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  • 123501.
    Wiese, Viktor
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Brake noise: A study in multi-tonal brake squeal2017Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Brake squeal is a major problem for the vehicle industry due to recla-mations and quality perception of vehicles, as well as the unpredictability of its occurrence. This report investigates the physical reasons behind a multi-tonal brake squeal generated in a motorcycle disc brake. It also covers why previous remedies to eliminate the noise has had an e↵ect, as well as trying to find a stable cost-e↵ective solution to the problem. The brake components are studied using numerical simulations as well as experimental analysis, the accuracy of which is investigated by analyzing a simple beam and compar-ing the results to analytical calculations. By performing a FEM-simulation of the di↵erent subsystems, the multi-tonal sound was tracked down to the ABS tone wheel, e.a. the sensory ring that is used for wheel speed mea-surements. By simulating the modes with altered tone wheel thickness, the modal pattern remains the same albeit reduced in frequency. A character-istic dimension between the tone wheels mounting points where found, as the frequency where these bending modes between the mounting points oc-curred closely correlated with the frequency content of the measured noise. A thinner tone wheel was then manufactured and field tested, these test results shows a reduction in frequency for the multi-tonal sound, thus the indications from the simulation is confirmed. Furthermore, an investigation in to brake disc properties is carried out in order to explain the reason why discs with altered geometry lacks the squealing problems of the original disc. This is done by a simulation of the sound propagation efficiency of the discs out-of-plane surfaces as well as an experimental study of the insertion loss from the friction surface between the brake disc and the brake pads to the tone wheel. The report ends with suggestions of design changes that can help combat the current issues, as well as problems of the same nature that might arise in future brake designs

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  • 123502.
    Wiesen, S.
    et al.
    Forschungszentrum Julich GmbH, Inst Energ & Klimaforschung Plasmaphys, D-52425 Julich, Germany.;Forsch Zentrum Julich GmbH, Inst Energie & Klimaforsch Plasmaphys, D-52425 Julich, Germany..
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Elevant, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ivanova, Darya
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Atom- och molekylfysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Tholerus, Simon
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Zychor, I.
    Inst Plasma Phys & Laser Microfus, PL-01497 Warsaw, Poland..
    Plasma edge and plasma-wall interaction modelling: Lessons learned from metallic devices2017Ingår i: Nuclear Materials and Energy, E-ISSN 2352-1791, Vol. 12, s. 3-17Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    Robust power exhaust schemes employing impurity seeding are needed for target operational scenarios in present day tokamak devices with metallic plasma-facing components (PFCs). For an electricity-producing fusion power plant at power density P-sep/R > 15 MW/m divertor detachment is a requirement for heat load mitigation. 2D plasma edge transport codes like the SOLPS code as well as plasma-wall interaction (PWI) codes are key to disentangle relevant physical processes in power and particle exhaust. With increased quantitative credibility in such codes more realistic and physically sound estimates of the life-time expectations and performance of metallic PFCs can be accomplished for divertor conditions relevant for ITER and DEMO. An overview is given on the recent progress of plasma edge and PWI modelling activities for (carbon-free) metallic devices, that include results from JET with the ITER-like wall, ASDEX Upgrade and Alcator C-mod. It is observed that metallic devices offer an opportunity to progress the understanding of underlying plasma physics processes in the edge. The validation of models can be substantially improved by eliminating carbon from the experiment as well as from the numerical system with reduced degrees of freedom as no chemical sputtering from amorphous carbon layers and no carbon or hydro-carbon transport are present. With the absence of carbon as the primary plasma impurity and given the fact that the physics of the PWI at metallic walls is less complex it is possible to isolate the crucial plasma physics processes relevant for particle and power exhaust. For a reliable 2D dissipative plasma exhaust model these are: cross-field drifts, complete kinetic neutral physics, geometry effects (including main-chamber, divertor and sub-divertor structures), SOL transport reflecting also the non-diffusive nature of anomalous transport, as well as transport within the pedestal region in case of significant edge impurity radiation affecting pedestal pressure and hence P-sep.

  • 123503. Wiesen, S.
    et al.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Elevant, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ivanova, Darya
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Jonsson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik, Atom- och molekylfysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Tholerus, Simon
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zychor, I.
    et al.,
    Effect of PFC Recycling Conditions on JET Pedestal Density2016Ingår i: Contributions to Plasma Physics, ISSN 0863-1042, E-ISSN 1521-3986, Vol. 56, nr 6-8, s. 754-759Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    There is experimental evidence that the pedestal dynamics in type-I ELMy H-mode discharges is significantly affected by a change in the recycling conditions at the tungsten plasma-facing components (W-PFCs) after an ELM event. The integrated code JINTRAC has been employed to assess the impact of recycling conditions during type-I ELMs in JET ITER-like wall H-mode discharges. By employing a heuristic approach, a model to mimic the physical processes leading to formation and release (i.e. outgassing) of finite near-surface fuel reservoirs in W-PFCs has been implemented into the EDGE2D-EIRENE plasma-wall interaction code being part of JINTRAC. As main result it is shown, that a delay in the density pedestal build-up after an ELM event can be provoked by reduced recycling induced by depleted W-PFC particle near-surface reservoirs. However the pedestal temperature evolution is barely affected by the change in recycling parameters suggesting that the presented model is incomplete.

  • 123504. Wiesen, S.
    et al.
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Elevant, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Ivanova, Darya
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för teknikvetenskap (SCI), Fysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Tholerus, Emmi
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Fusionsplasmafysik.
    Weckmann, Armin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Zychor, I.
    et al.,
    Modelling of plasma-edge and plasma-wall interaction physics at JET with the metallic first-wall2016Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T167, artikel-id 014078Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An overview is given on the recent progress on edge modelling activities for the JET ITER-like wall using the computational tools like the SOLPS or EDGE2D-EIRENE code. The validation process of these codes on JET with its metallic plasma-facing components is an important step towards predictive studies for ITER and DEMO in relevant divertor operational conditions, i.e., for detached, radiating divertors. With increased quantitative credibility in such codes more reliable input to plasma-wall and plasma-material codes can be warranted, which in turn results in more realistic and physically sound estimates of the life-time expectations and performance of a Be first-wall and a W-divertor, the same materials configuration foreseen for ITER. A brief review is given on the recent achievements in the plasma-wall interaction and material migration studies. Finally, a short summary is given on the availability and development of integrated codes to assess the performance of an JET-ILW baseline scenario also in view of the preparation for a JET DT-campaign.

  • 123505. Wiesen, S
    et al.
    Brezinsek, M
    Wischmeier, M
    de la Luna, E
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Groth, M
    Järvinen, A
    Losada, U
    Martin, A
    Impact of the JET ITER-Like Wall on H-Mode Plasma Fueling2016Ingår i: 26th IAEA Fusion Energy Conference, 17-22 October 2016, 2016Konferensbidrag (Refereegranskat)
  • 123506.
    Wiesen, S.
    et al.
    Forschungszentrum Julich, Inst Energie & Klimaforsch Plasmaphys, D-52425 Julich, Germany..
    Brezinsek, S.
    Forschungszentrum Julich, Inst Energie & Klimaforsch Plasmaphys, D-52425 Julich, Germany..
    Bonnin, X.
    ITER Org, Route Vinon Sur Verdon,CS90 046, F-13067 St Paul Les Durance, France..
    Delabie, E.
    Oak Ridge Natl Lab, POB 2009, Oak Ridge, TN 37831 USA..
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Groth, M.
    Aalto Univ, Espoo, Finland..
    Guillemaut, C.
    Univ Lisbon, Inst Plasmas & Fusao Nucl, IST, P-1049001 Lisbon, Portugal..
    Harrison, J.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Harting, D.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Henderson, S.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Huber, A.
    Forschungszentrum Julich, Inst Energie & Klimaforsch Plasmaphys, D-52425 Julich, Germany..
    Kruezi, U.
    ITER Org, Route Vinon Sur Verdon,CS90 046, F-13067 St Paul Les Durance, France..
    Pitts, R. A.
    ITER Org, Route Vinon Sur Verdon,CS90 046, F-13067 St Paul Les Durance, France..
    Wischmeier, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    On the role of finite grid extent in SOLPS-ITER edge plasma simulations for JET H-mode discharges with metallic wall2018Ingår i: Nuclear Materials and Energy, E-ISSN 2352-1791, Vol. 17, s. 174-181Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The impact of the finite grid size in SOLPS-ITER edge plasma simulations is assessed for JET H-mode discharges with a metal wall. For a semi-horizontal divertor configuration it is shown that the separatrix density is at least 30% higher when a narrow scrape-off layer (SOL) grid width is chosen in SOLPS-ITER compared to the case for which the SOL grid width is maximised. The density increase is caused by kinetic neutrals being not confined inside the divertor region because of the reduced extent of the plasma grid. In this case, an enhanced level of reflections of energetic neutrals at the low-field side (LFS) metal divertor wall is observed. This leads to a shift of the ionisation source further upstream which must be accounted for as a numerical artefact. An overestimate in the cooling at the divertor entrance is observed in this case, identified by a reduced heat flux decay parameters lambda(div)(q). Otherwise and further upstream the mid-plane heat decay length lambda(q) parameter is not affected by any change in divertor dissipation. This confirms the assumptions made for the ITER divertor design studies, i.e. that lambda(q) upstream is essentially set by the assumptions for the ratio radial to parallel heat conductivity. It is also shown that even for attached conditions the decay length relations lambda(ne)>lambda(Te)>lambda(q) hold in the near-SOL upstream. Thus for interpretative edge plasma simulations one must take the (experimental) value of lambda(ne) into account, rather than lambda(q), as the former actually defines the required minimum upstream SOL grid extent.

