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  • 1
    Electronic Resource
    Electronic Resource
    PRINCIPLES AND APPLICATION OF MAXIMUM KURTOSIS PHASE ESTIMATION (1988)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 36 (1988), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Methods of minimum entropy deconvolution (MED) try to take advantage of the non-Gaussian distribution of primary reflectivities in the design of deconvolution operators. Of these, Wiggins’(1978) original method performs as well as any in practice. However, we present examples to show that it does not provide a reliable means of deconvolving seismic data: its operators are not stable and, instead of whitening the data, they often band-pass filter it severely. The method could be more appropriately called maximum kurtosis deconvolution since the varimax norm it employs is really an estimate of kurtosis. Its poor performance is explained in terms of the relation between the kurtosis of a noisy band-limited seismic trace and the kurtosis of the underlying reflectivity sequence, and between the estimation errors in a maximum kurtosis operator and the data and design parameters.The scheme put forward by Fourmann in 1984, whereby the data are corrected by the phase rotation that maximizes their kurtosis, is a more practical method. This preserves the main attraction of MED, its potential for phase control, and leaves trace whitening and noise control to proven conventional methods. The correction can be determined without actually applying a whole series of phase shifts to the data. The application of the method is illustrated by means of practical and synthetic examples, and summarized by rules derived from theory. In particular, the signal-dominated bandwidth must exceed a threshold for the method to work at all and estimation of the phase correction requires a considerable amount of data.Kurtosis can estimate phase better than other norms that are misleadingly declared to be more efficient by theory based on full-band, noise-free data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2478.1988.tb02155.x
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  • 2
    Electronic Resource
    Electronic Resource
    TWO METHODS FOR CONTINUOUS MONITORING OF HARMONIC DISTORTION IN VIBROSEIS SIGNALS (1989)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 37 (1989), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: The quality of Vibroseis survey data can be improved by continuously monitoring the vibrator's baseplate and reaction mass accelerations. Equipment failures can be detected as they occur, rather than relying on similarity trials at the beginning and end of the day's production. Equipment faults can then be corrected as they happen and thus would not have a detrimental effect on the quality of the survey data. Source efficiency can be optimized by monitoring the amount of harmonic distortion generated by the vibrator at different drive levels on the different surfaces which may be encountered during a survey. Phase problems introduced by poor coupling of the baseplate to the ground can also be identified and addressed in the field.Rapid analysis of vibrator signals is required if continuous monitoring is to be useful. Frequency-time (f-t) analyses of vibrator signals are often used in processing centres, but are slow and require a large storage capacity which makes the technique unsuitable for a field analysis system.The two methods proposed to analyse vibrator signals entail the use of hodograms and time-varying notch filters. Hodograms provide a qualitative analysis of harmonic distortion and vibrator performance. A fast, time-varying notch filter gives quantitative and qualitative information about the harmonic distortion present in the signal and can be used to identify problems with vibrator behaviour. Both the hodogram and fast, time-varying notch filter methods can analyse the vibrator's reaction mass and baseplate accelerations as it progresses through its sweep and can present automatically interpreted results to the operator before moving to the next vibrator point.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2478.1989.tb02237.x
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  • 3
    Electronic Resource
    Electronic Resource
    LEAST-SQUARES FILTERS WITHOUT TRANSIENT ERRORS: AN EXAMINATION OF THE ERRORS IN LEAST-SQUARES FILTER DESIGN (1985)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 33 (1985), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: A new approach has been developed for the design of cross-equalization filters by the least-squares method. The filters estimated by this new exact method are subject to only two types of error: bias and random error. Cross-equalization filters estimated by a more conventional least-squares method are further subject to “transient error”. This type of error becomes important when designing filters from a data gate of a length comparable with the length of the filter, i.e., less than four times the length of the filter.The effect of altering various design parameters has been investigated for the new method. It has been found that the proportion of bias in the filter decreases as the effective filter length increases, whereas the random error in the filter decreases with increase in either the signal-to-noise ratio of the data or the ratio of the data duration to the filter length. The level of whitening applied to the auto-correlation matrix before inversion was not found to be a critical design parameter. Also, two techniques have been tested for reducing any anomalous d.c. component in the calculated filter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2478.1985.tb00771.x
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  • 4
    Electronic Resource
    Electronic Resource
