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  • 2000-2004  (97)
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  • 1
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The deformation of 9.4 mol% magnesia-partially-stabilized zirconia under compressive loads up to 1225 MPa was studied using mechanical testing with in situ neutron diffraction. The material shows obvious plastic deformation at applied stresses in excess of an estimated critical stress of 925 ± 20 MPa. Most of the accumulated strain occurred by transient room-temperature creep. Plastic deformation was associated with considerable stress-induced tetragonal-to-monoclinic transformation. The volume change calculated from the strain gauges correlates well with the amount of t→m transformation observed. Unlike previous studies of Ce-TZP and Y-TZP, ferroelasticity was not observed, nor was the t→o transformation observed. Minor microstructural changes were noted, including an increase in the root mean square internal strain of 0.05%, commensurate with an increase in internal stress of ∼100 MPa. It would appear that transformation selectivity was exercised with the transformation occurring first in tetragonal crystallites favorably oriented to the applied stress. The stress-induced monoclinic phase therefore exhibits a strong preferred orientation. Comparison is made with the other commercially interesting zirconia ceramics, Ce-TZP and Y-TZP, which have been studied using the same techniques.
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  • 2
    Electronic Resource
    Electronic Resource
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), S. 0 
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The synthesis of Ti3SiC2 by pressureless reactive sintering of Ti/SiC/C mixtures under an Ar atmosphere has been studied using in situ neutron diffraction. The intermediate phases TiCx and Ti5Si3Cx (x≤ 1) form first at ∼800–1400°C. These phases are consumed in the formation of Ti3SiC2, at ∼1500°C. After sintering, Ti5Si3Cx disappears but an amount of TiCx remains in the sample primarily as a surface layer. The studies appear to support a suggestion that the intermediate phases react to form Ti3SiC2 through a diffusion-controlled process. Prolonged stepwise heating under argon in some experiments resulted in decomposition of Ti3SiC2 above ∼1400°C and significant disproportionation of the sample.
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  • 3
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature biotechnology 19 (2001), S. 1117-1118 
    ISSN: 1546-1696
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: [Auszug] Embryonic stem (ES) cells are renewable pluripotent cells capable of generating any cell type of an organism. ES cell technology in mice has been one of the foundations of modern molecular biology, allowing targeted manipulations of the mouse genome. The recent isolation of human ES cells initiated ...
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  • 4
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature America Inc.
    Nature biotechnology 18 (2000), S. 675-679 
    ISSN: 1546-1696
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: [Auszug] Embryonic stem (ES) cells are clonal cell lines derived from the inner cell mass of the developing blastocyst that can proliferate extensively in vitro and are capable of adopting all the cell fates in a developing embryo. Clinical interest in the use of ES cells has been stimulated by studies ...
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  • 5
    ISSN: 1546-1696
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: [Auszug] Existing protocols for the neural differentiation of mouse embryonic stem (ES) cells require extended in vitro culture, yield variable differentiation results or are limited to the generation of selected neural subtypes. Here we provide a set of coculture conditions that allows rapid and efficient ...
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature biotechnology 22 (2004), S. 435-439 
    ISSN: 1546-1696
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: [Auszug] The purification of nucleic acids from microbial and mammalian cells is a crucial step in many biological and medical applications. We have developed microfluidic chips for automated nucleic acid purification from small numbers of bacterial or mammalian cells. All processes, such as cell isolation, ...
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  • 7
    ISSN: 1434-4475
    Keywords: Keywords. Homogeneous catalysis; Enantioselective hydrogenation; Heterocyclic arenes; Rh diphosphine complexes.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary.  The first case of an enantioselective hydrogenation of monosubstituted pyridines and furans with homogeneous rhodium diphosphine catalysts with low but significant enantioselectivities and catalyst activities is reported. Best enantioselectivities (ees of 24–27%) were obtained for the hydrogenation of 2- and 3-pyridine carboxylic acid ethyl ester and 2-furan carboxylic acid with catalysts prepared in situ from [Rh(nbd)2]BF4 and the chiral ligands diop, binap, or ferrocenyl diphosphines of the josiphos type. Turnover numbers (ton) were in the order of 10–20, turnover frequencies (tof) usually 1–2 h−1. Diphosphines giving 6- or 7-ring chelates led to higher ees than 1,2-diphosphines; otherwise, no clear correlation between ligand properties and catalytic performance was found. In some experiments black precipitates were observed at the end of the reaction, indicating the decomposition of the homogeneous catalysts for certain ligand/metal/substrate combinations.
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 18 (2000), S. 233-240 
    ISSN: 1434-6036
    Keywords: PACS. 75.30.Vn Colossal magnetoresistance - 78.70.Dm X-ray absorption spectra - 75.25.+z Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: X-ray absorption spectroscopy (XAS) and soft-X-ray magnetic circular dichroism (SXMCD) at the Mn L2,3-, Cr L2,3- and O-K edges of Sm0.5Ca0.5Mn1-xCrxO3 ( ) bulk polycrystalline samples have been performed at T=20 K below the ferromagnetic Curie temperature. We show the existence of a magnetic sublattice on each of the probed cations. Considering an electronically phase-separated system, results are compared with magnetization and resistivity measurements and a tentative correlation with magnetoresistance properties on such doped compounds is discussed.
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  • 9
    ISSN: 1434-6036
    Keywords: PACS. 61.80.Jh Ion radiation effects – 75.60.-d Domain effects, magnetization curves, and hysteresis – 85.70.Ge Ferrite and garnet devices
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The behavior of the magnetic properties of magnetite Fe3O4 irradiated by swift heavy ions is investigated by magnetization measurements. Although there is no induced structural phase transformation, both coercive field and saturation magnetization are sensitive to ion irradiation and exhibit different behaviors depending on the ion fluence range. In the low fluence regime, the coercive field increases, which is evidence for a strong pinning of magnetic domain boundaries by the induced defects. The magnetization shows a decrease in the saturation value and tends to reorient perpendicularly to the ion track axis. At high fluence, the initial magnetic properties of the sample are nearly restored. The changes in the magnitude and the direction of magnetization are interpreted by magnetostrictive effects related to the stress induced by irradiation. A phenomenological model is applied to reproduce the fluence evolution of the saturation magnetization, assuming relaxation of the stress induced around the core of defects of the tracks by overlapping effects at high fluence. The results are compared to those obtained in the case of yttrium iron garnet Y3Fe5O12.
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  • 10
    ISSN: 1572-9028
    Keywords: hydrogenation of aromatic nitro compounds ; Raney nickel ; vanadium promoter ; modified catalysts ; aryl hydroxylamine ; chloronitrobenzene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The effect of vanadium promotion of Raney nickel on aryl hydroxylamine accumulation in the catalytic hydrogenation of electron deficient aromatic nitro compounds was investigated. High accumulation of 70–80% was observed with unmodified Raney nickel. Vanadium promoters were able to modulate the accumulation and depending on the modifier used, an increase (up to 86%) or a decrease (down to 11%) was found. Higher rates were obtained in the former (up to a factor 1.3), lower ones in the latter case (down to a factor 0.1) compared to the unmodified system. Supported or unsupported NH4VO3 was usually the most efficient modifier for obtaining low accumulation and reasonable rates, but the optimum concentration and modification procedure had to be determined for every substrate separately. In cases of low accumulation, the vanadium promoters worked as disproportionation catalysts. Dehalogenation was not significantly influenced by the presence of promoters: in all cases dehalogenation took only place after both the nitro arene and aryl hydroxylamine compound had been consumed completely.
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