Oscillation Characteristics Research Articles

ANALYSE DES SERIES TEMPORELLES DES COLONNES VERTICALES DU DIOXYDE D’AZOTE ET DU FORMALDEHYDE ATMOSPHERIQUES A KINSHASA PAR LA DETECTION SYNCHRONE

This study concerns the analysis of atmospheric nitrogen dioxide and formaldehyde vertical column data in Kinshasa. The methodology uses the principle of synchronous detection. To do this, an algorithm was implemented and applied to search for the different harmonics in the spectra and to determine their respective characteristics. A multitude of harmonics was found in all frequency domains for each time series of the abundances of the considered atmospheric pollutants. The results of this study reveal an analysis technique capable of extracting weak signals embedded in a very high amplitude noise. In addition, apart from the information on the frequency, the analysis by synchronous detection makes it possible to obtain the phase and the amplitude of these signals extracted from the noise. Additionally, synchronous detection is able to find a particular oscillation buried in the noise and to determine its characteristics. It is therefore possible to study the phenomena associated with this oscillation (the rhythm of human activities, the alternation of seasons, the various tides, the Madden Julian or EL NINO oscillations) as well as the forces that maintain it (the various gravitational forces). The knowledge of the characteristics of a particular oscillation could also allow the exploration of the atmospheric environment of Kinshasa (emission site, altitude and relative abundance of atmospheric pollutants)

Effects of Tai Chi on anxiety and theta oscillation power in college students during the COVID-19 pandemic: A randomized controlled trial.

College students, especially during the COVID-19 pandemic, face substantial psychological stress. This study investigates the impact of Tai Chi (TC) practice on anxiety levels and theta oscillatory power activation characteristics among college students, aiming to provide empirical evidence for their psychological well-being. In this randomized controlled trial with 45 healthy college students, brainwave activity and changes in anxiety levels were measured. A 2 (TC group vs control group)×2 (pre-test vs post-test) factorial design was analyzed to explore TC's regulatory effects on brainwave activity and anxiety. Following 12 weeks of TC practice, the TC group exhibited a significant decrease in state-trait anxiety differences (-6.14±14.33), state anxiety differences (-3.45±7.57), and trait anxiety differences (-2.68±7.43), contrasting with an increase in the control group. Moreover, contrasting with a decrease in the control group, TC group demonstrated significance increased theta oscillatory power in C3, C4, F4, P3, T7, and T8, and a significant negative correlations were observed between state anxiety and F4-θ (r = -0.31, p = 0.04), T7-θ (r = -0.43, p = 0.01), and T8-θ (r = -0.30, p = 0.05). The positive influence of TC on college students' psychological well-being and brain function is evident, leading to reduced anxiety levels and increased theta oscillatory activity. While encouraging further research to delve into the mechanisms of TC on anxiety and theta brainwave characteristics, the study recommends actively promoting TC practice among college students to enhance mental health and address post-pandemic psychological challenges.

Detecting ALP wiggles at TeV energies

Axions and axion-like-particles (ALPs) are characterised by their two-photon coupling, which entails so-called photon-ALP oscillations as photons propagate through a magnetic field. These oscillations lead to distinctive signatures in the energy spectrum of high-energy photons from astrophysical sources, allowing one to probe the existence of ALPs. In particular, photon-ALP oscillations will induce energy dependent oscillatory features, or “ALP wiggles”, in the photon spectra. We propose to use the discrete power spectrum to search for ALP wiggles and present a model-independent statistical test. By using PKS 2155-304 as an example, we show that the method has the potential to significantly improve the experimental sensitivities for ALP wiggles, and that the ALP wiggles may be detected using the Cherenkov Telescope Array (CTA) for optimistic values of the photon-ALP coupling constant and the magnetic field. Moreover, we discuss how these sensitivities depend on the modelling of the magnetic field. We find that the use of realistic magnetic field models, due to their larger cosmic variance, substantially enhances detection prospects compared to the use of simplified models.

