Oscillation Characteristics Research Articles

Online Monitoring of Cable Insulation Degradation for Inverter-Fed Machine System Using PWM Switching Oscillations

Online cable condition monitoring is a reliability enhancement technique for inverter-fed machine systems, which requires high sensitivity with quantitative assessment capability to detect the incipient insulation degradation as early as possible. This article presents a noncontact cable condition monitoring method by utilizing the inverter's self-excited high-frequency (HF) PWM switching oscillations. As an HF resonance, the switching oscillation is sensitive to the small change of degrading cable insulation capacitance. First, the characteristic mode, i.e. the HF differential-mode, is selected for sensitive cable condition monitoring from the multi-modal switching oscillation in an inverter-fed machine system. Then, an online condition monitoring scheme is proposed, including the framework, the noncontact HF oscillation current sensor, and the indicator(s) of cable insulation condition estimated from the amplitude-frequency features of the characteristic oscillation mode. Finally, experimental work was carried out on a 20 m cable-connected 3-kW inverter-fed machine test rig and the results demonstrate the good sensitivity and robustness of the method.

Altered resting-state brain oscillation and the associated cognitive impairments in late-life depression with different depressive severity: An EEG power spectrum and functional connectivity study

ObjectiveCognitive impairments are prevalent in late-life depression (LLD). However, it remains unclear whether there are concurrent brain oscillation alterations in resting condition across varying level of depression severity. This cross-sectional study aims to investigate the characteristics of altered resting-state oscillations, including power spectrum and functional connectivity, and their association with the cognitive impairments in LLD with different depression severity. MethodsA total of 65 patients with LLD and 40 elder participants without depression were recruited. Global cognition and subtle cognitive domains were evaluated. A five-minute resting-state electroencephalography (EEG) was conducted under eyes-closed conditions. Measurements included the ln-transformed absolute power for power spectrum analysis and the weighted phase lag index (wPLI) for functional connectivity analysis. ResultsAttentional and executive dysfunction were exhibited in Moderate-Severe LLD group. Enhanced posterior upper gamma power was observed in both LLD groups. Additionally, enhanced parietal and fronto-parietal/occipital theta connectivity were observed in Moderate-Severe LLD group, which were associated with the attentional impairment. LimitationsLimitations include a small sample size, concomitant medication use, and a relatively higher proportion of females. ConclusionsCurrent study observed aberrant brain activity patterns in LLD across different levels of depression severity, which were linked to cognitive impairments. The altered posterior brain oscillations may be trait marker of LLD. Moreover, cognitive impairments and associated connectivity alterations were exhibited in moderate-severe group, which may be a state-like marker of moderate-to severe LLD. The study deepens understanding of cognitive impairments with the associated oscillation changes, carrying implications for neuromodulation targets in LLD.

Diurnal oscillations of epigenetic modifications are associated with variation in rhythmic expression of homoeologous genes in Brassica napus

BackgroundEpigenetic modifications that exhibit circadian oscillations also promote circadian oscillations of gene expression. Brassica napus is a heterozygous polyploid species that has undergone distant hybridization and genome doubling events and has a young and distinct species origin. Studies incorporating circadian rhythm analysis of epigenetic modifications can offer new insights into differences in diurnal oscillation behavior among subgenomes and the regulation of diverse expressions of homologous gene rhythms in biological clocks.ResultsIn this study, we created a high-resolution and multioscillatory gene expression dataset, active histone modification (H3K4me3, H3K9ac), and RNAPII recruitment in Brassica napus. We also conducted the pioneering characterization of the diurnal rhythm of transcription and epigenetic modifications in an allopolyploid species. We compared the evolution of diurnal rhythms between subgenomes and observed that the Cn subgenome had higher diurnal oscillation activity in both transcription and active histone modifications than the An subgenome. Compared to the A subgenome in Brassica rapa, the An subgenome of Brassica napus displayed significant changes in diurnal oscillation characteristics of transcription. Homologous gene pairs exhibited a higher proportion of diurnal oscillation in transcription than subgenome-specific genes, attributed to higher chromatin accessibility and abundance of active epigenetic modification types. We found that the diurnal expression of homologous genes displayed diversity, and the redundancy of the circadian system resulted in extensive changes in the diurnal rhythm characteristics of clock genes after distant hybridization and genome duplication events. Epigenetic modifications influenced the differences in the diurnal rhythm of homologous gene expression, and the diurnal oscillation of homologous gene expression was affected by the combination of multiple histone modifications.ConclusionsHerein, we presented, for the first time, a characterization of the diurnal rhythm characteristics of gene expression and its epigenetic modifications in an allopolyploid species. Our discoveries shed light on the epigenetic factors responsible for the diurnal oscillation activity imbalance between subgenomes and homologous genes’ rhythmic expression differences. The comprehensive time-series dataset we generated for gene expression and epigenetic modifications provides a valuable resource for future investigations into the regulatory mechanisms of protein-coding genes in Brassica napus.

