Articoli di riviste: "Temporal oscillators"

1

Horn, David, e Irit Opher. "Temporal Segmentation in a Neural Dynamic System". Neural Computation 8, n. 2 (15 febbraio 1996): 373–89. http://dx.doi.org/10.1162/neco.1996.8.2.373.

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Oscillatory attractor neural networks can perform temporal segmentation, i.e., separate the joint inputs they receive, through the formation of staggered oscillations. This property, which may be basic to many perceptual functions, is investigated here in the context of a symmetric dynamic system. The fully segmented mode is one type of limit cycle that this system can develop. It can be sustained for only a limited number n of oscillators. This limitation to a small number of segments is a basic phenomenon in such systems. Within our model we can explain it in terms of the limited range of narrow subharmonic solutions of the single nonlinear oscillator. Moreover, this point of view allows us to understand the dominance of three leading amplitudes in solutions of partial segmentation, which are obtained for high n. The latter are also abundant when we replace the common input with a graded one, allowing for different inputs to different oscillators. Switching to an input with fluctuating components, we obtain segmentation dominance for small systems and quite irregular waveforms for large systems.

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Lestienne, Rémy. "Intrinsic and Extrinsic Neuronal Mechanisms in Temporal Coding: A Further Look at Neuronal Oscillations". Neural Plasticity 6, n. 4 (1999): 173–89. http://dx.doi.org/10.1155/np.1999.173.

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Many studies in recent years have been devoted to the detection of fast oscillations in the Central Nervous System (CNS), interpreting them as synchronizing devices. We should, however, refrain from associating too closely the two concepts of synchronization and oscillation. Whereas synchronization is a relatively well-defined concept, by contrast oscillation of a population of neurones in the CNS looks loosely defined, in the sense that both its frequency sharpness and the duration of the oscillatory episodes vary widely from case to case. Also, the functions of oscillations in the brain are multiple and are not confined to synchronization. The paradigmatic instantiation of oscillation in physics is given by the harmonic oscillator, a device particularly suited to tell the time, as in clocks. We will thus examine first the case of oscillations or cycling discharges of neurones, which provide a clock or impose a “tempo” for various kinds of information processing. Neuronal oscillators are rarely just clocks clicking at a fixed frequency. Instead, their frequency is often adjustable and controllable, as in the example of the “chattering cells” discovered in the superficial layers of the visual cortex. Moreover, adjustable frequency oscillators are suitable for use in “phase locked loops” (PLL) networks, a device that can convert time coding to frequency coding; such PLL units have been found in the somatosensory cortex of guinea pigs. Finally, are oscillations stricto sensu necessary to induce synchronization in the discharges of downstream neurones? We know that this is not the case, at least not for local populations of neurones. As a contribution to this question, we propose that repeating patterns in neuronal discharges production may be looked at as one such alternative solution in relation to the processing of information. We review here the case of precisely repeating triplets, detected in the discharges of olfactory mitral cells of a freely breathing rat under odor stimulation.

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Levy, Chagai, Monika Pinchas e Yosef Pinhasi. "A New Approach for the Characterization of Nonstationary Oscillators Using the Wigner-Ville Distribution". Mathematical Problems in Engineering 2018 (11 luglio 2018): 1–14. http://dx.doi.org/10.1155/2018/4942938.

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Oscillators and clocks are affected by physical mechanisms causing amplitude fluctuations, phase noise, and frequency instabilities. The physical properties of the elements composing the oscillator as well as external environmental conditions play a role in the characteristics of the oscillatory signal produced by the device. Such instabilities demonstrate frequency drifts and modulation and spectrum broadening and are observed to be nonstationary processes in nature. Most of tools which are being used to measure and characterize oscillator stability are based on signal processing techniques, assuming time invariance during a temporal window, during which the signal is assumed to be stationary. This paper proposes a new time-frequency metric for the characterization of frequency sources. Our technique is based on the Wigner-Ville distribution, which extends the spectral measures to consist of the temporal nonstationary behavior of the processes affecting the accuracy of the clock. We demonstrate the use of the technique in the characterization of phase errors, frequency offsets, and frequency drift of oscillators.

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Levy, Chagai, Monika Pinchas e Yosef Pinhasi. "Characterization of Nonstationary Phase Noise Using the Wigner–Ville Distribution". Mathematical Problems in Engineering 2020 (20 aprile 2020): 1–7. http://dx.doi.org/10.1155/2020/1685762.

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Oscillators and atomic clocks, as well as lasers and masers, are affected by physical mechanisms causing amplitude fluctuations, phase noise, and frequency instabilities. The physical properties of the elements composing the oscillator as well as external environmental conditions play a role in the coherence of the oscillatory signal produced by the device. Such instabilities demonstrate frequency drifts, modulation, and spectrum broadening and are observed to be nonstationary processes in nature. Most of the tools which are being used to measure and characterize oscillator stability are based on signal processing techniques, assuming time invariance within a temporal window, during which the signal is assumed to be stationary. This letter proposes a new time-frequency approach for the characterization of frequency sources. Our technique is based on the Wigner–Ville time-frequency distribution, which extends the spectral measures to include the temporal nonstationary behavior of the processes affecting the coherence of the oscillator and the accuracy of the clock. We demonstrate the use of the technique in the characterization of nonstationary phase noise in oscillators.

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LABBI, ABDERRAHIM, RUGGERO MILANESE e HOLGER BOSCH. "ASYMPTOTIC SYNCHRONIZATION IN NETWORKS OF LOCALLY CONNECTED OSCILLATORS". International Journal of Bifurcation and Chaos 09, n. 12 (dicembre 1999): 2279–84. http://dx.doi.org/10.1142/s0218127499001759.

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In this paper, we describe the asymptotic behavior of a network of locally connected oscillators. The main result concerns asymptotic synchronization. The presented study is stated in the framework of neuronal modeling of visual object segmentation using oscillatory correlation. The practical motivations of the synchronization analysis are based on neurophysiological experiments which led to the assumptions that existence of temporal coding schemes in the brain by which neurons, with oscillatory dynamics, coding for the same coherent object synchronize their activities, while neurons coding for different objects oscillate with nonzero phase lags. The oscillator model considered is the FitzHugh–Nagumo neuron model. We restrict our study to the mathematical analysis of a network of such neurons. We firstly show the motivations and suitability of choosing FitzHugh–Nagumo oscillator, mainly for stimulus coding purposes, and then we give sufficient conditions on the coupling parameters which guarantee asymptotic synchronization of oscillators receiving the same external stimulation (input). We have used networks of such oscillators to design a layered architecture for object segmentation in gray-level images. Due to space limitations, description of this architecture and simulation results are briefly referred to by the end of the paper.

