Surface Structure and Catalytic COCO Oxidation Oscillations

A cellular automaton model is used to describe the dynamics of the catalytic oxidation of $CO$ on a $Pt(100)$ surface. The cellular automaton rules account for the structural phase transformations of the $Pt$ substrate, the reaction kinetics of the adsorbed phase and diffusion of adsorbed species. The model is used to explore the spatial structure that underlies the global oscillations observed in some parameter regimes. The spatiotemporal dynamics varies significantly within the oscillatory regime and depends on the harmonic or relaxational character of the global oscillations. Diffusion of adsorbed $CO$ plays an important role in the synchronization of the patterns on the substrate and this effect is also studied.Comment: Latex file with six postscript figures. To appear in Physica

On the Origin of Traveling Pulses in Bistable Systems

The interaction between a pair of Bloch fronts forming a traveling domain in a bistable medium is studied. A parameter range beyond the nonequilibrium Ising-Bloch bifurcation is found where traveling domains collapse. Only beyond a second threshold the repulsive front interactions become strong enough to balance attractive interactions and asymmetries in front speeds, and form stable traveling pulses. The analysis is carried out for the forced complex Ginzburg-Landau equation. Similar qualitative behavior is found in the bistable FitzHugh-Nagumo model.Comment: 5 pages, RevTeX. Aric Hagberg: http://t7.lanl.gov/People/Aric/; Ehud Meron:http://www.bgu.ac.il/BIDR/research/staff/meron.htm

A diffusion of innovations approach to investigate the brand name change of a higher education institution

Understanding the communication concepts behind promoting a brand name is essential to the successful adoption of that innovation. This research links diffusion of innovations theory, branding, and public relations by exploring the name change of a higher education institution. Extensive work has been done in the areas of branding and diffusion of innovations theory. However, this study links the two. The adoption of the University of Louisiana at Lafayette new name by its alumni was studied by analyzing the public relations campaign post-name change and by gathering background information on previous diffusion of innovations research and the importance of brand names to products, specifically higher education institutions. This background information set up a framework for testing diffusion of innovations theory with a marketing innovation. A survey was administered to a random sample of UL Lafayette out-of-state alumni to determine their opinions of the new university name, the rate of adoption of the new name, and the modes of communication utilized in the diffusion process. The approval rating of the new name by out-of-state alumni was split, with almost half of the respondents using the new name in everyday speech and a little more than half using it in everyday writing. In addition, while the public relations campaign did reach some out-of-state alumni, most learned of the new name through word-of-mouth and most were influenced to use the new name by other persons rather than by the university or university publications. The researcher also learned that the out-of-state alumni that approved and adopted the new name are also valuable supporters of the university through recruitment and funding. However, those who did not approve and adopt the new name now feel disconnected from their alma mater and do not choose to support it

Influence of auto-organization and fluctuation effects on the kinetics of a monomer-monomer catalytic scheme

We study analytically kinetics of an elementary bimolecular reaction scheme of the Langmuir-Hinshelwood type taking place on a d-dimensional catalytic substrate. We propose a general approach which takes into account explicitly the influence of spatial correlations on the time evolution of particles mean densities and allows for the analytical analysis. In terms of this approach we recover some of known results concerning the time evolution of particles mean densities and establish several new ones.Comment: Latex, 25 pages, one figure, submitted to J. Chem. Phy

Oscillatory instabilities during formic acid oxidation on Pt(100), Pt(110) and Pt(111) under potentiostatic control. II. Model calculations

A kinetic model is developed for the electrocatalytic oxidation of formic acid on Pt under potentiostatic control. The model development proceeds stepwise via a simple model of the electrocatalytic CO oxidation. The full model consists of four coupled, nonlinear ordinary differential equations. The scanned and stationary current/outer potential (I/U) behavior, stationary current oscillations, two-parameter bifurcation diagrams and stirring effects are simulated using realistic model parameters. The numerical findings are found to be consistent with the experimental results given by Strasser et al. The model reproduces period-1 as well as mixed-mode oscillations. Furthermore, a mechanistic analysis of the model was performed: two suboscillators are identified whose characteristics allow a plausible interpretation of the observed dynamics. After a classification of the suboscillators into previously described categories, an attempt is made to identify the minimal mechanistic requirements for electrochemical current oscillations

