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Spectral Density (spectral + density)
Kinds of 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] A test of homogeneity for autoregressive processesINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 3 2002Rafael Martínez Pedro Gómez Abstract In this paper, we introduce a new hypothesis test to determine whether or not two spectral densities are proportional. We deliberately limit our study to autoregressive processes and derive the asymptotic behaviour of the test. A test for autoregressive coefficient nullity or randomness is deduced. We derive asymptotic behaviour for these tests and show the usefulness of our test to detect speech in a noisy environment. Copyright © 2002 John Wiley & Sons, Ltd. [source] Comparison of decoupling methods for analyzing pressure fluctuations in gas-fluidized bedsAICHE JOURNAL, Issue 4 2010Yongmin Zhang Abstract Two methods of decoupling pressure fluctuations in fluidized beds by using the incoherent part (IOP) of absolute pressure (AP) and differential pressure (DP) fluctuations are evaluated in this study. Analysis is conducted first to demonstrate their similarities, differences, and drawbacks. Then, amplitudes, power spectral densities, mean frequencies, coherence functions, and filtering indices of the IOP of AP and DP fluctuations are calculated and compared based on experimental data from a two-dimensional fluidized column of FCC particles. Derived bubble sizes are also compared with the sizes of bubbles viewed in the two-dimensional bed. The results demonstrate the similarity of these two methods in filtering out global compression wave components from absolute pressure fluctuations, especially those generated from oscillations of fluidized particles and gas flow rate fluctuations. However, both methods are imperfect. Neither can filter out all the compression wave components and retain all the useful bubble-related wave components. Their amplitudes can be used to characterize global bubble property and quality of gas,solids contacting in bed, but they do not give accurate measurement of bubble sizes. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Surface texture characterization of injection-molded pigmented plasticsPOLYMER ENGINEERING & SCIENCE, Issue 9 2004Ingrid Ariño An appropriate description of the surface textures deliberately created on injection-molded plastic parts of interior car components is presented. A spatial wavelength-dependent analysis is used as an interesting alternative to the traditional roughness parameters. Auto-correlation functions and power spectral densities are examples of such spectral functions that include parameters both in amplitude and profile directions. Even fractal concepts can be useful descriptors. As an illustration, it is also shown how the effects on the surface topography of the plastic part of after-etching the mold can be assessed by suitable descriptors. An experimental evaluation of injection-molded plaques containing three different surface patterns was carried out using an optical profilometer, supplemented by contact stylus measurements. The ability to assess the topography of these plaques by means of a new fast photometric stereo-technique, denoted OptiTopo, was also evaluated. In its present form, however, this technique does not provide a detailed description of the topography of a pigmented plastic. Reasons for this and possible improvements are discussed. Polym. Eng. Sci. 44:1615,1626, 2004. © 2004 Society of Plastics Engineers. [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] Model updating using noisy response measurements without knowledge of the input spectrumEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 2 2005Ka-Veng Yuen Abstract A new probabilistic model identification methodology is proposed using measured response time histories only. The proposed approach requires that the number of independent measurements is larger than the number of independent excitations. Under this condition, no input measurements or any information regarding the stochastic model of the input is required. Specifically, the method does not require the response to be stationary and does not assume any knowledge of the parametric form of the spectral density of the input. Therefore, the method has very wide applicability. The proposed approach allows one to obtain not only the most probable values of the updated model parameters but also their associated uncertainties using only one set of response data. It is found that the updated probability distribution can be well approximated by a Gaussian distribution centered at the most probable values of the parameters. Examples are presented to illustrate the proposed method. Copyright © 2004 John Wiley & Sons, Ltd. [source] The effects of torsion and motion coupling in site response estimationEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 5 2003Mohammad R. Ghayamghamian Abstract Soil amplification characteristics are