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  • 122801.
    Zimmerer, Frank
    et al.
    Saarland University.
    Andreeva, Bistra
    Saarland University.
    Möbius, Bernd
    Saarland University.
    Malisz, Zofia
    KTH, Skolan för datavetenskap och kommunikation (CSC), Tal, musik och hörsel, TMH, Tal-kommunikation.
    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 Surprisal2017Ingår i: ESSV - 28. Konferenz Elektronische Sprachsignalverarbeitung 2017, Saarbrücken, 2017Konferensbidrag (Refereegranskat)
    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. 

  • 122802.
    Zimmerman, Robert W.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik (flyttat 20130630), Teknisk geologi och geofysik.
    The Imperial College lectures in petroleum engineering2018Samlingsverk (redaktörskap) (Övrigt vetenskapligt)
    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.

  • 122803.
    Zimmerman, Robert W.
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Mark- och vattenteknik (flyttat 20130630), Teknisk geologi och geofysik.
    Lutz, M.P
    Thermal and electrical conductivity of composites with graded interfaces2006Ingår i: International Journal of Advances in Science and Technology, ISSN 2229-5216, Vol. 45, s. 1097-1102Artikel i tidskrift (Refereegranskat)
  • 122804.
    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 fractures2004Ingår i: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 41, nr 3, s. 384-384Artikel i tidskrift (Refereegranskat)
    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.

  • 122805. Zimmermann, J.
    et al.
    Saravanan, B. K.
    Marz, R.
    Kamp, M.
    Forchel, A.
    Anand, Srinivasan
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Large dispersion in photonic crystal waveguide resonator2005Ingår i: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 41, nr 7, s. 414-415Artikel i tidskrift (Refereegranskat)
    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.

  • 122806. Zimmermann, J
    et al.
    Scherer, H
    Kamp, M
    Deubert, S
    Reithmaier, J P
    Forchel, A
    Marz, R
    Anand, Srinivasan
    KTH, Tidigare Institutioner, Elektronik.
    Photonic crystal waveguides with propagation losses in the 1 dB/mm range2004Ingår i: Journal of Vacuum Science & Technology B, ISSN 1071-1023, E-ISSN 1520-8567, Vol. 22, nr 6, s. 3356-3358Artikel i tidskrift (Refereegranskat)
    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.

  • 122807. Zimmermann, Kristian
    Cost and Weight Analysis of Ultra Thick Laminates for a Compact Landing Gear Fitting2011Ingår i: SICOMP 2011, 2011Konferensbidrag (Övrigt vetenskapligt)
  • 122808.
    Zimmermann, Kristian
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Ultra Thick Laminates for Compact Load Introduction Fittings2011Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

  • 122809. Zimmermann, Kristian
    et al.
    Siemetzki, Markus
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Analysis and Manufacturing of Ultra Thick Laminates for Future Aircraft Applications2008Ingår i: ECCM-13, 2008, 2008Konferensbidrag (Övrigt vetenskapligt)
    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.

  • 122810.
    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 elements2012Ingår i: Journal of reinforced plastics and composites (Print), ISSN 0731-6844, E-ISSN 1530-7964, Vol. 31, nr 3, s. 163-178Artikel i tidskrift (Refereegranskat)
    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.

  • 122811. Zimmermann,, Kristian
    et al.
    van den Broucke, B.
    Simulation of Process Induced Deformations in Ultra-thick Laminates Manufactured with Vacuum Assisted ProcessManuskript (preprint) (Övrigt vetenskapligt)
  • 122812. Zimmermann, Kristian
    et al.
    Zenkert, Dan
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Siemetzki, M.
    Testing and analysis of ultra thick composites2010Ingår i: Composites Part B: Engineering, ISSN 1359-8368, E-ISSN 1879-1069, Vol. 41, nr 4, s. 326-336Artikel i tidskrift (Refereegranskat)
    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.

  • 122813.
    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, Skolan för arkitektur och samhällsbyggnad (ABE), Centra, Centrum för transportstudier, 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, Skolan för arkitektur och samhällsbyggnad (ABE), Centra, Centrum för transportstudier, CTS.
    Capturing correlation with a mixed recursive logit model for activity-travel scheduling2018Ingår i: Transportation Research Part C: Emerging Technologies, ISSN 0968-090X, E-ISSN 1879-2359, Vol. 93, s. 273-291Artikel i tidskrift (Refereegranskat)
    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.

