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  • 101
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 10 (1994), S. 0 
    ISSN: 1475-2743
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract. The presence of spring barley plants increased the numbers of nematodes, particularly of plant-feeders, compared with fallow plots in a Scottish organic farming system. The addition of farmyard manure (FYM) had no detectable effect on nematode populations but poultry manure (PM) caused a considerable increase. The application of PM also altered the types of nematode present and favoured bacterial-feeders and rhabditids in particular. These changes suggest that PM causes shortterm (within a growing season) increases in microbiological activity and nutrient cycling, whereas FYM is more likely to bring about long-term changes.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 102
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 10 (1994), S. 0 
    ISSN: 1475-2743
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract. Topsoil (0–20 cm) and subsoil (60–100 cm) properties are compared at agricultural and nearby natural vegetation sites in São Paulo State. Differences are related to land use and climate, in order to estimate soil carbon storage under various ecosystems and also to study the effects of high-input agriculture on the chemical composition of soils with low activity clays. Within each land use, organic carbon in the topsoil is most strongly related to clay + silt content. This relationship is stronger for cropped, short savannah (cerrado) and tall savannah (cerradão) sites than for semi-deciduous and evergreen forest sites. Losses of topsoil carbon with cropping can be predicted if the initial carbon and the clay+silt contents are known. The greatest carbon losses after long term cultivation occurred in forest mineral topsoils, ranging from 6% for perudic clayey soils to 37% for ustic sandy soils. No significant difference in carbon content was found between the paired savannah-cultivated sites. In most of the originally less fertile soils cation exchange capacity was greater in the cultivated topsoil (Ap) than in the topsoil under savannah or forest (A1), probably because of liming and phosphate fertilization. Most subsoils at agricultural sites show increases in exchangeable bases (mainly Ca) and base saturation, but no significant change in pH.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 103
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 10 (1994), S. 0 
    ISSN: 1475-2743
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract. Bulk and undisturbed block samples of soil were collected from beneath five cricket tables and outfields managed by a local authority and used by local league cricketers. Thin sections made from the undisturbed blocks revealed considerable differences in soil structure and composition between the cricket tables. Topdressings of varying textures have been added to all the tables over the years. Texturally-layered profiles have built up beneath three of the tables because the topdressings have not been mixed. Horizontal organic mats often occur within and between the associated platy aggregates. Rooting is shallow under these tables, and the lower compacted layers often contain evidence for restricted drainage at certain times during the year. At one site, and to a lesser extent at another, greater mixing of the topdressings has been achieved by earthworms, but these seem to have been eradicated at the other sites. Although they create a better plant-growing medium, the earthworms seem to have had a detrimental effect on the playing quality of the cricket table.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 104
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 10 (1994), S. 0 
    ISSN: 1475-2743
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract. Nitrate leaching in lysimeters containing a tropical sandy agricultural soil was studied over two summers with maize (Zea mays L.) and one winter season with wheat (Triticum aestivum L.). The treatments included two moisture regimes and two nitrogen sources, cattle manure and inorganic fertilizer-N (either ammonium nitrate or ammonium sulphate) applied at 100 kg N/ha in the summers. Neither manure nor fertilizer-N was applied in the intervening winter. Leachate volume from the manured lysimeters was mostly larger than from fertilized ones because of poor growth and less evapotranspiration. The largest seasonal nitrate loads (17–39 kg N/ha) were obtained in the wet summer immediately after installation of the lysimeters. Nitrate loads in winter (3.7–18.6 kg N/ha) were larger than those obtained in fertilized (0.6 and 9.3 kg N/ha) and manured (0.3 and 3.0 kg N/ha) lysimeters for the two moisture regimes in the second summer. The drier conditions in the second summer decreased N-mineralization and leaching of manure.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 105
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 10 (1994), S. 0 
    ISSN: 1475-2743
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract. Field studies at five locations on farmer's fields irrigated with residual sodium carbonate water (RSC) indicated that gypsum applications at the rate of 100% of the gypsum requirement of soil plus the quantity of gypsum required to neutralize RSC in excess of 4 mEq/1 decreased SAR values, and improved infiltration rate, crop emergence and wheat grain yields. The soil pH decreased by 0.3–0.4 units. Once soils have been ameliorated by this treatment, further small applications of gypsum are needed to decrease the RSC in irrigation water and avoid further soil deterioration.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 106
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Soil use and management 10 (1994), S. 0 
    ISSN: 1475-2743
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract. At Woburn Experimental Farm (SE central England) sulphur (S) deficiency symptoms occurred in a winter oilseed rape crop grown in Lansome field on soil of the Cottenham series, but not on the Blithe series soil in the adjacent Mill Dam Close field. At maturity, the two crops produced a similar amount of dry matter but seed yield and harvest index were significantly less in Lansome. Total S uptake of the crop in Lansome was less than half of that in Mill Dam Close, which was similar to the amount normally found in a S sufficient crop. Both soils are of light texture (loamy sand and sandy clay loam for the Cottenham and Blithe series, respectively), and there was little difference in the extractable S concentration in the topsoils between the two fields. However, more extractable S was found in the subsoil of Blithe series, because it contains more free Fe and Al oxides and has a lower pH. These results show that any evaluation of the soil S supply needs to take into account the pool of available S in the subsoil.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 107
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: A slightly modified critical-state model was formulated in order to account for the volume-change behaviour at yield and failure observed in triaxial tests on unsaturated soils. Model parameters were specified for two soils (a sandy loam and a loam), each at three different soil-moisture contents. Maximum shear strain was integrated numerically for 36 cylindrical load paths with constant confining pressure (type I) or constant mean normal stress (type II). Predicted stress-strain relationships for load paths bringing soils from a normally-consolidated to a critical state were compared with stress-strain relationships observed for identical load paths in triaxial tests of the lubricated ends variety.The agreement between predicted and observed maximum shear strain depended on type of load path and soil-moisture content. The model failed to predict maximum shear strain at stress states close to critical. The absolute difference between observed and predicted strain was on average ≤0.05 for deviatoric stresses smaller than 90% of the critical-state values. The comparable maximum differences were 0.11 and 0.07 for load-path types I and II, respectively. The largest differences were found for the largest soil-moisture contents. The type of load path had a considerable effect on sample distortion, type I giving rise to larger (predicted and observed) maximum shear strain at common stress states.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 108
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: The Green & Ampt infiltration analysis is applied to the problem of the water uptake by aggregates when they are surrounded by water. Two situations are analysed, namely, when there is free escape of the displaced air and when there is no escape of the air. These extreme situations provide bounds for estimating the water uptake for the practical case when some air escapes through the aggregate's surface in the form of bubbles as the aggregate wets up. It is shown that the rate of water uptake is directly proportional to the square of the sorptivity of the aggregate material and inversely proportional to the square of the final water uptake. Experiments on spherical stabilized clay aggregates of different radii were in agreement with the theoretical analysis that predicted the observed very rapid wetting up. The analysis also showed that when there was free escape of air, the rate of advance of the wetting front into cylindrical and spherical aggregates decreased from an initially infinite value to a minimum value and then increased to an infinitely large value when the front reached the centre of the aggregate, in contrast to the continually decreasing rate into plate-like aggregates. This was demonstrated in experiments on the radial water movement into a fine sand contained in a cone.The analysis and experimental results indicate that preferential macropore flow in aggregated soils can be initiated very rapidly when air entrapment occurs within the aggregates.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 109
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: A simple model was employed to interpret the results of a series of measurements of gas diffusion in soil cores. The model divides air-filled porosity into three functional categories: arterial, marginal and remote. Diffusion along the axis of the core occurs through arterial pores; marginal pores do not contribute to axial diffusion; remote pores are isolated from gas transport. Simulations based on the model closely resembled data acquired from real cores. Optimizing the fit between real and simulated data gave estimates of the three functional pore fractions which generally made sense (compaction or wetting of cores resulted in reduced arterial and increased marginal porosities, for example). Dividing the pores into the different classes specified by the model was functionally equivalent (i.e. observable results were identical) to the introduction of a tortuosity factor to represent pore convolution. In order to account for observed diffusion rates in terms of pore convolution alone it is sometimes necessary to invoke implausibly high tortuosities; the introduction of marginal porosity renders this unnecessary without in any way compromising the ability of the model to simulate real diffusion data.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 110
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Assessment of gas diffusivity in situ gives a direct measure of the ability of soils to exchange gas with minimal soil disturbance. A versatile, readily portable probe for measuring the diffusion of a tracer gas through soil in situ is described. The radioactive tracer 85Kr is injected into a cell located at the end of the probe. The change in activity within the cell as the gas diffuses out is measured by a Geiger-Muller tube in the cell. The probe can be used by insertion either directly into an auger hole (buried-probe mode) or into a chamber pushed into the soil surface. A method to simulate diffusion numerically using Fick's equation for both methods of insertion is presented. In the tests reported, diffusivity was estimated by expanding or contracting the time axis of the simulation until it matched the observed count rates. A goodness-of-fit was attached to each diffusivity estimate. The probe was generally effective, giving diffusivities comparable to those measured in the laboratory on cores taken near the cell (buried-probe mode) or linked to the surface chamber. Poor fits were found for some diffusivities measured in the buried-probe mode on coarsely structured soils. These were attributed to non-uniform distribution of porosity and possible upward leakage of tracer when used at shallow depths in the buried-probe mode. However, thein situ diffusivities may be more representative than those measured in cores in the laboratory because of the greater sample volume. We show how the probe can be used to detect soil layers that restrict gas diffusivity and differences in aeration status between tillage treatments.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 111
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: The surface structure of many Australian red and red-brown earths frequently collapses (slakes) when dry, disturbed aggregates are wetted by rain or irrigation. The resulting fine matrix sets, on drying, to a strong, cohesive layer of up to 200 mm thick (hard setting). We investigated the mechanism of collapse and the extent to which the structure of aggregate beds Iron hard setting and non-hard setting soils collapsed when wetted by quick flooding or slowly with water at a suction of 200 mm, then drained in sequential steps of increasing suction and finally dried at 40°C. After flood wetting, but before draining, no collapse was observed due to the small effective stress prevalent in the flooded beds.After suction wetting, some collapse was measured owing to the effective stress (approximately 1.4 kPa) from the applied suction. On draining, flood-wetted beds collapsed extensively (volume strain 〉0.20), largely due to the disappearance of large pores (〉75 μm diameter). Suction-wetted beds collapsed less (volume strain 〈0.16) and retained more large pores. Hard setting soils collapsed more following both flood and suction wetting (volume strain 〉0.20 and 0.10, respectively), while non-hard setting soils did not collapse as extensively (volume strain 〈0.16 and 0.09, respectively). Results indicate that the mechanism causing collapse was independent of wetting method and involved two steps: (i) slaking of aggregates on wetting, and (ii) collapse of the aggregate bed on draining as a result of development of effective stress within the beds.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 112
