Phase Difference Of Oscillations Research Articles

Impacts of potential energy oscillations on the friction of graphene and BN lubricants

Abstract The frictional responses of graphene and boron nitride lubricants is studied from the perspective of the potential energy evolution. At a low normal load regime and high interface adhesion, friction can be effectively characterized by investigating the interfacial energy barrier formation process. By decomposing the energy evolution into strain and interfacial cohesive components, we find that the oscillation phase difference plays an essential role in the friction response and is controlled by the energy conversion between them. Analyses further reveal that the energy oscillations are excited by the vertical motion of the sliding asperity that induces periodic deformation and position changes in the lubrication systems. These new findings suggest the study of potential energy evolution is advantageous for understanding adhesive friction and infers the potential to leverage adhesion in 2D lubricant application through high conversion efficiency and out-of-phase oscillations between strain and cohesive energies.

Atypical instantaneous spatio-temporal patterns of neural dynamics in Alzheimer’s disease

Cognitive functions produced by large-scale neural integrations are the most representative ‘emergence phenomena’ in complex systems. A novel approach focusing on the instantaneous phase difference of brain oscillations across brain regions has succeeded in detecting moment-to-moment dynamic functional connectivity. However, it is restricted to pairwise observations of two brain regions, contrary to large-scale spatial neural integration in the whole-brain. In this study, we introduce a microstate analysis to capture whole-brain instantaneous phase distributions instead of pairwise differences. Upon applying this method to electroencephalography signals of Alzheimer’s disease (AD), which is characterised by progressive cognitive decline, the AD-specific state transition among the four states defined as the leading phase location due to the loss of brain regional interactions could be promptly characterised. In conclusion, our synthetic analysis approach, focusing on the microstate and instantaneous phase, enables the capture of the instantaneous spatiotemporal neural dynamics of brain activity and characterises its pathological conditions.

Multi‐Ion Oscillitons—Origin of Coherent Magnetospheric EMIC Waves

AbstractThe recent spacecraft observations by MMS and Van Allen Probes associated with electromagnetic ion cyclotron (EMIC) waves in the Earth magnetosphere emphasize the important role of multi‐ion plasma composition for generation and characteristics of these emissions. We show that main properties of the coherent EMIC waves can be explained with the concept of “multi‐ion oscillitons” (Sauer et al., 2001, https://doi.org/10.1029/2001GL013047). In a plasma with two types of ions of different masses (e.g., protons and oxygen ions), oscillitons arise from the exchange of momentum and energy between the two ion components, with the electromagnetic field acting as a mediator. At frequencies near cross‐over frequencies of different wave modes in the multi‐ion plasma the nonlinear resonance which strongly amplifies the seed unstable mode can be excited. A small phase difference in oscillations of different ion species leads to a nonlinear wave beating and generation of wave packets. The “resonance” frequency is characterized by a local maximum of the phase velocity and the coincidence of phase and group velocity. It is suggested that the oscillitons are triggered by the instability due to the proton temperature anisotropy and may survive outside the source region for long distances. The generation of coherent waves by oscillitons is of a general nature and may contribute to understand the manifold of phenomena in other space plasma environments in which the dynamics of minor ion admixtures cannot be neglected. The concept of oscillitons can also be applied to the momentum exchange between particle groups of the same mass, but different temperature.

A novel oscillation identification method for grid-connected renewable energy based on big data technology

With the development of big data technology, power system has entered the era of data analysis. With the help of the massive data provided by the wide area measurement system, the power system can be easily evaluated, and the abnormal operation status can be detected and positioned. As the increase of renewable energy permeability, more new abnormal operating status have appeared in the system. Aimed at the abnormal operation state in the development of new energy, this paper proposes an oscillation location scheme based on evidence theory and support vector machine, which makes up for the limitation of single oscillation location method. The result of location analysis of oscillation energy method, oscillation phase difference method and forced oscillation phase difference location method is fused by evidence theory.

Wave processes in the constructions of mechanisms and buildings

In the article a methodology for researching wave processes in weakly nonlinear homogeneous one-dimensional systems – elements of machine and building structures is proposed. It is based on D'Alembert's method of constructing solutions of wave equations and the asymptotic method of nonlinear mechanics. Resonant and non-resonant cases are considered. In the non-resonant case, the influence of viscoelastic forces and small periodic disturbances on the oscillatory process is taken into account. In the resonant case, the influence of the disturbing force and the phase difference of natural oscillations is considered. Numerical methods for linear differential equations were used to analyze the obtained differential equations.

