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  • 2351. Ahlen, N.
    et al.
    Johnsson, M.
    Larsson, A. K.
    Sundman, Bo
    KTH, Superseded Departments, Materials Science and Engineering.
    On the carbothermal vapour-liquid-solid (VLS) mechanism for TaC, TiC, and TaxTi1-xC whisker growth2000In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 20, no 14-15, p. 2607-2618Article in journal (Refereed)
    Abstract [en]

    The growth of TaC, TiC and TaxTi1-xC whiskers has been studied in some detail. The whiskers were synthesised via a vapour-liquid-solid (VLS) growth mechanism in the temperature range 1220-1400 degreesC. The starting materials were Ta2O5, TiO2, C, NaCl, and a catalyst metal (Ni, Co, Fe, and Cu were tested). The main reaction during synthesis was a carbothermal reduction of Ta2O5 and TiO2, and NaCl was added to form the oxochlorides and chlorides of Ta and Ti that account for the transport to the catalyst metal. The syntheses were made in a protecting Ar atmosphere. From experiments interrupted after different times at the synthesis temperature it is clear that sodium tantalates form as intermediate products, whereas sodium titanates cannot be identified. Only metals that are able to dissolve the elements building up the whiskers work as catalysts. Whisker growth starts either from a catalyst droplet in contact with carbon or from an oxide particle in contact with both catalyst metal and carbon. For TaC and TaxTi1-xC the only growth direction observed is [100], while TiC may grow either along [100] or along [111].

  • 2352.
    Ahlenius, Camilla
    et al.
    KTH, School of Computer Science and Communication (CSC).
    Tengvall, Tove
    KTH, School of Computer Science and Communication (CSC).
    Notisers påverkan på mobilanvändning2017Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The rapid development of portable technology and its integration in our way of living has led to discussions about the negative consequences of technology. Previous research has shown a correlation between major mobile phone usage and a low well-being, and within popular culture new phenomenona regarding technology has arisen, such as digital detox and to downgrade one’s smartphone to a phone with fewer features. Despite this, the trend indicates that smartphone usage is increasing. The smartphone is constantly calling for attention through notifications in form of short texts containing various announcements and information. The purpose of this study is to examine in which way notifications may affect mobile phone usage and if there is a connection between the amount of received notifications and one’s overall mobile phone usage. To investigate this, we implemented structured observations on the users unaffected smartphone usage as well as their usage when notifications were disabled. Surveys were added as a qualitative complement to the observations.

    The result of the study showed that the total amount of unlockings of the screen decreased while the time spent on the smartphone increased, which leads to the conclusion that when the users received fewer notifications the usage sessions became fewer in number but longer in duration. Checking the lock screen, i.e. to wake the smartphone without unlocking it, seemed to have become more frequent. This was due to that the users wanted to ensure they did not miss any important information, and in particular if someone was trying to get in touch with them. An absolute majority experienced the absence of notifications as bothersome, particularly concerning notifications from communication applications. No correlation was found between the users’ attitude to notifications and the way their smartphone usage changed.

  • 2353.
    Ahlenius, Elisabeth
    KTH, Superseded Departments, Structural Engineering.
    Explosionslaster och infrastrukturkonstruktioner: risker, värderingar och kostnader1999Licentiate thesis, monograph (Other scientific)
  • 2354. Ahlers, R.
    et al.
    Brandimarte, L.
    Kleemans, I.
    Sadat, S. H.
    Ambitious development on fragile foundations: Criticalities of current large dam construction in Afghanistan2014In: Geoforum, Vol. 54, p. 49-58Article in journal (Refereed)
  • 2355. Ahlfeldt, H.
    et al.
    Holm, J.
    Lindgren, S.
    Backlin, L.
    Vieider, C.
    Klinga, T.
    Kerzar, B.
    Nilsson, M.
    Svensson, M.
    Nilsson, S.
    Kjebon, Olle
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Schatz, Richard
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP. KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    20 GHz bandwidth of lasers flip-chip-mounted on microstructured carriers with integrated electrical waveguides1998In: Optical Communication, 1998. 24th European Conference on, 1998, Vol. 1, p. 205-206Conference paper (Refereed)
    Abstract [en]

    A flip-chip-mounting scheme for high-speed lasers has been realised. The mounting scheme involves a microstructured silicon carrier with integrated membrane transmission lines and self-aligning solder bumps

  • 2356.
    Ahlfors, Charlotta
    KTH, School of Electrical Engineering (EES), Electric Power and Energy Systems.
    On the impact of wind power on CO2 emissions in a power system2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This master thesis is carried out at KTH Royal Institute of Technology in Stockholmthe spring 2017. The project analyses the impact of wind power in a power system.A fictitious power system, created from the Nordic32 test system, is used for theanalysis. The power sources in the test system are hydro power, nuclear power, CHPand wind power, resembling Swedish conditions. The power production planning inthe system is solved as a mixed integer linear programming problem in GAMS withhourly resolution. From the result of the planning problem calculations of CO2emissions are carried out with Monte Carlo simulations. Different cases with differentamounts of wind power installed in the test system are studied via a stochasticMarkov model. The load model in the test system consists of hourly time seriesdata for a specific day. Furthermore, challenges with wind power as a continuouslyvarying power source are studied. These challenges are balance between productionand consumption in the power system, excess of power etc.The results show that increasing the wind power production results in a decreasein CO2 emissions. This can be seen from the different simulations in the project.However, the results show that increasing the wind power production means that thesystem becomes more sensitive to keep the power balance. Moreover, the dischargecapacity and the efficiency of the hydro power plants are important factors in thetest system.