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Baier, Gerold, e Sven Sahle. "Spatio-temporal patterns with hyperchaotic dynamics in diffusively coupled biochemical oscillators". Discrete Dynamics in Nature and Society 1, n. 2 (1997): 161–67. http://dx.doi.org/10.1155/s1026022697000162.

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We present three examples how complex spatio-temporal patterns can be linked to hyperchaotic attractors in dynamical systems consisting of nonlinear biochemical oscillators coupled linearly with diffusion terms. The systems involved are: (a) a two-variable oscillator with two consecutive autocatalytic reactions derived from the Lotka–Volterra scheme; (b) a minimal two-variable oscillator with one first-order autocatalytic reaction; (c) a three-variable oscillator with first-order feedback lacking autocatalysis. The dynamics of a finite number of coupled biochemical oscillators may account for complex patterns in compartmentalized living systems like cells or tissue, and may be tested experimentally in coupled microreactors.

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7

Treisman, Michel, Norman Cook, Peter L. N. Naish e Janice K. MacCrone. "The Internal Clock: Electroencephalographic Evidence for Oscillatory Processes Underlying Time Perception". Quarterly Journal of Experimental Psychology Section A 47, n. 2 (maggio 1994): 241–89. http://dx.doi.org/10.1080/14640749408401112.

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It has been proposed that temporal perception and performance depend on a biological source of temporal information. A model for a temporal oscillator put forward by Treisman, Faulkner, Naish, and Brogan (1990) predicted that if intense sensory pulses (such as auditory clicks) were presented to subjects at suitable rates they would perturb the frequency at which the temporal oscillator runs and so cause over- or underestimation of time. The resulting pattern of interference between sensory pulse rates and time judgments would depend on the frequency of the temporal oscillator and so might allow that frequency to be estimated. Such interference patterns were found using auditory clicks and visual flicker (Treisman & Brogan, 1992; Treisman et al., 1990). The present study examines time estimation together with the simultaneously recorded electroencephalogram to examine whether evidence of such an interference pattern can be found in the EEG. Alternative models for the organization of a temporal system consisting of an oscillator or multiple oscillators are considered and predictions derived from them relating to the EEG. An experiment was run in which time intervals were presented for estimation, auditory clicks being given during those intervals, and the EEG was recorded concurrently. Analyses of the EEG revealed interactions between auditory click rates and certain EEG components which parallel the interference patterns previously found. The overall pattern of EEG results is interpreted as favouring a model for the organization of the temporal system in which sets of click-sensitive oscillators spaced at intervals of about 12.8 Hz contribute to the EEG spectrum. These are taken to represent a series of harmonically spaced distributions of oscillators involved in time-keeping.

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8

Chaix, Amandine, Amir Zarrinpar e Satchidananda Panda. "The circadian coordination of cell biology". Journal of Cell Biology 215, n. 1 (10 ottobre 2016): 15–25. http://dx.doi.org/10.1083/jcb.201603076.

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Circadian clocks are cell-autonomous timing mechanisms that organize cell functions in a 24-h periodicity. In mammals, the main circadian oscillator consists of transcription–translation feedback loops composed of transcriptional regulators, enzymes, and scaffolds that generate and sustain daily oscillations of their own transcript and protein levels. The clock components and their targets impart rhythmic functions to many gene products through transcriptional, posttranscriptional, translational, and posttranslational mechanisms. This, in turn, temporally coordinates many signaling pathways, metabolic activity, organelles’ structure and functions, as well as the cell cycle and the tissue-specific functions of differentiated cells. When the functions of these circadian oscillators are disrupted by age, environment, or genetic mutation, the temporal coordination of cellular functions is lost, reducing organismal health and fitness.

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9

Mondal, Sirshendu, Vishnu R. Unni e R. I. Sujith. "Onset of thermoacoustic instability in turbulent combustors: an emergence of synchronized periodicity through formation of chimera-like states". Journal of Fluid Mechanics 811 (15 dicembre 2016): 659–81. http://dx.doi.org/10.1017/jfm.2016.770.

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Thermoacoustic systems with a turbulent reactive flow, prevalent in the fields of power and propulsion, are highly susceptible to oscillatory instabilities. Recent studies showed that such systems transition from combustion noise to thermoacoustic instability through a dynamical state known as intermittency, where bursts of large-amplitude periodic oscillations appear in a near-random fashion in between regions of low-amplitude aperiodic fluctuations. However, as these analyses were in the temporal domain, this transition remains still unexplored spatiotemporally. Here, we present the spatiotemporal dynamics during the transition from combustion noise to limit cycle oscillations in a turbulent bluff-body stabilized combustor. To that end, we acquire the pressure oscillations and the field of heat release rate oscillations through high-speed chemiluminescence ($CH^{\ast }$) images of the reaction zone. With a view to get an insight into this complex dynamics, we compute the instantaneous phases between acoustic pressure and local heat release rate oscillations. We observe that the aperiodic oscillations during combustion noise are phase asynchronous, while the large-amplitude periodic oscillations seen during thermoacoustic instability are phase synchronous. We find something interesting during intermittency: patches of synchronized periodic oscillations and desynchronized aperiodic oscillations coexist in the reaction zone. In other words, the emergence of order from disorder happens through a dynamical state wherein regions of order and disorder coexist, resembling a chimera state. Generally, mutually coupled chaotic oscillators synchronize but retain their dynamical nature; the same is true for coupled periodic oscillators. In contrast, during intermittency, we find that patches of desynchronized aperiodic oscillations turn into patches of synchronized periodic oscillations and vice versa. Therefore, the dynamics of local heat release rate oscillations change from aperiodic to periodic as they synchronize intermittently. The temporal variations in global synchrony, estimated through the Kuramoto order parameter, echoes the breathing nature of a chimera state.

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Wang, DeLiang, Joachim Buhmann e Christoph von der Malsburg. "Pattern Segmentation in Associative Memory". Neural Computation 2, n. 1 (marzo 1990): 94–106. http://dx.doi.org/10.1162/neco.1990.2.1.94.

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The goal of this paper is to show how to modify associative memory such that it can discriminate several stored patterns in a composite input and represent them simultaneously. Segmention of patterns takes place in the temporal domain, components of one pattern becoming temporally correlated with each other and anticorrelated with the components of all other patterns. Correlations are created naturally by the usual associative connections. In our simulations, temporal patterns take the form of oscillatory bursts of activity. Model oscillators consist of pairs of local cell populations connected appropriately. Transition of activity from one pattern to another is induced by delayed self-inhibition or simply by noise.

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Kaboodvand, Neda, Martijn P. van den Heuvel e Peter Fransson. "Adaptive frequency-based modeling of whole-brain oscillations: Predicting regional vulnerability and hazardousness rates". Network Neuroscience 3, n. 4 (gennaio 2019): 1094–120. http://dx.doi.org/10.1162/netn_a_00104.

