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H Schanz

Publications and source records attributed to H Schanz.

11 recordsLinked to original sources
PubMed2001

Effective coupling for open billiards.

We derive an explicit expression for the coupling constants of individual eigenstates of a closed billiard that is opened by attaching a waveguide. The Wigner time delay and the resonance positions resulting from the coupling constants are compared to an exact numerical calculation. Deviations can be attributed to evanescent modes in the waveguide and to the finite number of eigenstates taken into account. The influence of the shape of the billiard and of the boundary conditions at the mouth of the waveguide are also discussed. Finally we show that the mean value of the dimensionless coupling constants tends to the critical value when the eigenstates of the billiard follow random-matrix theory.

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↗
PubMed2000

Periodic-orbit theory of anderson localization on graphs

We present the first quantum system where Anderson localization is completely described within periodic-orbit theory. The model is a quantum graph analogous to an aperiodic Kronig-Penney model in one dimension. The exact expression for the probability to return to an initially localized state is computed in terms of classical trajectories. It saturates to a finite value due to localization, while the diagonal approximation decays diffusively. Our theory is based on the identification of families of isometric orbits. The coherent periodic-orbit sums within these families, and the summation over all families, are performed analytically using advanced combinatorial methods.

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↗
PubMed1992

[The incidence distribution and development of a trend of urinary stone substances. An evaluation of the data on over 210,000 urinary stone analyses from the area of the former DDR].

A computer analysis of more than 214,000 urinary stone analysis data recorded in 13 analysis centres in the GDR between 1970 and 1985 was performed. The relative frequencies of urinary stone constituents as pure substances and as main and secondary constituents were determined. Forty-eight percent of all calculi were monomineralic, and the sex ratio (male/female) was 1.96. In the so-called average calculus, mainly whewellite makes up 60.9% of its substance, weddellite 11.8%, uric acid 10.9%, apatite 4.76%, struvite 4.13%, ammonium urate 0.33%, and cystine 0.2%. Artefacts were found in 2.6% of the cases. Trend analysis shows a marked increase in the amount of whewellite and a reduction in the amounts or uric acid, struvite and cystine.

Electronic Data Processing↗
PubMed1991

An evaluation of the partial dopamine agonist terguride regarding positive symptoms reduction in schizophrenics.

Eleven schizophrenics (7 females) displaying an acute psychotic episode received the partial dopamine agonist terguride in doses up to 2 mg per day. Improvement in terms of positive symptoms reduction was observed in two cases only. In contrast, in a previous clinical trial targeted at negative schizophrenic symptoms, the majority of the patients appeared to have benefited from terguride application.

Adolescent↗