1,090 research outputs found
Disorder effects on the superconducting properties of BaFeCoAs single crystals
Single crystals of superconducting BaFeCoAs were exposed
to neutron irradiation in a fission reactor. The introduced defects decrease
the superconducting transition temperature (by about 0.3 K) and the upper
critical field anisotropy (e.g. from 2.8 to 2.5 at 22 K) and enhance the
critical current densities by a factor of up to about 3. These changes are
discussed in the context of similar experiments on other superconducting
materials
Conductance asymmetry in point-contacts on epitaxial thin films of Ba(FeCo)As
Point-contact spectroscopy is a powerful tool for probing superconductors.
One of the most common observations in the point-contact spectra on the
recently discovered ferropnictide superconductors is a large conductance
asymmetry with respect to voltage across the point-contact. In this paper we
show that the antisymmetric part of the point-contact spectrum between a silver
tip and an epitaxial thin film of Ba(FeCo)As shows
certain unique features. These features have an interesting evolution with
increasing temperature up to a temperature that is 30% larger than the critical
temperature of the superconductor. We argue that this evolution can be
associated with the rich normal state properties of these materials.Comment: 4 pages, 2 figure
Assessing amino acid racemization variability in coral intra-crystalline protein for geochronological applications.
Over 500 Free Amino Acid (FAA) and corresponding Total Hydrolysed Amino Acid (THAA) analyses were completed from eight independently-dated, multi-century coral cores of massive Porites sp. colonies. This dataset allows us to re-evaluate the application of amino acid racemization (AAR) for dating late Holocene coral material, 20 years after Goodfriend et al. (GCA56 (1992), 3847) first showed AAR had promise for developing chronologies in coral cores. This re-assessment incorporates recent method improvements, including measurement by RP-HPLC, new quality control approaches (e.g. sampling and sub-sampling protocols, statistically-based data screening criteria), and cleaning steps to isolate the intra-crystalline skeletal protein. We show that the removal of the extra-crystalline contaminants and matrix protein is the most critical step for reproducible results and recommend a protocol of bleaching samples in NaOCl for 48 h to maximise removal of open system proteins while minimising the induced racemization. We demonstrate that AAR follows closed system behaviour in the intra-crystalline fraction of the coral skeletal proteins. Our study is the first to assess the natural variability in intra-crystalline AAR between colonies, and we use coral cores taken from the Great Barrier Reef, Australia, and Jarvis Island in the equatorial Pacific to explore variability associated with different environmental conditions and thermal histories. Chronologies were developed from THAA Asx D/L, Ala D/L, Glx D/L and FAA Asx D/L for each core and least squares Monte Carlo modelling applied in order to quantify uncertainty of AAR age determinations and assess the level of dating resolution possible over the last 5 centuries. AAR within colonies follow consistent stratigraphic aging. However, there are systematic differences in rates between the colonies, which would preclude direct comparison from one colony to another for accurate age estimation. When AAR age models are developed from a combined dataset to include this natural inter-colony variability THAA Asx D/L, Glx D/L and Ala D/L give a 2σ age uncertainty of ±19, ±38 and ±29 year, for the 20th C respectively; in comparison 2σ age uncertainties from a single colony are ±12, ±12 and ±14 year. This is the first demonstration of FAA D/L for dating coral and following strict protocols 2σ precisions of ±24 years can be achieved across different colonies in samples from the last 150 years, and can be ±10 years within a core from a single colony. Despite these relatively large error estimates, AAR would be a valuable tool in situations where a large number of samples need to be screened rapidly and cheaply (e.g. identifying material from mixed populations in beach or uplift deposits), prior to and complementing the more time-consuming geochronological tools of U/Th or seasonal isotopic timeseries
Neutron Irradiation of Sm-1111
SmFeAsOF was irradiated in a fission reactor to a fast (E > 0.1
MeV) neutron fluence of 4x10^ m. The introduced defects increase
the normal state resistivity due to a reduction in the mean free path of the
charge carriers. This leads to an enhancement of the upper critical field at
low temperatures. The critical current density within the grains, Jc, increases
upon irradiation. The second maximum in the field dependence of Jc disappears
and the critical current density becomes a monotonically decreasing function of
the applied magnetic field
A diverse Pleistocene marsupial trackway assemblage from the Victorian Volcanic Plains, Australia
A diverse assemblage of late Pleistocene marsupial trackways on a lake bed in south-western Victoria provides the first information relating to the gaits and morphology of several megafaunal species, and represents the most speciose and best preserved megafaunal footprint site in Australia. The 60-110 ka volcaniclastic lacustrine sedimentary rocks preserve trackways of the diprotodontid Diprotodon optatum, a macropodid (probably Protemnodon sp.) and a large vombatid (perhaps Ramsayia magna or '. Phascolomys' medius) and possible prints of the marsupial lion, Thylacoleo carnifex. The footprints were imprinted within a short time period, demonstrating the association of the taxa present, rather than the time-averaged accumulations usually observed in skeletal fossil deposits. Individual manus and pes prints are distinguishable in some trackways, and in many cases some digital pad morphology is also present. Several parameters traditionally used to differentiate ichnotaxa, including trackway gauge and the degree of print in-turning relative to the midline, are shown to be subject to significant intraspecific variation in marsupials. Sexual dimorphism in the trackway proportions of Diprotodon, and its potential for occurrence in all large bodied, quadrupedal marsupials, is identified here for the first time
Evidence for electromagnetic granularity in polycrystalline Sm1111 iron-pnictides with enhanced phase purity
We prepared polycrystalline SmFeAsO1-xFx (Sm1111) bulk samples by sintering
and hot isostatic pressing (HIP) in order to study the effects of phase purity
and relative density on the intergranular current density. Sintered and HIPped
Sm1111 samples are denser with fewer impurity phases, such as SmOF and the
grain boundary wetting phase, FeAs. We found quite complex magnetization
behavior due to variations of both the inter and intragranular current
densities. Removing porosity and reducing second phase content enhanced the
intergranular current density, but HIPping reduced Tc and the intragranular
current density, due to loss of fluorine and reduction of Tc. We believe that
the HIPped samples are amongst the purest polycrystalline 1111 samples yet
made. However, their intergranular current densities are still small, providing
further evidence that polycrystalline pnictides, like polycrystalline cuprates,
are intrinsically granular.Comment: 14 pages, 6 figure
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