Functional differential equations of the neutral type: Oscillatory features of solutions

<abstract><p>This article delves into the behavior of solutions to a general class of functional differential equations that contain a neutral delay argument. This category encompasses the half-linear case and the multiple-delay case of neutral equations. The motivation to study this type of equation lies not only in the exciting analytical issues it presents but also in its numerous vital applications in physics and biology. We improved some of the inequalities that play a crucial role in developing the oscillation test. Then, we used an improved technique to derive several criteria that ensure the oscillation of the solutions of the studied equation. Additionally, we established a criterion that did not require imposing monotonic constraints on the delay functions and took into account their effect. We have supported the novelty and effectiveness of the results by analyzing and comparing them with previous results in the literature.</p></abstract>

An ensemble multi-scale framework for long-term forecasting of air quality.

The significance of accurate long-term forecasting of air quality for a long-term policy decision for controlling air pollution and for evaluating its impacts on human health has attracted greater attention recently. This paper proposes an ensemble multi-scale framework to refine the previous version with ensemble empirical mode decomposition (EMD) and nonstationary oscillation resampling (NSOR) for long-term forecasting. Within the proposed ensemble multi-scale framework, we on one hand apply modified EMD to produce more regular and stable EMD components, allowing the long-range oscillation characteristics of the original time series to be better captured. On the other hand, we provide an ensemble mechanism to alleviate the error propagation problem in forecasts caused by iterative implementation of NSOR at all lead times and name it improved NSOR. Application of the proposed multi-scale framework to long-term forecasting of the daily PM2.5 at 14 monitoring stations in Hong Kong demonstrates that it can effectively capture the long-term variation in air pollution processes and significantly increase the forecasting performance. Specifically, the framework can, respectively, reduce the average root-mean-square error and the mean absolute error over all 14 stations by 8.4% and 9.2% for a lead time of 100 days, compared to previous studies. Additionally, better robustness can be obtained by the proposed ensemble framework for 180-day and 365-day long-term forecasting scenarios. It should be emphasized that the proposed ensemble multi-scale framework is a feasible framework, which is applicable for long-term time series forecasting in general.

INTERMEDIATE STATES BETWEEN STATICS AND DYNAMICS AND SEISMIC EMISSION IN GRANULAR MEDIA

Seismic emission is the spontaneous emission of waves in a porous or fractured medium. There is still no explanation for the dependence of these phenomena on the parameters of the medium and the structure of the pore space, as well as for the transition from slow to fast movements. The paper proposes a description of the transition process from statics to dynamics using a model of structured continuum with an internal structure. The most important parameters of the model are the specific surface area and porosity of the medium. The reason for the emission is that the forces caused by internal stresses are only on average equal to zero over a representative volume, being different at each point of the medium. It is shown that the model of a structured continuum predicts the emission of waves under static load and gives an estimate of the emitted oscillation periods. In this case, the characteristic oscillation periods depend neither on the characteristic time of destruction of particles, nor on the loading time.

Fast-slow dynamics analysis in an externally excited smooth and discontinuous oscillator with a pair of irrational nonlinearities

The study of fast-slow oscillations in systems with irrational nonlinearity that may yield abundant dynamical mechanisms is not well developed. This paper aims to investigate the fast-slow dynamics in an excited mass-spring oscillator with a pair of irrational nonlinearities, which can undergo the dynamical transition from smooth to discontinuous characteristics depending on the values of a smoothness parameter. Three different types of fast-slow oscillations are reported in this interesting smooth and discontinuous (SD) oscillator with a pair of irrational nonlinearities. Due to the smooth and discontinuous characteristics of this SD oscillator, we consider its dynamical behaviors under the smooth and discontinuous cases, respectively. Based on the fast-slow analysis and the two-parameter bifurcation analysis, the smooth fast-slow dynamics associated with fold hysteresis and its turnover are revealed. In the discontinuous case, the system can be viewed as a piecewise-smooth dynamical system governed by three different subsystems in different regions divided by two nonsmooth boundaries. In particular, the nonsmooth boundaries can be divided into parts with different dynamical behaviors, including escaping and crossing lines. Unlike the smooth case, there is no change in the stability of the equilibrium in these three subsystems. However, transitions of system trajectory induced by crossing lines can account for the generation of fast-slow oscillations in the piecewise-smooth system. As a result, the smooth and piecewise-smooth fast-slow dynamics in the excited SD oscillator with a pair of irrational nonlinearities are revealed, which deepens the understanding of fast-slow dynamics of the dynamical systems with irrational nonlinearity.