  • 2357.
    Ahlfors, Charlotta
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Industrial Ecology.
    Bergkrantz, Malin
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Industrial Ecology.
    Energieffektivisering av en bandybana: Analys av kompressorkylteknik och fjärrvärmedriven absorptionskylteknik2015Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Today, the energy consumption in the world is increasing and Sweden is not an exception. Therefore, the continued work towards a sustainable development is essential in order for future generations to have the same opportunities as the people today. An important step towards this goal is to improve the energy efficiency until the next generations technology has been developed. As a result of this the energy resources of the earth could be saved which would lead to cost savings, due to the fact that operating costs would decrease with reduced energy consumption. A reduced electrical power generation would lead to reduced emissions of substances that affect the environment as well. The municipality of Västervik has worked towards a sustainable development for a long time; therefore energy efficiency in the public sector has been implemented.

    An analysis is done, based on a literature study and calculations, in purpose to decide if a change of the cooling system used for the outdoor ice rink in Gamleby would lead to reduced energy consumption and cost savings. The two different machines analysed are the existing compressor cooling machine and an alternative absorption cooling machine in combination with district heat from a local source. If excess of distinct heat could be used as heat source it would be positive for the environment and for sustainable development.

    Through calculations of the cooling demand, the sustainable economy and the CO2-emissions the following conclusions have been made. Since the coefficient of cooling performance is lower for the absorption cooling machine a switch of cooling system would result in a higher demand of energy (heat and power). Due to the different CO2-emission coefficients of the two energy sources a switch would lead to increase of CO2-emissions as well as reduce the efficiency of the resources of the earth.

    The investment cost for an absorption cooling machine is double the investment cost for a commercial compressor cooling machine. Therefore, calculations have shown that it would take 18 years until a change of the cooling system can be seen as cost-effective. This calculation is based on the most optimal conditions such as free district heating and a high value on the coefficient of performance. As well if the district heat would cost, a change would never be cost-effective. The life span of a cooling machine is approximately 25 years and due to the fact that the calculations for the optimal case are based on assumptions that are not confirmed, for instance the energy from the district heat would be free of charge, the authors of this study cannot recommend the change of cooling method for the ice rink seen through an economical perspective. To sum up, the conclusion is that a switch to absorption cooling will not result in an improvement in terms of energy efficiency, cost benefits or emission reduction. Instead, an analysis of the existing system should be made in order to identify efficiency improvement opportunities in areas such as optimization of the control system and reducing the cooling demand of the bandy ice by reducing heat transfer from the environment. 

  • 2358.
    Ahlfors, JOhanna
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Häggdahl, Josefin
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Framtidens modulskola: En jämförande studie av arbetsmiljön i en tillfällig och en befintlig skolbyggnad2016Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
  • 2359.
    AHLFVENGREN, ELLINOR
    et al.
    KTH, School of Industrial Engineering and Management (ITM).
    Blomqvist, Louise
    KTH, School of Industrial Engineering and Management (ITM).
    The effect of M&A activity on firms R&D intensity - A quantitative study on the Swedish biotechnological industry2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 2360. Ahlgren, B.
    et al.
    Hidell, Markus
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    Ngai, E. C. -H
    Internet of Things for Smart Cities: Interoperability and Open Data2016In: IEEE Internet Computing, ISSN 1089-7801, E-ISSN 1941-0131, Vol. 20, no 6, p. 52-56, article id 7781549Article in journal (Refereed)
    Abstract [en]

    The Internet of Things (IoT) has become a promising technology for addressing societal challenges by connecting smart devices and leveraging Big Data analytics to create smart cities worldwide. As the IoT scales up, it's important to provide interoperability among different devices. Yet current simple standard protocols lack sufficient openness and interoperability. IoT for smart cities needs to guarantee the accessibility of open data and cloud services to allow industries and citizens to develop new services and applications. Here, the authors provide a case study of the GreenIoT platform in Uppsala, Sweden, to demonstrate the idea of interoperability and open data for smart cities.

  • 2361. Ahlgren, B.
    et al.
    Ohlman, B.
    Axelsson, Erik
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101).
    Brown, Lars
    KTH, School of Information and Communication Technology (ICT).
    Subversion over OpenNetInf and CCNx2011In: Proceedings - Conference on Local Computer Networks, LCN, 2011, p. 1056-1063Conference paper (Refereed)
    Abstract [en]

    We describe experiences and insights from adapting the Subversion version control system to use the network service of two information-centric networking (ICN) prototypes: OpenNetInf and CCNx. The evaluation is done using a local collaboration scenario, common in our own project work where a group of people meet and share documents through a Subversion repository. The measurements show a performance benefit already with two clients in some of the studied scenarios, despite being done on un-optimised research prototypes. The conclusion is that ICN clearly is beneficial also for non mass-distribution applications. It was straightforward to adapt Subversion to fetch updated files from the repository using the ICN network service. The adaptation however neglected access control which will need a different approach in ICN than an authenticated SSL tunnel. Another insight from the experiments is that care needs to be taken when implementing the heavy ICN hash and signature calculations. In the prototypes, these are done serially, but we see an opportunity for parallelisation, making use of current multi-core processors.

  • 2362.
    Ahlgren Bergman, Malin
    KTH, School of Architecture and the Built Environment (ABE), Architecture.
    Fruängen Centrum: En kontextuell strategi för det offentliga rummet2017Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The subject matter of this thesis project is post-war suburban centres, and particularly the case of Fruängen. The main question has been how to intervene spatially in this type of context, without completely contradicting the spatial logic of the existing system. The intention has been to introduce specific and monumental architecture to a generic environment, and to strengthen the definition of its public spaces. 