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: At the groundwater–surface-water interface the last modification of discharging groundwater takes place. In this study the redox potential was measured in situ in four groundwater discharge areas with a size of 3–4 m2. Three of them were the upper reaches of streams in coniferous forests and one was an alder fen. Measurements were made at different seasons, with 50 and 100 platinum micro-electrodes respectively, in each area. Readings were taken in the upper 30 cm of the soil, at two depths.A method study showed that the electrodes needed a longer equilibrium time than is usually reported. The main finding of this study was the large spatial variation within soils in the discharge zone; regions as small as 10 cm in diameter could have redox potentials covering several hundred mV. It was not possible to identify a seasonal variation due to the large spatial variation. Differences in the distribution of the redox potential with depth may be explained by the structure of the peat affecting flow patterns and the residence time of water.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 113
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: The strength of soils is related to structural stability. Aggregate structure which collapses on wetting may set to a hard, consolidated layer on drying (hard setting). This process may be moderated by suction wetting and possibly by application of calcium, but the mechanism of moderation is not clear. We investigated the collapse-strength relationship and the mechanism by which wetting method and calcium act to reduce strength in hard setting and non-hard setting soils. Indirect tensile strength of aggregate beds that had been wetted with water or 10mM CaCI2 by rapid flooding or at a suction of 200 mm, was measured after draining to various suctions and drying at 40°C.The greater the volume strain during wetting and draining, the greater the tensile strength. Beds that were suction wetted, either with water or calcium solution, showed minimal collapse and did not develop high strength on drying. Water-flooded beds had the greatest dry strength while beds flooded with calcium solution developed significantly lower strength. The critical factor determining tensile strength of the beds appeared to be the presence of large (〉75 μm diameter) pores. The greater the volume strain on wetting, the smaller the proportion of larger pores and the greater the tensile strength on drying. Flood wetting caused more loss of large pores and closer packing of particles. Wetting with calcium solution did not affect the degree of collapse compared with that of water alone but did produce beds with larger pores than when wetted with water. Consequently the strength of the calcium-wetted beds was lower.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 114
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: We wished to determine whether soil-test P was affected by storing air-dry soil samples at room temperature. The soil samples had been collected from field experiments and air-dried (〈40°C) before measuring soil-test P (bicarbonate-extractable P). The samples were from field plots that had been treated with different applications of fertilizer P (superphosphate, rock phosphate) one or more years previously. Soil-test P was measured on two different sub samples of the same sample: either A, in the year the sample was collected; or B, after the sample had been stored at fluctuating room temperatures either from 2 to 8 years (four field experiments) or 17 years (59 field experiments). The room temperature ranged from 10 to 30°C, and averaged 17°C. The aim was to test whether soil-test P was systematically and consistently different between sub samples A and B.Differences between A and B were mostly small, and there were no consistent or systematic differences. For the Colwell soil test, applied to a range of south-western Australian soils, possible decreases in soil-test P due to continued reaction with the soil could not be detected using bicarbonate-extractable soil P, and storage of air-dry samples at room temperature did not significantly affect soil-test P measured up to 17 years later. We conclude that, provided fertilizer P has had time to react with soil in the field, no further changes in Colwell soil-test P occur during air-dry storage for up to 17 years at room temperature.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 115
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: A method for the measurement of Pb and Cd in equilibrium soil solutions involving soil equilibration with a dilute Ca electrolyte, centrifugation and filtration to 〈0.2 μm was evaluated. The procedure was subsequently used for the analysis of 100 Pb- and 30 Cd-contaminated soils. Solutions were analysed for Pb- and Cd using graphite-furnace AAS and the concentrations of Pb2+ and Cd2+ were estimated using standard speciation calculations.The concentrations of Pb and Cd found in the soil solutions were in the range 3.5–3600 μg dmp −3 and 2.7–1278 μg dm −3 respectively; both ranges represented less than 0.1% of the total metal concentration in the soils. Depending on solution pH, Pb +2 accounted for between 42–78% of Pb in solution while about 65% of Cd in solution was present as Cd+2. The concentrations of Pb2+ and Cd2+ in solution suggested that the soil solutions were undersaturated with respect to the solid phases PbC03 and CdC03 but supersaturated with respect to Pb5(P04)3Cl and, for some samples, Cd3(P04)2 respectively. However, for both metals, a good empirical relationship was obtained between the total metal concentration in soil (mol kg−1), free metal concentration in solution (mol dm−3) and solution pH. The relationships took the general form of a pH-dependent Freundlich adsorption equation:〈displayedItem type="mathematics" xml:id="mu1" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:13510754:EJSS59:EJSS_59_mu1"/〉For both lead and cadmium relationships, the values ofn and K1 were close to unity, so that the distribution coefficient could be estimated from pH and a single metal-dependent constant, K2. The algorithms appeared to be valid over a metal concentration range of four logarithmic units and pH range of 3.5–7.5.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 116
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: The effect of the presence of alpechín, wastewater from the olive-oil industry, on the reaction of three soils with Cd, Cu and Zn is studied. Adsorption of Cu and Zn by all the soils studied, and Cd by one of the soils, is markedly decreased by the presence of high doses of alpechín, while Cd adsorption by the other two soils increases in the presence of the residue. Adsorption of Cu and Zn in the absence of alpechín releases considerably more Ca than the exchangeable contents at a rate of about 0.5-1 moles of Ca for each mole of metal adsorbed, and this rate is decreased in most cases when alpechín is present. The behaviour of Cd with respect to Ca release is less definite. The relationships between solution concentrations and pH show that alpechín increases the mobility of Cd and Cu in the presence of some soils, while in the case of Zn no effect is evident.It is concluded that soil carbonate is the most relevant component involved in Cu or Zn retention, and, in the presence of alpechín, part of the carbonate surface is blocked and becomes unavailable for retention. Formation of soluble Cu complexes is suggested to occur in some cases.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 117
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: Any set of isotropic layers is equivalent, in the long wavelength limit, to a unique transversely isotropic (TI) layer; to find the elastic moduli of that layer is a solved problem. The converse problem is to find a set of isotropic layers equivalent to a given TI media. Here, explicit necessary and sufficient conditions on the TI stiffness moduli for the existence of an equivalent set of isotropic layers are found by construction of a minimal decomposition consisting of either two or three isotropic constituent layers. When only two constituents are required, their elastic properties are uniquely determined. When three constituents are required, two have the same Poisson's ratio and the same thickness fraction, and even then there is a one-parameter family of satisfactory minimal decompositions. The linear slip model for fractured rock (aligned fractures in an isotropic background) yields a restricted range of transverse isotropy dependent on only four independent parameters. If the ratio of the normal to tangential fracture compliance is small enough, the medium is equivalent to thin isotropic layering and in general its minimal decomposition consists of three constituents.
    Materialart: Digitale Medien
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  • 118
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 119
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 120
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: Information on the mass and the spatial location of an arbitrary source body can be obtained by performing suitable integrations of 3D gravity and magnetic data along an infinite straight line. No assumptions on the density/magnetization distribution or the shape and location of the source are required.For an oblique borehole, a relationship between the lower limit of the source mass and the distance to the body is obtained. The mass contrast and the magnetic moment of the source can also be estimated.For a vertical borehole, both gravity and vertical magnetic component anomalies have equal areas to the left and right of the depth axis.The particular case of a horizontal gallery not intersecting the body is also studied. If the source is intersected, a lower limit is estimated for the maximum thickness of the body along the gallery. Information on the vertical coordinate of the centre of mass of the source can also be obtained.Numerical tests with synthetic gravity data support the theoretical results.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 121
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: Refraction seismics with the shotpoints and the hydrophone cable on the sea-bottom, have become the standard geophysical method for investigating rock quality before constructing offshore tunnels in Norway. In connection with the construction of a sub-sea tunnel by the Norwegian Public Roads Administration, research work was carried out to compare two low-velocity zones, indicated by refraction seismics with other methods. A special resistivity cable for pole-dipole measurements on the sea-floor, with 10 m between the electrodes, was constructed. A 200 m long profile, crossing the two low-velocity zones, was measured with all combinations of electrode distances. The two zones were detected as low-resistivity zones. A special data processing technique to enhance the anomalies is described. Resistivity soundings in a seawater environment to detect fracture zones in the bedrock underneath the bottom sediments, are discussed. It is concluded that severely fractured zones, which may cause difficulties for the tunnel construction, can be detected both with sea-surface and sea-floor arrays using long electrode spacings.
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  • 122
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: In order to understand various aspects of radar wave propagation, a survey of electromagnetic wave behaviour relative to the geological characteristics of the formations prospected was undertaken. The sites chosen for the tests were a granite quarry and an underground schist working. By investigating an electrically resistive isotropic site and a conductive anisotropic site, it was demonstrated that non-conventional use of a radar system (antennae raised, various orientations of the transmitter/receiver, etc.) could improve data quality, and could allow information other than reflector depth to be collected (volume scattering intensity, isotropy, etc.). By studying wave propagation velocities, we underlined the difficulties encountered in establishing a velocity versus depth law, despite recourse to seismic data processing, such as NMO corrections. The results of field experiments, complemented by laboratory measurements of dielectric permittivities, clearly showed anisotropy effects: in the case of a path that is perpendicular to the schistosity plane, an electromagnetic wave propagates more slowly and is more attenuated than a wave parallel to the schistosity plane.
    Materialart: Digitale Medien
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  • 123
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: A 2D numerical finite-difference algorithm accounting for surface topography is presented. Higher-order, dispersion-bounded, cost-optimized finite-difference operators are used in the interior of the numerical grid, while non-reflecting absorbing boundary conditions are used along the edges. Transformation from a curved to a rectangular grid achieves the modelling of the surface topography. We use free-surface boundary conditions along the surface. In order to obtain complete modelling of the effects of wave propagation, it is important to account for the surface topography, otherwise near-surface effects, such as scattering, are not modelled adequately. Even if other properties of the medium, for instance randomization, can improve numerical simulations, inclusion of the surface topography makes them more realistic.
    Materialart: Digitale Medien
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  • 124
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: True-amplitude (TA) migration, which is a Kirchhoff-type modified weighted diffraction stack, recovers (possibly) complex angle-dependent reflection coefficients which are important for amplitude-versus-offset (AVO) inversion. The method can be implemented using existing prestack or post-stack Kirchhoff migration and fast Green's function computation programs. Here, it is applied to synthetic single-shot and constant-offset seismic data that include post-critical reflections (complex reflection coefficients) and caustics. Comparisons of the amplitudes of the TA migration image with theoretical reflection coefficients show that the (possibly complex) angle-dependent reflection coefficients are correctly estimated.
