Oscillatory Instability Research Articles

Bimodal Photothermal-driven Self-sustained Oscillator Based on MXene Structure

Soft robots capable of autonomous, continuous, fast, and adjustable motion speeds under constant external stimuli have great potential in environmental, industrial, military, and medical fields. Aiming at the difficulties of existing self-oscillators, including small oscillation range, difficulty of achieving non-reciprocal motion, and the slow forward speed of the resulting self-sustained soft robots. In this paper, a sunlight-driven self-oscillator based on MXene is prepared. By employing a bimorph structure and thermal regulation process, the self-oscillator exhibits two distinct oscillation modes: 'elastic' and 'plastic' deformation. These modes can be modulated within the same film by varying the light power. A broader amplitude range (3.6-302.3°, 3.3 times that of the existing studies) is achieved by attaching a load to the film's end to enhance the inertial force of movement. Non-reciprocal motion in both modes and stable oscillations in sunlight are achieved. Finally, a light-driven sailboat model is developed. The sailboat can achieve autonomous light-forward motion with a speed of up to 12.8 body length per minute (2.1 times that of existing studies), with its propulsion mechanism further explained through numerical simulation results. This research provides new strategies for constructing fast and large-amplitude self-oscillators and demonstrates the potential for applications in speed-adjustable autonomous forward devices.

Wind Velocity Induced Stable and Unstable Periodic Oscillations in a Harmonically Excited Aeroelastic Energy Harvester

Wind Velocity Induced Stable and Unstable Periodic Oscillations in a Harmonically Excited Aeroelastic Energy Harvester

An amplitude equation for the conserved-Hopf bifurcation-Derivation, analysis, and assessment.

We employ weakly nonlinear theory to derive an amplitude equation for the conserved-Hopf instability, i.e., a generic large-scale oscillatory instability for systems with two conservation laws. The resulting equation represents in the conserved case the equivalent of the complex Ginzburg-Landau equation obtained in the nonconserved case as an amplitude equation for the standard Hopf bifurcation. Considering first the case of a relatively simple symmetric two-component Cahn-Hilliard model with purely nonreciprocal coupling, we derive the nonlinear nonlocal amplitude equation with real coefficients and show that its bifurcation diagram and time evolution well agree with the results for the full model. The solutions of the amplitude equation and their stability are analytically obtained, thereby showing that in such oscillatory phase separation, the suppression of coarsening is universal. Second, we lift the two restrictions and obtain the amplitude equation in the generic case. It has complex coefficients and also shows very good agreement with the full model as exemplified for some transient dynamics that converges to traveling wave states.

Noise-to-State Stability of Random Coupled Kuramoto Oscillators via Feedback Control

This paper is intended to study noise-to-state stability in probability (NSSP) for random coupled Kuramoto oscillators with input control (RCKOIC). A feedback control is designed, which makes us give the existence and uniqueness of a solution for RCKOIC. Based on Kirchhoff’s matrix tree theorem in graph theory, an original and appropriate Lyapunov function for RCKOIC is established. With the help of the Lyapunov method and by resorting to some analysis skills, NSSP for RCKOIC with an arbitrarily coupled topological structure and second-order moment process stochastic disturbance is acquired. Finally, the effectiveness of the obtained results is verified by a numerical test and its simulation process.

CSIG-11. TUMOR-CELL INTRINSIC CALCIUM OSCILLATIONS DRIVE BRAIN METASTASIS

Abstract Calcium is a ubiquitous secondary messenger which regulates many cellular processes. Recently, we have shown that a subpopulation of glioblastoma cells can intrinsically generate calcium oscillations which drive proliferative signalling. Here, we set out to investigate whether such cancer cell autonomous oscillations are also present in secondary brain tumours. Employing longitudinal intravital two-photon microscopy in awake mice, we demonstrate that brain metastases of melanoma and lung cancer exhibit spontaneous calcium oscillations in vivo along the metastatic cascade. These oscillations are already observed during intravascular arrest and in in vitro monocultures, suggesting a tumour-cell intrinsic origin. We developed a fully automatic image analysis pipeline to accurately quantify calcium oscillations both in vivo and in vitro. Mathematical modelling of cytosolic and ER calcium stores can predict stable calcium oscillations with similar frequency and peak characteristics as those experimentally observed. We discovered that these oscillations are tightly regulated by an interplay of calcium-induced calcium release and store-operated calcium entry (SOCE). Similarly, SOCE-related ion channels are enriched in tissue from human melanoma brain metastases compared to healthy brain controls and calcium activity can also be observed ex vivo in patient-derived brain metastasis resections. Finally, by correlating calcium activity and EdU incorporation we discovered that the presence of calcium oscillations predicts their proliferative potential in vitro. Importantly, by intravital two-photon microscopy we show that calcium activity correlates with metastasis size in preclinical models, suggesting a potential new therapeutic angle from which to target brain metastases.