    The proposal consists of two buildings, an indoor bus terminal located on the existing bus station, and a library placed on the large parking lot behind the centre. New parking spaces in the bus terminal makes the placement of the library possible. 

    This project suggests that by dealing more efficiently with the traffic situation in a typical post-war centre, space can be created for new buildings on publicly owned land. This allows for the return of civic institutions to increasingly commercial centres and improved public spaces.

  • 2363.
    Ahlgren Bergman, Malin
    KTH, School of Architecture and the Built Environment (ABE), Architecture.
    School in Mariehäll: Elementary school in the new residential area Annedal2013Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    An elementary school in the Stockholm suburb Mariehäll, for children aged 6-11 as well as a daycare centre. The school will cater to approximately 700 students and a centre for art and culture, which will be available to the public. The school is located in the new residential area Annedal, adjacent to the local park and Bullerbytorget.

    This project explores the correlation between architecture and learning, with the purpose of creating an environment that meets the needs of students with difficulties in concentrating. This has influenced the orientation of the building and the classrooms, the organisation of the plan and the materials and colours used in the various rooms.

    The program is divided into two volumes – one which houses the actual school and daycare centre, and one which consists of administration and the centre for art and culture. These are connected by a souterrain storey which contains the school cafeteria, and entrances from the street and the square. The school grounds are located four meters above street level, which allows the roof of the lower volume to function as a part of the playground.

  • 2364.
    Ahlgren, Björn
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Astrophysical Constraints on Secret Neutrino Interactions2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 2365.
    Ahlgren, Björn
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Investigating subphotospheric dissipation in gamma-ray bursts by fitting a physical model2019Doctoral thesis, comprehensive summary (Other academic)
  • 2366.
    Ahlgren, Björn
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Subphotospheric dissipation in gamma-ray bursts observed by the Fermi Gamma-ray Space Telescope2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Gamma-ray bursts (GRBs) are the brightest events in the Universe, for a short time outshining the rest of the Universe combined, as they explode with isotropic equivalent luminosities up to $10^{54}$ erg s$^{-1}$. These events are believed to be connected to supernovae and to binary compact object mergers, such as binary neutron stars or neutron star -- black hole systems. The origin of the so-called prompt emission in GRBs remains an unsolved problem, although some progress is being made. Spectral analysis of prompt emission has traditionally been performed with the Band function, an empirical model with no physical interpretation, and it is just recently that physical models have started to be fitted to data. This thesis presents spectral analysis of GRB data from the Fermi Gamma-ray Space Telescope using a physical model for subphotospheric dissipation. The model is developed using a numerical code and implemented as a table model in {\scriptsize XSPEC}. Paper \rom{1} presents the model and provides a proof-of-concept of fitting GRB data with such a model. Specifically, two GRBs are fitted and compared with the corresponding Band function fits. In paper \rom{2}, a sample of 37 bursts are fitted with an extended version of the model and improved analysis tools. Overall, about a third of the fitted spectra can be described by the model. From these fits it is concluded that the scenario of subphotospheric dissipation can describe all spectral shapes present in the sample. The key characteristic of the spectra that are not fitted by the model is that they are very luminous. Within the context of the model, this suggests that the assumption of internal shocks as a dissipation mechanism cannot explain the full population of GRBs. Alternatively, additional emission components may required. The thesis concludes that subphotospheric dissipation is viable as a possible origin of GRB prompt emission. Furthermore, it shows the importance of using physically motivated models when analysing GRBs.

  • 2367.
    Ahlgren, Björn
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Subphotospheric dissipation in GRBs: fits to Fermi data constrain the dissipation scenario and reveal correlationsManuscript (preprint) (Other academic)
    Abstract [en]

     The emission mechanisms that give rise to the prompt emission in gamma-ray bursts (GRBs) is one of the main open questions in understanding these extreme explosions.

    We consider a model for subphotospheric dissipation which produces non-thermal spectra from the photosphere, by letting kinetic energy of the outow dissipate below the photosphere using a dissipation mechanism based on internal shocks. Building on the work of Ahlgren et al. (2015), we expand the model parameter space, compensate for adiabatic cooling, and improve the analysis tools. We create two table models for two dierent scenarios regarding the magnetisation, corresponding to no and moderate synchrotron emission, respectively. We t the models to time-resolved spectra of a sample of 37 Fermi GRBs and nd that  approximately a third of the spectra can be described by the models. From these ts we conclude that the scenario of subphotospheric dissipation can describe all spectral shapes present in the sample. However, we are not able to discriminate between no and moderate synchrotron emission. The key characteristic of spectra which are not tted by the model is that they are very luminous. Within the context of our model, we conclude that this is due to the assumption of internal shocks as a dissipation mechanism. Alternatively, some of these luminous bursts may require additional emission components.

  • 2368.
    Ahlgren, Björn
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    Byström, David
    KTH, School of Engineering Sciences (SCI), Theoretical Physics.
    A Study of Josephson Junction Characteristics.2011Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This Bachelor thesis has as its aim to investigate Josephson junctions by examining

    their I-V characteristics and to visualize various phenomena associated with Josephson

    junctions. Primarily, everything considered in this thesis uses a semi-classical model

    where quantum eects have been excluded. The thesis focuses on 1D arrays of Josephson

    junctions fed with direct current with the goal to study what occurs when many junctions

    are placed in a row. First a single Josephson junction is simulated and we observe a

    hysteresis in the I-V characteristics that is examined. Secondly a 1-D array is considered

    and the coupled system of dierential equations that follows is solved numerically, and

    from this data the properties of Josephson junctions are deduced. We discovered that this

    array generally has similar properties to a single Josephson junction. We also sought to

    replicate results obtained experimentally in the lab by David Haviland and his co-workers

    at KTH, but by simulations, to see how good our models are. We have produced data

    agreeing partly with the experimental results and we have had no directly contradicting

    outcomes from our simulations. An explicit relation between the number of Josephson

    junctions and the feature of the I-V characteristics was derived and the validity of our

    model was strengthened by the consistency of our results.

