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[pt] Com o avanço na medida dos parâmetros responsáveis por oscilação de neutrinos, podemos dizer que hoje a física de neutrinos está entrando na era da precisão, o que nos permite explorar cenários além de massas e misturas de três sabores de neutrinos, ou seja, podemos procurar uma nova física que cause algum efeito subdominante, que não pode ser explicado por oscilação usual. Podemos citar a anomalia de antineutrinos de reator e anomalia de Gálio, ambas serão explicadas posteriormente no capítulo 3. Propomos uma solução alternativa para estas duas anomalias, baseado em um cenário com grandes dimensões extras. Exploramos também a capacidade de um experimento com neutrinos ultramonocromáticos produzidos via efeito Mossbauer, de detectar ou vincular alguns cenários de nova física além do modelo padrão. Os cenários que consideramos nesta tese são: neutrinos esteréis, estes sendo a extensão mais simples do modelo de três sabores; o cenário com grandes dimensões espaciais extras; descoerência quântica como física não padrão; e por último e não menos importante o cenário com neutrinos de massa variável. Mostramos também o impacto, se assumimos a existência destes cenários, na determinação dos parâmetros de oscilação Delta m2 31 e Teta 13. / [en] With advances in the measurements of the neutrino oscillation parameters, we can assume that neutrino physics is going to a precision era, as a consequence we can explore new scenarios beyond the standard mass and mixing with three neutrino flavors , that is, we can look for a new physics that affects in a subleading way and that can not be explained by the standard oscillation framework. For instance, the reactor antineutrino and Gallium anomalies, both anomalies will be discussed in chapter 3. We propose an explanation for these anomalies based on a scenario with large extra dimension. We also explore the capability of an experiment with ultramonochromatic neutrinos based on M ossbauer effect detects or constrains some new physics scenarios beyond the standard model. In this thesis we consider: sterile neutrinos, large extra dimensions, non standard quantum decoherence and mass varying neutrinos. We also show the impact on the determination of the standard oscillation parameters delta m2 31 and teta 13 if we assume non standard physics scenarios.

The hippocampus is a brain structure involved in episodic memory and spatial cognition. Neuronal activity within the hippocampus exhibits intricate temporal patterning, including oscillatory and sequential dynamics, which are believed to underlie these cognitive processes. In individual cells, a temporal activity pattern called phase precession occurs which leads to the organisation of neuronal populations into sequences. These sequences are hypothesised to form a substrate for episodic memory and the representation of spatial trajectories during navigation. In this thesis, I present a novel theory of the phenomenological properties of these neuronal activity sequences. In particular, I propose that the sequential organisation of population activity is governed by the independent phase precession of each cell. By comparison of models in which cells are independent and models in which cells exhibit coordinated activity against experimental data, I provide empirical evidence to support this hypothesis. Further, I show how independent coding affords a vast capacity for the generation of sequential activity patterns across distinct environments, allowing the representation of episodes and spatial experiences across a large number of contexts. This theory is then extended to account for grid cells, whose activity patterns form a hexagonal lattice over external space. By analysing simple forms of phase coding in populations of grid cells, I show how previously undocumented constraints on phase coding in two dimensional environments are imposed by the symmetries of grid cell firing fields. To overcome these constraints, I propose a more complex phenomenological model which can account for phase precession in both place cells and grid cells in two dimensional environments. Using insights from this theory, I then propose a biophysical circuit mechanism for hippocampal sequences. I show that this biophysical circuit model can account for the proposed phenomenological coding properties and provide experimentally testable predictions which can distinguish this model from existing models of phase precession. Finally, I outline a scheme by which this biophysical mechanism can implement supervised learning using spike time dependent plasticity in order to learn associations between events occurring on behavioural timescales. The models presented in this thesis challenge previous theories of hippocampal circuit function and suggest a much higher degree of flexibility and capacity for the generation of sequences than previously believed. This flexibility may underlie our ability to represent spatial experiences and store episodic memories across a seemingly unlimited number of distinct contexts.

