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Dielectric elastomers are highly promising as functional materials for the rapidly developing field of flexible actuator and generator technology. They offer a unique combination of low densities and large reversible deformations of up to more than 100% in area, and consequently have great potential for many new types of application. However, implementation has been impeded by the lack of specialized materials. The elastomers that have so far been investigated suffer from a number of disadvantages, including the need for very high activation voltages and limited service lifetimes. This thesis describes an investigation of the use of elastomeric composites as dielectric elastomers with the aim of optimizing and improving their performance in actuators. The influence of materials properties on actuation was first analyzed on the basis of a simple physical model and materials properties derived from standard test methods. The implications for the actuation performance of three conventional dielectric elastomers were then considered in detail. A preliminary conclusion was that the actuation performance could be improved if the permittivity of the elastomers were to be increased by modification with ceramic or conductive fillers. However, actuation performance was shown to depend not only on the permittivity, but also on the elastic modulus, the electrical breakdown strength, and strain hardening. Thus, although significant increases in permittivity were achieved by this approach, actuation performance was compromised by an increase in modulus in the case of the ceramic fillers, and a dramatic drop in electrical breakdown strength, in the case of the conducting fillers. A more promising approach was therefore suggested to be the use of an organic conducting filler encapsulated in an insulating matrix. It was demonstrated that it is indeed possible to increase the permittivity of a given elastomer while maintaining a high electrical breakdown strength. Different processing routes were investigated in order to control the dispersion of the filler and tailor performance. The optimum filler concentration, i.e. that providing the best compromise between permittivity and stiffness, was determined to be approximately 16 vol%, resulting in an improvement by a factor of 2 in actuation strain for a given applied voltage over that obtained with the unmodified matrix. Higher filler concentrations were also argued to have considerable potential for use in generators, given that the observed increased permittivity was also associated with high electrical breakdown strengths and increased strains at break. A threefold increase in converted energy per working cycle was predicted for a composite containing 25.5 vol% fillers based on a simplified model for a dielectric elastomer generator. Whilst these results are extremely encouraging, it is concluded that the composite approach has, in general, only limited potential as a means of obtaining further increases in actuation performance. The major difficulty remains that the use of a relatively rigid second phase to increase dielectric performance will inevitably also increase the elastic modulus beyond a certain filler concentration. As argued in the final part of the thesis, the way forward may therefore ultimately depend on the development of new types of synthetic elastomeric matrix materials that combine intrinsic improvements in electrical response with reduced moduli.

ON 16 NOVEMBER 2000, the final report of the World Commission on Dams (WCD) was launched in London, in the presence of South Africa’s former president Nelson Mandela. This represented a remarkable milestone in the history of dam policy and politics. During its two-year existence, WCD had conducted the most extensive review of research and evidence regarding the planning, impacts, and management of large dams. It had engaged with numerous stakeholders around the globe. It also made comprehensive recommendations about how to improve dam planning and management.

Distributed power generation and cogeneration of heat and power is an attractive way toward a more rational conversion of fossil and bio fuels. Solid oxide fuel cell (SOFC) – gas turbine (GT) hybrid systems are emerging as the most promising candidates enabling the achievement of a cleaner and more efficient conversion of a large variety of resources across a broad power range covering from small to medium scale applications. This thesis introduces an innovative concept of SOFC-GT hybrid system that allows reaching efficiencies higher than the state of the art while enabling the carbon dioxide separation and avoiding fuel cell pressurisation technical issues. Several hybrid system design alternatives based on this concept are analysed through a thermodynamic optimisation approach combining process modelling, advanced process integration techniques and multi-objective optimisation. A number of optimal hybrid system configurations are determined for different design targets. The results consistently demonstrate the higher energy conversion performance and flexibility enabled with respect to the state of the art. The innovative concept analysis is extended to two applications for which SOFC-GT hybrid cycles are expected to provide the most significant impact toward sustainability: the small scale distributed generation and the conversion of renewable resources. A simplified version of the new hybrid system layout is especially developed for small scale distributed generation, typical of residential building applications (5-10 kWel). Experimental data are used to prove the technical feasibility of the system and to assess the performance potentially achievable with currently feasible technologies. The results of the analysis underline that energy conversion efficiencies higher than traditional centralised power generation can be achieved even at such a small scale. A systematic process integration and optimisation approach is used to assess the energy conversion performance of the original SOFC-GT hybrid cycle fuelled with hydrothermally gasified wet waste biomass. The analysis highlights the considerable potential of the integrated system that allows for converting wet waste biomass into electricity with First Law efficiency higher than 60% while simultaneously enabling the separation of the biogenic carbon dioxide.

