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  • 123901.
    Zetterberg, Per
    et al.
    KTH, School of Electrical Engineering (EES).
    Ottersten, Björn
    KTH, School of Electrical Engineering (EES).
    The spectrum efficiency of a base station antenna array system for spatially selective transmission2009In: Adaptive Antennas for Wireless Communications, John Wiley and Sons Inc. , 2009, p. 471-480Chapter in book (Other academic)
    Abstract [en]

    In this paper we investigate the spectrum efficiency gain using transmitting antenna arrays at the base stations of a mobile cellular network. The proposed system estimates the angular positions of the mobiles from the received data, and allows multiple mobiles to be allocated to the same channel within a cell. This is possible by applying a transmit scheme which directs nulls against co-channel users within the cell. It is shown that multiple mobiles per cell is an efficient way of increasing capacity in comparison with reduced channel reuse distance and narrow beams (without directed nulls). The effect of the spatial spread angle of the locally scattered rays in the vicinity of the mobile is also investigated.

  • 123902.
    Zetterberg, Per
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Ottersten, Björn
    KTH, Superseded Departments, Signals, Sensors and Systems.
    The Spectrum Efficiency of a Base-Station Antenna Array System for Spatially Selective Transmission1994In: IEEE 44th Vehicular Technology Conference, IEEE , 1994, p. 1517-1521Conference paper (Refereed)
    Abstract [en]

    The goal of this paper is to estimate the gain, in terms of system capacity at a given outage probability, which can be obtained by applying antenna arrays in the base stations of a mobile cellular network. For this purpose apropagation model which incorporates the angular distribution of the rays in the vicinity of the mobile is postulated. Also included in the model is the interference from co-channel cells. With the aid of the model, aweight selection algorithm is derived. The proposed system is simulated with different numbers of mobiles per channel in each cell and different numbers of antenna elements in the arrays. Also varied is the cluster size. This is done to determine the optimal trade-off between reduced cluster size and multiple mobiles per channel in each cell. The results show that it is possible to increase capacity between two and twelve times depending on thenumber of antennas in the arrays and the spread of the local scattering.

  • 123903. Zetterberg, T.
    et al.
    Astrom, B. T.
    Backlund, J.
    Burman, Magnus
    KTH, Superseded Departments, Aeronautical and Vehicle Engineering.
    On design of joints between composite profiles for bridge deck applications2001In: Composite structures, ISSN 0263-8223, E-ISSN 1879-1085, Vol. 51, no 1, p. 83-91Article in journal (Refereed)
    Abstract [en]

    Techniques for joining of pultruded composite profiles for bridge-deck applications are designed and analyzed. It is shown that both adhesively bonded and bolted joints can be designed to fulfill stringent requirements, but it is clear that the former is the preferred alternative. The methodology used to analyze a large composite structure composed of modular construction elements and to determine the load transfer between composite profiles is described.

  • 123904.
    Zetterberg Wallin, Georg
    KTH, School of Engineering Sciences (SCI).
    System architectural interfaces forautonomous trucks2014Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This thesis evaluates a proprietary interface developed by Scania that connects a third party developed autonomy solution to the electrical system of a Scania truck. The autonomy solution is developed for a mining application. While evaluating the interface the focus of the thesis narrows down to how to make the interface scalable and future proof. The content of this thesis is mainly based upon interviews and internal Scania documentation. In summary, the two main conclusions that could be drawn from this evaluation study are, that the interface needs to support a larger amount of requests from an external control to support that the interface is applicable in many areas. Secondly the idea of a modular electrical system must be carried on to autonomous applications as well and interface logic must be separated from core functionality of the electrical system.

  • 123905.
    Zetterberg Wallin, Georg
    et al.
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    Crétier, Matthieu
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Vehicle Dynamics.
    A supervised learning approach to estimate the drivers impact on fuel consumption: A heavy-duty vehicle case study2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The aim of this Master thesis is to provide a statistical analysis of the factors inuencing the fuel consumption, with a focus on the separation of the drivers' performance. The study is focused on the long haulage trucks, which correspond to the application where the fuel consumption becomes of primary interest from the economical point of view. Further developments of the work leads to a graphical representation of the outcomes on a map, highlighting in particular the segments of the road network having the highest variation of the driver-inuenced fuel consumption. The analysis dataset created is the combination of data coming from di erent sources and additional features computed based on them. The datasources are providing respectively the vehicles' operating data and congurations, the road network's characteristics and the weather information. The results obtained prove that it is possible to isolate the driver factor from the overall fuel consumption. This can be achieved by training a model composed by variables statistically chosen through a regression procedure. Further in the analysis the di erent driver factors are used in order to determine the fuel saving potential of the road stretches where the factors are computed. The results are gathered in multiple stages, based on the dimension of the dataset considered and the method used. Two methods are used to train the model: the least squares regression and the ridge regression. First the whole Swedish road network composed by primary roads is analyzed with least squares. 1195 road stretches belonging to this network present a dened and di erent than zero fuel saving potential varying between 0.003 and 83.71 l/100km. Then, a smaller portion of the same road network is analyzed after being provided with road slope information. The fuel saving potential estimated using ridge regression present values between 0.002 and 24.39 l/100km.

    From the geographical point of view little can be deduced from the analysis of the complete network. The E4 provided with slope data, on the contrary, allows a better insight, especially using ridge.

  • 123906.
    Zettergren, Carl
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Tavakoli, Mina
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Skillnad i skärmstorlek och skärmtyp: påverkan på inlärning2019Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In a more and more digitized society, the education has also been steeped in this digitization. This has lead to a rise in the production of video lectures which students, mostly at degree level, more often use for learning purposes. E-learning has many advantages since it, among other things, leads to an increased flexibility when studying. There are many previous studies on learning behaviours, screen sizes and video lectures. Earlier studies show that learning can differ depending on screen size but there are also studies showing the opposite. This bachelor’s thesis examines if screen size has an effect on how much one learns from watching a video lecture. This was done by grouping 34 test participants into three groups where they all watched a video lecture on three groups of screen sizes: small (4”-7”), medium (13”-17”) or large (27”). A few days before and directly after the test the contestants answered a survey with questions regarding the content in the specific video. The results are that differences between these screen sizes do not have a significant impact on how much one learns from a video lecture of interview type. This therefore means that one does not have to consider the screen size for that type of video lecture, either as a student or a video producer.

  • 123907.
    Zettergren, Herman
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management.
    Broms, Martin
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management.
    Bostadsförsäljning före ordinarie visning: Hur påverkas slutpriset vid försäljning före ordinarie visning?2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The objective of this study was to examine whether the final price of an apartment with the size of one-room and two-rooms in the Stockholm downtown area is affected of a sale before ordinary viewing. Further on we wanted to take part of how sellers, buyers and real esate agents is thinking during the process.  To obtain answers to our questions we performed a great quantitative analysis and a qualitative examination. The quantitative analysis was accomplished by comparing apartments that were sold before ordinary viewing to apartments that were sold after ordinary viewing. The qualitative examination consisted by interviews with sellers, buyers and real estate agents.  The result showed that two thirds of the apartments that were sold before ordinary viewing generated a higher final price per square meter, than the comparison objects. The average price per square meter was 104 534 SEK compared to 103 072 SEK. It turned our that the buyers acted like they did, because they believed that they saved money by buying before an ordinary viewing. Seen through the sellers´ perspective the most important part was to have a good contact with the real estate agent, to make sure they did a good affair. What mattered the most for the real estate agent was that the seller would be pleased and satisfied with the transaction. 

