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"Estudo da origem e do papel das oscilações elétricas em um modelo computacional do sistema olfativo de vertebrados". ; "Studying the origin and role of the electric oscillations in a computational model of vertebrate olfactory system."

Souza, Fábio Marques Simões de
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 28/07/2005 PT
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36.59%
Esse trabalho consiste no estudo de alguns mecanismos responsáveis pela geração das oscilações elétricas observadas no sistema olfativo de vertebrados e das possíveis funções que essas oscilações possam ter no processamento da informação olfativa. Da-se especial atenção ao papel desempenhado pelo ritmo respiratório e pelas sinapses químicas e elétricas nesse processo. Para realizar essa investigação, foram utilizados modelos computacionais que reproduzem aspectos da anatomia e da fisiologia do epitélio olfativo, do bulbo olfativo e do córtex piriforme. Os modelos foram desenvolvidos e simulados no neurossimulador GENESIS, funcionando no sistema operacional LINUX. A análise dos resultados foi feita no programa MATLAB (Mathworks™). Inicialmente, a tese faz uma descrição do substrato neurobiológico que compõe as camadas iniciais do sistema olfativo, incluindo o epitélio, bulbo e córtex olfativo, e de como a informação olfativa é processada por cada camada, discutindo a importância do sentido olfativo e a relevância da neurociência computacional no estudo da origem e do papel das oscilações elétricas existentes nesse sistema (Capítulo 1). O capítulo 2 descreve os materiais e métodos utilizados para a construção dos modelos computacionais e para análise dos resultados. O capítulo 3 faz uma descrição detalhada do modelo computacional utilizado e dos experimentos realizados com o modelo. Finalmente...

Oscilações inerciais sobre a plataforma continental Sudeste do Brasil ; Inertial oscillations on the South Brazil Bight

Leite, José Roberto Bairão
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 12/08/2014 PT
Relevância na Pesquisa
36.61%
Variações temporais na tensão de cisalhamento do vento, na Plataforma Continental Sudeste do Brasil (PCSE), perturbam o equilíbrio geostrófico gerando movimentos com frequências próximas à inercial local. Estas perturbações se propagam horizontalmente e verticalmente, interagindo com o fluxo médio e alterando as características hidrográficas e hidrodinâmicas. Foram analisados dados observacionais de corrente, registrados por correntógrafos fundeados às isóbatas de 50 m e 100 m, ao largo de Arraial do Cabo (RJ) e Ubatuba (SP), de vento registrados por bóias meteorológicas e de salinidade e temperatura perfilados em função da profundidade em estações hidrográficas, obtidos no âmbito do Projeto DEPROAS (Dinâmica do Ecossistema de Plataforma da Região Oeste do Atlântico Sul), entre 2001 e 2002. Os resultados das análises indicaram que a média de duração dos eventos de oscilações inerciais é 7,5 dias com desvio padrão de 3,8 dias, sendo 6,8 o número médio de oscilações em cada evento (desvio padrão de 3,3 oscilações). O período inercial efetivo médio foi calculado em 26,5 h com deslocamento médio da frequência inercial em 12,2%, devido ao desvio Doppler causado pelas interações com a vorticidade relativa do fluxo básico. As correntes inerciais horizontais...

Oscilações Subinerciais na Plataforma Continental Sudeste: Estudos Numéricos; Subinertial Oscillations in the South Brazil Bight: Numerical Studies

Gregorio, Helvio Prevelato
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 12/03/2014 PT
Relevância na Pesquisa
36.59%
Oscilações subinerciais da elevação da superfície livre do mar na Plataforma Continental Sudeste (PCSE) foram estudadas por meio de modelagem numérica computacional. Os campos atmosféricos utilizados nos experimentos foram obtidos da reanálise NCEP-DOE AMIP II e o modelo hidrodinâmico DELFT-3D Flow foi empregado. A validação dos resultados dos experimentos numéricos foi realizada por comparação com observações. Foram realizadas simulações para o verão de 2003, para o inverno de 2004 e para mais quatro cenários de ventos sintéticos, simulando a propagação de frentes frias climatológicas (obtidas neste estudo). Verificamos que na porção sul (norte) da região passaram 3,6 (2,9) frentes frias por mês durante o inverno e 3,4 (1,3) durante o verão. Esta diferença entre as regiões norte e sul mostrou que alguns eventos não percorreram toda a região, sendo isso mais frequente no verão. A passagem de frentes frias provocou a propagação de oscilações subinerciais da superfície do mar, confinadas junto à costa, com comprimento de onda de aproximadamente 2000 km, duração de 50 h e amplitude média de 0,3 m, tanto no verão quanto no inverno. Nas simulações em que as frentes frias não percorreram toda a PCSE...

