Plasma diagnostics in pulsed laser deposition of GaLaS chalcogenides

International audienceThe aim of this work is to characterize the ejection plume obtained by laser ablation of GaLaS (GLS) samples in order to better understand the ablation phenomena for optimizing the pulsed laser deposition of chalcogenide thin films. The dynamics of the plasma between target and substrate was investigated through time- and space-resolved optical emission spectroscopy. High-resolution optical spectra have been recorded in the UV-VIS range using a 500-mm focal length monochromator and a fast gate ICCD camera. From the space-time evolution of the optical signals, the velocities of various species (including neutrals and ions) have been derived. Using the relative intensity method, the space- and time-evolution of the excitation temperature and electronic density have been determined. A complex behavior of the laser ablation plasma has been revealed

A Hybrid Global Minimization Scheme for Accurate Source Localization in Sensor Networks

We consider the localization problem of multiple wideband sources in a multi-path environment by coherently taking into account the attenuation characteristics and the time delays in the reception of the signal. Our proposed method leaves the space for unavailability of an accurate signal attenuation model in the environment by considering the model as an unknown function with reasonable prior assumptions about its functional space. Such approach is capable of enhancing the localization performance compared to only utilizing the signal attenuation information or the time delays. In this paper, the localization problem is modeled as a cost function in terms of the source locations, attenuation model parameters and the multi-path parameters. To globally perform the minimization, we propose a hybrid algorithm combining the differential evolution algorithm with the Levenberg-Marquardt algorithm. Besides the proposed combination of optimization schemes, supporting the technical details such as closed forms of cost function sensitivity matrices are provided. Finally, the validity of the proposed method is examined in several localization scenarios, taking into account the noise in the environment, the multi-path phenomenon and considering the sensors not being synchronized

Atomic Parity Violation : Principles, Recent Results, Present Motivations

We review the progress made in the determination of the weak charge, Q\_w, of the cesium nucleus which raises the status of Atomic Parity Violation measurements to that of a precision electroweak test. Not only is it necessary to have a precision measurement of the electroweak asymmetry in the highly forbidden 6S-7S transition, but one also needs a precise calibration procedure. The 1999 precision measurement by the Boulder group implied a 2.5 sigma deviation of Q\_w from the theoretical prediction. This triggered many particle physicist suggestions as well as examination by atomic theoretical physicists of several sources of corrections. After about three years the disagreement was removed without appealing to "New Physics". Concurrently, an original experimental approach was developed in our group for more than a decade. It is based on detection by stimulated emission with amplification of the left- right asymmetry. We present our decisive, recent progress together with our latest results. We emphasize the important impact for electroweak theory, of future measurements in cesium possibly pushed to the 0.1% level. Other possible approaches are currently explored in several atoms

Neurons in Cat Primary Visual Cortex cluster by degree of tuning but not by absolute spatial phase or temporal response phase

Neighboring neurons in cat primary visual cortex (V1) have similar preferred orientation, direction, and spatial frequency. How diverse is their degree of tuning for these properties? Are they also clustered in their tuning for the spatial phase of a flashed grating ("absolute spatial phase") or the temporal phase of a drifting grating ("temporal response phase")? To address these questions, we used tetrode recordings to simultaneously isolate multiple cells at single recording sites and record their responses to flashed and drifting gratings of multiple orientations, spatial frequencies, and spatial/temporal phases. We recorded the responses of 761 cells presented with drifting gratings and 409 cells presented with flashed gratings. We found that orientation tuning width, spatial frequency tuning width and direction selectivity index all showed significant clustering. Absolute spatial phase and temporal response phase, however, showed no clustering. We also present an algorithm that improves the performance of spike-sorting algorithms, for use in analyzing cells recorded using tetrodes. A cluster of spikes corresponding to a putative cell obtained through automatic or manual spike sorting algorithms may contain spikes from other cells with similarly-shaped waveforms. Our algorithm preferentially removes contaminating spikes from other cells, thereby decreasing the level of contamination of each unit. We call this procedure "pruning", as it entails removing portions of the cluster that are determined to be more likely to contain contaminating spikes than the cluster as a whole. Testing of the algorithm on data in which "ground truth" is known shows excellent performance, for example on average giving a percentage reduction in false positive spikes 8.2 times the percentage reduction in true positive spikes, and reducing the degree of contamination by an average of about 13%

Measuring Entanglement using Programmable Holograms

The Einstein–Podolsky–Rosen (EPR) paradox proposes an entangled quantum state in high dimensional non-commuting observables, position and momentum. We experimentally demonstrate a novel method for measuring spatial correlations in joint position and joint momentum space for entangled photons in an EPR-like state. Research in the field of quantum optics can provide insight into quantum information processing, communication, quantum key distribution, and further investigation into the EPR paradox and locality. Unlike existing techniques, we take measurements of non-commuting observables using a static configuration. A 405nm pump laser incident on a Bismuth Borate nonlinear crystal produces an EPR state as a pair of 810nm photons through the process of spontaneous parametric downconversion. To measure spatial correlations, we take advantage of holograms displayed on digital micromirror devices (DMDs). This method allows for control over the basis that is measured only by changing what hologram is displayed on the DMD, without having to add lenses or other bulk optic components. The field interaction that generates a hologram can be computationally simulated and displayed on the DMD allowing for a momentum mode projection onto the incident state. Collection of joint position and joint momentum correlations provide an entanglement witness. Verification of entanglement using this technique provides the framework to investigate projections onto arbitrary states and explore further quantum communication advances

The Law of Employee Benefit Plans

What are commonly called “fringe benefits” in union agreements are formed out of threads taken from many parts of the fabric of law: a large skein of contract law; binding threads from the law of trusts, agency and taxation; and many colorful strands from a host of labor law statutes. The legal principles are for the most part not unique or novel. Rather, the accumulation of new economic and social arrangements has brought together a variety of familiar legal rules that take on the appearance of a system or body of interrelated legal doctrines. In light of the current Congressional investigations, there may soon be special legislation for employee benefit plans. Such legislation will be woven from threads of the present law on the subject; hence, this paper will undertake to trace the salient filaments of that law