242 research outputs found
Elimination of spurious states in the quasiparticle time blocking approximation
The quasiparticle time blocking approximation (QTBA) is considered as a model
for the description of excitations in open-shell nuclei. The QTBA is an
extension of the quasiparticle random phase approximation that includes
quasiparticle-phonon coupling. In the present version of the QTBA, the pairing
correlations are included within the framework of the BCS approximation. Thus,
in this model, the spurious states appear, which are caused by the
breaking of the symmetry related to the particle-number conservation. In this
work, the method is described which solves the problem of the spurious
states in the QTBA with the help of the projection technique. The method is
illustrated by calculations of excitations in Sn nucleus.Comment: 12 pages, 3 figures - To appear in the proceedings of the 59-th
International Meeting on Nuclear Spectroscopy and Nuclear Structure, June
15-19, 2009, Cheboksary, Russi
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
Indoor radon levels in relation to geology in southern Belgium
A statistical study of an indoor radon data set of about 1700 short-term measurements shows a striking relationship between indoor radon concentration and the geological factors, such as stratigraphic unit and rock type
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
Scalar ground-state observables in the random phase approximation
We calculate the ground-state expectation value of scalar observables in the
matrix formulation of the random phase approximation (RPA). Our expression,
derived using the quasiboson approximation, is a straightforward generalization
of the RPA correlation energy. We test the reliability of our expression by
comparing against full diagonalization in 0 h-bar omega shell-model spaces. In
general the RPA values are an improvement over mean-field (Hartree-Fock)
results, but are not always consistent with shell-model results. We also
consider exact symmetries broken in the mean-field state and whether or not
they are restored in RPA.Comment: 7 pages, 3 figure
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
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
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