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  • 126601.
    Zika-Wiktorsson, Annika
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Sundström, Per
    KTH, School of Technology and Health (STH).
    Engwall, Mats
    VINNOVA, Swedish Governmental Agency for Innovation Systems.
    Project Overload: An Exploratory Study of Work and Management in Multi-Project Settings2006In: International Journal of Project Management, ISSN 0263-7863, E-ISSN 1873-4634, Vol. 24, no 5, p. 385-394Article in journal (Refereed)
    Abstract [en]

    This study investigates psychosocial aspects of work in multi-project settings and how project members and project managers at operational level perceive their work situation. Work in a multi-project setting entails a complicated situation characterized by tight schedules, multi-tasking, increased coordination expenditures, and a large amount of set-up time when alternating between tasks. The study addresses the issue of project overload, a construct that in this study reflects perceived fragmentation, disruption and inefficiency, caused by switching between assignments for separate but simultaneous projects. An explorative approach was adopted for the study, and new models were created and investigated. The primary source of data was a web-based questionnaire. The questionnaire was administered to project co-workers (n = 392) in nine companies in Sweden (response rate: 81%). The companies represented manufacturing, pharmaceutical and construction industries, and all occupied a leading position on their respective markets. The results show that almost one-third of the respondents were under perceived project overload, and that 21% (p ≤ .001) of the variance on this variable could be explained by four factors. In order of magnitude, these factors were: (1) lack of opportunities for recuperation, (2) inadequate routines, (3) scarce time resources, and (4) a large number of simultaneous projects. Further, the study indicated that there are associations between high level of project overload and (a) high levels of psychological stress reactions, (b) decreased competence development, and (c) deviations from time schedules.

  • 126602.
    Zikeli, Florian
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. Technische Universität Wien, Austria.
    Ters, T.
    Fackler, K.
    Srebotnik, E.
    Li, Jiebing
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wheat straw lignin fractionation and characterization as lignin-carbohydrate complexes2016In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 85, p. 309-317Article in journal (Refereed)
    Abstract [en]

    Alkaline extracted and untreated wheat straw were ball-milled with liquid nitrogen cooling rendering them completely soluble in the solvent system dimethylsulfoxide-aqueous tetrabutylammonium hydroxide for subsequent fractionation into two lignin-carbohydrate complex fractions termed glucan-lignin and xylan-lignin according to their preferred association with glucan or arabinoxylan, respectively. This is the first description using this fractionation protocol for wheat straw. Eventually, acidolysis lignins were prepared from both lignin-carbohydrate complexes and structurally characterized using wet chemistry and NMR spectroscopy methods. Using the novel procedure we could reveal differences regarding wheat straw lignin association with polysaccharides, p-hydroxycinnamic acids and tricin as well as in their monomer composition. In glucan-lignin the lignin moiety was found to be linked mainly to glucan but also to branched arabinoxylan. Xylan-lignin, however, was rich in structures creating cross-links between lignin and linear arabinoxylan via ether-ester bridges by bi-functional ferulic acid. Inter-molecular ether-ester-linkages by ferulic acid connecting the lignin moieties of the two LCC fractions glucan-lignin and xylan-lignin were proposed. Alkaline extraction of the straw resulted in a strikingly lower recovery of xylan-lignin in the subsequent fractionation which was attributed to cleavage of ester linkages between ferulic acid and arabinoxylan. Structural characteristics indicated glucan-lignin and xylan-lignin deriving from different morphological origins of the cell wall.

  • 126603. Zikeli, Florian
    et al.
    Ters, Thomas
    Fackler, Karin
    Srebotnik, Ewald
    Li, Jiebing
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Fractionation of wheat straw Dioxane lignin reveals molar mass dependent structural differences2016In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 91, p. 186-193Article in journal (Refereed)
    Abstract [en]

    Dioxane lignin was isolated from ball-milled wheat straw by neutral dioxane-water extraction and subsequently molar-mass-fractionated by flash chromatography in dimethylformamide. The eluted lignin containing material was pooled into six distinct molar mass fractions that were in turn structurally characterized in detail by wet chemistry and NMR spectroscopy methods. Fractions of higher molar mass were found to be enriched in p-hydroxyphenyl units and contained more p-hydroxycinnamic acid units. They were found mainly associated with linear arabinoxylan, while in low-molar-mass fractions additional glucan contributions were found. Fractions of lower molar mass consisted of relatively more guaiacyl units and showed exclusive association with tricin units. One distinct lignin fraction with lower lignin content supposedly contained high ratios of arabinoxylan chains esterified by ferulic acid and cross-linked via ferulic acid dimerization, structures which were considered to represent lignin nucleation sites. High abundance of dibenzodioxocin type structures in this fraction indicated that they could be involved in cross-linking hemicelluloses networks with lignin moieties.

  • 126604.
    Zikeli, Florian
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. Vienna University of Technology, Austria.
    Ters, Thomas
    Fackler, Karin
    Srebotnik, Ewald
    Li, Jiebing
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Successive and quantitative fractionation and extensive structural characterization of lignin from wheat straw2014In: Industrial crops and products (Print), ISSN 0926-6690, E-ISSN 1872-633X, Vol. 61, p. 249-257Article in journal (Refereed)
    Abstract [en]

    A unique process for the fractionation of lignin from wheat straw is proposed: Ball milling for 8 h, followed by a direct and an acidolysis-assisted dioxane-water extraction. Four distinctly different lignin structures were thus obtained: (1) one free non-core lignin, which is a cellulose-lignin with lowest molar mass and highest contents of p-hydroxycinnamic acids, condensed phenolic hydroxyl groups and tricin moieties, and with a detectable amount of cinnamyl alcohols; (2) two core xylan-lignins differing in their degree of branching as indicated by their xylose/arabinose ratios of >4 and similar to 2, respectively; (3) one core cellulose-lignin which is the residual fraction resistant to all extractions. Based on the mass balance of Klason lignin the yields of these four fractions are 13.8%, 18.1%, 37.5% and 12.5%, respectively, thus accounting for 82% of the total KL in wheat straw. Therefore, the isolated lignin fractions could be considered as highly representative allowing a good insight into the different features of wheat straw lignin.

  • 126605.
    Zikopi, Eleni
    KTH, School of Electrical Engineering and Computer Science (EECS).
    A case study research on Scrum Framework2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Agile methods have been widely implemented in the industry while teaching these methods is a substantial part of Computer Science and Engineering program curricula. Evidencedriven data of agile practices, methods, and tools have been extracted based on empirical studies with students, however, there is an important need for more anecdotal evidence to confirm these findings. In order to fill this gap, this paper explores the perceptions and the applicability of the Scrum Framework in a student research team in an industrial context. Empirical data have been gathered through interviews with the case study participants combined with a survey. The analysis reveals that student experiences are mainly positive and that they can easily grasp the benefits of Scrum Framework. The challenges of implementing Scrum in such a setting mainly concern the balance between coach and self-organization, formulating accurate user stories when researching, finding the most suitable estimation method, as well as planning when conducting research. The empirical findings may potentially be extrapolated in student scrum teams or even in industrial settings. Finally, this research paper should encourage other researchers to investigate the adoption of Scrum in a student setting.

  • 126606.
    Zikou, Filippia
    KTH, School of Information and Communication Technology (ICT).
    Tweetopolitics: A Scalable Platform for Analyzing Swedish Elections on Twitter2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Due to its real-time, open and democratic nature in information dissemination Twitter has become a common-ground for civic opinion expression as well as observation. This is much anticipated on the wake of an electoral event. As a result, politicians spend considerable amount of resources on analyzing the positive and negative opinions shared with respect to their orientation. Ultimately they become keen on leveraging their popularity to increase their followers base through social media. This is where user profiling and recommendation systems become useful by eliciting social preferences of political parties and their respective followers, and leveraging such intelligence to suggest relevant parties to the interested followers. To this end, we present results of applying our user profiling approach on a Twitter dataset focus-crawled during the course of 2014 general elections of Sweden. Results of analyzing content of tweets show how parties speak of controversial topics, while results of network mining show how much interactions and popularities of the parties change during the month of Election.

