581 research outputs found
Gaseous fission product release during storage at various temperatures for HTGR-type fuels
Measurements were made of gaseous fission product releases from an HTGR-type fuel body under conditions simulating storage at temperatures up to 300/sup 0/C. The fuel was a recycle test element containing BISO-BISO coated fuel particles which had been irradiated for 701 effective full-power days in the Peach Bottom HTGR. Storage test temperatures were ambient (about 30/sup 0/C), 100, 150, 200, and 300/sup 0/C. The initial release rates of /sup 85/Kr varied after each change in temperature. A fairly stable release rate was reached that increased from approximately 60 ..mu..Ci/day at ambient temperature to approximately 1000 ..mu..Ci/day after 30 days at 200/sup 0/C and slowly decreased to about 200 ..mu..Ci/day after 554 days at 200/sup 0/C. In the experiment at 300/sup 0/C, a final release rate of 4000 ..mu..Ci/day was attained after 66 days. The releases of /sup 85/Kr were followed for about two and one-half years. The stabilized release rates for /sup 3/H were approximately 0.02 ..mu..Ci/day at ambient temperature, approximately 0.750 ..mu..Ci/day at 200/sup 0/C after 30 days, and 0.460 ..mu..Ci/day after 554 days. The final release rate at 300/sup 0/C was about 30 ..mu..Ci/day after 66 days.Over the lifetime of the experiment, approximately 22% of the initial /sup 85/Kr inventory was evolved and swept out, and approximately 4% of the initial /sup 3/H inventory was evolved and swept out. The activation energies calculated for the Kr and /sup 3/H evolution were approximately 7.8 kcal/mole and approximately 12.4 kcal/mole, respectively
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Observation and analysis of time-dependent closed orbit motion in the LAMPF Proton Storage Ring
When the stored beam is artificially offset in a section of the LAMPF Proton Storage Ring by changing selected ring dipole strengths, there is evidence for a small time dependence of the offset during the course of beam injection. A complete discussion of the time dependence of orbit offsets should take into account at least the following possibilities: (1) correlations between the injection timing pattern and ring dipole field ripple, (2) correlations between the injection timing pattern and changes of beam position monitor characteristics, and (3) growth of space-charge effects as the number of stored protons increases. Since there is no a priori reason to expect the correlations mentioned, we have analyzed the observed time dependence of the beam offset in terms of space-charge effects only, although the other possible causes cannot be ruled out. The buildup of circulating charge during proton injection leads to a shift of the betatron tune of individual protons because of space-charge forces; this shift can cause a change of the individual proton closed-orbit positions, and consequently a change in the position of the beam as a whole. At the end of a PSR injection cycle there are approximately 2.5 {times} 10{sup 13} protons stored in the ring. The observed time dependence of the beam offset indicates a horizontal-plane tune shift of {minus}0.03 {plus minus} 0.02; this is consistent with a theoretical estimate of a maximum expected space-charge tune shift of {minus}0.09 when 2.5 {times} 10{sup 13} protons are stored in the ring. 3 refs., 4 figs
Rotational and Vibrational Dynamics of Interstitial Molecular Hydrogen
The calculation of the hindered roton-phonon energy levels of a hydrogen
molecule in a confining potential with different symmetries is systematized for
the case when the rotational angular momentum is a good quantum number. One
goal of this program is to interpret the energy-resolved neutron time of flight
spectrum previously obtained for HC. This spectrum gives direct
information on the energy level spectrum of H molecules confined to the
octahedral interstitial sites of solid C. We treat this problem of
coupled translational and orientational degrees of freedom a) by construction
of an effective Hamiltonian to describe the splitting of the manifold of states
characterized by a given value of and having a fixed total number of phonon
excitations, b) by numerical solutions of the coupled translation-rotation
problem on a discrete mesh of points in position space, and c) by a group
theoretical symmetry analysis. Results obtained from these three different
approaches are mutually consistent. The results of our calculations explain
several hitherto uninterpreted aspects of the experimental observations, but
show that a truly satisfactory orientational potential for the interaction of
an H molecule with a surrounding array of C atoms has not yet been
developed.Comment: 53 pages, 9 figures, to appear in Phys. Rev B (in press). Phys. Rev.