Controlling turbulence in coupled map lattice systems using feedback techniques

We report the suppression of spatiotemporal chaos observed in coupled map lattices. Suppression is achieved using different feedback techniques, most of which are applicable to actual experimental situations. Results from application of feedback control to a single chaotic element (single map) are presented to demonstrate similarities in the dynamical response of a single system and an extended system under the influence of external feedback

Discrete dynamics by different concepts of majorization

For the description of complex dynamics of open systems an approach is given by different concepts of majorization (order structure). Discrete diffusion processes with both invariant object number and sink or source can be represented by the development of Young diagrams on lattices. As experimental example we investigated foam decay, dominated by sinks. The relevance of order structures for characterization of certain processes is discussed

Birhythmicity induced by perturbing an oscillating electrochemical system

We describe the generation of new limit cycles in electrochemical systems under the influence of external periodic perturbations. For certain specific parameters of a nonharmonic forcing function, two coexisting periodic orbits can be generated from a single limit cycle observed in the unperturbed dynamics. This inception of birhythmicity (bistability) is observed in both simulations and actual experiments involving potentiostatic electrodissolution of copper in an acetate buffer

Spiral waves in a surface reaction: Model calculations

A systematic study of spiral waves in a realistic reaction‐diffusion model describing the isothermal CO oxidation on Pt(110) is carried out. Spirals exist under oscillatory, excitable, and bistable (doubly metastable) conditions. In the excitable region, two separate meandering transitions occur, both when the time scales become strongly different and when they become comparable. By the assumption of surface defects of the order of 10 μm, to which the spirals can be pinned, the continuous distribution of wavelengths observed experimentally can be explained. An external periodic perturbation generally causes a meandering motion of a free spiral, while a straight drift results, if the period of the perturbation divided by the rotation period is a natural number

It's all about the interaction: listener responses as a discourse-organisational variable

Language is humanity’s key tool for communication. This entails the fact that it generally occurs in interaction between two or more individuals. However, we do not yet have a theory of language variation and change that integrates our understanding of the interactional nature of language with the variationist analysis. This is especially challenging for variables above the level of the phoneme, but also applies to phonological variables that are impacted by the interactional context they stand in. This thesis focuses on Listener Responses, a variable above the level of the phoneme, and presents a theory and methodology of sociolinguistic variation that allows us to develop (1) interactionally sensitive de1nitions of discourselevel variables, the envelope of variation, and to quantify them in an accountable manner, (2) coding schemes which situate the function-based variants in the interactional structure and thus allow for an analysis of structural constraints on variation, and (3) a way of applying inferential statistics to variation based on structural as well as social variables. With respect to phonological variables, this thesis shows how the level of (inter)action relates to the actual realisations we observe. This is done based on the example of Listener Responses as a discourseorganisational variable, and gender as a social variable. Listener Responses are de1ned as all the things Listener can do without taking over the 2oor. Their frequency is thus quanti1ed relative to the number of words in the longer stretch of talk produced by the main Speaker. In the data at hand here, cross-gender accommodation is observed, with female Listeners decreasing their response frequency when listening to men, and male Listeners increasing theirs when listening to women. Next, a taxonomy of Listener Response actions is developed based on existing interactional literature and a close structural and interactional analysis of the data. Seven Action Types are proposed, and used as a coding scheme in the next two analysis chapters. The third analysis chapter shows variation in the frequency of the individual Action Types based on Speaker and Listener gender. There is an important structural constraint on variation located at the level of interactional structure: those Action Types that are strongly predicated by what the main Speaker does in the segment preceding the response are more strongly in2uenced by the main Speaker, while the Listener has a greater impact on those that are not constrained by the preceding segment. Both the 1rst and this analysis chapter draw on zero-in2ated poisson regression analysis as a useful tool for the analysis of variation in frequency. The 1nal analysis chapter looks at the relationship between the different action types and the actual linguistic realisation of the utterance, thus linking the discourse-level to the phonetic and prosodic level. It demonstrates that the linguistic realisation of any Listener Response is tailored to the talk that has preceded it on all levels of linguistic structure, and that prosodic and lexical shape need to be considered together, particularly for lexical items that can be used to do different actions. Overall, this thesis contributes to sociolinguistic theory and methodology by presenting a way of integrating interactional and variationist analyses from the de1nition of the variable, the envelope of variation, an overall frequency operationalisation, describing and de1ning the variants, to exploring the link between interactional function and linguistic realisation. It can be extended to other variables, both linguistic and social