  • 2369.
    Ahlgren, Björn
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ahlberg, Erik
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Lundman, Christoffer
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Pe'er, Asaf
    Testing a model for subphotospheric dissipation in GRBs: fits to Fermi data constrain the dissipation scenario2019In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 485, p. 474-497Article in journal (Refereed)
    Abstract [en]

    It has been suggested that the prompt emission in gamma-ray bursts (GRBs) could be described by radiation from the photosphere in a hot fireball. Such models must be tested by directly fitting them to data. In this work we use data from the Fermi Gamma-ray Space Telescope and consider a specific photospheric model, in which the kinetic energy of a low-magnetization outflow is dissipated locally by internal shocks below the photosphere. We construct a table model with a physically motivated parameter space and fit it to time-resolved spectra of the 36 brightest Fermi GRBs with a known redshift. We find that about two-thirds of the examined spectra cannot be described by the model, as it typically underpredicts the observed flux. However, since the sample is strongly biased towards bright GRBs, we argue that this fraction will be significantly lowered when considering the full population. From the successful fits we find that the model can reproduce the full range of spectral slopes present in the sample. For these cases we also find that the dissipation consistently occurs at a radius of ∼1012 cm and that only a few per cent efficiency is required. Furthermore, we find a positive correlation between the fireball luminosity and the Lorentz factor. Such a correlation has been previously reported by independent methods. We conclude that if GRB spectra are due to photospheric emission, the dissipation cannot only be the specific scenario we consider here.

  • 2370.
    Ahlgren, Björn
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Oscar Klein Centre, Sweden.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Oscar Klein Centre, Sweden.
    Nymark, Tanja
    KTH, School of Engineering Sciences (SCI), Physics. KTH, School of Education and Communication in Engineering Science (ECE), Learning. Oscar Klein Centre, Sweden.
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Pe'er, A.
    Confronting GRB prompt emission with a model for subphotospheric dissipation2015In: Monthly Notices of the Royal Astronomical Society: Letters, ISSN 1745-3925, Vol. 454, no 1, p. L31-L35Article in journal (Refereed)
    Abstract [en]

    The origin of the prompt emission in gamma-ray bursts (GRBs) is still an unsolved problem and several different mechanisms have been suggested. Here, we fit Fermi GRB data with a photospheric emission model which includes dissipation of the jet kinetic energy below the photosphere. The resulting spectra are dominated by Comptonization and contain no significant contribution from synchrotron radiation. In order to fit to the data, we span a physically motivated part of the model's parameter space and create DREAM (Dissipation with Radiative Emission as A table Model), a table model for XSPEC. We show that this model can describe different kinds of GRB spectra, including GRB 090618, representing a typical Band function spectrum, and GRB 100724B, illustrating a double peaked spectrum, previously fitted with a Band+blackbody model, suggesting they originate from a similar scenario. We suggest that the main difference between these two types of bursts is the optical depth at the dissipation site.

  • 2371.
    Ahlgren, Björn
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Larsson, Josefin
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Valan, Vlasta
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Mortlock, Daniel
    Ryde, Felix
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Pe'er, Asaf
    Constraining subphotospheric dissipation in Gamma-ray Bursts using joint Fermi-Swift observationsManuscript (preprint) (Other academic)
  • 2372.
    Ahlgren, Björn
    et al.
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Ohlsson, Tommy
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Zhou, Shun
    KTH, School of Engineering Sciences (SCI), Theoretical Physics, Theoretical Particle Physics.
    Comment on "Is Dark Matter with Long-Range Interactions a Solution to All Small-Scale Problems of Λ Cold Dark Matter Cosmology?"2013In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 111, no 19, p. 199001-Article in journal (Refereed)
  • 2373.
    Ahlgren Cederlöf, Ebba
    et al.
    KTH, School of Engineering Sciences (SCI).
    Molin, Hilda
    KTH, School of Engineering Sciences (SCI).
    High-resolution photoluminescence spectroscopy of quantum dots2018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In this project we set up a high-resolution spectroscopy setup usinga fiber-based Fabry-P´erot interferometer to investigate epitaxial semiconductorquantum dots. We characterized the performance of the interferometerwith respect to four crucial parameters: reproducibility of measurements,resolution, transmission and stability. The setup is capable tomeasure linewidths of quantum dots with a resolution of up to 70 MHz.Using this setup, we performed high-resolution spectroscopy on a GaAsquantum dot measuring a linewidth of 5.9 ± 0.8 GHz, or 24.6 ± 3.2 μeV.Our results clearly show the applicability and challenges of fiber-basedFabry-P´erot interferometers for quantum dot spectroscopy.

  • 2374.
    Ahlgren, Hedvig
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Landström, Moa
    KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.).
    Success within Front End of Innovation- Recommendations for enabling creation anddevelopment of ideas at Atlas Copco,Construction Tools2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Several researchers talk about how the greatest source of competitive advantage is a firm's capability to be innovative, and it is a fact that economic growth is built upon innovations and ideas. Ideas belong to the early activities of innovation processes, which can be defined as he front end of innovation (FEI). FEI has clearly been stated to be crucial for the innovative performance of firms, but yet an area which many companies often lack of handling in a structured way.

