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  • 52451.
    Westman, Jonas
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Specifying Safety-Critical Heterogeneous Systems Using Contracts Theory2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Requirements engineering (RE) is a well-established practice that is also emphasized in safety standards such as IEC 61508 and ISO 26262. Safety standards advocate a particularly stringent RE where requirements must be structured in an hierarchical manner in accordance with the system architecture; at each level, requirements must be allocated to heterogeneous (SW, HW, mechanical, electrical, etc.) architecture elements and trace links must be established between requirements. In contrast to the stringent RE in safety standards, according to previous studies, RE in industry is in general of poor quality. Considering a typical RE tool, other than basic impact analysis, the tool neither gives feedback nor guides a user  when specifying, allocating, and structuring requirements. In practice, for industry to comply with the stringent RE in safety standards, better support for RE is needed, not only from tools, but also from principles and methods.

    Therefore, a foundation is presented consisting of an underlying theory for specifying heterogeneous systems and complementary principles and methods to specifically support the stringent RE in safety standards. This foundation is indeed suitable as a base for implementing guidance- and feedback-driven tool support for such stringent RE; however, the fact is that the proposed theory, principles, and methods provide essential support  regardless if tools are used or not.

    The underlying theory is a formal compositional contracts theory for heterogeneous systems. This contracts theory embodies the essential RE property of separating requirements on a system from assumptions on its environment. Moreover, the contracts theory formalizes the stringent RE effort of structuring requirements hierarchically with respect to the system architecture. Thus, the proposed principles and methods for supporting the stringent RE in safety standards are well-rooted in formal concepts and conditions, and are thus, theoretically sound. Not only that, but the foundation is indeed also tailored to be enforced by both existing and new tools considering that the support is based on precise mathematical expressions that can be interpreted unambiguously by machines. Enforcing the foundation in a tool entails support that guides and gives feedback when specifying heterogeneous systems in general, and safety-critical ones in particular.

  • 52452.
    Westman, Jonas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Embedded Control Systems.
    Nyberg, Mattias
    A Reference Example on the Specification of Safety Requirements using ISO 262622013In: Proceedings of Workshop DECS (ERCIM/EWICS Workshop on Dependable Embedded and Cyber-physical Systems) of the 32nd International Conference on Computer Safety, Reliability and Security - SAFECOMP 2013 - Workshop DECS (ERCIM/EWICS Workshop on Dependable Embedded and Cyber-physical Systems) of the 32nd International Conference on Computer Safety, Reliability and Security, France (2013), 2013Conference paper (Refereed)
    Abstract [en]

    ISO 26262 - "Road vehicles-Functional Safety" is a standard for the automotive industry, administered in an attempt to prevent potential accidents due to systematic and random failures in the Electrical/Electronic-system. In general, requirements in industry is often of poor quality and considering the strong emphasis on requirements management in ISO 26262, we believe that there is a strong need for guidance and experience-sharing on the speci cation of requirements in practice. We therefore present a reference example on the application of ISO 26262 in practice, where we perform a breakdown of a Safety Goal of an industrial system down to Software Safety Requirements on the C-code implementation. As a basis for structuring and formulating the requirements, we use the concepts of contracts and port variables.

  • 52453.
    Westman, Jonas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Nyberg, Mattias
    Conditions of Contracts for Separating Responsibilities in Heterogeneous Systems2017In: Formal methods in system design, ISSN 0925-9856, E-ISSN 1572-8102Article in journal (Refereed)
    Abstract [en]

    A general, compositional, and component-based contract theory is proposed for modeling and specifying heterogeneous systems, characterized by consisting of parts from different domains, e.g. software, electrical and mechanical. Given a contract consisting of assumptions and a guarantee, clearly separated conditions on a component and its environment are presented where the conditions ensure that the guarantee is fulfilled - a responsibility assigned to the component, given that the environment fulfills the assumptions. The conditions are applicable whenever it cannot be ensured that the sets of ports of components are partitioned into inputs and outputs, and hence fully support scenarios where components, characterized by both causal and acausal models, are to be integrated by solely relying on the information of a contract. An example of such a scenario of industrial relevance is explicitly considered, namely a scenario in a supply chain where the development of a component is outsourced. To facilitate the application of the theory in practice, necessary properties of contracts are also derived to serve as sanity checks of the conditions. Furthermore, based on a graph that represents a structuring of a hierarchy of contracts, sufficient conditions to achieve compositionality are presented.

  • 52454.
    Westman, Jonas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Nyberg, Mattias
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Contracts for Structuring and Specifying Requirements on Cyber-Physical Systems2015In: Cyber-Physical Systems: From Theory to Practice, CRC Press, 2015Chapter in book (Refereed)
    Abstract [en]

    A contract splits the responsibilities between a component and its environment into a guarantee that expresses an intended property under the responsibility of the component, given that the environment fulfills the assumptions. Building on recent works where contracts are proposed as a means to meet the challenges in the design of Cyber-Physical Systems (CPSs), a general contract framework is presented that supports the modelling of both individual components and architectures of CPS - at all levels of design, as well as the structuring and specification of requirements on the components using contracts. To facilitate the specification of requirements, constraints that restrict the portsover which a contract is expressed are introduced to serve as sanity checks that the component and the environment meet their respective responsibilities. Furthermore, a new graph, called a \emph{contract structure} is introduced to support the structuring and tracing of requirements on a CPS using contracts. As a proof-of-concept, the framework is used to specify and structure safety requirements on an industrial system, as proposed by ISO 26262.

  • 52455.
    Westman, Jonas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Nyberg, Mattias
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Environment-Centric Contracts for the Design of Cyber Physical Systems2014Report (Other academic)
    Abstract [en]

    A contract splits the responsibilities between a component and its environment into a guarantee that expresses an intended property under the responsibility of the component, given that the environment fulfills the assumptions. Although current contract theories are limited to express contracts over interfaces of components, specifications that are not limited to interfaces are used in practice and are needed in order to properly express safety requirements. A framework is therefore presented, generalizing current contract theory to environment-centric contracts - contracts that are not limited to the interface of components. The framework includes revised definitions of properties of contracts, as well as theorems that specifies exact conditions for when the properties hold. Furthermore, constraints are introduced, limiting the ports over which an environment-centric contract is expressed where the constraints constitute necessary conditions for the guarantee of the contract to hold in an architecture.

  • 52456.
    Westman, Jonas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Nyberg, Mattias
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics. Scania, Sweden.
    Extending Contract Theory with Safety Integrity Levels2015In: 2015 IEEE 16th International Symposium on High Assurance Systems Engineering (HASE), IEEE Computer Society, 2015, p. 85-92Conference paper (Refereed)
    Abstract [en]

    In functional safety standards such as ISO 26262 and IEC 61508, Safety Integrity Levels (SILs) are assigned to top-level safety requirements on a system. The SILs are then either inherited or decomposed down to safety requirements on sub-systems, such that if the sub-systems are sufficiently reliable in fulfilling their respective safety requirements, as specified by the SILs, then it follows that the system is sufficiently reliable in fulfilling the top-level safety requirement. Present contract theory has previously been shown to provide a suitable foundation to structure safety requirements, but does not include support for the use of SILs. An extension of contract theory with the notion of SILs is therefore presented. As a basis for structuring the breakdown of safety requirements, a graph, called a contract structure, is introduced that provides a necessary foundation to capture the notions of SIL inheritance and decomposition in the context of contract theory.

