2,259 research outputs found
Theory of double-resonant Raman spectra in graphene: intensity and line shape of defect-induced and two-phonon bands
We calculate the double resonant (DR) Raman spectrum of graphene, and
determine the lines associated to both phonon-defect processes, and two-phonons
ones. Phonon and electronic dispersions reproduce calculations based on density
functional theory corrected with GW. Electron-light, -phonon, and -defect
scattering matrix elements and the electronic linewidth are explicitly
calculated. Defect-induced processes are simulated by considering different
kind of idealized defects. For an excitation energy of eV, the
agreement with measurements is very good and calculations reproduce: the
relative intensities among phonon-defect or among two-phonon lines; the
measured small widths of the D, , 2D and lines; the line shapes; the
presence of small intensity lines in the 1800, 2000 cm range. We
determine how the spectra depend on the excitation energy, on the light
polarization, on the electronic linewidth, on the kind of defects and on their
concentration. According to the present findings, the intensity ratio between
the and 2D lines can be used to determine experimentally the electronic
linewidth. The intensity ratio between the and lines depends on the
kind of model defect, suggesting that this ratio could possibly be used to
identify the kind of defects present in actual samples. Charged impurities
outside the graphene plane provide an almost undetectable contribution to the
Raman signal
Electron Transport and Hot Phonons in Carbon Nanotubes
We demonstrate the key role of phonon occupation in limiting the high-field
ballistic transport in metallic carbon nanotubes. In particular, we provide a
simple analytic formula for the electron transport scattering length, that we
validate by accurate first principles calculations on (6,6) and (11,11)
nanotubes. The comparison of our results with the scattering lengths fitted
from experimental I-V curves indicates the presence of a non-equilibrium
optical phonon heating induced by electron transport. We predict an effective
temperature for optical phonons of thousands Kelvin.Comment: 4 pages, 1 figur
Kohn Anomalies and Electron-Phonon Interaction in Graphite
We demonstrate that graphite phonon dispersions have two Kohn anomalies at
the Gamma-E_2g and K-A'1 modes. The anomalies are revealed by two sharp kinks.
By an exact analytic derivation, we show that the slope of these kinks is
proportional to the square of the electron-phonon coupling (EPC). Thus, we can
directly measure the EPC from the experimental dispersions. The Gamma-E_2g and
K-A'1 EPCs are particularly large, whilst they are negligible for all the other
modes at Gamma and K.Comment: 4 pages, 2 figure
Child undernutrition in affluent societies: what are we talking about?
In this paper we set out to explore the prevalence of child undernutrition found in community studies in affluent societies, but a preliminary literature review revealed that, in the absence of a gold standard method of diagnosis, the prevalence largely depends on the measure, threshold and the growth reference used, as well as age. We thus go on to explore describe the common clinical ‘syndromes’ of child undernutrition: wasting, stunting and failure to thrive (weight faltering) and how we have used data from two population-based cohort studies, this paper to explore how much these different ‘syndromes’ overlap and the extent to which they reflect true undernutrition. This analysis revealed that when more than one definition is applied to the same children, a majority are below the lower threshold for only one measure. However, those with both weight faltering and low BMI in infancy, go on in later childhood to show growth and body composition patterns suggestive of previous undernutrition. In older children there is even less overlap and most children with either wasting or low fat seem to be simply growing at one extreme of the normal range. We conclude that in affluent societies the diagnosis of undernutrition is only robust when it relies on a combination of both, that is decline in weight or BMI centile and wasting
An agronomic evaluation of new safflower (Carthamus tinctorius L.) germplasm for seed and oil yields under Mediterraean climate conditions
Interest in oilseed crops for agro-industrial research and development projects has increased in the Mediterranean area, in recent years. Saffloower (Carthamus tinctorius L.) is of potential interest for agriculture mainly due to fatty acid content variability in the seed oil. The aim of this study was to assess the agronomic performance of 16 new safflower accessions together with safflower variety Montola 2000, used as a reference, in a semi-arid environment. Research was carried out in Sicily (Italy) from 2013–2014. Hierarchical cluster analysis carried out on the fatty acid composition of safflower accessions resulted in their division into four main groups. Linoleic, oleic and palmitic acids were the main fatty acids present in the accessions. Seed yield was 1.11 t ha-1 on average and seed oil content was found to be approximately 35.01% of dry matter on average. Positive and significant relationships between seed/oil yield and other tested traits were found. The carbon, hydrogen and nitrogen content as a percentage of dry matter varied greatly both for the above- and belowground
plant parts on average. This study confirms the interest of safflower for both food and non-food applications, offering interesting prospects in semi-arid regions
Phonon Linewidths and Electron Phonon Coupling in Nanotubes
We prove that Electron-phonon coupling (EPC) is the major source of
broadening for the Raman G and G- peaks in graphite and metallic nanotubes.
