Bounded geometry and leaves

The main theorem states that any complete connected Riemannian manifold of bounded geometry can be isometrically realized as a leaf with trivial holonomy in a compact Riemannian foliated space.Comment: 21 pages. To appear in Math. Nachr. arXiv admin note: text overlap with arXiv:1408.477

A universal Riemannian foliated space

It is proved that the isometry classes of pointed connected complete Riemannian $n$-manifolds form a Polish space, $\mathcal{M}_*^\infty(n)$, with the topology described by the $C^\infty$ convergence of manifolds. This space has a canonical partition into sets defined by varying the distinguished point into each manifold. The locally non-periodic manifolds define an open dense subspace $\mathcal{M}_{*,\text{lnp}}^\infty(n)\subset\mathcal{M}_*^\infty(n)$, which becomes a $C^\infty$ foliated space with the restriction of the canonical partition. Its leaves without holonomy form the subspace $\mathcal{M}_{*,\text{np}}^\infty(n)\subset\mathcal{M}_{*,\text{lnp}}^\infty(n)$ defined by the non-periodic manifolds. Moreover the leaves have a natural Riemannian structure so that $\mathcal{M}_{*,\text{lnp}}^\infty(n)$ becomes a Riemannian foliated space, which is universal among all sequential Riemannian foliated spaces satisfying certain property called covering-continuity. $\mathcal{M}_{*,\text{lnp}}^\infty(n)$ is used to characterize the realization of complete connected Riemannian manifolds as dense leaves of covering-continuous compact sequential Riemannian foliated spaces.Comment: 32 pages. Published in Topology Appl., 198 (2016), 47-8

Large perpendicular magnetic anisotropy in magnetostrictive Fe1−x_{1-x}Gax_x thin films

In this work we report the appearence of a large perpendicular magnetic anisotropy (PMA) in Fe$_{1-x}$Ga$_x$ thin films grown onto ZnSe/GaAs(100). This arising anisotropy is related to the tetragonal metastable phase in as-grown samples recently reported [M. Eddrief {\it et al.}, Phys. Rev. B {\bf 84}, 161410 (2011)]. By means of ferromagnetic resonance studies we measured PMA values up to $\sim$ 5$\times$10$^5$ J/m$^3$. PMA vanishes when the cubic structure is recovered upon annealing at 300$^{\circ}$C. Despite the important values of the magnetoelastic constants measured via the cantilever method, the consequent magnetoelastic contribution to PMA is not enough to explain the observed anisotropy values in the distorted state. {\it Ab initio} calculations show that the chemical ordering plays a crucial role in the appearance of PMA. Through a phenomenological model we are able to explain that an excess of next nearest neighbour Ga pairs (B$_2$-like ordering) along the perpendicular direction arises as the source of PMA in Fe$_{1-x}$Ga$_x$ thin films.Comment: 6 pages, 4 figure

Unusual Kondo physics in a Co impurity atom embedded in noble-metal chains

We analyze the conduction bands of the one dimensional noble-metal chains that contain a Co magnetic impurity by means of ab initio calculations. We compare the results obtained for Cu and Ag pure chains, as well as O doped Cu, Ag and Au chains with those previously found for Au pure chains. We find similar results in the case of Cu and Au hosts, whereas for Ag chains a different behavior is obtained. Differences and similarities among the different systems are analyzed by comparing the electronic structure of the three noble-metal hosts. The d-orbitals of Cu chains at the Fermi level have the same symmetry as in the case of Au chains. These orbitals hybridize with the corresponding ones of the Co impurity, giving rise to the possibility of exhibiting a two-channel Kondo physics.Comment: Accepted in IEEE Trans. Magn. - April 201

Influence du pastoralisme sur les populations acridiennes dans le massif du Siroua (Maroc)

Un foyer de grégarisation de #Dociostaurus maroccanus (Thunb.) a été étudié au cours de cinq missions annuelles (1988-1993). Le site d'étude est un pâturage d'altitude dans l'Anti-Atlas (2300 m) où les troupeaux estivent. Sur les 2850 ha de pâturages à #Poa bulbosa le nombre de moutons et de chèvres a été estimé à 7200 têtes (une tête pour 0,4 ha). Les acridiens (18 espèces) et leurs prédateurs (14 espèces d'insectes et oiseaux) sont cantonnés autour d'une prairie de fauche et des cultures irriguées (55 ha). Le site de ponte du criquet marocain est sur un parc à moutons de 2 hectares. La densité moyenne d'oothèques est de 77/m2, dont 37 % sont détruites par des larves de coléoptères (méloïdes) et des larves de diptères. #Falco naumanni Fleicher et #Pyrrhocorax pyrrhocorax docilis Gm. sont les prédateurs de criquets, importants sur le site. Les craves à bec rouge ont été observés déterrant les oothèques pour les manger. Il est connu que les moutons créent les conditions favorables à la grégarisation du criquet marocain. Nous montrons que le strict calendrier des activités pastorales influence aussi la dynamique des populations acridiennes : les éclosions ont lieu en mai dans un milieu non perturbé par les moutons et à l'abri des prédateurs jusqu'à la fenaison. La transhumance le 28 juillet, en pleine saison de ponte, modifie l'espace et les ressources trophiques disponibles. (Résumé d'auteur

On the fringe: tracking and evaluating changes in land use in the areas surrounding three national parks in Spain and Portugal

Naturbanization analyses territorial changes in the surroundings of national parks brought about by the arrival of new settlers and economic activities, both of which are attracted by the value of the environment and landscape. This paper presents a comparison of the naturbanization processes in three national parks in Spain and Portugal (Doñana and Sierra Nevada National Parks, and Peneda-Gêres National Park, respectively) and in their areas of influence. Data is taken from Corine-Land Cover (1990-2006), which is the only available source of information about land use and land cover changes in the whole of the European Union. These changes have been interpreted and analysed using the Cross Tabulation Matrix developed by Pontius (2004). Land use changes connected to naturbanization processes are measured using Gains and Loss measurements. The intensification of changes in land use is one of the most significant developments associated with these processes, which have implications for the sustainable development and conservation of these areas