    Materialart: Digitale Medien
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  • 125
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 126
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 127
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: The Fourier pseudospectral method has been widely accepted for seismic forward modelling because of its high accuracy compared to other numerical techniques. Conventionally, the modelling is performed on Cartesian grids. This means that curved interfaces are represented in a ‘staircase fashion‘causing spurious diffractions. It is the aim of this work to eliminate these non-physical diffractions by using curved grids that generally follow the interfaces.A further advantage of using curved grids is that the local grid density can be adjusted according to the velocity of the individual layers, i.e. the overall grid density is not restricted by the lowest velocity in the subsurface. This means that considerable savings in computer storage can be obtained and thus larger computational models can be handled.One of the major problems in using the curved grid approach has been the generation of a suitable grid that fits all the interfaces. However, as a new approach, we adopt techniques originally developed for computational fluid dynamics (CFD) applications. This allows us to put the curved grid technique into a general framework, enabling the grid to follow all interfaces. In principle, a separate grid is generated for each geological layer, patching the grid lines across the interfaces to obtain a globally continuous grid (the so-called multiblock strategy).The curved grid is taken to constitute a generalised curvilinear coordinate system, where each grid line corresponds to a constant value of one of the curvilinear coordinates. That means that the forward modelling equations have to be written in curvilinear coordinates, resulting in additional terms in the equations. However, the subsurface geometry is much simpler in the curvilinear space.The advantages of the curved grid technique are demonstrated for the 2D acoustic wave equation. This includes a verification of the method against an analytic reference solution for wedge diffraction and a comparison with the pseudospectral method on Cartesian grids. The results demonstrate that high accuracies are obtained with few grid points and without extra computational costs as compared with Cartesian methods.
    Materialart: Digitale Medien
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  • 128
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Calcium-rich pyromorphite [Pb5(PO4)3Cl] has been positively identified as the major lead-bearing phase in mine-waste soils from the South Pennine Orefield, UK, by a combination of EXAFS spectroscopy, ATEM and XRD. Evidence for a pyromorphite-like structure was provided by electron diffraction of individual Ca-rich, lead chlorophosphate grains in the soil using ATEM. Approximate unit-cell parameters derived from electron diffraction were used to identify peaks on the powder XRD trace obtained from the soil sample, allowing the cell parameters to be refined. The unit-cell parameters derived for the Ca-rich pyromorphite [a= 0.9789(7), c= 0.726(1) nm] are smaller than those reported for pure end-member pyromorphite (a= 0.998, c= 0.733 nm; Baker, 1966) and are sufficiently different to prevent positive identification by conventional XRD analysis. Lead absorption spectra and interatomic distances obtained from EXAFS performed on bulk soils confirmed the predominance of pyromorphite-like structure. EXAFS is shown to be a useful tool in the identification of soil minerals. It gives information about the local environment of one specific element in solids, be they crystalline or amorphous, and is unaffected by the limited chemical substitution of Ca for Pb.The identification of impure Pb minerals in soil by techniques other than XRD suggests that previous studies, based on XRD, may have underestimated the amount of soil Pb present as discrete Pb compounds.
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  • 129
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: The mineral forms of phosphorus in three urban sewage sludges were characterized using high-resolution solid-state phosphorus-31 nuclear magnetic resonance (NMR) coupled to a sequential extraction. The sludges studied were an anaerobically-digested and heat-treated sludge (Paris-Achères), an activated sludge (Briare) and an anaerobically-digested sludge (Nancy). NMR observations were conducted using both single-pulse and cross-polarization sequences in order to distinguish between 31P nuclei far from 1H nuclei, and 31P located within a fraction of a nanometre of 1H. This approach showed that a complex mixture of P species was present in these sludges. A mixture of hydrogenated octocalcium phosphates and apatites was observed in the three samples. Monetite was present in the anaerobically-digested sludge and brushite in the activated sludge. Dehydrogenated condensed calcium phosphates (compounds with a Ca:P ratio higher than 1.0 such as fluorapatite or tricalcium phosphate) and dehydrogenated pyrophosphates were also probably present in the anaerobically-digested sludge. A poorly-ordered wavellite was observed in the three sludges after the HCl extraction. However, results were inconclusive as to whether this mineral was present in the three sludges, or had been precipitated during the sequential extraction.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 130
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: The adsorption of a radioisotope of caesium, 137Cs, has been interpretation and ratio and solution measured on four soils with differing clay mineralogies. All measurements have been made using unwashed soils in suspensions shaken for 2 h at 20°C. The effects of concentration in potassium and caesium, the nature of the background electrolyte and the soil:solution ratio have been investigated. The results are expressed either as the distribution coefficient, KD or as Freundlich isotherms.The distribution coefficient of each of the soils decreases markedly as the concentration of caesium increases. The adsorption properties of the soils are not determined by the dominant clay mineralogy alone. Adsorption is always lower in 0.01 m CaCl2 solution than in water. The addition of potassium has relatively little effect on adsorption of trace amounts of caesium; however, KD decreases with increasing concentrations of stable caesium. The major reason for the dependence of KD on the soil: solution ratio is found to be the non-linear adsorption isotherm; the influence of the varying compositions of the solution and exchange complex is minor.The validity of the use of a single KD value as an indicator of adsorption capacity and the meaning of the relative values of the Freundlich parameters are considered. The implications of these findings for the use of radiotracers and the usefulness of KD as an indicator of bioavailability are discussed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 131
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: The paper examines the ability of a critical-state model to predict stresses and deformations of agricultural soil in a variety of laboratory shear and compression tests. The critical-state model used is a simple extension to the well-known Modified Cam Clay model. The extension provides a smoother transition from elastic to plastic behaviour and, amongst other things, introduces a capacity to model cyclic loading. The model is incorporated into a finite-element program.The model predictions are compared with: experimental observations of simple and direct shear tests with both constant normal stress and constant volume conditions; cyclic uniaxial compression tests; compaction tests in U-shaped and V-shaped boxes; and observations of some gross structural features caused by shear in direct-shear boxes. Predictions are made for both the compressing, strain-hardening and the expanding, strain-softening regimes of behaviour. In all cases the material properties for the model were obtained from tests other than those being used for the comparisons.The model predictions generally compare well with the various experimental results, although some numerical problems were encountered in strain-softening conditions. This demonstrates the versatility of the critical-state model for predicting fairly general stress and, deformation conditions in unsaturated soils using only five material-property constants. It also demonstrates that common laboratory strength and compression tests are adequate to measure the material properties.
    Materialart: Digitale Medien
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  • 132
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Critical state parameters were determined in constant cell volume triaxial tests on three remoulded agricultural topsoils, a sandy loam, a clay loam and a clay. Tests were made at a range of water contents. The normal consolidation lines tended to be linear on a semi-logarithmic plot up to a degree of saturation of c. 0.85, above which the soil was incompressible but highly deformable. The slopes of the projected critical state lines were slightly greater than the slopes of the normal consolidation lines for all three soils. For each soil, both lines pivoted about a point as water content increased and, for the two lighter-textured soils, the increases in compactibility tended to be greatest near the plastic limit. For all three soils, strength remained fairly constant with increasing water content until the soil was at around 70-85% of the cone penetrometer plastic limit. Strength then decreased with increasing water content, with the smallest decrease in the sandy loam.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 133
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: A device that infiltrated water over a small circular surface area having a radius ranging between 1.45 mm and 2.5 mm was used to measure the sorptivity of initially air-dry aggregates of size greater than 20 mm. The small infiltration area caused the water uptake to be dominated by capillarity that allowed the use of a simple formula to obtain the sorptivity from the steady-state flow rate that occurred very early after the start of imbibition. The results of measurements of sorptivity made on a fine sand agreed with those obtained from measurements on one-dimensional water infiltration into columns of the sand. Sorptivity measurements on stabilized aggregates of a clay soil and on air-dried field aggregates of a clay soil were easily made. The simplicity and rapidity of the method allowed measurements to be conveniently replicated.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 134
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Ninety years after the start of the Askov long-term fertilization experiment on sandy loam, bulk soil was taken from the 0–20 cm and 30–35 cm depths of unfertilized (UNF), animal-manure (FYM) treated and mineral-fertilized (NPK) plots and analysed for textural composition, carbon content, pH, CEC, particle density and plasticity limits. Undisturbed soil cores (100 cm3) from the 8–12 cm layer were brought to six different matric potentials and subjected to confined uniaxial compression, drop-cone penetration and annulus shear tests. Water-retention curves based on seven matric potentials were produced for undisturbed cores from the 8–12 and 30–35 cm layers. In the field, in situ shear strength of plough-layer soil was determined by a vane shear tester and a torsional shear box.FYM and NPK treatments increased the soil organic carbon content by 23 and 11% of the amount in UNF, respectively. Corresponding increases observed in CEC were 17 and 11%. The water content at the lower and upper plastic limits both decreased from FYM to NPK to UNF. Soil bulk density in the 0-20 cm layer was reduced in FYM and NPK treatments relative to UNF, whereas the volume of soil pores larger than 30 μm was unaffected by past fertilization.Soil receiving animal manure showed the greatest soil strength when exposed to annulus shear, drop-cone penetration and confined uniaxial compression tests, Shear strength measurements indicated that the UNF sandy loam soil reacted like a sand, the increase in soil strength upon drying primarily being due to increased internal friction. In contrast, soil from FYM and NPK treatments showed reactions typical of a loamy soil, the increase in soil strength during drying being caused by increased cohesion in the soil matrix. The field tests employed were unable to detect the management-induced differences in soil physical parameters found in the laboratory tests.This study shows that physical soil properties related to conditions for tillage and traffic, to crop development and erosion are significantly influenced by differences in soil organic matter levels resulting from contrasting methods of fertilizer management. Exhausting a loamy soil by long-term lack of fertilizer application severely affects the physical properties of the soil.
    Materialart: Digitale Medien
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  • 135
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Aggregates (9.5–12.7 mm) from ten soils were equilibrated at a range of matric suctions (Ψa) between 1 kPa and 100 MPa before immersion in water or wetting on a porous plate at zero suction. The soils were from cultivated and grassland sites and included hardsetting and non-hardsetting Australian and British soils as well as a Vertisol. The initial rate of wetting of each aggregate, and the composition and size distribution of the slaked fragments were measured. There was a significant inverse linear relation between the amount of slaking produced by plate wetting air-dry soil (Ψa=100 MPa) and its organic carbon content (r= 0.82***). The three cultivated hardsetting soils shared several common features. Their slaking was the most pronounced after plate wetting and occurred at the smallest Ψa(10 kPa). Their slaking also increased linearly with rate of wetting and the particle-size distribution of their slaked fragments varied significantly and considerably with Ψa. This last observation demonstrates that it is not always helpful to call the fragments produced by slaking, microaggregates.Possible explanations for our results and their agricultural implications are discussed.