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Whole-brain computational modeling based on structural connectivity has shown great promise in successfully simulating fMRI BOLD signals with temporal coactivation patterns that are highly similar to empirical functional connectivity patterns during resting state. Importantly, previous studies have shown that spontaneous fluctuations in coactivation patterns of distributed brain regions have an inherent dynamic nature with regard to the frequency spectrum of intrinsic brain oscillations. In this modeling study, we introduced frequency dynamics into a system of coupled oscillators, where each oscillator represents the local mean-field model of a brain region. We first showed that the collective behavior of interacting oscillators reproduces previously shown features of brain dynamics. Second, we examined the effect of simulated lesions in gray matter by applying an in silico perturbation protocol to the brain model. We present a new approach to map the effects of vulnerability in brain networks and introduce a measure of regional hazardousness based on mapping of the degree of divergence in a feature space.

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Boujo, E., e N. Noiray. "Robust identification of harmonic oscillator parameters using the adjoint Fokker–Planck equation". Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 473, n. 2200 (aprile 2017): 20160894. http://dx.doi.org/10.1098/rspa.2016.0894.

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We present a model-based output-only method for identifying from time series the parameters governing the dynamics of stochastically forced oscillators. In this context, suitable models of the oscillator’s damping and stiffness properties are postulated, guided by physical understanding of the oscillatory phenomena. The temporal dynamics and the probability density function of the oscillation amplitude are described by a Langevin equation and its associated Fokker–Planck equation, respectively. One method consists in fitting the postulated analytical drift and diffusion coefficients with their estimated values, obtained from data processing by taking the short-time limit of the first two transition moments. However, this limit estimation loses robustness in some situations—for instance when the data are band-pass filtered to isolate the spectral contents of the oscillatory phenomena of interest. In this paper, we use a robust alternative where the adjoint Fokker–Planck equation is solved to compute Kramers–Moyal coefficients exactly, and an iterative optimization yields the parameters that best fit the observed statistics simultaneously in a wide range of amplitudes and time scales. The method is illustrated with a stochastic Van der Pol oscillator serving as a prototypical model of thermoacoustic instabilities in practical combustors, where system identification is highly relevant to control.

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K. Macnamara, Cicely, e Mark A. J. Chaplain. "Spatio-temporal models of synthetic genetic oscillators". Mathematical Biosciences and Engineering 14, n. 1 (2017): 249–62. http://dx.doi.org/10.3934/mbe.2017016.

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Strömqvist, Gustav, Valdas Pasiskevicius, Carlota Canalias, Pierre Aschieri, Antonio Picozzi e Carlos Montes. "Temporal coherence in mirrorless optical parametric oscillators". Journal of the Optical Society of America B 29, n. 6 (9 maggio 2012): 1194. http://dx.doi.org/10.1364/josab.29.001194.

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15

PILIPCHUK, V. N. "TEMPORAL TRANSFORMATIONS AND VISUALIZATION DIAGRAMS FOR NONSMOOTH PERIODIC MOTIONS". International Journal of Bifurcation and Chaos 15, n. 06 (giugno 2005): 1879–99. http://dx.doi.org/10.1142/s0218127405013034.

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In this paper, a special nonsmooth transformation of time is combined with the shooting algorithm for visualization of the manifolds of periodic solutions and their bifurcations. The general class of nonlinear oscillators under smooth, nonsmooth, and impulsive loadings is considered. The corresponding boundary value problems with no singularities are obtained by introducing the periodic piecewise-linear (sawtooth) temporal argument. The Ueda circuit, that is Duffing's oscillator with no linear stiffness, is considered for illustration. It is shown that the temporal mode shape of the input can be responsible for qualitative features of the dynamics, such as transitions between the regular and random motions. The important role of unstable periodic orbits and their links with strange attractors are discussed.

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Chowdhury, Debajyoti, Chao Wang, Ai-Ping Lu e Hai-Long Zhu. "Understanding Quantitative Circadian Regulations Are Crucial Towards Advancing Chronotherapy". Cells 8, n. 8 (13 agosto 2019): 883. http://dx.doi.org/10.3390/cells8080883.

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Circadian rhythms have a deep impact on most aspects of physiology. In most organisms, especially mammals, the biological rhythms are maintained by the indigenous circadian clockwork around geophysical time (~24-h). These rhythms originate inside cells. Several core components are interconnected through transcriptional/translational feedback loops to generate molecular oscillations. They are tightly controlled over time. Also, they exert temporal controls over many fundamental physiological activities. This helps in coordinating the body’s internal time with the external environments. The mammalian circadian clockwork is composed of a hierarchy of oscillators, which play roles at molecular, cellular, and higher levels. The master oscillation has been found to be developed at the hypothalamic suprachiasmatic nucleus in the brain. It acts as the core pacemaker and drives the transmission of the oscillation signals. These signals are distributed across different peripheral tissues through humoral and neural connections. The synchronization among the master oscillator and tissue-specific oscillators offer overall temporal stability to mammals. Recent technological advancements help us to study the circadian rhythms at dynamic scale and systems level. Here, we outline the current understanding of circadian clockwork in terms of molecular mechanisms and interdisciplinary concepts. We have also focused on the importance of the integrative approach to decode several crucial intricacies. This review indicates the emergence of such a comprehensive approach. It will essentially accelerate the circadian research with more innovative strategies, such as developing evidence-based chronotherapeutics to restore de-synchronized circadian rhythms.

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Hong, H., T. I. Um, Y. Shim e M. Y. Choi. "Temporal association in a network of neuronal oscillators". Journal of Physics A: Mathematical and General 34, n. 24 (7 giugno 2001): 5021–31. http://dx.doi.org/10.1088/0305-4470/34/24/301.

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LEI, YOUMING, e FULI GUAN. "DISORDER INDUCED ORDER IN AN ARRAY OF CHAOTIC DUFFING OSCILLATORS". International Journal of Modern Physics C 23, n. 10 (ottobre 2012): 1250071. http://dx.doi.org/10.1142/s0129183112500714.

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This paper addresses the issue of disorder induced order in an array of coupled chaotic Duffing oscillators which are excited by harmonic parametric excitations. In order to investigate the effect of phase disorder on dynamics of the array, we take into account that individual uncoupled Duffing oscillator with a parametric excitation is chaotic no matter what the initial phase of the excitation is. It is shown that phase disorder by randomly choosing the initial phases of excitations can suppress spatio-temporal chaos in the system coupled by chaotic Duffing oscillators. When all the phases are the same and deterministic, the oscillators remain chaotic and asynchronous no matter what the common phase is. When driven asynchronously by introducing phase disorder, the oscillators coupled in the array appear more regular with increase of the amplitude of random phase, and the highest level of synchrony between them is induced by intermediate phase disorder, displaying a resonance like phenomenon caused from the transition of the coupled oscillators from chaos to periodic motion. Since varying the initial phases of excitations is more feasible than altering parameters intrinsic to the oscillators coupled in an array, this study provides a practical method for control and synchronization of chaotic dynamics in high-dimensional, spatially extended systems, which might have potential applications in engineering, neuroscience and biology.

