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Understanding how temperature affects biological systems is a central question in ecology and evolutionary biology. Anthropogenic climate change adds urgency to this topic, as the demise or success of species under climate change is expected to depend on how temperature affects important aspects of organismal performance, such as growth, development, survival and reproduction. Rates of biological processes generally increase with increasing temperature up to some maximal temperature. Variation in the slope of the initial, rising phase has attracted considerable interest and forms the focus of this thesis. I explore variation in growth rate-temperature relationships over several levels of biological organization, both between and within species, over individuals’ lifetime, depending on the ecological context and in relation to important life history characteristics such as generation length and winter dormancy.       Specifically, I examine how a clade of temperate damselflies have adapted to their thermal environment along a 3,600 km long latitudinal transect spanning from Southern Spain to Northern Sweden. For each of six species, I sampled populations from close to the northern and southern range margin, as well from the center of the latitudinal range. I reared larvae in the laboratory at several temperatures in order to measure indiviudal growth rates. Very few studies of thermal adaptation have employed such an extensive sampling approach, and my finding reveal variation in temperature responses at several levels of organization.       My main finding was that temperature responses became steeper with increasing latitude, both between species but also between latitudinal populations of the same species. Additional genetic studies revealed that this trend was maintained despite strong gene flow. I highlight the need to use more refined characterizations of latitudinal temperature clines in order to explain these findings. I also show that species differ in their ability to acclimate to novel conditions during ontogeny, and propose that this may reflect a cost-benefit trade-off driven by whether seasonal transitions occur rapidly or gradually during ontogeny.       I also carried out a microcosm experiment, where two of the six species were reared either separately or together, to determine the interacting effects of temperature and competition on larval growth rates and population size structure. The results revealed that the effects of competition can be strong enough to completely overcome the rate-depressing effects of low temperatures. I also found that competition had stronger effects on the amount of variation in growth rates than on the average value.       In summary, my thesis offers several novel insights into how temperature affects biological systems, from individuals to populations and across species’ ranges. I also show how it is possible to refine our hypotheses about thermal adaptation by considering the interacting effects of ecology, life history and environmental variation.

A probe for measuring the specific heat of superconductors at low temperatures and in high magnetic fields has been built and commissioned. The probe has been tested using the relaxation method on samples of copper and the accuracy of the data is 1.3 % between 5 K and 30 K, data taken using the long range pulse method has a resolution of 10 mK. Specific heat measurements have been performed on members of the series (Pb(_1)-(_x))Cu(_1.8x)Mo(_6)S(_8), (Sn(_1-x))Eu(_x)Mo(_6)S(_8) and (Pb(_1-x)M(_x))Mo(_6)S(_8) where M = Gd and Eu, from 3 K up to 30 K and in magnetic fields up to 15 T. Additional results from resistivity, susceptibility, magnetisation. X-ray diffraction, transmission electron microscopy and electron dispersive-ray measurements are also presented. These data have been compared to results from other authors and are analysed in terms of the BCS and GLAG theories of superconductivity and the magnetic properties of these materials. The mean field model has been used to calculate numerically the magnetic contribution to the specific heat (cm) of both ferromagnetic and antiferromagnetic systems as a function of temperature and applied field both above and below the ordering temperature. In addition an approximate analytic form for the magnetisation has been used to calculate Cm above the ordering temperature. Expressions have been derived for the saturation value of the peak in C(_m): C(^sat)(_m) = 1.1245n(_cell)RJI(J+1) and the temperature dependence of the peak with applied field ȡ(μ(_o)H(_ext))/ȡT(_peak)=6.540/g(_J)(J+1). They allow the simple calculation of the values of J and g(_J)(J + 1) from specific heat data. The magnetic contribution to the specific heat of the samples (Sn(_0.65)Eu(0.35)Mo(_6)S(_8)) and (Sn(0.50)Eu(_0.50)Mo(_6)S(_8)) have been modelled using these calculations and excellent agreement is found by considering the magnetic ions as free ions. The sample is accurately modelled by including an additional minority phase (Gd(_2)S(_3)). The approximate expressions have also been used to analyse data on high temperature superconductors producing values of J and g(_J)}{J + 1) consistent with a doublet ground state. The properties of Chevrel phase materials have been determined as a function of doping level. The critical temperature is degraded by doping but an increase in the critical current density is observed in the series (Pb(_1-x)Cu(_1-8x)Mo(_6)S(_8) for very low levels of doping. Increases of up to 28 % in the upper critical field, that are probably due to the compensation effect and an increase in the normal state resistivity, are also observed in the series (Sn(_1-x)Eu(_x)Mo(_6)S(_8)) at high levels of doping and in the series (Pb(_1-x)Gd(_x)Mo(_6)s(_8) for low levels of doping.