  • 52457.
    Westman, Jonas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Nyberg, Mattias
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Formal Architecture Modeling of Sequential C-Programs2016In: Formal Aspects of Component Software: 12th International Conference, FACS 2015, Niterói, Brazil, October 14-16, 2015, Revised Selected Papers, Springer, 2016, p. 312-329Conference paper (Refereed)
    Abstract [en]

    To enable verification of a complex C-program, so called compositional verification can be used where the specification for the C-program is split into a set of specifications organized such that the fact that the C-program satisfies its specification can be inferred from verifying that parts of the C-program satisfy their specifications. To support the approach in practice, specifications must be organized in parallel to a formal architecture model capturing the C-program as a hierarchical structure of components with well-defined interfaces. Previous modeling approaches lack support for formal architecture modeling of C-programs. Therefore, a general and formal approach for architecture modeling of sequential C-programs is presented, to support compositional verification, as well as to aid design and management of such C-programs in general.

  • 52458.
    Westman, Jonas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Nyberg, Mattias
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics. Scania.
    Preserving Contract Satisfiability Under Non-monotonic Composition2018In: Formal Techniques for Distributed Objects, Components, and Systems: 38th IFIP WG 6.1 International Conference, FORTE 2018, Held as Part of the 13th International Federated Conference on Distributed Computing Techniques, DisCoTec 2018, Madrid, Spain, June 18-21, 2018, Proceedings / [ed] Christel Baier, Luís Caires, Springer, 2018, Vol. 10854, p. 181-195Conference paper (Refereed)
    Abstract [en]

    A contracts theory embeds non-monotonic composition (with respect to implementation) if the fact that a composition of two components implements a specification S does not generally follow from one of these components implementing S. In contrast to monotonic composition, non-monotonic composition offers the additional expressiveness of specifying properties that only hold locally for a component since non-monotonic composition does not enforce all properties to be preserved when composing. Despite that this additional expressiveness is clearly needed, it implies that cases where monotony is indeed desired needs to be managed explicitly. The present paper elaborates on this topic by introducing a contracts theory embedding non-monotonic composition, and exploring conditions for ensuring monotonic composition in the context of this theory.

  • 52459.
    Westman, Jonas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Nyberg, Mattias
    Providing Tool Support for Specifying Safety-Critical Systems by Enforcing Syntactic Contract Conditions2018In: Requirements Engineering, ISSN 0947-3602, E-ISSN 1432-010XArticle in journal (Refereed)
    Abstract [en]

    Functional safety standards such as IEC 61508 and ISO 26262 advocate a particularly stringent requirements engineering where safety requirements must be structured in a hierarchical manner and specified in accordance with the system architecture. In contrast to the stringent requirements engineering in functional safety standards, according to previous studies, requirements engineering in industry is in general of poor quality. Contracts theory has been previously shown to be suitable for supporting such a stringent requirements engineering effort; this support has also been implemented in tools. However, to use these contract-based tools, requirements must be formalized, which is a major challenge in industry. Therefore, to support current industrial requirements engineering practice and the stringent requirements engineering in functional safety standards, it is shown how tool support can be provided even when requirements, and also architectures, are not formalized. This is achieved by enforcing syntactic, yet formal, conditions in contracts theory. Despite the need for further validation, initial findings in an industrial case study indicate high potential in realizing the proposed support in an industrial setting.

  • 52460.
    Westman, Jonas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Nyberg, Mattias
    Specifying and Structuring Requirements on Cyber-Physical Systems using Contracts2014Report (Other academic)
    Abstract [en]

    A contract splits the responsibilities between a component and its environment into a guarantee that expresses an intended property under the responsibility of the component, given that the environment fulfills the assumptions. Building on recent works where contracts are proposed as a means to meet the challenges in the design of Cyber-Physical Systems (CPSs), a general contract framework is presented that supports the modelling of both individual components and architectures of CPS - at all levels of design, as well as the structuring and specification of requirements on the components using contracts. To facilitate the specification of requirements, constraints that restrict the portsover which a contract is expressed are introduced to serve as sanity checks that the component and the environment meet their respective responsibilities. Furthermore, a new graph, called a contract structure is introduced to support the structuring and tracing of requirements on a CPS using contracts. As a proof-of-concept, the framework is used to specify and structure safety requirements on an industrial system, as proposed by ISO 26262.

  • 52461.
    Westman, Jonas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Nyberg, Mattias
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Gustavsson, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Gurov, Dilian
    KTH, School of Computer Science and Communication (CSC), Theoretical Computer Science, TCS.
    Formal Architecture Modeling of Sequential Non-Recursive C Programs2017In: Science of Computer Programming, ISSN 0167-6423, E-ISSN 1872-7964, Vol. 146, p. 2-27Article in journal (Refereed)
    Abstract [en]

    To manage the complexity of C programs, architecture models are used as high-level descriptions, allowing developers to understand, assess, and manage the C programs without having to understand the intricate complexity of the code implementations. However, for the architecture models to serve their purpose, they must be accurate representations of the C programs. In order to support creating accurate architecture models, the present paper presents a mapping from the domain of sequential non-recursive C programs to a domain of formal architecture models, each being a hierarchy of components with well-defined interfaces. The hierarchically organized components and their interfaces, which capture both data and function call dependencies, are shown to both enable high-level assessment and analysis of the C program and provide a foundation for organizing and expressing specifications for compositional verification.

  • 52462.
    Westman, Jonas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Nyberg, Mattias
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics. Scania, Sweden.
    Thydén, Oscar
    CPS Specifier - A Specification Tool for Safety-Critical Cyber-Physical Systems2016Conference paper (Refereed)
    Abstract [en]

    CPS Specifier is a specification tool for Cyber-Physical Systems. Founded on established theory and realized using general design and integration technologies and principles, e.g. Linked Data, CPS Specifier provides guidance-and feedback-driven support when authoring structured specifications in general, and for specifying and structuring requirements, in particular. The provided support is crucial in order to comply with functional safety standards such as IEC 61508 and ISO 26262 that require particularly stringent requirements engineering.

  • 52463.
    Westman, Jonas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Nyberg, Mattias
    Törngren, Martin
    Structuring Safety Requirements in ISO 26262 using Contract Theory2013Report (Other academic)
    Abstract [en]

    ISO 26262 - ''Road vehicles-Functional Safety'' is a standard for the automotive industry, administered in an attempt to prevent potential accidents due to systematic and random failures in the Electrical/Electronic-system. ISO 26262 is based on the principle of relying on safety requirements as the main source of information to enforce correctness of design. We show that the contract theory from the SPEEDS FP6 project provides a suitable foundation to structure safety requirements in ISO 26262. Contracts provide the necessary support to separate the responsibilities between a system and its environment by explicitly imposing requirements on the environment as assumptions, in order to guarantee the safety requirements. We show this by characterizing two levels of safety requirements with contracts for an industrial system where we also show how contract theory supports the verification of consistency and completeness of safety requirements.

  • 52464.
    Westman, Jonas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Embedded Control Systems.
    Nyberg, Mattias
    Törngren, Martin
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Embedded Control Systems.
    Structuring safety requirements in ISO 26262 using contract theory2013In: Computer Safety, Reliability, and Security: 32nd International Conference, SAFECOMP 2013, Toulouse, France, September 24-27, 2013. Proceedings, Springer Berlin/Heidelberg, 2013, Vol. 8153, p. 166-177Conference paper (Refereed)
    Abstract [en]

    ISO 26262 - ”Road vehicles-Functional Safety” is a standard for the automotive industry, administered in an attempt to prevent potential accidents due to systematic and random failures in the Electrical/Electronic-system. ISO 26262 is based on the principle of relying on safety requirements as the main source of information to enforce correctness of design. We show that the contract theory from the SPEEDS FP6 project provides a suitable foundation to structure safety requirements in ISO 26262. Contracts provide the necessary support to separate the responsibilities between a system and its environment by explicitly imposing requirements on the environment as assumptions, in order to guarantee the safety requirements. We show this by characterizing two levels of safety requirements with contracts for an industrial system where we also show how contract theory supports the verification of consistency and completeness of safety requirements.

