12,948 research outputs found
Displacement Data Assimilation
We show that modifying a Bayesian data assimilation scheme by incorporating
kinematically-consistent displacement corrections produces a scheme that is
demonstrably better at estimating partially observed state vectors in a setting
where feature information important. While the displacement transformation is
not tied to any particular assimilation scheme, here we implement it within an
ensemble Kalman Filter and demonstrate its effectiveness in tracking
stochastically perturbed vortices.Comment: 26 Pages, 9 figures, 5 table
Population bound effects on bosonic correlations in non-inertial frames
We analyse the effect of bounding the occupation number of bosonic field
modes on the correlations among all the different spatial-temporal regions in a
setting in which we have a space-time with a horizon along with an inertial
observer. We show that the entanglement between A (inertial observer) and R
(uniformly accelerated observer) depends on the bound N, contrary to the
fermionic case. Whether or not decoherence increases with N depends on the
value of the acceleration a. Concerning the bipartition A-antiR (Alice with an
observer in Rindler's region IV), we show that no entanglement is created
whatever the value of N and a. Furthermore, AR entanglement is very quickly
lost for finite N and for infinite N. We will study in detail the mutual
information conservation law found for bosons and fermions. By means of the
boundary effects associated to N finiteness, we will show that for bosons this
law stems from classical correlations while for fermions it has a quantum
origin. Finally, we will present the strong N dependence of the entanglement in
R-antiR bipartition and compare the fermionic cases with their finite N bosonic
analogs. We will also show the anti-intuitive dependence of this entanglement
on statistics since more entanglement is created for bosons than for their
fermion counterparts.Comment: revtex 4, 12 pages, 10 figures. Added Journal ref
Experimental Demonstration of >230{\deg} Phase Modulation in Gate-Tunable Graphene-Gold Reconfigurable Mid-Infrared Metasurfaces
Metasurfaces offer significant potential to control far-field light
propagation through the engineering of amplitude, polarization, and phase at an
interface. We report here phase modulation of an electronically reconfigurable
metasurface and demonstrate its utility for mid-infrared beam steering. Using a
gate-tunable graphene-gold resonator geometry, we demonstrate highly tunable
reflected phase at multiple wavelengths and show up to 237{\deg} phase
modulation range at an operating wavelength of 8.50 {\mu}m. We observe a smooth
monotonic modulation of phase with applied voltage from 0{\deg} to 206{\deg} at
a wavelength of 8.70 {\mu}m. Based on these experimental data, we demonstrate
with antenna array calculations an average beam steering efficiency of 50% for
reflected light for angles up to 30{\deg}, relative to an ideal metasurface,
confirming the suitability of this geometry for reconfigurable mid-infrared
beam steering devices
Thermodynamics of Quantum Jump Trajectories
We apply the large-deviation method to study trajectories in dissipative
quantum systems. We show that in the long time limit the statistics of quantum
jumps can be understood from thermodynamic arguments by exploiting the analogy
between large-deviation and free-energy functions. This approach is
particularly useful for uncovering properties of rare dissipative trajectories.
We also prove, via an explicit quantum mapping, that rare trajectories of one
system can be realized as typical trajectories of an alternative system.Comment: 5 pages, 3 figure
Facilitated spin models of dissipative quantum glasses
We introduce a class of dissipative quantum spin models with local
interactions and without quenched disorder that show glassy behaviour. These
models are the quantum analogs of the classical facilitated spin models. Just
like their classical counterparts, quantum facilitated models display complex
glassy dynamics despite the fact that their stationary state is essentially
trivial. In these systems, dynamical arrest is a consequence of kinetic
constraints and not of static ordering. These models display a quantum version
of dynamic heterogeneity: the dynamics towards relaxation is spatially
correlated despite the absence of static correlations. Associated dynamical
fluctuation phenomena such as decoupling of timescales is also observed.
