680 research outputs found
Spectrophotometry of planets, asteroids and satellites from the international ultraviolet explorer satellite
A total of 14 8 hour I.U.E. observing sessions resulted in 39 spectra of 11 asteroids and 9 solar type stars as well as 57 spectra at various locations on the disk of Jupiter. The Jupiter observations include a total of 5 center to limb series of spectra at various latitudes and a North South series along the central meridian. In the range from 2000-3000 A, the planet shows a striking decrease in brightness at latitudes greater than about 30 degrees, and exhibits limb brightening at low latitudes and limb darkening at high latitudes. Preliminary results indicate that about 6 km-amagats of clean hydrogen are required above a haze of absorbing aerosols to reproduce the limb brightening observed at 2500 A in the equatorial regions. At higher latitudes, the aerosols extend to even higher levels of the atmosphere. Comparison of the Jovian data with detailed model calculations and the analyses of the asteroid spectra are still in progress with other support
Kondo effect near the Van Hove singularity in biased bilayer graphene
Magnetic impurity adsorbed on one of the carbon planes of a bilayer graphene
is studied. The formation of the many-body SU(2) and SU(4) resonances close to
the bandgap is analyzed within the mean field Kotliar-Ruckenstein slave boson
approach. Impact of enhanced hybridization and magnetic instability of bilayer
doped near the Van Hove singularity on the screening of magnetic moment is
discussed.Comment: 10 pages, 8 figure
Interference effects in electronic transport through metallic single-wall carbon nanotubes
In a recent paper Liang {\it et al.} [Nature {\bf 411}, 665 (2001)] showed
experimentally, that metallic nanotubes, strongly coupled to external
electrodes, may act as coherent molecular waveguides for electronic transport.
The experimental results were supported by theoretical analysis based on the
scattering matrix approach. In this paper we analyze theoretically this problem
using a real-space approach, which makes it possible to control quality of
interface contacts. Electronic structure of the nanotube is taken into account
within the tight-binding model. External electrodes and the central part
(sample) are assumed to be made of carbon nanotubes, while the contacts between
electrodes and the sample are modeled by appropriate on-site (diagonal) and
hopping (off-diagonal) parameters. Conductance is calculated by the Green
function technique combined with the Landauer formalism. In the plots
displaying conductance {\it vs.} bias and gate voltages, we have found typical
diamond structure patterns, similar to those observed experimentally. In
certain cases, however, we have found new features in the patterns, like a
double-diamond sub-structure.Comment: 15 pages, 4 figures. To apear in Phys. Rev.
The Kondo effect in ferromagnetic atomic contacts
Iron, cobalt and nickel are archetypal ferromagnetic metals. In bulk,
electronic conduction in these materials takes place mainly through the and
electrons, whereas the magnetic moments are mostly in the narrow
-electron bands, where they tend to align. This general picture may change
at the nanoscale because electrons at the surfaces of materials experience
interactions that differ from those in the bulk. Here we show direct evidence
for such changes: electronic transport in atomic-scale contacts of pure
ferromagnets (iron, cobalt and nickel), despite their strong bulk
ferromagnetism, unexpectedly reveal Kondo physics, that is, the screening of
local magnetic moments by the conduction electrons below a characteristic
temperature. The Kondo effect creates a sharp resonance at the Fermi energy,
affecting the electrical properties of the system;this appears as a Fano-Kondo
resonance in the conductance characteristics as observed in other artificial
nanostructures. The study of hundreds of contacts shows material-dependent
lognormal distributions of the resonance width that arise naturally from Kondo
theory. These resonances broaden and disappear with increasing temperature,
also as in standard Kondo systems. Our observations, supported by calculations,
imply that coordination changes can significantly modify magnetism at the
nanoscale. Therefore, in addition to standard micromagnetic physics, strong
electronic correlations along with atomic-scale geometry need to be considered
when investigating the magnetic properties of magnetic nanostructures.Comment: 7 pages, 5 figure
Crossover from Kondo assisted suppression to co-tunneling enhancement of tunneling magnetoresistance via ferromagnetic nanodots in MgO tunnel barriers
Recently, it has been shown that magnetic tunnel junctions with thin MgO
tunnel barriers exhibit extraordinarily high tunneling magnetoresistance (TMR)
values at room temperature1, 2. However, the physics of spin dependent
tunneling through MgO barriers is only beginning to be unravelled. Using planar
magnetic tunnel junctions in which ultra-thin layers of magnetic metals are
deposited in the middle of a MgO tunnel barrier here we demonstrate that the
TMR is strongly modified when these layers are discontinuous and composed of
small pancake shaped nanodots. At low temperatures, in the Coulomb blockade
regime, for layers less than ~1 nm thick, the conductance of the junction is
increased at low bias consistent with Kondo assisted tunneling. In the same
