340 research outputs found
On invariants of almost symplectic connections
We study the irreducible decomposition under Sp(2n, R) of the space of
torsion tensors of almost symplectic connections. Then a description of all
symplectic quadratic invariants of torsion-like tensors is given. When applied
to a manifold M with an almost symplectic structure, these instruments give
preliminary insight for finding a preferred linear almost symplectic connection
on M . We rediscover Ph. Tondeur's Theorem on almost symplectic connections.
Properties of torsion of the vectorial kind are deduced
Shell corrections for finite depth potentials with bound states only
A new method of calculating unique values of ground-state shell corrections
for finite depth potentials is shown, which makes use of bound states only. It
is based on (i) a general formulation of extracting the smooth part from any
fluctuating quantity proposed by Strutinsky and Ivanjuk, (ii) a generalized
Strutinsky smoothing condition suggested recently by Vertse et al., and (iii)
the technique of the Lanczos factors. Numerical results for some
spherical heavy nuclei (Sn, Pb and 114) are
presented and compared to those obtained with the Green's function oscillator
expansion method.Comment: 5 pages, 2 tables and 3 figures. Accepted in Physics Letters
Comments on the nuclear symmetry energy
According to standard textbooks, the nuclear symmetry energy originates from
the {\it kinetic} energy and the {\it interaction} itself.
We argue that this view requires certain modifications.
We ascribe the physical origin of the {\it kinetic} term to the discreteness
of fermionic levels of, in principle arbitrary binary fermionic systems, and
relate its mean value directly to the average level density. Physically it
connects this part also to the isoscalar part of the interaction which, at
least in self-bound systems like atomic nuclei, decides upon the spatial
dimensions of the system. For the general case of binary fermionic systems
possible external confining potentials as well as specific boundary conditions
will contribute to this part. The reliability of this concept is tested using
self-consistent Skyrme Hartree-Fock calculations.Comment: 11 pages, 4 figure
Combinatorial nuclear level density by a Monte Carlo method
We present a new combinatorial method for the calculation of the nuclear
level density. It is based on a Monte Carlo technique, in order to avoid a
direct counting procedure which is generally impracticable for high-A nuclei.
The Monte Carlo simulation, making use of the Metropolis sampling scheme,
allows a computationally fast estimate of the level density for many fermion
systems in large shell model spaces. We emphasize the advantages of this Monte
Carlo approach, particularly concerning the prediction of the spin and parity
distributions of the excited states, and compare our results with those derived
from a traditional combinatorial or a statistical method. Such a Monte Carlo
technique seems very promising to determine accurate level densities in a large
energy range for nuclear reaction calculations.Comment: 30 pages, LaTex, 7 figures (6 Postscript figures included). Fig. 6
upon request to the autho
Saturation properties and incompressibility of nuclear matter: A consistent determination from nuclear masses
Starting with a two-body effective nucleon-nucleon interaction, it is shown
that the infinite nuclear matter model of atomic nuclei is more appropriate
than the conventional Bethe-Weizsacker like mass formulae to extract saturation
properties of nuclear matter from nuclear masses. In particular, the saturation
density thus obtained agrees with that of electron scattering data and the
Hartree-Fock calculations. For the first time using nuclear mass formula, the
radius constant =1.138 fm and binding energy per nucleon = -16.11
MeV, corresponding to the infinite nuclear matter, are consistently obtained
from the same source. An important offshoot of this study is the determination
of nuclear matter incompressibility to be 288 28 MeV using
the same source of nuclear masses as input.Comment: 14 latex pages, five figures available on request ( to appear in Phy.
Rev. C
RPA vs. exact shell-model correlation energies
The random phase approximation (RPA) builds in correlations left out by
mean-field theory. In full 0-hbar-omega shell-model spaces we calculate the
Hartree-Fock + RPA binding energy, and compare it to exact diagonalization. We
find that in general HF+RPA gives a very good approximation to the ``exact''
ground state energy. In those cases where RPA is less satisfactory, however,
there is no obvious correlation with properties of the HF state, such as
deformation or overlap with the exact ground state wavefunction.Comment: 6 pages, 7 figures, submitted to Phys Rev
Conceptualising a Dynamic Technology Practice in Education Using Argyris and Schön's Theory of Action
Despite substantial national effort to integrate technology in education, it seems that practitioners in the education system are not working in line with the given policy. Evidence from large-scale studies of studentsâ technology practices at school over the last decade show disparities in student practices. The observed gap between the micro and the macro level call for a closer exploration. Research that explores the influence of social and organizational factors may be useful for understanding the processes behind such gaps. Argyris and Schönâs âTheory of Actionâ (1978) is proposed as an example of an organizational theory that can be adopted in educational technology research to move towards understanding the complexities of technology practice. To encourage discourse and application of Argyris and Schönâs theory in the field of educational technology research, this paper introduces the theory, a review of its empirical application in research of teacher educationsâ technology practice and relevant conceptual work. The paper presents a conceptual framework based on Argyris and Schönâs theory that has been developed through two recent studies, and invites its application in future research and development
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