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T Dittrich

Publications and source records attributed to T Dittrich.

8 recordsLinked to original sources
PubMed2001

Classical and quantum periodically driven scattering in one dimension.

Irregular scattering at harmonically driven one-dimensional potential wells is studied both on the classical and the quantum level. We show that an ac-driven single square well, and a smooth well with oscillating bottom, are sufficient to generate chaotic scattering. For a square well with oscillating bottom, we introduce the concept of pseudointegrable scattering. The quantum dynamics of these models is treated using Floquet scattering theory, which is exact for arbitrary amplitude and frequency of the driving. In the deep quantum regime, scattering is dominated by multiphoton exchanges with the driving field, leading to complex resonance structures in transmission and reflection. For strong and fast driving, the ac-driven square well develops an effective double-well potential that introduces coherent tunneling in the scattering. We identify signatures of classical chaotic scattering in a phase-space representation of the quantum dynamics.

Journal Article↗
PubMed2001

Classical and quantum Hamiltonian ratchets.

We explain the mechanism leading to directed chaotic transport in Hamiltonian systems with spatial and temporal periodicity. We show that a mixed phase space comprising both regular and chaotic motion is required and we derive a classical sum rule which allows one to predict the chaotic transport velocity from properties of regular phase-space components. Transport in quantum Hamiltonian ratchets arises by the same mechanism as long as uncertainty allows one to resolve the classical phase-space structure. We derive a quantum sum rule analogous to the classical one, based on the relation between quantum transport and band structure.

Journal Article↗
PubMed1999

Spectral correlations in systems undergoing a transition from periodicity to disorder.

We study the spectral statistics for extended yet finite quasi-one-dimensional systems, which undergo a transition from periodicity to disorder. In particular, we compute the spectral two-point form factor, and the resulting expression depends on the degree of disorder. It interpolates smoothly between the two extreme limits-the approach to Poissonian statistics in the (weakly) disordered case, and the universal expressions derived in T. Dittrich, B. Mehlig, H. Schanz, and U. Smilansky, Chaos Solitons Fractals 8, 1205 (1997); Phys. Rev. E 57, 359 (1998); B. D. Simons and B. L. Altshuler, Phys. Rev. Lett. 70, 4063 (1993); and N. Taniguchi and B. L. Altshuler, ibid. 71, 4031 (1993) for the periodic case. The theoretical results agree very well with the spectral statistics obtained numerically for chains of chaotic billiards and graphs.

Journal Article↗
PubMed1990

Ion pair approach of ampicillin using in vitro methods.

The hydrophilic drug ampicillin (AP) was comprehensively studied in vitro with focus on an ion pair approach of AP. The influence of the counter ions in comparison with AP derivatives was studied on the water solubility, lipid partition, and transport across artificial lipid membranes as well as using an in vitro absorption model system. It was found that the water solubility of AP is pH dependent. The water solubility is markedly increased by derivatives such as bacampicillin (BAP). In contrast, the lipid partition and the transport across lipid membranes of AP were markedly enhanced by counter ions, particularly by dodecylsulfate (DS). However, ion pair formation is only in acidic solution (pH 2.5) possible. Taking this into account the same increase of the bioavailability of AP was obtained in the presence of DS as after application of BAP using the in vitro absorption model system.

Absorption↗