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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 1297-1302 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report frequency-dependent dipole and quadrupole polarizabilities of the oxygen molecule in its 3Σ−g ground state. These properties are obtained by means of the multiconfiguration self-consistent field method and used for the computation of the van der Waals coefficients of (O2)2 and the O2–Rg dimers, where Rg is He, Ne, Ar, and Kr. The required frequency-dependent polarizabilities of the rare gases were computed earlier by means of second-order many body perturbation theory.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 6270-6275 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A two-state diabatic model for high-energy photoionization is proposed and applied to the inner valence x-ray photoelectron spectrum of acetylene. The diabatic electronic representation is accomplished by calculating the first order nonadiabatic coupling over the vibrational normal modes. The photoionization overlap amplitudes are expressed in terms of this new basis which is related to the adiabatic representation via an orthogonal transformation. The nonadiabatic (vibronic) coupling leads to a significant redistribution of photoelectron intensity for the totally symmetric states in the inner valence region. This finding resolves previous ambiguities in the analysis of the spectrum.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 6211-6222 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A symmetry scheme based on the irreducible corepresentations of the full symmetry group of a molecular system is presented for use in relativistic calculations. Consideration of time-reversal symmetry leads to a reformulation of the Dirac–Hartree–Fock equations in terms of quaternion algebra. Further symmetry reductions due to molecular point group symmetry are then manifested by a descent to complex or real algebra. Spatial symmetry will be restricted to D2h and subgroups, and it will be demonstrated that the Frobenius–Schur test can be used to characterize these groups as a whole. The resulting symmetry scheme automatically provides maximum point group and time-reversal symmetry reduction of the computational effort, also when the Fock matrix is constructed in a scalar basis, that is, from the same type of electron repulsion integrals over symmetry-adapted scalar basis functions as in nonrelativistic theory. An illustrative numerical example is given showing symmetry reductions comparable to the nonrelativistic case. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 6208-6218 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The relativistic Dirac Hamiltonian that describes the motion of electrons in a magnetic field contains only paramagnetic terms (i.e., terms linear in the vector potential A) while the corresponding nonrelativistic Schrödinger Hamiltonian also contains diamagnetic terms (i.e., those from an A2 operator). We demonstrate that all diamagnetic terms relativistically arise from second-order perturbation theory and that they correspond to a "redressing" of the electrons by the magnetic field. If the nonrelativistic limit is taken with a fixed no-pair Hamiltonian (no redressing), the diamagnetic term is missing. The Schrödinger equation is normally obtained by taking the nonrelativistic limit of the Dirac one-electron equation, we show why nonrelativistic use of the A2 operator is also correct in the many-electron case. In nonrelativistic approaches, diamagnetic terms are usually considered in first-order perturbation theory because they can be evaluated as an expectation value over the ground state wave function. The possibility of also using an expectation value expression, instead of a second-order expression, in the relativistic case is investigated. We also introduce and discuss the concept of "magnetically balanced" basis sets in relativistic calculations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Biological cybernetics 39 (1980), S. 53-66 
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract The Clare Bishop Area (CBA) is a retinotopically organized cortical area in the cat brain connected to a great variety of visual areas in a very complex wax (Fig. 1). Experimental analysis is difficult because of the following aspects: 1. As the distance from the retina increases, the signal combinations necessary to analyse the system become more and more specific. 2. Feedback loops cannot be opened, so an unequivocal identification of CBA cell properties is impossible. 