Responses to recent climatic changes in the sediment of subarctic Lake Saanajärvi in northwestern Finnish Lapland are studied by comparison of various biological and sedimentological proxies with the 200-year long climate record, specifically reconstructed for the site using a data-set of European-wide meteorological data. The multi-proxy evidence of simultaneously changing diatom, Cladocera, and chrysophyte assemblages along with the increased rates of organic matter accumulation and pigment concentrations suggest that the lake has undergone a distinct typological change starting from the turn of the 20th century. This change, indicating an increase in lake productivity, parallels a pronounced rise in the meteorologically reconstructed mean annual and summer temperatures in the region between ca. 1850 and 1930's. We postulate that, during the Little Ice Age, the lake was not, or was only weakly, thermally stratified during summer, whereas the subsequent increase in air and hence epilimnetic water temperatures resulted in the development of the present summer stratification. The increased thermal stability of the lake created more suitable conditions for the growth of phyto- and zooplankton and changed the overall primary production from benthos to plankton. Mineral magnetic and carbonaceous particle records suggest long-distance pollution, particularly since the 1920's, yet the observed changes in lake biota and productivity can hardly be explained by this very minor background pollution; the 20th century species configurations are typical of neutral waters and do not indicate any response to pollution.

The constituent countries of the MENA region---defined in this thesis in conformity with the regional definition of the International Energy Agency and encompassing 17 Muslim countries in North Africa, in the Levant, on the Arabian Peninsula, and Iran---have developed very rapidly over the past decade. Two figures best exemplify the region's tremendous transformation: Total population has expanded by more than 20% and its aggregate economic output has more than doubled. As much as this development is desirable, said development trends have also dramatically reshaped the energy policy environment in the MENA region and began causing problems of their own---affecting the region's large oil exporters and its energy importers alike. Having traditionally enjoyed high energy security and handsome resource rents by virtue of their abundant and cheap fossil fuels, new realities in the domestic energy systems demand a new policy focus on domestic energy issues. Energy challenges have emerged which threaten security of supply, fiscal stability, and environmental integrity. The challenges differ in magnitude from country-to-country and reflect the specific national conditions and circumstances. However, given the similarity in the underlying drivers and the governing energy policies, the energy challenges resemble each other across borders. More specifically, ballooning domestic energy demand consumes a rising share of national energy production and thus increasingly imperils the constant flow of the much needed proceeds from oil and gas exports. In the MENA countries with less abundant hydrocarbon resources, domestic demand growth has heightened energy dependence and, to make matters worse, the tighter supply situation in the energy exporting neighbors may eventually also lead to a discontinuation of the preferential supply agreements which they have benefitted from in the past. As a further corollary of demand growth, massive capital-intensive infrastructure investments are necessary to keep pace with the growth on the demand side. The regional tradition to sell energy commodities domestically at prices non-competitive prices or even below cost, however, limits the national energy sectors' own capability of mustering the required capital. Finally, the universally observable heavily fossil fuel-dominated national energy mixes in the region render the study countries vulnerable to supply shocks. The virtually complete reliance on the regionally available hydrocarbons for meeting energy demand is also a principal contributor to environmental degradation and at the core of the large carbon footprint of energy consumption in MENA countries. Given current policies in combination with the emerging demographic and economic trends, these challenges must be expected to become more severe in the years to come. Rising living standards, especially in the region's expanding urban population, are likely to boost per capita energy consumption. The projected, continued demographic and economic growth will further drive commodity demand. And the supply side cannot be counted on to mitigate the challenges under given policies. On the contrary. Although no reliable production projections are available, it stands to reason that production from the region's most prolific oil and gas fields---some of which have been producing for several decades now---will increasingly require the use of costly secondary and tertiary recovery methods and that some will eventually [...]

