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  • 201.
    Becerra Garcia, Marley
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Self-consistent leader inception and propagation model —SLIM—: Response to some criticism2012Ingår i: Proceedings of the International Conference on Lightning Protection (ICLP), 2012, IEEE conference proceedings, 2012, s. 1-7Konferensbidrag (Refereegranskat)
    Abstract [en]

    The self-consistent leader inception and propagation model -SLIM- has been increasingly used to study the attachment of lightning flashes to grounded structures. However, criticism about some assumptions of SLIM has been raised in a recent publication. This paper intends to reply to this criticism and to openly discuss the validity of the model. Moreover, solid scientific evidence from theory and experiments is presented to support the validity of the assumptions considered by SLIM. It is shown that the streamer corona charge calculation and the leader inception condition used by SLIM give proper estimates which are completely justified. In addition, it is shown that the predictions of this state-of-the-art model based on the latest developments in the physics of leader discharges has been found in agreement with results available from laboratory, rocket triggered lightning experiments and field observations.

  • 202.
    Becerra, Marley
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Friberg, Andreas
    ABB Corporate Research, Västerås.
    Arc jets blown by outgassing polymers in air2014Ingår i: Proceedings of the 20th International Conference on Gas Discharges and Their Applications GD2014, GD2014 , 2014, s. 1-4Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper describes experimental results about the behaviour of arc jets transversely blown in the presence of outgassing polymers (POM –CH2O– or PMMA –C5H8O2–). The arc jets are ignited in air between copper electrodes under a 2 kA, 50 Hz AC current. High speed photography and optical emission spectroscopy are used to study the mechanism leading to the increase of the arc voltage when polymers are used instead of non-ablating materials (e.g. quartz). It is found that the transversal blowing flow caused by the injection of ablation vapours have a weak effect on the arc voltage build-up. Instead, the chemical changes in the plasma environment appear to better explain the observed increase in the arc voltage when polymers are used. 

  • 203.
    Becerra, Marley
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion. Division for Electricity, Uppsala University.
    Frid, Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    On the modeling of the production and drift of carriers in cyclohexane2013Ingår i: Annual Report - Conference on Electrical Insulation and Dielectric Phenomena, CEIDP, IEEE , 2013, s. 905-908Konferensbidrag (Refereegranskat)
    Abstract [en]

    The modeling of the mechanisms of generation, loss, multiplication and transport of charge carriers is vital for the simulation of the prebreakdown process in dielectric liquids. Unfortunately, there is a lack of suitable coefficients to describe the electron generation and transport of carriers in liquids, which hinders the development of numerical models with sufficient predictive power. In this paper, the drift-dominated continuity equations for electrons and ions are coupled with Poisson's equation in order to simulate the carrier production and drift in the liquid phase under positive and negative voltages in cyclohexane. The estimations of the model are compared with measurements of current-voltage characteristics and Trichel current pulses reported in the literature for needle-plane configurations. In the analysis, the electron generation mechanisms suggested for dielectric liquids are analyzed and discussed. It is found that estimations based on the Zener equation for field-dependent molecular ionization do not agree with measurements for negative sharp points. It is also shown that the proper estimation of the electric current in the liquid phase should consider a field-dependent attachment term as well as the electrohydrodynamic movement of the liquid.

  • 204.
    Becerra, Marley
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Long, Mengni
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Schulz, Wolfgang
    Austrian Electrotechnical Association (OVE), Department of Austrian Lightning Detection and Information (ALDIS).
    Thottappillil, Rajeev
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    On the Estimation of the Lightning Incidence to Offshore Wind FarmsManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Field observations have shown that the frequency of dangerous lightning events to wind turbines, calculated according to the IEC standard 61400-24:2010, is grossly underestimated.This paper intends to critically revisit the evaluation of the incidence of downward lightning as well as self-initiated and other-triggered upward flashes to off shore wind power plants. Three different farms are used as case studies. The conditions for interception of stepped leaders in downward lightning and the initiation of upward lightning is evaluated with the Self-consistent Leader Inception and Propagation Model (SLIM). The analysis show that only a small fraction of damages observed in the analysed parks can be attributed to downward lightning. It is also estimated that only a small fraction (less than 19%) of all active thunderstorms in the area of the analysed parks can generate sufficiently high thundercloud fields to self-initiate upward lightning. Furthermore, it is shown that upward flashes can betriggered even under low thundercloud fields once a sufficiently high electric field change is generated by a nearby lightning event. Despite of the uncertainties in the incidence evaluation, it is shown that upward flashes triggered by nearby positive cloud-to-ground flashes produce most of the dangerous lightning events to the casestudies.

  • 205.
    Becerra, Marley
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Pettersson, Jonas
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Bianchetti, Romeo
    ABB Corporate Research, Switzerland.
    On the Radiation Losses Introduced by the Vapour Layer Formed By Arc-Induced Ablation of Polymers in Air2016Konferensbidrag (Refereegranskat)
  • 206.
    Beckman, Claes
    Högskolan i Gävle, Ämnesavdelningen för elektronik.
    Center for RF-Measurement Technology2008Ingår i: Radio Science and Communication, RVK08, 2008Konferensbidrag (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    In February 2006 the Centre for RF Measurement Technology was established at the University of Gävle (HIG). The long term objectives of the centre are to establish world leading research in the area of RF Measurement Technology, support education of radio engineers for local, national and international radio companies at HIG, become a natural collaboration partner for leading industry companies and universities and to support local and national small and middle sized companies in the radio business.

    Today the centre has collaboration with more than 15 national and international companies within 3 major projects in the field of RF measurement technology research spanning from power amplifiers and antennas to electromagnetic interference in industrial environments.

    The annual research budget is in the area of 10 MSEK. In addition to the research projects the centre also supports education and collaboration with local industry, high schools and community.

    The centre is located easy to find, well equipped laboratories in Gävle Technology Park, next to the University of Gävle campus.

