Network satisfaction problems (NSPs) for finite relation algebras are computational decision problems, studied intensively since the 1990s. The major open research challenge in this field is to understand which of these problems are solvable by polynomial-time algorithms. Since there are known examples of undecidable NSPs of finite relation algebras it is advisable to restrict the scope of such a classification attempt to well-behaved subclasses of relation algebras. The class of relation algebras with a normal representation is such a well-behaved subclass. Many well-known examples of relation algebras, such as the Point Algebra, RCC5, and Allen’s Interval Algebra admit a normal representation. The great advantage of finite relation algebras with normal representations is that their NSP is essentially the same as a constraint satisfaction problem (CSP). For a relational structure B the problem CSP(B) is the computational problem to decide whether a given finite relational structure C has a homomorphism to B. The study of CSPs has a long and rich history, culminating for the time being in the celebrated proofs of the Feder-Vardi dichotomy conjecture. Bulatov and Zhuk independently proved that for every finite structure B the problem CSP(B) is in P or NP-complete. Both proofs rely on the universal-algebraic approach, a powerful theory that connects algebraic properties of structures B with complexity results for the decision problems CSP(B). Our contributions to the field are divided into three parts. Firstly, we provide two algebraic criteria for NP-hardness of NSPs. Our second result is a complete classification of the complexity of NSPs for symmetric relation algebras with a flexible atom; these problems are in P or NP-complete. Our result is obtained via a decidable condition on the relation algebra which implies polynomial-time tractability of the NSP. As a third contribution we prove that for a large class of NSPs, non-hardness implies that the problems can even be solved by Datalog programs, unless P = NP. This result can be used to strengthen the dichotomy result for NSPs of symmetric relation algebras with a flexible atom: every such problem can be solved by a Datalog program or is NP-complete. Our proof relies equally on known results and new observations in the algebraic analysis of finite structures. The CSPs that emerge from NSPs are typically of the form CSP(B) for an infinite structure B and therefore do not fall into the scope of the dichotomy result for finite structures. In this thesis we study NSPs of finite relation algebras with normal representations by the universal algebraic methods which were developed for the study of finite and infinite-domain CSPs. We additionally make use of model theory and a Ramsey-type result of Nešetril and Rödl. Our contributions to the field are divided into three parts. Firstly, we provide two algebraic criteria for NP-hardness of NSPs. Our second result is a complete classification of the complexity of NSPs for symmetric relation algebras with a flexible atom; these problems are in P or NP-complete. Our result is obtained via a decidable condition on the relation algebra which implies polynomial-time tractability of the NSP. As a third contribution we prove that for a large class of NSPs the containment in P implies that the problems can even be solved by Datalog programs, unless P = NP. As a third contribution we prove that for a large class of NSPs, non-hardness implies that the problems can even be solved by Datalog programs, unless P = NP. This result can be used to strengthen the dichotomy result for NSPs of symmetric relation algebras with a flexible atom: every such problem can be solved by a Datalog program or is NP-complete. Our proof relies equally on known results and new observations in the algebraic analysis of finite structures.