A Low Frequency Oscillation Disturbance Source Positioning Method Based on Oscillation Phase Difference

In the face of voltage sag which causes power quality problems, combined with the common short circuit fault types in power system, how to locate disturbance source quickly and accurately is an important problem in low frequency oscillation monitoring and control. The mechanism of the disturbance source affecting the unit in the network is analyzed. A low frequency oscillation source location method based on oscillation phase difference is proposed. Firstly, the electrical data of the dominant oscillation mode are extracted by empirical mode decomposition, then the oscillatory phase with physical meaning is calculated by Hilbert transform. According to the network information criterion, the location of the disturbance source can be traced, according to the power plant. The ground information criterion can check the specific disturbance source unit. The principle of the method is clear, only one electrical quantity is needed to participate in the calculation.

Моделирование переходного процесса с учетом изменения температуры электрической цепи

The article examines the influence of temperature on the transient process in the electrical circuits. It has been shown that the temperature change of active resistance can influence the character of the transient process in the electrical circuit. The numerical modeling of the differential equations system, which describes an electrical circuit considering resistance temperature increase, has shown the appearance of the phase difference of current-voltage oscillations between the compared variants.

Modelling sagittal and vertical phase differences in a lumped and distributed elements vocal fold model

The quality and timbre of disordered voices heavily rely on the vibration properties of the vocal folds. We discuss the representation of sagittal phase differences in vocal fold oscillations through a numerical biomechanical model involving lumped elements as well as distributed elements, i.e., delay lines. A dynamic glottal source model is proposed in which the fold displacement along the vertical and the sagittal dimensions is modelled using delay lines. In contrast to other models, with which the reproduction of sagittal phase differences is impossible (e.g., in two-mass models) or not easy to control (e.g., in 3D 16-mass and multi-mass models in general), the one proposed here provides direct control over the amount of phase delay between folds’ oscillations at the posterior and anterior part of the glottis, i.e., the sagittal axis, and at the superior and inferior part of the glottis, i.e., the vertical axis, while keeping the dynamic model simple and computationally efficient. The model is assessed by addressing the reproduction of oscillatory patterns observed in high-speed videoendoscopic data, in which sagittal phase differences are observed. Also, timing asymmetry parameters observed in hemi glottal area waveforms (GAWs) are used for fitting.

Jet deflection by two side-by-side arranged hydrofoils pitching in a quiescent fluid

The present work reports a computational study on the pitching of two identical NACA 0012 airfoils arranged in a side-by-side (parallel) configuration in a still medium. Pitching of airfoils arranged in a side-by-side (parallel) configuration in a still medium leads to the formation of a deflected jet. The angle at which the jet is deflected depends on the oscillation phase difference between the airfoils and the frequency of oscillation. The deflection angle is high at a lower frequency of oscillation for a given phase difference between the foils. The time-averaged jet deflection angle, thrust, and lift on airfoils are quantified for a range of frequencies (0.5 Hz–2 Hz) and phase differences (0°–180°) between the airfoils. The thrust force increases gradually with an increase in the phase difference between the foils until 120°, and beyond this, it decreases. The maximum jet deflection angle is found to be 28° when the phase difference is 45° for a frequency of 0.5 Hz. It is observed that the initially deflected jet switches toward the centerline position after specific periods of pitching. This switching of the jet from a deflected position toward the centerline initiates once the vortices from the lower foil interact completely with the upper foil. Some of these findings are relatively new in the domain of bio locomotion, which is useful for various related engineering applications.

상하단이 자유롭게 수평동요하는 수중 조파판에 의해 생성된 수면파의 근사해석

To derive a simplified analytic solution which can be utilized as a fundamental solution for the wave maker design, a segment of the wave board has been idealized as a submerged line segment in a two dimensional domain of a wave flume. The lower end of the line segment could be located at arbitrary depth of the wave flume and the upper end of the board could be also submerged to any depth from the free surface. The freely oscillating motion of the wave board is assumed to be defined by determining the condition of horizontal oscillation on both ends differently. The submerged wave board oscillating in horizontal direction could be specified by selecting the amplitude, frequency and the phase lag differently on lower and upper ends of the board. The simplified two dimensional wave generated by the wave board segment has been obtained by the first order perturbation method. It is found that the general solution of the freely oscillating wave board in two dimensional domain could be decomposed into the solution of flap motion with lower end hinge and swing motion with upper end hinge. The case study of the analytic solutions has been carried out to evaluate the effect on the wave height due to the difference of oscillation frequency, phase difference and variation of stroke between for the motion of both ends. It is found that the solution of the freely oscillating wave board could be utilized for the development of high performance wavemaker especially for irregular waves.