Moreover, we find that close to the classical limit quantum fluctuations can
enhance glassiness, as recently reported for quantum liquids.Comment: 7 pages, 6 figure
Secondary Frequency and Voltage Control of Islanded Microgrids via Distributed Averaging
In this work we present new distributed controllers for secondary frequency
and voltage control in islanded microgrids. Inspired by techniques from
cooperative control, the proposed controllers use localized information and
nearest-neighbor communication to collectively perform secondary control
actions. The frequency controller rapidly regulates the microgrid frequency to
its nominal value while maintaining active power sharing among the distributed
generators. Tuning of the voltage controller provides a simple and intuitive
trade-off between the conflicting goals of voltage regulation and reactive
power sharing. Our designs require no knowledge of the microgrid topology,
impedances or loads. The distributed architecture allows for flexibility and
redundancy, and eliminates the need for a central microgrid controller. We
provide a voltage stability analysis and present extensive experimental results
validating our designs, verifying robust performance under communication
failure and during plug-and-play operation.Comment: Accepted for publication in IEEE Transactions on Industrial
Electronic
Unveiling quantum entanglement degradation near a Schwarzschild black hole
We analyze the entanglement degradation provoked by the Hawking effect in a
bipartite system Alice-Rob when Rob is in the proximities of a Schwarzschild
black hole while Alice is free falling into it. We will obtain the limit in
which the tools imported from the Unruh entanglement degradation phenomenon can
be used properly, keeping control on the approximation. As a result, we will be
able to determine the degree of entanglement as a function of the distance of
Rob to the event horizon, the mass of the black hole, and the frequency of
Rob's entangled modes. By means of this analysis we will show that all the
interesting phenomena occur in the vicinity of the event horizon and that the
presence of event horizons do not effectively degrade the entanglement when Rob
is far off the black hole. The universality of the phenomenon is presented:
There are not fundamental differences for different masses when working in the
natural unit system adapted to each black hole. We also discuss some aspects of
the localization of Alice and Rob states. All this study is done without using
the single mode approximation.Comment: 16 pages, 10 figures, revtex4. Added Journal referenc
First Observations on the Re-Established Southeast Florida Recreational Swordfish Tournament Fishery
Recreational tournaments for swordfish (Xiphias gladius) existed in the Florida Straits between 1977 and 1983 before disappearing due to low catch rates and an overexploitation of the stock. The first recent swordfish tournament occurred in 2001 off southeast Florida with 13 participating vessels. In 2002, three swordfish tournaments were observed and anglers were interviewed to determine catch and gear characteristics of the re-established recreational fishery. A total of 156 vessels participated in these three tournaments, catching 112 swordfish and hooking an additional 48 animals. The combination of the recovery of the North Atlantic swordfish stock and the continuation of the 2001 closure of the Florida Straits to commercial pelagic longline fishing gear is expected to result in the continued expansion of the southeast Florida recreational swordfish fishery
Interplay Between Yu-Shiba-Rusinov States and Multiple Andreev Reflections
Motivated by recent scanning tunneling microscopy experiments on single
magnetic impurities on superconducting surfaces, we present here a
comprehensive theoretical study of the interplay between Yu-Shiba-Rusinov bound
states and (multiple) Andreev reflections. Our theory is based on a combination
of an Anderson model with broken spin degeneracy and nonequilibrium Green's
function techniques that allows us to describe the electronic transport through
a magnetic impurity coupled to superconducting leads for arbitrary junction
transparency. Using this combination we are able to elucidate the different
tunneling processes that give a significant contribution to the subgap
transport. In particular, we predict the occurrence of a large variety of
Andreev reflections mediated by Yu-Shiba-Rusinov bound states that clearly
differ from the standard Andreev processes in non-magnetic systems. Moreover,
we provide concrete guidelines on how to experimentally identify the subgap
features originating from these tunneling events. Overall, our work provides
new insight into the role of the spin degree of freedom in Andreev transport
physics.Comment: 15 pages, 10 figure
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