Experimental Observation of Simultaneously Existing Moving and Standing Patterns in a Gas-Discharge System

In a quasi 1-dimensional lateral gas-discharge system we observe experimentally sub- and supercritical bifurcations from a spatially homogeneous to an inhomogeneous distribution of the current density. Among other results we find for the first time the simultaneous existence of a nontrivial nonstationary pattern (travelling waves) with a nontrivial stationary pattern (periodic filaments) in a laterally extended dc-driven gas-discharge system.     

Sound velocity of CeAl2 in high magnetic fields

We report low temperature measurements of the C₄₄ sound velocity of CeAl₂ in magnetic fields up to 7 T. Between 5 K and 30 K the field softens C₄₄, below 5 K a more complicated behaviour is observed.     

Computational models of music perception and cognition I: The perceptual and cognitive processing chain

We present a review on perception and cognition models designed for or applicable to music. An emphasis is put on computational implementations. We include findings from different disciplines: neuroscience, psychology, cognitive science, artificial intelligence, and musicology. The article summarizes the methodology that these disciplines use to approach the phenomena of music understanding, the localization of musical processes in the brain, and the flow of cognitive operations involved in turning physical signals into musical symbols, going from the transducers to the memory systems of the brain. We discuss formal models developed to emulate, explain and predict phenomena involved in early auditory processing, pitch processing, grouping, source separation, and music structure computation. We cover generic computational architectures of attention, memory, and expectation that can be instantiated and tuned to deal with specific musical phenomena. Criteria for the evaluation of such models are presented and discussed. Thereby, we lay out the general framework that provides the basis for the discussion of domain-specific music models in Part II.     

Magnon dispersion in TbAl2

Slow neutron inelastic scattering has been used to determine the magnon dispersion relation in TbAl₂ at 4.6 K. Energies of magnons in symmetry points are in meV: Γ 1.7±0.1 and 6.0±0.1, X5.1±0.2 (degenerate); L3.0±0.1 and 7.4±0.1 for the acoustic and optical modes respectively. An analysis of the experimental curves in terms of interatomic exchange parameters shows long range order and oscillations in real space.     

Concentric-ring patterns in a dielectric barrier discharge system

We report on the first experimental observation of a concentric-ring pattern in a short planar dielectric barrier gas-discharge system and study its spatiotemporal behavior. While increasing the gas pressure the destabilization of the rings into a filamentary structure is observed. The charge carriers deposited on the dielectric electrodes determine the spatiotemporal behavior of the pattern.     

Magnetic excitations of HoAl2 in a magnetic field

The ground state spin wave excitation energies of single crystalline HoAl₂ have been studied at T= 4.2 K in external magnetic fields up to 7 T by means of inelastic neutron scattering. The results have been interpreted in terms of a cubic crystalline electric field using the parameters determined by magnetization measurements and an exchange interaction with the exchange parameters taken from the zero field measurements.     

A crystallographic description of experimentally identified formation reactions of Cu(In,Ga)Se2

This work describes solid-state reactions for the formation of the chalcopyrite compounds CuInSe₂, CuGaSe₂ and Cu(In,Ga)Se₂ on atomic scale. The most important chalcopyrite formation reactions which were identified by the authors by real-time in situ X-ray diffraction in preceding experiments are (A) CuSe+InSe→CuInSe₂, (B) Cu₂Se+2 InSe+Se→2 CuInSe₂ and (C) Cu₂Se+In₂Se₃→2 CuInSe₂. During the selenistaion of a metallic precursor containing gallium a separate fourth reaction occurs: (D) Cu₂Se+Ga₂Se₃→2 CuGaSe₂. The quaternary compound is finally formed by interdiffusion of CuInSe₂ with CuGaSe₂ (E). These five reactions differ in their activation energy and reaction speed. We explain these differences qualitatively by analysing the involved crystal structures for each reaction. It turns out that all reactions involved in the formation of Cu(In,Ga)Se₂ are promoted by epitaxial relations, which facilitates the formation of polycrystalline thin films at temperatures much below those necessary for single crystal growth. Recommendations for the growth of larger grains of Cu(In,Ga)Se₂ containing fewer defects are given.     

Measurement and 3D simulation of self-organized filaments in a barrier discharge

We report on pattern formation phenomena in the filamentary dielectric barrier discharge between plane glass electrodes. It is for the first time that a three-dimensional (3D) self-organized glow pattern was both observed in an actual experiment and directly calculated in a full 3D discharge simulation in a quantitative manner. Specifically, we investigate the genesis of periodic patterns during the first breakdowns. Despite our simple drift-diffusion discharge model, the correspondence of experimental and numerical findings is surprisingly good.     

Traveling pairs of spots in a periodically driven gas discharge system: collective motion caused by interaction

We report on a new type of interaction between solitary current density spots observed in an ac-driven gas discharge system. These spots behave as independent particles as long as they are far apart from each other. Upon collision, in most cases one of the spots is extinguished. However, we also observe the formation of stable bound pairs of spots that move rather fast. We argue that both the rapid motion and the binding itself are due to a pronounced symmetry breaking with respect to size and breakdown phase of the individual spots. Basic features of pairs of spots traveling due to a true two-spot mechanism are discussed.