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  • 122151.
    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.

  • 122152.
    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)
  • 122153.
    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.

  • 122154. 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.

  • 122155. 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.

  • 122156. Zimmermann, Kristian
    Cost and Weight Analysis of Ultra Thick Laminates for a Compact Landing Gear Fitting2011In: SICOMP 2011, 2011Conference paper (Other academic)
  • 122157.
    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.

  • 122158. 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.

  • 122159.
    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.

  • 122160. 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)
  • 122161. 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.

  • 122162.
    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.

  • 122163.
    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.

  • 122164. 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.

  • 122165.
    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.

  • 122166.
    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.

  • 122167. 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)
  • 122168.
    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

  • 122169.
    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.

  • 122170. 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.

  • 122171. 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.

  • 122172. 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.

  • 122173. 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.

  • 122174.
    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.

  • 122175.
    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.

  • 122176. 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.

  • 122177. 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.

  • 122178.
    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.

  • 122179. Zivkovic, Marija
    et al.
    Pereverza, Kateryna
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Industrial Ecology.
    Pasichnyi, Oleksii
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Industrial Ecology.
    Madzarevic, Aleksandar
    Ivezic, Dejan
    Kordas, Olga
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Industrial Ecology.
    Exploring scenarios for more sustainable heating: The case of Nis, Serbia2016In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 115, p. 1758-1770Article in journal (Refereed)
    Abstract [en]

    Sustainability transformation of the heating sector is recognised as being essential for reaching climate and environmental targets while improving the quality of life in cities worldwide. Participatory strategic planning enabled by scenario methods can be an important tool to guide this transformation, but methods for qualitative scenario analysis supporting stakeholder participation must be further developed and tested in the context of different cities. This paper presents results from integration of urban energy system modelling into the participatory strategic planning process implemented in the city of NE, which suffers problems typical of the heating sector in Serbia and the Western Balkans. The aim was to explore how the scenarios developed by local stakeholders could transform the NB heating system by 2030. Five scenarios developed within participatory backcasting project and a BAU scenario were analysed in terms of decarbonisation, energy security and energy efficiency using Long-range Energy Alternatives Planning System (LEAP). A final scenario "Efficiency for the green future" designed by the stakeholders for implementation in the city included high standards of energy efficiency in buildings, increased share of renewables in the heating energy mix, expanding the district heating system, deploying smart technologies and green architecture. The LEAP model demonstrated that this final scenario could lead to achievement of the desirable future vision developed by stakeholders for NB, through substantial improvements in energy efficiency and energy security, and to considerable emissions decreases by 2030 in comparison with the base year (2010) and the BAU scenario.

  • 122180. Zivkovic, Zoran
    et al.
    Booij, Olaf
    Kröse, Ben
    Topp, Elin Anna
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    Christensen, Henrik I.
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for Autonomous Systems, CAS.
    From sensors to human spatial concepts: An annotated data set2008In: IEEE Transactions on Robotics, ISSN 1552-3098, Vol. 24, no 2, p. 501-505Article in journal (Refereed)
    Abstract [en]

    An annotated data set is presented meant to help researchers in developing, evaluating, and comparing various approaches in robotics for building space representations appropriate for communicating with humans. The data consist of omnidirectional images, laser range scans, sonar readings, and robot odometry. A set of base-level human spatial concepts is used to annotate the data.

  • 122181.
    Ziyuan, Jiang
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Synthesis of GPU Programs from High-Level Models2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Modern graphics processing units (GPUs) provide high-performance general purpose computation abilities. They have massive parallel architectures that are suitable for executing parallel algorithms and operations. They are also throughput-oriented devices that are optimized to achieve high throughput for stream processing. Designing efficient GPU programs is a notoriously difficult task. The ForSyDe methodology is suitable to ease the difficulties of GPU programming. The methodology encourages software development from a high level of abstraction and then transforming the abstract model to an implementation through a series of formal methods. The existing ForSyDe models support the synchronous data flow (SDF) model of computation (MoC) which is suitable for modeling stream computations and is good for synthesizing efficient stream processing programs. There also exists high-level design models named parallel patterns that are suitable to represent parallel algorithms and operations. The thesis studies the method of modeling parallel algorithms using parallel patterns, and explores the way to synthesize efficient OpenCL implementation on GPUs for parallel patterns. The thesis also tries to enable the integration of parallel patterns into the ForSyDe SDF model in order to model stream parallel operations. An automation library that helps designing stream programs for parallel algorithms targeting GPUs is purposed in the thesis project. Several experiments are performed to evaluate the effectiveness of the proposed library regarding implementations of the high-level model.

