Antiphase Oscillations Research Articles

Strong Symmetry Breaking in Coupled, Identical Lengyel–Epstein Oscillators via Folded Singularities

We study pairs of symmetrically coupled, identical Lengyel-Epstein oscillators, where the coupling can be through both the fast and slow variables. We find a plethora of strong symmetry breaking rhythms, in which the two oscillators exhibit qualitatively different oscillations, and their amplitudes differ by as much as an order of magnitude. Analysis of the folded singularities in the coupled system shows that a key folded node, located off the symmetry axis, is the primary mechanism responsible for the strong symmetry breaking. Passage through the neighborhood of this folded node can result in splitting between the amplitudes of the oscillators, in which one is constrained to remain of small amplitude, while the other makes a large-amplitude oscillation or a mixed-mode oscillation. The analysis also reveals an organizing center in parameter space, where the system undergoes an asymmetric canard explosion, in which one oscillator exhibits a sequence of limit cycle canards, over an interval of parameter values centered at the explosion point, while the other oscillator executes small amplitude oscillations. Other folded singularities can also impact properties of the strong symmetry breaking rhythms. We contrast these strong symmetry breaking rhythms with asymmetric rhythms that are close to symmetric states, such as in-phase or anti-phase oscillations. In addition to the symmetry breaking rhythms, we also find an explosion of anti-phase limit cycle canards, which mediates the transition from small-amplitude, anti-phase oscillations to large-amplitude, anti-phase oscillations.

Signal Enhancement of a Differential Photoacoustic Cell by Connecting the Microphones via Capillaries.

Differential photoacoustic spectroscopy (DPAS) cells are usually excited on the first longitudinal ring mode, with a microphone situated in the middle of each of the two resonator tubes. However, it is known from other photoacoustic spectroscopy cell designs that connecting the microphones via a capillary can lead to signal enhancement. By means of finite element method (FEM) simulations, we compared such a photoacoustic spectroscopy (PAS) cell with a capillary to a DPAS cell with a capillary attached to each of the two resonators and showed that the behavior of both systems is qualitatively the same: In both the PAS and the DPAS cell, in-phase and anti-phase oscillations of the coupled system (resonator-capillary) can be excited. In the DPAS cell, capillaries of suitable length also increase the pressure signal at the microphones according to the FEM simulations. For different capillary diameters (1.2 mm/1.7 mm/2.2 mm), the respective optimal capillary length (36-37.5 mm) and signal amplification was determined (94%, 70%, 53%). According to the results of these FEM simulations, a significant increase in sensitivity can, therefore, also be achieved in DPAS cells by expanding them with thin tubes leading to the microphones.

Bistable dual cantilever flutter for potential wind energy harvesting applications

This paper examines the potential of bistable dual cantilever flutter (DCF) for wind energy harvesting applications. Two cantilever beams were placed side by side and perpendicular to the direction of the wind flow to create a unique phenomenon known as the DCF. Similar pole magnets were then attached to the free end of each beam to establish a bistable condition. A theoretical model was presented and was shown to agree well with the experimental measurement. The mass of the magnets caused the frequency of the beams to drop by approximately 4.5 times compared to the monostable DCF. When the two beams were placed 21.0 mm apart, the bistable beams achieved a stable state at a critical flutter speed of 5.3 ms−1 and displayed significantly large, anti-phase oscillations that is approximately three times larger than the monostable DCF. Further increase in this distance showed a decreasing trend with the critical flutter speed, which opposes the expected trend of the monostable DCF. Due to the bistable effect, significant flutter amplitudes were also obtained during a backward sweep when the wind speeds were incrementally reduced from high to low, recording a 73.2 % increase in bandwidth for one of the tested cases. This suggests the possibility of an ultra-wide bandwidth energy harvester. Finally, it was shown that the piezoelectric conversion method is more favourable for the bistable DCF whereas electromagnetic induction is preferred for the monostable DCF.

