2,048 research outputs found
Interface Ferromagnetism in a SrMnO3/LaMnO3 Superlattice
Resonant soft x-ray absorption measurements at the O K edge on a
SrMnO3/LaMnO3 superlattice show a shoulder at the energy of doped holes, which
corresponds to the main peak of resonant scattering from the modulation in the
doped hole density. Scattering line shape at the Mn L3,2 edges has a strong
variation below the ferromagnetic transition temperature. This variation has a
period equal to half the superlattice superperiod and follows the development
of the ferromagnetic moment, pointing to a ferromagnetic phase developing at
the interfaces. It occurs at the resonant energies for Mn3+ and Mn4+ valences.
A model for these observations is presented, which includes a double-exchange
two-site orbital and the variation with temperature of the hopping frequency
tij between the two sites.Comment: 8.1 pages, 6 figure
Interactions between trivalent rare earth oxides and mixed [Hbet][Tf2N]:H2O systems in the development of a one-step process for the separation of light from heavy rare earth elements
The factors, including ionic liquid:water ratios, temperature, solvent:solute contact times, and the effect of dissolved rare earth metal ions on the [Hbet][Tf2N]:H2O thermometric phase change are determined to develop a process for separating the light from the heavy rare earth metal oxides in [Hbet][Tf2N]:H2O mixtures. The relative solubility data for three light (La2O3, Nd2O3, and Eu2O3), two heavy (Y2O3 and Yb2O3) rare earth metal oxides (REOs), and Gd2O3 at different temperatures and different solute:solvent contact times are reported for 1:1 [Hbet][Tf2N]:H2O. The light REOs dissolve easily at 57 °C with the La and Eu reaching maximum solubility within minutes while the heavy REOs have very low solubilities at this temperature with negligible amounts being dissolved for contact times less than 80 min. Gd2O3 dissolves more slowly than the La, Eu, and Nd oxides at 57 °C reaching maximum solubility only after 160 min. Changing the [Hbet][Tf2N]:H2O ratio from 1:1 to 16:1 increases the time required to dissolve the REOs. The times taken to reach maximum solubility decrease for all of the REOs up to 95 °C, resulting in the separations between the light and heavy rare earth elements, and Gd becoming less distinct. The presence of rare earth metal ions in [Hbet][Tf2N]:H2O results in a reduction in the upper critical solution temperature (UCST) of the solvent from 55.6 °C to as low as 31.8 °C with Gd3+. The best separation of light from heavy REOs is achieved at 57 °C but better separation of Gd from the light REOs is achieved at 40 °C, below the solvent UCST. The best conditions for a one-step separation of light from heavy REOs in [Hbet][Tf2N]:H2O mixtures is achieved with 1:1 [Hbet][Tf2N]:H2O at 57 °C using short contact oxide:solvent times (maximum 5 min). Separations of light from heavy REOs, in waste phosphor samples, containing La2O3, CeO2, Eu2O3, Gd2O3, Tb3O4 and Y2O3, are also achieved even in the presence of high concentrations of heavy REOs using short contact times. The use of [Hbet][Tf2N]:H2O as a means of separating light and heavy REOs is aided by the ease of recycling the solvent which can be recycled and reused at least five times with little loss of solvent quality or efficiency
Novel sound absorption materials produced from air laid non-woven feather fibres
This research has investigated the use of feather fibres to produce sound absorption materials as an alternative to the oil derived synthetic plastics that currently dominate the sound absorption materials market. In this paper we show that clean and disinfected waste feathers from the poultry industry can be processed into fibres and air laid using commercial pilot plant facilities to form non-woven feather fibre composite mats. By varying the composition and processing conditions, materials with a range of different properties such as thickness and density were produced. The sound absorption coefficients of samples was determined using the impedance tube method (BS EN ISO 10534-2: 1998), using normal incidence sound between 80 and 1,600 Hz. The data reported shows that air laid non-woven feather fibre mats have improved sound absorption coefficients compared to other natural materials used for sound absorption for a given thickness, particularly in the problematic low frequency range between 250 to 800 Hz. We conclude that air laid non-woven feather fibres have high potential to be used as effective and sustainable sound absorption materials in aerospace, automotive, buildings, infrastructure and other applications where sound absorption is required
Extremal Optimization at the Phase Transition of the 3-Coloring Problem
We investigate the phase transition of the 3-coloring problem on random
graphs, using the extremal optimization heuristic. 3-coloring is among the
hardest combinatorial optimization problems and is closely related to a 3-state
anti-ferromagnetic Potts model. Like many other such optimization problems, it
has been shown to exhibit a phase transition in its ground state behavior under