  • 123507. Wiesen, S.
    et al.
    Brezinsek, S.
    Wischmeier, M.
    De La Luna, E.
    Groth, M.
    Jaervinen, A. E.
    De La Cal, E.
    Losada, U.
    De Aguilera, A. M.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. Association VR.
    Gao, Y.
    Guillemaut, C.
    Harting, D.
    Meigs, A.
    Schmid, K.
    Sergienko, G.
    Impact of the JET ITER-like wall on H-mode plasma fueling2017Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, nr 6, artikel-id 066024Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    JET ITER-like wall (ILW) experiments show that the edge density evolution is strongly linked with the poloidal distribution of the ionization source. The fueling profile in the JET-ILW is more delocalized as compared to JET-C (JET with carbon-based plasma-facing components PFCs). Compared to JET-C the H-mode pedestal fueling cycle is dynamically influenced by a combination of plasma-wall interaction features, in particular: (1) edge-localized modes (ELMs) induced energetic particles are kinetically reflected on W divertor PFCs leading to distributed refueling away from the divertor depending on the divertor plasma configuration, (2) delayed molecular re-emission and outgassing of particles being trapped in W PFCs (bulk-W at the high field side and W-coated CFCs at the low field side) with different fuel content and (3) outgassing from Be co-deposits located on top of the high-field side baffle region shortly after the ELM. In view of the results of a set of well diagnosed series of JET-ILW type-I ELMy H-mode discharges with good statistics, the aforementioned effects are discussed in view of H-mode pedestal fueling capacity. The ongoing modelling activities with the focus on coupled core-edge plasma simulations and plasma-wall interaction are described and discussed also in view of possible code improvements required.

  • 123508. Wiesenberger, M.
    et al.
    Einkemmer, L.
    Held, M.
    Gutierrez-Milla, A.
    Sáez, X.
    Iakymchuk, Roman
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Beräkningsvetenskap och beräkningsteknik (CST).
    Reproducibility, accuracy and performance of the FELTOR code and library on parallel computer architectures2019Ingår i: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 238, s. 145-156Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    FELTOR is a modular and free scientific software package. It allows developing platform independent code that runs on a variety of parallel computer architectures ranging from laptop CPUs to multi-GPU distributed memory systems. FELTOR consists of both a numerical library and a collection of application codes built on top of the library. Its main targets are two- and three-dimensional drift- and gyro-fluid simulations with discontinuous Galerkin methods as the main numerical discretization technique. We observe that numerical simulations of a recently developed gyro-fluid model produce non-deterministic results in parallel computations. First, we show how we restore accuracy and bitwise reproducibility algorithmically and programmatically. In particular, we adopt an implementation of the exactly rounded dot product based on long accumulators, which avoids accuracy losses especially in parallel applications. However, reproducibility and accuracy alone fail to indicate correct simulation behavior. In fact, in the physical model slightly different initial conditions lead to vastly different end states. This behavior translates to its numerical representation. Pointwise convergence, even in principle, becomes impossible for long simulation times. We briefly discuss alternative methods to ensure the correctness of results like the convergence of reduced physical quantities of interest, ensemble simulations, invariants or reduced simulation times. In a second part, we explore important performance tuning considerations. We identify latency and memory bandwidth as the main performance indicators of our routines. Based on these, we propose a parallel performance model that predicts the execution time of algorithms implemented in FELTOR and test our model on a selection of parallel hardware architectures. We are able to predict the execution time with a relative error of less than 25% for problem sizes between 10 −1 and 10 3 MB. Finally, we find that the product of latency and bandwidth gives a minimum array size per compute node to achieve a scaling efficiency above 50% (both strong and weak).

  • 123509.
    Wieser, Gabriella Stenberg
    et al.
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Odelstad, Elias
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Rymd- och plasmafysik. Swedish Inst Space Phys, Box 537, SE-75121 Uppsala, Sweden..
    Wieser, Martin
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Nilsson, Hans
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Goetz, Charlotte
    TU Braunschweig, Inst Geophys & Extraterrestrial Phys, D-38106 Braunschweig, Germany..
    Karlsson, Tomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Elektroteknik, Rymd- och plasmafysik.
    Andre, Mats
    Swedish Inst Space Phys, Box 537, SE-75121 Uppsala, Sweden..
    Kalla, Leif
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Eriksson, Anders I.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik. Swedish Inst Space Phys, Box 537, SE-75121 Uppsala, Sweden..
    Nicolaou, Georgios
    Swedish Inst Space Phys, Box 812, SE-98128 Kiruna, Sweden..
    Wedlund, Cyril Simon
    Univ Oslo, Dept Phys, POB 1048, N-0316 Oslo, Norway..
    Richter, Ingo
    TU Braunschweig, Inst Geophys & Extraterrestrial Phys, D-38106 Braunschweig, Germany..
    Gunell, Herbert
    Royal Belgian Inst Space Aeron, Ave Circulaire 3, B-1180 Brussels, Belgium.;Umeå Univ, Dept Phys, SE-90187 Umeå, Sweden..
    Investigating short-time-scale variations in cometary ions around comet 67P2017Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, s. S522-S534Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The highly varying plasma environment around comet 67P/Churyumov-Gerasimenko inspired an upgrade of the ion mass spectrometer (Rosetta Plasma Consortium Ion Composition Analyzer) with new operation modes, to enable high time resolution measurements of cometary ions. Two modes were implemented, one having a 4 s time resolution in the energy range 0.3-82 eV/q and the other featuring a 1 s time resolution in the energy range 13-50 eV/q. Comparing measurements made with the two modes, it was concluded that 4 s time resolution is enough to capture most of the fast changes of the cometary ion environment. The 1462 h of observations done with the 4 s mode were divided into hour-long sequences. It is possible to sort 84 per cent of these sequences into one of five categories, depending on their appearance in an energy-time spectrogram. The ion environment is generally highly dynamic, and variations in ion fluxes and energies are seen on time-scales of 10 s to several minutes.

  • 123510.
    Wiesinger, Jakob
    KTH, Skolan för elektroteknik och datavetenskap (EECS).
    Video Saliency Detection using Deep Learning2019Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    En deep learning-modell designas för att detektera fokuspunkter i video, dvs. förutspå vart människor kommer att rikta sin blick. Det neurala nätverkets arkitektur kombinerar flera innovationer inom fältet: två inputströmmar modellerar utseende och rörelse separat. Förtränad feature extraction detekterar objekt. Residual attention-moduler viktar om features. En ConvLSTM-modul säkerställer tidsmässig stabilitet i detektionen. Träningsdata består av både videoklipp och bilder, båda med motsvarande ögonfixeringsdata från eye trackers. Modellen utvärderas och visas prestera i klass med senaste forskningen.

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  • 123511.
    Wieslander, Simon
    et al.
    KTH, Skolan för industriell teknik och management (ITM), Tillämpad maskinteknik (KTH Södertälje).
    Landegren, Daniel
    KTH, Skolan för industriell teknik och management (ITM), Tillämpad maskinteknik (KTH Södertälje).
    Nätverksanslutning av verkstadsmaskiner med PLC för diagnostisering och visualisering av status2016Självständigt arbete på grundnivå (högskoleexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
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  • 123512. Wiesner, S.
    et al.
    Baalsrud Hauge, Jannicke
    KTH, Skolan för industriell teknik och management (ITM), Industriell ekonomi och organisation (Inst.). BIBA – Bremer Institut für Produktion und Logistik GmbH, Bremen, Germany.
    Haase, F.
    Thoben, K. -D
    Supporting the requirements elicitation process for cyber-physical product-service systems through a gamified approach2016Ingår i: IFIP WG 5.7 International Conference on Advances in Production Management Systems, APMS 2016, Springer New York LLC , 2016, s. 687-694Konferensbidrag (Refereegranskat)
    Abstract [en]

    Solutions are offered more and more in the form of Product- Service Systems (PSS), which combine tangible and intangible components into a comprehensive package for the customer. The rise of Internet of Things technology enables new ways of integrating products and services. So-called Cyber-Physical Systems (CPS) include the necessary sensors, actuators and software to provide reconfigurable functionalities for changing demands. However, engineering complexity is increased by the evolutionary aspect, as well as the increased number of stakeholders and system components involved over the whole life cycle. Understanding the underlying requirements is fundamental to establish a common perception of the targeted system among the manufacturer, service providers and the other stakeholders. This paper presents a gamified approach to elicit stakeholder requirements for the development of these complex systems. Four industrial users will use the gamified environment for refining their existing requirements. 

