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Добірка наукової літератури з теми "Oscillation modulating"

Автор: Grafiati

Опубліковано: 30 травня 2022

Оновлено: 31 травня 2022

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Статті в журналах з теми "Oscillation modulating"

Lagrange, Andre H. "Valproate Enhances Neuropeptide Y Expression: Modulating the Modulators." Epilepsy Currents 7, no. 4 (July 2007): 107–9. http://dx.doi.org/10.1111/j.1535-7511.2007.00167.x.

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Chronic Valproic Acid Treatment Triggers Increased Neuropeptide Y Expression and Signaling in Rat Nucleus Reticularis Thalami. Brill J, Lee M, Zhao S, Fernald RD, Huguenard JR. J Neurosci 2006;26:6813–6822. Valproate (VPA) can suppress absence and other seizures, but its precise mechanisms of action are not completely understood. We investigated whether VPA influences the expression of neuropeptide Y (NPY), an endogenous anticonvulsant. Chronic VPA administration to young rats (300–600 mg · kg–1 · d–1 in divided doses over 4 d) resulted in a 30–50% increase in NPY mRNA and protein expression in the nucleus reticularis thalami (nRt) and hippocampus, but not in the neocortex, as shown by real-time PCR, radioimmunoassay, and immunohistochemistry. No increased expression was observed after a single acute dose of VPA. Chronic treatment with the pharmacologically inactive VPA analog octanoic acid did not elicit changes in NPY expression. No significant expression changes could be shown for the mRNAs of the Y1 receptor or of the neuropeptides somatostatin, vasoactive intestinal polypeptide, and choleocystokinin. Fewer synchronous spontaneous epileptiform oscillations were recorded in thalamic slices from VPA-treated animals, and oscillation duration as well as the period of spontaneous and evoked oscillations were decreased. Application of the Y1 receptor inhibitor N2-(diphenylacetyl)- N-[(4-hydroxyphenyl)methyl]-d-arginine-amide (BIBP3226) enhanced thalamic oscillations, indicating that NPY is released during those oscillations and acts to downregulate oscillatory strength. Chronic VPA treatment significantly potentiated the effect of BIBP3226 on oscillation duration but not on oscillation period. These results demonstrate a novel mechanism for the antiepileptic actions of chronic VPA therapy.

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Chen, C. K., L. Wang, J. T. Yang, and L. T. Chen. "Experimental and Computational Analysis of Periodic Flow Structure in Oscillatory Gas Flow Meters." Journal of Mechanics 22, no. 2 (June 2006): 137–44. http://dx.doi.org/10.1017/s1727719100004433.

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AbstractThe oscillatory characteristics and dynamic structure of periodic flow in an oscillatory gas flow meter were studied experimentally and numerically. The flow oscillations were triggered by the Coanda effect and an universal correlation between Strouhal number and Reynolds number, Str = 1.09 × 10−3 for ReHD >800, was deduced based on spectral analysis of the pressure fluctuations in the flow channel. Numerical simulation indicated that the evolution of the flow patterns was classified into stages of induction and sustainable periodic oscillation. The transformation between the two stages was noticeably affected by the design of the feedback channels. The results further revealed that the development of the main vortex in the oscillating chamber and the small vortices at the entrance of the feedback channels concurrently modulate the mechanism of oscillation. The small vortices located at both entrances of the feedback channels play the role of a pair of modulating valves, which alternatively switch on and off the bypass flow through each feedback channel, thus reinforcing the periodic oscillation.

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Chen, Hua-Pin, San-Fu wang, Yu-Nan Chen, and Qi-Geng Huang. "Electronically Tunable Third-Order Quadrature Oscillator Using VDTAs." Journal of Circuits, Systems and Computers 28, no. 04 (March 31, 2019): 1950066. http://dx.doi.org/10.1142/s021812661950066x.

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This study proposes a new electronically tunable third-order quadrature oscillator using two multi-output voltage difference transconductance amplifiers (VDTAs) and three grounded capacitors. The proposed circuit provides three quadrature voltage outputs, two high-impedance quadrature current outputs, and one high-impedance current output with controllable amplitude. The proposed circuit can provide amplitude modulation/amplitude shift keying signals when the input bias current of the second VDTA is a modulating signal. The oscillation condition and oscillation frequency can be separately adjusted by the input bias currents of two multi-output VDTAs, and it is suitable for use on custom sensor networks. Experimental and H-Spice simulation results are given to confirm theoretical analyses.

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Marsh, Donald J., Olga V. Sosnovtseva, Alexey N. Pavlov, Kay-Pong Yip, and Niels-Henrik Holstein-Rathlou. "Frequency encoding in renal blood flow regulation." American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 288, no. 5 (May 2005): R1160—R1167. http://dx.doi.org/10.1152/ajpregu.00540.2004.

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With a model of renal blood flow regulation, we examined consequences of tubuloglomerular feedback (TGF) coupling to the myogenic mechanism via voltage-gated Ca channels. The model reproduces the characteristic oscillations of the two mechanisms and predicts frequency and amplitude modulation of the myogenic oscillation by TGF. Analysis by wavelet transforms of single-nephron blood flow confirms that both amplitude and frequency of the myogenic oscillation are modulated by TGF. We developed a double-wavelet transform technique to estimate modulation frequency. Median value of the ratio of modulation frequency to TGF frequency in measurements from 10 rats was 0.95 for amplitude modulation and 0.97 for frequency modulation, a result consistent with TGF as the modulating signal. The simulation predicted that the modulation was regular, while the experimental data showed much greater variability from one TGF cycle to the next. We used a blood pressure signal recorded by telemetry from a conscious rat as the input to the model. Blood pressure fluctuations induced variability in the modulation records similar to those found in the nephron blood flow results. Frequency and amplitude modulation can provide robust communication between TGF and the myogenic mechanism.

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Cho, Jun-Hyung, Hyo-Sang Jeong, and Hyuk-Kee Sung. "Spurious Tone Reduction and Signal Stabilization of Optoelectronic Oscillators by Low-Frequency RF Signal Modulation." Photonics 9, no. 5 (May 12, 2022): 339. http://dx.doi.org/10.3390/photonics9050339.

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In this study, the oscillation signal stabilization and spurious tone suppression of a directly modulated optoelectronic oscillator (DM-OEO) are simultaneously achieved by modulating a laser with a low-frequency radio frequency (RF) signal. The laser in the DM-OEO is modulated by a rectangular wave with a period inversely proportional to the frequency interval of the spurious tones and a duty cycle of 50%. The optical sidebands of the rectangular wave-modulated laser pulled the optical gain of the spurious tones of the DM-OEO, resulting in a spurious tone suppression and time stabilization in the DM-OEO signal. We achieve a 15 GHz DM-OEO with a 40.14 dB side-mode suppression ratio (SMSR) and 2.55 dB improvement in the oscillation power stability compared to that without RF modulation.

