| 1181. |
- Kosta, Antzela, 1990-
(författare)
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Analysis of the Age of Information in Status Update Systems
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rapid advances in wireless technology have taken us towards a pervasively connected world in which a vast array of wireless devices, from mobile phones to environmental sensors, seamlessly communicate with each other. In some of these systems the freshness of the transmitted information is of high importance. Characterization of time-critical information can be done through the so called real-time status updates that are messages, in the form of packets, carrying a timestamp of their generation. Status updates track time-varying content that needs to be transmitted from the generation point to a remote destination within a network. To quantify the freshness of information in networked systems a novel metric, different than delay or latency, termed as "age of information" (AoI) has been introduced. In this thesis, we focus on the communication systems' adaptability to meet stringent timeliness constraints.In Paper I, we expand the concept of information ageing by introducing the cost of update delay (CoUD) metric to characterize the cost of having stale information at the destination. Furthermore, we introduce the value of information of update (VoIU) metric that captures the degree of importance of the update received at the destination. A theoretical analysis and insights into the relation of cost and value are provided.Paper II investigates AoI in relation with throughput in a shared access setup with heterogeneous traffc. More specifically, we consider a shared access system consisting of a primary link and a network of secondary nodes, with multipacket reception (MPR) capabilities. To study the joint throughput-timeliness performance, we formulate two optimization problems considering both objectives and provide guidelines for the design of such a multiple access system fulfilling both timeliness and throughput requirements.Finally, in Paper III we investigate the AoI performance in various multiple access (MA) schemes, including scheduling and random access. We present analysis of the AoI with and without packet management at the transmission queue of the source nodes, considering that packet management is the capability to replace unserved packets at the queue whenever newer ones arrive. We incorporate the effect of channel fading and network path diversity in such a system and provide simulation results that illustrate the impact of network operating parameters on the performance of the different access protocols.
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| 1182. |
- Krantz, Venus, 1988-
(författare)
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Exploring localisation of the Sustainable Development Goals : Focusing on municipal organisations in a Swedish context
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Adopted in 2015, the 2030 Agenda and the seventeen Sustainable Development Goals (SDGs) call for integrated approaches and aim to “leave no one behind”. This licentiate thesis focuses on localisation of the SDGs in Swedish municipal organisations, and more specifically at early stages of SDG localisation processes. It investigates how the SDGs can be operationalised into municipal organisations and in what ways municipal organisations can engage with other actors in SDG localisation. The thesis takes it theoretical point of departure in governance, strategic planning, and management connected to sustainability and municipal organisations. This cover essay is based on three qualitative studies, mainly built on interviews but complemented with observations and document studies. The three studies explore SDG localisation from different perspectives. The first study focus on SDG operationalisation in a municipal organisation, the second on regional SDG collaboration and the third focuses on the intersection between SDG operationalisation and collaboration in municipal organisations. The findings (in this thesis) reveal that all studied municipalities showed ambitions to operationalise the SDGs holistically across sustainability dimensions (and sectors) through strategy and practices in the municipal organisation. The examples also show different levels and ways of how municipal organisations can engage with external actors in SDG localisation, from no specific external engagement to communicating the SDGs or initiating local SDG networks. In short, the SDGs can serve as a common denominator and contributes to learning, in both external and internal sustainability efforts. Moreover, the SDGs give municipal organisations an opportunity to approach a leader role to forward local sustainability. However, there is a tendency wanting to operationalise the SDGs internally before engaging with external actors, and hence, to act as a good example to have the credibility to engage other actors. Yet, this is challenging as the SDGs cover many areas. There is also a risk to get stuck in the details regarding operationalisation, hampering the municipal organisations to take a more active role in externally in SDG localisation. To manage this, it is suggested that SDG operationalisation and actor engagement should be approached as parallel (and intertwined) processes. This, and SDG localisation overall, puts a lot of pressure on municipal (SDG) process leaders, who need to have the mandate to act (i.e. placed centrally, organisational and political support) and have a generalist, flexible and open approach. This research contributes with knowledge and examples of SDG localisation and forwarding sustainability in municipal organisations, additionally it contributes theoretically to further understanding of the connections between sustainability management and local governance.