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This project proposes a solar-driven hybrid system for electricity generation and hydrogen production, which includes concentrated solar power (CSP), photovoltaic (PV), solid oxide electrolyser (SOEC). Electricity from the CSP and PV provides a continuous 24/7 supply to meet demand-side power consumption. When demand-side power consumption is low, the excess power is used to electrolyse water in the SOEC system. In this study, an SOEC is modelled, operation strategy for the solar-driven hybrid system is developed, the techno-economic performance of the overall system is evaluated, and sensitivity analysis is performed. For the modelling part, first develop an SOEC component in Matlab and Trnsys by considering the electrochemical model, thermal model and electric model. Second, design the hybrid system layout and simulate the system under 8760 hours in Matlab and Trnsys. The hybrid system is divided into five blocks: Heat Energy Source Block, Thermal Energy Storage Block, Rankine Cycle Block, Photovoltaic Block, Power to Hydrogen (PtH) Block. The operation strategy is: the heat is collected using a tower solar receiver and stored in tanks by heat transfer fluid molten salt. These thermal energy heats the water in heat exchangers and the resulting high temperature water vapour is used in steam turbine to generate electricity; at the same time part of the heat transfer fluid heats the feedwater in the PtH block and the resulting high temperature water vapour is used in SOEC for hydrogen production, if the operation temperature of steam in SOEC is not reached after heat exchange, the electric heater will heat the steam to raise the temperature. The CSP and PV provide electricity to demand side and SOEC. The produced hydrogen will be transported by truck or ship after compressed. For results part, the minimum CSP configurations to provide a 24/7 demand-side electricity consumption is a solar multiple (SM) with 2 and thermal storage (TES) size of 14 hours. SOEC stack has the best techno-economic performance at a nominal power of 275 Watt. The hybrid system has a levelised cost of electricity (LCOE) at 0.219 USD/kWh and a levelised cost of hydrogen (LCOH) at 7.5 USD/Kg. There are several sensitivity parameters for increase the energy productivity and decrease levelised cost. The larger the SM, the better the ability to generate power. The larger the TES size, the more the hourly generation is similar, otherwise it will fluctuate more. Increasing the SM results in a higher LCOE and a significantly lower LCOH. Increasing TES size also increases the LCOE, whereas the TES size has a marginal impact on the decrease of LCOH. Increased installed capacity inevitably leads to increased power generation. The increasing total power capacity makes the surplus power at the same demand side increase, so the SOEC runs at higher input power and the total hydrogen production increases, resulting in a lower LCOH. The effect of SOEC capacity on LCOH depends on the relationship between input power and SOEC nominal power. Higher operation temperature of SOEC leads to the lower the reversible voltage and an increasing consumption for water vapour. However, when the water vapour concentration is too high, the electrolysis current will instead drop, meaning that the rate of hydrogen production will drop.

Software Defined Radios (SDRs) lend themselves to flexibility and extensibility because they<br />depend on software to implement radio functionality. Cognitive Engines (CEs) introduce<br />intelligence to radio by monitoring radio performance through a set of meters and configuring<br />the underlying radio design by modifying its knobs. In Cognitive Radio (CR) applications,<br />CEs intelligently monitor radio performance and reconfigure them to meet it application<br />and RF channel needs. While the issue of introducing computational knobs and meters<br />is mentioned in literature, there has been little work on the practical issues involved in<br />introducing such computational radio controls.<br /><br />This dissertation decomposes the radio definition to reactive models for the CE domain<br />and real-time, or dataflow models, for the SDR domain. By allowing such design space<br />decomposition, CEs are able to define implementation independent radio graphs and rely on<br />a model transformation layer to transform reactive radio models to real-time radio models<br />for implementation. The definition of knobs and meters in the CE domain is based on<br />properties of the dataflow models used in implementing SDRs. A framework for developing<br />this work is presented, and proof of concept radio applications are discussed to demonstrate<br />how CEs can gain insight into computational aspects of their radio implementation during<br />their reconfiguration decision process.<br /> / Ph. D.

Because of its thermochemical qualities, ammonia is an attractive alternative to carbon-based fuels. Indeed, the lack of carbon atoms in its molecular structure and the ease of storage make its widespread use desirable. However, there are a number of technological challenges that must be overcome due to the slow burning rate and its large latent heat. The objective of the dissertation is to model ammonia spray flames because direct liquid fuel injection in a combustion chamber is an essential aspect of the design of practical devices. The topic has been divided into a number of sub-problems, which are examined in each chapter of the thesis, due to the lack of fundamental physical details of the individual processes occurring and modeling considerations that cannot be ignored anymore.To better understand how the large latent heat affects the spray dynamics, a campaign of direct numerical simulations is initially performed at various ambient temperatures. Then, conducting large eddy simulations is preferred to lower the computational cost. The assessment of the dispersion models showed that the available options, however, are unable to reproduce the averaged droplet distribution across the entire domain and an improved model is proposed. Droplet evaporation causes local inhomogeneities in the mixture, which simultaneously induces multiple combustion modes. The Darmstadt Multi-Regime Burner (MRB) was the ideal candidate to investigate the physical aspects in advance. The best option for capturing its flame structure was the physically-derived multi-modal manifold and a regime classification index is formulated and tested on the MRB.Then, a machine learning strategy based on neural networks is suggested to quicken the look-up procedure, and preliminary validation of the methodology revealed that a time reduction of 30% is achieved without affecting the results' accuracy.

