653 research outputs found
Similarity Renormalization Group for Nucleon-Nucleon Interactions
The similarity renormalization group (SRG) is based on unitary
transformations that suppress off-diagonal matrix elements, forcing the
hamiltonian towards a band-diagonal form. A simple SRG transformation applied
to nucleon-nucleon interactions leads to greatly improved convergence
properties while preserving observables, and provides a method to consistently
evolve many-body potentials and other operators.Comment: 5 pages, 6 figures (8 figure files); references updated and
acknowledgment adde
Low momentum nucleon-nucleon potential and shell model effective interactions
A low momentum nucleon-nucleon (NN) potential V-low-k is derived from meson
exhange potentials by integrating out the model dependent high momentum modes
of V_NN. The smooth and approximately unique V-low-k is used as input for shell
model calculations instead of the usual Brueckner G matrix. Such an approach
eliminates the nuclear mass dependence of the input interaction one finds in
the G matrix approach, allowing the same input interaction to be used in
different nuclear regions. Shell model calculations of 18O, 134Te and 135I
using the same input V-low-k have been performed. For cut-off momentum Lambda
in the vicinity of 2 fm-1, our calculated low-lying spectra for these nuclei
are in good agreement with experiments, and are weakly dependent on Lambda.Comment: 5 pages, 5 figure
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Forecast convergence score: a forecaster's approach to analysing hydro-meteorological forecast systems.
In this paper the properties of a hydro-meteorological forecasting system for forecasting river flows have been analysed using a probabilistic forecast convergence score (FCS). The focus on fixed event forecasts provides a forecaster's approach to system behaviour and adds an important perspective to the suite of forecast verification tools commonly used in this field. A low FCS indicates a more consistent forecast. It can be demonstrated that the FCS annual maximum decreases over the last 10 years. With lead time, the FCS of the ensemble forecast decreases whereas the control and high resolution forecast increase. The FCS is influenced by the lead time, threshold and catchment size and location. It indicates that one should use seasonality based decision rules to issue flood warnings
Block Diagonalization using SRG Flow Equations
By choosing appropriate generators for the Similarity Renormalization Group
(SRG) flow equations, different patterns of decoupling in a Hamiltonian can be
achieved. Sharp and smooth block-diagonal forms of phase-shift equivalent
nucleon-nucleon potentials in momentum space are generated as examples and
compared to analogous low-momentum interactions ("v_lowk").Comment: 4 pages, 9 figures (pdfLaTeX
Microscopically-based energy density functionals for nuclei using the density matrix expansion: Implementation and pre-optimization
In a recent series of papers, Gebremariam, Bogner, and Duguet derived a
microscopically based nuclear energy density functional by applying the Density
Matrix Expansion (DME) to the Hartree-Fock energy obtained from chiral
effective field theory (EFT) two- and three-nucleon interactions. Due to the
structure of the chiral interactions, each coupling in the DME functional is
given as the sum of a coupling constant arising from zero-range contact
interactions and a coupling function of the density arising from the
finite-range pion exchanges. Since the contact contributions have essentially
the same structure as those entering empirical Skyrme functionals, a
microscopically guided Skyrme phenomenology has been suggested in which the
contact terms in the DME functional are released for optimization to
finite-density observables to capture short-range correlation energy
contributions from beyond Hartree-Fock. The present paper is the first attempt
to assess the ability of the newly suggested DME functional, which has a much
richer set of density dependencies than traditional Skyrme functionals, to
generate sensible and stable results for nuclear applications. The results of
the first proof-of-principle calculations are given, and numerous practical
issues related to the implementation of the new functional in existing Skyrme
codes are discussed. Using a restricted singular value decomposition (SVD)
optimization procedure, it is found that the new DME functional gives
numerically stable results and exhibits a small but systematic reduction of our
test function compared to standard Skyrme functionals, thus justifying
its suitability for future global optimizations and large-scale calculations.Comment: 17 pages, 6 figure
Two-pion-exchange contributions to the pp\to pp\pi^0 reaction
Our previous study of the near-threshold pp\to pp\pi^0 reaction based on a
hybrid nuclear effective field theory is further elaborated by examining the
momentum dependence of the relevant transition operators. We show that the
two-pion exchange diagrams give much larger contributions than the one-pion
