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  • 1
    Electronic Resource
    Electronic Resource
    Uniform semiclassical calculation of the direct part of the photodissociation cross section of water (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 11749-11755 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The photodissociation cross section of water in the first absorption band naturally splits into two parts, a rather dominant and broad background, and a series of isolated resonances. We focus here on the semiclassical calculation of the background term. We compare various semiclassical methods of calculation, including the reflection approximation, the Wigner–Weyl series, Airy function approximations, and higher-order approximations in the time domain, and find that only the latter gives quantitative agreement. They are numerically efficient as they can be reduced to a 2-D spatial integration together with a Fourier transform. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479172
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  • 2
    Electronic Resource
    Electronic Resource
    Correlations in quantum time delay (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Chaos 3 (1993), S. 613-617 
    Details
    ISSN: 1089-7682
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The semiclassical periodic orbit content of the form factor K(λ ), the Fourier transform of the autocorrelation function, for the quantum time delay is analyzed. In analogy to the case of bounded systems, three regimes can be identified. For small λ isolated periodic orbits can be identified. For intermediate λ , there is a λ exp(−Γλ) regime, where Γ is the classical escape rate. For large λ , this changes into an exp( − γqmλ) law, where now γqm is related to an inverse lifetime of the resonances. The transition between the latter two regimes is determined by the density of resonances. The theoretical analysis is supported by numerical data for the three disk scattering system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.165925
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  • 3
    Electronic Resource
    Electronic Resource
    Magnetic field correlations in kinematic two-dimensional magnetohydrodynamic turbulence (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3477-3483 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The scaling properties of the second order magnetic structure function D2(B)(r) and the corresponding magnetic correlation function C2(B)(r) are derived for two-dimensional magnetohydrodynamic turbulence in the kinematic regime where the ratio of kinetic energy to magnetic energy is much larger than one. In this regime the magnetic flux function ψ can be treated as a passive scalar advected in a two-dimensional turbulent flow. Its structure function D2(ψ)(r) and the one for the magnetic field D2(B)(r) are connected by an exact relation. We calculate D2(ψ)(r) and thus D2(B)(r) within geometric measure theory over a wide range of scales r and magnetic Prandtl numbers Prm. The magnetic field correlations follow a r−4/3-scaling law and show an anticorrelation at the beginning of the Batchelor regime indicative of the formation of strongly filamented current sheets. Differences to the full dynamic regime, where the ratio of kinetic to magnetic energies is smaller than in the kinematic case, are discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873609
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  • 4
    Electronic Resource
    Electronic Resource
    Integrable four vortex motion (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 2796-2801 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It follows from the Poisson brackets between constants of motion that the motion of four vortices of zero net vorticity is integrable if the total momentum vanishes. The phase space motion of this integrable case is analyzed. One stable and several unstable uniformly rotating configurations are identified.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.867025
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  • 5
    Electronic Resource
    Electronic Resource
    Theoretical mechanics Crowd synchrony on the Millennium Bridge (2005)
    [s.l.] : Nature Publishing Group
    Nature 438 (2005), S. 43-44 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Soon after the crowd streamed on to London's Millennium Bridge on the day it opened, the bridge started to sway from side to side: many pedestrians fell spontaneously into step with the bridge's vibrations, inadvertently amplifying them. Here we model this unexpected and now notorious ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/438043a
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  • 6
    Electronic Resource
    Electronic Resource
    Finite lifetime of turbulence in shear flows (2006)
    [s.l.] : Nature Publishing Group
    Nature 443 (2006), S. 59-62 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Generally, the motion of fluids is smooth and laminar at low speeds but becomes highly disordered and turbulent as the velocity increases. The transition from laminar to turbulent flow can involve a sequence of instabilities in which the system realizes progressively more complicated states, or ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature05089
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  • 7
    Electronic Resource
    Electronic Resource
    Quantum effects of periodic orbits for the kicked top (1993)
    Springer
    The European physical journal 92 (1993), S. 221-233 
    Details
    ISSN: 1434-6036
    Keywords: 03.65.Sq ; 05.45.+b
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We analyze traces of powers of the time evolution operator of a periodically kicked top. Semiclassically, such traces are related to periodic orbits of the classical map. We derive the semiclassical traces in a coherent state basis and show how the periodic orbits can be recovered via a Fourier transform. A breakdown of the stationary phase approximation is detected. The quasi energy spectrum remains elusive due to lack of knowledge of sufficiently many periodic orbits. Divergencies of periodic orbit formulas are avoided by appealing to the finiteness of the quantum mechanical Hilbert space. The traces also enter the coefficients of the characteristic polynominal of the Floquet operator. Statistical properties of these coefficients give rise to a new criterion for the distinction of chaos and regular motion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01312181
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  • 8
    Electronic Resource
    Electronic Resource
    Periodic orbit analysis of the Lorenz attractor (1994)
    Springer
    The European physical journal 93 (1994), S. 259-266 
    Details
    ISSN: 1434-6036
    Keywords: 05.45.+b
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present an application of the periodic orbit formalism to the Lorenz attractor at the standard parameter values. The symbolic encoding of trajectories, the effects of symmetries and scaling properties of trajectories are discussed. Good results for the Hausdorff dimension and the Lyapunov exponent are obtained. The classical spectral density is computed and positions and widths of resonances are compared with those found in correlation functions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01316970
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  • 9
    Electronic Resource
    Electronic Resource
    Continued-fraction expansion of eigenvalues of generalized evolution operators in terms of periodic orbits (1993)
    Springer
    The European physical journal 92 (1993), S. 235-242 
    Details
    ISSN: 1434-6036
    Keywords: 05.45.+b
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new expansion scheme to evaluate the eigenvalues of the generalized evolution operator (Frobenius-Perron operator)H q relevant to the fluctuation spectrum and poles of the order-q power spectrum is proposed. The “partition function” is computed in terms of unstable periodic orbits and then used in a finite pole approximation of the continued fraction expansion for the evolution operator. A solvable example is presented and the approximate and exact results are compared; good agreement is found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01312182
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