As the largest global renewable source, hydropower shoulders a large portion of the regulation duty in many power systems. New challenges are emerging from variable renewable energy (VRE) sources, the increasing scale and complexity of hydropower plants (HPPs) and power grid. Stable and efficient operation of HPPs and their interaction with power systems is of great importance. Theoretical analysis, numerical simulation and on-site measurement are adopted as main study methods in this thesis. Various numerical models of HPPs are established, with different degrees of complexity for different purposes. The majority of the analysis and results are based on eight HPPs in Sweden and China. Stable operation (frequency stability and rotor angle stability) and efficient operation are two important goals. Regarding the stable operation, various operating conditions are analysed; the response time of primary frequency control (PFC) and the system stability of isolated operation are investigated. A fundamental study on hydraulic-mechanical-electrical coupling mechanisms for small signal stability of HPPs is conducted. A methodology is proposed to quantify the contribution to the damping of low frequency oscillations from hydraulic turbines. The oscillations, with periods ranging from less than one up to hundreds of seconds, are analysed. Regarding the efficient operation, a description and an initial analysis of wear and tear of turbines are presented; a controller filter is proposed as a solution for wear reduction of turbines and maintaining the frequency quality of power systems; then the study is further extended by proposing a framework that combines technical plant operation with economic indicators, to obtain relative values of regulation burden and performance of PFC. The results show that the coupling between the hydraulic-mechanical subsystem and the electrical subsystem can be considerable and should be considered with higher attention. Effectiveness and applicability of different numerical models are shown, supplying suggestions for further model optimization. For the influence from power systems on HPPs, the dynamic processes and corresponding control strategies of HPPs under diverse disturbances and requirements from power systems are addressed. For the influence from HPPs on power systems, quantifications of frequency quality and the hydraulic damping are conducted utilising proposed methodologies.

This thesis project is a theoretical and practical study on recommender systems (RSs). It aims to help the planning of course selection for students from the Master Programme in Computer Science in Uppsala University. To achieve the goal, the project implements a recommender service, which generates course selection recommendations based on these three factors:     (i) student users’ preferences     (ii)  course requirements from the university     (iii) best practices from senior students The implementation of the recommender service takes these three approaches:      applying frequent-pattern mining techniques on senior students’ course selection data ,  performing semantic queries on a simple knowledge organization system (SKOS) taxonomy file that classifies computing disciplines, applying constraint programming (CP) techniques for problem modelling and resolving when generating final course selection recommendations     The recommender service is implemented as a representational state transfer (REST) compliant web service, i.e., a RESTful web service. The result shows that aforementioned factors have positive impact on the output of the service. Preliminary user feedback gives encouraging rating on the quality of the recommendations.     This report will talk about recommender systems, the semantic web, constraint programming and the implementation details of the recommender service. It focuses on in-depth discussion of recommender systems and the recommender service’s implementation.

The genesis of atherosclerosis has previously been shown to be affected by the frictional load from the blood on the vessel wall, called the wall shear stress (WSS). Assessment of WSS can therefore provide important information for diagnoses, intervention planning, and follow‐up. Calculation of WSS requires high‐resolved velocity data from the vessel, which in turn can be obtained using computational fluid dynamics (CFD). In this work large eddy simulation LES was successfully used to simulate transitional flow in idealized as well as subject specific vessel models. It was shown that a scale resolving technique is to prefer for this application, since much valuable information otherwise is lost. Besides, Reynolds‐Averaged Navier‐Stokes (RANS) models have generally failed to predict this type of flow. Non‐pulsating flows of Reynolds numbers up to 2 000 in a circular constricted pipe showed that turbulence is likely to occur in the post‐stenotic region, which resulted in a complex WSS pattern characterized by large spatial as well temporal fluctuations in all directions along the wall. Time averaged streamwise WSS was relatively high, while time averaged circumferential WSS was low, meaning that endothelial cells in that region would be exposed to oscillations in a stretched state in the streamwise direction and in a relaxed state in the circumferential direction. Since every vessel is unique, so is also its WSS pattern. Hence the CFD simulations must be done in subject specific vessel models. Such can be created from anatomical information acquired with magnetic resonance imaging (MRI). MRI can also be used to obtain velocity boundary conditions for the simulation. This technique was used to investigate pulsating flow in a subject specific normal human aorta. It was shown that even the flow in healthy vessels can be very disturbed and turbulence like, and even for this case large WSS variations were seen. It was also shown that regions around branches from the aorta, known to be susceptible for atherosclerosis, were characterized by high time averaged WSS and high oscillatory shear index. Finally, the predictive capability of CFD was investigated. An idealized model of a human aorta with a coarctation and post‐stenotic dilatation was studied before and after a possible repair of the constriction. The results suggested that small remaining abnormalities in the geometry may deteriorate the chances for a successful treatment. Also, high values of shear rate and Reynolds stresses were found in the dilatation after the constriction, which previous works have shown means increased risk for thrombus formation and hemolysis.