  • 122814.
    Zimmermann, Maëlle
    et al.
    Department of Computer Science and Operations Research, Universit\'e de Montr\'eal, QC, Canada.
    Blom Västberg, Oskar
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Systemanalys och ekonomi. 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 schedulingManuskript (preprint) (Övrigt vetenskapligt)
    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.

  • 122815. Zimmermann, U.
    et al.
    Osterman, J.
    Kuylenstierna, D.
    Hallén, Anders.
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Konstantinov, A. O.
    Vetter, W. M.
    Dudley, M.
    Material defects in 4H-silicon carbide diodes2003Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 93, nr 1, s. 611-618Artikel i tidskrift (Refereegranskat)
    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.

  • 122816.
    Zimmermann, Uwe
    KTH, Tidigare Institutioner                               , Mikroelektronik och informationsteknik, IMIT.
    Design, Processing and Characterization of Silicon Carbide Diodes2003Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

  • 122817.
    Zimmermann, Uwe
    et al.
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Domeij, Martin
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Hallén, Anders
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Östling, Mikael
    KTH, Tidigare Institutioner, Mikroelektronik och informationsteknik, IMIT.
    Comparison between implanted and epitaxial pin-diodes on 4H-silicon carbide2004Ingår i: 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, s. 1037-1040Konferensbidrag (Övrigt vetenskapligt)
    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.

  • 122818. Zinkevich, M.
    et al.
    Aldinger, F.
    Sundman, Bo
    KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
    The Ringberg workshop 2005 on thermodynamic modeling and first-principles calculations2007Ingår i: Calphad, ISSN 0364-5916, E-ISSN 1873-2984, Vol. 31, nr 1, s. 2-3Artikel i tidskrift (Övrigt vetenskapligt)
  • 122819.
    Zinn, Alexandra
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Fastigheter och byggande.
    Framtidens studentbostadsmarknad2015Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Bostadsbristen för studenter, särskilt i större städer, har under en längre tid varit ett frekvent diskuterat ämne i Sverige. Stockholm har ett brett och starkt utbud av högre utbildning och regionen expanderar kontinuerligt. Regionen har idag cirka 80,000 studenter som slåss om färre än 13 000 studentbostäder. Detta medför en risk att studenter väljer bort Stockholm som studentstad.

    Denna studie syftar till att undersöka möjligheterna för studentbostadsmarknaden att utvecklas. Med ett kvalitativt tillvägagångsätt via intervjuer med fastighetsutvecklare och lärosäten identifierades fem problemområden som ligger till grund för detta examensarbete. De fem problemområdena är; Utformning av studentbostäder, uthyrning och hyreslagstiftning, ett utvecklat campus, högskolans roll, samt subventioner och bidrag.

    Examensarbetet avslutas med en presentation av en modell med två alternativ för nyproduktion av studentbostäder uppdelade efter studentbostäder som utvecklas på campus respektive utanför campus. Studentbostäder som ska byggas på campus föreslås i första hand att utformas som kollektivboende med lärosätet som ägare och att uthyrning ska ske till förstaårselever vid lärosätet. Studentbostäder som ska byggas utanför campus föreslås istället att utformas som studentettor eller tvåor vilka fastighetsbolag och stiftelser utvecklar, äger och hyr ut via ett kösystem.

    Slutsatsen för denna studie pekar på att det är viktigt att en meny av olika former av boende förs till studentbostadsmarknaden då studenter har olika preferenser samtidigt som lärosäten och fastighetsägare har olika intresse att bevaka gällande studenters boende.

  • 122820.
    ZINN, KRISTOFFER
    KTH, Skolan för industriell teknik och management (ITM), Industriell ekonomi och organisation (Inst.), Entreprenörskap och Innovation.
    Risk Management and the Tax Allocation Reserve2016Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    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.

  • 122821. Ziolek, Marcin
    et al.
    Cohen, Boiko
    Yang, Xichuan
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    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 films2012Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 14, nr 8, s. 2816-2831Artikel i tidskrift (Refereegranskat)
    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.

  • 122822. Ziolek, Marcin
    et al.
    Karolczak, Jerzy
    Zalas, Maciej
    Hao, Yan
    Tian, Haining
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    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 Cells2014Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, nr 1, s. 194-205Artikel i tidskrift (Refereegranskat)
    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.

  • 122823. Ziolek, Marcin
    et al.
    Tacchini, Ignacio
    Martinez, M. Teresa
    Yang, Xichuan
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Douhal, Abderrazzak
    A photo-induced electron transfer study of an organic dye anchored on the surfaces of TiO2 nanotubes and nanoparticles2011Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 13, nr 9, s. 4032-4044Artikel i tidskrift (Refereegranskat)
    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.

