427 research outputs found
Structural origins of electronic conduction in amorphous copper-doped alumina
We perform an {\it ab initio} modeling of amorphous copper-doped alumina
(a-AlO:Cu), a prospective memory material based on resistance
switching, and study the structural origin of electronic conduction in this
material. We generate molecular dynamics based models of a-AlO:Cu at
various Cu-concentrations and study the structural, electronic and vibrational
properties as a function of Cu-concentration. Cu atoms show a strong tendency
to cluster in the alumina host, and metallize the system by filling the band
gap uniformly for higher Cu-concentrations. We also study thermal fluctuations
of the HOMO-LUMO energy splitting and observe the time evolution of the size of
the band gap, which can be expected to have an important impact on the
conductivity. We perform a numerical computation of conduction pathways, and
show its explicit dependence on Cu connectivity in the host. We present an
analysis of ion dynamics and structural aspects of localization of classical
normal modes in our models
Strain-controlled band engineering and self-doping in ultrathin LaNiO films
We report on a systematic study of the temperature-dependent Hall coefficient
and thermoelectric power in ultra-thin metallic LaNiO films that reveal a
strain-induced, self-doping carrier transition that is inaccessible in the
bulk. As the film strain varies from compressive to tensile at fixed
composition and stoichiometry, the transport coefficients evolve in a manner
strikingly similar to those of bulk hole-doped superconducting cuprates with
varying doping level. Density functional calculations reveal that the
strain-induced changes in the transport properties are due to self-doping in
the low-energy electronic band structure. The results imply that thin-film
epitaxy can serve as a new means to achieve hole-doping in other (negative)
charge-transfer gap transition metal oxides without resorting to chemical
substitution
DXL: a sounding rocket mission for the study of solar wind charge exchange and local hot bubble X-ray emission
The Diffuse X-rays from the Local galaxy (DXL) mission is an approved
sounding rocket project with a first launch scheduled around December 2012. Its
goal is to identify and separate the X-ray emission generated by solar wind
charge exchange from that of the local hot bubble to improve our understanding
of both. With 1,000 cm2 proportional counters and grasp of about 10 cm2 sr both
in the 1/4 and 3/4 keV bands, DXL will achieve in a 5-minute flight what cannot
be achieved by current and future X-ray satellites.Comment: 15 Pages, 5 figures. Accepted for publication on Experimental
Astronom
Magnetic-field dependence of low-energy magnons, anisotropic heat conduction, and spontaneous relaxation of magnetic domains in the cubic helimagnet ZnCr2Se4
Anisotropic low-temperature properties of the cubic spinel helimagnet
ZnCr2Se4 in the single-domain spin-spiral state are investigated by a
combination of neutron scattering, thermal conductivity, ultrasound velocity,
and dilatometry measurements. In an applied magnetic field, neutron
spectroscopy shows a complex and nonmonotonic evolution of the spin-wave
spectrum across the quantum-critical point that separates the spin-spiral phase
from the field-polarized ferromagnetic phase at high fields. A tiny spin gap of
the pseudo-Goldstone magnon mode, observed at wave vectors that are
structurally equivalent but orthogonal to the propagation vector of the spin
helix, vanishes at this quantum critical point, restoring the cubic symmetry in
the magnetic subsystem. The anisotropy imposed by the spin helix has only a
minor influence on the lattice structure and sound velocity but has a much
stronger effect on the heat conductivities measured parallel and perpendicular
to the magnetic propagation vector. The thermal transport is anisotropic at T <
2 K, highly sensitive to an external magnetic field, and likely results
directly from magnonic heat conduction. We also report long-time thermal
relaxation phenomena, revealed by capacitive dilatometry, which are due to
magnetic domain motion related to the destruction of the single-domain magnetic
state, initially stabilized in the sample by the application and removal of
magnetic field. Our results can be generalized to a broad class of helimagnetic
materials in which a discrete lattice symmetry is spontaneously broken by the
magnetic order.Comment: 13 pages, 8 figures + Supplemental Materia
Feed supplementation with biochar may reduce poultry pathogens, including Campylobacter hepaticus, the causative agent of Spotty Liver Disease
Increased global regulation and restrictions on the non-therapeutic use of antibiotics in the poultry industry means that there is a need to identify alternatives that prevent infection while still conveying the growth and performance benefits afforded by their use. Biochars are produced by the incomplete pyrolysis of organic materials, with reports of use as a feed supplement and activity against pathogenic bacteria. In the current study the dose-dependent effects of biochar dietary inclusion in layer diets at 1%, 2% and 4% w/w were investigated to determine a) the efficacy of biochar as an anti-pathogenic additive on the intestinal microbiota and b) the optimal inclusion level. Biochar inclusion for anti-pathogenic effects was found to be most beneficial at 2% w/w. Poultry pathogens such as Gallibacterium anatis and campylobacters, including Campylobacter hepaticus, were found to be significantly lower in biochar fed birds. A shift in microbiota was also associated with the incorporation of 2% w/w biochar in the feed in two large scale trials on two commercial layer farms. Biochar inclusion for anti-pathogenic effects was found to be most beneficial at 2% w/w. Differential effects of the timing of biochar administration (supplementation beginning at hatch or at point of lay) were also evident, with greater impact on community microbial structure at 48 weeks of age when birds were fed from hatch rather than supplemented at point of lay.Nicky-Lee Willson, Thi T.H. Van, Surya P. Bhattarai, Jodi M. Courtice, Joshua R. McIntyre, Tanka P. Prasai, Robert J. Moore, Kerry Walsh, Dragana Stanle
White Paper: Shifting the goal post - from high impact journals to high impact data
The purpose of this white paper is to provide an overview of the ongoing initiatives at center level to respond to changing public expectations and to the challenge of improving the conduct of science by making research data widely available. We also attempt to provide a framework for implementing open access for research data to maximize CGIAR’s impact on development. The remainder of this paper proceeds as follows; firstly a summary of the diversity of research data produced by the centers is given, followed by an overview of the existing infrastructure for data management for each Center. Secondly, some of the limitations and barriers faced by the centers in their process to mainstream research data publishing are addressed. The paper concludes with recommendations for how these limitations and barriers can be tackled
First measurement of the Hubble Constant from a Dark Standard Siren using the Dark Energy Survey Galaxies and the LIGO/Virgo Binary–Black-hole Merger GW170814
International audienceWe present a multi-messenger measurement of the Hubble constant H 0 using the binary–black-hole merger GW170814 as a standard siren, combined with a photometric redshift catalog from the Dark Energy Survey (DES). The luminosity distance is obtained from the gravitational wave signal detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO)/Virgo Collaboration (LVC) on 2017 August 14, and the redshift information is provided by the DES Year 3 data. Black hole mergers such as GW170814 are expected to lack bright electromagnetic emission to uniquely identify their host galaxies and build an object-by-object Hubble diagram. However, they are suitable for a statistical measurement, provided that a galaxy catalog of adequate depth and redshift completion is available. Here we present the first Hubble parameter measurement using a black hole merger. Our analysis results in , which is consistent with both SN Ia and cosmic microwave background measurements of the Hubble constant. The quoted 68% credible region comprises 60% of the uniform prior range [20, 140] km s−1 Mpc−1, and it depends on the assumed prior range. If we take a broader prior of [10, 220] km s−1 Mpc−1, we find (57% of the prior range). Although a weak constraint on the Hubble constant from a single event is expected using the dark siren method, a multifold increase in the LVC event rate is anticipated in the coming years and combinations of many sirens will lead to improved constraints on H 0
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