In high-speed rail operations, contact wire irregularity (CWI) in a catenary is a common disturbance to the pantograph-catenary interaction performance, which directly affects the quality of current ...collection. To describe the pointwise stochastics of CWI, the power spectral density (PSD) function for CWI is proposed, and its effect on the pantograph-catenary interaction is investigated. First, a preprocessing procedure is proposed to eliminate the redundant information in the measured irregularities based on the ensemble empirical mode decomposition (EEMD). Then, the upper envelope of the irregularity, which contains all the information regarding the dropper positions on the contact wire, is extracted. A form of the PSD function is suggested for contact wire irregularities. A methodology is proposed to include the effect of random irregularities in the assessment of the interaction performance of a pantograph-catenary. A developed target configuration under dead load (TCUD) method is used to calculate the initial configuration of the catenary, in which the dropper points on the contact wire are placed on their exact positions. Finally, the effect of the random contact wire irregularities on the contact force is investigated through 500 numerical simulations at each operating speed. The present results indicate that random irregularities have a direct impact on the pantograph-catenary contact, including an increment in the dispersion of the contact force statistics. The stochastic analysis shows that over 70% of the results with irregularities are worse than the ideal result without irregularities.
This manuscript presents a systematic low-frequency noise analysis of inversion-mode vertically stacked silicon n-channel nanosheet MOSFETs on bulk wafers. Flicker noise due to carrier number ...fluctuations is shown as the dominant noise source, which is in line with previous reported studies on gate-all-around (GAA) nanowire nMOSFETs. In addition, the benchmark points out that the vertical stacking approach does not deteriorate the oxide trap density, since its normalized input-referred voltage noise Power Spectral Density at flat-band is lower compared to the data on non-stacked horizontal nanowire nMOSFETs. Another finding is that the Coulomb scattering mechanism dominates the mobility.
We show how LIGO is expected to detect coalescing binary black holes at z>1 that are lensed by the intervening galaxy population. Gravitational magnification, μ, strengthens gravitational-wave ...signals by μ without altering their frequencies, which if unrecognized leads to an underestimate of the event redshift and hence an overestimate of the binary mass. High magnifications can be reached for coalescing binaries, because the region of intense gravitational-wave emission during coalescence is so small (∼100 km), permitting very close projections between lensing caustics and gravitational-wave events. Our simulations use the current LIGO event-based mass function and incorporate accurate waveforms convolved with the LIGO power spectral density. Importantly, we include the detection dependence on sky position and orbital orientation, which for the LIGO configuration translates into a wide spread in observed redshifts and chirp masses. Currently, we estimate a detectable rate of lensed events 0.06−0.02+0.02 yr−1 that rises to 5−3+5 yr−1 at LIGO design sensitivity limit, depending on the high redshift rate of black hole coalescence.
•A multi-taper S-transform (MTST) method for estimating evolutionary power spectral density and coherence is provided.•The analytical expressions for the bias and variance of the EPSD and coherence ...estimators by the MTST method are deduced.•The superiority of the MTST method is numerically confirmed.•The MTST method is applied to the wind speed data recorded during Tropical Storm Wipha.
A multi-taper S-transform (MTST) method for estimating evolutionary power spectral density (EPSD) and coherence of multi-variate non-stationary processes is introduced in this paper. With a set of orthogonal time–frequency Hermite windows, the MTST method can simultaneously lead to sufficient resolution for the EPSD and coherence estimates and reduce their estimation variance. This method is applicable even in the case of only one realization available. The bias and variance of the EPSD and coherence estimators from the MTST method are deduced under the assumption that two univariate non-stationary processes are Gaussian and their auto-EPSDs have the same shape. The superiority of the MTST method is numerically confirmed through a comparison with the Priestley method and wavelet-based method. The applicability of the MTST method is finally demonstrated by applying the method to wind speed data measured during Tropical Storm Wipha.
