1,893 research outputs found
Strain-driven elastic and orbital-ordering effects on thickness-dependent properties of manganite thin films
We report on the structural and magnetic characterization of (110) and (001)
La2/3Ca1/3MnO3 (LCMO) epitaxial thin films simultaneously grown on (110) and
(001)SrTiO3 substrates, with thicknesses t varying between 8 nm and 150 nm. It
is found that while the in-plane interplanar distances of the (001) films are
strongly clamped to those of the substrate and the films remain strained up to
well above t=100 nm, the (110) films relax much earlier. Accurate determination
of the in-plane and out-of-plane interplanar distances has allowed concluding
that in all cases the unit cell volume of the manganite reduces gradually when
increasing thickness, approaching the bulk value. It is observed that the
magnetic properties (Curie temperature and saturation magnetization) of the
(110) films are significantly improved compared to those of (001) films. These
observations, combined with 55Mn-nuclear magnetic resonance data and X-ray
photoemission spectroscopy, signal that the depression of the magnetic
properties of the more strained (001)LCMO films is not caused by an elastic
deformation of the perovskite lattice but rather due to the electronic and
chemical phase separation caused by the substrate-induced strain. On the
contrary, the thickness dependence of the magnetic properties of the less
strained (110)LCMO films are simply described by the elastic deformation of the
manganite lattice. We will argue that the different behavior of (001) and
(110)LCMO films is a consequence of the dissimilar electronic structure of
these interfaces.Comment: 16 pages, 15 figure
Imported Fire Ant Infestation of Soybean Fields in the Southern United States
Moderate to heavy infestations of the imported fire ants (IFA), Solenopsis invicta Buren and S. richteri Forel, have reduced soybean production in the southern United States. In early surveys of crop damage, Wilson & Eads (1949) attributed a loss of about three percent of the soybean crop in three south Alabama counties to the ants. Adams et al. (1976, 1977) reported that 16.8 to 49.1 kg/ha of soybeans in Georgia and North Carolina were not harvested because of physical interference of S. invicta mounds with combine operation. Subsequent studies in Florida and Mississippi showed that IFA feeding on the germinating seed reduced the plant stand with an ultimate reduction of up to 600 kg/ha in soybean yield (Lofgren and Adams 1981, Adams et al. 1983). Apperson & Powell (1983) found that increased numbers of IFA correlated positively with reduced soybean yield in North Carolin
Imported Fire Ant Infestation of Soybean Fields in the Southern United States
Moderate to heavy infestations of the imported fire ants (IFA), Solenopsis invicta Buren and S. richteri Forel, have reduced soybean production in the southern United States. In early surveys of crop damage, Wilson & Eads (1949) attributed a loss of about three percent of the soybean crop in three south Alabama counties to the ants. Adams et al. (1976, 1977) reported that 16.8 to 49.1 kg/ha of soybeans in Georgia and North Carolina were not harvested because of physical interference of S. invicta mounds with combine operation. Subsequent studies in Florida and Mississippi showed that IFA feeding on the germinating seed reduced the plant stand with an ultimate reduction of up to 600 kg/ha in soybean yield (Lofgren and Adams 1981, Adams et al. 1983). Apperson & Powell (1983) found that increased numbers of IFA correlated positively with reduced soybean yield in North Carolin
Effect of growth pressure on coalescence thickness and crystal quality of GaN deposited on 4H-SiC
Cataloged from PDF version of article.The influence of growth pressure on the coalescence thickness and the crystal quality of GaN deposited on 4H-SiC by low pressure metalorganic vapor phase epitaxy was studied. It was shown that growth pressure has an impact on the surface roughness of epilayers and their crystal quality. GaN coalescence thicknesses were determined for the investigated growth pressures. The GaN layers were characterized by AFM and HRXRD measurements. HEMT structures were also fabricated and characterized. Among the growth pressures studied, 50, 125 and 200 mbar, 200 mbar was found to be most suitable for GaN/SiC epitaxy. (C) 2010 Elsevier B.V. All rights reserved
Observations on a parasitic nematode (Tetradonematidae) of fire ants, solenopsis (Formicidae), from Mato Grosso.