Apathy scores in Parkinson's disease relate to EEG components in an incentivized motor task.

Apathy is one of the most prevalent non-motor symptoms of Parkinson's disease and is characterized by decreased goal-directed behaviour due to a lack of motivation and/or impaired emotional reactivity. Despite its high prevalence, the neurophysiological mechanisms underlying apathy in Parkinson's disease, which may guide neuromodulation interventions, are poorly understood. Here, we investigated the neural oscillatory characteristics of apathy in Parkinson's disease using EEG data recorded during an incentivized motor task. Thirteen Parkinson's disease patients with apathy and 13 Parkinson's disease patients without apathy as well as 12 healthy controls were instructed to squeeze a hand grip device to earn a monetary reward proportional to the grip force they used. Event-related spectral perturbations during the presentation of a reward cue and squeezing were analysed using multiset canonical correlation analysis to detect different orthogonal components of temporally consistent event-related spectral perturbations across trials and participants. The first component, predominantly located over parietal regions, demonstrated suppression of low-beta (12-20 Hz) power (i.e. beta desynchronization) during reward cue presentation that was significantly smaller in Parkinson's disease patients with apathy compared with healthy controls. Unlike traditional event-related spectral perturbation analysis, the beta desynchronization in this component was significantly correlated with clinical apathy scores. Higher monetary rewards resulted in larger beta desynchronization in healthy controls but not Parkinson's disease patients. The second component contained gamma and theta frequencies and demonstrated exaggerated theta (4-8 Hz) power in Parkinson's disease patients with apathy during the reward cue and squeezing compared with healthy controls (HCs), and this was positively correlated with Montreal Cognitive Assessment scores. The third component, over central regions, demonstrated significantly different beta power across groups, with apathetic groups having the lowest beta power. Our results emphasize that altered low-beta and low-theta oscillations are critical for reward processing and motor planning in Parkinson's disease patients with apathy and these may provide a target for non-invasive neuromodulation.

A localized pallidal physiomarker in Meige syndrome.

Oscillatory patterns in local field potentials (LFPs) have been recognized as disease-specific physiomarkers, particularly in the context of Parkinson's disease and cervical dystonia. This characteristic oscillatory feature is currently employed in adaptive deep brain stimulation (aDBS). However, for other types of dystonia, especially Meige syndrome, a distinct physiomarker of this nature is yet to be identified. Local field potentials were recorded during microelectrode-guided deep brain stimulation surgery from 28 patients with primary Meige syndrome. Before surgery, the severity of patients' motor syndrome were assessed using the Burke-Fahn-Marsden Dystonia Rating Scale-Motor (BFMDRS-M). An instantaneous oscillation detection method was employed to identify true narrowband oscillations. Subsequently, a linear mixed effects model was utilized to examine the relationship between oscillatory activities (including power amplitude and burst duration) and symptom severity. The focal peaks of "oscillatory activities" detected were predominantly concentrated in the narrow theta band (4-8 Hz), constituting 81.5% of the total detected oscillations in all recording sites near active DBS contacts in the globus pallidus internus (GPi). The linear mixed effects model revealed a positive correlation between the theta burst duration and the severity of preoperative motor impairment, but no correlation with postoperative motor scores. Additionally, there was no significant lateralization effect observed between the left and right GPi. Our findings suggest that the exaggerated narrowband theta activity (mainly the burst duration) in the GPi is predictive of dystonia symptom severity and may be used as a physiomarker for optimized DBS target during surgery and adaptive DBS for the treatment of Meige syndrome.

Numerical study on dominant oscillation frequency of unstable steam jet under heaving condition

With its advanced efficiency in heat transfer, the steam direct contact condensation method is now extensively employed in many areas. The pressure oscillation characteristics of unstable steam jets under heaving conditions were investigated numerically in this study. The dominant oscillation frequency gradually rose with the decrease of the heaving period and the increase of the heaving amplitude. The dominant oscillation frequency under the heaving condition was higher than that under the static condition, with a maximum increase of 27.4%. The inertia and condensation dominated the evolution of steam bubbles at the necking stage under heaving conditions. With the decrease of the heaving period and the increase of heaving amplitude, the additional force induced by heaving movement increased, contributing to the condensation heat transfer enhancement. A dimensionless correlation predicting the dominant oscillation frequency at a low flow rate under heaving conditions was fitted, and the maximum error was within ±6.2%.

