3,153 research outputs found
Computational screening of magnetocaloric alloys
An exciting development over the past few decades has been the use of
high-throughput computational screening as a means of identifying promising
candidate materials for a variety of structural or functional properties.
Experimentally, it is often found that the highest-performing materials contain
substantial atomic site disorder. These are frequently overlooked in
high-throughput computational searches however, due to difficulties in dealing
with materials that do not possess simple, well-defined crystallographic unit
cells. Here we demonstrate that the screening of magnetocaloric materials with
the help of the density functional theory-based magnetic deformation proxy can
be extended to systems with atomic site disorder. This is accomplished by
thermodynamic averaging of the magnetic deformation for ordered supercells
across a solid solution. We show that the highly non-monotonic magnetocaloric
properties of the disordered solid solutions Mn(CoFe)Ge and
(MnNi)CoGe are successfully captured using this method.Comment: Main text: 8 pages, 6 figures. Supplemental Material: 2 pages, 2
figure
An Interstellar Conduction Front Within a Wolf-Rayet Ring Nebula Observed with the GHRS
With the High Resolution Spectrograph aboard the Hubble Space Telescope we
obtained high signal-to-noise (S/N > 200 - 600 per 17 km/s resolution element)
spectra of narrow absorption lines toward the Wolf-Rayet star HD 50896. The
ring nebula S308 that surrounds this star is thought to be caused by a
pressure-driven bubble bounded by circumstellar gas (most likely from a red
supergiant or luminous blue variable progenitor) pushed aside by a strong
stellar wind. Our observation has shown for the first time that blueshifted
(approximately 70 km/s relative to the star) absorption components of C IV and
N V arise in a conduction front between the hot interior of the bubble and the
cold shell of swept-up material. These lines set limits on models of the
conduction front. Nitrogen in the shell appears to be overabundant by a factor
~10. The P Cygni profiles of N V and C IV are variable, possibly due to a
suspected binary companion to HD 50896.Comment: 32 pages, Latex, to appear in the Astrophysical Journal, April, 199
First Measurement of Monoenergetic Muon Neutrino Charged Current Interactions
We report the first measurement of monoenergetic muon neutrino charged
current interactions. MiniBooNE has isolated 236 MeV muon neutrino events
originating from charged kaon decay at rest ()
at the NuMI beamline absorber. These signal -carbon events are
distinguished from primarily pion decay in flight and
backgrounds produced at the target station and decay pipe
using their arrival time and reconstructed muon energy. The significance of the
signal observation is at the 3.9 level. The muon kinetic energy,
neutrino-nucleus energy transfer (), and total cross
section for these events is extracted. This result is the first known-energy,
weak-interaction-only probe of the nucleus to yield a measurement of
using neutrinos, a quantity thus far only accessible through electron
scattering.Comment: 6 pages, 4 figure
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Francisella tularensis Transmission by Solid Organ Transplantation, 20171.
In July 2017, fever and sepsis developed in 3 recipients of solid organs (1 heart and 2 kidneys) from a common donor in the United States; 1 of the kidney recipients died. Tularemia was suspected only after blood cultures from the surviving kidney recipient grew Francisella species. The organ donor, a middle-aged man from the southwestern United States, had been hospitalized for acute alcohol withdrawal syndrome, pneumonia, and multiorgan failure. F. tularensis subsp. tularensis (clade A2) was cultured from archived spleen tissue from the donor and blood from both kidney recipients. Whole-genome multilocus sequence typing indicated that the isolated strains were indistinguishable. The heart recipient remained seronegative with negative blood cultures but had been receiving antimicrobial drugs for a medical device infection before transplant. Two lagomorph carcasses collected near the donor's residence were positive by PCR for F. tularensis subsp. tularensis (clade A2). This investigation documents F. tularensis transmission by solid organ transplantation
Imaging phonon-mediated hydrodynamic flow in WTe2
In the presence of interactions, electrons in condensed-matter systems can
behave hydrodynamically, exhibiting phenomena associated with classical fluids,
such as vortices and Poiseuille flow. In most conductors, electron-electron
interactions are minimized by screening effects, hindering the search for
hydrodynamic materials; however, recently, a class of semimetals has been
reported to exhibit prominent interactions. Here we study the current flow in
the layered semimetal tungsten ditelluride by imaging the local magnetic field
using a nitrogen-vacancy defect in a diamond. We image the spatial current
profile within three-dimensional tungsten ditelluride and find that it exhibits
non-uniform current density, indicating hydrodynamic flow. Our
temperature-resolve current profile measurements reveal a non-monotonic
temperature dependence, with the strongest hydrodynamic effects at
approximately 20 K. We also report ab initio calculations showing that
electron-electron interactions are not explained by the Coulomb interaction
alone, but are predominantly mediated by phonons. This provides a promising
avenue in the search for hydrodynamic flow and prominent electron interactions
in high-carrier-density materials.Comment: 11 pages, 4 figures + supplementary materia
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