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Instantaneous Frequency (instantaneous + frequency)
Selected AbstractsNumerical Treatment of Seismic Accelerograms and of Inelastic Seismic Structural Responses Using Harmonic WaveletsCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 4 2007Pol D. Spanos The effectiveness of the harmonic wavelets for capturing the temporal evolution of the frequency content of strong ground motions is demonstrated. In this regard, a detailed study of important earthquake accelerograms is undertaken and smooth joint time-frequency spectra are provided for two near-field and two far-field records; inherent in this analysis is the concept of the mean instantaneous frequency. Furthermore, as a paradigm of usefulness for aseismic structural purposes, a similar analysis is conducted for the response of a 20-story steel frame benchmark building considering one of the four accelerograms scaled by appropriate factors as the excitation to simulate undamaged and severely damaged conditions for the structure. The resulting joint time-frequency representation of the response time histories captures the influence of nonlinearity on the variation of the effective natural frequencies of a structural system during the evolution of a seismic event. In this context, the potential of the harmonic wavelet transform as a detection tool for global structural damage is explored in conjunction with the concept of monitoring the mean instantaneous frequency of records of critical structural responses. [source] 3D imaging of a reservoir analogue in point bar deposits in the Ferron Sandstone, Utah, using ground-penetrating radarGEOPHYSICAL PROSPECTING, Issue 3 2004Xiaoxian Zeng ABSTRACT Most existing reservoir models are based on 2D outcrop studies; 3D aspects are inferred from correlation between wells, and so are inadequately constrained for reservoir simulations. To overcome these deficiencies, we have initiated a multidimensional characterization of reservoir analogues in the Cretaceous Ferron Sandstone in Utah. Detailed sedimentary facies maps of cliff faces define the geometry and distribution of reservoir flow units, barriers and baffles at the outcrop. High-resolution 2D and 3D ground-penetrating radar (GPR) images extend these reservoir characteristics into 3D to allow the development of realistic 3D reservoir models. Models use geometric information from mapping and the GPR data, combined with petrophysical data from surface and cliff-face outcrops, and laboratory analyses of outcrop and core samples. The site of the field work is Corbula Gulch, on the western flank of the San Rafael Swell, in east-central Utah. The outcrop consists of an 8,17 m thick sandstone body which contains various sedimentary structures, such as cross-bedding, inclined stratification and erosional surfaces, which range in scale from less than a metre to hundreds of metres. 3D depth migration of the common-offset GPR data produces data volumes within which the inclined surfaces and erosional surfaces are visible. Correlation between fluid permeability, clay content, instantaneous frequency and instantaneous amplitude of the GPR data provides estimates of the 3D distribution of fluid permeability and clay content. [source] Detection and analysis of LNAPL using the instantaneous amplitude and frequency of ground-penetrating radar dataGEOPHYSICAL PROSPECTING, Issue 1 2002Luciana Orlando This paper reports the results of using the ground-penetrating radar (GPR) method to detect light non-aqueous phase liquids (LNAPL) floating on the water table in an area where the thickness of LNAPL present ranges from a few centimetres to several decimetres. To understand the GPR response in this context, GPR theoretical models are calculated using information from the literature and hydrogeological field data. The study revealed that in the case of LNAPL floating on the water table in a static condition, there is an increase in the reflection amplitude from the water table due to the decrease in the capillary fringe. Nevertheless the amplitude of reflection from the water table can discriminate the contaminated from the non-contaminated zone. Apart from an analysis of the real traces, the analysis of some attributes of the complex trace, instantaneous amplitude, phase and frequency, are also good tools to detect hydrocarbons floating on the water table. Such attributes, depending on both the signal frequency and the hydrocarbon thickness, can also give information about the thickness of the hydrocarbon layer. It is concluded that analysing the lateral variations in signal amplitude of the real trace and in the amplitude, phase and instantaneous frequency of the complex signal permits the delimiting of the area polluted by the hydrocarbon. [source] Naturalistic stimulus trains evoke reproducible subicular responses both within and between animals in vivoHIPPOCAMPUS, Issue 2 2010Beth Tunstall Abstract Previous investigation of CA1-evoked subicular responses has used either single low-frequency pulses (LF), paired-pulses (PP), or high-frequency bursts. Here we test for the first time how subiculum responds to naturalistic stimulation trains (NSTs). We recorded CA1-evoked