131 research outputs found
Promoting Truthful Behaviour in Participatory-Sensing Mechanisms
In this paper, the interplay between a class of nonlinear estimators and
strategic sensors is studied in several participatory-sensing scenarios. It is
shown that for the class of estimators, if the strategic sensors have access to
noiseless measurements of the to-be-estimated-variable, truth-telling is an
equilibrium of the game that models the interplay between the sensors and the
estimator. Furthermore, performance of the proposed estimators is examined in
the case that the strategic sensors form coalitions and in the presence of
noise.Comment: IEEE Signal Processing Letters, In Pres
Normalized coprime representations for time-varying linear systems
Copyright Ā© 2010 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.49th IEEE Conference on Decision and Control, Atlanta, USA, 15-17 December 2010By considering the behaviour of stabilizable and detectable, linear time-varying state-space models over doublyinfinite continuous time, we establish the existence of so-called normalized coprime representations for the system graphs; that is, stable and stably left (resp. right) invertible, image (resp. kernel) representations that are normalized with respect to the inner product on LĀ²(āā,ā); this is consistent with the notion of normalization used in the time-invariant setting. The approach is constructive, involving the solution of timevarying differential Riccati equations with single-point boundary conditions at either +ā or āā. The contribution lies in accommodating state-space models that may not define an exponential dichotomy
On Validating Closed-Loop Behaviour from Noisy Frequency-Response Measurements
It is shown how noisy closed-loop frequency-response measurements can be used to obtain pointwise in frequency bounds on the possible difference between the actual closed-loop system and the closed-loop comprising a nominal model of the plant and the stabilising controller. To this end, Vinnicombe's gap metric framework for robustness analysis plays a central role. Indeed, an optimisation problem and corresponding algorithm are proposed for estimating the chordal distance between the frequency responses of the nominal plant model and a plant that is consistent with the closed-loop data and a priori information, when projected onto the Riemann sphere
Implementing Homomorphic Encryption Based Secure Feedback Control for Physical Systems
This paper is about an encryption based approach to the secure implementation
of feedback controllers for physical systems. Specifically, Paillier's
homomorphic encryption is used to digitally implement a class of linear dynamic
controllers, which includes the commonplace static gain and PID type feedback
control laws as special cases. The developed implementation is amenable to
Field Programmable Gate Array (FPGA) realization. Experimental results,
including timing analysis and resource usage characteristics for different
encryption key lengths, are presented for the realization of an inverted
pendulum controller; as this is an unstable plant, the control is necessarily
fast
Physical properties of Ce3-xTe4 below room temperature
The physical properties of polycrystalline Ce3-xTe4 were investigated by
measurements of the thermoelectric properties, Hall coefficient, heat capacity,
and magnetization. The fully-filled, metallic x=0 compound displays a soft
ferromagnetic transition near 4K, and analysis of the corresponding heat
capacity anomaly suggests a doublet ground state for Ce^{3+}. The transition is
suppressed to below 2K in the insulating x=0.33 composition, revealing that
magnetic order in Ce3-xTe4 is driven by an RKKY-type interaction. The
thermoelectric properties trend with composition as expected from simple
electron counting, and the transport properties in Ce3Te4 are observed to be
similar to those in La3Te4. Trends in the low temperature thermal conductivity
data reveal that the phonons are efficiently scattered by electrons, while all
compositions examined have a lattice thermal conductivity near 1.2W/m/K at
200K.Comment: Submitted to Phys. Rev.
Spin reorientation in TlFe1.6Se2 with complete vacancy ordering
The relationship between vacancy ordering and magnetism in TlFe1.6Se2 has
been investigated via single crystal neutron diffraction, nuclear forward
scattering, and transmission electron microscopy. The examination of chemically
and structurally homogenous crystals allows the true ground state to be
revealed, which is characterized by Fe moments lying in the ab-plane below
100K. This is in sharp contrast to crystals containing regions of order and
disorder, where a competition between c-axis and ab-plane orientations of the
moments is observed. The properties of partially-disordered TlFe1.6Se2 are
therefore not associated with solely the ordered or disordered regions. This
contrasts the viewpoint that phase separation results in independent physical
properties in intercalated iron selenides, suggesting a coupling between
ordered and disordered regions may play an important role in the
superconducting analogues.Comment: Minor changes; updated references and funding acknowledgemen
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