  • 123513. Wiesner, S.
    et al.
    Seregni, M.
    Freitag, M.
    Baalsrud Hauge, Jannicke
    KTH. University of Bremen, Germany.
    Silvestro, A.
    Thoben, K. -D
    Effects of environmental dynamicity on requirements engineering for complex systems2017Ingår i: IFIP WG 5.7 International Conference on Advances in Production Management Systems, APMS 2017, Springer, 2017, Vol. 513, s. 255-262Konferensbidrag (Refereegranskat)
    Abstract [en]

    With customers demanding more and more holistic answers to their problems, solution providers respond with complex systems, integrating product, service and ICT elements into their offer. These solutions need to be aligned to a high number of requirements, coming not only from the individual customer but also from an environment of network partners, technology providers and other stakeholders. Especially for Product-Service Systems, where the solution provider takes responsibility in the operational phase, this environment is dynamic over the system life cycle. Stakeholders may enter or leave, as well as changing needs and technological capabilities. This makes the requirements towards the solution volatile, demanding a suitable Requirements Engineering approach. In this paper, it is discussed how environmental dynamicity can be monitored for its effect on requirements, with a special focus on organizational issues. Through a literature review and industrial case studies it is analysed, how it can be ensured that environmental changes can be taken into account in Requirements Engineering, leading to an optimal system configuration to address the customer problem.

  • 123514.
    Wiesner, Stefan
    et al.
    BIBA Bremer Inst Prod & Logist GmbH, Hochschulring 20, D-28359 Bremen, Germany..
    Baalsrud Hauge, Jannicke
    KTH, Skolan för industriell teknik och management (ITM).
    Sonntag, Paul
    Univ Bremen, Fac Prod Engn, Badgasteiner Str 1, D-28359 Bremen, Germany..
    Thoben, Klaus-Dieter
    BIBA Bremer Inst Prod & Logist GmbH, Hochschulring 20, D-28359 Bremen, Germany.;Univ Bremen, Fac Prod Engn, Badgasteiner Str 1, D-28359 Bremen, Germany..
    Applicability of Agile Methods for Dynamic Requirements in Smart PSS Development2019Ingår i: ADVANCES IN PRODUCTION MANAGEMENT SYSTEMS: PRODUCTION MANAGEMENT FOR THE FACTORY OF THE FUTURE, PT I / [ed] Ameri, F Stecke, KE VonCieminski, G Kiritsis, D, SPRINGER INTERNATIONAL PUBLISHING AG , 2019, s. 666-673Konferensbidrag (Refereegranskat)
    Abstract [en]

    Smart Product-Service Systems, i.e. solutions consisting of tangible and intangible components interacting with their environment through information and communication technology, are subject to various dynamic influences along the life cycle. Stakeholders to the solution may change, as well as their needs and technological capabilities. This makes the requirements for the solution volatile, uncertain, complex and ambiguous. The system scope and associated requirements are constantly changing. In this paper, it is discussed how agile methods can help to deal with these influences in the development phase. A literature review and an industrial case study are used for analysing the problem of dynamic requirements, and agile methods are identified that can be applied for Smart Product-Service Systems.

  • 123515.
    Wiest, Martina
    et al.
    University of Leoben.
    Gebretsadik, Elias Kassa
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Daves, Werner
    University of Leoben.
    Nielsen, Jens
    Chalmers University of technology.
    Ossberger, Heinz
    VAE.
    Assessment of methods for calculating contact pressure in wheel-rail/switch contact2008Ingår i: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 265, nr 9, s. 1439-1445Artikel i tidskrift (Refereegranskat)
    Abstract [en]

     Two models for wheel-rail rolling contact that are based on the half-space assumption are compared in this paper: Hertz and the non-Hertzian method implemented in the computer program CONTACT. These two models are further restricted by the assumption of linear-elastic material behaviour. Moreover, one elastic and one elastic-plastic finite element model of the contact are investigated with the commercial code ABAQUS. The finite element method is not limited by the half-space assumption or applicable to a linear-elastic material model only. The objective is to assess the four methods based on calculated contact pressure, contact patch size and penetration depth. Contact loads and contact locations, used as input data in the analysis, are taken from a vehicle dynamics simulation in the software GENSYS. The comparison is performed at a given cross-section in the crossing panel of a selected turnout design. To fulfil the requirements of the half-space assumption, the dimensions of the contact area must be small compared to the radii of curvature of the bodies in contact. On the selected cross-section, however, the half-space assumption does not hold since the smallest radius of rail curvature at the contact point is 13 mm, which is comparable to the largest semi-axis of the contact area. Nevertheless, it is found that the contact pressure distributions calculated using Hertz and CONTACT correlate well with those results obtained from the finite element method as long as no plastification of the material occurs.

  • 123516.
    Wieweg, William
    KTH, Skolan för elektroteknik och datavetenskap (EECS).
    Towards Arc Consistency in PLAS2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Schemaläggningsmodulen PLAS som är en del av ICE (Intelligent Control Environment) är ansvarig för planering och schemaläggning av stora mängder fordonsflottor. Denna process involverar skapandet av uppgifter som behöver utföras av fordonen. Utifrån denna information bestämmer PLAS vilka fordon som ska utföra vilka uppgifter, vilket är modellerat som villkorsuppfyllelseproblem. Att lösa villkorsuppfyllelseproblem är långsamt. För att förbättra prestandan, så finns det en mängd olika tekniker. En av dessa är bågkonsekvens, vilket involverar att betrakta ett villkorsuppfyllelseproblem och utvärdera dess variabler parvis genom att tillämpa villkoren mellan dem. Med hjälp av bågkonsekvens kan vi utröna kandidatlösningar för villkorsuppfyllelseproblemen snabbare, jämfört med ren sökning. Vidare, bågkonsenvens möjliggör upptäckande och bearbetning av inkonsekvenser i villkorsuppfyllelseproblem.

    Arbetet i denna masteruppsats omfattar genomförandet av en villkorslösare för symboliska villkor, innehållandes bågkonsekvensalgoritmen AC3. Vidare, så innefattar det genomförandet av en villkorsuppfyllelseproblemgenerator, baserad på grafmodellen Erdős-Rényi, inspirerad av kvasigruppkompletteringsproblem med hål, villket möjliggör utvärdering av villkorslösaren på stora problem. Med hjälp av villkorsuppfyllelseproblemgeneratorn så utfördes en mängd experiment för att utvärdera villkorslösaren. Vidare så kompletterades experimenten av en mängd scenarion utförda på manuellt skapade villkorsuppfyllelseproblem. Resultaten visar att prestandan skalar upp bra.

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  • 123517.
    Wiezell, Katarina
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Modelling and Experimental Investigation of the Dynamics in Polymer Electrolyte Fuel Cells2009Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In polymer electrolyte fuel cells (PEFC) chemical energy, in for example hydrogen, is converted by an electrochemical process into electrical energy. The PEFC has a working temperature generally below 100 °C. Under these conditions water management and transport of oxygen to the cathode are the parameters limiting the performance of the PEFC.

    The purpose of this thesis was to better understand the complex processes in different parts of the PEFC. The rate-limiting processes in the cathode were studied using pure oxygen while varying oxygen pressure and humidity. Mass-transport limitations in the gas diffusion layer using oxygen diluted in nitrogen or helium was also studied. A large capacitive loop was seen at 1-10 Hz with 5-20 % oxygen. When nitrogen was changed to helium, which has a higher binary diffusion coefficient, the loop decreased and shifted to a higher frequency.

    Steady-state and electrochemical impedance spectroscopy (EIS) models have been developed that accounts for water transport in the membrane and the influence of water on the anode. Due to water drag, the membrane resistance changes with current density. This gives rise to a low frequency loop in the complex plane plot. The loop appeared at a frequency of around 0.1 Hz and varied with D/Lm2, where D is the water diffusion coefficient and Lm is the membrane thickness. The EIS model for the hydrogen electrode gave three to four semicircles in the complex plane plot when taking the influence of water concentration on the anode conductivity and kinetics into account. The high-frequency semicircle is attributed to the Volmer reaction, the medium-frequency semicircle to the pseudocapacitance resulting from the adsorbed hydrogen, and the low-frequency semicircles to variations in electrode performance with water concentration. These low-frequency semicircles appear in a frequency range overlapping with the low-frequency semicircles from the water transport in the membrane. The effects of current density and membrane thickness were studied experimentally. An expected shift in frequency, when varying the membrane thickness was seen. This shift confirms the theory that the low-frequency loop is connected to the water transport in the membrane.