  • 207. Beckman, Claes
    Implications of Dual Band Functionality on Base Station Antenna Development1997Ingår i: Dual Band/Multi Band '97 / [ed] Center for EuroTelecomms, London, 1997Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    The recent growth in cellular communications has rapidly created a need for more radio channels. In order to make better use of the available frequency bands new access techniques such as TDMA (Time Division Multiple Access), FDMA (Frequency DMA) and CDMA (Code DMA) have been introduced. Still, the need for new channels is strong and new frequency bands have therefore been allocated for wireless communication systems.

    These new communication systems, e.g. the European Personal Communication Network (PCN: 1710-1880MHz) and the North American Personal Communication System (PCS: 1850-1990MHz), use frequencies about twice as high as their predecessors (e.g. AMPS: 824-894MHz and GSM: 880-960MHz). However, at a time when our downtown areas already are littered with antennas, operators are not keen to install more.

    One solution could be to replace existing GSM or AMPS antennas with dual band GSM/PCN or AMPS/PCS. This would reduce the windload of the towers, the number of feeder cables and the whole  cost of tower installations. If the dual band antennas were to be dual polarized also, the four antennas today being needed for receiving the PCN and GSM bands in a sector, could actually be replaced by one only.

  • 208.
    Beckman, Claes
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth. KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Performance analysis of applying up-link estimates in the down-link beamforming using a dual polarized array2000Ingår i: VTC2000-Spring. 2000 IEEE 51st Vehicular Technology Conference Proceedings (Cat. No.00CH37026), 2000, Vol. 2, s. 690-694 vol.2Konferensbidrag (Refereegranskat)
    Abstract [en]

    Most of the current and future mobile communications systems are frequency duplex systems, i.e. the up- and down-link are separated in frequency. Since the effect of the radio channel is not constant with frequency, this potentially limits the capacity gain using adaptive antennas. We use 150 MHz measurement data to simulate adaptive beamforming in a suburban environment. The information from the up-link at 1741 MHz is used for beamforming at this frequency as well as on the down-link at 1839 MHz. Our results show a reduction in C/I improvement of up to 10 dB between the up- and down-link

  • 209.
    Beckman, Claes
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth. KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS.
    Plausibility of assuming ideal arrays for direction of arrival estimation1996Ingår i: IEEE Antennas and Propagation Society International Symposium. 1996 Digest, 1996, Vol. 2, s. 1364-1367 vol.2Konferensbidrag (Refereegranskat)
    Abstract [en]

    In order to fulfil the increasing demands on capacity and coverage of mobile communication systems smart or intelligent antennas have been suggested. These antennas increase the spectral efficiency of a wireless system by using arrays of antenna elements to shape RF signals in particular directions. Generally, smart antennas can be divided into two approaches: switched multi-beam and adaptive. Adaptive antennas utilize sophisticated signal processing algorithms to continuously distinguish between the desired signal, multipath and interfering signal as well as to calculate their direction of arrival (DOA). This makes it possible to smoothly track users with main lobes and interferers with nulls and thereby constantly maximizing the SINR (signal-to-interference and noise ratio). The DOA is one of the most important parameter for an adaptive antenna system to estimate. It is also the main subject of this paper. We establish whether or not it is plausible to assume the array to be ideal (which is often assumed in array signal processing theory) when the received signals are actually collected with a physical array consisting of standard folded dipoles. In doing so we first measured the element patterns (or steering vectors) of a twelve element antenna array. The results were then used in array signal processing simulations. The performance of two DOA estimation algorithms, MUSIC and ESPRIT, are studied and compared.

  • 210. Beckman, Claes
    et al.
    Christian, Braun
    Engblom, Gunnar
    Antenna diversity for mobile telephones1998Ingår i: IEEE Antennas and Propagation Society International Symposium. 1998 Digest. Antennas: Gateways to the Global Network. Held in conjunction with: USNC/URSI National Radio Science Meeting (Cat. No.98CH36, Atlanta, GA, 1998, pp. 2220-2223 vol.4. / [ed] IEEE Antennas and Propagation Society, 1998, Vol. 4, s. 2220-2223Konferensbidrag (Refereegranskat)
    Abstract [en]

    There have been several studies made on new diversity antennas for the mobile telephones. The main idea has been to have a built-in (planar) antenna working together with the conventional external. The purpose of this paper is to examine the concept of diversity further and to design two different concepts, one with two external antennas and one with an external antenna combined with an in-built. For evaluation a MATLAB program developed by the Center for Personkommunikation, CPK, in Aalborg, Denmark, is used. Given the radiation pattern from each antenna and the incoming field distribution from the environment, this program calculates the diversity performance of the system assuming that selection combining is used to combine the signals

  • 211.
    Beckman, Claes
    et al.
    University of Gävle.
    Eklund, Lars
    Karlsson, Bo
    Lindmark, Björn
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    Ribbenfjärd, David
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Wirdemark, Per
    Verifying 3G licence requirements when every dB is worth a billion2006Ingår i: First European Conference on Antennas & Propagation: EuCAP 2006 / [ed] H. Lacoste & L. Ouwehand, 2006, s. 1-4Konferensbidrag (Refereegranskat)
    Abstract [en]

    In the year 2000, the Swedish Telecom regulator: “Post&Telestyrelsen”, PTS, granted in a “beauty contest” four licenses for operations of 3G systems. To verify the coverage and the license requirements, PTS, has developed a test procedure where the field strength of the primary Common Pilot Channel, CPICH, is measured in a drive test. Designing such a test constitutes a number of challenges mainly due to the fact that in 3G the accuracy in the measurement needs to be extremely high since even a small systematic error of ~1dB could in Sweden have the consequence that each operator would have to build an extra +1000 sites at a staggering cost of ~1billion SEK!

    The present paper gives an overview of the considerations behind the design of the test method used for verification of the 3G licence requirements in Sweden.