3. The nonlinear character seems to have a great influence on signal processing. To circumvent these problems, specific signal combinations leading to a separation of input subsystems have been developed (Hoffmann and v. Seelen, 1979). On grounds of practical experience and theoretic considerations, the signal combinations are usually restricted to combinations of deterministic and stochastic signals when analysing the CBA. The different methods of measurement are applied successively, the linearizing ones being used first so that a rough classification is possible. If the nonlinear features of the system have little effect, they can be linearized in the theoretical description, if not, a model consisting of a sequence of a linear dynamic system and a nonlinear one with a static, polynomial feature must be used for analysis by parameter estimation. The experimental part of this publication deals with the determination of a number of cell properties. Some hypotheses on the function of the CBA are tested. The results lead to the conclusion that further experiments, such as are discussed below, are necessary in the input subsystems, area 18 and 19. The experimental results of some other authors (Hubel and Wiesel, 1969; Turlejski, 1975; Turlejski and Michalski, 1975; Smith and Bauman, 1979; Spear and Bauman, 1979) are confirmed by the implications of the present results.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1434-601X
    Keywords: 21.10.−K ; 21.60.−n ; 25.70.−z ; 27.70.+q
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The strongly shape driving πh9/2[541]l/2− configuration with α=+1/2 exhibits some anomalous, and so far unexplained, features concerning the crossing frequency, ħωc, the aligned angular momentum, ix, and interaction strength, at the alignment of the first pair of i13/2 quasineutrons in several odd-Z rare earth-nuclei. The h9/2[541]1/2− and h11/2[523]7/2− bands have been studied in the stably deformed rare-earth nucleus163Tm to investigate these features. A difference in band crossing frequency of ∼ 80 keV between the two bands is found. Rotational bands built on these two configurations have been found to cross in the spin range I=25/2–29/2 ħ. Theγ-decay pattern between the two bands is established in the crossing region and analysed in terms of a moderate shape difference between them. A theoretical estimate of the size of the interaction strength between the two bands is presented and compared to the experimental value. The observed band structure in163Tm is very similar to that of167Lu which has 2 protons and 2 neutrons in addition. This observation is discussed in relation to the similarity of the yrast bands of the two even-even “core” nuclei162Er and166Yb, for which theγ-transition energies are identical within ∼0.2 keV below the vi13/2 crossing.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of low temperature physics 74 (1989), S. 293-318 
    ISSN: 1573-7357
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The maximum pinning force of a two-dimensional vortex lattice in a random potential is calculated. A connection is established between this threshold pinning force and the potential energy discontinuities due to elastic and plastic instabilities of the vortex lattice. Inspired by recent computer simulations, we assume that the fluctuations in the commensurability between the random potential and the vortex potential breaks the vortex system up into a set of flowing channels in between trapped regions. Two instability mechanisms and their contribution to the threshold force are discussed within this channel-flow picture. We find that three different regimes exist depending on, w, the width of the channels;w=∞,a 0〈w〈∞, and finallyw=a 0 , wherea 0 is the vortex lattice spacing. Weak pinning superconductors can pass through all three regimes as the reduced magnetic field is varied from 0 to 1, whereas strong pinning compounds can remain in the saturated region (w=a 0 ) for all values of the field. We compare the expression for the threshold force with experimental results for both strong and weak pinning samples. A satisfactory qualitative agreement is obtained between theory and experiment.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of statistical physics 66 (1992), S. 583-593 
    ISSN: 1572-9613
    Keywords: Lévy flight ; Hurst exponent ; Brownian motion ; scaling argument ; density correlations ; temporal fluctuations ; return times ; simulation ; power spectrum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We consider the density fluctuations of an ideal Brownian gas of particles performing Lévy flìghts characterized by the indexf. We find that the fluctuations scale as δN(t)∼ tH, where the Hurst exponentH locks onto the universal value 1/4 for Lévy flights with a finite root-mean-square range (f〉2). For Lévy flights with a finite mean range but infinite root-mean-square range (1〈f〈2) the Hurst exponent H=1/(2f). For infinite-range Lévy flights (f〈1) the Hurst exponent locks onto the value 1/2. The corresponding power spectrum scales with an exponent 1 + 2H, independent of dimension.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0009-286X
    Keywords: Chemistry ; Industrial Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Es wird über die theoretischen Grundlagen, die apparatebauliche Durchführung und einige experimentelle Ergebnisse des Trennverfahrens mit einer von den Autoren konstruierten Gaszentrifuge berichtet. Bei Stabilisierung des Rotorinhaltes durch Wasserstoffzusatz ergibt sich ein erhöhter Trenneffekt, der es erlaubt, verhältnismäßig große Mengen gasförmiger Isotope erheblich anzureichern.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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