This dissertation examines key areas in ontology through the intersection of metaphysics and physics. I argue that modern physics gives us good cause to look for new metaphysical models in place of the classical conceptions of ‘object' and ‘space'. Part I addresses the object in itself, wherein I argue that physics, along with various philosophical concerns, encourages us to re-evaluate the intrinsic/ extrinsic distinction in favour of new classifications. In particular, I use conclusions of relativity theory and the acquisition of mass via the Higgs field as indications of the inadequacy of intrinsicality, concluding that the distinction is more trouble than it is worth. Part II examines the intersection of objects and space, wherein I criticise substantivalism and promote singular fundamental ontologies like relationalism and supersubstantivalism. I examine phenomena like spatial expansion and field theory as well as separability issues more generally to emphasise the lack of rationale for a substance dualism of ‘object material' and ‘space material'. I also challenge the coherence of substantivalism's ‘occupation relation' and the ease of interpreting mathematical models into physical terms. I conclude that, again, the classical notion of ‘object' and its substantival framework are misplaced and should be put aside in favour of developing monistic ontologies. Part III looks at space in itself and the properties commonly attributed to it. I explore issues of separability using key experiments, and what makes spaces ‘physically real', before an extended examination of dimensions and dimensionality, highlighting the confusion physicists express toward such a ubiquitous concept in modern physical theories. I also explore how we use dimensions and reasons for adopting realist or instrumentalist approaches toward them, arguing that much more work should be focused on this area. I conclude with ways in which physics motivates new metaphysical models and suggest improvements for future methodological partnerships.

No description available.

Orientadores: Rubens Maciel Filho, Marcelo Embiruçu de Souza / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-09T00:35:59Z (GMT). No. of bitstreams: 1 Costa_MariaCarolinaBurgos_M.pdf: 1508476 bytes, checksum: 27959c176c0c329eb77aa2eff37a6b84 (MD5) Previous issue date: 2007 / Resumo: Um grande desafio relacionado com a pesquisa de polímeros tem sido o desenvolvimento de relações capazes de predizer as suas propriedades de uso final a partir das condições operacionais ¿ ou durante o processo de polimerização ou nas fases do processo de transformação. Estas relações podem ser utilizadas para otimizar as condições operacionais dos sistemas de transformação e produzir artigos com propriedades finais especificadas. O primeiro passo para isto é o conhecimento das relações entre propriedades intrínsecas e propriedades finais. O segundo passo é correlacionar as condições operacionais com as propriedades intrínsecas das resinas. Sendo assim, o principal objetivo do presente trabalho é desenvolver modelos empíricos para predição de propriedades finais de resinas de polietileno (PE) em função de suas propriedades intrínsecas, além de correlaciona r qualitativamente essas propriedades. Devido à grande variedade de resinas de polietileno existentes no mercado, as mesmas foram divididas em grupos, de acordo com a aplicação a que se destinam. Uma pesquisa foi realizada com a finalidade de se avaliar as propriedades mais importantes para cada aplicação final. Em seguida, foram encontradas equações compreendendo, para cada grupo de resinas, as seguintes classes de propriedades: propriedades mecânicas, térmicas, ópticas, propriedades de superfície de contato, reológicas e morfológicas. As propriedades intrínsecas selecionadas para caracterizar as resinas foram, índice de fluidez (MI), propriedade reológica que está inversamente relacionada com a viscosidade e com o peso molecular da resina; ¿stress exponent¿ (SE) / razão de expansão (SR), que é uma medida do caráter não-Newtoniano do polímero fundido, a qual pode ser usada para avaliar a processabilidade da resina; e densidade, que está diretamente relacionada com o grau de cristalinidade das resinas. Entre as propriedades intrínsecas existentes, as propriedades selecionadas exercem, em geral, uma influência significativa nas propriedades dos polímeros, além de serem facilmente mensuráveis na indústria. Além de uma extensa revisão bibliográfica, uma análise estatística prévia das correlações entre as variáveis foi realizada e, em seguida, foram escolhidas as variáveis de entrada de cada modelo. Para dois dos seis grupos de resinas estudados, a propriedade de SE / SR não foi usada como variável de entrada dos modelos, pois esta propriedade não é mensurável ou significativa para grande parte das resinas desses grupos. É importante destacar que os aditivos podem exercer influência considerável nas propriedades de uso final dos polímeros, ou seja, a influência dos aditivos torna ainda mais complexo o estudo para a predição das propriedades finais a partir das condições operacionais dos sistemas de polimerização. No entanto, não foi possível um controle da quantidade e qualidade dos aditivos envolvidos na produção das resinas e, dessa forma, um estudo envolvendo a influência dos aditivos nas propriedades de desempenho do polímero está além do escopo deste trabalho. Para o desenvolvimento deste trabalho, uma considerável quantidade de experimentos foi realizada, envolvendo 27 propriedades e 46 tipos de resinas, totalizando aproximadamente 870 resultados experimentais (Apêndice I), sendo que cada valor experimental apresentado representa uma média dos resultados obtidos para 5 amostras de cada tipo de resina. Em geral, os modelos desenvolvidos são capazes de reproduzir e predizer dados experimentais com precisão / Abstract: A great challenge related to polymers research has been the development of relations enabling prediction of polymer final properties according to the initial operational conditions - either during the polymerization process or the transformation process phases. These relations can be utilized to optimize the operational conditions of