Average Of Estimates Research Articles

Does Ocean Turbulence Peak at the Equator?: Revisited

In spite of the effects of several form of temporal variability that tend to mask geographical patterns in turbulence intensity, our evidence indicates that the turbulence is enhanced above the equatorial undercurrent in comparison to latitudes north and south of it. This evidence consists of three meridional transects of micro-structure observations across the equator (at 140°W in 1984 and 1987. and at 110°W in 1987) along with an equatorial station at 140°W and a longitudinal transect along the equator from 140°W to 110°W. All three meridional transects show a peak in averaged estimates of the turbulent kinetic energy dissipation rates, ε, at the equator, although in 1984 the peak was not significant at the 95% level. The major sources a temporal variability were the diurnal buoyancy flux variation and the wind stress variations, which had a typical period of a few days. After the diurnal variability is removed by averaging, it can be shown that, for similar wind stress, ε is larger over the undercurrent than away from it. Examination of the 16-m, 1-hour averaged ε, in terms of the vertical shear of horizontal velocity and the stratification (determined over similar space and time scales), indicated a tendency of this mean ε to vary with the Richardson number, Ri, when Ri<1. However, closer examination showed that the dependence of ε on Ri varied with depth. Therefore, a simple parameterization for mixing rates on Ri is not valid for all depth.

Statistical prediction of satellite magnetic anomalies

The geological utility of satellite magnetic observations is limited by orbital altitude variations which may be as large as a few hundred kilometres. This study investigates the use of fast and elegant statistical procedures for altitude normalization and gridding of magnetic anomaly data as an alternative to more commonly used equivalent source inversion procedures involving computationally extensive and complex least-squares matrix methods. A standard statistical approach for gridding satellite magnetic anomalies is to recompute numerically averaged values from three-dimensionally distributed observations which are within two standard deviations of an initially determined averaged anomaly estimate. The errors of this procedure for geological analysis are investigated using orbital anomaly simulations of lithospheric sources over a spherical earth. The simulations suggest that numerical averaging errors constitute small and relatively minor contributions to the total error-budget of higher orbital estimates (≳400 km), whereas for lower orbital estimates the error of averaging may increase substantially. A more complex statistical procedure involving least-squares collocation in 3-D is found to produce substantially more accurate anomaly estimates as the elevation of prediction is decreased towards the lithospheric sources. Moreover, 3-D collocation is computationally much more efficient and faster to apply than equivalent source inversion methods for altitude-normalizing and gridding magnetic anomaly data. Application of this procedure to MAGSAT magnetic observations of South America demonstrates its utility for producing accurately gridded magnetic anomalies at constant elevation for geological analysis.

Individual versus averaged estimates of parameters used in large scale emissions inventories

Development of emissions inventories for large geographic areas is currently based on the use of ‘mass balance’ equations to estimate the emissions from each source. The general equation used states that the emissions from a particular source for a specific pollutant in a specified time frame are equal to the product of the activity rate of the source in the selected time frame, an emission factor, which estimates the amount of pollutant emitted per unit activity, and additional parameters which vary according to the type of source whose emissions are being estimated. Values of the parameters used to estimate emissions are estimated in two different ways. ‘Individual’ estimates (an estimate for each source considered) are used for certain parameters; for other parameters, such as the emission factor, ‘averaged’ estimates (average values obtained by sampling a subset of the sources in a category) are used. The statistics resulting from the use of these two different methodologies are quite different. Derivation of the equations needed to calculate the mean square error in each case show that when the sources included in a category are homogeneous, then the averaged estimator may be better than individual estimates for estimating emissions from a particular source, but is worse for estimating sums. A numerical simulation was conducted to demonstrate these results. An example showing how to account for the effect of averaged estimators in a simple assessment is also included.