investigated using data from the Chibaken-Toho-Oki earthquake and its aftershocks recorded at Chiba dense array in Japan. The frequency-dependent amplification function of soil is calculated using uphole-to-downhole spectral ratio analysis, considering the horizontal components of shear wave. The identified spectral ratios consistently demonstrate the splitting of peaks in their resonance frequencies and low amplification values in comparison with a 1D model. The torsional behaviour and horizontal ground motion coupling are clarified as the reasons for these phenomena at the site. To prove the hypothesis, the torsional motion is directly evaluated using the data of the horizontal dense array in different depths at the site. The comparison between Fourier spectra of torsional motion and identified transfer functions reveals the peaks at the same frequencies. The wave equation including torsion and horizontal motion coupling is introduced and solved for the layered media by applying wave propagation theory. Using the developed model, the effects of torsional motion with horizontal motion coupling on soil transfer function are numerically examined. Splitting and low amplification at resonance frequencies are confirmed by the results of numerical analysis. Furthermore, the ground motion in two horizontal directions at the site is simulated using site geotechnical specification and optimizing the model parameters. The simulated and recorded motions demonstrate good agreement that is used to validate the hypothesis. In addition, the spectral density of torsional ground motions are compared with the calculated one and found to be well predicted by the model. Finally, the results are used to explain the overestimation of damping in back-calculation of dynamic soil properties using vertical array data in small strain level. Copyright © 2003 John Wiley & Sons, Ltd. [source] A high frequency kriging approach for non-stationary environmental processesENVIRONMETRICS, Issue 5 2001Montserrat Fuentes Abstract Emission reductions were mandated in the Clean Air Act Amendments of 1990 with the expectation that they would result in major reductions in the concentrations of atmospherically transported pollutants. The emission reductions are intended to reduce public health risks and to protect sensitive ecosystems. To determine whether the emission reductions are having the intended effect on atmospheric concentrations, monitoring data must be analyzed taking into consideration the spatial structure shown by the data. Maps of pollutant concentrations and fluxes are useful over different geopolitical boundaries, to discover when, where, and to what extent the U.S. Nation's air quality is improving or declining. Since the spatial covariance structure shown by the data changes with location, the standard kriging methodology for spatial interpolation cannot be used because it assumes stationarity of the process. We present a new methodology for spatial interpolation of non-stationary processes. In this method the field is represented locally as a stationary isotropic random field, but the parameters of the stationary random field are allowed to vary across space. A procedure for interpolation is presented that uses an expression for the spectral density at high frequencies. New fitting algorithms are developed using spectral approaches. In cases where the data are distributed exactly or approximately on a lattice, it is argued that spectral approaches have potentially enormous computational benefits compared with maximum likelihood. The methods are extended to interpolation questions using approximate Bayesian approaches to account for parameter uncertainty. We develop applications to obtain the total loading of pollutant concentrations and fluxes over different geo-political boundaries. Copyright © 2001 John Wiley & Sons, Ltd. [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] Quantum quadratic brownian oscillator model for absorption lineshapesISRAEL JOURNAL OF CHEMISTRY, Issue 2-3 2002Valeri Barsegov The absorption lineshape of a two-level chromophore coupled quadratically to a collective Gaussian solvation coordinate with an arbitrary Brownian oscillator spectral density is calculated exactly using a path-integral representation of the dipole correlation function in Liouville space. [source] Performance of a cryogenic silicon monochromator under extreme heat loadJOURNAL OF SYNCHROTRON RADIATION, Issue 2 2004Aleksandr Chumakov The performance of an indirectly cooled cryogenic silicon monochromator under heat loads up to 870,W has been studied. The investigation was performed over numerous parameters and included measurements of total flux, spectral density, rocking curves, angular beam profiles and crystal slope errors. An almost ideal monochromator performance was observed in the 270,570,W range of the heating power. At a heat load of ,400,W and under standard operation conditions, the crystal distortions did not exceed 1,µrad. At the highest