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| 1183. |
- Kunnath Ganesan, Unnikrishnan, 1989-
(författare)
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Distributed Massive MIMO : Random Access, Extreme Multiplexing and Synchronization
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The data traffic in wireless networks has grown tremendously over the past few decades and is ever-increasing. Moreover, there is an enormous demand for speed as well. Future wireless networks need to support three generic heterogeneous services: enhanced mobile broadband(eMBB), ultra-reliable low latency communication (URLLC) and massive machine type communication (mMTC). Massive MIMO has shown to be a promising technology to meet the demands and is now an integral part of 5G networks. To get high data rates, ultra densification of the network by deploying more base stations in the same geographical area is considered. This led to an increase in inter-cell interference which limits the capacity of the network. To mitigate the inter-cell interference, distributed MIMO is advocated. Cell-free massive MIMO is a promising technology to improve the capacity of the network. It leverages all the benefits from ultra densification, massive MIMO, and distributed MIMO technologies and operates without cell boundaries. In this thesis, we study random access, extreme multiplexing capabilities, and synchronization aspects of distributed massive MIMO. In Paper A studies the activity detection in grant-free random access for mMTC in cell-free massive MIMO network. An algorithm is proposed for activity detection based on maximum likelihood detection and the results show that the macro-diversity gain provided by the cell-free architecture improves the activity detection performance compared to co-located architecture when the coverage area is large. RadioWeaves technology is a new wireless infrastructure devised for indoor applications leveraging the benefits of massive MIMO and cell-free massive MIMO. In Paper B, we study the extreme multiplexing capabilities of RadioWeaves which can provide high data rates with very low power. We observe that the RadioWeaves deployment can spatially separate users much better than a conventional co-located deployment, which outweighs the losses caused by grating lobes and thus saves a lot on transmit power. Paper C studies the synchronization aspect of distributed massive MIMO. We propose a novel, over-the-air synchronization protocol, which we call as BeamSync, to synchronize all the different multi-antenna transmit panels. We also show that beamforming the synchronization signal in the dominant direction of the channel between the panels is optimal and the synchronization performance is significantly better than traditional beamforming techniques.
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| 1184. |
- Kärnell, Samuel, 1993-
(författare)
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Fluid Power Pumps and the Electrification : With a Focus on Discrete Displacement Control in Load Handling Applications
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- More and more vehicles are being electrified. Mobile working machines and heavy trucks are not excluded, and these machines are often hydraulically intense. Electrification entails new requirements for the hydraulic system and its components, and these requirements must be taken into consideration.Hydraulic systems have looked similar for a long time, but now there is an opportunity to advance. Many things change when a diesel engine is replaced with an electric motor. For example, variable-speed control becomes more relevant, electric regeneration becomes possible, and the use of multiple prime movers becomes an attractive alternative. The noise from the hydraulic system will also be more noticeable when the diesel engine is gone. Furthermore, the introduction of batteries to the system makes the energy more valuable, since batteries are heavy and costly compared to a diesel tank. Therefore, it is commercially viable to invest in the hydraulic system.This thesis revolves around the heart of the hydraulic system, that also is the root of all evil. That is the pump. Traditionally, a pump has had either a fixed displacement or a continuously variable displacement. Here, the focus is on something in between, namely a pump with discrete displacement. The idea of discrete displacement is far from unique, but has not been investigated in detail in combination with variable speed before. In this thesis, a novel design for a quiet pump with discrete displacement is presented and analysed. The results show that discrete displacement is relevant from an energy perspective for machines working extensively at high pressure levels and with low flow rates, and that a few discrete values are enough to make a significant difference. However, for other cycles, the possible energy gains are very limited, but the discrete displacement can be a valuable feature if downsizing the electric machine is of interest.
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| 1185. |
- Larsson, Felix, 1995-
(författare)
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Evaluation of Aircraft Actuator Technologies
- 2023
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The flight control actuation system is one of the most critical systems in an aircraft. A failure of this system cannot occur, since it would have catastrophic consequences. The environment it operates in is considered as highly demanding, with temperatures ranging from -50 to +60 degrees Celsius, speeds from 0 to Mach 2+ and G-forces from -3 up to 9. At the same time, the system shall be as small and lightweight as possible, since every gram and cm3 will decrease the available payload and/or increase the total aircraft size, which in turn increase the fuel-burn. The preferred choice of technology for actuators has, since the late 1930s, been hydraulics. Hydraulic actuators are characterized by high power density, high technical maturity, high safety, and high response. With emerging benefits from the electric domain, research during the last decade has been focusing on electrified alternatives as the future alternative for actuators. With varying requirements on the actuators depending on the type of air-craft platform, it is not trivial when it is a better alternative to electrify the actuators. For example, with smaller platforms, the forces acting on the actuators will be lower in comparison with larger aircraft. The purpose of this thesis was to investigate if, and when certain technology may be the preferred alternative with regards to size and weight, performance, power consumption and thermal characteristics. Also, it was investigated how to compare different topologies which utilize different technologies, and how certain technology may affect the requirements of surrounding systems in the platform. This work has led to three different approaches for comparison and evaluation of actuator technology that can be applied in early conceptual design of aircraft platforms. The first approach can be used to ensure comparability of the topologies to be studied. The second approach focuses on modeling of performance and thermal impact and can be applied to study static and dynamic behavior of different technologies. The third approach can be used to study how size and weight of actuators will be affected by operational requirements, with special emphasis on high-level modeling with few inputs.
