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In this thesis, I shall explore the theoretical and empirical expositions regarding the causal mechanisms of cognitive growth. I shall do this in order to determine if biological epistemic theories of cognitive systems can be justified. It will be necessary in this thesis for me to adopt a multidisciplinary stance from Philosophy and Psychology. It will try to investigate from these two perspectives what it means to be a cognitive creature. However, I shall argue, if taken singularly, each standpoint fails to provide an adequate account of cognition that is necessarily based on adaptive, evolutionary constructs. During this thesis I will primarily focus on the major arguments in Philosophy that show a tight coupling between language, cognition and rationality. More specifically I will examine in detail Donald Davidson’s holistic account of what it is to be a rational, cognitive creature. I will show in the thesis, through comparative experimental evidence, that the causal mechanisms of cognitive growth, and thus thought may not be language. Consequently, Philosophical arguments that are based on tight relationships of thought and language will not be able to deliver a true account of cognition. I will demonstrate that Davidson’s philosophy has suffered from not being able to ground his philosophical perspectives on the relationship of language, cognition and rationality within an empirical programme and consequently it makes fundamental errors. Davidson’s account does not take on board the recent (and not so recent) empirical based work on primates which show the possible mechanisms of cognitive growth, which are independent of language. Similarly, I will also show that Psychology, which does provide us with the means to deliver an empirical account of cognition, due to its history based on Behaviourism, does not have the right causal mechanisms nor language to talk about the nature of complex cognition. I will show how Associationistic Psychology mischaracterises what it is to be cognitive and consequently, like philosophy, cannot deliver an accurate ontology of cognition. I intend in this thesis to provide a bridge between the two schools by adopting a comparative psychological approach. By using this comparative perspective, a more accurate theory of cognition may be possible and one that is not contaminated by language or any other cultural symbolic systems. I aim by the end of the thesis to be in a position which will hopefully allow modification of Davidson’s condition on possessing beliefs, a creature must have beliefs about beliefs. This modification will be based on an evolutionary account of what may or may not eventually turn out to be the precursors of higher cognitive states.

Si,Ge,-, alloy is an emerging semiconductor material with many important potential applications in the electronic industry due to its adjustable physical, electronic and optical properties. It has been scrutinized for the fabrication of high-speed micro electronics (e.g., SiGe heterojunction bipolar transistors (HBT) and high electron mobility field effect transistors) and thermo-photovoltaics (e.g., photodetectors, solar cells, thermoelectric power generators and temperature sensor). Other applications of Si,Ge,-, include tuneable neutron and x-ray monochromators and y-ray detectors. In these applications, SixGel-, alloy is generally used in the form of epilayers that have to be deposited on a lattice-matched substrate (wafer). Therefore, SixGel-, bulk single crystals with a specific composition (x) are needed for the extraction of such wafers. LPEE (Liquid Phase Electroepitaxy) was considered as a technique of choice for the growth of single crystals. However, LPEE growth process needs a single crystal seed with the same composition as the crystal to be grown. Yet, such a seed substrate with particularly higher composition is not commercially available. In order to address this important issue in LPEE, a crystal growth technique, which is named "Liquid Phase Diffusion" (LPD), was developed and used to produce the needed seed substrate materials. This was the main motivation of the present research. This thesis presents a combined experimental and modelling study for LPD growth of compositionally graded, germanium-rich single crystals of 25 rnrn in diameter for use as lattice-matched seed substrates. The experimental part focuses on the design and development of a complete LPD grow system. The experimental set-up was tested by growing ten Si,Ge,-, single crystals. Grown crystals were characterized by macroscopic and microscopic examinations after chemical etching for delineation of the degree of . . . Abstract 111 single crystallinity and growth striations. Compositional mapping of selected crystals were performed by using Electron Probe Micro Analysis (EPMA) as well as Energy Dispersive X-ray analysis (EDX). It was shown that the LPD technique can be successfully utilized to obtain Si,Ge,-, single crystals up to 6-8 % at.Si with uniform radial composition distribution. The modeling part presents a rational continuum mixture model developed to study transport phenomena (heat and mass transfer, fluid flow) occurring during the LPD growth of Si,Ge,-, . Based on the continuum model developed, two and three-dimensional transient numerical simulations were carried out. The numerical simulation models presented account for some important physical features of the LPD growth process ofSi,Ge,-, , namely (1) a growth zone design on the thermal field, (2) the structure of the buoyancy induced convective flow and its effect on the growth and transport mechanisms, (3) the shape and evolution of the initial and progressing growth interfaces, and (4) the spatial and time variation of the crystal growth velocity. It was numerically shown that, as the name LPD implies, the growth of Si,Ge,-, by LPD is mainly a diffusion driven process except the initial stages of the growth process during which the natural convection in the solution zone is prominent and has significant effects on the composition of the grown crystal. The simulated evolution of the growth interface agrees with experimental observations. In addition, the numerical growth velocities are in good agreement with those of experiments. The numerical model developed can be used to study other crystal growth processes such as LPEE, Traveling Heater Method THM, and vertical Bridgman with slight modifications.

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30 clones of Betula pendula were produced using micro-propagation techniques and screened for root system variation. Shoot variation was assessed and the root systems divided into 3 root types; fine, woody, and non-woody. Dry weights, lengths, and various ratios were used in the analysis. There were differences in all the characteristics measured. Root system size could not usefully be predicted from shoot size. Four clones with contrasting root systems were chosen for further experiments. A sequential harvest experiment showed that all the characteristics changed with time, and that the clones grew and developed at different rates. Root distribution and development differed between the clones. A water status experiment indicated differences in rooting depth distribution which could be related to drought avoidance, but no growth differences were found. Two different nitrogen levels were used to show that root system differences had little effect on nitrogen uptake. One clone exhibited growth patterns which suggested that it would grow well in areas of chronic nutrient deficiency. The clone responses to phosphorus deficiency and mycorrhizal infection were also tested. One clone again showed growth patterns resembling those found in areas of chronic nutrient deficiency. Another clone responded poorly to mycorrhizal growth at high phosphorus concentrations. Ranking comparisons to the ranks found during the sequential harvest experiment showed that size was more important than age in determining development. Clone 14 seemed to be less plastic than the other clones, and shoot height and structural root production were controlled more by genotype than environment. The methods used, and some useful characteristics, were discussed in the context of tree selection programmes. Many suggestions for future work are given. These suggestions work towards the ultimate aim of the project to select root system types specifically suited to different environments.

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