A scheme for comparison of different strains of Friesians

International audienc

The use of non-additive components in selection policy

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Evidence for a possible influence of the fetus in the milk yield of the dam

International audienc

Der effect des foetus auf die milchleistung der betreffenden laktation

International audienc

Density Matrix Functional Calculations for Matter in Strong Magnetic Fields: I. Atomic Properties

We report on a numerical study of the density matrix functional introduced by Lieb, Solovej and Yngvason for the investigation of heavy atoms in high magnetic fields. This functional describes {\em exactly} the quantum mechanical ground state of atoms and ions in the limit when the nuclear charge $Z$ and the electron number $N$ tend to infinity with $N/Z$ fixed, and the magnetic field $B$ tends to infinity in such a way that $B/Z^{4/3}\to\infty$. We have calculated electronic density profiles and ground state energies for values of the parameters that prevail on neutron star surfaces and compared them with results obtained by other methods. For iron at $B=10^{12}$ G the ground state energy differs by less than 2 \% from the Hartree-Fock value. We have also studied the maximal negative ionization of heavy atoms in this model at various field strengths. In contrast to Thomas-Fermi type theories atoms can bind excess negative charge in the density matrix model. For iron at $B=10^{12}$ G the maximal excess charge in this model corresponds to about one electron.Comment: Revtex, 13 pages with 6 eps figures include

Matter in Strong Magnetic Fields

The properties of matter are significantly modified by strong magnetic fields, $B>>2.35\times 10^9$ Gauss ($1 G =10^{-4} Tesla$), as are typically found on the surfaces of neutron stars. In such strong magnetic fields, the Coulomb force on an electron acts as a small perturbation compared to the magnetic force. The strong field condition can also be mimicked in laboratory semiconductors. Because of the strong magnetic confinement of electrons perpendicular to the field, atoms attain a much greater binding energy compared to the zero-field case, and various other bound states become possible, including molecular chains and three-dimensional condensed matter. This article reviews the electronic structure of atoms, molecules and bulk matter, as well as the thermodynamic properties of dense plasma, in strong magnetic fields, $10^9G << B < 10^{16}G$. The focus is on the basic physical pictures and approximate scaling relations, although various theoretical approaches and numerical results are also discussed. For the neutron star surface composed of light elements such as hydrogen or helium, the outermost layer constitutes a nondegenerate, partially ionized Coulomb plasma if $B<<10^{14}G$, and may be in the form of a condensed liquid if the magnetic field is stronger (and temperature $<10^6$ K). For the iron surface, the outermost layer of the neutron star can be in a gaseous or a condensed phase depending on the cohesive property of the iron condensate.Comment: 45 pages with 9 figures. Many small additions/changes. Accepted for publication in Rev. Mod. Phy