22,767 research outputs found
Quantum Resonances of Weakly Linked, Mesoscopic, Superconducting Dots
We examine quantum properties of mesoscopic, Josephson coupled
superconducting dots, in the limit that charging effects and quantization of
energy levels within the dots are negligible, but quasi-particle transmission
into the weak link is not. We demonstrate that quasi-particle resonances lead
to current-phase relations, which deviate markedly from those of weak links
connecting macroscopic superconductors. Results for the steady state dc
Josephson current of two coupled dots are presented.Comment: Tex, 3 figures available on request to [email protected] (Andy
Martin
Non-destructive ultrasonic measurements of case depth
Two ultrasonic methods for nondestructive measurements of the depth of a case-hardened layer in steel are described. One method involves analysis of ultrasonic waves diffused back from the bulk of the workpiece. The other method involves finding the speed of propagation of ultrasonic waves launched on the surface of the work. Procedures followed in the two methods for measuring case depth are described
Giant Conductance Oscillations In Mesoscopic Andreev Interferometers
We analyze the electrical conductance of a two-dimensional, phase
coherent structure in contact with two superconductors, which is known to be an
oscillatory function of the phase difference between the
superconductors. It is predicted that for a metallic sample, the amplitude of
oscillation is enhanced by placing a normal barrier at the interface and that,
by tuning the strength of the barrier, can be orders of magnitude greater than
values observed in recent experiments. Giant oscillations can also be obtained
without a barrier, provided a crucial sum rule is broken. This can be achieved
by disorder induced normal scattering. In the absence of zero phase
inter-channel scattering, the conductance possesses a zero phase minimum.Comment: 4 pages of Revtex, 6 figures available on reques
Optimal softening for force calculations in collisionless N-body simulations
In N-body simulations the force calculated between particles representing a
given mass distribution is usually softened, to diminish the effect of
graininess. In this paper we study the effect of such a smoothing, with the aim
of finding an optimal value of the softening parameter. As already shown by
Merritt (1996), for too small a softening the estimates of the forces will be
too noisy, while for too large a softening the force estimates are
systematically misrepresented. In between there is an optimal softening, for
which the forces in the configuration approach best the true forces. The value
of this optimal softening depends both on the mass distribution and on the
number of particles used to represent it. For higher number of particles the
optimal softening is smaller. More concentrated mass distributions necessitate
smaller softening, but the softened forces are never as good an approximation
of the true forces as for not centrally concentrated configurations. We give
good estimates of the optimal softening for homogeneous spheres, Plummer
spheres, and Dehnen spheres. We also give a rough estimate of this quantity for
other mass distributions, based on the harmonic mean distance to the th
neighbour ( = 1, .., 12), the mean being taken over all particles in the
configuration. Comparing homogeneous Ferrers ellipsoids of different shapes we
show that the axial ratios do not influence the value of the optimal softening.
Finally we compare two different types of softening, a spline softening
(Hernquist & Katz 1989) and a generalisation of the standard Plummer softening
to higher values of the exponent. We find that the spline softening fares
roughly as well as the higher powers of the power-law softening and both give a
better representation of the forces than the standard Plummer softening.Comment: 16 pages Latex, 19 figures, accepted for publication in MNRAS,
corrected typos, minor changes mainly in sec.
Electric instability in superconductor-normal conductor ring
Non-linear electrodynamics of a ring-shaped Andreev interferometer
(superconductor-normal conductor-superconductor hybrid structure) inductively
coupled to a circuit of the dissipative current is investigated. The
current-voltage characteristics (CVC) is demonstrated to be a series of loops
with several branches intersecting in the CVC origin. The sensitivity of the
transport current to a change of the applied external magnetic flux can be
comparable to the one of the conventional SQUID's. Spontaneous arising of
coupled non-linear oscillations of the transport current, the Josephson current
and the magnetic flux in Andreev interferometers are also predicted and
investigated. The frequency of these oscillations can be varied in a wide
range, while the maximal frequency can reach
.Comment: 4 pages, 4 figure
Contribution of weak localization to non local transport at normal metal / superconductor double interfaces
In connection with a recent experiment [Russo {\it et al.}, Phys. Rev. Lett.
{\bf 95}, 027002 (2005)], we investigate the effect of weak localization on non
local transport in normal metal / insulator / superconductor / insulator /
normal metal (NISIN) trilayers, with extended interfaces. The negative weak
localization contribution to the crossed resistance can exceed in absolute
value the positive elastic cotunneling contribution if the normal metal phase
coherence length or the energy are large enough.Comment: 9 pages, 7 figures, minor modification
Forming disk galaxies in wet major mergers. I. Three fiducial examples
Using three fiducial Nbody+SPH simulations, we follow the merging of two disk
galaxies with a hot gaseous halo component each, and examine whether the merger
remnant can be a spiral galaxy. The stellar progenitor disks are destroyed by
violent relaxation during the merging and most of their stars form a classical
bulge, while the remaining form a thick disk and its bar. A new stellar disk
forms subsequently and gradually in the remnant from the gas accreted mainly
from the halo. It is vertically thin and well extended in its equatorial plane.
A bar starts forming before the disk is fully in place, contrary to what is
assumed in idealised simulations of isolated bar-forming galaxies. It has
morphological features such as ansae and boxy/peanut bulges. Stars of different
ages populate different parts of the box/peanut. A disky pseudobulge forms
also, so that by the end of the simulation, all three types of bulges coexist.
The oldest stars are found in the classical bulge, followed by those of the
thick disk, then by those in the thin disk. The youngest stars are in the
spiral arms and the disky pseudobulge. The disk surface density profiles are of
type II (exponential with downbending), and the circular velocity curves are
flat and show that the disks are submaximum in these examples: two clearly so
and one near-borderline between maximum and submaximum. On average, only
roughly between 10 and 20% of the stellar mass is in the classical bulge of the
final models, i.e. much less than in previous simulations.Comment: 17 pages, 8 figures, accepted for publication in ApJ. V2: replaced
Figure 4 with correct versio
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