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  • 1
    ISSN: 0273-1177
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1434-6036
    Keywords: PACS. 68.43.-h Chemisorption/physisorption: adsorbates on surfaces – 81.07.Pr Organic-inorganic hybrid nanostructures – 81.16.Be Chemical synthesis methods
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: Nano-sized cobalt clusters passivated by alkane-thiol molecules were obtained by the action of concentrated thiol solutions on micrometric cobalt particles. Thiol molecules caused an erosive process on the metal grains with the consequent formation of nano-sized metal debris and cobalt thiolate as by-product. The final material microstructure was composed by cobalt clusters embedded into a continuum cobalt thiolate matrix. Depending on the thiol molecule length, the material texture ranged from rubbery to waxy. These new types of nanocomposite materials were found to be crystalline, thermally stable up to ca. 300 °C, intensely red colored, and high hydrophobic. In addition, they generated polymeric structures when dissolved in non-polar solvents.
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  • 3
    ISSN: 1434-6036
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. In order to obtain faster hydrogen sorption kinetics, MgH2-Fe nanocomposites were prepared by high-energy ball milling. The MgH2 decomposition was studied in samples obtained by changing in a systematic way both the catalyst amount and the degree of microstructural refinement. To this purpose, blends containing increasing Fe concentration have been ball milled in processing conditions able to impart different amount of structural defects. The resulting samples have been characterized by X-ray diffraction to investigate the microstructural features and the phase composition, while the powder morphology and the degree of catalyst dispersion were analyzed by scanning electron microscopy. Differential scanning calorimetry was carried out to characterize the hydrogen desorption behavior of these nanocomposites. Experimental results clearly show that the characteristics of the desorption process are dominated, among other factors, by the morphology of the catalyst dispersion, which in turns depends on the processing conditions and blend composition. In order to achieve low desorption temperatures the homogeneous catalyst dispersion in micron-size particles throughout the structure is required. This condition can be achieved by suitable tuning of the milling conditions and of the catalyst amount.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0020-1693
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Micrometric, irregularly shaped Fe particles with a nanocrystalline structure have been prepared by mechanical attrition through ball-milling. Electron holography has been employed to visualize the stray field emerging from isolated Fe particles, both at 300 K and at selected temperatures T≤1200 K, from which indirect information on the magnetic domain configuration has been inferred. By complementary x-ray diffraction and transmission electron microscopy investigations a relationship has been established between the changes of the leakage field and of the microstructure upon annealing: it indicates that the structural evolution is accompanied by strong modifications in the interior magnetization pattern. This relationship finds explanation in the framework of the random anisotropy model, including temperature-induced reversible variations in the exchange correlation length and saturation magnetization. Moreover, the role played by the overall geometrical features of the particles in the determination of the actual domain configuration has been investigated. © 2001 American Institute of Physics.
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 2148-2152 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An automatic vibrating reed apparatus for internal friction and elastic modulus measurements in solids is described. The apparatus is equipped with a resistive heater for measurements up to 1400 K. A magnetic field (up to 250 kAt/m) is also available in the 300–1000 K range. Measurements as a function of temperature and/or magnetic field can be easily carried out. Data acquisition is controlled by a computer and originally written software allows automatic measurements and real time data analysis offering a user-friendly interface. The acquisition rate is nearly two orders of magnitude faster than that achieved manually. The use of the analyzer is straightforward and does not require a prolonged training of particularly skillful personnel. © 2001 American Institute of Physics.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 4219-4226 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nanocrystalline nickel was prepared by a planetary ball milling apparatus working in a vacuum of 10−4 Pa in the 150–300 K temperature range. The kinetic of the milling process and the microstructure evolution upon annealing were followed by x-ray diffraction and mechanical spectroscopy measurements. It was observed that thermal annealing up to 600 K induces a strong reduction of the internal strains without significant grain growth. Measurements of elastic energy dissipation and dynamic elastic modulus as a function of temperature showed that in the nanocrystalline samples, anelastic relaxation processes occur, with the activation energy of grain boundary diffusion. A systematic study of the magnetic field dependence of the dynamic modulus (ΔE effect) revealed a correlation between the ΔE magnitude and the strain values obtained by x-ray diffraction analysis. © 1998 American Institute of Physics.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Numerische Mathematik 86 (2000), S. 507-538 
    ISSN: 0945-3245
    Keywords: Mathematics Subject Classification (1991): 65F15, 65F30, 65H20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary. A general method for approximating polynomial solutions of second-order linear homogeneous differential equations with polynomial coefficients is applied to the case of the families of differential equations defining the generalized Bessel polynomials, and an algorithm is derived for simultaneously finding their zeros. Then a comparison with several alternative algorithms is carried out. It shows that the computational problem of approximating the zeros of the generalized Bessel polynomials is not an easy matter at all and that the only algorithm able to give an accurate solution seems to be the one presented in this paper.
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  • 9
    ISSN: 1572-946X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper we present the first results of the analysis of intermediate resolution (Δλ ∼ 3.5 Å) spectra of giants of the Sagittarius dwarf galaxy acquired using the ESO NTT telescope. From the deep CCD photometry of Marconi et al. (1998a) we have selected a sample of giants representative of the metallicity spread suggested by the comparison of the colour-magnitude diagram of Sagittarius with those of galactic globular clusters. The spectra have been used to measure radial velocities, to confirm the membership to Sagittarius, and to provide a metallicity estimate by using spectral synthesis techniques. The analyzed stars show a spread in metallicities in the range −1.0≤ [Fe/H]≤ +0.7, some 0.5 dex more metal-rich than the photometric estimates.
    Type of Medium: Electronic Resource
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  • 10
    Publication Date: 2013-12-23
    Description: We have used archival Hubble Space Telescope observations obtained with the Advanced Camera for Surveys to study the Hα emission properties of main-sequence stars in the globular cluster 47 Tucanae. Using a combination of multiband observations in the F 606 W , F 814 W and F 658 N bands, we search for stars showing Hα excess emission. An accurate photometric measurement of their Hα equivalent width allows us to identify objects with large Hα emission, which we attribute to mass accretion rather than enhanced chromospheric activity. The spatial position of some of these stars is coincident with that of known X-ray sources, and their location in the colour–magnitude diagram allows us to classify them as active binaries or cataclysmic variables (CVs). We show that this method, commonly adopted to study accreting discs in young stellar objects, can be successfully used to identify and characterize candidate CVs.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
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