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WANG, Xinlin, Xiaoyue QIU, Xuchu WENG, and Ping YANG. "Modulating working memory related-oscillation via entrainment of neural oscillation." Advances in Psychological Science 30, no. 4 (2022): 802. http://dx.doi.org/10.3724/sp.j.1042.2022.00802.

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Sihn, Duho, and Sung-Phil Kim. "Differential modulation of behavior by infraslow activities of different brain regions." PeerJ 10 (February 1, 2022): e12875. http://dx.doi.org/10.7717/peerj.12875.

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The oscillation phase of electroencephalograms (EEGs) is associated with behavioral performance. Several studies have demonstrated this association for relatively fast oscillations (>1 Hz); a similar finding has also been reported for slower oscillations, showing that behavioral performance is correlated with the phase of infraslow activity (ISA, 0.01–0.1 Hz) of electroencephalography (EEG). However, the previous study only investigated ISA in a local brain region using a relatively simple task (somatosensory discrimination task), leaving it difficult to determine how the EEG ISA for various brain regions is associated with behavioral performance. In addition, it is not known whether the EEG ISA phase modulates more complex behavioral task performance. In the present study, we analyzed the ISA of whole-brain EEG of participants performing various behaviors while playing video games. We found that behavior was associated with the specific oscillation phase of EEG ISA when that behavior was independent of other behaviors. In addition, we found that the EEG ISA oscillation phases modulating the different behaviors varied across brain regions. Our results suggest that the EEG ISA for different brain regions modulates behavioral performance in different ways and such modulation of EEG ISA can be generalized to diverse behaviors. This study may deepen the understanding of how EEG ISA modulates behavior and increases the applicability of EEG ISA.

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Kim, MinKyung, and UnCheol Lee. "Alpha oscillation, criticality, and responsiveness in complex brain networks." Network Neuroscience 4, no. 1 (January 2020): 155–73. http://dx.doi.org/10.1162/netn_a_00113.

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Brains in unconsciousness are characterized by significantly limited responsiveness to stimuli. Even during conscious wakefulness, responsiveness is highly dependent on ongoing brain activity, specifically, of alpha oscillations (∼10 Hz). We hypothesized that the variety of brain responses to external stimuli result from the interaction between state-specific and transient alpha oscillations and stimuli. To justify this hypothesis, we simulated various alpha oscillations in the human brain network, modulating criticality (a balanced state between order and disorder), and investigated specific alpha oscillation properties (instantaneous amplitude, phase, and global synchronization) that induce a large or small response. As a result, we found that the alpha oscillations near a critical state show a more complex and long-lasting response, which is more prominent when stimuli are given to globally desynchronized and low-amplitude oscillations. We also found specific phases of alpha oscillation that barely respond to stimuli, which implies the presence of temporal windows in the alpha cycle for a large or small response. The results explain why brain responses are so variable across conscious and unconscious states and across time windows even during conscious wakefulness, and emphasize the importance of considering ongoing alpha oscillations for effective brain stimulation.

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Kozhevnikov, Vasily, Andrey Kozyrev, Vladimir Konev, and Aleksey Klimov. "The phase stability of nanosecond Gunn oscillators." Vojnotehnicki glasnik 70, no. 2 (2022): 461–74. http://dx.doi.org/10.5937/vojtehg70-36094.

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Introduction/purpose: Detailed theoretical and experimental studies have been carried out in order to investigate the problem of a phase stability in electrodynamically uncoupled Gunn oscillators. Methods: The influence of modulating pulse instabilities has been investigated by means of computer simulation in the framework of a nonlinear one-dimensional theoretical model of the GaAs Gunn diode semiconductor active region. Experimental observations were also conducted including microwave measurements and antenna far-field estimation. They confirm the main theoretical results and extend the key work conclusions. Results: It was shown that the initial phase of the microwave oscillation out of the Gunn oscillator is independent of internal noises of the semiconductor structure and can be fixed only by the modulating voltage pulse. Conclusion: Gunn-diodes based microwave oscillators were stabilized using the leading edge of the voltage pulse from the modulating power supply. These results open up serious prospects for designing antenna phased arrays based on Gunn oscillators without mutual feedback (electrodynamically independent).

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Restrepo, Juan Camilo, Aldemar Higgins, Jaime Escobar, Silvio Ospino, and Natalia Hoyos. "Contribution of low-frequency climatic–oceanic oscillations to streamflow variability in small, coastal rivers of the Sierra Nevada de Santa Marta (Colombia)." Hydrology and Earth System Sciences 23, no. 5 (May 16, 2019): 2379–400. http://dx.doi.org/10.5194/hess-23-2379-2019.

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Abstract. This study evaluated the influence of low-frequency oscillations, that are linked to large-scale oceanographic–atmospheric processes, on streamflow variability in small tropical coastal mountain rivers of the Sierra Nevada de Santa Marta, Colombia. We used data from six rivers that had > 32 years of complete, continuous monthly streamflow records. This investigation employed spectral analyses to (1) explore temporal characteristics of streamflow variability, (2) estimate the net contribution to the energy spectrum of low-frequency oscillations to streamflow anomalies, and (3) analyze the linkages between streamflow anomalies and large-scale, low-frequency oceanographic–atmospheric processes. Wavelet analyses indicate that the 8–12-year component exhibited a quasi-stationary state, with a peak of maximum power between 1985 and 2005. These oscillations were nearly in phase in all rivers. Maximum power peaks occurred for the Palomino and Rancheria rivers in 1985 and 1995, respectively. The wavelet spectrum highlights a change in river variability patterns between 1995 and 2015, characterized by a shift towards the low-frequency oscillations' domain (8–12 years). The net contribution of these oscillations to the energy spectrum was as high as 51 %, a value much larger than previously thought for rivers in northwestern South America. The simultaneous occurrence of hydrologic oscillations, as well as the increase in the amplitude of the 8–12-year band, defined periods of extremely anomalous wet seasons during 1989–1990, 1998–2002 and 2010–2011, reflecting the role of low-frequency oscillations in modulating streamflow variability in these rivers. Cross-wavelet transform and wavelet coherence revealed high common powers and significant coherences in low-frequency bands (>96 months) between streamflow anomalies and Atlantic Meridional Oscillation (AMO), Pacific Decadal Oscillation (PDO) and the Tropical North Atlantic Index (TNA). These results show the role of large-scale, low-frequency oceanographic–climate processes in modulating the long-term hydrological variability of these rivers.