  • 123908. Zettergren, M. D.
    et al.
    Semeter, J. L.
    Dahlgren, Hanna
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics. Space Environment Physics, University of Southampton, Southampton, United Kingdom.
    Dynamics of density cavities generated by frictional heating: Formation, distortion, and instability2015In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 42, no 23, p. 10120-10125Article in journal (Refereed)
    Abstract [en]

    A simulation study of the generation and evolution of mesoscale density cavities in the polar ionosphere is conducted using a time-dependent, nonlinear, quasi-electrostatic model. The model demonstrates that density cavities, generated by frictional heating, can form in as little as 90 s due to strong electric fields of ∼120 mV/m, which are sometimes observed near auroral zone and polar cap arcs. Asymmetric density cavity features and strong plasma density gradients perpendicular to the geomagnetic field are naturally generated as a consequence of the strong convection and finite extent of the auroral feature. The walls of the auroral density cavities are shown to be susceptible to large-scale distortion and gradient-drift instability, hence indicating that arc-related regions of frictional heating may be a source of polar ionospheric density irregularities.

  • 123909.
    Zetterholm, Elisabeth
    et al.
    Department of Philosophy & Linguistics, Umeå University.
    Blomberg, Mats
    KTH, Superseded Departments, Speech, Music and Hearing.
    Elenius, Daniel
    KTH, Superseded Departments, Speech, Music and Hearing.
    A comparison between human perception and a speaker verification system score of a voice imitation2004In: Proc of Tenth Australian International Conference on Speech Science & Technology, 2004, p. 393-397Conference paper (Refereed)
    Abstract [en]

    A professional impersonator has been studied when training his voice tomimic two target speakers. A three-fold investigation has been conducted; acomputer-based speaker verification system was used, phonetic-acousticmeasurements were made and a perception test was conducted. Our ideabehind using this type of system is to measure how close to the target voice aprofessional impersonation might be able to reach and to relate this tophonetic-acoustic analyses of the mimic speech and human perception. Thesignificantly increased verification scores and the phonetic-acoustic analysesshow that the impersonator really changes his natural voice and speech in hisimitations. The results of the perception test show that there is no, or only asmall, correlation between the verification system and the listeners whenestimating the voice imitations and how close they are to one of the targetspeakers.

  • 123910.
    Zetterling, Carl-Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Dielectric issues for silicon carbide MOS devices1998In: 29th IEEE Semiconductor Interface Specialists Conference, 1998Conference paper (Refereed)
  • 123911.
    Zetterling, Carl-Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Electrical and transport properties of AlN1999In: Properties, processing and applications of gallium nitride and related semiconductors, Institution of Engineering and Technology, 1999, 1, p. 40-Chapter in book (Refereed)
  • 123912.
    Zetterling, Carl-Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Integrated circuits in silicon carbide for high-temperature applications2015In: MRS bulletin, ISSN 0883-7694, E-ISSN 1938-1425, Vol. 40, no 5, p. 431-438Article in journal (Refereed)
    Abstract [en]

    High-temperature electronic applications are presently limited to a maximum operational temperature of 225 degrees C for commercial integrated circuits (ICs) using silicon. One promise of silicon carbide (SiC) is high-temperature operation, although most commercial efforts have targeted high-voltage discrete devices. Depending on the technology choice, several processing challenges are involved in making ICs using SiC. Bipolar, metal oxide semiconductor field-effect transistors, and junction field-effect transistor technologies have been demonstrated in operating temperatures of up to 600 degrees C. Current technology performance and processing challenges relating to making ICs in SiC are reviewed in this article.

  • 123913.
    Zetterling, Carl-Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Present and Future Applications of Silicon Carbide Devices and Circuits2012In: Proceedings of the Custom Integrated Circuits Conference 2012, IEEE , 2012, p. 6330619-Conference paper (Refereed)
    Abstract [en]

    Silicon Carbide (SiC) is a wide bandgap semiconductor now reaching maturity. Discrete high-voltage SiC devices are commercially available from several suppliers for low-loss power conversion. Future applications may include integrated circuits for high-temperature and radiation-hard applications. This paper introduces SiC material properties, processing, devices, and circuits.

  • 123914.
    Zetterling, Carl-Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Process technology for silicon carbide devices2002 (ed. 1)Book (Other academic)
  • 123915.
    Zetterling, Carl-Mikael
    KTH, Superseded Departments, Electronic Systems Design.
    Silicon dioxide and aluminium nitride as gate dielectric for high temperature and high power silicon carbide MOSFETs1997Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Silicon carbide (SIC) is a wide bandgap semiconductor thathas been suggested as a replacement for silicon in applicationsusing high voltages, high frequencies, high temperatures orcombinations thereof. Several basic process steps need to bedeveloped for reliable manufacturing of long-term stableelectronic devices. One important process step is the formationof an insulator on the silicon carbide surface that may be usedas a) a gate dielectric, b) for device isolation or c) forpassivation of the surface. Silicon dioxide and aluminumnitride have been suggested for these purposes. This thesiscovers the investigation of some formation methods for boththese materials on 4H and 6H silicon carbide, and theelectrical characterisation of the resulting films.

    Commercially available n-type and p-type 4H and 6H SICwafers have been used, and both the silicon face and the carbonface have been investigated. Silicon dioxide has been formed byseveral methods: a) dry thermal oxidation with or without theaddition of TCA (trichloroethane), b) wet oxidation inpyrogenic steam or with awater bubbler, c) oxide deposition byPECVD (plasma enhanced chemical vapor deposition) or LPCVD (lowpressure chemical vapor deposition) and d) oxidation of aevaporated or LPCVD deposited sacrificial layer of silicon. Theinfluence of various cleaning methods prior to oxidation hasbeen studied, as well as post-oxidation and post-metallisationannealing. The aluminum nitride films were grown by MOCVD(metal organic chemical vapor deposition) under various processconditions.

    Oxidation kinetics have been studied for dry thermaloxidation at 1200 0C. The redistribution of aluminum (p-typedopant in SiC) during dry thermal oxidation has beeninvestigated using SIMS (secondary ion mass spectrometry). Themorphology of the aluminum nitride was determined using x-raydiffraction rocking curves, RHEED (reflection high energyelectron diffraction) and AFM (atomic force microscopy). Thequality of the silicon dioxide used as gate dielectric has beendetermined using breakdown field measurements. High frequencycapacitance-voltage measurements have been used on bothinsulators to a) verify thickness measurements made with othermethods, b) to determine fixed oxide charges by measuring theflatband voltage shifts and c) to quantitatively compare theamount of interface states.

    For electrical characterisation either aluminum, titanium ordoped polysilicon circular gate contacts of various sizes wereformed on the insulator surface. Flat MOS capacitors weremainly used for the electrical characterisation. U-grooved MOScapacitors, manufactured by RIE (reactive ion etching), wereused to test the quality of oxides grown on vertical surfaces.Two types of MOSFETs (metal oxide semiconductor field effecttransistors) have been fabricated: vertical U-grooved andlateral devices.