    The transport of chloride and non-diffusible solutes through soil (1985)
    Springer
    Irrigation science 6 (1985), S. 3-10 
    Details
    ISSN: 1432-1319
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary The mean velocity at which water flowed through large undisturbed cores of soil was determined from the breakthrough of surface-applied Cl−, using a transfer function based on the normal distribution of the logarithm of cumulative drainage. For soils ranging in texture from sandy loam to silty clay loam, mean pore water velocities varied from 7 to 30 cm h−1 for an input rate of 2 cm h−1. Antibiotic-resistant Escherichia coli applied to the soil surface appeared to be transported through large pores only (〉 10–15 μm diameter), and the relative concentration in the effluent (C/C0) did not change significantly with effluent volume. Mean C/C0 values for E. coli in these soils, which ranged from 0.003 to 0.94, could be predicted from the mean pore water velocity derived from Cl− transport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00272470
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  • 5
    Electronic Resource
    Electronic Resource
    The effect of phosphate nutrition of young rape plants on nitrate reductase activity and xylem exudation, and their relation to H ion efflux from the roots (1988)
    Springer
    Plant and soil 105 (1988), S. 257-263 
    Details
    ISSN: 1573-5036
    Keywords: Brassica napus ; H ion efflux ; nitrate accumulation ; nitrate reductase ; phosphate nutrition ; xylem exudation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Levels of nitrate reductase activity (N.R.A.) were measured in shoots and roots of P sufficient and P deficient rape plants and changes in N.R.A. examined in relation to the onset of H ion efflux from the roots. Rates of xylem exudation were measured and the sap analysed for nitrate, amino-N and phosphate content. The optimum concentration of phosphate in the leaves for N.R.A. was about 0.7%. Both high and low concentrations of phosphate within the leaves inhibited N.R.A in those leaves. This inhibition of N.R.A led to the accumulation of nitrate in the older parts of the shoots of P sufficient plants. Less accumulation of nitrate occurred in the P deficient plants since nitrate uptake by the plants decreased before any fall in N.R.A. Xylem exudation rates halved within 18 hours of depriving the plants of phosphate, and, since the composition of the sap remained constant, this indicated a reduced flux of nitrate into the xylem. The rate of xylem exudation continued to fall and by the end of the experiment was approximately one tenth of the rate in the P sufficient plants. The onset of H ion efflux from the terminal portions of the root preceded any effect on N.R.A by 2 days.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02376790
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  • 6
    Electronic Resource
    Electronic Resource
    The influence of phosphate nutrition on H ion efflux from the roots of young rape plants (1988)
    Springer
    Plant and soil 105 (1988), S. 247-256 
    Details
    ISSN: 1573-5036
    Keywords: Brassica napus ; cation-anion balance ; H ion efflux ; phosphate nutrition ; root growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Changes in pH around the roots of young rape plants were studied using a nutrient film technique which allowed either part or all of the root system to be subjected to specific nutrient treatments. The rapidity and direction of change of pH was assessed by embedding absorbing roots in a thin layer of agar containing bromocresol purple. Measurements were also made with a pH microelectrode placed next to the roots. Phosphate-fed plants were deprived of phosphate when 14 days old. Patterns of pH changes round the deprived roots were the same as with phosphate-fed plants until the plants had been deprived of P for three days, when H ion efflux started in the terminal portions of the roots. The lengths of root producing acid and amounts of H ion both increased as the plants became more P deficient. Both P fed and P deprived roots produced HCO3 ions but the net amount of HCO3 ion produced by the P deficient roots fell as did nitrate uptake rates. Cation-anion balances measured at the end of the experiment showed that uptake of all anions and K decreased in the P deprived plants but uptake of Ca and Mg were little altered. This resulted in a smaller ratio of anions to cations absorbed which was reflected in the reduced HCO3 ion efflux.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02376789
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  • 7
    Electronic Resource
    Electronic Resource
    Net mineralization and nitrification rates in a clay soil measured and predicted in permanent grassland from soil temperature and moisture content (1985)
    Springer
    Plant and soil 86 (1985), S. 151-172 
    Details
    ISSN: 1573-5036
    Keywords: Ammonification ; Clay soil ; Exchangeable ammonium ; Grassland ; Incubation ; Kinetics ; Nitrate ; Nitrification ; N cycle ; N mineralization ; Soil Moisture ; Soil temperature
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Net mineralization of N and net nitrification in field-moist clay soils (Evesham-Kingston series) from arable and grassland sites were measured in laboratory incubation experiments at 4, 10 and 20°C. Three depth fractions to 30 cm were used. Nitrate accumulated at all temperatures except when the soil was very dry (θ=0.13 cm3 cm−3). Exchangeable NH4-ions declined during the first 24 h and thereafter remained low. Net mineralization and net nitrification approximated to zero-order reactions after 24 h, with Q10 values generally 〈1.6. The effect of temperature on both processes was linear although some results conformed to an Arrhenius-type relationship. The dependence of net mineralization and net nitrification in the field soil on soil temperature (10 cm depth) and moisture (0–15, 15–25, 25–35 cm depths) was modelled using the laboratory incubation data. An annual net mineralization of 350 kg N ha−1 and net nitrification of 346 kg N ha−1 were predicted between September 1980 and August 1981. The model probably overstressed the effect of soil moisture relative to soil temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02182891
