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Power Spectral Density (power + spectral_density)
Selected AbstractsDynamic study of stacked packaging units by operational modal analysisPACKAGING TECHNOLOGY AND SCIENCE, Issue 3 2010Carlos Bernad Abstract Laboratory simulation of transport vibration has been the object of many studies in recent years due to the financial implications of potential customer claims in respect of damage caused during product distribution and the need for tools for packaging optimization. Most of these works concentrate on the special nature of transport vibrations and how to reproduce them: Power Spectral Density (PSD) profiles related to road and truck characteristics, the non-stationary aspects of the environment, the non-Gaussian characteristics of the recorded vibrations and the best procedures for meaningful laboratory testing. In the present work, a different point of view is applied to the issue. The paper deals with the dynamics of different corrugated stacked packaging units by means of operational modal analysis and a 6 degrees of freedom multi-axis shaker table. The results show the already known non-linear behaviour of the paperboard containers and the natural frequencies and modes likely to appear in the packaging. The relevance of bending-like modes in relation to laboratory testing is discussed. Copyright © 2010 John Wiley & Sons, Ltd. [source] Analysis of electrocardiographic changes in partial epileptic patients by combining eigenvector methods and support vector machinesEXPERT SYSTEMS, Issue 3 2009Elif Derya Übeyli Abstract: In the present study, the diagnostic accuracy of support vector machines (SVMs) on electrocardiogram (ECG) signals is evaluated. Two types of ECG beats (normal and partial epilepsy) were obtained from the Physiobank database. Decision making was performed in two stages: feature extraction by eigenvector methods and classification using the SVM trained on the extracted features. The present research demonstrates that the power levels of the power spectral densities obtained by eigenvector methods are features which represent the ECG signals well and SVMs trained on these features achieve high classification accuracies. [source] Three-Dimensional Surface Texture Characterization of Portland Cement Concrete PavementsCOMPUTER-AIDED CIVIL AND INFRASTRUCTURE ENGINEERING, Issue 3 2007Ala Abbas Ten PCC field cores of varying surface textures were included in the analysis. X-ray Computed Tomography (CT) was used to scan the upper portion of these cores, resulting in a stack of two-dimensional grayscale images. Image processing techniques were utilized to isolate the void pixels from the solid pixels and reconstruct the three-dimensional surface topography. The resulting three-dimensional surfaces were reduced to two-dimensional "map of heights" images, whereby the grayscale intensity of each pixel within the image represented the vertical location of the surface at that point with respect to the lowest point on the surface. The "map of heights" images were analyzed using four mathematical methods, namely the Hessian model, the Fast Fourier transform (FFT), the wavelet analysis, and the power spectral density (PSD). Results obtained using these methods were compared to the mean profile depth (MPD) computed in accordance with ASTM E1845. [source] Spectral analysis of electrocorticographic activity during pharmacological preconditioning and seizure induction by intrahippocampal domoic acidHIPPOCAMPUS, Issue 8 2010P.M. Sawant Abstract Previously we have shown that low-dose domoic acid (DA) preconditioning produces tolerance to the behavioral effects of high-dose DA. In this study, we used electrocorticography (ECoG) to monitor subtle CNS changes during and after preconditioning. Young adult male Sprague-Dawley rats were implanted with a left cortical electrode, and acute recordings were obtained during preconditioning by contralateral intrahippocampal administration of either low-dose DA (15 pmoles) or saline, followed by a high-dose DA (100 pmoles) challenge. ECoG data were analyzed by fast Fourier transformation to obtain the percentage of baseline power spectral density (PSD) for delta to gamma frequencies (range: 1.25,100 Hz). Consistent with previous results, behavioral analysis confirmed that low-dose DA preconditioning 60 min before a high-dose DA challenge produced significant reductions in cumulative seizure scores and high level seizure behaviors. ECoG analysis revealed significant reductions in power spectral density across all frequency bands, and high-frequency/high-amplitude spiking in DA preconditioned animals, relative to saline controls. Significant correlations between seizure scores and ECoG power confirmed that behavioral analysis is a reliable marker for seizure analysis. The reduction ofpower in delta to gamma frequency bands in contralateral cortex does not allow a clear distinction between seizure initiation and seizure propagation, but does provide objective confirmation that pharmacological preconditioning by DA reduces network seizure activity. © 2009 Wiley-Liss, Inc. [source] On the influence of trigger level in distribution vibration surveysPACKAGING TECHNOLOGY AND SCIENCE, Issue 4 2009Vincent Rouillard Abstract This paper follows on from recently published research that examined the effects of recording parameters on the outcomes of distribution vibration surveys. Whereas the previous research focused on the effects of the sampling period at which sub-records of the process are captured, this paper deals with another often-used recording parameter, namely, the vibration level trigger. The paper describes the development of a software tool that was designed specifically to study the influence of various sampling parameters on continuously recorded vibration data. This software tool was used to undertake a thorough statistical analysis on a vibration record set consisting of continuously sampled data measured from a wide variety of vehicle types and routes. The paper shows that the outcomes of vibration surveys are very sensitive to the trigger level and can produce highly distorted results by introducing a bias that nearly always overestimates the overall vibration levels. This is reflected in estimates of common descriptors of random vibration processes such as the average power spectral density (PSD), the peak-hold PSD and the overall root-mean-square values. The main outcome of this analysis is the formulation of a correction method based on relationships between the true mean and peak-hold PSDs and estimates from sampled data. The effect and significance of the proposed correction procedure is demonstrated, especially in the context of laboratory simulation of distribution vibrations. The paper concludes by making specific recommendations for configuring high-capacity field data recorders