493 research outputs found
Deep anterior lamellar keratoplasty for keratoconus: Elements for success
Advanced keratoconus may require keratoplasty when the patient can no longer achieve functional vision with glasses and contact lenses. Deep anterior lamellar keratoplasty (DALK) has become the surgical treatment of choice due to its undisputed advantages over penetrating keratoplasty including the reduced risk of intraoperative complications, the absence of endothelial immune rejection, and the longer graft survival. Albeit "big-bubble" DALK still represents the most popular surgical method, several modifications have been developed over the years. This allowed standardization of the technique, with improved success rates and clinical outcomes. This review presents an overview on the literature on DALK surgery for keratoconus. We discuss state-of-the art surgical techniques, current evidence on the clinical outcomes and complications as well as possible future directions
Carrier density dependence of 1/f noise in graphene explained as a result of the interplay between band-structure and inhomogeneities
http://www.gianlucafiori.org/articles/jstat_noise.pdf
We present a model for 1/f noise in graphene based on an analysis of the effect of charge trapping and detrapping events on the fluctuations of the number of charge carriers. Inclusion of a Gaussian distribution of fluctuations of the electrostatic potential enables us to reproduce all the various experimentally observed behaviors of the flicker noise power spectral density as a function of carrier density, both for monolayer and bilayer graphene. The key feature of a flicker noise minimum at the Dirac point that appears in bilayer graphene and sometimes also in monolayer graphene is explained in terms of the disappearance, when the number of electrons equals that of holes, of the carrier number fluctuations induced by trapping events. Such a disappearance is analyzed with two different approaches, in order to gain a better understanding of the physical origin of the effect, and to make some considerations about possible analogous phenomena in other semiconductors
A molecular state of correlated electrons in a quantum dot
Correlation among particles in finite quantum systems leads to complex
behaviour and novel states of matter. One remarkable example is predicted to
occur in a semiconductor quantum dot (QD) where at vanishing density the
Coulomb correlation among electrons rigidly fixes their relative position as
that of the nuclei in a molecule. In this limit, the neutral few-body
excitations are roto-vibrations, which have either rigid-rotor or
relative-motion character. In the weak-correlation regime, on the contrary, the
Coriolis force mixes rotational and vibrational motions. Here we report
evidence of roto-vibrational modes of an electron molecular state at densities
for which electron localization is not yet fully achieved. We probe these
collective modes by inelastic light scattering in QDs containing four
electrons. Spectra of low-lying excitations associated to changes of the
relative-motion wave function -the analogues of the vibration modes of a
conventional molecule- do not depend on the rotational state represented by the
total angular momentum. Theoretical simulations via the
configuration-interaction (CI) method are in agreement with the observed
roto-vibrational modes and indicate that such molecular excitations develop at
the onset of short-range correlation.Comment: PDF file only; 24 pages, 7 figures, 2 table. Supplementary
Information include
Molecular study on Senecio fontanicola (S. doria group, Asteraceae) and its conservation status
Senecio fontanicola is endemic to black-bog-rush fens of southern Austria, north-western Slovenia and north-eastern Italy. It is characterized by oblanceolate leaves, a low number of supplementary bracts and glabrous achenes and it grows in marshy spring areas, fens and reed beds, between elevations from 20 to 850 m . The species was never described with molecular traits and during the last decades, S. fontanicola showed a dramatic decline due to land reclamation for agriculture. Therefore, the present study aims to characterize S. fontanicola using the molecular barcoding technique and to updated its distribution to propose a global risk category for the species, based on IUCN criteria. The three molecular markers used in this study (trnH-psbA, rbcL, and ITS) clearly distinguished S. fontanicola from S. doria. s.s.and the revised distribution allowed the definition of the conservation status of the species, that is Endangered-EN B2ab(i,ii,iii,iv) following the B criterion of the IUCN guidelines
Molecular study on Senecio fontanicola (S. doria group, Asteraceae) and its conservation status
Senecio fontanicola is endemic to black-bog-rush fens of southern Austria, north-western Slovenia and north-eastern Italy. It is characterized by oblanceolate leaves, a low number of supplementary bracts and glabrous achenes and it grows in marshy spring areas, fens and reed beds, between elevations from 20 to 850 m . The species was never described with molecular traits and during the last decades, S. fontanicola showed a dramatic decline due to land reclamation for agriculture. Therefore, the present study aims to characterize S. fontanicola using the molecular barcoding technique and to updated its distribution to propose a global risk category for the species, based on IUCN criteria. The three molecular markers used in this study (trnH-psbA, rbcL, and ITS) clearly distinguished S. fontanicola from S. doria. s.s.and the revised distribution allowed the definition of the conservation status of the species, that is Endangered-EN B2ab(i,ii,iii,iv) following the B criterion of the IUCN guidelines
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