89 research outputs found
Electron spectroscopy of carbon materials: Experiment and theory
We present a comparative spectroscopic study of carbon as graphite, diamond and C60 using C1s K-edge electron energy-loss spectroscopy (EELS), X-ray emission spectroscopy, and theoretical modelling. The first principles calculations of these spectra are obtained in the local density approximation using a self-consistent Gaussian basis pseudo-potential method. Calculated spectra show excellent agreement with experiment and are able to discriminate not only between various carbon hybridisations but also local variation in environment. Core-hole effects on the calculated spectra are also investigated. For the first time, the EEL spectrum of carbyne is calculated
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Necrosis grasa subcutánea múltiple: correlación ecográficohistopatológica. Multiple encapsulated fat necrosis: histopathological relation to ultrasound findings
Encapsulated fat necrosis is a benign entity that has multiple possible conditions in the differential diagnosis. Because of this, the ultrasound and histological studies become highly relevant. We present a 14-year-old boy with this condition who exhibited numerous nodules that were detected after an intentional weight loss of 20kg. The ultrasound and histopathological examinations were necessary to confirm the diagnosis. Even though there is not a clear traumatic record in all cases, trauma constitutes the main hypothesis for its development, by decreasing the blood supply to the adipose tissue lobules and causing subsequent ischemic necrosis. Similar lesions have been described in the omentum and in the breast after surgical procedures or invasive diagnostic tests. In the ultrasound study, at least three presentation patterns have been described, which might match the three histological states, from early fat tissue degeneration to ultimate necrosis and even calcification. It is important to know the clinical characteristics, the ultrasound patterns, and the histological findings of this condition for an accurate diagnosis
Interstellar oxygen along the line of sight of Cygnus X-2
Interstellar dust permeates our Galaxy and plays an important role in many
physical processes in the diffuse and dense regions of the interstellar medium.
High-resolution X-ray spectroscopy, coupled with modelling based on laboratory
dust measurements, provides a unique probe to investigate the interstellar dust
properties along our line of sight towards Galactic X-ray sources. Here, we
focus on the oxygen content of the interstellar medium through its absorption
features in the X-ray spectra. To model the dust features, we perform a
laboratory experiment using the electron microscope facility located at the
University of Cadiz in Spain, where we acquire new laboratory data in the
oxygen K-edge. We study 18 dust samples of silicates and oxides with different
chemical compositions. The laboratory measurements are adopted for our
astronomical data analysis. We carry out a case study on the X-ray spectrum of
the bright low-mass X-ray binary Cygnus X-2, observed by XMM-Newton. We
determine different temperature phases of the ISM, and parameterize oxygen in
both gas (neutral and ionised) and dust form. We find Solar abundances of
oxygen along the line of sight towards the source. Due to both the relatively
low depletion of oxygen into dust form and the shape of the oxygen cross
section profiles, it is challenging to determine the precise chemistry of
interstellar dust. However, silicates provide an acceptable fit. Finally, we
discuss the systematic discrepancies in the atomic (gaseous phase) data of the
oxygen edge spectral region using different X-ray atomic databases, and also
consider future prospects for studying the ISM with the Arcus concept mission.Comment: Accepted for publication in A&A, 15 pages, 11 figure
Chemically active substitutional nitrogen impurity in carbon nanotubes
We investigate the nitrogen substitutional impurity in semiconducting zigzag
and metallic armchair single-wall carbon nanotubes using ab initio density
functional theory. At low concentrations (less than 1 atomic %), the defect
state in a semiconducting tube becomes spatially localized and develops a flat
energy level in the band gap. Such a localized state makes the impurity site
chemically and electronically active. We find that if two neighboring tubes
have their impurities facing one another, an intertube covalent bond forms.