  • 212.
    Beckman, Claes
    et al.
    University of Gävle.
    Lindmark, Björn
    Base station antennas for mobile communications2007Ingår i: 2007 IEEE International Symposium on Antennas and Propagation, 2007Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    This course gives the participants a general overview of the application, implementation and design of current and future base station antennas for mobile communications. It is aimed at microwave, RF- and antenna engineers in the wireless area, but also useful for researchers looking for relevant research topics and system engineers needing a deeper understanding of the antenna component of their system. The course explains underlying theoretical and practical implementation aspects of base station antennas in mobile communication networks of today and the future.

    The course is divided into three main parts:

    (i) System Aspects,

    (ii) BTS Antenna Design,

    (iii) Diversity and MIMO

    In the first part the fundamental parameters of a base station antenna are discussed in the context of radio network design. In particular we discuss parameters such as gain, radiation patterns, frequency bands and power handling and put them in the context of cell planning, propagation and capacity.

    In the second part a general overview of base station antenna design is given. In particular the design aspects of radiators, feed networks and reflectors are discussed. Furthermore, a general discussion of array synthesis for base station antennas is given.

    In the final part of the course we give an overview of the underlying theory of diversity and MIMO systems. In particular we discuss the requirements that these systems put on the base station antennas in order to be able to deliver the data rates expected from WiMAX and the long term evolution of 3G systems.

  • 213.
    Beckman, Claes
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Lindmark, Björn
    The evolution of base station antennas for mobile communications2007Ingår i: International Conference on Electromagnetics in Advanced Applications: ICEAA 07, IEEE conference proceedings, 2007, s. 85-92Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper gives a general overview of the design of base station antennas for mobile communications. It explains underlying theoretical and practical implementation aspects in mobile communication networks of today and the future. In the first part the fundamental parameters of a base station antenna are discussed in the context of radio network design. In particular we discuss parameters such as gain, radiation patterns, frequency bands and power handling and put them in the context of cell planning, propagation and capacity. In the final parts of the paper we give an overview of the underlying theory of diversity and MIMO systems.

  • 214.
    Beckman, Claes
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Centra, KTH Center för Trådlösa System, Wireless@kth.
    Smith, Gregory
    The Benefits of network Sharing2005Ingår i: Radiovetenskap och Kommunikation: RVK 2005, 2005, s. 147-151Konferensbidrag (Refereegranskat)
  • 215. Beckman, Claes
    et al.
    Wahlberg, Ulrik
    Widell, Svante
    Polarization Diversity Antennas1997Ingår i: Antenn 97: Nordiskt antennsymposium, 1997, s. 59-65Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this study we investigate how different types of  base station antenna polarization configurations, horizontal/vertical and slanted ±45 degrees, affect the diversity performance in different environments at 1800 MHz. The performance is determined by measurements where  envelope cross-correlation, mean signal levels and diversity gain are studied in urban and suburban small-cell environments. The results are compared with a two branch space diversity scheme, where the antennas are horizontally separated by 20l. The correlation values are in general low, less than 0.7 for more than 90% of the measurements. The horizontal/vertical system suffers though from differences in mean branch signal levels, compared to the ± 45° and space diversity system which always have comparable mean signal levels. The diversity gain of both dual polarized antenna systems are in general about 1dB less than the gain of spatial diversity. The ± 45° scheme performs also about 1dB better than the horizontal/vertical scheme in the urban area. The results indicates that the  ± 45° dual polarized scheme can be attractive in situations where hand-held portables are dimensioning for the cell planning.

  • 216.
    Behere, Sagar
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Inbyggda styrsystem.
    Liljeqvist, Björn
    EIS by Semcon.
    Towards Autonomous Architetures: An Automotive Perspective2012Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The use of embedded computers in modern automobiles is enabling increasingly autonomous features. Electronic power train management and applications in active safety, cooperative driving and navigation show an underlying trend of the transfer of responsibilities from the human driver to a vehicle's (semi-)autonomous subsystems. The logical culmination ofthis trend would be a completely autonomous vehicle. How should existing vehicle architectures be evolved to sustain the development and growth of autonomous functions? We explore the principal problems with existing architectures, caused due to ad hoc addition of (semi-) autonomous features and argue that it is time to rethink automotive architectures from an autonomous systems perspective. We introduce a pattern that can help architects and designers to think in terms of autonomy and suggest where the application of autonomous systems thinking should begin, in the context of architecture development.

  • 217.
    Behere, Sagar
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Mekatronik.
    Törngren, Martin
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Mekatronik.
    Systems Engineering and Architecting for Intelligent Autonomous Systems2017Ingår i: Automated Driving: Safer and More Efficient Future Driving / [ed] Watzenig, Daniel, Horn, Martin, Springer, 2017, s. 313-351Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    This chapter provides an overview of architecture and systems engineeringfor autonomous driving system, through a set of complementaryperspectives. For practitioners, a short term perspective uses the state of theart to dene a three layered functional architecture for autonomous driving,consisting of a vehicle platform, a cognitive driving intelligence, and o-board supervisory and monitoring services. The architecture is placed withina broader context of model based systems engineering (MBSE), for which wedene four classes of models: Concept of Operations, Logical Architecture,Application Software Components, and Platform Components. These classesaid an immediate or subsequent MBSE methodology for concrete projects.Also for concrete projects, we propose an implementation setup and technologiesthat combine simulation and implementation for rapid testing of autonomousdriving functionality in physical and virtual environments. Futureevolution of autonomous driving systems is explored with a long term perspectivelooking at stronger concepts of autonomy like machine consciousnessand self-awareness. Contrasting these concepts with current engineering practicesshows that scaling to more complex systems may require incorporatingelements of so-called constructivist architectures. The impact of autonomy onsystems engineering is expected to be mainly around testing and verication,while implementations shall continue experiencing an in ux of technologiesfrom non-automotive domains.