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Більше джерел

Дисертації з теми "Oscillation modulating"

Ozur, Anastasiia. "Thalamic modulation of the cortisal slow oscillation." Master's thesis, Université Laval, 2016. http://hdl.handle.net/20.500.11794/27030.

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Il est bien établi que le thalamus joue un rôle crucial dans la génération de l'oscillation lente synchrone dans le cortex pendant le sommeil lent. La puissance des ondes lente / delta (0.2-4 Hz) est un indicateur quantifiable de la qualité du sommeil. La contribution des différents noyaux thalamiques dans la génération de l’activité à ondes lentes et dans sa synchronisation n'est pas connue. Nous émettons l'hypothèse que les noyaux thalamiques de premier ordre (spécifiques) influencent localement l’activité à ondes lentes dans les zones corticales primaires, tandis que les noyaux thalamiques d'ordre supérieur (non spécifiques) synchronisent globalement les activités à ondes lentes à travers de larges régions corticales. Nous avons analysé les potentiels de champ locaux et les activités de décharges de différentes régions corticales et thalamiques de souris anesthésiées alors qu'un noyau thalamique était inactivé par du muscimol, un agoniste des récepteurs GABA. Les enregistrements extracellulaires multi-unitaires dans les noyaux thalamiques de premier ordre (VPM) et d'ordre supérieur (CL) montrent des activités de décharges considérablement diminuées et les décharges par bouffées de potentiels d'action sont fortement réduites après inactivation. Nous concluons que l'injection de muscimol réduit fortement les activités de décharges et ne potentialise pas la génération de bouffées de potentiel d'action à seuil bas. L'inactivation des noyaux thalamiques spécifiques avec du muscimol a diminué la puissance lente / delta dans la zone corticale primaire correspondante. L'inactivation d'un noyau non spécifique avec le muscimol a significativement réduit la puissance delta dans l'ensemble du cortex étudié. Nos expériences démontrent que le thalamus a un rôle crucial dans la génération de l'oscillation lente corticale.
It is well established that thalamus plays a crucial role in the generation of the synchronous slow oscillation in the cortex during non-REM sleep. The slow/delta power (0.2-4 Hz) is the main measured factor of the quality of sleep. However, the contribution of different thalamic nuclei to the generation of the slow wave activities and its synchronization is not known. We hypothesized that the first-order (specific) thalamic nuclei provide a control of slow waves in primary cortical areas, while higher-order (non-specific) thalamic nuclei may synchronize the slow-wave activities across wide cortical regions. We analyzed local field potentials and spiking activities from different cortical and thalamic areas of anesthetized mice while a thalamic nucleus was inactivated by the GABA-agonist muscimol. Extracellular multiunit recordings in first-order (VPM) and higher-order (CL) thalamic nuclei show dramatically decreased spiking activity and strongly reduced burst firing after inactivation with muscimol. We conclude that the injection of muscimol strongly reduced the spiking activity and does not potentiate the generation of low-threshold spike mediated bursts. Inactivation of specific thalamic nuclei with muscimol decreased the slow/delta power in the corresponding primary cortical area. The inactivation of a non-specific nucleus with muscimol significantly reduced the delta power in all investigated cortical areas. Our experiments demonstrate that the thalamus is required for the fine tuning of the cortical slow oscillation.

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Betterton, Ruth Traer. "Modulation of hippocampal gamma oscillations by acetycholine." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.691259.

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Neuronal oscillations involve the rhythmic, synchronous firing of populations of cells across a range of frequencies. Gamma oscillations (30 - 100Hz) occur during attention, sensory processing and learning and memory. Acetylcholine (ACh) release in the hippocampus is associated with increases in gamma oscillatory power and disruption of cholinergic inputs to the hippocampus and selective knockout of ACh receptor subtypes (AChRs) alter oscillatory activity. This suggests that ACh has a role in the modulation of gamma oscillations. To investigate this process we have utilised both in vitro brain slice and mathematical models.

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Ma, Rui, Martin Kreißig, Florian Protze, Frank Ellinger, Purbawati, Ruiz-Calaforra, Hem, and Ursula Ebels. "Spin Toqure Oscillator Based BFSK Modulation." IEEE / Institute of Electrical and Electronics Engineers Incorporated, 2017. https://tud.qucosa.de/id/qucosa%3A35059.

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This work presents a spin torque nano-oscillator (STNO) based binary frequency shift keying (BFSK) modulation schema implemented on a printed circuit board (PCB). Maximal input data rate reaches 20 Mbit/s. Depending on the STNO used, carrier frequency can range from 1 to 10 GHz. Both DC and AC currents flowing through the STNO can be tuned between 0 to 4 mA. Using one magnetic tunnel junction (MTJ) STNO, a 380 MHz frequency shift around the center frequency 9 GHz was observed, when the modulated current was toggled between 0.8 mA and 1.2 mA at a rate of 20 Mbit/s. This is the first work demonstrating that the STNOs are applicable for BFSK modulation on the wireless application level.

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Iemi, Luca [Verfasser]. "Spontaneous neural oscillations bias perception by modulating baseline excitability / Luca Iemi." Berlin : Medizinische Fakultät Charité - Universitätsmedizin Berlin, 2017. http://d-nb.info/1148425292/34.

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Gehlhaar, Robert. "Terahertz oscillation and stimulated emission from planar microcavities." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2007. http://nbn-resolving.de/urn:nbn:de:swb:14-1184931926949-93266.

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In the past decades, the miniaturization in optics led to new devices with structural sizes in the range of the light wavelength, where the photonic modes are con- fined and the number of states is limited. In the smallest microcavities, i.e. micrometer sized optical resonators, the propagation of only one mode is permitted that is simultaneously amplified internally. This particularly strong enhancement of the electric field is directly related to the quality factor of the cavity. By introducing an optical dipole into a high-Q microcavity, the spontaneous emission is amplified at the cavity mode frequency enabling stimulated emission in an inverted system. Although some of theses cavity e®ects can only be understood by quantum elec- trodynamic theory, most mechanisms are accessible by classical and semi-classical approaches. In this thesis, one-dimensional planar microcavities with quality factors up to 4500 have been fabricated by physical vapor deposition of dielectric thin films and organic active materials. A new cavity design based on anisotropic dielectric mirrors grown by oblique angle deposition microcavities with two energetically shifted orthogonally polarized modes is presented. The application of these anisotropic structures for terahertz di®erence signal generation is demonstrated in spectrally and time resolved transmission experiments, where optical beats with repetition rates in the terahertz range are observed. Optically pumped organic vertical cavity surface emitting lasers (VCSELs) have been realized by applying an organic solid state laser compound and high reflectance distributed Bragg reflectors. These lasers combine a very low laser threshold with small beam divergence and good stability. A transfer of the anisotropic design towards an organic VCSEL results in the generation of two perpendicularly polarized laser modes with a splitting adjustable by the fabrication conditions. The observation of an oscillation of two laser modes in a photomixing experiment proves a phase coupling mechanism. This demonstrates the potential of the anisotropic cavity design for a passive or active component in a terahertz radiation source or frequency generator. Furthermore, microcavities with two and three coupled resonators are investigated. By the application of time-resolved transmission experiments, spatial oscil- lations of the internal electric field - photonic Bloch oscillations - are successfully demonstrated. In combination with the anisotropic microcavities, this is a second concept for the modulation of transmitted light with terahertz frequencies. All experiments are accompanied by numerical or analytical models. Transmission experiments of continuously incident light and single laser pulses are compared with transfer matrix simulations and Fourier transform based approaches. For the modeling of emission experiments, a plane wave expansion method is successfully used. For the analysis of the organic VCSEL dynamics, we apply a set of rate equations that explains the gain switching process.

