Part A of 2 parts. / <p> This report is a study of the dynamic properties of semiconductor laser diodes. The measurement of some important laser diode parameters necessary for dynamic behaviour prediction is described. The relaxation oscillation behaviour for laser diodes pumped with nanosecond time scale current pulses is predicted using both an approximate analytic solution and computer simulations. This predicted behaviour is compared with experimental results. Dynamic experiments with an external cavity for extra optical feedback and a regenerative loop for optoelectronic feedback are also described and discussed. Details of the experimental setups and techniques used are given. </p> / Thesis / Master of Engineering (MEngr)

Computer simulations have become a vital tool in modern science. The ability to reliably move beyond the capabilities of experiment has allowed great insights into the nature of matter. To enable the study of a wide range of systems and properties a plethora of simulation techniques have been developed and refined, allowing many aspects of complex systems to be demystified. I have used a range of these to study a variety of systems, utilising the latest technology in high performance computing (HPC) and novel, nanoscale models. Monte Carlo (MC) simulation is a commonly used method to study the properties of system using statistical mechanics and I have made use of it in published work [1] to study the properties of ferrogels in homogeneous magnetic fields using a simple microscopic model. The main phenomena of interest concern the anisotropy and enhancement of the elastic moduli that result from applying uniform magnetic fields before and after the magnetic grains are locked in to the polymer-gel matrix by cross-linking reactions. The positional organization of the magnetic grains is influenced by the application of a magnetic field during gel formation, leading to a pronounced anisotropy in the mechanical response of the ferrogel to an applied magnetic field. In particular, the elastic moduli can be enhanced to different degrees depending on the mutual orientation of the fields during and after ferrogel formation. Previously, no microscopic models have been produced to shed light on this effect and the main purpose of the work presented here is to illuminate the microscopic behaviour. The model represents ferrogels by ensembles of dipolar spheres dispersed in elastic matrices. Experimental trends are shown to be reflected accurately in the simulations of the microscopic model while shedding light on the microscopic mechanism causing these effects. These mechanisms are shown to be related to the behaviour of the dipoles during the production of the gels and caused by the chaining of dipoles in magnetic fields. Finally, simple relationships between the elastic moduli and the magnetization are proposed. If supplemented by the magnetization curve, these relationships yield the dependencies of the elastic moduli on the applied magnetic field, which are often measured directly in experiments. While MC simulations are useful for statistical studies, it can be difficult to use them to gather information about the dynamics of a system. In this case, Molecular Dynamics (MD) is more widely used. MD generally utilises the classical equations of motion to simulate the evolution of a system. For large systems, which are often of interest, and multi-species polymers, the required computer power still poses a challenge and requires the use of HPC techniques. The most recent development in HPC is the use of Graphical Processing Units (GPU) for the fast solution of data parallel problems. In further published work [2], I have used a bespoke MD code utilising GPU acceleration in order to simulate large systems of block copolymers(BC) in solvent over long timescales. I have studied thin films of BC solutions drying on a flat, smooth surface which requires long timescales due to the ’slow’ nature of the process. BC’s display interesting self-organisation behaviour in bulk solution and near surfaces and have a wide range of potential applications from semi-conductors to self-constructing fabrics. Previous studies have shown some unusual behaviour of PI-PEO diblock co-polymers adsorbing to a freshly cleaved mica surface. These AFM studies showed polymers increasing in height over time and proposed the change of affinity of mica to water and the loss of water layers on the surface as a driver for this change. The MD simulation aimed to illuminate the process involved in this phenomena. The process of evaporation of water layers from a surface was successfully simulated and gave a good indication that the process of solvent evaporation from the surface and the ingress of solvent beneath the adsorbed polymer caused the increase in height seen in experiment.

Moral contractarianism, as demonstrated in the work of David Gauthier, is an attempt to derive moral principles from the non-moral premises of rational choice. However, this contractarian enterprise runs aground because it is unable to show that agents would commit to norms in a fairly realistic world where knowledge is limited in space and time, where random shocks are likely, and where agents can be arbitrarily differentiated from one another. In a world like this, agents will find that the most "rational" strategy is to behave "non-rationally," imitating the behavior of others in their vicinity and preserving a limited sort of ignorance.

Higher education professionals are always seeking new and better ways to prepare students for life after college—a goal that requires not only providing knowledge and experience in their chosen field, but also helping them stay engaged in the process. Recently, computer based simulations have magnified role playing and case study techniques that have been used in classrooms for many years. These simulations have found great success in many settings, including engineering, business, and medicine, but there have been very few computer simulations designed for writing classes. Given that some of the greatest challenges in such classes are teaching students to respond to a context, write to an audience, and stay engaged in the process, simulations have great potential to improve pedagogy in writing classes by providing a more authentic and engaging context. In this pilot study of a computer simulation designed for technical writing classes, we examined how the simulation affected these factors (authenticity and engagement). We combined qualitative and quantitative methods, doing surveys in three classes (the class using the simulation and two classes with other pedagogies) and focus groups with the simulation class. While the results of the survey were rather inconclusive, the surveys and focus groups combined taught us two main lessons: (1) the simulation needs to be believable to be effective—making it too much like a game can backfire with some students, and (2) students remain more interested when the simulation is complex and leaves them some autonomy concerning what happens. While not necessarily groundbreaking, knowing what worked and what didn’t in our simulation can provide valuable insights for future simulation designers.

Moral contractarianism, as demonstrated in the work of David Gauthier, is an attempt to derive moral principles from the non-moral premises of rational choice. However, this contractarian enterprise runs aground because it is unable to show that agents would commit to norms in a fairly realistic world where knowledge is limited in space and time, where random shocks are likely, and where agents can be arbitrarily differentiated from one another. In a world like this, agents will find that the most "rational" strategy is to behave "non-rationally," imitating the behavior of others in their vicinity and preserving a limited sort of ignorance.

The purpose of this thesis is to develop a testing environment for mobile robot experiments, to examine methods for multi-robot platooning through hostile environments, and test these algorithms on mobile robots. Such a system will allow us to rapidly address and test problems that arise concerning robot swarms and consequent interactions. In order to create this hardware simulation environment a test bed will be created using ROS or Robot Operating System. This platform is highly modular and extensible for future development. Trajectory generation for the robots will use smoothing splines, B-splines, and A* search. Each method has distinct properties which will be analyzed and rated with respect to its effectiveness with regards to robotic platooning. A few issues to be considered include: Is the optimal path taken with respect to distance and threats? Is the formation of the robots maintained or compromised during traversal of the path? And finally, what sorts of compromises or additions are needed to make each method effective? This work will be helpful for choosing route planning methods in future work and will provide a large code base for rapid prototyping.

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The complete set of Kubo conductivity tensors are computed for two- and three-dimensional linear magnetic null systems using collisionless single-particle simulations. Chaos regions are constructed for each case, along with the complete Lyapunov spectrum. It is found that stochastic frequency mixing of particle bounce motion, as well as gyromotion, contribute significantly to the conductivity. For many cases, the conductivity curve is well approximated by power-laws, resulting in a divergent value of the direct-current conductivity, while others can be described by a sum of Maxwellian curves. The energy dissipation of these systems is also briefly discussed.