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  • 1
    Electronic Resource
    Electronic Resource
    Nonunitary representations of the SU(2) algebra in the Dirac equation with a Coulomb potential (1999)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 40 (1999), S. 2324-2336 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A novel realization of the classical SU(2) algebra is introduced for the Dirac relativistic hydrogen atom defining a set of operators that allow the factorization of the problem. An extra phase is needed as a new variable in order to define the algebra. We take advantage of the operators to solve the Dirac equation using algebraic methods. A similar path to the one used in the angular momentum case is used; hence, the radial eigenfunctions so calculated comprise nonunitary representations of the algebra. One of the interesting properties of such nonunitary representations is that they are not labeled by integer nor by half-integer numbers, as occurs in the usual angular momentum representation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.532867
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  • 2
    Electronic Resource
    Electronic Resource
    Ergodic properties of infinite quantum harmonic crystals: An analytic approach (1996)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 37 (1996), S. 5111-5135 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: We prove that the quantum dynamics of a class of infinite harmonic crystals becomes ergodic and mixing in the following sense: if Hm is the m-particle Schrödinger operator, ωβ,m(A)=Tr(A exp−βHm)/Tr(exp−βHm) the corresponding quantum Gibbs distribution over the observables A,B,ψm,λ the coherent states in the mth particle Hilbert space, gm,λ=(exp−βHm)ψm,λ then limt→∞ limn→∞ limm→∞(1/T)∫T0〈eiHntAe−iHntψm,λ,ψ m,λ〉dt=limm→∞ ωβ,m(A) if the classical infinite dynamics is ergodic, and limt→∞ limn→∞ limm→∞ ωβ,m(e /iiHntAe−iHntB)=limm→∞ ωβ,m(A)limm→∞ωβ,m(B) if it is in addition mixing. The classical ergodicity and mixing properties are recovered as (h-dash-bar)→0, and limm→∞ ωβ,m(A) turns out to be the average over a classical Gibbs measure of the symbol generating A under Weyl quantization. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.531741
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  • 3
    Electronic Resource
    Electronic Resource
    Tau-function formalism for supersymmetric KP hierarchies (1995)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 36 (1995), S. 4898-4913 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: We consider the Manin–Radul and Jacobian supersymmetric KP hierarchies from the point of view of the tau-function formalism. Solutions of their associated systems of Sato equations are characterized in terms of correlation functions of supersymmetric vertex operators of superghost type. The expression of the wave functions of these hierarchies in terms of tau-functions is obtained and the corresponding bilinear identities are established. Explicit methods for generating soliton and rational solutions are given. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.530927
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  • 4
    Electronic Resource
    Electronic Resource
    Relaxation times in transient electric birefringence and electric-field light scattering of flexible polymer chains (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 7631-7639 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study in the present paper the response of a flexible macromolecular chain to the application or removal of an electric field. The polymer is mainly modeled as a Gaussian chain, and the case of freely jointed chains is also treated. We consider the dynamics of the chains, after the inception and subsequent cessation of an electric field. In particular, we calculate two properties. One of them is the time-dependent chain expansion, as measured by the components of the gyration tensor, that can be determined by transient electric-field light scattering. The other property is the transient electric birefringence, related to the reorientation of the chain segments. In this way, the dynamics of two different properties can be compared. The transient properties are analyzed in terms of a series of relaxation times. We propose the use of a mean relaxation time as a convenient representation of the rate of the dynamic process, and show that it can be deduced from simulation or experiments with more accuracy than the longest relaxation time. Our computational procedure is based on Brownian dynamics simulation. For Gaussian chains without hydrodynamic interaction, the results are compared with the predictions from the Rouse theory. We evaluate the influence of the strength of the force or field. Simulations are also carried out including hydrodynamic interactions, so that the importance of this effect can be assessed. We propose some combination of relaxation times with other macromolecular properties that take universal numerical values. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470282
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  • 5
    Electronic Resource
    Electronic Resource
    The structure of Nb3O and Nb3O+ determined by pulsed field ionization–zero electron kinetic energy photoelectron spectroscopy and density functional theory (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 103 (1995), S. 5335-5342 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The geometrical structures of the ground states of triniobium monoxide, Nb3O, and its cation, Nb3O+, have been determined by an experimental and theoretical study. Vibrationally resolved photoelectron spectra of an Nb3O cluster beam were obtained at 100 and 300 K using the pulsed field ionization-zero electron kinetic energy technique. The spectra were simulated by calculating multidimensional Franck–Condon factors using the geometries and harmonic vibrational frequencies obtained from density functional theory for the minimum energy structures of the ion and neutral molecule. The rather remarkable agreement between the experiment and the simulated spectra establishes that Nb3O and Nb3O+ have planar C2v structures with the oxygen atom bridging two niobium atoms. These are the most complex transition metal cluster structures to date to be characterized by gas phase spectroscopic techniques. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470568
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  • 6
    Electronic Resource
    Electronic Resource