  • 52465.
    Westman, Jonas
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Rodriguez-Navas, Guillermo
    MDH.
    Nyberg, Mattias
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Mechatronics.
    Verification of Requirements in Simulink Design Verifier and UPPAAL - an Industrial Case Study2016Report (Other academic)
    Abstract [en]

    Model checking has reached a state of maturity that allows its adoption for the verification of complex embedded systems, such as the ones found in vehicles. Little research has been carried out in order to determine how model checking can be integrated with the current design and verification practices at the industry. In this case study we take a real control subsystem of a Scania vehicle, specified as a Simulink model, and use two popular model checker (Simulink Design Verifier and Uppaal) for verifying its functional requirements according to the design specification. Our goal is to understand the real challenges faced by engineers performing model checking, and also to assess the possibilities and limitations of the available tools. The main difficulties encountered relate to the fact that most of the work still has to be performed manually, and depends significantly on the skills of the user. In particular, much effort has to be spent in formalizing the system requirements and in model-to-model transformation. This work shows that better tool support is required for these activities before model checking can be ready for widespread use in current development processes.

  • 52466.
    Westman, Maja
    KTH, School of Architecture and the Built Environment (ABE), Architecture.
    Opera i Stockholm, Stadsgårdskajen2011Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Opera i Stockholm,  kandidatprojekt i Arkitektur

  • 52467.
    Westman, Teresa
    KTH, School of Architecture and the Built Environment (ABE), Architecture.
    Hur långt kan vi gå?: En bilfri förort i Kymlinge2011Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [sv]

    Detta examensprojekt handlar om att utforma en stadsdel med bostäder som lever upp till visionerna för Stockholm och Sundbyberg inför 2020 och 2030.

    En bilfri förort, 15 minuter med tunnelbanan från Stockholms innerstad. Alldeles intill ett känsligt naturreservat. Kompakt boende, småskalig service och platsen präglas av en känsla av närhet. De boende ska använda lite yta, röra sig till fots, cykla och nyttja offentliga rum och kollektivtrafik i största möjliga utsträckning. Men de ska kunna leva ett fullgott urbant liv utan att behöva offra den bekvämlighet som ett liv i storstadsmiljö erbjuder.

  • 52468.
    Westmar, Olle
    KTH, School of Chemical Science and Engineering (CHE).
    Underjordsförvar av flygaska2012Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Vid avfallsförbränning utvinns energi men som biprodukt också den miljöfarliga flygaskan. Problemen med flygaskan har alltid varit många. Den har exporterats till Langøya i Norge för att hamna på underjordsdeponi vilket inte är ett hållbart alternativ då den beräknas vara uppfylld 2023-2025. Flertalet försök att genomgåtts för att hitta användningsområden men det vanligaste är att den deponeras. Flygaskan från avfallsförbränning innehåller höga halter av tungmetaller och salter och är miljöfarlig.

    Ett sätt att använda flygaskan är genom utfyllning av hålrum såsom gruvor eller oljelagringsrum som ej används. Detta innebär alltså att flygaskan nyttogörs och kan ses som en resurs istället för ett bekymmer. I grunden är det dock en typ av deponering.  

    Skall den deponeras finns det en rad säkerhetsrisker som måste gås igenom. Om inte hanteringen och deponeringen av askan kan göras helt sluten utan spill bör den förbehandlas. Ett vanligt förbehandlingssteg är inkapsling i cement.

    På Händelöverket i Norrköping finns det flera oljelagringsrum som tidigare var fyllda med olja men som idag används för just underjordsförvaring av flygaskor. Dessa rum har genomgått miljödomsbeslut där det ställs upp många krav på hur säkerheten skall gå till i rummen. En viktig parameter är hur det säkerställs att vätgashalten ej blir för hög då det råder en explosionsrisk om så är fallet.

    Underjordsdeponeringen av flygaska kan liknas den deponering som sker för kärnavfall, framförallt för låg- medelaktivt kärnavfall. Säkerhetsmetodiken som tagits fram av SKB bör kunnas anpassas för att göra det enklare att konstruera nya underjordsförvar för flygaskan.

    Ekonomiskt sätt är det betydligt billigare att använda befintliga bergrum och sedan preparera dem för förvaring jämfört med att konstruera helt nya förvar. Grovt uppskattat skulle kostnaden att bygga nytt underjordsförvar kosta ca 608 kr/m3 och för att rehabilitera en befintligt oljelagringsrum 45 kr/m3. Fördelen kan dock vara att vid ny byggnation av förvar kan lokaliseringen bestämmas och en placering nära hav är fördelaktigt då utlakningen av salter ej blir särskilt påverkande.

  • 52469. Westraadt, J. E.
    et al.
    Olivier, E. J.
    Neethling, J. H.
    Hedström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Odqvist, Joakim
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Xu, X.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Physical Metallurgy.
    Steuwer, A.
    A high-resolution analytical scanning transmission electron microscopy study of the early stages of spinodal decomposition in binary Fe-Cr2015In: Materials Characterization, ISSN 1044-5803, E-ISSN 1873-4189, Vol. 109, p. 216-221Article in journal (Refereed)
    Abstract [en]

    Spinodal decomposition (SD) is an important phenomenon in materials science and engineering. For example, it is considered to be responsible for the 475 degrees C embrittlement of stainless steels comprising the bcc (ferrite) or bct (martensite) phases. Structural characterization of the evolving minute nano-scale concentration fluctuations during SD in the Fe-Cr system is, however, a notable challenge, and has mainly been considered accessible via atom probe tomography (APT) and small-angle neutron scattering. The standard tool for nanostructure characterization, viz, transmission electron microscopy (TEM), has only been successfully applied to late stages of SD when embrit-dement is already severe. However, we here demonstrate that the structural evolution in the early stages of SD in binary Fe-Cr, and alloys based on the binary, are accessible via analytical scanning TEM. An Fe-36 wt% Cr alloy aged at 500 degrees C for 1, 10 and 100 h is investigated using an aberration-corrected microscope and it is found that highly coherent and interconnected Cr-rich regions develop. The wavelength of decomposition is rather insensitive to the sample thickness and it is quantified to 2, 3 and 6 nm after ageing for 1, 10 and 100 h, which is in reasonable agreement with prior APT analysis. The concentration amplitude is more sensitive to the sample thickness and acquisition parameters but the TEM analysis is in good agreement with APT analysis for the longest ageing time. These findings open up for combinatorial TEM studies where both local crystallography and chemistry is required.

  • 52470.
    Westén, Annelie
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    En numerisk modell för vätskekyld flänsad korsströmsvärmeväxlare inkluderande daggutfällning2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    There are many technical applications of heat exchangers in our community.A common type is the cross-flow heat exchangers in which the air-flow is perpendicularto the pipes with liquid. The area for heat convection is increasedby adding fins on the pipes. In this bachelor thesis, performed in the Schoolof Industrial Engineering and Management at KTH, the mentioned heat exchangeris studied. The goal is to create a numerical model for heat exchangersin ventilation systems that are used in big buildings in the climate of a Swedishsummer. This specific case requires that both heat- and mass transportis included in the model.The heat exchanger is divided in both the direction of the air-flow as well asthe liquid-flow in the model. This is done to make a step-wise calculation ofthe heat transfer. The temperature of the fins is depending on the temperatureand enthalpy of both flows. The temperature differs on the fins and iscalculates by dividing the fins in a net of temperature-points. The equilibriumsolution is iterated from heat conduction within the plate and heat convectionfrom the air-flow.The model is evaluated by simulating a test-case of typical data from a Swedishsummer through a heat exchanger with a geometry that could occur in a largebuilding. The result was a colder, dehumidified air flow out of the exchanger.Further evaluation of the model is made by extensive sensitivity analysis ofthe parameters which is allowed to change by the user. The analysis is madeby plotting the result and comparing with the equations in the model.The model has several restrictions. There are limitations of the number ofpipes and their placements. The model is based on steady-state.

