33,526 research outputs found
Single Cooper-pair pumping in the adiabatic limit and beyond
We demonstrate controlled pumping of Cooper pairs down to the level of a
single pair per cycle, using an rf-driven Cooper-pair sluice. We also
investigate the breakdown of the adiabatic dynamics in two different ways. By
transferring many Cooper pairs at a time, we observe a crossover between pure
Cooper-pair and mixed Cooper-pair-quasiparticle transport. By tuning the
Josephson coupling that governs Cooper-pair tunneling, we characterize
Landau-Zener transitions in our device. Our data are quantitatively accounted
for by a simple model including decoherence effects.Comment: 5 pages, 5 figure
Ground States of S-duality Twisted N=4 Super Yang-Mills Theory
We study the low-energy limit of a compactification of N=4 U(n) super
Yang-Mills theory on with boundary conditions modified by an S-duality
and R-symmetry twist. This theory has N=6 supersymmetry in 2+1D. We analyze the
compactification of this 2+1D theory by identifying a dual weakly coupled
type-IIA background. The Hilbert space of normalizable ground states is
finite-dimensional and appears to exhibit a rich structure of sectors. We
identify most of them with Hilbert spaces of Chern-Simons theory (with
appropriate gauge groups and levels). We also discuss a realization of a
related twisted compactification in terms of the (2,0)-theory, where the recent
solution by Gaiotto and Witten of the boundary conditions describing D3-branes
ending on a (p,q) 5-brane plays a crucial role.Comment: 104 pages, 5 figures. Revisions to subsection (6.6) and other minor
corrections included in version
Long Gamma-Ray Burst Progenitors: Boundary Conditions and Binary Models
The observed association of Long Gamma-Ray Bursts (LGRBs) with peculiar Type
Ic supernovae gives support to Woosley`s collapsar/hypernova model, in which
the GRB is produced by the collapse of the rapidly rotating core of a massive
star to a black hole. The association of LGRBs with small star-forming galaxies
suggests low-metallicity to be a condition for a massive star to evolve to the
collapsar stage. Both completely-mixed single star models and binary star
models are possible. In binary models the progenitor of the GRB is a massive
helium star with a close companion. We find that tidal synchronization during
core-helium burning is reached on a short timescale (less than a few
millennia). However, the strong core-envelope coupling in the subsequent
evolutionary stages is likely to rule out helium stars with main-sequence
companions as progenitors of hypernovae/GRBs. On the other hand, helium stars
in close binaries with a neutron-star or black-hole companion can, despite the
strong core-envelope coupling in the post-helium burning phase, retain
sufficient core angular momentum to produce a hypernova/GRB.Comment: 8 pp., 2 figs, Proceedings of 5th Stromlo Symposiu
Giant Flexoelectric Effect in Ferroelectric Epitaxial Thin Films
We report on nanoscale strain gradients in ferroelectric HoMnO3 epitaxial
thin films, resulting in a giant flexoelectric effect. Using grazing-incidence
in-plane X-ray diffraction, we measured strain gradients in the films, which
were 6 or 7 orders of magnitude larger than typical values reported for bulk
oxides. The combination of transmission electron microscopy, electrical
measurements, and electrostatic calculations showed that flexoelectricity
provides a means of tuning the physical properties of ferroelectric epitaxial
thin films, such as domain configurations and hysteresis curves.Comment: Accepted by Phys. Rev. Let
Herd Behaviors in Financial Markets
We investigate the herd behavior of returns for the yen-dollar exchange rate
in the Japanese financial market. It is obtained that the probability
distribution of returns satisfies the power-law behavior with the exponents (the time interval
one minute) and 3.36( one day). The informational cascade regime appears
in the herding parameter at one minute, while it occurs no
herding at one day. Especially, we find that the distribution of
normalized returns shows a crossover to a Gaussian distribution at one time
step day.Comment: 15 pages, 6 figure
Macromolecular separation through a porous surface
A new technique for the separation of macromolecules is proposed and
investigated. A thin mesh with pores comparable to the radius of gyration of a
free chain is used to filter chains according to their length. Without a field
it has previously been shown that the permeability decays as a power law with
chain length. However by applying particular configurations of pulsed fields,
it is possible to have a permeability that decays as an exponential. This
faster decay gives much higher resolution of separation. We also propose a
modified screen containing an array of holes with barb-like protrusions running
parallel to the surface. When static friction is present between the
macromolecule and the protrusion, some of the chains get trapped for long
durations of time. By using this and a periodic modulation of an applied
electric field, high resolution can be attained.Comment: 18 pages latex, 6 postscript figures, using psfi
(2,2)-Formalism of General Relativity: An Exact Solution
I discuss the (2,2)-formalism of general relativity based on the
(2,2)-fibration of a generic 4-dimensional spacetime of the Lorentzian
signature. In this formalism general relativity is describable as a Yang-Mills
gauge theory defined on the (1+1)-dimensional base manifold, whose local gauge
symmetry is the group of the diffeomorphisms of the 2-dimensional fibre
manifold. After presenting the Einstein's field equations in this formalism, I
solve them for spherically symmetric case to obtain the Schwarzschild solution.
Then I discuss possible applications of this formalism.Comment: 2 figures included, IOP style file neede
Renormalization analysis of intermittency in two coupled maps
The critical behavior for intermittency is studied in two coupled
one-dimensional (1D) maps. We find two fixed maps of an approximate
renormalization operator in the space of coupled maps. Each fixed map has a
common relavant eigenvaule associated with the scaling of the control parameter
of the uncoupled one-dimensional map. However, the relevant ``coupling
eigenvalue'' associated with coupling perturbation varies depending on the
fixed maps. These renormalization results are also confirmed for a
linearly-coupled case.Comment: 11 pages, RevTeX, 2 eps figure
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