4,136 research outputs found
Total scattering descriptions of local and cooperative distortions in the oxide spinel (Mg,Cu)Cr2O4 with dilute Jahn-Teller ions
The normal spinel oxide MgCr2O4 is cubic at room temperature while the normal
spinel CuCr2O4 is tetragonal as a consequence of the Jahn-Teller nature of Cu2+
on the tetrahedral sites. Despite different end-member structures, complete
solid solutions of Mg_{1-x}Cu_xCr2O4 can be prepared that display a first-order
structural transition with composition x = 0.43 at room temperature. Reverse
Monte Carlo analysis of total neutron scattering on data acquired between 300 K
and 15 K on samples with x = 0.10, 0.20, and 0.43 provides unbiased local and
average structure descriptions of the samples, including an understanding of
the transition from local Jahn-Teller distortions in the cubic phase to
cooperative distortions that result in a tetragonal structure. Distributions of
continuous symmetry measures help to understand and distinguish distorted and
undistorted coordination around the tetrahedral site in the solid solutions.
Magnetic exchange bias is observed in field-cooled hysteresis loops of samples
with dilute Cu2+ concentration and in samples with tetragonal--cubic phase
coexistence around 300 K.Comment: 10 pages, 14 figure
Exchange biasing of single-domain Ni nanoparticles spontaneously grown in an antiferromagnetic MnO matrix
Exchange biased composites of ferromagnetic single-domain Ni nanoparticles
embedded within large grains of MnO have been prepared by reduction of
NiMnO phases in flowing hydrogen. The Ni precipitates are 15-30
nm in extent, and the majority are completely encased within the MnO matrix.
The manner in which the Ni nanoparticles are spontaneously formed imparts a
high ferromagnetic- antiferromagnetic interface/volume ratio, which results in
substantial exchange bias effects. Exchange bias fields of up to 100 Oe are
observed, in cases where the starting Ni content in the precursor
NiMnO phase is small. For particles of approximately the same
size, the exchange bias leads to significant hardening of the magnetization,
with the coercive field scaling nearly linearly with the exchange bias field.Comment: 6 pages PDFLaTeX with 9 figure
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Effects of a Magazine’s Move to Online-only: Post-print Audience Attention and Readership Retention Revisited
For financial reasons, newspapers and magazines are increasingly going online-only. By doing so, some have returned to profitability, but with what consequences for their audiences? To expand the scant evidence base, we conducted a case study of the UK’s New Musical Express (NME) magazine. By analyzing quantitative audience data from official industry sources, we estimate total time spent with the NME by its British audience fell dramatically post-print—by 72%. This fall mirrors that suffered by The Independent newspaper, which went online-only two years earlier. We also report that the NME’s official net weekly and monthly readership increased post-print, although these results are difficult to compare with The Independent’s because the two titles differed in their print publication frequencies. We conclude that the attention periodicals attract via their print editions is unlikely to immediately transfer to their online editions should they go online-only. Building a fuller theory of print platform cessation, however—one that also encompasses changes in readership/reach—requires more comparable data. This case study provides further evidence to suggest that though, for newspapers and magazines, a post-print existence may be less costly, it is also more constrained, with much of the attention they formerly enjoyed simply stripped away
Impact of densitized lapse slicings on evolutions of a wobbling black hole
We present long-term stable and second-order convergent evolutions of an
excised wobbling black hole. Our results clearly demonstrate that the use of a
densitized lapse function extends the lifetime of simulations dramatically. We
also show the improvement in the stability of single static black holes when an
algebraic densitized lapse condition is applied. In addition, we introduce a
computationally inexpensive approach for tracking the location of the
singularity suitable for mildly distorted black holes. The method is based on
investigating the fall-off behavior and asymmetry of appropriate grid
variables. This simple tracking method allows one to adjust the location of the
excision region to follow the coordinate motion of the singularity.Comment: 10 pages, 8 figure
The local atomic quasicrystal structure of the icosahedral Mg25Y11Zn64 alloy
A local and medium range atomic structure model for the face centred
icosahedral (fci) Mg25Y11Zn64 alloy has been established in a sphere of r = 27
A. The model was refined by least squares techniques using the atomic pair
distribution (PDF) function obtained from synchrotron powder diffraction. Three
hierarchies of the atomic arrangement can be found: (i) five types of local
coordination polyhedra for the single atoms, four of which are of Frank-Kasper
type. In turn, they (ii) form a three-shell (Bergman) cluster containing 104
atoms, which is condensed sharing its outer shell with its neighbouring
clusters and (iii) a cluster connecting scheme corresponding to a
three-dimensional tiling leaving space for few glue atoms. Inside adjacent
clusters, Y8-cubes are tilted with respect to each other and thus allow for
overall icosahedral symmetry. It is shown that the title compound is
essentially isomorphic to its holmium analogue. Therefore fci-Mg-Y-Zn can be
seen as the representative structure type for the other rare earth analogues
fci-Mg-Zn-RE (RE = Dy, Er, Ho, Tb) reported in the literature.Comment: 12 pages, 8 figures, 2 table
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