  • 122824. Ziolek, Marcin
    et al.
    Yang, Xichuan
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    Douhal, Abderrazzak
    Interrogating the ultrafast dynamics of an efficient dye for sunlight conversion2010Ingår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, nr 28, s. 8098-8107Artikel i tidskrift (Refereegranskat)
    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.

  • 122825.
    Zioris, Stavros
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Vranjkovina, Alija
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Betongbyggnad.
    Evaluation of a Tramway’s Track Slab in Conventionally Reinforced Concrete or Steel Fibre Concrete2015Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Armeringen av betongkonstruktioner domineras av konventionell armering (armeringsjärn).

    Med den ständiga strävan mot utveckling och förbättring har inom teknikområdet nya

    innovativa och avancerade metoder introducerats. Det är på grund av bristen på normer,

    standarder som fiberarmerad betong begränsats till icke- bärande ändamål. Däremot har

    situationen förändrats under de senaste åren, redan idag kan man se konstruktioner där

    fiberarmering används till bärande ändamål.

    Amnet for den aktuella masterexamen var betongplatta i projektet ”Sparvag City” i Stockholm.

    Syftet var att utvärdera betongplattan, i form av att undersöka alternativa armeringsmöjligheter.

    I synnerhet undersöktes tre modeller; modell I- konventionellt armerad platta, modell IIstålfiberarmerad

    platta och modell III stålfiberarmerad platta kombinerad med konventionell

    armering. Modellernas möjligheter att uppfylla regelverkens krav undersöktes, men de

    jämfördes även ur ekonomiskt samt ergonomiskt perspektiv. En statisk linjär analys av

    betongplattan genomfördes i ett finit element program, Abaqus. Betongplattan utsattes för

    mekanisk belastning (egenvikt samt trafiklast) för vilken dimensionerande krafter extraherats.

    Därefter användes Eurocode 2 (EN 1992-1-1, 2004) och den svenska standarden för

    fiberarmerade betong konstruktioner (SS 812310:2014) för vidare konstruktionsberäkningar.

    Konstruktionsberäkningarna för betongplattan genomfördes i brottgränstillstånd för

    böjmoment samt tvärkraft, i brukgränsmotståndet undersöktes betongplattan för

    spänningsbegränsningar samt sprickkontroll.

    Konstruktionsberäkningarna kunde genomföras för modell I och III med de existerande

    föreskrifterna och kraven, men modellen med ”endast fibrer” kunde endast dimensionerna för

    böjmoment enligt SS 812310:2014. Därför kunde endast modell I och III fortsättningsvis

    jämföras med varandra. Från den ekonomiska jämförelsen erhölls det att modellen I var

    billigare än modell III, men att konstruktionstiden var längre. Dessutom var behoven för

    konventionell armering (armeringsjärn) betydligt mindre för modell III till skillnad från modell

    I. Modellernas innehåll av konventionell armering var avgörande för den ergonomiska

    bedömningen. Den mänskliga faktorn, som var relevanta för den ergonomiska bedömningens,

    gav jämförelsen av modellerna en annan dimension, där de viktiga mänskliga faktorerna

  • 122826.
    ZIRA, EIRINI
    KTH, Skolan för industriell teknik och management (ITM), Industriell ekonomi och organisation (Inst.), Entreprenörskap och Innovation.
    The Impact of Skill Mismatch on AggregateProductivity:cross-country analysis in OECD economies2016Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    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.

  • 122827. Zisis, G.
    et al.
    Manzo, Michele
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Gallo, Katia
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvantelektronik och -optik, QEO.
    Soergel, E.
    Mailis, S.
    UV laser-induced poling inhibition in proton exchanged LiNbO3 crystals2017Ingår i: Applied physics. B, Lasers and optics (Print), ISSN 0946-2171, E-ISSN 1432-0649, Vol. 123, nr 4, artikel-id 158Artikel i tidskrift (Refereegranskat)
    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.

  • 122828. Ziss, Dorian
    et al.
    Martin-Sanchez, Javier
    Lettner, Thomas
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Kvantnanofotonik.
    Halilovic, Alma
    Trevisi, Giovanna
    Trotta, Rinaldo
    Rastelli, Armando
    Stangl, Julian
    Comparison of different bonding techniques for efficient strain transfer using piezoelectric actuators2017Ingår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 121, nr 13, artikel-id 135303Artikel i tidskrift (Refereegranskat)
    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.