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Haggerty, Daniel Christopher. "Noradrenergic modulation of rat hippocampal neuronal oscillations in vitro." Thesis, University of Newcastle Upon Tyne, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.500920.

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Neuronal oscillations have been implicated in various cognitive functions in vivo and can be correlated to a variety of behavioural states. Hippocampal gamma (20-80 Hz) and theta (4-15 Hz) frequency neuronal oscillations have been reported to play a role in memory and representation of visuospatial information. Noradrenaline, a neurotransmitter released during arousal, is an important factor in information acquisition and ma}g of novel spatial information. The aim of this thesis was to investigate the cellular mechanisms by which noradrenaline modulates hippocampal gamma and theta frequency oscillations in the hippocampus in vitro.

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Fano, Silvia [Verfasser]. "Histaminergic modulation of gamma oscillations in rat hippocampus / Silvia Fano." Berlin : Freie Universität Berlin, 2013. http://d-nb.info/1035182475/34.

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Soukharev, Boris E., and Lon L. Hood. "Possible solar modulation of the equatorial quasi-biennial oscillation: Additional statistical evidence." AMER GEOPHYSICAL UNION, 2001. http://hdl.handle.net/10150/624003.

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Although the quasi-biennial oscillation (QBO) in the equatorial zonal wind is dominantly driven by wave forcing originating in the troposphere, a recent study suggests that certain properties of the QBO may vary slightly on the 11-year solar cycle timescale [Salby and Callaghan, 2000]. Here we report further statistical investigation using both equatorial wind data for levels from 50 to 1 hPa and longterm proxy solar ultraviolet flux time series (10.7-cm solar radio flux and sunspot numbers). Spectral analysis of the solar time series yields evidence for a significant spectral peak at periods between 25 and 30 months, approximately equivalent to the mean QBO period, as had also been noted by earlier authors [Shapiro and Ward, 1962]. Cross-spectral analysis of the 10.7-cm solar radio flux and equatorial zonal wind time series shows significant coherency at the QBO period at all available pressure levels. The phase lag of the wind data relative to the solar flux at the QBO period ranges from 0–1 months near the stratopause (1 hPa) to 20–24 months in the lower stratosphere (50 hPa). The nearly inphase relationship near the stratopause suggests a possible modulation of the QBO at this level by the radiative and photochemical effects of solar ultraviolet variations. The amplitudes of the solar variations at the QBO period tend to be larger under solar maximum than under solar minimum conditions. Composite analysis of the westerly and easterly phases of the equatorial zonal wind shows subtle but consistent differences in the durations of the westerlies and easterlies between solar maximum and minimum conditions.

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Copie, François. "Modulation instabilities in dispersion oscillating passive fiber-ring cavities." Thesis, Lille 1, 2017. http://www.theses.fr/2017LIL10111/document.

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Ces travaux de thèse portent sur l’instabilité paramétrique survenant dans les cavités optiques fibrées passives en anneau, induite par une modulation longitudinale de la dispersion chromatique. Dans les cavités optiques, le processus d’instabilité modulationnelle est connu pour être susceptible de déstabiliser l’état stationnaire et de le transformer en un train stable d’impulsions. Nous décrivons dans ce travail comment une variation longitudinale de la dispersion à l’intérieur de la cavité enrichie la dynamique de ce type de dispositif en engendrant un régime d’instabilité paramétrique. Nous détaillons l’étude théorique de ce nouveau mécanisme ce qui nous permet d’en identifier les signatures spectrales et temporelles, parmi lesquels, la génération de multiples pics de résonances dans le spectre optique et l’apparition d’une dynamique de doublement de période dans le domaine temporel. Nous avons réalisé de tels résonateurs afin de confirmer expérimentalement nos prédictions. Le modèle que nous avons retenu consiste à réaliser un anneau en soudant entre elles des fibres uniformes présentant des dispersions différentes. En terme de résultats, nous avons tout d’abord observé pour la première fois l’apparition des instabilités modulationnelle et paramétrique dans un même système, pour ensuite s’intéresser à leur dynamique. Cette dernière est accessible grâce à des méthodes de détection en temps réel à la fois spectrale et temporelle. Nous avons ainsi pu observer avec une précision remarquable l’émergence des instabilités, le doublement de période associé au régime paramétrique ainsi que l’apparition d’un nombre record de résonances paramétriques dans notre système
This thesis work deals with the parametric instability occurring in passive optical fiber-ring cavities, which is induced by a longitudinal modulation of the chromatic dispersion. In optical cavities, the modulation instability process is known to potentially destabilize the stationary state and turn it into a stable train of pulses. We describe in this work how a longitudinal variation of the dispersion inside the cavity enriches the dynamics of this type of device by entailing a regime of parametric instability. We detail the theoretical study of this new mechanism, which allows us to identify its spectral and temporal signatures, among which, the generation of multiple resonance peaks in the optical spectrum and the appearance of a period doubling dynamics in the time domain. We have realized such resonators in order to confirm experimentally our predictions. The model we have chosen simply consists in building a ring by splicing together uniform fibers characterized by different dispersions. In terms of results, we first observed the emergence of both modulational and parametric instabilities in the same system, before investigating their dynamics. The latter is accessible thanks to real-time spectral and temporal detection methods. We thus observed with remarkable precision the emergence of the instabilities, the period doubling associated to the parametric regime and the appearance of a record number of parametric resonances in our system

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Hood, Lon L. "QBO/solar modulation of the boreal winter Madden-Julian oscillation: A prediction for the coming solar minimum." AMER GEOPHYSICAL UNION, 2017. http://hdl.handle.net/10150/624342.