Under en lång tid har det satsats på att energieffektivisera byggnader under dess driftfas, då tidigare studier visar att driftfasen står för 85 procent av en byggnads totala energianvändning på 50 till 100 år, medan produktionsfasen står för 15 procent. Att bara ta hänsyn till klimatbelastning som uppstår under byggnadens bruk, har som konsekvens att energiförbrukningen förskjutits i fas, vilket resulterar i att energifördelningen har förflyttats till en ökad andel i produktionsfasen. Detta examensarbete syftar till att lyfta frågan om byggproduktionens energianvändning, genom att kartlägga hur mycket energi som förbrukas på plats i produktionskedet för att bygga ett flerbostadshus beläget i Umeå.  I detta examensarbete har tre olika stommaterial, platsgjuten betong, stål med prefabricerade betong och trä, undersökts och analyserats. För att projektet ska kunna genomföras har det utgåtts från ett referensobjekt, Kvarteret Sjörået på Tomtebo i Umeå som innefattar tre byggnader om fyra plan vardera, där endast ett fack av ett av husen undersöktes. Studien utgår från att fastställa det energikrävande momentet för de olika stommaterialen, för att sedan beräkna energiförbrukningen för dessa stommaterial baserat på det energikrävande momentet. Under projektets gång har olika aktörer inom byggbranschen kontaktats, simuleringar utförts i programmet TorkaS och en mängd olika antagande gjorts. Gällande mängder material har överförts från rapporten Livscykelanalys med fokus på energianvändning under tillverkningsfasen – en jämförelse mellan olika stommaterial av Mi Von Ahn. Resultatet som fås för det studerade referensobjektet visar att skillnaden i energianvändning för de olika stommaterialen är stor under produktionsfasen för referensobjektet. Resultatet visar att det går mest energi åt för att torka platsgjutna betongelement, då det krävs fläktar som i stort sätt drar mycket energi. När det är frågan om prefabricerade stomelement spelar stomelementens vikt stor roll, då det behövs lyftkranar som är anpassade efter byggelementens tyngd. Dessutom drar lyftkranarna olika mycket el, beroende på elementens vikt och lyfthastighet. Trästommen var mest fördelaktig i denna studie, på grund av stommens lätta vikt. Viktigt att poängtera är att resultatet för denna studie utgår från ett specifikt referensobjekt, vilket innebär att resultatet kan se annorlunda ut beroende på bland annat val av systemgränser. / For a long time the focus of energy efficiency in building constructions has mainly been focused on its operational phase, as previous studies show that the operational phase accounts for 85 percent of a building’s total energy consumption during its lifetime, estimated at 50 to 100 years, the production phase is estimated to account for 15 percent. By only accounting for the climate impact from buildings during the operational phase, has led to energy consumption shifting in phase, resulting in an increased share of the total energy distribution in the production phase. This thesis aims to highlight the issue of the energy consumption during the construction phase, by mapping how much energy is consumed on the spot in the production stage to build an apartment building located in Umeå. In this thesis three different framing materials has been examined and analyzed; in situ concrete, steel combined with precast concrete and wood. In order to implement the project, the main focus has been on a reference object, Kvarteret Sjörået in Tomtebo in Umeå, which includes three buildings of four floors each, where only one compartment of one of the buildings has been examined. The study of this thesis begins with determining the energy-consuming steps for each framing materials, followed by calculating the energy consumption of these frame materials. During the project contacts have been taken with various stakeholders from the construction industry in addition to simulations performed in the program TorkaS and a variety of adoption has been made. Regarding the amounts of material assumed consumption in this study a basis has been taken in the previous thesis Life cycle analysis with a focus on energy use during the manufacturing phase – a comparison of frame materials by Mi Von Ahn.  The result obtained for the reference object shows that the difference in energy consumption between the studied frame materials is high during the production phase of the reference object. The result further shows that in situ concrete frame is the most energy consuming alternative during the construction phase due to need of large fans that is consuming a lot of energy. When it comes to prefabricated frame materials the energy consumption is largely due to the need for cranes where one important aspect is the weight of the elements. In addition cranes use electricity depending on the elements weight and depending on the lifting speed. Wood was most advantageous in this study, because of its light weight body. Important to note is that the results of this study are based on a specific reference object, which means that the results may be different depending on many factors, for example the choice of system limits.