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van der Slot, Peter J. M., e Henry P. Freund. "Three-Dimensional, Time-Dependent Analysis of High- and Low-Q Free-Electron Laser Oscillators". Applied Sciences 11, n. 11 (28 maggio 2021): 4978. http://dx.doi.org/10.3390/app11114978.

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Free-electron lasers (FELs) have been designed to operate over virtually the entire electromagnetic spectrum, from microwaves through to X-rays, and in a variety of configurations, including amplifiers and oscillators. Oscillators can operate in both the low and high gain regime and are typically used to improve the spatial and temporal coherence of the light generated. We will discuss various FEL oscillators, ranging from systems with high-quality resonators combined with low-gain undulators, to systems with a low-quality resonator combined with a high-gain undulator line. The FEL gain code MINERVA and wavefront propagation code OPC are used to model the FEL interaction within the undulator and the propagation in the remainder of the oscillator, respectively. We will not only include experimental data for the various systems for comparison when available, but also present, for selected cases, how the two codes can be used to study the effect of mirror aberrations and thermal mirror deformation on FEL performance.

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VOLKOV, EVGENII I., e MAKSIM N. STOLYAROV. "TEMPORAL VARIABILITY GENERATED BY COUPLING OF MITOTIC TIMERS". Journal of Biological Systems 03, n. 01 (marzo 1995): 63–78. http://dx.doi.org/10.1142/s0218339095000071.

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Cell proliferation is considered as a periodic process which is governed by a two-variable relaxation timer. The collective behavior of a system composed of three identical relaxation oscillators is numerically studied under the condition that diffusion of the slow mode (inhibitor) dominates. The phase diagrams for cyclic and linear configurations show unexpectable diversity of stable periodic regimes, some of them are only observable under intermediate but reasonable values of coupling and stiffness. For cyclic configuration we demonstrate: (1) the existence of three periodic regimes with different periods and phase relations and unsymmetrical stable steady state (USSS); (2) the coexistence of in-phase oscillations and USSS; (3) the coexistence of periodic attractors and (4) the emergence of special kind of rotating wave which is manifested as two-loop limit cycle. The natural asymmetry of linear configuration leads to the appearance of many periodic attractors. The most of them are characterized by the large period oscillations of the middle element which has the step-like dependence of period versus coupling. The qualitative reasons for such a diversity and its possible role in the generation of cell cycle variability are discussed.

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Manna, Raj Kumar, Oleg E. Shklyaev e Anna C. Balazs. "Chemical pumps and flexible sheets spontaneously form self-regulating oscillators in solution". Proceedings of the National Academy of Sciences 118, n. 12 (15 marzo 2021): e2022987118. http://dx.doi.org/10.1073/pnas.2022987118.

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The synchronization of self-oscillating systems is vital to various biological functions, from the coordinated contraction of heart muscle to the self-organization of slime molds. Through modeling, we design bioinspired materials systems that spontaneously form shape-changing self-oscillators, which communicate to synchronize both their temporal and spatial behavior. Here, catalytic reactions at the bottom of a fluid-filled chamber and on mobile, flexible sheets generate the energy to “pump” the surrounding fluid, which also transports the immersed sheets. The sheets exert a force on the fluid that modifies the flow, which in turn affects the shape and movement of the flexible sheets. This feedback enables a single coated (active) and even an uncoated (passive) sheet to undergo self-oscillation, displaying different oscillatory modes with increases in the catalytic reaction rate. Two sheets (active or passive) introduce excluded volume, steric interactions. This distinctive combination of the hydrodynamic, fluid–structure, and steric interactions causes the sheets to form coupled oscillators, whose motion is synchronized in time and space. We develop a heuristic model that rationalizes this behavior. These coupled self-oscillators exhibit rich and tunable phase dynamics, which depends on the sheets’ initial placement, coverage by catalyst and relative size. Moreover, through variations in the reactant concentration, the system can switch between the different oscillatory modes. This breadth of dynamic behavior expands the functionality of the coupled oscillators, enabling soft robots to display a variety of self-sustained, self-regulating moves.

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Lewy, Hadas, Yossy Shub, Zvi Naor e Israel E. Ashkenazi. "TEMPORAL PATTERN OF LH SECRETION: REGULATION BY MULTIPLE ULTRADIAN OSCILLATORS VERSUS A SINGLE CIRCADIAN OSCILLATOR". Chronobiology International 18, n. 3 (gennaio 2001): 399–412. http://dx.doi.org/10.1081/cbi-100103964.

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Markman, G., V. Vasilchenko, S. Markman e K. Bar-Eli. "Spatial and temporal patterns in coupled Belousov-Zhabotinsky oscillators". Mathematical and Computer Modelling 31, n. 4-5 (febbraio 2000): 143–48. http://dx.doi.org/10.1016/s0895-7177(00)00032-7.

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Ernst, U., K. Pawelzik e T. Geisel. "Synchronization Induced by Temporal Delays in Pulse-Coupled Oscillators". Physical Review Letters 74, n. 9 (27 febbraio 1995): 1570–73. http://dx.doi.org/10.1103/physrevlett.74.1570.

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Isorna, Esther, Nuria de Pedro, Ana I. Valenciano, Ángel L. Alonso-Gómez e María J. Delgado. "Interplay between the endocrine and circadian systems in fishes". Journal of Endocrinology 232, n. 3 (marzo 2017): R141—R159. http://dx.doi.org/10.1530/joe-16-0330.

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The circadian system is responsible for the temporal organisation of physiological functions which, in part, involves daily cycles of hormonal activity. In this review, we analyse the interplay between the circadian and endocrine systems in fishes. We first describe the current model of fish circadian system organisation and the basis of the molecular clockwork that enables different tissues to act as internal pacemakers. This system consists of a net of central and peripherally located oscillators and can be synchronised by the light–darkness and feeding–fasting cycles. We then focus on two central neuroendocrine transducers (melatonin and orexin) and three peripheral hormones (leptin, ghrelin and cortisol), which are involved in the synchronisation of the circadian system in mammals and/or energy status signalling. We review the role of each of these as overt rhythms (i.e. outputs of the circadian system) and, for the first time, as key internal temporal messengers that act as inputs for other endogenous oscillators. Based on acute changes in clock gene expression, we describe the currently accepted model of endogenous oscillator entrainment by the light–darkness cycle and propose a new model for non-photic (endocrine) entrainment, highlighting the importance of the bidirectional cross-talking between the endocrine and circadian systems in fishes. The flexibility of the fish circadian system combined with the absence of a master clock makes these vertebrates a very attractive model for studying communication among oscillators to drive functionally coordinated outputs.

