The possibility of using conducting polymers as organic alternatives to widely used inorganic materials for thermoelectric (TE) applications has received much attention in the past few decades. Since conducting polymers are generally inefficient compared to inorganic TE materials, research into their underlying transport mechanisms is required to improve their efficiency. We use a model based on the effects of local thermal fluctuations to characterize the transport in conducting polymer composites. With this model, full linear responses for the current and electronic heat current are obtained. From these responses, the local temperature dependent conductivity, electronic contribution to the thermal conductivity, and Seebeck coefficient are extracted and related to those of the composite material through an effective medium theory. The resulting simple expressions for the TE transport properties are easy to use and can improve our understanding of transport in conducting polymers. An example of how to use the model is given for a parabolic tunneling barrier and comparisons to experimental data are also provided.

Magnetic nanoparticles (MNPs) have found use in a wide variety of biomedical applications including hyperthermia, imaging and drug delivery. Certain physical properties, such as the ability to generate heat in response to an alternating magnetic field, make these structures ideal for such purposes. This study's objective was to elucidate the mechanisms primarily responsible for RF MNP heating and determine how such processes affect polymer solutions that might be useful in drug delivery. 15-20 nm magnetite (Fe3O4) nanoparticles at 0.2% and 0.5% concentrations were heated with RF fields of different strengths (200 Oe, 400 Oe and 600 Oe) in water and in 0.5% gellan gum solution. Mixing and fan cooling were used in an attempt to improve accuracy of data collection. Specific absorption rate (SAR) values were determined experimentally for each combination of solvent, concentration and field strength. Theoretical calculation of SAR was performed using a model based on linear response theory. Mixing yielded greater precision in experimental determination of SAR while the effects of cooling on this parameter were negligible. Solutions with gellan gum displayed smoother heating over time but no significant changes in SAR values. This was attributed to low polymer concentration and lack of structural phase transition. The LRT model was found to be adequate for calculating SAR at low polymer concentration and was useful in identifying Neel relaxation as the dominant heating process. Heating trials with MNPs in 2% agar confirmed Neel relaxation to be primarily responsible for heat generation in the particles studied.

Sensory neurons assemble to form networks that process inputs coming from the senses. Through synaptic connections neurons interact and create complex dynamical states in response to these inputs. Networks with different connectivity patterns are thought to display different states and therefore subserve different computational goals. In this thesis, we mainly study brain rhythms, a dynamical state that occurs in various neural structures. Rhythms are emergent oscillations that typically occur in homogeneous recurrent networks, whose neurons have identical properties and are densely interconnected. Many sensory systems comprise neurons with opposite ON and OFF responses to inputs. We show that homogenous recurrent networks fail to sustain rhythms when ON and OFF neurons are present in equal proportions. This happens even when the network is subjected to spatially correlated inputs, which are known to promote synchronized oscillations. In this context, we adapted the so-called linear response theory to include networks containing ON and OFF neurons with different intrinsic properties. In this asymmetric case, oscillations can be recovered. A simpler approach is to segregate the ON and OFF populations, thus producing two oscillating subnetworks. The dynamics of purely feedforward networks are studied next. These networks are composed of two or more populations. The populations are connected in a serial fashion, but neurons are unconnected within the populations. This connectivity scheme is drastically different from the fully recurrent network. Yet, this network is shown to display oscillatorylike properties when subjected to spatially correlated stimulation under certain conditions. We also find that this network can implement various types of gain control, depending on the noise in the system and the strength of synaptic interactions. These results establish some unexpected links between feedforward and recurrent networks. Along the way, we apply our results and conclusions to a well-characterized sensory network, the electrosensory system of weakly electric fish.

Many social, biological and technological systems can be viewed as complex networks with a large number of interacting components. However despite recent advancements in network theory, a satisfactory description of dynamic processes arising in such cooperative systems is a subject of ongoing research. In this dissertation the emergence of dynamical complexity in networks of interacting stochastic oscillators is investigated. In particular I demonstrate that networks of two and three state stochastic oscillators present a second-order phase transition with respect to the strength of coupling between individual units. I show that at the critical point fluctuations of the global order parameter are characterized by an inverse-power law distribution and I assess their renewal properties. Additionally, I study the effect that different types of perturbation have on dynamical properties of the model. I discuss the relevance of those observations for the transmission of information between complex systems.