Experimental Study on Heat Transfer Characteristics of a ⊥-shaped Oscillating Heat Pipe Used in the Battery Thermal Management System

This paper introduces a ⊥-shaped oscillating heat pipe (OHP) with the purpose of improving the volumetric utilization of the battery thermal management system (BTMS) for electric vehicles. Distinguished from standard OHP structures, the evaporator and condenser sections of the ⊥-shaped OHP are oriented vertically in spatial arrangement. Experimental investigations were conducted on two types of ⊥-shaped OHPs and a standard OHP, employing filling ratios from 13.1% to 32.6%, working fluid mixtures of acetone with methanol, ethanol, and water, and thermal loads from 10 to 100W. The results indicate that all the OHPs with an acetone filling ratio of 19.6% exhibit minimum thermal resistance at 30W. When employing mixed working fluids, the acetone-ethanol and acetone-methanol combinations display the least and most temperature fluctuations, respectively. The OHP with mixed working fluids achieves no more improved thermal performance than the use of acetone. As the heating power increases, the operational stability of the ⊥-type OHP improves, however, the trend is opposite for the R-⊥-type OHP. In comparison to the standard OHP, the ⊥-type OHP demonstrates stronger oscillation stability at 100W and achieves a 3.3°C lower maximum temperature on the heat collector plate.

Stable and wideband-tunable optoelectronic oscillator utilizing a narrow-passband microwave photonic filter

Stable and wideband-tunable optoelectronic oscillator utilizing a narrow-passband microwave photonic filter

Evaluation of the Heat Transfer Performance of a Device Utilizing an Asymmetric Pulsating Heat Pipe Structure Based on Global and Local Analysis

PHPs (pulsating heat pipes) are widely used as an efficient heat transfer element in equipment thermal management and waste heat recovery due to their flexibility. The purpose of this study was to design a heat transfer device that utilizes an asymmetric pulsating heat pipe structure by adjusting the lengths of selected pipes within the entire circulation pipeline. In the experiment, a constant temperature water bath was used as the heat source, with heat dissipated in the condensing section via natural convection. An infrared thermal imager was used to record the temperature of the condensing section, and the local wall temperature distribution was measured in different channels of the condensing section. Based on an in-depth analysis of the wavelet frequency, the following research conclusions are drawn: Firstly, as the heat source temperature increases, the start-up time of the pulsating heat pipe is shortened, the operating state changes from start–stop–start to stable and continuous oscillation, and the oscillation mode changes from high amplitude and low frequency to low amplitude and high frequency. These changes are especially pronounced when the heat source temperature is 80 °C, which is when the thermal resistance reaches its lowest value of 0.0074 K/W, and the equivalent thermal conductivity reaches its highest value of 666.29 W/(m·K). Secondly, the flow and oscillation of the working fluid can be effectively promoted by appropriately shortening the length of the condensing section of the pulsating heat pipes or the heat transfer distance between the evaporation and condensing sections. Third, under a low-temperature heat source, the oscillation frequency of each channel of a pulsating heat pipe is found to be low based on wavelet analysis. However, as the heat source temperature increases, the energy content of the temperature signal of the working fluid in each channel changes from a low- to a high-frequency value, gradually converging to the same characteristic frequency. At this point, the working fluid in the pipes no longer flows randomly in multiple directions but rather in a single direction. Finally, we determined that the maximum oscillation frequency of working fluid in a PHP is around 0.7 HZ when using the water bath heating method.