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| 1186. |
- Lindberg, Therese, 1986-
(författare)
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Discrete Event Simulation of Bus Terminals
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Public transport is important to society as it provides spatial accessibility and reduces congestion and pollution in comparison to other motorized modes. To assure a high-quality service, all parts of the system need to be well-functioning and properly planned. One important aspect for the system's bus terminals is their capacity. This needs to be high enough to avoid congestion and queues and the delays these may lead to. During planning processes, various suggested designs and solutions for a terminal need to be evaluated. Estimating capacity and how well the suggestions will function is a challenging problem, however. It requires analysis of complex interactions and behaviour of the vehicles. This sort of analyses can preferably be carried out using microsimulation. Furthermore, a discrete event simulation approach can make use of the fact that the path of a vehicle through a terminal can readily be described by a sequence of events (such as arriving, starting to drive to a stop etc.).The overall aim of this thesis is to investigate how discrete event simulation can be used to evaluate bus terminal design and traffic control policies. The main contribution is the development of a method for bus terminal simulation. As a first step, a discrete event simulation model of a combined bus and tram stop is formulated. The model is tested on a real system where the current design is compared to an alternative one. The test shows that a model developed with a discrete event approach can be used to evaluate the situation at a stop and compare design alternatives. In the next step, a general discrete event simulation model of bus terminals is formulated. A modular approach is introduced, where a terminal can be constructed from a set of module building blocks. Another important contribution of the model is its spatial resolution that allows for queues and blockages to occur throughout the terminal. By applying the simulation model in a case study, it is shown that the model can be used to evaluate and compare various scenarios related to the layout, number of passengers and the outside traffic situation. Lastly, the bus terminal simulation model is used in a second case study in order to compare model output with empirical data. This study identified a number of factors that may have had an influence on differences between observations and simulation results and that is of interest to look further into. This includes the actual adherence to terminal rules and the effects of model parameters.
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| 1187. |
- Lindeberg, Fredrik, 1987-
(författare)
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Coordinating the Internet
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Många självklarheter i vårt digitala samhälle är beroende av Internet för att fungera. Allt från smarta dörrar för hemtjänster, till självscanningsapparaterna på ICA, till nyare bilar, moderna tillverkningsrobotar, telefoner och affärssystem. Den här licentiatavhandlingen reder ut vad Internet är, hur det styrs och vad det har för praktiska konsekvenser. Tidigare forskning finns bland annat inom telekommunikation där Internet liknas vid andra telekommunikationstjänster, så som kabel-TV eller mobiltelefoni, och inom digitalisering både inom management och informationssystem där Internet i det närmaste tas för givet som teknisk infrastruktur. Här tar jag en ansatts där jag förklarar Internet ur ett kombinerat tekniskt och organisatoriskt perspektiv.Studien är principiellt uppdelad i tre delar. Den första delen fokuserar på att begreppsmässigt hitta ett sätt att diskutera Internet utan att essentiella aspekter faller bort, såsom styrningen eller konsekvenser av den tekniska designen. Jag landar i att Internet är både ett tekniskt och ett organisatoriskt fenomen. Tekniskt i bemärkelsen att det handlar om digital paketbaserad kommunikation (dvs att olika paket kan ta olika väg och att det inte finns ett beroende på en viss specifik väg, eller “krets”), vilket kan särskiljas från exempelvis kretskopplad kommunikation (dvs en specific väg från sändare till mottagare) eller rent analog kommunikation. I denna tekniska dimension är Internet förhållandevis likt klassisk telekommunikation såsom kabel-TV och mobiltelefoni, och förlitar sig på best-effort paketbaserad kommunikation. I den andra dimensionen, styrning och organisation, är Internet ett explicit bottom-up fenomen som styrs med andra principer och ideal än klassisk telekommunikation. Till sin utformning är denna minsta möjliga koordination som krävs för att möjliggöra koordinering av de tekniska unika identifierare som behövs för att Internet ska fungera (dvs idag DNS- och BGP-flororna av protokoll för användning av namn och nummer på Internet). Båda dimensionerna, de organisatoriska och tekniska, följer samma designprinciper, och generellt är det meningsfullt att se Internet som en ekologi av aktörer snarare än en organisation i strikt teoretiska termer (exempelvis finns ingen tydlig