Study on flexible/rigid protection mechanism of hydrogen/methane premixed gas explosion in urban underground space

Explosion accidents are one of the factors that impede urban underground space development and utilization, and it is imperative to study safety precautions in case of an explosion in an urban underground space. Given this problem, a polyurethane sponge and carbon fiber board with Blocking Rates (BR) of 0.2, 0.4 and 0.6 were used to explore the combustion and explosion characteristics of hydrogen/methane premixed gas in a confined space in the presence of a flexible and rigid obstacle. The results indicated that both the flame and pressure exhibit Helmholtz oscillation characteristics in case of a rigid obstacle. When the BR of both flexible and rigid obstacle were 0.4, the explosion intensity index was the highest. It first increased and then declined with the increase of flexible obstacle BR. In the presence of a flexible obstacle, the Helmholtz oscillation phenomenon was completely suppressed, and explosion intensity indices were minimized, as the flexible obstacle BR increased, it first increased and then declined. Under the rigid obstacle preset conditions, the explosion hazard significantly increased compared to the flexible constructions. The research results provide a theoretical basis for protective facilities to suppress combustion and explosion phenomena in underground spaces.

An oscillating reaction network with an exact closed form solution in the time domain

BackgroundOscillatory behavior is critical to many life sustaining processes such as cell cycles, circadian rhythms, and notch signaling. Important biological functions depend on the characteristics of these oscillations (hereafter, oscillation characteristics or OCs): frequency (e.g., event timings), amplitude (e.g., signal strength), and phase (e.g., event sequencing). Numerous oscillating reaction networks have been documented or proposed. Some investigators claim that oscillations in reaction networks require nonlinear dynamics in that at least one rate law is a nonlinear function of species concentrations. No one has shown that oscillations can be produced for a reaction network with linear dynamics. Further, no one has obtained closed form solutions for the frequency, amplitude and phase of any oscillating reaction network. Finally, no one has published an algorithm for constructing oscillating reaction networks with desired OCs.ResultsThis is a theoretical study that analyzes reaction networks in terms of their representation as systems of ordinary differential equations. Our contributions are: (a) construction of an oscillating, two species reaction network [two species harmonic oscillator (2SHO)] that has no nonlinearity; (b) obtaining closed form formulas that calculate frequency, amplitude, and phase in terms of the parameters of the 2SHO reaction network, something that has not been done for any published oscillating reaction network; and (c) development of an algorithm that parameterizes the 2SHO to achieve desired oscillation, a capability that has not been produced for any published oscillating reaction network.ConclusionsOur 2SHO demonstrates the feasibility of creating an oscillating reaction network whose dynamics are described by a system of linear differential equations. Because it is a linear system, we can derive closed form expressions for the frequency, amplitude, and phase of oscillations, something that has not been done for other published reaction networks. With these formulas, we can design 2SHO reaction networks to have desired oscillation characteristics. Finally, our sensitivity analysis suggests an approach to constructing a 2SHO for a biochemical system.

Analysis of sub-synchronous oscillation characteristics of PMSGs based on transient energy

Analysis of sub-synchronous oscillation characteristics of PMSGs based on transient energy

Using oscillatory and aperiodic neural activity features for identifying idle state in SSVEP-based BCIs reduces false triggers

