Щоб переглянути інші типи публікацій з цієї теми, перейдіть за посиланням: POWER SPECTRUM CONDITION.
Статті в журналах з теми "POWER SPECTRUM CONDITION"
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-50 статей у журналах для дослідження на тему "POWER SPECTRUM CONDITION".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте статті в журналах для різних дисциплін та оформлюйте правильно вашу бібліографію.
1
Bhattarai, Shishir, and Prem Nath Maskey. "Effect of Linear Soil Condition on Seismic Inputs." Technical Journal 2, no. 1 (November 10, 2020): 48–55. http://dx.doi.org/10.3126/tj.v2i1.32829.
Повний текст джерелаАнотація:
Seismic inputs to structures in terms of risk consistent response spectrum and seismic hazard curves are developed at bedrock level considering ten independent seismic source zone in the vicinity of the Kathmandu valley. The seismic hazard curve is derived by assuming temporal occurrence of earthquakes to follow Poisson model. Response spectrum is developed using an empirical relationship of spectral ordinates with magnitude of earthquakes and epicentral distance. The seismic risk factor is introduced in response spectrum using conditional probabilities. Power spectral density function consistent with response spectrum is derived and ground acceleration time histories are derived from power spectral density function using Monte Carlo technique. To obtain free field hazard curves and ground motion parameters, one dimensional wave propagation analysis is used for two different underlying soil conditions.
2
Su, J. K., and B. Girod. "Power-spectrum condition for energy-efficient watermarking." IEEE Transactions on Multimedia 4, no. 4 (December 2002): 551–60. http://dx.doi.org/10.1109/tmm.2002.806535.
Повний текст джерела
3
Chandra, Rajorshi Sushovan, and Tarun Souradeep. "Primordial Power Spectrum reconstruction from CMB Weak Lensing Power Spectrum." Journal of Cosmology and Astroparticle Physics 2021, no. 10 (October 1, 2021): 081. http://dx.doi.org/10.1088/1475-7516/2021/10/081.
Повний текст джерелаАнотація:
Abstract We use the modified and improved Richardson-Lucy (IRL) deconvolution algorithm to reconstruct the Primordial Power Spectrum (PPS) from the Weak Lensing Power Spectrum CL ϕϕ reconstructed from CMB anisotropies. This provides an independent window to observe and constrain the PPS PR (k) along different k scales as compared to CMB Temperature Power Spectrum. The Weak Lensing Power Spectrum does not contain secondary variations in power and hence is cleaner, unlike the Temperature Power Spectrum which suffers from lensing which must be addressed during PPS reconstructions. We demonstrate that the physical behaviour of the weak lensing kernel is unique and reconstructs broad features over k. We provide an in-depth analysis of the error propagation using simulated data and Monte-Carlo sampling, using Planck best-fit cosmological parameters to simulate the data with cosmic variance limited error bars. The error and initial condition analyses provide a clear picture of the optimal reconstruction region for the estimator while providing a detailed statistical insight of the results. We also provide an algorithm for PR (k) sampling sparsity to be used based on the given data and errors, to optimize statistical significance. Eventually we plan to use this method on actual mission data and provide a cross reference to PPS reconstructed from other sectors and any possible features in them.
4
Zhang, Yu, Tong Zhu, and Jing Zhou. "Understanding Power Spectrum Density Transmissibility." Shock and Vibration 2016 (2016): 1–9. http://dx.doi.org/10.1155/2016/8479721.
Повний текст джерелаАнотація:
Power spectrum density transmissibility (PSDT) is a type of complex frequency domain function proposed recently. It describes the relation between cross-spectra of system outputs. Since PSDTs with same local-reference degree of freedom (DOF) combination but with different transferring output DOFs cross each other at the system’s poles under certain load condition, the functions have been used as the primary data in operational modal analysis (OMA) to extract modal parameters, and such technique is named as PSDT-based OMA (PSDTOMA). Because PSDT is a concept that appears recently, researches on which, especially, in-depth discussions aim at the essence and properties of PSDT are very rare. For appropriate application of PSDTOMA, it is necessary to perform further study on such problem obviously. In this paper, two paths to get PSDT, which, respectively, are referred to as PSDT estimator and PSDT syntheticism, are given firstly; some properties about PSDT are explored based on the PSDT syntheticism, and the relation between PSDT and single reference transmissibility function (STF) is analyzed. Finally, the above conclusions are verified with numerical values and experimental data.
5
Kunz, Torben, and Richard J. Greatbatch. "Effect of the Kinematic Lower Boundary Condition on the Spectral and Autocorrelation Structure of Annular Variability in the Troposphere." Journal of the Atmospheric Sciences 71, no. 6 (May 30, 2014): 2264–79. http://dx.doi.org/10.1175/jas-d-13-0104.1.
Повний текст джерелаАнотація:
Abstract The dynamical origin of the spectral and autocorrelation structure of annular variability in the troposphere is investigated by a deductive approach. Specifically, the structure of the power spectrum and autocorrelation function of the zonal-mean geopotential is analyzed for the case of a quasigeostrophic spherical atmosphere subject to a white noise mechanical forcing applied in a single Hough mode and concentrated at a particular level in the vertical, with vertically uniform Newtonian cooling and Rayleigh drag concentrated at a rigid lower boundary. Analytic expressions for the power spectrum are presented together with expressions for an approximate red noise (i.e., a Lorentzian-shaped) power spectrum. It is found that for an infinitely deep atmosphere the power spectrum can be well approximated by a red noise process for the first few Hough modes (associated with large Rossby heights), provided the distance from the forcing is not larger than about one Rossby height. When a frictional rigid lower boundary is included, however, the approximation is generally bad. The high-frequency part of the power spectrum exhibits near-exponential behavior and the autocorrelation function shows a transition from a rapid decay at short lags to a much slower decay at longer lags, if the thermal and mechanical damping time scales are sufficiently well separated. Since observed annular variability exhibits the same characteristics, the above results lead to the hypothesis that these characteristics may, to some extent, be intrinsic to the linear zonal-mean response problem—although the need for an additional contribution from eddy feedbacks is also implied by the results.
6
Liu, Yunjuan, and Dongsheng Chen. "An analysis on EEG power spectrum under pressure of girdle." International Journal of Clothing Science and Technology 27, no. 4 (August 3, 2015): 495–505. http://dx.doi.org/10.1108/ijcst-05-2014-0065.
Повний текст джерелаАнотація:
Purpose – The pressure exerted on the body by clothes is one important factor affecting the comfort of clothing, it is an effective method to evaluate pressure comfort by physiology and psychology. The purpose of this paper is to measure, electroencephalography (EEG), an index of brain activity in order to examine the effect on brain activity conditions caused by oppression exerted by clothing on the body. Design/methodology/approach – EEG power spectrum analysis was conduct to verify the electrophysiological characteristic of brain caused by pressure on the body by girdle. Findings – Experimental results showed that the intensity of α waves in the pressure condition is decreased compared to the non-pressure condition, and the somatosensory activated by pressure of girdle mainly in occipital, frontal and parietal region of brain. Originality/value – It was clarified that it is impossible to evaluate the clothes pressure by physiological technique of EEG, this study has enriched methods of evaluation pressure comfort.
7
Mnif, M., N. Smaoui, L. Triki, J. Donia, R. Feki, I. Gassara, S. Omri, et al. "EEG power spectrum analysis for Tunisian schizophrenic patients." European Psychiatry 66, S1 (March 2023): S1075. http://dx.doi.org/10.1192/j.eurpsy.2023.2283.