    What need to be considered for a successful FEI has laid the foundation of this thesis. The aim with the thesis is to investigate what are key success factors and common pitfalls for processes and activities within the FEI, and how these can be handled by management. The thesis is also investigating how ideas and innovations can be measured in order to take the right decisions for different types of ideas by a suitable level of decision-makers. The thesis was carried out as a case study at Construction Tools division at Atlas Copco who had expressed the same demand as many companies appear to struggle with: a structured FEI. The goal with the thesis is therefore to propose recommendations towards a successful FEI, including structures, methods, and tools for the case company. In order to do so, twelve semistructured qualitative interviews with internal employees followed by ten semi-structured qualitative interviews with external companies in different industries and sizes were conducted. Along with the case study, a literature study was also performed.

    The collected data were analyzed and benchmarked towards the literature and the research questions, which resulted in several conclusions which are both general as well as organizational specific for the case company. These are amongst others: a structured innovation portfolio management including clear budget allocation and innovation strategy; enabling a creative culture; separating staff for conducting work regarding disruptive ideas; involvement by top management in the development of ideas.

  • 2375.
    Ahlgren, Joel
    et al.
    KTH, School of Computer Science and Communication (CSC).
    Mikkola, Mattias
    KTH, School of Computer Science and Communication (CSC).
    Net Voting – Designing an Online Voting System.2011Independent thesis Advanced level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    We are currently in a time where old routines and ways are being converted to more easily accessible, digital ways. You can perform your bank errands and interact with authorities through the Internet. While many of our societies functions already have undergone this transformation, our elections are still very manual. In our report we present what we think are the biggest obstacles to implementing a net voting system in Sweden, how to solve these issues and present a system which we feel would be a good start to designing The Ultimate Net Voting System. We touch upon areas like authenticating voters, protecting their right to anonymous voting in sending and storing votes and ways to protect against attacks against this system. In the end, we present an abstract level of a system design which could begin to fulfill all requirements to make net voting a feasible solution.

  • 2376.
    Ahlgren, Joel
    et al.
    KTH, School of Computer Science and Communication (CSC), Media technology and interaction design.
    Mikkola, Mattias
    KTH, School of Computer Science and Communication (CSC), Media technology and interaction design.
    Net Voting – Designing an Online Voting System.2011Independent thesis Advanced level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    We are currently in a time where old routines and ways are being converted to more easily accessible, digital ways. You can perform your bank errands and interact with authorities through the Internet. While many of our societies functions already have undergone this transformation, our elections are still very manual. In our report we present what we think are the biggest obstacles to implementing a net voting system in Sweden, how to solve these issues and present a system which we feel would be a good start to designing The Ultimate Net Voting System. We touch upon areas like authenticating voters, protecting their right to anonymous voting in sending and storing votes and ways to protect against attacks against this system. In the end, we present an abstract level of a system design which could begin to fulfill all requirements to make net voting a feasible solution.

  • 2377.
    AHLGREN, LINNEA
    et al.
    KTH, School of Industrial Engineering and Management (ITM).
    AHLSTRAND, REBECCA
    KTH, School of Industrial Engineering and Management (ITM).
    Co-creation as a Market Entry Strategy Key areas to consider when entering a market by co-creating digital HR-tools2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 2378.
    Ahlgren, Linnea
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial Marketing and Entrepreneurship.
    Rebecca, Ahlstrand
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.), Industrial Marketing and Entrepreneurship.
    Co-creation as a Market Entry Strategy: Key areas to consider when entering a market by co-creating digital HR-tools2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Due to digitalization, companies face a wide range of opportunities and challenges when it comes to attracting, recruiting and retaining talents. To meet these, companies need to present and achieve originality regarding values and corporate culture. One possible solution to this may be customized Human Resource tools.  Co-creation is an increasingly common product development strategy to create customized tools. It is based on collaboration and joint production of value between a supplier and customer. Cocreation may be a favorable strategy for early stage companies to gain customers and enter the market. While there are a variety of market entry strategies, this study is based on the insufficient attention among these to the customer as a possible collaborator when entering. This lack of attention is noteworthy since theory shows that the customer is gaining increased power over a supplier’s business decisions, largely due to digitalization.  There is a need to introduce a strategy that defines how companies co-create with their customers and regards them as an allied. This close relationship provides mutual benefits, sustainable relationships and networks. Consequently, this study aims to investigate if a co-creation strategy can be used to enter a market for an early stage company. The study is based on inductive reasoning and qualitative research methods. It uses semi- structured interviews, active participating observations and a literature study to collect primary and secondary data. The study proposes that co-creation is a new type of market entry strategy and suggests three key areas to consider for an early stage company when entering. These areas are: development approach, ownership and product protection, and expectation and communication.

  • 2379.
    Ahlgren, Lucas
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Marin Puentes, Angie Melissa
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Livsmedelshandel i webbutiker: En tillgänglighetsundersökning med WCAG 2.02018Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    This study aims to evaluate the state of web accessibility in online grocery stores in Sweden. This with the aim of informing the food industry about how accessibility is prioritized today, in order to contribute, to the discussion about this subject becoming more active. The survey included seven Swedish grocery stores on the web: Ica, Coop, Mat.se, Mathem.se, Willys, Hemköp and City Gross. In each web store, accessibility was evaluated on three web pages: the start page, the product page for 1 liter of milk of the brand Arla and the checkout page. The starting point for evaluat-ing accessibility on these web pages was the WCAG 2.0 web standard, which is the recommended standard from the W3C to evaluate accessibility on the web. The study was conducted using an evaluation tool AChecker as well as manual evaluations. The result showed that there is a lot of difference between different web stores regarding accessibility according to WCAG 2.0 acces-sibility standards. Common to all online stores was that none of them met the lowest level of WCAG 2.0, Level A. City Gross broke against the most number of guidelines while Willys broke against the fewest number of guidelines in WCAG 2.0. Which indicates that accessibility is not a priority in these online grocery stores.