This allows us to directly measure the optical-phonon EPCs from the G and G-
linewidths. The experimental EPCs compare extremely well with those from
density functional theory. We show that the EPC explains the difference in the
Raman spectra of metallic and semiconducting nanotubes and their dependence on
tube diameter. We dismiss the common assignment of the G- peak in metallic
nanotubes to a Fano resonance between phonons and plasmons. We assign the G+
and G- peaks to TO (tangential) and LO (axial) modes.Comment: 5 pages, 4 figures (correction in label of fig 3
An adaptive stigmergy-based system for evaluating technological indicator dynamics in the context of smart specialization
Regional innovation is more and more considered an important enabler of
welfare. It is no coincidence that the European Commission has started looking
at regional peculiarities and dynamics, in order to focus Research and
Innovation Strategies for Smart Specialization towards effective investment
policies. In this context, this work aims to support policy makers in the
analysis of innovation-relevant trends. We exploit a European database of the
regional patent application to determine the dynamics of a set of technological
innovation indicators. For this purpose, we design and develop a software
system for assessing unfolding trends in such indicators. In contrast with
conventional knowledge-based design, our approach is biologically-inspired and
based on self-organization of information. This means that a functional
structure, called track, appears and stays spontaneous at runtime when local
dynamism in data occurs. A further prototyping of tracks allows a better
distinction of the critical phenomena during unfolding events, with a better
assessment of the progressing levels. The proposed mechanism works if
structural parameters are correctly tuned for the given historical context.
Determining such correct parameters is not a simple task since different
indicators may have different dynamics. For this purpose, we adopt an
adaptation mechanism based on differential evolution. The study includes the
problem statement and its characterization in the literature, as well as the
proposed solving approach, experimental setting and results.Comment: mail: [email protected]
Phonon surface mapping of graphite: disentangling quasi--degenerate phonon dispersions
The two-dimensional mapping of the phonon dispersions around the point of
graphite by inelastic x-ray scattering is provided. The present work resolves
the longstanding issue related to the correct assignment of transverse and
longitudinal phonon branches at . We observe an almost degeneracy of the
three TO, LA and LO derived phonon branches and a strong phonon trigonal
warping. Correlation effects renormalize the Kohn anomaly of the TO mode, which
exhibits a trigonal warping effect opposite to that of the electronic band
structure. We determined the electron--phonon coupling constant to be
166 in excellent agreement to calculations. These results
are fundamental for understanding angle-resolved photoemission,
double--resonance Raman and transport measurements of graphene based systems
CPAP after endoscopic procedures as add-on therapy for the treatment of tracheal stenosis: a case series
Tracheal stenosis represents a possible complication in intubated or tracheotomised patients. Tracheal resection is currently the gold standard for the treatment of complex stenosis while granulomas and simple stenosis (e.g., web-like) are often treated by endoscopic procedures, which do not consistently give satisfactory long-term results, due to frequent relapses. Administering continuous positive airway pressure (CPAP) after endoscopic procedures might represent a new add-on option for the treatment of this complication. In this case series are presented two patients with tracheal stenosis showed after the removal of tracheostomy tube, both treated with CPAP. The results were straightforward: CPAP treatment helped to keep stable the tracheal lumen, without adverse effects. No further endoscopic dilations were necessary thereafter, with a likely positive impact on patients' quality of life and on health expenditure
Structure and stability of graphene nanoribbons in oxygen, carbon dioxide, water, and ammonia
We determine, by means of density functional theory, the stability and the
structure of graphene nanoribbon (GNR) edges in presence of molecules such as
oxygen, water, ammonia, and carbon dioxide. As in the case of
hydrogen-terminated nanoribbons, we find that the most stable armchair and
zigzag configurations are characterized by a non-metallic/non-magnetic nature,
and are compatible with Clar's sextet rules, well known in organic chemistry.
In particular, we predict that, at thermodynamic equilibrium, neutral GNRs in
oxygen-rich atmosphere should preferentially be along the armchair direction,
while water-saturated GNRs should present zigzag edges. Our results promise to
be particularly useful to GNRs synthesis, since the most recent and advanced
experimental routes are most effective in water and/or ammonia-containing
solutions.Comment: accepted for publication in PR
- …