Embodied neuromechanical chaos through homeostatic regulation

In this paper, we present detailed analyses of the dynamics of a number of embodied neuromechanical systems of a class that has been shown to efficiently exploit chaos in the development and learning of motor behaviors for bodies of arbitrary morphology. This class of systems has been successfully used in robotics, as well as to model biological systems. At the heart of these systems are neural central pattern generating (CPG) units connected to actuators which return proprioceptive information via an adaptive homeostatic mechanism. Detailed dynamical analyses of example systems, using high resolution largest Lyapunov exponent maps, demonstrate the existence of chaotic regimes within a particular region of parameter space, as well as the striking similarity of the maps for systems of varying size. Thanks to the homeostatic sensory mechanisms, any single CPG “views” the whole of the rest of the system as if it was another CPG in a two coupled system, allowing a scale invariant conceptualization of such embodied neuromechanical systems. The analysis reveals chaos at all levels of the systems; the entire brain-body-environment system exhibits chaotic dynamics which can be exploited to power an exploration of possible motor behaviors. The crucial influence of the adaptive homeostatic mechanisms on the system dynamics is examined in detail, revealing chaotic behavior characterized by mixed mode oscillations (MMOs). An analysis of the mechanism of the MMO concludes that they stems from dynamic Hopf bifurcation, where a number of slow variables act as “moving” bifurcation parameters for the remaining part of the system

Design and synthesis of photoactive molecules based on metal dithiolenes

This work reports on the design, synthesis and characterization of some homoleptic and heteroleptic d8 metal (Ni, Pd, Pt) dithiolene complexes. Chapter 1 provides the background required to properly design metal dithiolenes exhibiting desired properties. Chapter 2 describes the synthesis & characterization of homoleptic radical monoanionic complexes showing multi-properties. Among these, a platinum complex prepared using a ligand containing a quinoxaline moiety connected through a dithieno bridge to the dithiolene core, shows unusual anti- Kasha solution proton dependent luminescence. The interaction of protons with these complexes is described with a view to understand their photo/electrocatalytic behaviour in aqueous acidic systems. Photocatalytic preliminary experiments on noble metal free homoleptic Ni-complex for hydrogen production from aqueous acidic solutions are described. Chapter 3 describes design, synthesis and characterization of chiral/achiral heteroleptic d8 metal dithiolene complexes, suitable as donor-metal-acceptor chromophores for 2nd order NLO applications. It describes how with the presence or absence of acid (protons) in solutions of complexes can afford two switchable chemical forms (having different electronic properties) which can possibly display contrast in their NLO response. It also describes, by inclusion of chirality in the acceptor ligand, a non-centrosymmetric arrangement of molecules in crystalline medium to preserve NLO response in the bulk. Moreover, the unusual proton dependent dual luminescent properties of some of these complexes are described. Lastly Chapter 4 contains conclusions, perspectives and appendices for this work

Model Order Reduction for Gas and Energy Networks

To counter the volatile nature of renewable energy sources, gas networks take a vital role. But, to ensure fulfillment of contracts under these circumstances, a vast number of possible scenarios, incorporating uncertain supply and demand, has to be simulated ahead of time. This many-query gas network simulation task can be accelerated by model reduction, yet, large-scale, nonlinear, parametric, hyperbolic partial differential(-algebraic) equation systems, modeling natural gas transport, are a challenging application for model order reduction algorithms. For this industrial application, we bring together the scientific computing topics of: mathematical modeling of gas transport networks, numerical simulation of hyperbolic partial differential equation, and parametric model reduction for nonlinear systems. This research resulted in the "morgen" (Model Order Reduction for Gas and Energy Networks) software platform, which enables modular testing of various combinations of models, solvers, and model reduction methods. In this work we present the theoretical background on systemic modeling and structured, data-driven, system-theoretic model reduction for gas networks, as well as the implementation of "morgen" and associated numerical experiments testing model reduction adapted to gas network models