Association of Scalp High-Frequency Oscillation Detection and Characteristics With Disease Activity in Pediatric Epilepsy

Introduction: High-frequency oscillation (HFO) in scalp electroencephalography is a promising new noninvasive prognostic epilepsy biomarker, but further data are needed to ascertain the utility of this parameter. The present work investigated the association between epileptic activity and scalp HFO in pediatric patients with various types of epilepsy, using multivariable regression models to correct for possible confounding factors. Methods: The authors analyzed 97 subjects who were divided into groups with active epilepsy (within 1 year of seizure), seizure-free epilepsy (>1 year without seizure), and nonepilepsy. Regarding the frequency of seizure occurrence as an indicator of epileptic activity, we categorized subjects into four groups (Daily/Weekly, Monthly, Yearly, and Rarely). Results: Multiple linear regression analysis showed that the scalp HFO detection rate was significantly higher in patients with active epilepsy than in those with nonepilepsy (β [95% confidence interval] = 2.77 [1.79–4.29]; P < 0.001). The association between scalp HFO detection rate and frequency of seizure occurrence was highest in the Daily/Weekly group (β [95% confidence interval] = 3.38 [1.57–7.27]; P = 0.002), followed by Monthly and Yearly groups (β [95% confidence interval] = 2.42 [1.02–5.73]; P = 0.046 and 0.36 [0.16–0.83]; P = 0.017). In addition, HFO duration, number of peaks, and number of channels detected were significantly higher in patients with active epilepsy. Conclusions: Pediatric patients with active epilepsy and high frequency of seizure occurrence exhibited a higher scalp HFO detection rate. These results may help to establish HFO detectable by noninvasive scalp electroencephalography as a biomarker of active epilepsy in pediatric patients.

Kneser-Type Oscillation Criteria for Half-Linear Delay Differential Equations of Third Order

This paper delves into the analysis of oscillation characteristics within third-order quasilinear delay equations, focusing on the canonical case. Novel sufficient conditions are introduced, aimed at discerning the nature of solutions—whether they exhibit oscillatory behavior or converge to zero. By expanding the literature, this study enriches the existing knowledge landscape within this field. One of the foundations on which we rely in proving the results is the symmetry between the positive and negative solutions, so that we can, using this feature, obtain criteria that guarantee the oscillation of all solutions. The paper enhances comprehension through the provision of illustrative examples that effectively showcase the outcomes and implications of the established findings.

Effect of Multi-Joint Clearance Coupling on Shimmy of Nose Landing Gear

The existence of joint clearances in the nose landing gear (NLG) is inevitable and significantly affects shimmy. It was found that the interaction of each joint clearance is closely related to the analysis of shimmy stability. In this study, the shimmy model of NLG with three-dimensional joint clearance was established by using LMS VirtualLab Motion. Based on the method of multibody dynamics (MBD), the load transfer mechanism at the joints of the NLG was analyzed, and the oscillation characteristics with multiple joint clearances were investigated. The results indicate that the radial and axial contact force of the joint decreases from bottom to top, and the radial contact forces are relatively high at the end positions of the connection shafts, resulting in uneven wear. When the joint clearance reaches a certain value, periodic shimmy of the NLG will occur, and an increase in torsional damping can reduce the amplitude of the shimmy. Therefore, this study reveals the influence of multi-position joint clearance coupling on shimmy, and provides a valuable insight for the maintenance and design of landing gear joints.

