19,675 research outputs found
Curved Graphene Nanoribbons: Structure and Dynamics of Carbon Nanobelts
Carbon nanoribbons (CNRs) are graphene (planar) structures with large aspect
ratio. Carbon nanobelts (CNBs) are small graphene nanoribbons rolled up into
spiral-like structures, i. e., carbon nanoscrolls (CNSs) with large aspect
ratio. In this work we investigated the energetics and dynamical aspects of
CNBs formed from rolling up CNRs. We have carried out molecular dynamics
simulations using reactive empirical bond-order potentials. Our results show
that similarly to CNSs, CNBs formation is dominated by two major energy
contribution, the increase in the elastic energy due to the bending of the
initial planar configuration (decreasing structural stability) and the
energetic gain due to van der Waals interactions of the overlapping surface of
the rolled layers (increasing structural stability). Beyond a critical diameter
value these scrolled structures can be even more stable (in terms of energy)
than their equivalent planar configurations. In contrast to CNSs that require
energy assisted processes (sonication, chemical reactions, etc.) to be formed,
CNBs can be spontaneously formed from low temperature driven processes. Long
CNBs (length of 30.0 nm) tend to exhibit self-folded racket-like
conformations with formation dynamics very similar to the one observed for long
carbon nanotubes. Shorter CNBs will be more likely to form perfect scrolled
structures. Possible synthetic routes to fabricate CNBs from graphene membranes
are also addressed
Margarine products quality monitoring using reflectance UV-VIS-SWNIR spectroscopy
Margarine is a term that can indicate any of a wide range of butter substitutes. Due to the great diversity of the raw material, margarine end-product quality characteristics are expected to be highly diversified. This article proposes the use of reflectance UV-VIS-SWNIR spectroscopy to monitor the margarine end-product quality properties. The main effort in this work was the development of a fast monitoring procedure to assess the quality of the manufactured margarines. 
The study was performed on two margarine products: regular margarine (less than 80% fat) and reduced-fat margarine (less than 60% fat). The nine product samples were collected during the production line normal operating conditions on different days. The samples had the surface cleaned in order to remove any sign of oxidized material. Then, spectra were collected by a reflectance probe normal to the sample surface. The samples temperature was recorded (10.0± 2.0ºC) and the probe-sample distance was kept constant for all the samples. The integration time was set to 40s for the collection of the five UV/VIS spectra per samples; the three VIS/NIR spectra per sample were collected using a 10s integration time.
The data analysis was performed on each product and for each spectral range independently. The spectra were normalized by its maximum intensity and the corrected for using a robust multiplicative scatter correction algorithm. A principal component analysis was performed to the pre-process spectra and the multivariate statistical process control limits were determined with bootstrap for each product/spectral range.
Results show that UV-VIS-SWNIR reflectance spectroscopy provides a quick and fast assessment of these products characteristics and thus it can be used as an indication of the overall product variability
Tipos nomenclaturais do Herbário IAN: organização, caracterização e divulgação.
Organizadores: Arion Tulio Aranda e Silvana Carvalho Thiengo
Mapping the train model for earthquakes onto the stochastic sandpile model
We perform a computational study of a variant of the ``train'' model for
earthquakes [PRA 46, 6288 (1992)], where we assume a static friction that is a
stochastic function of position rather than being velocity dependent. The model
consists of an array of blocks coupled by springs, with the forces between
neighbouring blocks balanced by static friction. We calculate the probability,
P(s), of the occurrence of avalanches with a size s or greater, finding that
our results are consistent with the phenomenology and also with previous models
which exhibit a power law over a wide range. We show that the train model may
be mapped onto a stochastic sandpile model and study a variant of the latter
for non-spherical grains. We show that, in this case, the model has critical
behaviour only for grains with large aspect ratio, as was already shown in
experiments with real ricepiles. We also demonstrate a way to introduce
randomness in a physically motivated manner into the model.Comment: 14 pages and 6 figures. Accepted in European Physical Journal
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