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LEONTINI, JUSTIN S., M. C. THOMPSON i K. HOURIGAN. "Three-dimensional transition in the wake of a transversely oscillating cylinder". Journal of Fluid Mechanics 577 (19.04.2007): 79–104. http://dx.doi.org/10.1017/s0022112006004320.
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A Floquet stability analysis of the transition to three-dimensionality in the wake of a cylinder forced to oscillate transversely to the free stream has been undertaken. The effect of varying the oscillation amplitude is determined for a frequency of oscillation close to the natural shedding frequency. The three-dimensional modes that arise are identified, and the effect of the oscillation amplitude on their structure and growth rate quantified.It is shown that when the two-dimensional wake is in the 2S configuration (which is similar to the Kármán vortex street), the three-dimensional modes that arise are similar in nature and symmetry structure to the modes in the wake of a fixed cylinder. These modes are known as modes A, B and QP and occur in this order with increasing Re. However, increasing the amplitude of oscillation causes the critical Reynolds number for mode A to increase significantly, to the point where mode B becomes critical before mode A. The critical wavelength for mode A is also affected by the oscillation, becoming smaller with increasing amplitude. Elliptic instability theory is shown also to predict this trend, providing further support that mode A primarily arises as a result of an elliptic instability.At higher oscillation amplitudes, the spatio-temporal symmetry of the two-dimensional wake changes and it takes on the P + S configuration, with a pair of vortices on one side of the wake and a single vortex on the other side, for each oscillation cycle. With the onset of this configuration, modes A, B and QP cease to exist. It is shown that two new three-dimensional modes arise from this base flow, which we call modes SL and SS. Both of these modes are subharmonic, repeating over two base-flow periods. Also, either mode can be the first to become critical, depending on the amplitude of oscillation of the cylinder.The emergence of these two new modes, as well as the reversal of the order of inception of the three-dimensional modes A and B, leads to the observation that for an oscillating cylinder wake there are four different modes that can lead the transition to three-dimensionality, depending on the amplitude of oscillation. Therefore this type of flow provides a good example for studying the effect of mode-order inception on the path taken to turbulence in bluff-body wakes.For the range of amplitudes studied, the maximum Re value for which the flow remains two-dimensional is 280.
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Ren, Linyuan, Yanan Wang, Weidong Ding, Anbang Sun, Burak Karadag, Zichen Deng i Jinyue Geng. "Discharge characteristics and mode transition of a ring-cusp magnetically confined plasma bridge neutralizer". Journal of Applied Physics 132, nr 8 (28.08.2022): 083301. http://dx.doi.org/10.1063/5.0101904.
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The discharge mode characteristics of cathodes may strongly influence the discharge stability and performance of electrostatic thrusters. In this article, discharge characteristics and mode transition phenomenon of the ring-cusp magnetically confined plasma bridge neutralizer (RCM-PBN) were experimentally studied using argon as the working gas. The dependences of anode current and oscillation amplitude on anode voltage, argon flow rate, heater power, and cathode-to-anode distance were investigated. Plasma properties were measured and plasma plume images were taken under different discharge modes. Two distinct discharge modes were observed during the experiments: high oscillation mode and low oscillation mode. In the high oscillation mode, the plasma plume appears dim, the anode current is low, and the oscillation level is more than 2%. While in the low oscillation mode, a spot-like structure close to the orifice is observed. The plume becomes brighter, the anode current increases, and the oscillation level decreases below 2%. The RCM-PBN was found to transition into the low oscillation mode by increasing anode voltage, flow rate, heater power and by decreasing the cathode-to-anode distance.
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Boriskov, Petr, Andrei Velichko, Nikolay Shilovsky i Maksim Belyaev. "Bifurcation and Entropy Analysis of a Chaotic Spike Oscillator Circuit Based on the S-Switch". Entropy 24, nr 11 (19.11.2022): 1693. http://dx.doi.org/10.3390/e24111693.
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This paper presents a model and experimental study of a chaotic spike oscillator based on a leaky integrate-and-fire (LIF) neuron, which has a switching element with an S-type current-voltage characteristic (S-switch). The oscillator generates spikes of the S-switch in the form of chaotic pulse position modulation driven by the feedback with rate coding instability of LIF neuron. The oscillator model with piecewise function of the S-switch has resistive feedback using a second order filter. The oscillator circuit is built on four operational amplifiers and two field-effect transistors (MOSFETs) that form an S-switch based on a Schmitt trigger, an active RC filter and a matching amplifier. We investigate the bifurcation diagrams of the model and the circuit and calculate the entropy of oscillations. For the analog circuit, the “regular oscillation-chaos” transition is analysed in a series of tests initiated by a step voltage in the matching amplifier. Entropy values are used to estimate the average time for the transition of oscillations to chaos and the degree of signal correlation of the transition mode of different tests. Study results can be applied in various reservoir computing applications, for example, in choosing and configuring the LogNNet network reservoir circuits.
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Cai, M. L., Z. D. Liu, Y. Jiang, Y. K. Wu, Q. X. Mei, W. D. Zhao, L. He, X. Zhang, Z. C. Zhou i L. M. Duan. "Probing a Dissipative Phase Transition with a Trapped Ion through Reservoir Engineering". Chinese Physics Letters 39, nr 2 (1.02.2022): 020502. http://dx.doi.org/10.1088/0256-307x/39/2/020502.
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Dissipation is often considered as a detrimental effect in quantum systems for unitary quantum operations. However, it has been shown that suitable dissipation can be useful resources in both quantum information and quantum simulation. Here, we propose and experimentally simulate a dissipative phase transition (DPT) model using a single trapped ion with an engineered reservoir. We show that the ion’s spatial oscillation mode reaches a steady state after the alternating application of unitary evolution under a quantum Rabi model Hamiltonian and sideband cooling of the oscillator. The average phonon number of the oscillation mode is used as the order parameter to provide evidence for the DPT. Our work highlights the suitability of trapped ions for simulating open quantum systems and shall facilitate further investigations of DPT with various dissipation terms.
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KANO, HIDEAKI, TAKASHI SAITO, AKIKATSU UEKI i TAKAYOSHI KOBAYASHI. "FIRST OBSERVATION OF DYNAMIC INTENSITY BORROWING INDUCED BY COHERENT MOLECULAR VIBRATIONS IN J-AGGREGATES REVEALED BY SUB-5-FS SPECTROSCOPY". International Journal of Modern Physics B 15, nr 28n30 (10.12.2001): 3817–20. http://dx.doi.org/10.1142/s0217979201008743.
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Sub-5-fs spectroscopy of porphyrin J-aggregates reveals for the first time coherent molecular vibration coupled to the Frenkel exciton. The oscillations with the frequency of 244cm-1 are described by a plus-cosine function for bleaching and a minus-cosine function for induced absorption. The coherent oscillation is explained by a modulated transition dipole moment, which is due to the transfer of an oscillator strength from the intense B-band to the weak Q-band through the ruffling mode with 244cm-1-frequency.
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Kikteva V. R., Kiseleva K. V., Kichin G. A., Skirdkov P. N. i Zvezdin K. A. "Impact of the mutual direction of Polarizer and Free Layer on the auto-oscillation mode of magnetic tunnel junctions (MTJs) of different geometry". Physics of the Solid State 65, nr 6 (2023): 893. http://dx.doi.org/10.21883/pss.2023.06.56097.03h.
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In this work we studied the auto-oscillation mode of structures based on magnetic tunnel junctions. During the experiment we studied how different values and orientation of the magnetic field affect the efficiency of the auto-oscillations regime for samples of various shapes. The auto-oscillation mode in samples was observed near the transition from one state of magnetization of the free layer to another. It was found that the maximum value of the power spectral density and its position relative to the frequency axis can be controlled by changing the magnitude and orientation of the external magnetic field. Keywords: Magnetic tunnel junction (MTJ), auto-oscillations, power spectral density, nanooscillator.
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Smirnov, Alexey, i Boris Smolnikov. "COLLINEAR CONTROL OF OSCILLATION MODES OF SPATIAL DOUBLE PENDULUM WITH VARIABLE GAIN". Cybernetics and Physics, Volume 10, 2021, Number 2 (1.10.2021): 88–96. http://dx.doi.org/10.35470/2226-4116-2021-10-2-88-96.