No description available.

Die vorliegende Arbeit befasst sich mit der Anwendung des kürzlich entwickelten 'Functional Approach' zur Elektrodynamik in Medien auf das Modell des freien homogenen Elektronengases. Basierend auf einer ausschließlich mikroskopischen Feldtheorie wird gezeigt, dass mittels universell gültiger Relationen zwischen Antwortfunktionen sowohl alle relevanten optischen als auch magnetischen (linearen) Materialeigenschaften allein aus der Strom-Strom-Korrelation gewonnen werden können. Dabei ist es essentiell, alle Berechnungen auf dem vollen Stromdichteoperator aufzubauen, also auf der Summe aus diamagnetischem, orbitalem und spinoriellem Anteil. Weiterhin wird anhand der magnetischen Suszeptibilität demonstriert, dass im Allgemeinen die Unterscheidung zwischen eigenen und direkten Antwortfunktionen nicht zu vernachlässigen ist. Schließlich wird mit dem „Lindhard-Integral-Theorem“ bewiesen, dass nicht nur der longitudinale, sondern auch der transversale Anteil des vollen frequenz- und wellenvektorabhängigen fundamentalen Antworttensors des freien Elektronengases komplett durch das charakteristische Lindhard-Integral bestimmt ist.:Introduction I Microscopic electrodynamics in media 1 Classical electrodynamics 1.1 Covariant formulation 1.2 Temporal gauge 1.3 Free Green function 1.4 Total functional derivatives 2 Electrodynamics in media 2.1 Field identifications 2.2 Fundamental response tensor 2.3 Universal response relations 2.4 Direct and proper response 2.5 Isotropic and combined limits 2.6 Full Green function 2.7 Wave equations in media and dispersion relations II Application to the free electron gas 3 Fundamental response tensor 3.1 Electromagnetic current density 3.2 Kubo-Greenwood formulae 3.3 Diamagnetic, orbital and spinorial contribution 3.4 Spin susceptibility vs. spinorial current response 4 London model and diamagnetic response 4.1 Interpretation as response function 4.2 Application of universal response relations 4.3 Spin correction 5 Full current response 5.1 Dimensionless formulae 5.2 Lindhard integral theorem 5.3 Laurent expansions 5.4 Optical properties 5.5 Magnetic properties Conclusion Appendix A - Notation Appendix B - Formulary B.1 Basic analysis and vector calculus B.2 Special relativity theory B.3 Fourier transformation B.4 Functional derivatives B.5 Projectors and Helmholtz' theorem B.6 Complex analysis Appendix C - Yang-Mills gauge theory C.1 Field strength tensor C.2 Minimal coupling principle C.3 Gauge invariant quantities and equations Appendix D - Periodic solids D.1 Partitioning of reciprocal space D.2 Homogeneous limit Appendix E - Electromagnetic spectrum Bibliography Acknowledgements Errata / This thesis is concerned with the application of the recently developed 'Functional Approach' to electrodynamics of media to the model of the free homogeneous electron gas. Based on an exclusively microscopic field theory it is shown that with the help of universally valid relations between response functions, all relevant optical and magnetic (linear) materials properties can be extracted from the mere current-current response. For this purpose, it is essential to base all calculations on the full current density operator, i.e. the sum of diamagnetic, orbital and spinorial contributions. Furthermore, we use the example of the magnetic susceptibility to demonstrate that the distinction between proper and direct response functions is in general crucial. Lastly, with the “Lindhard integral theorem” we prove that not only the longitudinal but also the transverse part of the full frequency- and wavevector-dependent fundamental response tensor of the free electron gas is completely determined by the characteristic Lindhard integral.:Introduction I Microscopic electrodynamics in media 1 Classical electrodynamics 1.1 Covariant formulation 1.2 Temporal gauge 1.3 Free Green function 1.4 Total functional derivatives 2 Electrodynamics in media 2.1 Field identifications 2.2 Fundamental response tensor 2.3 Universal response relations 2.4 Direct and proper response 2.5 Isotropic and combined limits 2.6 Full Green function 2.7 Wave equations in media and dispersion relations II Application to the free electron gas 3 Fundamental response tensor 3.1 Electromagnetic current density 3.2 Kubo-Greenwood formulae 3.3 Diamagnetic, orbital and spinorial contribution 3.4 Spin susceptibility vs. spinorial current response 4 London model and diamagnetic response 4.1 Interpretation as response function 4.2 Application of universal response relations 4.3 Spin correction 5 Full current response 5.1 Dimensionless formulae 5.2 Lindhard integral theorem 5.3 Laurent expansions 5.4 Optical properties 5.5 Magnetic properties Conclusion Appendix A - Notation Appendix B - Formulary B.1 Basic analysis and vector calculus B.2 Special relativity theory B.3 Fourier transformation B.4 Functional derivatives B.5 Projectors and Helmholtz' theorem B.6 Complex analysis Appendix C - Yang-Mills gauge theory C.1 Field strength tensor C.2 Minimal coupling principle C.3 Gauge invariant quantities and equations Appendix D - Periodic solids D.1 Partitioning of reciprocal space D.2 Homogeneous limit Appendix E - Electromagnetic spectrum Bibliography Acknowledgements Errata