    Keywords:silicon carbide, thermal oxidation, silicondioxide, metal organic chemical vapor deposition (MOCVD),aluminum nitride, capacitance-voltage measurements, MOSFET.

  • 123916.
    Zetterling, Carl-Mikael
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Dahlquist, Fanny
    Lundberg, Nils
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Rottner, K.
    Ramberg, L.
    Junction barrier Schottky diodes in 6H SiC1998In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 42, no 9, p. 1757-1759Article in journal (Refereed)
    Abstract [en]

    Junction barrier Schottky (JBS) diodes in 6H SiC have been fabricated and characterised electrically. This device, demonstrated in silicon technology, has the advantage of a low forward voltage drop comparable to that of Schottky diodes, as well as a high blocking voltage and low reverse leakage current of a pn junction. This is especially attractive for wide bandgap materials such as SiC in which pn junctions have a large forward voltage drop. The devices were capable of blocking up to 1100 V with a leakage current density of 0.15 A cm-2, limited by the leakage when the drift region was fully depleted, or breakdown of the SiC material itself. The forward conduction was limited by an on-resistance of 20 mΩ cm2, resulting in forward voltage drops of 2.6 V at 100 A cm-2. © 1998 Published by Elsevier Science Ltd. All rights reserved.

  • 123917.
    Zetterling, Carl-Mikael
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Dahlquist, Fanny
    Lundberg, Nils
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Rottner, Kurt
    Ramberg, Lennart
    High voltage silicon carbide Junction Barrier Schottky rectifiers1997In: Proceedings of the IEEE Cornell Conference on Advanced Concepts in High Speed Semiconductor Devices and Circuits, Ithaca, NY, USA, 1997, no Piscataway, NJ, United States, p. 256-263Conference paper (Refereed)
    Abstract [en]

    The Junction Barrier Schottky (JBS) diode has the advantage of a low forward voltage drop comparable to that of Schottky diodes, as well as a high blocking voltage and low reverse leakage current of a pn diode. This device, originally demonstrated in silicon technology, is especially attractive for wide bandgap materials such as silicon carbide (SiC) in which pn diodes have a large forward voltage drop. Two different JBS designs in 6H SiC have been fabricated, and the electrical characteristics have been compared to Schottky and pn diodes on the same wafer. Although the ion implanted pn diodes had remaining implant damage, the JBS diodes worked well. The JBS diodes were capable of blocking up to 1100 V with a leakage current density of 0.15 A/cm2, limited by the leakage when the drift region was fully depleted, or breakdown of the SiC material itself. The forward conduction was limited by an on-resistance of 20 mΩcm2.

  • 123918.
    Zetterling, Carl-Mikael
    et al.
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Hallén, Anders
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Hedayati, Raheleh
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Kargarrazi, Saleh
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Lanni, Luigia
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Malm, B. Gunnar
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Mardani, S.
    Norström, H.
    Rusu, Ana
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Suvanam, Sethu Saveda
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Tian, Ye
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.
    Bipolar integrated circuits in SiC for extreme environment operation2017In: Semiconductor Science and Technology, ISSN 0268-1242, E-ISSN 1361-6641, Vol. 32, no 3, article id 034002Article in journal (Refereed)
    Abstract [en]

    Silicon carbide (SiC) integrated circuits have been suggested for extreme environment operation. The challenge of a new technology is to develop process flow, circuit models and circuit designs for a wide temperature range. A bipolar technology was chosen to avoid the gate dielectric weakness and low mobility drawback of SiC MOSFETs. Higher operation temperatures and better radiation hardness have been demonstrated for bipolar integrated circuits. Both digital and analog circuits have been demonstrated in the range from room temperature to 500 °C. Future steps are to demonstrate some mixed signal circuits of greater complexity. There are remaining challenges in contacting, metallization, packaging and reliability.

  • 123919.
    Zetterling, Carl-Mikael
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Koo, S. -M
    Danielsson, Erik
    Liu, W.
    Lee, S. -K
    Domeij, Martin
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Lee, H. -S
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Challenges for High Temperature Silicon Carbide Electronics2003In: Materials Research Society Symposium - Proceedings, San Francisco, CA, 2003, Vol. 764, p. 15-25Conference paper (Refereed)
    Abstract [en]

    Silicon carbide has been proposed as an excellent material for high-frequency, high-power and high-temperature electronics. High power and high frequency applications have been pursued for quite some time in SiC with a great deal of success in terms of demonstrated devices. However, self-heating problems due to the much higher power densities that result when ten times higher electrical fields are used inside the devices needs to be addressed. High-temperature electronics has not yet experienced as much attention and success, possibly because there is no immediate market. This paper will review some of the advances that have been made in high-temperature electronics using silicon carbide, starting from process technology, continuing with device design, and finishing with circuit examples. For process technology, one of the biggest obstacles is long-term stable contacts. Several device structures have been electrically characterized at high temperature (BJTs and FETs) and will be compared to surface temperature measurements and physical device simulation. Finally some proposed circuit topologies as well as novel solutions will be presented.

  • 123920.
    Zetterling, Carl-Mikael
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Lanni, Luigia
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Ghandi, Reza
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Malm, B. Gunnar
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Future high temperature applications for SiC integrated circuits2011Conference paper (Refereed)
  • 123921.
    Zetterling, Carl-Mikael
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Lanni, Luigia
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Ghandi, Reza
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Malm, B. Gunnar
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Future high temperature applications for SiC integrated circuits2012In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 9, no 7, p. 1647-1650Article in journal (Refereed)
    Abstract [en]

    The main advantage of SiC is its high critical field for breakdown. This leads to much lower on-resistance for high voltage devices compared to silicon, but at a higher price that has to be offset by system gains. However, it is not straightforward to exploit this advantage, which is clear from the many different device types that are presently being commercialized. There are other advantages of SiC yet to be fully investigated: the possibility of high temperature operating electronics and radiation hard devices. If integrated circuits in SiC are also available, the system advantage is larger. Here temperature ranges higher than that of SOI should be aimed at, and some of these new application areas will be described. An overview of IC research will be ended with a description of our selected technology operated at 300 °C.

  • 123922.
    Zetterling, Carl-Mikael
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Liu, Wei
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Thermal modeling of multi-finger SiC power MESFETs2005In: 2005 International Semiconductor Device Research Symposium, 2005, Vol. 2005, p. 290-291Conference paper (Refereed)
    Abstract [en]

    The high critical electrical field of silicon carbide makes it possible to fabricate high power SiC devices, which can handle much higher power than the traditional silicon and gallium arsenide power devices1. SiC power MESFET is one of such devices available on the market for RF applications 2. Despite the high thermal conductivity of the material, the SiC devices may suffer severe self-heating when operating at very high power levels, especially if the gate pitch is small3. The self-heating phenomena of one- and multi-fingered SiC MESFETs were studied through 2D electro-thermal simulations and 2D and 3D steady-state thermal simulations. The device performance degradation caused by self-heating was observed, and is more profound for devices operating at room temperature than for devices working at elevated temperatures. The junction temperature and temperature distribution of devices fabricated on SiC substrates were estimated through both electro-thermal simulations and steady-state thermal simulations, and the results agree well (Fig. 1). Different layouts and gate pitches were investigated to optimize the trade-off between maximum operating temperature and the longest signal path, which limits the size of high-frequency devices (Fig. 2. and 3.).