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The Madden-Julian oscillation (MJO), also known as the 30-60day oscillation, is the strongest of the intraseasonal climate oscillations in the tropics and has significant derivative effects on extratropical circulation and intraseasonal climate. It has recently been shown that the stratospheric quasi-biennial oscillation (QBO) modulates the amplitude of the boreal winter MJO such that MJO amplitudes are larger on average during the easterly phase (QBOE) than during the westerly phase (QBOW). A major possible mechanism is the decrease in static stability in the lowermost stratosphere under QBOE conditions resulting from relative upwelling associated with the QBO-induced meridional circulation. Here evidence is presented that tropical upwelling changes related to the 11year solar cycle also modulate the boreal winter MJO. Based on 37.3years of MJO amplitude data, the largest amplitudes and occurrence rates, and the weakest static stabilities in the tropical lower stratosphere, occur during the QBOE phase under solar minimum (SMIN) conditions while the smallest amplitudes and strongest static stabilities occur during the QBOW phase under solar maximum (SMAX) conditions. Conversely, when the QBO and solar forcings are opposed (QBOW/SMIN and QBOE/SMAX), the difference in occurrence rates becomes statistically insignificant. During the coming solar minimum, at least one additional winter in the QBOE/SMIN category should occur (possibly as early as 2017/2018) during which especially large MJO amplitudes are expected and an initial test of these results will be possible. Plain Language Summary An ongoing issue in climate science is the extent to which upper atmospheric processes, including solar forcing, can influence tropospheric climate. It has recently been shown that an internal oscillation of the stratosphere, the quasi-biennial oscillation, can modulate the amplitude and occurrence rate of intraseasonal climate oscillations in the tropical Pacific during northern winter. These intraseasonal oscillations, the most important of which is the 30-60day Madden-Julian oscillation, have significant derivative effects on climate outside of the tropics, including impacts on rainfall events over the continental United States. Here evidence is presented that the amplitude of the Madden-Julian oscillation during northern winter is also modulated by the 11year solar cycle. The modulation is such that amplitudes and occurrence rates are largest under solar minimum conditions when the quasi-biennial oscillation is in its easterly phase and smallest under solar maximum conditions when the quasi-biennial oscillation is in its westerly phase. However, the available time record (37.3years of satellite measurements) is limited. During the coming solar minimum, at least one additional winter in the solar minimum/easterly category should occur (possibly as early as 2017/2018) during which larger-than-average amplitudes are expected and an initial test of the proposed relationship will be possible.

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Книги з теми "Oscillation modulating"

Wang, Bin. Intraseasonal Modulation of the Indian Summer Monsoon. Oxford University Press, 2018. http://dx.doi.org/10.1093/acrefore/9780190228620.013.616.

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The strongest Indian summer monsoon (ISM) on the planet features prolonged clustered spells of wet and dry conditions often lasting for two to three weeks, known as active and break monsoons. The active and break monsoons are attributed to a quasi-periodic intraseasonal oscillation (ISO), which is an extremely important form of the ISM variability bridging weather and climate variation. The ISO over India is part of the ISO in global tropics. The latter is one of the most important meteorological phenomena discovered during the 20th century (Madden & Julian, 1971, 1972). The extreme dry and wet events are regulated by the boreal summer ISO (BSISO). The BSISO over Indian monsoon region consists of northward propagating 30–60 day and westward propagating 10–20 day modes. The “clustering” of synoptic activity was separately modulated by both the 30–60 day and 10–20 day BSISO modes in approximately equal amounts. The clustering is particularly strong when the enhancement effect from both modes acts in concert. The northward propagation of BSISO is primarily originated from the easterly vertical shear (increasing easterly winds with height) of the monsoon flows, which by interacting with the BSISO convective system can generate boundary layer convergence to the north of the convective system that promotes its northward movement. The BSISO-ocean interaction through wind-evaporation feedback and cloud-radiation feedback can also contribute to the northward propagation of BSISO from the equator. The 10–20 day oscillation is primarily produced by convectively coupled Rossby waves modified by the monsoon mean flows. Using coupled general circulation models (GCMs) for ISO prediction is an important advance in subseasonal forecasts. The major modes of ISO over Indian monsoon region are potentially predictable up to 40–45 days as estimated by multiple GCM ensemble hindcast experiments. The current dynamical models’ prediction skills for the large initial amplitude cases are approximately 20–25 days, but the prediction of developing BSISO disturbance is much more difficult than the prediction of the mature BSISO disturbances. This article provides a synthesis of our current knowledge on the observed spatial and temporal structure of the ISO over India and the important physical processes through which the BSISO regulates the ISM active-break cycles and severe weather events. Our present capability and shortcomings in simulating and predicting the monsoon ISO and outstanding issues are also discussed.

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Center, Goddard Space Flight, ed. Modulation characteristics of a high-power semiconductor master oscillator power amplifier (MOPA). Greenbelt, Md: National Aeronautics and Space Administration, Goddard Space Flight Center, 1992.

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Q, Lee Richard, and United States. National Aeronautics and Space Administration., eds. Planar dielectric resonator stabilized HEMT oscillator integrated with CPW/aperture coupled patch antenna. [Washington, D.C.]: National Aeronautics and Space Administration, 1991.

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Pfurtscheller, Gert, and Fernando Lopes da Silva. EEG Event-Related Desynchronization and Event-Related Synchronization. Edited by Donald L. Schomer and Fernando H. Lopes da Silva. Oxford University Press, 2017. http://dx.doi.org/10.1093/med/9780190228484.003.0040.

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Event-related desynchronization (ERD) reflects a decrease of oscillatory activity related to internally or externally paced events. The increase of rhythmic activity is called event-related synchronization (ERS). They represent dynamical states of thalamocortical networks associated with cortical information-processing changes. This chapter discusses differences between ERD/ERS and evoked response potentials and methodologies for quantifying ERD/ERS and selecting frequency bands. It covers the interpretation of ERD/ERS in the alpha and beta bands and theta ERS and alpha ERD in behavioral tasks. ERD/ERS in scalp and subdural recordings, in various frequency bands, is discussed. Also presented is the modulation of alpha and beta rhythms by 0.1-Hz oscillations in the resting state and phase-coupling of the latter with slow changes of prefrontal hemodynamic signals (HbO2), blood pressure oscillations, and heart rate interval variations in the resting state and in relation to behavioral motor tasks. Potential uses of ERD-based strategies in stroke patients are discussed.

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Vlad, Serban E. Binary Periodic Signals and Flows. Nova Science Publishers, Incorporated, 2016.