  • 52471.
    Wetter, Erik
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    Straume, Kristoffer
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    Varför emitterar inte fler svenska företag högavkastande obligationer?2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [sv]

    Marknaden för så kallade ”High Yield Bonds” – högavkastande obligationer – har under det senaste årtiondet genomgått en remarkabel utveckling, särskilt i Europa. Ett ökat antal ”non-investment grade”-företag söker strategiskt att emittera dessa obligationer för att finansiera sina verksamheter, vare sig detrör sig om upprätthållandet av betalningsströmmar till leverantörer, anställda eller andra intressenter; kapitalanskaffning; företagsförvärv; refinansiering av lån; eller andra företagsrelaterade aktiviteter. Trots denna utveckling är marknaden för högavkastande obligationer i Sverige jämförelsevis liten. Följaktligen söker denna studie svara på varför så få högavkastande obligationer idag emitteras på den svenska marknaden. Våra resultat visar att den svenska finansmarknaden karaktäriseras av starka och långsiktiga relationer mellan företag och banker vilket effektivt reducerar företagens behov av alternativa finansieringskällor. För det andra, om vi betraktar den förhållandevis lilla volym svenska företag söker emittera, är inte många företag i den position att kunna emittera obligationer i de summor som för närvarande efterfrågas av investerarbasen. För det tredje tycks det också existera en kulturell faktor bland marknadsaktörerna; en tendens att undvika att verka på företagsobligationsmarknaden. Till sist har också en djupgående kunskapsbrist som alla marknadsaktörer tycks uppvisa ytterligare försvagat spridningen av högavkastande obligationer. Givet de snabba förändringarna finansbranschen genomgår idag, främst en konsekvens av de senaste årens kris och de efterföljande regleringarna som kommit till stånd, kommer banker, företag och investerare vara tvungna att förändra sitt beteende. Dessa förändringar kommer förmodligen innebära att obligationer – och särskilt högavkastande obligationer – blir en mer attraktiv lösning och kommer förmodligen att innebära att företagsobligationsmarknaden på sikt till sist etablerar sig i Sverige så som är fallet i resten av Europa och USA.

  • 52472.
    Wetterbrandt, Erik
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Service and Energy Systems.
    Luftburen värme, termisk komfort och energianvändning. Jämförelse av värmesystem för ett flerbostadshus2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Our society today is demanding more and more energy efficient construction of buildings. The lower the energy consumption of a build is, the less environmental impact it has. Because of this it is getting increasingly common to design buildings to meet the standard of environmental classification systems and low-energy requirements. Unfortunately it is still expensive to construct low-energy buildings. To save money, many designers are combining the heating- and ventilationsystem through so called ventilation heating systems. It is believed by many that these systems can maintain a good indoor climate for the users and still be cheap to construct and run.

    The goal of this study is to evaluate how well ventilation heating systems can perform with respect to energy use and indoor climate, compared to other systems. A good indoor climate consists of many things were some of the foremost are air quality and thermal comfort. To compare the different systems an apartment building in Stockholm has been modeled and simulated in the software IDA ICE.

    More than the simulations, a screening has been put together with the aim to evaluate how the industry views low-energy buildings and ventilation heating systems today.

    This study shows that it is getting more and more common to construct low-energy buildings in Sweden. That being said, it is not always the best solution. Although ventilation heating systems can perform well in theory, reality shows that's not usually the case due to exceeding maintenance and insight from all parties.

    After evaluating the simulations, the results indicate that the energy consumption of the ventilation heating system and the HVAC-system with radiators is almost equally good. At the same time the exhaust ventilation system with radiators and the exhaust ventilation system with floor heating has considerably worse energy consumption. We can also see that the HVAC-system with radiators and the exhaust ventilation system with floor heating provides a good indoor climate. Unfortunately the results show that the exhaust ventilation system with radiators and mainly the ventilation heating system provides worse indoor climate than the other systems. Even though the ventilation heating system can lower the installation costs during construction, these results indicate that the system provides a low energy use at the expense of the indoor climate.

    In addition to the four simulated heating systems, the ventilation heating system was simulated for a building designed to pass the low-energy building requirements according to FEBY. These results show that the energy consumption can be reduced even further while it has no significant improvement on the indoor climate.

    To summarize, this study has shown that ventilation heating systems can reduce the energy consumption in comparison with other heating systems. Unfortunately is this done at the expense of the indoor climate. This should be highlighted further while choosing heating system in low-energy buildings.

  • 52473.
    Wetterbrandt, Erik
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Björkman, Rasmus
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Utförande av Platta på Mark2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    I denna rapport undersöks om en platta på mark kan gjutas med en genomgående jämn tjocklek, istället för att ha en så kallad grundbalk längs med husets bärande väggar, och fortfarande uppnå samma hållfasthetskrav. För att göra detta undersöks om grundbalken kan ersättas med mer armering. Resultatet redovisas som grafer där armeringsarean är funktion för klarad spännvidd under plattan. Plattan utan grundbalk kommer inte upp i samma hållfasthet som plattan med grundbalk men klarar trots det referenshusets hållfasthetskrav. Utöver denna analys undersöks även om det här utförandet kan minska kostnaderna för grundläggningsarbetet. Resultatet påvisar besparingarna som kan göras är omfattande. Däremot är det svårt att veta om byggföretag idag kan möta dessa besparingar då de ofta har standardiserade plattgjutningsprocesser.

    Detta är fördjupningsdelen i ett arbete som också innefattar projektering och dimensionering av ett småhus. 

  • 52474.
    Wettergren, Carl
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Stenbäck, Kim
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Täckväxel2012Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The background to this project is that Trafikverket has major problems with its railway switches during the winter season. The problem occur when snow / ice prevents the moving parts in the rail switch to move into its switching position and allow trains to pass in the wanted direction. For the current situation, there is no single solution that can handle the extreme demands and conditions in Sweden. This report will give the reader an idea of how the inventor Visa Jääskeläinen’s proposal to solve today's railway switch problem can be realized. The basic idea is to mechanically prevent snow / ice from getting into unwanted places by covering a part of the track. This construction proposal should be the base for further development and for a future prototype. Visa's proposal is roughly a movable roof that protects areas where snow accumulates and is packed. While a railway switch is a dynamic system, more complex movements are needed to protect these areas. Täckväxeln is an additional module for existing 1:9 rail switches that you fit up for the winter season. It is about six meters long and covers the most critical part of the railway switch.