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This article is devoted to the study of controlled movements of spatial double pendulum with non-parallel cylindrical joints axes. The collinear control is used to swinging of the system by feedback. The most important property of collinear control is the ability of increasing system oscillations only on one oscillation mode. A modification of the collinear control law with variable gain depending on the energy level is investigated. It allows to control the system motions more flexible than in the case of constant gain. As a result, it is possible to observe a smooth transition from a linear oscillation mode to a nonlinear one with a gradual output to a steady oscillation motion with a given energy level. The obtained results are clearly illustrated by graph dependencies that demonstrate the swinging of the system on one oscillation mode from small to finite amplitudes.
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HASEGAWA, YOSHITAKA, RYUICHIRO TANAKA i YOSHISUKE UEDA. "ON RATIONAL PHASE-LOCKING OSCILLATIONS OF A SIMPLE SAWTOOTH OSCILLATOR WITH UJT". International Journal of Bifurcation and Chaos 11, nr 12 (grudzień 2001): 3003–32. http://dx.doi.org/10.1142/s0218127401004121.
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There are some reports about sawtooth oscillations on various systems. The authors constructed the sawtooth oscillator circuit exploiting a Uni-Junction Transistor (UJT), and investigated various nonautonomous-like oscillations induced by an external sinusoidal input. Different from the cases of ordinary differential equation (ODE) systems driven with some periodic oscillation, this input periodically alternates only the threshold of the mode transition. Many systems in various fields of electrical circuits, biology and so on utilize threshold variation or modulation between operational modes, and our system is a very simple representative. Though our circuit behaves as a piecewise-continuous ODE system, we will suggest one-dimensional map depending on the phase of the external sinusoidal input. And we will study the background about the existence of various rational locking mode in the analytic method, numerical investigations and circuit experiments, identifying our system as a discrete dynamical system. This paper reveals not only the existing regions of the respective modes, but also reports about respective itineraries of periodic solutions geometrically. Readers will see that the mode distribution constitutes a Cantor set structure.
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Iga, Keita. "Transition modes of rotating shallow water waves in a channel". Journal of Fluid Mechanics 294 (10.07.1995): 367–90. http://dx.doi.org/10.1017/s002211209500293x.
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Normal modes of shallow water waves in a channel wherein the Coriolis parameter and the depth vary in the spanwise direction are investigated based on the conservation of the number of zeros in an eigenfunction. As a result, it is generally shown that the condition for transition modes (Kelvin modes and mixed Rossby-gravity modes) to exist, besides Rossby and Poincaré modes, is determined only by boundary conditions. A Kelvin mode is interpreted as a modification of a Kelvin wave or a boundary wave along a closed boundary, and a mixed Rossby-gravity mode as a modification of an inertial oscillation or a boundary wave along an open boundary. Transition modes appearing in edge and continental-shelf waves, equatorial waves and free oscillations over a sphere are systematically understood by applying the theory in this paper.
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Aoyagi, Toshio, Takashi Takekawa i Tomoki Fukai. "Gamma Rhythmic Bursts: Coherence Control in Networks of Cortical Pyramidal Neurons". Neural Computation 15, nr 5 (1.05.2003): 1035–61. http://dx.doi.org/10.1162/089976603765202659.
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Much evidence indicates that synchronized gamma-frequency (20–70 Hz) oscillation plays a significant functional role in the neocortex and hippocampus. Chattering neuron is a possible neocortical pacemaker for the gamma oscillation. Based on our recent model of chattering neurons, here we study how gamma-frequency bursting is synchronized in a network of these neurons. Using a phase oscillator description, we first examine how two coupled chattering neurons are synchronized. The analysis reveals that an incremental change of the bursting mode, such as from singlet to doublet, always accompanies a rapid transition from antisynchronous to synchronous firing. The state transition occurs regardless of what changes the bursting mode. Within each bursting mode, the neuronal activity undergoes a gradual change from synchrony to antisynchrony. Since the sensitivity to Ca2+ and the maximum conductance of Ca2+ -dependent cationic current as well as the intensity of input current systematically control the bursting mode, these quantities may be crucial for the regulation of the coherence of local cortical activity. Numerical simulations demonstrate that the modulations of the calcium sensitivity and the amplitude of the cationic current can induce rapid transitions between synchrony and asynchrony in a large-scale network of chattering neurons. The rapid synchronization of chattering neurons is shown to synchronize the activities of regular spiking pyramidal neurons at the gamma frequencies, as may be necessary for selective attention or binding processing in object recognition.
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Zhang, Chao, Zhenhua Wan i Dejun Sun. "Mode transition and oscillation suppression in supersonic cavity flow". Applied Mathematics and Mechanics 37, nr 7 (29.06.2016): 941–56. http://dx.doi.org/10.1007/s10483-016-2095-9.
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Serykh, Ilya V., i Dmitry M. Sonechkin. "El Niño–Global Atmospheric Oscillation as the Main Mode of Interannual Climate Variability". Atmosphere 12, nr 11 (1.11.2021): 1443. http://dx.doi.org/10.3390/atmos12111443.
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The interannual variability of the global mean monthly anomalies of near-surface air temperature, sea-level pressure, wind speed near the surface, amount of precipitation and total cloudiness was investigated. The amplitudes of the anomalies of these hydrometeorological characteristics between opposite phases of the Global Atmospheric Oscillation (GAO) were calculated. The regional element of the GAO in the tropics of the Indian and Pacific Oceans is the Southern Oscillation. The results show that the oscillations of these characteristics are associated with the GAO not only in the tropical belt of the Earth but also in the middle and high latitudes, especially in the Arctic and northern Eurasia. The physical mechanism by which the transition of the GAO from the negative to the positive phase influences the weakening of the Pacific trade winds, and, as a consequence, the onset of El Niño is described.
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VÁSQUEZ FLORES, C., C. H. LENZI i G. LUGONES. "RADIAL PULSATIONS OF HYBRID NEUTRON STARS". International Journal of Modern Physics: Conference Series 18 (styczeń 2012): 105–8. http://dx.doi.org/10.1142/s201019451200829x.
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In this work we investigate the adiabatic radial oscillations of hybrid stars. We use a relativistic-mean-field model equation of state (EOS) to describe the hadron phase and the Nambu-Jona-Lasinio (NJL) model for the quark matter phase. We integrate the equations of relativistic radial oscillations using different parameterizations for the NJL model and investigate the effect of a first order hadron-quark phase transition on the fundamental oscillation mode. The results show that the period τ of the fundamental mode is characterized by a cusp on the maximum mass and is finite for some configurations beyond the maximum mass. We conclude that for hybrid stars with sharp discontinuities the standard stability criterion ∂M/∂εc > 0 is not coincident with the stability criterion based on the finiteness of τ.
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Luo, Jianqiang, Siqi Bu i Jiebei Zhu. "Transition from Electromechanical Dynamics to Quasi-Electromechanical Dynamics Caused by Participation of Full Converter-Based Wind Power Generation". Energies 13, nr 23 (27.11.2020): 6270. http://dx.doi.org/10.3390/en13236270.
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Previous studies generally consider that the full converter-based wind power generation (FCWG) is a “decoupled” power source from the grid, which hardly participates in electromechanical oscillations. However, it was found recently that strong interaction could be induced which might incur severe resonance incidents in the electromechanical dynamic timescale. In this paper, the participation of FCWG in electromechanical dynamics is extensively investigated, and particularly, an unusual transition of the electromechanical oscillation mode (EOM) is uncovered for the first time. The detailed mathematical models of the open-loop and closed-loop power systems are firstly established, and modal analysis is employed to quantify the FCWG participation in electromechanical dynamics, with two new mode identification criteria, i.e., FCWG dynamics correlation ratio (FDCR) and quasi-electromechanical loop correlation ratio (QELCR). On this basis, the impact of different wind penetration levels and controller parameter settings on the participation of FCWG is investigated. It is revealed that if an FCWG oscillation mode (FOM) has a similar oscillation frequency to the system EOMs, there is a high possibility to induce strong interactions between FCWG dynamics and system electromechanical dynamics of the external power systems. In this circumstance, an interesting phenomenon may occur that an EOM may be dominated by FCWG dynamics, and hence is transformed into a quasi-EOM, which actively involves the participation of FCWG quasi-electromechanical state variables.