Restoration of retinal images obtained through cataracts

An optical model for imaging the retina through cataracts has been developed. The images are treated as sample functions of stochastic processes. On the basis of the model a homomorphic Weiner filter can be designed that will optimally restore the cataractous image (in the mean-square-error sense). The design of the filter requires a priori knowledge of the statistics of either the cataract transmittance function or the noncataractous image. The cataract transmittance function, assumed to be low pass in nature, can be estimated from the cataractous image of the retina. The statistics of the noncataractous image can be estimated using an old, precataractous photograph of the same retina, which is frequently available. Various modes of this restoration concept were applied to clinical photographs and found to be effective. The best results were obtained with short-space enhancement using averaged short-space estimates of the spectra of the two images.

Microsphere determination of cochlear blood flow in chickens.

Chickens were injected with 9-micron-diameter radioactive microspheres. Cochleas were removed through the external auditory meatus, and the positions of all embedded microspheres were drawn under camera-lucida. Constant measurements of arterial pressures and postinjection blood-gas determinations confirmed that injections were made into normal circulatory systems. The averaged estimate of cochlear blood flow in chickens is 0.75 microliter/min. Variability in these data from chickens is similar to that reported from mammals. A potentially important but puzzling observation is an inverse relationship between blood flow to the cochlea and to the brain. The ease of cochlear extraction makes chickens ideal models for study of cochlear blood flow.

Equatorial Indian Ocean evaporation estimates from operational meteorological satellites and some inferences in the context of monsoon onset and activity

The estimation of evaporation from the sea surface is not yet achieved adequately by remote sensing techniques, in general. However, for approximate averaged estimates over moderate space and time scales over a specific tropical region, e.g., weekly values over the Indian Ocean as needed in monsoon moisture diagnosis, it may be possible to extrapolate satellite wind and humidity data to the ocean surface and then use bulk aerodynamic parameterization for estimating evaporation. In the present investigation, GOES low-level cloud winds and TIROS-N moisture profiles over the Indian Ocean are extrapolated to the ocean surface. The planetary boundary layer (PBL) wind shear is obtained over different sub-regions and periods during the monsoon season, by reference to objectively analysed fields. These shear values are applied to GOES satellite winds to obtain sea-surface winds. The humidity extrapolation was based on (i) an exponential fit for water vapour density and (ii) a vertical distribution of relative humidity approximately proportional to atmospheric pressure. The exchange coefficient is varied slightly depending on wind speed and boundary-layer stability inferred approximately from TIROS-N sea surface temperatures and temperature profiles. The evaporation estimate as based on these satellite parameters is assessed by comparison with ships' surface observations. Sensible heat exchange is also estimated and assessed. Some inferences based on these estimates are also presented, in relation to monsoon onset and activity.

Two‐ear correlation in statistical sound fields

The normalized correlation function R (f), connecting the signals at the left and right ears, was measured in a reverberant room as a function of frequency. Head diffraction effects are made evident by comparing these data to the correlation function predicted and observed for two mikes separated by a headwidth (15 cm) of space and moving in the same room. In contrast to the familiar two‐mike sine (δ) correlation (δ — kd), head diffraction gives a two‐ear correlation function, which is well described by sine (αδ)/[1 + (βδ)4]1/2, where α = 2.2 and β = 0.5. The dominant effect of head diffraction is to lower fD, the decoupling frequency [first zero of R (f)], to 500 Hz, about one‐half the no‐head value. The denominator in the fitted correlation function represents the near total independence of the signals at the two ears above fD. Thus, with head diffraction, the variance in a paired‐mike room with averaged pressure amplitude estimate at around 500 Hz, is already as small as that obtained sans head only at frequencies above 1200 Hz. [Work supported by NSF.]