A study on the application of cross-frequency coupling characteristics of neural oscillation in the diagnosis of mild cognitive impairment

In order to fully explore the neural oscillatory coupling characteristics of patients with mild cognitive impairment (MCI), this paper analyzed and compared the strength of the coupling characteristics for 28 MCI patients and 21 normal subjects under six different-frequency combinations. The results showed that the difference in the global phase synchronization index of cross-frequency coupling under δ-θ rhythm combination was statistically significant in the MCI group compared with the normal control group ( P = 0.025, d = 0.398). To further validate this coupling feature, this paper proposed an optimized convolutional neural network model that incorporated a time-frequency data enhancement module and batch normalization layers to prevent overfitting while enhancing the robustness of the model. Based on this optimized model, with the phase locking value matrix of δ-θ rhythm combination as the single input feature, the diagnostic accuracy of MCI patients was (95.49 ± 4.15)%, sensitivity and specificity were (93.71 ± 7.21)% and (97.50 ± 5.34)%, respectively. The results showed that the characteristics of the phase locking value matrix under the combination of δ-θ rhythms can adequately reflect the cognitive status of MCI patients, which is helpful to assist the diagnosis of MCI.

Modeling and numerical analysis of PID-controlled phase-change transpiration cooling

This paper innovatively introduces PID control to the phase-change transpiration cooling process and numerically investigates the multi-physics process of coupled control, flow, and heat transfer through mathematical modeling. Based on numerical simulations, the critical equal-amplitude oscillation characteristics in PID-controlled phase-change transpiration cooling, the PID tuning method for the cooling system's fast stabilization, and the applicability of PID tuning strategies at various control conditions are discussed. The discussions show that liquid phase change significantly influences the PID-controlled response process. The response process is prone to large temperature fluctuations and overshoots when the final phase change position is far from that in the corresponding open-loop process. In addition, the classical tuning parameters from the Ziegler-Nichols critical proportional tuning method are not fully applicable due to the significant heat transfer hysteresis in the liquid phase change and must be revised. After revision, the PID tuning strategy can contribute to excellent control consistency and reliability when the target temperature keeps away from the saturated temperature of the coolant or the feedback location moves within the superheated vapor area.

Microseismic oscillations as an indicator of tropical cyclones

The paper presents the results of recording microseismic oscillations in the frequency range of infrasonic waves performed during the periods of active influence of tropical cyclones on the water area of the Sea of Japan. The data were obtained by a coastal laser-interference measuring complex consisting of a two-axis laser strainmeter and a laser nanobarograph. A case study using remote sensing data shows that the world meteorological agencies stopped tracking the typhoon too early, while the cyclone retains its vortex structure and energy characteristics. The dynamics of changes in the characteristics of infrasound microseismic oscillations, which depend on the trajectory of typhoons and the duration of their impact on the sea area, is shown. Generalised results are given for some groups of typhoons having similar trajectories of movement, as a result of which the maximum amplitudes of microseismic infrasonic oscillations are manifested at different frequencies. During the passage of a category 5 typhoon in 2022, a microseismic signal formed by the interaction of the atmospheric vortex in the rear part of the cyclone with the field of quicksand waves was registered near the measuring site. As a result of registration by ground-based remote sensing methods of certain characteristics of microseismic signals generated during the passage of typhoons, it is possible to use the information to determine the parameters of tropical cyclone movement.

Hydrodynamic Response of a Large-Scale Mariculture Ship Based on Potential Flow Theory

The marine fishery will be the main form of the marine economy in the future. Simulating a hydrodynamic response under normal and extreme working conditions is the main means of structural analysis and design of a mariculture ship. In this paper, a simulation methodology is proposed based on potential flow theory, focusing on a semi-submersible large-scale mariculture ship with a rigid frame. Abaqus/Aqua 2020 software is used to establish a full-scale dynamic analysis model of the fishery. In the simulation, a nonlinear implicit integration method is applied, and the non-deterministic boundary conditions of the floating body are optimized using dynamic equilibrium principles. By varying the wave and flow conditions, the variations in mooring forces, vibration amplitudes, and average vibration values are analyzed. Furthermore, the dynamic changes in the overall spatial displacements of the fishery, characteristics of longitudinal and vertical oscillations, and mid-span deflections are analyzed. It is concluded that the mooring force is linearly correlated with the flow velocity, that a higher wave increases the longitudinal oscillation amplitude, and that a longer wave period leads to higher mooring forces and longitudinal heaving amplitude. These dynamic response and displacement results of the mariculture ship are expected to provide a basis for its design and safety assessment.

