Dominant Frequency Content Research Articles

Modified one Dimension Sub-Spaces in Non Linear Dynamic Analysis

The usual finite element methods reduce the infinite number of degree of freedom (D.O.F.) of system to a model with a limited number of D.O.F. while capturing the significant physical behavior. Base relation methods reduce number of D.O.F. in new coordinate. One of the base relation methods is gained from Ritz-Wilson vectors which is much better than the conventional base relation methods and eigen value methods in a lot of cases because of simpler and dependence on dynamic load. Also to be costly in large system calculations and to ignore loading parameter can be mentioned as the disadvantages of eigen vectors. Fewer number of required Ritz vectors in comparison with eigen values and considering place distribution of external loading and dominant frequency content of loading has pushed the researchers into applying Ritz vectors. Base alteration methods in nonlinear problems are not usually much applicable due to frequent matrix change of system. Generalized one dimensional subspace method presents an appropriate solution for geometric nonlinearity problems by means of Ritz-Wilson technique. In this article generalized one dimensional subspace method is combined with mode-acceleration technique in order to analyze nonlinear dynamic problems. Based on inside error component and generalized one dimensional subspace method, a modified criterion using mode-acceleration technique in order to update required base vectors for stiffness changes in nonlinear dynamic analysis is proposed. The results indicate that the accuracy and speed of the modified method are appropriate.

Examination of Selective Pulsed Laser Micropolishing on Microfabricated Nickel Samples Using Spatial Frequency Analysis

The precision of parts created by microfabrication processes is limited by surface roughness. Therefore, as a means of improving surface roughness, pulsed laser micropolishing on nickel was examined numerically and experimentally. A one-dimensional finite element method model was used to estimate the melt depth and duration for single 50–300 ns laser pulses. The critical frequency was introduced to predict the effectiveness of polishing in the spatial frequency domain. A 1064 nm Nd:YAG laser with 300 ns pulses was used to experimentally investigate pulsed laser polishing on microfabricated nickel samples with microscale line features. A microfabricated sample with 2.5 μm wide and 0.2 μm high lines spaced 5 μm apart and one with 5 μm wide and 0.38 μm high lines spaced 10 μm apart were polished with 300 ns long pulses of 47.2 J/cm2 and 44.1 J/cm2 fluences, respectively. The critical frequency for these experimental conditions was predicted and compared with the reduction in the average surface roughness measured for samples with two different spatial frequency contents. The average surface roughness of 5 μm and 10 μm wavelength line features were reduced from 0.112 μm to 0.015 μm and from 0.112 μm to 0.059 μm, respectively. Four regimes of pulsed laser micropolishing are identified as a function of laser fluence for a given pulse width: (1) at low fluences no polishing occurs due to insufficient melting, (2) moderate fluences allow sufficient melt time for surface wave damping and significant smoothing occurs, (3) increasing fluence reduces smoothing, and (4) high fluences cause roughening due to large recoil pressure and ablation. Significant improvements in average surface roughness can be achieved by pulsed laser micropolishing if the dominant frequency content of the original surface features is above the critical spatial frequency for polishing.

Steroid-dependent auditory plasticity for the enhancement of acoustic communication: Recent insights from a vocal teleost fish

The vocal plainfin midshipman fish ( Porichthys notatus) has become an excellent model for identifying neural mechanisms of auditory perception that may be shared by all vertebrates. Recent neuroethological studies of the midshipman fish have yielded strong evidence for the steroid-dependent modulation of hearing sensitivity that leads to enhanced coupling of sender and receiver in this vocal-acoustic communication system. Previous work shows that non-reproductive females treated with either testosterone or 17β-estradiol exhibit an increase in the degree of temporal encoding by the auditory saccular afferents to the dominant frequency content of male vocalizations produced during social-reproductive behaviors. The expanded frequency sensitivity of steroid treated females mimics the reproductive female’s auditory phenotype and is proposed to improve the detection and localization of calling conspecific mates during the summer breeding season. This review focuses on the novel form of steroid-dependent auditory plasticity that is found in the adult midshipman fish and its association with the reproductive biology and behavior of this species. Evidence for midshipman reproductive-state and steroid-dependent auditory plasticity is reviewed and the potential mechanisms that lead to this novel form of adaptive plasticity are discussed.