Antiferromagnetic–ferromagnetic heterostructure-based spin Hall nano-oscillator

Spin oscillators relying on ferromagnetic (FM) materials have been limited to frequency generation in the range of only a few gigahertz. In contrast, antiferromagnetic (AFM) material-based oscillators have a potential for beyond gigahertz range oscillations. However, the use of AFM oscillators is limited due to challenges in detecting and controlling magnetic orientation. This arises from the inherent lack of significant net magnetization in AFMs. This work focuses on exploring the dynamic characteristics of a spin Hall nano-oscillator (SHNO) that addresses these challenges by leveraging the inter-layer exchange interaction between AFM and FM layers. The proposed design demonstrates stable and power-efficient oscillation in the FM layer, relying on the dynamics of the AFM layer. The proposed AFM–FM-based SHNO design achieves a maximum frequency of 16.4 GHz at ISOT = 180 μA. Furthermore, considering the thermal effects at 300 K, the stable oscillation frequency is achieved at 15.94 GHz. The proposed device exhibits robust and tunable oscillations over a wide frequency range with a power consumption of 4 μW. Moreover, this oscillator achieves 3.35× and 2.44× higher oscillation frequency compared to spin torque nano-oscillators and conventional SHNO-based oscillators, respectively.

Effective mitigation of photodarkening-induced transverse mode instability in a monolithic fiber laser oscillator by 450 nm laser irradiation.

The photodarkening (PD) and transverse mode instability (TMI) effects are two main factors limiting the power increase and long-term stability of high-power fiber lasers. A prolonged burn-in test for an all-fiber laser oscillator below the TMI threshold was carried out. We observed the PD-induced TMI effects, which manifested as a sudden decrease in the output power due to higher-order mode leakage. After several minutes of exposure to a high-power density 450 nm laser diode (LD), the output power returned to its initial state, significantly enhancing the oscillator's stability. The 450 nm LD probably mitigates the accumulation of thermal effects by inhibiting the photodarkening effect, thus preventing the occurrence of the TMI effects and improving the stability of the oscillator's output power. Our work provides useful guidance for the development of high-stability fiber laser oscillators.

Study of immune response in a latent tuberculosis infection model

A simple mathematical model describing the immune response during the stage latent tuberculosis infection is established and analyzed. The main purpose of this study is to explore the sustained immune response of the immune system against invaded Mycobacterium tuberculosis in the stage of latent tuberculosis infection. First, the threshold R0 is defined to determine the occurrence of sustained immune response. Then, stability conditions are derived to show that the sustained immune response may converge to a constant or to a stable periodical oscillation, implying that the Mycobacterium tuberculosis, the infected macrophages, the activated uninfected macrophages, and the immune cells coexist to form the tuberculous granuloma structure. This structure may appear calcified if the system solution converges to a constant, or maintains a dynamic balance if the system solution undergoes a periodical oscillation. These findings well demonstrate the process of sustained immune response in the latent tuberculosis infection as the Mycobacterium tuberculosis is changing. Numerical examples are presented to illustrate the theoretical predictions.

Baleen stable isotopes reveal climate-driven behavioural shifts in North Atlantic fin whales

Climate variability impacts the structure and functioning of marine ecosystems and can trigger behavioural responses in organisms. We investigated whether such variability modulates diet and migration in the North Atlantic fin whale (Balaenoptera physalus). To reconstruct the dietary and migratory behaviours over time, we conducted stable isotope analysis of nitrogen (δ15N) and carbon (δ13C) along baleen plates from 29 fin whales sampled off southwestern (SW) Iceland in summer. We estimated a baleen growth rate of 16.1 ± 2.5 cm per year from the stable isotope oscillations observed along the baleens. We also assigned a deposition date for each baleen segment, thus obtaining isotopic sequential time series. We then assessed the potential association of these time series with the main climate patterns of the North Atlantic basin. Baleen δ15N and δ13C values are associated with the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO). During high AMO and low NAO periods, which tend to decrease krill abundance, there is an increase in both the mean and standard deviation of baleen δ15N values, suggesting that fin whales shift to higher trophic resources and expand their dietary niche. Additionally, high AMO periods, which relate to positive temperature anomalies, lead to a decrease in baleen δ13C values, suggesting that fin whales adjust their migratory routes and destinations towards higher latitudes. Significant variation in isotopic niche width between years also reflected these dietary and migratory behavioural shifts. This highlights the plasticity of the North Atlantic fin whale behaviour, a trait likely to strengthen the resilience of the species within the current context of rapid and intense climate variability.

Mode locking mechanism in Fourier-domain mode-locked optoelectronic oscillators.