Concentrating Solar Power (CSP) is one of the most promising renewable energybased electricity generation technologies to deal with the increasing demand of power consumption and environmental sustainability. With the aim of achieving the 2020 SunShot cost target for CSP of 60 USD/MWh, the United States Department of Energy presented, in May 2018, the Gen3 CSP initiative. In particular, the CSP Gen3 Liquid-Phase Pathway proposes to design a CSP system adopting liquid sodium as Heat Transfer Fluid (HTF) in the receiver, advanced high-temperature molten chloride salt as storage fluid and supercritical CO2 (sCO2) Brayton cycle as power cycle. Within this framework, the aim of this master thesis was to design the sodium-chloride salt Heat Exchanger (HX) by developing both a heat exchanger model and a sodiumsalt-sCO2 system model. To pursue these purposes, a completely new Modelica-based HX model was developed and added to the SolarTherm library. Furthermore, as an extension of earlier models, the sodium-salt-sCO2 CSP system (NaSaltsCO2System) was implemented in SolarTherm, by incorporating the HX model and linking it with other new and existing component models. As for the HX, a general model was developed for shell and tube heat exchangers, based on the TEMA guidelines, with the possibility of being customized in terms of media adopted, constraints, boundary conditions, and correlations. The model performs an optimization in order to select the internal geometry configuration that optimizes a user-defined objective-function. By employing the implemented HX model in the NaSaltsCO2System, the sodium-salt heat exchanger was designed aiming at minimizing the Levelized Cost of Electricity (LCOE), providing a complete geometry description, and an estimation of the performances and costs. The resulting NaSaltsCO2System model was found to be robust and able to perform annual simulations that allowed to estimate the energy performances of the CSP plant, as well as the LCOE. Considering the sodium-salt-sCO2 CSP system characterized by a receiver capacity of 543 MWth, 12 hours of Thermal Energy Storage (TES), and a 100 MWe power block, the LCOE resulted equal to 72.66 USD/MWh. The sodium-salt HX design that minimizes the LCOE resulted in a single-shell/single tube pass configuration, with vertical alignment, characterized by an overall height of 15 m, and a shell diameter of 1.8 m. It represents the 3.2% of the total capital cost of the plant. An interesting system-level optimization was then carried out on the combined receiver-heat exchanger block. It regarded the variation of the Log Mean Temperature Difference (LMTD) of the HX and highlighted the possibility to drop the LCOE down to 68.54 USD/MWh. The techno-economic investigations and the sensitivity analysis showed the flexibility and robustness of the HX model, as well as the importance of the NaSaltsCO2System. The latter lays the groundwork to explore potential improvements of this new generation of CSP systems, which can play a fundamental role in the future global energy mix. / Termisk solkraft (CSP) är en av de mest lovande elproduktionsteknologierna baserade på förnybar energi. Den kan bidra till hanteringen av den ökande efterfrågan på energi och miljömässig hållbarhet. I syfte att uppnå 2020 SunShot-kostnadsmålet för CSP på 60 USD/MWh presenterade USA:s energidepartement Gen3 CSPinitiativet. I synnerhet föreslår CSP Gen Liquid-Phase Pathway att utforma ett CSPsystem som använder flytande natrium som värmeöverföringsvätska i mottagaren, smält kloridsalt med hög temperatur som lagringsvätska, samt superkritisk CO2 (sCO2) Brayton-cykel som kraftcykel. Syftet för detta examensarbete var att utforma natriumkloridsaltets primära värmeväxlare genom att utveckla både en värmeväxlarmodell (HX) modell och en natriumsalt-sCO2-systemmodell. För att fullfölja dessa syften utvecklades HX-modellen först, sedan implementerades natriumsalt-sCO2 CSP-systemet NaSaltsCO2System. Båda verktygen utvecklades med hjälp av Modelica som programmeringsspråk. De finns nu tillgängliga i det öppna SolarTherm-biblioteket. När det gäller HX utvecklades en allmän modell för skal- och rörvärmeväxlare med möjligheten att anpassas när det gäller antagna medium, begränsningar, gränsvillkor och korrelationer. Dessutom utförde modellen en optimering för att välja den interna geometri-konfigurationen som optimerar en användardefinierad objektiv-funktion. Genom att använda den implementerade HX-modellen i NaSaltsCO2System designades natriumsalt-värmeväxlaren, vilket gav en fullständig konfiguration-beskrivning och en uppskattning av prestanda och kostnader. Den utvecklade NaSaltsCO2System-modellen visade sig vara robust och kapabel till att utföra simuleringar på årsbasis. Detta gjorde det möjligt att uppskatta CSP-anläggningens energiprestanda samt LCOE. Det utvecklade natriumsalt-sCO2 CSP-systemet som känneteckna des av en mottagarkapacitet på 543 MWth, 12 timmars TES och ett 100 MWe power block, resulterade i en LCOE på 72.66 USD/MWh. Natrium-salt HX-konstruktionen som minimerade LCOE resulterade i en enskalig/enkel rörpassningskonfiguration, med vertikal inriktning, kännetecknad av en total höjd av 15 m och en skaldiameter på 1.8 m. Det motsvarade 3.2% av anläggningens totala kapitalkostnad. Den mest intressanta systemoptimeringen genomfördes på det kombinerade blocket bestående av mottagare och värmeväxlare. Den behandlade variationen av HX:s LMTD och framhöll möjligheten att sänka LCOE till 68.54 USD/MWh. De teknisk-ekonomiska undersökningarna och känslighetsanalysen visade flexibiliteten och robustheten i HX-modellen, liksom vikten av NaSaltsCO2Systemet. Den senare lägger grunden för att utforska potentiella förbättringar av denna nya generation av CSP-system, som kan spela en grundläggande roll i den framtida globala energimixen.

