323 research outputs found
Properties of KCoAs and Alloys with Fe and Ru: Density Functional Calculations
Electronic structure calculations are presented for KCoAs and alloys
with KFeAs and KRuAs. These materials show electronic
structures characteristic of coherent alloys, with a similar Fermi surface
structure to that of the Fe-based superconductors, when the electron count
is near six per transition metal. However, they are less magnetic than the
corresponding Fe compounds. These results are discussed in relation to
superconductivity.Comment: 5 page
USING PRAISE TO INCREASE VISUAL ATTENDING IN AN ASYNCHRONOUS ONLINE LEARNING ENVIRONMENT: AN EYE TRACKING STUDY
With the emergence of online courses in the mid-1990s, the number of students enrolled in online courses has been growing at an exponential rate (Schwirzke, Vashaw, & Watson, 2018). This trend brings with it new problems, such as familiarity with evidence-supported behavioral techniques that will maintain student engagement and improve likelihood of academic success in online learning environments. The purpose of the present study was to examine how the use of praise may affect visual engagement with video lectures with the assistance of commercially available eye tracking technology. A secondary objective of the study was to identify how praise affects performance on post-lecture knowledge assessments of information delivered through online videos. Results indicated that three out of four undergraduate participants were visually engaged with the video lecture more when provided praise than in the absence of praise, while the fourth participant showed ceiling effects. Results also indicated that praise did not have a significant effect on post-lecture knowledge assessment accuracy. These results indicate that praise may have utility in improving visual engagement in online learning environments and that inexpensive eye tracking technology may be useful for measuring visual engagement in these environments
Superconductivity at 22 K in Co-doped BaFe2As2 Crystals
Here we report bulk superconductivity in BaFe1.8Co0.2As2 single crystals
below Tc = 22 K, as demonstrated by resistivity, magnetic susceptibility, and
specific heat data. Hall data indicate that the dominant carriers are
electrons, as expected from simple chemical reasoning. This is the first
example of superconductivity induced by electron doping in this family of
materials. In contrast to the cuprates, the BaFe2As2 system appears to tolerate
considerable disorder in the FeAs planes. First principles calculations for
BaFe1.8Co0.2As2 indicate the inter-band scattering due to Co is weak.Comment: 9 pages, 3 figure
Breaking through the Mermin-Wagner limit in 2D van der Waals magnets
The Mermin-Wagner theorem states that long-range magnetic order does not
exist in one- or two-dimensional (2D) isotropic magnets with short-ranged
interactions. The theorem has been a milestone in magnetism and has been
driving the research of recently discovered 2D van der Waals (vdW) magnetic
materials from fundamentals up to potential applications. In such systems, the
existence of magnetic ordering is typically attributed to the presence of a
significant magnetic anisotropy, which is known to introduce a spin-wave gap
and circumvent the core assumption of the theorem. Here we show that in
finite-size 2D vdW magnets typically found in lab setups (e.g., within
millimetres), short-range interactions can be large enough to allow the
stabilisation of magnetic order at finite temperatures without any magnetic
anisotropy for practical implementations. We demonstrate that magnetic ordering
can be created in flakes of 2D materials independent of the lattice symmetry
due to the intrinsic nature of the spin exchange interactions and finite-size
effects in two-dimensions. Surprisingly we find that the crossover temperature,
where the intrinsic magnetisation changes from superparamagnetic to a
completely disordered paramagnetic regime, is weakly dependent on the system
length, requiring giant sizes (e.g., of the order of the observable universe
~10 m) in order to observe the vanishing of the magnetic order at
cryogenic temperatures as expected from the Mermin-Wagner theorem. Our findings
indicate exchange interactions as the main driving force behind the
stabilisation of short-range order in 2D magnetism and broaden the horizons of
possibilities for exploration of compounds with low anisotropy at an atomically
thin level
BaT2As2 Single Crystals (T = Fe, Co, Ni) and Superconductivity upon Co-doping
The crystal structure and physical properties of BaFe2As2, BaCo2As2, and
BaNi2As2 single crystals are surveyed. BaFe2As2 gives a magnetic and structural
transition at TN = 132(1) K, BaCo2As2 is a paramagnetic metal, while BaNi2As2