  • 126607.
    Zildzic, Abdela
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Applied Mechanical Engineering (KTH Södertälje).
    Sundqvist, Filip
    KTH, School of Industrial Engineering and Management (ITM), Applied Mechanical Engineering (KTH Södertälje).
    Optimering av lagerstyrning och inköpsprocessen: En fallstudie genomförd inom virkesindustrin2018Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
  • 126608.
    Zima, Caroline
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Att rita ett Passivhus: Designprocessen utifrån arkitektoniska och tekniska förutsättningar2011Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This report examines the possibility of designing a passive house with several architectural

    and technical conditions that exist for passive houses. The focus lies on design where the

    architecture must interact with the passive house building technology. The building’s shape

    and size is then tested to see if the house can clear the U

    ‐values that are required for a

    passive house.

    By using the same structure as the one that Pumpkällhagen, which is another passivehouse

    south of Borås, has it is possible to test the building’s size and design on Rockwool’s website.

    Furthermore there are finished drawings of the building.

  • 126609. Zima-Bockarjova, Marija
    et al.
    Matevosyan, Julija
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Zima, Marek
    Söder, Lennart
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Sharing of Profit From Coordinated Operation Planning and Bidding of Hydro and Wind Power2010In: IEEE Transactions on Power Systems, ISSN 0885-8950, E-ISSN 1558-0679, Vol. 25, no 3, p. 1663-1673Article in journal (Refereed)
    Abstract [en]

    Depending on market rules, namely congestion management and balancing management, coordination between wind and hydro producers may be mutually beneficial. In this paper we propose a new collaboration scheme and a fair and transparent method, based on the Shapley value, for splitting the extra value caused by a coordinated bidding and operation strategy. We account for uncertainties in wind forecast and energy price evolution. We demonstrate the proposed approaches on a realistic system including congested lines, wind farm and a hydro plant consisting of several reservoir stages.

  • 126610.
    Zimm, Malin
    KTH, School of Architecture and the Built Environment (ABE), Architecture.
    Losing the plot: architecture and narrativity in fin-de siècle media cultures2005Doctoral thesis, monograph (Other scientific)
    Abstract [en]

    This thesis investigates the role of the term plot in mediating relations between architecture and narrativity. Examining organisational strategies in the creation of real and virtual spaces, it identifies literary works by novelists who have resisted, or subverted, plot conventions in fiction (Joris-Karl Huysmans, Edmond de Goncourt, Xavier de Maistre and Neal Stephenson), and introduces architectural spaces such as Thomas Edison’s film-studio Black Maria, and the plotless productions of early cinematography, to juxtapose concepts of plot and spatiality in a study of the production and consumption of pre-digital virtual spaces. Plot here relates therefore both to narrative sequentiality and spatial organisation – from "storyline" to "ground plan". The "plotless" narrative structure of Huysmans, Goncourt and de Maistre focuses on the interaction between man – the "writerin- residence" – and his domestic interior, functioning as an excitant or stimulant for the production of both material and imagined spaces. The media culture of late 19th century society saw the first significant attempts at moving image technology and its related spatialities – the Black Maria, the kinetoscope, the kinetograph, and the films produced by these, which had yet to find a narrative form. The architecture of the plotless novels and the proto-cinematic experiments of the late 19th century modulate between physical reality and fiction. They are ripe in their descriptive narrativity, expanding in the imagination of the consumer. Stephenson’s imaginative transposition of book media into a "Primer" – a new form of narrative media that develops its narrative content directly from the environmental context of its reader – concludes the discussion of the thesis, highlighting interrelations between fictive and real space, influencing both writer and reader. The refusal of narrative plot deprives the reader of causality, but emphasises the fictitious spatial creation in which the reader becomes immersed. These spaces, by virtue of their disengagement from plot, allow us to revisit the possibilities of virtual space without common preconceptions concerning the creation or experience of digital mediating technology.

  • 126611.
    Zimm, Malin
    KTH, Superseded Departments, School of Architecture.
    The Dying Dreamer - Architecture of Parallel Realities2003Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    The objective of this licentiate thesis is to investigatearchitectural experience and creation in virtual space and itsrepresentational problems. The thesis comprises three articlespublished during the years 2001-2003, and a website,www.arch.kth.se/~zimm.

    The articles investigate architecture as a transgressivestate between the virtual worlds of imagination and thedomestic interior, introducing obsessive dreambuilding as amethod of negotiating material fictions in real space. The mainrepresentative of this kind of architectural activity is thefictional character Baron des Esseintes in Joris-KarlHuysmans´ novel À Rebours (1884). Together with thearchitectural transformations created by the architect Sir JohnSoane and the artists Kurt Schwitters and Gregor Schneider, theprojects share and develop the theme of extreme individualityand explore the architectural imagination at work in the mindof the obsessive dreambuilder. These architects of parallelrealities create operative fields of artificiality andimagination, where architectural space splits into differentontological states, providing fields for observation ofperceptional and representational problems.

    Keywords:Architecture, Against Nature/À Rebours,Artifice, Artificiality, Domestic interior, Dream, Experience,Fiction, Hypertext, Huysmans, Imagination, Individuality,Interactivity, Interface, Obsession, Obsessive dreambuilding,Perception, Representation, Schwitters, Schneider, Soane,Symbolism, Virtual Reality

  • 126612.
    Zimm, Malin
    KTH, Superseded Departments, School of Architecture.
    Writers-in-residence: Goncourt and Huysmans at home without a plot2004In: Journal of Architecture, ISSN 1360-2365, E-ISSN 1466-4410, Vol. 9, no 3, p. 305-314Article in journal (Refereed)
  • 126613. Zimmer, F.
    et al.
    Friedrichs, M.
    Lapisa, Martin
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Niklaus, Frank
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Mueller, M.
    Bakke, T.
    Schenk, H.
    Lakner, H.
    The integration of mono-crystalline silicon micro-mirrors on CMOS for SLM applications2008In: International Conference on Multi-Material Micro Manufacture, 2008, p. 35-38Conference paper (Other academic)
  • 126614. Zimmer, Fabian
    et al.
    Bring, Martin
    List, Matthias
    Lapisa, Martin
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Niklaus, Frank
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Fabrication of mono-crystalline Silicon Micro-mirror Arrays using adhesive Wafer Transfer Bonding2009In: MikroSystemTechnik KONGRESS 2009, 2009Conference paper (Other academic)
    Abstract [en]

    Spatial light modulators (SLMs) based on indivvidually addressable micro-mirrors do show an increased use in projection displays, DUV lithography and adaptive optics. Mirror planarity and deflection characteristics are important issues for these applications. Mono-crystalline silicon as mirror material offers a great possibility to combine the perfect surface with the good mechanical properties of the crystalline material. Nevertheless, the challenge is the integration of mono-crystalline silicon in a CMOS process with low temperature budget (below 450deg C) and restricted material options. Thus, standard processes like epitaxial growth or re-crystallization of poly-silicon cannot be used. We will present a CMOS-compatible approach, using adhesive wafer transfer bonding with Benzocyclobutene (BCB) of a 300nm thin silicon membrane, located on a SOI donor wafer. After the bond process, the SOI donor wafer is grinded and spin etched to remove the handle silicon and the buried oxide layer, which results in a transfer of the mono-crystalline silicon membrane to the CMOS wafer. This technology is fully compatible for integration in a CMOS process, in order to fabricate SLMs, consisting of one million indivvidually addressable mono-crystalline silicon micro-mirrors. In this paper, we present fabrication process as well as first results of SLM devices with a pixel pitch of 16 micrometer.

