2,440 research outputs found
Computing Heavy Elements
Reliable calculations of the structure of heavy elements are crucial to
address fundamental science questions such as the origin of the elements in the
universe. Applications relevant for energy production, medicine, or national
security also rely on theoretical predictions of basic properties of atomic
nuclei. Heavy elements are best described within the nuclear density functional
theory (DFT) and its various extensions. While relatively mature, DFT has never
been implemented in its full power, as it relies on a very large number (~
10^9-10^12) of expensive calculations (~ day). The advent of leadership-class
computers, as well as dedicated large-scale collaborative efforts such as the
SciDAC 2 UNEDF project, have dramatically changed the field. This article gives
an overview of the various computational challenges related to the nuclear DFT,
as well as some of the recent achievements.Comment: Proceeding of the Invited Talk given at the SciDAC 2011 conference,
Jul. 10-15, 2011, Denver, C
Electromagnetic interferences from plasmas generated in meteoroids impacts
It is shown that the plasma, generated during an impact of a meteoroid with
an artificial satellite, can produce electromagnetic radiation below the
microwave frequency range. This interference is shown to exceed local noise
sources and might disturb regular satellite operations.Comment: 6 pages, no figures. This version macthes the published versio
Effects of sinking velocities and microbial respiration rates on the attenuation of particulate carbon fluxes through the mesopelagic zone
Author Posting. © American Geophysical Union, 2015. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Global Biogeochemical Cycles 29 (2015): 175–193, doi:10.1002/2014GB004935.The attenuation of sinking particle fluxes through the mesopelagic zone is an important process that controls the sequestration of carbon and the distribution of other elements throughout the oceans. Case studies at two contrasting sites, the oligotrophic regime of the Bermuda Atlantic Time-series Study (BATS) and the mesotrophic waters of the west Antarctic Peninsula (WAP) sector of the Southern Ocean, revealed large differences in the rates of particle-attached microbial respiration and the average sinking velocities of marine particles, two parameters that affect the transfer efficiency of particulate matter from the base of the euphotic zone into the deep ocean. Rapid average sinking velocities of 270 ± 150 m d−1 were observed along the WAP, whereas the average velocity was 49 ± 25 m d−1 at the BATS site. Respiration rates of particle-attached microbes were measured using novel RESPIRE (REspiration of Sinking Particles In the subsuRface ocEan) sediment traps that first intercepts sinking particles then incubates them in situ. RESPIRE experiments yielded flux-normalized respiration rates of 0.4 ± 0.1 day−1 at BATS when excluding an outlier of 1.52 day−1, while these rates were undetectable along the WAP (0.01 ± 0.02 day−1). At BATS, flux-normalized respiration rates decreased exponentially with respect to depth below the euphotic zone with a 75% reduction between the 150 and 500 m depths. These findings provide quantitative and mechanistic insights into the processes that control the transfer efficiency of particle flux through the mesopelagic and its variability throughout the global oceans.Funding was provided by the University of Alaska Fairbanks, Woods Hole Oceanographic Institution (WHOI) Rinehart Access to the Sea Program, the WHOI Coastal Oceans Institute, WHOI Academic Programs Office, and the National Science Foundation (NSF) for support of PAL (ANT-0823101), FOODBANCS, and WAPflux (ANT- 83886600) projects. A grant from the NSF Carbon and Water Program (06028416) supported the development of these methods.2015-08-2
Nuclear energy density optimization: Shell structure
Nuclear density functional theory is the only microscopical theory that can
be applied throughout the entire nuclear landscape. Its key ingredient is the
energy density functional. In this work, we propose a new parameterization
UNEDF2 of the Skyrme energy density functional. The functional optimization is
carried out using the POUNDerS optimization algorithm within the framework of
the Skyrme Hartree-Fock-Bogoliubov theory. Compared to the previous
parameterization UNEDF1, restrictions on the tensor term of the energy density
have been lifted, yielding a very general form of the energy density functional
up to second order in derivatives of the one-body density matrix. In order to
impose constraints on all the parameters of the functional, selected data on
single-particle splittings in spherical doubly-magic nuclei have been included
into the experimental dataset. The agreement with both bulk and spectroscopic
nuclear properties achieved by the resulting UNEDF2 parameterization is
comparable with UNEDF1. While there is a small improvement on single-particle
spectra and binding energies of closed shell nuclei, the reproduction of
fission barriers and fission isomer excitation energies has degraded. As
compared to previous UNEDF parameterizations, the parameter confidence interval
for UNEDF2 is narrower. In particular, our results overlap well with those
obtained in previous systematic studies of the spin-orbit and tensor terms.