  • 123923.
    Zetterling, Carl-Mikael
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Wongchotigul, K.
    Spencer, M. G.
    Harris, C. I.
    Wong, S. S.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Formation and high frequency CV-measurements of aluminum/aluminum nitride/6H silicon carbide structures1996In: Materials Research Society Symposium - Proceedings, San Francisco, CA, USA, 1996, Vol. 423, no Pittsburgh, PA, United States, p. 667-672Conference paper (Refereed)
    Abstract [en]

    Undoped single crystalline aluminum nitride films were grown by metal organic chemical vapor deposition (MOCVD) at 1200 °C. The precursors used were trimethylaluminum (TMA) and ammonia (NH3) in a hydrogen carrier flow, at a pressure of 10 Torr. Silicon carbide substrates of the 4H or the 6H polytype with an epilayer on the silicon face, were used to grow the 200 nm thick AlN films. Aluminum was evaporated and subsequently patterned to form MIS capacitors for high frequency (400 kHz) capacitance voltage measurements at room temperature. It was possible to measure the structure and characterize accumulation, depletion and deep depletion. However, it was not possible to invert the low doped SiC epilayer at room temperature. From an independent optical thickness measurement the relative dielectric constant of aluminum nitride was calculated to be 8.4. The films were stressed up to 50 Volts (2.5 MV/cm) without breakdown or excessive leakage currents. These results indicate the possibility to replace silicon dioxide with aluminum nitride in SiC field effect transistors.

  • 123924.
    Zetterling, Carl-Mikael
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    A novel UMOS capacitor test structure for SiC devices1996In: Solid-State Electronics, ISSN 0038-1101, E-ISSN 1879-2405, Vol. 39, no 9, p. 1396-1397Article in journal (Refereed)
    Abstract [en]

    In this paper we propose the use of U-grooved MOS capacitors to investigate oxides intended for U-grooved MOSFETs and IGBTs in silicon carbide. The UMOS capacitor uses only two mask layers, and has vertically etched walls and a gate contact that overlaps the step. We have manufactured UMOS capacitors in n-type 6H SiC with dry thermal gate oxides, and compared the capacitance voltage characteristics to those of flat reference capacitors. It was found that the general appearance of capacitance-voltage curves was unchanged by the addition of the vertical grooves, although the leakage through the oxide was increased. The oxide thickness on the sidewalls was approximately the same as on the flat parts of the devices. Copyright © 1996 Elsevier Science Ltd.

  • 123925.
    Zetterling, Carl-Mikael
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Comparison of thermal gate oxides on silicon and carbon face p-type 6H silicon carbide1994In: Materials Research Society Symposium - Proceedings, San Francisco, CA, USA, 1994, Vol. 339, no Pittsburgh, PA, United States, p. 209-214Conference paper (Refereed)
    Abstract [en]

    Monocrystalline 6H silicon carbide samples (n-type and p-type) with both carbon face and silicon face have been used to investigate gate oxide quality. The oxides were thermally grown in a dry oxygen ambient at 1523 K with or without the addition of TCA (Trichloroethane), or in wet pyrogenic steam at 1473 K. POCl3 doped polysilicon gates were used for electrical characterisation by capacitance-voltage measurements and breakdown field measurements. Large flatband voltage shifts indicate fixed oxide charges up to 1013 cm-2. The incorporation of aluminum in the oxides was monitored using SIMS (Secondary Ion Mass Spectrometry). Surprisingly high signals were interpreted as evidence of an aluminum-oxygen compound having been formed (ie Al2O3).

  • 123926.
    Zetterling, Carl-Mikael
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Electrical Properties of Thin Oxides for MOSFETs in the Poly-Si / SiO2 / 6H Silicon Carbide System1993In: Solid State Device Research Conference, 1993. ESSDERC ’93. 23rd European, 1993, p. 497-500Conference paper (Refereed)
    Abstract [en]

    This paper describes the fabrication of polysilicon / SiO2 / 6H silicon carbide structures with four different types of thin gate oxides. Wet and dry thermal oxidation, plasma-enhanced chemical vapor deposition (PECVD), and also an alternative method, oxidation of e-beam evaporated silicon, have been investigated. The four oxides were compared using capacitance-voltage measurements and breakdown field measurements. Breakdown fields exceeded 8 MV/cm for the thermal oxides, which is higher than previously published values.

  • 123927.
    Zetterling, Carl-Mikael
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Thermal oxidation of n- and p-type 6H-silicon carbide1994In: Physica scripta. T, ISSN 0281-1847, Vol. T54, p. 291-294Article in journal (Refereed)
  • 123928.
    Zetterling, Carl-Mikael
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Domeij, Martin
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Lee, H.-S.
    Silicon Carbide Power Device Technology2006Conference paper (Refereed)
  • 123929.
    Zetterling, Carl-Mikael
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Harris, C. I.
    Nordell, N.
    Wongchotigul, K.
    Spencer, M. G.
    Comparison of SiO2 and AlN as gate dielectric for SiC MOS structures1998In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 264-268, p. 877-880Article in journal (Refereed)
    Abstract [en]

    The electrical properties of silicon dioxide (thermal oxidation) and aluminum nitride (metal organic chemical vapor deposition) have been compared for use as gate dielectric for silicon carbide metal insulator semiconductor structures. High frequency capacitance voltage measurements at room temperature were used to investigate fixed charge and deep interface states. The deep interface states could be passivated with hydrogen if introduced during growth of silicon dioxide. Although results are promising for aluminum nitride, the morphology of the films grown so far do not allow a fair comparison with silicon dioxide.

  • 123930.
    Zetterling, Carl-Mikael
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Harris, C. I.
    Wood, P. C.
    Wong, S. S.
    UV-ozone precleaning and forming gas annealing applied to wet thermal oxidation of p-type silicon carbide1999In: Materials Science in Semiconductor Processing, ISSN 1369-8001, E-ISSN 1873-4081, Vol. 2, no 1, p. 23-27Article in journal (Refereed)
    Abstract [en]

    MOS capacitors using wet thermal oxidation of p-type 4H and 6H silicon carbide have been investigated using capacitance-voltage (CV) measurements. The interface state density was determined from displacements in the CV curves at room temperature after optical generation of carriers. Forming gas annealing at 400 °C after metallization was found to reduce the amount of deep interface states, and in combination with UV-ozone precleaning of the SiC substrates in a commercial system, the fixed oxide charge was also reduced.

  • 123931.
    Zetterling, Carl-Mikael
    et al.
    KTH, Superseded Departments, Electronics.
    Östling, Mikael
    KTH, Superseded Departments, Electronics.
    Nordell, Nils
    Schön, Oliver
    Deschler, Marc
    Influence of growth conditions on electrical characteristics of AlN on SiC1997In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 70, no 26, p. 3549-3551Article in journal (Refereed)
    Abstract [en]

    Undoped aluminum nitride films were grown on 4H or 6H silicon carbide substrates, using metalorganic chemical-vapor deposition at 1150°C. Different growth conditions were used, and two different V/III ratios were tested. Metal-insulator-semiconductor capacitors were made for high-frequency capacitance-voltage measurements at room temperature, from which the film thickness was determined. Accumulation, depletion, deep depletion, and inversion were seen for the best films, which also displayed peaks in x-ray diffraction rocking curves. Although large flatband voltage shifts occurred, indicating a fixed charge and interface trap problem, low conductance was observed. A flow of ammonia during ramp-up was found to improve the AlN films.