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Petkoski, Spase, e Viktor K. Jirsa. "Transmission time delays organize the brain network synchronization". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, n. 2153 (22 luglio 2019): 20180132. http://dx.doi.org/10.1098/rsta.2018.0132.

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The timing of activity across brain regions can be described by its phases for oscillatory processes, and is of crucial importance for brain functioning. The structure of the brain constrains its dynamics through the delays due to propagation and the strengths of the white matter tracts. We use self-sustained delay-coupled, non-isochronous, nonlinearly damped and chaotic oscillators to study how spatio-temporal organization of the brain governs phase lags between the coherent activity of its regions. In silico results for the brain network model demonstrate a robust switching from in- to anti-phase synchronization by increasing the frequency, with a consistent lagging of the stronger connected regions. Relative phases are well predicted by an earlier analysis of Kuramoto oscillators, confirming the spatial heterogeneity of time delays as a crucial mechanism in shaping the functional brain architecture. Increased frequency and coupling are also shown to distort the oscillators by decreasing their amplitude, and stronger regions have lower, but more synchronized activity. These results indicate specific features in the phase relationships within the brain that need to hold for a wide range of local oscillatory dynamics, given that the time delays of the connectome are proportional to the lengths of the structural pathways. This article is part of the theme issue ‘Nonlinear dynamics of delay systems’.

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Ahissar, Ehud. "Temporal-Code to Rate-Code Conversion by Neuronal Phase-Locked Loops". Neural Computation 10, n. 3 (1 aprile 1998): 597–650. http://dx.doi.org/10.1162/089976698300017683.

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Peripheral sensory activity follows the temporal structure of input signals. Central sensory processing uses also rate coding, and motor outputs appear to be primarily encoded by rate. I propose here a simple, efficient structure, converting temporal coding to rate coding by neuronal phase-locked loops (PLL). The simplest form of a PLL includes a phase detector (that is, a neuronal-plausible version of an ideal coincidence detector) and a controllable local oscillator that are connected in a negative feedback loop. The phase detector compares the firing times of the local oscillator and the input and provides an output whose firing rate is monotonically related to the time difference. The output rate is fed back to the local oscillator and forces it to phase-lock to the input. Every temporal interval at the input is associated with a specific pair of output rate and time difference values; the higher the output rate, the further the local oscillator is driven from its intrinsic frequency. Sequences of input intervals, which by definition encode input information, are thus represented by sequences of firing rates at the PLL's output. The most plausible implementation of PLL circuits is by thalamocortical loops in which populations of thalamic “relay” neurons function as phase detectors that compare the timings of cortical oscillators and sensory signals. The output in this case is encoded by the thalamic population rate. This article presents and analyzes the algorithmic and the implementation levels of the proposed PLL model and describes the implementation of the PLL model to the primate tactile system.

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Nikitin, D., I. Omelchenko, A. Zakharova, M. Avetyan, A. L. Fradkov e E. Schöll. "Complex partial synchronization patterns in networks of delay-coupled neurons". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, n. 2153 (22 luglio 2019): 20180128. http://dx.doi.org/10.1098/rsta.2018.0128.

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We study the spatio-temporal dynamics of a multiplex network of delay-coupled FitzHugh–Nagumo oscillators with non-local and fractal connectivities. Apart from chimera states, a new regime of coexistence of slow and fast oscillations is found. An analytical explanation for the emergence of such coexisting partial synchronization patterns is given. Furthermore, we propose a control scheme for the number of fast and slow neurons in each layer. This article is part of the theme issue ‘Nonlinear dynamics of delay systems’.

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29

Diebner, Hans H., Axel A. Hoff, Adolf Mathias, Horst Prehn, Marco Rohrbach e Sven Sahle. "Control and Adaptation of Spatio-temporal Patterns". Zeitschrift für Naturforschung A 56, n. 9-10 (1 ottobre 2001): 663–69. http://dx.doi.org/10.1515/zna-2001-0910.

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Abstract We apply a recently introduced cognitive system for dynamics recognition to a two-dimensional array of coupled oscillators. The cognitive system allows for both the control and the adaptation of spatio-temporal patterns of that array of oscillators. One array that shows Turing-pattems in a self-organizational manner is viewed as an externally presented dynamics (stimulus) which is mapped onto a mirror dynamics, whereby the latter is capable to simulate (simulus). Two of the parameters of the stimulus are thereby regarded to be unknown and have to be estimated by the cognitive system. The cognitive system itself consists of dynamical modules that are stimulated by the external dynamics in the sense of Pyragas' external force control mechanism and thereby yield measures of how good they match the stimulus. These measures are used as weights to construct the simulus. The adaptation process is performed "on the fly", i. e., without the storage of data. The proposed cognitive system, therefore, is a prominent candidate for the construction of a control device for a permanent real time observation of an external dynamical system in order to interfere instantaneously when necessary.

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30

Kocarev, Ljupčo, Predrag Janjić, Ulrich Parlitz e Toni Stojanovski. "Controlling spatio-temporal chaos in coupled oscillators by sporadic driving". Chaos, Solitons & Fractals 9, n. 1-2 (gennaio 1998): 283–93. http://dx.doi.org/10.1016/s0960-0779(97)00067-2.

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31

Yang, Zhenshan. "Temporal evolution of instantaneous phonons in time-dependent harmonic oscillators". Journal of Mathematical Physics 56, n. 3 (marzo 2015): 032102. http://dx.doi.org/10.1063/1.4914337.

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32

Belatreche, Ammar, Liam Maguire, Martin McGinnity, Liam McDaid e Arfan Ghani. "Computing with Biologically Inspired Neural Oscillators: Application to Colour Image Segmentation". Advances in Artificial Intelligence 2010 (12 maggio 2010): 1–21. http://dx.doi.org/10.1155/2010/405073.

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This paper investigates the computing capabilities and potential applications of neural oscillators, a biologically inspired neural model, to grey scale and colour image segmentation, an important task in image understanding and object recognition. A proposed neural system that exploits the synergy between neural oscillators and Kohonen self-organising maps (SOMs) is presented. It consists of a two-dimensional grid of neural oscillators which are locally connected through excitatory connections and globally connected to a common inhibitor. Each neuron is mapped to a pixel of the input image and existing objects, represented by homogenous areas, are temporally segmented through synchronisation of the activity of neural oscillators that are mapped to pixels of the same object. Self-organising maps form the basis of a colour reduction system whose output is fed to a 2D grid of neural oscillators for temporal correlation-based object segmentation. Both chromatic and local spatial features are used. The system is simulated in Matlab and its demonstration on real world colour images shows promising results and the emergence of a new bioinspired approach for colour image segmentation. The paper concludes with a discussion of the performance of the proposed system and its comparison with traditional image segmentation approaches.

