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  • Articles  (57)
  • Articles: DFG German National Licenses  (57)
  • Blackwell Publishers  (57)
  • 1995-1999  (57)
  • 1985-1989
  • Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition  (52)
  • Physics  (5)
  • Technology
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  • Articles  (57)
Source
  • Articles: DFG German National Licenses  (57)
Publisher
Years
  • 1995-1999  (57)
  • 1985-1989
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Topic
  • Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition  (52)
  • Physics  (5)
  • Technology
  • Economics  (64)
  • Geosciences  (5)
  • 1
    Electronic Resource
    Electronic Resource
    Multiple prediction using the homeomorphic-imaging technique (1998)
    Oxford BSL : Blackwell Publishers
    Geophysical prospecting 46 (1998), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: A new method for predicting different kinds of multiples and peg-leg reflections in unstacked seismic data is discussed. The basis for this method is the fact that kinematic properties of multiples can be represented as a combination of kinematic properties of primary reflections. The prediction is made using a two-step process. In the first step, the values for the angle of emergence and radius of curvature of the wavefront for primary reflections from ‘multiple-generating’ interfaces are obtained. These parameters are estimated directly from unstacked data for every source point using the homeomorphic-imaging technique. The second step consists of prediction of multiples from primary reflections that satisfy a so-called ‘multiple condition’. This condition is the equality of the absolute values of the angles of emergence calculated from the first step. This method is effective even in complex media and information on the subsurface geology is not required. The parameters are estimated directly from the unstacked data and do not require any computational efforts such as in wavefield extrapolation of data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2478.1998.990331.x
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  • 2
    Electronic Resource
    Electronic Resource
    Seismic and ultrasonic velocities in permafrost (1998)
    Oxford BSL : Blackwell Publishers
    Geophysical prospecting 46 (1998), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: We calculate the compressional- and shear-wave velocities of permafrost as a function of unfrozen water content and temperature. Unlike previous theories based on simple slowness and/or moduli averaging or two-phase models, we use a Biot-type three-phase theory that considers the existence of two solids (solid and ice matrices) and a liquid (unfrozen water). The compressional velocity for unconsolidated sediments obtained with this theory is close to the velocity computed with Wood's model, since Biot's theory involves a Wood averaging of the moduli of the single constituents. Moreover, the model gives lower velocities than the well-known slowness averaging theory (Wyllie's equation). For consolidated Berea sandstone, the theory underestimates the value of the compressional velocity below 0°C. Computing the average bulk moduli by slowness averaging the ice and solid phases and Wood averaging the intermediate moduli with the liquid phase yields a fairly good fit of the experimental data. The proportion of unfrozen water and temperature are closely related. Fitting the wave velocity at a given temperature allows the prediction of the velocity at the whole range of temperatures, provided that the average pore radius and its standard deviation are known.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2478.1998.1000333.x
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  • 3
    Electronic Resource
    Electronic Resource
    An experimental comparison of three direct methods of marine source signature estimation (1998)
    Oxford BSL : Blackwell Publishers
    Geophysical prospecting 46 (1998), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Three methods for estimation of the pressure wavefield generated by a marine airgun array are tested experimentally and compared. In the trial a variety of radiation angles and array configurations were used and some large synchronization errors were deliberately introduced. The source was equipped with near-field hydrophones and a subsource ministreamer. A tethered far-field hydrophone was used so that the three estimated far-field signatures could be compared with an independent measurement.The knowledge of the source signature is important for on-board source array QC, deconvolution, multiple attenuation, stratigraphic trap prediction, modelling and inversion, AVO analysis and reservoir monitoring.The methods perform very well and give estimates whose frequency-domain spectra match the measured spectra to within a few dB and within a few tens of degrees of phase over the tested bandwidth of 3.5–110 Hz. The time-domain error-energy is typically only a few per cent of the signal energy for radiation angles within about 30° of the vertical. The third method proved to be sensitive to an experimental shortcoming leading to overloading of the ministreamer and meaningful comparison was not possible for some test configurations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2478.1998.980334.x
