted photons. Combining this system with complete-angle illumination is found to be an important strategy toward improved imaging performance, resulting in a better-posed inversion problem. The appropriateness of reconstruction algorithms similar to those employed in x-ray computed tomography are showcased, and suggestions for model improvements are provided.     

Mode-locked laser operation of epitaxially grown Yb:Klu(WO4)2 composites

Mode locking based on an epitaxial composite of the monoclinic double tungstate crystal Yb:KLu(WO4)2 is realized. A 100 microm thin Yb:KLu(WO4)2 layer grown on a KLu(WO4)2 substrate is used as an active medium in a laser passively mode locked by a semiconductor saturable absorber. Pulse durations of 114 fs have been achieved for an average power of 31 mW at 1030 nm. Results in the femtosecond and picosecond regimes of the Yb:KLu(WO4)2/KLu(WO4)2 laser are presented. The great potential of Yb-doped tungstate composite structures as active elements for mode-locked laser systems is demonstrated.     

Effect of molecular binding to a semiconductor on metal/molecule/semiconductor junction behavior

Diodes made by (indirectly) evaporating Au on a monolayer of molecules that are adsorbed chemically onto GaAs, via either disulfide or dicarboxylate groups, show roughly linear but opposite dependence of their effective barrier height on the dipole moment of the molecules. We explain this by Au-molecule (electrical) interactions not only with the exposed end groups of the molecule but also with its binding groups. We arrive at this conclusion by characterizing the interface by in situ UPS-XPS, ex situ XPS, TOF-SIMS, and Kelvin probe measurements, by scanning microscopy of the surfaces, and by current-voltage measurements of the devices. While there is a very limited interaction of Au with the dicarboxylic binding groups, there is a much stronger interaction with the disulfide groups. We suggest that these very different interactions lead to different (growth) morphologies of the evaporated gold layer, resulting in opposite effects of the molecular dipole on the junction barrier height.     

Stationary spatial patterns during bulk CO electrooxidation on platinum

We present experimental studies and mathematical modeling on pattern formation during bulk CO electrooxidation on Pt ring electrodes. Profiles of the interfacial potential drop in front of the working electrode were recorded with a potential probe. Stationary self-organized potential patterns were observed under potentiostatic conditions in dilute acidic and basic supporting electrolytes. The amplitude and shape of these potential patterns can be modified by an appropriate local perturbation of the interfacial potential drop. A mathematical model of the formation of these patterns reveals that the homogeneous state becomes unstable through a subcritical Turing-like bifurcation and that several patterned electrode states coexist in wide parameter ranges.     

Computational models of music perception and cognition II: Domain-specific music processing

In Part I [Purwins H, Herrera P, Grachten M, Hazan A, Marxer R, Serra X. Computational models of music perception and cognition I: The perceptual and cognitive processing chain. Physics of Life Reviews 2008, in press, doi:10.1016/j.plrev.2008.03.004], we addressed the study of cognitive processes that underlie auditory perception of music, and their neural correlates. The aim of the present paper is to summarize empirical findings from music cognition research that are relevant to three prominent music theoretic domains: rhythm, melody, and tonality. Attention is paid to how cognitive processes like category formation, stimulus grouping, and expectation can account for the music theoretic key concepts in these domains, such as beat, meter, voice, consonance. We give an overview of computational models that have been proposed in the literature for a variety of music processing tasks related to rhythm, melody, and tonality. Although the present state-of-the-art in computational modeling of music cognition definitely provides valuable resources for testing specific hypotheses and theories, we observe the need for models that integrate the various aspects of music perception and cognition into a single framework. Such models should be able to account for aspects that until now have only rarely been addressed in computational models of music cognition, like the active nature of perception and the development of cognitive capacities from infancy to adulthood.     

Water peak suppression: time-frequency vs time-scale approach

Wavelets are the most popular time-scale analysis tool. A well-known application of wavelets in nuclear magnetic resonance spectroscopy is water peak extraction/suppression. However, spectroscopists are more familiar with frequency than scale. So, from a spectroscopist point of view, a time-scale analysis tool (i.e., wavelets) is not natural and a time-frequency approach would be much more satisfactory. We explain a time-frequency solution to this problem based on Gabor analysis. As the two formalisms are closely linked together we continuously emphasize their similarities and differences. In particular we show that, here, the Gabor method is as efficient as the wavelet approach, and we give some examples. Those remarks also apply to other NMR problems solved previously with the continuous wavelet transform, such as quantification or dynamical phase correction.