Upgrade of the pedagogic and popular science tool for holography to a colour version

In 2012, a pedagogic tool for monochromatic holography was realized for pedagogic and popular science purposes [Th. Voslion and A. Escarguel, Eur. J. Phys 33, 1803 (2012)]. Following its success, we decided to upgrade it to make larger colour holograms and new pedagogic experiments. The resulting kit includes all the necessary equipment to produce 4 " x 5 " colour holograms with a simple optical assembly and with an excellent vibration tolerance. The resulting holograms, in colour and bigger, are much more spectacular for science outreach purposes. For teaching purposes, some of the existing experiments have been upgraded, and new ones have been developed for university students and continuing education of teachers: colour reflection Denisyuk holograms, single shot transmission/reflection holograms, angular and wavelength multiplexing, holographic diffraction gratings with improved setup

Formation of spiral structures and radial convection in the edge region of a magnetized rotating plasma

The rotation of a cylindrical plasma column in a magnetic field has been studied in the linear section of the new plasma device Mistral. Under suitable conditions we observe a transition to a turbulent regime characterized by strong, bursty fluctuations at the edge of the column. The detection and the study of the spatio-temporal evolution of structures in the turbulent regime have been performed by means of a new enhanced conditional sampling technique. We have collected evidence of the development of a bent tail emanating from the plasma column. The charged particles inside the structure move along a spiral trajectory resulting in a net radial convection of the plasma to the walls. We show experimentally that a poloidal electric field is present inside the structures leading to the observed outwards radial E × B drift, in agreement with the expectations of recent and past theoretical works

New thylacocephalans from the Early Triassic Paris Biota (Bear Lake County, Idaho, USA).

International audienceTwo new genera and species of thylacocephalans (Arthropoda, Thylacocephala), Parisicaris triassica Charbonnier and Ligulacaris parisiana Charbonnier, are described from the early Spathian Paris Biota. These new occurrences are the first reports of thylacocephalans from Triassic rocks in North America. They considerably enlarge the spatiotemporal distribution of these enigmatic arthropods and highlight their relatively high generic richness during the Early Triassic. It also confirms that the Triassic was the taxonomically richest period for Thylacocephala

The Impact of the Species–Area Relationship on Estimates of Paleodiversity

Estimates of paleodiversity patterns through time have relied on datasets that lump taxonomic occurrences from geographic areas of varying size per interval of time. In essence, such estimates assume that the species–area effect, whereby more species are recorded from larger geographic areas, is negligible for fossil data. We tested this assumption by using the newly developed Miocene Mammal Mapping Project database of western North American fossil mammals and its associated analysis tools to empirically determine the geographic area that contributed to species diversity counts in successive temporal bins. The results indicate that a species–area effect markedly influences counts of fossil species, just as variable spatial sampling influences diversity counts on the modern landscape. Removing this bias suggests some traditionally recognized peaks in paleodiversity are just artifacts of the species–area effect while others stand out as meriting further attention. This discovery means that there is great potential for refining existing time-series estimates of paleodiversity, and for using species–area relationships to more reliably understand the magnitude and timing of such biotically important events as extinction, lineage diversification, and long-term trends in ecological structure

Optical diagnostics of a low frequency instability rotating around a magnetized plasma column

An argon magnetized plasma column is created with primary energetic electrons in the Mistral device. Low frequency instabilities regularly rotating around this column are observed with an ultra-fast camera and a spectroscopic device. Experimental results coupled to a coronal code show the presence of a few percents of fast (hot) electrons inside the ejected plasma. It also shows that ultra-fast camera analysis of the ejected plasma can only give information on the primary electron population. Finally, these results suggest that the radial decrease of the light emitted by the ejected plasma is essentially due to the radial decrease of the mean energy of the hot electrons