Fourier-domain mode-locked (FDML) optoelectronic oscillators (OEOs) are regarded as a promising candidate to generate linearly chirped microwave waveforms (LCMWs) with large time-bandwidth products. Nevertheless, up to date, the mode locking mechanism in FDML-OEOs is still not clear enough. Here, a comprehensive theoretical analysis is made to reveal the mode locking mechanism in FDML-OEOs. In particular, the phase relationship among numerous oscillation modes under stable oscillation is obtained. In addition, the FDML oscillation process originated from either noise or single-mode oscillation and is numerically simulated based on the model. Therefore, the initial oscillation process is comprehensively analyzed in the time domain, the Fourier domain, and the fractional Fourier domain, which provides a deep insight into the FDML oscillation process. Finally, the initial oscillation process of a FDML-OEO is captured in the experiment. The corresponding analysis is carried out to reveal the real mode locking mechanism, where the experimental results fit in with the theoretical and numerical results. This work provides a new approach for in-depth analysis of FDML-OEOs.

Hydrodynamic fluctuations near a Hopf bifurcation: Stochastic onset of vortex shedding behind a circular cylinder.

We investigate hydrodynamic fluctuations in the flow past a circular cylinder near the critical Reynolds number Re_{c} for the onset of vortex shedding. Starting from the fluctuating Navier-Stokes equations, we perform a perturbation expansion around Re_{c} to derive analytical expressions for the statistics of the fluctuating lift force. Molecular-level simulations using the direct simulation Monte Carlo method support the theoretical predictions of the lift power spectrum and amplitude distribution. Notably, we have been able to collect sufficient statistics at distances Re/Re_{c}-1=O(10^{-3}) from the instability that confirm the appearance of non-Gaussian fluctuations, and we observe that they are associated with intermittent vortex shedding. These results emphasize how unavoidable thermal-noise-induced fluctuations become dramatically amplified in the vicinity of oscillatory flow instabilities and that their onset is fundamentally stochastic.

Direct-modulated active mode-locking optoelectronic oscillator for microwave frequency comb signals

Abstract The optoelectronic oscillator (OEO) has been widely investigated to generate ultrapure microwave signals. For many applications, microwave signals with large bandwidth and multiple frequency bands, such as broadband microwave frequency comb (MFC) signals, are also needed. Conventional MFC signals are generated by active mode-locking OEO (AML-OEO) using devices such as Mach–Zehnder modulators (MZM) and delay fibers, which make the system structure more complicated and take a long time to build up stable oscillation at an oscillation mode. In this paper, A direct-modulated AML-OEO (DM-AML-OEO) is demonstrated with the advantages of compact design, cost-effectiveness, and straightforward integration. Mode-locked pulses are generated by direct-modulated Laser Diode (LD) which have low-phase noise. Furthermore, different comb spacings of MFC signals can be readily attained by adjusting the frequency of the active modulation signal (AMS) while supermodels are confined. In the experiments, the DM-AML-OEO produced MFC signals that exhibited a central frequency of 718 MHz and a frequency spacing of 100 kHz.

Oscillatory excitation of Faraday waves on the interface of immiscible fluids in a slotted channel

Recent studies of the oscillatory dynamics of the interface between fluids in Hele–Shaw cells have revealed a new type of instability termed the “oscillatory Saffman instability” in the case of fluids with high-viscosity contrast. The present study is dedicated to the experimental investigation of the dynamics of the interface between low-viscosity fluids of different densities oscillating in a vertical narrow channel. It is discovered that as the amplitude of oscillations increases, a threshold excitation of parametric oscillations of the interface in the form of a standing wave is observed in the plane of the fluid layer. This phenomenon bears a resemblance to Faraday waves, but the dependence of the standing wave wavelength on the oscillation frequency does not align with the classical dispersion relation for low-viscosity fluids. The damping effect of viscous boundary layers near the cell walls and the out-of-plane curvature of the oscillating interface leads to a decrease in the natural frequency of oscillations. The experiments demonstrate a significant role of the dimensionless layer thickness. With its decrease (increase in the dimensionless out-of-plane interface curvature), the threshold oscillation acceleration rises in accordance with a power law. To the best of the authors' knowledge, this type of instability has been discovered and studied for the first time. Another important finding is the excitation of intense time-averaged vortical flows in the channel plane within the supercritical region. The physical mechanism underlying the excitation of the time-averaged vortices is clarified, and the dimensionless parameters that govern their intensity are identified.