transformation systems and to produce devices with specified end-use properties. The first step for this is the information about the relationship s between end-use and intrinsic properties, while the second step is to correlate operation conditions with intrinsic properties of the resins. So, the main objective of the present work is to built-up empirical models to predict end -use properties of polyethylene (PE) resins as functions of its intrinsic properties and still correlate qualitatively these properties. Due to several types of polyethylene resins that are present in the market, the resins studied were separated in groups in accord to the final application of each ones. The research was carried out to evaluate the most important properties for each final application. Then, equations were found for each resins group, including the following classes of properties: mechanical, thermical, optical, contact surface, rheological and morphological properties. Intrinsic properties selected to characterize the resins were fluidity index (FI), which is opposite related to viscosity and molecular weight of the resin; stress exponent (SE) / expansion ratio (SR), which is a measure of the non-Newtonian character of the polymer melt and may be used to evaluate the processability of the polymer resin; and density, which is directly related with resins degree of crystallinity. Among the existing intrinsic properties, that ones which were selected exert, generally, a significant influence on the polymers properties, as well as being easily measurable in the industrial environment. Beyond an extensive literature revision, a previous statistic analysis of the correlations between variables was carried out, and then the input variables were chosen for each model. For two of six resins groups studied, the SE / SR properties were not used as a model input because these properties is not measured or meaningful for the greater part of the resins from those groups. It is important emphasize that the additives can exert considerable influence about end-use properties of polymers, thus, the additives influence makes even more complex the learning about a polymer final properties forecast from the operational conditions of the polymerization systems. However, a control of the additives amount and quality was not possible and a research including comprehensively the additives influence on polymers performance properties remaining beyond the scope of this work. In the curse of this research, a large number of experiments were carried out, embracing twenty seven properties and forty six resins, totalizing approximately eight hundred and seventy experimental results (Appendix I), and each experimental value presented represents a mean of the obtained results for five samples of each kind of resin. In general, models developed are able to reproduce and predict experimental data within experimental accuracy / Mestrado / Desenvolvimento de Processos Químicos / Mestre em Engenharia Química

La locomotion se définit par des mouvements répétés et coordonnés des membres droits et gauches et des muscles antagonistes d’une même articulation. L’activité locomotrice des rongeurs est générée par des groupes de neurones localisés dans la partie antérieure de l’élargissement lombaire; ce réseau de cellules est appelé Central Pattern Generator (CPG). Au cours de cette thèse, les études entreprises chez le rat nouveau-né ont eu pour but d’étudier les mécanismes cellulaires impliqués dans la genèse du rythme locomoteur. Le courant sodique persistant (INaP) joue un rôle important dans la genèse d’activités rythmiques de plusieurs structures supraspinales et notamment celles impliquées dans la mastication et la respiration. Curieusement, son existence et son implication dans la genèse d’activités rythmiques dans les structures du CPG locomoteur spinal n’ont jamais été abordées. A l’aide d’études électrophysiologiques, la thèse démontre l’existence de INaP et le caractérise pour la première fois au sein du CPG locomoteur. Ce courant est indispensable à la genèse du rythme locomoteur et joue un rôle fondamental dans l’émergence d’activités pacemakers au sein du CPG. Ces activités pacemakers émergent dans un contexte physiologique où des fluctuations dans la composition ionique du milieu extracellulaire interviennent au cours d’une activité locomotrice. L’ensemble de ces données suggère que le « cœur » du générateur de rythme pourrait être composé d’interneurones présentant une activité pacemaker dépendante de INaP dont la modulation pourrait être un élément fondamental à la fois dans le déclenchement et la modulation de l’activité locomotrice. / Identification of the cellular mechanisms underlying the generation of the locomotor rhythm is of longstanding interest to physiologists. Hindlimb locomotor movements are generated by lumbar neuronal networks, referred to as central pattern generators (CPG). Although rhythm generation mechanisms within the CNS can vary, the activation of a subthreshold depolarizing conductance is always needed to start the firing of individual neurons. Among various subthreshold membrane conductances, the persistent sodium current (INaP) is involved in rhythmic activity of numerous supraspinal neurons such as those involved in the generation of masticatory and respiratory rhythm. The thesis was aimed at identifying and characterizing INaP in the neonatal rodent locomotor CPG, determining its importance in shaping neuronal firing properties and its role in the operation of the locomotor circuitry. Using electrophysiological studies the thesis has characterized INaP for the first time in the locomotor CPG. This current is essential to the generation of the locomotor rhythm and plays a fundamental role in the emergence of pacemaker activity within the CPG. These pacemaker activities emerge in a physiological context in which fluctuations in the ionic composition of the extracellular environment occur during locomotion. This study provides evidence that INaP generates pacemaker activities in CPG interneurons and new insights into the operation of the locomotor network with a critical implication of INaP in stabilizing the locomotor pattern.

