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  • 1
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    German Medical Science GMS Publishing House; Düsseldorf
    In:  16. Deutscher Kongress für Versorgungsforschung (DKVF); 20171004-20171006; Berlin; DOCP061 /20170926/
    Publication Date: 2017-09-26
    Keywords: ddc: 610
    Language: German
    Type: conferenceObject
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  • 2
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    German Medical Science; Düsseldorf, Köln
    In:  Deutscher Kongress für Orthopädie und Unfallchirurgie; 70. Jahrestagung der Deutschen Gesellschaft für Unfallchirurgie, 92. Tagung der Deutschen Gesellschaft für Orthopädie und Orthopädische Chirurgie und 47. Tagung des Berufsverbandes der Fachärzte für Orthopädie; 20061002-20061006; Berlin; DOCW.4.2.1-1822 /20060928/
    Publication Date: 2007-03-09
    Keywords: ddc: 610
    Language: German
    Type: conferenceObject
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  • 3
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The article presents single step and cascade methods for converting the femtosecond radiation from a 1 kHz repetition rate Ti:sapphire regenerative amplifier to the near-infrared (1.2–1.5 μm and 1.6–2.2 μm), visible (554–593 nm), and for the first time to our knowledge to the vacuum ultraviolet spectral region well below 190 nm. Using only solid state materials (nonlinear optical crystals) femtosecond pulses are generated through phase-matched mixing processes down to 172.7 nm. The developed scheme for femtosecond parametric conversion provides nearly bandwidth limited femtosecond pulses, whose duration is comparable or even shorter than that of the pump pulses. The temporal gain narrowing in the optical parametric amplifier is identified as a pulse compression mechanism on the femtosecond time scale leading to generation of infrared light pulses as short as ≈50 fs. As a whole our all-solid state laser complex provides independently tunable and synchronized sub-200 fs light pulses simultaneously at several wavelengths and practically without relative jitter. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0044-2313
    Keywords: Chemistry ; Inorganic Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: At pressures up to 30 kb and temperatures of 1000-1500°C up to 25% of the Al3+ in the Al2SiO2-polymorph kyanite could be replaced by Cr3+ (composition (Al1.5Cr0.5)SiO5). The lattice constants a0, b0, c0 increase by this substitution, whereas the triclinic angles α, β, γ remain virtually unaffected. Cr3+ substitutes for Al in the chains of (AlO3+)-octahedra parallel to c0. The reflectance spectrum (240-1000 nm) exhibits the spin-forbidden ruby lines in addition to the spin-allowed transitions in Cr3+ in octahedral coordination. The half width (∼3.8 kK), position, and shape of the 10 Dq band indicates a symmetry not higher than D4h for the Cr3+-containing octahedra which is in accordance with structure refinement data for pure Kyanite (Burnham 1963).
    Notes: Bei Drücken bis zu 30 kb und Temperaturen von 1000-1500°C konnte in der Al2SiO5-Modifikation Disthen (Kyanit) Al3+ durch Cr3+ bis zu einer Zusammensetzung (Al1,5Cr0,5)SiO5 substituiert werden. Die Gitterkonstanten ao, bo, co steigen im Verlauf der Substitution an, die triklinen Achsenwinkel α, β, γ bleiben praktisch unverändert. Cr3+ wird in die co-parallelen Oktaederketten der Struktur eingebaut. Das Remissionsspektrum (240-1000 nm) zeigt außer den erlaubten d-d Übergängen des Cr3+ in oktaedrischer Koordination auch Interkombinationsbanden. Die Halbwertsbreite (∼ 3,8 kK), Lage und Gestalt der 10 Dq-Bande weist auf eine Symmetrie nicht höher als D4h der Cr3+-haltigen Oktaeder hin. Dies ist in Übereinstimmung mit der Strukturverfeinerung des reinen Disthens (Burnham 1963).
    Additional Material: 5 Ill.
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  • 5
    ISSN: 1432-2021
    Keywords: Key words Chromous silicate ; High-pressure ; Crystal chemistry ; Chromium dimer ; Metal-metal bonding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract The high-pressure behaviour of chromous orthosilicate, Cr2SiO4, has been studied by means of single-crystal X-ray diffraction and electronic absorption spectroscopy. X-ray diffraction data show that the structure remains orthorhombic to the highest pressure reached of 9.22 GPa. The compressibility of the unit-cell is strongly anisotropic with the c axis approximately six times more compressible than the a and b axes. A third-order Birch-Murnaghan equation of state fitted to the volume-pressure data yields V 0 = 610.10(3) Å3, K = 94.7(4) GPa, K′ = 8.32(14). Cr2SiO4 is therefore more compressible than the isostructural Cd analogue, even though its molar volume is smaller. This unusual behaviour can be attributed to the fact that the Cr atom is too small for the six-coordinated site that it occupies, and the site is therefore strongly distorted. Structure refinements indicate that under high pressures the Cr atom remains strongly displaced from the central position of the octahedron. Polarized and unpolarized electronic absorption spectra include a strong absorption band occuring at 18.300 cm−1 for E//c (which is parallel to the shortest Cr-Cr vector in the structure) which has an unusually large half width (5000 cm−1), indicative of electronic interaction between metal centres. Deconvolution of unpolarized high-pressure spectra show that the relative integrated intensity of this component increases linearly from 40% at 1 bar to 60% at 11.2 GPa. Both the structural changes and the absorption spectra at high pressures suggest that pairs of adjacent Cr atoms in chromous orthosilicate form chromium dimers with a weak metal-metal bond, which is consistent with the diamagnetic response found at ambient pressure.
