508 research outputs found
Quantum coherence generated by interference-induced state selectiveness
The relations between quantum coherence and quantum interference are
discussed. A general method for generation of quantum coherence through
interference-induced state selection is introduced and then applied to `simple'
atomic systems under two-photon transitions, with applications in quantum
optics and laser cooling.Comment: 17 pages, 7 figures, to be published in Journal of Modern Optics'
special issue on quantum interferenc
Tracking quasi-classical chaos in ultracold boson gases
We study the dynamics of a ultra-cold boson gas in a lattice submitted to a
constant force. We track the route of the system towards chaos created by the
many-body-induced nonlinearity and show that relevant information can be
extracted from an experimentally accessible quantity, the gas mean position.
The threshold nonlinearity for the appearance of chaotic behavior is deduced
from KAM arguments and agrees with the value obtained by calculating the
associated Lyapunov exponent.Comment: 4 pages, revtex4, submitted to PR
Continuous spin reorientation in antiferromagnetic films
We study anisotropic antiferromagnetic one-layer films with dipolar and
nearest-neighbor exchange interactions. We obtain a unified phase diagram as a
function of effective uniaxial D_e and quadrupolar C anisotropy constants. We
study in some detail how spins reorient continuously below a temperature T_s as
T and D_e vary.Comment: 3 LaTeX pages, 3 eps figures. Submitted to JMMM on 25 May 2006.
Accepted on 21 July 200
Continuous-wave Doppler-cooling of hydrogen atoms with two-photon transitions
We propose and analyze the possibility of performing two-photon
continuous-wave Doppler-cooling of hydrogen atoms using the 1S-2S transition.
"Quenching" of the 2S level (by coupling with the 2P state) is used to increase
the cycling frequency, and to control the equilibrium temperature. Theoretical
and numerical studies of the heating effect due to Doppler-free two-photon
transitions evidence an increase of the temperature by a factor of two. The
equilibrium temperature decreases with the effective (quenching dependent)
width of the excited state and can thus be adjusted up to values close to the
recoil temperature.Comment: 11 pages, 4 figures in eps forma
Low Metal Loading (Au, Ag, Pt, Pd) Photo‐Catalysts Supported on TiO2 for Renewable Processes
Photo‐catalysts based on titanium dioxide, and modified with highly dispersed metallic nanoparticles of Au, Ag, Pd and Pt, either mono‐ or bi‐metallic, have been analyzed by multiple characterization techniques, including XRD, XPS, SEM, EDX, UV‐Vis and N2 adsorption/desorption. Mono‐metallic photo‐catalysts were prepared by wet impregnation, while bi‐metallic photocatalysts were obtained via deposition‐precipitation (DP). The relationship between the physico‐chemical properties and the catalyst’s behavior for various photo‐synthetic processes, such as carbon dioxide photo‐reduction to liquid products and glucose photo‐reforming to hydrogen have been investigated. Among the tested materials, the catalysts containing platinum alone (i.e., 0.1 mol% Pt/TiO2) or bi‐metallic gold‐containing materials (e.g., 1 wt% (AuxAgy)/TiO2 and 1 wt% (AuxPtz)/TiO2) showed the highest activity, presenting the best results in terms of productivity and conversion for both applications. The textural, structural and morphological properties of the different samples being very similar, the main parameters to improve performance were function of the metal as electron sink, together with optoelectronic properties. The high activity in both applications was related to the low band gap, that allows harvesting more energy from a polychromatic light source with respect to the bare TiO2. Overall, high selectivity and productivity were achieved with respect to most literature data
Data Fusion of Left Ventricle Electro-Anatomic Mapping and Multislice Computerized Tomography for Cardiac Resynchronisation Therapy Optimization
Cardiac Resynchronization Therapy is a treatment for bi-ventricular asynchronism. It can be optimized by the identification of the most effective pacing sites. The aim of this study is to provide a helpful tool to perform this identification by the fusion of electrical and anatomical information resulting from Electro-Anatomic Mapping (EAM) data and Multislice Computerized Tomography (MSCT) imaging. EAM data provide an approximation of the left ventricle (LV) 3D-surface (SEAM). Left cardiac chambers are segmented from MSCT imaging and surfaces are reconstructed (SCT). In order to represent this information in a unified framework, a three steps method is proposed: (1) the LV is separated from the left auricle on SCT providing S ′ CT; (2) a semi-automatic rigid registration method; (3) activation time delays is applied to SEAM and S ′ CT are estimated on S ′ CT from the EAM data. This method results in a graphical interface offering to clinicians means to identify abnormal electrical activity sites
Atomic motion in tilted optical lattices
This paper presents a formalism describing the dynamics of a quantum particle
in a one-dimensional, time-dependent, tilted lattice. The formalism uses the
Wannier-Stark states, which are localized in each site of the lattice, and
provides a simple framework allowing fully-analytical developments. Analytic
solutions describing the particle motion are explicit derived, and the
resulting dynamics is studied.Comment: 6 pages, 2 figs, submitted to EPJD, Springer Verlag styl
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