    Materialart: Digitale Medien
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  • 136
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: We describe a least-squares inversion approach to estimating the subsurface resistivity structure from cross-hole or borehole-to-surface electromagnetic data. It is assumed that the resistivity distribution is symmetric about the axis of a borehole and that vertical magnetic dipoles are located on the borehole axis. The receivers are placed either in another borehole or on the earth's surface. The inversion scheme uses the finite-element and smoothness-constrained least-squares methods. The computational effort required to obtain partial derivatives is reduced considerably by using the reciprocity principle. Numerical simulations show that the reconstructions are generally in good agreement with the true structures when the assumption of an axisymmetric earth structure holds. An example involving the breakdown of this assumption, which can be obtained by interchanging the source and receiver boreholes, suggests that the inversion result may also be useful for locating a general 3D anomaly although artifacts are present.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 137
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: A crucial point in the processing of 3D seismic data is the migration step, both because of its 3D nature and the computational cost involved. The efficiency and accuracy of 3D migration are determined by the wavefield extrapolation technique employed. Wavefield extrapolation based on second-order differential operators of variable-length is very efficient and accurate at the same time. Compared to migration based on the McClellan transform and operator splitting, the use of variable-length second-order differential operators offers significant advantages. The 3D migration operator has an almost perfect circular symmetry. No positioning errors in the 45° azimuth between the in-line and cross-line directions are evident. The method is, in practice, only limited by spatial aliasing and does not require expensive interpolation of data to reduce numerical artifacts. This reduces the computational cost of 3D one-pass depth migration by a large factor.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 138
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: Differences between traveltimes from sonic to seismic frequencies, commonly known as drift, can be attributed to a combination of multiple scattering and absorption. The portion due to scattering can be estimated directly by calculating synthetic seismograms from sonic logs. A simple alternative approach is suggested by the long-wave equivalent averaging formulae for the effective elastic properties of a stack of thin layers, which gives the same traveltime delays as the low-frequency limit of the scattering dispersion. We consider the application of these averaging formulae over a frequency-dependent window with the hope of extending their use to frequencies higher than those allowed by the original validity conditions. However, comparison of the time delay due to window-averaging with the scattering dispersion predicted by the O'Doherty-Anstey formula reveals that it is not possible to specify a form of window that will fit the dispersion across the spectrum for arbitrary log statistics. A window with a width proportional to the wavelength squared matches the behaviour at the low-frequency end of the dispersive range for most logs, and allows an almost exact match of the drift across the entire spectrum for exponential correlation functions.We examine a real log, taken from a hole in nearly plane-layered geology, which displays strong quasi-cyclical variations on one scale as well as more random, smaller-scale fluctuations. The details of its drift behaviour are studied using simple models of the gross features. The form of window which gave a good theoretical fit to the dispersion for an exponential log correlation function can only fit the computed drift at high or low frequencies, confirming that there are at least two significant scale-lengths of fluctuation. A better overall fit is obtained for a window whose width is proportional to the wavelength. The calculated scattering drift is significantly less than that observed from a vertical seismic profile, but the difference cannot be wholly ascribed to absorption. This is because the source frequency of the sonic tool is not appropriate for its resolution (receiver spacing) so that the scattering drift from sonic to seismic frequencies cannot be fully estimated from the layer model derived from the log.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 139
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: The analytic signal (AS) is defined as the square root of the sum of the squares of the vertical and the two horizontal derivatives of the total magnetic field ΔT. This paper verifies theoretically that peaks of the AS correlate directly with their magnetic causative bodies and are positioned symmetrically over them, i.e. the main feature of the AS is that it is independent of the inclination of the magnetic field. This avoids the difficulties that are often faced in the conventional process of reduction to pole for ΔT, when the direction of magnetization of the causative bodies is not known. In addition, the AS has characteristics similar to the derivative features of the magnetic field, so that it is very sensitive to edge effects of the causative magnetic bodies. The theoretical derivations are tested by comparison with calculations on models, and, in a field example from Hunan Province, China, the AS is applied successfully to the interpretation of ΔT, whereas the conventional process of reduction to pole fails, due to the reverse magnetization of the causative body.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 140
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: An equivalent source procedure is derived for upward continuation of unevenly spaced gravity and magnetic data. The dipole layer is placed on a topographic relief approximated by a polyhedral surface, the stations being the vertices of the triangular faces. The dipoles have linear magnitudes, being directed along the normal vector over each triangle. The unknown values of the dipole magnitudes at each station are obtained by a suitable modification of the usual integral equation considering the discontinuity of the normal vector at each vertex of the dipole surface. Profile data processing is also studied. A numerical test outlines the accuracy and the limitations of the model for the case of a magnetic field significantly perturbed by a rough topographic relief.
    Materialart: Digitale Medien
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  • 141
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: We use a marine seismic dataset to examine the reflections from two gas sands, a lignitic sand and a cineritic bed, by means of their amplitude versus offset (AVO) responses. This offset-dependent signature is related to specific petrophysical and thus elastic situations or to peculiar interference patterns and may help to distinguish the nature of the amplitude anomalies on the stack sections.The prestack analysis is carried out on seismic data which have undergone an accurate true-amplitude processing.It is found that the lignitic-sand reflections exhibit a decreasing AVO while the two-gas sands show markedly increasing AVO trends. Also the reflections from the cineritic layer show increasing amplitudes with offset that may be due either to the petrophysical nature of the cinerites or to thin-layer interference or to both.In order to verify the reliability of the actual AVO responses we develop a detailed model from well data and compute a synthetic CMP seismogram. In order to account for mode conversions and thin-layer effects, the synthetic seismograms are computed using the reflectivity method. The wavelets used in the synthetics are retrieved from actual seismic and borehole data by means of wavelet processing. When finely layered structures are present, the estimation of a reliable wavelet is extremely important to get the correct synthetic AVO response. In particular, the AVO responses of the cineritic layer differ substantially if we make use in the computation of the synthetics of a Ricker wavelet or of a wavelet estimated through wavelet processing.The good match between the observed and modelled data confirms the reliability of the processing sequence and of the final AVO signatures.
    Materialart: Digitale Medien
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  • 142
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 143
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 144
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 145
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: The five-electrode resistivity configuration of Barker, who introduced the concept of offset resistivity measurements, is used in a profiling mode in the search for lateral variations of resistivity down to depths of a few tens of metres. Theoretical computations show that plotting simple pseudosections of offset measurements over faults is sufficient to reveal the fault position. The method is subsequently applied in the field for locating a buried fault in coal measures. Although offset pseudosections are often all that is required, apparent resistivity pseudosections are examined and compared to collations of 1D inversions of the sounding profile data and to computations over 2D models. It is shown that apparent restivity pseudosections may present a rather misleading picture.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 146
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: We present a layer-stripping method of migration for irregularly layered media in which first-order velocity discontinuities separate regions of constant or smoothly varying velocity. We use the reverse-time method to migrate seismic data layer by layer, from the surface downwards. As part of the migration of a given layer, the bottom boundary of the layer is defined based on power in the migrated signal, and a seismic section is collected along it. This new section serves as the boundary condition for migration in the next layer. This procedure is repeated for each layer, with the final image formed from the individual layer images. Layer-stripping migration consists of three steps: (1) layer definition, (2) wavefield extrapolation and imaging, and (3) boundary determination. The migration scheme when used with reverse-time extrapolation is similar to datuming with an imaging condition. The reverse-time method uses an explicit fourth-order time, tenth-order space, finite-difference approximation to the scalar wave equation.The advantages of layer-stripping reverse-time migration are: (1) it preserves the benefits of the reverse-time method by handling strong velocity contrasts between layers and steeply dipping structures; (2) it reduces computer memory and saves computation time in high-velocity layers, and (3) it allows interpretational control of the image.Post-stack layer-stripping reverse-time migration is illustrated with a synthetic CMP data example. Prestack migration is illustrated with a synthetic data set and with a marine seismic reflection profile across the Santa Maria Basin and the Hosgri Fault in central California.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 147
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: The aim of this study was to improve the quantitative determination of the plant opal content (i.e. phytoliths) in soils.The proposed method is based on: (i) the separation of plant opal from the silt and sand fractions of the soil, using heavy liquid flotation (aqueous solution of ZnBr2, density = 1.92 g cm−3); (ii) the subsequent determination of alkali-soluble silicon by atomic absorption spectrometry. Extraction and analytical procedures were tested on a broad sample of temperate and tropical soils with very different phytolith contents.Our investigations lead to the following conclusions: (i) a selective dissolution of opal in alkaline solutions (e.g. hot 0.5 m NaOH as proposed by Jones, 1969) is inaccurate so that a sink-float method must be used before any dissolution procedure; (ii) to dissolve opal completely, a 0.5 M NaOH dissolution treatment at 150°C can be easily and successfully carried out in steel PTFE-lined pressure vessels; (iii) the reproducibility of the determination is satisfactory for a step-by-step procedure (mean coefficient of variation = 13.4%).The comparison of this new method of quantitative assessment of soil opal with two other methods (gravimetric and phytolith-counting methods), shows very highly significant correlations (P〈0.001). Therefore, this procedure is a useful tool in studies connected with pedological and environmental history.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 148
