Unfiltered Data Research Articles

Reproducibility of the spectral turbulence analysis of the signal-averaged electrocardiogram.

Spectral turbulence analysis (STA) of the signal-averaged electrocardiogram (SAECG) is a recently proposed technique to identify patients with ventricular tachycardia as well as patients at risk for arrhythmic events after acute myocardial infarction (MI). The short-term reproducibility of this technique has been previously reported; our study evaluates the reproducibility of STA by shifting the reference points. Twenty patients with acute MI were recruited. SAECG was recorded 13 days after onset of the acute MI. Unfiltered data were transferred and analyzed by personal computer software for spectral turbulence analysis according to the standard condition; reference points of the segment of interest were shifted from QRS offset -10 ms and QRS onset -10 ms to QRS offset +10 ms and QRS onset +10 ms, step 2 ms. Thus, 10 analyses were computed. Reproducibility of the results was calculated using the coefficient of variation (CV) and the relative error (RE). The reproducibility of the classification (RC) was defined as the percentage of the identical classification compared with the standard segment. CV of the intersegment correlation standard deviation was statistically higher than the other parameters regardless of the lead considered. RE was not different in each parameter and in each lead. RC was > 90% in all parameters, except in spectral entropy which showed an RC > 80%. Reproducibility of the STA introducing a temporal shift in the analyzed segments was high in all considered parameters.

ERS‐1 altimeter fast delivery data quality flagging over land surfaces

Over land ice and land, satellite altimeters provide valuable topographic information, in spite of having been designed primarily to operate over the ocean. There is a need, however, for careful data quality assessment and screening as erroneous elevation measurements can be included within the telemetered data, especially when the range tracker encounters complex echoes, or rapidly varying topography. The ERS‐1 Fast Delivery (FD) data product provides an excellent source of near real‐time data, which has already been used for ice sheet mapping. This is a reduced data set consisting of on‐board parameters generated once per second. In this paper we show that by applying thresholds to two parameters, significant amounts of poorly tracked data can be eliminated. The effectiveness of this filtering technique is demonstrated by a comparison of filtered and unfiltered altimeter data with a digital elevation model. This filtering technique is applied to the first 35 day repeat cycle of FD data obtained over land to produce the first map of global topography from ERS‐1.

The Influence of the Andes Cordillera on Transient Disturbances

Abstract The influence of the Andes Cordillera on transient disturbances is investigated in this study using a lag-correlation analysis. This analysis shows that the unfiltered geopotential height data have a wavelike pattern moving to the east while tilting to the west in the vertical. When the wave approaches the Andes Cordillera, it exhibits orographic effects such as anticyclonic turning of a low-level disturbance trajectory, a zonal trajectory in the upper levels, distortions of the isolines of correlation, and an elongation of maximum correlation on the lee side of the Andes. The anticyclonic turning of the trajectory in the low-attitude levels and a zonal trajectory in upper levels implies a decrease in the vertical tilt of the system on the windward side and an increase in the tilt on the lee side. The increase of baroclinicity on the lee side results in baroclinic development as predicted from a linearly obtained normal-mode solution in the presence of mountains. A cross-correlation analysis of t...

On Currents and Vertical Mixing in Lake Ontario during Summer Stratification

Currents and vertical mixing characteristics were investigated on the basis of time series of current meter and temperature data from a summer-stratified period in Lake Ontario. The experimental set up consisted of seven current meters distributed in one vertical line from 12 m below the surface to 1 m above the lake bottom at a total depth of 143 m. The period considered for the analysis was from June to September, 1991. The currents showed pronounced oscillations with two significant kinetic energy peaks, one at about 17 hours due to inertial motions, and one at 10 days, probably due to meteorological forcing. The current shear in the hypolimnion was strong enough to overcome stability and generate turbulence (Richardson numbers below 0.25) and there was probably turbulence enough available to keep the matter (almost neutral buoyant particles) in the whole Nepheloid bottom layer in suspension. In the thermocline region the turbulence was mainly damped (Richardson numbers above 1), but some events with lower Richardson numbers were also calculated indicating increased mixing during these events. By analysing filtered and unfiltered current meter data it was found that the shear-generated turbulence in the hypolimnion was mainly due to the meteorologically forced currents. In the thermocline region, however, the vertical shear associated with the inertial oscillation had a greater impact on the mixing.