övergripande strategi, organisationsnummer eller löneutbetalare). Det är dessa designprinciper, som ligger väl i linje med systemarkitektursprinciper för datorsystem, som är orsaken till Internets lager-design där man (generellt) inte ska bry som om vad som händer på andra lager än sitt eget (beskrivet som “separation of concerns” eller i dubbel negation “high cohesion” i texten) samt att ha en minimalistisk ansatts till koordinering och enbart koordinera eller skapa beroenden mellan enheter (både tekniskt och organisatoriskt) när det verkligen behövs (beskrivet som “minimum coordination” eller “low coupling” i texten). Den andra delen fokuserar på hur Internet kan socialt påverkas eller förändras till något annat, eller till något med en annan funktion sett som en styrd organisation. Jag använder begreppet social robusthet, som motpol till teknisk robusthet som i hur man tekniskt kan förstöra Internet, för att diskutera dessa aspekter. Slutsatserna här mynnar ut i att Internets explicita bottom-up och problemsuppdelnings-design gör det märkbart svårt för någon att medvetet påverka Internet för att ändra dess beskaffenhet, och dessutom visar jag att även om man praktiskt lyckas ta över de formellt beslutande råden (exempelvis ICANNs och IETFs styrelser) så finns det inga formella eller praktiska hinder för att bara ignorera dem (dvs switching costs för just ICANN eller IETF är låga, om än tekniskt omständligt med att konfigurera om rötter och routing-tabeller, och betydligt enklare än att gå från IPv4 till IPv6 då utrustning kan behöva ersättas och därmed en betydligt högre switching cost). Med andra ord, det är enklare att byta ut Internets koordinerare än att byta ut Internet mot något som fungerar annorlunda. Däremot är den rådande politiska världsordningen ett hot mot Internet, eftersom den regelstyrda och koordinerade världsordningen inte längre är lika självklar som den varit tidigare. Den tredje och sista studien fokuserar på nätneutralitet, dvs rätten nätverksoperatörer har att fånga värde i andra dimensioner än trafikmängd, som en praktiskt effekt av hur Internet styrs och fungerar. Det primära praktiska bidraget är att nätneutralitet inte får ses som enbart en reglerings och lagstiftningfråga utan det är mer relevant att prata om i termer av nätneutralitet i praktiken. I den bemärkelsen är lagstiftningens vara eller inte vara mindre intressant än praktisk nätneutralitets vara eller inte vara och en tyngdpunktsförskjutning i den offentliga debatten hade fört diskussionen närmare hur Internet fungerar. Sammanfattningsvis ger Internets designprinciper att marknadskrafter, och ej direkt reglering, ska möjliggöra nätneutralitet. För att förtydliga, tanken är att det ska finnas konkurrens inom de flesta nivåer eller lager, och att det är av vikt att det finns konkurrens rakt igenom så att en kundvilja för paketneutralitet på tjänstenivå även påverkar nätägar- och infrastrukturnivå, så att det är användarnas efterfrågan som leder till nätneutralitet (om den användarviljan finns). Dock kan det mycket väl vara så att man som användare inte är intresserad av nätneutralitet och då ska tjänsteleverantörer, nätägare och infrastrukturoperatörer inte heller tvingas vara neutrala genom lagstiftning då det går stick i stäv med designprinciperna. Inte heller ska en grupps vilja kring nätneutralitet påverka andras möjligheter att välja.Genomgående identifierar jag två kolliderande världsbilder, den distribuerade regelstyrda och koordinerade ordningen i sitt perspektiv med sina förkämpar, och den mer integrerande och suveräna världsordningen med sitt perspektiv och sina förkämpar. Rent praktiskt uppfyller Internet en önskad funktion i den tidigare men ej i den senare, då Internet designmässigt är byggt för att tillåta snarare än kontrollera och bestämma. Exempelvis finns det inte inbyggda (tekniska) mekanismer i Internet för att till exempel möjliggöra statlig övervakning eller kontroll av material som finns tillgängligt, och då ligger det mer i statens intresse att ha kontrollerade telekommunikationstjänster, såsom kabel-TV, mobiltelefoni och liknande lösningar där man inte helt enkelt kan lägga på ett “extra lager” för att uppnå kryptering, anonymitet eller tillgång till andra tjänster.I texten använder jag perspektiven tillsammans med teknologi, marknader och byråkrati för att fånga upp dynamiken och strömningarna i Internet-ekologin och jämför med tekniska samhällsförändringar, som exempelvis järnvägsnät, postverk och finansiella marknader. Jag konstaterar att Internet har varit styrt av teknologiskt baserade värderingar, till skillnad från de andra exemplen som i huvudsak har utformats av dynamiken mellan byråkrati och marknad. I denna mån förelår jag att teknologi kan användas som strömning och motperspektiv till den klassiska uppställningen med byråkrati och marknad för att beskriva fenomen i digitaliseringens tidsålder.Avhandlingen sätter även pågående trender i ett bredare perspektiv mot både organisation och teknik, och trycker på vikten av att förstå delarna var för sig och tillsammans för att på ett rikare sätt måla upp helheten.
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| 1188. |
- Linder, Clara, 1994-
(författare)
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Catalytically active and corrosion resistant cobalt-based thin films