    Test of a simple model of the intermolecular potential of C60 on the series of KnC60, 0〈n≤6, crystals (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 8132-8137 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We perform a further test of a simple atom–atom model of the intermolecular potential of C60 by applying it to the alkali-metal doped crystals KnC60, 0〈n≤6. The model consists in an icosahedron of 12 Lennard-Jones interaction sites and no further refinement of its LJ parameters is performed. The electrostatic interactions due to the charges transferred by K atoms are taken into account. Several statical and dynamical properties, at room temperature and zero pressure, are calculated by constant-pressure molecular dynamics methods. Comparison with available experimental data shows that the icosahedron model plus an accumulative charge at each interaction site, gives good results for n≤4, but further improvement is needed for n=6. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469224
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  • 7
    Electronic Resource
    Electronic Resource
    Pseudospectral multireference single and double excitation configuration interaction (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 7564-7572 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present a pseudospectral formulation of the multireference single and double excitation configuration interaction method. A formal scaling advantage is achieved and practical timings are presented. The accuracy of the pseudospectral approximation within this method is probed for a variety of test cases. The method is typically accurate to within 1 mhartree while being up to six times faster than conventional codes. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469088
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  • 8
    Electronic Resource
    Electronic Resource
    Further dynamical studies of the dissociation and elimination reactions of methyl nitrite (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 10501-10510 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Classical trajectory calculations were performed to investigate the effects of molecular rotation, deuterium substitution, and the possibility of mode-specific effects in the two unimolecular channels that initiate the thermal decomposition of methyl nitrite (MeONO): O–N bond dissociation giving CH3O and NO and concerted elimination to produce CH2O and HNO. The calculations were carried out at a total energy of 140 kcal/mol, at which a microcanonical ensemble of excited molecules is maintained throughout the decomposition. Total and individual rate coefficients were evaluated under several types of initial sampling conditions: microcanonical (i.e., random) distribution of vibrational energy, selective excitation of normal modes, and various angular momentum orientations. Comparisons of the results obtained from random initial conditions and normal mode excitations show that there is significant enhancement of the decomposition rates for excitations of several vibrational modes (apparent non-RRKM behavior). The calculations predict rapid energy exchange among modes 465 (ONO bend), 715 (CO stretch), and 931 (O–N stretch) as well as strong coupling between modes 246 (CONO torsion) and 1670 (N(Double Bond)O stretch). The vibrational state distributions for the nascent NO species computed under excitations of modes 246 and 1670 are much broader than that obtained under random initial conditions. This gives further evidence for incomplete relaxation of vibrational energy on the time scale of reaction. Molecular rotation enhances the decomposition rates significantly. More specifically, exciting the symmetric top axis promotes elimination, while exciting either of the remaining two axes promotes dissociation. The presence of two-dimensional rotors at the dissociation transition state may explain the inverse isotope effect found in our previous classical trajectory calculations [J. Chem. Phys. 109, 8907 (1998)]. Finally, the importance of anharmonicity in the unimolecular density of states was estimated by fits of modified RRK schemes to our previously reported microcanonical rate coefficients. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480403
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  • 9
    Electronic Resource
    Electronic Resource
    High resolution Raman spectroscopy from vibrationally excited states populated by a stimulated Raman process. Transitions from v2=1 in 12C2H2 and 13C2H2 (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 519-524 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The Raman spectra of the Q branches of the ν1+ν2−ν2 band of 12C2H2 and of the ν1+ν2−ν2 and 2ν2+2ν5−ν2 bands of 13C2H2 were recorded at high resolution in the gaseous phase. To obtain the spectra a two-step pump/probe technique was used. In the first step, molecules were pumped from the ground to the v2=1 excited state by means of a double pulsed stimulated Raman process. Then, spectra corresponding to the transitions from this state to higher ones are recorded by means of a high resolution quasicontinuous stimulated Raman process. The analysis of the experimental data, taking into account the fourth-order anharmonic interaction coupling the excited states for the 13C isotopomer, provided unperturbed values for the rotational and distortion constants of the excited states and for the band origins. Accurate values for the x120 anharmonicity constant have been calculated directly from the energies of the v1=v2=1 states for the first time. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479331
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  • 10
    Electronic Resource
    Electronic Resource
    Unambiguous formalism of molecular vibrations: Use of redundant coordinates and canonical matrices (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 3302-3308 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This paper introduces a new approach to the problem of describing molecular vibrations in redundant valence coordinates. A consistent definition for canonical force field, which is different of that by Kuczera and Pupyshev et al., is outlined. This new definition is also generalized to other matrices like kinetic-energy matrices and transformation matrices between different sets of vibrational coordinates. The importance of such canonical matrices follows from the fact that they are uniquely determined and allow us to consider the redundant coordinates as though they were independent. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478195
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