3,541 research outputs found
A Cautionary Tale: The Coulomb Modified ANC for the State in O
We discuss the impact of the uncertainty ( keV) in the excitation
energy of the astrophysically important 6.356 MeV state of O
on the precision with which the Coulomb reduced ANC () for the
\left<^{17}\mathrm{O}(1/2^+_2) \mid \protect{^{13}\mathrm{C}} + \alpha
\right> overlap can be extracted from direct reaction data. We find a linear
dependence of on the binding energy, the value extracted
varying by a factor of 4 over the range --
MeV. This represents an intrinsic limit on the precision with which
can be determined which cannot be improved unless or until
the uncertainty in is reduced
Strong coupling effects in near-barrier heavy-ion elastic scattering
Accurate elastic scattering angular distribution data measured at bombarding
energies just above the Coulomb barrier have shapes that can markedly differ
from or be the same as the expected classical Fresnel scattering pattern
depending on the structure of the projectile, the target or both. Examples are
given such as 18O + 184W and 16O + 148,152Sm where the expected rise above
Rutherford scattering due to Coulomb-nuclear interference is damped by coupling
to the target excited states, and the extreme case of 11Li scattering, where
coupling to the 9Li + n + n continuum leads to an elastic scattering shape that
cannot be reproduced by any standard optical model parameter set. The recent
availability of high quality 6He, 11Li and 11Be data provides further examples
of the influence that coupling effects can have on elastic scattering.
Conditions for strong projectile-target coupling effects are presented with
special emphasis on the importance of the beam-target charge combination being
large enough to bring about the strong coupling effects. Several measurements
are proposed that can lead to further understanding of strong coupling effects
by both inelastic excitation and nucleon transfer on near-barrier elastic
scattering. A final note on the anomalous nature of 8B elastic scattering is
presented as it possesses a more or less normal Fresnel scattering shape
whereas one would a priori not expect this due to the very low breakup
threshold of 8B. The special nature of 11Li is presented as it is predicted
that no matter how far above the Coulomb barrier the elastic scattering is
measured, its shape will not appear as Fresnel like whereas the elastic
scattering of all other loosely bound nuclei studied to date should eventually
do so as the incident energy is increased, making both 8B and 11Li truly
"exotic".Comment: Review articl
Relationship between Population Dynamics and the Self-Energy in Driven Non-Equilibrium Systems
We compare the decay rates of excited populations directly calculated within
a Keldysh formalism to the equation of motion of the population itself for a
Hubbard-Holstein model in two dimensions. While it is true that these two
approaches must give the same answer, it is common to make a number of
simplifying assumptions within the differential equation for the populations
that allows one to interpret the decay in terms of hot electrons interacting
with a phonon bath. Here we show how care must be taken to ensure an accurate
treatment of the equation of motion for the populations due to the fact that
there are identities that require cancellations of terms that naively look like
they contribute to the decay rates. In particular, the average time dependence
of the Green's functions and self-energies plays a pivotal role in determining
these decay rates.Comment: Submitted to Entrop
General principles for the non-equilibrium relaxation of populations in quantum materials
We examine the problem of how excited populations of electrons relax after
they have been excited by a pump. We include three of the most important
relaxation processes: (i) impurity scattering; (ii) Coulomb scattering; and
(iii) electron-phonon scattering. The relaxation of an excited population of
electrons is one of the most fundamental processes measured in pump/probe
experiments, but its interpretation remains under debate. We show how several
common assumptions about non-equilibrium relaxation that are pervasive in the
field may not hold under quite general conditions. The analysis shows that
non-equilibrium relaxation is more complex than previously thought, but it
yields to recently developed theoretical methods in non-equilibrium theory. In
this work, we show how one can use many-body theory to properly interpret and
analyze these complex systems. We focus much of the discussion on implications
of these results for experiment.Comment: 13 pages, 10 figure
Microorganism study - Bacterial isolants from harsh environments Final report
Soil bacterial isolants from harsh environment
The Unusual Spitzer Spectrum of the Carbon Star IRAS 04496–6958: A Different Condensation Sequence in the LMC?
We present a new Spitzer Infrared Spectrograph (IRS) spectrum of the carbon star IRAS 04496-6958 in the Large Magellanic Cloud, which exhibits a fairly broad absorption feature at ~11 μm. This feature is consistent with SiC absorption, as seen in a few Galactic sources. Furthermore, the C2H2 (and other molecular) absorption bands are the deepest ever observed, indicative of a very high column density. While the Galactic sources with SiC absorption have cool colors (continuum temperature ≈300 K), IRAS 04496-6958 is much bluer, with a continuum temperature of ≈600 K. Based on the Galactic sample, SiC dust at this temperature should still display an emission feature at ~11 μm. If SiC is the cause of the absorption feature, it suggests a subtly different evolutionary path and a change to a different condensation sequence than assumed for Galactic carbon stars. An alternative explanation for this feature is molecular line absorption; however, currently available line lists are not sufficient to properly assess this hypothesis
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