Search for the Tunguska event in the Antarctic snow

The Tunguska explosion in 1908 is supposed to have been produced by the impact of a small celestial body. The absence of any identifiable crater together with the huge energy released by the event suggest that the impactor exploded in midair and that its material was widely spread over the Earth. The short term contribution of such exceptional events to the total accretion rate of extraterrestrial material by the Earth could be significant. Samples were chosen in a core electromechanically drilled in 1984 near South Pole Station. There, the low temperatures, preventing melting all year long, and the nearly regular snow fall rate provide good conditions for a reliable continuous record of any infalling material. In many samples Ir was below the detection limit of the instrumentation. The iridium infall averaged over 45 samples is given. In a few samples the iridium content is significantly higher than the average: the frequency and amplitude of such fluctuations can be explained by the presence on some filters of finite size cosmic particles. No significant systematic increase above the average level is observed in the part of the core corresponding to the Tunguska event. The two major results of this study are: (1) The presence of Tunguska explosion debris in the Antarctic snow is not confirmed; and (2) The estimate of the average iridium infall, is an order of magnitude lower than the Ganapathy's background but is close to the values measured in Antarctic snow and atmospheric samples by Takahashi et al. The results are also consistent with the flux of micrometeoroids deduced from optical and radar observations or derived from the study of Greenland cosmic dust collection but are lower than the flux at mid-latitude measured in paleocene-oligocene sediments from the central part of the Pacific Ocean

High flux polarized gamma rays production: first measurements with a four-mirror cavity at the ATF

The next generation of e+/e- colliders will require a very intense flux of gamma rays to allow high current polarized positrons to be produced. This can be achieved by converting polarized high energy photons in polarized pairs into a target. In that context, an optical system consisting of a laser and a four-mirror passive Fabry-Perot cavity has recently been installed at the Accelerator Test Facility (ATF) at KEK to produce a high flux of polarized gamma rays by inverse Compton scattering. In this contribution, we describe the experimental system and present preliminary results. An ultra-stable four-mirror non planar geometry has been implemented to ensure the polarization of the gamma rays produced. A fiber amplifier is used to inject about 10W in the high finesse cavity with a gain of 1000. A digital feedback system is used to keep the cavity at the length required for the optimal power enhancement. Preliminary measurements show that a flux of about $4\times10^6 \gamma$/s with an average energy of about 24 MeV was generated. Several upgrades currently in progress are also described

Organocatalysis for depolymerisation

Polymeric materials have been accumulating in the environment for decades as a result of the linear way of consuming plastics. Unfortunately, the current approaches followed to treat such a large amount of plastic waste, mainly involving physical recycling or pyrolysis, are not efficient enough. Recently, chemical degradation has emerged as a long-term strategy towards reaching completely sustainable cycles where plastics are polymerised, depolymerised, and then re-polymerised with minimal changes in their quantity or final properties. Organocatalysts, which are promising “green” substitutes for traditional organometallic complexes, are able to catalyse depolymerisation reactions yielding highly pure small molecules that are adequate for subsequent polymerisations or other uses. Moreover, by varying several reaction parameters (e.g. solvent, temperature, concentration, co-catalyst, etc.), the depolymerisation products can be tuned in innumerable possibilities, which further evidences the versatility of depolymerisation. In this review, we highlight the recent advances made by applying organocatalysts, such as organic bases, organic acids, and ionic compounds, to chemically degrade the most commonly used commercial polymers. Indeed, organocatalysis is envisaged as a promising tool to reach a circular and environmentally friendly plastic economy.Postprint (published version

Non-planar four-mirror optical cavity for high intensity gamma ray flux production by pulsed laser beam Compton scattering off GeV-electrons

As part of the R&D toward the production of high flux of polarised Gamma-rays we have designed and built a non-planar four-mirror optical cavity with a high finesse and operated it at a particle accelerator. We report on the main challenges of such cavity, such as the design of a suitable laser based on fiber technology, the mechanical difficulties of having a high tunability and a high mechanical stability in an accelerator environment and the active stabilization of such cavity by implementing a double feedback loop in a FPGA

CC9 Livestock-Associated Staphylococcus aureus Emerges in Bloodstream Infections in French Patients Unconnected With Animal Farming

We report 4 bloodstream infections associated with CC9 agr type II Staphylococcus aureus in individuals without animal exposure. We demonstrate, by microarray analysis, the presence of egc cluster, fnbA, cap operon, lukS, set2, set12, splE, splD, sak, epiD, and can, genomic features associated with a high virulence potential in human

Production of gamma rays by pulsed laser beam Compton scattering off GeV-electrons using a non-planar four-mirror optical cavity

As part of the positron source R&D for future $e^+-e^-$ colliders and Compton based compact light sources, a high finesse non-planar four-mirror Fabry-Perot cavity has recently been installed at the ATF (KEK, Tsukuba, Japan). The first measurements of the gamma ray flux produced with a such cavity using a pulsed laser is presented here. We demonstrate the production of a flux of 2.7 $\pm$ 0.2 gamma rays per bunch crossing ($\sim3\times10^6$ gammas per second) during the commissioning

THE FOUR-MIRROR LASER STACKING CAVITY FOR POLARIZED GAMMA-RAY/POSITRON GENERATION

Abstract A non planar four mirror cavity has been designed and constructed to demonstrate the production of high gamma ray fluxes from Compton scattering of laser and electron beams at ATF. A pulsed laser is amplified using the recent technology of Yb-doped photonic cristal fibres. Seeding the high finesse four-mirror cavity with this amplified laser beam will allow reaching average powers between 0.1MW and 1MW

The ThomX project status

Work supported by the French Agence Nationale de la recherche as part of the program EQUIPEX under reference ANR-10-EQPX-51, the Ile de France region, CNRS-IN2P3 and Université Paris Sud XI - http://accelconf.web.cern.ch/AccelConf/IPAC2014/papers/wepro052.pdfA collaboration of seven research institutes and an industry has been set up for the ThomX project, a compact Compton Backscattering Source (CBS) based in Orsay - France. After a period of study and definition of the machine performance, a full description of all the systems has been provided. The infrastructure work has been started and the main systems are in the call for tender phase. In this paper we will illustrate the definitive machine parameters and components characteristics. We will also update the results of the different technical and experimental activities on optical resonators, RF power supplies and on the electron gun

Development of a Method for Detection of Lactic Acid Bacteria Producing Exclusively the l-(+)- Isomer of Lactic Acid

A method was developed for the detection and isolation, within a population of lactic acid bacteria, of strains producing exclusively the l-(+)- isomer of lactic acid; the visual detection of colonies of these particular strains can be carried out directly on agar plates (50 to 70 colonies per plate). The method is based on an enzymatic stereospecific reaction involving d-(−)-lactate dehydrogenase and linked to a staining reaction; the diffusion area of the d-(−)- isomer stains red around the d-(−)- and the dl-lactic acid-producing colonies, while the colonies producing exclusively l-(+)-lactic acid are detected by the absence of the colored halo. The intensity of staining was increased when cellulose powder and Tween 20 were added to the agar medium