Повний текст джерелаАнотація:
IntroductionSchizophrenia (SCZ) is a common and disabling psychiatric condition. Its diagnosis is entirely clinical. Many researchers have looked into electroencephalogram (EEG) power spectrum analysis for SCZ to find specific abnormalities.Objectives The objective of this study was to analyze the EEG of patients with SCZ using power spectral density and to compare them with those of healthy controls, in order to look for specificities.Methods This was a cross-sectional, descriptive, and analytical case-control study conducted with patients followed for SCZ in the psychiatry "C" department at the Hedi Chaker hospital in Sfax. Healthy controls were included. Patients were assessed by the Positive and Negative schizophrenia scale (PANSS). All participants benefited from an EEG at rest condition at the service of the functional exploration at the Habib Bourguiba hospital in Sfax. We have measured the powers of each band using Welch power spectral density method called absolute power (AP). Statistical analyses were carried out.ResultsFifteen schizophrenics and 15 controls, all male, were included. The average age of schizophrenics and healthy controls was 40 years ±12.72 years and 47.93 ± 15.61 years respectively. There were no significant differences in age between patients and controls. Schizophrenics had a mean PANSS of 64.6±22.7.At the quantitative EEG, differences appeared to be insignificant. There was an overall decrease in AP for the alpha band particularly in the parietal and occipital lobes in schizophrenics (53,16 ± 48,83 μV2 and 75,17 ± 56,28 μV2 respectively) compared to controls (335,15 ± 994,73 μV2 and 400,24 ± 1109,95 μV2 respectively). There was also an overall decrease in AP for the different frequency bands in schizophrenics compared to controls. However, values persisted high in the temporal lobe for all frequency bands.ConclusionsIn conclusion, this decrease in AP for the alpha band in the parietal and occipital lobes in schizophrenics can be a sensitive biomarker for diagnosing SCZ.Disclosure of InterestNone Declared
8
Bouissou, P., P. Y. Estrade, F. Goubel, C. Y. Guezennec, and B. Serrurier. "Surface EMG power spectrum and intramuscular pH in human vastus lateralis muscle during dynamic exercise." Journal of Applied Physiology 67, no. 3 (September 1, 1989): 1245–49. http://dx.doi.org/10.1152/jappl.1989.67.3.1245.
Повний текст джерелаАнотація:
The relationship between intramuscular pH and the frequency components of the surface electromyographic (EMG) power spectrum from the vastus lateralis muscle was studied in eight healthy male subjects during brief dynamic exercise. The studies were carried out in placebo control and metabolic alkalosis induced by oral administration of NaHCO3. At the onset of exercise, blood pH was 0.08 units higher in alkalosis compared with placebo. Muscle lactate accumulation during exercise was higher in alkalosis (32 +/- 5 mmol/kg wet wt) than in placebo (17 +/- 4 mmol/kg wet wt), but no difference in intramuscular pH was found between the two conditions. The EMG power spectrum was shifted toward lower frequencies during fatigue in the control condition (10.1 +/- 0.9%), and these spectral shifts, evaluated from changes in the mean power frequency (MPF) of the EMG power spectrum, were further accentuated in alkalosis (19 +/- 2%). Although the changes in frequency components of EMG correlated with muscle lactate accumulation (r = 0.68, P less than 0.01), no direct relationship with muscle pH was observed. We conclude that alkalosis results in a greater reduction in MPF associated with a higher muscle lactate accumulation. However, the good correlation observed between the two variables is not likely causative, and a dissociation between intramuscular pH and the increase in the low-frequency content of EMG power spectrum appears during muscle fatigue.
9
Kornatowski, Eugeniusz. "Mechanical-Condition Assessment of Power Transformer Using Vibroacoustic Analysis." Key Engineering Materials 500 (January 2012): 40–44. http://dx.doi.org/10.4028/www.scientific.net/kem.500.40.
Повний текст джерелаАнотація:
This paper presents a method for vibroacoustic analysis of a transformer in the steady state. The standard approach to this problem has been based on analysis of the vibration frequency spectrum recorded with an accelerometer mounted on the transformer’s tank. To improve legibility of measurement results, the paper suggests the analysis method for the relative coefficient of harmonic frequency contents hnorm(f). The conducted experiment showed that high values of hnorm within a wide frequency range testify to deformation of windings and degradation of solid insulation.
10
Eastham, M. S. P., and K. M. Schmidt. "Absence of high-energy spectral concentration for Dirac systems with divergent potentials." Proceedings of the Royal Society of Edinburgh: Section A Mathematics 135, no. 4 (August 2005): 689–702. http://dx.doi.org/10.1017/s0308210500004078.
Повний текст джерелаАнотація:
It is known that one-dimensional Dirac systems with potentials q which tend to −∞ (or ∞) at infinity, such that 1/q is of bounded variation, have a purely absolutely continuous spectrum covering the whole real line. We show that, for the system on a half-line, there are no local maxima of the spectral density (points of spectral concentration) above some value of the spectral parameter if q satisfies certain additional regularity conditions. These conditions admit thrice-differentiable potentials of power or exponential growth. The eventual sign of the derivative of the spectral density depends on the boundary condition imposed at the regular end-point.
11
Eastham, M. S. P., and K. M. Schmidt. "Absence of high-energy spectral concentration for Dirac systems with divergent potentials." Proceedings of the Royal Society of Edinburgh: Section A Mathematics 135, no. 4 (August 2005): 689–702. http://dx.doi.org/10.1017/s0308210505000351.
Повний текст джерелаАнотація:
It is known that one-dimensional Dirac systems with potentials q which tend to −∞ (or ∞) at infinity, such that 1/q is of bounded variation, have a purely absolutely continuous spectrum covering the whole real line. We show that, for the system on a half-line, there are no local maxima of the spectral density (points of spectral concentration) above some value of the spectral parameter if q satisfies certain additional regularity conditions. These conditions admit thrice-differentiable potentials of power or exponential growth. The eventual sign of the derivative of the spectral density depends on the boundary condition imposed at the regular end-point.
12
DING, JIANMIN, and SHIU-WING TAM. "ASYMPTOTIC POWER SPECTRUM ANALYSIS OF CHAOTIC BEHAVIOR IN FLUIDIZED BEDS." International Journal of Bifurcation and Chaos 04, no. 02 (April 1994): 327–41. http://dx.doi.org/10.1142/s021812749400023x.
Повний текст джерелаАнотація:
The nonlinear behavior of fluidized beds is analyzed quantitatively using an asymptotic power spectrum method. A model based on kinetic theory is used to compute the voidage signals in a two-dimensional bubbling fluidized bed with a fluidization condition of U/Umf=4, where U is the fluidizing velocity and Umf is the minimum fluidizing velocity. The data for power versus frequency in the asymptotic frequency regime are shown to obey a power-law falloff. This means that the bubbling fluidization under such a fluidization condition cannot be a low-dimensional strange attractor. Pressure fluctuation data, obtained from a three-dimensional bubbling fluidized bed, are also analyzed and clearly show the power-law falloff. This is consistent with previous findings in that the correlation dimension for these data cannot be small (i.e., 2 or 3). The differences between our findings and others are discussed.
13
Martinez, Mathieu, Sergey Kotov, David De Vleeschouwer, Damien Pas, and Heiko Pälike. "Testing the impact of stratigraphic uncertainty on spectral analyses of sedimentary series." Climate of the Past 12, no. 9 (September 2, 2016): 1765–83. http://dx.doi.org/10.5194/cp-12-1765-2016.
