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Université de Fribourg

Planar LAAPDs: temperature dependence, performance, and application in low-energy X-ray spectroscopy

Ludhova, Livia ; Amaro, F. D. ; Antognini, A. ; Biraben, F. ; Cardoso, J. M. R. ; Conde, C. A. N. ; Covita, D. S. ; Dax, A. ; Dhawan, S. ; Fernandes, L. M. P. ; Hänsch, T. W. ; Hughes, V.-W. ; Huot, Olivier ; Indelicato, P. ; Julien, L. ; Knowles, Paul E. ; Kottmann, F. ; Lopes, J. A. M. ; Liu, Y.-W. ; Monteiro, C. M. B. ; Mulhauser, Françoise ; Nez, F. ; Pohl, R. ; Rabinowitz, P. ; Santos, J. M. F. dos ; Schaller, Lukas A. ; Taqqu, D. ; Veloso, J. F. C. A.

In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2005, vol. 540, p. 169-179

An experiment measuring the 2S Lamb shift in muonic hydrogen (μ-p) was performed at the Paul Scherrer Institute, Switzerland. It required small and compact detectors for 1.9 keV X-rays (2P–1S transition) with an energy resolution around 25% at 2 keV, a time resolution better than 100 ns, a large solid angle coverage, and insensitivity to a 5 T magnetic field. We chose Large Area Avalanche...

Université de Fribourg

Shedding light on El Farol

Challet, Damien ; Marsili, M. ; Ottino, Gabriele

In: Physica A: Statistical Mechanics and its Applications, 2004, vol. 332, p. 469-480

We mathematize El Farol bar problem and transform it into a workable model. We find general conditions on the predictor space under which the convergence of the average attendance to the resource level does not require any intelligence on the side of the agents. Secondly, specializing to a particular ensemble of continuous strategies yields a model similar to the Minority Game. Statistical...

Université de Fribourg

Magnon dispersion in field-induced magnetically ordered phases

Matsumoto, Masashige ; Normand, Bruce ; Rice, T. M. ; Sigrist, Manfred

In: Journal of Magnetism and Magnetic Materials, 2004, vol. 272-276, p. 267-268

The magnon dispersion in the field-induced and pressure-induced antiferromagnetically (AF) ordered phase in TlCuCl₃ are studied. In the pressure-induced AF phase, there are two transverse phase (Goldstone) modes and one gapped longitudinal amplitude mode. A magnetic field lifts the degeneracy, and it gives rise to three separated magnon branches in the field-induced AF phase, where the lowest...

Université de Fribourg

Circulating-current states and ring-exchange interactions in cuprates

Normand, Bruce ; Oleś, Andrzej M.

In: Physica C: Superconductivity, 2004, vol. 408-410, p. 252-253

We consider circulating charge- and spin-current states in a generalised Hubbard model for the CuO₂ planes in cuprates. We investigate the parameter regimes for these phases in microscopic calculations on small clusters. We demonstrate that a positive ring-exchange interaction enhances (suppresses) spin- (charge-)flux phases.

Université de Fribourg

Kosmotropes and chaotropes: modelling preferential exclusion, binding and aggregate stability

Moelbert, Susanne ; Normand, Bruce ; De Los Rios, Paolo

In: Biophysical Chemistry, 2004, vol. 112, p. 45-57

Kosmotropic cosolvents added to an aqueous solution promote the aggregation of hydrophobic solute particles, while chaotropic cosolvents act to destabilise such aggregates. We discuss the mechanism for these phenomena within an adapted version of the two-state Muller–Lee–Graziano model for water, which provides a complete description of the ternary water/cosolvent/solute system for small...

Université de Fribourg

Exchange constants and spin dynamics in Mn₁₂-acetate

Honecker, A. ; Fukushima, N. ; Normand, Bruce ; Chaboussant, G. ; Güdel, Hans-Ulrich

In: Journal of Magnetism and Magnetic Materials, 2005, vol. 290-291, p. 966-969

We have obtained new inelastic neutron scattering (INS) data for the molecular magnet Mn₁₂-acetate which exhibit at least six magnetic peaks in the energy range 5–35 meV. These are compared with a microscopic Heisenberg model for the 12 quantum spins localised on the Mn ions, coupled by four inequivalent magnetic exchange constants. A fit to the magnetic susceptibility under the constraint...

Université de Fribourg

Structure and electronic structure of quasicrystal and approximant surfaces: a photoemission study

Naumović, Dusanka

In: Progress in Surface Science, 2004, vol. 75, p. 205-225

The structure and electronic structure of different high-symmetry surfaces of either quasicrystalline or approximant Al–Pd–Mn were studied by means of photoemission-based techniques such as X-ray photoelectron diffraction (XPD) and ultraviolet photoelectron spectroscopy. We find that the twofold (2f), 3f and 5f surfaces of icosahedral Al–Pd–Mn exhibit all the symmetry elements of the...

Université de Fribourg

Kaonic nitrogen X-ray transition yields in a gaseous target

Ishiwatari, T. ; Beer, G. ; Bragadireanu, A. M. ; Cargnelli, M. ; Curceanu-Petrascu, C. ; Egger, J.-P. ; Fuhrmann, H. ; Guaraldo, C. ; Kienle, P. ; Koike, T. ; Iliescu, M. ; Itahashi, K. ; Iwasaki, M. ; Lauss, B. ; Lucherini, V. ; Ludhova, Livia ; Marton, J. ; Mulhauser, Françoise ; Ponta, T. ; Schaller, Lukas A. ; Seki, R. ; Sirghi, D. L. ; Sirghi, F. ; Strasser, P. ; Zmeskal, J.

In: Physics Letters B, 2004, vol. 593, p. 48-54

The first measurement of the yields of three kaonic nitrogen X-ray transitions, using the DEAR (DAΦNE Exotic Atom Research) setup at the DAΦNE collider of Frascati, is reported. The yields are 41.5±8.7(stat.)±4.1(sys.)% for the n=7→6 transition, 55.0±3.9(stat.)±5.5(sys.)% for the n=6→5 transition and 57.4±15.2(stat.)±5.7(sys.)% for the n=5→4 transition at a density ρ=3.4ρNTP. By...

Université de Fribourg

Optical response for a discrete stripe

Benfatto, Larra ; Morais Smith, Cristiane

In: Physica C: Superconductivity, 2004, vol. 408-410, p. 453-454

The optical response of a charge stripe in the presence of pinning impurities is investigated. We address the issue of a discrete description of the stripe, and discuss its quantitative relevance with respect to a continuum one in the light of recent optical-conductivity measurements in cuprate compounds.

Université de Fribourg

Hydrogen density in nanostructured carbon, metals and complex materials

Züttel, Andreas ; Wenger, Pascal ; Sudan, Patrick ; Mauron, Philippe ; Orimo, Shin-ichi

In: Materials Science and Engineering B, 2004, vol. 108, p. 9-18

The challenge in the research on hydrogen storage materials is to pack hydrogen atoms or molecules as close as possible. Hydrogen absorbed in metals can reach a density of more than 150 kg m⁻³ (e.g. Mg₂FeH₆ or Al(BH₄)₃) at atmospheric pressure. For metallic hydrides, however, due to the large atomic mass of the transition metals the gravimetric hydrogen density is limited to less than...