  • 218.
    Beijner, David
    KTH, Skolan för kemi, bioteknologi och hälsa (CBH), Medicinteknik och hälsosystem, Hälsoinformatik.
    Ökad lokal nytta av förnyelsebar energiproduktion med hybridkraftverk2018Självständigt arbete på grundnivå (högskoleexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Förnyelsebar och miljövänlig elproduktion är en förutsättning för det mer eller mindre miljömässigt positiva värdet hos de produkter och processer som förbrukar elenergi. Det räcker inte med att dessa produkter och processer är effektiva i sitt användande av el om denna el är producerad med icke förnyelsebara metoder. Målet simuleringsprogram som kan simulera ett hybridkraftverk som använder sig av vindkraft och vattenkraft. Resultatet av detta projekt är ett simuleringsprogram som kan uppskatta storleken på ett pumpkraftverk i form av hur många megawatt dess vattenturbin behöver vara samt hur stor reservoar som behövs. Dessutom uppskattas hur många vindkraftverk som krävs i kombination med vattenkraftverket för att nå en önskad minskning av elektricitet från icke förnyelsebara källor.  med detta projekt är skapandet av ett

  • 219. Belov, Ilja
    et al.
    Rydén, Jan
    Lindeblom, Joakim
    Zhang, Yafan
    RISE Acreo.
    Hansson, Torgny
    Bergner, Fredrik
    Leisner, Peter
    Application of CFD modelling for energy efficient humidity management of an electronics enclosure in storage under severe climatic conditions2008Konferensbidrag (Refereegranskat)
  • 220. Benbouzid, M. E. H.
    et al.
    Reyne, G.
    Meunier, G.
    Kvarnsjo, L.
    Engdahl, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Dynamic modelling of giant magnetostriction in Terfenol-D rods by the finite element method1995Ingår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 31, s. 1821-1824Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    As a contribution to the development of methods for the design and the analysis of devices based on giant magnetostrictive materials, a model for the simulation of the dynamic behaviour of the nonlinear magnetoelastic medium is presented. The coupled magnetic, magnetoelastic and mechanical equations that describe the magnetostrictive problem are solved by means of the finite element method. The thin sheets bending principle (surface splines) is used to introduce in the simulation the nonlinear properties of giant magnetostrictive materials, obtained by static characterizations

  • 221.
    Berg, Marcus
    et al.
    Uppsala University, Sweden.
    Thottappillil, Rajeev
    Uppsala University, Sweden.
    Scuka, Viktor
    Uppsala University, Sweden.
    Hydrophobicity estimation of HV polymeric insulating materials. Development of a digital image processing method.2001Ingår i: IEEE transactions on dielectrics and electrical insulation, ISSN 1070-9878, E-ISSN 1558-4135, Vol. 8, nr 6, s. 1098-1107Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Image analysis of water drop patterns on an inclined flat polymeric insulator surface has been performed in order to find a simple mathematical function that indicates the level of hydrophobicity of the insulator surface. A simple function, given the acronym average of normalized entropies (ANE), seems to correlate well with hydrophobicity as defined by the Swedish Transmission Research Institute (STRI) hydrophobicity classification. It is a composition of three other functions, viz. the standard deviation, the Shannon information entropy and the 'fraction of small differences'. All these are in turn based on the histogram of horizontal nearest-neighbor pixel differences for a given digital greyscale image of a water drop pattern. ANE is fairly independent of illumination intensity (exposure) as well as total gain and offset in a camera system (linear sensor). The experimental results also indicate that ANE is fairly independent of limited changes in the surface inclination, although this needs further investigation. Some of the various pitfalls associated with the photography of water drop patterns and processing of images are identified, together with possible solutions for avoiding them.

  • 222.
    Berger, Victor
    KTH, Skolan för datavetenskap och kommunikation (CSC).
    Anomaly detection in user behavior of websites using Hierarchical Temporal Memories: Using Machine Learning to detect unusual behavior from users of a web service to quickly detect possible security hazards.2017Självständigt arbete på avancerad nivå (masterexamen), 30 poäng / 45 hpStudentuppsats (Examensarbete)
    Abstract [en]

    This Master's Thesis focuses on the recent Cortical Learn-ing Algorithm (CLA), designed for temporal anomaly detection. It is here applied to the problem of anomaly detec-tion in user behavior of web services, which is getting moreand more important in a network security context.

    CLA is here compared to more traditional state-of-the-art algorithms of anomaly detection: Hidden Markov Models (HMMs) and t-stide (an N-gram-based anomaly detector), which are among the few algorithms compatible withthe online processing constraint of this problem.

    It is observed that on the synthetic dataset used forthis comparison, CLA performs signicantly better thanthe other two algorithms in terms of precision of the detection. The two other algorithms don't seem to be able tohandle this task at all. It appears that this anomaly de-tection problem (outlier detection in short sequences overa large alphabet) is considerably different from what hasbeen extensively studied up to now.

  • 223.
    Berggren, Andreas
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Design of Thermal Control System for the Spacecraft MIST2015Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In 2014 KTH Royal Institute of Technology initiated a space technology and research

    center, KTH Space Centre. MIST (MIniature Student saTellite) is the rst student

    project conducted at KTH Space Centre and also the rst student satellite from KTH

    with a predicted launch in 2017. This report includes the thermal analysis and control

    of the spacecraft MIST.

    One of the main systems in a spacecraft is the thermal control system. In order for

    the payloads and subsystems to withstand the harsh thermal environment in space a

    thorough thermal analysis is needed. In this project the thermal model has been built

    and thermal control design of the spacecraft has been started. As a start a preliminary

    thermal analysis was performed where the spacecraft was approximated as a sphere in

    order to get some estimates on the temperature in orbit due to the space environment.