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  • 4
    Electronic Resource
    Electronic Resource
    Joint estimation of AVO and kinematic parameters (1998)
    Oxford BSL : Blackwell Publishers
    Geophysical prospecting 46 (1998), S. 0 
    Details
    ISSN: 1365-2478
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences , Physics
    Notes: Conventional amplitude-versus-offset (AVO) analysis such as linear fitting of isotime samples after NMO correction does not give reliable results in the presence of interfering reflections or velocity errors. For this reason we propose a new method that is able to remove interference effects on the AVO of the target reflection and minimize the effects of residual moveout. The method is based on the minimization of the difference between observed data and a model that includes theoretical descriptions of the AVO and traveltimes. This minimization is carried out jointly with respect to AVO and kinematic parameters (velocities and traveltimes) and requires the a priori knowledge of the propagating wavelet. The kinematic parameters are given by the NMO equation extended to the fourth-order term and the AVO is described as a linear combination of a set of orthogonal functions. The AVO functions are derived from a statistical model of reflection amplitude in the presence of velocity error.Applications to synthetic and real data demonstrate the ability of the method to attenuate distortion effects on the AVO of the primary reflection by interfering coherent noise. The real data example pertains to a marine case where the primary event is contaminated by multiple reflections generated in the water layer and by another event, reflected from an interface deeper than the target, that merges with the examined reflections at the far-offsets. This causes a subtle tuning that distorts the AVO of the target. Our method attenuates the effects of the multiples and discriminates the ‘double event’ nature of the target reflection at the far-offsets.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2478.1998.970332.x
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  • 5
    Electronic Resource
    Electronic Resource
    Molecular Biology Made Simple and Fun (1998)
    Oxford, U.K. and Cambridge, USA : Blackwell Publishers
    Plant pathology 47 (1998), S. 0 
    Details
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3059.1998.0179c.x
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  • 6
    Electronic Resource
    Electronic Resource
    Spatial and temporal spread of powdery mildew (Erysiphe pisi) in peas (Pisum sativum) varying in quantitative resistance (1998)
    Oxford, U.K. and Cambridge, USA : Blackwell Publishers
    Plant pathology 47 (1998), S. 0 
    Details
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: A field experiment was conducted to assess the progress in time and spread in space of powdery mildew (caused by Erysiphe pisi) in pea (Pisum sativum) cultivars differing in resistance to the disease. Disease severity (proportion of leaf area infected) was measured in 19 × 23 m plots of cultivars Pania and Bolero (both susceptible) and Quantum (quantitatively resistant). Inoculum on infected plants was introduced into the centre of each plot. Leaves (nodes) were divided into three groups within the canopy (lower, middle, upper) at each assessment because of the large range in disease severity vertically within the plants. Disease severity on leaves at upper nodes was less than 4% until the final assessment 35 days after inoculation. Exponential disease progress curves were fitted to disease severity data from leaves at middle nodes. The mean disease relative growth rate was greater on Quantum than on Pania or Bolero, but it was delayed, resulting in an overall lower disease severity on Quantum. Gompertz growth curves were fitted to disease progress on leaves at lower nodes. Disease progress on Quantum was delayed compared with Pania and Bolero. The average daily rates of increase in disease severity from Gompertz curves did not differ between the cultivars on these leaves. Disease gradients in the plots from the inoculum focus to 12 m were detected at early stages of the epidemic, but the effects of background inoculum inputs and the rate of disease progress meant that these gradients decreased with time as the disease epidemic intensified. Spread was rapid, and there were no statistically significant differences between cultivar isopathic rates (Pania 2.2, Quantum 2.9 and Bolero 4.0 m d−1).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3059.1998.00231.x
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  • 7
    Electronic Resource
    Electronic Resource
    In memory of James Edward Vanderplank 1909–1997 (1998)
    Oxford, U.K. and Cambridge, USA : Blackwell Publishers
    Plant pathology 47 (1998), S. 0 
    Details
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3059.2998.00220.x
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  • 8
    Electronic Resource
    Electronic Resource