and applying correction strategies to ensure that vibration surveys yield statistically sound results. Copyright © 2009 John Wiley & Sons, Ltd. [source] Measurement and analysis of vibration levels for truck transport in Spain as a function of payload, suspension and speedPACKAGING TECHNOLOGY AND SCIENCE, Issue 8 2008Manuel-Alfredo Garcia-Romeu-Martinez Abstract The vibration levels that occur during transportation in vehicles are complex and play a significant role in the level of damage experienced by products when shipped. In the past decade, technology has allowed packaging engineers to measure and analyse the vibration levels in commercial shipments. Recent studies have measured vibration in shipping environments on a global basis to allow packaging designers to develop packaging to meet worldwide distribution challenges. The purpose of this study was to measure and develop simulation methods for truck transport in Spain. The study quantifies vibration characteristics in trucks as a function of speed, payload and suspension type. The shipments were instrumented with vibration data recorders to measure the vibration levels and a global position system to measure the truck speed. The recorders were mounted at the rear and front location of the trailer. Two different trucks, one with leaf spring suspension and the other with air ride suspension were studied using two different load conditions. The road surface was asphalt. The data is presented in the form of power spectral density that can be used to program electrohydraulic vibration tables using ASTM, ISTA and ISO vibration test methods. Results showed that the air ride vibration levels were lower than that of leaf spring suspension trailers. Overall, the vibration intensity was lower for both types of truck as compared with the levels measured in North America, China, India and Southeast Asia. Copyright © 2007 John Wiley & Sons, Ltd. [source] On the effects of sampling parameters when surveying distribution vibrationsPACKAGING TECHNOLOGY AND SCIENCE, Issue 8 2008Vincent Rouillard Abstract This paper presents the initial outcomes of a study aimed at better understanding the effects of recording parameters on the outcomes of distribution surveys. With the advent of vibration recorders with increasing capacity, there has been a corresponding increase in the number of studies aimed at evaluating and characterizing the random vibrations generated by transport vehicles across a wide variety of distribution environments. Oftentimes, the sampling and recording parameters used in these studies are not given adequate attention, resulting in statistical estimates that are open to interpretation. The paper shows how the selection of the sampling and recording parameters can have significant effects on much used descriptors of random vibration processes such as the average power spectral density (PSD), the peak-hold PSD and the root mean square distribution. The paper shows that the results of vibration surveys are most sensitive to the sampling period, especially when the vibrations are highly non-stationary. The paper concludes by making specific recommendations for configuring high-capacity vibration recorders to ensure that vibration surveys yield statistically sound results. Copyright © 2008 John Wiley & Sons, Ltd. [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] Enhanced reliability of magnetic tunnel junctions with thermal annealingPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 8 2004Kwang-Seok Kim Abstract Time-dependent dielectric breakdown (TDDB) of magnetic tunnel junctions (MTJs) under a constant voltage stress, tunneling magnetoresistance (TMR), and barrier properties, e.g. effective barrier height and thickness, were investigated as a function of thermal annealing temperatures. A Weibull failure distribution function was plotted in terms of time to breakdown (TBD) of MTJs. The TBD when 63 fraction of as-fabricated MTJs cumulatively failed increased significantly after thermal annealing at 210 °C while the TMR also increased from 8.85% to 14.22% before and after thermal annealing at 210 °C, respectively. We believe that the enhanced reliability of the MTJs is due to healing effect of bulk defects in the barrier during the annealing process, likely leading to the reduction of defect trap density. The reduction of bulk defects in the barrier was also confirmed by the lowered 1/f noise power spectral density from voltage fluctuation measurements. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Haze of polyethylene films,effects of material parameters and clarifying agentsPOLYMER ENGINEERING & SCIENCE, Issue 5 2002Erik Andreassen Effects of material parameters on the haze of blown films were analyzed. Four linearlow-density polyethylenes (two metallocene grades and two Ziegler-Natta grades) were studied in combination with three additives (two sorbitol-based clarifying agents and a low-molecular-weight long-chain branched polyethylene). One of the sorbitol-based additives reduced the haze of both the metallocene materials in this study, but did not have any positive effect on the two Ziegler-Natta materials. The variation in haze among the four base materials was directly related to the root-mean-square surface roughness (,). When considering all 16 material/additive combinations, the link between haze and surface topography was not a simple ,-haze relationship, but the haze was correlated with the average distance between adjacent surface profile peaks, the average slope, and the power spectral density at high lateral frequencies. Both of the mechanisms referred to in the literature, extrusion-induced haze and crystallization-induced haze, were probably active for the films in this study. [source] A framework for describing correlated excitation of solar p-modesASTRONOMISCHE NACHRICHTEN, Issue 5 2008W. J. Chaplin Abstract In a previous paper we suggested that, for a given p mode, the excitation function is the same as the component of the solar background noise that has an identical surface spherical harmonic projection (over the corresponding range of temporal frequency). An important consequence of this surmise is that the excitation of overtones of a given angular degree and azimuthal order will be correlated in time. In this note, we introduce the basic principles and a mathematical description of correlated mode excitation. We use simple, illustrative examples, involving two modes. Our treatment suggests that in the real observations, any signatures of the correlation would not appear as a correlation of the output amplitudes of overtones, but rather as subtle modifications to the power spectral density at frequencies between the central frequencies of the overtones. These modifications give a contribution to the observed peak asymmetries. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | |||||||||||||