    Furthermore the temperature decrease in eclipse was studied. Since most of the spacecraft

    will consist of Printed Circuit Boards (PCB) the thermal behavior of PCB has

    been investigated and as a part of this investigation a thermal vaccum chamber test

    was performed where the conductance from a PCB through the mounting interface to

    a metal plate was measured. This report will also guide the reader through the model

    built and assumptions made. As a part of the thermal control, Multi Layer Insulation

    (MLI) has been studied and modeled in two di erent ways which have been compared

    with each other in order to know the level of detail needed for the MLI model.

    Last but not least the design of the thermal control system has been started where some

    payloads have been wrapped in MLI and thermal contact conductance coecient has

    been changed in order to meet the thermal requirements of the payloads and subsystems.

  • 224.
    Bergkvist, Tommy
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Non-linear dynamics of Alfvén eigenmodes excited by fast ions in tokamaks2007Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The tokamak is so far the most promising magnetic configuration for achieving a net production of fusion energy. The D-T fusion reactions result in 3.5 MeV alpha-particles, which may destabilize Alfvén eigenmodes through wave-particle interaction. These instabilities redistribute the alpha-particles from the central region of the plasma towards the edge, where they are thermalized, and hence result in a reduced heating efficiency. The high-energy alpha-particles may even be thrown out of the plasma and may damage the wall.

    To investigate the destabilization of Alfvén eigenmodes by high-energy ions, ion cyclotron resonance heating (ICRH) and neutral beam injection (NBI) are often used to create a high-energy tail on the distribution function. The ICRH does not only produce high-energy anisotropic tails, it also decorrelates the wave-particle interaction with the Alfvén eigenmodes. Without decorrelation of the wave-particle interaction an ion will undergo a superadiabatic oscillation in phase space and there will be no net transfer of energy to the mode. For the thermal ions the decorrelation from collisions dominates while for the high-energy ions the decorrelation from ICRH dominates. As the unstable modes grow up, the gradients in phase space, which drive the mode, are reduced, resulting in a weaker drive. The dynamics of the system becomes non-linear due to a continuous restoration of the gradients by D-T reactions and ICRH.

    In this thesis the non-linear dynamics of toroidal Alfvén eigenmodes (TAEs) during ICRH has been investigated using the SELFO code. The SELFO code, which calculates the distribution function during ICRH self-consistently using a Monte-Carlo metod, has been upgraded to include interactions with TAEs. The fast decay of the mode amplitude as the ICRH is switched off, which is seen in experiments, as well as the oscillation of the mode amplitude as the distribution function is repetetively built up by the ICRH and flattened by the TAE has been reproduced using numerical simulations. In the presence of several unstable modes the dynamics become more complicated. The redistribution of an alpha-particle slowing down distribution function as well as the reduced heating efficiency in the presence of several modes has also been investigated.

  • 225.
    Bergkvist, Tommy
    et al.
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    Hellsten, Torbjörn
    KTH, Tidigare Institutioner                               , Elektrotekniska system.
    Self-consistent calculations of the distribution function and wave field during ICRF heating and global Alfvén wave excitation2004Ingår i: Proceeding of Theory of Fusions Plasmas, 2004, s. 123-132Konferensbidrag (Refereegranskat)
  • 226.
    Bergkvist, Tommy
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Holmström, Kerstin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Non-linear dynamics of Alfvén eigenmodes excited by thermonulcear alpha particles in the presence of ion cyclotron resonance heating2007Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 47, nr 9, s. 1131-1141Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Alfvén eigenmodes (AEs) excited by thermonuclear α-particles can degrade the heating efficiency by spatial redistribution of the resonant α-particles. Changes of the orbit invariants in phase space by collisions and interactions with other waves, such as magnetosonic waves during ion cyclotron resonance heating (ICRH), lead to changes in the phase between the α-particles and AEs, causing a decorrelation of the interactions and stronger redistribution of the α-particles. Cyclotron interactions increase the decorrelation of the AE interactions with the high-energy ions and hence a stronger radial redistribution of the high-energy α-particles by the AEs. Renewal of the distribution function by thermonuclear reactions and losses of α-particles to the wall lead to a continuous drive of the AEs and a radial redistribution of the α-particles. The condition for excitation of AEs is shown to depend on the heating scenario where heating at the low field side creates a significant population of high-energy non-standard orbits which drive the modes. The redistribution results in a reduction in the averaged α-particle energy and a degradation of the heating efficiency. The effect on the distribution function in the presence of several unstable modes is not additive and the particle redistribution is found to saturate with an increasing number of modes.

  • 227.
    Bergkvist, Tommy
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, T.
    Laxåback, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Non-linear study of fast particle excitation of global Alfvén eigenmodes during ICRH2005Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 45, s. 485-493Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-power ion–cyclotron resonance heating (ICRH) can produce centrally peaked fast ion distributions with wide non-standard drift orbits exciting Alfvén eigenmodes (AEs). The dynamics of the AE excitation depends not only on the anisotropy and the peaking of the fast ion distribution but also on the decorrelation of the AE interactions and the renewal of the fast ions resonant with the AE by ion–cyclotron interactions. A method of self-consistently including the evolution of the distribution function of fast ions during excitation of AEs and ICRH has been developed and implemented in the SELFO code. Numerical simulations of the AE dynamics and ICRH give a variation of the AE amplitude consistent with the experimentally observed splitting of the mode frequency. The experimentally observed fast damping of the mode as the ICRH is switched off is also evident in the simulations.

  • 228.
    Bergkvist, Tommy
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Self-consistent study of fast particle redistribution by Alfvén eigenmodes during Ion cyclotron resonance heating2005Ingår i: Proceedings of the 9th IAEA Technical Meeting on Energetic Particles in Magnetic Confinement Systems, 2005, s. 14-20Konferensbidrag (Refereegranskat)
  • 229.
    Bergman, David
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    The Effect of Partial Discharge Aging on the Dielectric Response of Polymers2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Det här arbetet undersökte effekten av partiella urladdningar (PD) på den komplexa

    permittiviteten i PVC, PC, PTFE, PE och PA6. Materialproverna utsattes för långvarig

    PD aktivitet och materialets komplexa permittivitet mättes med hjälp av dielektrisk

    spektroskopi (DS) före och efter att provet åldrats. Resultaten visade en förändring i

    förlustfaktorn i de testade materialen, några påverkades mer än andra och de uppvisade

    olika beteenden när de blev utsatta för PD åldring. Det var därför inte möjligt att hitta

    någon generell trend i den komplexa permittiviteten för de olika testade materialen.