Cells of the rodent medial entorhinal cortex (EC) possess cellular properties hypothesized to underlie the spatially periodic firing behaviors of 'grid cells' (GC) observed in vivo. Computational models have simulated experimental GC data, but a consensus as to what mechanism(s) generate GC properties has not been reached. Using whole cell patch-clamp and computational modeling techniques this thesis investigates resonance, rebound spiking and persistent spiking properties of medial EC cells to test potential mechanisms generating GC firing. The first experiment tested the voltage dependence of resonance frequency in layer II medial EC stellate cells. Some GC models use interference between velocity-controlled oscillators to generate GCs. These interference mechanisms work best with a linear relationship between voltage and resonance frequency. Experimental results showed resonance frequency decreased linearly with membrane potential depolarization, suggesting resonance properties could support the generation of GCs. Resonance appeared in medial EC but not lateral EC consistent with location of GCs. The second experiment tested predictions of a recent network model that generates GCs using medial EC stellate cell resonance and rebound spiking properties. Sinusoidal oscillations superimposed with hyperpolarizing currents were delivered to layer II stellate cells. Results showed that relative to the sinusoid, a limited phase range of hyperpolarizing inputs elicited rebound spikes, and the phase range of rebound spikes was even narrower. Tuning model parameters of the stellate cell population to match experimental rebound spiking properties resulted in GC spatial periodicity, suggesting resonance and rebound spiking are viable mechanisms for GC generation. The third experiment tested whether short duration current inputs can induce persistent firing and afterdepolarization in layer V pyramidal cells. During muscarinic acetylcholine receptor activation 1-2 second long current injections have been shown to induce persistent firing in EC principal cells. Persistent firing may underlie working memory performance and has been used to model GCs. However, input stimuli during working memory and navigation may be much shorter than 1-2 seconds. Data showed that input durations of 10, 50 and 100 ms could elicit persistent firing, and revealed time courses and amplitude of afterdepolarization that could contribute to GC firing or maintenance of working memory.

Goal-directed behavior requires flexible selection among action plans and updating behavioral strategies when they fail to achieve desired goals. Lateral prefrontal cortex (LPFC) is implicated in the execution of behavior-guiding rule-based cognitive control while anterior cingulate cortex (ACC) is implicated in monitoring processes and updating rules. Rule-based cognitive control requires selective processing while process monitoring benefits from combinatorial processing. I used a combination of computational and experimental methods to investigate how network oscillations and neuronal heterogeneity contribute to cognitive control through their effects on selective versus combinatorial processing modes in LPFC and ACC. First, I adapted an existing LPFC model to explore input frequency- and coherence-based output selection mechanisms for flexible routing of rate-coded signals. I show that the oscillatory states of input encoding populations can exhibit a stronger influence over downstream competition than their activity levels. This enables an output driven by a weaker resonant input signal to suppress lower-frequency competing responses to stronger, less resonant (though possibly higher-frequency) input signals. While signals are encoded in population firing rates, output selection and signal routing can be governed independently by the frequency and coherence of oscillatory inputs and their correspondence with output resonant properties. Flexible response selection and gating can be achieved by oscillatory state control mechanisms operating on input encoding populations. These dynamic mechanisms enable experimentally-observed LPFC beta and gamma oscillations to flexibly govern the selection and gating of rate-coded signals for downstream read-out. Furthermore, I demonstrate how differential drives to distinct interneuron populations can switch working memory representations between asynchronous and oscillatory states that support rule-based selection. Next, I analyzed physiological data from the LeBeau laboratory and built a de novo model constrained by the biological data. Experimental data demonstrated that fast network oscillations at both the beta- and gamma frequency bands could be elicited in vitro in ACC and neurons exhibited a wide range of intrinsic properties. Computational modeling of the ACC network revealed that the frequency of network oscillation generated was dependent upon the time course of inhibition. Principal cell heterogeneity broadened the range of frequencies generated by the model network. In addition, with different frequency inputs to two neuronal assemblies, heterogeneity decreased competition and increased spike coherence between the networks thus conferring a combinatorial advantage to the network. These findings suggest that oscillating neuronal populations can support either response selection (routing), or combination, depending on the interplay between the kinetics of synaptic inhibition and the degree of heterogeneity of principal cell intrinsic conductances. Such differences may support functional differences between the roles of LPFC and ACC in cognitive control.

Thesis. 1977. Sc.D.--Massachusetts Institute of Technology. Dept. of Physics. / M̲i̲c̲ṟo̲f̲i̲c̲ẖe̲ c̲o̲p̲y̲ a̲v̲a̲i̲ḻa̲ḇḻe̲ i̲ṉ A̲ṟc̲ẖi̲v̲e̲s̲ a̲ṉḏ S̲c̲i̲e̲ṉc̲e̲. / Vita. / Bibliography : leaves 167-170. / by Steven R. Rogers. / Sc.D.