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    FULLTEXT01
  • 123518.
    Wiezell, Katarina
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Gode, Peter
    KTH, Tidigare Institutioner                               , Kemiteknik.
    Lindbergh, Göran
    KTH, Tidigare Institutioner                               , Kemiteknik.
    Modelling and experimental studies of the membrane and hydrogen electrode in the PEFC: steady state and electrochemical impedance investigationsManuskript (preprint) (Övrigt vetenskapligt)
  • 123519.
    Wiezell, Katarina
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Holmström, Nicklas
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik, Tillämpad elektrokemi.
    Studying Low-Humidity Effects in PEFCs Using EIS II: Modeling2012Ingår i: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 159, nr 8, s. F379-F392Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electrochemical impedance spectroscopy (EIS) and steady-state models have been developed to investigate the influence of water transport on the membrane and electrode performance, with focus on the low-frequency impedance. Models for the membrane, hydrogen anode and oxygen cathode were connected in order to take the influence of water concentration on proton conductivity and hydrogen kinetics into account. At low frequencies, below 1 Hz, a pseudo-inductive loop was predicted, resulting from the overlap of the responses from anode and membrane. The anode response could be coupled to changes in the kinetics and polymer conductivity in the active layer, and the membrane response to changes in conductivity with changing water profile. The low frequency capacitive part was attributed to drying of the anode side of the membrane, while the inductive part was attributed to the rehydration of the membrane with water produced at the cathode. The loop appeared at a frequency proportional to 1/L-2, where L is the membrane thickness. The model was successfully fitted to experimental data at different membrane thicknesses, relative humidities and current densities. The modeled data follow the same trends as experimental data, giving an increase in impedance at dry conditions and with thicker membranes.

  • 123520.
    Wiezell, Katarina
    et al.
    KTH, Tidigare Institutioner, Kemiteknik.
    Lindbergh, Göran
    KTH, Tidigare Institutioner, Kemiteknik.
    Electrochemical impedance modeling of the proton conducting membrane in a PEFC2004Konferensbidrag (Refereegranskat)
    Abstract [en]

    An electrochemical impedance spectroscopy (EIS) model for water transport in the membrane in a polymer electrolyte fuel cell has been developed. Simulations show that an electrolyte can give a semi-circle in EIS if the resistivity or water concentration changes with current density. The magnitude of the loop is the sum of i-dR/di and dEconc/di, where E conc is the potential difference associated with the difference in water concentration between the anode and cathode side. The loop is capacitive for a positive sum and inductive for a negative sum. The characteristic frequency is proportional to the effective diffusivity of water and inversely proportional to the square of the membrane thickness. The model is based on the concentrated electrolyte theory, but similar results have also been obtained with a model for a diluted electrolyte. The influence of Econc is, however, omitted.

  • 123521.
    Wiezell, Katarina
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Gode, Peter
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Steady-State and EIS Investigations of Hydrogen Electrodes and Membranes in Polymer Electrolyte Fuel Cells: I. Modeling2006Ingår i: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 153, nr 4, s. A749-A758Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electrochemical impedance spectroscopy (EIS) and steady-state models have been developed for the porous hydrogen electrode with water concentration dependence and water transport in a polymer electrolyte fuel cell membrane. Because the hydrogen electrode performance is influenced by its water content, the hydrogen electrode model was coupled to the membrane model. The EIS model for the hydrogen electrode gave three to four loops in the complex plane plots. The high-frequency semicircle was attributed to the Volmer reaction and the medium-frequency semicircle to the hydrogen adsorption. The additional low-frequency loops were connected to changes in the hydrogen electrode performance with water concentration, due to changes in kinetics or proton conductivity. Those loops appear in a frequency range depending on the water transport in the membrane, changing with D/L-m(2), where D is the water diffusivity and L-m is the membrane thickness. Modeling of the membrane alone showed that the membrane gives rise to a loop in EIS. The difference between the high- and low-frequency intercepts of the loop is idR/di, where the high-frequency intercept is equal to the membrane resistance. The loop appears in the same frequency range as the hydrogen electrode low-frequency loops and thus overlaps.

  • 123522.
    Wiezell, Katarina
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Lindbergh, Göran
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Gode, Peter
    KTH, Skolan för kemivetenskap (CHE), Kemiteknik.
    Steady-state and EIS investigations of hydrogen electrodes and membranes in polymer electrolyte fuel cells: II. Experimental2006Ingår i: Journal of the Electrochemical Society, ISSN 0013-4651, E-ISSN 1945-7111, Vol. 153, nr 4, s. A759-A764Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Influence of water on membrane and anode performance was studied with steady-state and electrochemical impedance spectroscopy (EIS) measurements using a symmetrical cell with hydrogen on both sides. Both full-cell and half-cell measurements were performed. To obtain half-cell data a new reference electrode approach was demonstrated based on porous references in a four-electrode setup. A varying membrane resistance with current density was obtained using current interrupt and EIS measurements. The EIS measurements showed two semicircles at 10(4) Hz and 0.01-0.1 Hz, respectively. The first corresponds to hydrogen adsorption and the second to the water dependence of the electrode performance and membrane resistance. The low-frequency semicircle appears in a frequency range depending on the membrane thickness. The loop corresponding to the discharge of the double-layer capacitance through the Volmer reaction appears at frequencies too high to be experimentally measurable. The experimental data were in good agreement with the model developed in Part I of this paper. The model was also successfully fitted to experimental full cell data at different current densities and membrane thicknesses. The experiments confirmed that the low-frequency semicircle is attributed to the water dependence of both anode and membrane performance.

  • 123523.
    Wiezorek, Christian
    et al.
    Tech Univ Berlin, Fac Elect Engn & Comp Sci, Einsteinufer 11 EMH 1, Berlin, Germany..
    Parisio, Alessandra
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. Univ Manchester, Sch Elect & Elect Engn, Ferranti C5, Manchester M13 9PL, Lancs, England..
    Kyntaja, Timo
    Teknol Tutkimuskeskus VTT Oy, FI-02044 Helsinki, Finland..
    Elo, Joonas
    Teknol Tutkimuskeskus VTT Oy, FI-02044 Helsinki, Finland..
    Gronau, Markus
    Tech Univ Berlin, Fac Elect Engn & Comp Sci, Einsteinufer 11 EMH 1, Berlin, Germany..
    Johannson, Karl Henrik
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik.
    Strunz, Kai
    Tech Univ Berlin, Fac Elect Engn & Comp Sci, Einsteinufer 11 EMH 1, Berlin, Germany..
    Multi-location virtual smart grid laboratory with testbed for analysis of secure communication and remote co-simulation: concept and application to integration of Berlin, Stockholm, Helsinki2017Ingår i: IET Generation, Transmission & Distribution, ISSN 1751-8687, E-ISSN 1751-8695, Vol. 11, nr 12, s. 3134-3143Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The process of advancement and validation of smart grid technologies and systems calls for the availability of diverse expertise and resources. In response to this consideration, the virtual smart grid laboratory (VSGL) was developed as described in this study. At the core of the VSGL is a novel communication platform for seamlessly connecting geographically distributed laboratories with distinct competences. The platform has the dual purpose of opening access to resources of remote partner laboratory sites and offering the capability to emulate, analyse, and test smart grid communication networks involved in linking the distributed laboratory resources. The VSGL implementation is validated through a use case, in which the resources of R&D laboratories in three European countries are connected to form an aggregated system of distributed energy resources. The operation of the latter was coordinated through an energy management system based on model predictive control (MPC). The VSGL was found to be very suitable to meet the communication-specific requirements of such type of study. In addition, for this particular case the effectiveness of the MPC subject to diverse implementations of communication links was substantiated.

  • 123524.
    Wifstrand, Elsa
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Arkitektur.
    Onfill: Building on top of the Record Years2011Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
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    Onfill - Building on top of the Record Years
  • 123525.
    Wigaeus Tornqvist, Ewa
    et al.
    KTH, Skolan för teknik och hälsa (STH), Ergonomi.
    Hagberg, Mats
    Hagman, Maud
    Risberg, Eva Hansson
    Toomingas, Allan
    The influence of working conditions and individual factors on the incidence of neck and upper limb symptoms among professional computer users2009Ingår i: International Archives of Occupational and Environmental Health, ISSN 0340-0131, E-ISSN 1432-1246, Vol. 82, nr 6, s. 689-702Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To assess the influence of working conditions and individual factors on the incidence of neck and upper limb symptoms among professional computer users. The study is a prospective cohort study with an observation period of 10 months. A baseline questionnaire about symptoms in the neck, shoulder and arm/hand during previous month, individual factors, work content, physical and psychosocial work-related exposures was answered by 1,283 computer operators (response rate 84%). Incidence data were collected by ten monthly questionnaires regarding the occurrence of symptoms categorized into three gross body regions: neck, shoulders and arms/hands. A case, in the specific gross body region, was defined as a subject who was classified as non-symptomatic in that region at baseline or during minimum one follow-up period and later reported symptoms (a parts per thousand yen3 days). Univariable and multivariable incidence rate ratios with 95% confidence intervals for first occurrence of neck, shoulder and arm/hand cases, respectively, were calculated with Cox regression analysis. The incidence rate was 67, 41 and 47 cases per 100 person years for neck, shoulder and arm/hand symptoms, respectively. In the multivariable analyses, comfort of the computer work environment and gender were related to the incidence of symptoms in all body regions (RR = 1.5-1.9 for low comfort and 1.8-2.1 for females, respectively). Duration of mouse use predicted arm/hand symptoms (RR = 1.7 for a parts per thousand yen3 h/day) and job strain (high demands and low decision latitude) predicted neck symptoms (RR = 1.6 and 2.2 for medium and high strain, respectively). Additionally, age was related to neck and shoulder symptoms. Preventive strategies to reduce neck and upper limb symptoms among computer users should include measures to reduce mouse use, to increase the comfort of the work environment and to reduce job strain. Although the effect estimates were relatively weak to moderate, preventive measures may have a marked impact on the incidence of neck and upper limb symptoms in the general population because of the widespread use of computers in working life as well as at home.