    Flera av materialen uppvisade en förlustfaktor med -1/2 lutning vid låga frekvenser

    vilket motsvarar diffusion. -1/2 lutningen medför att förlustfaktorn och den dynamiska

    komponenten av den reella permittiviteten borde sammanfalla, vilket inte kunde ses.

    Det är därför osäkert huruvida det som observerats är en diffusionsprocess eller inte.

    Resultaten kan tyda på att PD-åldring orsakar en förändring i potentialfällors egenskaper

    i materialet. Således skulle rymdladdningar som deponeras på väggarna i kaviteten på

    grund av PD-aktiviteten kunna diffundera in i materialet där en del av laddningarna

    fastnar. Om en DS mätning görs innan de fångade laddningarna har fått tillräcklig tid

    att rekombinera eller ledas iväg, kan det påverka den komplexa permittiviteten. Detta

    visades genom att genomföra en DS mätning på ett åldrat prov av PC som fått vila i

    35 dagar. Mätningen visade att den komplexa permittiviteten hade återgått till nästan

    samma tillstånd som innan den åldrades. Mätproblem påträffades vilket påverkade

    mätningarna i detta arbete. Problemen antas vara orsakade av att mätelektroderna som

    användes till DS mätningarna inte var tillräckligt tunga för att eliminera små oönskade

    luftgap mellan elektroderna och provet. Dessutom erhölls ofullkomliga resultat för några

    av mätningarna vilket tros bero på att provets kapacitans befann sig på gränsen för vad

    mätinstrumentet kunde mäta.

  • 230. Bergqvist, A.
    et al.
    Engdahl, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    A phenomenological differential #x2010;relation #x2010;based vector hysteresis model1994Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 75, s. 5484-5486Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A phenomenological inherently vector hysteresis model employing simple differentials as a means of keeping track of the past history of the magnetic field is proposed. This results in a simple and computationally fairly efficient formulation for vector hysteresis of any dimension. An expression for determining model parameters from experimental data or from the Preisach function is given. The model exhibits rotational hysteresis and reduction of remanent magnetization by an orthogonal field and reduces to the classical Preisach model in one dimension. Details concerning the numerical implementation are discussed and computational examples demonstrating model properties are presented.

  • 231. Bergqvist, A.
    et al.
    Engdahl, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    A phenomenological magnetomechanical hysteresis model1994Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 75, nr 10, s. 5496-5498Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To obtain accurate design tools for applications involving giant magnetostrictive materials, magnetomechanical hysteresis effects should be taken into account. The problem consists of determining the magnetization and mechanical strain from the combined past history of magnetic field and mechanical stress. In this work, coupled magnetomechanical hysteresis has been modeled by using simple path #x2010;dependent differentials to accumulate the past history in functions related to the magnetization and strain through material #x2010;dependent parameters. By using anhysteretic curves and a few additional parameters to characterize a material, major, and minor loops with respect to both field and stress have been calculated for Terfenol #x2010;D and have shown good agreement with experiments.

  • 232. Bergqvist, A.
    et al.
    Engdahl, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    A stress-dependent magnetic Preisach hysteresis model1991Ingår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 27, s. 4796-4798Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The authors present a generalization of the classical Preisach model which handles coupled magnetic and mechanical hysteresis. Magnetostrictive materials are known to have hysteresis with respect to both magnetic field H and mechanical stress lambda;. To test the validity of the model, experiments where the two components H and lambda; have been verified in many different ways have been performed on Terfenol-D and compared to results computed from the model. Some of these results are presented. This stress-dependent model is found to have an accuracy comparable to that of the classical Preisach model

  • 233. Bergqvist, A.
    et al.
    Engdahl, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    A thermodynamic representation of pseudoparticles with hysteresis1995Ingår i: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 31, s. 3539-3541Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method of expressing pseudoparticles with hysteresis within a context of irreversible thermodynamics is investigated. The state of a pseudoparticle is uniquely determined by its magnetization and its evolution is governed by entropy maximization. Hysteresis appears if the free energy is a nonconvex function of magnetization. The vectorial nature of magnetization and dependence on rate are accounted for in a systematic manner. Some basic properties are derived for quasistatic processes. In particular, it is found that in the scalar case, the magnetization is a monotonically increasing functional with respect to field and that for quasistatic processes, this implies the wiping-out property

  • 234.
    Bergqvist, A.
    et al.
    KTH.
    Engdahl, Göran
    KTH.
    Homogenization of Laminated Cores for Eddy Current Calculations1998Ingår i: The 7th JointMMM-Intermag Conference, 1998. Abstracts, 1998, s. 51-51Konferensbidrag (Refereegranskat)
  • 235.
    Bergqvist, A.
    et al.
    KTH.
    Lundgren, A.
    KTH.
    Engdahl, Göran
    KTH.
    A Statistical Model for Domain Wall Motion Considering hysteresis1998Ingår i: The 7th Joint MMM-Intermag Conference, 1998. Abstracts, IEEE , 1998, s. 115-115Konferensbidrag (Refereegranskat)
  • 236. Bergqvist, A.
    et al.
    Tiberg, H.
    Engdahl, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Application of a vector Preisach model in a magnetic circuit1993Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 73, s. 5839-5841Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Magnetic hysteresis effects have been included in a finite #x2010;element description of a magnetic circuit by using the classical vector Preisach model for the constitutive relation between H and B. The influence of an external electric circuit is taken into account by adding equations derived from Faraday #x2019;s law. Computational results are presented for a magnetic circuit used in a magnetostrictive device.

