Search results for "determinant"
showing 10 items of 377 documents
Determinants of European parents' decision on the vaccination of their children against measles, mumps and rubella: A systematic review and meta-anal…
2016
ABSTRACT Low measles, mumps and rubella (MMR) immunization levels in European children highlight the importance of identifying determinants of parental vaccine uptake to implement policies for increasing vaccine compliance. The aim of this paper is to identify the main factors associated with partial and full MMR vaccination uptake in European parents, and combine the different studies to obtain overall quantitative measures. This activity is included within the ESCULAPIO project, funded by the Italian Ministry of Health. ORs and CIs were extracted, sources of heterogeneity explored and publication bias assessed. Forty-five papers were retrieved for the qualitative study, 26 of which were i…
Concentrations of Organochlorine Substances in Relation to Fish Size and Trophic Position: A Study on Perch (Perca fluviatilis L.)
2000
The aim of this study was to evaluate the importance of trophic position as a determinant of the concentrations of organochlorine substances (OCS) in fish. Perch (Perca fluvatilis) was selected since the species increases in trophic level over the course of its lifetime. The trophic position was characterized by stable isotope analysis of nitrogen and gut content. Perch (130 individuals) of different lengths and of both sexes were analyzed for polychlorinated biphenyls and chlorinated pesticides. There were no pronounced differences in the OCS concentrations between the perch sexes. Perch up to a length of 20 cm did not show any increase in OCS concentrations with increased length, despite …
Occupation Number Representation
2007
The first two chapters of this book presented angular momentum algebra as the basic tool of nuclear theory. That includes angular momentum coupling coefficients, spherical tensor operators and reduced matrix elements. In the preceding chapter we introduced the mean-field concept, along with associated many-nucleon wave functions, Slater determinants, describing configurations of non-interacting particles in mean-field single-particle orbitals.
Discriminating antiferromagnetic signatures in systems of ultracold fermions by tunable geometric frustration
2013
Recently, it has become possible to tune optical lattices continuously between square and triangular geometries. We compute thermodynamics and spin correlations in the corresponding Hubbard model using a determinant quantum Monte Carlo technique and show that the frustration effects induced by the variable hopping terms can be clearly separated from concomitant bandwidth changes by a proper rescaling of the interaction. An enhancement of the double occupancy by geometric frustration signals the destruction of nontrivial antiferromagnetic correlations at weak coupling and entropy $s\ensuremath{\lesssim}\mathrm{ln}(2)$ (and restores Pomeranchuk cooling at strong frustration), paving the way t…
Ferromagnetism of the Hubbard Model at Strong Coupling in the Hartree-Fock Approximation
2005
As a contribution to the study of Hartree-Fock theory we prove rigorously that the Hartree-Fock approximation to the ground state of the d-dimensional Hubbard model leads to saturated ferromagnetism when the particle density (more precisely, the chemical potential mu) is small and the coupling constant U is large, but finite. This ferromagnetism contradicts the known fact that there is no magnetization at low density, for any U, and thus shows that HF theory is wrong in this case. As in the usual Hartree-Fock theory we restrict attention to Slater determinants that are eigenvectors of the z-component of the total spin, {S}_z = sum_x n_{x,\uparrow} - n_{x,\downarrow}, and we find that the ch…
Relativistic positioning: errors due to uncertainties in the satellite world lines
2014
Global navigation satellite systems use appropriate satellite constellations to get the coordinates of an user -close to Earth- in an almost inertial reference system. We have simulated both GPS and GALILEO constellations. Uncertainties in the satellite world lines lead to dominant positioning errors. In this paper, a detailed analysis of these errors is developed inside a great region surrounding Earth. This analysis is performed in the framework of the so-called relativistic positioning systems. Our study is based on the Jacobian, J, of the transformation giving the emission coordinates in terms of the inertial ones. Around points of vanishing J, positioning errors are too large. We show …
Angular momentum projection of cranked Hartree-Fock states: Application to terminating bands inA~44nuclei
2007
We present the first systematic calculations based on the angular-momentum projection of cranked Slater determinants. We propose the Iy --> I scheme, by which one projects the angular momentum I from the 1D cranked state constrained to the average spin projection of =I. Calculations performed for the rotational band in 46Ti show that the AMP Iy --> I scheme offers a natural mechanism for correcting the cranking moment of inertia at low-spins and shifting the terminating state up by ~2 MeV, in accordance with data. We also apply this scheme to high-spin states near the band termination in A~44 nuclei, and compare results thereof with experimental data, shell-model calculations, and res…
Collective subspaces for large amplitude motion and the generator coordinate method
1979
The collection path $|\ensuremath{\varphi}(q)〉$ to be used in a microscopic description of large amplitude collective motion is determined by means of the generator coordinate method. By varying the total energy with respect to $|\ensuremath{\varphi}(q)〉$ and performing an adiabatic expansion a hierarchy of equations is obtained which determines uniquely a hierarchy of collective paths with increasing complexity. To zeroth order the $|\ensuremath{\varphi}(q)〉$ are Slater determinants, to first order they include 2p-2h correlations. In both cases simple noninterative prescriptions for an explicit construction of the path are derived. For a correlated path their solutions agree at the Hartree…
Isospin-breaking corrections to superallowed Fermi beta-decay in isospin- and angular momentum-projected nuclear Density Functional Theory
2012
Background: The superallowed beta-decay rates provide stringent constraints on physics beyond the Standard Model of particle physics. To extract crucial information about the electroweak force, small isospin-breaking corrections to the Fermi matrix element of superallowed transitions must be applied. Purpose: We perform systematic calculations of isospin-breaking corrections to superallowed beta-decays and estimate theoretical uncertainties related to the basis truncation, time-odd polarization effects related to the intrinsic symmetry of the underlying Slater determinants, and to the functional parametrization. Methods: We use the self-consistent isospin- and angular-momentum-projected nuc…
A time dependent RPA-theory for heavy ion reactions
1980
The time dependent Hartree Fock theory (TDHF) is generalized by incorporating 2p-2h correlations into the TDHF Slater determinant in order to improve the description of two-body observables. To this end a time dependent RPA theory (TDRPA) is formulated using the quasi boson approximation. The approach turns out to be readily applicable requiring only minor changes in the present time TDHF codes. The theory is exemplified by considering the spreading width of the fragment particle number in a nucleus-nucleus collision. The TDRPA states are furthermore used to formulate a scattering theory for heavy ion collisions which incorporates the quantum corrections of orderh2 by means of a gaussian pa…