  • 122829.
    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, Centra, SeRC - Swedish e-Science Research Centre. KTH, Centra, Science for Life Laboratory, SciLifeLab. KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. 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-32018Ingår i: eLIFE, E-ISSN 2050-084X, Vol. 7, artikel-id e42166Artikel i tidskrift (Refereegranskat)
    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.

  • 122830. Zivkovic, Marija
    et al.
    Pereverza, Kateryna
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik, Industriell ekologi.
    Pasichnyi, Oleksii
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik, Industriell ekologi.
    Madzarevic, Aleksandar
    Ivezic, Dejan
    Kordas, Olga
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Hållbar utveckling, miljövetenskap och teknik, Industriell ekologi.
    Exploring scenarios for more sustainable heating: The case of Nis, Serbia2016Ingår i: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 115, s. 1758-1770Artikel i tidskrift (Refereegranskat)
    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.

  • 122831. Zivkovic, Zoran
    et al.
    Booij, Olaf
    Kröse, Ben
    Topp, Elin Anna
    KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Centrum för Autonoma System, CAS.
    Christensen, Henrik I.
    KTH, Skolan för datavetenskap och kommunikation (CSC), Centra, Centrum för Autonoma System, CAS.
    From sensors to human spatial concepts: An annotated data set2008Ingår i: IEEE Transactions on Robotics, ISSN 1552-3098, Vol. 24, nr 2, s. 501-505Artikel i tidskrift (Refereegranskat)
    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.

  • 122832.
    Ziyuan, Jiang
    KTH, Skolan för elektroteknik och datavetenskap (EECS).
    Synthesis of GPU Programs from High-Level Models2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Moderna grafikbehandlingsenheter (GPU) tillhandahåller högpresterande generella syftes-beräkningsförmågor. De har massiva parallella arkitekturer som är lämpliga för att utföra parallella algoritmer och operationer. De är också streaminriktade enheter som är optimerade för att uppnå hög streaming för streamingbehandling. Att utforma effektiva GPU-program är en notoriskt svårt uppgift. ForSyDe-metoden är lämplig för att underlätta svårigheterna med GPU-programmering. Metodiken uppmuntrar mjukvaruutveckling från en hög nivå av abstraktion för att sedan omvandla den abstrakta modellen till en implementering genom en rad formella metoder. De befintliga ForSyDe-modellerna stöder synkron dataflöde (SDF) modell av beräkning (MoC) som är lämplig för modellering av streaming-beräkningar och är bra för att syntetisera effektiv streaming-bearbetningsprogram. Det finns också högkvalitativa designmodeller som kallas parallella mönster vilka är lämpliga för att representera parallella algoritmer och operationer. Avhandlingen analyserar metoden för modellering av parallella algoritmer med parallella mönster, och utforskar sättet att syntetisera effektiv OpenCL-implementering för GPU för parallella mönster. Avhandlingen försöker även att möjliggöra integration av parallella mönster i ForSyDe SDF-modellen för att modellera streaming parallella operationer. Ett automationsbibliotek som hjälper till att designa stream-program för parallella algoritmer som riktar sig mot GPU:er är avsedda för avhandlingsprojektet. Flera experiment utförs för att utvärdera effektiviteten hos det föreslagna biblioteket avseende implementering av högnivåmodellen.

  • 122833. Ziółek, M.
    et al.
    Martín, C.
    Sun, Licheng
    KTH, Skolan för kemivetenskap (CHE), Kemi, Organisk kemi.
    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 spectroscopy2012Ingår i: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 116, nr 50, s. 26227-26238Artikel i tidskrift (Refereegranskat)
    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.

  • 122834.
    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, Centra, Nordic Institute for Theoretical Physics NORDITA. NICPB, Ravala Pst 10, EE-10143 Tallinn, Estonia.
    Spacetime and dark matter from spontaneous breaking of Lorentz symmetry2018Ingår i: Classical and quantum gravity, ISSN 0264-9381, E-ISSN 1361-6382, Vol. 35, nr 23, artikel-id 235003Artikel i tidskrift (Refereegranskat)
    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.