  • 126615. Zimmer, Fabian
    et al.
    Lapisa, Martin
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Bakke, Thor
    Bring, Martin
    Stemme, Göran
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Niklaus, Frank
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    One-Megapixel Monocrystalline-Silicon Micromirror Array on CMOS Driving Electronics Manufactured With Very Large-Scale Heterogeneous Integration2011In: Journal of microelectromechanical systems, ISSN 1057-7157, E-ISSN 1941-0158, Vol. 20, no 3, p. 564-572Article in journal (Refereed)
    Abstract [en]

    In this paper, we demonstrate the first high-resolution spatial-light-modulator chip with 1 million tilting micromirrors made of monocrystalline silicon on analog high-voltage complementary metal-oxide-semiconductor driving electronics. This device, as result of a feasibility study, shows good optical and excellent mechanical properties. The micromirrors exhibit excellent surface properties, with a surface roughness below 1-nm root mean square. Actuated micromirrors show no imprinting behavior and operate drift free. Very large-scale heterogeneous integration was used to fabricate the micromirror arrays. The detailed fabrication process is presented in this paper, together with a characterization of the SLM devices. Large arrays of individually controllable micromirrors are the enabling component in high-perfomance mask-writing systems and promising for high throughput deep-ultraviolet maskless lithography systems. The adoption of new materials with enhanced characteristics is critical in meeting the challenging demands with regard to surface quality and operation stability in the future. Very large-scale heterogeneous integration may enable virtually any solid-state material to be integrated together with CMOS electronics. [2010-0272]

  • 126616.
    Zimmer, Fabian
    et al.
    Fraunhofer IPMS.
    Lapisa, Martin
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Bakke, Thor
    SINTEF, Norway.
    Bring, Martin
    Fraunhofer IPMS.
    Stemme, Göran
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Niklaus, Frank
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Very large scale heterogeneous system integration for 1-megapixel mono-crystalline silicon micro-mirror array on CMOS driving electronics2011In: 2011 IEEE 24th International Conference on Micro Electro Mechanical Systems (MEMS), 2011, p. 736-739Conference paper (Refereed)
    Abstract [en]

    In this paper we demonstrate the first high mirror-count 1-level spatial light modulator (SLM) chip with 1 million tilting micro-mirrors made of mono-crystalline silicon on analogue, high-voltage CMOS driving electronics. The device from a feasibility study shows good optical and excellent mechanical properties. The micro-mirrors exhibit excellent surface properties with a surface roughness below 1 nm RMS, actuated micro-mirrors show no imprinting behavior and operate drift-free. Very large scale heterogeneous system integration was used to fabricate the micro-mirror array; the process is presented in this paper together with a characterization of the fabricated device.

  • 126617. Zimmer, Fabian
    et al.
    Niklaus, Frank
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Lapisa, Martin
    KTH, School of Electrical Engineering (EES), Communication Theory.
    Ludewig, Thomas
    Bring, Martin
    Friedrichs, Martin
    Bakke, Thor
    Schenk, H.
    van der Wijngaart, Wouter
    KTH, School of Electrical Engineering (EES), Microsystem Technology.
    Fabrication of large-scale mono-crystalline silicon micro-mirror arrays using adhesive wafer transfer bonding2009In: Proceedings of SPIE - The International Society for Optical Engineering / [ed] David L. Dickensheets, Harald Schenk, Wibool Piyawattanametha, 2009, Vol. 7208, p. 720807-Conference paper (Refereed)
    Abstract [en]

    Today,spatial light modulators (SLMs) based on individually addressable micro-mirrors playan important role for use in DUV lithography and adaptiveoptics. Especially the mirror planarity and stability are important issuesfor these applications. Mono-crystalline silicon as mirror material offers agreat possibility to combine the perfect surface with the goodmechanical properties of the crystalline material. Nevertheless, the challenge isthe integration of mono-crystalline silicon in a CMOS process withlow temperature budget (below 450°C) and restricted material options. Thus,standard processes like epitaxial growth or re-crystallization of poly-silicon cannotbe used. We will present a CMOS-compatible approach, using adhesivewafer transfer bonding with Benzocyclobutene (BCB) of a 300nm thinsilicon membrane, located on a SOI-donor wafer. After the bondprocess, the SOI-donor wafer is grinded and spin etched toremove the handle silicon and the buried oxide layer, whichresults in a transfer of the mono-crystalline silicon membrane tothe CMOS wafer. This technology is fully compatible for integrationin a CMOS process, in order to fabricate SLMs, consistingof one million individually addressable mono-crystalline silicon micro-mirrors. The mirrors,presented here, have a size of 16×16 µm2. Deflection isachieved by applying a voltage between the mirrors and theunderlying electrodes of the CMOS electronics. In this paper, wewill present the fabrication process as well as first investigationsof the mirror properties.

  • 126618. Zimmer, Heiko
    et al.
    Jantsch, Axel
    KTH, School of Information and Communication Technology (ICT).
    A Fault Model Notation and Error-Control Scheme for Switch-to-Switch Buses in a Network-on-Chip2003In: Proceedings of the CODES-ISSS Conference, 2003Conference paper (Refereed)
  • 126619. Zimmer, Heiko
    et al.
    Jantsch, Axel
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Error-tolerant Interconnect Schemes2005In: Interconnect-Centric Design for Advanced SoC and NoC / [ed] Jari Nurmi, Hannu Tenhunen, Jouni Isoaho, Axel Jantsch, Springer, 2005, p. 155-176Chapter in book (Refereed)
    Abstract [en]

    The Network-on-Chip paradigm targets future Systems-on-Chip built of a large number of reusable, independent Intellectual-Property-blocks (IPs). A typical approach is to align these IPs as tiles in a regular manner, each associated with a wrapper providing access to the on-chip network. The network itself is a regular structure composed of switches/routers and the interconnecting links. The objective of implementing a Network-on-Chip is to decouple computation from communication by offering a uniform, reliable, and versatile communication platform for all the inter-IP communication required by a typical SoC application. Thus, the need for custom wiring to build an application-specific communication infrastructure is overcome. Furthermore, placement and routing are simplified for the whole NoC because both the IPs and the network components are encapsulated from one another except for a defined network interface providing network access in terms of services usable by the IP for all communication it requires with its surroundings. To fully exploit the advantages this approach offers, the network must provide defined, reliable communication services to the resources attached to it. This problem is far from trivial since the network links will most likely not be error-free in future deep submicron technology generations. While much work is done to develop robust transmission schemes, it is expected that especially crosstalk will seriously affect interconnect reliability. When the physical layer of an on-chip network fails despite all preventive measures taken, the effect should be controlled. This is what the error-tolerant interconnect schemes provide: They increase the network reliability and hide imperfections from the applications which use the communication services offered. Reliable network services are of great importance since applications have demands on communication that must be fulfilled to achieve correct application behaviour. In a classical approach, the communication infrastructure of a SoC is a combination of shared buses and custom designed interconnect to meet specific requirements. However, when all communication should be transported over a common medium, the on-chip network, it must be taken into account that the demands are different for different applications and may include bandwidth guarantees, integrity requirements or deadlines for completion of a specific task in real-time applications. Typically, an application running on a SoC is comprised of multiple processes associated to different NoC-resources. Naturally, the characteristics of data transport within one application are not uniform since different traffic types such as control messages, audio signals and video streams have to coexist. Even seemingly regular data streams become irregular during processing. For instance video streams are usually encoded such that only the delta between frames are transmitted, which makes the communicated data volume higly dependent on the video content. Closing the gap between the hardware platform's possibilities and the applications' requirements is the demanding task of error-tolerant interconnect schemes. Their aim is to provide a network with defined properties to the application. In the ideal case, what the applications see is an error-free communication medium fulfilling all their communication needs. Furthermore, this idea hides the physical implementation details of a specific technology. By providing defined services, the border between platform design (technology, layout, error-tolerant interconnect scheme) and application design (using communication at defined QoS-levels) is clear. Whichmeasures are taken to implement an error-tolerant interconnect scheme depends on the specific applications' requirements and the constraints imposed by the selected platform/architecture. Therefore, we give a general overview before focusing on one specific example.

