1,552 research outputs found
Cardiovascular Magnetic Resonance Imaging of Scar Development Following Pulmonary Vein Isolation: A Prospective Study
Aims Cardiovascular magnetic resonance (MR) provides non-invasive assessment of early (24-hour) edema and injury following pulmonary vein isolation (by ablation) and subsequent scar formation. We hypothesize that 24-hours after ablation, cardiovascular MR would demonstrate a pattern of edema and injury due to ablation and the severity would correlate with subsequent scar. Methods: Fifteen atrial fibrillation patients underwent cardiovascular MR prior to pulmonary vein isolation, 24-hours post (N = 11) and 30-days post (N = 7) ablation, with T2-weighted (T2W) and late gadolinium enhancement (LGE) imaging. Left atrial wall thickness, edema enhancement ratio and LGE enhancement were assessed at each time point. Volumes of LGE and edema enhancement were measured, and the circumferential presence of injury was assessed at 24-hours, including comparison with LGE enhancement at 30 days. Results: Left atrial wall thickness was increased 24-hours post-ablation (10.7±4.1 mm vs. 7.0±1.8 mm pre-PVI, p<0.05). T2W enhancement at 24-hours showed increased edema enhancement ratio (1.5±0.4 for post-ablation, vs. 0.9±0.2 pre-ablation, p<0.001). Edema and LGE volumes at 24-hours were correlated with 30-day LGE volume (R = 0.76, p = 0.04, and R = 0.74, p = 0.09, respectively). Using a 16 segment model for assessment, 24-hour T2W had sensitivity, specificity, and accuracy of 82%, 63%, and 79% respectively, for predicting 30-day LGE. 24-hour LGE had sensitivity, specificity, and accuracy of 91%, 47%, and 84%. Conclusions: Increased left atrial wall thickening and edema were characterized on cardiovascular MR early post-ablation, and found to correlate with 30-day LGE scar
Phase Modulated Thermal Conductance of Josephson Weak Links
We present a theory for quasiparticle heat transport through superconducting
weak links. The thermal conductance depends on the phase difference () of
the superconducting leads. Branch conversion processes, low-energy Andreev
bound states near the contact and the suppression of the local density of
states near the gap edge are related to phase-sensitive transport processes.
Theoretical results for the influence of junction transparency, temperature and
disorder, on the phase modulation of the conductance are reported. For
high-transmission weak links, , the formation of an Andreev bound state
at leads to suppression of the
density of states for the continuum excitations that transport heat, and thus,
to a reduction in the conductance for . For low-transmission
() barriers resonant scattering at energies
leads to an increase in the thermal conductance
as drops below (for phase differences near ).Comment: 4 pages, 3 figures Expanded discussion of boundary conditions for
Ricatti amplitude
Synchronization of active mechanical oscillators by an inertial load
Motivated by the operation of myogenic (self-oscillatory) insect flight
muscle, we study a model consisting of a large number of identical oscillatory
contractile elements joined in a chain, whose end is attached to a damped
mass-spring oscillator. When the inertial load is small, the serial coupling
favors an antisynchronous state in which the extension of one oscillator is
compensated by the contraction of another, in order to preserve the total
length. However, a sufficiently massive load can sychronize the oscillators and
can even induce oscillation in situations where isolated elements would be
stable. The system has a complex phase diagram displaying quiescent,
synchronous and antisynchrononous phases, as well as an unsual asynchronous
phase in which the total length of the chain oscillates at a different
frequency from the individual active elements.Comment: 5 pages, 4 figures, To appear in Phys. Rev. Let
Experimental Designs for Binary Data in Switching Measurements on Superconducting Josephson Junctions
We study the optimal design of switching measurements of small Josephson
junction circuits which operate in the macroscopic quantum tunnelling regime.
Starting from the D-optimality criterion we derive the optimal design for the
estimation of the unknown parameters of the underlying Gumbel type
distribution. As a practical method for the measurements, we propose a
sequential design that combines heuristic search for initial estimates and
maximum likelihood estimation. The presented design has immediate applications
in the area of superconducting electronics implying faster data acquisition.
