10,966 research outputs found
Performance measures for single-degree-of-freedom energy harvesters under stochastic excitation
We develop performance criteria for the objective comparison of different
classes of single-degree-of-freedom oscillators under stochastic excitation.
For each family of oscillators, these objective criteria take into account the
maximum possible energy harvested for a given response level, which is a
quantity that is directly connected to the size of the harvesting
configuration. We prove that the derived criteria are invariant with respect to
magnitude or temporal rescaling of the input spectrum and they depend only on
the relative distribution of energy across different harmonics of the
excitation. We then compare three different classes of linear and nonlinear
oscillators and using stochastic analysis tools we illustrate that in all cases
of excitation spectra (monochromatic, broadband, white-noise) the optimal
performance of all designs cannot exceed the performance of the linear design.
Subsequently, we study the robustness of this optimal performance to small
perturbations of the input spectrum and illustrate the advantages of nonlinear
designs relative to linear ones.Comment: 24 pages, 12 figure
A moment-equation-copula-closure method for nonlinear vibrational systems subjected to correlated noise
We develop a moment equation closure minimization method for the inexpensive
approximation of the steady state statistical structure of nonlinear systems
whose potential functions have bimodal shapes and which are subjected to
correlated excitations. Our approach relies on the derivation of moment
equations that describe the dynamics governing the two-time statistics. These
are combined with a non-Gaussian pdf representation for the joint
response-excitation statistics that has i) single time statistical structure
consistent with the analytical solutions of the Fokker-Planck equation, and ii)
two-time statistical structure with Gaussian characteristics. Through the
adopted pdf representation, we derive a closure scheme which we formulate in
terms of a consistency condition involving the second order statistics of the
response, the closure constraint. A similar condition, the dynamics constraint,
is also derived directly through the moment equations. These two constraints
are formulated as a low-dimensional minimization problem with respect to
unknown parameters of the representation, the minimization of which imposes an
interplay between the dynamics and the adopted closure. The new method allows
for the semi-analytical representation of the two-time, non-Gaussian structure
of the solution as well as the joint statistical structure of the
response-excitation over different time instants. We demonstrate its
effectiveness through the application on bistable nonlinear
single-degree-of-freedom energy harvesters with mechanical and electromagnetic
damping, and we show that the results compare favorably with direct Monte-Carlo
Simulations
One-way quantum computation with four-dimensional photonic qudits
We consider the possibility of performing linear optical quantum computation
making use of extra photonic degrees of freedom. In particular we focus on the
case where we use photons as quadbits. The basic 2-quadbit cluster state is a
hyper-entangled state across polarization and two spatial mode degrees of
freedom. We examine the non-deterministic methods whereby such states can be
created from single photons and/or Bell pairs, and then give some mechanisms
for performing higher-dimensional fusion gates.Comment: 10 figures (typos are corrected
Generating and verifying graph states for fault-tolerant topological measurement-based quantum computing in 2D optical lattices
We propose two schemes for implementing graph states useful for
fault-tolerant topological measurement-based quantum computation in 2D optical
lattices. We show that bilayer cluster and surface code states can be created
by global single-row and controlled-Z operations. The schemes benefit from the
accessibility of atom addressing on 2D optical lattices and the existence of an
efficient verification protocol which allows us to ensure the experimental
feasibility of measuring the fidelity of the system against the ideal graph
state. The simulation results show potential for a physical realization toward
fault-tolerant measurement-based quantum computation against dephasing and
unitary phase errors in optical lattices.Comment: 6 pages and 4 figures (minor changed
A Critical Analysis of Structural Contradictions in Open and Distance Higher Education Using Cultural-Historical Activity Theory
Drawing upon cultural-historical activity theory, this research analyzed the structural contradictions existing in a variety of educational activities among a group of alienated adult students in open and distance higher education
Deterministic amplification of Schroedinger cat states in circuit quantum electrodynamics
We propose a dynamical scheme for deterministically amplifying photonic
Schroedinger cat states based on a set of optimal state-transfers. The scheme
can be implemented in strongly coupled qubit-cavity systems and is well suited
to the capabilities of state of the art superconducting circuits. The ideal
analytical scheme is compared with a full simulation of the open
Jaynes-Cummings model with realistic device parameters. This amplification tool
can be utilized for practical quantum information processing in non-classical
continuous-variable states.Comment: A revised manuscript has 6 figure
A photonic-crystal optical antenna for extremely large local-field enhancement
We propose a novel design of an all-dielectric optical antenna based on photonic-band-gap confinement. Specifically, we have engineered the photonic-crystal dipole mode to have broad spectral response (Q ~70) and well-directed vertical-radiation by introducing a plane mirror below the cavity. Considerably large local electric-field intensity enhancement ~4,500 is expected from the proposed design for a normally incident planewave. Furthermore, an analytic model developed based on coupled-mode theory predicts that the electric-field intensity enhancement can easily be over 100,000 by employing reasonably high-Q (~10,000) resonators
Electronic properties of quantum dots formed by magnetic double barriers in quantum wires
The transport through a quantum wire exposed to two magnetic spikes in series
is modeled. We demonstrate that quantum dots can be formed this way which
couple to the leads via magnetic barriers. Conceptually, all quantum dot states
are accessible by transport experiments. The simulations show Breit-Wigner
resonances in the closed regime, while Fano resonances appear as soon as one
open transmission channel is present. The system allows to tune the dot's
confinement potential from sub-parabolic to superparabolic by experimentally
accessible parameters.Comment: 5 pages, 5 figure
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