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Graphene has displayed much promise as an electrical conductor and as a optical material. To date there is a large body of literature dedicated to the equilibrium properties of graphene. In this thesis the properties of graphene out of equilibrium are probed. Through combined optical and transport measurements the behaviour of hot electrons are probed at temperatures over five orders of magnitude from 50mK to 2000K. This wide range of temperatures allows access to the behaviour of quantum corrections at the lowest temperatures to the highest energy phonon modes. From ultrafast femtosecond laser pulses to steady state heating from an electric field the cooling of hot electron populations through coupling to various phonon modes in the graphene and the substrate are explored. Additionally the effect of an electric field on the weak localisation correction to the conductivity was separated from heating effects using applied magnetic fields combined with careful modelling of the heat transport properties of the graphene. Finally the desorption dynamics of oxygen bound to the surface are shown using a combination of transport and two pulse correlation technique using an ultrafast laser. Surprisingly the cooling of hot carriers in graphene at low energies shows substrate surface phonons as an important cooling mechanism, highlighting the importance of substrate choice in future graphene devices. In contrast at the very highest energy scales accessed only by photoexcitation the cooling is shown not to be influenced by the presence of a substrate, but out-of-plane phonon modes increase cooling of the hot optical phonons.

e appears to be significant potential for improving climate forecasts for SWA. The DoD still relies on long-term means to create climatological planning products to the field. We feel that by incorporating the anomalies associated with the climate variations discussed here, the DoD could add significant value to its climatology products.

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The twofold purpose of this investigation was to design and construct an apparatus for direct magnetic susceptibility measurements as a function of temperature and to provide the complete susceptibility characterization of the free radical galvinoxyl in the room temperature-liquid nitrogen range.

Abstract Grinding mills are generally very inefficient, difficult to control and costly, in terms of both power and steel consumption. Improved understanding of temperature behaviour in milling circuits can be used in the model-based control of milling circuits. The loss of energy to the environment from the grinding mill is significant hence the need for adequate modeling. The main objectives of this work are to quantify the various rates of energy loss from the grinding mill so that a reliable model for temperature behaviour in a mill could be developed. Firstly models of temperature behaviour in a grinding mill are developed followed by the development of a model for the overall heat transfer coefficient for the grinding mill as a function of the load volume, mill speed and the design of the liners and mill shell using the energy balances in order to model energy loss from the mill. The energy loss via convection through the mill shell is accounted for by quantifying the overall heat transfer coefficient of the shell. Batch tests with balls only were conducted. The practical aspect of the work involved the measurement of the temperatures of the mill load, air above the load, the liners, mill shell and the environmental temperature. Other measurements were: mill power and sound energy from the mill. Energy balances are performed around the entire mill. A model that can predict the overall heat transfer coefficient over a broad range of operating conditions was obtained. It was found that the overall heat transfer coefficient for the grinding mill is a function of the individual heat transfer coefficients inside the mill and outside the mill shell as well as the design of the liners and shell. It was also found that inside heat transfer coefficients are affected by the load volume and mill speed. The external heat transfer coefficient is affected by the speed of the mill. The values for the overall heat transfer coefficient obtained in this work ranged from 14.4 – 21W/m2K. iv List of Publications The author has published the following papers based on the contents of this dissertation as follows: Published conference abstract Kapakyulu, E., and Moys, M.H., 2005. Modelling of energy loss to the environment from the grinding mill, Proceedings of the Mineral Processing 2005’ Conference, SAIMM, Cape Town, South Africa, 4-5 Aug. pp 65-66 - SP03 Research Papers: Accepted for publication and currently in press in Minerals Engineering: Kapakyulu, E., and Moys, M.H., 2006. Modelling of energy loss to the environment from a grinding mill, Part I: Motivation, Literature Survey and Pilot Plant Measurements, (Currently in press in Minerals Engineering) Kapakyulu, E., and Moys, M.H., 2006. Modelling of energy loss to the environment from a grinding mill, Part II: Modeling the overall heat transfer coefficient, (Currently in press in Minerals Engineering)

