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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 2258-2266 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Monte Carlo simulation method has been used to investigate the spatial distribution of deposited energy for 1–10 keV electrons incident on solid hydrogen, nitrogen, neon, silicon, aluminum, and argon. In the simulation, elastic scattering cross sections are calculated exactly using the single-atom crystalline potentials. Inelastic energy loss processes for hydrogen are based on the ionization cross section from Green and Sawada [J. Atmos. Terr. Phys. 34, 1719 (1972)] and the gas-phase stopping power from Parks et al. [Nucl. Fus. 17, 539 (1977)]. For the heavier materials a modification of Gryzinski's [Phys. Rev. A 138, 305 (1965); 138, 322 (1965); 138, 336 (1965)] semiempirical expression for each core and valence electron excitation is used. The energy-deposition distribution of keV electrons and the ionization distribution of weakly bound electrons are practically equal, whereas the penetration depth distribution extends deeper into the material than the energy-deposition distribution. The energy-deposition distributions of keV electrons for light materials, except for hydrogen, can be represented quite well by a universal distribution. In addition, accurate Gaussian approximations for the different materials in the entire energy region from 1 to 10 keV have been evaluated. Parameters such as the mean penetration depth and the mean energy-deposition depth are included as well.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 126-134 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Solid samples of pure and doped deuterium were irradiated by keV electrons and the luminescence of these samples was measured between 200 and 700 nm. In order to separate the intrinsic emissions from impurity-induced luminescence, deuterium was doped with standard air impurities like N2, H2O, O2, and CO. In purified solid deuterium, an emission at 275 nm was observed for the first time and attributed to a transition in D*3 molecules produced via ionization of D2, formation of D3+, and subsequent recombination with electrons. Film-thickness dependence as well as timing experiments corroborate this interpretation.
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Weed research 42 (2002), S. 0 
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Summary Stem thickness of the weed Solanum nigrum and the crop sugarbeet was determined with a He–Ne laser using a novel non-destructive technique measuring stem shadow. Thereafter, the stems were cut close to the soil surface with a CO2 laser. Treatments were carried out on pot plants, grown in the greenhouse, at two different growth stages, and plant dry matter was measured 2–5 weeks after treatment. The relationship between plant dry weight and laser energy was analysed using two different non-linear dose–response regression models; one model included stem thickness as a variable, the other did not. A binary model was also tested. The non-linear model incorporating stem thickness described the data best, indicating that it would be possible to optimize laser cutting by measuring stem thickness before cutting. The general tendency was that more energy was needed the thicker the stem. Energy uses on a field scale are discussed.
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  • 4
    Electronic Resource
    Electronic Resource
    Oxford UK : Blackwell Science Ltd
    Weed research 41 (2001), S. 0 
    ISSN: 1365-3180
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Stems of Chenopodium album. and Sinapis arvensis. and leaves of Lolium perenne. were cut with a CO2 laser or with a pair of scissors. Treatments were carried out on greenhouse-grown pot plants at three different growth stages and at two heights. Plant dry matter was measured 2 to 5 weeks after treatment. The relationship between dry weight and laser energy was analysed using a non-linear dose–response regression model. The regression parameters differed significantly between the weed species. At all growth stages and heights S. arvensis was more difficult to cut with a CO2 laser than C. album. When stems were cut below the meristems, 0.9 and 2.3 J mm−1 of CO2 laser energy dose was sufficient to reduce by 90% the biomass of C. album and S. arvensis respectively. Regrowth appeared when dicotyledonous plant stems were cut above meristems, indicating that it is important to cut close to the soil surface to obtain a significant effect. When cutting L. perenne plants with 2-true leaves at a height of 2 cm from the soil surface with a laser, the biomass decreased significantly compared with plants cut by scissors, indicating a delay in regrowth. This delay was not observed for the dicotyledonous plants nor for the other growth stages of L. perenne.
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  • 5
    Electronic Resource
    Electronic Resource
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 31 (1998), S. 647-653 
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The introduction of synchrotron beamlines for high-energy X-ray diffraction raises new possibilities for texture determination of polycrystalline materials. The local texture can be mapped out in three dimensions and texture developments can be studied in situ in complicated environments. However, it is found that a full alignment of the two-dimensional detector used in many cases is impractical and that data-sets are often partially subject to geometric restrictions. Estimating the parameters of the traces of the Debye–Scherrer cones on the detector therefore becomes a concern. Moreover, the background may vary substantially on a local scale as a result of inhomogeneities in the sample environment etc. A set of image-processing tools has been employed to overcome these complications. An automatic procedure for estimating the parameters of the traces (taken as ellipses) is described, based on a combination of a circular Hough transform and nonlinear least-squares fitting. Using the estimated ellipses the background is subtracted and the intensity along the Debye–Scherrer cones is integrated by a combined fit of the local diffraction pattern. The corresponding algorithms are presented together with the necessary coordinate transform for pole-figure determination. The image-processing tools may be useful for the analysis of noisy or partial powder diffraction data-sets in general, provided flat two-dimensional detectors are used.
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillian Magazines Ltd.
    Nature 421 (2003), S. 43-44 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Supergranulation on the surface of the Sun is a pattern of horizontal outflows, outlined by a network of small magnetic features, with a distinct scale of 30 million metres and an apparent lifetime of one day. It is generally believed that supergranulation corresponds to a preferred ...
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 379 (1996), S. 235-237 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The recent discovery2 of how to measure the time taken by acoustic waves to travel inside the Sun is a powerful tool for studying the solar interior. This approach directly measures the travel time of acoustic waves between any point on the solar surface and a surrounding annulus. As a packet of ...
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  • 8
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Surface Science 167 (1986), S. 474-492 
    ISSN: 0039-6028
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Surface Science 125 (1983), S. 355-365 
    ISSN: 0039-6028
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0039-6028
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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