  • 52475.
    Wettergren, Carl
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Zetterström, Linda
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Noise reduction of pedestrian trucks for street unloading2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This report is the result of a Master’s Degree Thesis done at the Royal Institute of Technology, KTH, during October 2014 to April 2015. The project was commissioned by Lidl in collaboration with Stockholms Stad and Integrated Transport Research Labs at KTH, and is a part of the Off-peak project. The Aim of the project was to help Lidl perform quieter street unloadings during off-peak hours. The unloading, today, is done with electrical pedestrian trucks and roll containers. Information was gathered about the current equipment and the current method of unloading was studied through observations. There were three problematic areas identified: the uneven ground, the hardware and the user. These were studied further on a pedestrian truck which was borrowed from Lidl for the thesis work. A market study was performed to see what solutions existed on the market. Information was also gathered on Off-peak projects in other cities and what the benefits of such projects could be. Study visits were made to Toyota-BT in Mjölby and Karnag in Täby to gather further knowledge. A meeting was held with K.Hartwall at Integrated Transport Research Lab to discuss their current solutions. The three problematic areas were discussed during a midterm meeting. Two of them were selected for future work: an add-on module to keep the fork carriage from rattling and an aid for the drivers of the trucks that shows the noise level. Many iterations of brainstorming, testing and evaluating led to the final results. The testing showed that the module that was supposed to keep the fork carriage from rattling didn’t have the desired results. The choice was then made to develop a spring solution to keep the forks from bouncing of each other. This led to the development of a leaf spring solution that is mounted on the underside of the fork carriage. The development of an aid for the drivers led to the Noise Advisor which is a sound level meter that sits on the side of the trucks mast and gives visual feedback to the driver.

  • 52476. Wettergren, E E
    et al.
    Gussing, F
    Sest, Maike
    KTH, School of Biotechnology (BIO), Molecular Biotechnology (closed 20130101).
    Graslund, T
    Lundberg, Cecilia
    KTH, School of Biotechnology (BIO), Molecular Biotechnology (closed 20130101).
    Regulation of Endogenous GAD67 Expression Using Artificial Transcription Factors2011In: Molecular Therapy, ISSN 1525-0016, E-ISSN 1525-0024, Vol. 19, no 7Article in journal (Other academic)
  • 52477.
    Wetterling, John
    et al.
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. Department of Chemistry and Chemical Engineering, Chalmers University of Technology.
    Jonsson, S.
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology.
    Mattsson, Tuve
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. Department of Chemistry and Chemical Engineering, Chalmers University of Technology.
    Theliander, Hans
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Centres, Wallenberg Wood Science Center. Department of Chemistry and Chemical Engineering, Chalmers University of Technology.
    The Influence of Ionic Strength on the Electroassisted Filtration of Microcrystalline Cellulose2017In: Industrial & Engineering Chemistry Research, ISSN 0888-5885, E-ISSN 1520-5045, Vol. 56, no 44, p. 12789-12798Article in journal (Refereed)
    Abstract [en]

    The production of materials such as microfibrillated cellulose and cellulose nanocrystals is gathering significant research interest by combining mechanical strength and toughness with a low density, biodegradability and renewability. However, one of the challenges with production on an industrial scale is to obtain an energy-efficient solid-liquid separation which is difficult because of the high specific filtration resistance of these materials. This study investigates electroassisted filtration as a method to facilitate the dewatering of cellulosic materials and the influence of ionic strength on the electrofiltration behavior. Electroassisted filtration is found to improve the dewatering rate of the studied cellulosic material, and the potential improvement compared to pressure filtration increased with the specific surface area of the solid material. Increasing the ionic strength of the system increased the power demand of the electroassisted filtration, and the major potential for industrial application is thus for systems with a limited ionic strength.

  • 52478.
    Wetterling, John
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. Chalmers University of Technology, Sweden.
    Mattsson, Tuve
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. Chalmers University of Technology, Sweden.
    Theliander, Hans
    KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center. Chalmers University of Technology, Sweden.
    Modelling filtration processes from local filtration properties: The effect of surface properties on microcrystalline cellulose2017In: Chemical Engineering Science, ISSN 0009-2509, E-ISSN 1873-4405, Vol. 165, p. 14-24Article in journal (Refereed)
    Abstract [en]

    The influence of structure and charge of particles surfaces on the cake filtration behaviour of microcrystalline cellulose was investigated. The local filtration properties were evaluated experimentally and used to model the overall filtration behaviour. At suspension conditions where the microcrystalline cellulose particles are charged, a large pressure drop was observed close to the filter medium, thereby indicating that a rate-limiting skin layer was formed. Measurements of the local solidosity of the filter cake indicated that a secondary filter cake, with a negligible filtration resistance, formed above the rate-limiting skin layer. This behaviour was not observed when the surface roughness of the particles was increased or when the surface charge of the particles was neutralised by making a change to the pH of the suspension. The filtration behaviour of particles with these surface properties was instead dominated by the formation of a compressible filter cake. Local filtration properties of compressible filter cakes determined experimentally were used to successfully model the overall filtration behaviour. The filtration model used an empirical relationship to describe the pressure dependence of the local solidosity of the filter cake along with a cell model to describe the relationship between the solidosity and the permeability of the filter cake.

  • 52479.
    Wetterling, Jonas
    et al.
    KTH. Chalmers Univ Technol, Dept Chem & Chem Engn, S-41296 Gothenburg, Sweden.;Chalmers Univ Technol, Royal Inst Technol, Wallenberg Wood Sci Ctr, S-10044 Stockholm, Sweden..
    Sahlin, Karin
    KTH. Chalmers Univ Technol, Dept Chem & Chem Engn, S-41296 Gothenburg, Sweden.;Chalmers Univ Technol, Royal Inst Technol, Wallenberg Wood Sci Ctr, S-10044 Stockholm, Sweden..
    Mattsson, Tuve
    KTH. Chalmers Univ Technol, Dept Chem & Chem Engn, S-41296 Gothenburg, Sweden.;Chalmers Univ Technol, Royal Inst Technol, Wallenberg Wood Sci Ctr, S-10044 Stockholm, Sweden..
    Westman, Gunnar
    KTH. Chalmers Univ Technol, Dept Chem & Chem Engn, S-41296 Gothenburg, Sweden.;Chalmers Univ Technol, Royal Inst Technol, Wallenberg Wood Sci Ctr, S-10044 Stockholm, Sweden..
    Theliander, Hans
    KTH. Chalmers Univ Technol, Dept Chem & Chem Engn, S-41296 Gothenburg, Sweden.;Chalmers Univ Technol, Royal Inst Technol, Wallenberg Wood Sci Ctr, S-10044 Stockholm, Sweden..
    Electroosmotic dewatering of cellulose nanocrystals2018In: Cellulose (London), ISSN 0969-0239, E-ISSN 1572-882X, Vol. 25, no 4, p. 2321-2329Article in journal (Refereed)
    Abstract [en]

    One of the main challenges for industrial production of cellulose nanocrystals is the high energy demand during the dewatering of dilute aqueous suspensions. It is addressed in this study by utilising electroosmotic dewatering to increase the solid content of suspensions of cellulose nanocrystals. The solid content was increased from 2.3 up to 15.3 wt%, i.e. removal of more than 85% of all the water present in the system, at a much lower energy demand than that of thermal drying. Increasing the strength of the electric field increased not only the dewatering rate but also the specific energy demand of the dewatering operation: the electric field strength used in potential industrial applications is thus a trade-off between the rate of dewatering and the energy demand. Additionally, it was found that high local current intensity had the potential of degrading cellulose nanocrystals in contact with the anode. The maximum strength of the electric field applied should therefore be limited depending on the equipment design and the suspension conditions.