An intact pituitary vasopressin system is critical for building a robust circadian clock in the suprachiasmatic nucleus

The circadian clock is a biological timekeeping system that oscillates with a circa-24-h period, reset by environmental timing cues, especially light, to the 24-h day-night cycle. In mammals, a "central" clock in the hypothalamic suprachiasmatic nucleus (SCN) synchronizes "peripheral" clocks throughout the body to regulate behavior, metabolism, and physiology. A key feature of the clock's oscillation is resistance to abrupt perturbations, but the mechanisms underlying such robustness are not well understood. Here, we probe clock robustness to unexpected photic perturbation by measuring the speed of reentrainment of the murine locomotor rhythm after an abrupt advance of the light-dark cycle. Using an intersectional genetic approach, we implicate a critical role for arginine vasopressin pathways, both central within the SCN and peripheral from the anterior pituitary.

Strong Backreaction Regime in Axion Inflation.

We study the nonlinear dynamics of axion inflation, capturing for the first time the inhomogeneity and full dynamical range during strong backreaction, till the end of inflation. Accounting for inhomogeneous effects leads to a number of new relevant results, compared to spatially homogeneous studies: (i)the number of extra efoldings beyond slow-roll inflation increases very rapidly with the coupling, (ii)oscillations of the inflaton velocity are attenuated, (iii)the tachyonic gauge field helicity spectrum is smoothed out (i.e., the spectral oscillatory features disappear), broadened, and shifted to smaller scales, and (iv)the nontachyonic helicity is excited, reducing the chiral asymmetry, now scale dependent. Our results are expected to impact strongly on the phenomenology and observability of axion inflation, including gravitational wave generation and primordial black hole production.

Power allocation strategy for fuel cell distributed drive electric tractor based on adaptive multi-resolution analysis theory

Fuel cell distributed drive electric tractor (FCDET) provided a novel pathway for the development of green agricultural machinery technology. However, FCDET faced problems such as low traction efficiency, short endurance, and high hydrogen consumption. Relevant studies have shown that reasonable and effective power allocation strategy can improve the efficiency and reduce the energy consumption of fuel cell systems. In this paper, a drive power allocation strategy based on adaptive multi-resolution analysis theory (AMRA) was proposed. The strategy could realize effective decoupling between various energy sources, reduce the problems of frequent start-stop and large power fluctuation for fuel cells. We started with an equivalent circuit model of the fuel cell system, a total efficiency solution model, an energy dissipation model, and a drive motor response model. The first-time reconstruction strategy was based on Tunable Q-factor Wavelet Transform (TQWT) to obtain a subsequence that responds to the oscillatory characteristics of the power signal. The second-time reconstruction strategy took the low-frequency subsequence through Variational Mode Decomposition (VMD) into a number of discrete sub-signals with special sparse properties. Meanwhile, the Sparrow Search Algorithm (SSA) was used to obtain the optimal combined values of the modal decomposition layers and the quadratic penalty factor in the VMD on real time. Finally, the second-time decomposed subsequences and sub-signals were reconstructed according to the frequency characteristics, and the reconstructed power signals were redistributed among the individual energy sources. In order to validate the proposed power allocation strategy, we used the ET504-H prototype as a research object. The power information of plowing and transportation operating conditions was collected in Mengjin test base of China YTO Group. The MATLAB/Simulink-PXI joint simulation platform was set up and the driving motor bench test was carried out in the New Energy Key Laboratory of Henan Province. The results show that the AMRA-based FCDET drive power allocation strategy can effectively improve the energy utilization of the fuel cell system and the economy of the whole tractor operating unit. Compared to the power-following strategy under plowing and transportation conditions, the average efficiency of the fuel cell system was improved by 8.3 % and 3.3 %, the equivalent hydrogen consumption was reduced by 35.6 % and 43.89 %, respectively. The average efficiency of the drive motor was improved by 2.06 % and 2.08 %, the total energy consumption was reduced by 3.73 % and 2.6 %, respectively. This study can provide a theoretical foundation and a novel technical approach for the development of FCDET control system.