  • 122835.
    Zmijewski, Nicholas
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Effects of Watershed Dynamics on Water Reservoir Operation Planning: Considering the Dynamic Effects of Streamflow in Hydropower Operation2017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

  • 122836.
    Zmijewski, Nicholas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Bottacin-Busolin, Andrea
    University of Manchester, UK.
    Wörman, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Incorporating Hydrologic Routing into Reservoir Operation Models: Implications for Hydropower Production Planning2016Ingår i: Water resources management, ISSN 0920-4741, E-ISSN 1573-1650, Vol. 30, nr 2, s. 623-640Artikel i tidskrift (Refereegranskat)
    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.

  • 122837.
    Zmijewski, Nicholas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Wörman, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Coupled geomorphologic dispersion and reservoir managementManuskript (preprint) (Övrigt vetenskapligt)
  • 122838.
    Zmijewski, Nicholas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Wörman, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Hydrograph variances over different timescales in hydropower production networks2016Ingår i: Water resources research, ISSN 0043-1397, E-ISSN 1944-7973, Vol. 52, nr 8, s. 5829-5846Artikel i tidskrift (Refereegranskat)
    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.

  • 122839.
    Zmijewski, Nicholas
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Wörman, Anders
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Vattendragsteknik.
    Trade-Offs between phosphorous discharge and hydropower production using reservoir regulation2017Ingår i: Journal of water resources planning and management, ISSN 0733-9496, E-ISSN 1943-5452, Vol. 143, nr 9, artikel-id 04017052Artikel i tidskrift (Refereegranskat)
    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.

  • 122840.
    Zoghi, Sedigheh
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Samhällsplanering och miljö, Geodesi och satellitpositionering.
    On the statistical tests over Fennoscandian GNSS/levelling networks2015Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    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.

  • 122841.
    Zografos, Alexandros
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Kommunikationssystem, CoS, Radio Systems Laboratory (RS Lab).
    Wireless Sensor-based Agricultural Monitoring System2014Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Idag när energiresurser blir allt knappare och knappare blir de även mer värdefulla. I samband med befolkningstillväxten under förra århundradet har behovet av att hitta nya, mer effektiva och hållbara metoder inom jordbruket och livsmedelsproduktion blivit av allt större vikt. . För att underlätta denna process har vi designat, byggt och utvärderat ett system för precisionsjordbruk som ger bönder mer användbara data om jorden, vattenförsörjning och det allmänna tillståndet i sina områden på ett användarvänligt och lättillgängligt sätt. Vårt system syftar till att göra odling och bevattning effektivare då bonden kan fatta bättre underbyggda beslut och därmed spara tid och resurser.

    Mångfalden av läget och jordbrukets klimatpåverkan, tillsammans med andra miljöparametrar över tiden gör bondens beslutsprocess mer komplicerad än tidigare och kräver ytterligare empirisk kunskap. Att tillämpa trådlösa sensornätverk för övervakning av dessa parametrar och att presentera? denna information med en användarvänlig skräddarsydd webbtjänst kan göra det möjligt för jordbrukare att utnyttja på ett effektivt sätt nåde bästa resultaten från sitt jordbruk. Systemet kan skala utifrån varje bondes krav och den insamlade data kan utgöra en värdefull resurs för ett framtida jordbruk, utöver dess användning för dagens bondes beslut. Utformningen av systemet för precisionsjordbruk innehåller en prototyplösning avseende sensorplattformen och en anpassningsbar tjänst som kan användas på olika sätt och av flera enheter.

  • 122842.
    Zografos, Dimitrios
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Ghandhari, Mehrdad
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Estimation of Power System Inertia2016Ingår i: Power and Energy Society General Meeting (PESGM), 2016 17-21 July 2016, 2016Konferensbidrag (Refereegranskat)
    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.

  • 122843.
    Zografos, Dimitrios
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Ghandhari, Mehrdad
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Power system inertia estimation by approaching load power change after a disturbance2017Ingår i: Power & Energy Society General Meeting, 2017 IEEE, Chicago, IL, USA: Institute of Electrical and Electronics Engineers (IEEE), 2017Konferensbidrag (Refereegranskat)
    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.

  • 122844.
    Zografos, Dimitrios
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Ghandhari, Mehrdad
    KTH, Skolan för elektro- och systemteknik (EES), Elektriska energisystem.
    Eriksson, R.
    Power system inertia estimation: Utilization of frequency and voltage response after a disturbance2018Ingår i: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 161, s. 52-60Artikel i tidskrift (Refereegranskat)
    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.