In this thesis we derive novel results on the complexity of idempotent Mal'tsev condition satisfaction problems. For a Mal'tsev condition M, the idempotent M- satisfaction problem is the decision problem defined via: INPUT: A finite idempotent algebra A. QUESTION: Does A satisfy M? In particular we are able to prove that this decision problem is in the complexity class NP whenever M satisfi es one of the following conditions: 1. M is a strong Mal'tsev condition which implies the existence of a near unanimity term. 2. M is a strong Mal'tsev condition of height < 1 (see Definition 5.1.1). As a porism of these two results, we are able to derive the stronger result that the complexity of the idempotent M-satisfaction problem is in NP whenever M is a strong Mal'tsev condition which implies the existence of an edge term. On top of this we also outline a polynomial-time algorithm for the idempotent M-satisfaction problem when M is a linear strong Mal'tsev condition which implies the existence of a near unanimity term. We also examine the related search problem in which the goal is to produce operation tables of term operations of the algebra A which witness that A satisfies the Mal'tsev condition M whenever such terms exist (and otherwise correctly decide that such terms do not exist). We outline polynomial-time algorithms for this search problem for various strong Mal'tsev conditions. We close the thesis with a short list of open problems as suggested directions for further research. / Thesis / Doctor of Philosophy (PhD)

The ever-growing competition in current electronics industry has resulted in stringent time-to-market goals and reduced design time available to engineers. Lesser design time has subsequently raised a need for high-level synthesis design methodologies that raise the design to a higher level of abstraction. Higher level of abstraction helps in increasing the predictability and productivity of the design and reduce the number of bugs due to human-error. It also enables the designer to try out dierent optimization strategies early in the design stage. In-spite of all these advantages, high-level synthesis design methodologies have not gained much popularity in the mainstream design flow mainly because of the reasons like lack of readability and reliability of the generated register transfer level (RTL) code. The compiler framework presented in this thesis allows the user to draw high-level graphical models of the system. The compiler translates these models into synthesizeable RTL Verilog designs that exhibit their desired functionality following communicating sequential processes (CSP) model of computation. CSP model of computation introduces a good handshaking mechanism between different components in the design that makes designs less prone to timing violations during implementation and bottlenecks while in actual operation. / Master of Science

This thesis introduces a novel approach in which multiple heterogeneous devices collaborate to provide useful applications in an ad-hoc network. This thesis proposes a smart home as a particular ubiquitous computing scenario considering all the requirements given by the literature for succeed in this kind of systems. To that end, we envision a horizontally integrated smart home built up from independent components that provide services. These components are described with enough syntactic, semantic and pragmatic knowledge to accomplish spontaneous collaboration. The objective of these collaboration is domestic use, that is, the provision of valuable services for home residents capable of supporting users in their daily activities. Moreover, for the system to be attractive for potential customers, it should offer high levels of trust and reliability, all of them not at an excessive price. To achieve this goal, this thesis proposes to study the synergies available when an ontological description of home device functionality is paired with a formal method. We propose an ad-hoc home network in which components are home devices modelled as processes represented as semantic services by means of the Web Service Ontology (OWL-S). In addition, such services are specified, verified and implemented by means of the Communicating Sequential Processes (CSP), a process algebra for describing concurrent systems. The utilisation of an ontology brings the desired levels of knowledge for a system to compose services in a ad-hoc environment. Services are composed by a goal based system in order to satisfy user needs. Such system is capable of understaning, both service representations and user context information. Furthermore, the inclusion of a formal method contributes with additional semantics to check that such compositions will be correctly implemented and executed, achieving the levels of reliability and costs reduction (costs derived form the design, development and implementation of the system) needed for a smart home to succeed.

