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  • 1
    Electronic Resource
    Electronic Resource
    Methods to improve a periodontally involved terminal abutment of a cantilever fixed partial denture – a finite element stress analysis (1998)
    Oxford, UK : Blackwell Science Ltd
    Journal of oral rehabilitation 25 (1998), S. 0 
    Details
    ISSN: 1365-2842
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2842.1998.00234.x
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  • 2
    Electronic Resource
    Electronic Resource
    Free-volume distribution and positronium formation in amorphous polymers: Temperature and positron-irradiation-time dependence (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 4654-4661 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Positron annihilation lifetime spectroscopy was used to study the free-volume size distribution and the o-Ps (ortho-positronium) formation in two amorphous polymers. We performed positron lifetime measurements on poly(vinyl acetate) (PVAc) in the temperature range of 84–414 K and on poly(methyl methacrylate) (PMMA) in the temperature range of 84–454 K and as a function of time (〈200 h) at four temperatures (T=84, 149, 224, and 249 K). The glass transition temperature Tg and secondary transition temperature were determined from the average o-Ps lifetime τ3 versus temperature. The width of the o-Ps lifetime distribution was evaluated using the maximum entropy method (MELT). Analysis by the MELT program on the spectra shows that (i) the standard deviation σ(τ3) of the o-Ps lifetime distribution in PVAc and PMMA increases slightly with temperature in the glassy state, and then increases significantly with temperature above the glass transition temperature Tg; (ii) the σ(τ3) in PMMA has no observable variation as a function of positron irradiation time, which suggests that the measured free-volume distribution is not influenced by the positron irradiation. The o-Ps formation probability shows large variations with temperature, thermal history, and measuring time. These effects are discussed in the framework of the spur model. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475876
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of viscoelasticity of bulk polymer solution on the surface modes as probed by laser light scattering (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 109 (1998), S. 6103-6109 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The effects of surface tension, surface dilational modulus, stress relaxation time, and shear stress modulus on the surface laser light scattering (SLLS) spectrum of polymer solutions are investigated. The capillary wave component is significantly affected by both the stress relaxation time and the amplitude of the shear stress modulus. At moderate concentration, before crossing over to the elastic regime, a strong quasielastic component dominates the SLLS spectrum in polymer solution. In the viscoelastic regime, the capillary wave component of the SLLS spectrum is suppressed by the increase of the surface dilational modulus. The decrease of the surface tension gives rise to an effect similar to that caused by increasing the dilational modulus. However, at high polymer concentration in the elastic regime, the dilational modulus has only a negligible effect on the SLLS spectrum, in contrast to the effect of surface tension. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.477237
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  • 4
    Electronic Resource
    Electronic Resource
    Clear-cut experimental observation of the capillary wave to elastic wave crossover in concentrated polymer solutions (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 3827-3834 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A detailed experimental study of the surface laser light scattering (SLLS) spectrum of the polyisobutylene (PIB)/decane solution over a wide range of polymer concentration is carried out. In the dilute solution, the SLLS spectrum is found to be described adequately by a scattering theory from a capillary wave. As the polymer concentration increases, the solution viscoelasticity is found to play an important role in affecting the dynamics of surface waves. By comparing experiment with theory, a clear-cut capillary wave to elastic wave evolution in the PIB/decane solution is found. The nature of the quasielastic peak that appears in the SLLS spectrum of the viscoelastic polymer solution is delineated. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475771
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  • 5
    Electronic Resource
    Electronic Resource
    Dynamical response in an array of quantum-dot cells (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 2684-2689 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The time-dependent behavior of quantum cellular automata (QCA), chains of quantum-dot cells, is examined. Each cell consists of four quantum dots on the four corners of a square and contains two electrons. Cells interact with nearby cells via Coulomb potentials. We study the time evolution of the polarization of the cells due to the switching of a driver cell for the particular cases of linear chains and L-shaped configurations. Two different approaches are discussed. In the first one dissipation is not considered. For this case numerical results demonstrate that adiabatic switching can be used to implement QCA only for chains of two cells. In the second approach we explicitly include energy dissipation processes in a phenomenological way and obtain the time evolution of the polarization of the cells due to the switching of the driver cell. Dissipation processes are found to give rise to satisfactory response characteristics. For the cases studied no metastable states are found. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.368381