Variance Reduction for Ultrasonic Attenuation Measurements from Backscatter in Biological Tissue

Absfracf-Various averaging techniques can be used to reduce the variability of frequency-dependent attenuation estimates that are based on the power spectral density of acoustic backscatter signals from biological tissue. Three variance reduction methods are compared in terms of a consistently defined confidence interval. It is shown that the attenuation estimate based on averaged spectra from two C-planes is superior to the averaged attenuation estimate based on the pairs of spectra from individual A-lines. The superior technique yields results of equivalent accuracy with approximately 40 percent less data. This method is also shown to be asymptotically optimal in the sense of maximum likelihood estimation.

Analysis of blood velocity waveforms by phase shift averaging and autoregressive spectral estimation.

Analysis of blood velocity waveforms by phase shift averaging and autoregressive spectral estimation.

An exact solution to the Gaussian cloud approximation for gamma absorbed dose due to a ground-level release.

An exact solution is presented for the classical Gaussian cloud approximation for long-term averaged estimates of gamma absorbed dose due to a ground-level release of radioactive gases and particles. The solution is in the form of relatively simple functions and is much easier to implement than the traditional solution. Also, it is shown that the Gaussian cloud approximation predicts lower absorbed dose than the uniform cloud approximation. The difference is significant when the product of gamma attenuation coefficient and vertical dispersion coefficient is small. Since the Gaussian cloud approximation is based on a more realistic concentration distribution than the uniform cloud approximation, the calculations using the former should give more accurate estimates of the long-term averaged dose for the sector-averaged plume.

Calibration of subjective scaling responses

Subjective scaling is being used more frequently to assess the lighting characteristics of interiors, although there has been little attempt to validate the responses that subjects provide. It is argued that investigators using subjective scaling should calibrate their subjects in some way because idiosyncratic responses can alter averaged scaling estimates. In this experiment task contrast was varied and estimates of visual performance (speed and accuracy) were collected simultaneously with subjective responses on seven-point semantic scales. Subjects exhibited sterotypical behaviour on the performance measures; their scaling responses were quite idiosyncratic, although some subjective responses to the experimental parameters varied like the performance responses. It is argued that visual performance measures could be used to calibrate subjective scaling responses.

Validation of a Computer-Assisted Method for Estimating the Number and Volume of Gallstones Visualized by Cholecystography

It is likely that in the near future there will be widespread use of medicinal therapy to dissolve gallstones. The efficacy of medicinal therapy can best be determined by attempting to relate the total surface area of a collection of gallstones to the composition of bile in patients undergoing therapy. Surface area, in turn, can be directly related to gallstone size and number. In this study, involving 48 cholecystectomized patients, we have shown that standard cholecystography, together with a computer-assisted method of metrology, can effectively monitor the above parameters. Determinations of the standard deviation of 1) replicate readings (35.8%) and 2) averaged metrology estimates compared with actual stone volumes (42.9%), as well as correlation of actual stone volumes with averaged metrology estimates (r = 0.961), indicated the magnitude of assessed change in stone volume that would be necessary to accept a roentgenographic decrease or increase in stone size with 95% confidence. Even with the increased precision found in the computer-assisted method as described, to attain a 98% certainty of some volume change it was necessary to have metrology volume change of 50% or more. Actual stone counts were without significant error in 87.5% of the determinations.

Impulse response estimation with underwater explosive charge acoustic signals

A procedure is presented for estimating the impulse response of a linear system from noise contaminated measurements of random input and output signals. The estimation requires ensemble averaged estimates of input and output noise spectra and a priori assumed spectra of the system function and input signal. A minimum mean-square-error estimator is derived and its theoretical signal-to-noise ratio is shown to be a slowly increasing function of the measured signal-to-noise ratios. The procedure is applied to a set of measured underwater explosive charge acoustic signals. For this application additional techniques are presented for synthesizing source replica signals and for accurately determining bubble pulse periods. The result of the deconvolution is a single sharp spike with at least 20-dB bubble pulse suppression. With approximately 20-dB signal-to-noise ratio in the measured signals the processed signal-to-noise ratios range from 10 to 13 dB and are all within 1 dB of theoretical values. Peak-signal to rms-noise ratios are 41 and 38 dB before and after processing, respectively.