    Symptoms, aetiology and serological analysis of sweet potato virus disease in Uganda (1998)
    Oxford, U.K. and Cambridge, USA : Blackwell Publishers
    Plant pathology 47 (1998), S. 0 
    Details
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Sweet potato virus disease (SPVD) is the name used to describe a range of severe symptoms in different cultivars of sweet potato, comprising overall plant stunting combined with leaf narrowing and distortion, and chlorosis, mosaic or vein-clearing. Affected plants of various cultivars were collected from several regions of Uganda. All samples contained the aphid-borne sweet potato feathery mottle potyvirus (SPFMV) and almost all contained the whitefly-borne sweet potato chlorotic stunt closterovirus (SPCSV). SPCSV was detected by a mix of monoclonal antibodies (MAb) previously shown to react only to a Kenyan isolate of SPCSV, but not by a mixture of MAb that detected SPCSV isolates from Nigeria and other countries. Sweet potato chlorotic fleck virus (SPCFV) and sweet potato mild mottle ipomovirus (SPMMV) were seldom detected in SPVD-affected plants, while sweet potato latent virus (SPLV) was never detected. Isolates of SPFMV and SPCSV obtained by insect transmissions together induced typical symptoms of SPVD when graft-inoculated to virus-free sweet potato. SPCSV alone caused stunting and either purpling or yellowing of middle and lower leaves when graft-inoculated to virus-free plants of two cultivars. Similarly diseased naturally inoculated field plants were shown consistently to contain SPCSV. Both this disease and SPVD spread rapidly in a sweet potato crop.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3059.1998.00196.x
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  • 9
    Electronic Resource
    Electronic Resource
    Studies on dispersal of Septoria tritici pycnidiospores in wheat–clover intercrops (1998)
    Oxford, U.K. and Cambridge, USA : Blackwell Publishers
    Plant pathology 47 (1998), S. 0 
    Details
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Four experiments studied the effects of a clover understorey on pycnidiospore dispersal of Septoria tritici in a wheat–clover intercrop under simulated rain. Clover significantly reduced the dispersal of spores in a horizontal direction by 33% at a distance of 15 cm from a line inoculum source compared with a wheat monocrop. The clover also reduced the vertical movement of spores from infected leaves at the base of wheat plants by an average of 63% compared to the monocrop, and this suggests that the main movement of spores was from the base upwards. Splash experiments using blue colour marker showed the vertical decline of splash and the number of drops per cm2 with height caught on paper adjacent to trays of clover was described by the exponential decline model. The effect of clover in reducing vertical splash approached an asymptote as the leaf area index of the understorey increased. Simulated rain-splash increased the level of disease on the flag leaf and, in one experiment, there was a significant interaction between rain-splash and clover in reducing the number of lesions on the flag leaf. The level of disease resulting from one splash event was low, indicating that subsequent pathogen multiplication is probably required to bring about high severities of disease.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3059.1998.00200.x
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  • 10
    Electronic Resource
    Electronic Resource
    Incidence of weed reservoirs and vectors of tomato spotted wilt tospovirus on southern Tasmanian lettuce farms (1998)
    Oxford, U.K. and Cambridge, USA : Blackwell Publishers
    Plant pathology 47 (1998), S. 0 
    Details
    ISSN: 1365-3059
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Thrips species and tomato spotted wilt virus (TSWV) alternate weed hosts were surveyed on two lettuce farms in southern Tasmania during 1994 and 1995. Only one known vector species, Thrips tabaci, was found at either site, comprising on average 36.8% of the total monthly catch. A major peak of thrips activity in the summer corresponded with an increase of disease in autumn harvested lettuce. Two thrips species new for Tasmania were recorded, Pseudanaphothrips achaetus and Tenothrips frici. Infection patterns within the crop indicated that localized weed infestations were the most likely reservoir of virus. ELISA testing showed that TSWV was present in a range of dicotyledonous weed species, although usually infecting only a low percentage of the plants. Arctotheca calendula appeared to be the single most important reservoir host species at one property, whilst this species and Sonchus oleraceus, Malva sylvestris, Brassica rapa ssp. silvestris, Erodium moschatum and Trifolium sp. were probably the most important reservoirs at the other property. Two new natural TSWV host species were recorded, Erodium moschatum and Brassica rapa ssp. silvestris. The property with the highest incidence of TSWV-infected lettuce had a relatively higher proportion of virus-infected weeds but less thrips activity during the infection period.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3059.1998.00227.x
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