  • 123932.
    Zetterling, Carl-Mikael
    et al.
    KTH, Superseded Departments, Electronics.
    Östling, Mikael
    KTH, Superseded Departments, Electronics.
    Wongchotigul, K.
    Spencer, M. G.
    Tang, X.
    Harris, C. I.
    Nordell, N.
    Wong, S. S.
    Investigation of aluminum nitride grown by metal-organic chemical-vapor deposition on silicon carbide1997In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 82, no 6, p. 2990-2995Article in journal (Refereed)
    Abstract [en]

    Undoped single crystalline aluminum nitride films were grown on 4H and 6H SiC substrates using metal-organic chemical-vapor deposition at 1200°C. From in situ reflection high-energy electron diffraction, x-ray diffraction rocking curves, and cathodoluminescence spectra, the crystallinity of the films was confirmed. Atomic force microscopy showed that some films were substantially dominated by island growth, rather than step flow growth. Aluminum was evaporated to form metal-insulator-semiconductor (MIS) capacitors for high-frequency capacitance voltage measurements carried out at room temperature. Low leakage made it possible to measure the structures and characterize accumulation, depletion, deep depletion, and, in some cases, inversion. From independent optical thickness measurements, the relative dielectric constant of aluminum nitride was confirmed at 8.4. The flatband voltage of the AlN MIS capacitors on p-type SiC was close to the theoretical value expected. The films were stressed up to 60 V (3 MV/cm) without breakdown, but excessive leakage currents (>0.1 A/cm2), probably dominated by grain-boundary conduction, shifted the flatband voltage of the capacitors. These results indicate the possibility of replacing silicon dioxide with aluminum nitride in SiC field effect transistors using insulated gates.

  • 123933.
    Zetterling, Carl-Mikael
    et al.
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Östling, Mikael
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Yano, H.
    Kimoto, T.
    Matsunami, H.
    Linthicum, K.
    Davis, R. F.
    SiC MISFETs with MBE-grown AlN gate dielectric2000In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 338-342, p. 1315-1318Article in journal (Refereed)
    Abstract [en]

    Metal-Insulator-Semiconductor Field Effect Transistors (MISFETs) with ion implanted source and drain junctions have been made in 6H silicon carbide (SiC). Aluminum nitride (AlN) was used as the insulating gate dielectric, and was grown using molecular beam epitaxy (MBE). Gate controlled transistor operation was shown with an inversion layer mobility of 10-20 cm2/Vs. However, due to relaxation of the AlN film, the gate leakage was excessive, which precluded a thorough investigation of the transistor characteristics. This paper describes the manufacturing process and current voltage characteristics, and an improved process sequence is also proposed.

  • 123934.
    Zetterling, Fredrik
    KTH, Superseded Departments, Numerical Analysis and Computer Science, NADA.
    Phase Transformations in Computer Simulated Icosahedrally Ordered Phases2003Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Computer simulations play a profound and fundamental role inmodern theoretical physics, chemistry and materials science. Tounderstand the complex physics of metally liquids, metals,quasicrystals and metally glasses a working model imposing thelocal and global order is needed. Experiments and theory havepredicted the local order in liquid metals to beicosahedral.

    The current work has been done using molecular dynamicscomputer simulations of a monatomic system using a simplepair-potential for the interactions. Two new pair-potentialshas been developed, the Zetterling-1(Z1) and Zetterling-2(Z2)potentials. They are specifically modeled to impose icosahedralorder. The basis for the development of the potentials was theold Dzugutov potential which is known to freeze into adodecagonal quasicrystal. The new Zetterling potentials have alonger interaction range and a narrower first minimum. The morenarrow first minimum will enhance the local icosahedralordering and the longer interaction range was introduced toincorporate a second maximum in the potential mimicing theFriedel oscillations found in metallic systems. These Friedeloscillations are due to the singularity which arises at theFermi surface due to the screening of the positive charge bythe electron gas.

    Five papers are included in the study. The first two papersare studies of icosahedral clustering in the liquid andsupercooled liquid. The simulations in Paper I was done usingthe old Dzugutov potential while the new potentials were usedin Paper II using both molecular dynamics and the Basin Hoppingalgorithm presented in Chapter 5. Paper III considers theconcept of dynamical ergodicity in the context of thesuper-cooled liquid behaviour. The simulations were made usingthe old Dzugutov potential. Paper IVr eports a moleculardynamics simulation using the Dzugutov potential undersuper-cooling. A formation of icosahedrally structured domainswith distinctly slow diffusion which grows with cooling in alow-dimensional manner and percolate around Tc, the criticaltemperature of the mode-coupling theory. A sharp slowing downof the structural relaxation relative to diffusion is observed.It is concluded that this effect cannot be accounted for by thespatial variation in atomic mobility. The low-dimensionalclustering is discussed as a possible mechanism of fragility.Paper Vin vestigates the crystallization of a simple monatomicliquid model which utilizes the Zetterling-1 potential. Thesystem forms a thermodynamically stable solid phase exhibitingcubic symmetry. Its diffraction pattern is identified as thatof γ-brass, a tetrahedrally packed crystalline structurewith 52 atoms in the unit cell.

    Keywords:simple liquids, molecular dynamics, pairpotential, icosahedral cluster.

  • 123935.
    Zetterlund, Hanna
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Urban and Regional Studies.
    Rätten att gå till kungs: En genealogisk studie av besvärsrättens funktion och framtid i stadsplaneringens Sverige2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The primary aim of this paper is to broaden the perspective on third party rights of appeal in Swedish municipal planning and to study the underlying ideals that have formed the legislation in the Planning and Building Act. Currently the legislation is undergoing several changes and with the present housing crises in several Swedish cities the pressure to streamline the process is hard. Third party rights of appeals are viewed upon as time consuming obstacles, which both hinders the expansion in housing and economic growth. Several propositions on how to improve the legislation have been evaluated over the years, the most important proposal being the removal of the county administration board as the first of three instances for planning appeals. The research questions seeks to address the overall aim by using a genealogical lens to study the history of the right to appeal municipal development plans, and compare this to the parallel debate on the subject as well as the contemporary discussion. The bulk of material has been gathered through interviews with experts connected to the subject, and the study of official governmental investigations as well as newspaper articles. The theoretical part about planning ideals draws heavily on the work of Geriant Ellis on Ireland and his critics of the economic interests that form the debate there. The conclusions gathered from the study paints an image that differs from the one presented in the media of increasing problems with the Swedish appealing system. Instead it questions the proposed changes and their possible effect on the principals on legal security, citizen participation and democracy in the planning process. The percentage of appeald plans has been relatively consistent throughout the years since around the millenium, regardless of political majority, changes in legislation or economic fluctuations. The most noticable change, but surprisingly the least discussed; is the shift from appeals belonging to the political sphere of representative democracy, to the judicial sphere. This change has not been followed by any ideological discussions, and seemingly came out of necessity due to bureaucracy and the European convention. This change however, has not been communicated to the public; leading to that credence to the system as such has been left deminished. Swedish planning is at its core a political and value loaded issue, therefore making it a question of right or wrong by changing the system of appeal to a question of pure judicial nature should have raised a bigger ideological discussion. Especially before changing the system again towards being even more law oriented

