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  • 2501.
    Ahlstrom, Linda
    et al.
    Sahlgrenska akademin, Göteborgs universitet.
    Grimby-Ekman, Anna
    Sahlgrenska akademin, Göteborgs universitet.
    Hagberg, Mats
    Sahlgrenska akademin, Göteborgs universitet.
    Dellve, Lotta
    Sahlgrenska akademin, Göteborgs universitet.
    Measures of work ability and association with sick leave, symptoms and health: A prospective study of female workers on long term sick leave2010In: Scandinavian Journal of Work, Environment and Health, ISSN 0355-3140, E-ISSN 1795-990X, Vol. 36, no 5, p. 404-412Article in journal (Refereed)
  • 2502.
    Ahlstrom, Linda
    et al.
    Högskolan Borås.
    Larsson Fallman, Sara
    Högskolan Borås.
    Dellve, Lotta
    KTH, School of Technology and Health (STH), Health Systems Engineering, Ergonomics. Public Health and Community Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
    Return to work from long-term sick leave: a five-year prospective study of the importance of adjustment latitudes at work and home2014Conference paper (Other academic)
    Abstract [en]

    Background

    Adjustment latitude among employees, i.e. adjusting work to individual’s health capacity, has been associated with successful return to work (RTW) in cross-sectional studies. The aim is to investigate the long-term importance of adjustment latitude at the workplace and at home, as well as attitudes (own and colleagues) for increased work ability (WA), working degree (WD) and health-related quality of life (HRQoL) among female human service workers (HSW) on long-term sick leave in Sweden.

    Methods

    A cohort of female HSW (n=324) on long-term sick leave (>60 day) received a questionnaire at four times (0, 6, 12, 60 months). Prevalence ratios (PR) were used to examine possible relationships between explanatory factors and outcomes. Linear mixed models were used for longitudinal analysis of the repeated measurements of WA Score (0-10), WD (0-100%) and HRQoL (0-100). Analyses were performed with different models; the explanatory variables for each model were adjustment latitude, attitudes towards breaks at work, shared or single household and amount of household work.

    Result

    Having more adjustment latitude at work was associated with both increased WA and RTW compared to having few adjustment latitude opportunities. Adjustments related to working-pace were strongly associated with increased WD (PR 3.29(95%CI=1.71-6.26)), as were adjustments to working-place. Having opportunities to take short breaks at work, and a general acceptance at work to take short breaks was associated with increased WA. At home, a higher responsibility for household work (PR 1.98(95%CI=1.33-2.95)) was related to increased WA and RTW. Individuals with possibilities for adjustment latitude, especially pace and place, at work, and an acceptance to take breaks at work, increased in WA score significantly more over time and had higher WA score compared with individuals not having such opportunities at work. These prospective results were similar for the outcome WD and HRQoL.

    Conclusions

    The results highlight the importance of possibilities for adjustment latitude at work and at home, as well as accepting attitudes to take short breaks to increase WA and RTW among female human service workers previously on long-term sick leave.

  • 2503. AHLSTROM, M
    et al.
    JONSSON, B
    KARLSTROM, G
    ABINITIO MOLECULAR-ORBITAL CALCULATIONS ON HYDROGEN-BONDED AND NON-HYDROGEN-BONDED COMPLEXES - H2CO.H2O AND H2CO.H2S1979In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Vol. 38, p. 1051-1059Article in journal (Refereed)
  • 2504.
    Ahlström, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Aeroelastic FE modelling of wind turbine dynamicsIn: Computers & structures, ISSN 0045-7949, E-ISSN 1879-2243Article in journal (Refereed)
    Abstract [en]

    By designing wind turbines with very flexible components it is possible toreduce loads and consequently the associated cost. As a result, the increased flexibilitywill introduce geometrical nonlinearities. Design tools that can cope with those nonlinearitieswill therefore be necessary at some stage of the design process. The developedmodel uses the commercial finite element system MSC.Marc, which is an advanced finiteelement system focused on nonlinear design and analysis, to predict the structuralresponse. The aerodynamic model named AERFORCE, used to transform the wind toloads on the blades, is a Blade-Element/Momentum model, developed by The SwedishDefence Research Agency (FOI, previously named FFA). The paper describes the developedmodel with focus on component modelling to allow for geometrical nonlinearities.Verification results are presented and discussed for an extensively tested Danwin 180 kWstall-controlled wind turbine. Code predictions of mechanical loads, fatigue and spectralproperties, obtained at normal operational conditions, have been compared with measurements.The simulated results correspond well with measurements. Results from a bladeloss simulation are presented to exemplify the versatility of the developed code.

  • 2505.
    Ahlström, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Aerolastic simulation of wind turbine dynamics2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work in this thesis deals with the development of an aeroelastic simulation tool for horizontal axis wind turbine applications.

    Horizontal axis wind turbines can experience significant time varying aerodynamic loads, potentially causing adverse effects on structures, mechanical components, and power production. The needs for computational and experimental procedures for investigating aeroelastic stability and dynamic response have increased as wind turbines become lighter and more flexible.

    A finite element model for simulation of the dynamic response of horizontal axis wind turbines has been developed. The developed model uses the commercial finite element system MSC.Marc, focused on nonlinear design and analysis, to predict the structural response. The aerodynamic model, used to transform the wind flow field to loads on the blades, is a Blade-Element/Momentum model. The aerodynamic code is developed by The Swedish Defence Research Agency (FOI, previously named FFA) and is a state-of-the-art code incorporating a number of extensions to the Blade-Element/Momentum formulation. The software SOSIS-W, developed by Teknikgruppen AB was used to generate wind time series for modelling different wind conditions.

    The method is general, and different configurations of the structural model and various type of wind conditions can be simulated. The model is primarily intended for use as a research tool when influences of specific dynamic effects are investigated. Verification results are presented and discussed for an extensively tested Danwin 180 kW stall-controlled wind turbine. Code predictions of mechanical loads, fatigue and spectral properties, obtained at different conditions, have been compared with measurements. A comparison is also made between measured and calculated loads for the Tjæreborg 2 MW wind turbine during emergency braking of the rotor. The simulated results correspond well to measured data.

  • 2506.
    Ahlström, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Emergency stop simulation using a finite element model developed for large blade deflections2006In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 9, no 3, p. 193-210Article in journal (Refereed)
    Abstract [en]

    Predicting the load in every possible situation is necessary in order to build safe and optimized structures. A highly dynamical case where large loads are developed is an emergency stop. Design simulation tools that can cope with the upcoming non-linearities will be especially important as the turbines get bigger and more flexible. The model developed here uses the advanced commercial finite element system MSC.Marc, focused on non-linear design and analysis, to predict the structural response. The aerodynamic model named AERFORCE, used to transform the wind to loads on the blades, is a blade element momentum model. A comparison is made between measured and calculated loads for the Tjaere-borg wind turbine during emergency braking of the rotor. The simulation results correspond well with measured data. The conclusion is that the aeroelastic tool is likely to perform well when simulating more flexible turbines.

  • 2507.
    Ahlström, Anders
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Influence of wind turbine flexibility on loads and power production2006In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 9, no 3, p. 237-249Article in journal (Refereed)
    Abstract [en]

    Most aeroelastic codes used today assume small blade deflections and application of loads on the undeflected structure. However, with the design of lighter and more flexible wind turbines, this assumption is not obvious. By scaling the system mass and stiffness properties equally, it is possible to compare wind turbines of different degrees of slenderness and at the same time keep system frequencies the some in an undeformed state. The developed model uses the commercial finite element system MSC. Marc, focused on non-linear design and analysis, to predict the structural response. The aerodynamic model AERFORCE, used to transform the wind to loads on the blades, is a blade element momentum model. A comparison is made between different slenderness ratios in three wind conditions below rated wind speed. The results show that large blade deflections have a major influence on power production and the resulting structural loads and must be considered in the design of very slender turbines.

