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  • American Institute of Physics (AIP)  (14)
  • Oxford University Press
  • American Chemical Society (ACS)
  • 1985-1989  (14)
  • 1955-1959
  • 1
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An unusually pure Mnx Fe3−x O4 sample (x(approximately-equal-to)1.3) from a regionally metamorphosed ore body is expected to exhibit an approach to thermodynamic equilibrium unattainable in synthetic materials. This expectation is confirmed by the observation of (1) a small tetragonal distortion and (2) a complete ordering of Fe on the B sublattice. 57Fe Mössbauer spectra, obtained at 298, 175, 125, and 92 K and in an external field of 30 kG at 92 K, exhibit magnetic hyperfine splitting requiring the fitting of two subspectra, I and II. At 298 K, Heff =418 kOe, α=0.36 mm s−1 , and ε≈0 for the more intense subspectrum I, whereas for II Heff =403 kOe, δ=0.34 mm s−1 , and ε(approximately-equal-to)−0.15 mm s−1 . The two subspectra are not split by a 30 kG external field. Subspectra I and II correspond to Fe3+ ions located on a single magnetic sublattice. Subspectrum II is assigned to Fe3+ ions in regions with locally, large tetragonal distortions as a consequence of Mn3+clustering, which has often been invoked to explain the crystal chemistry and physical properties of Mnx Fe3−x O4 .
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Spectra of highly ionized praseodymium and dysprosium recorded from the Texas tokamak (TEXT) plasma have been analyzed in the 50–250-A(ring) range. The spectra contain high-intensity continuum bands in the region below 100 A(ring) and bright individual lines above this wavelength. Lines of highly ionized praseodymium and dysprosium have been identified. The highest ionization state reached in the 1-keV central electron temperature tokamak plasma was Cu i-like Pr xxxi. The composition of the bands is explained in terms of a new theoretical approach developed to treat large unresolved transition arrays. The brightness of the continuum is compared with that of intense spectral lines emitted in the same wavelength range.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 3028-3034 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using standard multilayer and effective medium models, we determine microstructures that optimize the near-IR-visible normal-incidence optical transmittance of electrically conducting metal films intended for use as semitransparent contacts for semiconductor devices such as photodetectors or photoelectrochemical converters. Various conditions are considered, including unpolarized and linearly polarized light and electrical conduction both parallel and perpendicular to the surface. For linearly polarized light, the optimum microstructure consists of parallel metal lines of nominally square cross section oriented perpendicular to the polarization vector of the incident light, regardless of the direction of electrical conduction. The line separation and cross-sectional dimensions must both be small compared to the wavelength λ. For unpolarized radiation, the optimum microstructure depends on the direction of electrical conduction. For conduction parallel to the surface, the optimum microstructure again consists of parallel lines with the lines oriented perpendicular to the residual linear polarization, if any, of the incident flux. For conduction perpendicular to the surface, the optimum microstructure consists of cylindrical metal posts of dimension small compared to λ. Expressions are derived that allow the thicknesses and refractive indices of protective antireflection coatings to be calculated to first order in the thicknesses of the metal films. The more general case of antireflection coatings for anisotropic structures is briefly discussed.
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 4949-4956 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The nuclear displacement operator (NDO) for Born–Oppenheimer electronic wave functions (BOEWF) is introduced and some recurrence formulas are obtained. The formulas for Born couplings and higher derivatives of BOEWF with respect to nuclear coordinates are derived from very general considerations and relations among these quantities are given. The series form, exponential, and integral forms of the NDO are exhibited. Particularly, it is proven that for the two-state systems the NDO has a very simple form by which it is convenient to study two-state dynamical processes. It is shown that the NDO satisfies a differential equation which is analogous to that for the time-evolution operator in the presence of a time-dependent perturbation. The physical meanings of these two operators are compared. It is demonstrated that the NDO is uniquely determined by the vector Born coupling matrix, and that the nuclear motion may be analyzed in terms of a local non-Abelian gauge transformation.