Damage precipitating cognitive decline in Alzheimer's disease (AD) begins long before behavioural alterations become clinically apparent. At this prodromal stage, communication between networks of neurons connecting different brain regions starts to break down; setting in motion a chain of events leading to clinical AD. A significant challenge facing Alzheimer's researchers today is finding a cheap, easy-to-perform test capable of detecting prodromal AD. Such a test would afford significant benefits to patients, including a chance of early intervention. Perhaps, more importantly, it would also aid development and testing of novel therapies aimed at combating AD before it causes irreversible damage. Since oscillations in electrical field activity are important for facilitating connectivity across the brain and have been seen to alter in AD, this work studied how oscillations and regional connectivity are affected in the AD brain. Specifically, local field oscillations were recorded from the hippocampus and prelimbic cortex (regions implicated in memory formation and maintenance) in a double transgenic AD model - the TASTPM mouse. Here, periods of predominant theta activity were assessed both spontaneously, under urethane anaesthesia and following electrical induction through dorsal periaqueductal gray (dPAG) stimulation. From these recordings, spectral power and connectivity between regions was assessed using both a traditional measure of functional connectivity (inter-region correlation) and through a novel information theoretic approach measuring effective connectivity (transfer entropy).Perhaps the most prominent finding from this study was the observation that young TASTPM mice, at an age prior to overt cognitive decline or plaque deposition, showed significant alterations in measures of both functional and effective connectivity. This suggests that such measures may be used as biomarkers predictive of prodromal AD and, as such, may be used to aid development of drugs targeted towards treatment of prodromal AD.This study also uncovered a number of interesting observations concerning hippocampal/prelimbic connectivity. Firstly, although spectral power and inter-regional correlation peaked at ∼ 3Hz, information flow between these structures was strongest at ∼6Hz. This suggests that low and high-band theta activity may fulfil separate functions. Secondly, at theta frequencies, information flowed predominantly from the prelimbic cortex to the hippocampus. However, during lower frequency activity, information flowed predominantly in the opposite direction. Suggesting that separate frequency bands may be important for routing information flow between these structures. Finally, the strength of information transfer was seen to oscillate at approximately double the frequency of its carrier signal, perhaps suggesting locking of information transfer to certain phases of an underlying oscillation. Therefore, oscillations may structure information transfer by temporal windowing and frequency-locked routing; processes which can be studied using measures of effective connectivity such as transfer entropy.

Zhang, Yaojun = / "November 2009." / Thesis (M.Phil.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (p. 109-111). / Abstracts in English and Chinese. / Zhang, Yaojun = / Abstract --- p.i / Acknowledgement --- p.iv / Chapter 1 --- Introduction --- p.1 / Chapter 2 --- Quasi-Normal Modes of Neutron Stars --- p.6 / Chapter 2.1 --- Equilibrium State of a Neutron Star --- p.6 / Chapter 2.2 --- Fluid Displacement and Metric Perturbation --- p.8 / Chapter 2.3 --- Axial Oscillations of Neutron Stars --- p.9 / Chapter 2.3.1 --- Wave Equation inside the Star --- p.9 / Chapter 2.3.2 --- Wave Equation outside the Star --- p.10 / Chapter 2.3.3 --- Location of Quasi-normal Modes --- p.10 / Chapter 2.4 --- Polar Oscillations of Neutron Stars - LD Formalism --- p.12 / Chapter 2.4.1 --- Equations inside the Star --- p.12 / Chapter 2.4.2 --- Equations outside the Star --- p.14 / Chapter 2.4.3 --- Location of Quasi-normal Modes --- p.16 / Chapter 2.5 --- Polar Oscillations of Neutron Stars - AAKS Formalism --- p.16 / Chapter 2.5.1 --- Equations