13,939 research outputs found
Oscillating chiral currents in nanotubes: a route to nanoscale magnetic test tubes
With a view to optimising the design of carbon-nanotube (CNT) windmills and
to maximising the internal magnetic field generated by chiral currents, we
present analytical results for the group velocity components of an electron
flux through chiral carbon nanotubes. Chiral currents are shown to exhibit a
rich behaviour and can even change sign and oscillate as the energy of the
electrons is increased. We find that the transverse velocity and associated
angular momentum of electrons is a maximum for non-metallic CNTs with a chiral
angle of 18. Such CNTs are therefore the optimal choice for CNT windmills
and also generate the largest internal magnetic field for a given longitudinal
current. For a longitudinal current of order amps, this field can be
of order Teslas, which is sufficient to produce interesting spintronic
effects and a significant contribution to the self inductance.Comment: 4 pages, 1 figur
Drive mechanism for production of simulated human breath
Simulated breath drive mechanism was developed as subsystem to breathing metabolic simulator. Mechanism reproduces complete range of human breath rate, breath depth, and breath waveform, as well as independently controlled functional residual capacity. Mechanism was found capable of simulating various individual human breathing characteristics without any changes of parts
Suppression of Giant Magnetoresistance by a superconducting contact
We predict that current perpendicular to the plane (CPP) giant
magnetoresistance (GMR) in a phase-coherent magnetic multilayer is suppressed
when one of the contacts is superconducting. This is a consequence of a
superconductivity-induced magneto-resistive (SMR) effect, whereby the
conductance of the ferromagnetically aligned state is drastically reduced by
superconductivity. To demonstrate this effect, we compute the GMR ratio of
clean (Cu/Co)_nCu and (Cu/Co)_nPb multilayers, described by an ab-initio spd
tight binding Hamiltonian. By analyzing a simpler model with two orbitals per
site, we also show that the suppression survives in the presence of elastic
scattering by impurities.Comment: 5 pages, 4 figures. Submitted to PR
Giant Backscattering Peak in Angle-Resolved Andreev Reflection
It is shown analytically and by numerical simulation that the angular
distribution of Andreev reflection by a disordered normal-metal --
superconductor junction has a narrow peak at the angle of incidence. The peak
is higher than the well-known coherent backscattering peak in the normal state,
by a large factor G/G_0 (where G is the conductance of the junction and
G_0=2e^2/h). The enhanced backscattering can be detected by means of ballistic
point contacts.Comment: Instituut-Lorentz, Leiden, The Netherlands, 4 pages, REVTeX-3.0, 3
figure
On the Inheritance of Resistance to Fowl Typhoid in Chickens
Studies at the Iowa Experiment Station during 1927 and 1928 indicate very clearly that selection is effective in increasing resistance to this disease
Semiclassical theory in Andreev billiards: beyond the diagonal approximation
Recently semiclassical approximations have been successfully applied to study
the effect of a superconducting lead on the density of states and conductance
in ballistic billiards. However, the summation over classical trajectories
involved in such theories was carried out using the intuitive picture of
Andreev reflection rather than the semiclassical reasoning. We propose a method
to calculate the semiclassical sums which allows us to go beyond the diagonal
approximation in these problems. In particular, we address the question of
whether the off-diagonal corrections could explain the gap in the density of
states of a chaotic Andreev billiard.Comment: 11 page
Random Scattering Matrices and the Circuit Theory of Andreev Conductances
The conductance of a normal-metal mesoscopic system in proximity to
superconducting electrode(s) is calculated. The normal-metal part may have a
general geometry, and is described as a ``circuit'' with ``leads'' and
``junctions''. The junctions are each ascribed a scattering matrix which is
averaged over the circular orthogonal ensemble, using recently-developed
techniques. The results for the electrical conductance reproduce and extend
Nazarov's circuit theory, thus bridging between the scattering and the bulk
approaches. The method is also applied to the heat conductance.Comment: 12 pages, RevTeX, including 2 figures with eps
Dermatofibroma: a curious tumor.
A tumor, such as a dermatofibroma, causes consternation among many patients, but it rarely creates problems on its own. Also called a histiocytoma, it remains one of the most common mesenchymal growths. Its etiology is unknown with the previous theory that it is a dermal response to injury, such as an insect bite, being challenged. As much as patients like to blame spiders or other arthropods for traumatizing an arm or leg, no definitive explanation is available for its etiology
Quantum-limited mass flow of liquid He
We consider theoretically the possibility of observing unusual quantum fluid
behavior in liquid He and solutions of He in He systems
confined to nano-channels. In the case of pure ballistic flow at very low
temperature conductance will be quantized in units of . We show that
these steps should be sensitive to increases in temperature. We also use of a
random scattering matrix simulation to study flow with diffusive wall
scattering. Universal conductance fluctuations analogous to those seen in
electron systems should then be observable. Finally we consider the possibility
of the cross-over to a one-dimensional system at sufficiently low temperature
where the system could form a Luttinger liquid
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