Search results for "SURF"
showing 10 items of 9629 documents
La métallurgie du fer au Sahel : Répartition spatiale de bas fourneaux au Sud-Ouest du Niger. Premiers résultats
2010
International audience; A 15 km à l'Est de Niamey (Sud-Ouest du Niger), une prospection pédestre exhaustive a permis de dénombrer plus de 4000 bas-fourneaux sur un bassin versant de 24 km². Ils sont identifiables par la présence de scories correspondant aux résidus de réduction du fer. Ce grand nombre de structures de réduction est lié au fonctionnement à usage unique des bas-fourneaux, qui est peu étudié dans la région ouest africaine. Les premières études de répartition spatiale montrent que l'implantation de ces bas-fourneaux est principalement soumise à la géomorphologie. Les forgerons ont installé leurs sites de réduction à proximité des talus de plateaux où affleure le minerai de fer …
Numerical analysis of masonry structures via interface models
2001
The present paper is devoted to the theoretical formulation and numerical implementation of an interface model suitable to simulate the behavior of mortar joints in masonry structures. The interface laws are formulated in the framework of elasto-plasticity for non-standard materials in order to simulate the softening response which occurs along the decohesion process in presence of shear and tension tractions. A variable material dilatancy parameter is introduced together with a further geometrical dilatancy related to the roughness of contact surfaces after joint fracture. An asperity model is adopted with the aim to describe the evolution of the contact surface shape during the loss of co…
Element-Selective Magnetic Imaging in Exchange-Coupled Systems by Magnetic Photoemission Microscopy
1998
We have used a photoemission microscope to obtain element-resolved magnetic contrast in stacked magnetic thin film systems. Magnetic information is thereby provided by X-ray magnetic circular dichroism. Elemental sensitivity, which is crucial for studying magnetic coupling phenomena in systems with several different layers, is achieved by tuning the energy of the illuminating photons to atomic absorption edges. We present measurements of a Ni-coated Co micropattern on Cu(001), and a wedged Co/Cr/Fe(001) sample. In the former sample the Ni magnetization is seen to follow the magnetization of the Co pattern, thereby changing from an out-of-plane easy axis in areas without underlying Co to in…
Coupled petrological-geodynamical modeling of a compositionally heterogeneous mantle plume
2018
Abstract Self-consistent geodynamic modeling that includes melting is challenging as the chemistry of the source rocks continuously changes as a result of melt extraction. Here, we describe a new method to study the interaction between physical and chemical processes in an uprising heterogeneous mantle plume by combining a geodynamic code with a thermodynamic modeling approach for magma generation and evolution. We pre-computed hundreds of phase diagrams, each of them for a different chemical system. After melt is extracted, the phase diagram with the closest bulk rock chemistry to the depleted source rock is updated locally. The petrological evolution of rocks is tracked via evolving chemi…
A rigidity theorem for the pair ${\cal q}{\Bbb C} P^n$ (complex hyperquadric, complex projective space)
1999
Given a compact Kahler manifold M of real dimension 2n, let P be either a compact complex hypersurface of M or a compact totally real submanifold of dimension n. Let \(\cal q\) (resp. \({\Bbb R} P^n\)) be the complex hyperquadric (resp. the totally geodesic real projective space) in the complex projective space \({\Bbb C} P^n\) of constant holomorphic sectional curvature 4\( \lambda \). We prove that if the Ricci and some (n-1)-Ricci curvatures of M (and, when P is complex, the mean absolute curvature of P) are bounded from below by some special constants and volume (P) / volume (M) \(\leq \) volume (\(\cal q\))/ volume \(({\Bbb C} P^n)\) (resp. \(\leq \) volume \(({\Bbb R} P^n)\) / volume …
Designed surface modes propagating along hyperbolic metamaterials
2013
We report on surface-wave propagation (SWP) that occurs in semi-infinite hyperbolic metamaterials whose optical axis is set in the interface plane. In practice it is implemented by a multi-layered metal-dielectric nanostructure that is cut normally to the layers. Our theoretical analysis shows that various conditions can be designed enabling distinct regimes of SWP. We concluded that hybridization of SWP polarization leads to tighter confinement near the interface as compared with conventional surface plasmon polaritons. By using the finite-element method (FEM), we demonstrate that the fields are enhanced on the walls of metallic films, and thus minimizing significantly its presence inside …
Analysis of static friction and elastic forces in a nanowire bent on a flat surface: A comparative study
2014
ZnO nanowires bent to a complex shape and held in place by static friction force from supporting flat surface are investigated experimentally and theoretically. The complex shapes are obtained by bending the nanowires inside a scanning electron microscope with a sharp tip attached to a nanopositioner. Several methods previously described in the literature are applied along with author's original method to calculate the distributed friction force and stored elastic energy in the nanowires from the bending profile. This comparative study evidences the importance of the usage of appropriate models for accurate analysis of the nanowires profile. It is demonstrated that incomplete models can lea…
The far south: the Pleistocene–Holocene transition in Nerja Cave (Andalucı́a, Spain)
2002
Abstract The archaeological site of Cueva de Nerja (Malaga, Spain) provides significant data about the bioclimatic conditions of one of the most southern European temperate regions. The bioclimatic and palaeogeographic changes that have occurred during the 20,000 years of human occupation of the site can be analysed by relating the geodynamic processes, the palaeobotany and the palaeofauna recovered from its archaeological deposits.
Inhibitoren der Korrosion (8) Über die Abhängigkeit der Korrosionsinhibierung des Eisens in Salzsäure von der Struktur quartärer Phosphoniumsalze
1971
Bei quartaren Phosphoniumsalzen be-steht zwischen der Inhibitorwirkung im sauren Medium unter Auschlus von Luft und den polarographisch ermittelten Re-duktionspotentialen keine direkte Bezie-hung. Die sterischen Faktoren der nach Aufnahme von zwei Elektronen entste-henden und an der Eisenoberflache fixierten Fragmente sind offenbar fur die Inhibitorwirkung hauptsachlich ver-antwortlich. Bisphoniumsalze mit gesattigten oder ungesattigten Brucken sind unter den oben genannten Bedingungen hervor-ragende Inhibitoren. Am wirksamsten sind Bisphosphoniumsalze mit Ketten von 4 bis 10 Methylengruppen zwischen den Phosphoniumzentren. Der starre p-Phenylenrest ist als Verknupfungs-prinzip weniger geei…
Oxidation, efflux, and isotopic fractionation of methane during autumnal turnover in a polyhumic, boreal lake
2007
[1] We studied the oxidation and efflux of methane (CH4) in a small, polyhumic lake, Mekkojarvi (southern Finland), during 6 weeks in autumn when the stability of the water mass first weakened, temporarily restabilized, and finally mixed completely. During the summer stratification period, CH4 had accumulated in the anoxic hypolimnion to high concentrations (>150 mmol m−3). Gradual mixing of the water column during the autumn allowed access to both oxygen and CH4 by aerobic methane-oxidizing bacteria (MOB) deeper in the water column. Thus the bulk (∼83–88%) of the CH4 accumulated in the hypolimnion was subsequently consumed by MOB while only 12–17% was lost from the lake to the atmosphere a…