  • 2508.
    Ahlström, Anders
    KTH, Superseded Departments, Mechanics.
    Simulating Dynamical Behaviour of Wind Power Structures2002Licentiate thesis, monograph (Other scientific)
    Abstract [en]

    The workin this thesis deals with the development of anaeroelastic simulation tool for horizontal axis wind turbineapplications.

    Horizontal axiswind turbines can experience significanttime varying aerodynamic loads, potentially causing adverseeffects on structures, mechanical components, and powerproduction. The need of computational and experimentalprocedures for investigating aeroelastic stability and dynamicresponse have increased as wind turbines become lighter andmore flexible.

    A finite element model for simulation of the dynamicresponse of horizontal axis wind turbines has been developed.The simulations are performed using the commercial finiteelement software SOLVIA, which is a program developed forgeneral analyses, linear as well as non-linear, static as wellas dynamic. The aerodynamic model, used to transform the windflow field to loads on the blades, is a Blade- Element/Momentummodel. The aerodynamic code is developed by FFA (TheAeronautical Research Institute of Sweden) and is astate-of-the-art code incorporating a number of extensions tothe Blade-Element/Momentum formulation. SOSIS-W, developed byTeknikgruppen AB was used to develop wind time series formodelling different wind conditions.

    The model is rather general, and different configurations ofthe structural model and various type of wind conditions couldeasily be simulated. The model is primarily intended for use asa research tool when influences of specific dynamic effects areinvestigated.

    Simulation results for the three-bladed wind turbine Danwin180 kW are presented as a verification example.

    Keywords:aeroelastic modelling, rotor aerodynamics,structural dynamics, wind turbine, AERFORCE, SOSIS-W,SOLVIA

  • 2509.
    Ahlström, Johan
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Björklund, Jacob
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Reglering av energikostnader med hjälp av energilagring i Danmark2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Compressed Air Energy Storage (CAES) implies compressing air, store it and expand it later on. CAES is together with Pumped Hydro Energy Storage (PHES) the only commercial viable bulk energy storage systems today. With respect to the geological conditions of low land in Denmark, two different types of CAES-technologies were further investigated for energy arbitrage.

    Denmark participates in the Nordic electricity market and the electricity trading occurs through Nord Pool Spot (Elspot) where the electricity price is determined specifically for every hour, the day before. The daily variation of prices in 2013 could from an empirical analysis locate hours with peak and off-peak prices.  The main goal of this report was therefore to investigate possible revenues with chosen energy storage system to buy electricity on off-peak price hours and store it, then sell it during peak price hours.

    Currently, there are two CAES facilities, one located in Huntorf, Germany, and one in Alabama, USA. A couple of different cases were investigated. Four cases, H1, H2, H3 and H4 are included in “Current Scenario” with similar features as the conventional CAES-facility, Huntorf. Conventional CAES-facilities use natural gas in the combustion chamber to heat up the air before the expansion phase to prevent the turbines from freezing. Two additional cases were investigated, A1 and A2 are included in the “Future Scenario” that is based on information about a planned future advanced adiabatic CAES facility called ADELE, by the energy company RWE in Germany.

    The calculations about the first case, H1 were based on the original performance characteristics with a total compressor capacity of 60 MW and a total output of 290 MW with charge-and discharge times of 4 and 2 hours respectively. The H2-case was assumed to be similar to the first H1-case with the only difference of a reduced consumption of natural gas by 25 %. The H3-case is based on the assumption of a compressor capacity of 480 MW and an output of 580 MW which gives the same charge- and discharge time of 1 hour. The H4-case is similar to H3 with the only difference of a reduced consumption of natural gas by 25 %. The A1-case concerns an AA-CAES facility of charge-and discharge time of 8 hours and 4 hours respectively with a compressor capacity of 200 MW and a total output of 260 MW. The second case assumes to have a total compressor capacity of 1600 MW and a total output of 1040 MW which gives the same discharge and charge time of 1 hour.

    The economic calculation model consists of two investment calculations, net present value- and payback-method. Calculations made, indicates that an investment in these observed CAES-cases under given assumptions is not economically profitable within the estimated economic and technical lifetime. The net present value ratio has a range of -1 for case H1 to -0,88 for case A1. The payback-time varies between having no payback at all (case H1) to 113 years for case A1.

    The calculations should be seen as rough estimations and just be considered as a hint for the future potential of CAES as a tool for energy arbitrage. The sensitivity analysis proves for the derived cases from the CAES-facility in Huntorf that a decreased price for natural gas did a huge impact on the operational revenues. Generally for all the different cases were that a reduction of the total plant investment, operation and maintenance costs and an increasing number of days with greater price variations would make the different CAES-cases more profitable.

    Advanced adiabatic CAES-facilities can potentially, with the necessary technical improvements, be a part of the future sustainable development.

  • 2510.
    Ahlström, Marcus
    KTH, School of Electrical Engineering and Computer Science (EECS), Media Technology and Interaction Design, MID.
    Broadening the Reading Experience on Mobile Devices using Tilt-based Input: An Explorative Design Study2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis is an explorative study aimed at the possibility of integrating tilt-based input to improve the reading experience on smartphones. Previous works from the early 2000s have been skeptical towards tilt-based navigation, deeming it unruly and imprecise. To investigate if today’s technology has unlocked new possibilities; two experimental reading methods were designed, created and tested iteratively on 20, respectively 18 participants. The first method is a reassessment of tilt-based auto-scrolling and the second is a novel approach comparable to tilt-based paging. Data from the reading sessions were collected quantitatively in tandem with qualitative data from post-session interviews. The results indicate good potential and a reading performance similar to the standard navigation method. The importance of accommodating people with different reading behaviours was also discussed.

  • 2511.
    Ahlström, Marcus
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Path Integral Monte Carlo Simulation of Helium-4 Nanodroplets2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 2512.
    Ahlström, Peter
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Entrepreneurship and innovation.
    Framtiden för Svensk TV: Hur hanteraran den förändring av marknaden för TVsom följer med internet2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The Swedish TV market is changing. The number of views moving from the traditional TV-screen to mobile platforms and TV-online is growing. The Swedish television programmers, such as TV4-gruppen, SBS, SVT and MTG has followed this trend and is currently delivering content to their viewers without any middle men through their respective play services. This study looks into how this technological change affects the television market from a consumer and business perspective.

    The study is based on a theoretical framework and empirical studies within the television market. The main theories used in this study is: The role of business models in capturing value in new technology and delivering this value to the market, how to handle technological change within organizations and dominant design.

    The study shows that the current change in the Swedish television market is already threatening to overthrow the traditional distributors of linear-TV when they no longer have a natural monopoly on the viewers through their distribution infrastructure. The study also shows that one of the major challenges in implementing a successful business model for nonliner-TV is the change of viewer behavior and how this change affects licensing and rights owners.

  • 2513.
    Ahlsén, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Naval Systems.
    Fartygsprojektering och Flytande havsbaserad vindkraft2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Den här rapporten behandlar tre områden anknutna till den gemensamma sektorn marina system. Inledningsvis beskrivs sjöfartsnäringens olika delar däribland olika typer av gods och fartygstyper samt sjöfartens aktörer och reglerande organ. Sjöfarten diskuteras med hänsyn till miljö och visar att godstransport till havs är relativt energieffektivt, men att alla typer av gods inte kan motiveras ur ett hållbart perspektiv.

    En inledande fartygsprojektering genomförs för ett transportscenario där 5500 ton kiwifrukt ska transporteras från Nya Zeeland till länder kring Östersjön inom en tidsrymd som garanterar att frukten håller god kvalitet. Fartygstypen är ett kylfartyg dimensionerat att rymma lasten, minimera motstånd och uppfylla stabilitetskriterier från IMO. För att uppfylla transportscenariot är fartyget designat för en marschfart på 20 knop, med ett deplacement på 12500 ton, en längd på 138 m, 21 m i bredd och ett djupgående på 7.7 m.