Coherent atomic oscillations and resonances between coupled Bose-Einstein condensates with time-dependent trapping potential

Abdullaev, F. Kh; Kraenkel, Roberto André
Fonte: Universidade Estadual Paulista Publicador: Universidade Estadual Paulista
Tipo: Artigo de Revista Científica Formato: 023613-023611
ENG
Relevância na Pesquisa
36.5%
The atomic tunneling between two tunnel-coupled Bose-Einstein condensates (BECs) in a double-well time-dependent trap was studied. For the slowly varying trap, synchronization of oscillations of the trap with oscillations of the relative population was predicted. Using the Melnikov approach, the appearance of the chaotic oscillations in the tunneling phenomena between the condensates was confirmed.

Outward potassium current oscillations in macrophage polykaryons: extracellular calcium entry and calcium-induced calcium release

Saraiva,R.M.; Masuda,M.O.; Oliveira-Castro,G.M.
Fonte: Associação Brasileira de Divulgação Científica Publicador: Associação Brasileira de Divulgação Científica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/11/1997 EN
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36.56%
Outward current oscillations associated with transient membrane hyperpolarizations were induced in murine macrophage polykaryons by membrane depolarization in the absence of external Na+. Oscillations corresponded to a cyclic activation of Ca2+-dependent K+ currents (IKCa) probably correlated with variations in intracellular Ca2+ concentration. Addition of external Na+ (8 mM) immediately abolished the outward current oscillations, suggesting that the absence of the cation is necessary not only for their induction but also for their maintenance. Oscillations were completely blocked by nisoldipine. Ruthenium red and ryanodine reduced the number of outward current cycles in each episode, whereas quercetin prolonged the hyperpolarization 2- to 15-fold. Neither low molecular weight heparin nor the absence of a Na+ gradient across the membrane had any influence on oscillations. The evidence suggests that Ca2+ entry through a pathway sensitive to Ca2+ channel blockers is elicited by membrane depolarization in Na+-free medium and is essential to initiate oscillations, which are also dependent on the cyclic release of Ca2+ from intracellular Ca2+-sensitive stores; Ca2+ ATPase acts by reducing intracellular Ca2+, thus allowing slow deactivation of IKCa. Evidence is presented that neither a Na+/Ca2+ antiporter nor Ca2+ release from IP3-sensitive Ca2+ stores participate directly in the mechanism of oscillation

Chronic Ketamine Reduces the Peak Frequency of Gamma Oscillations in Mouse Prefrontal Cortex Ex vivo

McNally, James M.; McCarley, Robert W.; Brown, Ritchie E.
Fonte: Frontiers Media S.A. Publicador: Frontiers Media S.A.
Tipo: Artigo de Revista Científica
EN_US
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Abnormalities in EEG gamma band oscillations (GBO, 30–80 Hz) serve as a prominent biomarker of schizophrenia (Sz), associated with positive, negative, and cognitive symptoms. Chronic, subanesthetic administration of antagonists of N-methyl-D-aspartate receptors (NMDAR), such as ketamine, elicits behavioral effects, and alterations in cortical interneurons similar to those observed in Sz. However, the chronic effects of ketamine on neocortical GBO are unknown. Thus, here we examine the effects of chronic (five daily i.p. injections) application of ketamine (5 and 30 mg/kg) and the more specific NMDAR antagonist, MK-801 (0.02, 0.5, and 2 mg/kg), on neocortical GBO ex vivo. Oscillations were generated by focal application of the glutamate receptor agonist, kainate (KA), in coronal brain slices containing the prelimbic cortex. This region constitutes the rodent analog of the human dorsolateral prefrontal cortex, a brain region strongly implicated in Sz-pathophysiology. Here we report the novel finding that chronic ketamine elicits a reduction in the peak oscillatory frequency of KA-elicited oscillations (from 47 to 40 Hz at 30 mg/kg). Moreover, the power of GBO in the 40–50 Hz band was reduced. These findings are reminiscent of both the reduced resonance frequency and power of cortical oscillations observed in Sz clinical studies. Surprisingly...

