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  • 1
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biochemical and Biophysical Research Communications 21 (1965), S. 448-453 
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Physica C: Superconductivity and its applications 177 (1991), S. 61-66 
    ISSN: 0921-4534
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The economic benefits of using site-specific weed management (SSWM) are related to the proportion of the field that is weed-infested, the number of weed patches and the spatial resolution of sampling and spraying technologies. In this paper we simulate different combinations of these factors using parameter values obtained for Avena sterilis ssp. ludoviciana growing in Spanish winter barley crops. The profitability of SSWM systems increased as the proportion of the field infested by this weed decreased and when patch distribution was more concentrated. Under most of the conditions tested, positive net returns for SSWM were obtained when the weed-infested area was smaller than 30%. The highest net return occurred using a 12 m × 12 m mapping and spraying resolution. The critical parameter that determined the economic viability of patch mapping and spraying resolution was the technology costs. The site specific strategy was economically superior to the standard strategy (overall herbicide application) in most cases. However, the differential between the two strategies decreased when the number of patches and the resolution of mapping and spraying increased, such that the highest net returns were obtained with a single patch covering 14% of the field and using a 12-m mapping and spraying resolution; whereas the worst net returns were obtained for all patch numbers when 64% of the field was infested and a 3-m mapping and spraying resolution was used.
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 1039-1042 
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In the present paper we extend to two dimensions the classical Langmuir–Blodgett law, which determines the maximum current ILB that can be accelerated by a given voltage across two infinitely long coaxial cylinders. Generalization of the ILB law is established by performing two-dimensional 2D particle-in-cell numerical experiments on a variety of cylindrical diode configurations with a finite-length emitter. It is found that the limiting current in two dimensions I2D follows a monotonically decreasing function of the emitter length-to-outer electrode radius ratio L/R as expressed by the fitting function I2D/ILB=1+0.1536/(L/R)+0.0183/(L/R)2 within 2.5% accuracy for simulation data in which the ratio of the outer to inner radii exceeds 3. © 2002 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 1486-1493 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Conceptual modeling of the multiaperture electrode system of a 5-cm-diam ring cusp ion thruster intended for producing a 1 mN thrust is described. A mathematical treatment of the ion extraction from the plasma has been developed to provide a method for calculating both the shape and potential of the plasma-emitting surface. The ion optics of the electrode system have been examined using a numerical code to evaluate the ion beam divergence. Close agreement is achieved between the predictions of the conceptual modeling presented here and published experimental results. © 1996 American Institute of Physics.
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  • 6
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: The ability to manage weed infestations in a spatially precise manner requires efficient and accurate methods of mapping weed distributions. A study was conducted to compare four different ground-based methods for collecting georeferenced information on infestations of Avena sterilis in winter wheat and barley. Sampling was performed at harvest by scoring panicle density, either from the ground or from a combine, by counting the number of panicle contacts with a stick moved horizontally over the crop canopy by an observer walking through the field, and by sampling A. sterilis seed rain on the ground. No significant differences were observed among the populations estimated by the four methods. A partial budget analysis of the in-season costs and benefits of spraying patches using these methods showed that visual scoring from the combine was the most appropriate method for the creation of weed management maps to be used for patch spraying in the following season. As a large variety of spatial patterns may be found in fields, the recommended sampling method might be field-specific and optimality should be verified for general use.
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  • 7
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Historical records on the field emergence of seedlings of Avena sterilis in winter cereal crops were used to develop thermal/hydrothermal models to predict the emergence of this weed as a function of meteorological conditions. When water was not a limiting factor, a Weibull function provided a good description of the relationship between thermal time and seedling emergence. The variability in the rate of seedling emergence observed under these conditions was associated with variation in the differential between measured and base temperatures. When water was limiting in the soil, the rate of seedling emergence was reduced, a different function was required to describe the process. The use of a hydrothermal model enabled the use of a single function to describe the patterns of seedling emergence of the nine site-years considered in the study. Using this model we can conclude that 70% seedling emergence will be reached, under very diverse conditions, within 300 hydrodegree days. The hydrothermal model proposed was validated with independent seedling emergence data, supporting the idea that this model is robust enough to be used as a predictive tool for seedling emergence of A. sterilis in a variety of conditions.
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  • 8
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Long-term experiments were conducted in two winter barley fields in central Spain to determine the spatial stability of Avena sterilis ssp. ludoviciana populations under annual applications of low rates of imazamethabenz herbicide. Weed density was sampled every year (over 5 years in the first field and over 3 years in the second) on the same grid locations prior to herbicide application. Although weed patches were stable in their location, weed density decreased in most of the years. In the first field, the populations decreased exponentially over the 5-year period. The rates of population decline were dependent on the initial density of the population, being higher for the central core of the patches and lower for the low-density areas. Under the conditions present in this experiment, it was possible to reduce heavy weed patches (up to 1200 seedlings m−2) down to relatively safe levels (18 seedlings m−2) in a period of 3 years using a density-specific control programme, applying low rates of herbicides when weed densities were below a given level (1000 seedlings m−2). However, under adverse environmental conditions, half rates of the herbicide failed to control the weed populations adequately. The stability of the location of patches of A. sterilis ssp. ludoviciana suggest that weed seedling distributions mapped in one year are good predictors of future seedling distributions. However, the actual densities established each year will depend on the control level achieved the previous year and the climatic conditions present during the establishment period.
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  • 9
    ISSN: 0304-4238
    Keywords: In vitro propagation ; Ophrys spp ; minitubers production ; terrestrial orchids
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The 9 March 1994 occultation of Ch08 (GSC248-01674)9 by Chiron was successfully observed with two telescopes: the 0.9-m telescope aboard NASA's Kuiper Airborne Observatory (KAO) flying near Recife, Brazil and the 0.5-m telescope at the South African Astronomical Observatory (SAAO) at Sutherland. We ...
    Type of Medium: Electronic Resource
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