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Nobre, Anna C. (Kia), and Gustavo Rohenkohl. Time for the Fourth Dimension in Attention. Edited by Anna C. (Kia) Nobre and Sabine Kastner. Oxford University Press, 2014. http://dx.doi.org/10.1093/oxfordhb/9780199675111.013.036.

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This chapter takes attention into the fourth dimension by considering research that explores how predictive information in the temporal structure of events can contribute to optimizing perception. The authors review behavioural and neural findings from three lines of investigation in which the temporal regularity and predictability of events are manipulated through rhythms, hazard functions, and cues. The findings highlight the fundamental role temporal expectations play in shaping several aspects of performance, from early perceptual analysis to motor preparation. They also reveal modulation of neural activity by temporal expectations all across the brain. General principles of how temporal expectations are generated and bias information processing are still emerging. The picture so far suggests that there may be multiple sources of temporal expectation, which can bias multiple stages of stimulus analysis depending on the stages of information processing that are critical for task performance. Neural oscillations are likely to provide an important medium through which the anticipated timing of events can regulate neuronal excitability.

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Частини книг з теми "Oscillation modulating"

Kraftmakher, Yaakov. "Measurement of Temperature Oscillations." In Modulation Calorimetry, 33–52. Berlin, Heidelberg: Springer Berlin Heidelberg, 2004. http://dx.doi.org/10.1007/978-3-662-08814-2_4.

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Sanguinetti, Joseph L. "Modulating Neural Oscillations with Transcranial Focused Ultrasound." In Rhythmic Advantages in Big Data and Machine Learning, 23–38. Singapore: Springer Singapore, 2022. http://dx.doi.org/10.1007/978-981-16-5723-8_2.

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Limes, Mark E. "Low-Frequency Modulation of Longitudinal Field: Modified Rabi Envelopes." In 129 Xe Relaxation and Rabi Oscillations, 89–103. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-13632-5_4.

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Kiwi, Miguel, Edmundo Lazo, and Jaime Rössler. "Periodic Modulation of a Logistic Oscillator." In Instabilities and Nonequilibrium Structures III, 59–64. Dordrecht: Springer Netherlands, 1991. http://dx.doi.org/10.1007/978-94-011-3442-2_5.

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Xie, Jinli, Jianyu Zhao, and Qinjun Zhao. "Topographic Modulations of Neural Oscillations in Spiking Networks." In Intelligent Computing Theories and Methodologies, 159–66. Cham: Springer International Publishing, 2015. http://dx.doi.org/10.1007/978-3-319-22180-9_16.

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Sakamoto, T., S. W. Hwang, Y. Nakamura, and K. Nakamura. "Envelope Modulation of Coulomb-Blockade Oscillations in Magnetic Fields." In Nanostructures and Quantum Effects, 107–11. Berlin, Heidelberg: Springer Berlin Heidelberg, 1994. http://dx.doi.org/10.1007/978-3-642-79232-8_14.

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Bromwich, David H., and Aric N. Rogers. "The El Niño-Southern Oscillation Modulation of West Antarctic Precipitation." In The West Antarctic Ice Sheet: Behavior and Environment, 91–103. Washington, D. C.: American Geophysical Union, 2013. http://dx.doi.org/10.1029/ar077p0091.

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Doungmo Goufo, Emile F., and A. Atangana. "Modulating Chaotic Oscillations in Autocatalytic Reaction Networks Using Atangana–Baleanu Operator." In Studies in Systems, Decision and Control, 135–58. Cham: Springer International Publishing, 2019. http://dx.doi.org/10.1007/978-3-030-11662-0_9.

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Sancristóbal, B., R. Vicente, A. J. Pons, G. Pipa, and J. Garcia-Ojalvo. "Modulating the Phase Coherence of Neuronal Population Oscillations in the Gamma Band." In Advances in Cognitive Neurodynamics (III), 475–81. Dordrecht: Springer Netherlands, 2013. http://dx.doi.org/10.1007/978-94-007-4792-0_64.

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Sarkar, Bishnu Charan, Suvra Sarkar, and Saumen Chakraborty. "Unstable PLL-Controller as FM Modulator and Detection of Modulating Self-Oscillations." In Advances and Applications in Nonlinear Control Systems, 369–98. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-30169-3_17.

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Тези доповідей конференцій з теми "Oscillation modulating"

Guyot, Daniel, Christian Oliver Paschereit, and Surya Raghu. "A Fluidic Actuator for Active Combustion Control." In ASME Turbo Expo 2008: Power for Land, Sea, and Air. ASMEDC, 2008. http://dx.doi.org/10.1115/gt2008-50797.

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In this work the performance of a fluidic actuator in an active combustion control scheme is demonstrated. The actuator was tested in two different burner configurations, a bluff body burner and a generic swirl-stabilized burner, where it modulated parts of the fuel flow. The oscillation frequency was controlled by varying the inlet mass flow of the actuator. Fluidic actuators are of special interest for fuel-based active control schemes featuring high frequency fuel flow modulation, as they are much more durable then conventional valves due to the absence of fast moving parts. Hot wire measurements were performed to investigate the fluidic actuator’s oscillation characteristics without combustion. The actuator was then incorporated into a bluff body burner and a swirl-stabilized burner, respectively, where it modulated parts of the fuel flow blended with nitrogen. Pressure and heat release fluctuations in the combustor were recorded and images of the flame were taken. For both burners the heat release response of the flame to fuel flow modulation was first studied during stable combustion. The spectra of the heat release signals showed a clear peak corresponding to the fluidics’ oscillation frequency, thus validating the ability of the actuator to influence the combustion process. As the next step, each of the two combustors was operated at conditions that featured a strong low-frequency combustion instability when no fuel was modulated. In case of the bluff body burner applying fuel modulation resulted in attenuation of the combustion instability for some oscillation frequencies. The attenuation was highest when modulating the fuel flow in between the fundamental instability frequency and its subharmonic. Modulating the fuel flow at the subharmonic, however, resulted in an amplification of the instable mode. Also when applied to the swirl burner, the fludics’ fuel flow modulation caused a significant reduction of the pressure oscillations, although the actuator could only be operated at oscillation frequencies much lower than the instability frequency due to the attached tubes. The results obtained in this work show that the fluidic actuator in use allows for fuel modulation and hence combustion control without the need for complex and fast moving parts, thus ensuring a long actuator lifetime. This makes the fluidic actuator highly appropriate for application in industrial gas turbines.