Azimuth estimation capabilities of the ARCESS regional seismic array

Abstract The effect of local geology and noise conditions on the performance of a small regional array is investigated by comparing the regional Pn backazimuth estimation capabilities of the ARCESS array in northern Norway to the NORESS array. A broadband frequency-wavenumber estimator was used to calculate backazimuths from the Pn arrival for each of 203 regional events recorded at ARCESS while varying element spacing, frequency band, and time window. Most of the errors in backazimuth are less than 20° when appropriate parameter combinations are used, and mean backazimuth errors are close to zero. The best results are obtained using a 13-element configuration that has a 1.4 km aperture and a maximum station spacing of about 600 m. With the 13-element configuration and the data filtered to include frequencies between 3 and 10 Hz, the mean errors for the 203 event data set are less than 0.9°, and S.D. are as small as 16.9°. There are differences seen in the backazimuth estimation capabilities of ARCESS and NORESS with specific parameter combinations. The larger aperture configurations (10- and 17-elements) have smaller means at ARCESS, although the precision is about the same. The estimates using unfiltered data at ARCESS are poor, because of local noise conditions that increase the level of background noise at low frequencies. Overall the precision is better at NORESS, but both regional arrays have the best results using the 13-element configuration and filtering the data in the middle frequency range (3 to 10 Hz). Other factors investigated include SNR and source region. Backazimuth estimation statistics improve if only events with 5 dB of SNR are included in the data set at both ARCESS and NORESS. The mean errors move closer to zero and standard deviations decrease. The differences between the two arrays are not as pronounced. There are some path effects from different source regions around the ARCESS array. However, combinations of small aperture configurations and middle (3 to 10 Hz) frequency bands work well for events over the entire distance range of 30 to 1200 km. ARCESS and NORESS have similar backazimuth estimation capabilities even though there are differences in the local geology and noise conditions. Because a 13-element configuration produces reliable results for both arrays, it would be reasonable to reduce the number of elements in a regional array. This in turn will reduce the costs associated with building and deploying small regional arrays.

Q estimates along the wasatch front in Utah derived from Sg and Lg wave amplitudes

Abstract This study develops estimates for the attenuation of peak vertical ground motions using a conventional, least-squares regression model applied to unfiltered and bandpass-filtered ground-motion data. The input data are from 88 earthquakes (1.0 ≤ M ≤ 3.3; epicentral distance range 10 to 450 km) located along the Utah-Idaho border and propagating Sg and Lg waves southward to seismograph stations along the Wasatch front in north central Utah. The regression model includes parameters to account for geometric spreading, anelastic attenuation with a power-law-frequency dependence, source, size, and station site effects. The maximum ground-motion amplitudes are derived from waves arriving about 3 sec, on the average, after the S -wave arrivals and are interpreted to be Sg in close (roughly 100 km or two crustal thicknesses) and Lg at greater distances. Accordingly, geometric spreading coefficients of 1.0 and 0.9 for body waves ( Sg ) and 0.83 (5/6) for higher-mode, Airy-phase surface waves ( Lg ) are chosen for testing. Similarly, a range of initial values of the power dependence of the attenuation (0.5 to 0.9) are also tested. The suite of estimates that result from regressing the amplitude data, while employing the family of fixed parameter values, leads to the following Q model: Q ( f ) = 97 f 0.80 for 3 Hz ≤ f ≤ 10 Hz. These results are important to the estimation of the seismic hazard for the study area. This pronounced level of attenuation, comparable to that found in California, has been reported in previous investigations of the study area using PSRV spectra, intensity attenuation and fall-off of Wood — Anderson seismogram amplitudes.