This thesis deals with the development and application of Monte Carlo simulations to study electron transport in bulk GaN in the wurtzite crystal structure and the properties of field effect transistors made from the material. There is a particular emphasis on transport in the high electric field regime and transistors operating at high voltages. The simulation model includes five sets of non-parabolic conduction band valleys which can be occupied by electrons during high field transport. The effects on electron transport of impurities and the relevant phonon scattering mechanisms have been considered. Results for electron transport at both low and high electric field are presented and compared with the properties of GaN in the zincblende structure, of other group-III nitride semiconductors, and of GaAs. The dependence of the transport properties on the material parameters is discussed and also with regard to the temperature, donor concentration and electric field magnitude and direction. The transport properties of electrons in wurtzite GaN n+-i(n)-n+ diodes are also explored, including the effect of the upper valleys and the temperature on hot electron transport. Simulations have also been carried out to model the steady-state and transient properties of GaN MESFETs that have recently been the subject of experimental study. It has been suggested that traps have a substantial effect on the performance of GaN field effect transistors and we have developed a model of a device with traps to investigate this suggestion. The model includes the simulation of the capture and release of electrons by traps whose charge has a direct effect on the current flowing through the transistor terminals. The influence of temperature and light on the occupancy of the traps and the /- V characteristics are considered. It is concluded that traps are likely to play a substantial role in the behaviour of GaN field effect transistors. Further simulations were performed to model electron transport in AlGaN/GaN hetero-junction FETs. So called HFET structures with a 78 nm Alo.2Gao.8N pseudomorphically strained layer have been simulated, with the inclusion of spontaneous and piezoelectric polarization effects in the strained layer. The polarization effects are shown to not only increase the current density, but also improve the electron transport by inducing a higher electron density close to the positive charge sheet that occurs in the channel.

The transport critical current density (J(_c)) of a 37 filament Bi-2223/Ag tape has been measured as a function of field and temperature from 4.2 K up to 90 K. Data have been obtained over a large current range from 10 mA up to 100 A and in fields up to 23 T with the tape in 3 orientations with respect to field. These comprehensive data have been used to test the predictions of the flux creep and weak link models used to explain J(_c) in Bi-2223 tapes. The J(_c)(B,T) dependence of optimised Bi-2223 tapes has been calculated using a curved film model. The model assumes perfect grain connectivity and that the local superconducting properties are equivalent to those in the best reported thin films. A comparison between the calculations and measured J(_c)(B,T) dependencies suggest that in high fields at 20 K, J(_c) in presently available industrially processed tapes is only a factor of 8 below the performance of ideal fully optimised tapes. Transport measurements have been made on Bi-2223 single filaments extracted from an alloy sheathed multifilamentary tape in liquid nitrogen at 77 K in fields up to 300 mT with the field aligned parallel and perpendicular to the a-b planes. Further Jc(B,T) data have been taken in a variable temperature insert at temperatures between 60 to 90 K in fields up to 15 T. In a study of the electric field-current density {E-J) characteristics of the c-axis orientated data at 77 K, negative curvature is observed in traces below 280 mT. However, the 280 mT trace exhibits both positive and negative curvature in different current regimes in contrast to the predictions of standard theory. A laboratory scale Bi-2223 superconducting magnet producing a maximum field of 1.29 T at 4.2 K has been designed and fabricated. The magnet comprises 6 resin impregnated double wound pancakes with a 40 mm bore fabricated via the react and wind route. Critical current density measurements have been made as a function of magnetic field, angle and strain at 4.2 K and 77 K on short samples of the constituent tape. The E-J characteristics of all component coils have been measured and a comparison with short sample data shows that minimal additional damage occurred beyond that produced by the bending strain on the tape and the long length variation in J(_c). Sufficient detail is provided for the non-specialist to assess the potential use of brittle superconducting tapes for magnet technology and construct a laboratory scale magnet.

<p>Processes where a molecule absorbs visible light and then converts the solar energy into chemical energy are important in many biological systems, such as photosynthesis and also in many technical applications e.g. photovoltaics. This thesis describes a part of a multidisciplinary project, aiming at a functional mimic of the natural photosynthesis, with the overall goal of production of a renewable fuel from sun and water. More specific, the thesis is focused on design and photophysical characterization of new photosensitizers, i.e. light absorbers that should be capable of transferring electrons to an acceptor and be suitable building blocks for supramolecular rod-like donor-photosensitizer-acceptor arrays.</p><p>The excited state lifetime, the excited state energy and the geometry are important properties for a photosensitizer. The work presented here describes a new strategy to obtain longer excited state lifetimes of the geometrically favorable Ru(II)-bistridentate type complexes, without a concomitant substantial decrease in excited state energy. The basic idea is that a more octahedral coordination around the Ru will lead to longer excited state lifetimes. In the first generation of new photosensitizers a 50-fold increase of the excited state lifetime was observed, going from 0.25 ns for the model complex to 15 ns for the best photosensitizer. The second generation goes another step forward, to an excited state lifetime of 810 ns. Furthermore, the third generation of new photosensitizers show excited state lifetimes in the 0.45 - 5.5 microsecond region at room temperature, a significant improvement. In addition, the third generation of photosensitizers are suitable for further symmetric attachment of electron donor and acceptor motifs, and it is shown that the favorable properties are maintained upon the attachment of anchoring groups. The reactivity of the excited state towards light-induced reactions is proved and the photostability is sufficient so the new design strategy has proven successful.</p>