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Search Results: 1 - 10 of 33180 matches for " Daniel Bloch "
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Comment on "Optical Response of Gas-Phase Atoms at Less than lambda/80 from a Dielectric Surface" published by K. A. Whittaker et al.
Daniel Bloch
Physics , 2014, DOI: 10.1103/PhysRevLett.114.049301
Abstract: Comment on "Optical Response of Gas-Phase Atoms at Less than lambda/80 from a Dielectric Surface" published by K. A. Whittaker, J. Keaveney, I. G. Hughes, A. Sargsyan, D. Sarkisyan, C. S. Adams in Phys. Rev. Lett. Lett 112 253201 (2014)
Resonant infiltration of an opal: reflection lineshape and contribution from in-depth regions
Isabelle Maurin,Daniel Bloch
Physics , 2015,
Abstract: We analyze the resonant variation of the optical reflection on an infiltrated artificial opal made of transparent nanospheres. The resonant infiltration is considered as a perturbation in the frame of a previously described one-dimensional model based upon a stratified effective index. We show that for a thin slice of resonant medium, the resonant response oscillates with the position of this slice. We derive that for adequate conditions of incidence angle, this spatially oscillating behavior matches the geometrical periodicity of the opal, and hence the related density of resonant infiltration. Close to these matching conditions, the resonant response of the global infiltration varies sharply in amplitude and shape with the incidence angle and polarization. The corresponding resonant reflection originates from a rather deep infiltration, up to several wavelengths or layers of spheres. Finally, we discuss the relationship between the present predictions and our previous observations on an opal infiltrated with a resonant vapor.
Spectroscopy in Extremely Thin Vapor Cells : Sensitivity Issues
Martial Ducloy,Daniel Bloch
Physics , 2005,
Abstract: This communication focuses on sensitivity issues - a long-time concern of J. Hall- in the spectroscopic analysis of Extremely Thin Cell of dilute vapor. With these small and often submicrometric slices of vapor, the most uncommon features are the relatively small number of interacting atoms, and the fact that essential results are already obtained in the frame of linear spectroscopy.
Atom-Wall interaction
Daniel Bloch,Martial Ducloy
Physics , 2005,
Abstract: This chapter deals with atom-wall interaction occurring in the "long-range" regime (typical distances: 1-1000 nm), when the electromagnetic fluctuations of an isolated atom are modified by the vicinity with a surface. Various regimes of interaction are discussed in an Introductory part, from Cavity Quantum ElectroDynamics modifications of the spontaneous emission, to Casimir effect, with emphasis on the atom-surface van der Waals interaction, characterized as a near-field interaction governed by a z-3 dependence. The major part of the Chapter focuses on the experimental measurements of this van der Waals interaction, reviewing various recent techniques, and insists upon optical techniques, and notably selective reflection spectroscopy which is particularly well-suited when excited atoms are considered. A review of various experiments illustrates the specific effects associated with a resonant coupling between the atomic excitation and surface modes, from van der Waals repulsion to surface-induced resonant transfer, and with anisotropy effects, including metastability transfer induced by a quadrupole contribution in the interaction. The effects of a thermal excitation of the surface -with a possible remote energy transfer to an atom-, and of interaction with nanobodies -which are intrinsically non planar- are notably discussed among the prospects.
Fluoxetine and Suicide Rates: Suicide and the Economy
Carlos A Camargo ,Daniel A Bloch
PLOS Medicine , 2006, DOI: 10.1371/journal.pmed.0030501
A Tabulation and Critical Analysis of the Wavelength-Dependent Dielectric Image Coefficient for the Interaction Exerted by a Surface onto a Neighbouring Excited Atom
Solomon Saltiel,Daniel Bloch,Martial Ducloy
Physics , 2006, DOI: 10.1016/j.optcom.2006.03.034
Abstract: The near-field interaction of an atom with a dielectric surface is inversely proportional to the cube to the distance to the surface, and its coupling strength depends on a dielectric image coefficient. This coefficient, simply given in a pure electrostatic approach by (eps-1) / (eps+1) with eps the permittivity, is specific to the frequency of each of the various relevant atomic transition : it depends in a complex manner from the bulk material properties, and can exhibit resonances connected to the surface polariton modes. We list here the surface resonances for about a hundred of optical windows whose bulk properties are currently tabulated. The study concentrates on the infrared domain because it is the most relevant for atom-surface interaction. Aside from this tabulation, we discuss simple hints to estimate the position of surface resonances, and how uncertainties in the bulk data for the material dramatically affect the predictions for the image coefficient. We also evaluate the contribution of UV resonances of the material to the non resonant part of the image coefficient.