•The hybrid spectral modeling method based on fault dynamics and LSTM is proposed.•Through overlapping weighted averaging, the PSD of planetary system is estimated.•The proposed method is verified ...via a planetary gearbox test rig.
It is the prerequisite for mechanical diagnosis to clarify the mapping relations between vibrations and damage conditions based on the dynamic model analyses and the systematic experiments. However, there is a certain deviation from the actual measurements in the existing planetary dynamic modeling methods which utilizes linear models or just considering simple non-linear factors. To solve the problem, the hybrid spectral modeling method based on the fault dynamics analysis and the long short-term memory (LSTM) network is proposed in this paper. Firstly, the response of several parts in planetary sets are simulated by the classical dynamic method. Then, as an exploratory attempt, an LSTM network is used to rectify the predicted spectral deviation caused by the over-simplification and parameter errors of the dynamic models. From the inputs of simulated spectral sequences of the several components, the LSTM successfully predicts the spectral sequence of the observation. Finally, by the overlapping weighted average, the power spectral density of the planetary system is estimated through the Welch method. The effectiveness and superiority of the proposed method are verified via the experimental data of a planetary gearbox test rig.
•The signal analysis step has been adopted in absolute surface error calibration for filtering out undesirable rotations angle.•The algorithm validation technology of the calibration was conducted ...using randomly generated surface profiles with power spectral density from experiment.•Quantitative analysis and calibration were performed to assess errors introduced by clamping stress, vibrations, airflow disturbances, angular errors and eccentricity.•The verification was conducted with standard mirror to prove the robustness, accuracy, and responsiveness.
A novel absolute surface calibration method for interferometer testing based on power spectral density analysis has been proposed. The method involves obtaining the loss of signal at different frequencies as a function of various rotation angles by signal analysis to choose the rotation angle for calibration. A model is developed to evaluate the calibration method by creating random surface shapes based on the Power Spectral Density. Using this algorithm, the precision of the absolute testing method during the testing process exceeds 0.28 %. Error propagation during the experimental process, such as testing optic clamping, angular errors, eccentricity, vibrations and airflow disturbances, were calibrated. Ultimately, the absolute detection test results were verified using high-precision flat mirrors. The experimental result indicates an RMS of 4.275 nm, 4.263 nm, and 4.265 nm in different rotation angle, and the calibrated result shows an RMS of 4.880 nm. The shape of surface errors in the absolute test results and calibration results is consistent.
Chinese high‐speed railway (HSR) network construction has expanded into earthquake‐prone areas. In this context, analyses of post‐seismic residual track irregularity and post‐seismic train speed ...threshold are vital. With a HSR bridge with track system taken as the study object, time‐domain signal for target post‐seismic residual track irregularity was constructed based on the Gaussian pulse translation theory. The response spectra of fitted post‐seismic residual track irregularity applicable to stochastic structures were established, thus providing irregularity input for ascertaining post‐seismic speed threshold. The results show that residual alignment irregularity has a large amplitude under transverse seismic actions; by contrast, cross‐level, gauge, and vertical irregularities showed small amplitudes. The evolution power spectral density (EPSD) of the stochastic post‐seismic residual track irregularities obeys a definite distribution in any frequency‐space coordinate. A uniquely deterministic target post‐seismic residual track irregularity can be constructed based on the stochastic irregularity set, and its safety guarantee rate can be precisely controlled by varying the significance level. Taking the first‐order transverse natural vibration period as the x‐axis and the amplitude of fitted post‐seismic residual track irregularity as the y‐axis, the response spectra of fitted post‐seismic residual track irregularity can be created. The irregularity response spectra are applicable to stochastic structures.
Multiple sclerosis (MS) is a neurodegenerative autoimmune disease affecting the central nervous system, leading to various neurological symptoms. Early detection is paramount to prevent enduring ...damage during MS episodes. Although magnetic resonance imaging (MRI) is a common diagnostic tool, this study aims to explore the feasibility of using electroencephalography (EEG) signals for MS detection, considering their accessibility and ease of application compared to MRI.