Image denoising with geometrical thresholds

Observation on the interpolation effect and selectivity of human visual perception can be used to construct a criterion to find and preserve geometrical details while denoising an image. An approach to denoise an image with such a criterion is introduced, through which the pointwise thresholding of wavelet coefficients is turned into a bandwise geometrical thresholding. Interestingly this method can make up for the loss of details in a pointwise thesholding procedure. Experimental results validate its good performance, particularly on images with dominant high frequency contents and faint directional details such as Barbara.

Partial Discharge Activity in Gas-Insulated System Under Composite Voltage

In the present study, the partial-discharge activity under nonstandard voltage formed by ac and dc voltages was studied. It is identified that the ac superposed with positive dc enhances the discharge activity in the medium and if the ac voltage is superposed with the negative dc, it can mitigate the discharge activity. The acoustic emission signal generated due to the partial discharges in gas-insulated systems under the composite voltage formed by ac superposed with dc voltage/ac/dc voltages, has a dominant frequency content at around 250 kHz.

Frequency Characteristics of Very Fast Transient Currents in a 245-kV GIS

The conducted as well as the induced voltages on control cables and control circuits due to transient electromagnetic (EM) fields generated during switching operations in a gas-insulated substation (GIS) depend on the waveshape of the very fast transient overvoltages and the associated very-fast transient currents (VFTCs). The aim of this paper is to build a basis for characterizing the VFTC generated in gas-insulated switchgear and the associated equipment during switching operations for the study of transient coupling phenomena. The peak magnitudes of VFTC and their dominant frequency content at various locations have been computed in a 245-kV GIS for different switching operations as well as substation configurations. Finally, the influence of the substation layout on the frequency spectrum, dominant frequencies, and the highest possible frequency component of the VFTC at various distances from the switch have been reported.

Study of electrical treeing phenomena in XLPE cable samples using acoustic techniques

Electrical trees were generated experimentally in the actual 33 kV underground XLPE cable insulation material under the AC voltages. A tree like structure and a bush type of tree structure can form from the point of defect site under the AC voltages. Acoustic emission technique was adopted to identify the point of inception, propagation and termination of electrical trees. A variation in the dominant frequency content of the acoustic signal was observed as and when the tree propagates in the insulation structure. The characteristic variation in the magnitude of the acoustic emission signal with time, indicates that tree propagation as an intermittent growth process. The energy content of the acoustic signal characterizes that the energy released due to partial discharges, at every step growth of the tree structure is not the same. The partial power measurement in the present study provides an indication to the growth process of electrical trees and to the near point of failure of polymer insulation material due to electrical treeing.

Wideband low frequency generation and detection of Lamb and Rayleigh waves using electromagnetic acoustic transducers (EMATs)

This paper describes a new type of non-contact electromagnetic transducer (EMAT) that can be used to generate both Lamb and Rayleigh waves on metal samples. The generated waves are wideband and low frequency with a dominant frequency content centred at approximately 200 kHz extending to around 500 kHz. The transducers have been used on both aluminium and steel, but operate more efficiently on aluminium due to its lower electrical resistance and density when compared to steel.

A blind interpretation of drill‐bit signals

The role of kurtosis in evaluating the quality of vertical seismic profiling (VSP) drill‐bit data is investigated. The calculations show how kurtosis depends on the dominant frequency, bandwidth, and phase content of a seismic signal. This analysis is applied to synthetic and real common‐offset and common‐shot drill‐bit seismograms to evaluate the prominence and quality of the first arrival and other coherent events. High values of kurtosis correspond to an isolated first arrival or to a compressed coherent noise event, while low values are typical of low S/N (distributed) ratio traces. Kurtosis analysis applied to drill‐bit VSP data while drilling proved to be successful at identifying high‐quality traces with little interpretational input.