São propostos modelos de 4 e de 12 vértices na rede quadrada para explicar a transição de fases antiferroelétrica observada no ácido quadrático (H IND. 2C IND. 4O IND. 4). A energia livre do modelo básico de 4 vértices se anula identicamente. A solução do modelo iônico de 12 vértices na aproximação de Bethe apresenta uma transição de segunda ordem. A existência desta transição de fases é assegurada por meio de um argumento de Peierls . A transição de fases do modelo de 12 vértices também é estudada pela técnica do grupo de renormalização fenomenológico. Conclui-se que a temperatura critica exata deve ser sistematicamente inferior àquela prevista pela aproximação de Bethe. Há evidências de que nü = 1. A mesma técnica foi empregada no estudo de um modelo de 16 vértices equivalente ao modelo de Ising, reproduzindo- se com boa precisão os cálculos exatos. Resultados experimentais mais recentes para O ácido quadrático indicam urna transição de primeira ordem. Mostra- se então que um modelo compressível de 12 vértices apresenta urna transição descontinua na aproximação de Bethe. / We consider 4 and 12 vertex models on the square lattice for the antiferroelectric phase transition in crystals of squaric acid (H IND. 2C IND. 4O IND. 4). The free energy of the basic 4 vertex model vanishes identically. In the framework of the Bethe approximation, the ionic 12 vertex model gives a second order phase transition. We use a Peierls argument to show that a phase transition does indeed occur in this model. Also, the phase transition in the 12 vertex model is studied by means of phenomenological renormalization group calculations. The exact critical temperature seems to be always lower than the prediction of the Bethe approximation. We present evidences that nü = 1 for this model. The same calculations were done for a 16 vertex model which is equivalent to the Ising model, the exact results being reproduced with good precision. Recent experimental data seem to support that the transition in squaric acid is indeed of first order. A compressible 12 vertex model is then shown to give a discontinuous transition.

Fuel cells are one of the most promising clean energy technologies under development. But a constraining factor in their further development is related to operating temperature ranges of current fuel cell systems, which is either low or high temperature. The intermediate temperature (200¡ÃƒÂ£C to 600¡ÃƒÂ£ C) would be the most desirable temperature range for a fuel cell for most applications, but there is no existing mature fuel cell technology in this range, mainly because of an absence of appropriate electrolytes. An effort to develop an intermediate-temperature molten-salt electrolyte fuel cell (IT-MSFC) was undertaken in this study. As a start, molten KOH was used as an electrolyte around 200¡ÃƒÂ£ C supported on a porous matrix. Tests used Pt loaded carbon cloth to be the electrode-catalyst layer, hydrogen and oxygen as fuel. The major challenge for this fuel cell was to hold electrolyte within a suitable porous support layer, without crossover of fuel gas during operation. Performance was short-lived, thus several ceramic materials were investigated in this research, including Zirconia felt, Zirconia disk, and porous NiO. To evaluate the properties of KOH molten salts working for IT-MSFCs, the performances were compared to fuel cell tests with KOH saturated solution and phosphoric acid with the same electrolyte support. KOH molten salt has large potential to work as electrolyte, with an open circuit voltage (OCV) of 1.0 V, and had linear performance curve between 1.0 V and 0.6 V, which is characteristic of fuel cells with low kinetic overpotentials. The highest performance was got by using porous NiO support in certain porosity range. Longevity of the fuel cell was a little better than the former, but still far from practical application. The result suggested that the capillarity, permeability and compatibility of support material are essential for performance of this type of fuel cell. Besides the problem of electrolyte II retention by the support matrix, unsuitable water management, degradation of the gas diffusion layer and catalyst may also reduce the fuel cell performance. Although this work is at a preliminary stage, it has demonstrated the immense potential of IT-MSFC, and a great deal of additional work will be required to produce a practical fuel cell.

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