Global slowing of network oscillations in mouse neocortex by diazepam

Scheffzük, Claudia; Kukushka, Valeriy I.; Vyssotski, Alexei L.; Draguhn, Andreas; Tort, Adriano B.L.; Branka, Jurij
Fonte: Universidade Federal do Rio Grande do Norte Publicador: Universidade Federal do Rio Grande do Norte
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.59%
SCHEFFZUK, C. , KUKUSHKA, V. , VYSSOTSKI, A. L. , DRAGUHN, A. , TORT, A. B. L. , BRANKACK, J. . Global slowing of network oscillations in mouse neocortex by diazepam. Neuropharmacology , v. 65, p. 123-133, 2013.; Benzodiazepines have a broad spectrum of clinical applications including sedation, anti-anxiety, and anticonvulsive therapy. At the cellular level, benzodiazepines are allosteric modulators of GABAA receptors; they increase the efficacy of inhibition in neuronal networks by prolonging the duration of inhibitory postsynaptic potentials. This mechanism of action predicts that benzodiazepines reduce the frequency of inhibition-driven network oscillations, consistent with observations from human and animal EEG. However, most of existing data are restricted to frequency bands beloww30 Hz. Recent data suggest that faster cortical network rhythms are critically involved in several behavioral and cognitive tasks. We therefore analyzed diazepam effects on a large range of cortical network oscillations in freely moving mice, including theta (4e12 Hz), gamma (40e100 Hz) and fast gamma (120e160 Hz) oscillations. We also investigated diazepam effects over the coupling between theta phase and the amplitude fast oscillations. We report that diazepam causes a global slowing of oscillatory activity in all frequency domains. Oscillation power was changed differently for each frequency domain...

Theta-associated high-frequency oscillations (110–160 Hz) in the hippocampus and neocortex

Tort, Adriano B.L.; Scheffer-Teixeira, Robson; Souza, Bryan C.; Draguhn, Andreas; Brankacˇk, Jurij
Fonte: Universidade Federal do Rio Grande do Norte Publicador: Universidade Federal do Rio Grande do Norte
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.5%
TORT, A. B. L. ; SCHEFFER-TEIXEIRA, R ; Souza, B.C. ; DRAGUHN, A. ; BRANKACK, J. . Theta-associated high-frequency oscillations (110-160 Hz) in the hippocampus and neocortex. Progress in Neurobiology , v. 100, p. 1-14, 2013.; We review recent evidence for a novel type of fast cortical oscillatory activity that occurs circumscribed between 110 and 160 Hz, which we refer to as high-frequency oscillations (HFOs). HFOs characteristically occur modulated by theta phase in the hippocampus and neocortex. HFOs can co-occur with gamma oscillations nested in the same theta cycle, in which case they typically peak at different theta phases. Despite the overlapping frequency ranges, HFOs differ from hippocampal ripple oscillations in some key characteristics, including amplitude, region of occurrence, associated behavioral state, and activity time-course (sustained vs intermittent). Recent in vitro evidence suggests that HFOs depend on fast GABAergic transmission and may also depend on axonal gap junctions. The functional role of HFOs is currently unclear. Both hippocampal and neocortical theta-HFO coupling increase during REM sleep, suggesting a role for HFOs in memory processing

Increase in Hippocampal Theta Oscillations during Spatial Decision Making

Belchior, Hindiael; Lopes-dos-Santos, Vitor; Tort, Adriano; Ribeiro, Sidarta
Fonte: Universidade Federal do Rio Grande do Norte Publicador: Universidade Federal do Rio Grande do Norte
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.5%
The processing of spatial and mnemonic information is believed to depend on hippocampal theta oscillations (5–12 Hz). However, in rats both the power and the frequency of the theta rhythm are modulated by locomotor activity, which is a major confounding factor when estimating its cognitive correlates. Previous studies have suggested that hippocampal theta oscillations support decision-making processes. In this study, we investigated to what extent spatial decision making modulates hippocampal theta oscillations when controlling for variations in locomotion speed. We recorded local field potentials from the CA1 region of rats while animals had to choose one arm to enter for reward (goal) in a four-arm radial maze. We observed prominent theta oscillations during the decision-making period of the task, which occurred in the center of the maze before animals deliberately ran through an arm toward goal location. In speed-controlled analyses, theta power and frequency were higher during the decision period when compared to either an intertrial delay period (also at the maze center), or to the period of running toward goal location. In addition, theta activity was higher during decision periods preceding correct choices than during decision periods preceding incorrect choices. Altogether...