  • 52480. Wetterlund, Elisabeth
    et al.
    Pettersson, Karin
    Magnusson, Mimmi
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
    Implications of system expansion for the assessment of well-to-wheel CO2 emissions from biomass-based transportation2010In: International journal of energy research (Print), ISSN 0363-907X, E-ISSN 1099-114X, Vol. 34, no 13, p. 1136-1154Article in journal (Refereed)
    Abstract [en]

    In this paper we show the effects of expanding the system when evaluating well-to-wheel (WTW) CO2 emissions for biomass-based transportation, to include the systems surrounding the biomass conversion system. Four different cases are considered: DME via black liquor gasification (BLG), methanol via gasification of solid biomass, lignocellulosic ethanol and electricity from a biomass integrated gasification combined cycle (BIGCC) used in a battery-powered electric vehicle (BPEV). All four cases are considered with as well as without carbon capture and storage (CCS). System expansion is used consistently for all flows. The results are compared with results from a conventional WTW study that only uses system expansion for certain co-product flows. It is shown that when expanding the system, biomass-based transportation does not necessarily contribute to decreased CO2 emissions and the results from this study in general indicate considerably lower CO2 mitigation potential than do the results from the conventional study used for comparison. It is shown that of particular importance are assumptions regarding future biomass use, as by expanding the system, future competition for biomass feedstock can be taken into account by assuming an alternative biomass usage. Assumptions regarding other surrounding systems, such as the transportation and the electricity systems are also shown to be of significance. Of the four studied cases without CCS, BIGCC with the electricity used in a BPEV is the only case that consistently shows a potential for CO2 reduction when alternative use of biomass is considered. Inclusion of CCS is not a guarantee for achieving CO2 reduction, and in general the system effects are equivalent or larger than the effects of CCS. DME from BLG generally shows the highest CO2 emission reduction potential for the biofuel cases. However, neither of these options for biomass-based transportation can alone meet the needs of the transport sector. Therefore, a broader palette of solutions, including different production routes, different fuels and possibly also CCS, will be needed.

  • 52481. Wettestad, J.
    et al.
    Eikeland, P. O.
    Nilsson, Måns
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment.
    EU climate and energy policy: A hesitant supranational turn?2012In: Global Environmental Politics, ISSN 1526-3800, E-ISSN 1536-0091, Vol. 12, no 2, p. 67-86Article in journal (Refereed)
    Abstract [en]

    This article examines the recent changes of three central EU climate and energy policies: the revised Emissions Trading Directive (ETS); the Renewables Directive (RES); and internal energy market (IEM) policy. An increasing transference of competence to EU level institutions, and hence "vertical integration," has taken place, most clearly in the case of the ETS. The main reasons for the differing increase in vertical integration are, first, that more member states were dissatisfied with the pre-existing system in the case of the ETS than in the two other cases. Second, the European Commission and Parliament were comparatively more united in pushing for changes in the case of the ETS. And, third, although RES and IEM policies were influenced by regional energy security concerns, they were less structurally linked to and influenced by the global climate regime than the ETS.

  • 52482.
    Weyrauch, Thomas
    KTH, School of Engineering Sciences (SCI), Solid Mechanics (Dept.).
    The Paperboard Testing-Machine: Development Process2011Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The design of a paperboard testing machine, developed in order to analyse the mechanical behaviour of paperboard during the combined of out-of-plane shear and compressive loading as in the deepdrawing process, is presented. The methodology to design a paperboard testing machine is discussed and the most appropriate concepts are compared and evaluated. The design process is presented in detail, and some pilot tests are performed to give an overview about the functionality of the manufactured prototype.

  • 52483. Weyres, Marco
    et al.
    Gross, James
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Effective Service Capacity Analysis of Interference-Limited Multi-Carrier Wireless Systems2013In: Proceedings of the 2013 19th European Wireless Conference (EW), VDE Verlag GmbH, 2013, p. 1-7Conference paper (Refereed)
    Abstract [en]

    A good utilization of a wireless network while still ensuring QoS-constraints for all users is a hard challenge for service providers. Especially for admission control or handover decisions it is important to have a good approximation of the possible rate a user can achieve with respect to QoS parameters like delay or outage probabilities. Since fourth generation cellular networks utilize a frequency reuse of one, especially terminals at the cell edge suffer from inter-cell interference. In order to provide them with rates that guarantee specific QoS parameters without reserving too much resources, a good prediction of their possible rates is needed. Unfortunately, the prediction of the rates in an interference-limited cell is a complex and hard problem. Hence, it is a common way to simplify calculations by treating interference as additional noise in the used system models. In this paper we derive closed-form solutions for the delay distribution of interference-limited cells with respect to an OFDMA and a round robin scheduling approach. These distributions can be used to predict the possible rates of users given their average received transmitter gains, interferer gains and their QoS-constraints in a very accurate way. We validate our derivations and show that a simplification by treating interference as noise leads to an underestimation of rates which lowers the cell throughput. Furthermore, we show that due to the resulting equations, there is no way to derive the rates for interference limited cells in a linear way from easier solutions given by noise-limited cells.

  • 52484. Weyrich, K.
    et al.
    Leelaruji, Rujiroj
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Kuehn, W.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Mitigating system's voltage instability through wide-area early warning signals and real-time HVDC control2012In: 2012 IEEE Workshop on Complexity in Engineering, COMPENG 2012 - Proceedings, IEEE , 2012, p. 107-112Conference paper (Refereed)
    Abstract [en]

    Two sequential approaches to prevent voltage instability are proposed in this article. The first approach utilizes synchrophasors in order to establish when the system is leading to a voltage instability and also to trigger the operation of HVDCs to relieve the system's stress. The second approach is used to ensure that HVDCs will operate securely when their transfer is pushed towards the maximum transferable power level.

  • 52485. Weyrich, K.
    et al.
    Leelaruji, Rujiroj
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Kuehn, W.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Real-time implementation of an Automatic Voltage Stabilizer for HVDC Control2012In: Innovative Smart Grid Technologies (ISGT Europe), 2012 3rd IEEE PES International Conference and Exhibition on, IEEE , 2012, p. 6465848-Conference paper (Refereed)
    Abstract [en]

    Classic HVDC systems are prone to voltage instability when operating on weak AC grids. This paper describes the implementation of a newly developed Automatic Voltage Stabilizer (AVS) in an existing CIGRÉ Benchmark Model for HVDC Controls and compares its performance with the Voltage Dependent Current Order Limitation (VDCOL) method. The tools used for the study are the eMegaSim OPAL-RT real-time simulator and the PSCAD/EMTDC digital simulator. With AVS, the power transfer can be optimized and kept at or close to the steady state stability limit thereby compensating for deficiencies of VDCOL. Using two different simulation environments provides important information on their capabilities to develop and improve future power system controls.

  • 52486. Weyrich, Kim
    et al.
    Kuehn, Walter
    Leelaruji, Rujiroj
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Vanfretti, Luigi
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Real-Time Implementation of an Automatic Voltage Stabilizer for HVDC Control2012In: IFAC 8th Power Plant and Power Systems Controls Symposium, 2012, 2012Conference paper (Other academic)
    Abstract [en]

    Classic HVDC systems are prone to voltage instability when operating on weak AC grids. Certain methods are available to cope with weak system conditions, one of which is VDCOL. This paper describes the implementation of a newly developed Automatic Voltage Stabilizer (AVS) in an existing CIGR´E Benchmark Model for HVDC Controls and compares its performance with the VDCOL method. The tools used for the study are the OPAL-RT real-time simulator and the PSCAD/EMTDC digital simulator. With AVS, the power transfer can be optimized and kept at or close to the steady state stability limit thereby compensating for deficiencies of VDCOL. Using two different simulation environments provides important information on their capabilities to develop and improve future power system controls.