Objective. In existing studies, rhythmic (oscillatory) components were used as main features to identify brain states, such as control and idle states, while non-rhythmic (aperiodic) components were ignored. Recent studies have shown that aperiodic (1/f) activity is functionally related to cognitive processes. It is not clear if aperiodic activity can distinguish brain states in asynchronous brain–computer interfaces (BCIs) to reduce false triggers. In this paper, we propose an asynchronous method based on the fusion of oscillatory and aperiodic features for steady-state visual evoked potential-based BCIs. Approach. The proposed method first evaluates the oscillatory and aperiodic components of control and idle states using irregular-resampling auto-spectral analysis. Oscillatory features are then extracted using the spectral power of fundamental, second-harmonic, and third-harmonic frequencies of the oscillatory component, and aperiodic features are extracted using the slope and intercept of the first-order polynomial of the spectral fit of the aperiodic component under a log-logarithmic axis. The process produces two types of feature pools (oscillatory, aperiodic features). Next, feature selection (dimensionality reduction) is applied to the feature pools by Bonferroni corrected p-values from two-way analysis of variance. Last, these spatial-specific statistically significant features are used as input for classification to identify the idle state. Main results. On a 7-target dataset from 15 subjects, the mix of oscillatory and aperiodic features achieved an average accuracy of 88.39% compared to 83.53% when using oscillatory features alone (4.86% improvement). The results demonstrated that the proposed idle state recognition method achieved enhanced performance by incorporating aperiodic features. Significance. Our results demonstrated that (1) aperiodic features were effective in recognizing idle states and (2) fusing features of oscillatory and aperiodic components enhanced classification performance by 4.86% compared to oscillatory features alone.

Multi‐Instruments Observation of Ionospheric‐Thermospheric Dynamic Coupling Over Mohe (53.5°N, 122.3°E) During the April 2023 Geomagnetic Storm

AbstractThe state and variations of the Ionosphere‐Thermosphere (I‐T) system are strongly influenced by dynamical processes, with these effects being amplified during intense space environment disturbances such as geomagnetic storms, producing multi‐scale disturbance features in the I‐T system. The redistribution of energy and momentum through the dynamical processes is currently not well understood. Unfortunately, the dearth of thermospheric observations has yielded limited studies capable of monitoring and analyzing the I‐T dynamical coupling during storms using co‐located measurements. This work examines the responses of the I‐T system during the April 2023 geomagnetic storm based on high‐resolution continuous I‐T system observations at Mohe observatory, a middle latitude station. Both large‐scale features and short‐period oscillations were identified in multiple key parameters of the I‐T system. Similar disturbed patterns in thermospheric winds occurred during the main and recovery phases of the geomagnetic storm. However, the oscillation features in many parameters of the I‐T system are only observed during the main phase. The results of concurrent I‐T system observations unveil the oscillation features of thermospheric winds, temperatures, the ionospheric F2 peak height, electron density, and total electron content. These findings reveal the important influence of wind divergence on thermospheric temperature disturbances and its modulatory effect on ionospheric disturbances.

Study on reduction of pressure oscillation in low-velocity steam jet condensation

To mitigate the high-amplitude pressure oscillations generated during the steam low-speed jet condensation process and reduce the risk of dynamic load damage to the suppression pool and its adjacent facilities, this study designed a temperature-rising cylinder scheme based on the characteristics of low-speed steam jet condensation pressure oscillation and studied the mitigation effect of this scheme through experiments. The experimental results showed that this scheme could effectively reduce the time of low-velocity steam jet condensation in the high-amplitude pressure oscillation region. For instance, at a steam mass flow rate of 30 kg/m2s, the time was reduced from 6300 s to 700 s, which significantly improves the safety of the pool and nearby facilities. Moreover, the scheme does not affect the suppression ability of the pool and can ensure the long-term effective operation of the suppression system.

Heat source/sink impact on wave oscillations of thermal and concentration boundary layer along inclined plate under lower gravitational region

The force of attraction between two masses increases as gravity increases. Gravity is very important mechanism for mass transfer characteristics across the inclined shape. The significant purpose of current study is to examine amplitude in mass transfer under reduced gravity-driven flow. The impact of heat source/sink on periodic mixed convective gravity-driven flow across the inclined plate has been evaluated. The oscillatory characteristics of heat rate and mass transmission are explored at three inclined angles π/6, π/4 and π/3. The gravity is assumed under maximum temperature difference. The governing dimensional model is transformed into non-dimensional equations with appropriate scaling variables. The non-dimensional equations are again reduced in non-oscillatory, real and imaginary parts. For smooth coding, the primitive formulation is used with finite difference method to change non-dimensional forms in algebraic system. The algebraic equations are solved with Gaussian elimination scheme to display velocity field, temperature distribution and rate of concentration numerically. The impact of heat source/sink ±δ, reduced gravity Rg, buoyancy variable λT, modified buoyancy factor λC, Prandtl factor Pr, reduced gravitation factor Rg, and Schmidt variable Sc on the oscillating behavior of shear stress, rate of fluctuating heat transfer, and rate of fluctuating mass transfer is secured. It is found that the amplitude of fluid velocity and temperature increases for each parameter under heat source +δ=0.4. It can be seen that concentration distribution increases as reduced gravity Rg increases under heat sink −δ=0.3. It can be seen that amplitude of shearing stress and heat transfer increases as heat source +δ increases. It is obtained that oscillation in mass transfer increases as heat source/sink ±δ increases under reduced gravitation Rg=1.2.

