1,870 research outputs found
Direct reaction measurements with a 132Sn radioactive ion beam
The (d,p) neutron transfer and (d,d) elastic scattering reactions were
measured in inverse kinematics using a radioactive ion beam of 132Sn at 630
MeV. The elastic scattering data were taken in a region where Rutherford
scattering dominated the reaction, and nuclear effects account for less than 8%
of the cross section. The magnitude of the nuclear effects was found to be
independent of the optical potential used, allowing the transfer data to be
normalized in a reliable manner. The neutron-transfer reaction populated a
previously unmeasured state at 1363 keV, which is most likely the
single-particle 3p1/2 state expected above the N=82 shell closure. The data
were analyzed using finite range adiabatic wave calculations and the results
compared with the previous analysis using the distorted wave Born
approximation. Angular distributions for the ground and first excited states
are consistent with the previous tentative spin and parity assignments.
Spectroscopic factors extracted from the differential cross sections are
similar to those found for the one neutron states beyond the benchmark
doubly-magic nucleus 208Pb.Comment: 22 pages, 7 figure
Epitaxial growth of Cu on Cu(001): experiments and simulations
A quantitative comparison between experimental and Monte Carlo simulation
results for the epitaxial growth of Cu/Cu(001) in the submonolayer regime is
presented. The simulations take into account a complete set of hopping
processes whose activation energies are derived from semi-empirical
calculations using the embedded-atom method. The island separation is measured
as a function of the incoming flux and the temperature. A good quantitative
agreement between the experiment and simulation is found for the island
separation, the activation energies for the dominant processes, and the
exponents that characterize the growth. The simulation results are then
analyzed at lower coverages, which are not accessible experimentally, providing
good agreement with theoretical predictions as well.Comment: Latex document. 7 pages. 3 embedded figures in separate PS files. One
bbl fil
Self-Regulation in a Web-Based Course: A Case Study
Little is known about how successful students in Web-based courses self-regulate their learning. This descriptive case study used a social cognitive model of self-regulated learning (SRL) to investigate how six graduate students used and adapted traditional SRL strategies to complete tasks and cope with challenges in a Web-based technology course; it also explored motivational and environmental influences on strategy use. Primary data sources were three transcribed interviews with each of the students over the course of the semester, a transcribed interview with the course instructor, and the students’ reflective journals. Archived course documents, including transcripts of threaded discussions and student Web pages, were secondary data sources. Content analysis of the data indicated that these students used many traditional SRL strategies, but they also adapted planning, organization, environmental structuring, help seeking, monitoring, record keeping, and self-reflection strategies in ways that were unique to the Web-based learning environment. The data also suggested that important motivational influences on SRL strategy use—self-efficacy, goal orientation, interest, and attributions—were shaped largely by student successes in managing the technical and social environment of the course. Important environmental influences on SRL strategy use included instructor support, peer support, and course design. Implications for online course instructors and designers, and suggestions for future research are offered
Search for the Production of Element 112 in the 48Ca + 238U Reaction
We have searched for the production of element 112 in the reaction of 231 MeV
48Ca with 238U. We have not observed any events with a "one event" upper limit
cross section of 1.6 pb for EVR-fission events and 1.8 pb for EVR-alpha events.Comment: 6 pages, 3 figures, submitted to Phys. Rev.
Prompt Optical Detection of GRB 050401 with ROTSE-IIIa
The ROTSE-IIIa telescope at Siding Spring Observatory, Australia, detected
prompt optical emission from Swift GRB 050401. In this letter, we present
observations of the early optical afterglow, first detected by the ROTSE-IIIa
telescope 33 s after the start of gamma-ray emission, contemporaneous with the
brightest peak of this emission. This GRB was neither exceptionally long nor
bright. This is the first prompt optical detection of a GRB of typical duration
and luminosity. We find that the early afterglow decay does not deviate
significantly from the power-law decay observable at later times, and is
uncorrelated with the prompt gamma-ray emission. We compare this detection with
the other two GRBs with prompt observations, GRB 990123 and GRB 041219a. All
three bursts exhibit quite different behavior at early times.Comment: 4 pages, 3 figures. Accepted for publication in ApJ Letter
Whole-genome sequencing of Theileria parva strains provides insight into parasite migration and diversification in the african continent
The disease caused by the apicomplexan protozoan parasite Theileria parva, known as East Coast fever or Corridor disease, is one of the most serious cattle diseases in Eastern, Central, and Southern Africa. We performed whole-genome sequencing of nine T. parva strains, including one of the vaccine strains (Kiambu 5), field isolates from Zambia, Uganda, Tanzania, or Rwanda, and two buffalo-derived strains. Comparison with the reference Muguga genome sequence revealed 34 814–121 545 single nucleotide polymorphisms (SNPs) that were more abundant in buffalo-derived strains. High-resolution phylogenetic trees were constructed with selected informative SNPs that allowed the investigation of possible complex recombination events among ancestors of the extant strains. We further analysed the dN/dS ratio (non-synonymous substitutions per non-synonymous site divided by synonymous substitutions per synonymous site) for 4011 coding genes to estimate potential selective pressure. Genes under possible positive selection were identified that may, in turn, assist in the identification of immunogenic proteins or vaccine candidates. This study elucidated the phylogeny of T. parva strains based on genome-wide SNPs analysis with prediction of possible past recombination events, providing insight into the migration, diversification, and evolution of this parasite species in the African continent
The magic nature of 132Sn explored through the single-particle states of 133Sn
Atomic nuclei have a shell structure where nuclei with 'magic numbers' of
neutrons and protons are analogous to the noble gases in atomic physics. Only
ten nuclei with the standard magic numbers of both neutrons and protons have so
far been observed. The nuclear shell model is founded on the precept that
neutrons and protons can move as independent particles in orbitals with
discrete quantum numbers, subject to a mean field generated by all the other
nucleons. Knowledge of the properties of single-particle states outside nuclear
shell closures in exotic nuclei is important for a fundamental understanding of
nuclear structure and nucleosynthesis (for example the r-process, which is
responsible for the production of about half of the heavy elements). However,
as a result of their short lifetimes, there is a paucity of knowledge about the
nature of single-particle states outside exotic doubly magic nuclei. Here we
measure the single-particle character of the levels in 133Sn that lie outside
the double shell closure present at the short-lived nucleus 132Sn. We use an
inverse kinematics technique that involves the transfer of a single nucleon to
the nucleus. The purity of the measured single-particle states clearly
illustrates the magic nature of 132Sn.Comment: 19 pages, 5 figures and 4 table
Wool and meat genetics - the joint possibilities
Wool and meat contribute to profit in sheep enterprises and both need to be considered in breeding programs. The relative responses expected from selection for a range of traits are presented and the realised responses that have been achieved in Merinos and variation in maternal breeds are illustrated. Knowledge of genetic parameters is required for the development of complex breeding objectives and selection indexes, comprehensive genetic evaluation of animals and the design of effective breeding programs. A review of world literature has highlighted the lack of accurate estimates of genetic parameters, especially for genetic correlations between trait groups. Analyses of a combined dataset from seven Australian Merino resource flocks comprising over 2000 sires and up to 100,000 records for each of various traits have provided accurate estimates of parameters to fill these gaps in current knowledge. The results show that there are no major genetic antagonisms between wool and meat traits and that improvement of both can be achieved by using appropriate selection indexes. Sheep Genetics Australia now provides a common system for genetic evaluation of Australian sheep, including across-flock estimated breeding values for a comprehensive range of traits and several standard indexes for various wool and meat breeding objectives
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