inside the Star --- p.16 / Chapter 2.5.2 --- Equations outside the Star --- p.19 / Chapter 2.5.3 --- Location of Quasi-normal Modes --- p.19 / Chapter 3 --- Decoupling of Spacetime Oscillations and Fluid Motion --- p.21 / Chapter 3.1 --- Motivation of Decoupling --- p.21 / Chapter 3.2 --- Expressing F in terms of S and H --- p.21 / Chapter 3.2.1 --- Inside the Star --- p.22 / Chapter 3.2.2 --- Outside the Star --- p.25 / Chapter 3.3 --- Constraint-free AAKS Formalism --- p.25 / Chapter 3.3.1 --- Equations inside the Star --- p.25 / Chapter 3.3.2 --- Equations outside the Star --- p.27 / Chapter 3.4 --- Cowling Approximation for Polar p-Mode --- p.29 / Chapter 3.4.1 --- Independent Fluid Motion --- p.29 / Chapter 3.4.2 --- Location of Polar p-Modes --- p.30 / Chapter 3.4.3 --- Numerical Results and Discussion --- p.31 / Chapter 3.5 --- Inverse-Cowling approximation for ω-Mode --- p.33 / Chapter 3.5.1 --- Independent Spacetime Oscillations --- p.33 / Chapter 3.5.2 --- Location of ω-Modes --- p.34 / Chapter 3.5.3 --- Numerical Results and Discussion --- p.34 / Chapter 4 --- Interplay between Matter and Spacetime --- p.37 / Chapter 4.1 --- Physical Insight --- p.37 / Chapter 4.2 --- Sturm-Liouville Eigenvalue Problem --- p.39 / Chapter 4.3 --- Energy of the Fluid --- p.40 / Chapter 4.4 --- Spacetime Oscillation Driven by Fluid Motion --- p.45 / Chapter 4.5 --- Damped Oscillation Caused by Radiation of Gravitational Wave --- p.46 / Chapter 4.6 --- Calculation of δωn in a Perturbative Way --- p.48 / Chapter 4.7 --- Numerical Results and Discussion --- p.49 / Chapter 5 --- Asymptotic Behavior of Spacetime Modes --- p.61 / Chapter 5.1 --- Motivation --- p.61 / Chapter 5.2 --- Asymptotic Behavior of Axial ω-modes for One-Layered Stars --- p.62 / Chapter 5.2.1 --- "Asymptotic Form of g(r*,ω)" --- p.63 / Chapter 5.2.2 --- "Asymptotic Form of f(r*, ω)" --- p.67 / Chapter 5.2.3 --- Asymptotic Behavior of Axial Quasi-Normal Modes --- p.69 / Chapter 5.3 --- Asymptotic Behavior of Polar ω-modes for One-Layered Stars --- p.71 / Chapter 5.3.1 --- High-Frequency Approximation --- p.71 / Chapter 5.3.2 --- Asymptotic Behavior of Polar Quasi-Normal Modes --- p.73 / Chapter 5.4 --- Relationship between Axial and Polar ω-Modes --- p.74 / Chapter 5.4.1 --- Application 1:ω-Modes of Quark Stars --- p.75 / Chapter 5.4.2 --- Application 2:ω-Modes of Polytropic Stars --- p.80 / Chapter 5.4.3 --- Application 3: The Influence of Surface Discontinuities --- p.89 / Chapter 5.4.4 --- Application 4:ω-Modes of Realistic Neutron Stars --- p.92 / Chapter 6 --- Conclusion and Outlook --- p.99 / Chapter A --- From Einstein Equation to LD Formalism --- p.101 / Chapter A.l --- The Linearized Perturbation Equations --- p.101 / Chapter A.1.1 --- The Perturbation of the Einstein Tensor --- p.102 / Chapter A.1.2 --- The Perturbation of the Energy-momentum Tensor --- p.103 / Chapter A.1.3 --- The Perturbed Einstein Equations --- p.104 / Chapter A.2 --- Some Symbolic Operation Results --- p.105 / Chapter A.3 --- Simplifications --- p.106

The objective of this thesis is to study the fluid oscillation modes in compact stars, understand their properties and infer stellar structures from their frequencies. The first part of the thesis focuses on the Newtonian theory of stellar pulsation and the Cowling approximation (CA), which neglects the change in gravitational potential. We modify the conventional CA, devise a more accurate version of the CA and calculate the first-order correction to the conventional CA. In the second part, we apply the variational approximation method proposed by Chandrasekhar [Astrophys. J. 139,664 (1963)] and δ-perturbation expansion proposed by Bender et. al. [J. Maths. Phys. 30, 1447 (1989)] to explain the universality in the relationships between the fundamental mode frequency and the moment of inertia of neutron stars, which was discovered by Lau et. al. [Astrophys. J. 714, 1234 (2010)]. We reveal that stiff equations of state are the conditions for the observed universality. In the third part, we consider the relativistic pulsation formulation and relativistic CAs for compact stars. We unify several known CAs with a single second-order differential equation. We also extend the modified CA derived from the formalism established by Allen et. al. [Phys. Rev. D 58, 124012 (1998)] to include the effect of buoyancy. Finally, we find the first-order and the second-order post-Newtonian expansions for the nonradial pulsations in quark stars. We derive an analytic formula expressing the fundamental mode frequency in terms of the compactness of quark stars. As a result, we are able to verify the universality mentioned above for quark stars. / 這論文是對在牛頓力學以及相對論框架下緻密星流體振盪的研究結果。