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Chishty, Wajid A., Joan Boulanger, and Sangsig Yun. "Experimental and Numerical Investigation of Spatial and Temporal Dispersion of Forced Fuel Oscillations." In ASME 2009 International Mechanical Engineering Congress and Exposition. ASMEDC, 2009. http://dx.doi.org/10.1115/imece2009-12595.

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In lean premixed combustors of gas turbine engines, fuel-air mixing is considered vital for controlling pollutant emissions as well as combustion instability. Enhancement in mixing may be obtained by modulating the fuel flow rate. Modulation of fuel flow is also a useful technique to actively control combustion instabilities arising from the pressure oscillations in the combustor and thrust augmenters. Effectiveness of the forced oscillations depends on the level of dispersion present in the system. Knowledge of dispersion levels is also important in determining the degree of mixing and therefore, the effectiveness of a premixer. This paper presents the experimental efforts undertaken to study the spatial and temporal dispersion of fuel flow rate oscillation introduced at the premixer inlet. Effects of oscillation amplitude and frequency are investigated at different bulk flow rates and at various locations in the premixer. Also presented is a review of the in-house numerical work done towards this end, using three computational methods. Results show that the degree of dispersion in fuel flow rate oscillations depends on modulation amplitude and frequency as well as advective velocity of the bulk flow.

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Song, Jinkwan, and Jong Guen Lee. "Characterization of Spray Formed by Liquid Jet Injected Into Oscillating Air Crossflow." In ASME Turbo Expo 2015: Turbine Technical Conference and Exposition. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/gt2015-43726.

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This paper presents experimental results on the characteristics of spray formed by a liquid (Jet-A) jet injected into an oscillating air crossflow. Ambient air pressure is raised up to 15.86 bar, and the corresponding aerodynamic Weber number and liquid-air momentum flux ratio are up to 1000 and 25, respectively. The level of modulated crossflow velocity is kept up to 20% of its mean value. For limited cases, the air crossflow is preheated. Planar Mie-scattering measurements are utilized to visualize changes of the spray penetration and cross-sectional spray area in the oscillating air crossflow, and PDPA measurements are used to measure the mean drop size and drop size distribution. Phase-synchronized PDPA measurement of droplet size under the modulation of crossflow shows that the modulating crossflow results in preferentially larger amount of smaller and bigger droplets than average-sized droplets. Global spray response of spray to modulating crossflow is characterized by using proper orthogonal decomposition (POD) analysis of Mie-scattering images and collecting (and hence determining gain of) Mie-scattering intensity of droplets at a fixed downstream distance. It is found that the dominant behavior of the spray is convective oscillation in the axial direction and the change of vertical penetration of the spray is almost negligible for the level of crossflow velocity modulation up to 20%. The gain of Mie-scattering intensity with respect to crossflow velocity modulation level gradually decreases as liquid-air momentum flux ratio increases. Also, per given momentum flux ratio and Weber number, the gain hardly varies with respect to crossflow modulation level, suggesting the response of spray increases in proportion to crossflow velocity modulation level.

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Kim, Kyu Tae, Jong Guen Lee, Bryan D. Quay, and Domenic A. Santavicca. "Experimental Investigation of the Nonlinear Response of Swirl Stabilized Flames to Equivalence Ratio Oscillations." In ASME Turbo Expo 2010: Power for Land, Sea, and Air. ASMEDC, 2010. http://dx.doi.org/10.1115/gt2010-23023.

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The nonlinear response of a swirl-stabilized flame to equivalence ratio oscillations was experimentally investigated in an atmospheric-pressure, high-temperature, lean-premixed model gas turbine combustor. To generate high-amplitude equivalence ratio oscillations, fuel was modulated using a siren type modulating device. The mixture ratio oscillations at the inlet of the combustion chamber were measured by the infrared absorption technique and the flame’s response, i.e., the fluctuation in the flame’s rate of heat release, was estimated by CH* chemiluminescence emission intensity. Phase-resolved CH* chemiluminescence images were taken to characterize the dynamic response of the flame. Results show that the amplitude and frequency dependence of the flame’s response to equivalence ratio oscillations is qualitatively consistent with the flame’s response to inlet velocity oscillations. The underlying physics of the nonlinear response of the flame to equivalence ratio oscillations, however, is associated with the intrinsically nonlinear dependence of the heat of reaction and burning velocity on the equivalence ratio. It was found that combustion cannot be sustained under conditions of high amplitude equivalence ratio oscillations. Lean blowoff occurs when the normalized amplitude of the equivalence ratio oscillation exceeds a threshold value. The threshold value is dependent on the mean equivalence ratio and modulation frequency.

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Ahsan, Syed N., and Matteo Aureli. "Modulation of Nonlinear Hydrodynamic Damping in Finite Amplitude Underwater Oscillations of Flanged Structures." In ASME 2015 Dynamic Systems and Control Conference. American Society of Mechanical Engineers, 2015. http://dx.doi.org/10.1115/dscc2015-9778.

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In this paper, we study the fluid-structure interaction problem of the harmonic oscillations of a flanged lamina in a quiescent, Newtonian, viscous fluid. Here, the flanges are introduced to elicit specific vortex-structure interactions, with the ultimate goal of modulating the nonlinear hydrodynamic damping experienced by the oscillating structure. The hydrodynamic forcing, incorporating added mass and hydrodynamic damping effects, is evaluated through boundary element method and computational fluid dynamics simulations. This allows to identify a model for the hydrodynamic forces in the form of a complex-valued function of three nondimensional parameters, describing oscillation frequency and amplitude and flange size. We find that the presence of the flanges results into larger fluid entrainment during the lamina oscillation, thus affecting the added mass. Further, we highlight the existence of a minimum in the hydrodynamic damping which is governed by complex dynamics of vortex-structure interaction. This peculiar phenomenon is discussed from physical grounds by analysis of the pertinent hydrodynamic fields. Finally, we propose a tractable form for the hydrodynamic function, to be used in the study of large amplitude underwater flexural vibrations of flanged structures.

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Shin, Yong-Jun, Steven M. Lipkin, Brandon Hencey, and Xiling Shen. "Disturbance Rejection Helps Modulate the p53 Oscillation." In ASME 2011 Dynamic Systems and Control Conference and Bath/ASME Symposium on Fluid Power and Motion Control. ASMEDC, 2011. http://dx.doi.org/10.1115/dscc2011-6046.

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Designing a system that adequately processes the input and that rejects the effects of disturbance is a central theme in feedback control theory. In this paper, we use the concept of “disturbance rejection” to analyze the oscillatory behavior of p53, a well-known tumor suppressor protein. Our analysis reveals that the p53 oscillation is not completely dictated by the p53-MDM2 negative feedback loop—it is also modulated by periodic DNA repair-related fluctuations. According to our disturbance rejection model, the feedback loop normally filters the effects of noise and fluctuations on p53, but upon DNA damage, it stops performing the filtering function so that DNA repair-related fluctuations can modulate the p53 oscillation. Our analysis suggests that the overexpression of MDM2, observed in many types of cancer, can make the feedback mechanism less responsive to the modulating signals after DNA damage occurs.

