Synchronization Behavior in Coupled Chemical Oscillators

Synchronization is a collective phenomenon emerging from the interactions of different dynamical systems. Systems with different characteristics adjust their behavior to a common behavior of the group. This collective behavior is observed in many biological, chemical, and physical systems. Examples from different fields include pacemaker heart cells, synchronization of neurons during epilepsy seizures, arrays of microwave oscillators, and robot manipulators. Studies of coupled oscillators have revealed different mechanisms by which discrete oscillators interact and organize to a uniform synchronized state from an incoherent state. The discovery of a new type of synchronization state, called the chimera state has further broadened the field of synchronization. A chimera state is made up of coexisting subpopulations of oscillators, each with same coupling structure, but with one exhibiting synchronous behavior and the other asynchronous behavior. The phenomena has been the focus of much theoretical and experimental research in the past decade. In this thesis, experimental and simulation studies of chimera states in populations of coupled chemical oscillators will be described and their relation to other synchronization states will be characterized. Experiments were carried out with the photosensitive Belousov-Zhabotinsky (BZ) chemical oscillators and a light feedback scheme. The dimensionless two-variable Zhabotinsky-Buchholtz-Kiyatin-Epstein (ZBKE) model of the BZ chemical system was used in simulations.;A two-group coupling model, which splits the oscillators into two subpopulations, was used in the first part of the study. The subpopulations are globally coupled, both within and between the subpopulations. The coupling of every oscillator with members of the other subpopulation is weaker than the coupling with members of its own subpopulation. In-phase, out-of-phase, and phase-cluster synchronized states, as well as the chimera state, were found in both experiments and simulations. The probability of finding a chimera state decreases with increasing intra-group coupling strength. The study also revealed that heterogeneity in the frequencies of the oscillators in the system decreases the lifetime of a chimera. This was evidenced by the collapse of the chimera state to a synchronized state in both experiments and simulations with heterogeneous oscillators.;Synchronized and mixed-state behaviors are observed in populations of nonlocally coupled chemical oscillators in a ring configuration. With nonlocal coupling, the nearest neighbors are strongly coupled and the coupling strength decreases exponentially with distance. Experimental studies show stable chimera states, phase cluster states and phase waves coexisting with unsychronized groups of oscillators. These are spontaneously formed from quasi-random initial phase distributions in the experiments and random initial phase distributions in simulations. Simulations with homogeneous and heterogeneous oscillators revealed that a finite spread of frequencies increases the probability of initiating a synchronized group, leading to chimera states. The effects of group size and coupling strength on chimera states, phase waves, phase clusters, and traveling waves are discussed. Complex behaviors in coexisting states were analyzed, consisting of periodic phase slips with identical oscillators and periodic switching with nonidentical oscillators. Fourier transform analysis was used to distinguish between states exhibiting high periodicity and chimera states, which show similar average behavior

Incorporating Sustainability into Engineering and Chemical Education Using E-Learning

The purpose of this study was to develop e-learning activities that could facilitate the integration of sustainability concepts and practices in engineering and chemical education. Using an online learning management system (LMS), undergraduate students in an applied chemistry program at a public university in Zimbabwe participated in an online discussion on the role of chemical reaction engineering in achieving environmental sustainability goals. In the second activity, the students were instructed to prepare a design report for a cost-effective and innovative wastewater treatment plant for a rural hospital. The design report was evaluated through peer review online. Quantitative and qualitative analyses were performed on the two online activities to evaluate student engagement, quality of responses and the incorporation of sustainability into their learning. In the online discussion, 97 comments were made averaging 120 words per comment. Furthermore, the students averaged 3.88 comments, with the majority of comments exhibiting simple and complex argumentation, a deep reflection and widespread use of terms associated with sustainability such as recycling, pollution, waste and the environment. Furthermore, the evaluation of peer reviews revealed that participants demonstrated they could identify the strengths and shortcomings in the design reports. Therefore, this study demonstrated that e-learning, particularly peer review and online discussion, could help chemistry and engineering students appreciate the need for chemical and engineering activities that encourage sustainable development