Повний текст джерелаАнотація:
Abstract. Spectral analysis is a key tool for identifying periodic patterns in sedimentary sequences, including astronomically related orbital signals. While most spectral analysis methods require equally spaced samples, this condition is rarely achieved either in the field or when sampling sediment core. Here, we propose a method to assess the impact of the uncertainty or error made in the measurement of the sample stratigraphic position on the resulting power spectra. We apply a Monte Carlo procedure to randomise the sample steps of depth series using a gamma distribution. Such a distribution preserves the stratigraphic order of samples and allows controlling the average and the variance of the distribution of sample distances after randomisation. We apply the Monte Carlo procedure on two geological datasets and find that gamma distribution of sample distances completely smooths the spectrum at high frequencies and decreases the power and significance levels of the spectral peaks in an important proportion of the spectrum. At 5 % of stratigraphic uncertainty, a small portion of the spectrum is completely smoothed. Taking at least three samples per thinnest cycle of interest should allow this cycle to be still observed in the spectrum, while taking at least four samples per thinnest cycle of interest should allow its significance levels to be preserved in the spectrum. At 10 and 15 % uncertainty, these thresholds increase, and taking at least four samples per thinnest cycle of interest should allow the targeted cycles to be still observed in the spectrum. In addition, taking at least 10 samples per thinnest cycle of interest should allow their significance levels to be preserved. For robust applications of the power spectrum in further studies, we suggest providing a strong control of the measurement of the sample position. A density of 10 samples per putative precession cycle is a safe sampling density for preserving spectral power and significance level in the Milankovitch band. For lower sampling density, the use of gamma-law simulations should help in assessing the impact of stratigraphic uncertainty in the power spectrum in the Milankovitch band. Gamma-law simulations can also model the distortions of the Milankovitch record in sedimentary series due to variations in the sedimentation rate.
14
Ren, Sun, Zhang, and Zhao. "The Effect of Light Source Line Width on the Spectrum Resolution of Dual-Frequency Coherent Detection Signals." Sensors 19, no. 23 (November 29, 2019): 5264. http://dx.doi.org/10.3390/s19235264.
Повний текст джерелаАнотація:
In this paper, the power spectrum resolution problem of dual-frequency coherent mixing signals is analyzed when the Doppler frequency difference is small. The power spectrum function formula of the four optical coherent mixing signals is obtained using statistical theory and the Wiener–Khinchin theorem. The influence of delay time and light source line width on the power spectrum of dual-frequency coherent signals is analyzed using this formula. The results show that delay time only affects the peak of the power spectrum of the coherent signal. An increase in the line width of the light source broadens the signal power spectrum and reduces the peak value. The necessary condition for distinguishing the Doppler frequency difference is that the theoretical Doppler frequency difference is greater than 1/5 times the line width of the light source.
15
Zakora, D. A. "Spectral properties of operators in the problem on normal oscillations of a mixture of viscous compressible fluids." Contemporary Mathematics. Fundamental Directions 69, no. 1 (March 31, 2023): 73–97. http://dx.doi.org/10.22363/2413-3639-2023-69-1-73-97.
Повний текст джерелаАнотація:
In this paper, we study a problem of normal oscillations of a homogeneous mixture of several viscous compressible fluids filling a bounded domain of three-dimensional space with an infinitely smooth boundary. Two boundary conditions are considered: the no-slip condition and the slip condition without shear stresses. It is proved that the essential spectrum of the problem in both cases is a finite set of segments located on the real axis. The discrete spectrum lies on the real axis, except perhaps for a finite number of complex conjugate eigenvalues. The spectrum of the problem contains a subsequence of eigenvalues with a limit point at infinity and a power-law asymptotic distribution.
16
Shabbir, Noman, Lauri Kütt, Bilal Asad, Muhammad Jawad, Muhammad Naveed Iqbal, and Kamran Daniel. "Spectrum Analysis for Condition Monitoring and Fault Diagnosis of Ventilation Motor: A Case Study." Energies 14, no. 7 (April 5, 2021): 2001. http://dx.doi.org/10.3390/en14072001.
Повний текст джерелаАнотація:
In modern power systems, since most loads are inductive by nature, there is an ongoing power quality issue and researchers’ interest in improving the power factor is widespread, as inductive loads have a low power factor that depletes the system’s capacity and has an adverse effect on the voltage level. The measurement and acute analysis of voltage- and current-level waveforms is essential to tackle power quality issues. This article presents a detailed case study and analysis of real-time data measured from a frequency converter, which is used to operate the motor of a ventilation system. The output of the frequency converter is a highly distorted current wave. A hybrid Fourier transform (FT)- and wavelet transform-based solution has been proposed here to diagnose and identify the causes of motor failure in the ventilation system. The traditional FT did not give a detailed analysis of this type of signal, which is highly contaminated by noise. Therefore, first, the signal is preprocessed for data denoising using the wavelet transform. Second, the Fourier analysis is performed on the filtered signal for frequency analysis and segregation of fundamental frequency components, higher-order harmonics, and suppressed noise. The spectrum analysis reveals that the noise is generated due to the rapidly switching circuits in the frequency converter and this unfiltered signal at the output of the frequency converter causes motor failure.
17
Huang, Qihong, Kaituo Zhang, He Huang, Bing Xu, and Feiquan Tu. "CMB Power Spectrum in the Emergent Universe with K-Essence." Universe 9, no. 5 (May 6, 2023): 221. http://dx.doi.org/10.3390/universe9050221.
Повний текст джерелаАнотація:
The emergent universe provides a possible method to avoid the Big Bang singularity by considering that the universe stems from a stable Einstein static universe rather than the singularity. Since the Einstein static universe exists before inflation, it may leave some relics in the CMB power spectrum. In this paper, we analyze the stability condition for the Einstein static universe in general relativity with k-essence against both the scalar and tensor perturbations. Furthermore, we find the emergent universe can be successfully realized by constructing a scalar potential and an equation of state parameter. Solving the curved Mukhanov–Sasaki equation, we obtain the analytical approximation for the primordial power spectrum, and then depict the TT-spectrum of the emergent universe. The results show that both the primordial power spectrum and CMB TT-spectrum are suppressed on large scales.
18
Yu, Xiao Guang, and Jian Liu. "Research on Fault Diagnosis and Application for Rolling Element Bearing Based on Fuzzy Analysis." Advanced Materials Research 189-193 (February 2011): 1358–61. http://dx.doi.org/10.4028/www.scientific.net/amr.189-193.1358.
Повний текст джерелаАнотація:
In order to simulate the fault of a single rolling bearing, this paper used the fault diagnosis lab desk to simulate some representative conditions of 30205 type of rolling element bearing, including regular condition, inner ring fault, outer ring fault and rolling body fault. It also adopted fuzzy theory to analyze signals and diagnose faults on the base of the MATLAB software desk. This paper also adopts the amplitude spectrum, the power spectrum, the envelope demodulated spectrum and the delayed correlation-envelop spectrum to diagnosis and analyze simulating signals. Comparatively, the fuzzy diagnosis theory is dependable．
19
KE, KE. "A GENERAL INITIAL CONDITION OF INFLATIONARY COSMOLOGY ON TRANS-PLANCKIAN PHYSICS." International Journal of Modern Physics A 20, no. 18 (July 20, 2005): 4331–35. http://dx.doi.org/10.1142/s0217751x05021178.
Повний текст джерелаАнотація:
We consider a more general initial condition satisfying the minimal uncertainty relationship. We calculate the power spectrum of a simple model in inflationary cosmology. The results depend on perturbations generated below a fundamental scale, e.g. the Planck scale.
20
Jiang, Ruilong, Jin Chen, Guangming Dong, Tao Liu, and Wenbin Xiao. "The weak fault diagnosis and condition monitoring of rolling element bearing using minimum entropy deconvolution and envelop spectrum." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 227, no. 5 (August 17, 2012): 1116–29. http://dx.doi.org/10.1177/0954406212457892.
Повний текст джерелаАнотація:
In vibration analysis, weak fault detect and diagnosis is of great importance. A method based on minimum entropy deconvolution and envelop spectrum analysis is proposed in this article. Minimum entropy deconvolution technique searches for an optimal set of filter coefficients to enhance the impulse making the filtered signal to contain clearer fault information. When there is a fault in bearing, it can be obviously reflected by the power spectral density estimation of the filtered signal even if the power spectral density estimation of original signal denies the information. The filtered signals are then analyzed by performing envelop spectrum analysis, where the bearing characteristic frequencies are quite clear for further diagnosis. The feasibility and validity of utilizing the minimum entropy deconvolution in weak fault diagnosis and condition monitoring is demonstrated by both simulation and experiments. The analysis of actual data from accelerated life test of rolling bearing shows that it can detect and diagnose fault 7 min earlier than RMS can reflect while the entire life takes 1962 min. This is considered to be significant in condition monitoring and early incipient fault diagnosis. The results of gearbox test also demonstrates the effective bearing fault diagnosis under strong noise and gear vibration interactions.