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  • 8
    Electronic Resource
    Electronic Resource
    Modelling growth responses of soil nitrifiers to additions of ammonium sulphate and ammonium chloride (1985)
    Springer
    Plant and soil 86 (1985), S. 425-439 
    Details
    ISSN: 1573-5036
    Keywords: Ammonium ; Chloride ; Growth ; Inhibition ; Monod model ; Nitrification ; Soil ; Sulphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Following the addition of 0–75 μmole N g−1 as ammonium chloride or ammonium sulphate to a sandy loam soil the nitrate formed was measured daily for a period of 15–17 days. The nitrate produced as a function of time was described using the Monod equation for microbial growth. An optimisation technique is described for obtaining, from the nitrification time course data, the maximum specific growth rate, the affinity constantant and an index limited by the concentration of ammonium in soil solution. Additions of more than 7.3 μmoles N g−1 soil as ammonium chloride were found to inhibit nitrification. The inhibition was interpreted as being caused by osmotic pressure or by chloride ion. A similar effect was not found with ammonium sulphate, because the salt concentration in the soil solution was restricted by the precipitation of calcium sulphate. The model developed was capable of accounting for nitrate production in the soil under non-steady state conditions of substrate concentrations and nitrifier biomass.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02145463
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  • 9
    Electronic Resource
    Electronic Resource
    The influence of nitrate nutrition on H+ efflux by young rape plants (Brassica napus cv. emerald) (1985)
    Springer
    Plant and soil 84 (1985), S. 403-415 
    Details
    ISSN: 1573-5036
    Keywords: Agar-pH indicator technique ; Cation-anion balance ; H ion efflux ; HCO3 ; ion efflux ; Nitrate nutrition ; Nitrate reductase ; Root growth ; Split root system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Changes in pH around the roots of young rape plants (Brassica napus cv. emerald) were studied using a nutrient film technique that allowed part or whole of the root system to be subjected to specific nutrient treatments. The rapidity and direction of pH change was assessed by imbedding absorbing roots in a thin film of agar containing bromocresol purple. When nitrate-fed plants were deprived of all sources of nitrogen at 15 or 17 days old, the release of H ions from the roots was immediate and uniformly distributed over the root length. When nitrate was witheld from half of the root system of nitrate-fed plants, the roots deprived of nitrate immediately started to produce H ions even though the nitrate-fed half of the root system continued to supply the whole of the plant with nitrate. However, the rate of H ion production in plants partly supplied with NO3 was less than in plants completely deprived of NO3. It is suggested that malate produced in the shoots, following nitrate reduction, may be redistributed to the roots deprived of nitrate. There, HCO3 produced by the decarboxylation of the malate masks some of the expected H ion efflux.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02275477
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  • 10
    Electronic Resource
    Electronic Resource
    The effect of high solute concentrations on nitrification rates in soil (1987)
    Springer
    Plant and soil 97 (1987), S. 37-45 
    Details
    ISSN: 1573-5036
    Keywords: Ammonium ; Chloride ; Inhibition ; Nitrification ; Osmotic pressure ; Sorbitol ; Sulphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary A short term nitrification assay (〈18 h) was used to assess the effect of high concentrations of different solutes on the rate of nitrate production. High solute concentrations were found to inhibit nitrification and the degree of inhibition was related both to the osmotic pressure of the soil solution and the osmoticum used. Ammonium chloride, ammonium sulphate and sorbitol were used as sources of osmotic pressure. The results showed that, with ammonium salts, no inhibition was observed with pressures less than 2 atm. Above these values, the severity of the inhibition followed the order ammonium chloride〉ammonium sulphate〉sorbitol up to the maximum osmotic pressure studied (25 atm). With ammonium chloride, a pressure of 3.5 atm. was sufficient to cause a 90% inhibition of nitrification rate. The inhibition produced by mixtures of ammonium chloride and sorbitol, each mixture generating an osmotic pressure of 5 atm. in the assay, was also investigated. The results suggest that inhibition by Cl-ion is disproportionate to its contribution to the osmotic pressure of the soil solution. The recovery of the nitrification rate, following exposure to high osmotic pressure solutions, was also investigated. It was found that the recovery of the nitrification rate was only partial, with the extent of the recovery diminishing as the severity of the initial osmotic stress applied increased. These results suggest that both reversible and irreversible mechanisms are involved in the inhibition of nitrification.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02149821
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