36,444 research outputs found
Fluctuating parts of nuclear ground state correlation energies
Background: Heavy atomic nuclei are often described using the
Hartree-Fock-Bogoliubov (HFB) method. In principle, this approach takes into
account Pauli effects and pairing correlations while other correlation effects
are mimicked through the use of effective density-dependent interactions.
Purpose: Investigate the influence of higher order correlation effects on
nuclear binding energies using Skyrme's effective interaction.
Methods: A cut-off in relative momenta is introduced in order to remove
ultraviolet divergences caused by the zero-range character of the interaction.
Corrections to binding energies are then calculated using the
quasiparticle-random-phase approximation (QRPA) and second order many-body
perturbation theory (MBPT2).
Result: Contributions to the correlation energies are evaluated for several
isotopic chains and an attempt is made to disentangle which parts give rise to
fluctuations that may be difficult to incorporate on the HFB level. The
dependence of the results on the cut-off is also investigated.
Conclusions: The improved interaction allows explicit summations of
perturbation series which is useful for the description of some nuclear
observables. However, refits of the interaction parameters are needed to obtain
more quantitative results
Noncommutative Solitons: Moduli Spaces, Quantization, Finite Theta Effects and Stability
We find the N-soliton solution at infinite theta, as well as the metric on
the moduli space corresponding to spatial displacements of the solitons. We use
a perturbative expansion to incorporate the leading 1/theta corrections, and
find an effective short range attraction between solitons. We study the
stability of various solutions. We discuss the finite theta corrections to
scattering, and find metastable orbits. Upon quantization of the two-soliton
moduli space, for any finite theta, we find an s-wave bound state.Comment: Second revision: Discussions of translation zero-modes in section 4
and scales in section 5 improved; web addresses of movies changed. First
revision: Section 6 is rewritten (thanks to M. Headrick for pointing out a
mistake in the original version); some references and acknowledgements added.
21 pages, JHEP style, Hypertex, 1 figure, 3 MPEG's at:
http://www.physto.se/~unge/traj1.mpg http://www.physto.se/~unge/traj2.mpg
http://www.physto.se/~unge/traj3.mp
Within-person structures of daily cognitive performance cannot be inferred from between-person structures of cognitive abilities
First published online: 09 June 2020Over a century of research on between-person differences has resulted in the consensus that human cognitive abilities are hierarchically organized, with a general factor, termed general intelligence or "g," uppermost. Surprisingly, it is unknown whether this body of evidence is informative about how cognition is structured within individuals. Using data from 101 young adults performing nine cognitive tasks on 100 occasions distributed over six months, we find that the structures of individuals' cognitive abilities vary among each other, and deviate greatly from the modal between-person structure. Working memory contributes the largest share of common variance to both between- and within-person structures, but the g factor is much less prominent within than between persons. We conclude that between-person structures of cognitive abilities cannot serve as a surrogate for within-person structures. To reveal the development and organization of human intelligence, individuals need to be studied over time
Graphical Tensor Product Reduction Scheme for the Lie Algebras so(5) = sp(2), su(3), and g(2)
We develop in detail a graphical tensor product reduction scheme, first
described by Antoine and Speiser, for the simple rank 2 Lie algebras so(5) =
sp(2), su(3), and g(2). This leads to an efficient practical method to reduce
tensor products of irreducible representations into sums of such
representations. For this purpose, the 2-dimensional weight diagram of a given
representation is placed in a "landscape" of irreducible representations. We
provide both the landscapes and the weight diagrams for a large number of
representations for the three simple rank 2 Lie algebras. We also apply the
algebraic "girdle" method, which is much less efficient for calculations by
hand for moderately large representations. Computer code for reducing tensor
products, based on the graphical method, has been developed as well and is
available from the authors upon request.Comment: 43 pages, 18 figure
A World of Fields
Trope ontology is exposed and confronted with the question where one trope ends and another begins. It is argued that tropes do not have determinate boundaries, it is arbitrary how tropes are carved up. An ontology, which I call field ontology, is proposed which takes this into account. The material world consists of a certain number of fields, each of which is extended over all of space. It is shown how field ontology can also tackle the problem of determin-able properties and the problem of completeness of things
Calculations of Hubbard U from first-principles
The Hubbard \emph{U} of the \emph{3d} transition metal series as well as
SrVO, YTiO, Ce and Gd has been estimated using a recently proposed
scheme based on the random-phase approximation. The values obtained are
generally in good accord with the values often used in model calculations but
for some cases the estimated values are somewhat smaller than those used in the
literature. We have also calculated the frequency-dependent \emph{U} for some
of the materials. The strong frequency dependence of \emph{U} in some of the
cases considered in this paper suggests that the static value of \emph{U} may
not be the most appropriate one to use in model calculations. We have also made
comparison with the constrained LDA method and found some discrepancies in a
number of cases. We emphasize that our scheme and the constrained LDA method
theoretically ought to give similar results and the discrepancies may be
attributed to technical difficulties in performing calculations based on
currently implemented constrained LDA schemes.Comment: 24 pages, 13 figures; Submitted to Phys. Rev.
Determination of the sticking probability of hydrocarbons on an amorphous hydrocarbons surface
Risk, Resources, and Education: Public Versus Private Financing of Higher Education
The paper develops a public education scheme that takes aspects of uncertainty in private educational investments explicitly into account. The social merits of public education schemes are related to the lack of markets in which students can insure against educational risks. A case is made for tuition fees that depend on expected returns of investments in education. The consideration of uncertainty provides a neglected link between educational choice, resource endowment, and productivity growth, which may serve to redefine the public role of education financing. Copyright 2002, International Monetary Fund
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