Although mature technologies at competitive prices are largely available, solar thermal is not yet playing the important role it deserves in the reduction of buildings fossil energy consumption. The generally low architectural quality characterizing existing building integrations of solar thermal systems pinpoints the lack of design as one major reason for the low spread of the technology. As confirmed by the example of photovoltaics, the improvement of the architectural quality of building integrated systems can increase the use of a solar technology even more than price and technique. This thesis investigates the possible ways to enhance the architectural quality of building integrated solar thermal systems, and focuses on integration into façade, where the formal constraints are major and have most impact. The architectural integration problematic is structured into functional, constructive and formal issues, so that integration criteria are given for each architectural category. As the functional and constructive criteria are already recognized by the scientific community, the thesis concentrates on the definition of the formal ones, yet underestimated or misunderstood. The results of a large European survey over architects and engineers perception of building integration quality are presented, showing that for architects formal issues are not a matter of personal taste, but that they relate to professional competences, and consequently can be described. The solar system characteristics having an impact on the formal quality of the integration are identified (formal characteristics), the related integration criteria are assessed, and finally integration guidelines to support architect integration design work are given. The limits imposed by the collectors available in the market are pointed out, showing that the lack of appropriate products is nowadays the main barrier to BIST (Building Integrated Solar Thermal) architectural quality. A methodology for the development of new solar thermal collectors systems responding at the same time to energy production needs and building integration requirements is defined. The importance to ensure, within the design team, the due professional competences in both these fields is stressed. Three progressive levels of system "integrability" are defined in the path leading to the concept of "active envelope systems" and the main role of facade manufacturers is highlighted. The methodology is applied to unglazed and glazed flat plate systems, and new façade system designs are proposed that show the relevance of the proposed approach.

Natural gas is defined as a combustible mixture of hydrocarbons coming from ground deposits and it is mainly used as a source of energy for burners and motors. Its consumption is increasing worldwide, as this represents a cheap and abundant source of energy, while releasing less CO2 emissions than other fossil fuels, in addition to low emissions of particulates. The diversification of the supply sources of gas and the increase of international trading through pipelines and liquefied natural gas (LNG) shipments makes the gas quality vary more than before, which is a rising challenge for the natural gas industry, as currently the vast majority of gas appliances and motors are unable to adapt to changes in gas quality. This will even worsen in the upcoming years with the multiplication of biogas sources and power-to-gas systems that will be added to the pipeline networks. In order to accomodate the appliances to changes in gas quality, compact and low cost natural gas quality transducers have to be developped for the natural gas industry. The present Thesis aimed at investigating the existing methods to determine natural gas quality for combustion, focusing on the determination of the Wobbe Index (WI), which is a key parameter to set up the air-fuel ratio of the combustion in burners and motors, and to qualify a new type of dynamic viscosity transducer developped at Laboratoire de Production Microtechnique (LPM) of EPFL for the determination of the combustion properties. Inference transducers are a new kind of transducers that allow determining the combustion parameters of the gas by relating to fundamental thermo-physical parameters, and not through the determination of the concentration of the gas constituents, as in gas chromatographs and spectrometers. Here, the dynamic viscosity is chosen as the most promising thermo-physical property of a natural gas to relate to the WI and the Higher Heating Value (HHV). The viscometer takes measurements proportional to the resistance to flow of a gas through a capillary under the action of pulses of heat, and it can be therefore be described as a thermal pumping gas viscometer. A mathematical model and a finite element model (FEM) are used to predict the behavior of the system and for thermal optimization, which are combined by a thermal characterization of the system. The miniature heater used to generate the heat pulses inside the viscometer is a key element of the transducer, and after reviewing potential technologies, the design choices are reported and the fabrication process is exposed, followed by a mechanical and thermal characterization. In order to determine and validate the conversion of the WI from the dynamic viscosity, theoretical relations are analyzed and empirical characterizations are done with a test and calibration setup allowing to create given mixes of gases. Finally, the degradation of the transducer to contaminants of natural gas is investigated, and the analysis is focused to the characterization of the corrosion by the sulfur compounds of natural gas. Test vehicles are developed to study the effect of sulfur corrosion on metallic parts, electronic substrates, silicone adhesives and wirebonds materials, and experiments are held with the dedicated test setups developed at LPM of EPFL.