Intricate interactions among constituent components are defining hallmarks of biological systems and sculpt physiology across different scales spanning gene networks to behavioural repertoires. Whereas interactions among channels and receptors define neuronal physiology, interactions among different cells specify the characteristic features of network physiology. From a single-neuron perspective, it is now evident that the somato-dendritic plasma membrane of hippocampus pyramidal neurons is endowed with several voltage-gated ion channels (VGICs) with varying biophysical properties and sub cellular expression profiles. Structural and physiological interactions among these channels define generation and propagation of electrical signals, thereby transforming neuronal dendrites to actively excitable membrane endowed with complex computational capabilities. In parallel to this complex network of plasma membrane channels is an elegantly placed continuous intraneuronal membrane of the endoplasmic reticulum (ER) that runs throughout the neuronal morphology. Akin to the plasma membrane, the ER is also endowed with a variety of channels and receptors, prominent among them being the inositol trisphosphate (InsP3) receptors (InsP3Rs) and ryanodine receptors (RyR), both of which are calcium release channels. Physiological interactions among these receptors transform the ER into a calcium excitable membrane, capable of active propagation of calcium waves and of spatiotemporal integration of neuronal signals. Thus, a neuron is endowed with two continuously parallel excitable membranes that actively participate in the bidirectional flow of intraneuronal information, through interactions among different channels and receptors on either membrane. Although the interactions among sets of channels and receptors present individually on either membrane are very well characterized, our understanding of cross-membrane interactions among channels and receptors across these two membranes has been very limited. Recent literature has emphasized the critical nature of such cross-membrane interactions and the several physiological roles played by such interactions. Such cross-channel interactions include ER depletion-induced signaling involving store-operated calcium channels, generation and propagation of calcium waves through interactions between plasma membrane and ER membrane receptors, and the plasticity of plasma membrane VGICs and receptors induced by ER Ca2+. Such tight interactions between these two membranes have highlighted several roles of the ER in the integration of intraneuronal information, in regulating signalling microdomains and in regulating the downstream signaling pathways that are regulated by these Ca2+ signals. Yet, our understanding about the functional interactions between the ion channels and receptors present on either of these membranes is very limited from the perspective of the combinatorial possibilities that encompass the span of channels and receptors across these two membranes. In this context, the first part of this thesis deals with two specific instances of such cross-membrane functional interactions, presented as two subparts with each probing different direction of impact. Specifically, whereas the first of these subparts deals with the impact of plasma membrane VGICs on the physiology of ER receptors, the second subpart presents an instance of the effect of ER receptor activation on plasma membrane VGIC. In the first subpart of the thesis, we establish a novel role for the A-type potassium current in regulating the release of calcium through inositol triphosphate receptors (InsP3R) that reside on the endoplasmic reticulum (ER) of hippocampus pyramidal neurons. Specifically, the A-type potassium current has been implicated in the regulation of several physiological processes including the regulation of calcium influx through voltage-gated calcium channels (VGCCs). Given the dependence of InsP3R open probability on cytosolic calcium concentration ([Ca2+]c) we asked if this regulation of calcium influx by A-type potassium current could translate into the regulation of release of calcium through InsP3Rs by the A-type potassium current. To answer this, we constructed morphologically realistic, conductance-based neuronal models equipped with kinetic schemes that govern several calcium signalling modules and pathways, and constrained the distributions and properties of constitutive components by experimental measurements from these neurons. Employing these models, we establish a bell-shaped dependence of calcium release through InsP3Rs on the density of A-type potassium current, during the propagation of an intraneuronal calcium wave initiated through established protocols. Exploring the sensitivities of calcium wave initiation and propagation to several underlying parameters, we found that ER calcium release critically depends on dendrite diameter and wave initiation occurred at branch points as a consequence of high surface area to volume ratio of oblique dendrites. Further, analogous to the role of A-type potassium channels in regulating spike latency, we found that an increase in the density of A-type potassium channels led to increases in the latency and the temporal spread of a propagating calcium wave. Next, we incorporated kinetic models for the metabotropic glutamate receptor (miler) signalling components and a calcium-controlled plasticity rule into our model and