Pseudo preexcitation syndrome

During the course of investigation for palpitations, a 62-year-old man underwent exercise testing using a MARQUETTE CASE 12 computerized exercise testing system. By stage III of the modified Bruce protocol, the computer-generated electrocardiogram appeared to show the development of exercise-induced preexcitation. Closer examination of the raw unfiltered data showed this to be a computer-generated artifact rather than true preexcitation. This artifact arose due to inherent limitations common to all computerized exercise testing systems and emphasizes the need to always review raw data, even when a seemingly clear-cut abnormality is present on a computer-averaged electrocardiogram.

Intraseasonal Variability of the Winter Circulation in the Southern Hemisphere Atmosphere

The intraseasonal variability of the Southern Hemisphere stratosphere and troposphere is studied using multilevel geopotential height data for nine winters (1979–87). The study uses empirical orthogonal function (EOF) analysis of unfiltered data at five tropospheric and five stratospheric levels. The four leading EOFs at all tropospheric levels exhibit the patterns previously detected at 500 mb. Study of the corresponding principal components (PCs) at each level shows that the quasi-stationary anomalies associated with the leading EOFs are equivalent barotropic and exhibit no preference for early, middle or late winter. The five leading EOFs in the stratosphere fall into two classes. The first three EOFs at all levels form the first class. This class represents anomalies that are dominated by zonal wavenumber one (wave 1), exhibit strong westward tilt with height and travel slowly eastward or remain stationary. Most cases of large, persistent PC values for this class occur in early winter. The fourth and fifth EOFs form the other class. This class represents anomalies that are dominated by wavenumber two, and tilt noticeably, but less strongly than the first class, westward with height. These anomalies tend to develop mostly in late winter and to travel eastward more rapidly. The intraseasonal variability in the stratosphere resides therewith, as expected, in structures dominated by the longest planetary waves. No systematic connections between tropospheric and stratospheric persistent anomalies are apparent in the dataset.

Investigation of turbulent jet impingement in a confined crossflow

Abstract : Measurements and computations are reported for the flow of a turbulent jet discharging into a crossflow confined between two parallel plates. For jet-to-crossflow velocity ratios R equal to 2 and 4, mean and fluctuating velocity components are measured by a laser Doppler anemometer. High order statistics of the streamwise velocity and its time derivative have been measured in the plane of symmetry of a jet in a confined crossflow. The existence of universal similarity of the fine scale structure of a developing turbulent velocity field and the validity of original Kolmogorov local similarity theory and later formulations were investigated. Construction of normalized spectral for energy content, dissipation, and higher order moments enable an examination of the Reynolds number dissipation, and higher order moments enable an examination of the Reynolds number dependence of these functions for the Re sub lamda range from 16 to 800. Estimates of the Kolmogorov constant, mu, ranging from 0.27 to 0.43 were obtained with the arithmetic average equal to 0.38. The fractal dimension of the fine scale structure was estimated from the functional relationship between the flatness of the velocity time derivative and Re sub lambda. For unfiltered data, the fractal dimension was estimated to be 2.45. However, with a + or - 12 sigma bandwidth, the fractal dimension increased to 2. 73.

Bond Price Data and Bond Market Liquidity

This paper attempts to characterize liquidity-driven noise in the CRSP Government Bond price data set by comparing these price records to the independently collected Shearson Lehman Brothers (SLB) Bond Data Base. We argue that discrepancies between the data sets are due largely to liquidity-driven price errors, and we show that they are systematically related to certain bond characteristics. On the other hand, these discrepancies are small in magnitude and are approximately mean zero. We examine data filters based on observable bond characteristics and show that these filters can reduce the noise in price records while preserving their mean zero nature. The effects of these errors on performance evaluation are investigated by comparing results using filtered and unfiltered data.