exchange diagram, even though the former is of higher order in the Weinberg
counting scheme. The relation between our results and an alternative counting
scheme, the momentum counting scheme, is also discussed.Comment: 11 pages, minor change, a few references are adde
AUSSAT battery life test program
AUSSAT Pty. Ltd., the Australian National Satellite organization, has contracted with the Hughes Aircraft Company (HAC) for the construction of 3 satellites based on the now familiar HS-376 product line. As part of the AUSSAT contract, HAC is conducting an extensive NiCd battery life test program. The life test program, objectives and test results to date are described. Particular emphasis is given to the evaluation of the FS2117 separator as a future replacement for the Pellon 2505 separator of which only a very limited quantity remains
Involvement of endothelins, peptides with potent vasoactive properties, in HIV-1 encephalopathy
International Educatorsâ Perspectives on the Purpose of Science Education and the Relationship between School Science and Creativity
This is the author accepted manuscript. The final version is available from Taylor & Francis (Routledge) via the DOI in this record.Background: Creativity across all disciplines is increasingly viewed as a fundamental
educational capability. Science can play a potentially important role in the nurturing of
creativity. Research also suggests that creative pedagogy, including interdisciplinary
teaching with Science and the Arts, can engage students with science. Previous studies
into teachersâ attitudes to the relationship between science and creativity have been
largely situated within national educational contexts.
Purpose: This study, part of the large EU funded CREATIONs project, explores
educatorsâ perspectives on the relationship between Science and Creativity across
national contexts drawn from Europe and beyond.
Sample and Methods: 270 educators, broadly defined to include primary (age 4-11) and
secondary (age 11-18) teachers and trainee teachers, informal educators and teacher
educators, responded to a survey designed to explore perceptions of the relationship
between science and creativity. Respondents were a convenience sample recruited by
project partners and through online media. The elements of the survey reported here
included Likert-scale questions, open response questions, and ranking questions in the
form of an electronic self-administered questionnaire. Exploratory factor analysis was
used to develop a combined attitude scale labelled âscience is creativeâ, with results
compared across nationalities and phases of education. Open question responses were
analysed thematically to allow more nuanced interpretation of the descriptive statistical
findings.
Results: The findings show broad agreement internationally and across phases that
science is a creative endeavour, with a small number of educators disagreeing about the
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relationship between science and creativity in the context of school science. Those who
disagreed were usually secondary science teachers, from England, Malta or outside
Europe (primarily from the United States). The role of scientific knowledge within
creativity in science education was found to be contentious.
Conclusions: That educators broadly see science as creative is unsurprising, but initial
exploration of educatorsâ perspectives internationally shows some areas of difference.
These were especially apparent for educators working in formal education, particularly
relating to the role of knowledge with respect to creativity in science. With current
interest in STEAM education, further investigation to understand potential mediating
factors of national educational contexts on teachersâ perspectives with respect to the
role of disciplinary knowledge(s) in creativity and their interaction in interdisciplinary
teaching and learning, is recommended.European Commissio
Chiral three-nucleon forces and bound excited states in neutron-rich oxygen isotopes
We study the spectra of neutron-rich oxygen isotopes based on chiral two- and
three-nucleon interactions. First, we benchmark our many-body approach by
comparing ground-state energies to coupled-cluster results for the same
two-nucleon interaction, with overall good agreement. We then calculate bound
excited states in 21,22,23O, focusing on the role of three-nucleon forces, in
the standard sd shell and an extended sdf7/2p3/2 valence space. Chiral
three-nucleon forces provide important one- and two-body contributions between
valence neutrons. We find that both these contributions and an extended valence
space are necessary to reproduce key signatures of novel shell evolution, such
as the N = 14 magic number and the low-lying states in 21O and 23O, which are
too compressed with two-nucleon interactions only. For the extended space
calculations, this presents first work based on nuclear forces without
adjustments. Future work is needed and open questions are discussed.Comment: 6 pages, 4 figures, published versio
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