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Search Results: 1 - 10 of 2506 matches for " Bernd Esser "
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Excitonic - vibronic coupled dimers: A dynamic approach
Bernd Esser,Holger Schanz
Physics , 1995, DOI: 10.1007/BF01313855
Abstract: The dynamical properties of exciton transfer coupled to polarization vibrations in a two site system are investigated in detail. A fixed point analysis of the full system of Bloch - oscillator equations representing the coupled excitonic - vibronic flow is performed. For overcritical polarization a bifurcation converting the stable bonding ground state to a hyperbolic unstable state which is basic to the dynamical properties of the model is obtained. The phase space of the system is generally of a mixed type: Above bifurcation chaos develops starting from the region of the hyperbolic state and spreading with increasing energy over the Bloch sphere leaving only islands of regular dynamics. The behaviour of the polarization oscillator accordingly changes from regular to chaotic.
Nonadiabatic couplings and incipience of quantum chaos
Holger Schanz,Bernd Esser
Physics , 1996, DOI: 10.1007/s002570050212
Abstract: The quantization of the electronic two site system interacting with a vibration is considered by using as the integrable reference system the decoupled oscillators resulting from the adiabatic approximation. A specific Bloch projection method is applied which demonstrates how besides some regular regions in the fine structure of the spectrum and the associated eigenvectors irregularities appear when passing from the low to the high coupling case. At the same time even for strong coupling some of the regular structure of the spectrum rooted in the adiabatic potentials is kept intact justifying the classification of this situation as incipience of quantum chaos.
Mixed Quantum-Classical versus Full Quantum Dynamics: Coupled Quasiparticle-Oscillator System
Holger Schanz,Bernd Esser
Physics , 1996, DOI: 10.1103/PhysRevA.55.3375
Abstract: The relation between the dynamical properties of a coupled quasiparticle-oscillator system in the mixed quantum-classical and fully quantized descriptions is investigated. The system is considered to serve as a model system for applying a stepwise quantization. Features of the nonlinear dynamics of the mixed description such as the presence of a separatrix structure or regular and chaotic motion are shown to be reflected in the evolution of the quantum state vector of the fully quantized system. In particular it is demonstrated how wave packets propagate along the separatrix structure of the mixed description and that chaotic dynamics leads to a strongly entangled quantum state vector. Special emphasis is given to view the system from a dynamical Born-Oppenheimer approximation defining integrable reference oscillators and elucidating the role of the nonadiabatic couplings which complements this approximation into a rigorous quantization scheme.
Spin-Boson Hamiltonian and Optical Absorption of Molecular Dimers
Christiane Koch,Bernd Esser
Physics , 1999, DOI: 10.1103/PhysRevA.61.022508
Abstract: An analysis of the eigenstates of a symmetry-broken spin-boson Hamiltonian is performed by computing Bloch and Husimi projections. The eigenstate analysis is combined with the calculation of absorption bands of asymmetric dimer configurations constituted by monomers with nonidentical excitation energies and optical transition matrix elements. Absorption bands with regular and irregular fine structures are obtained and related to the transition from the coexistence to a mixing of adiabatic branches in the spectrum. It is shown that correlations between spin states allow for an interpolation between absorption bands for different optical asymmetries.
Nonlinearity and trapping in excitation transfer: Dimers and Trimers.
Ivan Barvik,Bernd Esser,Holger Schanz
Physics , 1995, DOI: 10.1103/PhysRevB.52.9377
Abstract: We study the interplay between nonlinearity in exciton transport and trapping due to a sink site for the dimer and the trimer with chain configuration by a numerical integration of the discrete nonlinear Schroedinger equation. Our results for the dimer show, that the formation of a self trapped state due to the nonlinear coupling increases the life time of the exciton substantially. Self trapping can be enhanced by the sink for short times, but for long times it disappears. In the trimer consisting of a subdimer extended by a sink site exists a transition between states localized on the two sites of the subdimer before for larger nonlinear coupling self trapping on one site of the subdimer is observed. For large trapping rates the fear of death effect leads to an increasing life time of the excitation on both, the dimer and the trimer. The sink site is then effectively decoupled. We explain this effect using an asymptotic theory for strong trapping and demonstrate it by direct numerical computation.
Transfer and Decay of an Exciton Coupled to Vibrations in a Dimer
Holger Schanz,Ivan Barvik,Bernd Esser
Physics , 1996, DOI: 10.1103/PhysRevB.55.11308
Abstract: Transfer and decay dynamics of an exciton coupled to a polarization vibration in a dimer is investigated in a mixed quantum-classical picture with the exciton decay incorporated by a sink site. Using a separation of time scales, it is possible to explain analytically the most important characteristics of the model. If the vibronic subsystem is fast, these are the enhancement of nonlinear self trapping due to the sink and the slowing down of the exciton decay for large coupling or sink strength. Numerical results obtained recently for the DST approximation to the model are quantitatively explained and new dynamic effects beyond this approximation are found. If the vibronic subsystem is slow, the behavior of the system follows closely the predictions of the adiabatic approximation. In this regime, the exciton decay crucially depends on the initial conditions of the vibronic subsystem. In the transition regime between adiabatic and DST approximation, complex dynamics is observed by numerical computation. We discuss the correspondence to the chaotic behavior of the excitonic-vibronic coupled dimer without trap.
Genetics of fungi: retrospect and perspective
K. Esser
Micología Aplicada Internacional , 2001,
Abstract: This short survey on fungal genetics in the 20th century reflects the course of development from classical to molecular genetics and its implication to biotechnology.
Dendrochernes cyrneus (Arachnida: Pseudoscorpiones: Chernetidae) in Brandenburg
Esser, Jens
Arachnologische Mitteilungen , 2011, DOI: 10.5431/aramit4203
Abstract: The pseudoscorpion Dendrochernes cyrneus (L. Koch, 1873) is recorded for the first time in Brandenburg (Germany). The specimen was found in the ancient park of Sanssouci under the bark of a branch of a beech tree. The suitability of D. cyrneus as an indicator species for old-growth woodlands is discussed.
Comparative International Communication Projects: Overcoming the Challenges
Frank Esser
Brazilian Journalism Research , 2011,
Abstract:
J. Venema, Kiliaen van Rensselaer (1586-1643): Designing a New World
R. Esser
BMGN : Low Countries Historical Review , 2011,
Abstract:
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