  • 122845.
    Zografos, Dimitrios
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Ghandhari, Mehrdad
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Paridari, Kaveh
    KTH, Skolan för elektro- och systemteknik (EES), Elkraftteknik.
    Estimation of power system inertia using particle swarm optimization2017Ingår i: 2017 19th International Conference on Intelligent System Application to Power Systems, ISAP 2017, Institute of Electrical and Electronics Engineers (IEEE), 2017, artikel-id 8071383Konferensbidrag (Refereegranskat)
    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.

  • 122846.
    Zografos, Dimitrios
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Rabuzin, Tin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Ghandhari, Mehrdad
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elkraftteknik.
    Eriksson, Robert
    Prediction of Frequency Nadir by Employing a Neural Network Approach2018Ingår i: 2018 IEEE PES Innovative Smart Grid Technologies Conference Europe (ISGT-Europe), Institute of Electrical and Electronics Engineers (IEEE), 2018Konferensbidrag (Refereegranskat)
    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.

  • 122847.
    Zohdi, Zeynab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. 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, Skolan för teknikvetenskap (SCI), Tillämpad fysik.
    Moein, Mohammad Mahdi
    Karolinska Inst, Dept Clin Neurosci, Ctr Psychiat Res, SE-17176 Solna, Sweden..
    Abdel-Rehim, Mohamed
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik. 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 Spectrometry2019Ingår i: Molecules, ISSN 1420-3049, E-ISSN 1420-3049, Vol. 24, nr 7, artikel-id 1191Artikel i tidskrift (Refereegranskat)
    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.

  • 122848. Zois, D. -S
    et al.
    Levorato, Marco
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Mitra, U.
    Non-linear smoothers for discrete-time, finite-state Markov chains2013Ingår i: IEEE International Symposium on Information Theory: Proceedings, 2013, s. 2099-2103Konferensbidrag (Refereegranskat)
    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.

  • 122849. Zolesi, V. S.
    et al.
    Ganga, P. L.
    Scolamiero, L.
    Micheletti, A.
    Podio-Guidugli, P.
    Tibert, Gunnar
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Donati, A.
    Ghiozzi, M.
    On an innovative deployment concept for large space structures2012Ingår i: 42nd International Conference on Environmental Systems 2012, ICES 2012, American Institute of Aeronautics and Astronautics, 2012Konferensbidrag (Refereegranskat)
    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.

  • 122850.
    Zolfaghari, Anahita
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Transparant högtalare: Konstruktion, förpackning och montering2013Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Denna rapport beskriver ett examensarbete utfört på Institutionen för Maskinkonstruktion på Kungliga Tekniska högskolan (KTH) i samarbete med det svenska designföretaget People People. Projektet utfördes under sex månader och målet var att vidareutveckla en befintlig högtalare hos företaget samt att ta fram ett koncept för emballage. People People har tagit fram en högtalare i en låda av glas som tack vare sin transparens smälter in i sin omgivning och tar liten visuell plats. Den är tillräckligt stor för att kunna producera ljud av hög kvalitet. I elektroniklådan i högtalaren finns det möjlighet att koppla in en AirPortExpress som möjliggör trådlös uppspelning av musik från en enhet med WiFi. I dagsläget kan högtalaren levereras färdigmonterad men kunden kan även välja att få endast de ingående komponenterna levererade som ett do-it-yourself-kit (DIY-kit) och själv specialbeställa glaset från en lokal glasmästare. Syftet med examensarbetet är att optimera konstruktionen av högtalaren för att minska antalet lösa komponenter, minska tiden och kostnaden för montering i fabrik samt att öka användarvänligheten vid montering. Vidare ska elektroniken och dess utformning i högtalaren ses över. Elektroniken ska vara kompatibel för en bred marknad och komponenterna ska kopplas på ett sätt som är optimerat för en enkel inkoppling av AirPort Express. Vidare är syftet att ta fram koncept för emballagen, dels för den färdigmonterade produkten samt för DIY-kittet, så att de är optimerade för den pall de kommer lastas på och på så sätt miljövänliga. Genom färre monteringskomponenter minskades tiden för montering och med det kritiska momentet reducerades. De tre hörnskruvarna ersattes med en specialkonstruerad hörnbit för att underlätta och gör monteringen mer intuitiv. Elektroniklådan, som tidigare legat omsluten av glas på baksidan, monterades med lufttillförsel både fram och bak, vilket även möjliggjorde insättning av AirPort Express efter montering. Koncepten för emballagen som togs fram optimerades för transport och lastning på pall. Emballagen dimensionerades efter deras innehåll för att minska materialåtgång.

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