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Two Oxisols (Mena and Malanda), a Xeralf and a Xerert from Australia and an Andept (Patua) and a Fragiaqualf (Tokomaru) from New Zealand were used to examine the effect of pH and ionic strength on the surface charge of soil and sorption of cadmium. Adsorption of Cd was measured using water, 0.01 mol dmp−3 Ca(NO3)2, and various concentrations of NaNO3 (0.01–1.5 mol dm−3) as background solutions at a range of pH values (3–8).In all soils, the net surface charge decreased with an increase in pH. The pH at which the net surface charge was zero (point of net zero charge, PZC) differed between the soils. The PZC was higher for soils dominated by variable-charge components (Oxisols and Andept) than soils dominated by permanent charge (Xeralf, Xerert and Fragiaqualf). For all soils, the adsorption of Cd increased with an increase in pH and most of the variation in adsorption with pH was explained by the variation in negative surface charge. The effect of ionic strength on Cd adsorption varied between the soils and with the pH. In Oxisols, which are dominated by variable-charge components, there was a characteristic pH below which increasing ionic strength of NaNO3 increased Cd adsorption and above which the reverse occurred. In all the soils in the normal pH range (i.e. pH〉PZC), the adsorption of Cd always decreased with an increase in ionic strength irrespective of pH. If increasing ionic strength decreases cation adsorption, then the potential in the plane of adsorption is negative. Also, if increasing ionic strength increases adsorption below the PZC, then the potential in the plane of adsorption must be positive. These observations suggest that, depending upon the pH and PZC, Cd is adsorbed when potential in the plane of adsorption is either positive or negative providing evidence for both specific and non-specific adsorption of Cd. Adsorption of Cd was approximately doubled when Na rather than Ca was used as the index cation.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 149
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: The fate of 15N-labelled synthetic urine (50 g N m−2) applied to an irrigated pasture soil was studied using large undisturbed monolith lysimeters (800 mm diameter × 1200 mm deep). Over a period of 1 year, the pasture plants recovered the largest fraction of the applied 15N (43%) and approximately 20% of the applied 15N still remained in the soil, the majority of which was found in the topsoil (0–20 cm). Although the experiment was conducted under relatively intense rainfall and irrigation conditions, only 8% of the applied 15N was found to have leached below 1200 mm after 1 year. During this time, the average peak concentration of nitrate in the leachate reached 42 mg NO3−-N dm−3. The amount of nitrogen (N) lost by the process of denitrification was calculated as 28% of the applied 15N. This large loss of N to the atmosphere was attributed to the wet soil conditions which prevailed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 150
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Soil solution was obtained from potted rhizosphere or non-rhizosphere soils by water displacement or soil centrifugation. The pH of the displaced solutions was lower than that of bulk soils when solutions were obtained from non-rhizosphere soil, although it increased as plants grew. This increase probably reflected true changes in rhizosphere pH, generated by the uptake by plants of N03-N. In contrast, the pH of soil centrifugates was usually close to that of the bulk soils, implying that buffering by colloids had occurred during sampling. Concentrations of elements in solutions from non-rhizosphere soil were similar for both methods when soils were incubated at ambient pCO2. However, when non-rhizosphere soils were incubated at elevated pCO2, displacement solutions had lower pH values, and much larger concentrations of elements, compared to soil centrifugates.Comparison of mass flow of elements versus actual plant uptake showed that Ca and Mg accumulated, while K, Zn and Cd were depleted from the rhizosphere. Displacement solutions showed this accumulation or depletion of the elements more clearly than soil centrifugates. These differences were attributed to the fact that, at constant soil moisture, the rhizosphere developed mainly in larger pores, which were sampled by displacement. With centrifugation, a mixture of pore sizes was sampled, so that rhizosphere solution was only obtained when all of the soil had become rhizosphere.Soil centrifugates obtained after 22 days of growth also contained higher concentrations of organic carbon than displacement solutions, indicating contamination due to the disruption of roots and/or micro-organisms. We conclude that water displacement is suitable for sampling solution from light to medium textured rhizosphere or non-rhizosphere soils and that soil centrifugation is only of limited suitability.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 151
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Soil from Eutrochrept A horizons under long-term spruce forest (Sf), mixed deciduous forest (Df), permanent grassland (Gp) and arable rotation (Ar) was fractionated according to particle size and analysed for contents of C, N, lignin-derived phenols and carbohydrates.Whole soil from Sf, Df, Gp and Ar contained 84, 59, 73 and 25 g C kg−1 soil, respectively. For all sites, the C content declined and C/N ratio increased in the order: clay (〈2 μm), silt (2–20 μm), sand (20–2000 μm). Clay and silt were significantly lower in C in Ar than in Sf, Df and Gp, C associated with sand being substantially lower under arable rotation.The yield of lignin-derived phenols decreased and carboxyl functionality and methoxyl demethylation of lignin derivatives increased with decreasing particle size, indicating a progressive lignin alteration. Whole soil from Sf and Gp was substantially higher in vanillyl (V), syringyl (S) and cinnamyl (C) units (VSC) than soil from Df and Ar. Compared to whole soil, clay was depleted and sand enriched in VSC. Only sand appeared to be affected significantly by land use. Sand from Ar and Df was more enriched in VSC than sand from Gp and Sf.Whole soil carbohydrates decreased in the order: Gp〉Ar〉Df〉Sf. Sand- and clay-sized separates were enriched in carbohydrates compared to silt. Carbohydrates in sand were mainly of plant origin whereas microbially-derived sugars accounted for a larger proportion in the clay. Compared to Sf, Df and Gp, clay from Ar was enriched and sand depleted in microbial sugars.Lignin and carbohydrate distribution patterns indicate that organic matter was in a more advanced stage of decomposition in the sand separates from forest than from agricultural A horizons. The forest soils also show a higher degree of oxidative changes in lignin associated with clay. In contrast, differences between silt from the four A horizons were small.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 152
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: The effects of geometry upon diffusion from instantaneous sources is considered. Although surface area is important initially, it is the square of the volume of the source which determines flux from the source at large times. This asymptotic shape independence is demonstrated for spherical and cuboidal sources.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 153
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Water-stable macro-aggregate size fractions (〉2.0 mm, 1.0–2.0 mm, 0.5–1.0 mm and 0.25–0.5 mm) and non-aggregated soil from a sandy loam under long-term clover-based pasture and from grass pasture were analysed to determine the role of acid- and water-extractable carbohydrate C, total hyphal length, microbial biomass, organic C and total and mycorrhizal root length in stabilization of the aggregates. Aggregates were examined by scanning electron microscopy (SEM) and the particle-size distribution of the size fractions was also determined.Macro-aggregation increased under grass, relative to clover-based pasture; however, the properties of the aggregate fractions measured did not reflect this difference. Microbial-biomass C, extractable-carbohydrate C, hyphal length, total and mycorrhizal root length and organic C content of the soils were poorly correlated with macro-aggregation. Within the aggregates, the proportion of 250–1000-km sand was smaller and clay, silt and fine sand (20–250 μm) were greater relative to non-aggregated soil, suggesting that the 〉250-μm sand in the non-aggregated soil limited the stabilization of macro-aggregates. Under SEM, no enmeshment of aggregates by hyphae and roots was apparent. Although 50–160 m hyphae g−1 soil was found within the aggregates, calculations showed that on average only 5 to 13 lengths of hyphae were associated with each 250-μm cube of soil within the aggregates, and suggested little potential to stabilize the aggregates by enmeshing. On average, all 〉2.0-mm aggregates contained less than 3.6 mm of roots and less than 50% by weight of 〈2.0-mm aggregates contained a single length of root. The findings cast doubt about the role of hyphae and fine roots in the stabilization of macro-aggregates through an enmeshing mechanism in sandy soils.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 154
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Soil tillage is usually considered as a process having only an indirect influence on soil erosion. This paper describes the results of field experiments carried out with a mouldboard and a chisel plough showing that an important net downslope soil movement can be associated with soil tillage. Available experimental evidence suggests that the soil redistribution by tillage can be described by a diffusion-type equation, which allows the intensity of the process to be characterized by a single number, which may be called the diffusion constant. The experimentally determined values of the diffusion constant vary between 100 and 400 kg m−1 a−1. This implies that erosion and sedimentation rates associated with tillage may be more important than those associated with water erosion on much of the hilly arable land in western Europe. A comparison of recent hillslope evolution with model simulation results corroborates this conclusion. Therefore, tillage should be considered as a soil degradation process per se, rather than a process which makes the soil more sensitive to erosion.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 155
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: The diffusion of gas through a model of the structure of soil pores was simulated on a computer. This was done to test the model's usefulness for studying diffusion in real soil and to obtain insights into how soil pore geometry affects diffusion. A model of randomly-placed overlapping spheres was used to represent the soil solids, the pores being what remains. Various simulated porosities and average sphere radii produced pore networks which resembled those in real soil aggregates. Our diffusion simulations gave three results: steady-state flux, time delay and rate of increase of flux. The porosity and sphere size were varied to investigate their effects on these diffusion properties. Results were comparable with those from experimental work. Further analysis allowed us to express the geometry of pore simulations in terms of average pore path length and connectivity. Evidence of non-Fickian behaviour was obtained, particularly in the early stages of the simulated diffusion.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 156
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: The residual values of fertilizer P in six tropical soils were assessed from the response of grass in a pot experiment. The comparison was made between residues of P that had been applied to a previous crop (also grass) and fresh P applied to uncropped soil. Yields of dry matter and P uptakes were fitted to Mitscherlich and linear equations respectively, and the availabilities of fresh and residual P were assessed by fitted parameters of these equations.With sufficient residual P, the maximum yields were close to those obtained with fresh P, but residual P always had a lower availability than fresh P. The residual value was assessed by the ratio of the availability parameters for residual and fresh P and these values showed that there were differences between soils in the decline of P availability. Residual value was not directly related to the initial availability of P.The P uptake responses to both fresh and residual P were correlated significantly with buffer capacity for exchangeable sorption of phosphate and Al extracted by acid oxalate. This suggested that there is an available fraction of residual P, the uptake of which is influenced by the sorption and mobility of phosphate in soil, in the same way as for fresh fertilizer P.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 157