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Oxygen reduction reaction (ORR) has considerable potential for the pro-duction of electricity, issues with water splitting and many other applications in the energy sector. But in order to increase the efficiency of the reaction an electrocatalyst needs to be introduced.In today’s industrial devices precious and costly metals such as platinum (Pt) are used as catalysts. Other more abundant and cheaper alternatives, for example cobalt oxides, are therefore being investigated. In this thesis, pure cobalt (Co) thin films were synthesised to investigate if thin films can be used for the catalysis of ORR. This was successfully carried out by electrochemically modifying the thin films and grow catalytically ac-tive hexagonal cobalt oxide nanoparticles. Multicomponent system CoCrFeNi is an emerging alloy system with high research interest for its high corrosion resistance suitable for harsh environments in which the applications for ORR are found. In this thesis, CoCrFexNi were synthesised as thin films. The corrosion resistance of the films was investigated in addition to their catalytic activity. The effect of Fe content on these properties was also studied. The presence of Fe was crucial for the electrochemical activation of films and catalytic activity towards ORR. In summary, this thesis shows that cobalt based thin films can be used as catalysts combined with corrosion resistance for ORR applications.
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| 1189. |
- Lindfors, Axel, 1993-
(författare)
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Sustainability Solutions : Lessons on Assessment and Facilitation
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Sustainable development is one of the most influential visions guiding future societies. Encompassed within its vision are various domains where improvements are desirable such as, social equity, environmental degradation, climate change. In the work towards sustainable development firms, government authorities and individuals face various practical challenges tied to these sustainability domains. When facing these challenges, they may implement sustainability solutions, that is, solutions that are framed in the context of contributing to sustainable development. This thesis deals with a particular sub-set of such sustainability solutions, namely integrative and multi-functional solutions. These solutions are characterized by the ability to provide different functions through value creation within several different sustainability domains and require organisations, or units of organisations, to further integrate material, energy and informational flows in order to implement the solution. Integrative and multi-functional solutions may play an important part in the transition towards sustainable societies since the integration of material, energy and informational flows may bring with it synergistic benefits. Furthermore, the contribution of these solutions to several different sustainability domains reduces the risk of problem shifting, and it may be more cost-efficient to have one multi-functional sustainability solution than to have one for each sustainability- related challenge.However, if integration and multi-functionality are desirable characteristics of future socio-technological systems, we need ways to systematically assess them and facilitate their implementation. When it comes to the assessment, there is a need to find an assessment methodology that can handle capturing the synergistic benefits and multiple functions of such solutions. Furthermore, the methodology also has to conform to the value pluralism inherent to sustainable development. Dealing with this value pluralism when trying to assess which solution, among many, to implement can be challenging as comparative judgements have to handle potentially conflicting value orientations, goals, empirics and ontologies. As for the facilitation of their implementation, integrative and multi-functional solutions tend to be more difficult—or at least different—to implement than traditional single-minded solutions since they require traditionally separate organisations to cooperate Therefore, this thesis aims to contribute to understanding the process of implementing integrative and multi-functional solutions. Specifically the thesis explores how to select indicators for assessment, how assessments may aid decision-makers to deal with the value pluralism of sustainable development when making comparative judgements and how to strengthen the internal capacity of groups of actors to engage in collective action.Regarding the selection of indicators, the thesis suggests two different pathways. Either one may base indicator selections on stakeholder discussions, where stakeholders come to a consensus around which indicators are important to assess, or one may base indicators on operationalising pre-defined sustainability objectives: namely, sorting, contextualising and reformulating pre-defined sustainability objectives so that they fit the purpose of the assessment. A mix of both pathways is also possible, in other words, using both stakeholder discussions and the operationalisation of