Wave-packet dynamics in multilayer phosphorene

We investigate the dynamics of Gaussian wave packets in multilayer black phosphorus (BP). Time-dependent average position and velocity are calculated analytically and numerically by using a continuum model and a method based on the split-operator technique, respectively. By analyzing the wave-packet trajectories with nonvanishing initial momentum along $y$ direction, we observed transient spatial oscillations due to the effect known as zitterbewegung (ZBW). We also demonstrated, based on the Heisenberg picture and by the calculation of the velocity operators, that the trembling motion along the $y$ direction at small times is unavoidable even for null initial momentum. We verified that the ZBW is directly related to the splitting of the wave packet into two parts moving with opposite velocities, as similar to graphene, and the linear dependence on ${k}_{y}$ in out-of-diagonal terms in the Hamiltonian. In addition for phosphorene systems, the two portions of the propagated wave packets have an asymmetric shape for unbalanced $\left({[1,0]}^{T}\right)$ and phased different $\left({[1,i]}^{T}\right)$ initial pseudospin components, playing an important role in the amplitude, frequency and duration time of the transient oscillations. Electrons in the vicinity of the Fermi energy traveling in $N$-layer phosphorene also exhibit qualitatively similar trembling motion and transient character as found in the monolayer case, except by the oscillation phase difference and final group velocity achieved after the transient behavior. As a consequence of the anisotropy on the $N$-layer BP energy bands, effective masses and group velocities along the $x$ and $y$ directions, the wave packet propagates nonuniformly along the different directions and deforms into an elliptical shape. By comparing our analytical results with those ones obtained by the split-operator technique, we verified a good qualitative and quantitative agreement between them, except for very larger values of wave vector and after long time steps.

Cerebellar Lobulus Simplex and Crus I Differentially Represent Phase and Phase Difference of Prefrontal Cortical and Hippocampal Oscillations

SUMMARYThe cerebellum has long been implicated in tasks involving precise temporal control, especially in the coordination of movements. Here we asked whether the cerebellum represents temporal aspects of oscillatory neuronal activity, measured as instantaneous phase and difference between instantaneous phases of oscillations in two cerebral cortical areas involved in cognitive function. We simultaneously recorded Purkinje cell (PC) single-unit spike activity in cerebellar lobulus simplex (LS) and Crus I and local field potential (LFP) activity in the medial prefrontal cortex (mPFC) and dorsal hippocampus CA1 region (dCA1). Purkinje cells in cerebellar LS and Crus I differentially represented specific phases and phase differences of mPFC and dCA1 LFP oscillations in a frequency-specific manner, suggesting a site- and frequency-specific cerebellar representation of temporal aspects of neuronal oscillations in non-motor cerebral cortical areas. These findings suggest that cerebellar interactions with cerebral cortical areas involved in cognitive functions might involve temporal coordination of neuronal oscillations.

Effects of surface roughness on mixed convection nanoliquid flow over slender cylinder with liquid hydrogen diffusion

The influence of surface roughness on boundary layer flow characteristics over moving surfaces is of considerable research interest in recent times. In the present study, the effects of surface roughness on flow over moving slender cylinder are analyzed in presence of mixed convection nanoliquid boundary layer flow. The problem is modelled in terms of highly nonlinear dimensional partial differential equations, which are written in non-dimensional form with the help of non-similar transformations. The resulting equations are reduced to linear partial differential equations by utilizing Quasilinearization technique, which are discretized using implicit finite difference scheme. The results obtained during the numerical simulation are then depicted through graphs in terms of various profiles and gradients and are analyzed with proper physical explanations. The roughness of slender cylinder surface is represented in a deterministic model as a sine wave form and yields sinusoidal variations in the values of skin-friction coefficient, wall heat and mass transfer rates. It is observed that the surface roughness effects are more prominent away from the orifice. The local frequency of gradients increases (i.e. wavelength decreases) with the increase in the frequency of surface roughness (n). The addition of nanoparticles into the ordinary fluid enhances the skin-friction coefficient and wall mass transfer rate. However, due to its effects, significant reduction is observed in the wall heat transfer rate. The phase difference of gradient oscillations arising in presence of nanoparticles is suppressed further away from the origin due to surface roughness. Interestingly, the amplitude of gradient oscillations remain higher in case of nanoliquid in comparison with that in case of ordinary fluid. Furthermore, the magnitude of wall mass transfer rate of liquid hydrogen is higher than that of nanoparticle wall mass transfer rate, which signifies the higher diffusivity of nanoparticles. The results of present study are of practical relevance to industrial applications such as polymer fibre coating and coating of wires.

