2,693 research outputs found
Superconducting proximity effect in interacting double-dot systems
We study subgap transport from a superconductor through a double quantum dot
with large on-site Coulomb repulsion to two normal leads. Non-local
superconducting correlations in the double dot are induced by the proximity to
the superconducting lead, detectable in non-local Andreev transport that splits
Cooper pairs in locally separated, spin-entangled electrons. We find that the
-- characteristics are strongly asymmetric: for a large bias voltage of
certain polarity, transport is blocked by populating the double dot with states
whose spin symmetry is incompatible with the superconductor. Furthermore, by
tuning gate voltages one has access to splitting of the Andreev excitation
energies, which is visible in the differential conductance.Comment: 5 pages, 4 figure
Effect of dephasing on the current statistics of mesoscopic devices
We investigate the effects of dephasing on the current statistics of
mesoscopic conductors with a recently developed statistical model, focusing in
particular on mesoscopic cavities and Aharonov-Bohm rings. For such devices, we
analyze the influence of an arbitrary degree of decoherence on the cumulants of
the current. We recover known results for the limiting cases of fully coherent
and totally incoherent transport and are able to obtain detailed information on
the intermediate regime of partial coherence for a varying number of open
channels. We show that dephasing affects the average current, shot noise, and
higher order cumulants in a quantitatively and qualitatively similar way, and
that consequently shot noise or higher order cumulants of the current do not
provide information on decoherence additional or complementary to what can be
already obtained from the average current.Comment: 4 pages, 4 figure
Mitochondrial DNA lineages of Italian Giara and Sarcidano horses
Giara and Sarcidano are 2 of the 15 extant native Italian horse breeds with limited dispersal capability that originated from a larger number of individuals. The 2 breeds live in two distinct isolated locations on the island of Sardinia. To determine the genetic structure and evolutionary history of these 2 Sardinian breeds, the first hypervariable segment of the mitochondrial DNA (mtDNA) was sequenced and analyzed in 40 Giara and Sarcidano horses and compared with publicly available mtDNA data from 43 Old World breeds. Four different analyses, including genetic distance, analysis of molecular variance, haplotype sharing, and clustering methods, were used to study the genetic relationships between the Sardinian and other horse breeds. The analyses yielded similar results, and the FST values indicated that a high percentage of the total genetic variation was explained by between-breed differences. Consistent with their distinct phenotypes and geographic isolation, the two Sardinian breeds were shown to consist of 2 distinct gene pools that had no gene flow between them. Giara horses were clearly separated from the other breeds examined and showed traces of ancient separation from horses of other breeds that share the same mitochondrial lineage. On the other hand, the data from the Sarcidano horses fit well with variation among breeds from the Iberian Peninsula and North-West Europe: genetic relationships among Sarcidano and the other breeds are consistent with the documented history of this breed
Modelling a cell tower using SFM: automated detection of structural elements from skeleton extraction on a point cloud
The surveying and management of telecommunication towers poses a series of engineering challenges. Not only they must be regularly inspected for the purpose of checking for issues that require maintenance interventions, but they are often sub-let by their owners to communication companies, requiring a survey of the many (several thousand per company) installed appliances to check that they respect the established contracts. This requires a surveying methodology that is fast and possibly automated. Photogrammetric techniques using UAV-mounted cameras seem to offer a solution that is both suitable and economical. Our research team was asked to evaluate whether, from the information acquired by small drones it was possible to obtain geometric information on the structure, with what degree of accuracy and what level of detail. The workflow of this process is naturally articulated in three steps: the acquisition, the construction of the point cloud, and the extraction of geometries. The case study is a tower carrying antennas owned by several operators and placed in the industrial district of Cagliari. The article examines the problems found in modelling such structures using point clouds derived from the Structure-from-Motion technique, in order to obtain a model of nodes and beams suitable for the reconstruction of the structure's geometric elements, and possibly for a finite elements analysis or for populating GIS and BIM, either automatically or with minimal user intervention. In order to achieve this, we have used voxelization and skeleton extraction algorithms to obtain a 3D graph of the structure. The analysis of the results was carried out by varying the parameters relating to the voxel size, which defines the resolution, and the density of the points contained inside each voxel
Catching VY Sculptoris in a low state
Context. In the context of a large campaign to determine the system
parameters of high mass transfer cataclysmic variables, we found VY Scl in a
low state in 2008. Aims. Making use of this low state, we study the stellar
components of the binary with little influence of the normally dominating
accretion disc. Methods. Time-resolved spectroscopy and photometry of VY Scl
taken during the low state are presented. We analysed the light-curve and
radial velocity curve and use time-resolved spectroscopy to calculate Doppler
maps of the dominant emission lines. Results. The spectra show narrow emission
lines of Halpha, Hbeta, HeI, NaID, and FeII, as well as faint TiO absorption
bands that trace the motion of the irradiated secondary star, and Halpha and
HeI emission line wings that trace the motion of the white dwarf. From these
radial velocities, we find an orbital period of 3.84 h, and put constraints on
binary parameters such as the mass ratio M2/M1 of 0.43 and the inclination of
15 deg. With a secondary's mass between 0.3 and 0.35 Msol, we derive the mass
for the white dwarf as M1 = 0.6-0.1 Msol.Comment: 8 pages, 9 figures, accepted for publication in A&
Statistical model of dephasing in mesoscopic devices introduced in the scattering matrix formalism
We propose a phenomenological model of dephasing in mesoscopic transport,
based on the introduction of random phase fluctuations in the computation of
the scattering matrix of the system. A Monte Carlo averaging procedure allows
us to extract electrical and microscopic device properties. We show that, in
this picture, scattering matrix properties enforced by current conservation and
time reversal invariance still hold. In order to assess the validity of the
proposed approach, we present simulations of conductance and magnetoconductance
of Aharonov-Bohm rings that reproduce the behavior observed in experiments, in
particular as far as aspects related to decoherence are concerned.Comment: 6 pages, 6 figure
Omnidirectional and broadband absorption enhancement from trapezoidal Mie resonators in semiconductor metasurfaces
Light trapping in planar ultrathin-film solar cells is limited due to a small
number of optical modes available in the thin-film slab. A nanostructured
thin-film design could surpass this limit by providing broadband increase in
the local density of states in a subwavelength volume and maintaining efficient
coupling of light. Here we report a broadband metasurface design, enabling
efficient and broadband absorption enhancement by direct coupling of incoming
light to resonant modes of subwavelength-scale Mie nanoresonators defined in
the thin-film active layer. Absorption was investigated both theoretically and
experimentally in prototypes consisting of lithographically patterned,
two-dimensional periodic arrays of silicon nanoresonators on silica substrates.
A crossed trapezoid resonator shape of rectangular cross section is used to
excite broadband Mie resonances across the visible and near-IR spectra. Our
numerical simulations, optical absorption measurements and photocurrent
spectral response measurements demonstrate that crossed trapezoidal Mie
resonant structures enable angle-insensitive, broadband absorption. A short
circuit current density of 12.0 mA/cm2 is achieved in 210 nm thick patterned Si
films, yielding a 4-fold increase compared to planar films of the same
thickness. It is suggested that silicon metasurfaces with Mie resonator arrays
can provide useful insights to guide future ultrathin-film solar cell designs
incorporating nanostructured thin active layers.Comment: 15 pages, 5 figure
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