Weakly nonlinear analysis on synchronization and oscillation quenching of coupled mechanical oscillators

Various oscillatory phenomena occur in the world. Because some are associated with abnormal states (e.g. epilepsy), it is important to establish ways to terminate oscillations by external stimuli. However, despite the prior development of techniques for stabilizing unstable oscillations, relatively few studies address the transition from oscillatory to resting state in nonlinear dynamics. This study mainly analyzes the oscillation-quenching of metronomes on a platform as an example of such transitions. To facilitate the analysis, we describe the impulsive force (escapement mechanism) of a metronome by a fifth-order polynomial. By performing both averaging approximation and numerical simulation, we obtain a phase diagram for synchronization and oscillation quenching. We find that quenching occurs when the feedback to the oscillator increases, which will help explore the general principle regarding the state transition from oscillatory to resting state. We also numerically investigate the bifurcation of out-of-phase synchronization and beat-like solution. Despite the simplicity, our model successfully reproduces essential phenomena in interacting mechanical clocks, such as the bistability of in-phase and anti-phase synchrony and oscillation quenching occurring for a large mass ratio between the oscillator and the platform. We believe that our simple model will contribute to future analyses of other dynamics of mechanical clocks.

Sensory processing in humans and mice fluctuates between external and internal modes.

Perception is known to cycle through periods of enhanced and reduced sensitivity to external information. Here, we asked whether such slow fluctuations arise as a noise-related epiphenomenon of limited processing capacity or, alternatively, represent a structured mechanism of perceptual inference. Using 2 large-scale datasets, we found that humans and mice alternate between externally and internally oriented modes of sensory analysis. During external mode, perception aligns more closely with the external sensory information, whereas internal mode is characterized by enhanced biases toward perceptual history. Computational modeling indicated that dynamic changes in mode are enabled by 2 interlinked factors: (i) the integration of subsequent inputs over time and (ii) slow antiphase oscillations in the impact of external sensory information versus internal predictions that are provided by perceptual history. We propose that between-mode fluctuations generate unambiguous error signals that enable optimal inference in volatile environments.

Anomalies of Thermal Fields Revealed by Satellite Data during Preparatio n and Occurrence of Strong Earthquakes in the Region of the Baikal Rift Zone in 2008–2022

Long-term changes in thermal fields were studied before and during strong earthquakes with magnitudes from 5.1 to 5.6 that occurred in the region of the Baikal rift zone in 2008–2022. Satellite data were used for these studies. For the analysis we used the values of land surface temperature, temperature of the near-surface layer of the atmosphere, outgoing long-wave radiation, and relative humidity recorded using the AIRS instrument mounted on the Aqua satellite. During the periods of preparation and occurrence of these seismic events, anomalous variations in the parameters of thermal fields registered with satellite were revealed. They exceeded the average long-term values: for land surface temperature and temperature of the near-surface layer of the atmosphere by 5–10%, for outgoing long-wave radiation by 11–15%, and for relative humidity by 6–10%. A strong negative correlation was found between changes in the temperature of the near-surface layer of the atmosphere and relative humidity (correlation coefficient of –0.75), as well as antiphase oscillations between the values of the outgoing long-wave radiation and relative humidity. The obtained results can be used for studies of the precursor variability of thermal fields during monitoring of seismic hazard zones.

Nonlinear Rigid-Elastic Coupled Modeling and Oscillation Mechanism Analysis of Rotor-Body-Slung-Load System

In order to reveal the mechanism of Category II rotor-body-slung-load coupled oscillation (RBSLCO) with the frequency range of 2.5~8 Hz, a novel nonlinear rigid-elastic coupled model is presented for the helicopter and slung load system (HSLS) with explicit formulation. The slung load system model is coupled with the current rigid-elastic coupled helicopter model, considering fuselage hook point rigid-elastic coupled movements, cable stretching, and hook point force from the slung load system. The results show that carrying the heaviest load is the vital state for Category II RBSLCO. As slung load mass ratio increases, rotor-fuselage coupling becomes stronger and the oscillation frequency shifts slightly, causing a maximum of 15% reduction in stability margin. In addition, even when the load is lightweight, another form of Category II RBSLCO may appear involving fuselage bending and cable stretching. This Category II RBSLCO behaves like the vertical bouncing but is divided into a high-frequency anti-phase oscillation and a relatively low-frequency in-phase oscillation.