Slow Oscillations in the Mouse Hippocampus Entrained by Nasal Respiration

Yanovsky, Yevgenij; Ciatipis, Mareva; Draguhn, Andreas; Tort, Adriano B.L.; Brankacˇk, Jurij
Fonte: Universidade Federal do Rio Grande do Norte Publicador: Universidade Federal do Rio Grande do Norte
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.53%
Different types of network oscillations occur in different behavioral, cognitive, or vigilance states. The rodent hippocampus expresses prominentoscillations atfrequencies between 4 and 12Hz,which are superimposed by phase-coupledoscillations (30 –100Hz).These patterns entrain multineuronal activity over large distances and have been implicated in sensory information processing and memory formation. Here we report a new type of oscillation at near- frequencies (2– 4 Hz) in the hippocampus of urethane-anesthetized mice. The rhythm is highly coherent with nasal respiration and with rhythmic field potentials in the olfactory bulb: hence, we called it hippocampal respiration-induced oscillations. Despite the similarity in frequency range, several features distinguish this pattern from locally generatedoscillations: hippocampal respiration-induced oscillations have a unique laminar amplitude profile, are resistant to atropine, couple differentlytooscillations, and are abolished when nasal airflow is bypassed bytracheotomy. Hippocampal neurons are entrained by both the respiration-induced rhythm and concurrent oscillations, suggesting a direct interaction between endogenous activity in the hippocampus and nasal respiratory inputs. Our results demonstrate that nasal respiration strongly modulates hippocampal network activity in mice...

Les oscillations torsionnelles dans la zone de convection solaire

Beaudoin, Patrice
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
FR
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36.62%
Nous analysons les oscillations torsionnelles se développant dans une simulation magnétohydrodynamique de la zone de convection solaire produisant des champs magnétiques de type solaire (champs axisymétriques subissant des inversions de polarités régulières sur des échelles temporelles décadaires). Puisque ces oscillations sont également similaires à celles observées dans le Soleil, nous analysons les dynamiques zonales aux grandes échelles. Nous séparons donc les termes aux grandes échelles (force de Coriolis exercée sur la circulation méridienne et les champs magnétiques aux grandes échelles) de ceux aux petites échelles (les stress de Reynolds et de Maxwell). En comparant les flux de moments cinétiques entre chacune des composantes, nous nous apercevons que les oscillations torsionnelles sont maintenues par l’écoulement méridien aux grandes échelles, lui même modulé par les champs magnétiques. Une analyse d’échange d’énergie confirme ce résultat, puisqu’elle montre que seul le terme comprenant la force de Coriolis injecte de l’énergie dans l’écoulement. Une analyse de la dynamique rotationnelle ayant lieu à la limite de la zone stable et de la zone de convection démontre que celle-ci est fortement modifiée lors du passage de la base des couches convectives à la base de la fine tachocline s’y formant juste en-dessous. Nous concluons par une discussion au niveau du mécanisme de saturation en amplitude dans la dynamo s’opérant dans la simulation ainsi que de la possibilité d’utiliser les oscillations torsionnelles comme précurseurs aux cycles solaires à venir.; We study torsional oscillations developping in a magnetohydrodynamic simulation of the solar convective layers producing solar-like magnetic cycles (large-scale axisymmetric fields subjected to regular polarity reversals). Since these oscillations are similar to those observed in the Sun...