The critical role of phase difference in theta oscillation between bilateral parietal cortices for visuospatial working memory

Visual working memory (VWM) refers to people’s ability to maintain and manipulate visual information on line. Its capacity varies between individuals, and neuroimaging studies have suggested a link between one’s VWM capacity and theta power in the parietal cortex. However, it is unclear how the parietal cortices communicate with each other in order to support VWM processing. In two experiments we employed transcranial alternate current stimulation (tACS) to use frequency-specific (6 Hz) alternating current to modulate theta oscillation between the left and right parietal cortex with either in-phase (0° difference, Exp 1), anti-phase (180° difference, Exp 2), or sham sinusoidal current stimulation. In Experiment 1, in-phase theta tACS induced an improved VWM performance, but only in low-performers, whereas high-performers suffered a marginally-significant VWM impairment. In Experiment 2, anti-phase theta tACS did not help the low-performers, but significantly impaired high-performers’ VWM capacity. These results not only provide causal evidence for theta oscillation in VWM processing, they also highlight the intricate interaction between tACS and individual differences—where the same protocol that enhances low-performers’ VWM can backfire for the high-performers. We propose that signal complexity via coherent timing and phase synchronization within the bilateral parietal network is crucial for successful VWM functioning.

FSI DYNAMIC RESPONSE ANALYSES OF A CONICAL ORIFICE VALVE DURING WORKING PROCESS WITH SEVERAL MAJOR INFLUENCES

Based on a 3-D fluid-structure interaction dynamics model and direct coupling solving method, the nonlinear dynamic response characteristics, such as variable flow rate, pressure difference and valve opening, of a conical orifice valve are numerically simulated to show its whole working process of opening and closing under inlet fluid velocity pulse excitation. Especially, the high-frequency fluctuation characteristics of valve opening are investigated in details. The wavelet analysis method for short unstationary process data is employed to analyze the time-frequency spectrum of the valve opening response. Practical verification of the solution algorithms is performed using different time-integration methods and time steps. Then, a series of numerical experiments are conducted to compare the effects of each change of several system parameters, such as valve core mass, spring parameters and hydraulic oil parameters, and excitation parameters, such as inlet fluid velocity amplitude and ulse width. The numerical experiment results show that the different fluid integration algorithms influence the solution results quite much; the influences of change in valve core mass or fluid compressibility on the valve opening oscillation frequency are significant; oil viscosity change leads to oscillation phase difference; different spring stiffnesses and preloads change the maximum valve opening; the initial collisions between valve core and seat result in increase of the valve opening oscillation frequency.

Experimental Investigation of Energy Dissipation in Presliding Spherical Contacts Under Varying Normal and Tangential Loads

Interfacial damping in assembled structures is difficult to predict and control since it depends on numerous system parameters such as elastic mismatch, roughness, contact geometry, and loading profiles. Most recently, phase difference between normal and tangential force oscillations has been shown to have a significant effect on interfacial damping. In this study, we conduct microscale (asperity-scale) experiments to investigate the influence of magnitude and phase difference of normal and tangential force oscillations on the energy dissipation in presliding spherical contacts. Our results show that energy dissipation increases with increasing normal preload fluctuations and phase difference. This increase is more prominent for higher tangential force fluctuations, thanks to larger frictional slip along the contact interface. We also show that the energy dissipation and tangential fluctuations are related through a power law. The power exponents we identify from the experiments reveal that contacts deliver a nonlinear damping for all normal preload fluctuation amplitudes and phase differences investigated. This is in line with the damping uncertainties and nonlinearities observed in structural dynamics community.