  • 126620.
    Zimmer, Loïc
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Adaptive filtering for maritime target tracking from an airborne radar2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Maritime target tracking from an airborne radar faces many issues due to the features of theenvironment, the targets to be tracked and the movement of the radar platform. Therefore, aunique tracking algorithm is not always able to reach the best possible performance for everyencountered situation. It needs to self-adapt to the environment and to the targets which areobserved in order to always be as ecient as possible. Adaptability is thus a key issue of radartracking.Several implementations of the mathematical Bayesian estimation theory, commonly called lters,have been used in the literature in order to estimate as precisely as possible targets trajectory.Depending on the situations and the assumptions that are considered, some of themare expected to perform better. This thesis suggests to look deeper into the tracking techniquesthat can be found in the literature and compare them in order to dene more precisely the advantagesof each of them over the others. This should enable to wisely choose the method thatis most likely to provide the best performance for a given situation. In particular, the nonlinearconversion between the Cartesian coordinates with which the state vector is dened and thespherical coordinates used for the measurements is investigated. A measure of nonlinearity isintroduced, studied and used to compare the extended Kalman lter and the particle lter.The size of the detected maritime targets is a special feature that makes it possible to draw amaneuverability-based classication which enables to adapt the tracking technique to be used.Joint tracking and classication (JTC) has already been described in the literature with a specicmeasurement model. This thesis makes this model more realistic using a random distribution ofthe reection point on the target's shape. The tracking method is modied to take into accountthis new measurement model and some simulations are run.This modied JTC algorithm proves to be more ecient than the JTC structure presented inthe literature. Eventually, this thesis shows that nonlinearity is a paramount issue that needsto be considered to implement an ecient self-adapatable radar tracking algorithm, this beingespecially true for extended targets.

  • 126621.
    Zimmer, Michael
    et al.
    University of California, Berkeley.
    Broman, David
    University of California, Berkeley and Linköping University.
    Shaver, Chris
    University of California, Berkeley.
    Lee, Edward A.
    University of California, Berkeley.
    FlexPRET: A Processor Platform for Mixed-Criticality Systems2014In: Proceedings of the 20th IEEE Real-Time and Embedded Technology and Application Symposium (RTAS), IEEE conference proceedings, 2014, p. 101-110Conference paper (Refereed)
    Abstract [en]

    Mixed-criticality systems, in which multiple tasks of varying criticality execute on a single hardware platform, are an emerging research area in real-time embedded systems. High-criticality tasks require spatial and temporal isolation guarantees for independent verification, and the task set should efficiently utilize hardware resources. Hardware-based isolation is desirable but often underutilizes hardware resources, which can consist of multiple single-core, multicore, or multithreaded processors. We present FlexPRET, a processor designed specifically for mixed-criticality systems by allowing each task to make a trade-off between hardware-based isolation and efficient processor utilization. FlexPRET uses fine-grained multithreading with flexible scheduling and timing instructions to provide this functionality.

  • 126622.
    Zimmerer, Frank
    et al.
    Saarland University.
    Andreeva, Bistra
    Saarland University.
    Möbius, Bernd
    Saarland University.
    Malisz, Zofia
    KTH, School of Computer Science and Communication (CSC), Speech, Music and Hearing, TMH, Speech Communication and Technology.
    Ferragne, Emmanuel
    CNRS Université Lyon 2.
    Pellegrino, François
    CNRS Université Lyon 2.
    Brandt, Erika
    Saarland University.
    Perzeption von Sprechgeschwindigkeit und der (nicht nachgewiesene) Einfluss von Surprisal2017In: ESSV - 28. Konferenz Elektronische Sprachsignalverarbeitung 2017, Saarbrücken, 2017Conference paper (Refereed)
    Abstract [de]

    In zwei Perzeptionsexperimenten wurde die Perzeption von Sprech- geschwindigkeit untersucht. Ein Faktor, der dabei besonders im Zentrum des In- teresses steht, ist Surprisal, ein informationstheoretisches Maß für die Vorhersag- barkeit einer linguistischen Einheit im Kontext. Zusammengenommen legen die Ergebnisse der Experimente den Schluss nahe, dass Surprisal keinen signifikanten Einfluss auf die Wahrnehmung von Sprechgeschwindigkeit ausübt. 

  • 126623.
    Zimmerman, Robert W.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Engineering Geology and Geophysics.
    The Imperial College lectures in petroleum engineering2018Collection (editor) (Other academic)
    Abstract [en]

    This book presents, in a self-contained form, the equations of fluid flow in porous media, with a focus on topics and issues that are relevant to petroleum reservoir engineering. No prior knowledge of the field is assumed on the part of the reader, and particular care is given to careful mathematical and conceptual development of the governing equations, and solutions for important reservoir flow problems. Fluid Flow in Porous Media starts with a discussion of permeability and Darcy's law, then moves on to a careful derivation of the pressure diffusion equation. Solutions are developed and discussed for flow to a vertical well in an infinite reservoir, in reservoirs containing faults, in bounded reservoirs, and to hydraulically fractured wells. Special topics such as the dual-porosity model for fractured reservoirs, and fluid flow in gas reservoirs, are also covered. The book includes twenty problems, along with detailed solutions. As part of the Imperial College Lectures in Petroleum Engineering, and based on a lecture series on the same topic, this book provides the introductory information needed for students of the petroleum engineering and hydrology.

  • 126624.
    Zimmerman, Robert W.
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Engineering Geology and Geophysics.
    Lutz, M.P
    Thermal and electrical conductivity of composites with graded interfaces2006In: International Journal of Advances in Science and Technology, ISSN 2229-5216, Vol. 45, p. 1097-1102Article in journal (Refereed)
  • 126625.
    Zimmerman, R.W.
    et al.
    Dept. of Earth Science/Engineering, Imperial College, London.
    Al-Yaarubi, A
    Pain, C.C
    Grattoni, C.A
    Non-linear regimes of fluid flow in rock fractures2004In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 41, no 3, p. 384-384Article in journal (Refereed)
    Abstract [en]

    We have conducted high-resolution Navier-Stokes simulations and laboratory measurements of fluid flow in a natural sandstone fracture. First, epoxy casts were made of the two opposing fracture surfaces. The surface profiles of the two surfaces were then measured at a vertical resolution of ±2 μm, every 20 μm in the x and y-directions, over 2 cm × 2 cm regions of the fracture. These data were then used to create a finite-element mesh for the fracture void space, and the Navier-Stokes equations were solved within this domain. Flow experiments were also conducted within the same fracture casts, over a range of flowrates. The simulations confirm the existence of a weak inertia regime for Reynolds numbers in the range of 1-10, in which the non-Darcy pressure drop varies with the cube of the flowrate. Although of theoretical interest, this effect is, however, probably too small to be of engineering interest. At Reynolds numbers above about 20, both the simulations and experiments exhibit a Forchheimer-type regime, in which the non-Darcy pressure drop is quadratic in the flowrate.

  • 126626. Zimmermann, J.
    et al.
    Saravanan, B. K.
    Marz, R.
    Kamp, M.
    Forchel, A.
    Anand, Srinivasan
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Large dispersion in photonic crystal waveguide resonator2005In: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 41, no 7, p. 414-415Article in journal (Refereed)
    Abstract [en]

    Group delay and chromatic dispersion of a Fabry-Perot resonator embedded in a photonic crystal waveguide have been directly measured at 1.55 mu m avelength using the phase-shift technique. The photonic crystal waveguide resonator was fabricated in an InGaAsP/InP heterostructure and was designed to show a channel spacing of 100 GHz. Group velocity dispersion up to 250 ps/nm was observed.

  • 126627. Zimmermann, J
    et al.
    Scherer, H
    Kamp, M
    Deubert, S
    Reithmaier, J P
    Forchel, A
    Marz, R
    Anand, Srinivasan
    KTH, Superseded Departments, Electronics.
    Photonic crystal waveguides with propagation losses in the 1 dB/mm range2004In: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 22, no 6, p. 3356-3358Article in journal (Refereed)
    Abstract [en]

    High-quality photonic crystal waveguides have been fabricated in the InGaAsP/InP and GaAs/AlGaAs material systems aimed at the communication wavelengths of 1.55 and 1.31 mum. The waveguides consist of omitted rows of holes in a triangular lattice of air holes etched into the semiconductor heterostructures by electron cyclotron resonance reactive ion etching. Efficient waveguiding has been observed in optical transmission measurements, with waveguide losses ranging from 1.5 dB/mm for a waveguide with three missing row of holes (W3) to 0.2 dB/mm for seven missing rows (W7). (C) 2004 American Vacuum Society.

