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  • Artikel  (8)
  • 36.40.+d
  • Springer  (8)
  • American Institute of Physics
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  • 1995-1999  (8)
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  • Artikel  (8)
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  • Springer  (8)
  • American Institute of Physics
  • Elsevier
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  • 1995-1999  (8)
  • 1990-1994
  • 1965-1969
  • 1955-1959
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  • 1
    Digitale Medien
    Digitale Medien
    Springer
    The European physical journal 98 (1995), S. 421-428 
    ISSN: 1434-6036
    Schlagwort(e): 36.40.+d ; 33.70.Jg ; 67.40.Yv
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We examine the effects of impurities (“doping”) and rotational excitation on the structural and energetic properties of helium clusters. Quantum Monte Carlo (QMC) techniques are used to study ground and rotationally excited states of pure and doped clusters. We use exponentially correlated wave functions and treat the molecular impurities as rigid. Whereas pure HeN show essentially monotonic decay of density from a central maximum value, addition of impurities induces local ordering of He to an extent dependent on the impurity-He binding. Rotational excitation of HeN gives rise to extremely large centrifugal distortions. The location of impurities also appears to change upon rotational excitation. The implications of these distortions on impurity spectra are discussed for SF6HeN, and compared to recent experimental results.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    ISSN: 1432-0649
    Schlagwort(e): 36.40.+d ; 42.65.Dr
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Spatial distributions of rotational temperatures and molecular number densities of C2H2 and H2 were measured with CARS during the production of ultrafine SiC powders in a laser pyrolytic process flame. By means of a CO2 laser, the reaction gases SiH4 and C2H2 (or alternatively C2H4) are converted into SiC and H2. From the CARS measurements temperature gradients are determined between 8.8 × 105 K/m and 1.6 × 106 K/m with corresponding heating rates of 1.8 × 106 K/s and 1.3 × 106 K/s. The CARS data also allow an estimation of the gas expansion behaviour in the reaction zone. Moreover, they show that diffusive velocity components of the hydrogen in the hot reaction zone do not exceed 0.4 m/s.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Applied physics 60 (1995), S. 49-55 
    ISSN: 1432-0630
    Schlagwort(e): 42.65.An ; 36.40.+d ; 31.20.Sy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract Using wave functions determined from ground-state local-density calculations, we have calculated the wave-dispersed free response of the optical nonlinear polarizabilityγ (3)(−3ω;ω,ω,ω), for the C60 molecule andχ (3)(−3ω;ω,ω,ω) i.e. Third-Harmonic Generation (THG) for films using a sum-over-states approach. The influence of screening was determined by applying an external static electric field in separate selfconsistent calculations to evaluate induced dipole moments which was used to determine the static linear and nonlinear polarizabilities. The polarizabilities calculated in the static limit were used to determine an effective screening parameter which was, in turn, used together with an RPA approach to calculate screened wave-dispersed, third-order nonlinear optical properties such asγ (3)(−3ω;ω,ω,ω) andχ (3)(−3ω;ω,ω,ω). Comparing evaluated polarizabilities with experimental values we found that the non-resonant free polarizability compares well in absolute magnitude with experimental results. Inclusion of screening results in a polarizability about two orders of magnitude below the experimental values.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Springer
    The European physical journal 32 (1995), S. 337-341 
    ISSN: 1434-6079
    Schlagwort(e): 36.40.+d ; 79.60.−i ; 36.20.Kd
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract In the photoemission process of a core level electron a satellite structure may appear due to the simultaneous excitations of valence electrons (many-electron effects). We study this phenomenon in Au55 aggregates. In this calculation we assume that the excitations can be limited to the 6s electrons which are described by means of tight-binding Hamiltonians in the initial (no core hole) and the final (hole present on a core level) states. An extension of a Anderson's formula strictly valid for the bulk is discussed and the possible use of the phase shift concept is analyzed. Our calculated satellite structure depends only on two parameters: Δ, the core hole attractive diagonal term and β, the normal transfer integral. We fix Δ/β=3 by comparison of our results to experiment performed on Au55 (P Ph3)12Cl6 compounds. The various experimental features are roughly reproduced by the calculation (number of peaks as well as their intensities and positions). Another interpretation of the experimental structure was proposed in the original experimental work. A more extensive investigation on other polyhedral metallic aggregates is necessary for allowing a choice between the two models.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    The European physical journal 34 (1995), S. 135-138 
    ISSN: 1434-6079
    Schlagwort(e): 71.50.+t ; 36.40.+d
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The temperature of a sodium fluoride cluster beam produced by laser vaporization is estimated from the rotationally-resolved laser spectroscopy of the Na2 dimer. The cluster beam is obtained by laser vaporization of a sodium rod in a mixture of helium containing a small amount (1%) of SF6. Both rotational and vibrational temperatures (respectively 170 K and 400 K) are much higher than expected from a simple theoretical model of a supersonic beam. These temperatures can be lowered to 70 K and 250 K respectively by cooling the nozzle to liquid nitrogen temperature.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    The European physical journal 35 (1995), S. 273-278 
    ISSN: 1434-6079
    Schlagwort(e): 36.40.+d ; 72.15.Gd ; 75.30.Cr
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We present a simple theory for the cluster size dependence of the average cluster magnetic moment of transition metal clusters. Assuming a local environmental dependence of the atomic magnetic moments, the cluster magnetization exhibits a magnetic shell structure, reflecting the atomic structure of the cluster. Thus, the observed oscillations of the average cluster magnet moment may serve as a fingerprint of the cluster geometry. We also discuss the giant magnetoresistance (GMR) exhibited by an ensemble of magnetic clusters embedded in a metallic matrix. It is shown that the magnetic anisotropy affects strongly the magnetization of the cluster ensemble under certain conditions. Since the GMR depends on the cluster ensemble magnetization, it can be used to determine the cluster magnetic anisotropy energy.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    The European physical journal 32 (1995), S. 329-336 
    ISSN: 1434-6079
    Schlagwort(e): 36.40.+d ; 78.20.−e
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract We investigate the effects of the atomic cores on the Mie resonance in lithium metal clusters, perturbing a jellium Hamiltonian with zero-range pseudopotentials. The resonance is red-shifted with respect to the classical formula by core effects, most important of which is the increased effective mass due to the core potentials. Much of the large shift seen in lithium clusters is thereby explained if the strength of the pseudopotentials is taken from band structure calculations. However, such pseudopotentials cause the resonance to be greatly broadened, contrary to observation.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    ISSN: 1434-6079
    Schlagwort(e): 36.40.+d ; 35.20.Wg ; 34.10.+x
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract Laser ablation of YMCuO metal-composite-oxides (M=Ba, Sr, Ca, Mg) in high vacuum produced cluster ions with various sizes and compositions. Mass spectra of the cluster ions were recorded by a home-built time-of-flight (TOF) mass spectrometer and the mass distributions were analyzed by a statistical model. For YBa2Cu3O7−x (YBCO) high-Tc superconducting samples, six series of cluster ions were observed. Replacement of barium in the metal-composite-oxide sample with other alkaline earth metal, such as strontium, calcium, or magnesium, not only removed the superconductivity, but also changed the compositions and distributions of the laser generated cluster ions. For instance, copper was only found in the compositions of cluster ions generated from YBCO sample. From comparison of the experimental results, interactions among components of the metal-composite-oxides and the function of alkaline earth metal in superconducting material were discussed.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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