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SANTHIAH, M., P. PHILOMINATH, I. RAJA MOHAMED e K. MURALI. "ORDERED AND CHAOTIC PHENOMENA IN TWO COUPLED FORCED LCR OSCILLATORS SHARING A COMMON NONLINEARITY". International Journal of Bifurcation and Chaos 21, n. 01 (gennaio 2011): 161–75. http://dx.doi.org/10.1142/s0218127411028349.

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This paper suggests a simple mechanism of sharing a common nonlinearity among the linear oscillators to exhibit some interesting phenomena. Here, we present fourth-order nonautonomous circuit capable of showing a large variety of dynamical behaviors in three different modes of operation. In particular, a new phenomenon of coexistence of attractors leading to torus behavior when two identical oscillators sharing a common nonlinearity and many spatio-temporal patterns when more oscillators sharing a nonlinearity are presented. The results of numerical simulations, hardware experimental realization and analytical studies are presented.

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34

Hegazi, Sara, Christopher Lowden, Julian Rios Garcia, Arthur H. Cheng, Karl Obrietan, Joel D. Levine e Hai-Ying Mary Cheng. "A Symphony of Signals: Intercellular and Intracellular Signaling Mechanisms Underlying Circadian Timekeeping in Mice and Flies". International Journal of Molecular Sciences 20, n. 9 (13 maggio 2019): 2363. http://dx.doi.org/10.3390/ijms20092363.

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Abstract (sommario):

The central pacemakers of circadian timekeeping systems are highly robust yet adaptable, providing the temporal coordination of rhythms in behavior and physiological processes in accordance with the demands imposed by environmental cycles. These features of the central pacemaker are achieved by a multi-oscillator network in which individual cellular oscillators are tightly coupled to the environmental day-night cycle, and to one another via intercellular coupling. In this review, we will summarize the roles of various neurotransmitters and neuropeptides in the regulation of circadian entrainment and synchrony within the mammalian and Drosophila central pacemakers. We will also describe the diverse functions of protein kinases in the relay of input signals to the core oscillator or the direct regulation of the molecular clock machinery.

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35

Crook, Sharon M., G. Bard Ermentrout e James M. Bower. "Spike Frequency Adaptation Affects the Synchronization Properties of Networks of Cortical Oscillators". Neural Computation 10, n. 4 (1 maggio 1998): 837–54. http://dx.doi.org/10.1162/089976698300017511.

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Oscillations in many regions of the cortex have common temporal characteristics with dominant frequencies centered around the 40 Hz (gamma) frequency range and the 5–10 Hz (theta) frequency range. Experimental results also reveal spatially synchronous oscillations, which are stimulus dependent (Gray&Singer, 1987;Gray, König, Engel, & Singer, 1989; Engel, König, Kreiter, Schillen, & Singer, 1992). This rhythmic activity suggests that the coherence of neural populations is a crucial feature of cortical dynamics (Gray, 1994). Using both simulations and a theoretical coupled oscillator approach, we demonstrate that the spike frequency adaptation seen in many pyramidal cells plays a subtle but important role in the dynamics of cortical networks. Without adaptation, excitatory connections among model pyramidal cells are desynchronizing. However, the slow processes associated with adaptation encourage stable synchronous behavior.

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36

Kim, Jinkyu, e Dongkeon Kim. "Temporal finite element methods through the extended framework of Hamilton’s principle". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 231, n. 2 (9 agosto 2016): 263–78. http://dx.doi.org/10.1177/0954406216642481.

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With basic ideas of mixed Lagrangian formulation and sequential assigning process for initial conditions, the extended framework of Hamilton’s principle (EHP) was recently developed for continuum dynamics. Unlike the original Hamilton’s principle, this new variational framework can fully take initial conditions into account for both linear and nonlinear dynamics, so that it provides a sound base to apply a finite element scheme over the temporal domain without any ambiguity. This paper describes temporal finite element approach stemming from the extended Hamilton’s principle, which focuses initially on classical single-degree-of-freedom oscillators such as Kelvin–Voigt damped oscillator and an elasto-viscoplastic model. In each case, an appropriate weak form is provided and a corresponding formulation is discretized in the temporal domain with the adoption of Galerkin’s method. Basic numerical properties are investigated for the developed numerical algorithms with several computational examples for the elasto-viscoplastic model. For the underlying conservative system, the present method is symplectic and unconditionally stable with respect to the time step. On the other hand, the method provides unconditionally stable and noniterative algorithm for the elasto-viscoplastic model.

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König, Peter, Bernd Janosch e Thomas B. Schillen. "Stimulus-Dependent Assembly Formation of Oscillatory Responses: III. Learning". Neural Computation 4, n. 5 (settembre 1992): 666–81. http://dx.doi.org/10.1162/neco.1992.4.5.666.

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A temporal structure of neuronal activity has been suggested as a potential mechanism for defining cell assemblies in the brain. This concept has recently gained support by the observation of stimulus-dependent oscillatory activity in the visual cortex of the cat. Furthermore, experimental evidence has been found showing the formation and segregation of synchronously oscillating cell assemblies in response to various stimulus conditions. In previous work, we have demonstrated that a network of neuronal oscillators coupled by synchronizing and desynchronizing delay connections can exhibit a temporal structure of responses, which closely resembles experimental observations. In this paper, we investigate the self-organization of synchronizing and desynchronizing coupling connections by local learning rules. Based on recent experimental observations, we modify synchronizing connections according to a two-threshold learning rule, involving synaptic potentiation and depression. This rule is generalized to its functional inverse for weight changes of desynchronizing connections. We show that after training, the resulting network exhibits stimulus-dependent formation and segregation of oscillatory assemblies in agreement with the experimental data. These results indicate that local learning rules during ontogenesis can suffice to develop a connectivity pattern in support of the observed temporal structure of stimulus responses in cat visual cortex.

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38

Bloch, Guy, Erik D. Herzog, Joel D. Levine e William J. Schwartz. "Socially synchronized circadian oscillators". Proceedings of the Royal Society B: Biological Sciences 280, n. 1765 (22 agosto 2013): 20130035. http://dx.doi.org/10.1098/rspb.2013.0035.

