1,828 research outputs found
Universal Rashba Spin Precession of Two-Dimensional Electrons and Holes
We study spin precession due to Rashba spin splitting of electrons and holes
in semiconductor quantum wells. Based on a simple analytical expression that we
derive for the current modulation in a broad class of experimental situations
of ferromagnet/nonmagnetic semiconductor/ferromagnet hybrid structures, we
conclude that the Datta-Das spin transistor (i) is feasible with holes and (ii)
its functionality is not affected by integration over injection angles. The
current modulation shows a universal oscillation period, irrespective of the
different forms of the Rashba Hamiltonian for electrons and holes. The analytic
formulas approximate extremely well exact numerical calculations of a more
elaborate Kohn--Luttinger model.Comment: 7 pages, 2 eps figures included, minor change
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
Short communication: Study on epilithic diatoms in the Kozluk Creek (Arapgir-Malatya, Turkey)
Being the most important members of phytoplankton and phytobenthos, both of which are the primary producers of surface water resources, algae play a very important role in the biological productivity of waters with their oxygen production through photosynthesis and they synthesize the organic materials. Furthermore, with their high levels of protein, algae are used as human and animal food as well as being used in the production of organic fertilizers and organic vitamins. Another reason for algae currently being among the most researched organisms is their easy and inexpensive productions in culture media. With the recognition of the importance of algae in standing waters and streams, the number of studies conducted on these organisms has rapidly increased. In Turkey, the number of studies on algae in streamsis quite high [(Altuner and Gurbuz (1989), Altuner and Gurbuz (1991) Yıldız (1991) , Yildiz and Ozkiran (1994), Ertan and Morkoyunlu (1998), Sahin (1998), Cetin and Yavuz (2001), Solak et al. (2012), Sivaci and Dere (2007), Mumcu et al. (2009), Pala and Caglar (2008)]
Protective effects of curcumin and vitamin E on carbon tetrachloride-induced nephrotoxicity in rats
The present investigation reports the protective effects of curcumin (CMN) and vitamin E against CCl4 induced oxidative stress and nephrotoxicity in rats. The toxicant CCl4 was used to induce nephrotoxicity at a dose of 1 ml/kg as 1:1(v/v) mixture with liquid paraffin twice
weekly for 8 weeks. Plasma total protein, albumin, urea and creatinine concentrations were measured to assess the renal function. Antioxidant status in the kidney was estimated by determining the activities of glutathione peroxidase (GPx), glutathione reductase (GR), glutathione-S-transferase (GST), catalase (CAT) and superoxide dismutase (SOD) as well as by histopathological examination. CCl4 caused elevated levels of urea and creatinine while it decreased levels of total protein and albumin in plasma. Furthermore, CCl4 treated rats showed marked depletion of renal endogenous antioxidant enzymes. Oral administration of curcumin (100 mg/kg, daily for 8 weeks) and in combination with vitamin E (three times weekly for 8 weeks) showed significantly attenuated renal dysfunction by increased activity of antioxidant
enzymes in kidney. It also increased the concentrations of plasma total protein and albumin, while reducing the concentration of urea and creatinine. Kidney sections of CCl4 induced rats showed deleterious alterations in micro anatomy. However, curcumin and vitamin E treatment prevented kidney damage induced by CCl4. This study reveals that curcumin in combination with vitamin E possesses strong antioxidant and kidney protective activity compared to curcumin alone
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
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
Local Density of States in Mesoscopic Samples from Scanning Gate Microscopy
We study the relationship between the local density of states (LDOS) and the
conductance variation in scanning-gate-microscopy experiments on
mesoscopic structures as a charged tip scans above the sample surface. We
present an analytical model showing that in the linear-response regime the
conductance shift is proportional to the Hilbert transform of the
LDOS and hence a generalized Kramers-Kronig relation holds between LDOS and
. We analyze the physical conditions for the validity of this
relationship both for one-dimensional and two-dimensional systems when several
channels contribute to the transport. We focus on realistic Aharonov-Bohm rings
including a random distribution of impurities and analyze the LDOS-
correspondence by means of exact numerical simulations, when localized states
or semi-classical orbits characterize the wavefunction of the system.Comment: 8 pages, 8 figure
Formation of quantum dots in the potential fluctuations of InGaAs heterostructures probed by scanning gate microscopy
The disordered potential landscape in an InGaAs/InAlAs two-dimensional
electron gas patterned into narrow wires is investigated by means of scanning
gate microscopy. It is found that scanning a negatively charged tip above
particular sites of the wires produces conductance oscillations that are
periodic in the tip voltage. These oscillations take the shape of concentric
circles whose number and diameter increase for more negative tip voltages until
full depletion occurs in the probed region. These observations cannot be
explained by charging events in material traps, but are consistent with Coulomb
blockade in quantum dots forming when the potential fluctuations are raised
locally at the Fermi level by the gating action of the tip. This interpretation
is supported by simple electrostatic simulations in the case of a disorder
potential induced by ionized dopants. This work represents a local
investigation of the mechanisms responsible for the disorder-induced
metal-to-insulator transition observed in macroscopic two-dimensional electron
systems at low enough density
Non-local Andreev transport through an interacting quantum dot
We investigate sub-gap transport through a single-level quantum dot tunnel
coupled to one superconducting and two normal-conducting leads. Despite the
tendency of a large charging energy to suppress the equilibrium proximity
effect, a finite Andreev current through the dot can be achieved in
non-equilibrium situations. We propose two schemes to identify non-local
Andreev transport. In one of them, the presence of strong Coulomb interaction
leads to negative values of the non-local conductance as a clear signal of
non-local Andreev transport.Comment: 5 pages, 4 figure
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