UNEDF2 can be viewed as an all-around Skyrme EDF that performs reasonably well
for both global nuclear properties and shell structure. However, after adding
new data aiming to better constrain the nuclear functional, its quality has
improved only marginally. These results suggest that the standard Skyrme energy
density has reached its limits and significant changes to the form of the
functional are needed.Comment: 18 pages, 13 figures, 12 tables; resubmitted for publication to Phys.
Rev. C after second review by refere
Nuclear energy density optimization: Large deformations
A new Skyrme-like energy density suitable for studies of strongly elongated
nuclei has been determined in the framework of the Hartree-Fock-Bogoliubov
theory using the recently developed model-based, derivative-free optimization
algorithm POUNDerS. A sensitivity analysis at the optimal solution has revealed
the importance of states at large deformations in driving the parameterization
of the functional. The good agreement with experimental data on masses and
separation energies, achieved with the previous parameterization UNEDF0, is
largely preserved. In addition, the new energy density UNEDF1 gives a much
improved description of the fission barriers in 240Pu and neighboring nuclei.Comment: 16 pages, 11 figures, accepted for publication in Phys. Rev.
Search for correlation effects in linear chains of trapped ions
We report a precise search for correlation effects in linear chains of 2 and
3 trapped Ca+ ions. Unexplained correlations in photon emission times within a
linear chain of trapped ions have been reported, which, if genuine, cast doubt
on the potential of an ion trap to realize quantum information processing. We
observe quantum jumps from the metastable 3d 2D_{5/2} level for several hours,
searching for correlations between the decay times of the different ions. We
find no evidence for correlations: the number of quantum jumps with separations
of less than 10 ms is consistent with statistics to within errors of 0.05%; the
lifetime of the metastable level derived from the data is consistent with that
derived from independent single-ion data at the level of the experimental
errors 1%; and no rank correlations between the decay times were found with
sensitivity to rank correlation coefficients at the level of |R| = 0.024.Comment: With changes to introduction. 5 pages, including 4 figures. Submitted
to Europhys. Let
A novel drug management system in the Febuxostat versus Allopurinol Streamlined Trial:A description of a pharmacy system designed to supply medications directly to patients within a prospective multicenter randomised clinical trial
Background: Trials of investigational medicinal products are required to adhere to strict guidelines with regard to the handling and supply of medication. Information technology offers opportunities to approach clinical trial methodology in new ways. This report summarises a novel pharmacy system designed to supply trial medications directly to patients by post in the Febuxostat versus Allopurinol Streamlined Trial.Method: A bespoke web-based software package was designed to facilitate the direct supply of trial medications to Febuxostat versus Allopurinol Streamlined Trial participants from a pharmacy based in the Medicines Monitoring Unit, University of Dundee.Results: To date, 65,467 packs of medication have been dispensed using the system to 3978 patients. Up to 238 packs per day have been dispensed.Conclusion: The Medicines Monitoring Unit Febuxostat versus Allopurinol Streamlined Trial drug management system is an effective method of administering the complex drug supply requirements of a large-scale clinical trial with advantages over existing arrangements. A low rate of loss to follow-up in the Febuxostat versus Allopurinol Streamlined Trial may be attributable to the drug management system.</p
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