  • 2380.
    Ahlgren, Marcus
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematical Statistics.
    Claims Reserving using Gradient Boosting and Generalized Linear Models2018Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    One fundamental function of an insurance company revolves around calculating the expected claims costs for which the insurer has to compensate its policyholders for. This is the process of claims reserving which is practised by actuaries using statistical methods. Over the last few decades statistical learning methods have become increasingly popular due to their ability to find complex patterns in any type of data. However, they have not been widely adapted within the insurance sector. In this thesis we evaluate the capability of claims reserving with the method of gradient boosting, a non-parametric statistical learning method that has proven to be successful within multiple other disciplines which has made it very popular. The gradient boosting technique is compared with the generalized linear model(GLM) which is widely used for modelling claims. We compare the models by using a claims data set provided by Länsförsäkringar AB which allows us to train the models and evaluate their performance on data not yet seen by the models. The models were implemented using R. The results show that the GLM has a lower prediction error. Also, the gradient boosting method requires more fine tuning to handle claims data properly while the GLM already possesses certain features that makes it suitable for claims reserving without making as many adjustments in the model implementation. The advantage of capturing complex dependencies in data is not fully utilized in this thesis since we only work with 6 predictor variables. It is more likely that gradient boosting can compete with GLM when predicting more complicated claims.

  • 2381.
    Ahlgren, Markus
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematical Statistics.
    Internal Market Risk Modelling for Power Trading Companies2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Since the financial crisis of 2008, the risk awareness has increased in the -financial sector. Companies are regulated with regards to risk exposure. These regulations are driven by the Basel Committee that formulates broad supervisory standards, guidelines and recommends statements of best practice in banking supervision. In these regulations companies are regulated with own funds requirements for market risks.

    This thesis constructs an internal model for risk management that, according to the "Capital Requirements Regulation" (CRR) respectively the "Fundamental Review of the Trading Book" (FRTB), computes the regulatory capital requirements for market risks. The capital requirements according to CRR and FRTB are compared to show how the suggested move to an expected shortfall (ES) based model in FRTB will affect the capital requirements. All computations are performed with data that have been provided from a power trading company to make the results fit reality. In the results, when comparing the risk capital requirements according to CRR and FRTB for a power portfolio with only linear assets, it shows that the risk capital is higher using the value-at-risk (VaR) based model. This study shows that the changes in risk capital mainly depend on the different methods of calculating the risk capital according to CRR and FRTB respectively and minor on the change of risk measure.

  • 2382.
    Ahlgren, Mats
    KTH, Superseded Departments, Physics.
    Studies of quantum interference effects in icosahedral quasicrystals and amorphous superconductors1997Doctoral thesis, comprehensive summary (Other scientific)
  • 2383.
    Ahlgren, Max
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management.
    Goldmann, Jacob
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management.
    The Internationalization of Swedish SMEs: how does internationalization affect individual firm’s capital and credit risk structure?2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    In this master thesis we examine how the level of internationalization, i.e. a firm’s relative exposure to foreign sales, affects individual SMEs in Sweden. Since it is conducted using a data sample with Swedish SMEs its applicability in other countries may vary. The aspects concerned in which the internationalization affects the firm’s structure is limited to the areas of capital structure, credit risk and the factors affecting credit risk. Altman’s Z-score model is employed to approximate a firm’s credit risk and the debt ratio represents the firm’s capital structure. The purpose of the thesis is to increase the knowledge and provide insights on how internationalization affects SMEs in general and in Sweden in particular. Knowledge on how internationalization affects firms is scarce and by this thesis we have extended the known area of the topic and shed light on this relatively unexplored SME aspect. Our hope is that by highlighting differences (and similarities) in credit risk attributes of high and low internationalized firms SMEs this will improve their financial transparency and ease their attracting and access to external sources of capital. To examine the effects of internationalization on Swedish SMEs we have employed statistical techniques, most importantly regression analysis.

    Our study has not only implications for academics, but for all parts that has any interest in efficient credit scoring models and to understand credit risk characteristics and how internationalization affects SMEs. Banks, policy makers and credit rating agencies are constantly pursuing improvements in the efficiency and accuracy of quantifying credit risk by developing credit-scoring models. Banks because they want to minimize credit losses and maximize profitability and policy makers to secure a viable business environment for companies to nurture economic growth, employment, innovation and the country’s competitiveness. The SME segment has received extra attention lately due to the financing barriers they are facing.

    Our results are contradictory to some earlier research in the area and in line with other. This implies that the characteristics and relationship of SMEs credit risk and internationalization changes over time and/or differs between countries, perhaps even between regions within national borders. For example we arrived at the conclusion that our basic model indicates a positive relationship between internationalization and credit risk, in line with both Rugman (2009) and Caves (2007). Our analysis shows no significant difference in the firm’s capital structure depending on the internationalization, although younger companies tended to have a higher level of internationalization. This finding is contradictory to the research conducted by Burgman (2009) and the reports carried out by the European Commission whose report reaches the conclusion that older firms had a higher level of international exposure. 