This finding opens an intriguing possibility for tunnel junctions, as well as
the functionalization of suitably doped carbon nanotubes by selectively forming
chemical bonds with ligands at the impurity site. If the intertube bond density
is high enough, a highly packed bundle of interlinked single-wall nanotubes can
form.Comment: 4 pages, 4 figures; major changes to the tex
BN domains included into carbon nanotubes: role of interface
We present a density functional theory study on the shape and arrangement of
small BN domains embedded into single-walled carbon nanotubes. We show a strong
tendency for the BN hexagons formation at the simultaneous inclusion of B and N
atoms within the walls of carbon nanotubes. The work emphasizes the importance
of a correct description of the BN-C frontier. We suggest that BN-C interface
will be formed preferentially with the participation of N-C bonds. Thus, we
propose a new way of stabilizing the small BN inclusions through the formation
of nitrogen terminated borders. The comparison between the obtained results and
the available experimental data on formation of BN plackets within the single
walled carbon nanotubes is presented. The mirror situation of inclusion of
carbon plackets within single walled BN nanotubes is considered within the
proposed formalism. Finally, we show that the inclusion of small BN plackets
inside the CNTs strongly affects the electronic character of the initial
systems, opening a band gap. The nitrogen excess in the BN plackets introduces
donor states in the band gap and it might thus result in a promising way for
n-doping single walled carbon nanotubes
Atomic Configuration of Nitrogen Doped Single-Walled Carbon Nanotubes
Having access to the chemical environment at the atomic level of a dopant in
a nanostructure is crucial for the understanding of its properties. We have
performed atomically-resolved electron energy-loss spectroscopy to detect
individual nitrogen dopants in single-walled carbon nanotubes and compared with
first principles calculations. We demonstrate that nitrogen doping occurs as
single atoms in different bonding configurations: graphitic-like and
pyrrolic-like substitutional nitrogen neighbouring local lattice distortion
such as Stone-Thrower-Wales defects. The stability under the electron beam of
these nanotubes has been studied in two extreme cases of nitrogen incorporation
content and configuration. These findings provide key information for the
applications of these nanostructures.Comment: 25 pages, 13 figure
High speed e-beam writing for large area photonic nanostructures-a choice of parameters
Photonic nanostructures are used for many optical systems and applications. However, some high-end applications require the use of electron-beam lithography (EBL) to generate such nanostructures. An important technological bottleneck is the exposure time of the EBL systems, which can exceed 24 hours per 1 cm2. Here, we have developed a method based on a target function to systematically increase the writing speed of EBL. As an example, we use as the target function the fidelity of the Fourier Transform spectra of nanostructures that are designed for thin film light trapping applications, and optimize the full parameter space of the lithography process. Finally, we are able to reduce the exposure time by a factor of 5.5 without loss of photonic performance. We show that the performances of the fastest written structures are identical to the original ones within experimental error. As the target function can be varied according to different purposes, the method is also applicable to guided mode resonant grating and many other areas. These findings contribute to the advancement of EBL and point towards making the technology more attractive for commercial applications
Modelos de crecimiento y producción en España: historia, ejemplos contemporáneos y perspectivas
En el presente trabajo se presenta una revisión sobre los modelos forestales desarrollados en España durante los últimos años, tanto para la producción maderable como no maderable y, para la dinámica de los bosques (regeneración, mortalidad). Se presentan modelos tanto de rodal completo como de clases diamétricas y de árbol individual. Los modelos desarrollados hasta la fecha se han desarrollado a partir de datos procedentes de parcelas permanentes, ensayos y el Inventario Forestal Nacional. En el trabajo se muestran los diferentes submodelos desarrollados hasta la fecha, así como las plataformas informáticas que permiten utilizar dichos modelos. Se incluyen las principales perspectivas
de desarrollo de la modelización forestal en España.In this paper we present a review of forest models developed in Spain in recent years for both timber and non timber production and forest dynamics (regeneration, mortality). Models developed are whole stand, size (diameter) class and individual-tree. The models developed to date have been developed using data from permanent plots, experimental
sites and the National Forest Inventory. In this paper we show the different sub-models developed so far and the friendly use software. Main perspectives of forest modeling in Spain are presented.The models described in this paper were funded by
different regional, national and European projects, and
some of them were elaborated by the authors. This
work was funded by the Spanish Government by the
SELVIRED network (code AGL2008-03740) and the
strategic project «Restauración y Gestión Forestal»
(code PSE-310000-2009-4)
Modélisation de la qualité des stations et de la croissance individuelle des arbres dans des peuplements purs et mélangés de Pinus brutia dans le nord-est de la Grèce
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