Frequency Bands Of Spectrum Research Articles

Noise prediction via large eddy simulation: Application to radial fans

In this study, aerodynamics and aeroacoustics of two radial fans are investigated by using a hybrid computational aeroacoustics method. Unsteady turbulent flow field of both fans is simulated with large eddy simulation (LES).Acoustic sources are computed based on the pressure fluctuations. Inhomogeneous wave equation, which accounts for the propagation, diffraction and scattering of the acoustic waves, is solved to determine the far field sound pressure level with the boundary element method. Numerical results are validated with experimental data. Sound pressure level distribution in narrow band frequency spectrum and directivity of the acoustic waves are predicted numerically with a high accuracy. Results of the LES provide an insight into the turbulent flow and noise generation mechanisms, which can be utilized to reduce fan noise. © 2009 Institute of Noise Control Engineering.

Dispersion Diagram Characteristics of Periodic Array of Dielectric and Magnetic Materials Based Spheres

In this paper, the characteristics of electromagnetic (EM) waves supported by three dimensional (3D) periodic arrays of dielectric and magneto-dielectric spheres are theoretically investigated. The sphere particles have the potential to offer electric and magnetic dipole modes, where their novel arrangements engineer desired metamaterial performance. A full wave spherical modal analysis is applied to express the electromagnetic fields in terms of the electric and magnetic dipole modes and the higher order terms. Imposing the boundary conditions, determine the required equations for obtaining <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">kd</i> -beta <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> dispersion characteristics. A metamaterial constructed from unit-cells of two different spheres is created, where one set of spheres develops electric modes, and the other set establishes magnetic modes. It is demonstrated that such a composite of high dielectric spheres provides double negative (DNG) metamaterial in a narrow frequency band spectrum where kd,betad<1. We also investigate the dispersion diagram for a 3D array of one-set of highly coupled dielectric spheres. Here, the couplings between the electric and magnetic dipoles of the spheres generate hybrid modes, resulting in a backward wave medium for <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">kd</i> > 1. The developments of DNG and backward wave metamaterials utilizing 3D array of magneto-dielectric spheres located inside space, and dielectric spheres embedded in a negative mu host, are also addressed. The use of magnetic materials allows accomplishing wider dispersion characteristic bandwidths and tunable feasibility.

Temporal Coding: Assembly Formation Through Constructive Interference

Temporal coding is studied for an oscillatory neural network model with synchronization and acceleration. The latter mechanism refers to increasing (decreasing) the phase velocity of each unit for stronger (weaker) or more coherent (decoherent) input from the other units. It has been demonstrated that acceleration generates the desynchronization that is needed for self-organized segmentation of two overlapping patterns. In this letter, we continue the discussion of this remarkable feature, giving also an example with several overlapping patterns. Due to acceleration, Hebbian memory implies a frequency spectrum for pure pattern states, defined as coherent patterns with decoherent overlapping patterns. With reference to this frequency spectrum and related frequency bands, the process of pattern retrieval, corresponding to the formation of temporal coding assemblies, is described as resulting from constructive interference (with frequency differences due to acceleration) and phase locking (due to synchronization).

Underwater radiated noise due to the piling for the Q7 Offshore Wind Park

The Q7 is the second offshore wind farm in the Dutch sector of the North Sea and, at 23 km off the Dutch coast, the world's first to be located outside the 12-mile limit. To support the wind turbines, monopiles (54 metres long steel pipes with a diameter of 4 metres) are hammered into the seabed using a pile-driver. The underwater radiated noise during the impulsive hammering of 9 out of 61 monopiles was monitored. Although there is a wide concern about the impact of piling noise on the marine life in the area, there are no criteria for the maximum acceptable noise levels. A quantitative comparison of the results of various studies in which the underwater noise from pile driving has been measured and reported is difficult, due to the lack of standardization in the level definitions and data processing. The Q7 data have been analyzed in terms of a broadband sound exposure level, peak pressure and pulse duration and a 1/3-octave band frequency spectrum of the sound pressure at different hydrophone locations, for each hammer stroke that has been recorded. The results are discussed in relation to the stroke energy and the hydrophone distance and depth.

