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  • 1995-1999  (76)
  • 1930-1934  (5)
  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 82 (1997), S. 1876-1881 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The process of ion bombardment is investigated for the fabrication of Mo/Si multilayer x-ray mirrors using e-beam evaporation. The ion treatment is applied immediately after deposition of each of the Si layers to smoothen the layers by removing an additional thickness of the Si layer. In this study the parameters of Kr+ ion bombardment have been optimized within the energy range 300 eV–2 keV and an angular range between 20° and 50°. The optical performance of the Mo/Si multilayers is determined by absolute measurements of the near-normal-incidence reflectivity at 14.4 nm wavelength. The multilayer structures are analyzed further with small-angle reflectivity measurements using both specular reflectivity and diffuse x-ray scattering. The optimal smoothening parameters are obtained by determining the effect of ion bombardment on the interface roughness of the Si layer. The optimal conditions are found to be 2 keV at 50° angle of incidence with respect to the surface. These settings result in 47% reflectivity at 85° (λ=14.4 nm) for a 16-period Mo/Si multilayer mirror, corresponding to an interface roughness of 0.21 nm rms. Analysis shows that the interface roughness is determined by ion induced viscous flow, an effect which increases with ion energy as well as angle of incidence. In order to determine the effect of intermixing of the Si and Mo atoms, the penetration depth of the Kr+ ions is calculated as a function of ion energy and angle of incidence. Furthermore, the angular dependence of the etch yield, obtained from the in situ reflectivity measurements, is investigated in order o determine the optimal ion beam parameters for the production of multilayer mirrors on curved substrates. © 1997 American Institute of Physics.
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 81 (1997), S. 6112-6119 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We discuss a new method to characterize multilayer structures with grazing-incidence reflectivity measurements using hard x-ray radiation, such as Cu-Kα or Mo-Kα radiation. The method is based on the analysis of the reverse Fourier transforms of the reflectivity at the Bragg peaks in q-space, the reflectivity data being obtained from an angular scan (θ−2θ). This method is faster than curve fitting of the reflectivity data, results in an accurate value of the density and thickness of both materials, and needs no pre-assumptions about the material composition and the parameters of the multilayer. The method makes a distinction between interface roughness and layer thickness errors, and is independent of measurement of the critical angle. A minor disadvantage is that only an average value of the layer thickness is determined, rather than the individual layer thicknesses. As an example our method is used to analyze small-angle reflectivity measurements of Mo/Si and Co/C multilayers. The parameters thus obtained are used to model a structure, which is subsequently used to predict the near-normal incidence reflectivity at soft x-ray wavelengths. The accuracy thus found corresponds to a relative error of 5%. The densities of a Mo/Si multilayer are determined independently with critical angle measurements to verify the values obtained from the grazing incidence reflectivity measurements. The results of the analysis of the Co/C multilayer are compared to values obtained using a conventional method based on the kinematical theory. However, the conventional method requires additional data of soft x-ray reflectivity measurements. The new method yields the same values for the multilayer parameters but does not require the extra soft x-ray measurements. © 1997 American Institute of Physics.
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  • 3
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Industrial & engineering chemistry 25 (1933), S. 184-187 
    ISSN: 1520-5045
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 4700-4708 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: To optimize the growth process of Mo/Si multilayers, the effect of an elevated substrate temperature during deposition has been studied in the temperature range between 300 K and 550 K. Multilayer properties, such as interface roughness, d-spacing, and structure of the layers, have been investigated during deposition and cool-down, after cool-down, and during heating. A number of techniques have been used: small-angle, near-normal incidence, and in situ reflectivity measurements. It is found that the increased substrate temperature changes the interface roughness to a minimum value for samples produced at 488 K. Also, a change of the d-spacing as a function of time and temperature is observed and is explained by annihilation of free volume of the Si layer. The atomic structures of the layers deposited at different temperatures have been analyzed with high resolution electron microscopy (TEM), which shows that both materials are amorphous for the entire temperature range investigated. At the extremes of the temperature range investigated irregular layer structures, such as ripples and V-shaped structures, have been observed by TEM. © 1998 American Institute of Physics.