Hydrogen lines in correlated plasmas

Hydrogen line shapes broadened by Stark effects are calculated for a dense hydrogen plasma created by a Nd:YAG laser focussed into liquid water. The electronic density and temperature deduced from the experiment allow to use a Debye Hückel model for the interaction potential between the plasmas ions screened by the electrons. The Stark broadened line shapes, obtained in the frame of the Model Microfield Method, both for the electronic and ionic contributions, are based upon accurate Monte Carlo hydrogen field distributions functions, calculated on a neutral point together for the electrons (OCP) and for the ions (screened Coulombic field). The theoretical description allows to cover a wide range of thermodynamical conditions and to predict the emissivity (and opacity)of astrophysical and laboratory plasmas

Characterisation of coherent rotating modes in a magnetised plasma ă column using a mono-sensor tomography diagnostic

International audienceIn this paper, we report on the core plasma evolution during the ă rotation of coherent modes in a magnetized plasma column. The study ă makes use of an original tomographic diagnostic based on a single ă sensor. The experimental observations demonstrate that the mode shape is ă constant during the plasma rotation, therefore confirming an a priori ă assumption of single position measurements. The experimental set-up and ă the numerical inversion method used to interpret the data are presented. ă The results are then compared to two-dimensional probe measurements to ă assess their perturbative character and to give further details on the ă mode characteristics. A pi/2 phase shift between the electrostatic ă potential and density perturbation is evidenced. Published by AIP ă Publishing

Smithian and spathian (early triassic) ammonoid assemblages from terranes: paleoceanographic and paleogeographic implications

Early Triassic paleobiogeography is characterised by the stable supercontinental assembly of Pangea. However, at that time, several terranes such as the South Kitakami Massif (SK), South Primorye (SP) and Chulitna (respectively, and presently located in Japan, eastern Russia and Alaska) straddled the vast oceans surrounding Pangea. By means of quantitative biogeographical methods including Cluster Analysis, Non-metric Multidimensional Scaling and Bootstrapped Spanning Network applied to Smithian and Spathian (Early Triassic) ammonoid assemblages; we analyze similarity relationships between faunas and suggest paleopositions for the above-cited terranes. Taxonomic similarities between faunas indicate that primary drivers of the ammonoid distribution were Sea Surface Temperature and currents. Possible connections due to current-controlled faunal exchanges between both sides of the Panthalassa are shown and terranes such as SK, SP and Chulitna played an important role as stepping stones in the dispersal of ammonoids. SK and SP terranes show strong sub-equatorial affinities during the Smithian, thus suggesting a location close to South China. At the same time, the Chulitna terrane shows strong affinities with equatorial faunas of the eastern Panthalassa. This paleoceanographic pattern was markedly altered during the Spathian, possibly indicating significant modifications of oceanic circulation at that time, as illustrated by the development of a marked intertropical faunal belt across Tethys and Panthalassa

Ion velocity analysis of rotating structures in a magnetic linear plasma device

International audienceThe MISTRAL device is designed to produce a linear magnetized plasma column. It has been used a few years ago to study a nonlinear low frequency instability exhibiting an azimuthal number m = 2. By changing the experimental configuration of MISTRAL, this work shows experimental results on an m = 1 rotating instability with strongly different behavior. The spatio-temporal evolution of the ion velocity distribution function given by a laser-induced fluorescence diagnostic is measured to infer the radial and azimuthal velocities, ion fluxes, and electric fields. The naive image of a plasma exhibiting a global rotation is again invalidated in this m = 1 mode but in a different way. Contrary to the m = 2 mode, the rotation frequency of the instability is lower than the ion cyclotron frequency and ions exhibit a complex behavior with a radial outward flux inside the unstable arm and azimuthal ion fluxes always directed toward the unstable arm. The azimuthal ion velocity is close to zero inside the ionization region, whereas the radial ion velocity grows linearly with radius. The radial electric field is oriented inward inside the unstable arm and outward outside. An axial velocity perturbation is also present, indicating that contrary to the m = 2 mode, the m = 1 mode is not a flute mode. These results cannot be easily interpreted with existing theories

Si II transition probabilities measurements in a laser induced plasma

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