Spectral Evaluation of Hypernasality in Children with Repaired Cleft Palate

Objective: To identify the characteristics of the spectrum of hypernasality in relation to the formant amplitudes for the vowel ‘a’ (∂ in the International Phonetic Association alphabet chart of vowels) for children with repaired cleft palate and the relationship of hypernasality with other acoustic parameters.Patients and Methods: Fifty three children with repaired cleft palate were divided into 2 groups, based on perceptual speech rating: moderate to severe hypernasality (n = 33) and mild hypernasality (n = 20). The control group comprised 20 children without cleft palate. Sound segments ‘ka’ containing the vowel ‘a’ were recorded, digitised, and analysed to identify formant pattern, breathiness values, and amplitudes for one-third octave band frequency spectra using computer software.Results: Differences in frequency values obtained between the hypernasal groups and normal children for the fundamental frequency (F0) and formants F1 and F2 were not statistically significant. Significant differences in breathiness values were obtained for children with moderate to severe hypernasalality and those with mild hypernasality compared with normal children. Spectral analysis revealed an increase in amplitudes in frequency bands between F1 and F2 and spectral dips at 630 to 800 Hz band and at F2 with an additional Fn peak at 800 to 1000 Hz band in subjects with moderate to severe hypernasality.Conclusions: Formant amplitude measurement using one-third octave frequency band spectral analysis revealed characteristic features for the hypernasal vowel ‘a’ as an increase in amplitudes in some frequency bands and an additional spectral peak Fn between F1 and F2.

Extracting the main patterns of natural time series for long-term neurofuzzy prediction

A combination of singular spectrum analysis and locally linear neurofuzzy modeling technique is proposed to make accurate long-term prediction of natural phenomena. The principal components (PCs) obtained from spectral analysis have narrow band frequency spectra and definite linear or nonlinear trends and periodic patterns; hence they are predictable in large prediction horizon. The incremental learning algorithm initiates a model for each of the components as an optimal linear least squares estimation, and adds the nonlinear neurons if they help to reduce error indices over training and validation sets. Therefore, the algorithm automatically constructs the best linear or nonlinear model for each of the PCs to achieve maximum generalization, and the long-term prediction of the original time series is obtained by recombining the predicted components. The proposed method has been primarily tested in long-term prediction of some well-known nonlinear time series obtained from Mackey–Glass, Lorenz, and Ikeda map chaotic systems, and the results have been compared to the predictions made by multi-layered perceptron (MLP) and radial basis functions (RBF) networks. As a real world case study, the method has been applied to the long-term prediction of solar activity where the results have been compared to the long-term predictions of physical precursor and solar dynamo methods.

Changes in the frequency power spectrum of fetal heart rate in the course of pregnancy.

The aim of this study was to examine changes in the heart rate variability based on the frequency power spectrum of healthy fetuses during the second and third trimester of pregnancy. We analyzed 222 fetal magnetocardiograms recorded in 49 healthy singleton pregnancies between the 16th and 42nd week. Discrete Fourier transformation was performed on the time-based step function of the RR-intervals. Changes of spectral density in the frequency spectrum in various bands between 0.003 to 1 Hz, including low-frequency (LF: 0.04-0.15 Hz) and high-frequency (HF: 0.15-0.40 Hz) bands, were examined as a function of gestational age. Spectral density between 0.003 to 1.0 Hz increased with gestational age with large changes, in particular, at lower frequencies. At approximately the 32nd week, the rate of increase in power slowed substantially. Prior to this time, the rates of change in power were different for the bands 0.003 to 0.40 Hz, 0.40 to 0.60 Hz and 0.60 to 1.0 Hz. LF and HF showed similar development, with HF increasing slightly more rapidly. We conclude that characteristic spectral bands that increase in spectral density at different rates during the second and third trimester may be identified. They most likely reflect developmental changes and behavioral states during pregnancy.

Linear and nonlinear vibrations and waves in optical or acoustic superlattices (photonic or phonon crystals)

A model of a dielectric or an elastic superlattice is proposed which describes quite simply the frequency spectrum of electromagnetic or acoustic waves. The frequency band spectrum of a one-dimensional lattice consists of minibands, which narrow down with increasing frequency (so that the forbidden bands in the spectrum broaden with increasing frequency). An elementary analysis of the spectrum of a one-dimensional lattice reveals the presence of many forbidden frequency bands in this case as well. It is shown that dynamic equations for superlattices can be generalized to the nonlinear case, leading to equations of the type of the nonlinear Schrodinger equation for the lattice. Soliton excitations are described and the particle-like dynamics of solitons is demonstrated. Local vibrations near point defects of different complexity in superlattices are studied and graphically illustrated. The existence of Bloch oscillations of a wave packet in a superlattice in a homogeneous external field is discussed.

On the nature of internal wave spectra near a continental slope

Amongst the most energetic motions in the deep ocean are internal waves supported by stable vertical stratification in density. Previously, these waves were considered freely propagating as described by a smooth continuum internal wave band (IWB) frequency spectrum. We studied details of the IWB using yearlong current observations from the Bay of Biscay. Instead of observing continuum IWB spectra near a continental slope, we show that (at least) the first half‐decade of the IWB is dominated by motions at localized frequencies determined by strong non‐linear interactions between waves at the fundamental semidiurnal tidal and atmospherically induced inertial frequencies.