  • 123526.
    Wigardt, Oliver
    KTH, Skolan för industriell teknik och management (ITM), Maskinkonstruktion (Inst.).
    Design of a stabilizer for the Slotborer2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Platinautvinning är antagligen en av the farligaste gruvindustrierna. På följd av det har gruvmaskiner som Slotborer utvecklats för att göra utvinningsprocessen säkrare. Slotborern är ett ganska nytt koncept och har problem med vibrationer i borrsträngen när den blir längre.Den här rapporten föreslår fyra koncept för att dämpa/stabilisera dessa vibrationer och ett av dessa koncept var sedan vidare utvecklat efter en evaluering. Det koncept som vidareutvecklats använder sig av massdämpare för att dämpa/stabilisera borrsträngen. Massdämparna är justerbara vilket gör dem effektiva över ett större frekvensområde. Några mätvärden från riktiga borrningar var analyserade och analytiska och matematiska modeller var utvecklade att ha ett liknande beteende som det från mätningarna. Modellerna var sedan utvidgade och massdämparna var implementerade in i modellerna för att analysera deras effekt på systemet. När de analytiska modellerna för massdämparna vara klara nog, började konstruktions- och dimensioneringsarbetet av projektet. Dämparen/stabilisatorn var från början konstruerad för att direkt dämpa vibrationer på 2 – 5 Hz, men på grund av väldigt höga spänningar i massdämparna var frekvensspannet ändrat till 3,5 – 6-7 Hz. Ingen verifiering genom empiriska studier var gjorda men några bra analytiska resultat åstadkoms.

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  • 123527.
    Wigder, Chaya
    KTH, Skolan för elektroteknik och datavetenskap (EECS).
    Word embeddings for monolingual and cross-language domain-specific information retrieval2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Flera studier har visat att ordinbäddningsmodeller är användningsbara för många olika språkteknologiuppgifter. Denna avhandling undersöker hur ordinbäddningsmodeller kan användas i sökmotorer för både enspråkig och tvärspråklig domänspecifik sökning. Experiment gjordes för att optimera hyperparametrarna till ordinbäddningsmodellerna och för att hitta det bästa sättet att vikta ord efter hur viktiga de är i dokumentet eller sökfrågan. Dessutom undersöktes metoder för att skapa domänspecifika tvåspråkiga inbäddningar. Systemet jämfördes med en baslinje utan inbäddningar baserad på cosinuslikhet, och för både enspråkiga och tvärspråkliga sökningar var systemet som använde enspråkiga inbäddningar bättre än baslinjen. Däremot var de tvåspråkiga inbäddningarna, särskilt för domänspecifika ord, av låg kvalitet och gav för dåliga resultat för direkt användning inom sökmotorer.

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  • 123528. Wigenius, Jens
    et al.
    Björk, Per
    Hamedi, Mahiar
    Linköping University, Sweden.
    Aili, Daniel
    Supramolecular assembly of designed α-helical polypeptide-based nanostructures and luminescent conjugated polyelectrolytes2010Ingår i: Macromolecular Bioscience, ISSN 1616-5187, E-ISSN 1616-5195, Vol. 10, nr 8, s. 836-841Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Designed polypeptides with controllable folding properties are utilized as supramolecular templates for fabrication of ordered nanoscale molecular and fibrous assemblies of LCPs. The properties of the LCPs as well as the three dimensional conformation of the polypeptide-scaffold determine how the polymers are arranged in the supramolecular construct, which highly affects the properties of the hybrid material. The ability to control the polypeptide conformation and assembly into fibers provides a promising route for tuning the optical properties of LCPs and for fabrication of complex functional supramolecules with well defined structural properties.

  • 123529. Wigenius, Jens
    et al.
    Hamedi, Mahiar
    Inganäs, Olle
    Limits to Nanopatterning of Fluids on Surfaces in Soft Lithography2008Ingår i: Advanced Functional Materials, ISSN 1616-301X, E-ISSN 1616-3028, Vol. 18, nr 17, s. 2563-2571Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Soft lithographic microcontact printing using the residual polydimethylsiloxane (PDMS) found in elastomeric PDMS stamps is demonstrated to lead to unstable prints with sub-micrometer dimensions. The statics and dynamics of the process have been followed with time-resolved atomic force microscopy, imaging ellipsometry, water contact angle measurement, and optical diffraction. It is proposed that this instability places a fundamental limitation on patterning by macromolecular fluids, which is of general relevance to soft lithography and nanoimprint lithography with low viscosity polymers.

  • 123530. Wigenius, Jens
    et al.
    Persson, Gustav
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Experimentell biomolekylär fysik.
    Widengren, Jerker
    KTH, Skolan för teknikvetenskap (SCI), Tillämpad fysik, Experimentell biomolekylär fysik.
    Inganäs, Olle
    Interactions Between a Luminescent Conjugated Oligoelectrolyte and Insulin During Early Phases of Amyloid Formation2011Ingår i: Macromolecular Bioscience, ISSN 1616-5187, E-ISSN 1616-5195, Vol. 11, nr 8, s. 1120-1127Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aggregates of misfolded proteins play an important role in diseases such as Alzheimer's. Here it is demonstrated how the anionic oligothiophene p-FTAA interacts with and influences pre-fibrillar protein assemblies during the earlier stages of in vitro fibrillation. Conjugated polythiophenes have previously been demonstrated to detect and discriminate between different types of protein aggregates and also introduce luminescent or conductive properties to these nanoscale fiber structures. Fluorescence spectroscopy, DLS, TEM and FCS are employed to follow the interplay between p-FTAA and insulin during in vitro fibrillation.

  • 123531.
    Wigenstam, Frida
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Byggteknik och design.
    Upprättande av mall för fuktsäkerhetsbeskrivning: Genom granskning av projekt ur fuktsäkerhetssynpunkt2011Självständigt arbete på grundnivå (högskoleexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Under 1990-talet uppdagades ett stort antal byggprojekt där bristande fuktsäkerhetsåtgärder

    under byggprocessen lett till omfattande fuktskador. Även nyligen utförda undersökningar

    visar att problemen med fuktskador snarare ökat än minskat under senare år. Fukt anses vara

    en av de främsta faktorerna som orsakar besvär på grund av brister i inomhusmiljön och

    orsakar dessutom onödiga kostnader och minskat förtroende för byggbranschen.

    I examensarbetet har tre projekt granskats för att undersöka hur arbetet med fuktsäkerhet har

    fungerat under byggprocessen. Fokus har lagts på att identifiera fuktkritiska byggnadsdelar

    och kontrollera hur dessa har beaktats främst under projekterings- och byggskede. Målet med

    granskningen har varit att få en överblick över Karlstad kommuns arbete med fuktsäkerhet för

    att kunna skapa riktlinjer inför framtida projekt. Den information som granskningen gett har

    använts som underlag för upprättandet av en mall för en Fuktsäkerhetsbeskrivning.

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  • 123532. Wiget, R.
    et al.
    Andersson, G.
    Andreasson, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Dimarogonas, Dimos V.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Johansson, Karl H.
    KTH, Skolan för elektro- och systemteknik (EES), Reglerteknik. KTH, Skolan för elektro- och systemteknik (EES), Centra, ACCESS Linnaeus Centre.
    Dynamic simulation of a combined AC and MTDC grid with decentralized controllers to share primary frequency control reserves2015Ingår i: 2015 IEEE Eindhoven PowerTech, PowerTech 2015, IEEE conference proceedings, 2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    The use of multi-terminal HVDC grids is a promising option to tackle the coming challenges in long distance power transmission, but the combined operation of HVDC and AC grids will bring certain challenges. The dynamic interaction from the fast controllable converter station with the rotational inertia dependent AC grids has to be investigated in detail, as well as how the converter stations will be controlled in the static and dynamic case. This paper will focus on the dynamic case and proposes a decentralized controller structure to control the HVDC converter power set-points. The proposed controller does not rely on real-time communication nor on a slack bus. A simulation study is presented to demonstrate the implementation of the controller.