Influence mechanism and virtual power system stabiliser method of virtual synchronous generator for low‐frequency oscillation of power system

AbstractThe virtual synchronous generator (SG) (VSG) can not only enhance the inertia of the grid, but also introduce the oscillation characteristics of SG, which is easy to interact with the power angle of SG in the grid, and even produce low‐frequency oscillation (LFO). The authors first construct a two‐machine interconnected power system model containing VSG and traditional SG. The model is linearised to construct the state space equations to obtain the Phillips–Heffron model with VSG. The LFO path of action between VSG and SG is analysed. To reduce the negative damping torque provided by VSG to SG through this path, a virtual power system stabiliser (VPSS) is proposed and the controller parameters are adjusted according to the phase compensation method. Finally, the effectiveness of VPSS is verified by modal analysis and simulation comparison.

Results of the Study of Resonant Oscillations in the Northern Part of the Shelf of the Peter the Great Gulf, the Sea of Japan

To study the features of resonant oscillations in the water column of the Peter the Great Gulf of the Sea of Japan, in situ measurements were carried out on its shelf, combined with numerical simulation of these processes. The observational data were obtained from autonomous bottom pressure gauges in Novik Bay in the winter of 2016. In the calculations, a spectral-difference model was used, modified to account for the ice cover, and implemented on an irregular triangular grid. The atmospheric forcing used in the model had periods from 15 to 55 min. As a result, characteristic series of spatio-temporal parameters for resonant oscillations of the studied water area were determined. The locations of the peaks on the simulated resonance curves correspond to the locations of well-defined maxima of the energy spectrum according to in situ measurements, hence indicating the possibility of a significant resonant amplification of level fluctuations by wave and periodic wind effects. The novelty of this study is inclusion of the winter period, when the surface of the bay is partially covered with ice.

Two-phase flow characterization for metal concentric tubes with capacitance measurement

The two-phase flow characteristics for the concentric tube would be different to a plain tube. But the existing research focused on the two-phase flow in circular tubes, without concentric structures. The purpose of this paper was to reveal the two-phase flow characteristics for R134a in both horizontal and vertical upward flow between two concentric tubes by capacitance sensors. The capacitive signals corresponding to different vapor qualities were measured with the mass fluxes from 18.37 kg m−2 s−1 to 64.31 kg m−2 s−1. The experimental data showed that the value of the time-averaged capacitive signal was mainly determined by the vapor quality. The measured capacitance was independent of the mass flux and electrode width, but greatly influenced by the flow direction. The result in horizontal flow was flatter when the fluid was closer to the single-phase and steeper at moderate vapor quality (from 0.1 to 0.9), while it was close to a straight line in vertical upward flow. Moreover, the capacitive signals had oscillation characteristics. By the probability density function, it was found that the amplitude features and oscillation levels were related to the flow patterns. The amplitude degree reflected the stability of the two-phase flow. The oscillation levels could be explained by the flow pattern transition. The corresponding relationship between flow patterns and oscillation characteristics was discovered, which could provide more information for the identification of flow patterns.

Experimental investigations of combustion oscillation modes in a large-aspect-ratio dual-mode combustor equipped with multi-strut

The annular scramjet combustor is considered one of the best configurations for a wide-speed-range combined engine, owing to its superior thermal protection performance and optimal geometric compatibility with rockets and turbines. To investigate the effect of fuel injection methods on the flame oscillation characteristics in the annular combustor, a scaled-down experiment was conducted on a fan-shaped combustor with a high aspect ratio equipped with multiple struts, utilizing liquid kerosene as the fuel. A series of experiments were conducted at the combustor inlet conditions of Ma = 2.7, Pt = 1.68 MPa, and Tt = 1640 K. High-speed cameras and pressure measurements were used in the experiments, and the flame images were processed using proper orthogonal decomposition. The findings revealed that under single-strut and multi-strut injection conditions, the flame oscillated in two modes: shear layer oscillation and central flame oscillation. As the equivalent ratio of injection strut increased, the oscillation frequency increased from 25 to 284 Hz, and the oscillation mode transition caused by the adverse pressure gradient occurred. The flashback was closely related to the combustion mode, and the distinct flame propagation processes under supersonic and subsonic flow conditions resulted in different oscillation characteristics. The experiment demonstrated that the flashback issue could be mitigated by increasing the spacing between the fuel injection struts. The study in this paper will provide important references for future research on flame oscillation and propagation characteristics in high-aspect-ratio annular combustors.

