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  • 1
    Digitale Medien
    Digitale Medien
    Lattice instability at a fast moving crack tip (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4332-4336 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A molecular dynamics method is used to analyze the dynamic propagation of an atomistic crack tip. The simulation shows that the crack propagates at a relatively constant global velocity which is well below the Rayleigh wave velocity. However the local propagation velocity oscillates violently, and it is limited by the longitudinal wave velocity. The crack velocity oscillation is caused by a repeated process of crack tip blunting and sharpening. When the crack tip opening displacement exceeds a certain critical value, a lattice instability takes place and results in dislocation emissions from the crack tip. Based on this concept, a criterion for dislocation emission from a moving crack tip is proposed. The simulation also identifies the emitted dislocation as a source for microcrack nucleation. A simple method is used to examine this nucleation process. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.363383
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  • 2
    Digitale Medien
    Digitale Medien
    Simulation of nucleation and emission of dislocations by molecular-dynamics method (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 2393-2399 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The nucleation and emission of dislocations from the crack tip under mode II loading are analyzed by the molecular-dynamics method in which the Finnis–Sinclair potential has been used. A suitable atom lattice configuration is employed to allow one to fully analyze the nucleation, emission, dissociation, and pileup of the dislocations. The calculated results show that although the pure mode II loading is applied, the crack tip generally exhibits a combined mode. The stress distributions before the dislocation emission are in agreement with the elasticity solution, but are not after the emission. The critical stress intensity factor corresponding to the dislocation nucleation KIIe is dependent on the loading rate K(overdot)II. The separations of a pair of partial dislocations and the full dislocations are also dependent on the loading rate. When the first partial dislocation is blocked, a pileup of dislocations can be set up. It is also found that the dislocation can move at subsonic wave speed (less than the shear wave speed) or at transonic speed (greater than the shear wave speed but less than the longitudinal wave speed) depending on the loading rate, but at the longitudinal wave speed which just corresponds to K(overdot)II=1.15 MPa (square root of)m/ps for copper, the atom lattice breaks down. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.358764
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  • 3
    Digitale Medien
    Digitale Medien
    Anisotropy dependence of the focused field radiated into a piezoelectric half-space by an interdigital transducer (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 52 (1988), S. 456-458 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Bulk waves radiated into an anisotropic half-space by an interdigital transducer are studied theoretically. The mechanical displacements of excited waves are obtained by asymptotic evaluation of an integral whose singularities give rise to both Rayleigh surface waves and angularly focused bulk waves. By applying the analysis to singly rotated Y cuts of quartz with propagation normal to the x axis, it is shown that the orientation and width of the main lobe are very sensitive to frequency and crystal orientation.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.99442
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  • 4
    Digitale Medien
    Digitale Medien
    Formation of epitaxially strained islands by controlled annealing (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 205-207 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A three-dimensional continuum method is developed to simulate the formation of epitaxially strained islands during controlled annealing. In the formulation, the strain energy density, surface energy and surface energy anisotropy are taken into account. Our simulations show that no surface energy anisotropy leads to spherical caps while high anisotropy leads to elongated islands. Under the present framework, a relatively uniform and regular island array can be obtained at a certain annealing time from a random surface. An almost perfectly uniform and regular island array can be obtained at a certain annealing time from a random surface with one dominant wavelength, which is in a specific range; for long-time annealing, these island arrays are undergoing ripening. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.124320
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  • 5
    Digitale Medien
    Digitale Medien
    Vertical self-alignment of quantum dots in superlattice (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 74 (1999), S. 1809-1811 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Self-alignment of quantum dots separated by spacer layers is investigated by using a three-dimensional finite element method. We find that the morphology of the top islands is not just simply a reproduction of the buried islands. It is dependent on the arrangement of the buried islands, the interruption time, and the spacer layer thickness. If the buried islands are uniform and regular, with appropriate choice of their spacing and aspect ratio and with a thin spacer layer, there exists a regime in which the steady-state top islands are always uniform and regular, vertically aligned, and stable against small perturbations. For a thicker spacer layer, due to the change of the strain energy density distribution on top of the spacer layer, the top islands are misaligned with the buried islands. If the buried islands are not uniform and regular, our simulations demonstrate the top islands may self-assemble into more uniform and regular arrangements. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.123093
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  • 6
    Digitale Medien
    Digitale Medien
    Three-dimensional analysis of shape transitions in strained-heteroepitaxial islands (2001)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 78 (2001), S. 2706-2708 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A continuum model of shape transitions in strained heteroepitaxial islands predicts that small islands are hut shaped, while larger islands are domed. The volume of a stable hut can exceed that of a stable dome, however, indicating that the stability of hut-shaped islands plays an important role in shape transition, in addition to energy changes associated with the transition. A hut-shaped island loses stability upon reaching a critical volume, which depends on the anisotropy in surface energy. Impingement between islands reduces the critical volume by nucleating new facets at the base of a hut, which subsequently trigger a shape transition. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1354155
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  • 7
    Digitale Medien
    Digitale Medien
    Electrical conductivity enhancement in nanocrystalline (RE2O3)0.08(ZrO2)0.92 (RE=Sc, Y) thin films (2000)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 77 (2000), S. 3409-3411 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Dense, crack-free, uniform, and homogeneous (RE2O3)0.08(ZrO2)0.92 (RE=Sc, Y) nanocrystalline thin films were fabricated by a simple sol-gel method and characterized by impedance studies. At temperatures beyond 600 °C, the electrical conductivity of (Sc2O3)0.08(ZrO2)0.92 and (Y2O3)0.08(ZrO2)0.92 nanocrystals in pure cubic phase was ten times higher than that of the corresponding bulk materials. The decrease of grain boundary resistance related to interfacial effect is predominately responsible for the electrical conductivity enhancement. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1328099
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  • 8
    Digitale Medien
    Digitale Medien
    Ammonium diaqua(ethylenediaminetetraacetato)scandium(III) trihydrate (1999)
    Oxford [u.a.] : International Union of Crystallography (IUCr)
    Acta crystallographica 55 (1999), S. 1418-1420 
    Details
    ISSN: 1600-5759
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108270199008057
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  • 9
    Digitale Medien
    Digitale Medien
    Optical design of the NSRL undulator beamline (1998)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 5 (1998), S. 559-561 
    Details
    ISSN: 1600-5775
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: The optical design of the NSRL undulator beamline is presented. The NSRL undulator has 29 periods of 9.2 cm that produce a photon energy of 7.7–124 eV with the fundamental and third harmonics at a ring energy of 800 MeV. The beamline consists of a typical Kirkpatrick–Baez prefocusing mirror system, a modified spherical-grating monochromator (SGM) and a refocusing toroidal mirror. The monochromator has two including angles of 148 and 157° with two plane mirrors inserted into the entrance arm in order to cover the wide energy range with high grating diffraction efficiency. Calculation shows that the resolving power of the monochromator can be greater than 5000 with the slits fully opened and 20000 with a 20 µm opening of the slits. The spot at the sample is about 1.5 (H) mm × 0.5 (V) mm.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0909049598000478
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  • 10
    Digitale Medien
    Digitale Medien
    Synthesis and structure of pentacoordinate tin(IV) complexes
    Amsterdam : Elsevier
    Journal of Organometallic Chemistry 375 (1989), S. 173-181 
    Details
    ISSN: 0022-328X
    Quelle: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Thema: Chemie und Pharmazie
    Materialart: Digitale Medien
    URL: http://linkinghub.elsevier.com/retrieve/pii/0022-328X(89)85111-3
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