25,888 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
Antioxidants of natural plant origins: from sources to food industry applications
ReviewIn recent years, great interest has been focused on using natural antioxidants in food
products, due to studies indicating possible adverse effects that may be related to the consumption of
synthetic antioxidants. A variety of plant materials are known to be natural sources of antioxidants,
such as herbs, spices, seeds, fruits and vegetables. The interest in these natural components is
not only due to their biological value, but also to their economic impact, as most of them may be
extracted from food by-products and under-exploited plant species. This article provides an overview
of current knowledge on natural antioxidants: their sources, extraction methods and stabilization
processes. In addition, recent studies on their applications in the food industry are also addressed;
namely, as preservatives in different food products and in active films for packaging purposes and
edible coatingsinfo:eu-repo/semantics/publishedVersio
Structural studies of mesoporous ZrO-CeO and ZrO-CeO/SiO mixed oxides for catalytical applications
In this work the synthesis of ZrO-CeO and
ZrO-CeO/SiO were developed, based on the process to form
ordered mesoporous materials such as SBA-15 silica. The triblock copolymer
Pluronic P-123 was used as template, aiming to obtain crystalline single phase
walls and larger specific surface area, for future applications in catalysis.
SAXS and XRD results showed a relationship between ordered pores and the
material crystallization. 90% of CeO leaded to single phase homogeneous
ceria-zirconia solid solution of cubic fluorite structure (Fmm). The
SiO addition improved structural and textural properties as well as the
reduction behavior at lower temperatures, investigated by XANES measurements
under H atmosphere
Scaling Laws for Non-Intercommuting Cosmic String Networks
We study the evolution of non-interacting and entangled cosmic string
networks in the context of the velocity-dependent one-scale model. Such
networks may be formed in several contexts, including brane inflation. We show
that the frozen network solution , although generic, is only a
transient one, and that the asymptotic solution is still as in the
case of ordinary (intercommuting) strings, although in the present context the
universe will usually be string-dominated. Thus the behaviour of two strings
when they cross does not seem to affect their scaling laws, but only their
densities relative to the background.Comment: Phys. Rev. D (in press); v2: final published version (references
added, typos corrected
Radial dependence of line profile variability in seven O9--B0.5 stars
Massive stars show a variety of spectral variability: presence of discrete
absorption components in UV P-Cygni profiles, optical line profile variability,
X-ray variability, radial velocity modulations. Our goal is to study the
spectral variability of single OB stars to better understand the relation
between photospheric and wind variability. For that, we rely on high spectral
resolution, high signal-to-noise ratio optical spectra collected with the
spectrograph NARVAL on the Telescope Bernard Lyot at Pic du Midi. We
investigate the variability of twelve spectral lines by means of the Temporal
Variance Spectrum (TVS). The selected lines probe the radial structure of the
atmosphere, from the photosphere to the outer wind. We also perform a
spectroscopic analysis with atmosphere models to derive the stellar and wind
properties, and to constrain the formation region of the selected lines. We
show that variability is observed in the wind lines of all bright giants and
supergiants, on a daily timescale. Lines formed in the photosphere are
sometimes variable, sometimes not. The dwarf stars do not show any sign of
variability. If variability is observed on a daily timescale, it can also (but
not always) be observed on hourly timescales, albeit with lower amplitude.
There is a very clear correlation between amplitude of the variability and
fraction of the line formed in the wind. Strong anti-correlations between the
different part of the temporal variance spectrum are observed. Our results
indicate that variability is stronger in lines formed in the wind. A link
between photospheric and wind variability is not obvious from our study, since
wind variability is observed whatever the level of photospheric variability.
Different photospheric lines also show different degrees of variability.Comment: 13 pages, 9 figures + appendix. A&A accepted. Figures degraded for
arxiv submissio
Multicolored Temperley-Lieb lattice models. The ground state
Using inversion relation, we calculate the ground state energy for the
lattice integrable models, based on a recently obtained baxterization of non
trivial multicolored generalization of Temperley-Lieb algebras. The simplest
vertex and IRF models are analyzed and found to have a mass gap.Comment: 15 pages 2 figure
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