21
Alshehawy, Abdelrahman M., Diaa-Eldin A. Mansour, Mohsen Ghali, Matti Lehtonen, and Mohamed M. F. Darwish. "Photoluminescence Spectroscopy Measurements for Effective Condition Assessment of Transformer Insulating Oil." Processes 9, no. 5 (April 21, 2021): 732. http://dx.doi.org/10.3390/pr9050732.
Повний текст джерелаАнотація:
Condition assessment of insulating oil is crucial for the reliable long-term operation of power equipment, especially power transformers. Under thermal aging, critical degradation in oil properties, including chemical, physical, and dielectric properties, occurs due to the generation of aging byproducts. Ultraviolet-visible (UV-Vis) spectroscopy was recently proposed for the condition assessment of mineral oil. However, this absorption technique may involve all electronic states of the investigated material which typically yield a broad spectrum, and thus cannot precisely reflect the electronic structure of aged oil samples. It also cannot be implemented as an online sensor of oil degradation. In this paper, photoluminescence (PL) spectroscopy is introduced, for the first time, for effective condition assessment of insulating oil. The PL technique involves emission processes that only occur between a narrow band of electronic states that are occupied by thermalized electrons and consequently yields a spectrum that is much narrower than that of the absorption spectrum. Aged oil samples with different aging extents were prepared in the laboratory using accelerated aging tests at 120 °C, under which 1 day of laboratory aging is equivalent to approximately 1 year of aging in the field. These aged samples were then tested using PL spectroscopy with a wavelength ranging from 150 nm to 1500 nm. Two main parameters were evaluated for quantitative analysis of PL spectra: The full width at half-maximum and the enclosed area under the PL spectra. These parameters were correlated to the aging extent. In conjunction with PL spectroscopy, the aged oil samples were tested for the dielectric dissipation factor as an indication of the number of aging byproducts. Interestingly, we find a correlation between the PL spectra and the dielectric dissipation factor. The results of PL spectroscopy were compared to those of UV-Vis spectroscopy for the same samples and the parameters extracted from PL spectra were compared to the aging b-products extracted from UV-Vis spectra. Finally, the corresponding physical mechanisms were discussed considering the obtained results and the spectral shift for each spectrum. It was proved that PL spectroscopy is a promising technique for the condition assessment of insulating oil when compared to conventional transformer oil assessment measuring techniques and even to other optical absorption techniques.
22
Putilov, Arcady A., Olga G. Donskaya, and Evgeniy G. Verevkin. "Generalizability of Frequency Weighting Curve for Extraction of Spectral Drowsy Component From the EEG Signals Recorded in Eyes-Closed Condition." Clinical EEG and Neuroscience 48, no. 4 (October 11, 2016): 259–69. http://dx.doi.org/10.1177/1550059416673271.
Повний текст джерелаАнотація:
One of the critical barriers to reducing the threats of sleep loss to public health, safety, and productivity is a lack of practical tools for quick identification of objective level of sleepiness. We examined a novel sleepiness measure named “spectral drowsy component score” to provide evidence for generalizability of a frequency weighting curve required for calculation of this measure. Each spectral drowsy component score is a sum of 16 weighted ln-transformed single-Hz power densities (1-16 Hz) obtained by the fast Fourier transformation of an electroencephalographic signal recorded during the first minute after closing the eyes. A set of 16 weights (frequency weighting curve) is derived empirically. One type of such curve is a correlation spectrum. It consists of 16 coefficients of correlation of a group-averaged experimental time course of sleepiness with16 time courses of single-Hz power densities. Sleepiness is determined either subjectively (by self-scoring on the Karolinska Sleepiness Scale) or objectively (as sleep latency). Another type is a differential spectrum reflecting difference between 2 sets of 16 power densities obtained for either distant phases of sleep deprivation experiment or distinct alertness-sleepiness substates. Analysis of 3 datasets collected in sleep deprivation experiments with, in total, 160 participants showed that, despite differences in the protocols of these experiments and ages of their participants, the forms of frequency weighting curves always resembled one another. Such resemblance led to practical identity of scoring results. We concluded that spectral drowsy component scoring might be implemented into quick, simple, direct, transparent, and objective test of sleepiness.
23
Lee, W. B., C. F. Cheung, and S. To. "Friction-induced fluctuation of cutting forces in the diamond turning of aluminium single crystals." Proceedings of the Institution of Mechanical Engineers, Part B: Journal of Engineering Manufacture 217, no. 5 (May 1, 2003): 615–31. http://dx.doi.org/10.1243/095440503322011344.
Повний текст джерелаАнотація:
This paper presents a multidisciplinary approach to the analysis of the fluctuation of cutting forces in the diamond turning of crystalline materials. The analysis is based on a microplasticity model for shear angle prediction and a cutting force model incorporating a friction variable which is estimated from the power spectrum analysis. The results reveal that the pattern of periodic fluctuation of the microcutting forces is not only due to the crystallographic orientation of the materials being cut but also to the friction between the chip and the tool face. The frictional effect is found to cause a change in the pattern and the periodicity of the fluctuation of the cutting force. The power spectrum predicted from the cutting force model incorporates a friction variable which can be chosen to match the experimental power spectrum, thus providing a new way to assess the frictional condition, and can be used as a diagnostic tool to monitor the tool wear and cutting conditions during diamond turning.
24
Gielniak, Jaroslaw, and Magdalena Czerniak. "Investigation of Distribution Transformers Vibrations in Terms of Core and Winding Condition Assessment." Energies 15, no. 1 (December 21, 2021): 13. http://dx.doi.org/10.3390/en15010013.
Повний текст джерелаАнотація:
This work refers to the criterion values used to assess the state of the active part of the transformer based on the analysis of the effective value of the total vibration acceleration and the frequency spectrum. It was proved in the work that the criteria values should be differentiated for transformers of different rated power. Transformers with lower rated power are characterized by lower RMS values of vibration acceleration than units with higher rated power, which cannot remain without impact on the criteria values. Trend analysis of the total aRMS values may reveal increasing defects before the currently applicable criteria values are exceeded. In addition, the influence of the position of the sensor on the frequency spectrum of the obtained signals was analyzed. It was proved that the sensors should be mounted in the middle of the transformer tank, between its lower part and the cover. The dependence of RMS value of vibration acceleration on no-load losses was also determined for transformers of different types but the same rated power. This relationship will not have a large share in the total vibrations of the transformer, due to slight changes in the value of aRMS occurring for all analyzed units.
25
Shi, Qi, Bifen Shu, Jingxiang Jiang, and Yuqi Zhang. "Effect of Optical–Electrical–Thermal Coupling on the Performance of High-Concentration Multijunction Solar Cells." Applied Sciences 12, no. 12 (June 9, 2022): 5888. http://dx.doi.org/10.3390/app12125888.
Повний текст джерелаАнотація:
In the process of high-concentration photovoltaic (HCPV) power generation, multijunction cells work in the conditions of high radiation and high current. Non-uniformity of focusing, the mismatch between the focusing spectrum caused by the dispersion effect and the spectrum of multijunction solar cell design and the increase in cell temperature are the key factors affecting the photoelectric performance of the multijunction solar cell. The coupling effect of three factors on the performance of multijunction solar cell intensifies its negative impact. Based on the previous research, the light intensity and spectral characteristics under Fresnel lens focusing are calculated through the optical model, and the optical–electrical–thermal coupling model under non-uniform illumination is established. The results show that obvious changes exist in the concentration spectrum distribution, energy and non-uniformity along different optical axis positions. These changes lead to serious current mismatch and transverse current in the multijunction solar cell placed near the focal plane which decreases the output power. The lost energy makes the cell temperature highest near the focal plane. In the condition of passive heat dissipation with 500 times geometric concentration ratio, the output power of the solar cell near the focal plane decreases by 35% and the temperature increases by 15%. Therefore, optimizing the placement position of the multijunction cell in the optical axis direction can alleviate the negative effects of optical–electrical–thermal coupling caused by focusing non-uniformity, spectral mismatch and rising cell temperature, and improve the output performance of the cell. This conclusion is verified by the experimental result.