    Avslutningsvis identifieras kriterier och förutsättningar för flytande havsbaserad vindkraft. Detta med syfte genomföra en inledande projektering av en vindkraftpark stor nog att Gotland kan täcka sin elkonsumtion med endast förnybara energikällor. Parken anläggs längs en ny kabelanslutning mellan Gotland och fastlandet utom synhåll från såväl Gotland, Öland och fastlandet. Området uppfyller krav på vindförhållanden och utgörs av 24 vindkraftverk med kapacitet på 5 MW vardera.

  • 2514.
    Ahlsén, David
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Naval Systems.
    Experimental and numerical fluid-structure interaction analysis of a suspended rod subjected to forced vibrations2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This study is evaluating Solid-Acoustic Finite Element modelling as a method for calculating structural vibration response in water. When designing for example vehicles, it is important to avoid vibrational resonance in any part of the structure, as this causes additional noise and reduced lifespan. It is known that vibration response can be affected by the surrounding medium, i.e. water for marine applications.Previous studies show that this effect is both material and geometry dependant why it is hard to apply standardised design rules. An alternative approach is direct calculation using full Fluid Structure Interaction (FSI) by Computational Fluid Dynamics (CFD) and Finite Element Methods (FEM) which is a powerful but slow and computationally costly method.Therefore, there exists a need for a faster and more efficient calculation method to predict how structures subjected to dynamic loads will respond when submerged in water. By modelling water as an acoustic medium, viscous effects are neglected and calculation time can be drastically reduced. Such an approximation is a linearization of the problem and can be suitable when all deformations are assumed to be small and there are no other nonlinear effects present.This study consists of experimental tests where vibrational response was measured for rod shaped test specimens which were suspended in a water filled test rig and excited using an electrodynamic shaker. A Solid-Acoustic Finite Element model of the same experiment was created, and the test and simulation results were compared. The numerical results were shown to agree well with experiments up to 450 Hz. Above 450 Hz differences occur which is probably due to a simplified rig geometry in the numerical model.

  • 2515.
    Ahltorp, Magnus
    KTH, School of Computer Science and Communication (CSC).
    A Personalizable Reading Aid for Second Language Learners of Japanese.2012Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Magnus Ahltorp

    A Personalizable Reading Aid for Second Language Learners of Japanese

    Second language learners of Japanese today have access to vast amounts of authentic Japanese text, audio and video material. A challenge that the Japanese learner faces though, is that the process of looking up words in a dictionary is prohibitively slow. In this thesis, I describe a personalizable system that helps the user read Japanese text by providing pronunciation information and English explanations at the user's request. I also describe the user-centered development of the system and the results of each iteration of user testing. The resulting system and user testing show that it is feasible to provide an immersive reading experience that both beginners and more advanced language learners can use to take command of a crucial part of their own learning.

  • 2516.
    Ahltorp, Magnus
    et al.
    KTH.
    Skeppstedt, M.
    Dalianis, H.
    Kvist, M.
    Using text prediction for facilitating input and improving readability of clinical text2013In: Studies in Health Technology and Informatics, IOS Press, 2013, no 1-2, p. 1149-Conference paper (Refereed)
    Abstract [en]

    Text prediction has the potential for facilitating and speeding up the documentation work within health care, making it possible for health personnel to allocate less time to documentation and more time to patient care. It also offers a way to produce clinical text with fewer misspellings and abbreviations, increasing readability. We have explored how text prediction can be used for input of clinical text, and how the specific challenges of text prediction in this domain can be addressed. A text prediction prototype was constructed using data from a medical journal and from medical terminologies. This prototype achieved keystroke savings of 26% when evaluated on texts mimicking authentic clinical text. The results are encouraging, indicating that there are feasible methods for text prediction in the clinical domain.

  • 2517. Ahlund, John
    et al.
    Nilson, Katharina
    Palmgren, Pål
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Gothelid, Emmanuelle
    Schiessling, Joachim
    Göthelid, Mats
    Martensson, Nils
    Puglia, Carla
    Molecular growth determined by surface domain patterns2008In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 112, no 17, p. 6887-6890Article in journal (Refereed)
    Abstract [en]

    The growth of iron phthalocyanine (FePc) on InSb(001) c(8 x 2) at submonolayer coverage has been investigated with scanning tunneling microscopy (STM). FePc adsorbs flat centered on the In rows both at 70 K and at room temperature (RT). However, the shapes of the two-dimensional molecular islands are fundamentally different; while the RT growth results in chainlike structures along the [I 10] direction, as already observed for other Pc's adsorbed on the same surface, the islands are prolonged along [110], i.e., perpendicular to the substrate rows, at 70 K. These observations are explained on the basis of a recently observed new surface phase at low temperature, resulting in structural domains on the surface. The molecular growth front follows the propagating domain boundary that freezes at low temperature.

  • 2518.
    Ahlund, Rasmus
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Ögren, Oscar
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Soil and Rock Mechanics.
    Pore pressures and settlements generated from two different pile drilling methods2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    For piling works in sensitive soil, especially in inner city projects, it is essential to be aware of the available methods and to choose the most suitable method to minimize the risk of damaging existing buildings or endanger the workers at the construction site. Down-the-hole drilling of piles is a relatively safe method and can be separated into drilling with air powered hammers and water powered hammers. This study compares water powered drilling with air powered drilling and shows that the impact on the soil generated by air powered drilling is larger than that from water powered drilling.

    A field study was carried out where 4 piles were drilled, two with air powered DTH drilling and two with water powered DTH drilling. The drilling was carried out in clay resting on an approximately 4 m layer of silt and friction soil. The total soil depth was about 12- 15 m. To analyze the soil influence, settlements were measured at ground level and in depth and pore pressure was measured in the middle of the clay layer. This study distinguished two major problems when drilling through this type of soil. The first is the risk of over-drilling in the friction layer. The second problem is the risk of increasing the pore pressure in the clay. Both these problems were experienced when using air powered drilling but for the water powered case only a small pore pressure increase and no over-drilling was observed. In conclusion, drilling with water has less influence on the soil in the sense that it gives a smaller effect on the pore water pressure and causes smaller settlements.

  • 2519.
    Ahluwalia, A.
    et al.
    Italy.
    De Maria, C.
    Italy.
    Lantada, A. D.
    Spain.
    Pietro, L. D.
    Italy.
    Ravizza, A.
    Italy.
    Mridha, Mannan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Health Informatics and Logistics.
    Madete, J.
    Kenya.
    Makobore, P. N.
    Uganda.
    Aabloo, A.
    Estonia.
    Kitsing, R.
    Estonia.
    Leivobits, A.
    Estonia.
    Towards open source medical devices current situation, inspiring advances and challenges2018In: BIODEVICES 2018 - 11th International Conference on Biomedical Electronics and Devices, Proceedings; Part of 11th International Joint Conference on Biomedical Engineering Systems and Technologies, BIOSTEC 2018, SciTePress, 2018, p. 141-149Conference paper (Refereed)
    Abstract [en]

    Open Source Medical Devices may be part of the solution towards the democratization of medical technologies pursuing Universal Health Coverage as part of the Sustainable Development Goals for United Nations. Recent technological advances, especially in information and communication technologies, combined with innovative collaborative design methodologies and manufacturing techniques allow for the mass-personalization of biodevices and help to optimize the related development times and costs, while keeping safety in the foreground through the whole life cycle of medical products. These advantages can be further promoted by adequately fostering collaboration, communication, high value information exchange, and sustainable partnerships and by extending the employment of open source strategies. To this end, within the UBORA project, we are developing a framework for training the biomedical engineers of the future in open-source collaborative design strategies and for supporting the sharing of information and the assessment of safety and efficacy in novel biodevices. An essential part of this open-source collaborative framework is the UBORA e-infrastructure, which is presented in this study, together with some initial success cases. Main future challenges, connected with regulatory harmonization, with educational issues and with accessible and open design and manufacturing resources, among others, are also presented and discussed.

