Helmet and active streamers from radio observations

Large coronal regions disconnected from any calcium plages and identified by their thermal emission at 169 mHz play a basic role in the sector structure of the interplanetary medium. It was concluded that these coronal regions are to be interpreted as streamers

Magnetic Moment Formation in Quantum Point Contacts

We study the formation of local magnetic moments in quantum point contacts. Using a Hubbard-like model to describe point contacts formed in a two dimensional system, we calculate the magnetic moment using the unrestricted Hartree approximation. We analyze different type of potentials to define the point contact, for a simple square potential we calculate a phase diagram in the parameter space (Coulomb repulsion - gate voltage). We also present an analytical calculation of the susceptibility to give explicit conditions for the occurrence of a local moment, we present a simple scaling argument to analyze how the stability of the magnetic moment depends on the point contact dimensions.Comment: 7 pages, 2 figure

Vies moyennes de quelques niveaux du noyau 19F

Les énergies d'excitations et les vies moyennes de 9 niveaux du 19 F d'énergie inférieure à 6 MeV ont été déterminées à l'aide de la réaction 18O(d, nγ) 19F. De ces vies moyennes, mesurées à partir de la méthode du déplacement Doppler, ont été déduites certaines largeurs de transition M1 qui sont comparées aux prédictions de modèles en couches

Spin order in the one-dimensional Kondo and Hund lattices

We study numerically the one-dimensional Kondo and Hund lattices consisting of localized spins interacting antiferro or ferromagnetically with the itinerant electrons, respectively. Using the Density Matrix Renormalization Group we find, for both models and in the small coupling regime, the existence of new magnetic phases where the local spins order forming ferromagnetic islands coupled antiferromagnetically. Furthermore, by increasing the interaction parameter $|J|$ we find that this order evolves toward the ferromagnetic regime through a spiral-like phase with longer characteristic wave lengths. These results shed new light on the zero temperature magnetic phase diagram for these models.Comment: PRL, to appea

A new approach for perovskites in large dimensions

Using the Hubbard Hamiltonian for transition metal-3d and oxygen-2p states with perovskite geometry, we propose a new scaling procedure for a nontrivial extension of these systems to large spatial dimensions $D$. The scaling procedure is based on a selective treatment of different hopping processes for large $D$ and can not be generated by a unique scaling of the hopping element. The model is solved in the limit $D \rightarrow \infty$ by the iterated perturbation theory and using an extended non-crossing approximation. We discuss the evolution of quasi particles at the Fermi-level upon doping, leading to interesting insight into the dynamical character of the charge carriers near the metal insulator instability of transition metal oxide systems, three dimensional perovskites and other strongly correlated transition metal oxides.Comment: 5 pages (TeX) with 2 figures (Postscript

The effect of Coulomb interaction at ferromagnetic-paramagnetic metallic perovskite junctions

We study the effect of Coulomb interactions in transition metal oxides junctions. In this paper we analyze charge transfer at the interface of a three layer ferromagnetic-paramagnetic-ferromagnetic metallic oxide system. We choose a charge model considering a few atomic planes within each layer and obtain results for the magnetic coupling between the ferromagnetic layers. For large number of planes in the paramagnetic spacer we find that the coupling oscillates with the same period as in RKKY but the amplitude is sensitive to the Coulomb energy. At small spacer thickness however, large differences may appear as function of : the number of electrons per atom in the ferromagnetics and paramagnetics materials, the dielectric constant at each component, and the charge defects at the interface plane emphasizing the effects of charge transfer.Comment: tex file and 7 figure

Accueillir l’enfant illégitime : modalités, enjeux, limites de la benignitas canonica. Des théories romano-canoniques aux pratiques sociales (XIIe-XVe siècles)

This paper purposed to study figures of children considered as bastards through medieval sources, as rejected and stigmatized one because they were born outside of wedlock but also as children whom society and parents had to take care, who were symbolically, legally and judicially protected. They could not inherit of their father, at least in theory, but those had to feed and educate them, or to contribute by alimenta to do it. Canonists diverged from romanists who nevertheless defined what nutrire or alere meant because from the second part of the twelfth century, popes and decretalists, step by step, demonstrate that parents had to take care of their children, even those who had been born spurii. The idea that supported this form of representation of bastards had nothing to do with favor prolis but simply sollicitudo or benignitas canonica that obliged everyone to put at the first rank the jus naturale instead of human laws that might had restricted bastard’s rigths. But those canonical demonstrations had to be precisely qualified by notarial or judicial sources that proved fatherhood obligations but also difficulties for spurii. Those medieval representations, sometimes paradoxal ones, were finally compared with conclusions of some anthropological studies

Electron-Doped Manganese Perovskites: The Polaronic State

Using the Lanczos method in linear chains we study the ground state of the double exchange model including an antiferromagnetic super-exchange in the low concentration limit. We find that this ground state is always inhomogeneous, containig ferromagnetic polarons. The extention of the polaron spin distortion, the dispersion relation and their trapping by impurities, are studied for diferent values of the super exchange interaction and magnetic field. We also find repulsive polaron polaron interaction.Comment: 4 pages, 6 embedded figure