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Hill, Sean, i Giulio Tononi. "Modeling Sleep and Wakefulness in the Thalamocortical System". Journal of Neurophysiology 93, nr 3 (marzec 2005): 1671–98. http://dx.doi.org/10.1152/jn.00915.2004.
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When the brain goes from wakefulness to sleep, cortical neurons begin to undergo slow oscillations in their membrane potential that are synchronized by thalamocortical circuits and reflected in EEG slow waves. To provide a self-consistent account of the transition from wakefulness to sleep and of the generation of sleep slow waves, we have constructed a large-scale computer model that encompasses portions of two visual areas and associated thalamic and reticular thalamic nuclei. Thousands of model neurons, incorporating several intrinsic currents, are interconnected with millions of thalamocortical, corticothalamic, and both intra- and interareal corticocortical connections. In the waking mode, the model exhibits irregular spontaneous firing and selective responses to visual stimuli. In the sleep mode, neuromodulatory changes lead to slow oscillations that closely resemble those observed in vivo and in vitro. A systematic exploration of the effects of intrinsic currents and network parameters on the initiation, maintenance, and termination of slow oscillations shows the following. 1) An increase in potassium leak conductances is sufficient to trigger the transition from wakefulness to sleep. 2) The activation of persistent sodium currents is sufficient to initiate the up-state of the slow oscillation. 3) A combination of intrinsic and synaptic currents is sufficient to maintain the up-state. 4) Depolarization-activated potassium currents and synaptic depression terminate the up-state. 5) Corticocortical connections synchronize the slow oscillation. The model is the first to integrate intrinsic neuronal properties with detailed thalamocortical anatomy and reproduce neural activity patterns in both wakefulness and sleep, thereby providing a powerful tool to investigate the role of sleep in information transmission and plasticity.
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Peppa, Sofia, Lambros Kaiktsis, Christos E. Frouzakis i George S. Triantafyllou. "Computational Study of Three-Dimensional Flow Past an Oscillating Cylinder Following a Figure Eight Trajectory". Fluids 6, nr 3 (5.03.2021): 107. http://dx.doi.org/10.3390/fluids6030107.
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The paper presents a computational study of three-dimensional flow past a cylinder forced to oscillate in a uniform stream, following a figure-eight trajectory. Flow simulations were performed for Re = 400, for different cases, defined in terms of the oscillation mode (‘counter-clockwise’ or ‘clockwise’), for values of the ratio, F, of the transverse oscillation frequency to the Strouhal frequency close to 1.0. The results demonstrate that, for F ≤ 1.0, counter-clockwise cylinder motion is associated with positive power transfer from the flow to the cylinder, corresponding to excitation; for the clockwise motion, power transfer is negative at intermediate to high amplitudes, corresponding to damping. For the clockwise mode, in the range F = 0.9–1.1, a transition to two-dimensional vortex street is identified for transverse oscillation amplitude exceeding a critical value. This results from the induced suction of vortices, which moves vortex formation and shedding closer to the cylinder surface, thus resulting in a narrower wake, characterized by an effective lower Reynolds number. Both oscillation modes are characterized by higher harmonics in the lift force spectrum, with the third harmonic being very pronounced, while even harmonics are present for the case of clockwise mode, resulting from a wake transition to a “S + P” mode.
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Konenkov, NV, MA Korzhavchikov, VA Stepanov i OE Trunina. "Quadrupole mass filter acceptance in stability island created by double-frequency quadrupole excitation". European Journal of Mass Spectrometry 24, nr 4 (26.02.2018): 315–21. http://dx.doi.org/10.1177/1469066718760164.
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Increase in quadrupole mass filter resolution at separation in narrow band stability island (X-band) formed by biharmonic resonance excitation of ion oscillation is discussed. X-band and the normal working quadrupole mass filter modes are compared at theoretical resolution of 10,000 and different separation times. Transmission curves, acceptance ellipses parameters, and acceptance characteristics are obtained by numerical simulation. Transmission coefficients are approximately the same in both modes. Dependence of acceptance ellipses parameters on ion inlet phases has a complicated oscillating form in the X-band mode. Acceptance contours calculated for given transition levels have been compared. At low acceptance level, the combined acceptance in the X-band mode was found to be one order of magnitude higher than in the normal mode.
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Абдуллина, Г. И., Л. Г. Аскинази, А. А. Белокуров, Н. А. Жубр, В. А. Корнев, С. В. Крикунов, С. В. Лебедев, Д. B. Разуменко i А. С. Тукачинский. "Определение локализации альфвеновских колебаний в плазме токамака ТУМАН-3М". Письма в журнал технической физики 44, nr 3 (2018): 47. http://dx.doi.org/10.21883/pjtf.2018.03.45578.17063.
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AbstractThe Alfvén oscillations have been studied in ohmically heated deuterium discharges with LH-transition in the TUMAN-3M tokamak in order to clarify their location in a plasma column. The Alfvén oscillation location was determined by comparison of the oscillation frequency measured with magnetic probes and that calculated from local density assuming the typical dispersion relation for Alfvén waves f = (2π)^−1 k _|| v _ A , where v _ A is the Alfvén velocity and k _|| is the the parallel wave number in the direction of the magnetic field. It was found that they are localized in central part of plasma column inside r / a < 0.5 region. Candidate sets of mode numbers have been determined.
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Yu, Z. B., Q. Li, X. Chen, F. Z. Guo, X. J. Xie i J. H. Wu. "Investigation on the oscillation modes in a thermoacoustic Stirling prime mover: mode stability and mode transition". Cryogenics 43, nr 12 (grudzień 2003): 687–91. http://dx.doi.org/10.1016/s0011-2275(03)00183-8.
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Yeh, Sang-Wook, Yune-Jung Kang, Yign Noh i Arthur J. Miller. "The North Pacific Climate Transitions of the Winters of 1976/77 and 1988/89". Journal of Climate 24, nr 4 (15.02.2011): 1170–83. http://dx.doi.org/10.1175/2010jcli3325.1.
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Abstract This paper examines characteristic changes in North Pacific sea surface temperature (SST) variability during the boreal winter (December–February) for two subperiods (1956–88 and 1977–2009) during which the 1976/77 and the 1988/89 climate transitions occurred. It is found that the Pacific decadal oscillation (PDO)-like SST variability plays a dominant role in the 1976/77 climate transition, while both the North Pacific Gyre Oscillation (NPGO)-like and PDO-like SST variability contribute to the 1988/89 climate transition. Furthermore, the leading mode changes from PDO-like SST variability during the period 1956–88 to NPGO-like SST variability during the period 1977–2009, indicative of an enhancement of NPGO-like SST variability since 1988. Changes in sea level pressure across the 1976/77 climate transition project strongly onto the Aleutian low pressure system. But sea level pressure changes across the 1988/89 climate transition project primarily onto the North Pacific Oscillation, which is associated with remote changes in the Arctic Oscillation over the polar region as well. This contributes to enhancing the NPGO-like SST variability after 1988. The authors also analyze the output from an ensemble of Tropical Ocean and Global Atmosphere (TOGA) experiments in which the observed SSTs are inserted only at grid points in the tropics between 20°S and 20°N. The results indicate that the changes in the North Pacific atmosphere in the 1976/77 climate transition are mostly due to the tropics, whereas those in the 1988/89 climate transition are not.
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Lindsay, Christopher J., J. M. Joel Ong i Sarbani Basu. "Near-core Acoustic Glitches Are Not Oscillatory: Consequences for Asteroseismic Probes of Convective Boundary Mixing". Astrophysical Journal 950, nr 1 (1.06.2023): 19. http://dx.doi.org/10.3847/1538-4357/acccf5.
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Abstract Asteroseismology has been used extensively in recent years to study the interior structure and physical processes of main-sequence stars. We consider prospects for using pressure modes (p-modes) near the frequency of maximum oscillation power to probe the structure of the near-core layers of main-sequence stars with convective cores by constructing stellar model tracks. Within our mass range of interest, the inner turning point of p-modes as determined by the Jeffreys–Wentzel–Kramers–Brillouin (JWKB) approximation evolves in two distinct phases during the main sequence, implying a sudden loss of near-core sensitivity during the discontinuous transition between the two phases. However, we also employ non-JWKB asymptotic analysis to derive a contrasting set of expressions for the effects that these structural properties will have on the mode frequencies, which do not encode any such transition. We show analytically that a sufficiently near-core perturbation to the stellar structure results in nonoscillatory, degree-dependent perturbations to the star’s oscillation mode frequencies, contrasting with the case of an outer glitch. We also demonstrate numerically that these near-core acoustic glitches exhibit strong angular degree dependence, even at low degree, agreeing with the non-JWKB analysis, rather than the degree-independent oscillations that emerge from JWKB analyses. These properties have important implications for using p-modes to study near-core mixing processes for intermediate-mass stars on the main sequence, as well as for the interpretation of near-center acoustic glitches in other astrophysical configurations, such as red giants.