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  • 5
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Industrial and engineering chemistry 3 (1931), S. 253-254 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 6
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    Industrial and engineering chemistry 3 (1931), S. 254-255 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
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  • 7
    ISSN: 1617-4623
    Keywords: Key words Genetic recombination ; Ribosomal DNA ; Topoisomerase II ; Radiation ; Genome instability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Pat1 protein of Saccharomyces cerevisiae was identified during a screen for proteins that interact with topoisomerase II. Previously, we have shown that pat1Δ mutants exhibit a slow-growth phenotype and an elevated frequency of both mitotic and meiotic chromosome mis-segregation. Here, we have studied the effects of deleting the PAT1 gene on chromosomal stability, with particular reference to rates of homologous recombination within the rDNA locus. This locus was analyzed because rDNA-specific hyperrecombination is known to occur in conditional top2 mutants. We show that pat1Δ strains mimic top2 mutants in displaying an elevated rate of intrachromosomal excision recombination at the rDNA locus, but not elsewhere in the genome. The elevated rate of recombination is dependent upon Rad52p, but not upon Rad51p or Rad54p. However, pat1Δ strains display additional manifestations of more general genomic instability, in that they show mild sensitivity to UV light and an increased incidence of interchromosomal recombination between heteroalleles.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 1 (1998), S. 123-127 
    ISSN: 1434-6036
    Keywords: PACS. 47.20.-k Hydrodynamics stability - 68.10.-m Fluid surfaces and fluid-fluid interfaces
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The first stages of finger formation in a Hele-Shaw cell with lifting plates are investigated by means of linear stability analysis. At the beginning of lifting the square of the wavenumber of the dominant mode results to be proportional to the lifting rate (in qualitative agreement with the available experimental data), to the square of the length of the cell occupied by the more viscous fluid, and inversely proportional to the cube of the cell gap. This dependence on the cell parameters is significantly different of that found in the standard cell. On the other hand, our results show that the wavelength of the dominant mode decreases with lifting time, also in agreement with several experimental observations.
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  • 9
    ISSN: 1572-8889
    Keywords: Cotesia glomerata ; C. rubecula ; Pieris ; Mamestra ; Plutella ; crucifers ; Brassica ; Tropaeolum ; Crataegus ; parasitoid ; foraging behavior ; infochemical ; olfaction ; preferences
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract To determine and compare innate preferences of the parasitoid speciesCotesia glomerata andC. rubecula for different plant-herbivore complexes, long-range (1-m) foraging behavior was studied in dual-choice experiments in a wind tunnel. In this study we tested the hypothesis that naive females of the specialistC. rubecula should show more pronounced preferences for different plant-herbivore complexes than females of the generalistC. glomerata. The herbivore species used were the pieridsPieris brassicae, P. rapae, P. Napi, andAporia crataegi and the nonhostsPlutella xylostella andMamestra brassicae. All herbivore species feed mainly on cabbage and wild crucifers, exceptAporia crataegi, which feeds on species of Rosaceae. Both parasitoid species preferred herbivore-damaged plants over nondamaged plants. NeitherC. rubecula norC. glomerata discriminated between plants infested by different caterpillar species, not even between plants infested by host-and nonhost species. Both parasitoid species showed preferences for certain cabbage cultivars and plant species. No differences were found in innate host-searching behavior betweenC. glomerata andC. rubecula. The tritrophic system cabbage-caterpillars-Cotesia sp. seems to lack specificity on the herbivore level, whereas on the plant level differences in attractiveness to parasitoids were found.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Acta informatica 32 (1995), S. 189-207 
    ISSN: 1432-0525
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Notes: Abstract We investigate the property of self-stabilization in bounded Petri nets. We give characterizations for both self-stabilizing bounded ordinary Petri nets (i.e., Petri nets without multiple arcs) and self-stabilizing bounded general Petri nets (i.e., Petri nets with multiple arcs). These characterizations allow us to determine the complexity of deciding self-stabilization for each of these classes. In particular, we show the self-stabilization problem to be PTIME-complete for bounded ordinary Petri nets and PSPACE-complete for bounded general Petri nets.
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