Spectral function of the Anderson impurity model at finite temperatures

Using the functional renormalization group (FRG) and the numerical renormalization group (NRG), we calculate the spectral function of the Anderson impurity model at zero and finite temperatures. In our FRG scheme spin fluctuations are treated non-perturbatively via a suitable Hubbard-Stratonovich field, but vertex corrections are neglected. A comparison with our highly accurate NRG results shows that this FRG scheme gives a quantitatively good description of the spectral line-shape at zero and finite temperatures both in the weak and strong coupling regimes, although at zero temperature the FRG is not able to reproduce the known exponential narrowing of the Kondo resonance at strong coupling.Comment: 6 pages, 3 figures; new references adde

Nonequilibrium Spin Dynamics in the Ferromagnetic Kondo Model

Motivated by recent experiments on molecular quantum dots we investigate the relaxation of pure spin states when coupled to metallic leads. Under suitable conditions these systems are well described by a ferromagnetic Kondo model. Using two recently developed theoretical approaches, the time-dependent numerical renormalization group and an extended ow equation method, we calculate the real-time evolution of a Kondo spin into its partially screened steady state. We obtain exact analytical results which agree well with numerical implementations of both methods. Analytical expressions for the steady state magnetization and the dependence of the long-time relaxation on microscopic parameters are established. We find the long-time relaxation process to be much faster in the regime of anisotropic Kondo couplings. The steady state magnetization is found to deviate significantly from its thermal equilibrium value.Comment: 4 pages, 3 figures, final version as accepted by Physical Review Letter

Theory of Optical Tweezers

We derive a partial-wave (Mie) expansion of the axial force exerted on a transparent sphere by a laser beam focused through a high numerical aperture objective. The results hold throughout the range of interest for practical applications. The ray optics limit is shown to follow from the Mie expansion by size averaging. Numerical plots show large deviations from ray optics near the focal region and oscillatory behavior (explained in terms of a simple interferometer picture) of the force as a function of the size parameter. Available experimental data favor the present model over previous ones.Comment: 4 pages, 3 figure

Application of Lippmann interference photography to data storage

Lippmann's interference photography is an elegant process to record coloured images in the volume of a sensitive material. We propose to use this technique for wavelength multiplexed data storage in a page-oriented approach. Using computer simulations, we demonstrate that the capacities reached with this technique are similar to those reached by volume holographic data storage

Detection of the tagged or untagged photons in acousto-optic imaging of thick highly scattering media by photorefractive adaptive holography

We propose an original adaptive wavefront holographic setup based on the photorefractive effect (PR), to make real-time measurements of acousto-optic signals in thick scattering media, with a high flux collection at high rates for breast tumor detection. We describe here our present state of art and understanding on the problem of breast imaging with PR detection of the acousto-optic signal

On the Relation between Solar Activity and Clear-Sky Terrestrial Irradiance

The Mauna Loa Observatory record of direct-beam solar irradiance measurements for the years 1958-2010 is analysed to investigate the variation of clear-sky terrestrial insolation with solar activity over more than four solar cycles. The raw irradiance data exhibit a marked seasonal cycle, extended periods of lower irradiance due to emissions of volcanic aerosols, and a long-term decrease in atmospheric transmission independent of solar activity. After correcting for these effects, it is found that clear-sky terrestrial irradiance typically varies by about 0.2 +/- 0.1% over the course of the solar cycle, a change of the same order of magnitude as the variations of the total solar irradiance above the atmosphere. An investigation of changes in the clear-sky atmospheric transmission fails to find a significant trend with sunspot number. Hence there is no evidence for a yet unknown effect amplifying variations of clear-sky irradiance with solar activity.Comment: 16 pages, 7 figures, in press at Solar Physics; minor changes to the text to match final published versio

Design of interactive stations for patients suffering from severe impairmentscaused byAlzheimer’sdisease (the Tipatsma device)

Les troubles de la déambulation et de la manipulation incessante d’objets sont un phénomène fréquent chez les malades à un stade avancé de la maladie d’Alzheimer. Leur prise en charge est très complexe pour les institutions et peu de solutions satisfaisantes ont jusqu’à présent été proposées. Tableau interactif pour patients atteints de troubles sévères de la maladie d’Alzheimer (Tipatsma) se veut porteur d’une solution à destination de ces patients et de leur entourage. S’inscrivant dans une proposition thérapeutique non médicamenteuse, il met à portée de main un support d’activités sensorimotrices et cognitives placé sur le parcours de déambulation. Cet article retrace le processus itératif de conception et d’évaluation de la matérialisation de ce dispositif, dans une démarche constructiviste. Les deux itérations successives ont permis de mieux cerner les besoins des patients et d’apporter de nouvelles pistes pour l’amélioration des solutions proposées

Macrospin approximation and quantum effects in models for magnetization reversal

The thermal activation of magnetization reversal in magnetic nanoparticles is controlled by the anisotropy-energy barrier. Using perturbation theory, exact diagonalization and stability analysis of the ferromagnetic spin-s Heisenberg model with coupling or single-site anisotropy, we study the effects of quantum fluctuations on the height of the energy barrier. Opposed to the classical case, there is no critical anisotropy strength discriminating between reversal via coherent rotation and via nucleation/domain-wall propagation. Quantum fluctuations are seen to lower the barrier depending on the anisotropy strength, dimensionality and system size and shape. In the weak-anisotropy limit, a macrospin model is shown to emerge as the effective low-energy theory where the microscopic spins are tightly aligned due to the ferromagnetic exchange. The calculation provides explicit expressions for the anisotropy parameter of the effective macrospin. We find a reduction of the anisotropy-energy barrier as compared to the classical high spin-s limit.Comment: 10 pages, 11 figure

How Small Firms in the High Quality Food Sector Can Improve Their Business Performance: The Ligurian Oil Case Study

This paper proposes a methodology to create market value in the high quality food sector. The research starts from the consumer’s opinion about the attributes characterizing a high quality food, then a market research shows which are the attributes able to increase the good value in the different distribution channels. The paper shows how attributes are market and channel dependent, therefore attribute able to create value in certain markets and channels are uninflected in others. The methodology proposed is concretely applied on a case study: the Italian Extra virgin olive oil sector with a particular focus on the Ligurian olive oil, one of the most appreciated Italian oil. Likewise the methodology can be implemented form many other high quality food