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  • 6
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Synthetic melilites on the join Ca2MgSi2O7 (åkermanite) — Ca2FeSi2O7 (iron åkermanite) with Fe/(Fe+Mg) from 0.0 to 0.7 exhibit, at room temperature, an incommensurate phase with a rectangular modulation of a wavelength of about 19 Å in the [110] direction. Upon increase of temperature, they transform to a commensurate melilite structure at about 80° C for Fe/(Fe+Mg)=0.0 and about 250° C for Fe/(Fe+Mg)=0.6. In addition to the T(2) positions of the melilite structure filled by Si, the incommensurate phase exhibits two distinguishable T(1) sites containing the Mg and Fe2+. These two sites merge into one site during the phase transition from the incommensurate to the commensurate phase. A structural model for the incommensurate phase is based on the misfit between the tetrahedral (Mg, Fe2+)Si2O 7 4− sheets and the Ca2+ ions.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Physics and chemistry of minerals 15 (1988), S. 417-418 
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
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  • 8
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Cr2SiO4 has been prepared both as quench crystals and as an apparently stable subsolidus phase, at T=1600 and 1650 °C, P=37 kbar on Cr2SiO4 and Cr-SiO3 bulk compositions. Crystal structure determination by Rietveld analysis of X-ray powder data from 3 samples show the structure, in space group Fddd, to be related to that of Cd2SiO4 (thenardite Na2SO4-V structure) but with approximately “square planar” coordination of the Cr2+ (d 4) atom. In one of the axial ligand positions, normal to the strongly bonded CrO4 equatorial plane, is found a Cr atom (Cr-Cr=2.75 Å). Stereochemistry permits this contact to be a weak metal-metal bond, though it cannot be ruled out to be a non-bonded result of polyhedral connectivity.
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  • 9
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract Ti K-edge XANES spectra have been collected on a series of Ti-bearing silicate glasses with metasilicate and tetrasilicate compositions. The intensity of the preedge feature in these spectra has been found to change with glass composition and varies from 29 to 58% (normalized intensity) suggesting a variation in structural environent around the absorbing atom. The pre-edge peak intensity increases for the alkali titanium tetrasilicate glasses from 35% to 58% in the order Li 〈 Na 〈 K 〈 Rb, Cs whereas for the metasilicate compositions there is a maximum for the K-bearing glass. The pre-edge peak intensity remains constant for the alkaline earth titanium metasilicate glasses, Ca and Sr (34%) but increases slightly for Ba (41%). As the intensity of this feature is inversely correlated with coordination number, a comparison of the pre-edge intensity data for the investigated glasses with those of materials of known coordination number leads us to establish a regression equation and to infer that the average coordination number of Ti in these glasses ranges from 4.8 to 5.8. Large alkali cations appear to stabilize a relatively low average coordination number for Ti in silicate melts. The Ti structural environment results appear also to vary as a function of SiO2 content within the K2O-TiO2-SiO2 system. A number of physical properties of the melts from which these glasses were quenched and of other Ti-bearing silicate melts, have been determined in recent years. Clear evidence of a variable coordination number of Ti, consistent with the interpretation of the present XANES data is available from density measurements. These and other property determinations are compared with the present spectroscopic observations in an attempt to relate structure and properties in these melts which contain a major component with variable coordination number.
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  • 10
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  Garnets along the join Mg4Si4O12 (majorite end member) – Mg3Al2Si3O12 (pyrope) synthesized at 2000 °C, 19 GPa are, after quench, tetragonal in the compositional range up to 20 mol% pyrope, but cubic at higher Al contents. Lattice constants a tet and a tet in the tetragonal compositional range converge with increasing pyrope contents towards the lattice constant of the cubic garnets. The elastic strain and the intensity of the (222) reflection as a function of composition indicate a second-order phase transition near 20 mol% pyrope. From the wedge-like shape of pseudomerohedral twins and their interaction near 90° twin-boundary corners, as well as from the absence of growth-induced dislocations, it is concluded that the Al-poor garnets are also cubic at synthesis conditions but invert by (Mg,Si) ordering on the octahedral sites into tetragonal phases of space group I41/a upon quench. This implies that the cubic-to-tetragonal phase transition in Mg4Si4O12 garnet occurs below 2000 °C at 19 GPa and at even lower temperatures in more aluminous compositions. A composition-dependent Landau model is consistent with a direct transformation from Ia3d to I41/a. Comparison of the T-X stability field of majorite-pyrope garnets with the chemistry of majorite-rich garnets expected to occur in the Earth's transition zone shows that the latter will be cubic under all conditions. Softening of elastic constants, which commonly accompanies ferroelastic phase transitions, may affect the seismic velocities of garnets in the deeper transition zone where majorite contents are highest.
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