2,474 research outputs found
Avaliação por Cromatografia Líquida de Alta Eficiência (Hplc) da Interação Atrazina-Carboximetilcelulose.
bitstream/CNPDIA/10488/1/CT38_2000.pd
Restoring observed classical behavior of the carbon nanotube field emission enhancement factor from the electronic structure
Experimental Fowler-Nordheim plots taken from orthodoxly behaving carbon
nanotube (CNT) field electron emitters are known to be linear. This shows that,
for such emitters, there exists a characteristic field enhancement factor (FEF)
that is constant for a range of applied voltages and applied macroscopic fields
. A constant FEF of this kind can be evaluated for classical CNT
emitter models by finite-element and other methods, but (apparently contrary to
experiment) several past quantum-mechanical (QM) CNT calculations find
FEF-values that vary with . A common feature of most such
calculations is that they focus only on deriving the CNT real-charge
distributions. Here we report on calculations that use density functional
theory (DFT) to derive real-charge distributions, and then use these to
generate the related induced-charge distributions and related fields and FEFs.
We have analysed three carbon nanostructures involving CNT-like nanoprotrusions
of various lengths, and have also simulated geometrically equivalent classical
emitter models, using finite-element methods. We find that when the
DFT-generated local induced FEFs (LIFEFs) are used, the resulting values are
effectively independent of macroscopic field, and behave in the same
qualitative manner as the classical FEF-values. Further, there is fair to good
quantitative agreement between a characteristic FEF determined classically and
the equivalent characteristic LIFEF generated via DFT approaches. Although many
issues of detail remain to be explored, this appears to be a significant step
forwards in linking classical and QM theories of CNT electrostatics. It also
shows clearly that, for ideal CNTs, the known experimental constancy of the FEF
value for a range of macroscopic fields can also be found in appropriately
developed QM theory.Comment: A slightly revised version has been published - citation below -
under a title different from that originally used. The new title is:
"Restoring observed classical behavior of the carbon nanotube field emission
enhancement factor from the electronic structure
LATTES: a novel detector concept for a gamma-ray experiment in the Southern hemisphere
The Large Array Telescope for Tracking Energetic Sources (LATTES), is a novel
concept for an array of hybrid EAS array detectors, composed of a Resistive
Plate Counter array coupled to a Water Cherenkov Detector, planned to cover
gamma rays from less than 100 GeV up to 100 TeVs. This experiment, to be
installed at high altitude in South America, could cover the existing gap in
sensitivity between satellite and ground arrays.
The low energy threshold, large duty cycle and wide field of view of LATTES
makes it a powerful tool to detect transient phenomena and perform long term
observations of variable sources. Moreover, given its characteristics, it would
be fully complementary to the planned Cherenkov Telescope Array (CTA) as it
would be able to issue alerts.
In this talk, a description of its main features and capabilities, as well as
results on its expected performance, and sensitivity, will be presented.Comment: Proceedings of the 35th International Cosmic Ray Conference
(ICRC2017), Busan, South Korea. Presented by R. Concei\c{c}\~{a}o. 8 pages;
v2: correct affiliation + journal referenc
Avaliação do efeito cicatrizante da quitosana por aplicação tópica em ratos.
bitstream/CNPDIA-2009-09/11045/1/DOC29_2007.pd
Selecting New \u3cem\u3eBrachiaria humidicola\u3c/em\u3e Hybrids for Western Brazilian Amazon
Brachiaria humidicola is a perennial and stoloniferous forage grass, with excellent adaptation to infertile soils and waterlogging. Producers in northern Brazil have become interested in this species, especially after the degradation of large areas of lowly permeable soils sown with B. brizantha cv. Marandu, which is highly intolerant of soil waterlogging (Andrade and Valentim 2006). However, since only 3 cultivars of B. humidicola are registered in Brazil (Mapa 2013), there is a need to develop new cultivars adapted to the range of environmental conditions experienced. Recently, Embrapa Beef Cattle obtained intraspecific hybrids of B. humidicola that need to be evaluated agronomically, aiming at subsequent grazing trials and future releases. The objective of this study was to evaluate and select apomictic and sexual hybrids of B. humidicola in the environmental conditions of the state of Acre, in western Brazilian Amazon
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