EEG correlates of acute and chronic paroxetine treatment in depression

Single dose administration of efficacious antidepressant agents elicit characteristic pharmaco-electroencephalographic (EEG) profiles in healthy volunteers but acute and chronic pharmaco-EEG profiling of antidepressant action in depressed patients has been relatively lacking. This study sought to examine the quantitative topographic EEGs of depressed patients in response to paroxetine treatment. Thirty male patients, meeting DSM-IV criteria for major depression, were examined before and after a single 20 mg dose. These, and an additional 40 patients, were also assessed following 6 weeks of treatment. Eyes-closed resting EEG, collected from 21 scalp sites, was spectrally analyzed to yield regional measures of absolute/relative power and mean frequency in delta, theta, alpha, beta and total spectrum frequency bands. Chronic treatment resulted in a significant reduction in scores on the Hamilton Rating Scale for Depression (HAM-D), with 80% of treatment completers exhibiting a >50% reduction in depression ratings at the end of the 6th week. Acute paroxetine did not alter EEG in patients but chronic treatment was associated with significant alterations as shown by diffuse decreases in alpha power and increases in slow (delta and theta) and anterior fast (beta) wave power, Mean theta and alpha (occipital) frequency were slowed while mean total frequency was accelerated at frontal sites and decreased at occipital sites. The chronic pharmaco-EEG response pattern reflects both sedating and activating actions in regional specific areas which are relevant to the pathophysiology and the pharmacotherapeutic treatment of depression.

Using the cyclostationary properties of chaotic signals for communications

Cyclostationary signals have an expectation value which varies periodically in time. Chaotic signals that have large components at some discrete frequencies in their power spectra can be cyclostationary. The cyclostationarity persists even if the discrete frequency components are removed from the chaotic signal, leaving a signal with a purely broad band frequency spectrum. In this brief, a communications system is created by modulating information onto the periodic parts of a chaotic signal and then removing the periodic parts from the frequency spectrum. At the receiver, the periodic parts of the spectrum are restored by means of a nonlinear operation. This system is demonstrated both in simulations and real circuits, and the performance of this system is measured in simulations. Finally, some of the reasons why such a scheme might be useful are discussed.

On a simple model of the photonic or phononic crystal

A model is proposed for a one-dimensional dielectric or elastic superlattice (SL) that relatively simply describes the frequency spectrum of electromagnetic or acoustic waves. The band frequency spectrum is reduced to minibands contracting with increasing frequency. A procedure is suggested for obtaining local states near a defect in a SL, and the simplest of these states is described. Conditions for the initiation of Bloch oscillations of a wave packet in a SR are discussed.

Is there paradoxical arousal reaction in the EEG subdelta range in patients during anesthesia?

Different anesthetic drugs can produce different electroencephalographic (EEG) patterns. Nondrug induced influences, such as surgical stimulation, may also alter the EEG in anesthetized patients. Increases of delta activity are interpreted as signs of deepening of anesthesia. These EEG patterns are sometimes also found in frontal leads after surgical stimulation during isoflurane anesthesia. However, to avoid incorrect anesthetic management under EEG monitoring, this phenomenon of "paradoxical arousal" must be taken into consideration. This study demonstrates that, after surgical stimulation, frontal activity was enhanced in the 2-3 Hz and 3-4 Hz frequency bands. On the other hand, in the subdelta range (the 0.05-1 Hz and 1-2 Hz frequency bands), there was an opposite reaction. This significant (p<0.001, according to ANOVA and Dunn's method) reduction of EEG power as a result of the surgical stimuli was found in 25 patients (mean age, 49.1+/-16.3 years) scheduled for elective neurosurgical intervention in the lumbosacral region. This report shows some of the problems arising from the common practice of arbitrarily subdividing a power spectrum in frequency bands.

Hybrid-mode computation of propagation and attenuation characteristics of parallel coupled microstrips with finite metallization thickness

The hybrid-mode mixed spectral domain approach (MSDA) is formulated to investigate the dispersion nature of multiple coupled microstrip lines with arbitrary metallization thickness. Incorporated into the solution procedure, a new set of basis functions with /spl delta//sup -1/3/ field singularity near conductor edges is found to be effective in calculating both the phase and attenuation constants. The computation of conductor loss is based on the perturbation procedure. Over a broad band of frequency spectrum, excellent agreement is obtained between the calculated results and existing experiment data for the metallic losses of a single microstrip and effective dielectric constants of coupled lines. The influence of finite metallization thickness on the frequency dependent modal propagation and attenuation characteristics is presented for both a three-line and four-line structure.