Perceived Dimensions for Combinations of Drug Substances

8 experienced users of “street-drugs” estimated the over-all similarity of 11 drug-substance combinations based on their own experiences with such combinations. Their similarity estimations were analyzed using multidimensional scaling procedures (namely, the Stone-Coles method). Four judgmental factor-dimensions were extracted and identified (tentative labels: I. Psychedelic drugs in combination with other substances vs pot in combination with downers; II. stimulant-depressant; III. psychedelic drugs vs other drugs, IV. LSD in combination with other substances) which accounted for 92% of the variance of the averaged similarity estimates. These particular judgmental factor-dimensions were similar to those extracted from judgments pertaining to single drugs as stimuli.

Automated spectral analysis of neurophysiological data using intermediate magnetic tape storage

A software package for the Digital Equipment Corporation Lab-8 Computer is described which performs frequency domain analysis of biological input-output signals where each signal may consist of either a continuous analog record or a series of point events in time such as action potentials. The data to be analysed is first stored in digital format on a DECtape magnetic tape storage device and is then accessed by a series of programs which sample the data, perform the fast Fourier transform upon the sampled data and then compute averaged spectral estimates from the Fourier coefficients. Intermediate data samples and final spectral estimates are stored on a DF32 magnetic disc unit as files within the Disc Monitor System. Ancillary programs are provided which allow visual and numerical examination of the data at various stages of the process. Access to the data and arithmetic manipulation of the data is provided through the interpretive language FOCAL.

The MEDEX medical occupation concept in subjective medical occupation-profession multidimensional space.

Members of a MEDEX training staff (N = 13) estimated the similarity of 16 medical occupations-professions (including the MEDEX concept). Evaluative dimensions utilized by these judges to form their judgments of scale similarity were extracted using a recently proposed multidimensional scaling method-model. Five judgmental factor-dimensions were identified (tentative labels: I. Amount of training—degree of responsibility—prestige; II. Therapist; III. Nurse; IV. Technician; and V. Hospital nursing staff authority) which accounted for up to 86% of the variance of the averaged similarity estimates. These factor-dimensions as well as the methodology employed were discussed. Future research was suggested.

Microwave Spectrum, Dipole Moment, and Barrier to Internal Rotation of Fluoral

About 700 transitions have been measured and assigned in the microwave spectrum of the ground vibrational state and first excited torsional state of natural and deuterated trifluoroacetaldehyde. Most of these lines occurred as doublets due to tunneling through the barrier to internal rotation of the trifluoromethyl group. The splittings of these doublets were used in conjunction with a recently published computer program to compute independent values of the barrier in the ground state of the normal isotopic species and the excited states of both isotopes. The final averaged barrier estimate is 885±75 cal/mole, the first such value of a three-fold barrier of a CF3 group to be obtained from microwave splittings. This barrier is considerably lower than that (1150 cal/mole) for acetaldehyde. In general the fit with a rigid—rigid model is good but not perfect. The dipole components are estimated to be μ = 0.15 D and μb = 1.64 D. Two novel techniques employed in the assignment of the very intense and rich fluoral spectrum were the assignment, by least-squares polynomial curve fitting, of a Q-branch series of quite high J values as the initial step in solving the spectrum, and the application of the double resonance technique to the location of the weak R-branch spectrum of the excited state.

FOREST FIRE WEATHER

SUMMARY The article discusses briefly:— 1. The use of the term “Fire Hazard” in W.A.2. A method of checking Hazards, based on wood cylinder moisture contents, by averaged personal estimates from field officers.3. Some common causes of error in personal estimations of Fire Hazard.4. The basis of forecasting Fire Weather.5. The relation of weather to Fire Hazard (with diagram).6. A description of the variation in weather between the two Forest Fire Weather Regions of W.A.