Parasitic nematodes, Tetradonema sp. (Mermithoidea: Tetradonematidae) were obwserved in the fire ant. Solenopsis invicta Buren, for the first time. Five colonies in a sample of 14 colonies from one site in Mato Grosso were infected. The infection rate among adult workers was 12..5% in one colony and less than 5% in each of the remaining colonies. Adult reproductive males and females, eggs, and juvenile nematodes were observed in the haemocoel of male and worker ants. The infected worker ants often can be recognized by their slightly enlarged gasters, the dorsal scierites of which vable changes in behavior: infected adult males contained normal sperm. An attempt to transmit the nematode to colonies of S. invicta in the United States was unsuccessful.TÃtulo em português: Observações sobre um nematóide parasito (Tetradonematidae) da formiga lava-pé, Solenopsis (Formicidae), em Mato Grosso
Electronic self-doping of Mo-states in A2FeMoO6 (A=Ca, Sr and Ba) half-metallic ferromagnets - a Nuclear Magnetic Resonance study
A systematic study of (A,A')2FeMoO6 (A,A'=Ca, Sr, Ba) ferromagnetic oxides
with double perovskite structure has been performed using 95,97Mo and 57Fe NMR
spectroscopy. These oxides are isoelectronic but have substantially different
Curie temperatures. The NMR analysis provides clear evidence that the magnetic
moment at Mo sites is not constant but varies sensitively with the ionic size
of the alkaline ions. The 95,97Mo frequency, and thus the electronic charge at
Mo ions, is found to be smaller in Ba and Ca than in Sr-based oxides. The
charge release from Mo sites is accompanied by an uptake at Fe sites, and thus
a self-doping Fe-Mo process is observed. This process is controlled by relevant
structural parameters: the Fe-O-Mo bond length and bending. A clear
relationship between the Curie temperature and the magnetic moment and thus
electron density at Mo sites has been disclosed. The relevance of these
findings for the understanding of ferromagnetic coupling in double perovskites
is discussed.Comment: 26 pages, 8 figure
Interlayer Exchange Coupling Mediated by Valence Band Electrons
The interlayer exchange coupling mediated by valence band electrons in
all-semiconductor IV-VI magnetic/nonmagnetic superlattices is studied
theoretically. A 3D tight-binding model, accounting for the band and magnetic
structure of the constituent superlattice components is used to calculate the
spin-dependent part of the total electronic energy. The antiferromagnetic
coupling between ferromagnetic layers in EuS/PbS superlattices is obtained, in
agreement with the experimental evidences. The results obtained for the
coupling between antiferromagnetic layers in EuTe/PbTe superlattices are also
presented.Comment: 8 pages, 6 figures, to be submitted to Phys.Rev.
'Surely the most natural scenario in the world’: Representations of ‘Family’ in BBC Pre-school Television
Historically, the majority of work on British children’s television has adopted either an institutional or an audience focus, with the texts themselves often overlooked. This neglect has meant that questions of representation in British children’s television – including issues such as family, gender, class or ethnicity - have been infrequently analysed in the UK context. In this article, we adopt a primarily qualitative methodology and analyse the various textual manifestations of ‘family’, group, or community as represented in a selected number of BBC pre-school programmes. In doing so, we question the (limited amount of) international work that has examined representations of the family in children’s television, and argue that nuclear family structures do not predominate in this sphere
Open access resource for cellular-resolution analyses of corticocortical connectivity in the marmoset monkey
Understanding the principles of neuronal connectivity requires tools for efficient quantification and visualization of large datasets. The primate cortex is particularly challenging due to its complex mosaic of areas, which in many cases lack clear boundaries. Here, we introduce a resource that allows exploration of results of 143 retrograde tracer injections in the marmoset neocortex. Data obtained in different animals are registered to a common stereotaxic space using an algorithm guided by expert delineation of histological borders, allowing accurate assignment of connections to areas despite interindividual variability. The resource incorporates tools for analyses relative to cytoarchitectural areas, including statistical properties such as the fraction of labeled neurons and the percentage of supragranular neurons. It also provides purely spatial (parcellation-free) data, based on the stereotaxic coordinates of 2 million labeled neurons. This resource helps bridge the gap between high-density cellular connectivity studies in rodents and imaging-based analyses of human brains
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