pre-defined sustainability objectives to motivate and justify the selection of indicators. As for how assessments may aid decision-makers, the thesis advocates for a discursive approach based on the primacy of decision support tools over decision-making tools. Meaning that the tools should support informed decisions but not make them for the decisionmaker. Here, contributions are made in the form of motivations for the discursive, qualitative approach to decision-making and exemplify how decision support tools may be designed, and a method is presented and developed that enables this kind of informed comparative judgements. This method builds on multicriteria decision analysis methodology but makes a few key contributions to the selection of indicators (mentioned previously) and to how to compare different alternatives and judge which of the alternatives is the preferred. Finally, contributions are made to the practice of facilitating integrative and multi-functional solutions through showing how the theory of institutional capacity building can be used to guide design, development and evaluation of interventions aimed at facilitating such solutions. Institutional capacity building represents the ability of groups of actors to engage in collective action, something that seems to be often needed to implement integrative and multi-functional solutions. Historically, this theory has been used to study how different events influenced the capacity of actors to engage in collective action. However, in research performed within the bounds of this thesis, the theory is expanded for use in a proactive manner, thereby contributing with insights and inspiration to others that may seek to facilitate the implementation process of integrative and multi-functional solutions.
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| 1190. |
- Lindmark, Gustav, 1983-
(författare)
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Methods and algorithms for control input placement in complex networks
- 2018
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The control-theoretic notion of controllability captures the ability to guide a systems behavior toward a desired state with a suitable choice of inputs. Controllability of complex networks such as traffic networks, gene regulatory networks, power grids etc. brings many opportunities. It could for instance enable improved efficiency in the functioning of a network or lead to that entirely new applicative possibilities emerge. However, when control theory is applied to complex networks like these, several challenges arise. This thesis consider some of these challenges, in particular we investigate how control inputs should be placed in order to render a given network controllable at a minimum cost, taking as cost function either the number of control inputs or the energy that they must exert. We assume that each control input targets only one node (called a driver node) and is either unconstrained or unilateral.A unilateral control input is one that can assume either positive or negative values but not both. Motivated by the many applications where unilateral controls are common, we reformulate classical controllability results for this particular case into a more computationally-efficient form that enables a large scale analysis. We show that the unilateral controllability problem is to a high degree structural and derive theoretical lower bounds on the minimal number of unilateral control inputs from topological properties of the network, similar to the bounds that exists for the minimal number of unconstrained control inputs. Moreover, an algorithm is developed that constructs a near minimal number of control inputs for a given network. When evaluated on various categories of random networks as well as a number of real-world networks, the algorithm often achieves the theoretical lower bounds.A network can be controllable in theory but not in practice when completely unreasonable amounts of control energy are required to steer it in some direction. For unconstrained control inputs we show that the control energy depends on the time constants of the modes of the network, and that the closer the eigenvalues are to the imaginary axis of the complex plane, the less energy is required for control. We also investigate the problem of placing driver nodes such that the control energy requirements are minimized (assuming that theoretical controllability is not an issue). For the special case with networks having all purely imaginary eigenvalues, several constructive algorithms for driver node placement are developed. In order to understand what determines the control energy in the general case with arbitrary eigenvalues, we define two centrality measures for the nodes based on energy flow considerations: the first centrality reflects the network impact of a node and the second the ability to control it indirectly. It turns out that whether a node is suitable as driver node or not largely depends on these two qualities. By combining the centralities into node rankings we obtain driver node placements that significantly reduce the control energy requirements and thereby improve the “practical degree of controllability”.
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