  • 123936.
    Zetterlund, Katrin
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Naruszewicz, Adam
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Tillämpning av nya beräkningsmetoder för branddimensionering av  träkonstruktioner - analyser och jämförelser2010Independent thesis Advanced level (professional degree), 30 credits / 45 HE creditsStudent thesis
    Abstract [en]

    To build high-rise buildings made of timber has for long been limited by national laws, due to the lack of knowledge in engineering solutions. Frame structures made of wood has for a long time been associated with major fire hazards and consequently lower safety and this connection is still being made today. The increased environmental awareness in recent years has contributed to the exploitation of indigenous building materials, including wood from our own Swedish forests and has become increasingly common. Increased knowledge about how structures behave in fire and how they can be protected in order to achieve safe timber structures has resulted in a growing interest in these structures in the construction industry. Research in the area is constantly updated and new laws allow any number of storeys in wooden buildings in Sweden as long as the performance requirements are fulfilled.

    The main part of this work has involved calculations of the fire resistance and load bearing capacity of floor and wall constructions. The calculations are based on different models, both old and new. There are many alternative ways to handle the problems. The report presents three different approaches that have been generalized into three calculation methods. The names used here for the methods are the same as the two manuals: Brandsäkra trähus version 2 and Fire Safety In Timber Buildings, as well as the standard Eurocode 5, where a detailed description of the methods of calculation are introduced.

    This work has resulted in a number of updated tables in order to exemplify the fire resistance and load bearing capacity during fire for selected timber structures according to the latest calculation methods. In addition, values of bearing capacity for cross-laminated structures are included. The tables are grouped according to type of construction, namely, walls and floors.  A selection of relevant structures of varying claddings can be found in the tables, including single gypsum plasterboard, double plasterboard and gypsum plasterboard with plywood behind that protect underlying wood studs. Tables of cross-laminated elements are presented separately. Cross laminated structures are composed of 3, 5 or 7 layers of timber and can be either unprotected or protected with a single gypsum board. The thickness of the load bearing and non-bearing layers has also been varied in different ways in order to investigate how the bearing capacity is affected. Finally obtained values are discussed and compared.

     

  • 123937.
    Zetterlund, Nils
    et al.
    KTH, Superseded Departments, Physics.
    Lindblad, Thomas
    KTH, Superseded Departments, Physics.
    Ekblad, Ulf
    KTH, Superseded Departments, Physics.
    The minimum risk angle for automatic target recognition using the intersecting cortical model2004In: Proc. Seventh Int. Conf. Inf. Fusion, 2004, p. 1014-1021Conference paper (Refereed)
    Abstract [en]

    While kids easily find 3-D objects like animals in a scene (e.g. a photograph), this is still not the case for algorithms running on von Neumann computers or neural network chips. The present investigation has two goals: Finding "signatures" of the object in the scene and trying to find out at which observation angle the chance of correct identification is the best. By signatures we mean a vector of reasonable size (say 50 elements). Clearly a cow looks different from the back or from the side. A car is probably more easily identified viewed from the front than it is from above. For a plane it may be the other way around. Thus if we define a general but compact "signature" of the object, it will surely depend on the viewing angle. The problem of finding the most optimal viewing angle is dealt with in this paper.

  • 123938.
    Zetterman, Joachim
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Health Informatics and Logistics.
    Prediktiv simulation: En undersökning om möjligheten att minskaslöseri vid ett industriföretag med hjälp av digitala simuleringar2018Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The industrial company Scania CV AB is a world leader in the manufacturing of commercial vehicles. They offer a modular systems that include heavy trucks and buses that can be configured to a range of different needs. However, this adaptability leads to a problem where each order can have a large variance of assemblers that are re-quired during the manufacturing process. In other words, variant assemblers have a workflow that can shift from high workload to low workload and vice versa in a short period of time. To solve this problem a prototype will be developed. This prototype will be used to check if it’s possible to optimize the work schedule for variant assem-blers with the help of predictive simulations.

    The result of the study became an implementation in form of a prototype. This prototype is built up in two layers; a data layer and a simulation layer. The data layer provides the simulation layer with two different datasets. The first dataset is based on historical data and is derived from Scania’s production in Zwolle. The second dataset is based on synthetic data which is formed with a high utilization rate in order to mimic a better production situation with less product variants to assemble. The simulation layer consists of a DES-model that is modelled after a station in the final assembly of Zwolle. After a simulation has been executed, this layer generates a simulation result in form of a graph that presents the utilization rate for a group of variant assemblers. This will happened for each dataset in the data layer, in this case two times. The simulation result that got produced shows that it’s possible to create a simulation with predictive characteristics. A long term solution for Scania’s problem statement requires more research within the possibility of combining different technologies such as DES with predictive methods such as ML and GAs.

  • 123939.
    Zetterquist, Martin
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Effektmätning i pump2011Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The interest for power and energy measurement has greatly raised with todays increasing electricity prices and enviromental awareness. In the search for energy efficient solutions, the measurements are more complex due to increasing of non linear components. Harmonics and non sinusoidal voltages put high demands on sampling and filtering. Meanwhile, the price must be controlled so the customer still will find it interesting to invest in smaller plants. ITT W&WW asks for a robust, heat resistant power meter with compact dimensions to allow mounting inside the casing of a pump. It should be able to measure the power, both from a regular power supply and fed from a VFD. The accuracy needs not to be on reference level, but the price/performance-ratio is an important parameter. Synchronous sample is tested, but is not considered suitable. Several test kits designed for 50 Hz AC, turn out to also measure VFD feed loads with good accuracy.

  • 123940.
    Zetterqvist, Robert
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Fault localization in IP-based communication infrastructure: Improving network information systems through active equipment integration2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 123941.
    Zettersten, Theodor
    KTH, School of Information and Communication Technology (ICT).
    Parallel Architecture for Real-Time Video Games2010Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    As the number CPU cores increases, game-developers struggle to extract as much performance as possible from the underlying hardware. Aside from difficulties in designing software for concurrency, the extensive use of middleware further limits the opportunity for parallelization. Over recent years, several customized parallel solutions for real-time game applications have been developed, threading specific functionality, but a more generic solution is necessary for the future.

    The purpose of this project is to design, implement and evaluate an architecture for parallelizing real-time gaming and simulation software. The focus is on scheduling and state-management components that enables transparent performance scalability, for an N-core machine, while suiting a traditional game-framework

    A generic design is proposed which allows a game-framework to be configured for several scheduling strategies, depending on the specific application’s requirements. A standard has been created which, synchronously or asynchronously, executes wrapped units of work, tasks, in iterative cycles.

     Furthermore, a centralized state manager has been developed, tailored for a distributed component-based entity-system, supporting two major synchronization strategies: either deferring state-change notifications to an exclusive propagation point, or immediately propagating state-changes with locks to guarantee thread-safety.