  • 126628. Zimmermann, Kristian
    Cost and Weight Analysis of Ultra Thick Laminates for a Compact Landing Gear Fitting2011In: SICOMP 2011, 2011Conference paper (Other academic)
  • 126629.
    Zimmermann, Kristian
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Ultra Thick Laminates for Compact Load Introduction Fittings2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Composites are increasingly often used for thick and compact structures with the clear aim to reduce the overall weight and cost of an aircraft. But classic applications of composites are thinner structures with limited out of plane loads. Analysis and test methods are therefore commonly developed and used for thinner structures and neglect the special challenges involved with thicker laminates. In addition composites are increasingly becoming interesting for fittings and joints since the surrounding structures are either built or being developed in composites a well. Using metallic fitting and joints can cause additional thermal stresses and /or corrosion due to the material mix of composites and metals. Due to the enlarged field of application for composites, there is an increasing demand for suitable analysis, test and manufacturing methods. Compact and highly loaded composite structures are prone to be subjected to high and multidirectional loads. This causes an atypical load situation for composites, which usually are subjected to plane loads to best exploit the strength of the fibers. Due to the orthotropic nature of the material a large amount of design variables are introduced. The design of any composite part is highly manufacturing driven, meaning that the final shape is determined by manufacturing capabilities. Thick composites provide a cost effective alternative and can generate a distinct weight benefit over standard metallic components and hence will a play a significant role in future aircraft developments. Analysis, testing and manufacturing methods have to be developed and adapted for that purpose. A reliable analysis is only possible if accurate 3D material properties are available. Analysis capabilities have to be assessed using empirical test data in order to judge the applicability. The presented work has its emphasis on the analysis and testing of structural components manufactured in thick composites. The generated data from a comprehensive manufacturing and test program is also used as basis for a cost and weight study under the assumption of a highly automized serial production. The results further underline the potential of thick composites.  In a first approach, standard 2D finite element methods are used for a topology investigation. In order to fully capture the behavior of the material 3D methods are quickly implemented. An extensive test program with full scale samples and coupons is used to improve and evolve the analysis. An open mold manufacturing cycle minimizes tooling costs and provides optimum flexibility for frequent design changes. A strong link between the analysis, the manufacturing and the design is maintained throughout the developments in order to generate a material suitable design solution. Although the ultimate goal is to manufacture a specific component, the topics are approached as generic as possible in order to provide a basis for future studies with similar boundary conditions. Despite the fact that the material creates countless design variables, an affordable approach for the analysis of thick composite structures is provided using standard 3D composite brick elements. The initial problem of missing reliable 3D material properties is counteracted with tests of full scale sub- components and modified short beam shear tests. A new cure cycle for thick laminates is presented and analyzed to assess process induced stresses and deformations. A large landing gear fitting component is designed and manufactured and can be regarded as an excellent demonstrator of ultra thick composites. With a maximum wall thickness of 90mm, the component provides a weight reduction of 18% and a cost benefit of approximately 20% compared to the metallic counterpart. The potential of composites applied to a compact and highly loaded fitting is demonstrated and suitable analysis methods are established. A need for future tests to provide reliable and generic 3D material properties is identified. To provide a weight and cost benefit it is crucial to find a design topology suitable for composites.

  • 126630. Zimmermann, Kristian
    et al.
    Siemetzki, Markus
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Analysis and Manufacturing of Ultra Thick Laminates for Future Aircraft Applications2008In: ECCM-13, 2008, 2008Conference paper (Other academic)
    Abstract [en]

    Compact and highly loaded composite components experience extensive transverse shear stress concentrations in areas of load introduction and curved sections. Standard 3D multilayered composite brick elements are employed to analyze UTL. For the purpose of validation several full-scale test components with T-cross section have been manufactured with thicknesses ranging from 60-90mm. In a first approach single non interactive failure criteria have been used due to the uncertainty of out of plane material properties. Despite the fact that the used element type provides a simple mean of modeling and analyzing UTL, it is found that the element formulation strictly limits the accuracy of transverse shear stress prediction. The quadratic or even linear approximation of in plane displacements does not account for the irregular distribution in thickness direction [1]. Global deformations of the geometry can however be calculated with good results. Most failure modes experienced, are found to be dominated by transverse shear or out of plane peeling stresses. Particularly in the region of load introduction. For the analysis of the final landing gear fitting material restricted correction factors are introduced. In addition to the T-Sections, large so called ‘Double Corners’ are tested in both in plane and out of plane direction to develop effective countermeasures for premature failure modes, such as throat washers and load distribution plates. The utilized modified VAP cycle has significant benefits compared to closed mould processes, such as reduced tooling costs and high flexibility. For curved UTL sections spring back effects and preform compression rates are considered to improve laminate quality.

  • 126631.
    Zimmermann, Kristian
    et al.
    EADS Innovation Works, Munich, Germany.
    Van den Broucke, B.
    Assessment of process-induced deformations and stresses in ultra thick laminates using isoparametric 3D elements2012In: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 31, no 3, p. 163-178Article in journal (Refereed)
    Abstract [en]

    Shape distortions are a common problem experienced during the manufacturing of fiber reinforced plastics and are commonly investigated for thinner components. The following study presents the analysis of shape distortions and residual stresses in Ultra-thick laminates using a coupled thermomechanical approach. Existing studies frequently use high resolution meshes with multiple elements over ply thickness. This approach is not feasibly for thicker structures due to the computational effort. A new curing cycle, adapted to the requirements of Ultra-thick laminates, is deployed. Residual stresses need to be quantified and accounted for in the structural analysis. Several test components are manufactured in non-crimped fabric, to generate comparable data on heat distribution within the laminate and to measure the spring-in angle. For the FE analysis 3D stacked composite brick elements are used. These combine several plies within each element and present an efficient way to analyse thicker composite structures. Substantial residual stresses are calculated in the curved section of the laminate. A discrepancy in the calculated and measured spring-in angle is most likely explained by the usage of a single-sided steel tooling and several debulking steps.

  • 126632. Zimmermann,, Kristian
    et al.
    van den Broucke, B.
    Simulation of Process Induced Deformations in Ultra-thick Laminates Manufactured with Vacuum Assisted ProcessManuscript (preprint) (Other academic)
  • 126633. Zimmermann, Kristian
    et al.
    Zenkert, Dan
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Lightweight Structures.
    Siemetzki, M.
    Testing and analysis of ultra thick composites2010In: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 41, no 4, p. 326-336Article in journal (Refereed)
    Abstract [en]

    For the development of a composite main landing gear fitting in carbon fiber reinforced plastics the behavior and performance of Ultra Thick Laminate components is investigated. Material thicknesses exceeds 60 mm. For the purpose of validation a test program is arranged using T-cross sections subjected to multiple load cases. The components are manufactured entirely with non crimped fabrics (NCF) using an adapted open mould manufacturing process. In addition to these T-Sections large full scale subcomponents of the entire fitting are manufactured and tested. As main topic of this paper standard FE methods are investigated and validated for thick structures using the generated test results. Due to the presence of transverse shear and normal stresses a 3D modeling approach is chosen. Transverse shear and normal stresses are indentified as main failure cause and failure is mainly initiated in the curved regions. Solid composite brick elements offer an efficient way to model thick structures. These are incapable of calculating accurate shear stresses on a ply level; usable results are however achieved by discretisation of the component with multiple elements over thickness. In addition stress gradients in the failure region are small; stress variations on a ply level are minimal. Out of plane material properties are not available and initial assumptions are made. Material correction factors (degradation) are introduced and discussed.