A miniature tunable quadrature shadow oscillator with orthogonal control

This article presents a new design of a quadrature shadow oscillator. The oscillator is realized using one input and two outputs of a second-order filter cell together with external amplifiers in a feedback configuration. The oscillation characteristics are controlled via the external gain without disturbing the internal filter cell, following the concept of the shadow oscillator. The proposed circuit configuration is simple with a small component-count. It consists of, two voltage-different transconductance amplifiers (VDTAs) along with a couple of passive elements. The frequency of oscillation (FO) and the condition of oscillation (CO) are controlled orthogonally via the dc bias current and external gain. Moreover, with the addition of the external gain, the frequency range of oscillation can be further extended. The proposed work is verified by computer simulation with the use of 180 nm complementary metal–oxide–semiconductor (CMOS) model parameters. The simulation gives satisfactory results of two sinusoidal output signals in quadrature with some small total harmonic distortions (THD). In addition, a circuit experiment is performed using the commercial operational transconductance amplifiers LM13700 as the active components. The circuit experiment also demonstrates satisfactory outcome which confirms the validity of the proposed circuit.

Temporal characteristics of hypersonic flows over a double wedge with Reynolds number

Laminar hypersonic flows at Mach 7.10 with unit Reynolds numbers of 5.2×104, 1.04×105, and 4.14×105 m−1 over a 30°/55° double-wedge configuration were studied to investigate the spatial–temporal characteristics of the flow in a time-accurate manner. Close comparisons were made between previous kinetic and current continuum approaches to test the validity of the continuum assumption, especially considering the presence of large gradients associated with shock–shock and shock–boundary layer interactions, as well as spanwise instabilities. Previous results from direct simulation Monte Carlo, which inherently predicts rarefied effects such as velocity slip and temperature jumps, were found to be in very close agreement with the current work, even for the lowest Reynolds number. The impact of velocity slip and temperature jumps on flow and surface parameters was investigated, and comparisons were made with a no-slip and constant temperature wall model. The temporal and spatial variation of two- and three-dimensional flows were thoroughly investigated using two-dimensional (2D), three-dimensional (3D) periodic sidewall boundary conditions, and a full 3D configuration consistent with existing experimental data. Close comparisons among the 2D and 3D cases were made. The characteristics of 2D periodic oscillations were reported for the moderate Reynolds number case for the first time. The presence of spanwise instabilities, even at a relatively low free stream pressure of about 100 Pa, establishes that the flow field depends on spanwise effects and is fully 3D. High-fidelity numerical schlieren videos captured strong spanwise oscillations for 3D configurations.

Application of heat transfer at the combustor wall to attenuate self-excited thermoacoustic oscillations

Self-sustained thermoacoustic oscillations (also known as combustion instability) arise in combustors when pressure and heat release fluctuations couple to produce high-energy sound waves. The need for diverse strategies to control these oscillations will increase as future design moves towards highly efficient, lean combustors. In this work, the impact of heat transfer at the combustor wall on the generation of thermoacoustic oscillations is examined through computational fluid dynamics. Characteristics of the thermoacoustic oscillations generated across cases with a range of thermal boundary conditions are compared to an adiabatic reference case. The amplitude of limit cycle oscillations in a Rijke tube is seen to decrease as wall temperatures increase. A stable combustor with a negative growth rate is observed when the full outer wall is heated to 900 K, and a sound pressure level reduction of 75 dB is achieved. The most efficient stable configuration is achieved when only the inlet duct wall is heated to 1000 K, requiring a minimum of 430 W of input power. The present work introduces an alternative stable combustor design and demonstrates that optimizing the temperature distribution of the combustor wall can effectively dampen thermoacoustic oscillations.