    To evaluate the proposed architecture a demo application has been developed to run a flocking behavior simulation with typical game-related functional blocks such as: rendering, physics, AI, input handling etc. The demo achieves scalable performance benefits through exploiting dataparallelism and dynamically batching entity-processing to maintain an appropriate taskgranularity. A comparison between the two major synchronization strategies revealed a marginal performance benefit when deferring state-change notifications and supporting exclusive propagation.

  • 123942.
    Zetterström, Jeanette
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Design Methodology for Protective Structures of Glass Fibre Reinforced Plastic Exposedto Trawling2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Complex subsea oil and gas components installed on the seabed require protective structures,traditionally made of steel or glass fibre reinforced plastic – GRP. The most critical load case is trawlfishing, where trawl weights of several tons are dragged along the seabed.This master thesis work aims to develop a design methodology for such protective GRP covers and is acontinuation of the master theses work performed by REINERTSEN Jonas Elgered and Marco Nikolic in2011.The trawl load case, which is suitable for a dynamic analysis since much energy is transferred over ashort period of time, is modelled with LS DYNA, using one model built up with shell elements and onewith thick shell elements.The idea is for the methodology to work as a tool for evaluating lamina thicknesses and layups for earlycover-geometry designs.

  • 123943.
    Zeuner, Katharina D.
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Paul, Matthias
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Lettner, Thomas
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Reuterskiold Hedlund, Carl
    KTH, School of Electrical Engineering and Computer Science (EECS), Electronics.
    Schweickert, Lucas
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Steinhauer, Stephan
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Yang, Lily
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Zichi, Julien
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Hammar, Mattias
    KTH, School of Electrical Engineering and Computer Science (EECS), Electronics.
    Jöns, Klaus D.
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Zwiller, Val
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    A stable wavelength-tunable triggered source of single photons and cascaded photon pairs at the telecom C-band2018In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 112, no 17, article id 173102Article in journal (Refereed)
    Abstract [en]

    The implementation of fiber-based long-range quantum communication requires tunable sources of single photons at the telecom C-band. Stable and easy-to-implement wavelength-tunability of individual sources is crucial to (i) bring remote sources into resonance, (ii) define a wavelength standard, and (iii) ensure scalability to operate a quantum repeater. So far, the most promising sources for true, telecom single photons are semiconductor quantum dots, due to their ability to deterministically and reliably emit single and entangled photons. However, the required wavelength-tunability is hard to attain. Here, we show a stable wavelength-tunable quantum light source by integrating strain-released InAs quantum dots on piezoelectric substrates. We present triggered single-photon emission at 1.55 mu m with a multi-photon emission probability as low as 0.097, as well as photon pair emission from the radiative biexciton-exciton cascade. We achieve a tuning range of 0.25 nm which will allow us to spectrally overlap remote quantum dots or tuning distant quantum dots into resonance with quantum memories. This opens up realistic avenues for the implementation of photonic quantum information processing applications at telecom wavelengths. 

  • 123944. Zevenbergen, J.
    et al.
    Ferlan, M.
    Mattsson, Hans-Åke
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Pre-emption rights compared: Netherlands, Slovenia and Sweden2008In: Real Property Transactions. Procedures, Transaction Costs and Models, Delft University Press, 2008, p. 261-279Chapter in book (Other academic)
  • 123945. Zevenhoven, R.
    et al.
    Mukherjee, A. B.
    Bhattahcharya, Prosun
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630).
    Arsenic Flows in the Environment of the European Union: A Synoptic Review2007In: Arsenic in Soil and Groundwater Environment: Biogeochemical Interactions, Health Effects and Remediation, Trace Metals and other Contaminants in the Environment, Elsevier, 2007, p. 527-547Chapter in book (Refereed)
    Abstract [en]

    During the last two decades, a number of studies were made directed towards the problem of As in groundwater, the mechanisms by which As is released from natural sources and its toxic effects on humans, animals and terrestrial plants in developing countries. There has been negligible focus on As in waste and other materials in modern industrial societies. This work evaluates materials containing As, waste from those and their flows in the European Union (EU-15 states), based on the data available since the 1990s. Due to its high toxicity, the recovery of As in metallurgical industries has been sharply reduced in recent years, although two facilities continue with the production of arsenic trioxide in the EU-15. The uses of As are documented for the glass industry, in wood preservation, in photochemical devices and many other applications. Atmospheric emission of As has decreased substantially since the mid-1990s. But still, coal combustion and metallurgical industry are the main sources of atmospheric emission of As in the EU-15. Arsenic is also an intrinsic part of fly ashes, copper-chromium-arsenic (CCA)-impregnated wood products and sewage sludges. The generation of waste within the EU-15 is enormous and As concentrations vary from 1.8 to 10 mg/kg. This indicates that through waste, 31-88 t of As are disposed off in landfills annually. The leaching of As from landfills has been observed in EU-15 states. Automotive shredder residue contains 20-25 mg/kg As and its disposal in landfills contributes 4-6 t/year As to the EU-15 soils.

  • 123946. Zevenhoven-Onderwater, M.
    et al.
    Backman, R.
    Skrifvars, B. J.
    Hupa, M.
    Liliedahl, Truls
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Rosén, Christer
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Sjöström, Krister
    KTH, Superseded Departments, Chemical Engineering and Technology.
    Engvall, Klas
    Hallgren, A.
    The ash chemistry in fluidised bed gasification of biomass fuels. Part II: Ash behaviour prediction versus bench scale agglomeration tests2001In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 80, no 10, p. 1503-1512Article in journal (Refereed)
    Abstract [en]

    This paper is part II in a series of two. Ash behaviour modelling of the gasification of four biomass fuels is compared with pilot-scale experiments carried out in a pressurised fluidised bed gasifier at the Royal Institute of Technology (KTH) and an atmospheric test rig of Termiska Processer AB (TPS). Experiments were provocative with respect to agglomeration of the bed material. Thus, in the experiments, the agglomeration was allowed to happen without any corrective changes in the operation. Small-scale experiments showed clear defluidisation in five cases. Some degree of bed disturbance or agglomeration occurred in seven out of 13 cases. In nine of these cases, agglomerates were also found in the samples analysed with SEM/EDX analyses. In six out of 13 cases, the thermodynamic multi-phase multi-component equilibrium calculations were in agreement with SEM/EDX analysis, i.e. predicted fort-nation of agglomerates. In two cases, no or small amounts of agglomerates were predicted, nor were these found with SEM/EDX analysis. In two cases out of 13, the modelling predicted some degree of agglomeration while no agglomerates could be detected with SEM/EDX analysis. However, in these cases, agglomerates were found in the pilot-scale experiments. Thus it is shown that the thermodynamic multi-phase multi-component equilibrium calculations are a useful prediction tool for the formation of agglomerates in (pressurised) fluidised bed gasification of biomass fuels thereby enhancing the understanding of the chemistry involved.