  • 237. Bergqvist, Anders
    et al.
    Engdahl, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    A model for Magnetomechanical Hysteresis and Losses in Magnetostrictive Materials1996Ingår i: J. Appl. Phys., Vol. 79, nr 8Artikel i tidskrift (Refereegranskat)
  • 238. Bergqvist, Anders
    et al.
    Lundgren, Anders
    Engdahl, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Experimental testing of an anisotropic vector hysteresis model1997Ingår i: IEEE Transactions on Magnetics, Vol. 33, nr 5, s. 4152-54Artikel i tidskrift (Refereegranskat)
  • 239. Bergqvist, Anders
    et al.
    Lundgren, Anders
    Stillesjö, Fredrik
    Engdahl, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Statistical modelling of magnetic and magnetostrictive properties due to domain wall motion1999Ingår i: Journal of Applied Physics, s. 5190-5192Artikel i tidskrift (Refereegranskat)
  • 240. Bergqvist, J.
    et al.
    Lundgren, A.
    Engdahl, Göran
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Computationally efficient vector hysterisis model using flux density as known variable1998Ingår i: Non-linear electromagnetic systems, s. 463-Artikel i tidskrift (Refereegranskat)
  • 241.
    Bergsåker, Claudia
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Impact of transformer core size on the reactive power requirement of power transformers due to GIC2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Geomagnetiskt inducerade strömmar (GIC) är ett naturfenomen som uppstår till följd av solstormar.

    Vid en solstorm kastas stora mängder magnetiserad plasma ut från solens yta, och när denna

    plasma når jorden uppstår  uktuationer i det jordmagnetiska fältet. Detta kan leda till att DCstr

    ömmar induceras i långa transmissionsledsningar. Dessa överströmmar påverkar kraftsystemet

    på  era olika sätt, bland annat har de en stor påverkan på transformatorer. Då överströmmen

     yter genom transformatorlindningarna ökar det reaktiva eektuttaget för transformatorn, vilket

    kan leda till spänningsinstabilitet i systemet. En fråga som legat till grund för detta projekt är huruvida

    en ökning av transformatorkärnans storlek gör transformatorns reaktiva eektuttag mindre

    känsligt för GIC. För att undersöka detta har en ny transformatormodell använts; den såkallade

    hybridmodellen som kombinerar dualitetsprincipen med en matrisrepresentation av transformatorn.

    Denna modell, som nyligen implementerats i simuleringsprogrammet PSCAD, har använts för att

    simulera GIC i transformatorer med kärnor av olika storlekar. Resultaten från dessa simuleringar

    indikerar att större transformatorkärna medför mindre förändring av det reaktiva eektuttaget när

    transformatorn utsätts för GIC. Det är även tydligt att det reaktiva eektuttaget som funktion av

    GIC är en icke-linjär funktion när hybridmodellen används. Denna funktion har tidigare ansetts

    vara linjär.

  • 242.
    Bergsåker, Henrik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Possnert, G.
    Likonen, J.
    Koivuranta, S.
    Coad, J. P.
    Van Renterghem, W.
    Uytdenhouwen, I.
    Widdowson, A. M.
    Microscopically nonuniform deposition and deuterium retention in the divertor in JET with ITER-like wall2015Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, s. 956-960Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The divertor surfaces in JET with ITER-like wall (ILW) have been studied using micro ion beam analysis (mu-IBA) methods and scanning electron microscopy (SEM). Deposited layers with beryllium as main constituent had been formed during plasma operations through 2011-2012. The deuterium trapping and impurity deposition were non-uniform, frequently enhanced within pits, cracks and valleys, regions reaching in size from 10 mu m to 200 mu m. The impurity deposition and fuel retention were correlated with the surface slope with respect to the direction of ion incidence. Typically more than 70% of the total measured areal density of trapped D was found in less than 30% of the surface area. This is of consequence for the interpretation of other surface analyses and in extrapolation from fuel retention in JET with ITER-like wall and rough divertor surfaces to ITER with smoother surfaces.

  • 243.
    Bernal, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Signalbehandling.
    A Comparison of Kalman Filtering Techniques Applied to the Alignment Problem2015Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 244.
    Bernard, C.
    et al.
    University of Padova.
    Bolognani, S.
    University of Padova.
    Peretti, L.
    University of Padova.
    Zigliotto, M.
    University of Padova.
    Steering chain HIL simulator for steer-by-wire systems2006Konferensbidrag (Refereegranskat)
  • 245.
    Berntsson, Lars-Olof
    et al.
    Volvo Technology AB.
    Blom, Hans
    Volvo Technology AB.
    Chen, DeJiu
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Inbyggda styrsystem.
    Cuenot, Philippe
    Siemens VDO.
    Donandt, Jörg
    Daimler AG.
    Eklund, Ulrich
    Volvo Cars.
    Freund, Ulrich
    ETAS GmbH.
    Frey, Patrick
    ETAS GmbH.
    Gérard, Sébastien
    CEA List , Commissariat à l'Énergie Atomique Saclay.
    Jansson, Pontus
    Mecel AB.
    Johansson, Rolf
    Mentor Graphics Corp..
    Lönn, Henrik
    Volvo Technology AB.
    Reiser, Mark-Oliver
    Technical University of Berlin.
    Selin, Dennis
    Volvo Cars.
    Servat, David
    CEA List , Commissariat à l'Énergie Atomique Saclay.
    Sjöstedt, Carl-Johan
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Inbyggda styrsystem.
    Tessier, Patrick
    CEA List , Commissariat à l'Énergie Atomique Saclay.
    Reiser, Mark-Oliver
    Technical University of Berlin.
    Törner, Fredrik
    Volvo Car Corp..
    Törngren, Martin
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.), Inbyggda styrsystem.
    Weber, Matthias
    Carmeq GmbH.
    EAST-ADL 2.0 Specification2008Rapport (Refereegranskat)
    Abstract [en]