regime we observe a suppression of the TMR. For slightly thicker layers, and
correspondingly larger nanodots, the TMR is enhanced at low bias, consistent
with co-tunneling.Comment: Nano Letters (in press
Spintronic transport and Kondo effect in quantum dots
We investigate the spin-dependent transport properties of quantum-dot based
structures where Kondo correlations dominate the electronic dynamics. The
coupling to ferromagnetic leads with parallel magnetizations is known to give
rise to nontrivial effects in the local density of states of a single quantum
dot. We show that this influence strongly depends on whether charge
fluctuations are present or absent in the dot. This result is confirmed with
numerical renormalization group calculations and perturbation theory in the
on-site interaction. In the Fermi-liquid fixed point, we determine the
correlations of the electric current at zero temperature (shot noise) and
demonstrate that the Fano factor is suppressed below the Poissonian limit for
the symmetric point of the Anderson Hamiltonian even for nonzero lead
magnetizations. We discuss possible avenues of future research in this field:
coupling to the low energy excitations of the ferromagnets (magnons), extension
to double quantum dot systems with interdot antiferromagnetic interaction and
effect of spin-polarized currents on higher symmetry Kondo states such as
SU(4).Comment: 11 pages, 5 figures. Proceedings of the 3rd Intl. Conf. on Physics
and Applications of Spin-Related Phenomena in Semiconductors, Santa Barbara,
200
Inheritance of signs of «many-flowered» common wheat and evaluation of productivity of the spike of F2 hybrids
Parameters of spike productivity in plants varieties Novosibirskaya 67 (N67), Saratovskaya 29 (S29), Puza-4 and «many-flowered» line Skle 123-09 were assessed in two years with different weather conditions. It was shown that «many-flowered» line Skle 123-09 is significantly higher in the number of grains per spike and number of grains per spikelet than varieties N67, S29 and Puza-4, and that the expression of «many-flowering» depends on the environmental conditions and the genetic background. It was shown that the «many-flowering» is a genetic trait and is therefore workable. A study of hybrids F2 ĐĄ29ĂSkle123-09, N67ĂSkle 123-09, P-4ĂSkle 123-09 isolated plants with fan-shaped cones and a high number of grains per spikelet as Skle 123-09 and having the best performance of other features as ear varieties recipients. The seeds of these plants will be used to secure «flowering». Two-factor analysis of variance showed that the number of grains per spike knotted depends on growing conditions, genotype and their interaction. Variability of grains per spikelet in drought-resistant varieties of S29 and Puza-4 is mainly dependent on the genotype and, to a lesser extent, on the «genotypeĂenvironment» interaction. In variety N67 created for West Siberia, only genotype is a factor. The weight of a grain per ear primarily is primarily affected by «genotypeĂenvironment» (almost 60 %), while the influence of «genotypeĂenvironmental» was half as strong. The variability of «masse of one grain» in F2 hybrids (S29, P-4ĂSkle123-09) is influenced by environmental factors, genotype and their interplay. Genotype accounts for the highest impact (> 70 %). F2 hybrids (N67ĂSkle 123-09) share the greatest variability in the «genotypeĂenvironment» interaction (77 %)
Spin-Polarized Transprot through Double Quantum Dots
We investigate spin-polarized transport phenomena through double quantum dots
coupled to ferromagnetic leads in series. By means of the slave-boson
mean-field approximation, we calculate the conductance in the Kondo regime for
two different configurations of the leads: spin-polarization of two
ferromagnetic leads is parallel or anti-parallel. It is found that transport
shows some remarkable properties depending on the tunneling strength between
two dots. These properties are explained in terms of the Kondo resonances in
the local density of states.Comment: 8 pages, 11 figure
Painful knee joint after ACL reconstruction using biodegradable interference screws- SPECT/CT a valuable diagnostic tool? A case report
With the presented case we strive to introduce combined single photon emission computerized tomography and conventional computer tomography (SPECT/CT) as new diagnostic imaging modality and illustrate the possible clinical value in patients after ACL reconstruction. We report the case of a painful knee due to a foreign body reaction and delayed degradation of the biodegradable interference screws after ACL reconstruction. The MRI showed an intact ACL graft, a possible tibial cyclops lesion and a patella infera. There was no increased fluid collection within the bone tunnels. The 99mTc-HDP-SPECT/CT clearly identified a highly increased tracer uptake around and within the tibial and femoral tunnels and the patellofemoral joint. On 3D-CT out of the SPECT/CT data the femoral graft attachment was shallow (50% along the Blumensaat's line) and high in the notch. At revision arthroscopy a diffuse hypertrophy of the synovium, scarring of the Hoffa fat pad and a cyclops lesion of the former ACL graft was found. The interference screws were partially degraded and under palpation and pressure a grey fluid-like substance drained into the joint. The interference screws and the ACL graft were removed and an arthrolysis performed
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