282 research outputs found
Edge-functionalized and substitutional doped graphene nanoribbons: electronic and spin properties
Graphene nanoribbons are the counterpart of carbon nanotubes in
graphene-based nanoelectronics. We investigate the electronic properties of
chemically modified ribbons by means of density functional theory. We observe
that chemical modifications of zigzag ribbons can break the spin degeneracy.
This promotes the onset of a semiconducting-metal transition, or of an
half-semiconducting state, with the two spin channels having a different
bandgap, or of a spin-polarized half-semiconducting state -where the spins in
the valence and conduction bands are oppositely polarized. Edge
functionalization of armchair ribbons gives electronic states a few eV away
from the Fermi level, and does not significantly affect their bandgap. N and B
produce different effects, depending on the position of the substitutional
site. In particular, edge substitutions at low density do not significantly
alter the bandgap, while bulk substitution promotes the onset of
semiconducting-metal transitions. Pyridine-like defects induce a
semiconducting-metal transition.Comment: 12 pages, 5 figure
UV-B Physiological Changes Under Conditions of Distress and Eustress in Sweet Basil
UV-B radiation has been previously reported to induce protective or deleterious effects on plants depending on the UV-B irradiation doses. To elucidate how these contrasting events are physiologically coordinated, we exposed sweet basil plants to two UV-B doses: low (8.5 kJ m-2 day-1, 30 min exposure) and high (68 kJ m-2 day-1, 4 h exposure), with the plants given both doses once continuously in a single day. Physiological tests during and after both UV-B exposures were performed by comparing the stress-induced damage and adverse effects on photosynthetic activity, the concentration and composition of photosynthetic and non-photosynthetic pigments, and stress-related hormones biosynthesis in basil plants. Our results showed that upon receiving a high UV-B dose, a severe inactivation of oxygen evolving complex (OEC) activity at the PSII donor side and irreversible PSII photodamage caused primarily by limitation of the acceptor side occurred, which overloaded protective mechanisms and finally led to the death of the plants. In contrast, low UV-B levels did not induce any signs of UV-B stress injuries. The OEC partial limitation and the inactivation of the electron transport chain allowed the activation of photoprotective mechanisms, avoiding irreversible damage to PSII. Overall results indicate the importance of a specific response mechanisms regulating photoprotection vs irreversible photoinhibition in basil that were modulated depending on the UV-B doses
Parathyroidectomy for adults with primary hyperparathyroidism
© 2018 The Cochrane Collaboration. This is a protocol for a Cochrane Review (Intervention). The objectives are as follows: To assess the effects of parathyroidectomy for adults with PHPT. We will also compare the effects of different types of parathyroidectomy on people with PHPT.Published versio
Case report of an atypical early onset X-linked retinoschisis in monozygotic twins
Background: X-linked Retinoschisis (XLRS) is one of the most common macular degenerations in young males, with a worldwide prevalence ranging from 1:5000 to 1:20000. Clinical diagnosis of XLRS can be challenging due to the highly variable phenotypic presentation and limited correlation has been identified between mutation type and disease severity or progression.
Case presentation: We report the atypical early onset of XLRS in 3-month-old monozygotic twins. Fundus examination was characterized by severe bullous retinal schisis with pre-retinal and intraretinal haemorrhages. Molecular genetic analysis of the RS1 was performed and the c.288G > A (p. Trp96Ter) mutation was detected in both patients.
