167 research outputs found
Robust Subspace System Identification via Weighted Nuclear Norm Optimization
Subspace identification is a classical and very well studied problem in
system identification. The problem was recently posed as a convex optimization
problem via the nuclear norm relaxation. Inspired by robust PCA, we extend this
framework to handle outliers. The proposed framework takes the form of a convex
optimization problem with an objective that trades off fit, rank and sparsity.
As in robust PCA, it can be problematic to find a suitable regularization
parameter. We show how the space in which a suitable parameter should be sought
can be limited to a bounded open set of the two dimensional parameter space. In
practice, this is very useful since it restricts the parameter space that is
needed to be surveyed.Comment: Submitted to the IFAC World Congress 201
A Learning Based Approach to Control Synthesis of Markov Decision Processes for Linear Temporal Logic Specifications
We propose to synthesize a control policy for a Markov decision process (MDP)
such that the resulting traces of the MDP satisfy a linear temporal logic (LTL)
property. We construct a product MDP that incorporates a deterministic Rabin
automaton generated from the desired LTL property. The reward function of the
product MDP is defined from the acceptance condition of the Rabin automaton.
This construction allows us to apply techniques from learning theory to the
problem of synthesis for LTL specifications even when the transition
probabilities are not known a priori. We prove that our method is guaranteed to
find a controller that satisfies the LTL property with probability one if such
a policy exists, and we suggest empirically with a case study in traffic
control that our method produces reasonable control strategies even when the
LTL property cannot be satisfied with probability one
Distribution-Aware Sampling and Weighted Model Counting for SAT
Given a CNF formula and a weight for each assignment of values to variables,
two natural problems are weighted model counting and distribution-aware
sampling of satisfying assignments. Both problems have a wide variety of
important applications. Due to the inherent complexity of the exact versions of
the problems, interest has focused on solving them approximately. Prior work in
this area scaled only to small problems in practice, or failed to provide
strong theoretical guarantees, or employed a computationally-expensive maximum
a posteriori probability (MAP) oracle that assumes prior knowledge of a
factored representation of the weight distribution. We present a novel approach
that works with a black-box oracle for weights of assignments and requires only
an {\NP}-oracle (in practice, a SAT-solver) to solve both the counting and
sampling problems. Our approach works under mild assumptions on the
distribution of weights of satisfying assignments, provides strong theoretical
guarantees, and scales to problems involving several thousand variables. We
also show that the assumptions can be significantly relaxed while improving
computational efficiency if a factored representation of the weights is known.Comment: This is a full version of AAAI 2014 pape
An Inductorless Bias-Flip Rectifier for Piezoelectric Energy Harvesting
Piezoelectric vibration energy harvesters have drawn much interest for powering self-sustained electronic devices. Furthermore, the continuous push toward miniaturization and higher levels of integration continues to form key drivers for autonomous sensor systems being developed as parts of the emerging Internet of Things (IoT) paradigm. The synchronized switch harvesting (SSH) on inductor and synchronous electrical charge extraction are two of the most efficient interface circuits for piezoelectric energy harvesters; however, inductors are indispensable components in these interfaces. The required inductor values can be up to 10 mH to achieve high efficiencies, which significantly increase overall system volume, counter to the requirement for miniaturized self-power systems for IoT. An inductorless bias-flip rectifier is proposed in this paper to perform residual charge inversion using capacitors instead of inductors. The voltage flip efficiency goes up to 80% while eight switched capacitors are employed. The proposed SSH on capacitors circuit is designed and fabricated in a 0.35-μm CMOS process. The performance is experimentally measured and it shows a 9.7x performance improvement compared with a full-bridge rectifier for the case of a 2.5-V open-circuit zero-peak voltage amplitude generated by the piezoelectric harvester. This performance improvement is higher than most of the reported state-of-the-art inductor-based interface circuits, while the proposed circuit has a significantly smaller overall volume enabling system miniaturization.EPSRC (Grant number: EP/L010917/1
Diagnosis and Repair for Synthesis from Signal Temporal Logic Specifications
We address the problem of diagnosing and repairing specifications for hybrid
systems formalized in signal temporal logic (STL). Our focus is on the setting
of automatic synthesis of controllers in a model predictive control (MPC)
framework. We build on recent approaches that reduce the controller synthesis
problem to solving one or more mixed integer linear programs (MILPs), where
infeasibility of a MILP usually indicates unrealizability of the controller
synthesis problem. Given an infeasible STL synthesis problem, we present
algorithms that provide feedback on the reasons for unrealizability, and
suggestions for making it realizable. Our algorithms are sound and complete,
i.e., they provide a correct diagnosis, and always terminate with a non-trivial
specification that is feasible using the chosen synthesis method, when such a
solution exists. We demonstrate the effectiveness of our approach on the
synthesis of controllers for various cyber-physical systems, including an
autonomous driving application and an aircraft electric power system
A new electrode design method in piezoelectric vibration energy harvesters to maximize output power
A resonant vibration energy harvester typically comprises of a clamped anchor and a vibrating shuttle with a proof mass. Piezoelectric materials are embedded in locations of high strain in order to transduce mechanical deformation into electrical charge. Conventional design for piezoelectric vibration energy harvesters (PVEH) usually utilizes piezoelectric materials and metal electrode layers covering the entire surface area of the cantilever with no consideration provided to examine the trade-off involved with respect to maximize output power. This paper reports on the theory and experimental verification underpinning optimization of the active electrode area in order to maximize output power. The calculations show that, in order to maximize the output power of a PVEH, the electrode should cover the piezoelectric layer from the peak strain area to a position, where the strain is a half of the average strain in all the previously covered area. With the proposed electrode design, the output power can be improved by 145% and 126% for a cantilever and a clamped-clamped beam, respectively. MEMS piezoelectric harvesters are fabricated to experimentally validate the theory.EPSRC (Grant EP/L010917/1
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