Relevance of sub-surface chip layers for the lifetime of magnetically trapped atoms

We investigate the lifetime of magnetically trapped atoms above a planar, layered atom chip structure. Numerical calculations of the thermal magnetic noise spectrum are performed, based on the exact magnetic Green function and multi layer reflection coefficients. We have performed lifetime measurements where the center of a side guide trap is laterally shifted with respect to the current carrying wire using additional bias fields. Comparing the experiment to theory, we find a fair agreement and demonstrate that for a chip whose topmost layer is metallic, the magnetic noise depends essentially on the thickness of that layer, as long as the layers below have a much smaller conductivity; essentially the same magnetic noise would be obtained with a metallic membrane suspended in vacuum. Based on our theory we give general scaling laws of how to reduce the effect of surface magnetic noise on the trapped atoms.     

Radiation enhanced silicon self-diffusion and the silicon vacancy at high temperatures

We report proton radiation enhanced self-diffusion (RESD) studies on Si-isotope heterostructures. Self-diffusion experiments under irradiation were performed at temperatures between 780 degrees C and 872 degrees C for various times and proton fluxes. Detailed modeling of RESD provides direct evidence that vacancies at high temperatures diffuse with a migration enthalpy of H(m)(V)=(1.8+/-0.5) eV significantly more slowly than expected from their diffusion at low temperatures, which is described by H(m)(V)<0.5 eV. We conclude that this diffusion behavior is a consequence of the microscopic configuration of the vacancy whose entropy and enthalpy of migration increase with increasing temperature.     

Finding finite-time invariant manifolds in two-dimensional velocity fields

For two-dimensional velocity fields defined on finite time intervals, we derive an analytic condition that can be used to determine numerically the location of uniformly hyperbolic trajectories. The conditions of our main theorem will be satisfied for typical velocity fields in fluid dynamics where the deformation rate of coherent structures is slower than individual particle speeds. We also propose and test a simple numerical algorithm that isolates uniformly finite-time hyperbolic sets in such velocity fields. Uniformly hyperbolic sets serve as the key building blocks of Lagrangian mixing geometry in applications. (c) 2000 American Institute of Physics.     

Rectangle exchange transformations

We define rectangle exchange transformations analogously to interval exchange transformations. An interval exchange transformation is a mapping of the unit interval onto itself obtained by cutting the interval up into a finite number of subintervals and rearranging the pieces. A rectangle exchange transformation is a mapping of the unit square onto itself obtained by cutting the square up into a finite number of rectangular pieces and rearranging the pieces. We give a minimality condition for rectangle exchange transformations. We deal with various examples of ergodic rectangle exchange transformations. Related questions are discussed.With 2 Figures     

On the statistical behaviour of molecular vibronic energy levels

Electronic spectra of polyatomic molecules often exhibit a high density of complicated energy levels, making a detailed analysis of the individual levels unfavourable. In these cases, statistical tests provide an appropriate means for analysing the spectra. Fluctuation measures are presented and evaluated for calculated and experimental molecular spectra as examples. The results are compared with the predictions of random matrix theory.     

Problems arising in the development of optical communication systems

The report starts with a survey of methods and feasibilities for the application of optical transmission systems in present and in future communication networks. Transmission systems with 1.12 Gbit/s offer new prospects for developing integrated communication systems. Therefore for this bitrate the use of optical components and the attainable repeater distances are discussed in detail. Finally an experimental model of an integrated broadband network is presented allowing to study the unsolved problems of using optical transmission channels in complex transmission and switching systems.     

Buchbesprechungen

Ohne Zusammenfassung

---

Book Reviews

---

Notices Bibliographiques

     

Die Bestimmung des Isomerenverhältnisses und Strukturermittlung substituierter Methylmetallocene durch kernmagnetische Resonanz

Zusammenfassung Eine rasche und einfache Bestimmung des Isomerenverhältnisses sowie die Strukturermittlung von substituierten Methylmetallocenen ist mit Hilfe derKMR-Spektroskopie auf Grund der chemischen Verschiebungen und der relativen Intensitäten der Signale der Ringmethylprotonen möglich.DieKMR-Spektren von etwa 50 (z. Teil neuen) isomeren Derivaten des Methyl- und 1,1-Dimethylferrocens, Methylcyclopentadienyl-Mn-tricarbonyls (Methylcymantrens) und Toluol-Cr-tricarbonyls (Methylbenchrotrens) werden mitgeteilt. Für einige wichtige Substitutionsreaktionen wurden die Isomerenverteilungen ermittelt und daraus die relativen Reaktivitäten der Ringpositionen berechnet.

---

A rapid and simple determination of the isomer distribution as well as the elucidation of structure of substituted methyl metallocenes is possible byNMR spectroscopy on the basis of the chemical shifts and relative intensities of the signals of the ring methylprotons.TheNMR spectra of appr. 50 (partly new) isomeric derivatives of methyl and 1.1-dimethylferrocene, methylcyclopentadienyl-Mn-tricarbonyl (methyl cymantrene) and toluene-Cr-tricarbonyl (methyl benchrotrene) are reported. For some important substitution reactions the isomer ratios were determined and from these the site reactivities were calculated.

---

---

Mit 1 Abbildung

---

31. Mitt.:H. Egger undH. Falk, Mh. Chem.97, 1590 (1966).