  • 2520.
    Ahluwalia, Arti
    et al.
    Univ Pisa, Dept Ingn Informaz, Bioengn, Pisa, Italy..
    De Maria, Carmelo
    Univ Pisa, Dept Ingn Informaz, Bioengn, Pisa, Italy..
    Diaz Lantada, Andres
    UPM, ETSII, Dept Mech Engn, Madrid, Spain..
    Madete, June
    Univ Pisa, Res Ctr E Piaggio, Pisa, Italy.;Kenyatta Univ, Nairobi, Kenya..
    Makobore, Philippa Ngaju
    Uganda Ind Res Inst, Instrumentat Div, Kampala, Uganda..
    Ravizza, Alice
    Univ Pisa, Pisa, Italy..
    Di Pietro, Licia
    Mridha, Mannan
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems, Health Informatics and Logistics.
    Munoz-Guijosa, Juan Manuel
    UPM, ETSII, Dept Mech Engn, Madrid, Spain..
    Tanarro, Enrique Chacon
    UPM, ETSII, Dept Mech Engn, Madrid, Spain..
    Torop, Janno
    Tartu Ulikool, Inst Technol, Tartu, Estonia..
    Biomedical Engineering Project Based Learning: Euro-African Design School Focused on Medical Devices2018In: International Journal of Engineering ,Science and Innovative Technology, ISSN 0949-149X, E-ISSN 2277-3754, Vol. 34, no 5, p. 1709-1722Article in journal (Refereed)
    Abstract [en]

    Biomedical engineering (BME) has the potential of transforming medical care towards universal healthcare by means of the democratization of medical technology. To this end, innovative holistic approaches and multidisciplinary teams, built upon the gathering of international talent, should be encouraged within the medical industry. However, these transformations can only be accomplished if BME education also continuously evolves and focuses on the internationalization of students, the promotion of collaborative design strategies and the orientation towards context relevant medical needs. In this study we describe an international teaching-learning experience, the "UBORA (Swahili for 'excellence') Design School". During an intensive week of training and collaboration 39 engineering students lived through the complete development process for creating innovative open-source medical devices following the CDIO ("conceivedesign-implement-operate") approach and using the UBORA e-infrastructure as a co-design platform. Our post-school survey and analyses showed that this integral teaching-learning experience helped to promote professional skills and could nurture the future generation of biomedical engineers, who could transform healthcare technology through collaborative design oriented to open source medical devices.

  • 2521.
    Ahlvar, Mathias
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management.
    Berg, Fredrik
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management.
    Investment companies as an investment – Could a person without experience from investments bee helped by the active ownership of investment companies?2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this essay we have been studying the development of investment companies that is traded at

    Mid Cap and Large Cap at the Stockholm stock market. We took out five investment companies at random from the mentioned markets above. We used these companies as benchmarking for the study. To measure the development we looked at the change in the stock price and the total yield over the given time period, we then compared these to three random portfolios of 8 stocks each and the index called Six-Return index. All the companies in the random portfolios have another type of owner structure and lack Investment Company as a big owner. Those companies have a more divided ownership. In the essay we also look at the yield with consideration to the

    risk that is taken in the given investment in forms of Sharpe ratio and standard deviation for each portfolio. To get some extra insight we have interviewed Investor AB and Investment AB

    Latour. Both companies are leading investment companies in Sweden. The time period for the essay is 10 years and is stretching from 2004-01-01 until 2014-01-01.

    The results from the paper are that investment companies in general had a higher yield then the index and portfolios that was used as comparison. The results for the investment companies are better in terms of change in stock price and in yield but also with the consideration of the risk. The explanation of the results lies in several variables where the active ownership of the investment companies is the major part of the explanation and net asset discount together with the high dividend is another part. With these result investment companies is supposedly a very good investment for t

    hose that can’t beat the market, which would mean a great deal of all

    investors.

  • 2522.
    Ahlvik, Patrik
    KTH, School of Architecture and the Built Environment (ABE), Architecture.
    Nya Operan Stockholm: Förslag till nytt operahus i Stockholm2015Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    New Opera Stockholm

    My thesis is a proposal for a new opera house in Stockholm at Galärparken on the southern island of Djurgården, already one of Sweden's most visited tourist activity areas that I believe a new opera house will thrive on. Like a big boat building has comfortably settled to correct the Strandvägskajen with land bridge lowered. It is an opera in Stockholm and the National Opera in Sweden. With its 70,000 sqm it will give the opera a better room for a live opera, ballet and concert activities than can fit within the existing opera house today.

    The debate on giving Stockholm a new opera house has a long history, the current oscarianska opera has become too small and outdated to keep today's technically demanding operas; both Copenhagen, Oslo, Helsinki and Gothenburg have dared to invest and built their new opera houses in the last decade, now it's Stockholm's turn!

  • 2523.
    Ahlén, Patrik
    KTH, School of Engineering Sciences (SCI), Aeronautical and Vehicle Engineering, Aerodynamics.
    Computation of the Aerodynamic Characteristics of Propellers Using the BEMT-method Including the Condition of Stalled Flow2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The flow around a propeller is complex in nature and has to date still not been completely understood. However, since predicting the aerodynamic characteristics of propellers is an important aspect of the design of aircraft, a number of methods have been devised that by using simplifying assumptions is able to predict the aerodynamic coefficients of interest. One such is the blade element momentum theory method (BEMT-method) which have been found to give accurate results at high advance ratios. At lower advance numbers, where the flow over at least part of the propeller blade is stalled, the theory has traditionally not been found to be as accurate. This report presents a program written in Matlab that, by using the BEMT-method, is capable of predicting the aerodynamic characteristics for a given propeller in the whole operating region, i.e. including low advance ratios. The report include a derivation of the BEMT-equations, as well as a more general discussion of the aerodynamic of propellers, especially focusing on the issues that are important at low advance ratios. The report presents the results from the calculations for a two bladed propeller used on a racing plane, and discuss the issues surrounding the accuracy of the results.

    The BEMT-method have also been used for the calculation of other types of rotors and as an example of this, this report also shows how the BEMT-method can be used for predicting the aerodynamic characteristics of a wind turbine and gives an example of a computation. The result from both of the performed computations shows that the results from the BEMT-method where the blades operate with attached flow has good agreement, while when the flow is stalled the accuracy is less good. Although not numerically in agreement, the results show somewhat of a qualitative agreement.

  • 2524.
    Ahmad, Aftab
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Effective development of haptic devices using a model-based and simulation-driven design approach2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Virtual reality (VR)-based surgical simulators using haptic devices can increase the effectiveness of surgical training for surgeons when performing surgical procedures in hard tissues such as bones or teeth milling. The realism of virtual surgery through a surgical simulator depends largely on the precision and reliability of the haptic device, which reflects the interaction with the virtual model. The quality of perceptiveness (sensation, force/torque) depends on the design of the haptic device, which presents a complex design space due to its multi-criteria and conflicting character of functional and performance requirements. These requirements include high stiffness, large workspace, high manipulability, small inertia, low friction, high transparency, and cost constraints.

    This thesis proposes a design methodology to improve the realism of force/torque feedback from the VR-based surgical simulator while fulfilling end-user requirements.

    The main contributions of this thesis are:

    1. The development of a model-based and simulation-driven design methodology, where one starts from an abstract, top-level model that is extended via stepwise refinements and design space exploration into a detailed and integrated systems model that can be physically realized.