Let t:[a,b] → ft be a C2 family of \"good\" C4 e piecewise expanding unimodal maps, with a critical point c, that is transversal to the topological classes of such maps. Given a lipchitzian observable ∅, consider the function ℛ∅(t)=∫∅dµt, where µt is the unique bsolutely continuous invariant probability of ft. We show a central limit theorem for the modulus of continuity of ℝ∅, that is limh→0m{t ∈ [a,b] : t + h ∈ [a,b] e 1/(Ψ(t)(-log|h|)½)((ℛ∅(t + h) - ℛ∅(t))/h) ≤ y} converges to 1/(2π)½ ∫y-∞e-s2/2ds. Now, let us consider a C2+ε expanding map f : 𝕊1 → 𝕊1 and a C1+ε periodic function v : 𝕊1 → ℝ. We show that the unique bounded solution of the twisted cohomological equation v(x) = α(f(x)) - Df(x)α(x) is either of class C1+ε or nowhere differentiable. We also prove that if α is nowhere differentiable, them the modulus of continuity of α satisfies a central limit theorem, that is, there is α &gt 0 such that limh→0µ{x : (α(x + h) - α(x))/(σ𝓁h(-log|h|)½) ≤ y} = 1/(2π)½ ∫y-∞e-t2/2dt, where µ is the absolutely continuous invariant probability of f. / Seja t:[a,b] → ft uma família C2 \"boa\" de transformações unimodais expansoras por pedaços com um ponto crítico c, que é transversal às classes topológicas de tais transformações. Dado um observável lipschitziano ∅, considere a função ℛ∅(t)=∫∅dµt, onde µt é a única probabiidade invariante absolutamente contínua de ft. Mostramos um teorema do limite central para o módulo de continuidade de ℝ∅, isto é limh→0m{t ∈ [a,b] : t + h ∈ [a,b] e 1/(Ψ(t)(-log|h|)½)((ℛ∅(t + h) - ℛ∅(t))/h) ≤ y} converge para 1/(2π)½ ∫y-∞e-s2/2ds. Vamos considerar agora f : 𝕊1 → 𝕊1 uma transformação expansora de classe C2+ε e v : 𝕊1 → ℝ uma função periódica de classe C1+ε. Mostramos que a única solução limitada da equação cohomológica torcida v(x) = α(f(x)) - Df(x)α(x) ou é de classe C1+ε ou não possui derivada em ponto algum. Mostramos também que se α não possui derivada em ponto algum, então o módulo de continuidade de α satisfaz um teorema do limite central, isto é, existe α &gt 0 tal que limh→0µ{x : (α(x + h) - α(x))/(σ𝓁h(-log|h|)½) ≤ y} = 1/(2π)½ ∫y-∞e-t2/2dt, onde µ é a probabilidade invariante absolutamente contínua associada a f.