The role of strategy and redundancy in diagnostic reasoning
Ralph F Bloch, Daniel Hofer, Sabine Feller, Maria Hodel
BMC Medical Education , 2003, DOI: 10.1186/1472-6920-3-1
Abstract: Using an interactive computer simulation that includes 21 unique cases with seven sensory loss patterns and either concordant, neutral or discordant textual information, 21 3rd year medical students, 21 6th year and 21 senior neurology residents each examined 15 cases over the course of one session. An additional 23 psychology students examined 24 cases over two sessions, 12 cases per session. Subjects also took a seven-item MCQ exam of seven classical patterns presented visually.Knowledge of sensory patterns and diagnostic accuracy are highly correlated within groups (R2 = 0.64). The total amount of information gathered for incorrect diagnoses is no lower than that for correct diagnoses. Residents require significantly fewer tests than either psychology or 6th year students, who in turn require fewer than the 3rd year students (p < 0.001). The diagnostic accuracy of subjects is affected both by level of training (p < 0.001) and concordance of clinical information (p < 0.001). For discordant cases, refutation testing occurs significantly in 6th year students (p < 0.001) and residents (p < 0.01), but not in psychology or 3rd year students. Conversely, there is a stable 55% excess of confirmatory testing, independent of training or concordance.Knowledge and practice are both important for diagnostic success. For complex diagnostic situations reasoning components employing redundancy seem more essential than those using strategy.A major part of the undergraduate medical curriculum is dedicated to teaching the art and science of diagnosing illness and disease. Furthermore, when assessing the clinical competence of medical students, examiners must infer knowledge and reasoning skills from the behavior and the responses of the candidates.It stands to reason then that medical teachers should possess a thorough understanding of diagnostic reasoning as a "basic science" of medical education. In reality, however, our comprehension of the diagnostic reasoning process is hazy a
Theoretical study of dark resonances in micro-metric thin cells
Horacio Failache,Lorenzo Lenci,Arturo Lezama,Daniel Bloch,Martial Ducloy
Physics , 2007, DOI: 10.1103/PhysRevA.76.053826
Abstract: We investigate theoretically dark resonance spectroscopy for a dilute atomic vapor confined in a thin (micro-metric) cell. We identify the physical parameters characterizing the spectra and study their influence. We focus on a Hanle-type situation, with an optical irradiation under normal incidence and resonant with the atomic transition. The dark resonance spectrum is predicted to combine broad wings with a sharp maximum at line-center, that can be singled out when detecting a derivative of the dark resonance spectrum. This narrow signal derivative, shown to broaden only sub-linearly with the cell length, is a signature of the contribution of atoms slow enough to fly between the cell windows in a time as long as the characteristic ground state optical pumping time. We suggest that this dark resonance spectroscopy in micro-metric thin cells could be a suitable tool for probing the effective velocity distribution in the thin cell arising from the atomic desorption processes, and notably to identify the limiting factors affecting desorption under a grazing incidence.
Three dimensional confinement of vapor in nanostructures for sub-Doppler optical resolution
Philippe Ballin,Elias Moufarej,Isabelle Maurin,Athanasios Laliotis,Daniel Bloch
Physics , 2013, DOI: 10.1063/1.4809668
Abstract: We confine a Cs thermal vapor in the interstitial regions of a glass opal. We perform linear reflection spectroscopy on a cell whose window is covered with a thin film (10 or 20 layers) of ~ 1000 nm (or 400 nm) diameter glass spheres, we observe sub-Doppler structures in the optical spectrum for a large range of oblique incidences. This original feature associated with the inner (3-dimension) confinement of the vapor in the interstitial regions of the opal, evokes a Dicke narrowing. We finally consider possible micron-size references for optical frequency clocks based on weak, hard to saturate, molecular lines.
The optical interface of a photonic crystal: Modeling an opal with a stratified effective index
Isabelle Maurin,Elias Moufarej,Athanasios Laliotis,Daniel Bloch
Physics , 2014,
Abstract: An artificial opal is a compact arrangement of transparent spheres, and is an archetype of a three-dimensional photonic crystal. Here, we describe the optics of an opal using a flexible model based upon a stratified medium whose (effective) index is governed by the opal density in a small planar slice of the opal. We take into account the effect of the substrate and assume a well- controlled number of layers, as it occurs for an opal fabricated by Langmuir-Blodgett deposition. The calculations are performed with transfer matrices, and an absorptive component in the effective index is introduced to account for the light scattering. This one-dimensional formalism allows quantitative predictions for reflection and transmission, notably as a function of the ratio between the irradiation wavelength and the sphere diameter, or as a function of the incidence angle or of the polarization. It can be used for an irradiation from the substrate side or from the vacuum side and can account for defect layers. The interface region between the opal and the substrate (or vacuum) is shown to have a strong influence, regardless of the exact opal structure. This break in the periodicity at the interface is a general, but often ignored feature, of any external coupling to a photonic crystal. Our calculations provide also the main features of the Bragg peak for reflection, including its width and strength. Comparisons of this versatile model with experiments show that despite its simplicity, it is powerful enough to explain numerous observations.
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