Conclusions: Early onset XLRS is associated with a more progressive form of the disease, characterized by large bullous peripheral schisis involving the posterior pole, vascular abnormalities and haemorrhages. The availability of specific technology permitted detailed imaging of the clinical picture of unusual cases of XLRS. The possible relevance of modifying genes should be taken into consideration for the future development of XLRS gene therapy
Interplay between edge states and simple bulk defects in graphene nanoribbons
We study the interplay between the edge states and a single impurity in a
zigzag graphene nanoribbon. We use tight-binding exact diagonalization
techniques, as well as density functional theory calculations to obtain the
eigenvalue spectrum, the eigenfunctions, as well the dependence of the local
density of states (LDOS) on energy and position. We note that roughly half of
the unperturbed eigenstates in the spectrum of the finite-size ribbon hybridize
with the impurity state, and the corresponding eigenvalues are shifted with
respect to their unperturbed values. The maximum shift and hybridization occur
for a state whose energy is inverse proportional to the impurity potential;
this energy is that of the impurity peak in the DOS spectrum. We find that the
interference between the impurity and the edge gives rise to peculiar
modifications of the LDOS of the nanoribbon, in particular to oscillations of
the edge LDOS. These effects depend on the size of the system, and decay with
the distance between the edge and the impurity.Comment: 10 pages, 15 figures, revtex
Optical properties and charge-transfer excitations in edge-functionalized all-graphene nanojunctions
We investigate the optical properties of edge-functionalized graphene
nanosystems, focusing on the formation of junctions and charge transfer
excitons. We consider a class of graphene structures which combine the main
electronic features of graphene with the wide tunability of large polycyclic
aromatic hydrocarbons. By investigating prototypical ribbon-like systems, we
show that, upon convenient choice of functional groups, low energy excitations
with remarkable charge transfer character and large oscillator strength are
obtained. These properties can be further modulated through an appropriate
width variation, thus spanning a wide range in the low-energy region of the
UV-Vis spectra. Our results are relevant in view of designing all-graphene
optoelectronic nanodevices, which take advantage of the versatility of
molecular functionalization, together with the stability and the electronic
properties of graphene nanostructures.Comment: J. Phys. Chem. Lett. (2011), in pres
On the nature of Delta Scuti star HD 115520
Observing Delta Scuti stars is most important as their multi-frequency
spectrum of radial pulsations provide strong constraints on the physics of the
stars interior; so any new detection and observation of these stars is a
valuable contribution to asteroseismology. While performing uvby-beta
photoelectric photometry of some RR Lyrae stars acquired in 2005 at the
Observatorio Astronomico Nacional, Mexico, we also observed several standard
stars, HD115520 among them. After the reduction this star showed indications of
variability. In view of this, a new observing run was carried out in 2006
during which we were able to demonstrate its variability and its nature as a
Delta Scuti star. New observations in 2007 permitted us to determine its
periodic content with more accuracy. This, along with the uvby-beta
photoelectric photometry allowed us to deduce its physical characteristics and
pulsational modes.Comment: 6 pages. To be published in Journal of Physics: Conference Series.
Proc. of the workshop Helioseismology, Asteroseismology and MHD Connections
held in Gottingen, Germany, 20-24 August 200
The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the extended Baryon Oscillation Spectroscopic Survey and from the second phase of the Apache Point Observatory Galactic Evolution Experiment
The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in
operation since July 2014. This paper describes the second data release from
this phase, and the fourteenth from SDSS overall (making this, Data Release
Fourteen or DR14). This release makes public data taken by SDSS-IV in its first
two years of operation (July 2014-2016). Like all previous SDSS releases, DR14
is cumulative, including the most recent reductions and calibrations of all
data taken by SDSS since the first phase began operations in 2000. New in DR14
is the first public release of data from the extended Baryon Oscillation
Spectroscopic Survey (eBOSS); the first data from the second phase of the
Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2),
including stellar parameter estimates from an innovative data driven machine
learning algorithm known as "The Cannon"; and almost twice as many data cubes
from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous
release (N = 2812 in total). This paper describes the location and format of
the publicly available data from SDSS-IV surveys. We provide references to the
important technical papers describing how these data have been taken (both
targeting and observation details) and processed for scientific use. The SDSS
website (www.sdss.org) has been updated for this release, and provides links to
data downloads, as well as tutorials and examples of data use. SDSS-IV is
planning to continue to collect astronomical data until 2020, and will be
followed by SDSS-V.Comment: SDSS-IV collaboration alphabetical author data release paper. DR14
happened on 31st July 2017. 19 pages, 5 figures. Accepted by ApJS on 28th Nov
2017 (this is the "post-print" and "post-proofs" version; minor corrections
only from v1, and most of errors found in proofs corrected
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