26
Howard, I. M. "Higher-order spectral techniques for machine vibration condition monitoring." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 211, no. 4 (April 1, 1997): 211–19. http://dx.doi.org/10.1243/0954410971532622.
Повний текст джерелаАнотація:
The vibration signals measured from rotating machinery can be very complex and a number of machine malfunctions can create complicated modulation patterns which are sometimes difficult to detect and to understand. Conventional linear spectral analysis will be of limited use in particular instances when frequency components interact together to form new spectral components due to some non-linear process. Under these circumstances, various signal processing tools are available for performing sophisticated analysis of the measured vibration to detect the non-linear interaction of frequency components and hence changes in machine performance and condition. This paper presents two higher-order spectral analysis techniques, the bispectrum and the trispectrum, and demonstrates how they can be used to detect phase coherence between various frequency components. The theoretical relationship of the higher-order spectral techniques to the power spectrum is given along with the derivation of the normalized bispectrum and trispectrum using the Fourier series of phase- related signals to show that the higher-order spectral analysis techniques can detect various forms of phase coupling between frequency components as well as the strength of the phase coupling. The particular case of modulation is investigated to show the applicability of the higher-order spectral techniques to detect amplitude and phase modulation.
27
Wang, D. Y., and Y. Ma. "Reacceleration of Relativistic Electrons by Turbulent Alfvén Waves in Radio Jets." Symposium - International Astronomical Union 195 (2000): 439–41. http://dx.doi.org/10.1017/s0074180900163442.
Повний текст джерелаАнотація:
Relativistic electrons may be effectively accelerated by turbulent Alfvén waves in radio jets. The acceleration spectrum is a power law with the electron energy as high as γ ~ 106, but the spectrum index is ~ 1.2 in the condition of diffusion approximation, which is less than the observation value.
28
Wang, Er Bing, Hong Zhou, and Ying Zhen Liang. "Transfer Characteristic Research of Power Assisted Steering Pump Noise." Key Engineering Materials 439-440 (June 2010): 384–89. http://dx.doi.org/10.4028/www.scientific.net/kem.439-440.384.
Повний текст джерелаАнотація:
The characteristics of hybrid electric vehicles’ noise and vibration are different when compared with traditional vehicles, especially in idle condition. Taking the noise level of driver location as reference, this paper investigates the influence of noise of power assisted steering pump equipped in a HEV under idle condition, and figure out how it transfers into cavity using spectrum analysis, vibrational energy transfer analysis, and FRF (frequency response function) analysis etc. It is proved that air-borne noise rather than structure-borne noise is the main source. Test verification is consistent with the analysis result, and appropriate acoustic treatment can be effective in improving the noise level inside the vehicle in idle condition.
29
Bohatyrewicz, Patryk, Janusz Płowucha, and Jan Subocz. "Condition Assessment of Power Transformers Based on Health Index Value." Applied Sciences 9, no. 22 (November 14, 2019): 4877. http://dx.doi.org/10.3390/app9224877.
Повний текст джерелаАнотація:
In electric power systems, health index algorithms are mostly used for evaluation of the transformer population. In this method, some assessment criteria are insensitive when it comes to judging the technical state of the edges of the age spectrum. This paper presents a new health index calculation method that aims to improve the overall effectiveness of the assessment. The proposed algorithm is based on regularly conducted oil diagnostics and easily available maintenance data to enable estimation and updating of the device’s health status in short intervals from an operational point of view. This method is compared to another health index algorithm built from the same parameters, but with different weights and an alternative result assessment philosophy. The two health index calculation methods are tested on a population of 96 power transformers and then compared to results obtained with an expert system, which is based on much more advanced diagnostic tests to determine the technical condition of the unit. The results of the experiment show that proper selection of weighting factors of the transformer’s technical condition parameters during health index calculation may help in simplifying its assessment while maintaining satisfactory accuracy in comparison to a highly advanced expert method.
30
Speth, Tamara, Benjamin Rusak, Tara Perrot, Kimberly Cote, and Penny Corkum. "Sleep Architecture and EEG Power Spectrum Following Cumulative Sleep Restriction: A Comparison between Typically Developing Children and Children with ADHD." Brain Sciences 13, no. 5 (May 8, 2023): 772. http://dx.doi.org/10.3390/brainsci13050772.
Повний текст джерелаАнотація:
No studies have looked at the effects of cumulative sleep restriction (CSR) on sleep architecture or the power spectrum of sleep EEG (electroencephalogram) in school-age children, as recorded by PSG (polysomnography). This is true for both typically developing (TD) children and children with ADHD (attention deficit/hyperactivity disorder), who are known to have more sleep difficulties. Participants were children (ages 6–12 years), including 18 TD and 18 ADHD, who were age- and sex-matched. The CSR protocol included a two-week baseline and two randomized conditions: Typical (six nights of sleep based on baseline sleep schedules) and Restricted (one-hour reduction of baseline time in bed). This resulted in an average of 28 min per night difference in sleep. Based on ANOVAs (analysis of variance), children with ADHD took longer to reach N3 (non-rapid eye movement), had more WASO (wake after sleep onset) (within the first 5.1 h of the night), and had more REM (rapid eye movement) sleep than TD children regardless of condition. During CSR, ADHD participants had less REM and a trend toward longer durations of N1 and N2 compared to the TD group. No significant differences in the power spectrum were found between groups or conditions. In conclusion, this CSR protocol impacted some physiological aspects of sleep but may not be sufficient to cause changes in the power spectrum of sleep EEG. Although preliminary, group-by-condition interactions suggest that the homeostatic processes in children with ADHD may be impaired during CSR.
31
Huang, Guo Xing, Zhi Yuan Li, Yin Huang, and You Meng Lu. "Research on the Whole Condition Loaded Noise Measurement Circuit of Power Capacitor." Applied Mechanics and Materials 490-491 (January 2014): 1647–51. http://dx.doi.org/10.4028/www.scientific.net/amm.490-491.1647.
Повний текст джерелаАнотація:
Power capacitor is one of the key equipments of the high-voltage direct current (HVDC) transmission system. It is also the main noise source difficult to control. Presently in the world, there are none explicit requirement and regulation on the evaluation and measurement of the noise generated by the power capacitor, which has seriously restricted the development of the further research on the noise control in power capacitor. So the research on the noise measurement method and technology has extremely important significance in scientifically evaluating the noise of power capacitor. Power capacitor in HVDC Converter Station under practical conditions has apparent fundamental frequency and rich harmonic frequency components. In order to simulate this condition, a whole condition loaded bridge circuit of noise measurement on power capacitor has been designed and studied. Two arms of the bridge are used to load fundamental frequency and a parallel resonance compensation inductance is used to reduce the fundamental current, while the other two arms are used to load harmonic frequency. The harmonic frequency load power supply composed of harmonic signal generator and power amplifier which can simultaneously load any combination of harmonics under 48th to simulate the various actual working conditions. The tests indicated that the noise spectrum measured under the designed circuit completely accorded with the one in HVDC Converter Station.
32
Fu, Lian Qing, Li Sheng Yang, He Tang, and Ya Ning Ma. "Anti-Stealth Radar with Spread Spectrum Technology." Key Engineering Materials 474-476 (April 2011): 2079–84. http://dx.doi.org/10.4028/www.scientific.net/kem.474-476.2079.
