3,475 research outputs found
Impurities and electronic localization in graphene bilayers
We analyze the electronic properties of bilayer graphene with Bernal stacking
and a low concentration of adatoms. Assuming that the host bilayer lies on top
of a substrate, we consider the case where impurities are adsorbed only on the
upper layer. We describe non-magnetic impurities as a single orbital hybridized
with carbon's pz states. The effect of impurity doping on the local density of
states with and without a gated electric field perpendicular to the layers is
analyzed. We look for Anderson localization in the different regimes and
estimate the localization length. In the biased system, the field induced gap
is partially filled by strongly localized impurity states. Interestingly, the
structure, distribution and localization length of these states depend on the
field polarization.Comment: 7 pages, 6 figure
Tuning the proximity effect in a superconductor-graphene-superconductor junction
We have tuned in situ the proximity effect in a single graphene layer coupled
to two Pt/Ta superconducting electrodes. An annealing current through the
device changed the transmission coefficient of the electrode/graphene
interface, increasing the probability of multiple Andreev reflections. Repeated
annealing steps improved the contact sufficiently for a Josephson current to be
induced in graphene.Comment: Accepted for publication in Phys. Rev.
Bilayer graphene under pressure: Electron-hole Symmetry Breaking, Valley Hall Effect, and Landau Levels
The electronic structure of bilayer graphene under pressure develops very
interesting features with an enhancement of the trigonal warping and a
splitting of the parabolic touching bands at the K point of the reciprocal
space into four Dirac cones, one at K and three along the T symmetry lines. As
pressure is increased, these cones separate in reciprocal space and in energy,
breaking the electron-hole symmetry. Due to their energy separation, their
opposite Berry curvature can be observed in valley Hall effect experiments and
in the structure of the Landau levels. Based on the electronic structure
obtained by Density Functional Theory, we develop a low energy Hamiltonian that
describes the effects of pressure on measurable quantities such as the Hall
conductivity and the Landau levels of the system.Comment: 11 pages, 9 figure
Supersymmetry of FRW barotropic cosmologies
Barotropic FRW cosmologies are presented from the standpoint of
nonrelativistic supersymmetry. First, we reduce the barotropic FRW system of
differential equations to simple harmonic oscillator differential equations.
Employing the factorization procedure, the solutions of the latter equations
are divided into the two classes of bosonic (nonsingular) and fermionic
(singular) cosmological solutions. We next introduce a coupling parameter
denoted by K between the two classes of solutions and obtain barotropic
cosmologies with dissipative features acting on the scale factors and spatial
curvature of the universe. The K-extended FRW equations in comoving time are
presented in explicit form in the low coupling regime. The standard barotropic
FRW cosmologies correspond to the dissipationless limit K =0Comment: 6 page
Radiation Induced Membrane Changes and Programmed Cell Death: Possible Interrelationships
A short review of the evidence that lymphocyte membranes are a target for the initiation of irradiation induced programmed cell death (PCD) is given. It is assumed that for lymphocytes PCD represents an essential physiological mechanism in order to prevent degeneration of the biological system involved. Initiation of PCD can be obtained by a pharmacological activation as well as with irradiation. In both cases, protein kinase-C (PKC) is involved in the signal transduction from the cellular membrane to the nucleus where, by means of a metabolically active process, DNA fragmentation is induced. It is hypothesized that processes connected to lipid peroxidation in the cell membrane constitute a primary effect of irradiation induced PCD, where membrane fluidization or a compensatory process aimed to the maintenance of membrane fluidity (membrane homeoviscosity hypothesis) are likely to be involved
Measurements of Stellar Inclinations for Kepler Planet Candidates II: Candidate Spin-Orbit Misalignments in Single and Multiple-Transiting Systems
We present a test for spin-orbit alignment for the host stars of 25 candidate
planetary systems detected by the {\it Kepler} spacecraft. The inclination
angle of each star's rotation axis was estimated from its rotation period,
rotational line broadening, and radius. The rotation periods were determined
using the {\it Kepler} photometric time series. The rotational line broadening
was determined from high-resolution optical spectra with Subaru/HDS. Those same
spectra were used to determine the star's photospheric parameters (effective
temperature, surface gravity, metallicity) which were then interpreted with
stellar-evolutionary models to determine stellar radii. We combine the new
sample with the 7 stars from our previous work on this subject, finding that
the stars show a statistical tendency to have inclinations near 90, in
alignment with the planetary orbits. Possible spin-orbit misalignments are seen
in several systems, including three multiple-planet systems (KOI-304, 988,
2261). Ideally these systems should be scrutinized with complementary
techniques---such as the Rossiter-McLaughlin effect, starspot-crossing
anomalies or asteroseismology---but the measurements will be difficult owing to
the relatively faint apparent magnitudes and small transit signals in these
systems.Comment: 11 pages, 9 figures, accepted for publication in Ap
Polymeric templating synthesis of anatase TiOâ‚‚ nanoparticles from low-cost inorganic titanium sources
A novel facile and cost-effective synthesis method for anatase TiOâ‚‚ nanoparticles has been developed by using poly-acrylic acid hydrogel as template at room temperature. The newly developed synthesis method avoids the use of hazardous reagents and/or hydrothermal steps, and enables production of highly active TiOâ‚‚ nanoparticles from low cost inorganic titanium sources. The synthesized TiOâ‚‚ nanoparticles have been studied in several applications including dye-sensitized solar cells as a photoanode as well as in organics degradation of methyl orange in aqueous media. Good photocatalytic performances were obtained in both applications
Influence of water deficits on grape berry growth
The effects of early and late water deficits on pericarp cell division and enlargement of Syrah berries (Vitis vinifera L.) was determined by DNA extraction and quantification. Different periods and different levels of water deficit were applied between anthesis and maturity to grapevines growing under controlled water supply in two consecutive years. DNA extraction profiles showed that water deficit did not affect cell division. Reduction of berry size and berry weight was caused exclusively by a decrease of pericarp volume, independent of the intensity of the water deficit or the stage of berry development. Decreased cell volume as a result of an early water deficit from flowering to veraison was irreversible. These results support the hypothesis that early water deficits modify the structural properties of the cell components and consequently cell wall extensibility, thereby limiting the subsequent enlargement of pericarp cells.
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