6,473 research outputs found
Prevalence of obstructive coronary artery disease and prognosis in patients with stable symptoms and a zero-coronary calcium score
© The Author 2017. Published by Oxford University Press on behalf of the European Society of Cardiology.Aims: CT calcium scoring (CTCS) and CT cardiac angiography (CTCA) are widely used in patients with stable chest pain to exclude significant coronary artery disease (CAD). We aimed to resolve uncertainty about the prevalence of obstructive coronary artery disease and long-term outcomes in patients with a zero-calcium score (ZCS). Methods and results: Consecutive patients with stable cardiac symptoms referred for CTCS or CTCS and CTCA from chest pain clinics to a tertiary cardiothoracic centre were prospectively enrolled. In those with a ZCS, the prevalence of obstructive CAD on CTCA was determined. A follow-up for all-cause mortality was obtained from the NHS tracer service. A total of 3914 patients underwent CTCS of whom 2730 (69.7%) also had a CTCA. Half of the patients were men (50.3%) with a mean age of 56.9 years. Among patients who had both procedures, a ZCS was present in 52.2%, with a negative predictive value of 99.5% for excluding ≥70% stenosis on CTCA. During a mean follow-up of 5.2 years, the annual event rate was 0.3% for those with ZCS compared with 1.2% for CS ≥1. The presence of non-calcified atheroma on CTCA in patients with ZCS did not affect the prognostic value (P = 0.98). Conclusion: In patients with stable symptoms and a ZCS, obstructive CAD is rare, and prognosis over the long-term is excellent, regardless of whether non-calcified atheroma is identified. A ZCS could reliably be used as a 'gatekeeper' in this patient cohort, obviating the need for further more expensive tests.Peer reviewedFinal Published versio
Steady States of a Microwave Irradiated Quantum Hall Gas
We consider effects of a long-wavelength disorder potential on the Zero
Conductance State (ZCS) of the microwave-irradiated 2D electron gas. Assuming a
uniform Hall conductivity, we construct a Lyapunov functional and derive
stability conditions on the domain structure of the photo-generated fields. We
solve the resulting equations for a general one-dimensional and certain
two-dimensional disorder potentials, and find non-zero conductances,
photo-voltages, and circulating dissipative currents. In contrast, weak white
noise disorder does not destroy the ZCS, but induces mesoscopic current
fluctuations.Comment: 4 pages, 2 colour figure
Topological string entanglement
We investigate how topological entanglement of Chern-Simons theory is
captured in a string theoretic realization. Our explorations are motivated by a
desire to understand how quantum entanglement of low energy open string degrees
of freedom is encoded in string theory (beyond the oft discussed classical
gravity limit). Concretely, we realize the Chern-Simons theory as the
worldvolume dynamics of topological D-branes in the topological A-model string
theory on a Calabi-Yau target. Via the open/closed topological string duality
one can map this theory onto a pure closed topological A-model string on a
different target space, one which is related to the original Calabi-Yau
geometry by a geometric/conifold transition. We demonstrate how to uplift the
replica construction of Chern-Simons theory directly onto the closed string and
show that it provides a meaningful definition of reduced density matrices in
topological string theory. Furthermore, we argue that the replica construction
commutes with the geometric transition, thereby providing an explicit closed
string dual for computing reduced states, and Renyi and von Neumann entropies
thereof. While most of our analysis is carried out for Chern-Simons on S^3, the
emergent picture is rather general. Specifically, we argue that quantum
entanglement on the open string side is mapped onto quantum entanglement on the
closed string side and briefly comment on the implications of our result for
physical holographic theories where entanglement has been argued to be crucial
ingredient for the emergence of classical geometry.Comment: 48 pages + appendices, many tikz fgures. v2: added clarification
Complex resonance frequencies of a finite, circular radiating duct with an infinite flange
Radiation by solid or fluid bodies can be characterized by resonance modes.
They are complex, as well as resonance frequencies, because of the energy loss
due to radiation. For ducts, they can be computed from the knowledge of the
radiation impedance matrix. For the case of a flanged duct of finite length
radiating on one side in an infinite medium, the expression of this matrix was
given by Zorumski, using a decomposition in duct modes. In order to calculate
the resonance frequencies, the formulation used in Zorumski's theory must be
modified as it is not valid for complex frequencies. The analytical development
of the Green's function in free space used by Zorumski depends on the integrals
of Bessel functions which become divergent for complex frequencies. This paper
proposes first a development of the Green's function which is valid for all
frequencies. Results are applied to the calculation of the complex resonance
frequencies of a flanged duct, by using a formulation of the internal pressure
based upon cascade impedance matrices. Several series of resonance modes are
found, each series being shown to be related to a dominant duct mode. Influence
of higher order duct modes and the results for several fluid densities is
presented and discussed
A zero-current-switching based three-phase PWM inverter having resonant circuits on AC-side
The authors present a zero-current-switching (ZCS)-based three-phase PWM (pulse-width-modulated) inverter having small resonant circuits on the AC side, whose resonant frequency is 50 kHz. The ZCS inverter can greatly reduce the switching losses and electromagnetic noise. The principle of ZCS operation, the design of the resonant circuits, and the control sequence are described from theoretical and practical points of view. Experimental results obtained from a ZCS PWM inverter driving an induction motor of 2.2 kW are shown to verify the practicability of this device </p
Spin-phonon coupling in antiferromagnetic chromium spinels
The temperature dependence of eigenfrequencies and intensities of the IR
active modes has been investigated for the antiferromagnetic chromium spinel
compounds CdCr2O4, ZnCr2O4, ZnCr2S4, ZnCr2Se4, and HgCr2S4 by IR spectroscopy
for temperatures from 5 K to 300 K. At the transition into the magnetically
ordered phases, and driven by spin-phonon coupling, most compounds reveal
significant splittings of the phonon modes. This is true for geometrically
frustrated CdCr2O4, and ZnCr2O4, for bond frustrated ZnCr2S4 and for ZnCr2Se4,
which also is bond frustrated, but dominated by ferromagnetic exchange. The
pattern of splitting is different for the different compounds and crucially
depends on the nature of frustration and of the resulting spin order. HgCr2S4,
which is almost ferromagnetic, exhibits no splitting of the eigenfrequencies,
but shows significant shifts due to ferromagnetic spin fluctuations.Comment: 15 pages, 6 figure
On universal decoherence under gravity: a perspective through the Equivalence Principle
In Nature Phys. 11, 668 (2015) (Ref. [1]), a composite particle prepared in a
pure initial quantum state and propagated in a uniform gravitational field is
shown to undergo a decoherence process at a rate determined by the
gravitational acceleration. By assuming Einstein's Equivalence Principle to be
valid, we demonstrate, first in a Lorentz frame with accelerating detectors,
and then directly in the Lab frame with uniform gravity, that the dephasing
between the different internal states arise not from gravity but rather from
differences in their rest mass, and the mass dependence of the de Broglie
wave's dispersion relation. We provide an alternative view to the situation
considered by Ref. [1], where we propose that gravity plays a kinematic role in
the loss of fringe visibility by giving the detector a transverse velocity
relative to the particle beam; visibility can be easily recovered by giving the
screen an appropriate uniform velocity. We finally propose that dephasing due
to gravity may in fact take place for certain modifications to the
gravitational potential where the Equivalence Principle is violated.Comment: 5 pages, 3 figure
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