B (in press
The Local Bubble and Interstellar Material Near the Sun
The properties of interstellar matter (ISM) at the Sun are regulated by our
location with respect to the Local Bubble (LB) void in the ISM. The LB is
bounded by associations of massive stars and fossil supernovae that have
disrupted natal ISM and driven intermediate velocity ISM into the LB interior
void. The Sun is located in such a driven ISM parcel. The Local Fluff has a
bulk velocity of 19 km/s in the LSR, and an upwind direction towards the center
of the gas and dust ring formed by the Loop I supernova remnant interaction
with the LB. When the ram pressure of the LIC is included in the total LIC
pressure, and if magnetic thermal and cosmic ray pressures are similar, the LIC
appears to be in pressure equilibrium with the local hot bubble plasma.Comment: Proceedings of Symposium on the Composition of Matter, honoring
Johannes Geiss on the occasion of his 80th birthday. Space Science Reviews
(in press
Lattice-switch Monte Carlo
We present a Monte Carlo method for the direct evaluation of the difference
between the free energies of two crystal structures. The method is built on a
lattice-switch transformation that maps a configuration of one structure onto a
candidate configuration of the other by `switching' one set of lattice vectors
for the other, while keeping the displacements with respect to the lattice
sites constant. The sampling of the displacement configurations is biased,
multicanonically, to favor paths leading to `gateway' arrangements for which
the Monte Carlo switch to the candidate configuration will be accepted. The
configurations of both structures can then be efficiently sampled in a single
process, and the difference between their free energies evaluated from their
measured probabilities. We explore and exploit the method in the context of
extensive studies of systems of hard spheres. We show that the efficiency of
the method is controlled by the extent to which the switch conserves correlated
microstructure. We also show how, microscopically, the procedure works: the
system finds gateway arrangements which fulfill the sampling bias
intelligently. We establish, with high precision, the differences between the
free energies of the two close packed structures (fcc and hcp) in both the
constant density and the constant pressure ensembles.Comment: 34 pages, 9 figures, RevTeX. To appear in Phys. Rev.
SIRT1-NOX4 Signaling Axis Regulates Cancer Cachexia
Approximately one third of cancer patients die due to complexities related to cachexia. However, the mechanisms of cachexia and the potential therapeutic interventions remain poorly studied. We observed a significant positive correlation between SIRT1 expression and muscle fiber cross-sectional area in pancreatic cancer patients. Rescuing Sirt1 expression by exogenous expression or pharmacological agents reverted cancer cell-induced myotube wasting in culture conditions and mouse models. RNA-seq and follow-up analyses showed cancer cell-mediated SIRT1 loss induced NF-κB signaling in cachectic muscles that enhanced the expression of FOXO transcription factors and NADPH oxidase 4 (Nox4), a key regulator of reactive oxygen species production. Additionally, we observed a negative correlation between NOX4 expression and skeletal muscle fiber cross-sectional area in pancreatic cancer patients. Knocking out Nox4 in skeletal muscles or pharmacological blockade of Nox4 activity abrogated tumor-induced cachexia in mice. Thus, we conclude that targeting the Sirt1-Nox4 axis in muscles is an effective therapeutic intervention for mitigating pancreatic cancer-induced cachexia
Stable isotope food-web analysis and mercury biomagnification in polar bears ( Ursus maritimus )
Mercury (Hg) biomagnification occurs in many ecosystems, resulting in a greater potential for toxicological effects in higher-level trophic feeders. However, Hg transport pathways through different food-web channels are not well known, particularly in high-latitude systems affected by the atmospheric Hg deposition associated with snow and ice. Here, we report on stable carbon and nitrogen isotope ratios, and Hg concentrations, determined for 26, late 19th and early 20th century, polar bear ( Ursus maritimus ) hair specimens, collected from catalogued museum collections. These data elucidate relationships between the high-latitude marine food-web structure and Hg concentrations in polar bears. The carbon isotope compositions of polar bear hairs suggest that polar bears derive nutrition from coupled food-web channels, based in pelagic and sympagic primary producers, whereas the nitrogen isotope compositions indicate that polar bears occupy > fourth-level trophic positions. Our results show a positive correlation between polar bear hair Hg concentrations and δ 15 N. Interpretation of the stable isotope data in combination with Hg concentrations tentatively suggests that polar bears participating in predominantly pelagic food webs exhibit higher mercury concentrations than polar bears participating in predominantly sympagic food webs.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73930/1/j.1751-8369.2009.00114.x.pd
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