  • 122182. Ziółek, M.
    et al.
    Martín, C.
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Douhal, A.
    Effect of electrolyte composition on electron injection and dye regeneration dynamics in complete organic dye sensitized solar cells probed by time-resolved laser spectroscopy2012In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, no 50, p. 26227-26238Article in journal (Refereed)
    Abstract [en]

    Femtosecond time-gated fluorescence and nanosecond flash photolysis studies of seven complete, real titania nanoparticle solar cells sensitized with an efficient organic dye (TH305) were performed in order to investigate the role of the electrolyte composition on the charge transfer dynamics. The electron injection rate constants were found to range from 0.4 to 3.5 ps-1 in iodide-based electrolyte, and they well correlate with the shift of the conduction band edge potential of titania. The lithium cation additives resulted in 2 times faster electron injection rate constant (3.55 ps-1) with respect to that when larger sodium cations were used (1.86 ps-1). However, in the presence of a pyridine derivative component in the electrolyte solution, the electron injection rate constant decreased several times (0.38 ps-1 for Li+ and 0.54 ps-1 for Na+), while the electron injection efficiency was found to be still very high, 96-100%. The dye regeneration by the redox couple under relatively low fluence of excitation beam (0.4 mJ/cm2 giving about 4 electrons per titania nanoparticle) proceeds with an average rate constant of about 40 × 10 3 s-1 and efficiency close to 100%, independent of the electron composition. However, for a larger fluence (2 mJ/cm2) excitation, a titania-dye electron recombination process competes with the dye regeneration and lowers the solar cell efficiency. The effect of self-quenching, high vibrational levels of the dye excited state, and the neat solvent on the electron injection process are also discussed. This study clearly shows that for TH350-based DSSCs the best performance is obtained using Li+ and TBP as additives to the iodide electrolyte, giving the highest open circuit voltage and almost 100% efficiency of electron injection and dye regeneration.

  • 122183.
    Zlosnik, Tom
    et al.
    Czech Acad Sci, Inst Phys, CEICO, Slovance 1999-2, Prague 18221, Czech Republic..
    Urban, Federico
    Czech Acad Sci, Inst Phys, CEICO, Slovance 1999-2, Prague 18221, Czech Republic..
    Marzola, Luca
    NICPB, Ravala Pst 10, EE-10143 Tallinn, Estonia..
    Koivisto, Tomi S.
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. NICPB, Ravala Pst 10, EE-10143 Tallinn, Estonia.
    Spacetime and dark matter from spontaneous breaking of Lorentz symmetry2018In: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 35, no 23, article id 235003Article in journal (Refereed)
    Abstract [en]

    It is shown that a spontaneously-broken gauge theory of the Lorentz group contains Ashtekar's chiral formulation of general relativity accompanied by dust. From this perspective, gravity is described entirely by a connection omega valued in the Lie algebra of the complexified Lorentz group and a Lorentz-charged scalar field tau. The model is 'pre-geometric' in the sense that the spacetime metric may be constructed only in the symmetry-broken regime. We speculate on the extent to which this dust may account for dark matter and on the behaviour of the theory in regimes where the symmetry is not broken.

  • 122184.
    Zmijewski, Nicholas
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Effects of Watershed Dynamics on Water Reservoir Operation Planning: Considering the Dynamic Effects of Streamflow in Hydropower Operation2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Water reservoirs are used to regulate river discharge for a variety of reasons, such as flood mitigation, water availability for irrigation, municipal consumption and power production purposes. Recent efforts to increase the amount of renewable power production have seen an increase in intermittent climate-variable power production due to wind and solar power production. The additional variable energy production has increased the need for regulating the capacity of the electrical system, to which hydropower production is a significant contributor. The hydraulic impact on the time lags of flows between production stations have often largely been ignored in optimization planning models in favor of computational efficiency and simplicity. In this thesis, the hydrodynamics in the stream network connecting managed reservoirs were described using the kinematic-diffusive wave (KD) equation, which was implemented in optimization schemes to illustrate the effects of wave diffusion in flow stretches on the resulting production schedule. The effect of wave diffusion within a watershed on the variance of the discharge hydrograph within a river network was also analyzed using a spectral approach, illustrating that wave diffusion increases the variance of the hydrograph while the regulation of reservoirs generally increases the variance of the hydrograph over primarily short periods. Although stream hydrodynamics can increase the potential regulation capacity, the total capacity for power regulation in the Swedish reservoir system also depends significantly on the variability in climatic variables. Alternative formulations of the environmental objectives, which are often imposed as hard constraints on discharge, were further examined. The trade-off between the objectives of hydropower production and improvement of water quality in downstream areas was examined to potentially improve the ecological and aquatic environments and the regulation capacity of the network of reservoirs.