The presented experimental results confirm the usefulness of the method. KEY
WORDS: optimal design, D-optimality, logistic regression, complementary log-log
link, quantum physics, escape measurement
Response of thin-film SQUIDs to applied fields and vortex fields: Linear SQUIDs
In this paper we analyze the properties of a dc SQUID when the London
penetration depth \lambda is larger than the superconducting film thickness d.
We present equations that govern the static behavior for arbitrary values of
\Lambda = \lambda^2/d relative to the linear dimensions of the SQUID. The
SQUID's critical current I_c depends upon the effective flux \Phi, the magnetic
flux through a contour surrounding the central hole plus a term proportional to
the line integral of the current density around this contour. While it is well
known that the SQUID inductance depends upon \Lambda, we show here that the
focusing of magnetic flux from applied fields and vortex-generated fields into
the central hole of the SQUID also depends upon \Lambda. We apply this
formalism to the simplest case of a linear SQUID of width 2w, consisting of a
coplanar pair of long superconducting strips of separation 2a, connected by two
small Josephson junctions to a superconducting current-input lead at one end
and by a superconducting lead at the other end. The central region of this
SQUID shares many properties with a superconducting coplanar stripline. We
calculate magnetic-field and current-density profiles, the inductance
(including both geometric and kinetic inductances), magnetic moments, and the
effective area as a function of \Lambda/w and a/w.Comment: 18 pages, 20 figures, revised for Phys. Rev. B, the main revisions
being to denote the effective flux by \Phi rather than
Avoided Critical Behavior in O(n) Systems
Long-range frustrating interactions, even if their strength is infinitesimal,
can give rise to a dramatic proliferations of ground or near-ground states. As
a consequence, the ordering temperature can exhibit a discontinuous drop as a
function of the frustration. A simple model of the doped Mott insulator, where
the short-range tendency of the holes to phase separate competes with
long-range Coulomb effects, exhibits this "avoided critical" behavior. This
model may serve as a paradigm for many other systems.Comment: 4 pages, 2 figure
Topological properties of superconducting junctions
Motivated by recent developments in the field of one-dimensional topological
superconductors, we investigate the topological properties of s-matrix of
generic superconducting junctions where dimension should not play any role. We
argue that for a finite junction the s-matrix is always topologically trivial.
We resolve an apparent contradiction with the previous results by taking into
account the low-energy resonant poles of s-matrix. Thus no common topological
transition occur in a finite junction. We reveal a transition of a different
kind that concerns the configuration of the resonant poles
Macroscopic Symmetry Group Describes Josephson Tunneling in Twinned Crystals
A macroscopic symmetry group describing the superconducting state of an
orthorhombically twinned crystal of YBCO is introduced. This macroscopic
symmetry group is different for different symmetries of twin boundaries.
Josephson tunneling experiments performed on twinned crystals of YBCO determine
this macroscopic symmetry group and hence determine the twin boundary symmetry
(but do not experimentally determine whether the microscopic order parameter is
primarily d- or s-wave). A consequence of the odd-symmetry twin boundaries in
YBCO is the stability of vortices containing one half an elementary flux
quantum at the intersection of a twin boundary and certain grain boundaries.Comment: 6 pages, to be published in the Proceedings of the MOS96 Conference
in the Journal of Low Temperature Physic
Mean Field Theory of Josephson Junction Arrays with Charge Frustration
Using the path integral approach, we provide an explicit derivation of the
equation for the phase boundary for quantum Josephson junction arrays with
offset charges and non-diagonal capacitance matrix. For the model with nearest
neighbor capacitance matrix and uniform offset charge , we determine,
in the low critical temperature expansion, the most relevant contributions to
the equation for the phase boundary. We explicitly construct the charge
distributions on the lattice corresponding to the lowest energies. We find a
reentrant behavior even with a short ranged interaction. A merit of the path
integral approach is that it allows to provide an elegant derivation of the
Ginzburg-Landau free energy for a general model with charge frustration and
non-diagonal capacitance matrix. The partition function factorizes as a product
of a topological term, depending only on a set of integers, and a
non-topological one, which is explicitly evaluated.Comment: LaTex, 24 pages, 8 figure
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