174 research outputs found
Entry length for the rocket meteorological radiation shield
Thermal entry length of temperature sensor placement in tubular radiation shiel
Point defect interactions with extended defects in semiconductors
FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOWe performed a theoretical investigation of the interaction of point defects (vacancy and self-interstitials) with an intrinsic stacking fault in silicon using ab initio total-energy calculations. Defects at the fault and in the crystalline environment display a different behavior, which is evidenced by changes in formation energy and electronic structure. The formation energies for the vacancy and the [110]-split interstitial are lower at the intrinsic stacking fault than those in the crystal, indicating that in nonequilibrium conditions, intrinsic stacking faults can act, together with other extended defects, as a sink for point defects, and also that in equilibrium conditions, there can be a higher concentration of such defects at the fault than that in bulk silicon. [S0163-1829(99)03631-0].We performed a theoretical investigation of the interaction of point defects (vacancy and self-interstitials) with an intrinsic stacking fault in silicon using ab initio total-energy calculations. Defects at the fault and in the crystalline environment display a different behavior, which is evidenced by changes in formation energy and electronic structure. The formation energies for the vacancy and the [110]-split interstitial are lower at the intrinsic stacking fault than those in the crystal, indicating that in nonequilibrium conditions, intrinsic stacking faults can act, together with other extended defects, as a sink for point defects, and also that in equilibrium conditions, there can be a higher concentration of such defects at the fault than that in bulk silicon.60747114714FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOFAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULOCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOSem informaçãoSem informaçãoThe authors acknowledge partial support from the Brazilian funding agencies FAPESP and CNPq. Computer calculations were performed at the facilities of CENAPAD-SP
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
A metaphylactic treatment with double dose oxytetracycline reduces the risk of bovine respiratory disease in feedlot calves
El objetivo del presente estudio fue evaluar el efecto del tratamiento metafiláctico con oxitetraciclina (OTC), a simple y doble dosis, en bovinos con alto riesgo de padecer enfermedad respiratoria bovina (ERB). El estudio se realizó en un establecimiento de engorde a corral donde se utilizaron 2.754 terneros que fueron considerados de alto riesgo de padecer ERB.
Se utilizó un diseño en bloque completamente al azar donde se consideró al animal como la unidad experimental y el corral (n=10) como bloque. Se formaron tres grupos experimentales: 1- control (CTL) el cual permaneció sin tratamiento, 2- recibió OTC 20 mg/kg SC (OTC20) y 3- recibió OTC 40 mg/kg SC (OTC40). El riesgo de ERB fue evaluado a través de una regresión logística. Los animales del grupo CTL tuvieron 2,85 y 7,14 veces más chances de enfermarse de ERB que los animales de los grupos OTC20 y OTC40 respectivamente (
Machine learning of microscopic ingredients for graphene oxide/cellulose interaction
Understanding the role of microscopic attributes in nanocomposites allows for
a controlled and, therefore, acceleration in experimental system designs. In
this work, we extracted the relevant parameters controlling the graphene oxide
binding strength to cellulose by combining first-principles calculations and
machine learning algorithms. We were able to classify the systems among two
classes with higher and lower binding energies, which are well defined based on
the isolated graphene oxide features. By a theoretical X-ray photoelectron
spectroscopy analysis, we show the extraction of these relevant features.
Additionally, we demonstrate the possibilities of a refined control within a
machine learning regression between the binding energy values and the system's
characteristics. Our work presents a guiding map to the control graphene
oxide/cellulose interaction
Orientational Defects in Ice Ih: An Interpretation of Electrical Conductivity Measurements
We present a first-principles study of the structure and energetics of
Bjerrum defects in ice Ih and compare the results to experimental electrical
conductivity data. While the DFT result for the activation energy is in good
agreement with experiment, we find that its two components have quite different
values. Aside from providing new insight into the fundamental parameters of the
microscopic electrical theory of ice, our results suggest the activity of traps
in doped ice in the temperature regime typically assumed to be controlled by
the free migration of L defects.Comment: 4 pages, 4 Figures, 1 Tabl
Emergence of magnetism in graphene materials and nanostructures
Magnetic materials and nanostructures based on carbon offer unique
opportunities for future technological applications such as spintronics. This
article reviews graphene-derived systems in which magnetic correlations emerge
as a result of reduced dimensions, disorder and other possible scenarios. In
particular, zero-dimensional graphene nanofragments, one-dimensional graphene
nanoribbons, and defect-induced magnetism in graphene and graphite are covered.
Possible physical mechanisms of the emergence of magnetism in these systems are
illustrated with the help of computational examples based on simple model
Hamiltonians. In addition, this review covers spin transport properties,
proposed designs of graphene-based spintronic devices, magnetic ordering at
finite temperatures as well as the most recent experimental achievements.Comment: tutorial-style review article -- 18 pages, 19 figure
Hdac6 regulates Tip60-p400 function in stem cells
In embryonic stem cells (ESCs), the Tip60 histone acetyltransferase activates genes required for proliferation and silences genes that promote differentiation. Here we show that the class II histone deacetylase Hdac6 co-purifies with Tip60-p400 complex from ESCs. Hdac6 is necessary for regulation of most Tip60-p400 target genes, particularly those repressed by the complex. Unlike differentiated cells, where Hdac6 is mainly cytoplasmic, Hdac6 is largely nuclear in ESCs, neural stem cells (NSCs), and some cancer cell lines, and interacts with Tip60-p400 in each. Hdac6 localizes to promoters bound by Tip60-p400 in ESCs, binding downstream of transcription start sites. Surprisingly, Hdac6 does not appear to deacetylate histones, but rather is required for Tip60-p400 binding to many of its target genes. Finally, we find that, like canonical subunits of Tip60-p400, Hdac6 is necessary for robust ESC differentiation. These data suggest that Hdac6 plays a major role in the modulation of Tip60-p400 function in stem cells. DOI: http://dx.doi.org/10.7554/eLife.01557.001
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