3,514 research outputs found
Diffusion of a liquid nanoparticle on a disordered substrate
We perform molecular dynamic simulations of liquid nanoparticles deposited on
a disordered substrate. The motion of the nanoparticle is characterised by a
'stick and roll' diffusive process. Long simulation times (),
analysis of mean square displacements and stacking time distribution functions
demonstrate that the nanoparticle undergoes a normal diffusion in spite of long
sticking times. We propose a phenomenological model for the size and
temperature dependence of the diffusion coefficient in which the activation
energy scales as .Comment: Accepted for publication in Phys. Rev.
Mechanisms for Lasing with Cold Atoms as the Gain Medium
We realize a laser with a cloud of cold rubidium atoms as gain medium, placed
in a low-finesse cavity. Three different regimes of laser emission are observed
corresponding respectively to Mollow, Raman and Four Wave Mixing mechanisms. We
measure an output power of up to 300 W and present the main properties of
these different lasers in each regime
Pressure dependence of the oxygen isotope effect in YBaCuO
We have carried out measurements of the pressure dependence to 1.2 GPa of the
oxygen isotope effect on in the high- superconductor
YBaCuO using a clamp cell in a SQUID magnetometer. This compound
lies close to, but just above, the 1/8 doping point where in
LaSrCuO marked anomalies in isotope effects occur. Both
isotopes show the same very large pressure dependence of with the result
that the isotope exponent remains low (0.08) but increases slightly with
increasing pressure. This is discussed in terms of stripe suppression, a
competing pseudogap and the effect of superconducting fluctuations.Comment: 4 pages, 1 figures, submitted to Phys. Rev.
Influence of Ablation on Differential Arc Resistance
The influence of ablation on the du/di behavior of an arc in a model gas circuit breaker was examined. Specifically the transition from a state without ablation in the nozzle towards states with ablation was of interest, since prior work indicated that for high currents the voltage becomes constant or du/di gets even positive if ablation is present. Measurements with different blow pressures and rectangular DC currents of varying amplitude were compared, using PMMA-nozzles and dry air as blowing gas. Ablation was measured by weighing the nozzle, scanning the cross section, and using a coordinate measuring machine. The results agreed well, and confirmed that higher pressure shifts the du/di curve towards more favorable values
Determining the Time Constant of Arcs at Arbitrary Current Levels
For the development and optimization of gas circuit breakers and switchgear, a detailed understanding of the arc related processes is of great importance. Ideally, analytical or numerical models with predicitive capability can be found and used during the design process preceding costly and time-consuming experiments.In the present contribution, we report on a novel measurement and evaluation technique to determine the thermal arc time constant ("thermal inertia") that is commonly used in simple black-box models to describe the arc's dynamical properties. The method is introduced and applied to example arcs under varying blow gas conditions in air
Isotope Effect in the Superfluid Density of HTS Cuprates: Stripes, Pseudogap and Impurities
Underdoped cuprates exhibit a normal-state pseudogap, and their spins and
doped carriers tend to spatially separate into 1- or 2-D stripes. Some view
these as central to superconductivity, others as peripheral and merely
competing. Using LaSrCuZnO we show that an oxygen
isotope effect in and in the superfluid density can be used to
distinguish between the roles of stripes and pseudogap and also to detect the
presence of impurity scattering. We conclude that stripes and pseudogap are
distinct, and both compete and coexist with superconductivity.Comment: Revised submission to PRL with added appendix on a possible isotope
effect in the effective mass, 4 pages, 3 figure
Risk analysis to support operation and maintenance of an ageing dock-gate for the Port of Marseille Authority
The dry dock n°10 is a strategic infrastructure of the Port of Marseille Authority: its dimensions (465 x 85 m) place it among the biggest dry docks in Europe. Built in the seventies, it is isolated from the sea by a dock-gate in prestressed concrete. Faced to the ageing of this dock-gate, the Port of Marseille Authority wished to make the most of its knowledge in order to assess the feasibility of two considered operation scenarios: use the dry dock for ship repair or for building new civil engineering structures. In this context, OXAND and the Port of Marseille Authority worked together so as to obtain formal and objective decision-making indicators. These indicators took into account the different operation stakes of the dry dock (security, availability), the condition diagnosis and the ageing prognosis of components and facilities of the dock-gate, along with adapted maintenance actions and related costs. The risk analysis methodology used for this study allowed (1) to characterize the risks linked to each foreseen operation scenario, (2) to identify the most appropriate actions to control these risks, integrating operation constraints (e.g.: need to put the dock-gate in dry dock), (3) to rank these actions regarding their cost/benefit ratio and thus (4), to build a maintenance plan
Absence of an isotope effect in the magnetic resonance in high- superconductors
An inelastic neutron scattering experiment has been performed in the
high-temperature superconductor to search for an
oxygen-isotope shift of the well-known magnetic resonance mode at 41 meV.
Contrary to a recent prediction (I. Eremin, {\it et al.}, Phys. Rev. B {\bf
69}, 094517 (2004)), a negligible shift (at best +0.2 meV) of the
resonance energy is observed upon oxygen isotope substitution
(OO). This suggests a negligible spin-phonon interaction in
the high- cuprates at optimal doping.Comment: 3 figure
X-Ray Scattering at FeCo(001) Surfaces and the Crossover between Ordinary and Normal Transitions
In a recent experiment by Krimmel et al. [PRL 78, 3880 (1997)], the critical
behavior of FeCo near a (001) surface was studied by x-ray scattering. Here the
experimental data are reanalyzed, taking into account recent theoretical
results on order-parameter profiles in the crossover regime between ordinary
and normal transitions. Excellent agreement between theoretical expectations
and the experimental results is found.Comment: 9 pages, Latex, 1 PostScript figure, to be published in Phys.Rev.
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