Nanoscale Quantized Oscillations in Thin‐Film Growth Greatly Enhance Transconductance in Organic Transistors

AbstractA growth mode of pentacene thin films deposited by high vacuum sublimation where the morphology versus thickness h “rings” back and forth between rough 3D films with pyramid islands and smooth 2D films with ziqqurat islands is discovered. The roughness σ versus h exhibits seamless coherent oscillations whose amplitude and wavelength increase as integer multiples of 1.5 ML thickness. The quantized oscillations are reconducted to dynamic wetting/dewetting transitions involving the upper layers of pentacene film. Importantly, the transconductance of organic field effect transistors, either in solid state or electrolyte‐gated, exhibits antiphase oscillations with one‐decade swing. Charge mobilities in the wetting regime reach 0.1 cm2 V−1 s−1, in line with high‐end values reported for thin‐film pentacene transistors. Controlling this growth mode enables the limitations of charge transport imposed by the roughening transition to be overcome, a universal feature of high vacuum growth to date.

Phase-resolved frequency-domain analysis of the photoemission spectra for photoexcited 1T-TaS2 in the Mott insulating charge density wave state

We investigate the nonequilibrium electronic structure of 1T-TaS2 by time- and angle-resolved photoemission spectroscopy. We observe that strong photoexcitation induces the collapse of the Mott gap, leading to the photo-induced metallic phase. It is also found that the oscillation of photoemission intensity occurs as a result of the excitations of coherent phonons corresponding to the amplitude mode of the charge density wave (CDW). To study the dynamical change in the band dispersions modulated by the CDW amplitude mode, we perform analyses by using frequency-domain angle-resolved photoemission spectroscopy (FDARPES). We find that two different peak structures exhibit anti-phase oscillation with respect to each other by retrieving the amplitude and phase parts of the FDARPES spectra. They are attributed to the minimum and maximum band positions in energy, where the single band is oscillating between them synchronizing with the CDW amplitude mode. We further find that the flatband constructed as a result of CDW band folding survives during the oscillation while the Mott gap is significantly reduced. Our results suggest the CDW phase is robust, and the lattice modulation corresponding to the CDW amplitude mode dynamically modulates the Mott gap.

Sea level variation in the Arctic Ocean since 1979 based on ORAS5 data

The Arctic is currently experiencing unprecedented changes across all components of the climate system, primarily driven by global warming. As an important indicator of climate change in the Arctic, sea level reflects variations in both the atmosphere and ocean. This paper analyzes the sea level variation of the Arctic Ocean over the past four decades using ORAS5 data, which is the product of the latest reanalysis-analysis system produced by the European Centre for Medium-Range Weather Forecasts (ECMWF). ORAS5 accurately reproduces the main spatial features of the climatology and temporal evolution of sea surface height (SSH) in the Arctic Ocean, as observed by satellite altimeters, and reveals that seasonal variability is the most significant property of the sea level variation in this region. The seasonal cycle of SSH is closely linked to atmospheric circulation and sea ice formation. The first two dominant modes of the annual-mean SSH in the Arctic Ocean exhibit significant decadal variability. The first mode can be explained by the Ekman transport of wind related to the Arctic Oscillation (AO), which leads to antiphase changes in SSH on the continental shelves and in the deep basins. The second mode shows an antiphase oscillation of SSH between the Eurasian and Canadian Arctic Archipelago (CAA) sides and is driven by the wind anomaly associated with the Arctic dipole anomaly (DA). Due to the decadal variations associated with climate modes, particularly the AO, sea level in the Arctic Ocean has been continuously rising since the mid-1990s or early 2000s, with the most rapid sea level rise occurring in the Beaufort Sea.

Chaotic chimera attractors in a triangular network of identical oscillators.