available heat load of 870,W, the crystal distortions were about 7,µrad. [source] Unit-root testing: on the asymptotic equivalence of Dickey,Fuller with the log,log slope of a fitted autoregressive spectrumJOURNAL OF TIME SERIES ANALYSIS, Issue 3 2010Evangelos E. Ioannidis In this article we consider the problem of testing for the presence of a unit root against autoregressive alternatives. In this context we prove the asymptotic equivalence of the well-known (augmented) Dickey,Fuller test with a test based on an appropriate parametric modification of the technique of log-periodogram regression. This modification consists of considering, close to the origin, the slope (in log,log coordinates) of an autoregressively fitted spectral density. This provides a new interpretation of the Dickey,Fuller test and closes the gap between it and log-periodogram regression. This equivalence is based on monotonicity arguments and holds on the null as well as on the alternative. Finally, a simulation study provides indications of the finite-sample behaviour of this asymptotic equivalence. [source] A superharmonic prior for the autoregressive process of the second-orderJOURNAL OF TIME SERIES ANALYSIS, Issue 3 2008Fuyuhiko Tanaka Abstract., The Bayesian estimation of the spectral density of the AR(2) process is considered. We propose a superharmonic prior on the model as a non-informative prior rather than the Jeffreys prior. Theoretically, the Bayesian spectral density estimator based on it dominates asymptotically the one based on the Jeffreys prior under the Kullback,Leibler divergence. In the present article, an explicit form of a superharmonic prior for the AR(2) process is presented and compared with the Jeffreys prior in computer simulation. [source] Simulation of Real-Valued Discrete-Time Periodically Correlated Gaussian Processes with Prescribed Spectral Density MatricesJOURNAL OF TIME SERIES ANALYSIS, Issue 2 2007A. R. Soltani Abstract., In this article, we provide a spectral characterization for a real-valued discrete-time periodically correlated process, and then proceed on to establish a simulation procedure to simulate such a Gaussian process for a given spectral density. We also prove that the simulated process, at each time index, converges to the actual process in the mean square. [source] Estimation of the location and exponent of the spectral singularity of a long memory processJOURNAL OF TIME SERIES ANALYSIS, Issue 1 2004Javier Hidalgo Abstract., We consider the estimation of the location of the pole and memory parameter ,0 and d of a covariance stationary process with spectral density We investigate optimal rates of convergence for the estimators of ,0 and d, and the consequence that the lack of knowledge of ,0 has on the estimation of the memory parameter d. We present estimators which achieve the optimal rates. A small Monte-Carlo study is included to illustrate the finite sample performance of our estimators. [source] Nonlinear functionals of the periodogramJOURNAL OF TIME SERIES ANALYSIS, Issue 5 2002GILLES FAY A central limit theorem is stated for a wide class of triangular arrays of nonlinear functionals of the periodogram of a stationary linear sequence. Those functionals may be singular and not-bounded. The proof of this result is based on Bartlett decomposition and an existing counterpart result for the periodogram of an independent and identically distributed sequence, here taken to be the driving noise. The main contribution of this paper is to prove the asymptotic negligibility of the remainder term from Bartlett decomposition, feasible under short dependence assumption. As it is highlighted by applications (to estimation of nonlinear functionals of the spectral density, robust spectral estimation, local polynomial approximation and log-periodogram regression), this extends may results until then tied to Gaussian assumption. [source] Averaged Periodogram Spectral Estimation with Long-memory Conditional HeteroscedasticityJOURNAL OF TIME SERIES ANALYSIS, Issue 4 2001Marc Henry The empirical relevance of long-memory conditional heteroscedasticity has emerged in a variety of studies of long time series of high frequency financial measurements. A reassessment of the applicability of existing semiparametric frequency domain tools for the analysis of time dependence and long-run behaviour of time series is therefore warranted. To that end, in this paper the averaged periodogram statistic is analysed in the framework of a generalized linear process with long-memory conditional heteroscedastic innovations according to a model specification first proposed by Robinson (Testing for strong serial correlation and dynamic conditional heteroscedasticity in multiple regression. J. Economet. 