  • 52487. Whalen, Joann
    et al.
    Xu, Charles (Chunbao)
    Shen, Fei
    Kumar, Amit
    Eklund, Mats
    Yan, Jinyue
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes. Mälardalen University, Sweden.
    Sustainable biofuel production from forestry, agricultural and waste biomass feedstocks2017In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 198, p. 281-283Article in journal (Refereed)
  • 52488. White, B. T.
    et al.
    Lewis, R.
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Lyu, Yezhe
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    The contribution of iron oxides to the wet-rail phenomenon2016In: Civil-Comp Proceedings, ISSN 1759-3433, Vol. 110Article in journal (Refereed)
    Abstract [en]

    This paper reviews the current literature regarding iron oxide formation in the wheel-rail contact in order to assess the possible role of iron oxides in the "Wet-Rail" phenomenon, which causes low adhesion between the wheel and the rail. The paper discusses the structure and formation of oxides from a chemical perspective before analysing the direct tribological effects and outlining the techniques that have been used to study the oxide layers. This paper also suggests how knowledge of the subject could be expanded and how further understanding of the "Wet-Rail" phenomenon could lead to better mitigation methods, resulting in both economic and safety benefits.

  • 52489.
    White, B. T.
    et al.
    Univ Sheffield, Dept Mech Engn, Sheffield, S Yorkshire, England..
    Nilsson, R.
    SLL, Stockholm, Sweden..
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Arnall, A. D.
    Univ Sheffield, Dept Mech Engn, Sheffield, S Yorkshire, England..
    Evans, M. D.
    Univ Sheffield, Dept Mech Engn, Sheffield, S Yorkshire, England..
    Armitage, T.
    Arup, Sheffield, S Yorkshire, England..
    Fisk, J.
    Arup, Sheffield, S Yorkshire, England..
    Fletcher, D. I.
    Univ Sheffield, Dept Mech Engn, Sheffield, S Yorkshire, England..
    Lewis, R.
    Univ Sheffield, Dept Mech Engn, Sheffield, S Yorkshire, England..
    Effect of the presence of moisture at the wheel-rail interface during dew and damp conditions2018In: Proceedings of the Institution of mechanical engineers. Part F, journal of rail and rapid transit, ISSN 0954-4097, E-ISSN 2041-3017, Vol. 232, no 4, p. 979-989Article in journal (Refereed)
    Abstract [en]

    Incidents involving low levels of adhesion between the wheel and rail are a recurrent issue in the rail industry. The problem has been mitigated using friction modifiers and traction enhancers, but a significant number of incidents still occur throughout the year. This study looks at the environmental conditions that surround periods of low adhesion in order to provide an insight into why low adhesion events occur. Network Rail Autumn data, which provided details on the time and location of low adhesion incidents, were compared against weather data on a national and then local scale. Low adhesion incidents have often been attributed to contamination on the rails, such as organic leaf matter, but these incidents also occur when no contamination is visible. The time, date and location of incidents were linked to local weather data to establish any specific weather conditions that could lead to these events. The effects of precipitation, temperature and humidity on rails were analysed in order to further the understanding of low adhesion in the wheel-rail contact, which will lead to adopting better methods of mitigating this problem.

  • 52490. White, Ben
    et al.
    Lewis, Roger
    Olofsson, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Lyu, Yezhe
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    The Contribution of Iron Oxides to theWet-Rail Phenomenon2016In: Proceedings of the Third International Conference on Railway Technology: Research, Development and Maintenance / [ed] J. Pombo, Stirlingshire, Scotland, 2016Conference paper (Refereed)
    Abstract [en]

    This paper reviews the current literature regarding iron oxide formation in the wheel-rail contact in order to assess the possible role of iron oxides in the “Wet-Rail” phenomenon, which causes low adhesion between the wheel and the rail. The paper discusses the structure and formation of oxides from a chemical perspective before analysing the direct tribological effects and outlining the techniques that havebeen used to study the oxide layers. This paper also suggests how knowledge of the subject could be expanded and how further understanding of the “Wet-Rail” phenomenon could lead to better mitigation methods, resulting in both economic andsafety benefits.

  • 52491. White, Jesse F.
    et al.
    Allertz, Carl
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Boron partitioning between SiO2-CaO-MgO slags and liquid silicon at controlled nitrogen potential2013In: International Journal of Materials Research - Zeitschrift für Metallkunde, ISSN 1862-5282, E-ISSN 2195-8556, Vol. 104, no 7, p. 650-656Article in journal (Refereed)
    Abstract [en]

    During refining of silicon using slag treatment, boron dissolved in the silicon is extracted to a liquid oxide (slag) phase. In this investigation the partitioning of boron between SiO2-CaO-MgO slags and liquid silicon was examined at 1873 K over a range of slag compositions and CO-N-2 gas mixtures. It was found that the distribution of boron is strongly dependent on the nitrogen partial pressure as well as the slag composition. The greatest partition ratios were achieved at 0.6 atm CO/0.4 atm N-2 with low silica content in the slag. The concentration of MgO in the slag seems to have little or no impact on the boron partition ratio.

  • 52492. White, Jesse F.
    et al.
    Allertz, Carl
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    The thermodynamics of boron extraction from liquid silicon using SiO2-CaO-MgO stag treatment2013In: International Journal of Materials Research - Zeitschrift für Metallkunde, ISSN 1862-5282, E-ISSN 2195-8556, Vol. 104, no 3, p. 229-234Article in journal (Refereed)
    Abstract [en]

    In the refining of solar-grade silicon using slag treatment, boron dissolved in the silicon is oxidized and rejected to a liquid oxide (slag) phase. In this study the partitioning of boron between liquid silicon and SiO2-CaO-MgO slags was examined at 1 873 K over a range of slag compositions and oxygen partial pressures. It was found that the distribution of boron is indeed dependent on both the slag composition and the oxygen partial pressure. The concentration of MgO seems to have little impact on the partition ratio.

  • 52493. White, Jesse F.
    et al.
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Mass Transfer in Slag Refining of Silicon with Mechanical Stirring: Transient Kinetics of Ca and B Transfer2015In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 46, no 1, p. 135-144Article in journal (Refereed)
    Abstract [en]

    Mechanical stirring was demonstrated to be a potent means to increase the mass transfer rates of B and Ca in slag refining of silicon, and optimal stirring conditions were attained with only a modest kinetic energy input into the melt. Experiments were undertaken to measure mass transfer rates between liquid silicon and CaO-SiO2 slags at 1823 K (1550 degrees C) with varying stirring speed and slag composition. A remarkable feature of this system is the extreme fluctuation in interfacial area-these changes occur very rapidly and are difficult to capture. As little as 50 rpm stirring speed promotes, significant transient increases in interfacial area. At stirring speeds above 100 rpm, the rates of mass transfer do not increase significantly, so it is evident that above this threshold mass transfer in the bulk phases and interfacial area generation are already maximized. With a sufficiently high content of CaO in the slag, interfacial phenomena induced by the mass flux of calcium facilitate emulsification, and this is explained from a thermodynamic standpoint. It is likely that the calcium transfer enhances boron transfer by increasing the available interfacial area.

  • 52494.
    White, Jesse F.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Lee, Jaewoo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Hessling, Oscar
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Glaser, Björn
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Reactions Between Liquid CaO-SiO2 Slags and Graphite Substrates2017In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 48, no 1, p. 506-515Article in journal (Refereed)
    Abstract [en]

    In this study, the spreading and infiltration behavior of liquid slag in contact with different grades of graphite was investigated. The wetting and infiltration of slag into graphite were found to be highly material dependent. The reduction of silica by carbon is a characteristic of the system, and it generates gaseous products as evidenced by the observation of bubble formation. The higher the temperature and silica activity of the slag is, the greater the slag infiltration and the faster the rate of spreading. Silicon infiltrated into the graphite substrates much deeper than the oxide phases, indicating gas-phase transport of SiO(g) into the graphite pores. Fundamentally, in this system where the liquid and substrate are reacting, the driving force for spreading is the movement of the system toward a lower total Gibbs energy. Reduction of silica in the slag near the interface may eventually lead to the formation of a solid, CaO-rich layer, slowing down or stopping the reduction reaction.

