3,979 research outputs found
Evidence for strong extragalactic magnetic fields from Fermi observations of TeV blazars
Magnetic fields in galaxies are produced via the amplification of seed
magnetic fields of unknown nature. The seed fields, which might exist in their
initial form in the intergalactic medium, were never detected. We report a
lower bound ~gauss on the strength of intergalactic
magnetic fields, which stems from the nonobservation of GeV gamma-ray emission
from electromagnetic cascade initiated by tera-electron volt gamma-ray in
intergalactic medium. The bound improves as if magnetic
field correlation length, , is much smaller than a megaparsec. This
lower bound constrains models for the origin of cosmic magnetic fields.Comment: 14 pages, 3 figure
The U.S. demographic transition
agriculture;manufacturing;technological change
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
Real space investigation of structural changes at the metal-insulator transition in VO2
Synchrotron X-ray total scattering studies of structural changes in rutile
VO2 at the metal-insulator transition temperature of 340 K reveal that
monoclinic and tetragonal phases of VO2 coexist in equilibrium, as expected for
a first-order phase transition. No evidence for any distinct intermediate phase
is seen. Unbiased local structure studies of the changes in V--V distances
through the phase transition, using reverse Monte Carlo methods, support the
idea of phase coexistence and point to the high degree of correlation in the
dimerized low-temperature structure. No evidence for short range V--V
correlations that would be suggestive of local dimers is found in the metallic
phase.Comment: 4 pages, 5 figure
Beyond BAO: improving cosmological constraints from BOSS with measurement of the void-galaxy cross-correlation
We present a measurement of the anisotropic void-galaxy cross-correlation
function in the CMASS galaxy sample of the BOSS DR12 data release. We perform a
joint fit to the data for redshift space distortions (RSD) due to galaxy
peculiar velocities and anisotropies due to the Alcock-Paczynski (AP) effect,
for the first time using a velocity field reconstruction technique to remove
the complicating effects of RSD in the void centre positions themselves. Fits
to the void-galaxy function give a 1% measurement of the AP parameter
combination at redshift , where
is the angular diameter distance and the Hubble parameter, exceeding the
precision obtainable from baryon acoustic oscillations (BAO) by a factor of
~3.5 and free of systematic errors. From voids alone we also obtain a 10%
measure of the growth rate, . The parameter
degeneracies are orthogonal to those obtained from galaxy clustering. Combining
void information with that from BAO and galaxy RSD in the same CMASS sample, we
measure (at 0.8% precision),
kmsMpc (1%) and
(4.9%), consistent with cosmic microwave background
(CMB) measurements from Planck. These represent a factor \sim2 improvement in
precision over previous results through the inclusion of void information.
Fitting a flat cosmological constant CDM model to these results in
combination with Planck CMB data, we find up to an 11% reduction in
uncertainties on and compared to use of the corresponding BOSS
consensus values. Constraints on extended models with non-flat geometry and a
dark energy of state that differs from show an even greater improvement.Comment: 22 pages, 15 figures. Accepted for publication in Phys.Rev.D. v2
corrects small error in likelihood analysis; minor changes to figures and
text, cosmological results unchanged. Reconstruction and void-finding code
available at https://github.com/seshnadathur/Revolver, likelihood analysis
code available at https://github.com/seshnadathur/void-galaxy-cosmo-fitte
Recommended from our members
From Waste-Heat Recovery to Refrigeration: Compositional Tuning of Magnetocaloric Mn 1+ x Sb
- …