    2. A methodology for creating an analytical and compact model of the quasi-static stiffness of a haptic device, which considers the stiffness of actuation systems, flexible links and passive joints.

    3. A robust design optimization approach to find the optimal numerical values for a set of design parameters to maximize the kinematic, dynamic and kinetostatic performances of a 6-degrees of freedom (DOF) haptic device, while minimizing its sensitivity to variations in manufacturing tolerances and cost, and also satisfying the allowed variations in the performance indices.

    4. A cost-effective approach for force/torque feedback control using force/torque estimated through a recursive least squares estimation.

    5. A model-based control strategy to increase transparency and fidelity of force/torque feedback from the device by compensating for the natural dynamics of the device, friction in joints, gravity of platform, and elastic deformations.

     

  • 2525.
    Ahmad, Aftab
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Kinematisk och dynamisk modellering av den haptiska enheten TAU i sex frihetsgrader2009Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The thesis presents an optimally designed kinematic structure for a new 6-DOF haptic device

    based on TAU configuration. The configuration of the TAU-2 proposed by Suleman Khan and

    Kjell Andersson [1] was modified and its mobility was verified by using Grübler criterion to

    have a 6 DOF. Analytical kinematic models for the inverse and forward kinematics were

    developed for the haptic TAU configuration to determine a set of optimal design parameters.

    Kinematic performance indices such as volume of the workspace, kinematic isotropy and pay

    load index, were defined based on the singular values of the Jacobian matrix. The Jacobian

    matrix was scaled to homogenize the physical units. The Jacobian matrix dependent on the

    position and orientation of the end-effector gives local isotropy and pay load index, so global

    design indices were defined, which represent the performance of the mechanism in the whole

    workspace. A multi-objective function was defined based on the minimum of the global design

    indices in order to find a set of optimal design parameters. Genetic algorithm (GA) was used for

    optimization due to the nonlinearity of the multi-objective function. The optimal design

    parameters were obtained by minimizing the payload index while maximizing the volume index

    and isotropy indices.

    A close form dynamic model was developed using Lagrange mechanics to describe the dynamic

    behavior of the configuration. A trigonometric helical trajectory was developed in Cartesian

    space for each degree of freedom for the moving platform while moving along the trajectory

  • 2526.
    Ahmad, Aftab
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Andersson, Kjell
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    A comparative study of friction estimation and compensation using extended, iterated, hybrid, and unscented kalman filters2013In: Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference - 2013, ASME Press, 2013Conference paper (Refereed)
    Abstract [en]

    Transparency is a key performance evaluation criterion for haptic devices, which describes how realistically the haptic force/torque feedback is mimicked from a virtual environment or in case of master-slave haptic device. Transparency in haptic devices is affected by disturbance forces like friction between moving parts. An accurate estimate of friction forces for observer based compensation requires estimation techniques, which are computationally efficient and gives reduced error between measured and estimated friction. In this work different estimation techniques based on Kalman filter, such as Extended Kalman filter (EKF), Iterated Extended Kalman filter (IEKF), Hybrid extended Kalman filter (HEKF) and Unscented Kalman filter (UKF) are investigated with the purpose to find which estimation technique that gives the most efficient and realistic compensation using online estimation. The friction observer is based on a newly developed friction smooth generalized Maxwell slip model (S-GMS). Each studied estimation technique is demonstrated by numerical and experimental simulation of sinusoidal position tracking experiments. The performances of the system are quantified with the normalized root mean-square error (NRMSE) and the computation time. The results from comparative analyses suggest that friction estimation and compensation based on Iterated Extended Kalman filter both gives a reduced tracking error and computational advantages compared to EKF, HEKF, UKF, as well as with no friction compensation.

  • 2527.
    Ahmad, Aftab
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Andersson, Kjell
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    A deterministic and probabilistic approach for robust optimal design of a 6-DOF haptic device2014In: Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference--2013: Volume 3 B, 2013, ASME Press, 2014, p. V03BT03A032-Conference paper (Refereed)
    Abstract [en]

    This work suggests a two-stage approach for robust optimal design of 6-DOF haptic devices based on a sequence of deterministic and probabilistic analyses with a multi-objective genetic algorithm and the Monte-Carlo method. The presented model-based design robust optimization approach consider simultaneously the kinematic, dynamic, and kinetostatic characteristics of the device in both a constant and a dexterous workspace in order to find a set of optimal design parameter values for structural configuration and dimensioning. Design evaluation is carried out based on local and global indices, like workspace volume, quasi-static torque requirements for the actuators, kinematic isotropy, dynamic isotropy, stiffness isotropy, and natural frequencies of the device. These indices were defined based on focused kinematic, dynamic, and stiffness models. A novel procedure to evaluate local indices at a singularity-free point in the dexterous workspace is presented. The deterministic optimization approach neglects the effects from variations of design variables, e.g. due to tolerances. A Monte-Carlo simulation was carried out to obtain the response variation of the design indices when independent design parameters are simultaneously regarded as uncertain variables. It has been observed that numerical evaluation of performance indices depends of the type of workspace used during optimization. To verify the effectiveness of the proposed procedure, the performance indices were evaluated and compared in constant orientation and in dexterous workspace.

  • 2528.
    Ahmad, Aftab
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Andersson, Kjell
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    A model-based and simulation driven design approach for haptic devices2013In: Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference--2013, ASME Press, 2013, p. V02BT02A014-Conference paper (Refereed)
    Abstract [en]

    The output from a design process of high precision and reliable haptic devices for surgical training like bones and teeth is a complex design. The complexity is largely due to the multi-criteria and conflicting character of the functional requirements. These requirements include high stiffness, large workspace, high manipulability, small inertia, low friction, and high transparency. The requirements are a basis for generating design concepts. The concept evaluation relies to a large extent on a systematic usage of kinematic, dynamic, stiffness, and friction models. The design process can benefit from a model-based and simulation driven approach, where one starts from an abstract top-level model that is extended via stepwise refinements and design space exploration into a complete realization of the system. Such an approach is presented and evaluated through a test case where a haptic device, based on a Stewart platform, has been designed and realized. It can be concluded, based on simulation and experimental results that the performance of this optimally designed haptic device satisfies the stated user requirements. This indicates that the methodology can support the development of an optimal haptic device. However, more test cases are needed to further verify the presented methodology.

  • 2529.
    Ahmad, Aftab
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Andersson, Kjell
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Elements.
    An approach to stiffness analysis methodology for haptic devices2011In: 2011 3rd International Congress on Ultra Modern Telecommunications and Control Systems and Workshops (ICUMT), IEEE conference proceedings, 2011, , p. 8p. 1-8Conference paper (Refereed)
    Abstract [en]

    In this work a new methodology is proposed to model the static stiffness of a haptic device. This methodology can be used for other parallel, serial and hybrid manipulators. The stiffness model considers the stiffness of; actuation system; flexible links and passive joints. For the modeling of the passive joints a Hertzian contact model is introduced for both spherical and universal joints and a simply supported beam model for universal joints. For validation of the stiffness model a modified JP Merlet kinematic structure has been used as a test case. A parametric Ansys FEM model was developed for this test case and used to validate the resulting stiffness model. The findings in this paper can provide an additional index to use for multi-objective structural optimization to find an optimum compromise between a lightweight design and the stiffness performance for high precision motion within a larger workspace.

