729 research outputs found
Temporal Evolution of Soot Particles from C2H2/O2 Combustion in a Closed Chamber
An experimental study of soot formation in C2H2/O2 flames at different C/O ratios in a closed chamber was carried out. The evolution temporal behavior and the volume fraction of soot particles were determined by laser extinction. It was found that total time for the soot formation phenomenon in flames from C2H2/O2 with C/O ratio > 0.75 or C2H2/O2/Ar with C/O ratio = 1.00 was around 3.0-4.0 ms after ignition. At almost the same time the excited radicals reached their maximum emission intensity and the gases under combustion reached their maximum pressure. The micrographs show compact and approximately spherical soot particles with diameters within 60-150 nm. However, soot aggregates are not compact and they present a netlike structure similar to that of an aerogel.Neste trabalho, realizou-se um estudo da formação de partículas de fuligem durante a combustão de misturas de C2H2/O2 em diferentes razões C/O. A evolução temporal e a fração de volume das partículas de fuligem foram obtidas através da extinção de um feixe de laser. Constatou-se que o tempo total de formação da fuligem nas chamas de C2H2/O2 com razão C/O > 0.75 ou de C2H2/O2/Ar com razão C/O = 1.00 é de cerca de 3.0-4.0 ms, após o início da reação. O máximo de emissão dos radicais excitados e o máximo da pressão nestas reações, ocorrem praticamente neste mesmo intervalo de tempo. Observou-se a formação de partículas de fuligem compactas e aproximadamente esféricas com 60-150 nm de diâmetro. Entretanto, os agregados não são compactos e mostram uma estrutura de rede que se assemelha a de um aerogel.4753Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP
A wide band gap metal-semiconductor-metal nanostructure made entirely from graphene
A blueprint for producing scalable digital graphene electronics has remained
elusive. Current methods to produce semiconducting-metallic graphene networks
all suffer from either stringent lithographic demands that prevent
reproducibility, process-induced disorder in the graphene, or scalability
issues. Using angle resolved photoemission, we have discovered a unique one
dimensional metallic-semiconducting-metallic junction made entirely from
graphene, and produced without chemical functionalization or finite size
patterning. The junction is produced by taking advantage of the inherent,
atomically ordered, substrate-graphene interaction when it is grown on SiC, in
this case when graphene is forced to grow over patterned SiC steps. This
scalable bottomup approach allows us to produce a semiconducting graphene strip
whose width is precisely defined within a few graphene lattice constants, a
level of precision entirely outside modern lithographic limits. The
architecture demonstrated in this work is so robust that variations in the
average electronic band structure of thousands of these patterned ribbons have
little variation over length scales tens of microns long. The semiconducting
graphene has a topologically defined few nanometer wide region with an energy
gap greater than 0.5 eV in an otherwise continuous metallic graphene sheet.
This work demonstrates how the graphene-substrate interaction can be used as a
powerful tool to scalably modify graphene's electronic structure and opens a
new direction in graphene electronics research.Comment: 11 pages, 7 figure
New electronic orderings observed in cobaltates under the influence of misfit periodicities
We study with ARPES the electronic structure of CoO2 slabs, stacked with
rock-salt (RS) layers exhibiting a different (misfit) periodicity. Fermi
Surfaces (FS) in phases with different doping and/or periodicities reveal the
influence of the RS potential on the electronic structure. We show that these
RS potentials are well ordered, even in incommensurate phases, where STM images
reveal broad stripes with width as large as 80\AA. The anomalous evolution of
the FS area at low dopings is consistent with the localization of a fraction of
the electrons. We propose that this is a new form of electronic ordering,
induced by the potential of the stacked layers (RS or Na in NaxCoO2) when the
FS becomes smaller than the Brillouin Zone of the stacked structure
Significant reduction of electronic correlations upon isovalent Ru substitution of BaFe2As2
We present a detailed investigation of Ba(Fe0.65Ru0.35)2As2 by transport
measurements and Angle Resolved photoemission spectroscopy. We observe that Fe
and Ru orbitals hybridize to form a coherent electronic structure and that Ru
does not induce doping. The number of holes and electrons, deduced from the
area of the Fermi Surface pockets, are both about twice larger than in
BaFe2As2. The contribution of both carriers to the transport is evidenced by a
change of sign of the Hall coefficient with decreasing temperature. Fermi
velocities increase significantly with respect to BaFe2As2, suggesting a
significant reduction of correlation effects. This may be a key to understand
the appearance of superconductivity at the expense of magnetism in undoped iron
pnictides
Silicon intercalation into the graphene-SiC interface
In this work we use LEEM, XPEEM and XPS to study how the excess Si at the
graphene-vacuum interface reorders itself at high temperatures. We show that
silicon deposited at room temperature onto multilayer graphene films grown on
the SiC(000[`1]) rapidly diffuses to the graphene-SiC interface when heated to
temperatures above 1020. In a sequence of depositions, we have been able to
intercalate ~ 6 ML of Si into the graphene-SiC interface.Comment: 6 pages, 8 figures, submitted to PR
EQUIPT: protocol of a comparative effectiveness research study evaluating cross-context transferability of economic evidence on tobacco control
This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial.This article has been made available through the Brunel Open Access Publishing Fund.Tobacco smoking claims 700 000 lives every year in Europe and the cost of tobacco smoking in the EU is estimated between €98 and €130 billion annually; direct medical care costs and indirect costs such as workday losses each represent half of this amount. Policymakers all across Europe are in need of bespoke information on the economic and wider returns of investing in evidence-based tobacco control, including smoking cessation agendas. EQUIPT is designed to test the transferability of one such economic evidence base-the English Tobacco Return on Investment (ROI) tool-to other EU member states
First direct observation of a nearly ideal graphene band structure
Angle-resolved photoemission and X-ray diffraction experiments show that
multilayer epitaxial graphene grown on the SiC(000-1) surface is a new form of
carbon that is composed of effectively isolated graphene sheets. The unique
rotational stacking of these films cause adjacent graphene layers to
electronically decouple leading to a set of nearly independent linearly
dispersing bands (Dirac cones) at the graphene K-point. Each cone corresponds
to an individual macro-scale graphene sheet in a multilayer stack where
AB-stacked sheets can be considered as low density faults.Comment: 5 pages, 4 figure
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