  • 122185.
    Zmijewski, Nicholas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Bottacin-Busolin, Andrea
    University of Manchester, UK.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Incorporating Hydrologic Routing into Reservoir Operation Models: Implications for Hydropower Production Planning2016In: Water resources management, ISSN 0920-4741, E-ISSN 1573-1650, Vol. 30, no 2, p. 623-640Article in journal (Refereed)
    Abstract [en]

    Increased reliance on variable and intermittent energy sources is likely to lead to a change in the production strategies of hydropower, thereby increasing the importance of accurate forecasting of production. For optimization models applied to water reservoirs, the computational cost increases with the number of reservoirs and future time-steps considered, often requiring simplification of the physical description of the flow dynamics. Here it is demonstrated that deficiency of the model of the flow dynamics on stream-reaches gives rise to errors in short-term planning, which leads to sub-optimal production. Here a simplified hydraulic model based on the kinematic-diffusion wave model was incorporated in the optimization of reservoir production planning. The time-lag distributions of the streams were evaluated for River Dalälven and implemented in a computationally efficient form of the kinematic-diffusion wave equation incorporated in a production optimization algorithm for a series of reservoirs. Compared to using a single time-lag for the water transfer on flow reaches between hydropower stations, the wave diffusion was found to affect the management as a deviation between the actual production and the planned production. The deviation was found to increase with increasing short-term regulation and decreasing Peclet number below about 10. For a sufficiently high Peclet number and long wavelength characterizing individual stream reaches, the distribution of time-lags become sufficiently narrow to motivate being replaced by a simpler description such as the constant time-lag.

  • 122186.
    Zmijewski, Nicholas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Coupled geomorphologic dispersion and reservoir managementManuscript (preprint) (Other academic)
  • 122187.
    Zmijewski, Nicholas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Hydrograph variances over different timescales in hydropower production networks2016In: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 52, no 8, p. 5829-5846Article in journal (Refereed)
    Abstract [en]

    The operation of water reservoirs involves a spectrum of timescales based on the distribution of stream flow travel times between reservoirs, as well as the technical, environmental, and social constraints imposed on the operation. In this research, a hydrodynamically based description of the flow between hydropower stations was implemented to study the relative importance of wave diffusion on the spectrum of hydrograph variance in a regulated watershed. Using spectral decomposition of the effluence hydrograph of a watershed, an exact expression of the variance in the outflow response was derived, as a function of the trends of hydraulic and geomorphologic dispersion and management of production and reservoirs. We show that the power spectra of involved time-series follow nearly fractal patterns, which facilitates examination of the relative importance of wave diffusion and possible changes in production demand on the outflow spectrum. The exact spectral solution can also identify statistical bounds of future demand patterns due to limitations in storage capacity. The impact of the hydraulic description of the stream flow on the reservoir discharge was examined for a given power demand in River Dalälven, Sweden, as function of a stream flow Peclet number. The regulation of hydropower production on the River Dalälven generally increased the short-term variance in the effluence hydrograph, whereas wave diffusion decreased the short-term variance over periods of <1 week, depending on the Peclet number (Pe) of the stream reach. This implies that flow variance becomes more erratic (closer to white noise) as a result of current production objectives.