demonstrate that the presence of mGluRs induced a leftward shift in a BCM-like synaptic plasticity profile. Finally, we show that the A-type potassium current could regulate the relative contribution of ER calcium to synaptic plasticity induced either through 900 pulses of various stimulus frequencies or through theta burst stimulation. These results establish a novel form of interaction between active dendrites and the ER membrane and suggest that A-type K+ channels are ideally placed for inhibiting the suppression of InsP3Rs in thin-caliber dendrites. Furthermore, they uncover a powerful mechanism that could regulate biophysical/biochemical signal integration and steer the spatiotemporal spread of signalling micro domains through changes in dendritic excitability. In the second subpart, we turned our focus to the role of calcium released through InsP3Rs in regulating the properties of VGICs present on the plasma membrane, thereby altering neuronal intrinsic properties that are dependent on these VGICs. Specifically, the synaptic plasticity literature has focused on establishing necessity and sufficiency as two essential and distinct features in causally relating a signalling molecule to plasticity induction, an approach that has been surprisingly lacking in the intrinsic plasticity literature. Here, we complemented the recently established necessity of inositol trisphosphate (InsP3) receptors (InsP3R) in a form of intrinsic plasticity by asking if ER InsP3R activation was sufficient to induce plasticity in intrinsic properties of hippocampus neurons. To do this, we employed whole-cell patch-clamp recordings to infuse D-myo-InsP3, the endogenous ligand for InsP3Rs, into hippocampus pyramidal neurons and assessed the impact of InsP3R activation on neuronal intrinsic properties. We found that such activation reduced input resistance, maximal impedance amplitude and temporal summation, but increased resonance frequency, resonance strength, sag ratio, and impedance phase lead of hippocampus pyramidal neurons. Strikingly, the magnitude of plasticity in all these measurements was dependent upon [InsP3], emphasizing the graded dependence of such plasticity on InsP3R activation. Mechanistically, we found that this InsP3-induced plasticity depended on hyperpolarization-activated cyclic-nucleotide gated (HCN) channels. Moreover, this calcium-dependent form of plasticity was critically reliant on the release of calcium through InsP3Rs, the influx of calcium through N-methyl-D -aspartate receptors and voltage-gated calcium channels, and on the protein kinase A pathway. These results delineate a causal role for InsP3Rs in graded adaptation of neuronal response dynamics through changes in plasma membrane ion channels, thereby revealing novel regulatory roles for the endoplasmic reticulum in neural coding and homeostasis. Whereas the first part of the thesis dealt with bidirectional interactions between ER membrane and plasma membrane channels/receptors within a neuron, second part focuses on cross-cellular interactions, specifically between ER membrane on astrocytes and dendritic plasma membrane of neurons. Specifically, the universality of ER-dependent calcium signalling ensures that its critical influence extends to regulating the physiology of astrocytes, an abundant form of glial cells in the hippocampus. Due to the presence of calcium release channels on ER membrane, astrocytes are calcium excitable, whereby they respond to neuronal activity by increase in their cytosolic calcium levels. Specifically, astrocytes respond to the release of neurotransmitters from neuronal presynaptic terminals through activation of metabotropic receptors expressed on their plasma membrane. Such activation results in the mobilization of cytosolic InsP3 and subsequent release of calcium through InsP3 on the astrocytes ER membrane. These ER-dependent [Ca2+]c elevations in astrocytes then result in the release of gliotransmitters from astrocytes, which bind to corresponding receptors located on neuronal plasma membrane resulting in voltage-deflections and/or activation of signaling pathways in the neuron. Although it is well established that gliotransmission constitutes an important communication channel between astrocytes and neurons, the impact of gliotransmission on neurons have largely been centered at the cell body of the neurons. Consequently, the impact of the activation of astrocytic InsP3R on neuronal dendrites, and the role of dendritic active conductances in regulating this impact have been lacking. This lacuna in mapping the spatial spread of gliotransmission in neurons is especially striking because most afferent synapses impinge on neuronal dendrites, and a significant proportion of information processing in neurons is performed in their dendritic arborization. Additionally, given that active dendritic conductances play a pivotal role in regulating the impact of fast synaptic neurotransmission on neurons, we hypothesized that such active-dendritic regulation should extend to the impact of slower extrasynaptic gliotransmission on neurons. The second part of the thesis is devoted to testing this hypothesis using dendritic and paired astrocyte-neuron electrophysiological recordings, where we also investigate the specific roles of active dendritic conductances in regulating the impact of gliotransmission initiated through activation of astrocytic InsP3Rs. In testing this hypothesis, in the second part of