With the growth of wireless networks and the increase in personal internet use for a wide diversity of applications, the importance of the quality of service (QoS) delivered to clients has become of great importance. In order to evaluate QoS, this study explores the application of the linear response surface analysis (LRSA) technique as an evaluation tool for QoS factors such as Throughput and Delay. An 802.11n prototype wireless network is constructed in order to capture QoS data that is then used to construct LRSA models in order to evaluate the QoS factors. The LRSA models are maximised and minimised while constraining specific measured QoS factors and the subsequent results are analysed. Based on this analysis, recommendations for the improvement of wireless networks are made as well as the use of the LRSA technique to evaluate QoS within a wireless network. / Thesis (MSc (Computer Science))--North-West University, Potchefstroom Campus, 2013

With the growth of wireless networks and the increase in personal internet use for a wide diversity of applications, the importance of the quality of service (QoS) delivered to clients has become of great importance. In order to evaluate QoS, this study explores the application of the linear response surface analysis (LRSA) technique as an evaluation tool for QoS factors such as Throughput and Delay. An 802.11n prototype wireless network is constructed in order to capture QoS data that is then used to construct LRSA models in order to evaluate the QoS factors. The LRSA models are maximised and minimised while constraining specific measured QoS factors and the subsequent results are analysed. Based on this analysis, recommendations for the improvement of wireless networks are made as well as the use of the LRSA technique to evaluate QoS within a wireless network. / Thesis (MSc (Computer Science))--North-West University, Potchefstroom Campus, 2013

Submitted by Santos Davilene (davilenes@ufba.br) on 2017-05-30T21:33:41Z No. of bitstreams: 1 tesededoutorado_thiago_bomfim_final.pdf: 1432533 bytes, checksum: e5fc0b79704aaec51e9363c8b86f6553 (MD5) / Approved for entry into archive by Vanessa Reis (vanessa.jamile@ufba.br) on 2017-06-01T12:41:44Z (GMT) No. of bitstreams: 1 tesededoutorado_thiago_bomfim_final.pdf: 1432533 bytes, checksum: e5fc0b79704aaec51e9363c8b86f6553 (MD5) / Made available in DSpace on 2017-06-01T12:41:44Z (GMT). No. of bitstreams: 1 tesededoutorado_thiago_bomfim_final.pdf: 1432533 bytes, checksum: e5fc0b79704aaec51e9363c8b86f6553 (MD5) / Nesta tese estudamos classes robustas de sistemas dinâmicos não-uniformemente expansores. Inicialmente provamos a diferenciabilidade da pressão topológica e de estados de equilíbrio e suas densidades com respeito ao sistema dinâmico, obtendo fórmulas precisas para as derivadas. Tais resultados, que decorrem da uniformidade do gap espectral dos respectivos operadores de transferência obtida a partir da técnica de cones e métricas projetivas, têm fortes consequências nas propriedades estatísticas do sistema dinâmico. De fato, provamos que a média e a variância obtidos do teorema central do limite variam diferenciavelmente com a dinâmica e também que vale um princípio de grandes desvios cuja função taxa varia diferenciavelmente com a dinâmica. Mais ainda, obtemos que a função taxa de decaimento de correlações em tempo-n para a medida de máxima entropia e diferenciável com respeito ao sistema dinâmico com derivada assintótica a zero. / No estudo das propriedades erg´odicas destas classes de sistemas dinˆamicos foi inclu´ıda tamb´em uma descri¸c˜ao topol´ogica sobre o formalismo multifractal associado a m´edias de Birkhoff e sequˆencias n˜ao necessariamente aditivas motivadas pelo estudo de expoentes de Lyapunov em dimens˜ao alta. Para estados de equil´ıbrio que exibem a propriedade de Gibbs fraco, provamos que a press˜ao topol´ogica do conjunto de pontos cuja m´edia de Birkhoff est´a afastada da m´edia espacial correspondente ao ´unico estado de equil´ıbrio pode ser expressa em termos press˜ao topol´ogica de todo sistema e da taxa grandes desvios. Extens˜oes para sistemas dinˆamicos com singularidades, fluxos e difeomorfismos hiperbólicos bem como conjuntos irregulares associados a medidas empíricas foram também obtidos.