Atoms in microcavities : detection and spectroscopy

This thesis presents work undertaken with cold rubidium atoms interacting with an optical microcavity. The optical microcavity used is unique in its design, being formed between an optical fibre and silicon micromirror. This allows direct optical access to the cavity mode, whilst the use of microfabrication techniques in the design means that elements of the system are inherently scalable. In addition, the parameters of the system are such that a single atom has a substantial impact on the cavity field. In this system, two types of signal arise from the atoms' interaction with the cavity field; a `reflection' signal and a `fluorescence' signal. A theoretical description for these signals is presented, followed by experiments which characterise the signals under a variety of experimental conditions. The thesis then explores two areas: the use of the microcavity signals for atom detection and the investigation of how higher atom numbers and, as a result, a larger cooperative interaction between the atoms and the cavity field, impacts the signals. First, the use of these signals to detect an effective single atom and individual atoms whilst falling and trapped is explored. The effectiveness of detection is parameterised in terms of detection confidence and signal to noise ratio, detection fidelity and dynamic range. In the second part of this thesis, the effect of higher atom numbers on the reflection and fluorescence signals is investigated. A method for increasing the atom number is presented, alongside experiments investigating the impact on the measured signals. This is followed by experiments which explore the dispersive nature of the atom-cavity interaction by measuring the excitation spectrum of the system in reflection and fluorescence. In doing so, it is shown that, for weak coupling, these two signals are manifestly different

Design and synthesis of photoactive molecules based on metal dithiolenes

This work reports on the design, synthesis and characterization of some homoleptic and heteroleptic d8 metal (Ni, Pd, Pt) dithiolene complexes. Chapter 1 provides the background required to properly design metal dithiolenes exhibiting desired properties. Chapter 2 describes the synthesis & characterization of homoleptic radical monoanionic complexes showing multi-properties. Among these, a platinum complex prepared using a ligand containing a quinoxaline moiety connected through a dithieno bridge to the dithiolene core, shows unusual anti- Kasha solution proton dependent luminescence. The interaction of protons with these complexes is described with a view to understand their photo/electrocatalytic behaviour in aqueous acidic systems. Photocatalytic preliminary experiments on noble metal free homoleptic Ni-complex for hydrogen production from aqueous acidic solutions are described. Chapter 3 describes design, synthesis and characterization of chiral/achiral heteroleptic d8 metal dithiolene complexes, suitable as donor-metal-acceptor chromophores for 2nd order NLO applications. It describes how with the presence or absence of acid (protons) in solutions of complexes can afford two switchable chemical forms (having different electronic properties) which can possibly display contrast in their NLO response. It also describes, by inclusion of chirality in the acceptor ligand, a non-centrosymmetric arrangement of molecules in crystalline medium to preserve NLO response in the bulk. Moreover, the unusual proton dependent dual luminescent properties of some of these complexes are described. Lastly Chapter 4 contains conclusions, perspectives and appendices for this work

American Square Dance Vol. 55, No. 6 (June 2000)

Monthly square dance magazine that began publication in 1945

Near field interactions in terahertz metamaterials

Terahertz (THz) frequencies comprise the portion of the electromagnetic spectrum more energetic than microwaves, but less energetic than infrared light. The THz band presents many opportunities for condensed matter physics and optics engineering. From the physics perspective, advances in the generation and detection of THz radiation have opened the door for spectroscopic studies of a range of solid-state phenomena that manifest at THz frequencies. From an engineering perspective, THz frequencies are an under-used spectral region, ripe for the development of new devices. In both cases, the challenge for researchers is to overcome a lack of sources, detectors, and optics for THz light, termed the THz Gap. Metamaterials (MMs), composite structures with engineered index of refraction, n, and impedance, Z, provide one path towards realizing THz optics. MMs are an ideal platform for the design of local EM field distributions, and far-field optical properties. This is especially true at THz frequencies, where fabrication of inclusions is easily accomplished with photolithography. Historically, MM designs have been based around static configurations of resonant inclusions that work only in a narrow frequency band, limiting applications. Broadband and tunable MMs are needed to overcome this limit. This dissertation focuses on creating tunable and controllable MM structures through the manipulation of electromagnetic interactions between MM inclusions. We introduce three novel MM systems. Each system is studied computationally with CST-Studio, and experimentally via THz spectroscopy. First, we look at the tunable transmission spectrum of two coupled split ring resonators (SRRs) with different resonant frequencies. We show that introducing a lateral displacement between the two component resonators lowers the electromagnetic coupling between the SRRs, activating a new resonance. Second, we study an SRR array, coupled to a non-resonant closed ring array. We show that lowering the interaction strength through lateral displacement changes the MM oscillator strength by ~ 40% and electric field enhancement by a factor of 4. Finally, we show that interactions between a superconducting SRR array and a conducting ground plane result in a temperature and field strength dependent MM absorption. The peak absorption changes by ~ 40% with increasing electric field and by ~ 66% with increasing temperature