  • 2530.
    Ahmad, Aftab
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Andersson, Kjell
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    An Optimization Approach Toward a Robust Design of Six Degrees of Freedom Haptic Devices2015In: Journal of mechanical design (1990), ISSN 1050-0472, E-ISSN 1528-9001, Vol. 137, no 4, article id 042301Article in journal (Refereed)
    Abstract [en]

    This work presents an optimization approach for the robust design of six degrees of freedom (DOF) haptic devices. Our objective is to find the optimal values for a set of design parameters that maximize the kinematic, dynamic, and kinetostatic performances of a 6-DOF haptic device while minimizing its sensitivity to variations in manufacturing tolerances. Because performance indices differ in magnitude, the formulation of an objective function for multicriteria performance requirements is complex. A new approach based on Monte Carlo simulation (MCS) was used to find the extreme values (minimum and maximum) of the performance indices to enable normalization of these indices. The optimization approach presented here is formulated as a methodology in which a hybrid design-optimization approach, combining genetic algorithm (GA) and MCS, is first used. This new approach can find the numerical values of the design parameters that are both optimal and robust (i.e., less sensitive to variation and thus to uncertainties in the design parameters). In the following step, with design optimization, a set of optimum tolerances is determined that minimizes manufacturing cost and also satisfies the allowed variations in the performance indices. The presented approach can thus enable the designer to evaluate trade-offs between allowed performance variations and tolerances cost.

  • 2531.
    Ahmad, Aftab
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Kjell, Andersson
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    A model-based and simulation-driven methodology for design of haptic devices2014In: Mechatronics (Oxford), ISSN 0957-4158, E-ISSN 1873-4006, Vol. 24, no 7, p. 805-818Article in journal (Refereed)
    Abstract [en]

    High precision and reliable haptic devices are highly complex products. The complexity that has to be carefully treated in the design process is largely due to the multi-criteria and conflicting character of the functional and performance requirements. These requirements include high stiffness, large work-space, high manipulability, small inertia, low friction, high transparency, as well as cost constraints. The requirements are a basis for creating and assessing design concepts. Concept evaluation relies to a large extent on a systematic usage of kinematic, dynamic, stiffness, friction, and control models. The design process can benefit from a model-based and simulation-driven approach, where one starts from an abstract top-level model that is extended via stepwise refinements and design space exploration into a detailed and integrated systems model that can be physically realized. Such an approach is presented, put in context of the V-model, and evaluated through a test case where a haptic device, based on a Stewart platform, is designed and realized. It can be concluded, based on simulation and experimental results that the performance of this deterministically optimized haptic device satisfies the stated user requirements. Experiences from this case indicate that the methodology is capable of supporting effective and efficient development of high performing haptic devices. However, more test cases are needed to further validate the presented methodology.

  • 2532.
    Ahmad, Aftab
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Kjell, Andersson
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    An optimization approach towards a robust design of 6-DOF haptic devicesManuscript (preprint) (Other academic)
  • 2533.
    Ahmad, Aftab
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Kjell, Andersson
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Model-based control strategy for 6-DOF haptic devicesManuscript (preprint) (Other academic)
  • 2534.
    Ahmad, Aftab
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Kjell, Andersson
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Machine Design (Div.).
    Sellgren, Ulf
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Boegli, Max
    Evaluation of friction models for haptic devices2013Conference paper (Refereed)
    Abstract [en]

    In this work different friction models are evaluated to determine how well these models are suited for performance simulation and control of a 6-DOF haptic device. The studied models include, Dahl model, LuGre model, Generalized Maxwell slip model (GMS), smooth Generalized Maxwell slip model (S-GMS) and Differential Algebraic Multistate (DAM) friction model. These models are evaluated both numerically and experimentally with an existing 6-DOF haptic device that is based on a Stewart platform. In order to evaluate how well these models compensate friction, a model-based feedback friction compensation strategy along with a PID controller were used for position fracking accuracy The accuracies of the friction compensation models are examined separately for both low-velocity and high-velocity motions of the system. To evaluate these models, we use criteria based on fidelity to predict realistic friction phenomena, easiness to implement, computational efficiency and easiness to estimate the model parameters. Experimental results show that friction compensated with GMS, S-GMS and DAA4 models give better accuracy in terms of standard deviation, Root Mean Squared Error, and maximum error between a reference and measured trajectory. Based on the criteria of fidelity, ease of implementation and ease to estimate model parameters, the S-GMS model, which represents a smooth transition between sliding and pre-sliding regime through an analytical set of differential equations, is suggested.

  • 2535.
    Ahmad, Arslan
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering. Brabant Water NV, 5200 BC 's-Hertogenbosch, The Netherlands.
    Evaluation and optimization of advanced oxidation coagulation filtration (AOCF) to produce drinking water with less than 1 μg/L of arsenic2014Report (Other academic)
    Abstract [en]

    Arsenic is an extremely poisonous element. It has been reported to cause contamination of drinking water sources in many parts of the world. The current drinking water permissible limit for arsenic in the European Union is 10 μg/L. The World Health Organization has a general rule that no substance may have a higher lifetime risk of more than 1 in 100,000. However, several studies on toxicity of arsenic suggest that purely based on health effects the arsenic limit of 10 μg/L is not sufficient. The main goal of this research was to develop an efficient arsenic removal technology that could be able to produce drinking water with an arsenic concentration of less than 1 μg/L. For this purpose, an innovative three step technique, Advanced Oxidation - Coagulation - Filtration (AOCF), was investigated through bench-scale and pilot scale experiments in the Netherlands at the water treatment plant of Dorst. Firstly, prior to the investigations on AOCF, the existing arsenic removal at the water treatment plant was investigated. Secondly, through a series of bench-scale experiments, the optimum type of coagulant, its combination dose with the selected chemical oxidant and optimum process pH were determined. Eventually, the partially optimized technique from the bench-scale was implemented at the pilot scale physical model of water treatment plant Dorst where AOCF was evaluated for arsenic removal and its effect on the removal of other common undesirable groundwater constituents. The optimized AOCF technology consistently removed arsenic from groundwater to below 1 ug/L when implemented at pilot scale. The overall effluent quality also remained acceptable. The method is efficient with both types of filtration media tested in this research i.e., virgin sand and metal oxide coated sand, however virgin sand media showed slightly better arsenic removal efficiency.

  • 2536.
    Ahmad, Arslan
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    Evaluation of organic residues and their mixtures with Peepoos to produce fertilizer.2014Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Peepoo, self-sanitising, biodegradable toilet is characterized by low carbon to nitrogen (C-N) ratio and low dry matter (DM) content. Principal nutrients (nitrogen (N), phosphorous (P) and potassium (K)) are also not in a balance as required by most crops. It was expected that the mixing of used Peepoos with other organic materials might balance its chemical characteristics. In this thesis, availability and suitability of common organic materials produced in Kenya has been investigated for mixing with used Peepoo bags to obtain a balanced fertilizer product from the crop nutrition aspect. Seven organic residues were selected from the list of 13 on the basis of their availability near the processing site in Nairobi. The selected residues were then chemically analyzed for their individual plant nutrient content. The analysis results were used subsequently to simulate the chemical composition of a wide range of Peepoo-Residue mixtures. The evaluation of the theoretical mixtures based on DM content, C-N ratio and NPK ratio showed that the majority of investigated mixtures had DM content below 60 %. Majority of the mixtures showed C-N ratio between 10-1:1. All the mixtures deviated from the common nutrient uptake ratio of crops (1:0.5:1.4). Composite mixtures with more than 2 ingredients resulted in a balanced fertilizer product. The study concludes and recommends that the composite mixtures with more than two ingredients should be considered for practical processing of Peepoos into a commercial fertilizer product.

