1,725 research outputs found
A new neutron study of the short range order inversion in FeCr
We have performed new neutron diffuse scattering measurements in
FeCr solid solutions, in a concentration range 0x0.15, where
the atomic distribution shows an inversion of the short range order. By
optimizing the signal-background ratio, we obtain an accurate determination of
the concentration of inversion x =0.110(5). We determine the near neighbor
atomic short range order parameters and pair potentials, which change sign at
x. The experimental results are compared with previous first principle
calculations and atomistic simulations.Comment: 6 pages; 6 figure
Fermi edge singularity in a non-equilibrium system
We report exact results for the Fermi Edge Singularity in the absorption
spectrum of an out-of-equilibrium tunnel junction. We consider two metals with
chemical potential difference V separated by a tunneling barrier containing a
defect, which exists in one of two states. When it is in its excited state,
tunneling through the otherwise impermeable barrier is possible. We find that
the lineshape not only depends on the total scattering phase shift as in the
equilibrium case but also on the difference in the phase of the reflection
amplitudes on the two sides of the barrier. The out-of-equilibrium spectrum
extends below the original threshold as energy can be provided by the power
source driving current across the barrier. Our results have a surprisingly
simple interpretation in terms of known results for the equilibrium case but
with (in general complex-valued) combinations of elements of the scattering
matrix replacing the equilibrium phase shifts.Comment: 4 page
Void-induced cross slip of screw dislocations in fcc copper
Pinning interaction between a screw dislocation and a void in fcc copper is
investigated by means of molecular dynamics simulation. A screw dislocation
bows out to undergo depinning on the original glide plane at low temperatures,
where the behavior of the depinning stress is consistent with that obtained by
a continuum model. If the temperature is higher than 300 K, the motion of a
screw dislocation is no longer restricted to a single glide plane due to cross
slip on the void surface. Several depinning mechanisms that involve multiple
glide planes are found. In particular, a depinning mechanism that produces an
intrinsic prismatic loop is found. We show that these complex depinning
mechanisms significantly increase the depinning stress
Complex Organic Molecules at High Spatial Resolution Toward Orion-KL I: Spatial Scales
Here we present high spatial resolution (<1 arcsecond) observations of
molecular emission in Orion-KL conducted using the Combined Array for Research
in Millimeter-Wave Astronomy (CARMA). This work was motivated by recent
millimeter continuum imaging studies of this region conducted at a similarly
high spatial resolution, which revealed that the bulk of the emission arises
from numerous compact sources, rather than the larger-scale extended structures
typically associated with the Orion Hot Core and Compact Ridge. Given that the
spatial extent of molecular emission greatly affects the determination of
molecular abundances, it is important to determine the true spatial scale for
complex molecules in this region. Additionally, it has recently been suggested
that the relative spatial distributions of complex molecules in a source might
give insight into the chemical mechanisms that drive complex chemistry in
star-forming regions. In order to begin to address these issues, this study
seeks to determine the spatial distributions of ethyl cyanide [C2H5CN],
dimethyl ether [(CH3)2O], methyl formate [HCOOCH3], formic acid [HCOOH],
acetone [(CH3)2CO], SiO, methanol [CH3OH], and methyl cyanide [CH3CN] in
Orion-KL at \lambda = 3 mm. We find that for all observed molecules, the
molecular emission arises from multiple components of the cloud that include a
range of spatial scales and physical conditions. Here we present the results of
these observations and discuss the implications for studies of complex
molecules in star-forming regions.Comment: Accepted for publication in the Astrophysical Journal Supplement;
Part 1 of a 2 paper series; 37 page
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