A prominent type of collective dynamics in networks of coupled oscillators is the coexistence of coherently and incoherently oscillating domains known as chimera states. Chimera states exhibit various macroscopic dynamics with different motions of the Kuramoto order parameter. Stationary, periodic and quasiperiodic chimeras are known to occur in two-population networks of identical phase oscillators. In a three-population network of identical Kuramoto-Sakaguchi phase oscillators, stationary and periodic symmetric chimeras were previously studied on a reduced manifold in which two populations behaved identically [Phys. Rev. E 82, 016216 (2010)1539-375510.1103/PhysRevE.82.016216]. In this paper, we study the full phase space dynamics of such three-population networks. We demonstrate the existence of macroscopic chaotic chimera attractors that exhibit aperiodic antiphase dynamics of the order parameters. We observe these chaotic chimera states in both finite-sized systems and the thermodynamic limit outside the Ott-Antonsen manifold. The chaotic chimera states coexist with a stable chimera solution on the Ott-Antonsen manifold that displays periodic antiphase oscillation of the two incoherent populations and with a symmetric stationary chimera solution, resulting in tristability of chimera states. Of these three coexisting chimera states, only the symmetric stationary chimera solution exists in the symmetry-reduced manifold.

Intermittent swimming of two self-propelled flexible fins with laterally constrained heaving motions in a side-by-side configuration

Inspired by the intermittent locomotion of fish schools, numerical simulations are performed with two self-propelled flexible fins in a side-by-side configuration with anti-phase oscillation actuated by laterally constrained heaving motions. For an intermittent swimming gait, one type of the half-tail-beating mode (HT mode) and two types of multiple-tail-beating modes coasting at the smallest (MTS mode) and largest (MTL mode) lateral gap distances are applied. Similar to the continuous-tail-beating mode (CT mode), equilibrium lateral gap distances between two fins with HT and MTL modes exist, whereas two fins with MTS mode do not maintain a lateral equilibrium state. Although the cycle-averaged lateral force acting on two fins with CT and MTL modes is mostly determined by an outward deflected jet and enhanced positive pressure between two fins, an added-mass lateral force related to an asymmetric flapping kinematics by passive flexibility also plays an important role in MTL mode to achieve a stable state with a lateral gap distance smaller than that in CT mode. When the cruising speed or the cycle-averaged input power is identical in a stable state, the cost of transport (COT) for two fins with MTL mode is smaller than that with CT mode due to not only a benefit from the intermittent swimming gait but also an enhanced schooling benefit with a small equilibrium lateral gap distance. The COT for two fins with CT mode is reduced further when the bending rigidity increases, whereas it is opposite with MTL mode.

Observation of hydrodynamic plasmons and energy waves in graphene.

Thermally excited electrons and holes form a quantum-critical Dirac fluid in ultraclean graphene and their electrodynamic responses are described by a universal hydrodynamic theory. The hydrodynamic Dirac fluid can host intriguing collective excitations distinctively different from those in a Fermi liquid1-4. Here we report the observation of the hydrodynamic plasmon and energy wave in ultraclean graphene. We use the on-chip terahertz (THz) spectroscopy technique to measure the THz absorption spectra of a graphene microribbon as well as the propagation of the energy wave in graphene close to charge neutrality. We observe a prominent high-frequency hydrodynamic bipolar-plasmon resonance and a weaker low-frequency energy-wave resonance of the Dirac fluid in ultraclean graphene. The hydrodynamic bipolar plasmon is characterized by the antiphase oscillation of massless electrons and holes in graphene. The hydrodynamic energy wave is an electron-hole sound mode with both charge carriers oscillating in phase and moving together. The spatial-temporal imaging technique shows that the energy wave propagates at a characteristic speed of [Formula: see text] near the charge neutrality2-4. Our observations open new opportunities to explore collective hydrodynamic excitations in graphene systems.

Collective excitations in three-band superconductors

We investigate equilibrium states, magnetic response and the normal oscillations of internal degrees of freedom (Higgs modes and Goldstone modes) of three-band superconductors accounting the terms of both internal proximity effect and the ``drag'' effect (intergradient interaction) in the Lagrangian. Both the Goldstone mode and the Higgs mode are split into three branches each: common mode oscillations and two modes of anti-phase oscillations, which are analogous to the Leggett mode in two-band superconductors. It is demonstrated that the second and third branches are nonphysical, and they can be removed by special choice of coefficients at the ``drag'' terms in Lagrangian. As a result, three-band superconductors are characterized by only single coherence length. Spectrum of the common mode Higgs oscillations has been obtained. The magnetic penetration depth is determined with densities of superconducting electrons in each band, although the drag terms renormalize the carrier masses.