Monitoring changes in time of chaotic nonlinear systems.

We extend our method for classifying signals from chaotic nonlinear dynamical systems to the problem of monitoring chaotic nonlinear dynamical systems with the goal of detecting that the state of a system has changed. One potential application would be to systems where the changes are not easily detectable by spectral analysis or other linear techniques. The method is expected to be most useful in comparison to other techniques when there are other signals or noise present, some of which have a broad band frequency spectrum, and the signal of interest is associated with either a low dimensional dynamical system or a low dimensional chaotic attractor. The method is applied to data from a laboratory model of a fluidized bed reactor and to data from a gyroscope as well as to numerically generated signals from mathematical models. For the dynamical systems considered in the paper, the proposed method provides significantly better discrimination than spectral analysis. (c) 1995 American Institute of Physics.

Controlling high frequency chaos in circular YIG films

High power ferromagnetic resonance experiments involving thin circular YIG films produce chaotic oscillations with broad band frequency spectra in the 0.5–25 MHz range. To eliminate chaotic oscillations, a delayed feedback of the ac component of the ferromagnetic resonance signal was used to modulate one of the system parameters, the applied static magnetic field. The chaotic oscillations were converted to oscillations of reduced periodicity, and ultimately the quiescent state, as the gain in the feedback loop was increased. Similar results have been obtained in numerical simulations.

Computer Simulation of Molecular Motions in Liquids: Infrared Spectra of Water and Heavy Water

Abstract The infrared spectra of liquid water and heavy water are calculated from molecular dynamics simulations using different spectroscopic properties. A flexible simple point charged (SPC) molecular model is assumed. The near, mid and far infrared spectra calculated from simulations are compared with experimental data. Special attention is paid to the relationship between the frequency bands of spectra and the nature of the microscopic motions. The usefulness of molecular dynamics simulation for interpreting the spectroscopic measurements is discussed.

Infant distress vocalizations in the Southern African Lesser Bushbaby (Galago moholi)

Infant lesser bushbabies are typically able, from the earliest age, to utter distress vocalizations which appear to have major adaptive significance. Distress vocalizations of infant G. moholi were analyzed by means of a digital storage oscilloscope. Three kinds of sound analyses were carried out: analysis of the sound wave signal, sequential spectrum analysis, and fast Fourier transformation. We emphasize analysis of the frequency spectrum. Three distress calls were identified-the “click call”, the “crackle”, and the “chirp”-which we report for the first time. Click calls were typically composed of short, high-pitched pulses (clicks) uttered in fast, repetitive sequences with a broad band frequency spectrum containing frequencies up to 60 kHz. These acoustic characteristics appear to be particularly well suited for accurate spatial localization of the sound source. The main function of the click call is apparently to alert and to guide the mother to a lost or endangered infant. These basic acoustic characteristics-related to sound localization-are shared to some extent, with the other two distress calls. However, the three calls appear to represent different degrees of distress, with the click call being the basic, call, the crackle corresponding to a greater degree of distress, and the chirp possibly signaling extreme distress such as physical pain.

Transmission characteristics of finite-width conductor-backed coplanar waveguide

This paper presents theoretical and experimental results for a finite-width conductor-backed coplanar waveguide (FW-CBCPW). The guiding characteristics of FW-CBCPW are investigated first by the rigorous method of mode matching. An FW-CBCPW through line is then placed within a test fixture commonly used in laboratories, and the scattering parameters of the through line are obtained theoretically by approximating the FW-CBCPW as a simple system of coupled transmission lines. Experimental results are shown to agree very well with the theoretical ones. In particular, the anomalous behavior observed in the transmission characteristic of the through line is related to the resonant phenomenon of the terminated side planes which are short-circuited at both input and output ends due to the test fixture. Finally, a technique of mode suppression in the side-plane regions is suggested for the improvement of signal transmission over a broad band of frequency spectrum. The effects of extra higher order modes on the transmission characteristics at high frequencies are also discussed. >

ＡＥによる摩擦・摩耗の研究 摩耗形態とＡＥ信号

This paper deal with the characteristics of acoustic emission (AE) signal which generated by friction and wear. The experiments carried out changed the finishing method of plate specimens for produce a typical wear mode. As experimental results, the correlation was observed between the friction and wear phenomena and the amplitude of AE signal or the AE frequency spectrum. The summary of results is shown below. In the abrasive wear mode, wear rate is relatively high, but the AE count rate and the amplitude of AE signal are small. In the adhesive wear mode, wear rate is small, but the amplitude of AE signal is larger. In the abrasive wear and adhesive wear mode, AE signal in the 1-1.5MHz frequency spectrum band was observed.