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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Discrete & computational geometry 22 (1999), S. 297-315 
    ISSN: 1432-0444
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mathematics
    Notes: Abstract. We present an easy to survey constructive method using only basic mathematics which allows us to define a homeomorphism between any compact real algebraic variety and some components of the configuration space of a mechanical linkage. The aim is to imitate addition and multiplication in the framework of weighted graphs in the euclidean plane that permit a ``mechanical description'' of polynomial functions, and thus of varieties.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-2099
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract A temporary increase in the incidence of infant leukaemia in Greece was reported by Petridou et al., which was attributed to in utero exposure to ionising radiation resulting from the Chernobyl accident. We performed a similar analysis based on the data of the German Childhood Cancer Registry in order to check whether the observation could be confirmed by means of independent data. Applying the same definitions as Petridou et al., we also observed an increased incidence of infant leukaemia in a cohort of children born after the Chernobyl accident. More detailed analyses, regarding areas with different contamination levels and dose rate gradients over time after the accident, showed, however, no clear trend with regard to exposure. It would therefore appear less likely that the observed effect was caused by exposure to ionising radiation due to the Chernobyl accident.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 62 (1996), S. 181-185 
    ISSN: 1432-0630
    Keywords: 72.70 ; 85.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Heterojunctions, such as ZnO/CdS/CuGaSe2, were fabricated for photovoltaic applications. Optimization of device structures based on monocrystalline CuGaSe2 led to the highest-to-date power conversion efficiencies for CuGaSe2 solar cells. At room temperature under 100 mW/cm2 AM1.5 illumination a maximum cell efficiency of 9.7% was achieved, given by an open-circuit voltage of 946 mV, a short circuit current density of 15.5 mA/cm2, and a fill factor of 66.5%. Preparation and performance of the optimum device are described. Current voltage characteristics dependent on illumination intensity and temperature, spectral response and electron-beam-induced current measurements were performed to determine the device parameters as well as to analyse the current transport and loss mechanisms. Tunneling, assisted by defect levels in the CdS layer, seems to play a major role. High injection effects are observed at forward bias ofV 〉 0.5 V or an illumination level ofP 〉 10 mW/cm2. Under such conditions, as well as at low temperatures, the non-zero series resistance comes into play. Effects of the shunt resistance, however, are negligible in all cases.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 62 (1996), S. 181-185 
    ISSN: 1432-0630
    Keywords: PACS: 72.70; 85.60
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract.  Heterojunctions, such as ZnO/CdS/CuGaSe2, were fabricated for photovoltaic applications. Optimization of device structures based on monocrystalline CuGaSe2 led to the highest-to-date power conversion efficiencies for CuGaSe2 solar cells. At room temperature under 100 mW/cm2 AM1.5 illumination a maximum cell efficiency of 9.7% was achieved, given by an open-circuit voltage of 946 mV, a short circuit current density of 15.5 mA/cm2, and a fill factor of 66.5%. Preparation and performance of the optimum device are described. Current voltage characteristics dependent on illumination intensity and temperature, spectral response and electron-beam-induced current measurements were performed to determine the device parameters as well as to analyse the current transport and loss mechanisms. Tunneling, assisted by defect levels in the CdS layer, seems to play a major role. High injection effects are observed at forward bias of V〉0.5 V or an illumination level of P〉10 mW/cm2. Under such conditions, as well as at low temperatures, the non-zero series resistance comes into play. Effects of the shunt resistance, however, are negligible in all cases.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-0630
    Keywords: PACS: 61.16.Ch; 68.35.Bs
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: 2 ) has been investigated by contact-mode atomic force microscopy (AFM) in air. Both the terraces and the monolayer step itself were reproducibly imaged at atomic resolution in the repulsive-force regime at forces between tip apex and sample of the order of 10-9 N. Several kinks were also imaged at atomic resolution. Details of the atomic registry of subsequent Se-Nb-Se sandwich layers as well as the arrangement of the individual atoms at the kink sites were resolved. The results are in perfect quantitative agreement with the lattice structure known from X-ray analysis and indicate that true atom-by-atom lateral resolution of microscopic defects is feasible by AFM in the contact mode and under ambient conditions.
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  • 6
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using neutron diffraction (ND), muon-spin rotation/relaxation (μSR), and57Fe-Mössbauer spectroscopy (MS) we have investigated magnetic properties of the normal spinel (Zn)[Fe2]O4. In compounds which are slowly cooled from 1200°C to room temperature inversion is below detection limits. AtT N = 10.5 K the spinel exhibits long-range antiferromagnetic order (LRO). The transition as seen in thermal-scan spectra by MS is very sharp. However, ND andμSR experiments show that already at temperatures of ∼ 10T N a short-range antiferromagnetic ordering (SRO) develops which extends through ∼70% of the sample volume just aboveT N . BelowT N SRO and LRO coexist. At 4.2 K still ∼25% of the sample is short-range ordered. The regions over which the SRO extends have a size of ∼ 3 nm. Their fluctuation rates are in the GHz range. Modern ab initio cluster calculations successfully describe the magnetic hyperfine fields as well as the electric field gradient (EFG) tensor at the Fe sites. Covalency of the Fe-O and Zn-O bonds is important. The physical origin of the regions exhibiting SRO, however, remains unresolved at this point.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Using the 93.31 keV Mössbauer transition in67Zn we have investigated hyperfine interactions and lattice-dynamic effects of nanostructured hexagonal (wurtzite) ZnO. The nanocrystals with particle sizes between 3 and 30 ran were produced by a reactive-gas sublimation method and were subsequently compacted into solid bodies under external pressure. The nanocrystalline materials were used as sources in Mössbauer emission experiments. A drastic increase of the asymmetry parameter was found fromη=0 (single crystal) toη≈0.5 (nanostructured material). Our theoretical Hartree-Fock cluster calculations show that displacements of the Zn atoms off the hexagonal symmetry axis as small as 0.005 Å can lead to such enhancedη parameters. The Lamb-Mössbauer factorf drastically drops when the particle size is reduced below ∼ 10 nm. Two lattice-dynamic models are discussed which successfully describe this behavior.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Plant systematics and evolution 78 (1929), S. 284-288 
    ISSN: 1615-6110
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Plant systematics and evolution 77 (1928), S. 227-238 
    ISSN: 1615-6110
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Plant systematics and evolution 77 (1928), S. 68-76 
    ISSN: 1615-6110
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
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