460 research outputs found
Delayed feedback control in quantum transport
Feedback control in quantum transport has been predicted to give rise to
several interesting effects, amongst them quantum state stabilisation and the
realisation of a mesoscopic Maxwell's daemon. These results were derived under
the assumption that control operations on the system be affected
instantaneously after the measurement of electronic jumps through it. In this
contribution I describe how to include a delay between detection and control
operation in the master equation theory of feedback-controlled quantum
transport. I investigate the consequences of delay for the state-stabilisation
and Maxwell's-daemon schemes. Furthermore, I describe how delay can be used as
a tool to probe coherent oscillations of electrons within a transport system
and how this formalism can be used to model finite detector bandwidth.Comment: 13 pages, 5 figure
Controlling surface morphologies by time-delayed feedback
We propose a new method to control the roughness of a growing surface, via a
time-delayed feedback scheme. As an illustration, we apply this method to the
Kardar-Parisi-Zhang equation in 1+1 dimensions and show that the effective
growth exponent of the surface width can be stabilized at any desired value in
the interval [0.25,0.33], for a significant length of time. The method is quite
general and can be applied to a wide range of growth phenomena. A possible
experimental realization is suggested.Comment: 4 pages, 3 figure
Feedback control of flow alignment in sheared liquid crystals
Based on a continuum theory, we investigate the manipulation of the
non-equilibrium behavior of a sheared liquid crystal via closed-loop feedback
control. Our goal is to stabilize a specific dynamical state, that is, the
stationary "flow-alignment", under conditions where the uncontrolled system
displays oscillatory director dynamics with in-plane symmetry. To this end we
employ time-delayed feedback control (TDFC), where the equation of motion for
the ith component, q_i(t), of the order parameter tensor is supplemented by a
control term involving the difference q_i(t)-q_i(t-\tau). In this diagonal
scheme, \tau is the delay time. We demonstrate that the TDFC method
successfully stabilizes flow alignment for suitable values of the control
strength, K, and \tau; these values are determined by solving an exact
eigenvalue equation. Moreover, our results show that only small values of K are
needed when the system is sheared from an isotropic equilibrium state, contrary
to the case where the equilibrium state is nematic
Stabilizing continuous-wave output in semiconductor lasers by time-delayed feedback
The stabilization of steady states is studied in a modified Lang-Kobayashi
model of a semiconductor laser. We show that multiple time-delayed feedback,
realized by a Fabry-Perot resonator coupled to the laser, provides a valuable
tool for the suppression of unwanted intensity pulsations, and leads to stable
continuous-wave operation. The domains of control are calulated in dependence
on the feedback strength, delay time (cavity round trip time), memory parameter
(mirror reflectivity), latency time, feedback phase, and bandpass filtering,
Due to the optical feedback, multistable behavior can also occur in the form of
delay-induced intensity pulsations or other modes for certain choices of the
control parameters. Control may then still be achieved by slowly ramping the
injection current during turn-on.Comment: 12 pages, 17 figure
Effects of external global noise on the catalytic CO oxidation on Pt(110)
Oxidation reaction of CO on a single platinum crystal is a reaction-diffusion
system that may exhibit bistable, excitable, and oscillatory behavior. We
studied the effect of a stochastic signal artificially introduced into the
system through the partial pressure of CO. First, the external signal is
employed as a turbulence suppression tool, and second, it modifies the
boundaries in the bistable transition between the CO and oxygen covered phases.
Experiments using photoemission electron microscopy (PEEM) together with
numerical simulations performed with the Krischer-Eiswirth-Ertl (KEE) model are
presented.Comment: 15 pages, 7 figures, accepted in J. Chem. Phy
Equation of motion method for Full Counting Statistics: Steady state superradiance
For the multi-mode Dicke model in a transport setting that exhibits
collective boson transmissions, we construct the equation of motion for the
cumulant generating function. Approximating the exact system of equations at
the level of cumulant generating function and system operators at lowest order,
allows us to recover master equation results of the Full Counting Statistics
for certain parameter regimes at very low cost of computation. The
thermodynamic limit, that is not accessible with the master equation approach,
can be derived analytically for different approximations.Comment: 7 pages, 3 figures, revised version, accepted by PR
Nonpolar resistance switching of metal/binary-transition-metal oxides/metal sandwiches: homogeneous/inhomogeneous transition of current distribution
Exotic features of a metal/oxide/metal (MOM) sandwich, which will be the
basis for a drastically innovative nonvolatile memory device, is brought to
light from a physical point of view. Here the insulator is one of the
ubiquitous and classic binary-transition-metal oxides (TMO), such as Fe2O3,
NiO, and CoO. The sandwich exhibits a resistance that reversibly switches
between two states: one is a highly resistive off-state and the other is a
conductive on-state. Several distinct features were universally observed in
these binary TMO sandwiches: namely, nonpolar switching, non-volatile threshold
switching, and current--voltage duality. From the systematic sample-size
dependence of the resistance in on- and off-states, we conclude that the
resistance switching is due to the homogeneous/inhomogeneous transition of the
current distribution at the interface.Comment: 7 pages, 5 figures, REVTeX4, submitted to Phys. Rev. B (Feb. 23,
2007). If you can't download a PDF file of this manscript, an alternative one
can be found on the author's website: http://staff.aist.go.jp/i.inoue
Control of Synchronization in two-layer power grids
In this work we suggest to model the dynamics of power grids in terms of a
two-layer network, and use the Italian high voltage power grid as a
proof-of-principle example. The first layer in our model represents the power
grid consisting of generators and consumers, while the second layer represents
a dynamic communication network that serves as a controller of the first layer.
In particular, the dynamics of the power grid is modelled by the Kuramoto model
with inertia, while the communication layer provides a control signal for
each generator to improve frequency synchronization within the power grid. We
propose different realizations of the communication layer topology and
different ways to calculate the control signal. Then we conduct a systematic
survey of the two-layer system against a multitude of different realistic
perturbation scenarios, such as disconnecting generators, increasing demand of
consumers, or generators with stochastic power output. When using a control
topology that allows all generators to exchange information, we find that a
control scheme aimed to minimize the frequency difference between adjacent
nodes operates very efficiently even against the worst scenarios with the
strongest perturbations
Feedback-controlled transport in an interacting colloidal system
Based on dynamical density functional theory (DDFT) we consider a
non-equilibrium system of interacting colloidal particles driven by a constant
tilting force through a periodic, symmetric "washboard" potential. We
demonstrate that, despite of pronounced spatio-temporal correlations, the
particle current can be reversed by adding suitable feedback control terms to
the DDFT equation of motion. We explore two distinct control protocols with
time delay, focussing on either the particle positions or the density profile.
Our study shows that the DDFT is an appropriate framework to implement
time-delayed feedback control strategies widely used in other fields of
nonlinear physicsComment: 6 pages, 5 figure
Control of unstable steady states by time-delayed feedback methods
We show that time-delayed feedback methods, which have successfully been used
to control unstable periodic ortbits, provide a tool to stabilize unstable
steady states. We present an analytical investigation of the feedback scheme
using the Lambert function and discuss effects of both a low-pass filter
included in the control loop and non-zero latency times associated with the
generation and injection of the feedback signal.Comment: 8 pages, 11 figure
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