  • 122188.
    Zmijewski, Nicholas
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Trade-Offs between phosphorous discharge and hydropower production using reservoir regulation2017In: Journal of water resources planning and management, ISSN 0733-9496, E-ISSN 1943-5452, Vol. 143, no 9, article id 04017052Article in journal (Refereed)
    Abstract [en]

    The management of water flow using reservoirs for the purpose of hydropower production can have significant impacts on solute transport. Reducing the phosphorous load to downstream areas can be of great importance for aquatic habitats associated with recipient waters, as well as for the overall health of coastal and estuary areas. This study demonstrates a combined operation of a network of reservoirs with the objectives of hydropower production and improvement of water quality in downstream areas using a multiobjective approach and incorporating the transport of phosphorous in the watershed. A genetic optimization method was used to determine the trade-off between power production and mitigation of phosphorous discharge in the reservoir network of the Dalälven River, Sweden. The phosphorous export can be reduced (-5%) with a limited loss of power production (-4.3%), but further reduction is associated with a significant loss in total power production. The trade-off between the two objectives is determined using Pareto diagrams and examined for varying particulate conditions.

  • 122189.
    Zoghi, Sedigheh
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    On the statistical tests over Fennoscandian GNSS/levelling networks2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In Geodesy and Surveying we work with a large amount of observations which alwayscontains different types of errors. The errors decrease the quality of the observations andpropagate to the results. Therefore, detection and removing the gross errors are of vitalimportance. The Global Navigation Satellite Systems (GNSS) can be used to measure theellipsoidal height and by subtracting an existing geoid height from that, the orthometric heightcan be determined. There is a simple linear relation amongst these triple heights, whichcannot be fulfilled due to the presence of different types of error. One of the important sort ofthese errors is gross errors.This study concerns about investigation and detection of blunders or gross errors on the 4346GNSS/levelling points over Fennoscandia. Each country has its own data set with specificprecision. The well-known gravity model EGM08 is used to compute the geoid heights withrespect to WGS84 reference ellipsoid. We have a large amount of data and we expect thattheir errors follow the normal distribution. The main aim of this thesis is to apply some datascreening methods both before and after adjustment process in such a way that the normaldistribution of the data set is achieved by eliminating the erroneous data. This will be done byperforming the pre- and post-adjustment data screening. For the pre-adjustment we performeddata filtering, test of normality of observations and test of their variances for theGNSS/levelling data over Sweden, Denmark, Norway and Finland. We used the 4-, 5- and 7-parameter corrective surfaces for modelling the systematic trends of the differences betweenthe EGM08 geoid model and the ellipsoidal and orthometric height differences. The test ofnormality of residuals, global test of variance, Baarda’s data snooping and Tau test will beperformed after the removal of the trends. Numerical studies show that the GNSS/levellingdata of Sweden, Denmark and Finland are of good qualities, but the claimed errors for thedata are rather optimistic. The situation was complicated for the data of Norway and we couldnot see the normality of the data and even the claimed accuracies seem to be optimistic.

  • 122190.
    Zografos, Alexandros
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Wireless Sensor-based Agricultural Monitoring System2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Today energy resources are becoming scarcer and therefore more valuable. In conjunction with the population growth over last century, the need for finding new, more efficient, and sustainable methods of agricultural cultivation and food production has become more critical. To facilitate this process, we are designing, building, and evaluating a system for precision agriculture which provides farmers with useful data about the soil, the water supply, and the general condition of their fields in a user friendly, easily accessible manner. Our system aims to make cultivation and irrigation more efficient as the farmer is able to make better informed decisions and thus save time and resources.

    The diversity of location and climatic effects upon agricultural cultivation, along with other environmental parameters over time makes the farmer’s decision-making process more complicated and requires additional empirical knowledge. Applying wireless sensor networks for monitoring environmental parameters and combining this information with a user-customized web service may enable farmers to exploit their knowledge in an efficient way in order to extract the best results from their agricultural cultivation. The system can scale based on each farmer’s demands and the resulting ensemble of collected information may represent a valuable resource for future use, in addition to its use for real-time decision making. The design of the precision agriculture system contains a prototype solution regarding the sensor platform and a customizable service that can be utilized in different ways and by several entities.