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Freezing significantly influences the amount and chemical form of extractable soil phosphorus and, therefore, has important consequences regarding plant nutrient availability. Much of the current evidence relies on field-based observations and tends to be rather contradictory. The present work reports the specific effects various freezing episodes have on phosphorus availability. Experimental treatments included the freezing rate and the time soil remained frozen together with the number of freeze/thaw cycles. These laboratory incubations used two soils, an iron humus podzol and a peaty podzol, sub-samples of which were equilibrated at three different soil-moisture contents. Concentrations of phosphorus in soil solutions and acetic acid extracts (Ac-P) were measured. Freezing had the greatest effect on the organic (Op) horizon of the peaty podzol, where the amounts of total dissolved phosphorus (TDP) and Ac-P increased from 0.58 to 3.21 and from 11.8 to 19.3 mg P kg−1, respectively. TDP in soil solution was subdivided into three broad categories, dissolved (molybdate) reactive (MRP), organic (DOP) and condensed (DCP). The rather variable effect that freeze/thaw episodes had on these fractions highlighted the problems associated with attributing the ‘freezing effect’ to any single process.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 158
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Retention of V(V) by three Finnish mineral soils from 10−4m and 10−5m sodium vanadate solutions was investigated at room temperature in the pH range 2.3–7.5. In adsorption experiments, 0.02 m KCl was used as ionic medium, and the samples were left to equilibrate for 72 h. The solid: solution ration was 1:100 (m: v). Maximum adsorption occurred at pH ∼4, where 70–80% of the added V (350–400 μg g−1 from 10−4m solution and 35–40 μg g−1 from 10−5m solution) was retained by each soil. Retention was significant even at pH 6, where adsorption of a similar anion, molybdate, is negligible. Desorption of the retained V was measured by adding 50.0 cm3 of 0.02 M KCl into weighed soil samples and shaking for 17 h in a mechanical stirrer. Only a minor part of retained V could be removed from each soil by the KCl treatment.Retention of different ionic species of V from 10−5m solution is approximated using values of log K obtained from the literature. In these calculations, kaolin is used as a reference material.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 159
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: The occurrence of greigite (Fe3S4) in soils is reported for the first time. It forms irregularly-shaped aggregations within plant cells in the Gr2 horizon of a gley soil developed from colluvial material. Greigite was identified by X-ray diffraction and magnetic measurements and was investigated by optical and transmission electron microscopy. Biogenic formation is proposed, based on the elongated shape of single greigite crystals, and sulphur isotope analyses, which showed a depletion in 34S relative to the soil-water sulphate. The cell-edge length of 0.98639±0.00003 nm is significantly smaller than values reported for sedimentary greigite. The mean coherence length of 27 nm agrees with TEM observations and indicates that the single greigite crystals lie in the superparamagnetic region. However, the fine aggregates show magnetically single-domain behaviour. Greigite is the only carrier of a stable magnetic remanence in the soil profile studied.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 160
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Equations are developed to predict the distribution of Fe2+ between solid and solution phases in a reduced soil undergoing oxidation at different pHs, based on cation-exchange equilibria and electrical neutrality in the solid and solution. The equations satisfactorily explained experimental results. They are incorporated in the model of Fe2+ diffusion and oxidation developed in Part II, and the model is also extended to allow for O2 consumption in processes other than Fe2+ oxidation. The resultant predictions are tested against measured profiles of Fe(II), Fe(III) and pH in cylinders of reduced soil exposed to O2 at one end. When oxidation rate constants measured in stirred soil suspensions were used to run the model, the predicted rates of O2 consumption were too great and the spread of the oxidation front too small. Satisfactory agreement was achieved for oxidation rate constant values about one-eighth of those measured in the stirred suspensions. The findings are consistent with the rate of Fe2+ oxidation in soil being controlled by access of O2 to Fe2+ sorption sites, as suggested in Part I. The revised model allows a study of the effects of Fe2+ oxidation on the mobility of other cations in reduced soils, e.g. nutrient cations in the rice rhizosphere. Fez+ oxidation and the accompanying acidification may greatly impede cation mobility in reduced soils.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 161
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: High spatial resolution is obtained from a gamma-ray transmission density gauge by restricting the measured counts to a narrow band of the energy spectrum, close to the emission energy peak. The effect on measurement accuracy of any movement of this measurement window relative to the energy peak was investigated. The findings were related to anticipated energy peak movements in a proposed LED-based gain-stabilization system.Movements of the energy peaks during recording of unstabilized spectra prevented direct comparisons of spectra at different positions. A simulation procedure was, therefore, developed in which movements of the measurement window relative to sets of stable calibration spectra were examined.When analysing spectra, recorded using a gauge with a different gain-stabilization system, accuracy was found to be unaffected by simulated peak movements of up to 0.03 MeV in the direction of increasing energy. However, movements of stabilized spectra in the direction of decreasing energy, and of unstabilized spectra in either direction, increased measurement errors to twice the level of inherent measurement errors within 0.02 MeV, with errors in bulk density of up to 0.7 Mg m−3 for movements of 0.1 MeV. The spectra of the new LED-based stabilization system are expected to behave in a manner similar to the unstabilized system, therefore requiring regular monitoring of the peak position.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 162
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: We have determined electrical conductivity (Ee) and total dissolved salts (S) in saturation extracts from 39 soil samples from the Baza basin (Province of Granada, south-east Spain). Ee ranged from 2.8 to 110dS m−3, and S from 2 to 444 8 dm−3.The relationship between S and Ee was not linear. When the saturation extracts were diluted with progressively larger quantities of distilled water and their electrical conductivity calculated (Eec) with the equation〈displayedItem type="mathematics" xml:id="mu1" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:13510754:EJSS153:EJSS_153_mu1"/〉where Ed and Ew are the conductivity of the diluted extract and the distilled water and f is the dilution factor, the relationship between S and Eec tended to become linear.The highest linear correlation coefficient relating S (mg dm−3) and Eec (dS m−1) was reached when Eec, values were calculated for dilutions with a conductivity (Ed) between 0.1 and 0.3 dS m−1 (E*ec). The regression equation was S= 490 E*ec with r2= 0.999. This relationship can be used in all saturation extracts, regardless of the concentration and type of ions present.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 163
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: The consequences of slow diffusion of strongly adsorbed solutes into soil aggregates are not fully understood. The distribution of 32P after diffusing down a soil column cannot be explained from a consideration of liquid-phase impedance factor and isotopic exchange alone, as can that of 36CI.A model was developed that considers the soil to provide linked parallel intra-aggregate and inter-aggregate pathways. With this geometry, simulations agreed fairly well with experimental data when the intra-aggregate impedance factor was 0.001, using other model parameters that had been determined in independent equilibration studies. With this intra-aggregate impedance factor, the model yielded straight-line plots for chloride and the overall impedance factor derived agreed closely with the experimental one. The intra-aggregate impedance factor for 32P also agreed with the rate of reaction of the rapidly-exchanging P fraction previously determined. The slowly-exchanging P fraction has little influence on the P concentration profiles up to 10 d, but the small exchanged amount does have an effect at run times of 57 d.The slow intra-aggregate diffusion of strongly adsorbed solutes decreases the amount adsorbed from a surface source of supply, and it also decreases the amount that is taken up by a surface sink. However, the interaggregate solution concentration remote from a source of supply is considerably increased, which may be important if the solute is a pollutant or a nutrient.
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  • 164
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: A pot experiment was conducted to study changes over time of Cd and Zn in soil solution and in plants. Radish was grown in a soil which had been contaminated with heavy metals prior to 1961. Constant amounts of a fertilizer solution (NH4NO3, KNO3) were added daily. Soil solution was obtained at intervals by displacement with water.The cumulative additions of small amounts of fertilizers were made equal to the plants' requirements at the final harvest but were found to exceed them during most of the experiment. Excess fertilizers caused substantial increases of major (K, Ca, Mg) and heavy-metal (Cd, Zn) ions in soil solutions and a decrease in soil pH, probably due to ion-exchange mechanisms and the dissolution of carbonates.Uptake of Cd and Zn into leaves was correlated with the mass flow of Cd (adjusted r2= 0.798) and Zn (adjusted r2= 0.859). Uptake of K, Ca and Mg by the plants was independent of their concentrations in solution.It is concluded that, in order to study effects of plants on heavy-metal availability and obtain soil solution that has not been altered by fertilizer ions, nutrients must be added according to the needs and growth of the plants. This could be achieved by linking fertilizer additions to the rate of transpiration, as nutrient uptake and transpiration were closely correlated in this experiment.
    Materialart: Digitale Medien
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  • 165
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Measurements of total organic C, δ13C and δ14C are given for topsoils taken from six experimental sites in southern England. At each site, some of the samples were collected before and some after the thermonuclear tests of the early 1960s, so that pre- and post-bomb samples could be compared for radiocarbon content. The current Rothamsted model for the turnover of organic C in soil gave an acceptable fit to the data from five of the sites, apart from one aberrant radiocarbon measurement. The annual input of C to the topsoil was calculated for the five sites from these fits; the values obtained were: 0.15 t C ha−1 a−l for a site on silty clay loam, kept bare by hand weeding since 1870; 0.2 for unmanured spring barley growing on a sandy loam; 2.95 for a fertilized all-arable rotation on a loamy sand; 1.9 for the same fertilized all-arable rotation on a silty loam and 2.5 from this rotation on a calcareous silty loam. The corresponding values for Net Primary Production at the five sites were 0.15, 0.76, 5.16, 5.71 and 5.46 t C ha−1 a−l. In fitting the model to the radiocarbon data it was necessary to postulate that all these sites contained substantial quantities of biologically-inert organic matter, ranging from 2.2 to 10.0 t C ha−1.
    Materialart: Digitale Medien
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  • 166
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Iron (hydr)oxides are active phosphate sorbents in soils and sediments, but no information exists on phosphate (P) sorption by natural hematites. In this study, we characterized the chemical, mineralogical and P-sorption properties of 14 hematite-rich natural materials of different origins. Phosphate sorption was described by a modified Freundlich equation including a time term. Phosphate sorbed at 1d at an equilibrium concentration of 1 mg P dm−3 ranged widely (0.2–1.7 μmol m−2). After 1 d, hematites showed a marked slow sorption. At 75 d, and an equilibrium concentration of 6mg P dm−3, the total amount of P sorbed ranged between 0.8 and 4.1 μmol mp−2. Phosphate-sorption capacity was influenced by the morphology of the coherently scattering domains: the shorter the domains in the crystallographic c relative to the a direction, the lower the P-sorption capacity. This has been observed by other authors in synthetic hematites and agrees with the idea that the prismatic faces, which have singly co-ordinated Fe-OH groups, are more active in P-sorption than other faces. The average P sorption capacity of hematites was similar to that of natural goethites (2.6 μmol P m−2) but, in contrast to these, variability among samples was high. In comparison with goethites, hematites show slower sorption and lower affinity for phosphate.
