205 research outputs found
Entry length for the rocket meteorological radiation shield
Thermal entry length of temperature sensor placement in tubular radiation shiel
Surface magnetization in non-doped ZnO nanostructures
We have investigated the magnetic properties of non-doped ZnO nanostructures
by using {\it ab initio} total energy calculations. Contrary to many proposals
that ferromagnetism in non-doped semiconductors should be induced by intrinsic
point defects, we show that ferromagnetism in nanostructured materials should
be mediated by extended defects such as surfaces and grain boundaries. This
kind of defects create delocalized, spin polarized states that should be able
to warrant long-range magnetic interactions.Comment: 8 pages, 3 figure
Formation of Atomic Carbon Chains from Graphene Nanoribbons
The formation of one-dimensional carbon chains from graphene nanoribbons is
investigated using it ab initio molecular dynamics. We show under what
conditions it is possible to obtain a linear atomic chain via pulling of the
graphene nanoribbons. The presence of dimers composed of two-coordinated carbon
atoms at the edge of the ribbons is necessary for the formation of the linear
chains, otherwise there is simply the full rupture of the structure. The
presence of Stone-Wales defects close to these dimers may lead to the formation
of longer chains. The local atomic configuration of the suspended atoms
indicates the formation of single and triple bonds, which is a characteristic
of polyynes.Comment: 4 pages, 5 figure
Accidental poisoning with Wedelia glauca (“sunchillo”) in a bull confirmed by analysis of rumen content
Wedelia glauca is an invasive, perennial plant of the Asteraceae family native to South America. Its toxicity is attributed to the presence of a hepatotoxic terpenoid known as atractyloside, a powerful inhibitor of cellular respiration and ATP synthesis. Cattle are the most frequently poisoned species, and the course of this poisoning is hyperacute or acute. Occasionally, it is possible to find fragments of plants in the rumen contents and indentify the dermis structure of the plants, as they do not undergo significant changes in spite of the mechanic and enzymatic activities occurring in the rumen. The macroscopic and microscopic anatomopathologic findings of a natural Wedelia glauca poisoning case in a Hereford bull are reported. It was confirmed by micrographic analysis of plant fragments found in the rumen contents and also in bales used to feed those animals
Substrate suppression of oxidation process in pnictogen monolayers
2D materials present an interesting platform for device designs. However,
oxidation can drastically change the system's properties, which need to be
accounted for. Through {\it ab initio} calculations, we investigated
freestanding and SiC-supported As, Sb, and Bi mono-elemental layers. The
oxidation process occurs through an O spin-state transition, accounted for
within the Landau-Zener transition. Additionally, we have investigated the
oxidation barriers and the role of spin-orbit coupling. Our calculations
pointed out that the presence of SiC substrate reduces the oxidation time scale
compared to a freestanding monolayer. We have extracted the energy barrier
transition, compatible with our spin-transition analysis. Besides, spin-orbit
coupling is relevant to the oxidation mechanisms and alters time scales. The
energy barriers decrease as the pnictogen changes from As to Sb to Bi for the
freestanding systems, while for SiC-supported, they increase across the
pnictogen family. Our computed energy barriers confirm the enhanced robustness
against oxidation for the SiC-supported systems
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