  • 123533.
    Wigman, Igor
    KTH, Skolan för teknikvetenskap (SCI), Matematik (Inst.).
    Fluctuations of the nodal length of random spherical harmonics2010Ingår i: Communications in Mathematical Physics, ISSN 0010-3616, E-ISSN 1432-0916, Vol. 298, nr 3, s. 787-831Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using the multiplicities of the Laplace eigenspace on the sphere (the space of spherical harmonics) we endow the space with Gaussian probability measure. This induces a notion of random Gaussian spherical harmonics of degree n having Laplace eigenvalue E = n(n + 1). We study the length distribution of the nodal lines of random spherical harmonics. It is known that the expected length is of order n. It is natural to conjecture that the variance should be of order n, due to the natural scaling. Our principal result is that, due to an unexpected cancelation, the variance of the nodal length of random spherical harmonics is of order log n. This behaviour is consistent with the one predicted by Berry for nodal lines on chaotic billiards (Random Wave Model). In addition we find that a similar result is applicable for "generic" linear statistics of the nodal lines.

  • 123534. Wigren, C.
    et al.
    Andersen, J. N.
    Nyholm, R.
    Göthelid, M.
    Hammar, M.
    KTH, Tidigare Institutioner (före 2005), Fysik.
    Törnevik, C.
    Karlsson, U. O.
    Sm- and Yb-induced reconstructions of the Si(111) surface1993Ingår i: Physical Review B, ISSN 0163-1829, Vol. 48, nr 15, s. 11014-11019Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Low-energy electron diffraction, scanning tunneling microscopy, and photoelectron spectroscopy results from the submonolayer Sm- and Yb-induced surface structures are presented. Several similar metal-induced surface reconstructions are found to exist for Yb and Sm on Si(111) for low submonolayer coverages: 3×2, 5×1, and 7×1. At higher submonolayer coverage, Yb induces a 2×1 reconstruction while Sm induces a (3 × 3) R30°-like reconstruction. Yb is found to be divalent in all structures, whereas the Sm valence increases with increasing coverage. In the 3×2 structure only divalent Sm is present, in the 5×1 and 7×1 structures a small amount of trivalent Sm appears, and, finally, in the (3 × 3) R30°structure approximately half of the Sm atoms are trivalent. The surface Fermi-level position in the band gap for the different Sm and Yb reconstructions has been measured. The difference in valence stability between Sm and Yb is suggested to be the cause of the difference in the high-coverage structures found and the differences in pinning level for the two elements observed for the 5×1 and 7×1 structures. © 1993 The American Physical Society.

  • 123535. WIGREN, C
    et al.
    ANDERSEN, JN
    NYHOLM, R
    KARLSSON, Ulf O
    EPITAXIAL SILICIDE FORMATION IN THE MG/SI(111) SYSTEM1993Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 289, nr 3, s. 290-296Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The silicide formation has been studied in the Mg/Si(111) system by IOW energy electron diffraction (LEED) and photoelectron spectroscopy. It has been found that an epitaxial Mg2Si silicide is responsible for the (2/3 square-root e x 2/3 square-root 3)R30-degrees reconstruction in this system. The thickness of the silicide is limited due to the very low formation temperature for this silicide. The Fermi level is positioned 0.59 +/- 0.06 eV above the valence band maximum in the Si substrate and the valence band maximum in the epitaxial silicide is positioned 0.3 +/- 0.1 eV below the Fermi level.

  • 123536. WIGREN, C
    et al.
    ANDERSEN, JN
    NYHOLM, R
    KARLSSON, Ulf O
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    FORMATION OF SM SILICIDES ON SI(111) - COMPOSITION AND EPITAXY1993Ingår i: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 293, nr 3, s. 254-259Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The formation of Sm silicides on Si(111) by means of solid phase epitaxy has been studied with low energy electron diffraction, Auger electron spectroscopy and photoelectron spectroscopy of the Sm 4f level and Si 2p level. A limited reaction is found to occur already at room temperature whereas at higher temperatures a strongly intermixed Sm/Si layer showing some long range order is formed. The Sm atoms of this intermixed phase are found to be completely trivalent in accordance with expectations. The intermixed layer consists of two silicides with different compositions, one of them being SmSi2-x, the other being tentatively ascribed to SmSi.

  • 123537. WIGREN, C
    et al.
    ANDERSEN, JN
    NYHOLM, R
    KARLSSON, Ulf O
    KTH, Skolan för informations- och kommunikationsteknik (ICT).
    GROWTH AND EPITAXY OF YB SILICIDES ON SI(111)1991Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films, ISSN 0734-2101, E-ISSN 1520-8559, Vol. 9, nr 3, s. 1942-1945Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Yb silicides have been grown epitaxially on the Si(111) surface using solid-state epitaxy with annealing to 400-degrees-C. The amount of deposited Yb was varied from parts of a monolayer to films being about 40 monolayer thick. Auger- and photoelectron spectroscopy showed that Si segregates into the Yb overlayer at room temperature and that a strong reaction occurs during annealing to 400-degrees-C leading to the formation of thick silicides. The epitaxial silicides showed a 1 x 1 or a unroofed-radical 3 x unroofed-radical 3 low-energy electron diffraction pattern depending on the detailed preparation procedure. The composition of the silicide was found to be YbSi2-x.

  • 123538. WIGREN, C
    et al.
    ANDERSEN, JN
    NYHOLM, R
    KARLSSON, Ulf O
    NOGAMI, J
    BASKI, AA
    QUATE, CF
    ADSORPTION-SITE DETERMINATION OF ORDERED YB ON SI(111) SURFACES1993Ingår i: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 47, nr 15, s. 9663-9668Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Low-energy-electron-diffraction (LEED), scanning-tunneling-microscopy (STM), and photoelectron-spectroscopy measurements have been performed on the ordered submonolayer surface reconstructions of Yb on Si(111). Two of these reconstructions, namely, 3 X 1 and 2 X 1, have been studied in detail. STM and LEED revealed that what was considered to be the 3 X 1 reconstruction is actually a 3 X 2 reconstruction. By combining STM and photoelectron-spectroscopy results from the 3 X 2 and 2 X 1 reconstructions, we conclude that the Yb atoms are adsorbed in bridge sites.

  • 123539.
    Wigren, Emma
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Fastigheter och byggande.
    Carlsson, Patrik
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Fastigheter och byggande.
    Moms på bostadshyra: möjliga effekter på bostadsmarknaden2018Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Sveriges bostadsmarknad upplevs i nuläget redan som ansträngd med hänsyn till att bemöta efterfrågan hos befolkningen. I förhållande till befolkningsmängden hade Sverige lägst produktionstakt av bostäder i Norden under 2000-talet fram till 2016. Dessutom förväntas populationen i Sverige öka med drygt en miljon människor i varierande åldrar till 2026, vilket sätter ytterligare press på byggandet än tidigare. Utan att förändra nuvarande boendetäthet bedöms behovet till 600 000 nya bostäder i hela landet mellan 2016–2025. Otillräcklig arbetskraft pekas ut som det största hindret för bostadsbyggandet av Konjunkturinstitutet. Vidare framgår det att produktionskostnaderna av nyproducerade hyresrätter i flerbostadshus ökat markant med nästan 250 % de senaste 20 åren. Trots att det i Stockholms län byggs på rekordhöga nivåer sedan miljonprogrammet på 1970-talet, redogör samtliga kommuner ett underskott på bostäder. Något alla i hela länet, med undantag för två kommuner, tror kommer kvarstå om tre år. Ett sätt att stödja produktion och stimulera bostadsbyggandet är medel genom statliga subventioner. Det är inte sällan subventioner riktas mot byggandet av hyresrätter eftersom att de upprättas gentemot en reglerad hyresmarknad, vilket försvårar de ekonomiska kalkylerna och investeringsmöjligheterna. SABO, Hyresgästföreningen och Fastighetsägarna har tillsammans redovisat ett förslag om att införa en låg momsprocentsats på bostadshyra. Införandet kan betraktas som en subvention i och med att det bidrar till förbättrade ekonomiska förutsättningar vid nybyggnation, renoveringar samt förvaltning av hyresfastigheter då skatten tillåter avdrag på ingående moms förutsatt vidare försäljning, alltså utgående moms. I början på året kom EU-kommissionen med förslag om nya direktiv som bland annat öppnar upp möjligheten att införa moms på bostadshyra, något som enligt dagens regelverk inte är tillåtet. Syftet med rapporten har varit att utvärdera reformens möjliga effekter på bostadsmarknaden med tyngdpunkt på ett eventuellt ökat byggande av hyresrätter, där befintlig litteratur i ämnet samt intervjuer av utvalda aktörer med bred kunskap och erfarenhet inom bostadsmarknaden utgjort grunden till analys för arbetet. Det konstaterades att det råder tveksamheter kring om subventioner bidrar till någon positiv effekt eller inte. Att de flesta subventioner dessutom är begränsade i tid bidrar till osäkerhet om ett visst stöd kommer att försvinna alternativ tillkomma i framtiden, vilket i sin tur frambringar ojämna produktionsnivåer.