This thesis is concerned with exploring methods for making computing systems more resilient to problems in the network communication, both in the setting of existing infrastructure but also in the case where no infrastructure is available. Specifically, we target a situation called network partitions which means that a computer or device network is split in two or more parts that cannot communicate with each other. The first of the two tracks in the thesis is concerned with upholding system availability during a network partition even when there are integrity constraints on data. This means that the system will optimistically accept requests since it is impossible to coordinate nodes that have no means of communicating during finite intervals; thus requiring a reconciliation process to take place once the network is healed. We provide several different algorithms for reconciling divergent states of the nodes, one of which is able to allow the system to continue accepting operations during the reconciliation phase as opposed to having to stop all invocations.  The algorithms are evaluated analytically, proving correctness and the conditions for termination.  The performance of the algorithms has been analysed using simulations and as a middleware plugin in an emulated setting. The second track considers more extreme conditions where the network is partitioned by its nature. The nodes move around in an area and opportunistically exchange messages with nodes that they meet. This as a model of the situation in a disaster area where the telecommunication networks are disabled. This scenario poses a number of challenges where protocols need to be both partition-tolerant and energy-efficient to handle node mobility, while still providing good delivery and latency properties. We analyse worst-case latency for message dissemination in such intermittently connected networks. Since the analysis is highly dependent on the mobility of the nodes, we provide a model for characterising connectivity of dynamic networks. This model captures in an abstract way how fast a protocol can spread a message in such a setting. We show how this model can be derived analytically as well as from actual trace files. Finally, we introduce a manycast protocol suited for disaster area networks. This protocol has been evaluated using simulations which shows that it provides very good performance under the circumstances, and it has been implemented as a proof-of-concept on real hardware.

This thesis contributes to three research areas in software security, namely security requirements and intrusion prevention via static analysis and runtime detection. We have investigated current practice in security requirements by doing a field study of eleven requirement specifications on IT systems. The conclusion is that security requirements are poorly specified due to three things:  inconsistency in the selection of requirements, inconsistency in level of detail, and almost no requirements on standard security solutions. A follow-up interview study addressed the reasons for the inconsistencies and the impact of poor security requirements. It shows that the projects had relied heavily on in-house security competence and that mature producers of software compensate for poor requirements in general but not in the case of security and privacy requirements specific to the customer domain. Further, we have investigated the effectiveness of five publicly available static analysis tools for security. The test results show high rates of false positives for the tools building on lexical analysis and low rates of true positives for the tools building on syntactical and semantical analysis. As a first step toward a more effective and generic solution we propose decorated dependence graphs as a way of modeling and pattern matching security properties of code. The models can be used to characterize both good and bad programming practice as well as visually explain code properties to programmers. We have implemented a prototype tool that demonstrates how such models can be used to detect integer input validation flaws. Finally, we investigated the effectiveness of publicly available tools for runtime prevention of buffer overflow attacks. Our initial comparison showed that the best tool as of 2003 was effective against only 50 % of the attacks and there were six attack forms which none of the tools could handle. A follow-up study includes the release of a buffer overflow testbed which covers 850 attack forms. Our evaluation results show that the most popular, publicly available countermeasures cannot prevent all of these buffer overflow attack forms.