  • 123947. Zevenhoven-Onderwater, Maria
    et al.
    Backman, Rainer
    Skrifvars, Bengt-Johan
    Hupa, Miko
    Liliendahl, Truls
    Rosén, Christer
    Sjöström, Krister
    Engvall, Klas
    KTH, Superseded Departments (pre-2005), Chemical Engineering and Technology.
    Hallgren, Anders
    KTH, Superseded Departments (pre-2005), Chemical Engineering and Technology.
    The ash chemistry in fluidised bed gasification of biomass fuels. Part I: Predicting the chemistry of melting ashes and ash-bed material interaction2001In: Fuel, ISSN 0016-2361, E-ISSN 1873-7153, Vol. 80, no 10, p. 1489-1502Article in journal (Refereed)
    Abstract [en]

    This paper is part I in a series of two describing the modelling of the ash-chemistry of seven biomass fuels under reducing, pressurised conditions in fluidised bed gasification by means of thermodynamic multi-phase multi-component equilibrium (TPCE) calculations. The fuels considered were Salix, a Scandinavian forest residue, Miscanthus, Reed Canary Grass, Eucalyptus, Arundo Donax and Lucerne. The composition and amount of phases have been calculated for the gasification of the fuel as such and in presence of an excess amount of calcite, dolomite, magnesium olivine sand and sand by using TPCE calculations in a temperature interval of 600-900°C and a pressure of 10 bar. It was found that interaction of inorganic compounds released from the fuels with bed material is a prerequisite for the formation of bed agglomerates. The presence of an excess of dolomite decreased the amount of alkali components in the bed, thereby increasing the amount of alkali components volatilised. A silica bed, however, binds most alkali released from the fuel, retaining it in the bed as low melting alkali silicates. The chances of experiencing operating problems due to bed agglomeration may increase hereby significantly. Calculations at atmospheric pressure show that the amounts of melt present will be smaller when compared to pressurised conditions, thereby decreasing the chances of bed agglomeration. In a pressurised gasifier using calcite or dolomite as bed material a small amount of an alkali carbonate rich melt can be expected at temperatures above 620°C with each of the seven biomass fuels fired. In silica-rich cases such as when firing Miscanthus, Reed Canary Grass, Arundo Donax or using a Si-rich bed material a melt can be expected at temperatures above 770°C. The amount of melt is rather high, i.e. 12-100% of the original ash formed. In the case of a magnesium olivine sand bed an alkali melt can be expected at 620°C. At temperatures above 800°C, a silicate melt can form as well. The amount of melt was hi gh, i.e. 60-300% of the original ash formed, showing a significant contribution of the bed material.

  • 123948. Zewde, Mesfin
     Transactifying a Computer Game2009Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    One of the latest concurrent programming technologies is Software Transactional Memory (STM). This degree project studied the use of STM by taking the large open-source computer game Globulation2 and modifying it from a non-concurrent version to several concurrent versions – a lock-based version and a STM version with finer granularity, as well as an additional STM version with coarser granularity. The different game versions were to be compiled with a STM compiler, which resulted in an evaluation of existing STM compilers. The first choice LLVM and Tanger turned out to be unable to compile the game versions because Tanger lacked an irrevocable mode and support for exceptions inside transactions as well as basic C++ support needed by the game, including memory operators new and delete and the C++ STL. Together with an instability that was detected while using the LLVM compiler and Tanger, LLVM and Tanger were finally considered too unstable to use as the STM compiler for this project. Instead the Intel C++ STM compiler was chosen as the STM compiler for the project, and could successfully be used to compile the different game versions.

    Performance data from the game versions was gathered by timing different parts of the code, including the simulation part of the game’s main loop where most of the game computation is done. Using the collected data a comparison of the game versions’ performance and how well they scaled when increasing the number of threads was made. The results showed that the STM versions of the game performed worse than the lock-based version and did not scale well when the number of threads was increased. The coarser-grained STM version did however have better performance and scaled better than the finer-grained STM version. Switches to irrevocable mode, transaction overhead and to some extent transaction retries were identified as possible reasons for the bad performance and scaling of the STM version. An attempt was also made to use an experimental version of the Intel C++ STM compiler that integrated the SwissTM STM library, but it was not ready to use, and SwissTM could not be used or evaluated in this project.

  • 123949.
    Zguns, Pjotrs A.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Department of Physics and Astronomy, Uppsala University, Box 516, 75121 Uppsala, Sweden .
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Materials Center Leoben Forschung GmbH, A-8700 Leoben, Austria.
    Skorodumova, Natalia
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Department of Physics and Astronomy, Uppsala University, Box 516, 75121 Uppsala, Sweden .
    Ordering and phase separation in Gd-doped ceria: a combined DFT, cluster expansion and Monte Carlo study2017In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 19, no 39, p. 26606-26620Article in journal (Refereed)
    Abstract [en]

    Ordering of dopants and oxygen vacancies is studied for Gd-doped ceria (x(Gd) <= 0.25) by means of a combined density functional theory (DFT) and cluster expansion approach, where the cluster interactions derived from DFT calculations are further used in Monte Carlo simulations. The methodology is meticulously tested and the stability of the obtained solutions with respect to the volume change, applied exchange-correlation approximation and other modelling parameters is carefully analysed. We study Gd and vacancy ordering in the case of thermodynamic equilibrium and vacancy ordering for quenched Gd configurations. We find that at the thermodynamic equilibrium there exists a transition temperature (T-C) below which phase separation into C-type Gd2O3 and pure CeO2 occurs. The phase separation is observed in the whole studied concentration range and the transition temperature increases with concentration from ca. 600 (x(Gd) = 0.03) to 1000 K (x(Gd) = 0.25). Above T-C the distribution of Gd is random, oxygen vacancies tend to cluster in the coordination shells along < 1, 1/2, 0 > and < 1, 1, 1 >, and the nearest neighbour position is preferred for Gd-vacancy. In the quenched Gd case, where Gd atoms are immobilised below 1500 K, the vacancy ordering is significantly frustrated. In fact, we observe an oxygen freezing transition below temperature T-F approximate to T-C - 350 K, which is close to temperatures at which a change in the conductivity slope is observed experimentally.

  • 123950.
    Zguns, Pjotrs A.
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala Univ, Dept Phys & Astron, Box 516, S-75121 Uppsala, Sweden.
    Ruban, Andrei V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Leoben Forsch GmbH, Mat Ctr, A-8700 Leoben, Austria..
    Skorodumova, Natalia V.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Uppsala Univ, Dept Phys & Astron, Box 516, S-75121 Uppsala, Sweden.
    Phase diagram and oxygen-vacancy ordering in the CeO2-Gd2O3 system: a theoretical study2018In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 17, p. 11805-11818Article in journal (Refereed)
    Abstract [en]

    We present the phase diagram of Ce1-xGdxO2-x/2 (CGO), calculated by means of a combined Density Functional Theory (DFT), cluster expansion and lattice Monte Carlo approach. We show that this methodology gives reliable results for the whole range of concentrations (x x(Gd) <= 1). In the thermodynamic equilibrium, we observe two transitions: the onset of oxygen-vacancy (O-Va) ordering at ca. 1200-3300 K for concentrations x(Gd) = 0.3-1, and a phase separation into CeO2 and C-type Gd2O3 occurring below ca. 1000 K for all concentrations. We also model 'quenched' systems, with cations immobile below 1500 K, and observe that the presence of random-like cation configurations does not prevent C-type vacancy ordering. The obtained transition temperatures for Va ordering agree rather well with existing experimental data. We analyse the effect of vacancy ordering and composition on the lattice parameters and relaxation pattern of cations.

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