Photo-electrochemical (PEC) devices allow for converting solar energy into chemical energy and for the production of energetically dense solar fuels. Light absorption, charge separation and transport, electrochemical reactions, and ionic transport are required in such devices, all processes happening simultaneously. PEC devices - compared to competing, conventional PV-electrolysis systems - offer the promise of less complexity in design and implementation and more flexibility in their use. Nevertheless, PEC devices' economic and performance competitiveness is not well understood, given their low technology readiness level. No study has considered accurate multi-physical, multi-scale, and multi-dimensional performance models, degradation aspects, and uncertainty in the performance and cost metrics. Addressing some of these unknowns and focusing on the conversion of solar energy into two different solar fuels (H2 from water and CO from CO2), the objective of this thesis is threefold: (i) conduct a system-level techno-economic analysis based on a systematic and physical performance model (including degradation), and address uncertainty via a probabilistic approach (Monte Carlo (MC) method); (ii) based on the insight gained from the techno-economic analysis, identify most promising design and operational principles, substantiated by experimental investigation of an example case to assess practical feasibility; and (iii) develop two intricate multi-dimensional, multi-physical models: one for an innovative PEC device designed to operate with water vapor, and the other for a PEC device utilizing concentrated solar light engaged in the conversion of CO2 to CO. Overall, this thesis provides a combination of experimental demonstration and simulation tools to conduct feasibility studies, predict costs, and provide design guidelines and operational conditions for PEC devices in diverse electrochemical processes. This scope extends the use of PEC devices beyond the traditional liquid water splitting reaction, encompassing applications such as water vapor splitting, energy storage, and CO2 reduction.

The resonant excitation of free electrons in metallic nanostructures enables extreme near field intensities along with a deep sub-wavelength localization of the electromagnetic energy. This has been exploited to enhance light-matter interaction down to the single molecule level, to localize heat, and tailor radiation into the far field, all applications of optical antennas. Importantly, the rise and advances in the field of plasmonics over the last ten years have been tightly bound to the development of nanofabrication techniques. The present thesis shows how different nanofabrication approaches can be combined and exploited to produce optical antennas with single nanometer interparticle distances, full geometric and material control and increased fabrication throughput and reliability. Different nanofabrication techniques are first developed for the manufacturing of aperture-type antennas that target applications in fluorescence enhancement for the study of biological systems. The fabrication of high-resolution (~20 nm) bowtie nanoapertures via reactive ion etching through stencils is demonstrated to be an efficient approach to upscale the lithographic fabrication of a master, the stencil, to produce a number of functional samples in an aluminum thin film. Fluorescence measurements are performed on living cells, a proof of concept of the system for the sub-wavelength illumination of dynamic lipid membranes. This initial work preludes to the investigation of the dimer in a box geometry that provides further near field enhancement and confinement in order to reach measurement volumes down to the few tens of zeptolitres and over three orders of magnitude fluorescent enhancement. A second part of the work is dedicated to the investigation and exploitation of colloidal nanoparticle assembly. Although these elements possess unique intrinsic properties, their deterministic positioning is crucial to harness their full potential. An initial study enables understanding and exploitation of the various mechanisms underlying the capillary assembly of gold nanorods onto topographic templates. Novel topographic trap geometries are realized, including three dimensional barriers and funnels to reach unity yield, nanometric positioning and 1° orientation accuracy. Further on, complex nanorod trimers of dolmen geometry are assembled and characterized, revealing the unique potential of nanoparticle assembly in creating plasmonic structures with few-nm gaps. ¿ Finally, two projects exploit the developed nanofabrication capabilities to investigate material-based opportunities for nanoantennas. First, heterostructures composed of two coupled elements made of different material, respectively gold-silver and gold-aluminum, are investigated. High-resolution electron beam lithography and sub-10 nm layer-to-layer alignment is used to produce dimers with fully controlled geometry and interparticle gap in order to reveal the underlying mechanisms of detuned plasmonic pairs. Finally, the very last section offers an outlook beyond metallic nanostructures relying on high index dielectric, silicon nanodiscs. These silicon elements rely on Mie resonances rather than their plasmonic counterpart in metals. The gradual contribution of both strong electric and magnetic dipoles in silicon structures is compared to the properties of metal discs and used to produce vivid color palettes visible under bright field microscopy and naked eye.