  • 122191.
    Zografos, Dimitrios
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Estimation of Power System Inertia2016In: Power and Energy Society General Meeting (PESGM), 2016 17-21 July 2016, 2016Conference paper (Refereed)
    Abstract [en]

    Information about power system inertia is of utmost importance for the Transmission System Operators (TSOs), so that it can be guaranteed that the stability of the system is not under risk. A new offline inertia estimation method is proposed in this paper. The method includes the calculation of the total power change after a disturbance in the system, based on selection of appropriate time ranges of the Rate Of Change Of Frequency(ROCOF) curve. Nordic32 test system is used for the simulations, where different disturbances, load dynamics and data processing tools are considered. Finally, a comparison of the proposed method to two methods proposed in the past takes place.

  • 122192.
    Zografos, Dimitrios
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Power system inertia estimation by approaching load power change after a disturbance2017In: Power & Energy Society General Meeting, 2017 IEEE, Chicago, IL, USA: Institute of Electrical and Electronics Engineers (IEEE), 2017Conference paper (Refereed)
    Abstract [en]

    The substitution of conventional synchronous power plants by intermittent generation leads to reduced power system inertia. This transition deteriorates system's frequency response and necessitates the estimation of power system inertia, so that adequate power resources are preserved. An offline estimation method is proposed in this paper, which aims to estimate the power change of the loads due to voltage dependency after a disturbance. To do that, data available at the generator buses are employed. The proposed method is applied on a modified version of Nordic32 test system under twenty different scenarios, which include generator and load disconnections. Finally, a comparison with two offline methods presented in the past literature takes place and demonstrates the advantages and disadvantages of the proposed method.

  • 122193.
    Zografos, Dimitrios
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power Systems.
    Eriksson, R.
    Power system inertia estimation: Utilization of frequency and voltage response after a disturbance2018In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 161, p. 52-60Article in journal (Refereed)
    Abstract [en]

    Power system inertia is gradually being reduced due to the ongoing replacement of conventional synchronous power plants by intermittent generation. This affects the frequency response of the system and necessitates the estimation of power system inertia, so that sufficient power reserves are retained. This paper contributes with a novel disturbance-based inertia estimation method, that simultaneously estimates the power change after a disturbance. The proposed method accommodates the frequency and voltage dynamics, which significantly affect the system's power change, and hence the inertia estimation. Two separate approaches – that are also capable of standing alone – are combined, in order to accommodate the dynamics. An extended version of the Nordic32 test system is used for the application of the method, where several case studies and a comparison are investigated, so as to examine the method's accuracy and robustness.

  • 122194.
    Zografos, Dimitrios
    et al.
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Paridari, Kaveh
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    Estimation of power system inertia using particle swarm optimization2017In: 2017 19th International Conference on Intelligent System Application to Power Systems, ISAP 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, article id 8071383Conference paper (Refereed)
    Abstract [en]

    Power system inertia is being globally reduced, due to the substitution of conventional synchronous power plants by intermittent generation. This threatens the frequency stability of the system and makes the estimation of power system inertia necessary, so that proactive measures can be imposed. A disturbance-based method is proposed in this paper, which estimates the total inertia constant of the power system. The method applies particle swarm optimization (PSO) to minimize a cost function, which is defined based on the swing equation. To do that, data available at the generator buses are employed. The proposed method is applied on the Nordic57 test system under twenty different scenarios, which include generator and load disconnections. Furthermore, a comparison with two methods presented in the literature is performed and demonstrates the higher performance of the proposed method, in the sense of the mean and the variance of the errors.

  • 122195.
    Zografos, Dimitrios
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Rabuzin, Tin
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Ghandhari, Mehrdad
    KTH, School of Electrical Engineering and Computer Science (EECS), Electric Power and Energy Systems.
    Eriksson, Robert
    Prediction of Frequency Nadir by Employing a Neural Network Approach2018In: 2018 IEEE PES Innovative Smart Grid Technologies Conference Europe (ISGT-Europe), Institute of Electrical and Electronics Engineers (IEEE), 2018Conference paper (Refereed)
    Abstract [en]

    The increased integration rate of inverter-interfaced devices is affecting the frequency response of the modern power systems. This leads to an increase of the variability of the power generation and to a reduction of the total system's inertia. This evolution of the system necessitates the prediction of frequency metrics, so that the frequency stability of the system can be guaranteed and that necessary mitigation measures can be taken. This paper proposes a method to predict the frequency nadir by using a Neural Network (NN) approach. As the approach uses measurements during a first short time period after the event, it more accurately predicts the frequency nadir compared to using static values. Several inputs for the NN are examined and when the appropriate ones are selected, a highly accurate prediction is accomplished.

