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  • 06  (2)
  • 12.20.Fv  (2)
  • Atomic, Molecular and Optical Physics  (2)
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  • 1
    ISSN: 1434-601X
    Schlagwort(e): 14.80.Pb ; 13.10. + q ; 12.20.Fv
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Motivated by the observation of energy- and momentum-correlatede + e − pairs in heavy ion collisions, a search for resonances ine + e − scattering at the corresponding energies has been made. Thee + e − decay channel is analyzed in a time window from ∼ 10−13 s to ∼ 10−11 s with a set-up optimized for low-background detection of delayede + e − decays. The two-photon decay channel of a hypothetical resonance is investigated by measuring the two-photon annihilation-in-flight excitation function. New upper limits for the partiale + e − decay width Γee of a few meV are derived for total centre-of-mass energies √s between 1.78 and 1.92 MeV, taking into account the dilepton as well as the two-photon decay of a neutral resonance.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 22 (1980), S. 185-187 
    ISSN: 1432-0630
    Schlagwort(e): 06 ; 07 ; 61.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract New methods for thermal-equilibrium investigations of atomic vacancies or of dislocation movements in metals require measurements of minute resistance fluctuations. The accuracy of such measurements is limited by thermal noise from the resistor. The present paper proposes a method for analysing resistance fluctuations independent of voltage noise.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 48 (1989), S. 233-236 
    ISSN: 1432-0630
    Schlagwort(e): 06 ; 07 ; 61.70
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract A novel method is presented for measuring the spectral density of resistance fluctuations without the explicit determination of the voltage background noise (Johnson noise, pre-amplifier noise). The output of a standard ac bridge excited by a single-frequency alternating current is demodulated by two phase-sensitive detectors which operate in quadrature. When the phase difference between excitation and detection is properly set, the real part of the cross-spectral density of the two demodulators shows only the spectral density of the resistance fluctuations and not the disturbing background noise. The feasibility of our new method is demonstrated by measurements of 1/f noise of a thin-film A1 sample.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    ISSN: 1434-601X
    Schlagwort(e): 13.10.+q ; 12.20.Fv ; 14.80.Pb
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract A monoenergetic positron (e +) beam (ΔT/T〈5·10−4) from the Stuttgart pelletron accelerator and a 4.6 mg/cm2 Be target has been employed to investigatee + e −scattering in the MeV region in a large solid angle with high statistics by means of a novel positionsensitive detector system. Superimposed on the Bhabha scattering, a structure has been found at ane + kinetic energy of 2263 keV (810 keV excitation energy in thee + e −rest frame). From the energy-integrated resonance cross-section of $$\sigma _{res} \cdot \Gamma _{res}^{e^ + e^ - } $$ ≅30 b·eV (c.m.) and the standard resonance cross-section we estimate partial resonance widths $$\Gamma _{res}^{e^ + e^ - } $$ ≅72 meV or 24 meV for total angular momenta J=0 or J=1, respectively. The structure, which has not been predicted within the framework of quantum electrodynamics, coincides with one of the sum energies of the correlatede + e −lines observed in heavy-ion collisions.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 19 (1981), S. 113-130 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: Semilocal pseudopotentials have been determined for first-row (Li to Ne), second row (Na to Ar), and third-row atoms (K, Ca). Core-valence correlation is included by adjusting the pseudopotentials to experimental energies of ions with a single valence electron. Correlation within the valence shell is taken into account by using the spin-density functional formalism. The approximations involved in this approach are tested for atomic ionization energies as well as binding energies of monohydrides and alkali diatomics, agreement with experiment is usually satisfactory, but in certain applications density functionals should be already included in the fitting of the local part of the pseudopotential. In addition, 3s/3p and 3s/2p basis sets (for first and second row, respectively), designed for use in connection with our pseudopotentials, are given; it is shown that they yield reasonable results for both SCF and correlation energies.
    Zusätzliches Material: 3 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    International Journal of Quantum Chemistry 9 (1975), S. 775-787 
    ISSN: 0020-7608
    Schlagwort(e): Computational Chemistry and Molecular Modeling ; Atomic, Molecular and Optical Physics
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie
    Notizen: A method is described for calculating cohesive energies of solids in the single-determinant approximation including the full Hartree-Fock exchange. The method involves (1) the construction of a rapidly convergent series in vectors of the direct and reciprocal lattice for the Fock matrix, (2) a decoupling procedure for the k-dependence of the Fock matrix, which works even in the case of strong interatomic overlap. An application to Li and Be is given. Agreement with experiment to 10% is achieved for the cohesive energies and to 5% for the equilibrium lattice constants.
    Zusätzliches Material: 2 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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