  • 126634.
    Zimmermann, Maelle
    et al.
    Univ Montreal, Dept Comp Sci & Operat Res, Montreal, PQ, Canada.;CIRRELT Interuniv Res Ctr Entreprise Networks Log, Montreal, PQ, Canada..
    Västberg, Oskar Blom
    KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Transport Studies, CTS.
    Frejinger, Emma
    Univ Montreal, Dept Comp Sci & Operat Res, Montreal, PQ, Canada.;CIRRELT Interuniv Res Ctr Entreprise Networks Log, Montreal, PQ, Canada..
    Karlström, Anders
    KTH, School of Architecture and the Built Environment (ABE), Centres, Centre for Transport Studies, CTS.
    Capturing correlation with a mixed recursive logit model for activity-travel scheduling2018In: Transportation Research Part C: Emerging Technologies, ISSN 0968-090X, E-ISSN 1879-2359, Vol. 93, p. 273-291Article in journal (Refereed)
    Abstract [en]

    Representing activity-travel scheduling decisions as path choices in a time-space network is an emerging approach in the literature. In this paper, we model choices of activity, location, timing and transport mode using such an approach and seek to estimate utility parameters of recursive logit models. Relaxing the independence from irrelevant alternatives (IIA) property of the logit model in this setting raises a number of challenges. First, overlap in the network may not fully characterize perceptual correlation between paths, due to their interpretation as activity schedules. Second, the large number of states that are needed to represent all possible locations, times and activity combinations imposes major computational challenges to estimate the model. We combine recent methodological developments to build on previous work by Blom Vastberg et al. (2016) and allow to model complex and realistic correlation patterns in this type of network. We use sampled choices sets in order to estimate a mixed recursive logit model in reasonable time for large-scale, dense time-space networks. Importantly, the model retains the advantage of fast predictions without sampling choice sets. In addition to estimation results, we present an extensive empirical analysis which highlights the different substitution patterns when the IIA property is relaxed, and a cross-validation study which confirms improved out-of-sample fit.

  • 126635.
    Zimmermann, Maëlle
    et al.
    Department of Computer Science and Operations Research, Universit\'e de Montr\'eal, QC, Canada.
    Blom Västberg, Oskar
    KTH, School of Architecture and the Built Environment (ABE), Transport Science, System Analysis and Economics. Royal Institute of Technology.
    Frejinger, Emma
    Department of Computer Science and Operations Research, Universit\'e de Montr\'eal, QC, Canada.
    Karlström, Anders
    Capturing correlation with a mixed recursive logit model for activity-travel schedulingManuscript (preprint) (Other academic)
    Abstract [en]

    Representing activity-travel scheduling decisions as path choices in a time-space network is an emerging approach in the literature. In this paper, we model choices of activity, location, timing and transport mode using such an approach and seek to estimate utility parameters. Relaxing the independence from irrelevant alternatives (IIA) assumption of the logit model in this setting raises a number of challenges. First, overlap in the network may not fully characterize the correlation between paths, due to their interpretation as activity schedules. Second, the large number of states that are needed to represent all possible locations, times and activity combinations imposes major computational challenges to estimate the model. We combine recent methodological developments to extend previous work that allow to model complex and realistic correlation patterns in this type of network. The resulting model is a mixed recursive logit which keeps the advantages of the recursive logit for prediction. We use sampled choices sets in order to estimate the model in reasonable time for large-scale, dense time-space networks. In addition to estimation results, we present an extensive empirical analysis which highlights the different substitution patterns when the IIA property is relaxed, and a cross-validation study which confirms improved out-of-sample fit.

  • 126636. Zimmermann, U.
    et al.
    Osterman, J.
    Kuylenstierna, D.
    Hallén, Anders.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Konstantinov, A. O.
    Vetter, W. M.
    Dudley, M.
    Material defects in 4H-silicon carbide diodes2003In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 93, no 1, p. 611-618Article in journal (Refereed)
    Abstract [en]

    Crystallographic defects revealed by synchrotron white beam x-ray topography, electron beam induced current, optical microscopy, and electroluminescence are correlated with the electrical characteristics of medium-voltage epitaxial 4H-silicon carbide diodes. Diodes that include macroscopic crystallographic defects show a significantly reduced reverse breakdown voltage with typical microplasma current fluctuations under reverse bias. Microplasma current paths are revealed by increased electroluminescence both under forward and reverse bias of the diodes and coincide with the locations of screw dislocations in the epitaxial layers of the diodes. The role of crystallographic imperfections on the formation of stacking faults responsible for the degradation of bipolar silicon carbide components is discussed.

  • 126637.
    Zimmermann, Uwe
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Design, Processing and Characterization of Silicon Carbide Diodes2003Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Electronic power devices made of silicon carbide promisesuperior performance over today's silicon devices due toinherent material properties. As a result of the material'swide band gap of 3.2eV, high thermal conductivity, itsmechanical and chemical stability and a high critical electricfield, 4H-silicon carbide devices have the potential to be usedat elevated temperatures and in harsh environments. Shortercarrier lifetimes and a reduction in the necessary width of thelow-doped drift zone in silicon carbide devices compared totheir silicon counterparts result in faster switching speedsand lower switching losses and thus in much more efficientpower devices.

    High-voltage 4H-silicon carbide diodes have been fabricatedin a newly developed processing sequence, using standardsilicon process equipment. Epitaxial layers grown by chemicalvapor deposition (CVD) on commercial 4H-silicon carbidesubstrates were used as starting material for both mesa-etchedepitaxial and implanted p+n-n+ planar diodes, Schottky diodesand merged pn-Schottky (MPS) diodes, together with additionaltest structures. The device metallization was optimized to givea low contact resistivity on implanted and epitaxial layers anda sufficiently high Schottky barrier with a singlemetallization scheme. Different high-field termination designshave been tested and breakdown voltages of up to 4 kV onimplanted, field-ring terminated diodes were achieved,corresponding to 80% of the critical electric field. A 5kVepitaxial diode design with a forward voltage drop of 3.5V at acurrent density of 100Acm-2 equipped with an implanted junctiontermination extension (JTE) was also fabricated.

    A new measurement setup was designed and built with thecapability of measuring current-voltage and capacitance-voltagecharacteristics of semiconductor devices at reverse biases upto 10kV. Together with these electrical measurements, theresults of other characterization techniques were used toidentify performance limiting defects in the fabricated siliconcarbide diodes. Increased forward voltage drop of bipolardevices during on-state operation was studied and it was shownthat the stacking faults causing forward degradation arevisible in scanning electron microscopy. With the help ofsynchrotron white-beam X-ray diffraction topographs (SWBXT),electron beam induced current (EBIC) and electroluminescencemeasurements of silicon carbide diodes, the role of screwdislocations as a dominant source of device failure in the formof localized microplasma breakdown was identified. Screwdislocations with and without open core have been found tocause a 20-80% reduction in the critical electric field of4H-silicon carbide diodes, both for low-voltage (150V) andhigh-voltage (~5kV) designs. While micropipes have almost beeneliminated from commercial silicon carbide material,closed-core screw dislocations are still abundant withdensities in the order of 10000cm-2 in state-of-the-art siliconcarbide epitaxial layers.

  • 126638.
    Zimmermann, Uwe
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Domeij, Martin
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Hallén, Anders
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Östling, Mikael
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Comparison between implanted and epitaxial pin-diodes on 4H-silicon carbide2004In: SILICON CARBIDE AND RELATED MATERIALS 2003, PRTS 1 AND 2 / [ed] Madar, R; Camassel, J, ZURICH-UETIKON: TRANS TECH PUBLICATIONS LTD , 2004, Vol. 457-460, p. 1037-1040Conference paper (Other academic)
    Abstract [en]

    Two sets of pin-diodes with epitaxially grown anode regions and implanted anode regions, respectively, were processed on the same low-doped n-type epitaxial layer. The designed breakdown voltage for the epitaxial layer was 5 kV with punch-through at about 2 kV. The almost ideal forward voltage drop of less than 3.5 V at current densities of 100 A cm(-2) of the epitaxial diodes indicates high-level carrier injection into the low-doped epitaxial layer, which is also supported by the results of reverse recovery measurements. At current densities above 10 A cm(-2) the forward voltage drop of the implanted pin-diodes is significantly higher than that of the epitaxial diodes.

  • 126639. Zinkevich, M.
    et al.
    Aldinger, F.
    Sundman, Bo
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    The Ringberg workshop 2005 on thermodynamic modeling and first-principles calculations2007In: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 31, no 1, p. 2-3Article in journal (Other academic)
  • 126640.
    Zinn, Alexandra
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management.
    Framtidens studentbostadsmarknad2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The shortage for student housing, especially in larger cities, has during a longer time period been a frequently discussed topic in Sweden. Stockholm has a wide and strong offer of higher education and the region is continuously expanding. The Stockholm region has about 80 000 students but less than 13 000 student apartments. This results in a risk that students deselect Stockholm as a city to study in.