Étude numérique des origines hémodynamiques des oscillations dans des réseaux de capillaires

Tawfik, Yasmine
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
FR
Relevância na Pesquisa
36.53%
En simulant l’écoulement du sang dans un réseau de capillaires (en l’absence de contrôle biologique), il est possible d’observer la présence d’oscillations de certains paramètres comme le débit volumique, la pression et l’hématocrite (volume des globules rouges par rapport au volume du sang total). Ce comportement semble être en concordance avec certaines expériences in vivo. Malgré cet accord, il faut se demander si les fluctuations observées lors des simulations de l’écoulement sont physiques, numériques ou un artefact de modèles irréalistes puisqu’il existe toujours des différences entre des modélisations et des expériences in vivo. Pour répondre à cette question de façon satisfaisante, nous étudierons et analyserons l’écoulement du sang ainsi que la nature des oscillations observées dans quelques réseaux de capillaires utilisant un modèle convectif et un modèle moyenné pour décrire les équations de conservation de masse des globules rouges. Ces modèles tiennent compte de deux effets rhéologiques importants : l’effet Fåhraeus-Lindqvist décrivant la viscosité apparente dans un vaisseau et l’effet de séparation de phase schématisant la distribution des globules rouges aux points de bifurcation. Pour décrire ce dernier effet...

Spontanoszillationen der Pupillenweite : Untersuchung unter konstanten Beleuchtungsbedingungen bei unterschiedlicher zentralnervöser Aktivierung; Spontaneous pupillary oscillations : Investigation in constant light conditions at different alertness level

Warga, Max Roland
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
DE_DE
Relevância na Pesquisa
36.59%
Zielsetzung: Dunkelheit ist eine der Hauptbedingungen für den Pupillographischen-Schläfrigkeitstest (PST), der die durch Schläfrigkeit induzierten spontanen Oszillationen der Pupillenweite misst. Ziel der Studie war es, den Einfluss der lichtinduzierten Oszillationen auf Schläfrigkeitswellen zu untersuchen und anschließend lichtinduzierte Oszillationen im Zustand hoher zentralnervöser Aktivierung näher zu bestimmen. Methode: Spontane Pupillenoszillationen wurden bei gesunden Probanden (n=12) in 3 Schlafentzugsversuchen bei Leuchtdichten von 2, 40 und 400 cd/m² mit dem PST aufgezeichnet. Der PST basiert auf der Infrarot-Videopupillographie. Zwischen den Messnächten lagen mind. 10 Tage, um kumuliertes Schlafdefizit zu vermeiden. In einem 2. Experiment wurden Probanden (n=12) im Zustand hoher zentralnerv. Aktivierung untersucht. Die Messzeit wurde von 11 min. auf 5,5 min. reduziert. Diesmal wurde mit 4 Leuchtdichten (0 / 0,5 / 2 / 40 cd/m²) jede halbe Stunde am Vormittag gemessen. Ergebnis: Das Amplitudenspektrum 0,8 Hz und der PUI nahmen am deutlichsten bei 40 und 400 cd/m² während des Schlafentzugsversuches zu (bei 40 cd/m² signifikant), während der Anstieg bei 2 cd/m² am schwächsten zu sehen war. Bei den Vormittagsmessungen der wachen Probanden zeigte sich bei den lichtinduzierten Pupillenoszillationen ein Anstieg des Amplitudenspektrums 0...

Linear Oscillations of Compact Stars in the Cowling Approximation; Lineare Schwingungen von kompakten Sternen im Rahmen der Cowling-Näherung

Gaertig, Erich
Fonte: Universidade de Tubinga Publicador: Universidade de Tubinga
Tipo: Dissertação
EN
Relevância na Pesquisa
36.65%
During their evolution, relativistic stars may undergo oscillations which can become unstable under certain conditions. Newly born neutron stars are expected to oscillate wildly during their creation shortly after a supernovae collapse. They are also expected to oscillate if they are members of binary systems and there is tidal interaction or mass and angular momentum transfer from the companion star. Rotation strongly affects these oscillations and perturbed stars can become unstable if they rotate faster than some critical velocities. During these oscillatory phases of their lives, compact stars emit copious amounts of gravitational waves which together with viscosity tend to suppress the oscillations. These oscillations are divided into distinct families according to the restoring force; each of these classes providing valuable information about the stars interior. It is therefore of particular interest to investigate pulsations of relativistic objects. During the last two decades, these studies have become even more important due to the relations of the oscillations and instabilities to the emission of gravitational waves and the possibility of getting information about the stellar parameters (mass, radius, equation of state) by the proper analysis of the oscillation spectrum. Still...