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Abstract (sommario):

Daily rhythms of physiology and behaviour are governed by an endogenous timekeeping mechanism (a circadian ‘clock’). The alternation of environmental light and darkness synchronizes (entrains) these rhythms to the natural day–night cycle, and underlying mechanisms have been investigated using singly housed animals in the laboratory. But, most species ordinarily would not live out their lives in such seclusion; in their natural habitats, they interact with other individuals, and some live in colonies with highly developed social structures requiring temporal synchronization. Social cues may thus be critical to the adaptive function of the circadian system, but elucidating their role and the responsible mechanisms has proven elusive. Here, we highlight three model systems that are now being applied to understanding the biology of socially synchronized circadian oscillators: the fruitfly, with its powerful array of molecular genetic tools; the honeybee, with its complex natural society and clear division of labour; and, at a different level of biological organization, the rodent suprachiasmatic nucleus, site of the brain's circadian clock, with its network of mutually coupled single-cell oscillators. Analyses at the ‘group’ level of circadian organization will likely generate a more complex, but ultimately more comprehensive, view of clocks and rhythms and their contribution to fitness in nature.

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Kurz, Felix T., Miguel A. Aon, Brian O'Rourke e Antonis A. Armoundas. "Wavelet analysis reveals heterogeneous time-dependent oscillations of individual mitochondria". American Journal of Physiology-Heart and Circulatory Physiology 299, n. 5 (novembre 2010): H1736—H1740. http://dx.doi.org/10.1152/ajpheart.00640.2010.

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Mitochondrial inner membrane potential oscillations in cardiac myocytes synchronize under oxidative or metabolic stress, leading to synchronized whole cell oscillations. Gaining information about the temporal properties of individual mitochondrial oscillators is essential to comprehend the network's intrinsic spatiotemporal organization. We have developed methods to detect individual mitochondrial tetramethylrhodamine ethyl ester fluorescence oscillations and assess their dynamical properties using wavelet analysis. We demonstrate that these advanced signal processing tools can provide quantitative spatiotemporal information about intermitochondrial coupling. We have found that the mean frequency of selected groups of continuously oscillating mitochondria was 16.49 ± 1.04 mHz, whereas the mean frequency in the normalized mean global wavelet spectrum was 22.84 ± 1.80 mHz ( n = 9 myocytes). In conclusion, this novel methodology will help shed new light on the dynamical properties of the mitochondrial network on the verge of synchronization.

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40

Clerico, Eugenia M., Vincent M. Cassone e Susan S. Golden. "Stability and lability of circadian period of gene expression in the cyanobacterium Synechococcus elongatus". Microbiology 155, n. 2 (1 febbraio 2009): 635–41. http://dx.doi.org/10.1099/mic.0.022343-0.

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Molecular aspects of the circadian clock in the cyanobacterium Synechococcus elongatus have been described in great detail. Three-dimensional structures have been determined for the three proteins, KaiA, KaiB and KaiC, that constitute a central oscillator of the clock. Moreover, a temperature-compensated circadian rhythm of KaiC phosphorylation can be reconstituted in vitro with the addition of KaiA, KaiB and ATP. These data suggest a relatively simple circadian system in which a single oscillator provides temporal information for all downstream processes. However, in vivo the situation is more complex, and additional components contribute to the maintenance of a normal period, the resetting of relative phases of circadian oscillations, and the control of rhythms of gene expression. We show here that two well-studied promoters in the S. elongatus genome report different circadian periods of expression under a given set of conditions in wild-type as well as mutant genetic backgrounds. Moreover, the period differs between these promoters with respect to modulation by light intensity, growth phase, and the presence or absence of a promoter-recognition subunit of RNA polymerase. These data contrast sharply with the current clock model in which a single Kai-based oscillator governs circadian period. Overall, these findings suggest that complex interactions among the circadian oscillator, perhaps other oscillators, and other cellular machinery result in a clock that is plastic and sensitive to the environment and to the physiological state of the cell.

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SHABUNIN, A., V. ASTAKHOV e V. ANISHCHENKO. "DEVELOPING CHAOS ON BASE OF TRAVELING WAVES IN A CHAIN OF COUPLED OSCILLATORS WITH PERIOD-DOUBLING: SYNCHRONIZATION AND HIERARCHY OF MULTISTABILITY FORMATION". International Journal of Bifurcation and Chaos 12, n. 08 (agosto 2002): 1895–907. http://dx.doi.org/10.1142/s021812740200556x.

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The work is devoted to the analysis of dynamics of traveling waves in a chain of self-oscillators with period-doubling route to chaos. As a model we use a ring of Chua's circuits symmetrically coupled via a resistor. We consider how complicated are temporal regimes with parameters changing influences on spatial structures in the chain. We demonstrate that spatial periodicity exists until transition to chaos through period-doubling and tori birth bifurcations of regular regimes. Temporal quasi-periodicity does not induce spatial quasi-periodicity in the ring. After transition to chaos exact spatial periodicity is changed by the spatial periodicity in the average. The periodic spatial structures in the chain are connected with synchronization of oscillations. For quantity researching of the synchronization we propose a measure of chaotic synchronization based on the coherence function and investigate the dependence of the level of synchronization on the strength of coupling and on the chaos developing in the system. We demonstrate that the spatial periodic structure is completely destroyed as a consequence of loss of coherence of oscillations on base frequencies.

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42

LABAVIC, DARKA, e HILDEGARD MEYER-ORTMANNS. "Temporal self-similar synchronization patterns and scaling in repulsively coupled oscillators". Indian Academy of Sciences – Conference Series 1, n. 1 (18 dicembre 2017): 101–8. http://dx.doi.org/10.29195/iascs.01.01.0019.

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43

Oppo, Gian-Luca, Andrew J. Scroggie, Scott Sinclair e Massimo Brambilla. "Complex spatio-temporal dynamics of optical parametric oscillators close to threshold". Journal of Modern Optics 47, n. 11 (settembre 2000): 2005–14. http://dx.doi.org/10.1080/09500340008232452.

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44

Karantonis, Antonis, Michael Pagitsas, Yasuyuki Miyakita e Seiichiro Nakabayashi. "Manipulation of spatio-temporal patterns in networks of relaxation electrochemical oscillators". Electrochimica Acta 50, n. 25-26 (settembre 2005): 5056–64. http://dx.doi.org/10.1016/j.electacta.2005.02.072.

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45

Wasserman, Danit, Sapir Nachum, Meital Cohen, Taylor P. Enrico, Meirav Noach-Hirsh, Jasmin Parasol, Sarit Zomer-Polak et al. "Cell cycle oscillators underlying orderly proteolysis of E2F8". Molecular Biology of the Cell 31, n. 8 (1 aprile 2020): 725–40. http://dx.doi.org/10.1091/mbc.e19-12-0725.