Under de senaste årtiondena har ansvarfullt företagande (CSR) varit ett ämne som erhållit allt mer fokus inom forskning och således även för företag och samhället i stort. CSR är ett ämne som är högst aktuellt då globalisering är ett faktum och medför att de företag som är verksamma idag bär ett globalt ansvar, då dessa är stora aktörer i en värld som kantas av ekonomiska kriser, miljöproblem och humanitär försummelse. Det ökade intresset från samhället för CSR har medfört att företagen idag ser detta som en strategisk investering och företags satsning i hållbarhetsaktiviteter har kommit att erhålla en allt större del av företags verksamhet. Frågan kvarstår om detta endast är en investering som ökar företagets etik och moral eller om det faktiskt är lönsamt, och även om lönsamma företag ökar sin investering i hållbarhetsarbete. En stor mängd forskning har utförts för att undersöka förhållandena mellan hållbarhet och lönsamhet, dock utan att konsensus i forskningsgrenen har uppkommit.       Grundat på den nuvarande forskningssituationen syftade denna studie till att undersöka vilken effekt ansvarsfullt företagande har på olika lönsamhetsmått, samt vilken effekt de olika lönsamhetsmåtten har på ansvarsfullt företagande, i företag registrerade på large cap och mid cap på Nasdaq OMX Stockholm. För att besvara studiens problemformulering och uppfylla studiens syfte har en kvantitativ forskningsansats brukats och ett urval av företag listade på large och mid cap Nasdaq OMX Stockholm har undersökts. För att sätta ett mått på ansvarsfullt företagande (CSP) har en innehållsanalys av företags årsrapporter och hållbarhetsrapporter genomförts, lönsamhetsmåtten (CFP) har utgått från redovisningsbaserade mått (ROE och ROA) samt ett marknadsbaserat mått (total avkastning). Vidare undersöks även relationen mellan variablerna, CSP och CFP, med en tidsaspekt och kontrollvariablerna storlek, risk, FoU och industritillhörighet har brukats. De teorier som har använts för att förklara CFP:s effekt på CSP är slappa resurser och direktörsopportunism, och effekten CSP har på CFP har teorierna intressentteorin, resursbaserad synvinkel och kompromissteorin använts.  Det resultat som framkommit genom de multipla regressionerna som testat studiens hypoteser visar att ROE:s effekt på CSP är positiv, medan både ROA:s och avkastningens effekt på CSP är neutral. Slutsatsen blir således delad då lönsamhetsmåttet ROE visar att företag som har en högre lönsamhet kommer investera mer i hållbarhet, denna effekt knyts samman med teorin om slappa resurser. Å andra sidan visar både ROA och avkastning på en neutral effekt på CSP vilket ej kan knytas till varken slappa resurser eller direktöropportunism. Vidare när istället CSP:s effekt på ROE, ROA och avkastning undersökts visar samtliga på en neutral påverkan. Den slutsats som kan dras från detta resultat är att hållbarhetsarbete ej empiriskt kan säkerställa en högre eller lägre lönsamhet, och varken intressentteorin, resursbaserad synvinkel eller kompromissteorin kan förklara resultatet. Med icke-konklusiva resultat föreslår författarna för vidare forskning inom området där mer forskning i den svenska kontexten är nödvändig.