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Pihnastyi, Oleh, i Svіtlana Chernіavska. "Using the asymptotic approximation of the Maxwell element model for the analysis of stress in a conveyor belt". Eastern-European Journal of Enterprise Technologies 6, nr 7 (114) (21.12.2021): 77–84. http://dx.doi.org/10.15587/1729-4061.2021.247526.
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The features of the propagation of dynamic stresses in a conveyor belt, the material properties of which correspond to the Maxwell element model, are considered. Analytical expressions are presented for calculating the dynamic elastic modulus, the loss modulus, and the angle of mechanical loss depending on the frequency of longitudinal oscillations in the belt of an extended transport conveyor. To analyze the dynamic stress propagation process, dimensionless parameters are introduced that characterize the specific features of the viscoelastic process in a conveyor belt, the material properties of which correspond to the Maxwell element model. The transition to the dimensionless Maxwell element model is made and the analysis of the relationship between stress and deformation of a conveyor belt element for extremely large and small values of dimensionless parameters is made. The substantiation of the scope of the Maxwell element model is given. It is shown that at sufficiently high frequencies of longitudinal stress oscillations in a conveyor belt, at which the oscillation period is much less than the characteristic oscillation decay time, the relationship between stress and deformation of the conveyor belt element corresponds to Hooke's law. A qualitative analysis of the relaxation time was carried out for a conveyor belt material, the properties of which correspond to the Maxwell element model. The analysis of the propagation of dynamic stresses in the conveyor belt for the characteristic operating modes of the transport conveyor is carried out. The conveyor operating mode with a constant deformation rate of the belt element; the mode in which a constant load is suddenly applied to the belt element; the conveyor operating mode with an instantly applied load to the belt element were investigated. It was determined that in cases where the characteristic process time significantly exceeds the stress relaxation time in the conveyor belt or the longitudinal oscillation period is much less than the stress relaxation time in the conveyor belt, the Maxwell element model can be replaced with a sufficient degree of accuracy by the Hooke element model.
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TATENO, KATSUMI, HIDEYUKI TOMONARI, HATSUO HAYASHI i SATORU ISHIZUKA. "PHASE DEPENDENT TRANSITION BETWEEN MULTISTABLE STATES IN A NEURAL NETWORK WITH RECIPROCAL INHIBITION". International Journal of Bifurcation and Chaos 14, nr 05 (maj 2004): 1559–75. http://dx.doi.org/10.1142/s0218127404010138.
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We studied multistable oscillatory states of a small neural network model and switching of an oscillatory mode. In the present neural network model, two pacemaker neurons are reciprocally inhibited with conduction delay; one pacemaker neuron inhibits the other via an inhibitory nonpacemaker interneuron, and vice versa. The small network model shows bifurcations from quasi-periodic oscillation to chaos via period 3 with increase in the synaptic weight of the reciprocal inhibition. The route to chaos in the network model is different from that in the single pacemaker neuron. The network model exhibits several multistable states. In a regime of a weak inhibitory connection, in-phase beat, out-of-phase beat (period 3), and chaotic oscillation coexist at the multistable state. We can switch an oscillatory mode by an excitatory synaptic input to one of the pacemaker neurons through an afferent path. In a strong inhibitory connection regime, in-phase beat and out-of-phase beat (period 4) coexist at the multistable state. An excitatory synaptic input through the afferent path leads to the transition from the in-phase beat to the out-of-phase beat. The transition from the out-of-phase beat to the in-phase beat is induced by an inhibitory synaptic input via interneurons. A conduction delay, furthermore, causes the spontaneous transition from the in-phase beat to the out-of-phase beat. These transitions can be explained by phase response curves.
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Zhileykin, Mikhail M., Pavel V. Sirotin, Sergey S. Nosikov i Nikolay N. Pulyaev. "Method for detecting the loss of stability of the movement of tractors when towing a trailer or a coupled unit". Tractors and Agricultural Machinery 90, nr 1 (23.05.2023): 39–48. http://dx.doi.org/10.17816/0321-4443-321266.
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BACKGROUND:Currently, combines and tractors, being the most energy-intensive transport and technological machines for agricultural purposes, largely determine the possibility of transition to an efficient and environmentally friendly agricultural economy, and also provide the technical aspect of the transformation of the agro-industrial complex into the leading sector of the countrys industry. One of the sources of dynamic loads in the units and subsystems of tractor equipment are self-oscillating modes.
AIMS:Study of the conditions for the occurrence of self-oscillating processes in the design of wheeled tractor trains and development of methods to increase the handling and safety of their movement by means of reducing the galloping and yawing of the tractor-tractor when towing heavy loads.
METHODS:It has been established that due to the coupling of oscillations along the longitudinal displacement of a truck tractor and a trailer with oscillations along the vertical displacement of the center of mass and with pitch angle oscillations of the truck tractor, when an auto-oscillatory mode occurs in the interaction zone of an elastic wheel with a solid surface, the same mode of self-oscillation will occur along the mentioned degrees of freedom. Moreover, it is possible to specify the sequence of occurrence of self-oscillating modes in different zones of the tractor train design.
RESULTS:First, self-oscillations are excited in the contact patch of a wheel with a solid surface when a complete slip occurs, then self-oscillations along the pitch angle of a truck tractor body begin and after that self-oscillations along the vertical displacement of the center of mass of a truck tractor occur. Folding angle oscillations of a tractor train are associated with oscillations of the translational motion of wheel centers, which lead to the emergence of an self-oscillating mode, both with partial and full slip in the interaction zone of an elastic tire with a solid surface. Since the self-oscillations of each of the wheels occur at random times, the self-oscillations of a truck tractor along the folding angle will be chaotic.
CONCLUSIONS:The practical value of the study lies in the possibility of using the proposed methods to identify the danger of self-oscillating processes in the design of promising types of agricultural machinery.
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LO JACONO, DAVID, JUSTIN S. LEONTINI, MARK C. THOMPSON i JOHN SHERIDAN. "Modification of three-dimensional transition in the wake of a rotationally oscillating cylinder". Journal of Fluid Mechanics 643 (24.12.2009): 349–62. http://dx.doi.org/10.1017/s0022112009992370.
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A study of the flow past an oscillatory rotating cylinder has been conducted, where the frequency of oscillation has been matched to the natural frequency of the vortex street generated in the wake of a stationary cylinder, at Reynolds number 300. The focus is on the wake transition to three-dimensional flow and, in particular, the changes induced in this transition by the addition of the oscillatory rotation. Using Floquet stability analysis, it is found that the fine-scale three-dimensional mode that typically dominates the wake at a Reynolds number beyond that at the second transition to three-dimensional flow (referred to as mode B) is suppressed for amplitudes of rotation beyond a critical amplitude, in agreement with past studies. However, the rotation does not suppress the development of three-dimensionality completely, as other modes are discovered that would lead to three-dimensional flow. In particular, the longer-wavelength mode that leads the three-dimensional transition in the wake of a stationary cylinder (referred to as mode A) is left essentially unaffected at low amplitudes of rotation. At higher amplitudes of oscillation, mode A is also suppressed as the two-dimensional near wake changes in character from a single- to a double-row wake; however, another mode is predicted to render the flow three-dimensional, dubbed mode D (for double row). This mode has the same spatio-temporal symmetries as mode A.
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Iwagami, Sho, Ryoya Tabata, Taizo Kobayashi, Yuji Hattori i Kin’ya Takahashi. "Numerical study on edge tone with compressible direct numerical simulation: Sound intensity and jet motion". International Journal of Aeroacoustics 20, nr 3-4 (24.03.2021): 283–316. http://dx.doi.org/10.1177/1475472x211003296.
