1,224 research outputs found
Interplay between the electrical transport properties of GeMn thin films and Ge substrates
We present evidence that electrical transport studies of epitaxial p-type
GeMn thin films fabricated on high resistivity Ge substrates are severely
influenced by parallel conduction through the substrate, related to the large
intrinsic conductivity of Ge due to its small bandgap. Anomalous Hall
measurements and large magneto resistance effects are completely understood by
taking a dominating substrate contribution as well as the measurement geometry
into account. It is shown that substrate conduction persists also for well
conducting, degenerate, p-type thin films, giving rise to an effective
two-layer conduction scheme. Using n-type Ge substrates, parallel conduction
through the substrate can be reduced for the p-type epi-layers, as a
consequence of the emerging pn-interface junction. GeMn thin films fabricated
on these substrates exhibit a negligible magneto resistance effect. Our study
underlines the importance of a thorough characterization and understanding of
possible substrate contributions for electrical transport studies of GeMn thin
films.Comment: 9 pages, 9 figure
Lattice Dynamics and Intermolecular Forces in Organic Molecular Crystals
Recent developments in the theory and the application of determination
of intermolecular forces are discussed for the computer simulation of the lattice dynamics of organic molecular crystals. Different atom-atom potentials for carbon, hydrogen, halogens, oxygen and nitrogen are presented. The influences of hydrogen bonds and multipolar forces are illustrated with some examples. Such potentials are applied to glutaric and squaric acid, hexachloroethane, malononitrile and parachlorobenzamide
Clustering in a precipitate free GeMn magnetic semiconductor
We present the first study relating structural parameters of precipitate free
Ge0.95Mn0.05 films to magnetisation data. Nanometer sized clusters - areas with
increased Mn content on substitutional lattice sites compared to the host
matrix - are detected in transmission electron microscopy (TEM) analysis. The
films show no overall spontaneous magnetisation at all down to 2K. The TEM and
magnetisation results are interpreted in terms of an assembly of
superparamagnetic moments developing in the dense distribution of clusters.
Each cluster individually turns ferromagnetic below an ordering temperature
which depends on its volume and Mn content.Comment: accepted for publication in Phys. Rev. Lett. (2006). High resolution
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EC-90-102 Nebraska Spring Small Grain Variety Tests 1990
Extension circular 90-102 is about Nebraska spring small grain variety tests 1990
Enquête qualitative 2016 - Bibliothèque municipale de Lyon
La Bibliothèque municipale de Lyon a mené, en complément des enquêtes quantitatives (Baromètres 2013 et 2015), une enquête qualitative qui précise encore les attentes du public lyonnais. Elle a l’originalité d’interroger non seulement des abonnés et « décrocheurs », mais aussi des non usagers de la bibliothèque.
Associant dans l’examen des entretiens des méthodes linguistiques d’analyse de discours, elle révèle non seulement des pratiques (culturelles, numériques, de lecture) et des stratégies (d’information, d’approvisionnement, d’appropriation), mais aussi la prégnance des représentations et des « insécurités culturelles » qui président à la fréquentation, aux usages, à la prise d’information… En quoi cette enquête, aboutissant à des préconisations concrètes que la BmL prendra le temps d’examiner pour compléter son Projet d’Etablissement, dans les années qui viennent, dépasse aussi le cadre lyonnais et peut contribuer à une meilleure compréhension du public en général
Factors shaping community assemblages and species co-occurrence of different trophic levels
Species assemblages are the results of various processes, including dispersion and habitat filtering. Disentangling the effects of these different processes is challenging for statistical analysis, especially when biotic interactions should be considered. In this study, we used plants (producers) and leafhoppers (phytophagous) as model organisms, and we investigated the relative importance of abiotic versus biotic factors that shape community assemblages, and we infer on their biotic interactions by applying three-step statistical analysis. We applied a novel statistical analysis, that is, multiblock Redundancy Analysis (mbRA, step 1) and showed that 51.8% and 54.1% of the overall variation in plant and leafhopper assemblages are, respectively, explained by the two multiblock models. The most important blocks of variables to explain the variations in plant and leafhopper assemblages were local topography and biotic factors. Variation partitioning analysis (step 2) showed that pure abiotic filtering and pure biotic processes were relatively less important than their combinations, suggesting that biotic relationships are strongly structured by abiotic conditions. Pairwise co-occurrence analysis (step 3) on generalist leafhoppers and the most common plants identified 40 segregated species pairs (mainly between plant species) and 16 aggregated pairs (mainly between leafhopper species). Pairwise analysis on specialist leafhoppers and potential host plants clearly revealed aggregated patterns. Plant segregation suggests heterogeneous resource availability and competitive interactions, while leafhopper aggregation suggests host feeding differentiation at the local level, different feeding microhabitats on host plants, and similar environmental requirements of the species. Using the novel mbRA, we disentangle for the first time the relative importance of more than five distinct groups of variables shaping local species communities. We highlighted the important role of abiotic processes mediated by bottom-up effects of plants on leafhopper communities. Our results revealed that in-field structure diversification and trophic interactions are the main factors causing the co-occurrence patterns observed.Fil: Trivellone, Valeria. Swiss Federal Institute for Forest, Snow and Landscape Research; SuizaFil: Bougeard, Stephanie. French Agency for Food, Environmental and Occupational Health Safety; FranciaFil: Giavi, Simone. Swiss Federal Institute for Forest, Snow and Landscape Research; SuizaFil: Krebs, Patrik. Swiss Federal Institute for Forest, Snow and Landscape Research; SuizaFil: Balseiro, Diego. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - CĂłrdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de CĂłrdoba. Facultad de Ciencias Exactas FĂsicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Dray, Stephane. UniversitĂ© Claude Bernard Lyon 1; FranciaFil: Moretti, Marco. Swiss Federal Institute for Forest, Snow and Landscape Research; Suiz
Hole spin dynamics and hole factor anisotropy in coupled quantum well systems
Due to its p-like character, the valence band in GaAs-based heterostructures
offers rich and complex spin-dependent phenomena. One manifestation is the
large anisotropy of Zeeman spin splitting. Using undoped, coupled quantum wells
(QWs), we examine this anisotropy by comparing the hole spin dynamics for high-
and low-symmetry crystallographic orientations of the QWs. We directly measure
the hole factor via time-resolved Kerr rotation, and for the low-symmetry
crystallographic orientations (110) and (113a), we observe a large in-plane
anisotropy of the hole factor, in good agreement with our theoretical
calculations. Using resonant spin amplification, we also observe an anisotropy
of the hole spin dephasing in the (110)-grown structure, indicating that
crystal symmetry may be used to control hole spin dynamics
All-electrical measurements of direct spin Hall effect in GaAs with Esaki diode electrodes
We report on measurements of direct spin Hall effect in a lightly n-doped
GaAs channel. As spin detecting contacts we employed highly efficient
ferromagnetic Fe/(Ga,Mn)As/GaAs Esaki diode structures. We investigate bias and
temperature dependence of the measured spin Hall signal and evaluate the value
of total spin Hall conductivity and its dependence on channel conductivity and
temperature. From the results we determine skew scattering and side jump
contribution to the total spin hall conductivity and compare it with the
results of experiments on higher conductive n-GaAs channels[Phys. Rev. Lett.
105,156602(2010)]. As a result we conclude that both skewness and side jump
contribution cannot be fully independent on the conductivity of the channel.Comment: 14 pages, 4 figure
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