  • 122196.
    Zohdi, Zeynab
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics. Karolinska Inst, Dept Clin Neurosci, Ctr Psychiat Res, SE-17176 Solna, Sweden ; Univ Bu Ali Sina, Dept Chem, Hamadan 65174, Iran.
    Hashemi, Mahdi
    Univ Bu Ali Sina, Dept Chem, Hamadan 65174, Iran..
    Uheida, Abdusalam
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Moein, Mohammad Mahdi
    Karolinska Inst, Dept Clin Neurosci, Ctr Psychiat Res, SE-17176 Solna, Sweden..
    Abdel-Rehim, Mohamed
    KTH, School of Engineering Sciences (SCI), Applied Physics. Karolinska Inst, Dept Clin Neurosci, Ctr Psychiat Res, SE-17176 Solna, Sweden Dept Appl Phys, SE-16440 Stockholm, Sweden..
    Graphene Oxide Tablets for Sample Preparation of Drugs in Biological Fluids: Determination of Omeprazole in Human Saliva for Liquid Chromatography Tandem Mass Spectrometry2019In: Molecules, ISSN 1420-3049, E-ISSN 1420-3049, Vol. 24, no 7, article id 1191Article in journal (Refereed)
    Abstract [en]

    In this study, a novel sort of sample preparation sorbent was developed, by preparing thin layer graphene oxide tablets (GO-Tabs) utilizing a mixture of graphene oxide and polyethylene glycol on a polyethylene substrate. The GO-Tabs were used for extraction and concentration of omeprazole (OME) in human saliva samples. The determination of OME was carried out using liquid chromatography-tandem mass spectrometry (LC-MS/MS) under gradient LC conditions and in the positive ion mode (ESI+) with mass transitions of m/z 346.3 -> 198.0 for OME and m/z 369.98 -> 252.0 for the internal standard. Standard calibration for the saliva samples was in the range of 2.0-2000 nmol L-1. Limits of detection and quantification were 0.05 and 2.0 nmol L-1, respectively. Method validation showed good method accuracy and precision; the inter-day precision values ranged from 5.7 to 8.3 (%RSD), and the accuracy of determinations varied from -11.8% to 13.3% (% deviation from nominal values). The extraction recovery was 60%, and GO-Tabs could be re-used for more than ten extractions without deterioration in recovery. In this study, the determination of OME in real human saliva samples using GO-Tab extraction was validated.

  • 122197. Zois, D. -S
    et al.
    Levorato, Marco
    KTH, School of Electrical Engineering (EES), Automatic Control. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Mitra, U.
    Non-linear smoothers for discrete-time, finite-state Markov chains2013In: IEEE International Symposium on Information Theory: Proceedings, 2013, p. 2099-2103Conference paper (Refereed)
    Abstract [en]

    The problem of enhancing the quality of system state estimates is considered for a special class of dynamical systems. Specifically, a system characterized by a discrete-time, finite-state Markov chain state and observed via conditionally Gaussian measurements is assumed. The associated mean vectors and covariance matrices are tightly intertwined with the system state and a control input selected by a controller. Exploiting an innovations approach, finite-dimensional, non-linear approximate MMSE smoothing estimators are derived for the Markov chain system state. The resulting smoothers are driven by a control policy determined by a stochastic dynamic programming algorithm, which minimizes the MSE filtering error, and was proposed in our earlier work. An application of the smoothers derived in this paper is presented for the problem of physical activity detection in wireless body sensing networks, which illustrates the performance enhancement due to smoothing.

  • 122198. Zolesi, V. S.
    et al.
    Ganga, P. L.
    Scolamiero, L.
    Micheletti, A.
    Podio-Guidugli, P.
    Tibert, Gunnar
    KTH, School of Engineering Sciences (SCI), Mechanics, Structural Mechanics.
    Donati, A.
    Ghiozzi, M.
    On an innovative deployment concept for large space structures2012In: 42nd International Conference on Environmental Systems 2012, ICES 2012, American Institute of Aeronautics and Astronautics, 2012Conference paper (Refereed)
    Abstract [en]

