3,366 research outputs found
Hadamard States and Two-dimensional Gravity
We have used a two-dimensional analog of the Hadamard state-condition to
study the local constraints on the two-point function of a linear quantum field
conformally coupled to a two-dimensional gravitational background. We develop a
dynamical model in which the determination of the state of the quantum field is
essentially related to the determination of a conformal frame. A particular
conformal frame is then introduced in which a two-dimensional gravitational
equation is established.Comment: 7 pages, no figur
On Cosmological Implication of the Trace Anomaly
We establish a connection between the trace anomaly and a thermal radiation
in the context of the standard cosmology. This is done by solving the covariant
conservation equation of the stress tensor associated with a conformally
invariant quantum scalar field. The solution corresponds to a thermal radiation
with a temperature which is given in terms of a cut-off time excluding the
spacetime regions very close to the initial singularity. We discuss the
interrelation between this result and the result obtained in a two-dimensional
schwarzschild spacetime.Comment: 8 pages, no figure
Age-dependent dynamic electrophysiological field potential behavior of atrioventricular node during experimental AF in rabbit
Introduction: Electrophysiological studies have demonstrated a relationship between aging and atrioventricular (AV) nodal conduction and refractoriness. The aim of the present study was to determine the effects of nodal aging on dynamic AV nodal field potential recording during atrial fibrillation (AF) in rabbit. Methods: Two groups of male New Zealand rabbits (neonatal 2-week-olds and adult 12-week-olds, n=14 each group) were used in this study. Field potential recordings were executed by silver electrodes with a diameter of 100 μM. Pre-defined stimulation protocols of AF, zone of concealment (ZOC) and concealed conduction for determination of the electrophysiological properties of the AV-node were separately applied in each group. Results: Results of the study showed that mean ventricular rate (HH) during atrial fibrillation was smaller in the neonatal compared to the adult group (229.1 ± 8.3 versus 198.6 ± 13.1 msec, respectively). Also ventricular distribution conduction pattern showed two peaks in the adult and one peak in the neonatal group. Analyzing the zone of concealment in different rates and after concealed beat indicated that the zone of concealment in neonates were significantly smaller compared with adult rabbits and increasing zone of concealment, which is accompanied with increasing ventricular rate is abrogated in the neonatal group (5 ± 3.3, 12.2 ± 6.3 msec). Conclusion: The results of this study showed that the electrophysiological protective dynamic behavior of the AV node during atrial fibrillation is smaller in neonates compared to adults. Narrower zone of concealment, abrogation rate dependent trend of the zone of concealment and shorter nodal refractoriness can account for the specific nodal electrophysiological properties of neonatal rabbits
Coexistence of bulk and surface states probed by Shubnikov-de Haas oscillations in BiSe with high charge-carrier density
Topological insulators are ideally represented as having an insulating bulk
with topologically protected, spin-textured surface states. However, it is
increasingly becoming clear that these surface transport channels can be
accompanied by a finite conducting bulk, as well as additional topologically
trivial surface states. To investigate these parallel conduction transport
channels, we studied Shubnikov-de Haas oscillations in BiSe thin films,
in high magnetic fields up to 30 T so as to access channels with a lower
mobility. We identify a clear Zeeman-split bulk contribution to the
oscillations from a comparison between the charge-carrier densities extracted
from the magnetoresistance and the oscillations. Furthermore, our analyses
indicate the presence of a two-dimensional state and signatures of additional
states the origin of which cannot be conclusively determined. Our findings
underpin the necessity of theoretical studies on the origin of and the
interplay between these parallel conduction channels for a careful analysis of
the material's performance.Comment: Manuscript including supplemental materia
Optimal Wavelength Allocation in Hybrid Quantum-Classical Networks
An efficient algorithm for optimal allocation of wavelengths in a hybrid dense-wavelength-division-multiplexing system, carrying both quantum and classical data, is proposed. The transmission of quantum bits alongside intense classical signals on the same fiber faces major challenges arising from the background noise generated by classical channels. Raman scattering, in particular, is shown to have detrimental effects on the performance of quantum key distribution systems. Here, by using an optimal wavelength allocation technique, we minimize the Raman induced background noise on quantum channels, hence maximize the achievable secret key generation rate for quantum channels. It turns out the conventional solution that the optimal arrangement would involve splitting the spectrum into only two bands, one for quantum and one for classical channels, is only a suboptimal one. We show that, in the optimal arrangement, we might need several quantum and classical bands interspersed among each other
- …