9,765 research outputs found
Reflection high-energy electron diffraction experimental analysis of polycrystalline MgO films with grain size and orientation distributions
Analysis of biaxial texture of MgO films grown by ion-beam-assisted deposition (IBAD) has been performed using a quantitative reflection high-energy electron diffraction (RHEED) based method. MgO biaxial texture is determined by analysis of diffraction spot shapes from single RHEED images, and by measuring the width of RHEED in-plane rocking curves for MgO films grown on amorphous Si3N4 by IBAD using 750 eV Ar+ ions, at 45° incidence angle, and MgO e-beam evaporation. RHEED-based biaxial texture measurement accuracy is verified by comparison with in-plane and out-of-plane orientation distribution measurements made using transmission electron microscopy and x-ray rocking curves. In situ RHEED measurements also enable the analysis of the evolution of the biaxial texture which narrows with increasing film thickness. RHEED-based measurements of IBAD MgO biaxial texture show that the minimum in-plane orientation distribution depends on the out-of-plane orientation distribution, and indicates that the minimum obtainable in-plane orientation on distribution is 2°
{Tris[2-(imidazol-2-ylmethylimino)ethyl]methylammonium}iron(II) tris(perchlorate) dihydrate
The title complex, [Fe(C19H27N10)](ClO4)3·2H2O, is a new polymorph of an iron(II) Schiff base complex of tris(2-aminoethyl)methylammonium with imidazole-2-carboxaldehyde. The octahedral FeII atom is bound to three facial imidazole N atoms with average Fe—Nimidazole and Fe—Nimine bond distances of 1.963 (5) and 1.951 (5) Å, respectively. The central N atom of the tripodal ligand is outside the bonding distance at 3.92 Å. The crystal packing is stabilized by the hydrogen-bonding interactions between the two water molecules (acceptor) and two of the three imidazole NH groups (donor). The third imidazole NH group (donor) forms a hydrogen bond to one of the three perchlorate counter-ions (acceptor)
The magnetic phase of the perovskite CaCrO studied with SR
We investigated the magnetic phase of the perovskite CaCrO by using the
muon spin relaxation technique accompanied by susceptibility measurements. A
thermal hysteresis loop is identified with a width of about 1 K at the
transition temperature. Within the time scale of the muon lifetime, a static
antiferromagnetic order is revealed with distinct multiple internal fields
which are experienced in the muon interstitial sites below the phase-transition
temperature, . Above , lattice deformations are indicated by
transverse-field muon-spin rotation and relaxation suggesting a magneto-elastic
mechanism.Comment: 5 pages, 4 figures. Accepted for publication in PR
Fe I Oscillator Strengths for the Gaia-ESO Survey
The Gaia-ESO Public Spectroscopic Survey (GES) is conducting a large-scale
study of multi-element chemical abundances of some 100 000 stars in the Milky
Way with the ultimate aim of quantifying the formation history and evolution of
young, mature and ancient Galactic populations. However, in preparing for the
analysis of GES spectra, it has been noted that atomic oscillator strengths of
important Fe I lines required to correctly model stellar line intensities are
missing from the atomic database. Here, we present new experimental oscillator
strengths derived from branching fractions and level lifetimes, for 142
transitions of Fe I between 3526 {\AA} and 10864 {\AA}, of which at least 38
are urgently needed by GES. We also assess the impact of these new data on
solar spectral synthesis and demonstrate that for 36 lines that appear
unblended in the Sun, Fe abundance measurements yield a small line-by-line
scatter (0.08 dex) with a mean abundance of 7.44 dex in good agreement with
recent publications.Comment: Accepted for publication in Mon. Not. R. Astron. So
The Herbertsmithite Hamiltonian: SR measurements on single crystals
We present transverse field muon spin rotation/relaxation measurements on
single crystals of the spin-1/2 kagome antiferromagnet Herbertsmithite. We find
that the spins are more easily polarized when the field is perpendicular to the
kagome plane. We demonstrate that the difference in magnetization between the
different directions cannot be accounted for by Dzyaloshinksii-Moriya type
interactions alone, and that anisotropic axial interaction is present.Comment: 8 pages, 3 figures, accepted to JPCM special issue on geometrically
frustrated magnetis
Assessment of Metal Mining-Contaminated River Sediments in England and Wales
This report reviews how sediments and floodplain soils have been contaminated by abandoned metal mines and recommends what the Environment Agency should do about this issue
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Laser-Induced Spall Of Aluminum And Aluminum Alloys At High Strain Rates
We conducted laser-induced spall experiments aimed at studying how a material's microstructure affects the tensile fracture characteristics at high strain rates (> 10(6) s(-1)). We used the Z-Beamlet Laser at Sandia National Laboratory to drive shocks and to measure the spall strength of aluminum targets with various microstructures. The targets were recrystallized, high-purity aluminum (Al-HP RX), recrystallized aluminum + 3 wt.% magnesium (Al-3Mg RX), and cold-worked aluminum + 3 wt.% magnesium (Al-3Mg CW). The Al-3Mg RX and Al-3Mg CW are used to explore the roles that solid-solution alloying and cold-work strengthening play in the spall process. Using a line-VISAR (Velocity Interferometer System for Any Reflector) and analysis of recovered samples, we were able to measure spall strength and determine failure morphology in these targets. We find that the spall strength is highest for Al-HP RX. Analysis reveals that material grain size plays a vital role in the fracture morphology and spall strength results.Mechanical Engineerin
A late Pleistocene long pollen record from Lake Urmia, NW Iran
A palynological study based on two 100-m long cores from Lake Urmia in northwestern Iran provides a vegetation record spanning 200 ka, the longest pollen record for the continental interior of the Near East. During both penultimate and last glaciations, a steppe of Artemisia and Poaceae dominated the upland vegetation with a high proportion of Chenopodiaceae in both upland and lowland saline ecosystems. While Juniperus and deciduous Quercus trees were extremely rare and restricted to some refugia, Hippophaë rhamnoides constituted an important phanerophyte, particularly during the upper last glacial sediments. A pronounced expansion in Ephedra shrub-steppe occurred at the end of the penultimate late-glacial period but was followed by extreme aridity that favoured an Artemisia steppe. Very high lake levels, registered by both pollen and sedimentary markers, occurred during the middle of the last glaciation and upper part of the penultimate glaciation. The late-glacial to early Holocene transition is represented by a succession of Hippophaë, Ephedra, Betula, Pistacia and finally Juniperus and Quercus. The last interglacial period (Eemian), slightly warmer and moister than the Holocene, was followed by two interstadial phases similar in pattern to those recorded in the marine isotope record and southern European pollen sequences
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