    Large deployable space structures are mission-critical technologies for which deployment failure cannot be an option. The difficulty to fully reproduce and test on ground the deployment of large systems dictates the need for extremely reliable architectural concepts. In 2010, ESA promoted a study focused at the pre-development of breakthrough architectural concepts offering superior reliability. The study, which was performed as an initiative of ESA Small Medium Enterprises Office (http://www.esa.int/SME/), by Kayser Italia at its premises in Livorno (Italy), with Universita' di Roma TorVergata (Rome, Italy) as sub-contractor and consultancy from KTH (Stockholm, Sweden), led to the identification of an innovative large deployable structure of "tensegrity" type, which achieves the required reliability because it permits a drastic reduction in the number of articulated joints in comparison with non-tensegrity architectures. The identified target application was in the field of large antenna reflectors. The project focused on the overall architecture of a deployable system and the related design implications. With a view toward verifying experimentally the performance of the deployable structure, a reduced-scale breadboard model was designed and manufactured. A gravity off-loading system was designed and implemented, so as to check deployment functionality in a 1-g environment. Finally, a test campaign was conducted, to validate the main design assumptions as well as to ensure the concept's suitability for the selected target application. The test activities demonstrated satisfactory stiffness, deployment repeatability, and geometric precision in the fully deployed configuration. The test data were also used to validate a finite element model, which predicts a good static and dynamic behavior of the full-scale deployable structure.

  • 122199.
    Zolfaghari, Anahita
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Transparant högtalare: Konstruktion, förpackning och montering2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This report describes a master thesis conducted at the Machine Department at the KTH Royal Institute of Technology in collaboration with the Swedish design company People People. The project was done during six months and the goal was to further develop an existing speaker that People People had developed and to generate concepts for the packaging. People People has developed a speaker in a box of glass that owing to its transparency blends into its environment and takes up little visual space. The speaker is large enough to produce high quality sound. In the electronics box in the speaker, it is possible to connect an AirPort Express that enables wireless music playback from a device connected to WiFi. In the current situation, the speaker is delivered fully assembled, but the customer can also choose to have only the components delivered as a do-it-yourself kit (DIY kit) and make a special order for the glass from a local glazier. The aim of the project was to optimize the design of the speaker in order to reduce the number of separate components, reduce the time and cost of installation in the factory and to facilitate the mounting. Furthermore, the electronics and the design of the speaker were to be reviewed. The electronics must be compatible for a wide market and the components must be connected in a way that is optimized for an easy connection to AirPort Express. A further aim was to develop the concept of the packages, both in the pre-assembled product, and DIY kit, so that they are optimized for the transport and in that way more environmentally friendly. With fewer components, the time of mounting and the critical moment was reduced. The three corners of the screws were replaced with a specially designed corner piece to facilitate and make the installation more intuitive. The electronics box that previously was enclosed by glass on the backside, was fitted with air supply both front and back, which enabled the insertion of AirPort Express after mounting. The concepts for the packages that were developed were optimized for transport. The packaging was design after the dimensions of the product in order to reduce material consumption.

  • 122200.
    Zolfaghari, Anahita
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Waldner, Carl-Johan
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Bogramp till FRED 252010Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Fred 25 is a boat that is supposed to be accessible to everyone, regardless of mobility. It is a 7.5 m long aluminum boat with ramp at the bow. The objective in the development of the boat has been that one wheelchair bound skipper can manage the boat all by himself. There are a number of problems with the boat to be resolved. In this project the focus has been on developing an inexpensive and effective sealing of the ramp and a locking of the ramp that goes to automate. These problems must be solved with minimal changes to the boat's current design. Developing the bow ramp with these requests is absolutely possible. However, it was difficult to obtain optimal solutions in which few or no changes could be made on the boat. This leads to solutions that counteract the built-in errors rather than erase them.For sealing the bottom of the ramp, the concept chosen consisted of a rubber mat that attaches to the outside of the ramp and the hull underneath the ramp.In order to seal the sides of the ramp a tubular rubber ledge was chosen. The rubber ledge clamps over the rib of the ramp and fills the gap between the ramp and the hull. The newly developed locking for the ramp follows the same principle as before i.e. a board with holes that folds over two locking bolts. Earlier this maneuver has been done manually, but with this new solution the board is hoisted up with the ramp and folds over the bolts automatically. Tests on the boat Fred 25 with the modifications which this project has resulted in has to be made for full evaluation.

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