Locating Method of Disturbance Source of Low Frequency Oscillation Based on Oscillation Phase Difference

Fast and accurate location of low frequency oscillation disturbance source is crucial to the safe and stable operation of power system. This paper firstly analyzes the mechanism that how the disturbance source unit influence the other units in the power grid. Then, the oscillation phase distribution relation of the points in the tie-line is derived based on the simplified model of two machine oscillation and the method for locating the disturbance source is proposed based on the oscillation phase difference. The empirical mode decomposition is used to extract the electric quantity data of the dominant oscillation mode and the Hilbert Transform is used to calculate the oscillation phase with physical meaning. The oscillation phase difference is calculated to describe the oscillation phase relationship between two points. The orientation of the disturbance source can be traced by the network information criterion and the specific disturbance unit can be located by the local information criterion of the power plants. The principle of this method is clear and only one kind of electric quantity is involved in calculation. Finally, this paper verifies the applicability of this method by the low frequency oscillation simulation of one actual power grid. The results show that this method is of good accuracy and has potential value of engineering application.

Determination of electrostatic force and its characteristics based on phase difference by amplitude modulation atomic force microscopy

Electrostatic force measurement at the micro/nano scale is of great significance in science and engineering. In this paper, a reasonable way of applying voltage is put forward by taking an electrostatic chuck in a real integrated circuit manufacturing process as a sample, applying voltage in the probe and the sample electrode, respectively, and comparing the measurement effect of the probe oscillation phase difference by amplitude modulation atomic force microscopy. Based on the phase difference obtained from the experiment, the quantitative dependence of the absolute magnitude of the electrostatic force on the tip-sample distance and applied voltage is established by means of theoretical analysis and numerical simulation. The results show that the varying characteristics of the electrostatic force with the distance and voltage at the micro/nano scale are similar to those at the macroscopic scale. Electrostatic force gradually decays with increasing distance. Electrostatic force is basically proportional to the square of applied voltage. Meanwhile, the applicable conditions of the above laws are discussed. In addition, a comparison of the results in this paper with the results of the energy dissipation method shows the two are consistent in general. The error decreases with increasing distance, and the effect of voltage on the error is small.

Indirect coupling between two cavity modes via ferromagnetic resonance

We experimentally realize an indirect coupling between two cavity modes via strong coupling with ferromagnetic resonance in Yttrium Iron Garnet. We find that some indirectly coupled modes of this system can have a higher microwave transmission than the individual uncoupled modes. Using a coupled harmonic oscillator model, the influence of the oscillation phase difference between the two cavity modes on the nature of the indirect coupling is revealed. The properties of the indirectly coupled modes can be controlled using an external magnetic field or by tuning the cavity height. The relation between cavity transmission and the relative phase difference between cavity modes should be useful for developing tunable optical devices and improved information processing technologies.

Discrepancies between Multi-Electrode LFP and CSD Phase-Patterns: A Forward Modeling Study.

Multi-electrode recordings of local field potentials (LFPs) provide the opportunity to investigate the spatiotemporal organization of neural activity on the scale of several millimeters. In particular, the phases of oscillatory LFPs allow studying the coordination of neural oscillations in time and space and to tie it to cognitive processing. Given the computational roles of LFP phases, it is important to know how they relate to the phases of the underlying current source densities (CSDs) that generate them. Although CSDs and LFPs are distinct physical quantities, they are often (implicitly) identified when interpreting experimental observations. That this identification is problematic is clear from the fact that LFP phases change when switching to different electrode montages, while the underlying CSD phases remain unchanged. In this study we use a volume-conductor model to characterize discrepancies between LFP and CSD phase-patterns, to identify the contributing factors, and to assess the effect of different electrode montages. Although we focus on cortical LFPs recorded with two-dimensional (Utah) arrays, our findings are also relevant for other electrode configurations. We found that the main factors that determine the discrepancy between CSD and LFP phase-patterns are the frequency of the neural oscillations and the extent to which the laminar CSD profile is balanced. Furthermore, the presence of laminar phase-differences in cortical oscillations, as commonly observed in experiments, precludes identifying LFP phases with those of the CSD oscillations at a given cortical depth. This observation potentially complicates the interpretation of spike-LFP coherence and spike-triggered LFP averages. With respect to reference strategies, we found that the average-reference montage leads to larger discrepancies between LFP and CSD phases as compared with the referential montage, while the Laplacian montage reduces these discrepancies. We therefore advice to conduct analysis of two-dimensional LFP recordings using the Laplacian montage.