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  • 5
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Formulation of the expectations of eight operators required for the evaluation of the Born corrections, the Born couplings, and higher derivatives of the Born–Oppenheimer wave functions are derived for the case of a Gaussian-lobe orbital (GLO) basis. The relative simplicity of these analytical formulas is a special advantage of GLO and reduces the computer time in these calculations. Some operators treated here require a modification of the Slater rules. As examples of applications of these techniques, ab initio calculations of the orbital stresses and the Born corrections for the ground state X 1Σ+g and excited states 1Σ+g(II), C, C' 3Πu, and 3Πu(II) of N2 are reported. The obtained results show that the Born correction near the avoided crossing region strongly depends upon the nuclear separation; in this region configuration interaction makes an important contribution.
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  • 6
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electrochemical techniques are applied to a study of selected intrinsic physical properties (independent of dopant) of polyacetylene, (CH)x. Electrochemical voltage spectroscopy (EVS) is used to characterize the energies of charge injection and removal for both cis-(CH)x and trans-(CH)x. The difference in charge injection and ejection potentials is shown to give a direct measure of the approximate semiconductor band gap and the results are compared with similar data from optical measurements. Charge injection and ejection potentials are used to define the redox potentials of (CH)x and are used in conjunction with equilibrium potential measurements at varying oxidation or reduction levels of polyacetylene to present a unifying concept to the electrochemistry of (CH)x.
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 45-48 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The design and construction of an imaging bandpass electron energy analyzer which operates in the intermediate magnetic field of a photoelectron spectromicroscope is described. Image electrons injected parallel to the magnetic field are guided, using crossed magnetic and nonuniform electrostatic fields, to a low-pass electron mirror and subsequently a high-pass retardation filter. The nonuniform electrostatic fields compensate for the energy-dependent dispersion of the crossed fields. A bandwidth-limited photoelectron image demonstrates the spatial integrity of the image after passage through the image bandpass filter. The performance of the device as an energy analyzer is assessed. An energy resolution of less than 30 meV is demonstrated and thermionic electron spectra are presented with electron energies ranging from 10 to 200 eV with a 250-meV bandwidth. Area-selected photoelectron spectra from Au and W show UPS and XPS performance of the device. In the case of Au, the spectrum was obtained from a 400-×400-nm area.
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  • 8
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 1494-1500 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An electron energy analyzer which acts as a bandpass filter while maintaining the spatial integrity of an electron image in a uniform magnetic field is described. It embodies some new electron-optical properties. Image electrons injected parallel to the magnetic field are guided, using crossed electrostatic and magnetic fields, to a low-pass electron mirror and then through a high-pass retardation filter. Nonuniform electrostatic deflection fields are used to compensate for the energy-dependent dispersion of the crossed fields. A simple computer modeling method used to design the electrostatic fields is described. A test analyzer was constructed to operate in a 0.0125-T (125 G) uniform magnetic field to investigate its properties. Bandpass filtered images of an 18-eV electron source demonstrating the removal of energy-dependent dispersion and the narrowing of the bandwidth to 100 meV are presented. Another application of the analyzer, to obtain an energy spectrum from a spatially extended electron source, is demonstrated.
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  • 9
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 3057-3062 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A nonperturbative theory of predissociation based upon an effective Hamiltonian is presented. For a model diatomic system in which a (bound-state) Morse potential-energy curve is crossed by an (unbound-state) exponential potential-energy curve, the exact effective Hamiltonian may be obtained in high precision for any well behaved interaction potential. The real and imaginary parts of the eigenvalues of the effective Hamiltonian give the (shifted) energies and widths, respectively, of the predissociative states. Numerical results are obtained and compared with both a semiclassical approximation and those derived from solutions of coupled Schrödinger equations. In the weak-coupling regime the agreement between the present method and semiclassical results is good, and better in general than the coupled-equations results, which apparently suffer from instability problems. For couplings of intermediate strength, the semiclassical method breaks down, as do fully quantum-mechanical first-order perturbation approximations, as is demonstrated by comparison with the converged nonperturbative results. Fixed points of the spectrum appear at "resonance'' values of the coupling strength which bring the exact energy eigenvalue into resonance with one of the adiabatic levels so that the imaginary part (level width) of the former vanishes. Thus beyond a critical coupling strength, stronger coupling enhances the stability of a resonance.
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  • 10
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 5984-5985 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The nature of the metastable state of hydrogen trimers described by Ga and Kuppermann (ref.1) is further discussed. The analysis is based on linewidth measurements in the emission spectrum of the trimer, the quantum mechanical selection rules, and earlier beam and photoionization measurements.(AIP)
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