Power Spectrum Density Analysis Research Articles

Wavelet-Based Multiresolution Analysis of Pavement Profiles as a Diagnostic Tool

Discrete wavelet transform (DWT) was proposed as a new diagnostic tool for locating various frequency-related features of profiles, such as repeated waves and short-lived surface distress, that affect ride quality. The shortcomings of power spectrum density (PSD) analysis in evaluating the distribution of energy of a profile between various frequency bandwidths were pointed out. The theoretical background and the basics of the DWT decomposition algorithm are discussed. Advantages of DWT analysis over PSD analysis in detection of short-lived features of the profile are illustrated by an example. The results of both the PSD and DWT analyses of three profile data, taken from data collected as a part of an ongoing research project sponsored by New Jersey Department of Transportation, are presented. The results indicate that DWT analysis can capture both short-lived high-frequency and long-lived low-frequency features of the profile and, consequently, provides a better representation of the profile characteristics. The application of DWT in the development of new ride indices is also discussed.

Wavelet-Based Multiresolution Analysis of Pavement Profiles as a Diagnostic Tool

Discrete wavelet transform (DWT) was proposed as a new diagnostic tool for locating various frequency-related features of profiles, such as repeated waves and short-lived surface distress, that affect ride quality. The shortcomings of power spectrum density (PSD) analysis in evaluating the distribution of energy of a profile between various frequency band-widths were pointed out. The theoretical background and the basics of the DWT decomposition algorithm are discussed. Advantages of DWT analysis over PSD analysis in detection of short-lived features of the profile are illustrated by an example. The results of both the PSD and DWT analyses of three profile data, taken from data collected as a part of an ongoing research project sponsored by New Jersey Department of Transportation, are presented. The results indicate that DWT analysis can capture both short-lived high-frequency and long-lived low-frequency features of the profile and, consequently, provides a better representation of the profile characteristics. The application of DWT in the development of new ride indices is also discussed.

Children with spastic hemiplegia are equally able as controls in maintaining a precise percentage of maximum force without visually monitoring their performance

In this study the hypothesis was tested that children with spastic hemiplegia rely more on externally guided visual feedback when trying to keep force constant with their affected hand (AH) as compared to their non-affected hand (NAH) and as compared to controls. An isometric force task in which a cursor had to be moved to a visually specified target that disappeared half way the task, was performed by 19 children with cerebral palsy (CP), spastic hemiplegia, aged between 5 and 16 years and an aged matched control group. It was found that the absolute deterioration of performance after withdrawal of target visualization did differ between AH, NAH and controls. The absolute error was smaller and the variability was larger in the hemiplegic hand. However, the normalized force error and co-efficient of variation increased similarly between groups. Furthermore, power spectrum density analysis of the force signal showed that both hands in both groups had a similar loss in the energy in the 2–3 Hz range when target visualization was removed. These results suggest that CP children are equally able to produce stable force without visually monitoring their performance than children without CP, provided they are allowed to operate within their own force range.

Physiological noise in murine solid tumours using T2*-weighted gradient-echo imaging: a marker of tumour acute hypoxia?

T2*-weighted gradient-echo magnetic resonance imaging (T2*-weighted GRE MRI) was used to investigate spontaneous fluctuations in tumour vasculature non-invasively. FSa fibrosarcomas, implanted intramuscularly (i.m.) in the legs of mice, were imaged at 4.7 T, over a 30 min or 1 h sampling period. On a voxel-by-voxel basis, time courses of signal intensity were analysed using a power spectrum density (PSD) analysis to isolate voxels for which signal changes did not originate from Gaussian white noise or linear drift. Under baseline conditions, the tumours exhibited spontaneous signal fluctuations showing spatial and temporal heterogeneity over the tumour. Statistically significant fluctuations occurred at frequencies ranging from 1 cycle/3 min to 1 cycle/h. The fluctuations were independent of the scanner instabilities. Two categories of signal fluctuations were reported: (i) true fluctuations (TFV), i.e., sequential signal increase and decrease, and (ii) profound drop in signal intensity with no apparent signal recovery (SDV). No temporal correlation between tumour and contralateral muscle fluctuations was observed. Furthermore, treatments aimed at decreasing perfusion-limited hypoxia, such as carbogen combined with nicotinamide and flunarizine, decreased the incidence of tumour T2*-weighted GRE fluctuations. We also tracked dynamic changes in T2* using multiple GRE imaging. Fluctuations of T2* were observed; however, fluctuation maps using PSD analysis could not be generated reliably. An echo-time dependency of the signal fluctuations was observed, which is typical to physiological noise. Finally, at the end of T2*-weighted GRE MRI acquisition, a dynamic contrast-enhanced MRI was performed to characterize the microenvironment in which tumour signal fluctuations occurred in terms of vessel functionality, vascularity and microvascular permeability. Our data showed that TFV were predominantly located in regions with functional vessels, whereas SDV occurred in regions with no contrast enhancement as the result of vessel functional impairment. Furthermore, transient fluctuations appeared to occur preferentially in neoangiogenic hyperpermeable vessels. The present study suggests that spontaneous T2*-weighted GRE fluctuations are very likely to be related to the spontaneous fluctuations in blood flow and oxygenation associated with the pathophysiology of acute hypoxia in tumours. The disadvantage of the T2*-weighted GRE MRI technique is the complexity of signal interpretation with regard to pO2 changes. Compared to established techniques such as intravital microscopy or histological assessments, the major advantage of the MRI technique lies in its capacity to provide simultaneously both temporal and detailed spatial information on spontaneous fluctuations throughout the tumour.