  • 2384. Ahlgren, Niklas
    et al.
    Karlsson, Thomas
    Larsson, Robin
    Spacecraft Department, OHB Sweden, Sweden.
    Noteborn, Ron
    PRISMA Mission Extension: Adapting Mission Operations to New and Changing Mission Objectives2012In: SpaceOps 2012 Conference, American Institute of Aeronautics and Astronautics, 2012Conference paper (Refereed)
    Abstract [en]

    The PRISMA in-orbit test-bed was launched in June 2010 to demonstrate strategies and technologies for formation flying and rendezvous. OHB Sweden is the prime contractor for the project which is funded by the Swedish National Space Board (SNSB) with support from DLR, CNES, and DTU. In early September of 2011, 15 months after launch, all primary mission objectives of the PRISMA formation flying satellites had been achieved and mission success was declared. Since a significant amount of delta-V capability still remained an open call for new experiments was issued, inviting both old and new experimenters to use the capabilities of the formation. Several interested parties took the opportunity to perform their own experiments with an existing platform, each coming with new mission objectives not previously planned to be flown on the PRISMA satellites. Some of these experiments were close to what had already been achieved within the nominal mission, but some included new ways of using the formation not envisioned by the spacecraft designers. The new experiments span from data collection in specific relative orbits, with a separation from a few meters to several kilometers, to entirely new modules within the on-board software. Changing from a pre-planned technology demonstration mission to operating a commercial resource required adaptation of the original operational concept, taking into account the different levels of experience of the customers and managing the satellites between experiments. This paper describes how these new mission objectives were integrated in operations and how a sometimes very short turn-around between initial concept and experiment execution was implemented with the aid of well established validation processes, high degrees of on-board autonomy and a flexible operations team.

  • 2385.
    AHLGREN, OSKAR
    KTH, School of Industrial Engineering and Management (ITM), Applied Mechanical Engineering (KTH Södertälje).
    SPICE UP APQP2013Independent thesis Basic level (university diploma), 10 credits / 15 HE creditsStudent thesis
  • 2386.
    Ahlgren, Per
    University College of Borås.
    A note on search formulation redundancy1998In: Journal of Documentation, ISSN 0022-0418, E-ISSN 1758-7379, Vol. 54, no 3, p. 352-354Article in journal (Refereed)
  • 2387.
    Ahlgren, Per
    Stockholm University, Sweden.
    Den norska modellen sett från Sverige2008In: Forskningspolitikk, ISSN 0333-0273, Vol. 31, no 1, p. 18-18Article in journal (Other academic)
  • 2388.
    Ahlgren, Per
    University College of Borås.
    On a cognitive search strategy1999In: Digital libraries: interdisciplinary concepts, challenges and opportunities, 1999, Vol. 1, p. 245-253Conference paper (Refereed)
  • 2389.
    Ahlgren, Per
    University College of Borås.
    Passage retrieval: en introduktion till ett aktuellt forskningsområde2000In: Svensk biblioteksforskning, ISSN 0284-4354, E-ISSN 1653-5235, no 2, p. 5-20Article in journal (Other academic)
  • 2390.
    Ahlgren, Per
    University College of Borås.
    Query expansion2001In: Human IT, ISSN 1402-1501, E-ISSN 1402-151X, no 4, p. 157-176Article in journal (Other academic)
  • 2391.
    Ahlgren, Per
    University College of Borås.
    The effects of indexing strategy-query term combination on retrieval effectiveness in a Swedish full text database2004Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis deals with Swedish full text retrieval and the problem of morphological variation of query terms in thedocument database. The study is an information retrieval experiment with a test collection. While no Swedish testcollection was available, such a collection was constructed. It consists of a document database containing 161,336news articles, and 52 topics with four-graded (0, 1, 2, 3) relevance assessments.

    The effects of indexing strategy-query term combination on retrieval effectiveness were studied. Three of five testedmethods involved indexing strategies that used conflation, in the form of normalization. Further, two of these threecombinations used indexing strategies that employed compound splitting. Normalization and compound splittingwere performed by SWETWOL, a morphological analyzer for the Swedish language. A fourth combinationattempted to group related terms by right hand truncation of query terms. A search expert performed the truncation.The four combinations were compared to each other and to a baseline combination, where no attempt was made tocounteract the problem of morphological variation of query terms in the document database.

    Two situations were examined in the evaluation: the binary relevance situation and the multiple degree relevancesituation. With regard to the binary relevance situation, where the three (positive) relevance degrees (1, 2, 3) weremerged into one, and where precision was used as evaluation measure, the four alternative combinationsoutperformed the baseline. The best performing combination was the combination that used truncation. Thiscombination performed better than or equal to a median precision value for 41 of the 52 topics. One reason for therelatively good performance of the truncation combination was the capacity of its queries to retrieve different partsof speech.

    In the multiple degree relevance situation, where the three (positive) relevance degrees were retained, retrievaleffectiveness was taken to be the accumulated gain the user receives by examining the retrieval result up to givenpositions. The evaluation measure used was nDCG (normalized cumulated gain with discount). This measurecredits retrieval methods that (1) rank highly relevant documents higher than less relevant ones, and (2) rankrelevant (of any degree) documents high. With respect to (2), nDCG involves a discount component: a discount withregard to the relevance score of a relevant (of any degree) document is performed, and this discount is greater andgreater, the higher position the document has in the ranked list of retrieved documents.