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Abstract (sommario):

We uncovered interlocking mechanisms regulating the temporal proteolysis of the transcriptional repressor E2F8 in cycling cells including SCFCyclin F in G2, dephosphorylation of Cdk1 sites, and activation of APC/CCdh1, but not APC/CCdc20 during mitotic exit and G1. Differential stabilization under limited APC/C activity allows E2F8 to reaccumulate during late G1 and coregulate S-phase entry.

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46

Mathewson, Kyle E., Christopher Prudhomme, Monica Fabiani, Diane M. Beck, Alejandro Lleras e Gabriele Gratton. "Making Waves in the Stream of Consciousness: Entraining Oscillations in EEG Alpha and Fluctuations in Visual Awareness with Rhythmic Visual Stimulation". Journal of Cognitive Neuroscience 24, n. 12 (dicembre 2012): 2321–33. http://dx.doi.org/10.1162/jocn_a_00288.

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Abstract (sommario):

Rhythmic events are common in our sensory world. Temporal regularities could be used to predict the timing of upcoming events, thus facilitating their processing. Indeed, cognitive theories have long posited the existence of internal oscillators whose timing can be entrained to ongoing periodic stimuli in the environment as a mechanism of temporal attention. Recently, recordings from primate brains have shown electrophysiological evidence for these hypothesized internal oscillations. We hypothesized that rhythmic visual stimuli can entrain ongoing neural oscillations in humans, locking the timing of the excitability cycles they represent and thus enhancing processing of subsequently predictable stimuli. Here we report evidence for entrainment of neural oscillations by predictable periodic stimuli in the alpha frequency band and show for the first time that the phase of existing brain oscillations cannot only be modified in response to rhythmic visual stimulation but that the resulting phase-locked fluctuations in excitability lead to concomitant fluctuations in visual awareness in humans. This entrainment effect was dependent on both the amount of spontaneous alpha power before the experiment and the level of 12-Hz oscillation before each trial and could not be explained by evoked activity. Rhythmic fluctuations in awareness elicited by entrainment of ongoing neural excitability cycles support a proposed role for alpha oscillations as a pulsed inhibition of cortical activity. Furthermore, these data provide evidence for the quantized nature of our conscious experience and reveal a powerful mechanism by which temporal attention as well as perceptual snapshots can be manipulated and controlled.

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Schillen, Thomas B., e Peter König. "Stimulus-Dependent Assembly Formation of Oscillatory Responses: II. Desynchronization". Neural Computation 3, n. 2 (giugno 1991): 167–78. http://dx.doi.org/10.1162/neco.1991.3.2.167.

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Recent theoretical and experimental work suggests a temporal structure of neuronal spike activity as a potential mechanism for solving the binding problem in the brain. In particular, recordings from cat visual cortex demonstrate the possibility that stimulus coherency is coded by synchronization of oscillatory neuronal responses. Coding by synchronized oscillatory activity has to avoid bulk synchronization within entire cortical areas. Recent experimental evidence indicates that incoherent stimuli can activate coherently oscillating assemblies of cells that are not synchronized among one another. In this paper we show that appropriately designed excitatory delay connections can support the desynchronization of two-dimensional layers of delayed nonlinear oscillators. Closely following experimental observations, we then present two examples of stimulus-dependent assembly formation in oscillatory layers that employ both synchronizing and desynchronizing delay connections: First, we demonstrate the segregation of oscillatory responses to two overlapping but incoherently moving stimuli. Second, we show that the coherence of movement and location of two stimulus bar segments can be coded by the correlation of oscillatory activity.

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48

Arantes, Pablo, e Ronaldo Mangueira Lima Júnior. "Using a coupled-oscillator model of speech rhythm to estimate rhythmic variability in two Brazilian Portuguese varieties (CE and SP)". Cadernos de Linguística 2, n. 4 (4 settembre 2021): e577. http://dx.doi.org/10.25189/2675-4916.2021.v2.n4.id577.

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This paper presents preliminary results of a semi-automatic methodology to extract three parameters of a dynamic model of speech rhythm. The model attempts to analyze the production of rhythm as a system of coupled oscillators which represent syllabicity and phrase stress as levels of temporal organization. The estimated parameters are the syllabic oscillator entrainment rate (alpha), the syllabic oscillator decay rate (beta), and the coupling strength between the oscillators (w0). The methodology involves finding the <alpha, beta, w0> combination that minimizes the distance between natural duration contours and simulated contours generated using several combinations of the parameters. The distance between natural and model-generated contours was measured in two ways by comparing: (1) plain or overt syllable to syllable duration and (2) relative change along both contours.We applied this methodology to read speech produced by five speakers of the state of Ceará (CE) and eight speakers of the state of São Paulo (SP). Mean w0 and alpha values are compatible with the view that Brazilian Portuguese is a mixed-rhythm language. Results from two bayesian hierarchical regression models do not suggest a difference between SP and CE speakers, but indicate a difference between the two methods, with the relative change method generating lower alpha values and higher w0 values, and the reverse for the plain duration method.

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Pitts, SiNae, Elizabeth Perone e Rae Silver. "Food-entrained circadian rhythms are sustained in arrhythmic Clk/Clk mutant mice". American Journal of Physiology-Regulatory, Integrative and Comparative Physiology 285, n. 1 (luglio 2003): R57—R67. http://dx.doi.org/10.1152/ajpregu.00023.2003.

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Daily scheduled feeding is a potent time cue that elicits anticipatory activity in rodents. This food-anticipatory activity (FAA) is controlled by a food-entrainable oscillator (FEO) that is distinct from light-entrained oscillators of the suprachiasmatic nucleus (SCN). Circadian rhythms within the SCN depend on transcription-translation feedback loops in which CLOCK protein is a key positive regulator. The Clock gene is expressed in rhythmic tissues throughout the brain and periphery, implicating its widespread involvement in the functioning of circadian oscillators. To examine whether CLOCK protein is also necessary for the FEO, the effect of daily food restriction was studied in homozygous Clock mutant ( Clk/Clk) mice. The results show that Clk/Clk mutant mice exhibit FAA, even when their circadian wheel-running behavior is arrhythmic. As in wild-type controls, FAA in Clk/Clk mutants persists after temporal feeding cues are removed for several cycles, indicating that the FEO is a circadian timer. This is the first demonstration that the Clock gene is not necessary for the expression of a circadian, food-entrained behavior and suggests that the FEO is mediated by a molecular mechanism distinct from that of the SCN.

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Moon, F. C., e M. Kuroda. "Spatio-temporal dynamics in large arrays of fluid-elastic, Toda-type oscillators". Physics Letters A 287, n. 5-6 (settembre 2001): 379–84. http://dx.doi.org/10.1016/s0375-9601(01)00375-9.

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