Some characteristics of quasi-biennial geomagnetic oscillations of solar origin

The monthly means of the geomagnetic index aa and of the relative sunspot numbers were used to analyse the quasi-biennial oscillations (QBO) in geomagnetic activity related to an analogous variation in solar activity. Statistical methods of time series analysis were applied: autocorrelation and power spectrum, cross-correlation, complex demodulation, and the digital filter technique. The aim of this investigation was not only the detection of QBO in geomagnetic activity, which has been done by various authors, but also the determination of the time variation of the period, phase and amplitude of these oscillations in the given time interval with reference to the results of Apostolov [2] and Apostolov and Letfus [4]. The following main results have been obtained: The characteristic period of QBO in geomagnetic activity is shorter and varies in a narrower interval than that in sunspot activity; the lifetime of the oscillations is about 22 years and roughly coincides with Hale's cycle; the amplitude of QBO in geomagnetic activity has its maximum on the decreasing branch of the sunspot cycle; the QBO in geomagnetic activity follows the analogous variation in sunspot activity with a delay of 2 to 6 months for various solar cycles, as compared with the 3 to 22 moths for the raw, unfiltered data. The causes of the differences in the characteristics of QBO in geomagnetic and sunspot activity are considered and it is shown that these differences do not contradict the solar control of this phenomenon.

Joint three-dimensional inversion of gravity and magnetic data from Jombo Hill alkaline complex, Kenya

Jombo alkaline complex is the largest of the alkaline complexes in Kenya. It has been the subject of several geological and geochemical studies. However, the surface geology puts few constraints on the subsurface shape of the intrusion which we here attempt to determine by simultaneous inversion of gravity and aeromagnetic data. The major feature of the gravity map is an elliptical high >800g.u. in amplitude centred near Jombo Hill. When the filtered magnetic map is reduced to the pole and pseudo-gravity transformed, a strikingly similar anomaly is revealed, suggesting a common source. Using an iterative least-squares technique, joint inversion of the gravity and unfiltered magnetic data for a three-dimensional model established that both data sets can be adequately modelled by a thick slab tapering upwards from c . 29 km depth and striking approximately E-W. Only the upper c . 18 km is magnetized which we interpret as an indication of the depth to the Curie isotherm. The body is predicted to be of ultramafic composition capped by the exposed syenites and ijolites.

Processing of Unfiltered Data from an Inertial Survey System of Local Level Type

Processing of Unfiltered Data from an Inertial Survey System of Local Level Type

Winter depression tracks and climatological jet streams in the Southern Hemisphere during the FGGE year

AbstractA band‐pass filter transparent to fluctuations in the 2£5‐6 day period range is applied to a set of twice‐daily analyses covering the 1979 (FGGE year) winter of the Southern Hemisphere. Fields analysed include MSL pressure, 500mb height, 300mb wind, and the meridional heat flux due to transient eddies at 850mb. Variance maxima in these filtered fields indicate regions of high cyclonic activity, with favoured cyclolysis areas in the vicinity of the Antarctic coastline also showing up in the MSL pressure statistics. Using these results, supplemented by data on the distribution of cyclogenesis, we are able to identify the major depression tracks. In this analysis, extensive use is made of studies relating satellite‐observed cloud vortices to the various stages of cyclonic development. In general, it appears there was significantly more activity in the eastern hemisphere than in the western during the 1979 winter.By evaluating the terms in the time‐averaged zonal momentum equation (using the unfiltered data set), it is possible to assess the role of transient eddies in the maintenance of the time‐mean zonal flow. This analysis shows that Coriolis acceleration associated with poleward time‐mean ageostrophic flow at the tropopause level dominates the forcing of the jet centred around 25°S, but that convergence of eddy momentum flux maintains the higher latitude jet around 50°S. However, a significant contribution to the latter jet comes from poleward ageostrophic flow south of Africa.