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A two-dimensional model of the edge tone is studied by a highly accurate and reliable method of direct numerical simulation of the compressible Navier-Stokes equations, and used to verify key features observed in previous experimental and numerical studies, and to discover new features related to the jet motion and the edge tone generation mechanism. The first and second modes of the edge tone that are numerically reproduced agree well with Brown’s equation. In the mode transition region, dynamical mode transition is observed at a fixed jet velocity. For both first and second modes, the pressure distributions are antisymmetric with respect to the edge plate, and the sound intensity is proportional to the fifth power of the jet velocity. These results are consistent with the edge tone being radiated from a dipole-like source. Spatial profiles of the velocity and the velocity variance of the oscillating jet are also investigated for each mode over a range of the jet velocity including the mode transition regime. The amplitude of the velocity oscillation becomes constant with increasing jet velocity, while a measure of the amplitude of the velocity variance profile, which is introduced to characterize the strength of the jet fluctuation and named the ’fluctuation strength’, is proportional to the third power of the jet velocity. Some properties of the fluctuation strength correspond to properties of the sound intensity, including the first mode having larger amplitude than the second mode, and the way of deviating from the power law at smaller values of jet velocity and in the mode transition region. It is proposed that the third-power law exhibited by behavior of the fluctuation strength could be related to the increase of the skewness observed in the velocity profile with increase of jet velocity, and a model calculation is used to support this proposal.
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Li, Yang, Jifan Shi i Kazuyuki Aihara. "Mean-field analysis of Stuart–Landau oscillator networks with symmetric coupling and dynamical noise". Chaos: An Interdisciplinary Journal of Nonlinear Science 32, nr 6 (czerwiec 2022): 063114. http://dx.doi.org/10.1063/5.0081295.
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This paper presents analyses of networks composed of homogeneous Stuart–Landau oscillators with symmetric linear coupling and dynamical Gaussian noise. With a simple mean-field approximation, the original system is transformed into a surrogate system that describes uncorrelated oscillation/fluctuation modes of the original system. The steady-state probability distribution for these modes is described using an exponential family, and the dynamics of the system are mainly determined by the eigenvalue spectrum of the coupling matrix and the noise level. The variances of the modes can be expressed as functions of the eigenvalues and noise level, yielding the relation between the covariance matrix and the coupling matrix of the oscillators. With decreasing noise, the leading mode changes from fluctuation to oscillation, generating apparent synchrony of the coupled oscillators, and the condition for such a transition is derived. Finally, the approximate analyses are examined via numerical simulation of the oscillator networks with weak coupling to verify the utility of the approximation in outlining the basic properties of the considered coupled oscillator networks. These results are potentially useful for the modeling and analysis of indirectly measured data of neurodynamics, e.g., via functional magnetic resonance imaging and electroencephalography, as a counterpart of the frequently used Ising model.
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Гинзбург, Н. С., А. С. Сергеев, Е. Р. Кочаровская, А. М. Малкин, Е. Д. Егорова i В. Ю. Заславский. "Дифракционная селекция мод в гетеролазерах с планарными брэгговскими структурами". Физика и техника полупроводников 54, nr 9 (2020): 974. http://dx.doi.org/10.21883/ftp.2020.09.49842.38.
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Within the coupled waves method complemented by quasi-optical approach, we investigate a possibility of diffraction mode selection with respect to the transverse mode index in lasers with planar Bragg resonators. Allowable values of the Fresnel parameter are determined which provide for establishment of stationary single-mode oscillation regime with narrow angle spectrum due to diffraction losses from the edges of the Bragg structure. We show that at larger values of the Fresnel parameter, oscillation stability can be improved by shifting the operating transition frequency to the eigenfrequency of the highest-Q longitudinal mode of the Bragg resonator.
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Palies, Paul, Milos Ilak i Robert Cheng. "Transient and limit cycle combustion dynamics analysis of turbulent premixed swirling flames". Journal of Fluid Mechanics 830 (5.10.2017): 681–707. http://dx.doi.org/10.1017/jfm.2017.575.
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Premixed low swirling flames (methane–air and hydrogen–methane–air) are experimentally investigated for three different regimes. Stable, local transient to instability and limit cycle regimes corresponding to three distinct equivalence ratios are considered. Dynamic mode decomposition is applied to the hydrogen–air–methane flame to retrieve the modes frequencies, growth rates and spatial distributions for each regime. The results indicate that a vortical wave propagating along the flame front is associated with the transition from stability to instability. In addition, it is shown that a key effect on stability is the location of the non-oscillating (0 Hz) flame component. The phase-averaged unsteady motion of the flames over one cycle of oscillation shows the vortical wave rolling up the flame front. The Rayleigh index maps are formed to identify the region of driving and damping of the self-sustained oscillation, while the flame transfer function phase leads to the propagation mode of the perturbations along the flame front. The second mechanism identified concerns the swirl number fluctuation induced by the mode conversion. By utilizing hypotheses for the flow field and the flame structure, it is pointed out that those mechanisms are at work for both flames (methane–air and hydrogen–methane–air) and their effects on the unsteady heat release are determined. Both unsteady heat release contributions, the vortical wave induces flame surface fluctuations and swirl number oscillation induces unsteady turbulent burning velocity, are in phase opposition and of similar amplitudes.
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Kravtsov, S., P. Berloff, W. K. Dewar, M. Ghil i J. C. McWilliams. "Dynamical Origin of Low-Frequency Variability in a Highly Nonlinear Midlatitude Coupled Model". Journal of Climate 19, nr 24 (15.12.2006): 6391–408. http://dx.doi.org/10.1175/jcli3976.1.
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Abstract A novel mechanism of decadal midlatitude coupled variability, which crucially depends on the nonlinear dynamics of both the atmosphere and the ocean, is presented. The coupled model studied involves quasigeostrophic atmospheric and oceanic components, which communicate with each other via a constant-depth oceanic mixed layer. A series of coupled and uncoupled experiments show that the decadal coupled mode is active across parameter ranges that allow the bimodality of the atmospheric zonal flow to coexist with oceanic turbulence. The latter is most intense in the regions of inertial recirculation (IR). Bimodality is associated with the existence of two distinct anomalously persistent zonal-flow modes, which are characterized by different latitudes of the atmospheric jet stream. The IR reorganizations caused by transitions of the atmosphere from its high- to low-latitude state and vice versa create sea surface temperature anomalies that tend to induce transition to the opposite atmospheric state. The decadal–interdecadal time scale of the resulting oscillation is set by the IR adjustment; the latter depends most sensitively on the oceanic bottom drag. The period T of the nonlinear oscillation is 7–25 yr for the range of parameters explored, with the most realistic parameter values yielding T ≈ 20 yr. Aside from this nonlinear oscillation, an interannual Rossby wave mode is present in all coupled experiments. This coupled mode depends neither on atmospheric bimodality, nor on ocean eddy dynamics; it is analogous to the mode found previously in a channel configuration. Its time scale in the model with a closed ocean basin is set by cross-basin wave propagation and equals 3–5 yr for a basin width comparable with the North Atlantic.
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Neverova, G. P., O. L. Zhdanova i E. Ya Frisman. "Modeling the Dynamics of Predator-Prey Community with Age Structures". Mathematical Biology and Bioinformatics 14, nr 1 (20.02.2019): 77–93. http://dx.doi.org/10.17537/2019.14.77.
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A model of the predator-prey community has been proposed with specific stages of individual development and the seasonality of breeding processes. It is assumed each of the species has an age structure with two stages of development. The case typical for the community “Arctic fox – rodents” is modeled. An analytical and numerical study of the model proposed is made. It is shown that periodic, quasi-periodic and chaotic oscillations can occur in the system, as well as a shift in the dynamics mode as a result of changes in the current sizes of the community’s populations. The model proposed demonstrates long-period oscillations with time delay like auto-oscillations in the classical model of Lotka-Volterra. It is shown that a transition from stable dynamics to quasi-periodic oscillations and vise verse is possible in the system, while an increase in the values of the half capturing saturation coefficient reduces the possibility of quasiperiodic oscillation emergence. Simulations demonstrate the growth in predator’s consumption of the prey average number expands the zones of multistability and quasi-periodic dynamics in the stability area of nontrivial fixed point. Therefore, the variation of the current population size of the community can lead to a change in the dynamic mode observed. The scenarios of transition from stationary dynamics to community’s population fluctuations are analyzed with different values of population parameters determining the dynamics of both species and their interaction coefficient. The model shows both sustainable community development and various complex fluctuations of interacting species. At the same time, the prey dynamics affects the predator one: the prey population fluctuations initiate predator oscillations like prey’s fluctuations, while the intrapopulation parameters of the predator can give to both stationary and fluctuating dynamic modes.