    This study aims to investigate the possibilities for the student housing market to develop. With a qualitative method through interviews with various actors on the market five problem areas were identified. The five problem areas that lay ground for this thesis are; design of student housing, rental and lease law, a developed campus, the university’s role, and subsidies and grants.

    The thesis concludes with a presentation of a model with two options for the construction of new student housing, broken down by student housing developed on campus and off campus. Student housing that will be built on campus are proposed primarily to take the form of collective accommodation with the university as owner and the leasing should be made to freshmen at the university. Student housing that will be built off campus are instead suggested to be developed as one or two room apartments that real estate companies develop, own, and lease through a queuing system.

    The conclusion of this study indicate that it is important that a menu of various forms of accommodation are brought to the student housing market as students have different preferences combined with the universities’ and property owners’ different interests regarding students’ accommodation

  • 126641.
    ZINN, KRISTOFFER
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Entrepreneurship and innovation.
    Risk Management and the Tax Allocation Reserve2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This paper aims to investigate if there exist a relation between the use of the tax allocation reserve and financial risk management among Swedish corporations. In order to perform the study the literature on risk management is reviewed. The fields within the risk management theory that have an impact on the incentives to use the tax allocation reserve is identified and described. A binary logit model is applied to empirically test if a statistical relationship between the use of the tax allocation reserve and risk management exist. To determine the use of the tax allocation reserve a binary choice variable is created and tested against the theories of transaction costs, coordination of financing and investment policies and the reduction of corporate tax. The model is applied on financial statement data of firms operating in Sweden from 2009 to 2011. Reported results reveal evidence that there exist a statistical relationship between the use of the tax allocation reserve and the theories of transaction costs and the coordination of financing and investment policies, and suggest that their occur risk management related activities in the application of the tax allocation reserve among firms operating in Sweden. The findings also suggest that tax incentives impact the utilization of the tax allocation reserve.

  • 126642. Ziolek, Marcin
    et al.
    Cohen, Boiko
    Yang, Xichuan
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Paulose, Maggie
    Varghese, Oomman K.
    Grimes, Craig A.
    Douhal, Abderrazzak
    Femtosecond to millisecond studies of electron transfer processes in a donor-(pi-spacer)-acceptor series of organic dyes for solar cells interacting with titania nanoparticles and ordered nanotube array films2012In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, no 8, p. 2816-2831Article in journal (Refereed)
    Abstract [en]

    Time-resolved emission and absorption spectroscopy are used to study the photoinduced dynamics of forward and back electron transfer processes taking place between a recently synthesized series of donor-(pi-spacer)-acceptor organic dyes and semiconductor films. Results are obtained for vertically oriented titania nanotube arrays (inner diameters 36 nm and 70 nm), standard titania nanoparticles (25 nm diameter) and, as a reference, alumina nanoparticle (13 nm diameter) films. The studied dyes contain a triphenylamine group as an electron donor, cyanoacrylic acid part as an electron acceptor, and differ by the substituents in a spacer group that causes a shift of its absorption spectra. Despite a red-shift of the dye absorption band resulting in an improved response to the solar spectrum, smaller electron injection rates and smaller extinction coefficients result in reduced dye sensitized solar cell (DSSC) conversion efficiencies. For the most efficient dye, TPC1, electron injection from the hot locally excited state to titania on a time scale of about 100 fs is suggested, while from the relaxed charge transfer state it proceeds in a non-exponential way with time constants from 1 ps to 50 ps. Our results imply that the latter process involves the trap states below the conduction band edge (or the sub-bandgap tail of the acceptor states), localized close to the dye radical cation, and is accompanied by fast electron recombination to the parent dye's ground state. This process should limit the efficiency of DSSCs made using these types of organic dyes. The residual, slower recombination can be described by a stretched exponential decay with a characteristic time of 0.5 ms and a dispersion parameter of 0.33. Both the electron injection and back electron transfer dynamics are similar in titania nanoparticles and nanotubes. Variations between the two film types are only found in the time resolved emission transients, which are explained in terms of the difference in local electric fields affecting the position of the emission bands.

  • 126643. Ziolek, Marcin
    et al.
    Karolczak, Jerzy
    Zalas, Maciej
    Hao, Yan
    Tian, Haining
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Douhal, Abderrazzak
    Aggregation and Electrolyte Composition Effects on the Efficiency of Dye-Sensitized Solar Cells. A Case of a Near-Infrared Absorbing Dye for Tandem Cells2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 1, p. 194-205Article in journal (Refereed)
    Abstract [en]

    Time-resolved laser spectroscopy studies of complete solar cells sensitized with a near-infrared absorbing dye (HY103) and filled with different electrolytes are applied to explain their macroscopic parameters (efficiency and short-circuit current). Particular attention is paid to the effect of coadsorbent, size of cations in electrolyte (lithium vs guanidine ones), and addition of tert-butylpyridine. A complete deactivation scheme in the cell is revealed, and the rates of electron injection and all other processes are explored. For the most efficient electrolyte, the electron injection rate constants are 0.21 ps(-1) from monomers and 0.07 ps(-1) from H-aggregates. Moreover, two important and novel findings are revealed: energy transfer from the excited state of monomers to H-aggregates (with rate constants from 0.04 to 0.25 ps(-1)) and the decrease of internal conversion rate in HY103 attached to the nanoparticles (0.01 ps(-1)) with respect to that of free dye in solution (0.06 ps(-1)). Thus, our study gives more clues to better understand the photobehavior of dye-sensitized solar cells.

  • 126644. Ziolek, Marcin
    et al.
    Tacchini, Ignacio
    Martinez, M. Teresa
    Yang, Xichuan
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Douhal, Abderrazzak
    A photo-induced electron transfer study of an organic dye anchored on the surfaces of TiO2 nanotubes and nanoparticles2011In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, no 9, p. 4032-4044Article in journal (Refereed)
    Abstract [en]

    We report on femtosecond-nanosecond (fs-ns) studies of the triphenylamine organic dye (TPC1) interacting with titania nanoparticles of different sizes, nanotubes and nanorods. We used time-resolved emission and absorption spectroscopy to measure the photoinduced dynamics of forward and back electron transfer processes taking place in TPC1-titania complexes in acetonitrile (ACN) and dichloromethane (DCM) solutions. We observed that the electron injection from the dye to titania occurs in a multi-exponential way with the main contribution of 100 fs from the hot excited charge-transfer state of anchored TPC1. This process competes with the relaxation of the excited state, mainly governed by solvation, that takes place with average time constants of 400 fs in ACN and 1.3 ps in DCM solutions. A minor contribution to the electron injection process takes place with longer time constants of about 1-10 ps from the relaxed excited state of TPC1. The latter times and their contribution do not depend on the size of the nanoparticles, but are substantially smaller in the case of nanotubes (1-3 ps), probably due to the caging effect. The contribution is also smaller in DCM than in ACN. The efficient back recombination takes place also in a multi-exponential way with times of 1 ps, 15 ps and 1 ns, and only 20-30% of the initial injected electrons in the conduction band are left within the first 1 ns after excitation. The faster recombination rates are suggested due to those originating from the free electrons in the conduction band of titania or the electrons in the shallow trap states, while the slower recombination is due to the electrons in the deep trap states. The results reported here should be relevant to a better understanding of the photobehaviour of an organic dye with promising potential for use in solar cells. They should also help to determine the important factors that limit the efficiency of solar cells based on the triphenylamine-based dyes for solar energy conversion.