the thesis, we first demonstrate a significantly large increase in the amplitude of astrocytically originating spontaneous slow excitatory potentials (SEP) in distal dendrites compared to their perisomatic counterparts. Employing specific neuronal infusion of pharmacological agents, we show that blocking HCN channels increased the frequency, rise-time and width of dendritically-recorded spontaneous SEPs, whereas blockade of A-type potassium channels enhanced their amplitude. Next, through paired neuron-astrocytes recordings, we show that our conclusions on the differential roles of HCN and A-type potassium channels in modulating spontaneous SEPs also extended to SEPs induced through infusion of InsP3 in a nearby astrocyte. Additionally, employing subtype-specific receptor blockers during paired neuron-astrocyte recordings, we provide evidence that GluN2B-and GluN2D-containing NMDARs predominantly mediate perisomatic and dendritic SEPs, respectively. Finally, using morphologically realistic conductance-based computational models, we quantitatively demonstrate that dendritic conductances play an active role in mediating compartmentalization of the neuronal impact of gliotransmission. These results unveil an important role for active dendrites in regulating the impact of gliotransmission on neurons, and suggest astrocytes as a source of dendritic plateau potentials that have been implicated in localized plasticity and place cell formation. This thesis is organized into six chapters as follows: Chapter 1 lays the motivations for the questions addressed in the thesis apart from providing the highlights of the results presented here. Chapter 2 provides the background literature for the thesis, introducing facts and concepts that forms the foundation on which the rest of the chapters are built upon. In chapter 3, we present quantitative analyses of the physiological interactions between A-type potassium conductances and InsP3Rs in CA1 pyramidal neurons. In chapter 4, using electrophysiological recordings, we investigate the role of calcium released through InsP3Rs in induction of plasticity of intrinsic response dynamics, and demonstrate that this form of plasticity is consequent to changes in neuronal HCN channels. In chapter 5, we systematically map the spatial dynamics of the impact of gliotransmission on neurons across the somato-apical trunk, also unveiling the role of neuronal HCN and A-type potassium channels in compartmentalizing such impact. Finally, chapter 6 concludes the thesis highlighting its major contributions and discussing directions of future research.

No description available.

No description available.

Quasi-particles formed in lithium niobate after pulse exposure were investigated by transient absorption and photoluminescence spectroscopy as well as numerical simulations. This includes the formation process, the transport through the crystal, interim pinning on defects during the relaxation process, and the final recombination with deep centers. It was shown that the charge-transport through the crystal can be described by a hopping transport including different types of hops between regular or defective lattice sites, i.e., the transport includes a mixture of free and bound small polarons. Furthermore, the different types of hops connected with varying activation energies and their distribution are responsible for an altered temporal decay curve when changing the crystal composition or temperature. Additionally, it was shown that the hitherto accepted recombination model is insufficient to describe all transient absorption and luminescence effects in lithium niobate under certain experimental conditions, i.e., long-living absorption dynamics in the blue/UV spectral range do not follow the typical polaron dynamics and cannot be described under the assumption of charge compensation. However, similar decay characteristics between self-trapped excitons known from photoluminescence spectroscopy and the unexpected behavior of the transient absorption were found leading to a revised model. This includes, besides the known polaron relaxation and recombination branch, a significant role of self-trapped excitons and their pinning on defects (pinned STEs). Since the consideration of further absorption centers in the relaxation path after pulse exposure might result in misinterpretations of previously determined polaron absorption cross-sections and shapes, the necessity to perform a review became apparent. Therefore, a supercontinuum pump-probe experiment was designed and all measurements applied under the same experimental conditions (temperature, polarization) so that one can extract the absorption amplitudes of the single quasi-particles in a spectral range of 0.7-3.0eV. The detailed knowledge might be used to deconvolve the absorption spectra and transform them to number densities of the involved centers which enables one to obtain an easier insight into recombination and decay dynamics of small polarons and self-trapped excitons. As the hopping transport of quasi-particles and the concept of pinned STEs might be fundamental processes, a thorough understanding opens up the possibility of their exploitation in various materials. In particular, results presented herein are not only limited to lithium niobate and its applications; an extension to a wide range of further strongly polar crystals in both their microscopic processes and their use in industry can be considered.