New methods of time series analysis of non-stationary EEG data: eigenstructure decompositions of time varying autoregressions

Objective: Those who analyze EEG data require quantitative techniques that can be validly applied to time series exhibiting ranges of non-stationary behavior. Our objective is to introduce a new analysis technique based on formal non-stationary time series models. This novel method provides a decomposition of the time series into a set of ‘latent’ components with time-varying frequency content. The identification of these components can lead to practical insights and quantitative comparisons of changes in frequency structure over time in EEG time series. Methods: The technique begins with the development of time-varying autoregressive models of the EEG time series. Such models have been previously used in EEG analysis but we extend their utility by the introduction of eigenstructure decomposition methods. We review the basis and implementation of this method and report on the analysis of two channel EEG data recorded during 3 generalized tonic–clonic seizures induced in an individual as part of a course of electroconvulsive therapy for major depression. Results: This technique identified EEG patterns consistent with prior reports. In addition, it quantified a decrease in dominant frequency content over the seizures and suggested for the first time that this decrease is continuous across the end of the seizures. The analysis also suggested that the seizure EEG may be best modeled by the combination of multiple processes, whereas post-ictally there appears to be one dominant process. There was also preliminary evidence that these features may differ as a function of ECT therapeutic effectiveness. Conclusions: Eigenanalysis of time-varying autoregressive models has promise for improving the analysis of EEG time series.

Dominant frequency content of ocular microtremor from normal subjects.

Ocular microtremor (OMT) is a high frequency tremor of the eyes present during fixation and probably related to brainstem activity (Coakley, D. (1983). Minute eye movement and brain stem function. CRC Press, FL.). Published observations on the frequency of OMT have varied widely. Ocular microtremor was recorded in 105 normal healthy subjects using the Piezoelectric strain gauge technique. The dominant frequency content of a signal was determined using the peak counting method. Values recorded ranged from 70 to 103 Hz, the mean frequency being 83.68 Hz (S.D. +/- 5.78 Hz).

VIBRATION REDUCTION BY USING PERIODIC SUPPORTS IN A PIPING SYSTEM

In this paper, the applicability of the periodic characteristics of wave stop and wave propagation bands are investigated for piping systems conveying fluid by employing the wave approach and are proved through experiments. The inviscid fluid dynamic forces acting on a pipe due to internal fluid flow are approximated by the plug-flow model with the slender-body theory. This paper shows that if the dominant frequency contents in the excitation loads are known, a proper design of periodic supports for reducing the vibration in those frequency bands is possible. Therefore, the periodic support design may be effective in vibration reduction in a piping system.

Evoked Otoacoustic Emissions and Cochlear Transduction Processes

Some aspects of the generation of evoked otoacoustic emissions (EOAEs) are discussed. This signal is generated within the periphery of the auditory organ and is shown to contain responses from localized regions of the cochlea. From deconvolution of the responses from normal hearing subjects it appears that EOAEs are linearly related to the input stimulus, for acoustic impulses (clicks) and sinusoidal bursts, within the same ear. Short-time Fourier analysis is shown to reveal the composite time structure of these signals; the dominant frequency content and post-stimulus times are discussed.

Transmission Survey Using Seismic Guided Waves: Cadiz, Ohio: ABSTRACT

When seismic survey energy is initiated within a coal seam, internally reflected S and P waves constructively interfere to form a seam wave. The seam wave is a high-frequency, dispersive wave which may exhibit both Rayleigh-type and Love-type modes. Since the seam wave is confined to the coal seam, its frequency content and dispersion characteristics are a function of the elastic properties and thickness of the coal seam. Large variations in the elastic properties or thickness of the coal seam, such as faults, sand bodies and pinch-outs, will affect the frequency and dispersion of the seam wave. Seam-wave studies applied to coals in the eastern United States are few. The paper gives an acount of a transmission survey shot across a block of coal in the Oak Park Mine located near Cadiz, Ohio. The coal seam, under investigation is the lower Freeport (6A) which is 54 in. (14 cm) thick at the Oak Park Mine. Conducting an underground seismic survey presents many difficulties including: (1) mine accessibility; (2) underground-safety regulations; (3) source and receiver coupling; and (4) maneuverability. Comparison of the observed dispersion and predicted dispersion of the seam wave reveals its dominant mode and frequency content. End_of_Article - Last_Page 1013------------