variation of a system parameter: the graph's mean vertex degree. This phase
transition is often associated with the instances of highest complexity. We use
extremal optimization to measure the ground state cost and the ``backbone'', an
order parameter related to ground state overlap, averaged over a large number
of instances near the transition for random graphs of size up to 512. For
graphs up to this size, benchmarks show that extremal optimization reaches
ground states and explores a sufficient number of them to give the correct
backbone value after about update steps. Finite size scaling gives
a critical mean degree value . Furthermore, the
exploration of the degenerate ground states indicates that the backbone order
parameter, measuring the constrainedness of the problem, exhibits a first-order
phase transition.Comment: RevTex4, 8 pages, 4 postscript figures, related information available
at http://www.physics.emory.edu/faculty/boettcher
Probing the Role of the Barrier Layer in Magnetic Tunnel Junction Transport
Magnetic tunnel junctions with a ferrimagnetic barrier layer have been
studied to understand the role of the barrier layer in the tunneling process -
a factor that has been largely overlooked until recently. Epitaxial oxide
junctions of highly spin polarized La0.7Sr0.3MnO3 and Fe3O4 electrodes with
magnetic NiMn2O4 (NMO) insulating barrier layers provide a magnetic tunnel
junction system in which we can probe the effect of the barrier by comparing
junction behavior above and below the Curie temperature of the barrier layer.
When the barrier is paramagnetic, the spin polarized transport is dominated by
interface scattering and surface spin waves; however, when the barrier is
ferrimagnetic, spin flip scattering due to spin waves within the NMO barrier
dominates the transport.Comment: 10 pages, 3 figure
Studies on the hyperplasia ('regeneration') of the rat liver following partial hepatectomy. Changes in lipid peroxidation and general biochemical aspects
Using the experimental model of partial hepatectomy in the rat, we have examined the relationship between cell division and lipid peroxidation activity. In rats entrained to a regime of 12 h light/12 h dark and with a fixed 8 h feeding period in the dark phase, partial hepatectomy is followed by a rapid regeneration of liver mass with cycles of synchronized cell division at 24 h intervals. The latter phenomenon is indicated in this study by pulses of thymidine kinase activity having maxima at 24 h, 48 h and 72 h after partial hepatectomy. Microsomes prepared from regenerating livers show changes in lipid peroxidation activity (induced by NADPH/ADP/iron or by ascorbate/iron), which is significantly decreased relative to that in microsomes from sham-operated controls, again at 24 h, 48 h and 72 h after the operation. This phenomenon has been investigated with regard to possible underlying changes in the content of microsomal fatty acids, the microsomal enzymes NADPH:cytochrome c reductase and cytochrome P-450, and the physiological microsomal antioxidant alpha-tocopherol. The cycles of decreased lipid peroxidation activity are apparently due, at least in part, to changes in microsomal alpha-tocopherol content that are closely associated in time with thymidine kinase activity
Sexually dimorphic expression of secreted frizzled-related (SFRP) genes in the developing mouse Mullerian duct
In developing male embryos, the female reproductive tract primordia (Müllerian ducts) regress due to the production of testicular anti-Müllerian hormone (AMH). Because of the association between secreted frizzled-related proteins (SFRPs) and apoptosis, their reported developmental expression patterns and the role of WNT signaling in female reproductive tract development, we examined expression of Sfrp2 and Sfrp5 during development of the Müllerian duct in male (XY) and female (XX) mouse embryos. We show that expression of both Sfrp2 and Sfrp5 is dynamic and sexually dimorphic. In addition, the male-specific expression observed for both genes prior to the onset of regression is absent in mutant male embryos that fail to undergo Müllerian duct regression. We identified ENU-induced point mutations in Sfrp5 and Sfrp2 that are predicted to severely disrupt the function of these genes. Male embryos and adults homozygous for these mutations, both individually and in combination, are viable and apparently fertile with no overt abnormalities of reproductive tract development
Exhaustive enumeration unveils clustering and freezing in random 3-SAT
We study geometrical properties of the complete set of solutions of the
random 3-satisfiability problem. We show that even for moderate system sizes
the number of clusters corresponds surprisingly well with the theoretic
asymptotic prediction. We locate the freezing transition in the space of
solutions which has been conjectured to be relevant in explaining the onset of
computational hardness in random constraint satisfaction problems.Comment: 4 pages, 3 figure
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