1,080 research outputs found
Density Matrix Expansion for Low-Momentum Interactions
A first step toward a universal nuclear energy density functional based on
low-momentum interactions is taken using the density matrix expansion (DME) of
Negele and Vautherin. The DME is adapted for non-local momentum-space
potentials and generalized to include local three-body interactions. Different
prescriptions for the three-body DME are compared. Exploratory results are
given at the Hartree-Fock level, along with a roadmap for systematic
improvements within an effective action framework for Kohn-Sham density
functional theory.Comment: 50 pages, 10 figure
Do Historical Cost Financial Statements Comply with the Objectives of SFAC 1?
The Financial Accounting Standards Board has issued Statements of Financial Accounting Concepts to provide the objectives which financial reporting should comply with. As the economic environment and markets have changed, there has been some controversy over whether historical cost information complies with these objectives. This paper reviews the objectives and comes to the conclusion that historical cost is satisfactory for the present, but a change will probably be needed in the future. Several alternatives are discussed and a gradual change to a valuation basis is recommended. User and preparer opinions are discussed and the recommendations take into account their opposition to change. The main conclusion of the paper is that SFAC 1 basically says that financial reporting should provide users with the information they need and want. Historical cost information seems to be satisfactory now, but a move to supplemental information is also considered positive. Any change occurring in financial reporting will have to be implemented slowly and build on what users already understand.B.S. (Bachelor of Science
Isovector part of nuclear energy density functional from chiral two- and three-nucleon forces
A recent calculation of the nuclear energy density functional from chiral
two- and three-nucleon forces is extended to the isovector terms pertaining to
different proton and neutron densities. An improved density-matrix expansion is
adapted to the situation of small isospin-asymmetries and used to calculate in
the Hartree-Fock approximation the density-dependent strength functions
associated with the isovector terms. The two-body interaction comprises of
long-range multi-pion exchange contributions and a set of contact terms
contributing up to fourth power in momenta. In addition, the leading order
chiral three-nucleon interaction is employed with its parameters fixed in
computations of nuclear few-body systems. With this input one finds for the
asymmetry energy of nuclear matter the value MeV,
compatible with existing semi-empirical determinations. The strength functions
of the isovector surface and spin-orbit coupling terms come out much smaller
than those of the analogous isoscalar coupling terms and in the relevant
density range one finds agreement with phenomenological Skyrme forces. The
specific isospin- and density-dependences arising from the chiral two- and
three-nucleon interactions can be explored and tested in neutron-rich systems.Comment: 14 pages, 7 figures, to be published in European Physical Journal
Between Science Education and Environmental Education : How Science Motivation Relates to Environmental Values
Science education and environmental education are important gates to prepare the next generation for our society’s current and upcoming challenges. While in the informal sector, environmental education acts independently, on the formal side, science education hosts environmental issues within its interdisciplinary context. As both educational efforts traditionally bear different emphases, the question may arise of whether formal science classes can act as an appropriate host. Against the background of the declining motivation to learn science in secondary school, possible synergies between both educational efforts may have vanished. For an investigation of such linkages between science motivation and environmental perception, we monitored adolescents’ motivation to learn sciences and their environmental values. By analyzing data from 429 Irish secondary school students, we reconfirmed existing scales by using confirmatory factor analysis (CFA) and investigated potential relations via SEM. Besides gender differences, we identified a significant relationship between positive ‘green’ attitude sets and the individual motivation to learn science—positive environmental preferences predict a high science motivation, primarily intrinsic motivation. Taking advantage of this relationship, individual motivation may find support from environmental educational initiatives with the focus on green values. Especially girls, who evidentially tend to have a lower motivation in science learning, may be addressed in that way
Fully microscopic shell-model calculations with realistic effective hamiltonians
The advent of nucleon-nucleon potentials derived from chiral perturbation
theory, as well as the so-called V-low-k approach to the renormalization of the
strong short-range repulsion contained in the potentials, have brought renewed
interest in realistic shell-model calculations. Here we focus on calculations
where a fully microscopic approach is adopted. No phenomenological input is
needed in these calculations, because single-particle energies, matrix elements
of the two-body interaction, and matrix elements of the electromagnetic
multipole operators are derived theoretically. This has been done within the
framework of the time-dependent degenerate linked-diagram perturbation theory.
We present results for some nuclei in different mass regions. These evidence
the ability of realistic effective hamiltonians to provide an accurate
description of nuclear structure properties.Comment: 6 pages, 9 figures, talk presented at INPC2010, Vancouver, July 4 -9
2010. Accepted for publication in Journal of Physics: Conference Serie
Nuclear energy density functional from chiral two- and three-nucleon interactions
An improved density-matrix expansion is used to calculate the nuclear energy
density functional from chiral two- and three-nucleon interactions. The
two-body interaction comprises long-range one- and two-pion exchange
contributions and a set of contact terms contributing up to fourth power in
momenta. In addition we employ the leading order chiral three-nucleon
interaction with its parameters and fixed in
calculations of nuclear few-body systems. With this input the nuclear energy
density functional is derived to first order in the two- and three-nucleon
interaction. We find that the strength functions and
of the surface and spin-orbit terms compare in the relevant
density range reasonably with results of phenomenological Skyrme forces.
However, an improved description requires (at least) the treatment of the
two-body interaction to second order. This observation is in line with the
deficiencies in the nuclear matter equation of state that remain
in the Hartree-Fock approximation with low-momentum two- and three-nucleon
interactions.Comment: 16 pages, 12 figures, submitted to Eur. Phys. J.
High-momentum tails from low-momentum effective theories
In a recent work \cite{Anderson:2010aq}, Anderson \emph{et al.} used the
renormalization group (RG) evolution of the momentum distribution to show that,
under appropriate conditions, operator expectation values exhibit factorization
in the two-nucleon system. Factorization is useful because it provides a clean
separation of long- and short-distance physics, and suggests a possible
interpretation of the universal high-momentum dependence and scaling behavior
found in nuclear momentum distributions. In the present work, we use simple
decoupling and scale-separation arguments to extend the results of Ref.
\cite{Anderson:2010aq} to arbitrary low-energy -body states. Using methods
that are reminiscent of the operator product expansion (OPE) in quantum field
theory, we find that the high-momentum tails of momentum distributions and
static structure factors factorize into the product of a universal function of
momentum that is fixed by two-body physics, and a state-dependent matrix
element that is the same for both and is sensitive only to low-momentum
structure of the many-body state. As a check, we apply our factorization
relations to two well-studied systems, the unitary Fermi gas and the electron
gas, and reproduce known expressions for the high-momentum tails of each.Comment: 22 pages, 0 figure
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