Auslander Systems

The authors generalize the dynamical system constructed by J. Auslander in 1959, resulting in perhaps the simplest family of examples of minimal but not strictly ergodic systems. A characterization of unique ergodicity and mean-L-stability is given. The new systems are also shown to have zero topological entropy and fail to be weakly rigid. Some results on the set of idempotents in the enveloping semigroup are also achieved

Honey bee colony losses

No description supplie

IP Cluster Points Idempotents, And Recurrent Sequences

We consider the dynamical system (M,S) where M is the orbit closure of a nonperiodic recurrent sequence of O\u27s and 1\u27s (for example, the Morse sequence) and S is the shift map. The enveloping semigroup is E(M) = {Sⁿ : n ∈ Z} where the closure is taken in the topology of pointwise convergence. H. Furstenberg was the first to establish the existence of relationships between recurrence, IP sets, and idempotents in the enveloping semigroup, and the first author has proven that the closure of the set of idempotents coincides with the IP cluster points. In this paper the authors compute this set for (M,S) and shed light on other combinatorial properties of generalized Morse sequences

Microwave device investigations

Materials, devices and novel schemes for generation, amplification and detection of microwave and millimeter wave energy are studied. Considered are: (1) Schottky-barrier microwave devices; (2) intermodulation products in IMPATT diode amplifiers; and (3) harmonic generation using Read diode varactors

Tricritical behaviour in deterministic aperiodic Ising systems

We use a mixed-spin model, with aperiodic ferromagnetic exchange interactions and crystalline fields, to investigate the effects of deterministic geometric fluctuations on first-order transitions and tricritical phenomena. The interactions and the crystal field parameters are distributed according to some two-letter substitution rules. From a Migdal-Kadanoff real-space renormalization-group calculation, which turns out to be exact on a suitable hierarchical lattice, we show that the effects of aperiodicity are qualitatively similar for tricritical and simple critical behaviour. In particular, the fixed point associated with tricritical behaviour becomes fully unstable beyond a certain threshold dimension (which depends on the aperiodicity), and is replaced by a two-cycle that controls a weakened and temperature-depressed tricritical singularity.Comment: Formatting improved. 7 pages, 2 figures (included). Journal reference adde

Hypernatural Numbers as Ultrafilters

In this paper we present a use of nonstandard methods in the theory of ultrafilters and in related applications to combinatorics of numbers

On the Absorption of X-rays in the Interstellar Medium

We present an improved model for the absorption of X-rays in the ISM intended for use with data from future X-ray missions with larger effective areas and increased energy resolution such as Chandra and XMM, in the energy range above 100eV. Compared to previous work, our formalism includes recent updates to the photoionization cross section and revised abundances of the interstellar medium, as well as a treatment of interstellar grains and the H2molecule. We review the theoretical and observational motivations behind these updates and provide a subroutine for the X-ray spectral analysis program XSPEC that incorporates our model.Comment: ApJ, in press, for associated software see http://astro.uni-tuebingen.de/nh