Interaction of vibroimpact lattice and screen sieve in anti-phase oscillation mode

Introduction. One of basic technological operations in construction technology is a process of classification of fine grained mineral materials, for example, natural sand. The related actual problem is connected with increasing performance and effectiveness of screening of sand medium, in particular reducing the contamination of screening surface of vibrating screens from seal particles and sticking in sieve holes wedge-shaped grains. The solution of this problem concludes in performing by the use of vibroimpact screens of various operating principle. One of innovative vibroimpact screen constructions is a screen with vibroimpact lattice, mounted under sieve with a gap on spring elements, which provides an impulse impact on all sieve surface area. Such construction provides increasing the effectiveness of sieve cleaning due to the transfer to sieve impact impulse in each screen oscillation period and reducing its excessive damage and abrasion by increasing the area of vibroimpact lattice and sieve interaction. The purpose of the work is to determinate functional relationships of dynamical interaction between elements of three-mass vibroimpact ‘screen body – vibroimpact lattice – sieve’ system for providing the necessary value of impact impulse transferred to sieve in relation to screen body oscillation frequency and amount of gap between lattice and sieve.Materials and methods. The research is based on a method of mathematical modelling. On the first stage the research is being conducted with using two-mass ‘screen body – vibroimpact lattice’ model without consideration the impact between lattice and sieve for determination the oscillation frequency range of in-phase oscillation regime and gap values providing an impact between lattice and sieve. For the calculation of displacement of screen elements and for research the relationships of its parameters in selected range the three-mass model of vibroimpact model of screen with one impact pair is used on a second stage of research.Results. As a result of calculation obtained the functional relationships of correlation of the gap between vibroimpact lattice and screen sieve and oscillation frequency on the impact impulse transferred to sieve and sieve double amplitude were obtained. The developed recommendations for practical using of obtained relationships for adjustment operating regimes of vibroimpact screen which allow to establish the screen operating oscillation frequency and value of gap between lattice and sieve for providing high effectiveness of sieve holes cleaning from contaminating particles.Discussion and Conclusions. Performed mathematical modelling allowed to obtain dependencies of influence of gap between sieve and vibroimpact lattice and screen elements oscillation frequency on impulse transferred on screen sieve and sieve double amplitude. Developed practical recommendations of obtained dependencies allow to perform an effective adjustment of vibroimpact screen operating regimes and reduce the labor intensity of works being performed during its starting-up and maintenance.

Определениe рациональных режимных параметров виброударного грохота

The paper deals with the problem of vibroimpact screen operating regimes selection for the regime of anti-phase oscillations of its elements. The criteria of effective screen operation accepted are impact impulse transferred to sieve from vibroimpact lattice and sieve double amplitude, which provide effective regimes of sieve cleaning from clogging particles and maintenance of preset sieve oscillations regime for support of technological parameters of material screening. Using the developed mathematical model and program the computational experiment was conducted for operating oscillation frequency range from 105 rad/s to 160 rad/s and adjustment gap between vibroimpact lattice and sieve for operating range from 0 to 5,5 mm. Influences of oscillation frequency and adjustment gap on impact impulse transferred to sieve and sieve double amplitude are obtained in the form of regression equations. On its base the recommendations for determining effective operating regimes of vibroimpact screen are offered. Obtained regularities explain nonlinear behavior of two-mass vibroimpulse oscillating system according to its operating parameters changing and show principal opportunities of system control. Also obtained results could find an application in screen operating regimes adjustment during commissioning and start-up operation and screen operation period, and could decrease labor costs and fasten the procedure of rational screen operating parameters searching.

Phase-flip transition in volume-mismatched pairs of coupled 1-pentanol drops.