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Sattinger, Stanley S., Yedidia Neumeier, Aharon Nabi, Ben T. Zinn, David J. Amos, and Douglas D. Darling. "Sub-Scale Demonstration of the Active Feedback Control of Gas-Turbine Combustion Instabilities." In ASME 1998 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1998. http://dx.doi.org/10.1115/98-gt-258.

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Described are sub-scale tests that successfully demonstrate active feedback control as a means of suppressing damaging combustion oscillations in natural-gas-fueled, lean-premix combustors. The control approach is to damp the oscillations by suitably modulating an auxiliary flow of fuel injected near the flame. The control system incorporates state observer software that can ascertain the frequency, amplitude, and phase of the dominant modes of combustion oscillation, and a sub-scale fuel flow modulator that responds to frequencies well above 1 kHz. The demonstration was conducted on a test combustor that could sustain acoustically coupled combustion instabilities at preheat and pressurization conditions approaching those of gas-turbine engine operation. With the control system inactive, two separate instabilities occurred with combined amplitudes of pressure oscillations exceeding 70 kPa (10 psi). The active control system produced four-fold overall reduction in these amplitudes. With the exception of an explainable control response limitation at one frequency, this reduction represented a major milestone in the implementation of active control.

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Guyot, Daniel, and Christian Oliver Paschereit. "Active Control of Combustion Instability Using Symmetric and Asymmetric Premix Fuel Modulation." In ASME Turbo Expo 2007: Power for Land, Sea, and Air. ASMEDC, 2007. http://dx.doi.org/10.1115/gt2007-27342.

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Active instability control was applied to an atmospheric swirl-stabilized premixed combustor using open loop and closed loop control schemes. Actuation was realised by two on-off valves allowing for symmetric and asymmetric modulation of the premix fuel flow while maintaining constant time averaged overall fuel mass flow. Pressure and heat release fluctuations in the combustor as well as NOx, CO and CO2 emissions in the exhaust were recorded. In the open loop circuit the heat release response of the flame was first investigated during stable combustion. For symmetric fuel modulation the dominant frequency in the heat release response was the modulation frequency, while for asymmetric modulation it was its first harmonic. In stable open loop control a reduction of NOx emissions due to fuel modulation of up to 19% was recorded. In the closed loop mode phase-shift control was applied while triggering the valves at the dominant oscillation frequency as well as at its second subharmonic. Both, open and closed loop control schemes were able to successfully control a low-frequency combustion instability, while showing only a small increase in NOx emissions compared to, for example, secondary fuel modulation. Using premixed open loop fuel modulation, attenuation was best when modulating the fuel at frequencies different from the dominant instability frequency and its subharmonic. The performance of asymmetric fuel modulation was generally slightly better than for symmetric modulation in terms of suppression levels as well as emissions. Suppression of the instability’s pressure rms level of up to 15.7 dB was recorded.

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Yadav, Sneha, C. Vineeth, K. K. Kumar, R. K. Choudhary, Tarun K. Pant, and Surendra Sunda. "Role of the phase of Quasi-Biennial Oscillation in modulating the influence of SSW on Equatorial Ionosphere." In 2019 URSI Asia-Pacific Radio Science Conference (AP-RASC). IEEE, 2019. http://dx.doi.org/10.23919/ursiap-rasc.2019.8738274.

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Karmarker, Ashwini, Jacqueline O’Connor, and Isaac Boxx. "Relative Effects of Velocity- and Mixture-Coupling in a Thermoacoustically Unstable, Partially-Premixed Flame." In ASME Turbo Expo 2021: Turbomachinery Technical Conference and Exposition. American Society of Mechanical Engineers, 2021. http://dx.doi.org/10.1115/gt2021-59113.

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Abstract Combustion instability, which is the result of a coupling between combustor acoustic modes and unsteady flame heat release rate, is a severely limiting factor in the operability and performance of modern gas turbine engines. This coupling can occur through different coupling pathways, such as flow field fluctuations or equivalence ratio fluctuations. In realistic combustor systems, there are complex hydrodynamic and thermo-chemical processes involved, which can lead to multiple coupling pathways. In order to understand and predict the mechanisms that govern the onset of combustion instability in real gas turbine engines, we consider the influences that each of these coupling pathways can have on the stability and dynamics of a partially-premixed, swirl-stabilized flame. In this study, we use a model gas turbine combustor with two concentric swirling nozzles of air, separated by a ring of fuel injectors, operating at an elevated pressure of 5 bar. The flow split between the two streams is systematically varied to observe the impact on the flow and flame dynamics. High-speed stereoscopic particle image velocimetry, OH planar laser-induced fluorescence, and acetone planar laser-induced fluorescence are used to obtain information about the velocity field, flame, and fuel-flow behavior, respectively. Depending on the flow conditions, a thermoacoustic oscillation mode or a hydrodynamic mode, identified as the precessing vortex core, is present. The focus of this study is to characterize the mixture coupling processes in this partially-premixed flame as well as the impact that the velocity oscillations have on mixture coupling. Our results show that, for this combustor system, changing the flow split between the two concentric nozzles can alter the dominant harmonic oscillation modes in the system, which can significantly impact the dispersion of fuel into air, thereby modulating the local equivalence ratio of the flame. This insight can be used to design instability control mechanisms in real gas turbine engines.

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Звіти організацій з теми "Oscillation modulating"

Wang, Guimei, Timur Shaftan, Victor Smalyuk, Y. Li, and James Rose. Rapid Crossing of a Resonance During Tune Modulation by Synchrotron Oscillations. Office of Scientific and Technical Information (OSTI), May 2016. http://dx.doi.org/10.2172/1504886.

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Parzen, G. Tune modulation due to synchrotron oscillations and chromaticity, and the dynamic aperture. Office of Scientific and Technical Information (OSTI), March 1994. http://dx.doi.org/10.2172/10142134.

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Parzen, George. Tune Modulation Due to Synchrotron Oscillations and Chromaticity, and the Dynamic Aperture. Office of Scientific and Technical Information (OSTI), March 1994. http://dx.doi.org/10.2172/1119382.

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Ng, K. Y. One-turn map investigation on space-charge modulation of betatron tune by synchrotron oscillation. Office of Scientific and Technical Information (OSTI), September 2005. http://dx.doi.org/10.2172/875516.

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