  • 52495.
    White, Jesse Franklin
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Equilibrium and Kinetic Considerations in Refining of Silicon2013Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The purity requirements for photovoltaic-grade (PV) silicon are very stringent. In PV applications, purified silicon is either doped with boron or phosphorous, so the levels of these particular elements have to be tightly controlled. An alternative process route to photovoltaic-grade silicon that has been successfully implemented on an industrial scale is a multi-step process comprising carbothermic reduction, slag refining, hydrometallurgical extraction, and finally directional solidification. There are many fundamental aspects of the process that are not fully understood and need to be defined.

     

    In the refining of silicon using slag treatment, boron dissolved in the silicon is oxidized and rejected to a liquid oxide (slag) phase. The partitioning of boron between liquid silicon and SiO2–CaO–MgO slags was examined at 1873. It was found that the distribution of boron is strongly dependent on the oxygen partial pressure and nitrogen partial pressure, as well as the slag composition. The concentration of MgO seems to have little impact on the partition ratio. The greatest partition ratios were achieved at 0.6 atm CO / 0.4 atm N2 with low silica content in the slag.

     

    Experiments were carried out to study mass transfer rates between liquid silicon and CaO–SiO2 slag using mechanical stirring at 1823 K. The evidence suggests that the reduction of calcium oxide at the interface leads to a rapid, temporary drop in the apparent interfacial tension. At low apparent interfacial tension, mechanical agitation facilitates the dispersion of metal into the slag phase, which dramatically increases the interfacial area; here it has been estimated to increase by at least one order of magnitude. As the reaction rate slows down, the apparent interfacial tension increases and the metal re-coalesces. The rates of mass transfer of both Ca and B were found to increase by agitating the melt, which shows that without forced convection, the overall kinetic rates are mass-transfer controlled. From a reactor design perspective, this is ideal since it should be simpler to achieve optimal mixing conditions with less kinetic energy input into the melt.

     

    The infiltration of silicon into graphite was found to be highly dependent on the internal structure of the graphite substrate. It was confirmed that the heating history of silicon in contact with a graphite substrate strongly influences the melting behavior, which is likely attributed to a gas-solid reaction that forms SiC below the liquidus temperature of silicon and alters the surface properties of the graphite. It was also observed that a partial pressure of CO greater than 0.05 atm in the inlet gas leads to SiC formation on the surface of the silicon and severely hinders proper melting. 

  • 52496.
    White, Jesse Franklin
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Mass Transfer in Slag Refining of Silicon with Mechanical Stirring: Rates of Ca and B TransfeManuscript (preprint) (Other academic)
  • 52497.
    White, Jesse Franklin
    et al.
    Elkem AS, Technology, Kristiansand, Norway .
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Mass Transfer in Slag Refining of Silicon with Mechanical Stirring: Transient Interfacial Phenomena2014In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 45, no 1, p. 96-105Article in journal (Refereed)
    Abstract [en]

    Experiments have been carried out to study the rates of mass transfer between liquid silicon and CaO-SiO2 slag with impeller stirring at 1823 K (1550 A degrees C). The occurrence of transient interfacial phenomena related to the mass transfer of calcium has been observed; the evidence suggests that the reduction of calcium oxide at the interface leads to a rapid, temporary drop in the apparent interfacial tension. At low apparent interfacial tension, mechanical agitation facilitates the dispersion of metal into the slag phase, which dramatically increases the interfacial area; here, it has been estimated to increase by at least one order of magnitude. As the reaction rate slows down, the apparent interfacial tension increases and the metal recoalesces. The incidental transfer of calcium very likely promotes the transfer of boron by increasing the interfacial area. Mechanical mixing appears to be an extremely effective means to increase the reaction rate of boron extraction and could feasibly be implemented in the industrial slag refining of silicon to improve reaction rates.

  • 52498.
    White, Jesse Franklin
    et al.
    Elkem AS, Technology, Kristiansand, Norway .
    Ma, Luyao
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Forwald, Karl
    Du, Sichen
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Micro-Modelling.
    Reactions Between Silicon and Graphite Substrates at High Temperature: In Situ Observations2014In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 45, no 1, p. 150-160Article in journal (Refereed)
    Abstract [en]

    Graphite as a refractory material has found wide application in many process steps to produce photovoltaic silicon. In the current study, the melting behavior of silicon in contact with different grades of graphite was investigated. The infiltration of silicon into graphite was found to be highly dependent on the internal structure of the graphite substrate. It was confirmed that the heating history of silicon in contact with a graphite substrate strongly influences the melting behavior, which is likely attributed to a gas-solid reaction that forms SiC at less than the liquidus temperature of silicon and alters the surface properties of the graphite. It was also observed that a concentration of CO greater than 5 pct in the inlet gas leads to SiC formation on the surface of the silicon and severely hinders melting.

  • 52499.
    White, Jesse
    et al.
    KTH, School of Industrial Engineering and Management (ITM).
    Lee, Jaewoo
    KTH.
    Hessling, Oscar
    KTH.
    Glaser, Bjoern
    KTH, School of Industrial Engineering and Management (ITM).
    Interactions between liquid CaO–SiO2 slags and graphite substrates2017In: Advances in Molten Slags, Fluxes, and Salts: Proceedings of the 10th International Conference on Molten Slags, Fluxes and Salts 2016, Springer International Publishing AG , 2017, p. 565-572Conference paper (Refereed)
    Abstract [en]

    In this study, the spreading and infiltration behavior of slag in contact with different grades of graphite was investigated. The wetting and infiltration of slag into graphite were found to be highly material dependent. Temperature and silica content of the slag also have a major influence on how slag spreads and infiltrates: The higher the temperature and silica content, the greater the slag infiltration, and the faster the rate of spreading. Reactions that generate gaseous products occurred during spreading of slag on graphite was evidenced by the observation of bubble formation. Silicon infiltrated into the graphite substrates much deeper than the slag phase, indicating gas-phase transport of silicon-bearing vapor species. Complete wetting of the interface and reduction of silica in the slag near the interface may lead to passivation by formation of a solid, CaO-rich layer.

  • 52500.
    White, Peta
    KTH, Superseded Departments (pre-2005), Speech, Music and Hearing.
    A study of the effects of vocal intensity variation on children’s voices using long-term average spectrum (LTAS) analysis1997In: TMH-QPSR, ISSN 1104-5787, Vol. 38, no 1, p. 119-131Article in journal (Other academic)
    Abstract [en]

    It has been well documented in adult studies that, as overall vocal intensity increases, the resulting increase in partials is greater in higher than in lower frequencies. Investigations involving children’s normal productions are uncommon however, and there is, as a consequence, little knowledge of how children’s vocal function differs from that of adults. Using long term average spectrum (LTAS) analysis, this study investigates the effects of vocal intensity variation on the voices of fifteen schoolchildren aged 10 years, singing in soft, mid and loud voice. Mean amplitudes, dynamic range, and gain in each frequency band were calculated, and means are presented as normative data for children’s vocal productions. Observed systematic effects of vocal loudness as well as male-female differences in the averaged spectra are discussed, and comparisons with adult data made.

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