: This thesis applies neural network feature selection techniques to multivariate time series data to improve prediction of a target time series. Two approaches to feature selection are used. First, a subset enumeration method is used to determine which financial indicators are most useful for aiding in prediction of the S&P 500 futures daily price. The candidate indicators evaluated include RSI, Stochastics and several moving averages. Results indicate that the Stochastics and RSI indicators result in better prediction results than the moving averages. The second approach to feature selection is calculation of individual saliency metrics. A new decision boundary-based individual saliency metric, and a classifier independent saliency metric are developed and tested. Ruck's saliency metric, the decision boundary based saliency metric, and the classifier independent saliency metric are compared for a data set consisting of the RSI and Stochastics indicators as well as delayed closing price values. The decision based metric and the Ruck metric results are similar, but the classifier independent metric agrees with neither of the other metrics. The nine most salient features, determined by the decision boundary based metric, are used to train a neural network and the results are presented and compared to other published results. (AN)

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Nonlinear Time Series Analysis.

This review provides a detailed overview of the energy harvesting technologies associated with piezoelectric materials along with the closely related sub-classes of pyroelectrics and ferroelectrics. These properties are, in many cases, present in the same material, providing the intriguing prospect of a material that can harvest energy from multiple sources including vibration, thermal fluctuations and light. Piezoelectric materials are initially discussed in the context of harvesting mechanical energy from vibrations using inertial energy harvesting, which relies on the resistance of a mass to acceleration, and kinematic energy harvesting which directly couples the energy harvester to the relative movement of different parts of a source. Issues related to mode of operation, loss mechanisms and using non-linearity to enhance the operating frequency range are described along with the potential materials that could be employed for harvesting vibrations at elevated temperatures. In addition to inorganic piezoelectric materials, compliant piezoelectric materials are also discussed. Piezoelectric energy harvesting devices are complex multi-physics systems requiring advanced methodologies to maximise their performance. The research effort to develop optimisation methods for complex piezoelectric energy harvesters is then reviewed. The use of ferroelectric or multi-ferroic materials to convert light into chemical or electrical energy is then described in applications where the internal electric field can prevent electron–hole recombination or enhance chemical reactions at the ferroelectric surface. Finally, pyroelectric harvesting generates power from temperature fluctuations and this review covers the modes of pyroelectric harvesting such as simple resistive loading and Olsen cycles. Nano-scale pyroelectric systems and novel micro-electro-mechanical-systems designed to increase the operating frequency are discussed.

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Piezoelectric and ferroelectric materials and structures for energy harvesting applications

High-Performance Piezoelectric Energy Harvesters and Their Applications

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Analysis of observed chaotic data

Materials science is recognized as one of the main factors driving development and economic growth. Since the silicon industrial revolution of the 1950s, research and developments in materials and solid state science have radically impacted and transformed our society by enabling the emergence of the computer technologies, wireless communications, Internet, digital data storage, and widespread consumer electronics. Today's emergent topics in solid state physics, such as nano-materials, graphene and carbon nano-tubes, smart and advanced functional materials, spintronic materials, bio-materials, and multiferroic materials, promise to deliver a new wave of technological advances and economic impact, comparable to the silicon industrial revolution of the 1950s.The surge of interest in multiferroic materials over the past 15 years has been driven by their fascinating physical properties and huge potential for technological applications. This article addresses some of the fundamental aspects of solid-state mult...

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Fundamentals of Multiferroic Materials and Their Possible Applications

A particular attention is devoted to analyze the dynamics of a strongly nonlinear energy harvester having fractional order viscoelastic flexible material. The strong nonlinearity is obtained from the magnetic interaction between the end free of the flexible material and three equally spaced magnets. Periodic responses are computed using the KrylovBogoliubov averaging method, and the effects of fractional order damping on the output electric energy are analyzed. It is obtained that the harvested energy is enhanced for small order of the fractional derivative. Considering the order and strength of the fractional viscoelastic property as control parameter, the complexity of the system response is investigated through the Melnikov criteria for horseshoes chaos, which allows us to derive the mathematical expression of the boundary between intra-well motion and bifurcations appearance domain. We observe that the order and strength of the fractional viscoelastic property can be effectively used to control chaos in the system. The results are confirmed by the smooth and fractal shape of the basin of attraction as the order of derivative decreases. The bifurcation diagrams and the corresponding Lyapunov exponents are plotted to get insight into the nonlinear response of the system.

Analysis of tristable energy harvesting system having fractional order viscoelastic material

A turbulent wind source for possible energy harvesting is considered. To increase the amplitude of vibration, we apply a magnetopiezoelastic oscillator having a double well Duffing potential. The output voltage response of the system for different level of wind excitations is analyzed. The energy harvesting appeared to be the most efficient for the conditions close to the stochastic resonance region where the potential barrier was overcame.

Performance of a piezoelectric energy harvester driven by air flow

An electromechanical energy harvesting system with a fractional order current–voltage relationship for the electrical circuit and fractional power law in the restoring force of its mechanical part is considered to act as an energy harvester. Our results show that, under a single-well potential configuration, for a small amplitude of the perturbation, as the order of derivative increases, the resonant amplitude of mechanical vibration decreases while the bending degree (hardening case) remains fairly constant. For a large amplitude of the perturbation, the output power is increased due to the hardening effects. Under a double-well configuration, the fractional power stiffness $$\alpha $$
 strongly affects the crossing well dynamics (large amplitude motion) and consequently the output electrical power. The harvested electric power appears to be maximal for deterministic and random excitation for small $$\alpha $$
 . High-level noise intensity is found to reduce the output power in the region of resonance and surprisingly increases the output in other regions of $$\alpha $$
 . For sufficiently large amplitude of harmonic excitation, this effect is realized in a stochastic resonance.

Nonlinear analysis of energy harvesting systems with fractional order physical properties

This paper proposes a rotational energy harvester using a piezoelectric bistable buckled beam to harvest low-speed rotational energy. The proposed harvester consists of a piezoelectric buckled beam with a center magnet, and a rotary magnet pair with opposite magnetic poles mounted on a revolving host. The magnetic plucking is used to harvest the angular kinetic energy of the host. The nonlinear snap-through mechanism is utilized to improve the vibration displacement and output voltage of the piezoelectric layer over a wide rotation frequency range. Theoretical simulation and experimental results show that the proposed energy harvester can yield a stable average output power ranging between 6.91-48.01 μW over a rotation frequency range of 1-14 Hz across a resistance load of 110 kΩ. Furthermore, dual attraction magnets were employed to overcome the suppression phenomenon at higher frequencies, which yields a broadband and flat frequency response over 6-14 Hz with the output power reaching 42.19-65.44 μW, de...

A piezoelectric energy harvester for broadband rotational excitation using buckled beam

An electromechanical system with flexible arm is considered. The mechanical part is a linear flexible beam and the electrical part is a nonlinear self-sustained oscillator. Oscillatory solutions are obtained using an averaging method. Chaotic behavior is studied via the Lyapunov exponent. The synchronization of regular and chaotic states of two such devices is discussed and the stability boundaries for the synchronization process are derived using the Floquet theory. We compare the results obtained from a finite difference simulation to those from the classical modal approach.

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C. A. Kitio Kwuimy

Papers

Analysis of tristable energy harvesting system having fractional order viscoelastic material

Performance of a piezoelectric energy harvester driven by air flow

Nonlinear analysis of energy harvesting systems with fractional order physical properties

A piezoelectric energy harvester for broadband rotational excitation using buckled beam

Dynamics, chaos and synchronization of self-sustained electromechanical systems with clamped-free flexible arm