An investigation of Martian atmospheric trace species using laboratory and computer-based simulation

The study of trace gas species in the Martian atmosphere has the potential to shed new light on wide-ranging topics such as the search for life and the history of liquid water on the planet. Investigating the way that molecules such as ozone, water and HCl are cycled in the atmosphere will give insights into the interactions taking place between the atmosphere, lithosphere and any potential biosphere. Numerous missions are currently being planned; for example the NASA/ESA Trace Gas Orbiter which will probe the trace constituents of the Martian atmosphere and to try to explain recent observations such as the Tharsis methane plumes and the presence of perchlorate in the North polar plains. Currently there are two Mars General Circulation Models (MGCMs) that have fully coupled photochemistry modules: the 3D Mars Global Multiscale Model (GM3) and the Laboratoire de Météorologie Dynamique (LMD) MGCM. Both modules focus on odd-hydrogen (HOx) and odd-oxygen (Ox) chemistry and are not yet capable of simulating more complex chemical interactions. However, the benefit of fully-coupled MGCMs is that both the chemistry and the global transport of trace species can be investigated. In the current project we plan to study the more exotic chemical reactions occurring in the Martian atmosphere and to constrain their mechanisms and rates using both laboratory analogues and computerbased simulation

Towards AMR Simulations of Galaxy Formation

Numerical simulations present a fundamental building block of our modern theoretical understanding of the Universe. As such the work in this thesis is primarily concerned with understanding fundamental differences that lie between the different hydrodynamic schemes. In chapter 3 I outline the optimisations I make to the FLASH code to enable larger simulations to be run. These include developing and testing a new FFT gravity solver. With these complete, in chapter 4 I present results from a collaborative code comparison project in which we test a series of different hydrodynamics codes against a suite of demanding test problems with astrophysical relevance. As the problems have known solutions, we can quantify their performance and are able to develop a resolution criteria which allows for the two different types to be reliably compared. In chapter 5 we develop an analytic model for ram pressure stripping of the hot gaseous haloes of galaxies in groups and clusters. We test the model against a suite of hydrodynamic simulations in the SPH GADGET-2 code. To ensure that the spurious suppression of hydrodynamic instabilities by SPH codes does not bias our results, I compare our findings to those obtained with the FLASH AMR code and find excellent agreement. Chapter 6 presents work in which we unambiguously determine the origin of the difference between the entropy cores formed in AMR and SPH codes. By running mergers of model clusters we are able to systematically explore the various proposed mechanisms and determine that turbulent mixing generates the higher entropy cores within AMR codes but is suppressed in SPH codes. The startling differences between the two hydrodynamic schemes presented in chapter 6 leads me to investigate their affect upon different sub-grid physical recipes. In chapter 7 I present the implementation of a sub-grid star formation recipe in FLASH and find strong differences in the way the two codes model pressure laws. I extend the work in chapter 8 by implementing a kinetic supernova feedback mechanism in FLASH and contrasting it with the results from the GADGET-2 code. I find that AMR codes dissipate energy much more efficiently than in SPH codes

Living with the Semantic Gap: Experiences and remedies in the context of medical imaging

Semantic annotation of images is a key concern for the newly emerged applications of semantic multimedia. Machine processable descriptions of images make it possible to automate a variety of tasks from search and discovery to composition and collage of image data bases. However, the ever occurring problem of the semantic gap between the low level descriptors and the high level interpretation of an image poses new challenges and needs to be addressed before the full potential of semantic multimedia can be realised. We explore the possibilities and lessons learnt with applied semantic multimedia from our engagement with medical imaging where we deployed ontologies and a novel distributed architecture to provide semantic annotation, decision support and methods for tackling the semantic gap problem

Artequakt: Generating tailored biographies from automatically annotated fragments from the web

The Artequakt project seeks to automatically generate narrativebiographies of artists from knowledge that has been extracted from the Web and maintained in a knowledge base. An overview of the system architecture is presented here and the three key components of that architecture are explained in detail, namely knowledge extraction, information management and biography construction. Conclusions are drawn from the initial experiences of the project and future progress is detailed

Numerical simulations of the possible atmospheric origin of Martian perchlorate

The first detection of perchlorate salts in the Martian regolith was made by NASA’s Phoenix Mars lander in the northern polar plains. Perchlorate salts are important as they can lead to the formation of brines, are a possible energy source for microbes and can be used as a marker for climate change from wet to dry conditions. There is currently no known mechanism of perchlorate production on Mars though an atmospheric chemical pathway resulting in perchlorate has been proposed