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Bejarano, Luis, i Fei-Fei Jin. "Coexistence of Equatorial Coupled Modes of ENSO*". Journal of Climate 21, nr 12 (15.06.2008): 3051–67. http://dx.doi.org/10.1175/2007jcli1679.1.
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Abstract To study the regimes of leading ocean–atmosphere coupled modes of relevance to the El Niño–Southern Oscillation (ENSO) phenomenon, a comprehensive eigenmode analysis of an intermediate coupled model linearized with respect to an array of basic states is performed. Different kinds of leading modes are found to coexist and become unstable under wide ranges of basic states and parameter conditions. In particular, the two most important modes have periods of around 4 and 2 yr. They are referred to as the quasi-quadrennial (QQ) and the quasi-biennial (QB) modes, respectively. The positive coupled feedback destabilizes and quantizes the near-continuous spectrum for the low-frequency modes of the upper-ocean dynamics, giving rise to these leading modes with distinct periodicities. The primary mechanism for the phase transition of the QQ mode is due to the slow oceanic dynamic adjustment of equatorial heat content, which is consistent with the simple conceptual recharge oscillator, whereas anomalous advection of sea surface temperature by equatorial zonal current anomalies plays a dominant role in the phase transition of the QB mode. The coexistence of these ENSO-like coupled modes under the present climate conditions may provide an explanation for the observed rich variations in ENSO behaviors.
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Verma, Suyash, Muhammad S. U. Khalid i Arman Hemmati. "On association of lift generation, wake topology and kinematics of oscillating foils". International Journal of Micro Air Vehicles 14 (styczeń 2022): 175682932110739. http://dx.doi.org/10.1177/17568293211073959.
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The association of lift generation and evolution of wake topology behind an oscillating foil with combined heaving and pitching motion is investigated numerically at a range of bluereduced frequency (0.16 [Formula: see text] 0.48), phase offset (0[Formula: see text] [Formula: see text] 315[Formula: see text]) and Reynolds number (1000 [Formula: see text] 4000). The pitch-dominated kinematics that coincide with the range of [Formula: see text] 120[Formula: see text] and [Formula: see text] 225[Formula: see text] suggests that leading edge vortices are suppressed while trailing edge vortices dominate the wake with increasing reduced frequency. This corresponds to a transition in wake topology from a [Formula: see text] to a reverse Von Kármán wake mode. Contrarily, heave dominated kinematics (120[Formula: see text] [Formula: see text] 225[Formula: see text]) did not exhibit any wake topology transition with increasing [Formula: see text]. The temporal lift variation associated with heave-dominated regime further revealed a symmetric feature in terms of the time taken to attain peak lift generation within an oscillation cycle. This temporal symmetry was, however, lost as kinematics transitioned from heave- to pitch-dominated regime. Analyzing the wake evolution and lift features at quarter phase of an oscillation cycle revealed the existence of a correspondence between the two processes during the heave- and pitch-dominated kinematics.
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Sourav, Kumar, Pavan Kumar Yadav, Phanindra Tallapragada i Deepak Kumar. "Simultaneous streamwise and cross-stream oscillations of a diamond oscillator at low Reynolds numbers". Physics of Fluids 34, nr 6 (czerwiec 2022): 063601. http://dx.doi.org/10.1063/5.0096416.
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A two-dimensional stabilized space-time finite-element-based in-house solver is used to explore flow around an elastically mounted rigid diamond oscillator undergoing undamped vortex-induced vibrations in transverse and stream-wise directions simultaneously. The computations are carried over a reduced velocity ([Formula: see text]) range of 1–12 keeping the Reynolds number ( Re) and the mass ratio ([Formula: see text]) fixed at 100 and 10, respectively. In the current investigation, a five-branch response behavior with the presence of an “upper branch” is identified, which is absent for transverse-only oscillations. A shift in normalized time-averaged phase difference ([Formula: see text]) from 0 to 1 is related to the transition from the upper to the lower branch. The non-dimensional oscillation frequencies in both streamwise and cross-stream directions ( Fx and Fy, respectively) collapse on the upper branch, matching the oscillator's non-dimensional natural frequency ( FN). This leads to periodic single-looped “raindrop-shaped” cylinder trajectories. On this branch, the vortex-shedding mode is asymmetric, and the mean lift is non-zero ([Formula: see text]). For all other response branches, [Formula: see text] and the vortex-shedding modes are symmetric. The presence of multiple frequencies in the in-line oscillations makes the initial branch quasi-periodic, whereas all other response branches are periodic. The addition of in-line motion modifies the fluid loading on the oscillator significantly.
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Li, Tianming. "Phase Transition of the El Niño–Southern Oscillation: A Stationary SST Mode". Journal of the Atmospheric Sciences 54, nr 24 (grudzień 1997): 2872–87. http://dx.doi.org/10.1175/1520-0469(1997)054<2872:ptoten>2.0.co;2.
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Rodriguez-Vera, Geidy, Rosario Romero-Centeno, Christopher L. Castro i Víctor Mendoza Castro. "Coupled Interannual Variability of Wind and Sea Surface Temperature in the Caribbean Sea and the Gulf of Mexico". Journal of Climate 32, nr 14 (20.06.2019): 4263–80. http://dx.doi.org/10.1175/jcli-d-18-0573.1.
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Abstract This work describes dominant patterns of coupled interannual variability of the 10-m wind and sea surface temperature in the Caribbean Sea and the Gulf of Mexico (CS&GM) during the period 1982–2016. Using a canonical correlation analysis (CCA) between the monthly mean anomalies of these fields, four coupled variability modes are identified: the dipole (March–April), transition (May–June), interocean (July–October), and meridional-wind (November–February) modes. Results show that El Niño–Southern Oscillation (ENSO) influences almost all the CS&GM coupled modes, except the transition mode, and that the North Atlantic Oscillation (NAO) in February has a strong negative correlation with the dipole and transition modes. The antisymmetric relationships found between the dipole mode and the NAO and ENSO indices confirm previous evidence about the competing remote forcings of both teleconnection patterns on the tropical North Atlantic variability. Precipitation in the CS and adjacent oceanic and land areas is sensitive to the wind–SST coupled variability modes from June to October. These modes seem to be strongly related to the interannual variability of the midsummer drought and the meridional migration of the intertropical convergence zone in the eastern Pacific. These findings may eventually lead to improving seasonal predictability in the CS&GM and surrounding land areas.
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Kang, Qi, Di Wu, Li Duan, Liang Hu, Jia Wang, Pu Zhang i Wenrui Hu. "The effects of geometry and heating rate on thermocapillary convection in the liquid bridge". Journal of Fluid Mechanics 881 (25.10.2019): 951–82. http://dx.doi.org/10.1017/jfm.2019.757.
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The experimental study on thermocapillary convection in liquid bridges of large Prandtl number has been carried out on Tiangong-2 in space. The purpose of these experiments is to study the oscillation instability of thermocapillary convection, and to discover and recognize the mechanism of destabilization of thermocapillary convection in the microgravity environment in space. In this paper, the geometry of a half-floating-zone liquid bridge is featured by the aspect ratio Ar and volume ratio Vr, and its influence on critical conditions of oscillatory thermocapillary convection is studied. More than 700 sets of space experiments have been finished. The critical conditions and oscillation characteristics of thermocapillary convection instability in the Ar–Vr parameter space have been fully obtained under microgravity conditions for the first time. It is found that the Ar–Vr parameter space can be divided into two regions of different critical conditions and oscillation characteristics: the region of low frequency oscillation, and the region of high frequency oscillation. More importantly, we obtain the complete configuration of these two stability neutral curves, and find that the low frequency mode is a ‘’ type curve. Based on this, we discuss the influence of heating rate on the oscillation mode. It is found that the heating rate affects the selection of critical mode, which results in a jump change of critical temperature difference. The findings of this study are helpful to better understand the critical modes and transition processes of thermocapillary convection in liquid bridges with different configurations.
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ROWLEY, CLARENCE W., TIM COLONIUS i AMIT J. BASU. "On self-sustained oscillations in two-dimensional compressible flow over rectangular cavities". Journal of Fluid Mechanics 455 (25.03.2002): 315–46. http://dx.doi.org/10.1017/s0022112001007534.