    Samtidigt kan stöd vara nödvändigt för att fastighetsägare inte ensamma ska behöva bära risken i projekt. En låg momsprocentsats på bostadshyra är dock svår att likställa med andra subventioner då reformen skulle innebära en mer långsiktig lösning, vilket i sin tur är väsentligt för att försäkra att investeringar på bostadsmarknaden är stabila över tid. Även om nya direktiv från EU skulle möjliggöra ett införande av reformen bedöms den tidigast kunna realiseras år 2022. Förslaget skulle innebära möjlighet till förbättring i att balansera ut skattemässiga orättvisor som idag råder mellan upplåtelseformer, och på så sätt göra hyresrätten mer attraktiv. Dock saknar reformen i nuläget förslag på finansiering vilket bidrar till ytterligare svårigheter att driva det vidare. Förhoppningarna om förbättrade kalkyler för fastighetsägare och byggherrar riskerar dessutom att korrelera med ett flertal effekter som motverkar reformens syfte. En mer påtaglig effekt är svårigheten i att säkerhetsställa att vinsten tillfaller fastighetsägaren. Förekommer en ökad betalningsförmåga hos byggherrar skulle det kunna driva upp prisnivåerna både avseende mark, material och tjänster och därmed förhindra ett ökat byggande. Förbättrade kalkyler kan underlätta för flera av de utmaningar som kan utpekas på bostadsmarknaden men reformen löser inte problemen i dess utgångspunkt. Att reformen därför skulle kunna fungera på kort sikt, innan andra delmarknader hinner priskompensera, är inte omöjligt. Största delen av reformens ämnade syfte med ökat byggande, fler renoveringar och förbättrade förutsättningar för hyresrätter riskerar att således gå förlorade om inte frågan om finansiering kan lösas gemensamt med att korrelerade negativa effekter begränsas.

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  • 123540. Wigren, R.
    et al.
    Wilhelmsson, Mats
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Fastigheter och byggande.
    Housing stock and price adjustments in 12 west European countries between 1976 and 19992007Ingår i: Housing, Theory and Society, ISSN 1403-6096, E-ISSN 1651-2278, Vol. 24, nr 2, s. 133-154Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Housing investment has both a direct and an indirect effect on economic growth. It is therefore of great importance to understand the mechanisms underlying the housing market. This paper uses an error-correction model to analyse the dynamics of the housing markets in 12 West European countries for the period 1976-99. The empirical results indicate that it is, to some degree, possible to consider the European housing market as one market. The relationships between housing stock and its macroeconomic determinants are robust across countries. Furthermore, the results show that the price and cost elasticity of the housing supply are low. Shocks on demand and supply have small effects on the housing stock (low speed of adjustment on quantity). On average, shocks take 4 years before being fully incorporated into the housing stock. On the other hand, shocks have a substantial effect on prices (high speed of adjustment on price). Supply-side and demand-side shocks have an instant effect on housing prices.

  • 123541.
    Wigren, Rune
    et al.
    Uppsala, IBF.
    Wilhelmsson, Mats
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Centra, Centrum för bank och finans, Cefin.
    Construction investments and economic growth in Western Europe2007Ingår i: Journal of Policy Modeling, ISSN 0161-8938, E-ISSN 1873-8060, Vol. 29, nr 3, s. 439-451Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The research task in the present study is to examine the statistical relationship between gross domestic product and a broad group of construction and, furthermore, the presence of crowding-out within the construction industry in Europe. The empirical analyzes support the findings of no crowding-out effect within the construction industry. Contrary, it seems that investments in especially infrastructure will have a complementary filling-in effect by an increase in both residential and other building construction. The Granger causality tests are not conclusive. However, the results imply that GDP Granger cause total construction in the short run, but not vice versa. Furthermore, infrastructure investments Granger causes GDP in the short run. The overall conclusion is that public infrastructure policies have an effect on short-run economic growth but only a weak effect on the long run and that there exist a filling-in effect from other types of construction. Furthermore, residential construction does have a long-run effect on economic growth.

  • 123542. Wigren, T.
    et al.
    Händel, Peter
    Harmonic signal modeling using adaptive nonlinear function estimation1996Ingår i: Acoustics, Speech, and Signal Processing, 1996. ICASSP-96. Conference Proceedings., 1996 IEEE International Conference on, 1996, Vol. 5, s. 2952-2955Konferensbidrag (Refereegranskat)
    Abstract [en]

    It is well-known that sine waves produce harmonic overtones when passed through static nonlinear functions. This paper describes a new algorithm where an arbitrary periodic signal is estimated recursively. The estimated signal model is typically parameterised as a real sine wave with unknown frequency in cascade with a piecewise linear function. A recursive Gauss-Newton prediction error identification algorithm for joint estimation of the driving frequency and the parameters of the nonlinear output function can then be derived. The approach handles colored measurement disturbances and gives a direct measure of the size of the nonlinearity that corresponds to the harmonic spectrum. The Cramer-Rao bound (CRB) is also calculated in the paper

  • 123543. Wigren, T.
    et al.
    Remle, S.
    Wahlberg, Bo
    KTH, Tidigare Institutioner, Signaler, sensorer och system.
    Analysis of a low-complexity change detection scheme2000Ingår i: International journal of adaptive control and signal processing (Print), ISSN 0890-6327, E-ISSN 1099-1115, Vol. 14, nr 5, s. 481-503Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In many applications, for example in fault detection, it is important to discriminate between changes in system dynamics and abrupt changes in the disturbance level. A new low-complexity change detection method based on the average behaviour of the estimated impulse response parameters of the normalized least mean-square (NLMS) algorithm is presented. The solution includes second-order Kalman filters based on exponential transient models for parameter convergence. Explicit formulas for time-varying state covariances and Kalman gains are given. The receiver operating characteristics (ROC) is also computed and used for performance evaluation. The effects of the approximations in the averaging analysis that occur for high adaptation gains are handled with an experimental ROC analysis.

  • 123544.
    Wigsén, Oskar
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Fastigheter och byggande.
    Swedish real estate firms’ capital structure determinants: A pre- versus post-crisis comparative study2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Att få förståelse för den underliggande tanken bakom ett företags kapitalstruktur är något som forskare undersökt i decennium. Detta till trots, har en fullt förklarande teoretisk modell som beskriver hur och varför ett företag väljer att ha en viss kapitalstruktur. Resultat från tidigare studier visar på stor tvetydighet och det har förklarats av att företags kapitalstrukturer tenderar att skilja åt beroende diverse omvärldsfaktorer som det makroekonomiska klimatet, ett lands politiska situation och dess rättsliga system. Mot bakgrund  av detta syftar denna studie till att undersöka vilka faktorer som påverkar ett företags kapitalstruktur, då det är ett relativt outforskat område i Sverige, vidare har det undersökts hur den senaste finanskrisen påverkat ett företags kapitalstruktur för att öka förståelsen kring faktorernas dynamik. Utgångspunkten för studiens teoretiska ramverk är Modigliani och Millers teori (1958), som, baserat på antagandet att ett företag försöker maximera dess värde, fastställde att ett företags värde är oberoende av dess kapitalstruktur på en perfekt marknad. Efterföljande forskning byggde vidare på teorin för att anpassa den till ett mer realistiskt marknadsscenario. De två mest etablerade teorierna som uppkommit är avvägningsteorin och hackordningsteorin. Avvägningsteorin menar att ett företag aktivt belånar sig för att maximalt utnyttja ränteavdraget för att minimera skatten och teorin hävdar att ett företag kommer fortsätta att belåna sig fram till dess att den förväntade kostnaden av en konkurs överstiger värdet av ränteavdraget. Hackordningsteorin antar det existerar en hierarkisk följd av finansieringsalternativ utifrån ett företags preferenser, där intern finansiering antas premieras, fram extern finansiering där skuldfinansiering föredras framför nyemission. Faktorerna som antas påverka kapitalstrukturen i fastighetsföretag undersöks och analyseras utifrån dessa två teorier och det kommer att genomföras genom utförandet av en paneldata-regression. Studiens resultat antyder att svenska noterade fastighetsföretag väljer finansieringspolicy i linje med avvägningsteorin då ett företags likviditet och andel anläggningstillgångar korrelerar positivt med dess skuldsättning. The komparativa studien antyder att företag före den finansiella krisen hade en finansieringspolicy som var av en opportunistisk natur som inte kunde förklaras av någon av de två teorierna. Efter krisen blev företag mer riskmedvetna och applicerade en finansieringspolicy som kunde förklaras av både avvägningsteorin och hackordningsteorin.  