has a structural phase transition at T0 = 131 K, followed by superconductivity
below Tc = 0.69 K. The bulk superconductivity in Co-doped BaFe2As2 below Tc =
22 K is demonstrated by resistivity, magnetic susceptibility, and specific heat
data. In contrast to the cuprates, the Fe-based system appears to tolerate
considerable disorder in the transition metal layers. First principles
calculations for BaFe1.84Co0.16As2 indicate the inter-band scattering due to Co
is weak.Comment: Accepted to Physica
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Immobilization of high-level defense wastes in SYNROC-D: recent research and development results on process scale-up
SYNROC is a titanate-based ceramic waste form being developed to immobilize high-level nuclear reactor wastes. SYNROC-D is a unique variation of SYNROC designed to contain high-level defense wastes, particularly those in storage at the Savannah River Plant (SRP). We review recent research and development on SYNROC-D processing options and report on work in progress on various unit operations. The overall immobilization process can be divided into three general parts: (1) slurry preparation (formulation, reactant addition and blending); (2) powder processing (spray drying, calcination/redox control); and (3) mineralization (densification). Powder processing research is directed toward development of a slurry-fed, fluidized-bed calciner based on the ICPP design. Densification research is focused on use of hot isostatic pressing (HIP) or hot uniaxial pressing (HUP). The successful use of both have been demonstrated
Local circuit amplification of spatial selectivity in the hippocampus
Local circuit architecture facilitates the emergence of feature selectivity in the cerebral cortex1. In the hippocampus, it remains unknown whether local computations supported by specific connectivity motifs2 regulate the spatial receptive fields of pyramidal cells3. Here we developed an in vivo electroporation method for monosynaptic retrograde tracing4 and optogenetics manipulation at single-cell resolution to interrogate the dynamic interaction of place cells with their microcircuitry during navigation. We found a local circuit mechanism in CA1 whereby the spatial tuning of an individual place cell can propagate to a functionally recurrent subnetwork5 to which it belongs. The emergence of place fields in individual neurons led to the development of inverse selectivity in a subset of their presynaptic interneurons, and recruited functionally coupled place cells at that location. Thus, the spatial selectivity of single CA1 neurons is amplified through local circuit plasticity to enable effective multi-neuronal representations that can flexibly scale environmental features locally without degrading the feedforward input structure
Systematics of the Giant Monopole Resonance from Inelastic Alpha Scattering
Journals published by the American Physical Society can be found at http://publish.aps.org
Giant-Resonances in Ca-40
Journals published by the American Physical Society can be found at http://publish.aps.org
Data incongruence and the problem of avian louse phylogeny
Recent studies based on different types of data (i.e. morphological and molecular) have supported conflicting phylogenies for the genera of avian feather lice (Ischnocera: Phthiraptera). We analyse new and published data from morphology and from mitochondrial (12S rRNA and COI) and nuclear (EF1-) genes to explore the sources of this incongruence and explain these conflicts. Character convergence, multiple substitutions at high divergences, and ancient radiation over a short period of time have contributed to the problem of resolving louse phylogeny with the data currently available. We show that apparent incongruence between the molecular datasets is largely attributable to rate variation and nonstationarity of base composition. In contrast, highly significant character incongruence leads to topological incongruence between the molecular and morphological data. We consider ways in which biases in the sequence data could be misleading, using several maximum likelihood models and LogDet corrections. The hierarchical structure of the data is explored using likelihood mapping and SplitsTree methods. Ultimately, we concede there is strong discordance between the molecular and morphological data and apply the conditional combination approach in this case. We conclude that higher level phylogenetic relationships within avian Ischnocera remain extremely problematic. However, consensus between datasets is beginning to converge on a stable phylogeny for avian lice, at and below the familial rank
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