Повний текст джерелаАнотація:
The paper addresses the realization of anti-stealth radar and the problems which modern radars are confronted with. With the application of spread spectrum technology to radars, the capability of anti-stealth and anti-jamming is improved. Signal-to-noise (SNR) of the receiver increases through raising the launching power. Intercept probability decreases by transmitting multiple PN codes. Range of radar detector increases on condition that the intercept probability is unchanged. Simulation results show the validity of the proposed method.
33
Villafaina, Santos, Daniel Collado-Mateo, Juan P. Fuentes-García, Ricardo Cano-Plasencia, and Narcís Gusi. "Impact of Fibromyalgia on Alpha-2 EEG Power Spectrum in the Resting Condition: A Descriptive Correlational Study." BioMed Research International 2019 (April 1, 2019): 1–6. http://dx.doi.org/10.1155/2019/7851047.
Повний текст джерелаАнотація:
Objective. The objective of this prospective cross-sectional study was to analyze the differences between patients with fibromyalgia and non-pain controls in terms of EEG power in the eyes-closed resting state. This study also aims to evaluate potential correlations between EEG power and subjective pain.Methods. The fibromyalgia patients were recruited by the Extremadura Association of Fibromyalgia (AFIBROEX) in Cáceres, Spain. Age- and sex-matched healthy controls (1:1 ratio) were recruited from university facilities and people close to the AFIBROEX by public calls. All underwent EEG during a 1-minute resting period with their eyes closed. The theta, alpha-1, alpha-2, beta-1, beta-2, and beta-3 frequency bands were analyzed by using EEGLAB. Self-reported visual analog scale pain scores were determined just prior to EEG.Results. A total of 62 women participated in the study, 31 of them diagnosed with fibromyalgia and 31 healthy controls. Fibromyalgia group exhibited a significantly lower alpha-2 in C4, T3, P4, Pz, and O2 compared to the healthy controls. Interestingly, pain correlated negatively with alpha-2 in Cz, P4, and Pz only in the fibromyalgia group.Conclusion. The fibromyalgia group exhibited decrease alpha-2 power in central, temporoparietal, and occipital brain areas. Furthermore, higher values of pain correlated with lower level of alpha-2 power in Cz, P4, and Pz. These findings may point the importance of alpha-2 power in pain in women with fibromyalgia.
34
Chen, Guilin, Yong Wu, Qijun Pan, Fuli Ning, and Peng Jiang. "Analysis and Optimization of Impact Condition of Power Conditioning Inverter Based on ANSYS." MATEC Web of Conferences 232 (2018): 04003. http://dx.doi.org/10.1051/matecconf/201823204003.
Повний текст джерелаАнотація:
This paper uses the professional finite element analysis software ANSYS to process a certain type of power regulating inverter. The overall finite element model of the inverter is established then the three-way impact condition is analysed according to the requirements of GJB 1060.1-91. Through the modal analysis in ANSYS software, the natural frequency and natural vibration mode of the inverter are calculated. Based on modal analysis of the inverter, the DDAM shock spectrum analysis function is used to analyse the impact condition of the inverter. Through the calculation of the impact condition, the deformation and stress state of the inverter structure under various working conditions are obtained. By analysing the calculation results, the weak position of the inverter structure is found and the corresponding optimization scheme is proposed to improve the dynamic performance and improve the electron. The overall dynamic performance of the inverter cabinet also provides an important reference for the design of subsequent electronic cabinets.
35
Ma, Qiong, Yingwei Fan, and Hongxiang Kang. "Quantitative evaluation of the supercontinuum laser eye dazzling effect: in vivo experimental research." Laser Physics Letters 19, no. 10 (August 26, 2022): 105601. http://dx.doi.org/10.1088/1612-202x/ac8751.
Повний текст джерелаАнотація:
Abstract To quantitatively evaluate the dazzling effect of each spectrum band of the supercontinuum laser, we conducted experimental research to explore the safety and dazzling of animal eyes. Under the condition of dark adaptation, the rabbit eyes were irradiated with different power densities and spectral bands by frontal incident mode for 0.25 s, which was repeated ten times. The fundus of the rabbit eyes was examined using an ophthalmoscope, and the upper limit of safe power density was explored. Rabbit eyes were irradiated with different doses of dazzling light for 0.1 s. Visual electrophysiological signals were collected dynamically, and the recovery time of the electroretinogram (ERG)-b wave amplitude of the rabbit eyes was recorded and analyzed after laser irradiation. When the power density was 8.0 mW cm−2 in visible spectrum (vs.), the recovery time of the ERG-b wave in the rabbit eye was 4.11 ± 0.67 s. When the power density was 12.0 mW cm−2 in the full spectrum (FS), the recovery time of the ERG-b wave in the rabbit eye was 4.16 ± 0.55 s. The recovery time of the ERG-b wave was 4.50 ± 0.94 s at a power density of 4.6 mW cm−2 in FS-1 and 3.81 ± 0.11 s at a power density of 5.0 mW cm−2 in the FS-2. When the power density was 628.00 mW cm−2 in infrared spectrum (IS), the recovery time of the ERG-b wave was only 0.84 ± 0.09 s. The reference values for the upper limit of the safe irradiation power density of the supercontinuum laser are set as follows: 25.2 mW cm−2 in vs., 118.4 mW cm−2 in IS and 105.0 mW cm−2 in FS. The vs., FS, FS-1 and FS-2 of the supercontinuum laser had a good dazzling effect on rabbit eyes, and the dazzling effect was enhanced with increasing radiation power density, but the IS had little dazzling effect.
36
Wilczek, M., H. Xu, and Y. Narita. "A note on Taylor's hypothesis under large-scale flow variation." Nonlinear Processes in Geophysics 21, no. 3 (June 2, 2014): 645–49. http://dx.doi.org/10.5194/npg-21-645-2014.
Повний текст джерелаАнотація:
Abstract. Experimental investigations of turbulent velocity fields often invoke Taylor's hypothesis (also known as frozen turbulence approximation) to evaluate the spatial structure based on time-resolved single-point measurements. A crucial condition for the validity of this approximation is that the turbulent fluctuations are small compared to the mean velocity, in other words, that the turbulence intensity must be low. While turbulence intensity is a well-controlled parameter in laboratory flows, this is not the case in many geo- and astrophysical settings. Here we explore the validity of Taylor's hypothesis based on a simple model for the wavenumber-frequency spectrum that has recently been introduced as a generalization of Kraichnan's random sweeping hypothesis. In this model, the fluctuating velocity is decomposed into a large-scale random sweeping velocity and small-scale fluctuations, which allows for a precise quantification of the influence of large-scale flow variations. For turbulence with a power-law energy spectrum, we find that the wavenumber spectrum estimated by Taylor's hypothesis exhibits the same power-law as the true spectrum, yet the spectral energy is overestimated due to the large-scale flow variation. The magnitude of this effect, and specifically its impact on the experimental determination of the Kolmogorov constant, are estimated for typical turbulence intensities of laboratory and geophysical flows.
37
Suslina, T. A. "Asymptotics of the Spectrum of Variational Problems Arising in the Theory of Fluid Oscillations." Contemporary Mathematics. Fundamental Directions 67, no. 2 (December 15, 2021): 363–407. http://dx.doi.org/10.22363/2413-3639-2021-67-2-363-407.
Повний текст джерелаАнотація:
This work is a survey of results on the asymptotics of the spectrum of variational problems arising in the theory of small oscillations of a fluid in a vessel near the equilibrium position. The problems were posed by N. D. Kopachevsky in the late 1970s and cover various fluid models. The formulations of problems are given both in the form of boundary-value problems for eigenvalues in the domain R3, which is occupied by the fluid in the equilibrium state, and in the form of variational problems on the spectrum of the ratio of quadratic forms. The common features of all the problems under consideration are the presence of an elliptic constraint (the Laplace equation for an ideal fluid or a homogeneous Stokes system for a viscous fluid), as well as the occurrence of the spectral parameter in the boundary condition on the free (equilibrium) surface . The spectrum in the considered problems is discrete; the spectrum distribution functions have power-law asymptotics.