  • 123545.
    Wigsén, Oskar
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Fastigheter och byggande.
    The Occurrence of Earnings Management in Swedish Real Estate Companies – a quantitative study2016Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Background and aim: All of the publicly listed companies in the EU have since January 2005 been required to implement the new international accounting standard IAS/IFRS in their financial statements. One of the new regulations that were included in the standard was the IAS 40 – Investment Property, which regulates the valuation and reporting of a company’s investment properties. IAS 40 introduced two different approaches to valuate investment properties; the cost method and the fair value method. The latter one created debate and controversy because of concerns regarding its applicability on assets not traded on an efficient market. The foundation of the fair value method is to value an asset to its fair value, which is the amount that can be expected to be received if the asset would have been sold the time of the valuation. If an asset is regularly traded on an efficient market the information of the value can be retrieved directly from recent market transactions. However, if the asset is not traded on an efficient market the management needs to make own assumptions when assessing the value, which is thus subject to bias. This creates opportunities for the management to manipulate the earnings.

    The purpose of this study is to determine whether Swedish real estate companies use the fair value method as a tool to manipulate earnings by implementing earnings management techniques.

    Methodology: Two hypotheses were developed to answer the research question. They were tested by conducting a statistical analysis. Hypothesis 1 was tested by performing a linear regression analysis and the second hypothesis was tested by a chi-square-test.

    Result and conclusion: The results from statistical analysis were ambiguous. Although a specific earnings management technique could not be proven to be used it was not possible to eliminate the possibility of real estate companies performing some kind of earnings management technique to manipulate the earnings.

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  • 123546. Wigö, Hans
    Effects of intermittent air velocity on thermal and draught perception during transient temperature conditions2008Ingår i: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 7, nr 1, s. 59-66Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    : Previous research has shown that air movement has a significant influence on humans' thermal comfort. For persons feeling cool, air movement tends to be perceived as draught, whilst when feeling warm air movements may provide a desired cooling effect. In the transition zone it therefore seems difficult to use constant air velocity as a tool for cooling without creating draught problems. Nevertheless, from an energy saving perspective it appears to be far more efficient to use enhanced convective cooling, induced by the air movement, to cool only the occupants instead of the entire building. One possible way to use air movement as a method to improve thermal comfort without resultant draught problems could be to use intermittent air velocity instead of constant velocity. The present paper reports results from three experiments where subjects have been exposed to velocity variations, showing support for the hypothesis that it is possible to cool humans and reduce the percentage of occupants who are dissatisfied with the room temperature, without creating draught problems, through intermittent cooling.

  • 123547.
    Wigö, Hans
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap.
    Technique and human perception of intermittent air velocity variation2005Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Objectives. The main objective of the present thesis was to evolve a controlled intermittent velocity field and to examine the impact of this type of dynamic indoor climate on human’s psychology and physiology. The prediction was that intermittent velocity variation could provide occupants with the desired cooling without causing draught and that this intermittent change of the indoor climate would influence peoples’ affect and cognitive performance.

    Methods. All experiments were performed in a classroom-like environment where groups of subjects were exposed to a temperature increase and step changes in air velocity. The changes or intermittent variations in air velocity consisted of elevated speed during five minutes, which were repeated three times. To reduce the influence of individual thermal preferences all measures were collected twice and the statistical analyses were based on the change scores in these measures.

    Results. The obtained results showed that, intermittent velocity variation may provide occupants with the desired cooling without causing draught. Subjects exposed to velocity variations were significantly less affected by the temperature rise in the room, compared to the control group. Moreover, the method reduced the expected increase of occupants who perceived the temperature condition as uncomfortable. The findings concerning air movements demonstrate that very few perceived the condition as draughty, after being exposed to the three high velocity pulses.

    The results concerning affect showed a significant effect on high activation, in the temperature range 21 - 24oC when the velocity variations made the subjects rate the temperature as slightly lowered over time, they kept their level of activation. In the higher temperature interval, 25 - 27oC, unactivated unpleasantness increased and activated pleasantness decreased significantly more in subjects in the constant velocity condition than it did for subjects in the velocity variation condition. In sum, all results concerning affect, the significant ones and tendencies point in the same direction. Subjects exposed to velocity variation report changes, over time, indicating higher activation and more positive feelings.

    No differences in cognitive performances were shown between the air velocity conditions. However, a tendency to a significant result (p = 0.10) in an attention task was shown, indicating that subjects in the velocity variation condition increased their speed in a short-term memory search, compared to subjects in the constant velocity condition.

    In the temperature range 21- 24oC, where the perception of the room temperature was measured at 0, 5 and 10 minutes respectively after the last high velocity period, the difference in MTV scores between the two groups, did decrease over time. Ten minutes after the last pulse the difference in MTV scores between the two groups was not significant. This suggests that the high velocity period should be repeated every10 to 15 minutes to keep the expected rise in subjects who judged the thermal conditions as uncomfortable down.

    The skin temperature was not affected neither by the rise in ambient temperature (from 21 to 24oC over 80 minutes) nor the periods (3 x 5 minutes) of high velocity. A consequence of this result is that the human temperature regulation system permitted an increased heat loss during the high velocity pulse, and hence a reduction of the body’s internal stored heat. For uncovered body parts the increase in heat loss was 20 % during the high velocity pulse. Summarised over the whole exposure time the three pulses produced a total energy loss that was only 2 % higher compared to constant low velocity.

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  • 123548.
    Wigö, Hans
    et al.
    Univ Gavle, Dept Technol & Built Environm.
    Knez, Igor
    Psychological impact of air velocity variations in ventilated room2005Ingår i: Ergonomics, ISSN 0014-0139, E-ISSN 1366-5847, Vol. 48, nr 9, s. 1086-1096Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two experiments investigated the psychological impact of two velocity conditions (constant low velocity (V1) and variations of low and high velocity (V2)) in two temperature conditions (Experiment 1: an air temperature increase from 21 degrees C to 24 degrees C; Experiment 2: an air temperature increase from 25 degrees C to 27 degrees C) in females and males, aged 16 to 18 years, under realistic classroom conditions during an exposure period of 80 min. It was predicted that the V2 room condition compared to the V 1 room condition would be more beneficial for subjects' perceived room temperature and air quality, self-reported affect and cognitive performance. The results obtained showed no significant effects on cognitive performance. However and as predicted, in Experiment 1, the subjects in the V2 compared to those in the V1 room condition felt that the air temperature decreased (while it de facto increased) and reported a constant level of high activation. In Experiment 2, the subjects in the V2 room condition felt that the air temperature increased less and reported that their unactivated unpleasantness increased less and activated pleasantness decreased less than it did for subjects in the V 1 room condition. All this indicates, as was suggested by Wigo et al. (2002), that a cooling effect, induced by air velocity variations, might be beneficial for subjects in a ventilated room and that their perceived pleasantness of the indoor climate could be met at a higher room temperature than otherwise.

  • 123549.
    Wigö, Hans
    et al.
    Univ Gavle, Dept Technol & Built Environm.
    Knez, Igor
    Univ Gavle, Dept Technol & Built Environm.
    Sandberg, M.
    Effects of velocity variations in ventilated rooms on comfort, affect and cognitive performance2002Ingår i: Proceedings of Indoor Air 2002 (9th International Conference on Indoor Air Quality and Climate) - June 30 - July 5, 2002 - Monterey, 2002, s. 635-640Konferensbidrag (Refereegranskat)
    Abstract [en]

    96 human subjects (18 years age students from a Swedish high school) were submitted in an experimental room furnished as a classroom to different air flows issued from different ventilation systems : displacement with constant air flow rate, alternating between displacement (floor diffusers) and mixing ventilation (ceiling diffusers) with constant flow rate, mixing ventilation with varying flow rate, displacement with constant flow rate and with ceiling fans to generate air motions alternatively on and off. Activuty of the subjects was composed of tasks allowing to estimate their intellectual performance. A questionnaire also concerned their perception of comfort. Air velocity variations did not affect thermal comfort but had a positive effect on perceived indoor air quality and on cognitive performance.

  • 123550. Wigö, Hans
    et al.
    Nilsson, Håkan O.
    Application of a thermal manikin to evaluate heat loss rates from people caused by variations in air velocity and air temperature2004Ingår i: The International Journal of Ventilation, ISSN 1473-3315, E-ISSN 2044-4044, Vol. 3, nr 3Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Heat loss monitoring from a thermal manikin was undertaken representing an occupant in a classroom during a lesson period of 80 minutes in which the room temperature was increased from 21 to 24°C for various airflow velocity configurations. A group of subjects was exposed to various conditions of temperature and airflow rate so that the impact of these variations on their surface/skin temperature could be determined. It was found that skin temperature remained stable and close to 34°C for all conditions of exposure. Thus, over the temperature and air velocity range considered, these new findings verified the suitability of using a thermal manikin, set to steady uniform surface temperature, to determine the heat loss characteristics from occupants subjected to intermittent velocity       variation. When the manikin was exposed to a high velocity pulse, the heat loss from the       whole body increased by 10% while the heat loss from exposed areas (hands and face) increased by 20 % (when compared to no velocity pulse). After the 80 minutes monitoring period, the total energy loss from a manikin exposed to velocity variations was 2% higher than when exposed to constant low velocity.

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