Dynamics of pulsational mode in the EiBI gravity fabric

We systematically theorise a model formalism to investigate the linear pulsational mode dynamics excitable in self-gravitating dust molecular clouds (DMCs) in the framework of the Eddington-inspired Born-Infeld (EiBI) gravity. The adopted spherical DMC consists of thermalized lighter (non-inertial) electrons and ions, both treated analogously as the Boltzmann species, whereas the partially ionised heavier (inertial) dust grains as the constitutive neutral and charged dust fluids. The model closure comes from the coupling gravito-electrostatic Poisson equations governing the resultant potential distributions sourced in the material and charge density fields. Application of spherical normal mode (Fourier-based) analysis transforms the model DMC into a quartic linear dispersion relation with diverse atypical multi-parametric dispersion coefficients. A numerical platform is constructed for an illustrative dispersion analysis. It shows that the positive EiBI parameter, dust charge number, and cloud size act as stabilizing agents against the inward non-local self-gravity. In contrast, a negative EiBI parameter, dust mass, and equilibrium dust population density play destabilizing roles. The modal propagatory and oscillatory features are portrayed graphically and interpreted elaborately. The reliability of our calculation scheme is validated in light of the closely related results previously reported in the literature. The analyses presented here could be relevant in the context of understanding astrophysical structure formation dynamics through the self-gravitational canonical condensation processes in diverse real astronomic environs.

Characteristics of sub-synchronous oscillation in grid-connected wind farm system

With the rapid development of wind power, wind turbines are accompanied by a large quantity of power electronic converters connected to the grid, causing changes in the characteristics of the power system and leading to increasingly serious sub-synchronous oscillation (SSO) problems, which urgently require the generalized classification and characterization of the emerging oscillation problems. This paper classifies and characterizes the emerging types of SSO caused by grid-connected wind turbines to address these issues. Finally, the impact of the typical system parameters changes on the oscillation pattern is analyzed in depth to provide effective support for the subsequent suppression and prevention of SSO.

Hole behavior captured by analysis of instantaneous amplitude and phase of sarcosynced oscillations reveals wave characteristics of sarcomeric oscillations

In this study, we performed signal analysis based on instantaneous amplitude and phase of sarcomeric oscillations, which are generated by skeletal muscle under constant calcium concentration conditions and in which sarcomeres repeatedly contract and relax autonomously. In addition to the changes in sarcomere length that have been attracting attention, we named the Z-line oscillations that partition sarcomeres sarcosynced oscillations, and analyzed their instantaneous amplitude and phase. As a result, the behavior of pairs of sarcosynced oscillations and sarcomeric oscillations, which are produced when propagating waves propagate in one direction or collide, was clearly visualized. By focusing on the behavior of the hole, which is a dip in the instantaneous amplitude accompanied by a sudden jump in the instantaneous phase in sarcosynced oscillations, we were able to discern the wave characteristics. Transient disruption occurred in the propagating waves even when they traveled in one direction. Its properties were captured by the sarcomeric defect hole (SD hole), a dip in the instantaneous amplitude accompanied by a jump in the instantaneous phase in sarcosynced oscillations. When propagating waves collide, the collision site, its persistence, movement, and disappearance process are captured as sarcomeric collision holes (SC holes) of sarcosynced oscillations. These holes are important indicators for understanding the oscillation properties of sarcomeres. In conclusion, although sarcosynced oscillations and sarcomeric oscillations are closely related, they exhibit different oscillations, and the study of the SD holes and SC holes caused by them will contribute to a detailed understanding of the muscle characteristics of sarcomeres. This finding has important implications for improving our understanding of the efficiency of muscle function and its regulatory mechanisms.