    Materialart: Digitale Medien
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  • 167
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    European journal of soil science 45 (1994), S. 0 
    ISSN: 1365-2389
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: The sorption of phosphate on amorphous aluminium hydroxides was investigated using 27Al and 71P solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, following the effect of different exposures to soluble phosphate. The spectra obtained were compared with the spectrum of amorphous aluminium phosphate. Aluminium in the unreacted hydroxide had a 100% octahedral co-ordination. When dried at 200°C and exposed to soluble phosphate, very little (maximum 0.1%) amorphous aluminium hydroxide transformed to a tetrahedral co-ordination (A1 bound by oxygen bridges to four P atoms), even after 120d. The tetrahedral co-ordination exists in aluminium phosphate gel, although most of its A1 atoms exhibit an octahedral co-ordination. For the aluminium hydroxide dried at 200°C, no formation of aluminium phosphate in which aluminium is in octahedral co-ordination could be detected, not even when the aluminium hydroxide was exposed to a phosphate solution for 120 d. We concluded that the formation of aluminium phosphate is restricted to the surface of the hydroxide. Most of the phosphate which is bound to the aluminium oxide however may not have formed a ‘bulk solid’ aluminium phosphate, but is adsorbed on the internal and external surface of the oxide. The same amorphous aluminium hydroxide, dried at 70°C instead of 200°C, is converted much more rapidly to aluminium phosphate when exposed to soluble phosphate. We propose a P-induced weathering mechanism to describe P sorption on amorphous aluminium hydroxides at high P concentrations. In addition to NMR, phosphate adsorption experiments conducted on aluminium hydroxides dried at different temperatures produced evidence that the porosity of the aluminium hydroxide aggregated particles can also be a factor controlling the rate of phosphate uptake from solution, if the aggregate is stable (is not resuspended) in solution.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 168
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: A method of non-invasive NMR in the earth's field has been developed and is now used for groundwater surveys to depths of investigation of 100 m or more.A circular wire loop of diameter 100 m, laid out on the ground, is employed to excite and receive the NMR signal in the earth's field. However, in areas with high electromagnetic noise, the NMR measurements may be inaccurate.To overcome this problem, a noise-reducing figure-of-eight-shaped antenna, consisting of two touching coils each of diameter 50 m, has been utilized.Using this antenna, the NMR signal has been calculated for different depths of water-saturated layers with various inclinations of the geomagnetic field. The model calculations and experimental data have been compared and found to be mutually consistent. The two-coil antenna is shown to be suitable for studies at depths of up to 30–40 m, which is of practical importance for engineering geology.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 169
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: A general inversion scheme based on a genetic algorithm is developed to invert seismic observations for anisotropic parameters. The technique is applied to the inversion of shear-wave observations from two azimuthal VSP data sets from the Conoco test site in Oklahoma. Horizontal polarizations and time-delays are inverted for hexagonal and orthorhombic symmetries. The model solutions are consistent with previous studies using trial and error matching of full waveform synthetics. The shear-wave splitting observations suggest the presence of a shear-wave line singularity and are consistent with a dipping fracture system which is known to exist at the test site. Application of the inversion scheme prior to full waveform modelling demonstrates that a considerable saving in time is possible whilst retaining the same degree of accuracy.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 170
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: A numerical simulation of electromagnetic propagation through a multilayered medium is performed in order to explain and interpret the signal received from the radar sounding of a temperate glacier. During the winter of 1990, several radar profiles were obtained on the Mont-de-Lans glacier in the French Alps with a ground penetrating radar which uses a phase modulation of the transmitted pulse by coded sequences. The pulse compression is obtained by applying the matched filter to the received signal, which provides a range-resolution of about 8 m in the ice. The profiles recorded on the temperate glacier do not show a single clear reflection from the ice-bedrock interface, but they exhibit widely distributed energy decreasing with depth. This may be due to the inhomogeneous inner structure of the temperate glacier and we use a simple model of a layered medium to compute a simulation of the propagation. Thus, partial reflection at each layer and scattering from a rough basal interface may explain the observed signal. A computer-based technique is used to locate on the data the bottom of the glacier in order to estimate the ice thickness. The results from the different radar profiles are consistent and are a good fit to the thickness which has been determined by other geophysical methods.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 171
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: Both approximate and exact formulations for the interaction of an incident elastic wave with a cased borehole are presented. In the approximate method, simple and explicit formulae are derived for the pressure in fluid at low frequencies. In the exact method, elastic potentials in each annulus are represented as a superposition of fundamental solutions to the Helmholtz equations. Continuity of displacements and stresses across layer boundaries are used to determine unknown coefficients. A global matrix algorithm is employed to compute simultaneously these coefficients in individual layers. Calculations show that, in cased boreholes, the borehole effects on downhole seismic measurements are more significant than in open boreholes. A strong resonance occurs in the fluid for SV-wave incidence from a soft formation. This resonance is prominent even at very high frequencies because the tube-wave velocity is raised well above the formation shear velocity by the steel pipe. At a particular angle of incidence of a plane P-wave, the pressure in the fluid is near zero at low frequencies (the cased borehole screening phenomenon). For hard formations and frequencies above 1 kHz, the cased borehole influence on a downhole geophone measurement is significant, especially at grazing incidence. For soft formations, both the pressure in the fluid and the solid displacement on the borehole wall show strong dependence on frequency and angle of incidence, even at low frequencies.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 172
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: Seismograms predicted from acoustic or elastic earth models depend very non-linearly on the long wavelength components of velocity. This sensitive dependence demands the use of special variational principles in waveform-based inversion algorithms. The differential semblance variational principle is well-suited to velocity inversion by gradient methods, since its objective function is smooth and convex over a large range of velocity models. An extension of the adjoint state technique yields an accurate estimate of the differential semblance gradient. Non-linear conjugate gradient iteration is quite successful in locating the global differential semblance minimum, which is near the ordinary least-squares global minimum when coherent data noise is small. Several examples, based on the 2D primaries-only acoustic model, illustrate features of the method and its performance.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 173
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: Evidence from borehole susceptibility logs and the spectral analysis of aeromagnetic data suggests that the three-dimensional distribution of magnetization within the crust can be described as fractal. This property can be exploited in magnetic interpretation methods which explicitly require statistical information on the spatial variation of magnetization. Specifically, we address the problem of magnetic source depth estimation through downward continuation and gridding aeromagnetic survey data using the method of kriging.When magnetic data are continued downwards the depth at which the power spectrum flattens out (the ‘white’ depth) can be taken to be an estimate of the top of the source distribution. This procedure assumes that individual sources are uncorrelated with each other. Taking into account the correlation of the magnetization using a fractal description leads to a reduction in this depth estimate.Gridding of randomly distributed magnetic measurements using kriging requires an estimate of the covariance of the data. Compared with the assumption of a white (uncorrelated) magnetization distribution, using fractal covariances for kriging produces gridded estimates which more closely reflect the statistics of the underlying magnetization process and produce maps with a justifiable degree of smoothness.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 174
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: The superposition integral expressing the field due to a magnetic source body is relatively simple to evaluate in the case of a homogeneous magnetization. In practice this generally requires that any remnant component is uniform and the susceptibility of the body is sufficiently low to permit the assumption of a uniform induced magnetization. Under these conditions the anomalous magnetic field due to a polyhedral body can be represented in an intuitive and physically appealing manner. It is demonstrated that the components of the magnetic field H can be expressed as a simple combination of the potentials due to two elementary source distributions. These are, firstly, a uniform double layer (normally directed dipole moment density) located on the planar polygonal faces of the body and, secondly, a uniform line source located along its edges. In practice both of these potentials (and thus the required magnetic field components) are easily computed. The technique is applicable to polyhedra with arbitrarily shaped faces and the relevant expressions for the magnetic field components are suitable for numerical evaluation everywhere except along the edges of the body where they display a logarithmic singularity.
    Materialart: Digitale Medien
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  • 175
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: Improving the accuracy of NMO corrections and of the corresponding interval velocities entails implementing a better approximation than the formula used since the beginning of seismic processing. The exact equations are not practical as they include many unknowns. The approximate expression has only two unknowns, the reflection time and the rms velocity, but becomes inaccurate for large apertures of the recording system and heterogeneous vertical velocities. Several methods of improving the accuracy have been considered, but the gains do not compensate for the dramatic increase in computing time. Two alternative equations are proposed: the first containing two parameters, the reflection time and the focusing time, is not valid for apertures much greater than is the standard formula, but has a much faster computing time and does not stretch the far traces; the other, containing three parameters, the reflection time, like focusing time and the tuning velocity, retains high frequencies for apertures about twice those allowed by the standard equation. Its computing time can be kept within the same limits. NMO equations, old and new, are designed strictly for horizontal layering, but remain reliable as long as the rays travel through the same layers in both the down and up directions.An equation, similar to Dix's formula, is given to compute the interval velocities. The entire scheme can be automated to produce interval-velocity sections without manual picking.
    Materialart: Digitale Medien
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  • 176
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: The Bjøirnøya West Basin lies between latitudes 73° and 74°, longitudes 16°E and 18°E, contains at least 8 km of sediments deposited from the Late Jurassic, and is of considerable interest for hydrocarbon exploration. The Cenozoic extensional tectonics in the basin can be clearly seen from seismic data with normal faulting and from subsidence curves with rapid subsidence. The extension occurred during the Late Palaeocene with active extension lasting about 6 million years (m.y.) followed by thermal cooling. The tectonic subsidence within the study area shows a three-phase development: phase 1, synrift (58–52 Ma (million years before the present day)), is characterized by rapid subsidence; phase 2, postrift (52–5 Ma), by slow subsidence with occasional uplift; and phase 3 (5–0 Ma), by rapid subsidence. An adaptive finite-element model, with consideration of the radiogenic heat production in the lithosphere, has been used to model the subsidence and heat flow. The modelling of subsidence shows the β-factor distribution varying from 1.9 to 3.5 with an average of 2.4 for the uniform lithospheric extension. The heat-flow modelling predicts a rapid increase of heat flow during the Early Palaeocene. The maximum heat flow at about 52 Ma, which could be as much as 3.0 hfu (10−6 cal/cm2/s), was followed by a decrease in heat flow. A plate-weakening model has been proposed to explain the rapid subsidence for the last 5 m.y. by flexure of the elastic lithosphere which is weakened by a decrease in elastic thickness caused by an increase of the temperature gradient in the lithosphere. The plate-weakening model predicts a heat-flow increase at 5 Ma of up to 2.0 hfu. Our study, using quantitative modelling of the tectonic subsidence, provides a partial (if not a full) understanding of the tectonic development and thermal evolution of the Bjønøya West Basin.
    Materialart: Digitale Medien
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  • 177
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical prospecting 42 (1994), S. 0 
    ISSN: 1365-2478
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Geologie und Paläontologie , Physik
    Notizen: We present a discrete modelling scheme which solves the elastic wave equation on a grid with vertically varying grid spacings. Spatial derivatives are computed by finite-difference operators on a staggered grid. The time integration is performed by the rapid expansion method. The use of variable grid spacings adds flexibility and improves the efficiency since different spatial sampling intervals can be used in regions with different material properties. In the case of large velocity contrasts, the use of a non-uniform grid avoids spatial oversampling in regions with high velocities. The modelling scheme allows accurate modelling up to a spatial sampling rate of approximately 2.5 gridpoints per shortest wavelength. However, due to the staggering of the material parameters, a smoothing of the material parameters has to be applied at internal interfaces aligned with the numerical grid to avoid amplitude errors and timing inaccuracies. The best results are obtained by smoothing based on slowness averaging. To reduce errors in the implementation of the free-surface boundary condition introduced by the staggering of the stress components, we reduce the grid spacing in the vertical direction in the vicinity of the free surface to approximately 10 gridpoints per shortest wavelength. Using this technique we obtain accurate results for surface waves in transversely isotropic media.
    Materialart: Digitale Medien
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  • 178
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    New technology, work and employment 9 (1994), S. 0 
    ISSN: 1468-005X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Sociologie , Wirtschaftswissenschaften
    Notizen: Here the author examines the development and implementation of a computer-based system within a financial services organization. It highlights emerging paradoxes within the developments of systems design which utilise quality management methodologies to support IT intensive business processes.
    Materialart: Digitale Medien
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  • 179
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Business ethics 3 (1994), S. 0 
    ISSN: 1467-8608
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Philosophie , Wirtschaftswissenschaften
    Notizen: Managerial effort has been moving from maintaining a “steady state” to wrestling with the challenge of continuing change and the ethical dilemmas which this can present. Is it possible to formulate an “ethics of change” to guide individuals in such circumstances? The author is a senior lecturer at Cranfield University, Bedford MK43 OAL, UK, and a visiting research associate at the London School of Economics. His principal interests concern the management of organisational change in settings where technology is either the key driver of change, or is the key enabler of some aspect of organisational or process redesign.