A deterministic analysis of limit cycle oscillations in recursive digital filters due to quantization; A deterministic analysis of limit cycle oscillations in recursive digital filters due to quantization; NA; NA

Hess, Sigurd; Hess, Sigurd
Fonte: Monterey, California ; Naval Postgraduate School; Monterey, California ; Naval Postgraduate School Publicador: Monterey, California ; Naval Postgraduate School; Monterey, California ; Naval Postgraduate School
Tipo: Thesis; Thesis Formato: 276 p.: ill.;28 cm.; 276 p.: ill.;28 cm.
EN_US; EN_US
Relevância na Pesquisa
36.5%
A deterministic analysis of the limit cycle oscillations which occur in fixed-point implementations of recursive digital filters due to roundoff and truncation quantization after multiplication operations, is performed. Amplitude bounds, based upon a correlated nonstochastic signal approach and Lyapunov's direct method, as well as an approximate expression for the frequency of zero-input limit cycles, are derived and tested for the two-pole filter. The limit cycles are represented on a successive value phase-plane diagram from which certain symmetry properties are derived. Similar results are developed for other second-order digital filter configurations, and the' parallel and cascade forms. The results are extended to include limit cycles under in-put signal conditions. A basic design relationship between the number of significant digits required for the realization of a filter algorithm with a desired signal-to-noise (limit cycle) ratio is stated; A deterministic analysis of the limit cycle oscillations which occur in fixed-point implementations of recursive digital filters due to roundoff and truncation quantization after multiplication operations, is performed. Amplitude bounds, based upon a correlated nonstochastic signal approach and Lyapunov's direct method...

Analyse de l'activité en ondes lentes et des oscillations lentes chez les somnambules

Perrault, Rosemarie
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
FR
Relevância na Pesquisa
36.69%
Le somnambulisme est une parasomnie commune, caractérisée par des éveils incomplets lors des stades de sommeil lent, au cours desquels les individus atteints présentent des comportements moteurs d’une complexité variable accompagnés de confusion et d’un jugement altéré. La littérature actuelle suggère que ce trouble serait associé à des particularités de l’activité en ondes lentes et des oscillations lentes, deux indices de l’intégrité du processus homéostatique et de la profondeur du sommeil. Toutefois, en raison de certaines lacunes méthodologiques dans les études existantes, le rôle de ces marqueurs électroencéphalographiques dans la pathophysiologie du somnambulisme reste à éclaircir. Notre premier article a donc investigué d’éventuelles anomalies de l’activité en ondes lentes et des oscillations lentes chez les somnambules, en comparant leur sommeil au cours de la nuit entière à celui de participants contrôles. De plus, comme les somnambules semblent réagir différemment (en termes de fragmentation du sommeil notamment) des dormeurs normaux à une pression homéostatique accrue, nous avons comparé l’activité en ondes lentes et les oscillations lentes en nuit de base et suite à une privation de sommeil de 38 heures. Les résultats de nos enregistrements électroencéphalographiques chez 10 somnambules adultes et neuf participants contrôles montrent une élévation de la puissance spectrale de l’activité en ondes lentes et de la densité des oscillations lentes en nuit de récupération par rapport à la nuit de base pour nos deux groupes. Toutefois...

Feedback control of oscillations in combustion and cavity flows

Illingworth, Simon J
Fonte: University of Cambridge; Department of Engineering Publicador: University of Cambridge; Department of Engineering
Tipo: Thesis; doctoral; PhD
EN
Relevância na Pesquisa
36.59%
This thesis considers the control of combustion oscillations, motivated by the susceptibility of lean premixed combustion to such oscillations, and the long and expensive development and commissioning times that this is giving rise to. The controller used is both closed-loop, employing an actuator to modify some system parameter in response to a measured signal, and adaptive, meaning that it is able to maintain control over a wide range of operating conditions. The controller is applied to combustion systems with annular geometries, where instabilities can occur both longitudinally and azimuthally, and which require multiple sensors and multiple actuators for control. One of the requirements of Lyapunov-based adaptive control which is particularly troublesome for combustion systems is then addressed: that the sign of the high-frequency gain of the open-loop system is known. We address it by using an adaptive controller which employs a Nussbaum gain, and successfully apply it experimentally to combustion oscillations in a Rijke tube. Another type of fluid-acoustic resonance is then considered: the compressible flow past a shallow cavity. We start by finding a linear model of the cavity flow's dynamics, or its `transfer function'...