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Numerical simulations are used to investigate the resonant instabilities in two-dimensional flow past an open cavity. The compressible Navier–Stokes equations are solved directly (no turbulence model) for cavities with laminar boundary layers upstream. The computational domain is large enough to directly resolve a portion of the radiated acoustic field, which is shown to be in good visual agreement with schlieren photographs from experiments at several different Mach numbers. The results show a transition from a shear-layer mode, primarily for shorter cavities and lower Mach numbers, to a wake mode for longer cavities and higher Mach numbers. The shear-layer mode is characterized well by the acoustic feedback process described by Rossiter (1964), and disturbances in the shear layer compare well with predictions based on linear stability analysis of the Kelvin–Helmholtz mode. The wake mode is characterized instead by a large-scale vortex shedding with Strouhal number independent of Mach number. The wake mode oscillation is similar in many ways to that reported by Gharib & Roshko (1987) for incompressible flow with a laminar upstream boundary layer. Transition to wake mode occurs as the length and/or depth of the cavity becomes large compared to the upstream boundary-layer thickness, or as the Mach and/or Reynolds numbers are raised. Under these conditions, it is shown that the Kelvin–Helmholtz instability grows to sufficient strength that a strong recirculating flow is induced in the cavity. The resulting mean flow is similar to wake profiles that are absolutely unstable, and absolute instability may provide an explanation of the hydrodynamic feedback mechanism that leads to wake mode. Predictive criteria for the onset of shear-layer oscillations (from steady flow) and for the transition to wake mode are developed based on linear theory for amplification rates in the shear layer, and a simple model for the acoustic efficiency of edge scattering.
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KIM, HWA-MIN, i YOUNG-DAE JUNG. "Transitions in the surface dust-ion-acoustic mode in a self-gravitating semi-bounded magnetized dusty plasma". Journal of Plasma Physics 73, nr 5 (październik 2007): 785–91. http://dx.doi.org/10.1017/s0022377806006283.
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AbstractThe transitions and the self-gravitational effects on the surface dust-ion-acoustic mode are investigated in semi-bounded magnetized dusty plasmas. We find that there is a dust-ion-acoustic resonance mode in small wave number regions. Furthermore, we find that the self-gravitational effects enhance the resonance frequency. However, the surface wave starts to propagate as the wave number increases. The transition position between the resonance oscillation and the wave propagation is shifted to the smaller wave number domain as self-gravitational effects increase. In addition, the resonance frequency is found to decrease with decreasing strength of the magnetic field in small wave number domains.
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Киктева, В. Р., К. В. Киселева, Г. А. Кичин, П. Н. Скирдков i К. А. Звездин. "Влияние взаимного направления поляризатора и свободного слоя на автогенерацию магнитных туннельных переходов (МТП) разной геометрии". Физика твердого тела 65, nr 6 (2023): 932. http://dx.doi.org/10.21883/ftt.2023.06.55646.03h.
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In this work we studied the auto-oscillation mode of structures based on magnetic tunnel junctions. During the experiment we studied how different values and orientation of the magnetic field affect the efficiency of the self-generation regime for samples of various shapes. The auto-oscillation mode in samples was observed near the transition from one state of magnetization of the free layer to another. It was found that the maximum value of the power spectral density and its position relative to the frequency axis can be controlled by changing the magnitude and orientation of the external magnetic field.
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Zhan, Feibiao, Yingteng Zhang, Jian Song i Shenquan Liu. "Canard Mechanism and Rhythm Dynamics of Neuron Models". Mathematics 11, nr 13 (27.06.2023): 2874. http://dx.doi.org/10.3390/math11132874.
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Canards are a type of transient dynamics that occur in singularly perturbed systems, and they are specific types of solutions with varied dynamic behaviours at the boundary region. This paper introduces the emergence and development of canard phenomena in a neuron model. The singular perturbation system of a general neuron model is investigated, and the link between the transient transition from a neuron model to a canard is summarised. First, the relationship between the folded saddle-type canard and the parabolic burster, as well as the firing-threshold manifold, is established. Moreover, the association between the mixed-mode oscillation and the folded node type is unique. Furthermore, the connection between the mixed-mode oscillation and the limit-cycle canard (singular Hopf bifurcation) is stated. In addition, the link between the torus canard and the transition from tonic spiking to bursting is illustrated. Finally, the specific manifestations of these canard phenomena in the neuron model are demonstrated, such as the singular Hopf bifurcation, the folded-node canard, the torus canard, and the “blue sky catastrophe”. The summary and outlook of this paper point to the realistic possibility of canards, which have not yet been discovered in the neuron model.
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Brekhov, K. A., N. A. Ilyin, E. D. Mishina, P. A. Prudkovskii i G. Kh Kitaeva. "The temperature dependence of the photoinduced soft mode in Sn2P2S6 crystal". International Journal of Modern Physics B 33, nr 08 (30.03.2019): 1950061. http://dx.doi.org/10.1142/s0217979219500619.
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In this paper, we present the results of the temperature dependence studies of the photoinduced phonon mode which appears in a ferroelectric-semiconductor Sn2P2S6 (SPS) crystal under the influence of femtosecond laser pulses. We show that its behavior reminds the soft mode one near the phase transition. However, the observed decrease in the oscillation frequency in the vicinity of Curie temperature Tc is much weaker than previously reported. This can be explained by the shadowing of the pure soft mode by its interaction with other photoinduced modes.
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Chen, Tao, Songbai Xue, Bo Wang, Peizhuo Zhai i Weimin Long. "Study on Short-Circuiting GMAW Pool Behavior and Microstructure of the Weld with Different Waveform Control Methods". Metals 9, nr 12 (7.12.2019): 1326. http://dx.doi.org/10.3390/met9121326.
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In order to study internal relation among the behavior of the weld pool, the microstructure of weld bead and the waveform of short-circuiting gas metal arc welding (S-GMAW), a high speed photograph-images analysis system was formed to extract characteristics of weld pool behavior. Three representative waveform control methods were used to provide partly and fully penetrated weld pools and beads. It was found that the behavior of the weld pool was related to the instantaneous power density of the liquid bridge at the break-up time. Weld pool oscillation was triggered by the explosion of the liquid bridge, the natural oscillation frequencies were derived by the continuous wavelet transform. The change of weld pool state caused the transition of oscillation mode, and it led to different nature oscillation frequencies between partial and full penetration. Slags flow pattern could be an indication of the weld pool flow. Compared with the scattered slags on fully penetrated weld pool, slag particles accumulated on partially penetrated weld pools. The oscillating promoted the convection of the welding pool and resulted in larger melting width and depth, the grain size, and the content of pro-eutectoid ferrite in the weld microstructure of S235JR increased, the content of acicular ferrite decreased.
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Nabatian, Negar, Xiaofei Xu i Njuki Mureithi. "POD ANALYSIS OF THREE-DIMENSIONAL HARMONICALLY FORCED WAKE FLOW OF A CIRCULAR CYLINDER". Transactions of the Canadian Society for Mechanical Engineering 39, nr 4 (grudzień 2015): 789–803. http://dx.doi.org/10.1139/tcsme-2015-0063.
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A 3D numerical simulation of a circular cylinder wake is presented in this paper. The cylinder is harmonically forced in the stream-wise direction. The objective of the present work is to investigate the effect of the oscillation amplitude on the secondary transition of the wake. The frequency of the lift force is then linked to the form of the vortex shedding mode. The relation between these vortex shedding modes using POD analysis of the transverse velocity and the unsteady lift coefficient of 3D simulation is in good agreement with the 2D model. Results show that the 3D spanwise effect, which can change the wake structure, is suppressed at Re = 200 by streamwise oscillation of the cylinder. Thus the 2D analysis can effectively model the temporal instability of the wake flow.
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Hud, V., I. Hevko, O. Lyashuk, O. Hevko, I. Shust i M. Sokol. "Research of resonance vibrations of the system «Telescopic screw — bulk medium» caused by torsional vibrations". Bulletin of the Karaganda University. "Physics" Series 98, nr 2 (30.06.2020): 119–26. http://dx.doi.org/10.31489/2020ph2/119-126.