We have explored a variety of synchronization domains and observed phase-flip transition in a pair of coupled 1-pentanol drops as a function of the volume mismatch. Both experimental observations and numerical studies are presented. The experiments were carried out in a rectangular channel in a ferroin deionized water solution premixed with some volume of pentanol. A single pentanol drop (≥3μL) performs back and forth oscillations along the length of the channel due to the well-known Marangoni forces. In the present work, for a pair of drops, the drop 1 volume was changed from 3 to 5 μL in steps of 1μL, whereas the drop 2 volume was varied from 1 to 3 μL in steps of 0.5μL. A systematic investigation of all the possible combinations of the drop volumes showed the presence of three different types of synchrony-in-phase, antiphase, and phase-switched. In-phase synchronization was robust for a volume mismatch of >3.0μL between the two drops. On the other hand, antiphase synchronization was robust when the volume mismatch was <2.0μL. The phase-switched state is a synchronized state involving a phase-flip transition in the time domain. This state was observed for the intermediate range of volume mismatch. Numerically, the system has been investigated using two Stuart-Landau oscillators interacting via a coupling function in the form of Lennard-Jones potential. The numerical results suitably capture both in-phase and antiphase oscillations for a pair of volume-mismatched pentanol drops.

Mixing in arrays of villi-like actuators

This paper is concerned with computational modeling of fluid mixing by arrays of villi-like actuators. There are numerous applications of such actuators motivated by the motility and mixing induced by natural villi in the small intestine, such as microbial fuel cells and swimming robots—understanding how mixing occurs from viscous-dominated to inertia-dominated flows is paramount. Here, we analyze mixing in two-dimensional arrays of actuators, where neighboring actuators perform in-phase or anti-phase oscillations. We show that in both these cases, the temporal behavior becomes progressively more complex as inertia, or the Reynolds number, is increased. This behavior is classified into three regimes or stages with distinct behaviors and flow structures. We show that mixing can be substantially enhanced in the direction parallel to the wall the actuators are mounted on. We show this mixing is effectively constrained to a peripheral region or layer above the actuator tips. This layer is thicker in the anti-phase case than the in-phase case; however, in both cases this layer thickness saturates at high Reynolds number. Particle tracking results are used to define a mixing number, which shows the anti-phase pattern to be the most effective at mixing both along and across this peripheral layer, and this is linked to the flow structures generated in each stage. Our results provide a map for a range of behaviors that can be achieved through coordinated active motions of villi-like structures that we hope will be useful for the design of future robotics and fluidic-control systems.

Guidance of the resonance energy flow in the mechanism of coupled magnetic pendulums

This paper presents a methodology of controlling the resonance energy exchange in mechanical system consisting of two weakly coupled magnetic pendulums interacting with the magnetic field generated by coils placed underneath. It is shown that properly guided magnetic fields can effectively change mechanical potentials in a way that the energy flow between the oscillators takes the desired direction. Studies were considered by using a specific set of descriptive functions characterizing the total excitation level, its distribution between the pendulums, and the phase shift. The developed control strategies are based on the observation that, in the case of antiphase oscillation, the energy is moving from the pendulum subjected to the repelling magnetic field, to the oscillator under the attracting field. In contrast, during the inphase oscillations, the energy flow is reversed. Therefore, closed-loop controller requires only the information about phase shift, which is easily estimated from dynamic state signals through the coherency index. Advantage of suggested control strategy is that the temporal rate of inputs is dictated by the speed of beating, which is relatively slow compared to the carrying oscillations.

Устойчивые и неустойчивые динамические процессы в автоколебательной системе с тремя степенями свободы

The work is devoted to the study of the dynamic instability of coherent regimes of a system of two self-oscillators with a strong mutual resonant coupling. It is shown that this system can generate synchronous oscillations at three different frequencies, they correspond to the basic types of oscillations-modes: one in-phase and two anti-phase. A qualitative analysis of the influence of the characteristics of the resonant coupling on the stability of natural synchronous modes of oscillations has been carried out. An analytical criterion for the instability of in-phase oscillations and the conditions for its fulfillment are considered. The possibility of suppressing the stability of antiphase oscillations is discussed. The method of numerical simulation was used to study the temporal and spectral characteristics of oscillatory processes in various modes, including chaotic. Variants of the system behavior under competition and mode suppression accompanied by self-modulation processes are demonstrated. The features of dynamic chaos tuning and diagnostics of its components are discussed. The possibility of obtaining chaotic signals with a continuous spectrum in a band exceeding an octave is shown.