38
Kmita, Grzegorz, Michał Kozupa, Gianluca Bustreo, Miljenko Hrkac, Roberto Zannol, and Karolina Kolber. "Noise and Vibration Measurements for the Assessment of Damping Efficiency in Power Transformers." Applied Mechanics and Materials 798 (October 2015): 135–39. http://dx.doi.org/10.4028/www.scientific.net/amm.798.135.
Повний текст джерелаАнотація:
Power transformers emit a very characteristic harmonic sound during operation. The sound spectrum consists of the harmonics of double frequency of the power grid with the fundamental of 100Hz or 120Hz in different countries around the world. This fundamental frequency dominates in the sound spectrum during the load condition while the higher harmonics are representative for the no-load operating state. Regardless of loading conditions, all the harmonics build rather unpleasant noise, which is difficult to suppress. Moreover, this noise is sometimes difficult to measure and interpret, due to the harmonic nature and a content of harmonics of relatively low frequencies.This paper presents the exemplary study on the assessment of noise damping efficiency, performed with the use of laser vibrometry and sound intensity measurements, which can provide the most complete information, when it comes to the identification of the sources of noise as well as to the proper evaluation of damping solutions.
39
REN, JIE, HONG-GUANG ZHANG, and XIN-HE MENG. "EXPLORING TRANS-PLANCKIAN PHYSICS AND THE CURVATURE EFFECT BY THE PRIMORDIAL POWER SPECTRUM WITH WMAP FIVE-YEAR DATA." International Journal of Modern Physics D 18, no. 09 (September 2009): 1343–53. http://dx.doi.org/10.1142/s0218271809015126.
Повний текст джерелаАнотація:
The vacuum inflation with a boundary condition specified at a short distance scale in a generally primeval nonflat universe, and implications of the correspondingly modified primordial power spectrum via the WMAP data are investigated. We obtain a general form of the modified primordial power spectrum including the effects of both the possibly new physics scale and the spatial curvature. The modulation of the primordial power spectrum due to new physics is of the order H/Λ, where H is the Hubble parameter during inflation and Λ is the new physics scale which is key to inflation, while the modulation from the curvature effect is of the order K/k2, where K is the spatial curvature before inflation and k is the comoving wave number. We also find that a closed universe before inflation is favored by WMAP five-year data.
40
Guo, Zhi Ping, Lian Lei Wang, Wei Zhou, Wen Liang Li, Chao Zhang, and Bao Zong Li. "The Vibration Response Analysis for a Car Left Front Shaft Head Based on User Conditions." Applied Mechanics and Materials 52-54 (March 2011): 1187–92. http://dx.doi.org/10.4028/www.scientific.net/amm.52-54.1187.
Повний текст джерелаАнотація:
As one of the main reason of fatigue failure, vibration has received more attention in reliability and comfort research on vehicles. The shock from bumpy roads has a great impact to the fatigue of vehicle parts and components. The method of survey user conditions is described for the road test in the article, and three accelerating data of X, Y, Z directions of a vehicle left shaft position have been obtained with the typical user condition. Through studied the data, we have obtained the load spectrum and the power spectral density data of one car. The obtained quantitative results from the analysis can be used for evaluating the comfort of using vehicle.
41
Wei, Xin, Rui Wei Huang, Shao Hui Lai, and Z. H. Xie. "Vibration Analysis of ID Slicing Process and Wafer Measurement." Key Engineering Materials 315-316 (July 2006): 641–45. http://dx.doi.org/10.4028/www.scientific.net/kem.315-316.641.
Повний текст джерелаАнотація:
ID (inner-diameter) slicing is widely used in cutting ingots currently. In this paper, the deflection (axial vibration) and vibration (radial vibration) signals in different slicing conditions of the silicon wafers were measured online and analyzed. The effects of the vibration signals on the machining accuracy and surface roughness of sliced wafers were investigated based on the measurement and analysis of the surface roughness, warpage and TTV (total thickness vibration) of the sliced wafers. The results show that the changes of surface roughness, warpage and TTV of the sliced wafers exhibit approximately consistence with the changes of the power spectrums of the acquired vibration signals in different working stage of the blade. The vibration and deflection signals can give evidence of the changes in the cutting forces and blade performance during slicing. The power spectrum of the signals is useful for monitoring the blade wear and tension condition and predicting the surface quality and machining accuracy of the sliced wafers.
42
Vrankic, Miroslav, Saša Vlahinić, Zoran Šverko, and Ivan Markovinović. "EEG-Validated Photobiomodulation Treatment of Dementia—Case Study." Sensors 22, no. 19 (October 5, 2022): 7555. http://dx.doi.org/10.3390/s22197555.
Повний текст джерелаАнотація:
In this article, we perform a case study of the impact of photobiomodulation (PBM) on brain power spectrum and connectivity in an elderly person with a Self Administered Gerocognitive Exam (SAGE) score indicating probable memory and thinking disorder. First, we designed and realized the prototype of a near-infrared (NIR) device for PBM. Analysing the alpha band of the power spectrum, we found a positive long-term effect in nine out of sixteen electrodes in the eyes-open condition (OE) and in twelve out of sixteen electrodes in the eyes-closed condition (CE), while in the theta band, a positive long-term effect was found in nine out of sixteen electrodes for OE and seven out of sixteen electrodes for CE. When considering the theta-alpha ratio (TAR), the positive long-term effect is found on thirteen of sixteen electrodes for OE and on fourteen of sixteen electrodes for CE. A connectivity analysis using the imaginary component of the complex Pearson correlation coefficient (imCPCC) was also performed, and a global efficiency measure based on connectivity matrices with thresholds was calculated. The global efficiency calculated for the long-term effect was higher than before stimulation by a factor of 5.24 for the OE condition and by a factor of 1.25 for the CE condition. This case study suggests that PBM could have positive effects on improving desired brain activity, measured as improvement in power spectrum and connectivity measures in theta and alpha bands, for elderly people with memory and thinking disorders.
43
MÜLLER, V., B. KOTCHOUBEY, J. PERELMOUTER, W. LUTZENBERGER, N. BIRBAUMER, A. SCHICK, and C. RECKHARDT. "EFFECTS OF DISTURBING AUDITORY NOISE ON THE COMPLEXITY OF ELECTROCORTICAL ACTIVITY." International Journal of Bifurcation and Chaos 11, no. 04 (April 2001): 1159–67. http://dx.doi.org/10.1142/s0218127401002638.
Повний текст джерелаАнотація:
The effects of disturbing noise on the nonlinear electrical brain (EEG) dynamics were investigated in a sample of 12 healthy volunteers. The prediction that a high intensity noise increases the dimensional complexity of brain activity as compared to a low intensity noise, was confirmed using a deterministic chaos algorithm. Further, there was a tendency for rest conditions to have a higher dimensional complexity than the condition in which the low-intensity noise was presented. Although a Fourier-analysis of the EEG revealed a difference in the alpha power between the rest condition at the end of the experiment and the noise conditions, no effect of noise intensity on the EEG power spectrum was obtained. The data indicate that the disturbing effect of a loud noise results in the recruitment of additional cortical networks and thus increases the complexity of cortical cell assemblies.
44
Li, Wan Qing, Wei Wang, Le Ting Lin, Bei Min Xie, Ming Chao Xia, Ping Zhu Liu, and Wei Ma. "Research on the Vibration Condition On-Line Monitoring System for EHV Power Transformer." Applied Mechanics and Materials 734 (February 2015): 675–79. http://dx.doi.org/10.4028/www.scientific.net/amm.734.675.