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The article outlines the relevance of using the principle of telescopy in the process of creation screw conveyors, which nowadays are folded to obtain significant lengths, which makes their designs expensive and structurally unreasonably complicated. It has been shown an experimental equipment, which provides measurement results of the research process in a wide range with high accuracy in an automated control mode with the necessary data capture. Based on the constructed mathematical model, the dependences of the angular perturbation velocity on the physicomechanical and geometric parameters of the «telescopic screw — bulk medium» system have been obtained. Because of analytical relations describing the laws of variation of characteristic parameters for its oscillation resonance case have been received. It has been proved that for resonant oscillations, when there are significant angular velocities of rotation, the natural frequency of the bending oscillations is smaller and at the same time the amplitude of the transition through the resonance is smaller. The results of the amplitude of the transverse oscillations of the system for different values of the angular velocity of rotation in time during the transition through the internal resonance, which largely depends on the physicomechanical and geometric characteristics of the motion of the medium, have been presented.
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Anwar, Muhammad Usman, Maha M. A. Lashin, Niaz B. Khan, Adnan Munir, Mohammed Jameel, Riaz Muhammad, Kamel Guedri i Ahmed M. Galal. "Effect of Variation in the Mass Ratio on Vortex-Induced Vibration of a Circular Cylinder in Crossflow Direction at Reynold Number = 104: A Numerical Study Using RANS Model". Journal of Marine Science and Engineering 10, nr 8 (17.08.2022): 1126. http://dx.doi.org/10.3390/jmse10081126.
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This study reports on the numerical analysis of the impact of mass ratio on the Vortex-Induced Vibration (VIV) phenomenon of an elastically rigid cylinder, oscillating freely in a crossflow direction. Reynolds-averaged Navier–Stokes (RANS) equations with (k-ω SST) model were used to analyze the flow behavior, amplitude ratio and vortex shedding patterns. The study was performed at constant Reynold number (Re) = 104 with reduced velocity (Ur) ranging from 2 to 14 and mass ratio (m*) of 2.4 and 11. The mass ratio was defined as the ratio between mass of the vibrating cylinder and mass of the fluid displaced. It was found that increasing the mass ratio from 2.4 to 11 resulted in decrease in amplitude response by 80%, 71% and 31% at initial branch, upper to lower transition region and lower branch, respectively. However, the amplitude in the upper branch decreased only 8% at high mass ratio. The peak amplitude observed in the present study was lower than previous experimental and DES results. However, the RANS k-ω SST well captured the vortex shedding modes of 2S, 2P, P + S, and 2T. In 2S mode, two single pairs of vortices were formed, whereas in 2P mode two pairs were generated in single oscillation. Similarly, P + S meant one pair and one individual vortex; whereas 2T mode meant two triplets of vortices generated in one oscillation. The study concluded that increase in mass ratio results in shortening of the lock-in region and decrease in amplitude response.
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Dyks, J., P. Weltevrede i C. Ilie. "Circular polarization in radio pulsar PSR B1451−68: coherent mode transitions and intrabeam interference". Monthly Notices of the Royal Astronomical Society 501, nr 2 (4.12.2020): 2156–73. http://dx.doi.org/10.1093/mnras/staa3762.
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ABSTRACT The radio emission of pulsar B1451−68 contains two polarization modes of similar strength, which produce two clear orthogonal polarization angle tracks. When viewed on a Poincaré sphere, the emission is composed of two flux patches that rotate meridionally as a function of pulse longitude and pass through the Stokes V poles, which results in transitions between orthogonal polarization modes (OPMs). Moreover, the ratio of power in the patches is inversed once within the profile window. It is shown that the meridional circularization is caused by a coherent OPM transition (COMT) produced by a varying mode ratio at a fixed quarter-wave phase lag. The COMTs may be ubiquitous and difficult to detect in radio pulsar data, because they can leave no trace in polarized fractions and they are described by equation similar to the rotating vector model. The circularization, which coincides with flux minima at lower frequency, requires that profile components are formed by radiation with an oscillation phase that increases with longitude in steps of 90○ per component. The properties can be understood as an interference pattern involving two pairs of linear orthogonal modes (or two non-orthogonal elliptic waves). The frequency-dependent coherent superposition of coplanar oscillations can produce the minima in the pulse profile, and thereby the illusion of components as separate entities. The orthogonally polarized signal that is left after such negative interference explains the enhancement of polarization degree that is commonly observed in the minima between profile components.
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Feszty, D., K. J. Badcock i B. E. Richards. "Utilising CFD in the investigation of high-speed unsteady spiked body flows". Aeronautical Journal 106, nr 1058 (kwiecień 2002): 161–74. http://dx.doi.org/10.1017/s0001924000012963.
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AbstractUnsteady spiked body flows were simulated by a second order time-accurate CFD method. Laminar, axisymmetric flow was considered at Mach 2.21 and Mach 6 freestreams and Reynolds’ numbers based on the blunt body diameter of 0.12 million and 0.13 million, respectively. A spiked forward facing cylinder with spike lengths between LID = 1.00 and LID = 2.40 was used as the model geometry. Following the numerical method’s verification, the individual flow modes of oscillation and pulsation were examined. The frequency of the events was found in good agreement with the experiment, while the pressure amplitudes were overpredicted in the Mach 6 cases. Analysis of the numerical results showed that the oscillation flow mode was driven by a viscous mechanism, whereas the pulsation by an inviscid one. The hysteresis phenomenon in the transition between the two flow modes was predicted qualitatively.
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Zhang, Yin, Guodong Ren, Aatef Hobiny, Bashir Ahmad i Jun Ma. "Mode transition in a memristive dynamical system and its application in image encryption". International Journal of Modern Physics B 34, nr 27 (6.10.2020): 2050244. http://dx.doi.org/10.1142/s0217979220502446.
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Chaotic systems can be used for secure communication and image encryption by applying a variety of encryption algorithms. While most of the low-dimensional chaotic systems and maps can be estimated by using phase reconstruction and thus the safety in signal processing and propagation is attacked. In this paper, an initial-dependent dynamical system, which is developed from the Rössler system by adding memristive function and disturbance function on the memristive variable [Formula: see text], is presented for realizing image encryption and bifurcation analysis is supplied in detail. Time-varying disturbance from sampled variables is applied to control the memristive variable and the dependence of mode oscillation on initial values is enhanced. As a result, the dynamics of this memristive system is switched between different oscillation modes (e.g., periodical to chaotic, chaotic to chaotic) by activating the initial value, memristive gain and disturbance gain, respectively. From a dynamical viewpoint, the involvement of stochastic adjustment on the memristive variable can reset the initial value and then induce time-varying parameter regulation or switch on certain parameter embedded in the memristive nonlinearity and function, and thus the dynamics dependence on the initial setting is enhanced. Standard bifurcation analysis is carried out on this memristive system and then the sampled time series are used for image encryption, furthermore, the reliability for this scheme is discussed and suggestions for further study are supplied in the end.
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Miraval Zanon, A., S. Campana, A. Ridolfi, P. D’Avanzo i F. Ambrosino. "X-ray study of high-and-low luminosity modes and peculiar low-soft-and-hard activity in the transitional pulsar XSS J12270−4859". Astronomy & Astrophysics 635 (marzec 2020): A30. http://dx.doi.org/10.1051/0004-6361/201936356.
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XSS J12270−4859 (henceforth J12270) is the first low-mass X-ray binary to exhibit a transition, taking place at the end of 2012, from an X-ray active state to a radio pulsar state. The X-ray emission based on archival XMM-Newton observations is highly variable, showing rapid variations (∼10 s) from a high X-ray luminosity mode to a low mode and back. A flaring mode has also been observed. X-ray pulsations have been detected during the high mode only. In this work we present two possible interpretations for the rapid swings between the high and low modes. In the first scenario, this phenomenon can be explained by a rapid oscillation between a propeller state and a radio-ejection pulsar state, during which the pulsar wind prevents matter from falling onto the neutron star surface. In the second scenario, a radio pulsar is always active, the intra-binary shock is located just outside the light cylinder in the high mode, while it expands during the low mode. At variance with other transitional pulsars, J12270 shows two instances of the low mode: a low-soft and low-hard mode. Performing an X-ray spectral analysis, we show that the harder component, present in the low-hard spectra, is probably related to the tail of the flare emission. This supports the understanding that the flare mechanism is independent of the high-to-low mode transitions.