論文第一部分集中討論牛頓力學下流體振盪以及近似方法。這近似方法忽略重力勢的擾動，令系統由四階微分方程減少為二階微分方程。我們修正了已往的近似方法和提出一個更精準的近似方法。第二部分包括變分近似方法。我們利用該方法和δ微擾理論解釋基本模式頻率的普通性。第三部分包括相對論框架下緻密星流體振盪和近似方法。我們以一條二階微分方程總結之前出現的近似方法並且在近似方法中加入浮力。最後，我們執行一階和二階的後牛頓展開，以分析夸克星的基本模式。我們驗證了展開的準確度和發現了基本模式頻率的方程。 / Chan, Tsang Keung = 有關在緻密星中流體振盪的研究 / 陳增強. / Thesis M.Phil. Chinese University of Hong Kong 2013. / Abstracts also in Chinese. / Title from PDF title page (viewed on 07, October, 2016). / Chan, Tsang Keung = You guan zai zhi mi xing zhong liu ti zhen dang de yan jiu / Chen Zengqiang. / Detailed summary in vernacular field only.

No presente trabalho foram estudados alguns aspectos não lineares da catálise da oxidação de etileno glicol (EG) sob platina em meio alcalino (KOH). A dinâmica do sistema foi investigada através de voltametria cíclica, séries temporais de corrente e potencial e por espectroscopia de impedância eletroquímica. (EIE). Os resultados da EIE revelaram a presença de uma região de resistência diferencial negativa escondida nas proximidades o pico principal obtido na voltametria cíclica. De modo geral o sistema se mostrou apto a oscilar tanto sob regime potenciostático quanto galvanostático e por longos períodos de tempo apresentando uma miríade de estados dinâmicos que incluem oscilações harmônicas, de baixa e alta amplitudes, períodos 2, 3, 4 e modos mistos, além da duplicação de período na transição para o caos. A concentração tanto de EG como de KOH tiveram caráter essencial nos padrões temporais observados. A complexidade dos períodos aumenta com o aumento da concentração de EG resultando em 90% do tempo em que o sistema passa oscilando devotado às oscilações caóticas quando a concentração de EG é de 1,6 M. O aumento da densidade de corrente produz um efeito contrário nos padrões, ou seja, quanto mais alta é a corrente mais simples são os períodos. A influência de alguns produtos de oxidação parcial do EG foi estudada em diferentes condições. Os resultados das mudanças de morfologia das oscilações são racionalizados em termos das eventuais conexões com os intermediários de reação formados durante o processo de oxidação que, por sua vez, dependem da concentração do álcool e da densidade de corrente. / In the present work were studied some nonlinear aspects of the catalytic oxidation of ethylene glycol (EG) on platinum electrodes in alkaline media (KOH). The system\'s dynamics was investigated by means of cyclic voltammetry, current and potential time series, and electrochemical impedance spectroscopy (EIS). The EIS results reveal the presence of a hidden negative differential resistance around the main voltammetric peak. Overall, the system was able to oscillate for several periods, displaying a myriad of dynamic states which includes harmonic, small and large amplitude, periods 2, 3, and 4, and mixed-mode oscillations, as well as period doubling transition to chaos. The concentration of both EG and KOH were found to play an essential role in the temporal patterns observed. The complexity of the periods increase with EG concentration resulting in 90% of the oscillating time devoted to chaotic patters when EG concentration is 1.6 M. The increment of the current density produces an opposite behavior of the patters: the higher the applied current the simpler the oscillatory dynamics. The influence of some products of partial EG oxidation was studied under different conditions and compared. The results of the changes in the oscillatory morphology are rationalized in terms of its eventual connection with reaction intermediates formed during the oxidation process that, in turn, depends on the alcohol concentration and on the current density.