    Materialart: Digitale Medien
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  • 180
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Business ethics 3 (1994), S. 0 
    ISSN: 1467-8608
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Philosophie , Wirtschaftswissenschaften
    Notizen: Stakeholder theory aims at identifying those who have rights or interests at stake in business behaviour. Can we turn the tables and also consider what ethical responsibilities various stakeholders may have for the good behaviour of business? The author is Editor of this Review. This article contains material which also appeared in the Hugh Kay Memorial Lecture for 1993 delivered by the author under the auspices of the Christian Association of Business Executives, London.
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  • 181
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Business ethics 3 (1994), S. 0 
    ISSN: 1467-8608
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Philosophie , Wirtschaftswissenschaften
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 182
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Business ethics 3 (1994), S. 0 
    ISSN: 1467-8608
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Philosophie , Wirtschaftswissenschaften
    Notizen: Karl Homann & Franz Blome-Drees (1992). Wirtschafts- und Unternehmensethik. Vandenhoeck & Ruprecht. Göttingen. pp. 207. paperback, 19.80 DM. ISBN 3-8252-1721-3
    Materialart: Digitale Medien
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  • 183
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Business ethics 3 (1994), S. 0 
    ISSN: 1467-8608
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Philosophie , Wirtschaftswissenschaften
    Notizen: Brief thumbnail sketches capture group interest and show the relevance of ethical considerations in real life situations. Bill Bain has considerable experience of business and is currently a PhD student at the Management School of London University's Imperial College, 53 Prince's Gate, Exhibition Road, London SW7 2PG.
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  • 184
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Business ethics 3 (1994), S. 0 
    ISSN: 1467-8608
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Philosophie , Wirtschaftswissenschaften
    Notizen: Games have become a standard tool in management education. The authors have cooperated on developing just such a teaching aid for business people and management students interested in playing the business game ethically. Dr Higginson is Director of The Ridley Hall Foundation, Ridley Hall, Cambridge, CB3 9HG and Geoff Moore is Principal Lecturer at Newcastle Business School, University of Northumbria at Newcastle, Newcastle upon Tyne NE1 8ST.
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  • 185
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Business ethics 3 (1994), S. 0 
    ISSN: 1467-8608
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Philosophie , Wirtschaftswissenschaften
    Notizen: Despite the social, economic and ethical problems facing government in the Czech Republic, there are positive signs of a growing concern for ethical business, including the development of codes of conduct and a striking example of new corporate social responsibility. Dr Bohatá is a member of the Economics Institute of the Academy of Sciences, Politickych Veznu 7, 111 21 Prague 1, and an Associate Editor of this Review.
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  • 186
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Business ethics 3 (1994), S. 0 
    ISSN: 1467-8608
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Philosophie , Wirtschaftswissenschaften
    Notizen: The media, advertising and public relations are all regulated in some degree by ethical codes of practice, but do they work and do they help practitioners? The author is Senior Lecturer in public relations and philosophy at Leeds Business School, Leeds Metropolitan University, Leeds LS2 8AF. She is currently preparing material for a new MA in Business Policy and Ethics, to be offered jointly by Leeds Metropolitan University and the University of Leeds.
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  • 187
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Business ethics 3 (1994), S. 0 
    ISSN: 1467-8608
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Philosophie , Wirtschaftswissenschaften
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 188
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Business ethics 3 (1994), S. 0 
    ISSN: 1467-8608
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Philosophie , Wirtschaftswissenschaften
    Notizen: Most large frauds develop only gradually and incidentally. When things fall apart it is politic to call it anything but fraud. The author is a member of the Department of Sociology, University of Liverpool, POB 147, Liverpool L69 3BX.
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  • 189
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Business ethics 3 (1994), S. 0 
    ISSN: 1467-8608
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Philosophie , Wirtschaftswissenschaften
    Notizen: Georges Enderle, Karl Homann, Martin Honecker, Walter Kerber, Horst Steinmann (editors), Lexikon der Wirtschaftsethik. Freiburg im Breisgau, Verlag Herder, 1993. pp. 690, ISBN 3-451-22336-8.
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  • 190
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Business ethics 3 (1994), S. 0 
    ISSN: 1467-8608
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Philosophie , Wirtschaftswissenschaften
    Notizen: Action needs to be taken on the ethical issues raised by the commercialising of sport if its integrity is to be maintained and its ethical base is not to be eroded further. The author has worked as an independent consultant in the leisure sector for a number of years and has recently joined the Research Unit of Britain's Sports Council. The views expressed by her in this article are not necessarily those held by the Sports Council.
    Materialart: Digitale Medien
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  • 191
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Business ethics 3 (1994), S. 0 
    ISSN: 1467-8608
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Philosophie , Wirtschaftswissenschaften
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 192
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    New technology, work and employment 9 (1994), S. 0 
    ISSN: 1468-005X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Sociologie , Wirtschaftswissenschaften
    Notizen: The computing occupations are in a state of transition between a technical service and something more central to organizational power and decision-making. This process has had complex implications for the nature of computing work and for careers. There is no certainty that embryonic changes will carry through. But neither should the chances of these occupations of mounting a ‘collective mobility project’ be written off early.
    Materialart: Digitale Medien
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  • 193
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    New technology, work and employment 9 (1994), S. 0 
    ISSN: 1468-005X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Sociologie , Wirtschaftswissenschaften
    Notizen: The relationship between new information and communication technology and organizations is the subject of considerable debate. So too is the nature of organizational transformation. ‘Business process re-engineering’, with its emphasis upon the strategic deployment of information systems, brings both debates together. But does it resolve any of the issues?
    Materialart: Digitale Medien
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  • 194
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    New technology, work and employment 9 (1994), S. 0 
    ISSN: 1468-005X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Sociologie , Wirtschaftswissenschaften
    Notizen: Teaching Company Scheme programmes involve employing graduates known as Teaching Company Associates in companies on projects which are jointly supervised by academics and company staff. This article presents findings of a study of the effectiveness of these programmes in transferring university expertise in science, technology and management, to industry.
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  • 195
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    New technology, work and employment 9 (1994), S. 0 
    ISSN: 1468-005X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Sociologie , Wirtschaftswissenschaften
    Notizen: This article critically examines the phenomenon of ‘Reengineering’ (or Business Process Reengineering: as it is sometimes called) as a transfer of ‘just-in-time’ techniques developed in manufacturing to the office environment. The article concludes that its most likely diffusion will be for ‘downsizing’ and ‘cost-reduction’, and may result in a modest degree of success in only some of its applications to manufacturing and office environments.
    Materialart: Digitale Medien
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  • 196
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    New technology, work and employment 9 (1994), S. 0 
    ISSN: 1468-005X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Sociologie , Wirtschaftswissenschaften
    Notizen: This article is concerned with the application in a case study of three inter-related theoretical issues: new perspectives on technological change, learning organizations, and the question of market versus hierarchy in the relationships between firms. The case study is of the software manual printing industry in Ireland, and its relationship with the major, international software companies.
    Materialart: Digitale Medien
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  • 197
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    New technology, work and employment 9 (1994), S. 0 
    ISSN: 1468-005X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Sociologie , Wirtschaftswissenschaften
    Notizen: Drawing on empirical material from comparative research on jobbing printing in Iceland and Sweden, the author argues that the typesetting process has been subjected to deskilling, and he stresses that the development has been far more complex than often is realised. He concludes that gender, firm size, and production run and variety, must be considered in order to explain the diversity in the typesetting process.
    Materialart: Digitale Medien
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  • 198
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    New technology, work and employment 9 (1994), S. 0 
    ISSN: 1468-005X
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Sociologie , Wirtschaftswissenschaften
    Notizen: Book reviews in this article:Technclogy in Working Order: Studies of Work, Interaction, and Technology Graham Button (Ed.)Communication, Technology and the Development of People Bernard WoodsPhotonic Technology and Industrial Policy: US Responses to Technological Change Ernest StembergBeyond Taylorism: Computerization and the New Industrial Relations Lorraine GiordanoJapanization at Work John BrattonWorking for the Japanese Stephanie JonesTechnology and Work in German Industry Norbert Altmann, Christoph Kohler and Pamela Meil (Eds.)Towards Global Localisation: The Computing and Telecommunications Industries in Britain and France Philip Cooke, Frank Moulaert, Erik Swyngedouw, Olivier Weinstein, Peter Wells, Martine Lemattre and Patrice GrevetNew Technology and Practical Police Work S. Ackroyd, R. Harper, J. A. Hughes, D. Shapiro and K. Soothill
    Materialart: Digitale Medien
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  • 199
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Ground water monitoring & remediation 14 (1994), S. 0 
    ISSN: 1745-6592
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik , Geologie und Paläontologie
    Notizen: Hydrogen gas was discovered within the steel casing above standing water in a percussion-drilled borehole on the Hanlord Site in south-central Washington state. In situ measurements of the borehole fluids indicated anoxic, low-Eh (〈-400 mV) conditions. Ground water sampled from adjacent wells in the same formation indicated that the ground water was oxygenated. H2 was generated during percussion drilling, due to the decomposition of borehole waters as a result of aqueous reactions with drilled sediment and steel from the drilling tools or casing. The generation of H2 within percussion-drilled boreholes that extend below the water table may be more common than previously realized. The ambient concentration of H2 produced during drilling was limited by microbial activity within the casing-resident fluids. H2 was generated abiotically in the laboratory, whereby sterilized borehole slurry samples produced 100 times more H2 than unsterilizcd samples. It appears that H2 is metabolized by microorganisms and concentrations might be significantly greater if not for microbial metabolism.
    Materialart: Digitale Medien
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  • 200
    Digitale Medien
    Digitale Medien
    Oxford, UK : Blackwell Publishing Ltd
    Ground water monitoring & remediation 14 (1994), S. 0 
    ISSN: 1745-6592
    Quelle: Blackwell Publishing Journal Backfiles 1879-2005
    Thema: Energietechnik , Geologie und Paläontologie
    Notizen: Measurement accuracy was increased by nearly one order of magnitude by outfitting the thermal-pulse flowmeter (TFM) with an inflatable packer. To accurately measure slow water velocities in boreholes greater than 15 cm diameter, it is necessary to divert borehole fluids through the TFM by inflating a packer. During calibration it was noted that the TFM's accuracy decreased as the borehole diameter increased. With Lhe packer inflated the TFM has a useful flow measurement range of 0.08 to 15 L/min (with flow velocities of 0.24 ± 0.012 cm/inin to 45.7 ± 0.61 cm/min, respectively, in 20-cm-diameter pipe), compared to 0.8 to 57 L/min for a packcrless TFM. A computer interlace was added to the TFM to provide a real-time graphical display of the differential voltage output from the TFM, a running mean and standard deviation of the pulse-response time, and a mean flow rate and velocity based on calibration curve fits.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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