Vibro Acoustic Response of the Satellite Telescope (1st Report, Lower Frequency Response Analysis)

The goal of this research is to analyze vibration response when the main mirror in a Satellite Solar-B optical telescope assembly (OTA) is subjected to acoustic load. First, we determined the maximum frequency for the frequency range in this analysis from the results of vibration tests and acoustic tests. Next, we derived a frequency response analysis method using BEM, and calculated the internal sound pressure in the OTA. We then considered this internal sound pressure as the input, conducted a Power Spectrum Density (PSD) analysis using an FEM model, and analyzed the vibration response of the OTA. Results of these studies indicate good correlation between the results from the proposed simulation and the results of the acoustic test.

Measurement of the Reynolds stress structure and turbulence characteristics of the wind above a two-dimensional trapezoidal shape of hill

Wind tunnel experiments were carried out to measure the mean velocity and turbulence structure of the wind flow over a two-dimensional trapezoidal shape of hill. The quadrant analysis technique was employed to analyze the structure of the Reynolds stress. Analysis of the turbulent velocity spectrum of the wind above the hill under different wind attack angles is conducted. The fractional speed-up ratios of the present measured results are found in agreement with the wind tunnel data of Lemelin et al. (J. Wind Eng. Ind. Aerodyn. 28 (1988) 117) for the case of the wind attack angle of 30°. Measurements of the mean velocity profiles disclose that the speed-up phenomenon is mostly manifest at Z/ H=0.6 for the case of wind attack angle of 10°. Turbulence intensity profiles measured at different locations show that the turbulence intensity decreases as shifting from far upstream location of the hill ( X/ H=−20) to the downstream location at the center of hill ( X/ H=0). The decrease of the turbulence intensity is obviously at the distance close to the surface of the hill. Results of the quadrant analysis indicate that the sweep and ejection events are the major contributors to the Reynolds stress. Others like inward and outward interaction events make negative contributions. The values of the stress fractions of ejection and sweep events become the lowest as the wind attack angle is 20°. Analysis of the turbulent velocity power spectrum density shows that the spectrum density is increasing in the lower-frequency region as the wind attack angle increases. The power spectrum density is found to decrease for increase in the wind attack angle at the higher-frequency region.

On the influence of noise on the critical and oscillatory behavior of a predator–prey model: coherent stochastic resonance at the proper frequency of the system

Noise-induced changes in the critical and oscillatory behavior of a prey–predator system are studied using power spectrum density and spectral amplification factor (SAF) analysis. In the absence of external noise, the population densities exhibit three kinds of asymptotic behavior, namely: absorbing state, fixed point (FP) and an oscillatory regime with a well defined proper (natural) frequency. The addition of noise destabilizes the FP phase inducing a transition to a new OR. Surprisingly, it is found that when a periodic signal is added to the control parameter, the system responds robustly, without relevant changes in its behavior. Nevertheless, the coherent stochastic resonance phenomenon is found only at the proper frequency. Also, a method based on SAF allows us to locate very accurately the transition points between the different regimes.

Anisotropic scaling of hard disk surface structures

We present a detailed study of the surface roughness of a computer hard disk using atomic force microscopy and light scattering. The power spectrum density analysis showed that the surface possesses an anisotropic scaling behavior and has both random roughness and periodic roughness components. Quantitative anisotropic correlation length (ξ) and roughness exponent (α) for the directions parallel and perpendicular to the grooves are obtained. A novel in-plane (measurement parallel to the sample surface) light scattering technique is shown to be particularly useful for the analysis of the rough surface parallel to the grooves.