  • 2537.
    Ahmad, Arslan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Bhattacharya, Prosun
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Environmental arsenic in a changing world2019In: Groundwater for Sustainable Development, ISSN 2352-801X, Vol. 8, p. 169-171Article in journal (Refereed)
  • 2538.
    Ahmad, Arslan
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering. Hoofd Ingenieursbureau, Brabant Water N.V., 's-Hertogenbosch, Netherlands .
    Van De Wetering, S.
    Groenendijk, M.
    Bhattacharya, Prosun
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering.
    Advanced Oxidation-Coagulation-Filtration (AOCF) - An innovative treatment technology for targeting drinking water with <1 μg/L of arsenic2014In: One Century of the Discovery of Arsenicosis in Latin America (1914-2014): As 2014 - Proceedings of the 5th International Congress on Arsenic in the Environment, CRC Press, 2014, p. 817-819Conference paper (Refereed)
    Abstract [en]

    Advanced Oxidation-Coagulation-Filtration (AOCF) has been investigated for producing drinking water with less than 1 μg L-1 of As through a series of bench scale and pilot scale experiments. At bench scale, the suitable coagulant, its combination dose with KMnO4 oxidant, the optimum process pH and kinetics of As removal were determined. The optimized AOCF technique was capable of consistently reducing the As concentration to below 1 μg L-1 when implemented at pilot scale and did not adversely affect the already existing removal processes of Fe, Mn and NH4 +. Dual media filter solved the filter run time reduction issue.

  • 2539.
    Ahmad, Ashfaq
    et al.
    Univ Engn & Technol, ACTSENA Res Grp, Taxila 47050, Pakistan..
    Arshad, Farzana
    Univ Engn & Technol, ACTSENA Res Grp, Taxila 47050, Pakistan..
    Naqvi, Syeda I.
    Univ Engn & Technol, ACTSENA Res Grp, Taxila 47050, Pakistan..
    Amin, Yasar
    KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK. Univ Engn & Technol, ACTSENA Res Grp, Taxila 47050, Pakistan.
    Tenhunen, Hannu
    KTH, School of Information and Communication Technology (ICT), Centres, VinnExcellence Center for Intelligence in Paper and Packaging, iPACK. Univ Turku, Dept Informat Technol, TUCS, FIN-20520 Turku, Finland..
    Design, Fabrication, and Measurements of Extended L-Shaped Multiband Antenna for Wireless Applications2018In: Applied Computational Electromagnetics Society Journal, ISSN 1054-4887, Vol. 33, no 4, p. 388-393Article in journal (Refereed)
    Abstract [en]

    This article expounds a multi-band compact shaped antenna, which is based on CPW ground plane. FR-4 with a thickness of 1.6 mm is used as a substrate for the proposed antenna. The proposed antenna is capable of operating at 1.56 GHz for (Global Positioning System), 2.45 GHz (Wireless Local Area Network) and 4.49 GHz (Aeronautical Mobile Telemetry (AMT) fixed services). The efficiency at 1.56, 2.45, and 4.49 GHz is 79.7, 76.9 and 76.7%, respectively. The VSWR of the presented antenna is less than 1.5 at all the desired resonance modes, which confirms its good impedance matching. The performance of the proposed antenna is evaluated in terms of VSWR, return loss, radiation pattern and efficiency. CST (R) MWS (R) software is used for simulations. In order to validate the simulation results, a prototype of the designed antenna is fabricated and a good agreement is found between the simulated and measured results.

  • 2540.
    Ahmad, Bilal
    KTH, School of Information and Communication Technology (ICT).
    ID-REPLICATION FOR PEER-TO-PEER SYSTEMS2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Replication provides fault-­tolerance in distributed systems. This thesis presents ID-­replication, which is a new replication scheme for structured overlays. We first discuss the shortcomings of existing replication schemes and show how ID-­replication does not suffer from many of these issues. We present a detailed design, algorithmic specification and evaluation of ID-­replication.

    ID-replication is less sensitive to churn which makes it better suited for building consistent services on top of it and for working in asynchronous networks where inaccurate failure detections are a norm. ID­‐replication does not require requests to go through a particular replica before forwarding them to another node for processing and thus does not suffer from the bottleneck. ID-­‐replication provides variable replication degree, which makes it suitable for systems which need to provide extra backup for more critical data. It also makes the system easily handle hotspots/popular and is easier to load balance.

    We evaluate ID­‐replication and provide a comprehensive comparison of ID-­replication with SL-­replication, which is among the most popular replication scheme in use today.

  • 2541.
    Ahmad Khan, Naveed
    KTH, School of Electrical Engineering (EES), Electrical Energy Conversion.
    Power Loss Modeling of Isolated AC/DC Converter2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Several research activities at KTH are carried out related to Isolated AC/DC converters in order to improve the design and efficiency. Concerning the improvement in the mentioned constraints, losses of the elements in the prototype converter are modeled in this thesis work. The obtained loss model is capable of calculating the losses under different circumstances. The individual contribution of losses for each element at different conditions can be obtained, which is further useful in improving the design and therefore, efficiency. The losses in different elements of the converter, including power semiconductor devices, RC-snubbers, transformer and filter inductor at different operating points can be computed by using the obtained model. The loss model is then validated by comparing the analytical results with the measurements. The results based on developed loss model show consistency with the measured losses. The comparison at different conditions shows that, the difference between measured and analytical results ranges between 10% to 20 %. The difference is due to those losses which are disregarded because of their negligible contribution. On the other hand, it is also observed that if the neglected losses are counted, the difference reduces up to 10%.

  • 2542. Ahmad, M. Rauf
    et al.
    Pavlenko, Tatjana
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.).
    A U-classifier for high-dimensional data under non-normality2018In: Journal of Multivariate Analysis, ISSN 0047-259X, E-ISSN 1095-7243, Vol. 167, p. 269-283Article in journal (Refereed)
    Abstract [en]

    A classifier for two or more samples is proposed when the data are high-dimensional and the distributions may be non-normal. The classifier is constructed as a linear combination of two easily computable and interpretable components, the U-component and the P-component. The U-component is a linear combination of U-statistics of bilinear forms of pairwise distinct vectors from independent samples. The P-component, the discriminant score, is a function of the projection of the U-component on the observation to be classified. Together, the two components constitute an inherently bias-adjusted classifier valid for high-dimensional data. The classifier is linear but its linearity does not rest on the assumption of homoscedasticity. Properties of the classifier and its normal limit are given under mild conditions. Misclassification errors and asymptotic properties of their empirical counterparts are discussed. Simulation results are used to show the accuracy of the proposed classifier for small or moderate sample sizes and large dimensions. Applications involving real data sets are also included. 

  • 2543.
    Ahmad, Maqsood
    KTH, School of Information and Communication Technology (ICT).
    Anonymous Authentication Using Secure Multi-Party Computations2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Typical authentication systems provide a method to allow registered users access to protected resources after the user successfully authenticates. A user successfully authenticates by proving his or her valid identity if he or she is a registered user. During a typical authentication process, the authentication server can directly or indirectly learn the actual identity of the user who authenticates. However, the user might not want any one to know the actual identity of the user, while still able to authenticate. This problem of user’s anonymous authentication is the focus of this thesis project. This thesis project provides a solution for user’s anonymous authentication using Secure Multi-party Computation (SMPC). In SMPC, the user information is distributed among the authentication servers, using a secret sharing scheme, in such a way that none of the authentication servers individually possesses all the information of a user.

    However, these authentication servers can validate the user using some SMPC arithmetic operations. This thesis project provides a model for anonymous authentication and couples this anonymous authentication system with the Open Authentication Protocol (OAuth) to allow the user access to protected resources on the server. The model is explained using UML collaborations and SDL state transition diagrams. An analysis of the model is provided to ensure the security of the proposed system. A skeleton of the proposed model is provided which needs to be completed with appropriate code to realize the functionalities. This thesis project also provides an implementation of a simplified prototype which represents the core of the proposed model for anonymous authentication

  • 2544.
    Ahmad, Mirwary
    et al.
    KTH, School of Information and Communication Technology (ICT).
    Kaur, Birgeet
    KTH, School of Information and Communication Technology (ICT).
    Sustainability Aspects in ICT Engineering Thesis Works2016Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    An evaluation of thesis reports performed by students from the degree programme Computer Engineering, TIDAB, that was made by UKÄ, The Swedish Higher Education Authority, showed that there was a lack of consideration of environmental and sustainability aspects in the thesis reports, leading to many students not meeting the criteria in the degree objectives regarding this aspect. The purpose of this bachelor thesis is to improve students’ ability in considering the important aspects of sustainability in their thesis works, by providing them with guidelines which they can follow and implement during their thesis work that will enable them to reach the level ‘Very High Quality’.