Solar activity and total atmospheric ozone

Analyses are presented of the association between two parameters of solar activity (Lyman‐α and 10.7 cm flux) and global total ozone as determined from Nimbus observations for the period April‐December 1970 (IRIS observations)and April 1970 ‐ April 1972 (BUV observations); and between Lyman‐α and global total ozone as observed at ground stations and the ozone concentration in the lower and middle stratosphere in the subtropics for the period 1969‐1972. It is shown that the high correlations discussed in other published studies between these solar parameters and nine months of IRIS data resulted from the use of a very limitedseasonally unfiltered data set.

Solar-generated quasi-biennial geomagnetic variation

The existence of highly correlated quasi-biennial variations in the geomagnetic field and in solar activity is demonstrated. The analysis uses a numerical filter technique applied to monthly averages of the geomagnetic horizontal component and of the Zurich relative sunspot number. Striking correlations are found between the quasi-biennial geomagnetic variations determined from several magnetic observatories located at widely different longitudes, indicating a worldwide nature of the obtained variation. The correlation coefficient between the filtered Dst index and the filtered relative sunspot number is found to be -0.79 at confidence level greater than 99% with a time-lag of 4 months, with solar activity preceding the Dst variation. The correlation between the unfiltered data of Dst and of the sunspot number is also high with a similar time-lag. Such a timelag has not been discussed in the literature, and a further study is required to establish the mode of sun-earth relationship that gives this time delay.

Trend surface and residual analysis

Trend surfaces are continuous graphical and analytical representations by which the spatial distribution of a social variable can be evaluated. Analytical expressions, concepts and computational techniques of developing trend surfaces, residuals and criteria for evaluating them are presented. Contour mapping is employed as an integral part of the presentation and methodology of the analysis. Of computer graphic displays, contouring is the only one that lends itself to the type of further mathematical modeling such as by trend surfaces. Trend surfaces and residuals are complementary constructs. In contrast to usage of the residual in sociology as the error term in the general linear model, residuals are treated as probable loci of anomalous but significant variation of the mapped variable. Qualitative and quantitative aspects of, and theoretical and practical limitations to selection of best-fitting surfaces and residuals are discussed. Distortion of mapping can be encountered by clustering of data points and boundary effects. Applications of trend surfaces and residuals to social variables appearing in the economic georgraphy literature are reported.Contour mappings of unfiltered data, a trend surface model and complementary residuals demonstrate aspects and principles of the techniques applied to population data for Nassau and Suffolk Counties, New York, 1960-1970. Besides arrays of relative highs, lows, regional and local gradients, dominant features, such as a plateau of 100 percent change in population which covers most of the western portion of Suffolk County and the barrier effect of the Suffolk County line on population settlement over the period, emerge from the mapped models. Application of trend surfaces and residuals to social, ecological data is suggested as one model of computer data reduction and analysis of large volumes of regional and census data.

Mixed Lubrication and Surface Topography of Rolling Contacts

Measurements of friction torque in a tapered roller bearing are made over a range of axial loads at low rotational speeds. Under these conditions considerable metallic contact between surface asperities occurs. Experimental and theoretical values of no-contact time are compared. The usually adopted ratio of calculated film thickness to gross surface r.m.s. value is shown to be a less meaningful measure of the quality of lubrication than one based on the r.m.s. after filtering out contributions due to asperities of wavelength greater than twice the Hertzian width. An analysis of the statistical properties of worn and unworn surfaces is made. Digital filtering of the power spectrum reveals differences that are not apparent in the unfiltered data. Asperities of long and very short wavelengths, compared with the Hertzian width, are shown to be little affected during running-in whilst those of intermediate size are removed.

Monte Carlo experiment to determine the statistical uncertainty for the average 24-hour wave derived from filtered and unfiltered data

To test whether the diurnal variation is more reliably determined from filtered data, a daily harmonic analysis is made before and after filtering an adequate sequence of synthetic bihourly values containing only random noise and a 24-hour wave of constant phase and amplitude. For each of three filters it is shown, empirically, that the statistical uncertainty of the 24-hour wave from N days of such filtered data does not differ significantly from that from N days of unfiltered data. The filters were of different bandwidths and each was designed to pass the 24-hour wave.