Syftet med denna undersökning är att ta fram en taxonomi för databashanteringssystem (DBMS) som kan förenkla valet av DBMS, då det kan vara en lång och komplicerad process. Taxonomin klassificerar kriterier hos DBMS som anses viktiga i en litteraturstudie av flertalet artiklar. Arbetet visar även på en strukturerad process för att gå från krav till val av databashanterare i form av ett poängsystem som använder sig av taxonomin och DBMS rangordning på olika kriterier. Valprocessen tar ställning till de val och krav som användaren lämnat och slutligen tilldelas denne ett förslag, utan att kräva tid och avancerade kunskaper. / The purpose of this study is to develop a taxonomy for database management systems (DBMS) that can simplify the choice of DBMS, when this usually can be a long and complicated process. The taxonomy classifies criteria of DBMS that are considered important in the literature of several articles. The work also shows a structured process to go from requirements to the choice of the DBMS in form of a score based system that uses the taxonomy and the management system’s ranking on different criteria. User choices and other mandatory information is taken into consideration by the process to represent the most suitable DBMS, without requiring time and advanced skills of the user.

Forecasts are used to predict the uncertain outcome of a variable. These predictions are made to get an understanding of likely future scenarios which allows planning in advance. Forecasts are commonly used in inventory control systems to estimate the future demand. This estimation along with the estimated precision of the forecast can be used to determine adequate safety stocks. In extension, forecasts of the future demand can be used to support decisions regarding the replenishment of inventories.     This thesis involves forecasting of the demand of pharmaceutical drugs. In particular, drugs that are referred to as generics. The demand of generics can fluctuate heavily due to the substitution system and can therefore be troublesome to forecast. The main objective of this thesis is to design a suitable forecast approach for the demand of generics, and to examine how these forecasts can be used to control the replenishment of inventories. The project was executed at a pharmaceutical drug distributor and hopes to enlighten some new techniques that can be used to improve the handling of generics. To achieve the objective of this thesis, the initial focus was on the current state. The currently used methods where studied and compared with theories and methods described in literature. Assumptions and theories on which the currently used methods are based on could thus be identified. These assumptions where later assessed as either reasonable or unreasonable. Finally, a new forecast approach was designed to account for the insights gained from evaluating the current methods. The result of this thesis is a forecast approach suitable to forecast the demand of generics that account for the fluctuation in demand which occurs due to the substitution system. It assumes that the demand has a constant demand model, but an alternative method suitable for the trend model is also given. It is proposed that tracking signals are used to monitor the forecast such that systematic errors are identified. Furthermore, the literature review indicates that alternatives to the current method used to determine the reorder point should be considered for occasionally demanded generics.

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The paper industry is a highly energy consuming process which also facing huge challenges as the global demand of paper products constantly decreasing. Therefore, the importance of energy optimizing the process becomes more and more crucial. The purpose of this work was to contribute to the energy optimization work at Kvarnsveden paper mill in Borlänge by mapping the energy consumption and analyzing particular areas with potential of optimization. Furthermore, analysis of the process parameters tinting colors, moisture profile and the pulp refiners in order to decrease the material losses were performed. The results from the analysis of tinting colors and moisture profiles provided the operators with reference intervals which stated how to run the parameters in order to produce paper of approved quality. The purpose of analyzing the refiners was to investigate if the quality of the mass could be predicted by specific energy instead of Freeness and average fiber length, which is the method used today. The result of this analysis shows that this is not possible today. However, specific energy is a valuable parameter in order to predict process malfunctions. The result of the energy mapping shows that the total specific energy consumption to produce one ton paper is 4,1 MWh/ton. Furthermore the energy mapping shows that every ton of paper that doesn’t clear the quality control and has to be re-produced consumes additional 1,3 MWh/ton of energy, which means that the total amount of energy for reproduced paper is 5,4 MWh. The amount of energy that is necessary to re-produce shows the importance of producing quality approved paper the first time, and since PM12 is capable of producing 1 ton/min at normal operating speed, the amount of paper that has to be re-produced can increase very fast. Hopefully, the results from the analysis of tinting colors and moisture profile will contribute to a decreased amount of papers that has to be re-produced. Furthermore the energy mapping shows some areas with energy optimization potential. Partly by maintenance and repairs of heat exchangers and steam condensers and partly by terminate the heating of buildings that has no use in the production today.