    A literature study was performed thoroughly in conjunction with reviewing previous thesis reports and conducting expert interviews as an approach to find a solution to the problem.

    The outcome of the analysis was three methods that was developed, which the students can use as guidelines in their thesis work. A set of guidelines, a table with skill sets and the SEMAT Essence Kernel card for sustainable development was the resulting methods that will help the students to at minimum accomplish the criteria for ‘High Quality’ on the objective "Demonstrate an understanding of technology capabilities and limitations, its role in society and people’s responsibility for its use, including social and economic aspects, environmental and safety aspects" when the methods are followed.

  • 2545. Ahmad, Muhammad Ashfaq
    et al.
    Akram, Nadeem
    Raza, Rizwan
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    Structural and electrical characterisation of nanostructure electrodes for SOFCs2014In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 39, no 30, p. 17487-17491Article in journal (Refereed)
    Abstract [en]

    This paper reports the effects of sintering temperature on structure, particle size and conductivity of electrodes (Sn0.2Zn0.8Fe0.2O & Sn0.8Zn0.2Fe0.2O). The electrode material was prepared by the chemical method combining a solid state reaction. Structural analyses were performed using X-ray diffraction and scanning electron microscopy. The particle size of the material obtained using Scherrer's formula was 50-60 nm and the nanostructure's surface was studied using electrochemical characterisations tools. Electrical conductivity was determined using the 4-probe DC method, which was compared with the 4-probe AC method. These results suggest a promising substitute for the conventional electrodes of solid oxide fuel cells (SOFCs). It is known that a sintering temperature above 1000 degrees C causes an increase in density and a reduction of porosity. Therefore, we optimised the sintering temperature at 1000 degrees C and obtained electrical conductivity of about 5 S Thus, this electrode could play a vital role in the development of high performance SOFCs at intermediate temperatures.

  • 2546.
    Ahmad, Muhammad Bilal
    KTH, School of Electrical Engineering (EES), Communication Networks.
    Macro and Femto Network Aspectsfor Realistic LTE usage scenarios with Interference Management2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 2547.
    Ahmad, Muhammad Nabi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geoinformatik och Geodesi.
    Development of MetroMan with Open Source & Commercial web GIS technologies2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 2548.
    Ahmad, Nawaz
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. KTH Royal Institute of Technology.
    Numerical Modeling and Analysis of Small Gas Turbine Engine: Part I: Analytical Model and Compressor CFD2009Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The thesis work aims at devising analytical thermodynamic model and numerical modeling of the compressor of a small gas turbine to be operated on producer gas with lower heating contents. The turbine will serve as a component of “EXPLORE-Biomass Based Polygeneration” project to meet the internal electrical power requirements of 2-5 KW. The gas turbine engine is of radial type (one stage radial compressor, one stage radial turbine). Small gas turbines give less electrical efficiencies especially when operated with lower heating contents fuels like producer gas. This necessitates for optimum designing of components of the entire machine.

    Detailed analytical thermodynamic modeling of the engine has been analyzed for both internally and externally fired gas turbine cycles. Efforts are put on optimum utilization of energy available in the cycle and to enhance the efficiency thereby including various components.

    Numerical modeling of compressor using CFX has been performed for both steady and unsteady states. First different mesh sizes have been investigated followed by study of RMS residual targets on the results. Compressor performance has been studied for various speed lines. Thereafter, detailed steady state and unsteady simulations are performed for various cases including compressor single blade passage, 360 degree complete compressor, compressor connected with straight inlet pipe and for the compressor connected with 90 degree bended pipe.

    The operating point of the entire engine is analyzed. The numerical results are compared with each other and then to the ones from the 1D modeling. A good agreement has been found between the numerical results. Compared to 1D modeling, CFD presents higher performance at higher mass flow rates. However, for lower mass flow rates both 1D model and CFD present a similar performance.  

  • 2549.
    Ahmad, Nawaz
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering. KTH Royal Institute of Technology.
    REACTIVE TRANSPORT MODELLING OF DISSOLVED CO2 IN POROUS MEDIA: Injection into and leakage from geological reservoirs2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The geological sequestration of carbon dioxide (CO2) is one of the options of controlling the greenhouse gas emissions. However, leakage of CO2 from the storage reservoir is a risk associated with geological sequestration. Over longer times, large-scale groundwater motion may cause leakage of dissolved CO2 (CO2aq).

    The objectives of this thesis are twofold. First, the modelling study analyzes the leakage of CO2aq along the conducting pathways. Second, a relatively safer mode of geological storage is investigated wherein CO2aq is injected in a carbonate reservoir. A reactive transport model is developed that accounts for the coupled hydrological transport and the geochemical reactions of CO2aq in the porous media. The study provides a quantitative assessment of the impact of advection, dispersion, diffusion, sorption, geochemical reactions, temperature, and heat transport on the fate of leaking CO2aq.

    The mass exchange between the conducting pathway and the rock matrix plays an important role in retention and reactions of leaking CO2aq. A significant retention of leaking CO2aq is caused by its mass stored in aqueous and adsorbed states and its consumption in reactions in the rock matrix along the leakage pathway. Advection causes a significant leakage of CO2aq directly from the reservoir through the matrix in comparison to the diffusion alone in the rock matrix and advection in a highly conducting, but thin fracture. Heat transport by leaking brine also plays an important role in geochemical interactions of leaking CO2aq

    Injection of CO2aq is simulated for a carbonate reservoir. Injected CO2-saturated brine being reactive causes fast dissolution of carbonate minerals in the reservoir and fast conversion of CO2aq through considered geochemical reactions. Various parameters like dispersion, sorption, temperature, and minerals reaction kinetics are found to play important role in the consumption of CO2aq in reactions.

  • 2550.
    Ahmad, Nawaz
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering. Policy Wing, Ministry of Petroleum and Natural Resources, Government of Pakistan, Pakistan.
    Wörman, Anders
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Hydraulic Engineering.
    Bottacin-Busolin, Andrea
    Sanchez-Vila, Xavier
    Reactive transport modeling of leaking CO2-saturated brine along a fractured pathway2015In: International Journal of Greenhouse Gas Control, ISSN 1750-5836, E-ISSN 1878-0148, Vol. 42, p. 672-689Article in journal (Refereed)
    Abstract [en]

    One concern regarding the underground storage of carbon dioxide (CO2) is its potential leakage from reservoirs. Over short period of time, the leakage risk is related mainly to CO2 as a separate supercritical fluid phase. However, over longer periods upon complete dissolution of injected CO2 in the fluid, the leakage risk is associated with dissolved phase CO2. Over the geological time scales, large-scale groundwater motion may cause displacement of brine containing dissolved CO2 along the conducting pathways. In this paper, we present a comprehensive modeling framework that describes the reactive transport of CO2-saturated brine along a fracture in the clay caprock based on the future, hypothetical leakage of the dissolved phase CO2. This study shows that the transport of leaked dissolved CO2 is significantly retarded by a combination of various physical and geochemical processes, such as mass exchange between conducting fracture and the neighboring rock matrix through molecular diffusion, sorption and calcite dissolution in the rock matrix. Mass stored in aqueous and adsorbed states in the rock matrix caused retention of dissolved CO2 along the leakage pathway. Calcite dissolution reaction in the rock matrix resulted in consumption of leaking dissolved CO2 and reduced its mass along the leakage pathway. Consumption and retention of dissolved CO2 along the leakage pathway have important implications for analyzing the potential reduction of CO2 fluxes from storage reservoirs over large periods and long travel pathways.

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