  • 126645. Ziolek, Marcin
    et al.
    Yang, Xichuan
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Douhal, Abderrazzak
    Interrogating the ultrafast dynamics of an efficient dye for sunlight conversion2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 28, p. 8098-8107Article in journal (Refereed)
    Abstract [en]

    We report on studies of the recently synthesized compound (TPC1) with a promising potential use in dye-sensitized solar cells. We used steady-state as well as femtosecond (fs) to nanosecond (ns) time-resolved emission techniques to understand its behaviour under different conditions of solvation and light excitation. In polar solvents the equilibrium between TPC1 normal and anion structures was found to depend on solvent H-bond acceptor ability and concentration of the dye. We observed a correlation between the contribution of the normal form in the total absorption spectrum and solar energy conversion efficiency of the photovoltaic devices prepared in different baths, which are high in dichloromethane and low in tetrahydrofurane. Both forms exhibit a large charge transfer character in the excited state manifested by a large Stokes shift between absorption and emission maxima (up to 9000 cm(-1) in acetonitrile). The lifetime of the relaxed state of the normal structure varies significantly with the solvent polarity (from 80 ps in acetonitrile to 1.8 ns in n-hexane), and it is considerably shorter than that of the anion one (1.2-2.6 ns). The ultrafast relaxation processes are dominated by the solvation dynamics which is the fastest in acetonitrile (below 1 ps) and the slowest in ethanol (about 25 ps, the amplitude-averaged time). The results reported here should be relevant to a better understanding of the photobehaviour of metal-free dyes for solar cells and help in the design of new and more efficient dyes for conversion of light to electricity.

  • 126646.
    Zioris, Stavros
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Vranjkovina, Alija
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Concrete Structures.
    Evaluation of a Tramway’s Track Slab in Conventionally Reinforced Concrete or Steel Fibre Concrete2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The dominant reinforcement used widely for concrete structures is conventional steel bars

    (rebars). Nevertheless, the perpetual effort toward evolution and development could not exclude

    the engineering field, thus new innovative and sophisticated methods are introduced. It is true

    that, due to lack of extended regulations and standards, the fibre reinforced concrete (FRC) was

    limited to non-structural applications. However, the last years the situation is changing rapidly

    and already the applications of FRC include actual structural members.

    The subject of the current thesis was a tramway’s track slab from “Sparvag City” project in

    Stockholm. The aim was to evaluate the track slab, in terms of alternative reinforcing ways. In

    particular three models were examined; model I – conventional reinforcement, model II – steel

    fibre reinforced concrete (SFRC) and model III – SFRC with conventional reinforcement. The

    assessment was performed from structural, regulations – compliance, economic and ergonomic

    perspective. A static linear analysis of the track slab was performed using Abaqus; a finite

    element analysis (FEA) software. The track slab was subjected only to mechanical loads (selfweight

    and traffic actions) and thus, the design internal forces were extracted. Thereafter,

    Eurocode 2 (EN 1992-1-1, 2004) and Swedish standards for FRC structures (SS 812310:2014)

    were utilized for the reinforcement design of the models. The design was performed in ultimate

    limit state (ULS), for bending moment and shear resistance, and in serviceability limit state

    (SLS), for stress limitation and crack control.

    Model I and III were successfully designed abiding with the respective regulations and

    requirements, while “only fibres” model was considered valid only for bending moment

    resistance according to SS 812310:2014. Consequently only models I and III were compared

    with each other. From the economic comparison it was obtained that model I was less

    expensive than model III, but on the other hand its construction time was larger. Furthermore

    model III contained significantly less total rebars’ mass in comparison to model I. This

    particularity was crucial for the ergonomic assessment. The human factors, that were relevant

    to the ergonomic assessment, improved the quality of the comparison and the extracted

    inferences, but also introduced aspects impossible to be put against economic facts as an

    equal quantity. Thus, there was not a final proposal as the best solution for the thesis subject.

  • 126647.
    ZIRA, EIRINI
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Entrepreneurship and innovation.
    The Impact of Skill Mismatch on AggregateProductivity:cross-country analysis in OECD economies2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The present study explores the relationship between skill mismatch in twomain categories, numeracy and literacy, and aggregate productivity as derivedfrom a decomposition of productivity into within-rm productivityand allocative eciency. Skill mismatch is considered a rather persistentphenomenon with long lasting eects in various aspects. In the analysiscovered, OECD Survey of Adult Skills (PIAAC) database was employed forthe aggregated indicators of skill mismatch while productivity was measuredusing ORBIS commercial database. The key ndings reveal a strong andnegative relationship between skill mismatch in numeracy and productivity,which stems from a negative relationship between the same category and thewithin-rm labor productivity. Under-skilling in numeracy exhibits a negativeeect on productivity while over-skilling seems not to be related in thecurrent specication. Based on the relationship between competition andproductivity, market power is used to control for the competition in dierentsectors. The results suggest that higher market share translates to higherproductivity and the relationship is statistically signicant.

  • 126648. Zisis, G.
    et al.
    Manzo, Michele
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Gallo, Katia
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Electronics and Quantum Optics, QEO.
    Soergel, E.
    Mailis, S.
    UV laser-induced poling inhibition in proton exchanged LiNbO3 crystals2017In: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 123, no 4, article id 158Article in journal (Refereed)
    Abstract [en]

    The applicability of the UV laser-induced poling inhibition method for ferroelectric domain engineering in proton exchanged lithium niobate planar waveguides is investigated. Our results indicate that intense UV irradiation of proton exchanged lithium niobate samples can, indeed, produce poling inhibited domains in this material under certain irradiation conditions. However, there is strong indication that the temperature gradient that is formed during UV irradiation modifies the local proton concentration leading to changes in the refractive index profile of the original planar waveguide.

  • 126649. Ziss, Dorian
    et al.
    Martin-Sanchez, Javier
    Lettner, Thomas
    KTH, School of Engineering Sciences (SCI), Applied Physics, Quantum Nano Photonics.
    Halilovic, Alma
    Trevisi, Giovanna
    Trotta, Rinaldo
    Rastelli, Armando
    Stangl, Julian
    Comparison of different bonding techniques for efficient strain transfer using piezoelectric actuators2017In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 121, no 13, article id 135303Article in journal (Refereed)
    Abstract [en]

    In this paper, strain transfer efficiencies from a single crystalline piezoelectric lead magnesium niobatelead titanate substrate to a GaAs semiconductor membrane bonded on top are investigated using state-of-the-art x-ray diffraction (XRD) techniques and finite-element-method (FEM) simulations. Two different bonding techniques are studied, namely, gold-thermo-compression and polymer-based SU8 bonding. Our results show a much higher strain-transfer for the "soft" SU8 bonding in comparison to the "hard" bonding via gold-thermo-compression. A comparison between the XRD results and FEM simulations allows us to explain this unexpected result with the presence of complex interface structures between the different layers.

  • 126650.
    Zivanov, Jasenko
    et al.
    MRC, Lab Mol Biol, Cambridge, England..
    Nakane, Takanori
    MRC, Lab Mol Biol, Cambridge, England..
    Forsberg, Björn O.
    Stockholm Univ, Dept Biochem & Biophys, Sci Life Lab, Stockholm, Sweden..
    Kimanius, Dari
    Stockholm Univ, Dept Biochem & Biophys, Sci Life Lab, Stockholm, Sweden..
    Hagen, Wim J. H.
    European Mol Biol Lab, Struct & Computat Biol Unit, Heidelberg, Germany.;European Mol Biol Lab, Cryoelectron Microscopy Serv Platform, Heidelberg, Germany..
    Lindahl, Erik
    KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, Centres, Science for Life Laboratory, SciLifeLab. KTH, School of Engineering Sciences (SCI), Applied Physics. Stockholm Univ, Dept Biochem & Biophys, Sci Life Lab, Stockholm, Sweden..
    Scheres, Sjors H. W.
    MRC, Lab Mol Biol, Cambridge, England..
    New tools for automated high-resolution cryo-EM structure determination in RELION-32018In: eLIFE, E-ISSN 2050-084X, Vol. 7, article id e42166Article in journal (Refereed)
    Abstract [en]

    Here, we describe the third major release of RELION. CPU-based vector acceleration has been added in addition to GPU support, which provides flexibility in use of resources and avoids memory limitations. Reference-free autopicking with Laplacian-of-Gaussian filtering and execution of jobs from python allows non-interactive processing during acquisition, including 2D-classification, de novo model generation and 3D-classification. Per-particle refinement of CTF parameters and correction of estimated beam tilt provides higher resolution reconstructions when particles are at different heights in the ice, and/or coma-free alignment has not been optimal. Ewald sphere curvature correction improves resolution for large particles. We illustrate these developments with publicly available data sets: together with a Bayesian approach to beam-induced motion correction it leads to resolution improvements of 0.2-0.7 angstrom compared to previous RELION versions.

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