The study involved the analysis of EEG signals during rest from 17 MS patients and 27 healthy volunteers to investigate MS-healthy patterns. Power spectral density features (PSD) were extracted from the 32-channel EEG signals. The study employed Linear Discriminant Analysis (LDA), Support Vector Machine (SVM), Classification and Regression Trees (CART), and k-Nearest Neighbor (kNN) classifiers to identify channels with the highest accuracy. Notably, the study achieved 100% accuracy in MS detection using the “Fp1” and “Pz” channels with the LDA classifier. A statistical analysis, utilizing the independent sample t-test, was conducted to explore whether PSD features of these channels differed significantly between healthy individuals and those with MS.
The results of the study demonstrate that effective detection of MS can be achieved using PSD features from only two channels of the EEG signal. Specifically, the “Fp1” and “Pz” channels exhibited 100% accuracy in MS detection with the LDA classifier. The statistical analysis further explored and confirmed the significant differences in PSD features between healthy individuals and MS patients.
The study concludes that the proposed method, utilizing PSD features from specific EEG channels, offers a straightforward and efficient diagnostic approach for the effective detection of MS. The findings suggest the potential utility of EEG signals as a non-invasive and accessible alternative for MS detection, highlighting the importance of further research in this direction.
•Introduction of the first healthy-MS classification method achieving 100% accuracy using only two channels of EEG signals obtained during rest.•Utilization of band powers, band power ratios, and relative powers of subbands obtained through the Fast Fourier Transform (FFT) during the resting state for classification purposes.•Implementation of subject-independent classification through Leave-One Subject Out Cross Validation, ensuring robustness and generalizability of the classification model.•Comprehensive classification of all possible channel pairs in EEG using various algorithms such as LDA, SVM, CART, and kNN, followed by comparison of their performances to determine the most effective approach.
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•A defect in organic coating was investigated by SECM and electrochemical noise.•The reactivity of the defect can be evaluated by probe approach curves.•Amplitude of EN and power ...spectral density are indicators for corrosion reactivity.
The electrochemical reactivity of a defect in organic coating was investigated by electrochemical noise (EN) and scanning electrochemical microscopy (SECM). Time dependent EN spectra and SECM image on a metal with defective organic coating was measured, and corresponding EN frequency domain spectra and probe approach curves (PACs) were used to obtain electrochemical reactivity information within the coating defects. All time domain and frequency domain analyses, and SECM measurements were successful indicators of corrosion intensity within the defect. The amplitude of electrochemical current noise (ECN) and the low-frequency plateau of the power spectral density (PSD) WL increased significantly with corrosion intensity.
Due to the independence of input spectra, the transmissibility-based operational modal analysis (OMA) methods have been developed rapidly over the last two decades. The response transmissibility (RT) ...methods can extract the modal parameters from multiple different load cases while the power spectral density transmissibility (PSDT) methods just use one single load case by combining multiple transfer outputs. Their ability to identify modal parameters under non-white excitations has been claimed, verified and applied by many researches. However, some problems, such as the robustness under different load conditions, the extent of noise influence and the application conditions, still arise when they are applied in the real field. Moreover, the comparison between different transmissibility-based methods on the identification accuracy and robustness is rare, which is significant for users to select the very method for their tasks.
Four representative transmissibility-based OMA methods are considered and compared in this paper. The influence factors of RT and PSDT functions are analyzed first and the results reveal the requirements of the load case for four OMA methods. A numerical example is used to assess and compare the robustness of four methods to measurement noises, damping ratio of non-white noise excitations, non-fully-excited load cases and harmonic excitations, and their identification ability is further evaluated through a real field example. The results show that the transmissibility-based OMA methods are independent of input spectra only under certain conditions and some user-defined parameters play important roles in their identification ability.
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