field potentials from dorsal rat subiculum in response to LF, PP, and two NST patterns. The latter were derived from CA1 place cell activity; NST1 contained bursts of stimuli presented in two main episodes, while the burst-patterned stimuli in NST2 were spaced more evenly. NSTs generated significantly greater field responses compared with LF or PP patterns. Response patterns to either NST were significantly correlated across trial repeats in 9 out of 10 rats, supporting a robust postsynaptic encoding of CA1 input by subiculum. Correlations between NST responses were also observed across experiments; however, these were more variable than those within experiments. The relationship between response magnitude and activation history revealed a strong correlation between magnitude and NST instantaneous frequency for NST1 but was weaker for NST2. In addition, the number of stimuli within a prior 500 ms window was a determining factor for response magnitude for both NSTs. Overall, the robust reproducibility in subicular responses within rats suggests that information within NSTs is faithfully transmitted through the CA1-subiculum axis. However, variation in response sequences across rats suggests that encoding patterns to the same input differ across the subiculum. Changes in the ratio of target bursting and regularly spiking neurons along the subicular proximodistal axis may account for this variation. The activation history of this connection also appears to be a strong determining factor for response magnitude. © 2009 Wiley-Liss, Inc. [source] Time,frequency higher-order spectra with adjustment to the instantaneous frequency variationINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 3 2010L. Gelman Abstract Novel time,frequency techniques are proposed: the short time instantaneous higher-order spectra (HOS) with adjustment to measured or known a priori time variation of the instantaneous frequency of transient signals. It is shown that the proposed transforms are more effective than the non-instantaneous HOS (i.e. without adjustment to time variation of the instantaneous frequency) in recognizing a non-stationary nonlinearity. Copyright © 2008 John Wiley & Sons, Ltd. [source] AM,FM techniques in the analysis of optical coherence tomography signalsJOURNAL OF BIOPHOTONICS, Issue 6-7 2009Costas Pitris Abstract The subtle tissue changes associated with the early stages of malignancies, such as cancer, are not clearly discernible even at the current, improved, resolution of optical coherence tomography (OCT) systems. However, these changes directly affect the spectral content of the OCT image that contains information regarding these unresolvable features. Spectral analysis of OCT signals has recently been shown to provide additional information, resulting in improved contrast, directly related to scatterer size changes. Amplitude modulation,frequency modulation (AM,FM) analysis, a fast and accurate technique for the estimation of the instantaneous frequency, phase, and amplitude of a signal, can also be applied to OCT images to extract scatterer-size information. The proposed technique could make available an extremely valuable tool for the investigation of disease characteristics that now remain below the resolution of OCT and could significantly improve the technology's diagnostic capabilities. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The use of intrinsic mode functions to characterize shock and vibration in the distribution environmentPACKAGING TECHNOLOGY AND SCIENCE, Issue 1 2005Vincent Rouillard Abstract This paper describes an innovative approach, based on the instrinsic mode functions (IMFs), to characterize the nature of mechanical vibration encountered in transport vehicles. The paper highlights the importance of understanding the nature of transport vibration and shows that their accurate characterization is essential for the optimization of protective packaging. Although there have been numerous studies aimed at characterizing random vibration during transport, the majority of those have been limited to applying relatively conventional signal analysis techniques, such as the average power spectral density (PSD). This paper investigates the benefits offered by the recently introduced Hilbert,Huang transform when characterizing non-stationary random vibration in comparison with more traditional Fourier analysis-based techniques. The paper describes the operation of the Hilbert,Huang transform, which was developed to assist in the analysis of non-Gaussian and non-stationary random data. The Hilbert,Huang transform is based on the empirical mode decomposition (EMD) technique used to produce a finite number of IMFs, which, as a set, provide a complete description of the process. It is shown how these IMFs are well suited to the application of the Hilbert,Huang transform to determine the magnitude and instantaneous frequency of each IMF. The technique is applied to various records of random vibration data collected from transport vehicles in order to illustrate the benefits of the method in characterizing the nature of non-stationarities present in transport vibration. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||