A straightforward method to compute average stochastic oscillations from data samples

J?lvez, Jorge
Fonte: BMC Publicador: BMC
Tipo: Article; published version
EN
Relevância na Pesquisa
36.59%
This is the final version of the article. It first appeared from BioMed Central via http://dx.doi.org/10.1186/s12859-015-0765-z; Background: Many biological systems exhibit sustained stochastic oscillations in their steady state. Assessing these oscillations is usually a challenging task due to the potential variability of the amplitude and frequency of the oscillations over time. As a result of this variability, when several stochastic replications are averaged, the oscillations are flattened and can be overlooked. This can easily lead to the erroneous conclusion that the system reaches a constant steady state. Results: This paper proposes a straightforward method to detect and asses stochastic oscillations. The basis of the method is in the use of polar coordinates for systems with two species, and cylindrical coordinates for systems with more than two species. By slightly modifying these coordinate systems, it is possible to compute the total angular distance run by the system and the average Euclidean distance to a reference point. This allows us to compute confidence intervals, both for the average angular speed and for the distance to a reference point, from a set of replications. Conclusions: The use of polar (or cylindrical) coordinates provides a new perspective of the system dynamics. The mean trajectory that can be obtained by averaging the usual cartesian coordinates of the samples informs about the trajectory of the center of mass of the replications. In contrast to such a mean cartesian trajectory...

Incessant excitation of the Earths free oscillations: global comparison of superconducting gravimeter records

Nawa, Kazunari; Suda, Naoki; Fukao, Yoshio; Sato, Tadahiro; Tamura, Yoshiaki; Shibuya, Kazuo; McQueen, Herbert; Virtanen, Heikki; Kaariainen, Jussi
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.53%
Records of superconducting gravimeters (SGs) at Canberra (Australia), Esashi (Japan), Metsahovi (Finland) and Syowa Stations (Antarctica) were analyzed to search for further evidence of background free oscillations of the Earth. Spectrograms for 1-year period and averaged power spectra for seismically quiet periods were obtained for each of the stations. Anomalous features of the oscillations observed at Syowa Station, such as an apparent seasonal variation and a high intensity at frequencies between 3 and 4 mHz, were absent at the other SG stations. Among the SG stations used in this study, the background free oscillations were detected most consistently and distinctly at Canberra, where the noise level was comparable to that at the IDA quietest station, while that at Syowa Station was close to the critical limit for detecting the oscillations. The background free oscillations provide a good reference to evaluate the noise level in the milliHertz band. (C) 2000 Elsevier Science B.V. All rights reserved.

Respiratory and non respiratory oscillations of the skin blood flow: A window to the junction of the sympathetic fibers to the skin blood vessels

Estañol,Bruno; Sentíes-Madrid,Horacio; Elías,Yolanda; Coyac,Plácido; Martínez-Memije,Raúl; Infante,Óscar; Tellez-Zenteno,José Francisco; García-Ramos,Guillermo
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2008 EN
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Objective of the study: The skin blood flow (SBF) has been known to oscillate in frequency and amplitude. The nature and type of these oscillations have remained obscure. We studied the oscillations of the SBF in frequency and amplitude with non invasive techniques during normal breathing at rest and compared it to the oscillations during rhythmic paced breathing at 6 cycles per minute. Subjects and methods: Thirty healthy subjects were studied under normothermic conditions. The following variables were recorded: 1) EKG signal; 2) SBF signal given by an infrared photoplethysmograph; 3) respiratory movements (RM). A correlation of the frequency of the respiration, the SBF and the EKG was made. The variability of the amplitudes of the SBF, RR intervals and pulse intervals was analyzed in the time domain and with spectral analysis using Fourier analysis. Results: We found no clear respiratory modulation of the amplitude of the SBF during natural breathing at rest. With default breathing there was a low frequency oscillations (LF 0.04 to 0.15 Hz) modulation of the amplitude of the SBF that was non respiratory in nature. During rhythmic breathing at 0.1 Hz there was a strong modulation at LF of the SBF with a typical waxing and waning appearance...