Small‐signal stability criterion of the PMSG‐based wind power delivery system via VSC‐HVDC

AbstractThis paper presents an analytical examination of the small‐single stability (SSS) criterion of the permanent magnet synchronous generator (PMSG)‐based wind power delivery system via voltage source converter‐based high voltage direct current (VSC‐HVDC). First, a small‐signal model of the PMSG‐based WPDS is developed. Then, the SSS criterion, driven by the phase‐locked loop of the PMSG in the sub‐synchronous timescale, is derived. The derived SSS criterion provides analytical insights into why and how the loading condition, the grid connection, and the control parameters affect the system’s SSS. It is unambiguously revealed that increasing loading conditions of the PMSG or/and the grid connection of the WPDS to VSC‐HVDC shall bring about a higher risk of oscillatory instability. Hence, analytical derivation of the SSS criterion helps better understand the instability mechanism in the PMSG‐based WPDS via VSC‐HVDC. In addition, while the derivation of the SSS criterion presupposes identical dynamics among PMSGs, this derived criterion can still be approximately utilized to assess the SSS of the PMSG‐based WPDS via VSC‐HVDC, irrespective of whether the dynamics of the PMSGs are similar or different. Finally, the SSS criterion is demonstrated and evaluated through three examples of the PMSG‐based WPDS via VSC‐HVDC.

Dual‐channel, high‐frequency optoelectronic oscillators utilizing optically‐injected lasers

AbstractWe propose a novel approach to dual‐channel optoelectronic oscillators (OEOs) with enhanced frequency band by leveraging directly modulated (DM) semiconductor lasers under optical injection. In this configuration, the frequency‐tuned optical signal from a master laser is introduced into a single‐mode slave laser, facilitating multioptical‐mode operation. The resulting multiple optical frequencies emitted by the slave laser facilitates a DM‐OEO signal at a frequency exceeding the laser's intrinsic modulation bandwidth. Through the deployment of a dual‐channel OEO based on the DM multimode laser signal, stable oscillation signals have been successfully achieved simultaneously at 15 and 18 GHz with phase noise levels of 96.43 and 95.62 dBc/Hz, respectively, at a 10‐kHz offset frequency.

Frequency stabilization of self-sustained oscillations in a sideband-driven electromechanical resonator

We present a method to stabilize the frequency of self-sustained vibrations in micromechanical and nanomechanical resonators. The method refers to a two-mode system with the vibrations at significantly different frequencies. The signal from one mode is used to control the other mode. In the experiment, self-sustained oscillations of micromechanical modes are excited by pumping at the blue-detuned sideband of the higher-frequency mode. Phase fluctuations of the two modes show near-perfect anticorrelation. They can be compensated in either of the modes by a stepwise change of the pump phase. The phase change of the controlled mode is proportional to the pump phase change, with the proportionality constant independent of the pump amplitude and frequency. This finding allows us to stabilize the phase of one mode against phase diffusion using the measured phase of the other mode. We demonstrate that phase fluctuations of either the high-frequency mode or the low-frequency mode can be significantly reduced. The results open new opportunities in generating stable vibrations in a broad frequency range via parametric down-conversion in nonlinear resonators. Published by the American Physical Society 2024

Wheel Slip Equilibrium Point Model Reference Adaptive Control Based PID Controller for Antilock Braking System: A New Approach

This paper presents a new approach to wheel slip control in Antilock Braking System (ABS) using an Approximated First Order Wheel Slip (AFOWS) Model Reference Adaptive Control (MRAC) based PID (AFOWS-MRAC-PID) controller. An ABS was modeled in a MATLAB/Simulink environment using a quarter car model with the proposed controller. Simulations were conducted with a wide range of adaptation gains (50, 100, 150, 200, and 250) to study the effectiveness of the proposed control system. The results revealed that the proposed system could track and maintain 10% wheel slip and eliminate oscillation (instability) in terms of overshoot associated with conventional PID controllers, particularly on wet and snowy road surfaces, using adaptation gains of 150, 200, and 250. Overall, the proposed system provided the best performance in terms of stopping distance, vehicle braking velocity, and braking torque on all road surfaces with an adaptation gain of 250, although braking on dry road surfaces was the most effective.