    In the multiple degree relevance situation, the five combinations were evaluated under four different user scenarios,where each scenario simulated a certain user type. Again, the four alternative combinations outperformed thebaseline, for each user scenario. The truncation combination had the best performance under each user scenario.This outcome agreed with the performance result in the binary relevance situation. However, there were alsodifferences between the two relevance situations. For 25 percent of the topics and with regard to one of the four userscenarios, the set of best performing combinations in the binary relevance situation was disjunct from the set of bestperforming combinations in the multiple degree relevance situation. The user scenario in question was such thatalmost all importance was placed on highly relevant documents, and the discount was sharp.

    The main conclusion of the thesis is that normalization and right hand truncation (performed by a search expert)enhanced retrieval effectiveness in comparison to the baseline, irrespective of which of the two relevance situationswe consider. Further, the three indexing strategy-query term combinations based on normalization were almost asgood as the combination that involves truncation. This holds for both relevance situations.

  • 2392.
    Ahlgren, Per
    Stockholm University.
    The SNIP indicator in relation to the Norwegian model2014In: Proceedings of the 19th International Conference on Science and Technology Indicators, 2014, p. 6-13Conference paper (Refereed)
  • 2393.
    Ahlgren, Per
    Stockholm University.
    Two elements of evaluative bibliometrics in Sweden: The national indicator and the bibliometric unit of Stockholm University2015In: Ronald Rousseau and the development of Scientomerics in China.: The 8th International Conference on Scientometrics and  University Evaluation, 2015, p. 66-75Conference paper (Other academic)
  • 2394.
    Ahlgren, Per
    et al.
    KTH, School of Education and Communication in Engineering Science (ECE).
    Colliander, C.
    Sjögårde, Peter
    KTH, School of Education and Communication in Engineering Science (ECE). Department of ALM, Uppsala University, Uppsala, Sweden.
    Exploring the relation between referencing practices and citation impact: A large-scale study based on Web of Science data2018In: Journal of the Association for Information Science and Technology, ISSN 2330-1635, E-ISSN 2330-1643, Vol. 69, no 5, p. 728-743Article in journal (Refereed)
    Abstract [en]

    In this large-scale contribution, we deal with the relationship between properties of cited references of Web of Science articles and the field normalized citation rate of these articles. Using nearly 1 million articles, and three classification systems with different levels of granularity, we study the effects of number of cited references, share of references covered by Web of Science, mean age of references and mean citation rate of references on field normalized citation rate. To expose the relationship between the predictor variables and the response variable, we use quantile regression. We found that a higher number of references, a higher share of references to publications within Web of Science and references to more recent publications correlate with citation impact. A correlation was observed even when normalization was done with a finely grained classification system. The predictor variables affected citation impact to a larger extent at higher quantile levels. Regarding the relative importance of the predictor variables, citation impact of the cited references was in general the least important variable. Number of cited references carried most of the importance for both low and medium quantile levels, but this importance was lessened at the highest considered level.

  • 2395.
    Ahlgren, Per
    et al.
    Stockholm University.
    Colliander, Cristian
    Document-document similarity approaches and science mapping: Experimental comparison of five approaches2009In: Journal of Informetrics, ISSN 1751-1577, E-ISSN 1875-5879, Vol. 3, no 1, p. 49-63Article in journal (Refereed)
  • 2396.
    Ahlgren, Per
    et al.
    Stockholm University.
    Colliander, Cristian
    Textual content, cited references, similarity order, and clustering: An experimental study in the context of science mapping2009In: Proceedings of the 12th International Conference on Scientometrics and Informetrics (Volume 2), 2009, p. 862-873Conference paper (Refereed)
  • 2397.
    Ahlgren, Per
    et al.
    Stockholm University, Sweden.
    Colliander, Cristian
    Persson, Olle
    Field normalized citation rates, field normalized journal impact and Norwegian weights for allocation of university research funds2012In: Scientometrics, ISSN 0138-9130, E-ISSN 1588-2861, Vol. 92, no 3, p. 767-780Article in journal (Refereed)
    Abstract [en]

    We compared three different bibliometric evaluation approaches: two citation-based approaches and one based on manual classification of publishing channels into quality levels. Publication data for two universities was used, and we worked with two levels of analysis: article and department. For the article level, we investigated the predictive power of field normalized citation rates and field normalized journal impact with respect to journal level. The results for the article level show that evaluation of journals based on citation impact correlate rather well with manual classification of journals into quality levels. However, the prediction from field normalized citation rates to journal level was only marginally better than random guessing. At the department level, we studied three different indicators in the context of research fund allocation within universities and the extent to which the three indicators produce different distributions of research funds. It turned out that the three distributions of relative indicator values were very similar, which in turn yields that the corresponding distributions of hypothetical research funds would be very similar.

  • 2398.
    Ahlgren, Per
    et al.
    Stockholm University.
    Grönqvist, Leif
    Evaluation of retrieval effectiveness with incomplete relevance data: theoretical and experimental comparison of three measures2008In: Information Processing & Management, ISSN 0306-4573, E-ISSN 1873-5371, Vol. 44, no 1, p. 212-225Article in journal (Refereed)
  • 2399.
    Ahlgren, Per
    et al.
    University College of Borås.
    Grönqvist, Leif
    Measuring retrieval effectiveness with incomplete relevance data2006In: Current research in information sciences and technologies: multidisciplinary approaches to global information systems, 2006, p. 74-78Conference paper (Refereed)
  • 2400.
    Ahlgren, Per
    et al.
    University College of Borås.
    Grönqvist, Leif
    Retrieval evaluation with incomplete relevance data: a comparative study of three measures2006In: Proceedings of the 15th ACM International Conference on Information and Knowledge Management, 2006, p. 872-873Conference paper (Refereed)
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