62,720 research outputs found
Relation between directed polymers in random media and random bond dimer models
We reassess the relation between classical lattice dimer models and the
continuum elastic description of a lattice of fluctuating polymers. In the
absence of randomness we determine the density and line tension of the polymers
in terms of the bond weights of hard-core dimers on the square and the
hexagonal lattice. For the latter, we demonstrate the equivalence of the
canonical ensemble for the dimer model and the grand-canonical description for
polymers by performing explicitly the continuum limit. Using this equivalence
for the random bond dimer model on a square lattice, we resolve a previously
observed discrepancy between numerical results for the random dimer model and a
replica approach for polymers in random media. Further potential applications
of the equivalence are briefly discussed.Comment: 6 pages, 3 figure
Ebolavirus is evolving but not changing: No evidence for functional change in EBOV from 1976 to the 2014 outbreak
The 2014 epidemic of Ebola virus disease (EVD) has had a devastating impact in West Africa. Sequencing of ebolavirus (EBOV) from infected individuals has revealed extensive genetic variation, leading to speculation that the virus may be adapting to humans, accounting for the scale of the 2014 outbreak. We computationally analyze the variation associated with all EVD outbreaks, and find none of the amino acid replacements lead to identifiable functional changes. These changes have minimal effect on protein structure, being neither stabilizing nor destabilizing, are not found in regions of the proteins associated with known functions and tend to cluster in poorly constrained regions of proteins, specifically intrinsically disordered regions. We find no evidence that the difference between the current and previous outbreaks is due to evolutionary changes associated with transmission to humans. Instead, epidemiological factors are likely to be responsible for the unprecedented spread of EVD
The Ultra-Fast Outflow of WKK 4438: Suzaku and NuSTAR X-ray Spectral Analysis
Previous X-ray spectral analysis has revealed an increasing number of AGNs
with high accretion rates where an outflow with a mildly relativistic velocity
originates from the inner accretion disk. Here we report the detection of a new
ultra-fast outflow (UFO) with a velocity of in addition to a relativistic disk reflection
component in a poorly studied NLS1 WKK~4438, based on archival \nustar and
\suzaku observations. The spectra of both \suzaku and \nustar observations show
an Fe~\textsc{xxvi} absorption feature and the \suzaku data also show evidence
for an Ar~\textsc{xviii} with the same blueshift. A super-solar argon abundance
() and a slight iron over-abundance
() are found in our spectral
modelling. Based on Monte-Carlo simulations, the detection of the UFO is
estimated to be around at 3 significance. The fast wind most likely
arises from a radius of away from the central black hole. The disk
is accreting at a high Eddington ratio (). The
mass outflow rate of the UFO is comparable with the disk mass inflow rate
(), assuming a maximum covering factor.
The kinetic power of the wind might not be high enough to have influence in AGN
feedback () due to a relatively
small column density (~cm). However note that
both the inferred velocity and the column density could be lower limits owing
to the low viewing angle ().Comment: 7 pages, 3 figures, accepted by MNRA
Electric dipole sheets in BaTiO/BaZrO superlattices
We investigate two-dimensional electric dipole sheets in the superlattice
made of BaTiO and BaZrO using first-principles-based Monte-Carlo
simulations and density functional calculations. Electric dipole domains and
complex patterns are observed and the complex dipole structures with various
symmetries (e.g. Pma2, Cmcm and Pmc2_{1}) are further confirmed by density
functional calculations, which are found to be almost degenerate in energy with
the ferroelectric ground state of the Amm2 symmetry, therefore strongly
resembling magnetic sheets. More complex dipole patterns, including vortices
and anti-vortices, are also observed, which may constitute the intermediate
states that overcome the high energy barrier of different polarization
orientations previously predicted by Lebedev\onlinecite{Lebedev2013}. We also
show that such system possesses large electrostrictive effects that may be
technologically important
Zero-Bias Anomalies in Narrow Tunnel Junctions in the Quantum Hall Regime
We report on the study of cleaved-edge-overgrown line junctions with a
serendipitously created narrow opening in an otherwise thin, precise line
barrier. Two sets of zero-bias anomalies are observed with an enhanced
conductance for filling factors and a strongly suppressed conductance
for . A transition between the two behaviors is found near . The zero-bias anomaly (ZBA) line shapes find explanation in
Luttinger liquid models of tunneling between quantum Hall edge states. The ZBA
for occurs from strong backscattering induced by suppression of
quasiparticle tunneling between the edge channels for the Landau
levels. The ZBA for arises from weak tunneling of quasiparticles
between the edge channels.Comment: version with edits for clarit
Advanced water window x-ray microscope design and analysis
The project was focused on the design and analysis of an advanced water window soft-x-ray microscope. The activities were accomplished by completing three tasks contained in the statement of work of this contract. The new results confirm that in order to achieve resolutions greater than three times the wavelength of the incident radiation, it will be necessary to use aspherical mirror surfaces and to use graded multilayer coatings on the secondary (to accommodate the large variations of the angle of incidence over the secondary when operating the microscope at numerical apertures of 0.35 or greater). The results are included in a manuscript which is enclosed in the Appendix
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