Roughness Characterization of Si(110) Etched in TMAH by Atomic Force Microscopy

AbstractWe have investigated the roughness of a silicon (110)-oriented surface after being etched with 20% TMAH (Tetra-methyl Ammonium Hydroxide). We have used an Atomic Force Microscope to determine the roughness exponent α using three different methods: fractal, power spectrum density and scaling analysis. The value of the parameter α was identified to be close to 1/2. This value is different from the KPZ value, which is 0.4 in 2+1 dimension

Rotation induced stabilization of air convection in a bottom heated diverging cylinder rotating about its own axis

Rotation induced stabilization of air convection in a vertical, diverging cylinder heated from below and rotated steadily about its own axis is studied experimentally. The cylinder has a smaller circular cross section at its bottom end. In the experiments, the transient variations of the air temperature at selected locations are measured to explore the effects of rotation rate and diverging angle on the temporal stability of the flow. Data are collected for the diverging angle varied from 0–30°, imposed temperature difference from 5–15°C and rotation rate up to 346.1 rpm. The measured data show that the ranges of the rotation rate to stabilize the flow are wider for diverging cylinders than those for a right cylinder at ξ = 0°. Thus, it is possible to use a crucible with a diverging section to grow large and high quality bulk crystals. A power spectrum density analysis of the data for the unstable flow at high rotation rates indicates that the flow oscillation is mainly time periodic and dominated by a single fundamental frequency. Moreover, the oscillation frequency varies nonmonotonically with the rotation rate. Flow regime maps delineating stable and unstable states are also provided for practical applications.

Time-averaged and reverse transition in oscillatory air convection in a differentially heated rotating cubic cavity

An experimental study was carried out to investigate the time-averaged and unsteady thermal characteristics in an inclined cubic air cavity, subject to differential heating across a pair of side walls and subject to rotation about an axis which is normal to the insulated bottom wall and through the geometric center of the cavity. Specifically, the air temperature in the cavity at selected locations was measured for both steady and unsteady flows. Results were obtained for the cavity height H = 10 and 15 cm, temperature difference ΔT ranging from 2 to 10°C, rotation rate Ω from 0 to 452.9 rpm and inclined angle φ from 0 to 90° (heated from below). Time records of the air temperature showed the presence of the flow re-stabilization in two different ranges of the rotation rates. Thus, the transient oscillatory flow can be stabilized by increasing the cavity rotation when the rotation rate is in these ranges. This flow restabilization is more pronounced for a higher inclined angle. Moreover, a power spectrum density analysis of the time records indicated that at low rotation rates the amplitudes of the temperature oscillation are location dependent, but the oscillation frequencies at various locations for a given set of ΔT, Ω and φ are the same.

Visual evoked potentials (VEPs) in senile dementia (Alzheimer type) and in non-organic behavioural disorders in the elderly; Comparison with EEG parameters

Forty-two patients with senile dementia of the Alzheimer type were compared with normal subjects (51) and with elderly patients with non-organic psychiatric disorders (40). All were examined by EEG (routine visual inspection and power spectrum density analysis) and VEP (pattern reversal) testing. In dementia the late components (N130, P165, N220) of the VEP are delayed, but the EEG was abnormal more often than the VEP.

COIL-STRETCH TRANSITION OF MACROMOLECULES IN LAMINAR FLOW AROUND A SMALL CYLINDER

The analysis of mass transfer from a small cylindrical wire in a dilute polymer solution by using an electrochemical technique is reported here. Steady state measurements showed a large decrease of the mass transfer rate with respect to the newtonian behaviour, starting from a critical flow rate value. This phenomenon was ascribed to the fast stretching of the polymers coils which occurs when the elongational gradient in the upstream vicinity of the wire, equals the reciprocal of the polymer relaxation time. Fluctuations concurrently arise at the transition and result from an hydrodynamic instability induced by the viscosity increase during elongation. From a power spectrum density analysis, it was demonstrated that these instabilities actually take place near the stagnation point upstream.

The relationships among sequences with applications to geological data

Power spectrum density analysis of isotopic variations and other temperature-dependent parameters in the Caribbean cores P6304-8 and P6304-9 yields spectrums which to good approximation are identical with the power spectrum of summer insolation variation at 65°N. Identification of the various peaks in the spectrums as astronomical frequencies leads to an accurate method for determining the sedimentation rate in the cores. These rates are in good agreement with those obtained by correlating these cores with others that have been absolutely dated.