Crossover between magnetism and superconductivity in low H-doped LaFeAsO

By a systematic study of the hydrogen-doped LaFeAsO system by means of dc resistivity, dc magnetometry, and muon-spin spectroscopy we addressed the question of universality of the phase diagram of rare-earth-1111 pnictides. In many respects, the behaviour of LaFeAsO_(1-x)H_(x) resembles that of its widely studied F-doped counterpart, with H^- realizing a similar (or better) electron-doping in the LaO planes. In a x = 0.01 sample we found a long-range SDW order with T_n = 119 K, while at x = 0.05 the SDW establishes only at 38 K and, below T_c = 10 K, it coexists at a nanoscopic scale with bulk superconductivity. Unlike the abrupt M-SC transition found in the parent La-1111 compound, the presence a crossover region makes the H-doped system qualitatively similar to other Sm-, Ce-, or Nd-1111 families.Comment: to appear in Journal of Physics: Condensed Matte

Application of LaBr3 detector for neutron resonance densitometry

A method to determine the amount of nuclear materials in melted fuel resulting from a nuclear accident such as the one occurred at the Fukushima Daiichi nuclear power plants has not yet been established. The problem is complex due to the expected presence of 10B and other strong neutron absorbing impurities. For this reason, neutron resonance densitometry, combining neutron resonance transmission analysis and neutron capture analysis, is proposed and a feasibility study has been defined. In this contribution a method to account for the presence of 10B is presented and investigated. The study includes GEANT4 simulations to study the performance of a new well type gamma-ray detector based on LaBr3 scintillators. In the design of the detector the main emphasis was on the capability to separate the full energy peak corresponding to the 478-keV gamma ray resulting from the 10B(n,αγ) reaction from the contribution of the 662-keV gamma ray due to the decay of 137Cs. In addition, experiments have been carried out at the time-of-flight facility GELINA of the EC-JRC-IRMM to test the capabilities of a LaBr3 detector for NRCA applications, in particular to determine impurities present in the melted fuel. A neutron resonance capture gamma-ray experiment with a natSe sample was performed using a LaBr3 scintillator in parallel with a Ge-detector. The results of these measurements demonstrate that a LaBr3 detector is suitable for NRCA as a part of neutron resonance densitometry.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Drake Antarctic Agile Meteor Radar (DrAAMER) First Results: Configuration and Comparison of Mean and Tidal Wind and Gravity Wave Momentum Flux Measurements with SAAMER

A new-generation meteor radar was installed at the Brazilian Antarctic Comandante Ferraz Base (62.1degS) in March 2010. This paper describes the motivations for the radar location, its measurement capabilities, and comparisons of measured mean winds, tides, and gravity wave momentum fluxes from April to June of 2010 and 2011 with those by a similar radar on Tierra del Fuego (53.8degS). Motivations for the radars include the "hotspot" of small-scale gravity wave activity extending from the troposphere into the mesosphere and lower thermosphere (MLT) centered over the Drake Passage, the maximum of the semidiurnal tide at these latitudes, and the lack of other MLT wind measurements in this latitude band. Mean winds are seen to be strongly modulated at planetary wave and longer periods and to exhibit strong coherence over the two radars at shorter time scales as well as systematic seasonal variations. The semidiurnal tide contribute most to the large-scale winds over both radars, with maximum tidal amplitudes during May and maxima at the highest altitudes varying from approx.20 to >70 m/s. In contrast, the diurnal tide and various planetary waves achieve maximum winds of approx.10 to 20 m/s. Monthly-mean gravity wave momentum fluxes appear to reflect the occurrence of significant sources at lower altitudes, with relatively small zonal fluxes over both radars, but with significant, and opposite, meridional momentum fluxes below approx.85 km. These suggest gravity waves propagating away from the Drake Passage at both sites, and may indicate an important source region accounting in part for this "hotspot"

Proposal of neutron resonance densitometry for particle like debris of melted fuel using NRTA and NRCA

Neutron resonance densitometry (NRD) has been proposed to quantify nuclear materials in particle-like debris of melted fuel formed in a severe accident of nuclear reactors such as the Fukushima Daiichi nuclear power plants. NRD is a method that combines NRTA (neutron resonance transmission analysis) and NRCA (neutron resonance capture analysis) using a pulsed neutron generator and the TOF (time of flight) technique. NRTA is used to quantify the amount of Pu and U isotopes. NRCA is used to identify matrix materials, such as B and Fe, which are present in the melted fuel. A special gamma-ray spectrometer has been designed to apply NRCA in the presence of highly radioactive materials. The applicability of the NRD method has been studied using Monte Carlo simulations and neutron TOF experiments at the GELINA facility of the EC-JRC-IRMM. We conclude that NRD has a potential to determine the quantities of Pu and U isotopes in particle-like debris of melted fuel with counting statistics uncertainties less than 1%, even in the presence of 2.5 w% natB and 9 w% 56Fe.JRC.D.4-Standards for Nuclear Safety, Security and Safeguard

Accurately accounting for effects on times-of-flight caused by finite field-transition times during the ejection of ions from a storage trap: A study for TOF and MRTOF mass spectrometry

In applied forms of time-of-flight mass spectrometry utilizing ion storage devices prior to an analysis device, a non instantaneous electric ejection pulse applied in the region of ion storage is used to accelerate ions into the time-of-flight analyzer. The calculated mass value of the ions from the time-of-flight is dependent on the duration of the field transition up to full strength. For novel applications dedicated to precision measurements, such as multi-reflection time-of-flight mass spectrometry of short-lived isotopes, the goal is to continuously decrease the measurement uncertainty while providing a mass accuracy on the same order. Even though dynamic-field models for time-of-flight mass spectrometry have been considered in the past for technological advances, it is important to study the accuracy of the measured mass in this context. Using a simplified linear model for the field transition, we provide a basic investigation of the scenario, and discuss the deviation from the classical "mass-over-charge" dependency of the ions' time-of-flight, which becomes violated. The emerging mass discrepancy depends on the distance between the mass of the ion used for calibration and that of the ion of interest and, in extreme cases, can increase to about one percent for systems with short times-of-flight. However, for typical conditions in single-reference multi-reflection time-of-flight mass spectrometry, mass deviations caused by this effect typically remain below the 1 ppm level. If a mass calibration using two or more ion species is possible during the measurement, the effect becomes negligible for appropriate choices of reference masses.Comment: 14 pages, 9 figure

Zebrafish hoxd4a Acts Upstream of meis1.1 to Direct Vasculogenesis, Angiogenesis and Hematopoiesis

10.1371/journal.pone.0058857PLoS ONE83