47 (1991), 67,84). It is shown that the averaged periodogram estimate of the spectral density of a short-memory process remains asymptotically normal with unchanged asymptotic variance under mild moment conditions, and that for strongly dependent processes Robinson's averaged periodogram estimate of long memory (Semiparametric analysis of long memory time series. Ann. Stat. 22 (1994), 515,39) remains consistent. [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] Measurements and analysis of the noise spectral density of YBCO filmsPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2006A. Taoufik Abstract We studied the voltage noise spectral density SV(f, T, H ) dependence on frequency f, temperature T and applied magnetic field H in YBa2Cu3O7,, films. The voltage noise spectral density SV(f ) as a function of frequency exhibits 1/f behavior according to a Lorentzian shape A [(1 + ,f /f0)B ]C, where A, f0, B, C constants which are determined and compared for many values of H . The influence of temperature and magnetic field is clearly observed as a function of temperature, SV(T ) is found to vanish at Tg, the temperature of vortex glass transition, according to a (T , Tg)x law. We interpreted those results by the formation of a large distribution of glass vortex domains. Approaching Tg, these domains grow in size and lifetime, while at Tg those parameters diverge. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [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] Zero dimensional exciton-polaritonsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 10 2006A. Baas The cover picture from the article [1] shows, in the left parts of the three diagrams, the measured photoluminescence intensity as a function of energy and emission angle for a 3 ,m (left diagram), 9 ,m (middle diagram) and 19 ,m-diameter quasi-circular mesa (right diagram). The white lines are the energy dispersions of 2D polariton modes. For clarity, intensities above 1485 meV have been multiplied by a constant factor, as indicated. The right parts of the diagrams contain intensity plots of the simulated polariton spectral density for cylindrical mesas of the same diameters, yielding very good quantitative agreement of the 0D polariton states in the circular mesas. This confirms the coexistence of 0D and 2D microcavity polaritons in these semiconductor structures. This paper is an invited presentation from the 8th International Workshop on Nonlinear Optics and Excitation Kinetics. Further articles from NOEKS 8 are published in phys. stat. sol. (c) 3, No. 7 (2006). [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] Exact formulas for the Hodrick-Prescott filterTHE ECONOMETRICS JOURNAL, Issue 1 2008Tucker McElroy Summary, The Hodrick,Prescott (HP) filter is widely used in the field of economics to estimate trends and cycles from time series data. For certain applications,such as deriving implied trend and cycle models and obtaining filter weights,it is desirable to express the frequency response of the HP as the spectral density of an ARMA model; in other words, to accomplish the spectral factorization of the HP filter. This paper presents an exact approach to this problem, which makes it possible to provide exact algebraic formulas for the HP filter coefficients in terms of the HP's signal-to-noise ratio. [source] Beat-to-Beat QT Interval Variability Is Primarily Affected by the Autonomic Nervous SystemANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2008Ph.D., Takanao Mine M.D. Background: Beat-to-beat QT interval variability is associated with life-threatening arrhythmias and sudden death, however, its precious mechanism and the autonomic modulation on it remains unclear. The purpose of this study was to determine the effect of drugs that modulate the autonomic nervous system on beat-to-beat QT interval. Method: RR and QT intervals were determined for 512 consecutive beats during fixed atrial pacing with and without propranolol and automatic blockade (propranolol plus atropine) in 11 patients without structural heart disease. Studied parameters included: RR, QTpeak (QRS onset to the peak of T wave), QTend (QRS onset to the end of T wave) interval, standard deviation (SD) of the RR, QTpeak, and QTend (RR-SD, QTpeak-SD, and QTend-SD), coefficients of variation (RR- CV, QTpeak-CV, and QTend-CV) from time domain analysis, total power (TP; RR-TP, QTpeak-TP, and QTend-TP), and power spectral density of the low-frequency band (LF; RR-LF, QTpeak-LF, and QTend-LF) and the high-frequency band (HF; RR-HF, QTpeak-HF and QTend-HF). Results: Administration of propranolol and infusion of atropine resulted in the reduction of SD, CV, TP, and HF of the QTend interval when compared to controlled atrial pacing (3.7 ± 0.6 and 3.5 ± 0.5 vs 4.8 ± 1.4 ms, 0.9 ± 0.1 and 0.9 ± 0.1 vs 1.2 ± 0.3%, 7.0 ± 2.2 and 7.0 ± 2.2 vs 13.4 ± 8.1 ms2, 4.2 ± 1.4 and 4.2 ± 1.2 vs 8.4 ± 4.9 ms2, respectively). Administration of propranolol and atropine did not affect RR interval or QTpeak interval indices during controlled atrial pacing. Conclusions: Beat-to-beat QT interval variability is affected by drugs that modulate the autonomic nervous system. [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] | ||||||||||||||||||||||