    This specification of the EAST ADL 2.0 is based on the EAST-ADL developed in the EAST EEA projectand has been further refined and harmonized with on-going modelling appraches in the automotiveindustry. It presents the modeling infrastructure, i.e. how the modeling elements should be represented inthe language and the UML representation. For each package a usage example is provided.The EAST-ADL 2.0 is harmonized with AUTOSAR.The metamodel and UML profile of EAST ADL 2.0 is defined in two steps: A domain (automotive)metamodel is defined, capturing only the domain specific needs of the language, without adding the UML2details. The basic concepts of UML are used for this purpose, such as classes, compositions andassociations. Based on the domain metamodel, a UML2 profile for the domain metamodel is defined,specifying stereotypes with properties and constraints.Comments on the content of this document are welcomed, and should be directed to <coordinator@atesst.org>.Please download the latest available specification and the XMI file ready for use in UML2 tools from the <atesst.org> website.

  • 246.
    Bertilsson, Kent
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Simulation and Optimization of SiC Field Effect Transistors2004Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Silicon Carbide (SiC) is a wide band-gap semiconductor material with excel-lent material properties for high frequency, high power and high temperature elec-tronics. In this work different SiC field-effect transistors have been studied using theoretical methods, with the focus on both the devices and the methods used. The rapid miniaturization of commercial devices demands better physical models than the drift-diffusion and hydrodynamic models most commonly used at present.

    The Monte Carlo method is the most accurate physical methods available and has been used in this work to study the performance in short-channel SiC field-effect devices. The drawback of the Monte-Carlo method is the computational power required and it is thus not well suited for device design where the layout requires to be optimized for best device performance. One approach to reduce the simulation time in the Monte Carlo method is to use a time-domain drift-diffusion model in contact and bulk regions of the device. In this work, a time-domain drift-diffusion model is implemented and verified against commercial tools and would be suitable for inclusion in the Monte-Carlo device simulator framework.

    Device optimization is traditionally performed by hand, changing device pa-rameters until sufficient performance is achieved. This is very time consuming work without any guarantee of achieving an optimal layout. In this work a tool is developed, which automatically changes device layout until optimal device per-formance is achieved. Device optimization requires hundreds of device simulations and thus it is essential that computationally efficient methods are used. One impor-tant physical process for RF power devices is self heating. Self heating can be fairly accurately modeled in two dimensions but this will greatly reduce the computa-tional speed. For realistic influence self heating must be studied in three dimensions and a method is developed using a combination of 2D electrical and 3D thermal simulations. The accuracy is much improved by using the proposed method in comparison to a 2D coupled electro/thermal simulation and at the same time offers greater efficiency. Linearity is another very important issue for RF power devices for telecommunication applications. A method to predict the linearity is imple-mented using nonlinear circuit simulation of the active device and neighboring passive elements.

  • 247.
    Bertling, Lina
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Larsson, Mats B-O
    MML Åhus.
    Wallnerström, Carl Johan
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Review of the Swedish Network Performance Assessment Model2008Rapport (Övrigt vetenskapligt)
    Abstract [en]

    The Swedish energy agency (STEM), has developed a new regulatory model to supervise the revenues of the Distribution System Operators (DSO), referred to as the Network Performance Assessment Model (NPAM). The fundamental idea of the NPAM is that the electrical distribution system provides customer values, and the DSO is allowed to collect revenue corresponding to these values. The NPAM calculates customer values for a fictive electrical distribution system, with a total cost referred to as the Network Performance Assessment (NPA). The allowed debiting rate for a DSO is defined by the quotient of the revenue and the NPA. If the debiting rate is higher than a certain value, defined by the Energy Market Inspection (EMI) at STEM, the DSO is placed under review and could be forced to pay back revenue to customers. A lawsuit is currently in progress on this use of the NPAM, which has highlighted drawbacks in the model. This paper provides a comprehensive presentation of the NPAM. It describes in detail the different input data for the model, the steps in the calculations and the resulting cost factors. The paper also presents for the first time details on the theory underlying the calculations.

  • 248.
    Bertling, Lina M.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    On evaluation of RCM for maintenance management of electric power systems2005Ingår i: 2005 IEEE POWER ENGINEERING SOCIETY GENERAL MEETING, 2005, s. 2638-2640Konferensbidrag (Refereegranskat)
    Abstract [en]

    This panel presentation aims to propose a possible solution for how to evaluate the effect of RCM as a tool for maintenance management. The starting point is a general understanding of the RCM methodology. Further on, a quantitative approach for relating the impact of component maintenance on system reliability and total cost is introduced. The method, referred to as reliability-centred asset maintenance method (RCAM) is being developed within a research group at KTH in Sweden. Finally the presentation comments on ongoing research to evaluate the introduction of RCM. The aim of RCM is to optimize the maintenance achievements in a systematic way.

  • 249.
    Bertling, Lina M.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Allan, R
    Eriksson, Roland
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    A reliability-centred asset maintenance method for assessing the impact of maintenance in power distribution systems2005Ingår i: 2005 IEEE Power Engineering Society General Meeting, 2005, s. 2649-2649Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper proposes a method for comparing the effect of different maintenance strategies on system reliability and cost. This method relates reliability theory with the experience gained from statistics and practical knowledge of component failures and maintenance measures. The approach has been applied to rural and urban distribution systems. In particular, a functional relationship between failure rate and maintenance measures has been developed for a cable component. The results show the value of using a systematic quantitative approach for investigating the effect of different maintenance strategies.

  • 250.
    Bertling, Lina
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Wallnerström, Carl Johan
    KTH, Skolan för elektro- och systemteknik (EES), Elektroteknisk teori och konstruktion.
    Nätnyttomodellens tillförlitlighet med avseende på små förändringar i indata2006Rapport (Övrigt vetenskapligt)
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