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  • 6
    Electronic Resource
    Electronic Resource
    Ultrafast optical response of the Au–BaO thin film stimulated by femtosecond pulse laser (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 7855-7859 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The pump-probe method was applied to study the dependence of the transient optical transmissivity upon time delay for the Au–BaO composite thin film stimulated by a femtosecond pulsed laser. It was observed that the light absorption of the thin film increased rapidly and then resumed its initial value in several picoseconds. Optical relaxation is a process in which nonequilibrium electrons, excited by laser pulses and originating from Au ultrafine particles, return to the equilibrium state. In this article, the value of the electron-phonon coupling constant g of gold ultrafine particles in the composite thin film was calculated theoretically. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367960
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  • 7
    Electronic Resource
    Electronic Resource
    Luminescence improvement of SrS:Ce thin films by rapid thermal annealing: Evidence of energy-transfer model for SrS:Ce electroluminescent devices (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 7958-7964 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: SrS:Ce thin films and electroluminescent (EL) devices have been deposited on Si substrate using the rf magnetron reactive sputtering method and subsequently submitted to various thermal treatments. The effects of rapid thermal annealing (RTA) on the properties of SrS:Ce thin films and EL devices have been investigated and compared with results obtained using a conventional furnace. Subsequently, the higher temperature of RTA treatment not only remarkably improves the crystallization of SrS phosphor film in the (200) plane but also reduces oxygen interdiffusion problems and enhances both the interface states (Eit) as well as bulk trap (Ebt) densities. These effects all are important factors in yielding brighter electroluminescence. Furthermore, a physical band model based on energy-transfer concept is proposed to elucidate the electroluminescent mechanism of SrS:Ce EL devices. All evidence reveals that the efficient luminous center formed by the Ce atom associated with the Ebt bulk trap is the basis of this energy-transfer model in SrS:Ce EL devices. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367977
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  • 8
    Electronic Resource
    Electronic Resource
    Energy state of Nd3+ doped in barium sodium niobate crystals (1998)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 83 (1998), S. 2560-2562 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nd-doped barium sodium niobate (Ba2Na)1−xNdxNb5O15 (BNN:Nd), with x=0.025 and a Curie temperature of 537±2 °C, crystallizes with a filled tungsten bronze-type structure in the tetragonal system. The lattice constants are a=b=1.2446(1) and c=0.3991(1) nm at room temperature. There are two formulas per unit cell. The five typical deep energy levels, formed by the Nd3+ ions doped in the A1 and A2 sites, are 2.36, 2.12, 1.68, 1.55, and 1.43 eV. Investigating the green and yellow second-harmonic generation shows that the BNN:Nd crystal can be expected as a useful material for the green, especially for the yellow laser radiation at room temperature. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.367016
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  • 9
    Electronic Resource
    Electronic Resource
    Deep level defects in n-type GaN grown by molecular beam epitaxy (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 1211-1213 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Deep-level transient spectroscopy has been used to characterize electronic defects in n-type GaN grown by reactive molecular-beam epitaxy. Five deep-level electronic defects were observed, with activation energies E1=0.234±0.006, E2=0.578±0.006, E3=0.657±0.031, E4=0.961±0.026, and E5=0.240±0.012 eV. Among these, the levels labeled E1, E2, and E3 are interpreted as corresponding to deep levels previously reported in n-GaN grown by both hydride vapor-phase epitaxy and metal organic chemical vapor deposition. Levels E4 and E5 do not correspond to any previously reported defect levels, and are characterized for the first time in our studies. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121016
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  • 10
    Electronic Resource
    Electronic Resource
    Persistent photoconductivity and defect levels in n-type AlGaN/GaN heterostructures (1998)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 72 (1998), S. 2745-2747 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Persistent photoconductivity effects have been characterized in n-type Al0.15Ga0.85N/GaN heterostructures using both monochromatic light and room light illumination. Time constants of ∼1×104 s have been observed, and measurements of photocurrent specta performed using various illumination geometries and techniques have shown that defect levels exist in both the Al0.15Ga0.85N and GaN layers. Broad distributions of defect levels with excitation energies lower than the bandgap energies are found in both Al0.15Ga0.85N and GaN, and evidence is observed that these levels contribute significantly to the aforementioned persistent photoconductivity effects. The photocurrent spectra also reveal the presence of a level with an excitation energy of 3.36 eV that contributes to the persistent photoconductivity in the heterostructure. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.121077
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