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  • 1
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The timing of early human dispersal to Asia is a central issue in the study of human evolution. Excavations in predominantly lacustrine sediments at Majuangou, Nihewan basin, north China, uncovered four layers of indisputable hominin stone tools. Here we report magnetostratigraphic results that ...
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillian Magazines Ltd.
    Nature 410 (2001), S. 565-567 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] When a force deforms an elastic object, practical experience suggests that the resulting displacement will be in the same direction as the force. This property is known as positive stiffness. Less familiar is the concept of negative stiffness, where the deforming force and the resulting ...
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillian Magazines Ltd.
    Nature 423 (2003), S. 974-976 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Transient luminous events in the atmosphere, such as lighting-induced sprites and upwardly discharging blue jets, were discovered recently in the region between thunderclouds and the ionosphere. In the conventional picture, the main components of Earth's global electric circuit include ...
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  • 4
    ISSN: 1572-8862
    Keywords: silicon nanoparticles ; nanoclusters ; photoluminescence ; TEM
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Photoluminescence (PL) from alkyl-terminated silicon nanocrystallites as a function of size has been studied. Ultraviolet–blue luminescence (390–410 nm) is observed from as-prepared silicon nanoclusters with diameters from 3 to 8 nm. After 1 h of annealing at 162°C in 2-methoxyethyl ether (diglyme), the λ max of PL shifts from 360 to 420 nm. High-resolution transmission electron microscopy (HRTEM) images show that individual silicon nanoparticles are fused to form pairs of nanoparticles. FTIR spectra show that the alkyl groups remain on the surface of silicon nanoparticles. As the temperature is raised to 250°C for 1 h, the PL no longer shows any peak in the visible light region. TEM images show that the silicon nanoparticles are aggregated and fused uniformly in one single dimension, to form a strip, and these strips parallel each other. When the temperature is raised to 350°C these silicon nanoparticles form a large piece of silicon textile network, showing that functionalized alkyl surface does not persist above this temperature. A strong Si–O–Si asymmetric stretching vibration appears between 1000 and 1100 cm−1 at the expense of the C–H vibrational modes and there is no more change after 3 h of annealing at 250 or 350°C. These results provide strong evidence that the PL originates from quantum confinement.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 14 (1995), S. 460-463 
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 6
    ISSN: 1435-1536
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
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  • 7
    ISSN: 1573-5036
    Keywords: chelate ; ecology ; membrane transport ; plant iron nutrition ; plant-microbial interactions ; rhizosphere
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Most bacteria, fungi, and some plants respond to Fe stress by the induction of high-affinity Fe transport systems that utilize biosyrthetic chelates called siderophores. To competitively acquire Fe, some microbes have transport systems that enable them to use other siderophore types in addition to their own. Bacteria such as Escherichia coli achieve this ability by using a combination of separate siderophore receptors and transporters, whereas other microbial species, such as Streptomyces pilosus, use a low specificity, high-affinity transport system that recognizes more than one siderophore type. By either strategy, such versatility may provide an advantage under Fe-limiting conditions; allowing use of siderophores produced at another organism's expense, or Fe acquisition from siderophores that could otherwise sequester Fe in an unavailable form. Plants that use microbial siderophores may also be more Fe efficient by virtue of their ability to use a variety of Fe sources under different soil conditions. Results of our research examining Fe transport by oat indicate parity in plant and microbial requirements for Fe and suggest that siderophores produced by root-colonizing microbes may provide Fe to plants that can use the predominant siderophore types. In conjunction with transport mechanisms, ecological and soil chemical factors can influence the efficacy of siderophores and phytosiderophores. A model presented here attempts to incorporate these factors to predict conditions that may govern competition for Fe in the plant rhizosphere. Possibly such competition has been a factor in the evolution of broad transport capabilities for different siderophores by microorganisms and plants.
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  • 8
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract High-dose chromium implantation resulted in complex changes in the structure, chemistry, and oxidation behaviour of beta-type single-crystal silicon carbide. Detailed analytical studies indicated that, in addition to the primary process of surface doping, chromium implantation of silicon carbide to 3.90×1017 ions cm−2 at 200 keV was accompanied by many secondary processes such as surface sputtering, lattice damaging, and silicon depletion/carbon enrichment in the implanted region. These changes resulted in accelerated oxidation of the implanted samples by a factor of 1.14 as compared with the unimplanted crystals in 1 atm of flowing oxygen at 1100°C. The oxidation layer exhibited interesting structural and compositional inhomogeneity which could be explained based upon chromium mobility variation in the implanted region. The presence of densely populated chromium oxide precipitates in the outer region of the oxidation layer played a significant role in keeping the degree of oxidation acceleration low under the detrimental influence of lattice damages and silicon deletion/carbon enrichment. It was concluded that the potential of chromium implantation to improve the oxidation resistance of silicon carbide can be realized only when the implantation-induced secondary effects are suppressed.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    International journal of fracture 52 (1991), S. 293-306 
    ISSN: 1573-2673
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The deformation field near the tip of a tensional crack impinging upon a normally loaded bimaterial frictional interface is studied. By allowing the two materials to slide with respect to each other along the interface the high stresses around the crack tip are relaxed. The region of slip as well as the stress distribution inside the slip zone is obtained as a function of the far field loading parameter.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Experimental mechanics 25 (1985), S. 251-254 
    ISSN: 1741-2765
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The analogy used to solve some thermoelastic problems is extended to include a region with an eccentric hole. The relation is shown to be a little more complicated in this case than in the one for the concentric hole. Three bending tests of an analogous thin plate are required. As an experimental proof, an eccentric circular region is considered and mental proof, an eccentric circular region is considered and the analogous thin plate is prepared. The heat-conduction equation is first solved to give the required temperature terms. The measured strains on the plate and the coefficients specified from the transverse loads and moments applied to the plate are combined effectively to get the estimated thermal stress. The experimentally estimated thermal stress of the region and the numerical result are shown to be in agreement.
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