Повний текст джерелаАнотація:
The paper introduces a design scheme for the Extra High Voltage (EHV) transformer condition on-line monitoring system, which is based on the collection and analysis of the transformer winding and core vibration signals. This system is composed of vibration acceleration signal sensors and the signal analyzing computer where the collected vibration signal is saved and processed. The analyzing computer can accomplish the missions of data acquisition control, data analysis and the historical data query. Vibration characteristic values of transformer winding and core include peak to peak value, spectrum, kurtosis, and the amplitude 100Hz component and its higher harmonic components. They are extracted, and the characteristic trend curves are drawn by data analysis, so that EHV transformer on-line monitoring and fault diagnosis are accomplished.
45
Wu, Zai Xin, Yong Wei Wang, and Tao Liu. "Analysis of Vibration Signals of Scroll Compressor Based on Information Entropy." Applied Mechanics and Materials 401-403 (September 2013): 1523–28. http://dx.doi.org/10.4028/www.scientific.net/amm.401-403.1523.
Повний текст джерелаАнотація:
In order to make a quantitative description for the running status of the scroll compressor, a fault diagnosis method of information entropy is proposed on the basis of the theory of entropy. This method is based on singular spectrum entropy in time domain, power spectrum entropy in frequency domain, wavelet power spectrum entropy and wavelet space feature spectrum entropy in time-frequency domain, which is used as the comprehensive appraisal index of quantitative feature for vibration status of scroll compressor. Under condition of invariable speed operation, the identification of natural frequency of is carried out. Meanwhile, the influence of the axial vibration of moving scroll, radial compliance mechanism and slight liquid slugging on the scroll compressor is analyzed quantitatively. Three forms of periodic cataclysm of moving scroll under variable speed operation and the variation of information entropy with rotational speed are disclosed.
46
Novoselov, E. M., D. A. Polkoshnikov, V. A. Savelyev, A. S. Strakhov, and A. A. Skorobogatov. "Method of condition monitoring of rotor windings of the medium voltage induction motors of power plant auxiliaries in start-up modes." Vestnik IGEU, no. 4 (2019): 31–44. http://dx.doi.org/10.17588/2072-2672.2019.4.031-044.
Повний текст джерелаАнотація:
A promising method of monitoring rotor winding condition of induction electric motors ensuring higher reliability of their operation is spectral analysis of the external magnetic field signal. Modern methods of external magnetic field analysis use only the spectrum of this signal in the steady-state operation mode, which does not allow effective monitoring on a number of medium voltage electric motors of power plant auxiliaries operating with long start-ups (for example, machines with variable load, with a double squirrel cage, etc.). It is possible to evaluate the rotor winding condition of such machines in start-up modes, which means that an important task is to study the frequency-time spectra of the external magnetic field of the above-mentioned electric motors and to develop a method for monitoring the state of their rotor windings in the startup mode. In the study, the authors used two-dimensional models of two different types of motors representing drives of the mechanisms of draft systems at power stations. Both models are developed in the ANSYS software package. The calculation of the external magnetic field was carried out using the finite element method. The modelling was done for cases with or without defects. Signal processing was per-formed using the Fourier window transform method in the MatLab software package. Frequency-time spectra of the external magnetic field were built in the start-up mode on models of the investigated induction motors with the following defects: with dynamic eccentricity, with one broken bar of the rotor winding and without the indicated defects. The research results allowed us to develop a method for monitoring the rotor winding state of medium voltage electric motors of power plant auxiliaries operating with long start-ups. The method is based on detecting lower side frequencies of the fictitious rotor winding harmonics in the frequency-time spectrum during the startup. Their specific feature is «reflection» in the spectrum from the time axis. The developed method of monitoring rotor winding condition of the above-mentioned induction electric motors allows increasing the reliability of their operation by timely detection of faults in the rotor windings.
47
Li, Zhen Jia, Yao Nan Cheng, Guang Yu Tan, S. Y. Ning, and Z. G. Wang. "Study on Groove Optimization Technology Based on the Power Spectrum Analysis." Materials Science Forum 471-472 (December 2004): 211–15. http://dx.doi.org/10.4028/www.scientific.net/msf.471-472.211.
Повний текст джерелаАнотація:
Based on the milling force testing system, we have experimented with the waved-edge milling insert and the great milling insert developed by Harbin University of Science and Technology, the American Metal milling insert, the ISCAR hackle milling insert and the flat milling insert, and then compare the insert milling capability of various grooves milling inserts. We have discussed the dynamic milling force under the incontinuous cutting condition, especially the characteristic of time and frequency. Based on the power spectrum analysis of the five types of milling inserts, we have found that the insert whose groove is formed from the curve or curly plane of the period function has an advantage on minishing the milling force and resisting to vibration. The right insert geometry parameters have great effect on improving the cutting capability. By the power spectrum analysis, we found that the complex 3-D grooves milling insert is superior to the flat milling insert on minishing milling force and vibration. The analysis result proves that using power spectrum analysis in groove optimization is viable.
48
Asad, Bilal, Toomas Vaimann, Anouar Belahcen, Ants Kallaste, Anton Rassõlkin, Payam Shams Ghafarokhi, and Karolina Kudelina. "Transient Modeling and Recovery of Non-Stationary Fault Signature for Condition Monitoring of Induction Motors." Applied Sciences 11, no. 6 (March 21, 2021): 2806. http://dx.doi.org/10.3390/app11062806.
Повний текст джерелаАнотація:
This paper presents the modeling and the broken rotor bar fault diagnostics by time–frequency analysis of the motor current under an extended startup transient time. The transient current-based nonstationary signal is retrieved and investigated for its time–frequency response to segregate the rotor faults and spatial harmonics. For studying the effect of reduced voltage on various parameters and the theoretical definition of the fault patterns, the winding function analysis (WFA)-based model is presented first. Moreover, an algorithm to improve the spectrum legibility is proposed. It is shown that by efficient utilization of the attenuation filter and consideration of the area containing the maximum power spectral density, the diagnostic algorithm gives promising results. The results are based on the machine’s analytical model and the measurements taken from the laboratory setup.
49
Chen, Peng, Masatoshi Taniguchi, Toshio Toyota, and Zhengja He. "Fault diagnosis method for machinery in unsteady operating condition by instantaneous power spectrum and genetic programming." Mechanical Systems and Signal Processing 19, no. 1 (January 2005): 175–94. http://dx.doi.org/10.1016/j.ymssp.2003.11.004.
Повний текст джерела
50
Jasika, Ranko, Jovan Mrvić, and Stefan Obradović. "Insulation stresses of power equipment exposed to non-standard overvoltage waveforms." Zbornik radova Elektrotehnicki institut Nikola Tesla, no. 32 (2022): 27–41. http://dx.doi.org/10.5937/zeint32-41430.
Повний текст джерелаАнотація:
During its operation, electrical equipment is constantly exposed to overvoltages of various waveforms, such as lightning discharges, switching operations, faults, etc. Therefore, adequate selection of overvoltage protection and equipment insulation withstand voltages are key factors in increasing system reliability. In general, insulation coordination is carried out by analyzing the insulation behavior for standard impulse and switching overvoltage waveforms. However, overvoltages that occur in operating conditions can significantly deviate from the standard waveforms of insulation withstand voltages, in terms of the front time, the duration of the wave, the existence of highfrequency components as result of reflections in the facility and other factors. This paper presents possible methods of assessing the behavior of equipment insulation for real voltage waves to which the insulation is exposed during exploitation and which deviate from standard waveforms, by analysis in the frequency domain. As there are different components in the overvoltage signal at different frequencies, which a different energy, the main goal of this paper is to analyze the insulation characteristics of a specific transformer from the point of view of the energy spectral density of the voltage wave that occurs at its terminals when an atmospheric discharge occurs. The analysis is based on the determination of the safety margin on the entire frequency spectrum of the overvoltage wave, that is, on the calculation of the so-called FDSF (Frequency Domain Severity Factor). The calculation results show that although the overvoltage amplitude is lower than the withstand voltage of the transformer insulation with an appropriate safety margin (the condition of the classic approach to insulation coordination is satisfied), the spectrum analysis of the voltage wave in the frequency domain shows that the insulation may still be compromised.