Lewis Dartnell

Academic

Postgraduate Work University College London 2003 - 2008
PhD Martian radiation environment and astrobiological implications
Life on Mars? Using Geant4 to model the subsurface radiation environment Powerpoint presentation delivered 6^th October 2005 to the GEANT4-SPENVIS workshop, Leuven, Belgium. Thumbnail links to the Workshop website, from which the presentation can be downloaded. Are we all Martians? Poster produced for the Perspectives Poster Competition at the BA Festival of Science. Dublin, September 2005. Placed as Runner-Up. The BA website here gives a list of all the Winners and links to pdf files of the posters. The thumbnail to the right links to a .jpg version of my poster. Mars Crustal magnetism, radiation environment, and implications for astrobiology Powerpoint presentation delivered February 2005 as part of the Astrobiology and Planetary Exploration (APEX) lecture series, UCL.
MRes Modelling Biological Complexity
Major research project Illusions disrupting the accurate perception of velocity and position This study constitutes the generation of a new kind of motion illusion. Stimuli are created that distort not only the perception of object velocity, but also its position. The long-range and short-range motion detection mechanisms are stimulated with separate signals to create a powerful illusion of either accelerated or retarded velocity. The consequences of such an illusion are explored with respect to the distinctive dynamic patterns displayed by certain cephalopod species when hunting prey or escaping predators. The following animations were created to illustrate a lecture given on the results of this research project. The thumbnails download a .mov file. Alternatively, you could download all three as a single zip file here. For best results, make sure your player is set to 'Loop'. Scrolling gabor function A sine grating enveloped in a guassian window so as to merge smoothly with the background, and phase shifted each time step to give the impression of smooth scrolling. Wacky Race Although the two moving gabors are exactly level, the right-hand one always appears to be slipping ahead. Mind Mess The gabor is moving in a true circle at constant speed, but the motion illusion distorts the shape of the path and the gabor also seems to speed up and slow down. Miniprojects Motion illusions & active camouflaging It has been well established that the pattern of colouration on many animals is adaptive and confers a survival advantage by concealment, either from predators or prey. The first section of this report reviews different general camouflaging strategies to evade visual detection. The second section discusses different models for explaining the mechanism of neural computation in the visual system. Both edge detectors and motion detectors are treated in detail. Section 3 examines two examples where the camouflage system appears to be exploiting a specific feature of the observer’s visual processing pathway. Section 4 begins the investigation into optical illusions designed specifically as novel methods of masking movement. Several different active camouflage strategies are discussed, including minimisation of apparent motion, and percepts of accelerated or retarded velocity. These illusions are run through a programme simulating the action of the Multi-channel Gradient Model of motion perception to obtain an objective quantification of the perceptual effects. Section 5 addresses the question as to whether these illusions are employed in nature to disrupt motion perception. The common cuttlefish, along with other cephalopods, produces a characteristic kinetic pattern that may represent an adaptation to generate the motion illusions examined in this research. Two alternative hypotheses for the function of the display are discussed, both of which are novel to the best of the author’s knowledge. MRes core skills Understanding the Macro with the Micro: Using plankton to study ocean-wide ecology Information about some of the smallest organisms in the sea, plankton, has recently been used to address two of the most pressing issues of our time: global climate change and the sustainable harvesting of the oceans. Here we explain how plankton data are collected and present an overview of the diverse uses of this valuable data set. (link opens a reduced .jpg in a new window) This poster was produced in collaboration with Trevor Graham It is on display at the SAHFOS centre, Marine Biological Association, Plymouth. Runge-Kutta and the Lorenz Attractor The Lorenz Attractor was one of the first chaotic systems to be discovered by mathematicians. Here a Mathematica programme has been written to perform a technique of numerical apporximation, the 4th-order Runge-Kutta method, to calculate and plot trajectories through 3-space.

Undergraduate Work The Queen's College, Oxford. 1999 - 2002
Specialisations for microchiropteran echolocation and moth defence co-evolution	The suborder Microchiroptera contains approximately 800 species of bats with a sophisticated biosonar system used to actively interrogate the local environment and analyse the returned echoes to extract information on obstacles and potential prey in the flight path. Most are insectivorous and hunt with aerial-hawkng or gleaning tactics, although some, such as Noctilio leporinus, predate on fish and use echolocation to detect localised surface ripples. Much research has been conducted into the neurophysiology of echolocation with its superb acoustic discrimination capabilities, including very fine temporal and frequency resolution. This review covers firstly bat call design and hunting behaviour, and the neural basis of their capabilities. The second half deals with the question of a bat-moth co-evolutionary arms race.	Achieved a First grade
Is Humpback Whale Song a Language?	The humpback whale, Megaptera novaeangliae, produces the most complex vocalisations of all 77 cetacean species, which have been dubbed by Payne and MacVay (1971) as “songs”. These songs are hierarchical in nature, with rules seemingly governing their organisation and evolution over breeding seasons. No one hypothesis of the song’s function adequately explains its complexity and structure, except perhaps for the theory that it constitutes the first non-human language yet discovered. Buck and Suzuki (1999) have applied Information theory to analyse a sample of humpback song converted into a stream of symbols using a self-organising neural network (SONN). This theory can be used to determine the maximum amount of information contained within a coded sequence by the unpredictability of the next symbol. Different assumptions can be made about the nature of the sequence; the next symbol is randomly determined (thus no hierarchical structure is possible within the sequence), or the probability of the next symbol is dependent on the previous one, or two symbols (0th, 1st and 2nd Order Markov models respectively). It was found that a first-order assumption could not reasonably model humpback song, meaning that humpback song possesses a hierarchical structure suggestive of language. The low rate of information transmission, about 0.1 - 0.6 bits per second, may ensure reliable communication over long distances in noisy, unpredictable acoustic conditions. Language, as opposed to simple communicative signals, has a deep-structure that is both hierarchical and recursive. This recursiveness means that words sometimes greatly separated in a sentence must agree (for example in gender or plurality); so called “long-distance dependency”. Words of the same category (for example adjectives or nouns) behave similarly with respect to syntactically correct positioning within a sentence, and thus language also contains a lexical category structure. Elman (1992) has demonstrated that a partially recursive artificial neural network trained on a set of English sentences can detect and internally represent both recursive and lexical category structure. This study constitutes a novel approach to analysis of humpback song for signs of language. A network architecturally identical to Elman’s was used to test song for evidence of lexical category structure, detection of which would provide support for the language hypothesis.	Achieved a First grade

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