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  • 1. Abdullah, Omed Gh.
    et al.
    Tahir, Dana A.
    Kadir, K.
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Kurdistan Institution for Strategic Studies and Scientific Research, Iraq.
    Optical and structural investigation of synthesized PVA/PbS nanocomposites2015In: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 26, no 9, p. 6939-6944Article in journal (Refereed)
    Abstract [en]

    Polymer nanocomposite based on polyvinyl alcohol (PVA) and lead sulfide (PbS) in the average radius of (1.88-2.23) nm, have been synthesized using the chemical reduction rote and solution casting technique for different concentrations of PbS. The characterization of the polymer nanocomposite films were carried out using UV-visible spectroscopy, SEM, and XRD. The effect of various concentration of PbS NP on the optical properties of the composite has been studied to understand the optimum conditions for the synthesis process. The nanocomposite film shows high UV and visible light absorptions in the wavelength range of (200-500) nm, which correspond to the characteristics of the PbS NPs. The significant decreasing trend of the direct allowed band gap of the nanocomposite was observed upon increasing the Pb source concentration, from (6.27 eV) for pure PVA to (2.34 eV) for 0.04 M PbS concentration, which is much higher than the energy gap of bulk PbS value (0.41 eV). The calculated values of the static refractive index of Cauchy dispersion model were in the range of (1.09-1.20). X-ray diffraction analysis confirmed the cubic nanocrystalline PbS phase formation.

  • 2. Barbeiro, A. R.
    et al.
    Ureba, Ana
    Stockholm University, Faculty of Science, Department of Physics. Universidad de Sevilla, Spain; Instituto de Biomedicina de Sevilla, IBIS, Spain; Karolinska Institutet, Sweden.
    Baeza, J. A.
    Linares, R.
    Perucha, M.
    Jimenez-Ortega, E.
    Velazquez, S.
    Mateos, J. C.
    Leal, A.
    3D VMAT Verification Based on Monte Carlo Log File Simulation with Experimental Feedback from Film Dosimetry2016In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 11, no 11, article id e0166767Article in journal (Refereed)
    Abstract [en]

    A model based on a specific phantom, called QuAArC, has been designed for the evaluation of planning and verification systems of complex radiotherapy treatments, such as volumetric modulated arc therapy (VMAT). This model uses the high accuracy provided by the Monte Carlo (MC) simulation of log files and allows the experimental feedback from the high spatial resolution of films hosted in QuAArC. This cylindrical phantom was specifically designed to host films rolled at different radial distances able to take into account the entrance fluence and the 3D dose distribution. Ionization chamber measurements are also included in the feedback process for absolute dose considerations. In this way, automated MC simulation of treatment log files is implemented to calculate the actual delivery geometries, while the monitor units are experimentally adjusted to reconstruct the dose-volume histogram (DVH) on the patient CT. Prostate and head and neck clinical cases, previously planned with Monaco and Pinnacle treatment planning systems and verified with two different commercial systems (Delta4 and COMPASS), were selected in order to test operational feasibility of the proposed model. The proper operation of the feedback procedure was proved through the achieved high agreement between reconstructed dose distributions and the film measurements (global gamma passing rates > 90% for the 2%/2 mm criteria). The necessary discretization level of the log file for dose calculation and the potential mismatching between calculated control points and detection grid in the verification process were discussed. Besides the effect of dose calculation accuracy of the analytic algorithm implemented in treatment planning systems for a dynamic technique, it was discussed the importance of the detection density level and its location in VMAT specific phantom to obtain a more reliable DVH in the patient CT. The proposed model also showed enough robustness and efficiency to be considered as a pre-treatment VMAT verification system.

  • 3. Bertels, Koen
    et al.
    Jacques, Jean-Marie
    Boman, Magnus
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Risk and crises management in complex systems2005In: Micro, meso, macro: addressing complex systems couplings / [ed] Hans Liljenstörm, Uno Svedin, New Jersey: World Scientific, 2005, p. 305-316Chapter in book (Other academic)
  • 4. Biteus, Jonas
    et al.
    Lindgren, Tony
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Planning Flexible Maintenance for Heavy Trucks using Machine Learning Models, Constraint Programming, and Route Optimization2017In: SAE International Journal of Materials & Manufacturing, ISSN 1946-3979, E-ISSN 1946-3987, Vol. 10, no 3, p. 306-315Article in journal (Refereed)
    Abstract [en]

    Maintenance planning of trucks at Scania have previously been done using static cyclic plans with fixed sets of maintenance tasks, determined by mileage, calendar time, and some data driven physical models. Flexible maintenance have improved the maintenance program with the addition of general data driven expert rules and the ability to move sub-sets of maintenance tasks between maintenance occasions. Meanwhile, successful modelling with machine learning on big data, automatic planning using constraint programming, and route optimization are hinting on the ability to achieve even higher fleet utilization by further improvements of the flexible maintenance. The maintenance program have therefore been partitioned into its smallest parts and formulated as individual constraint rules. The overall goal is to maximize the utilization of a fleet, i.e. maximize the ability to perform transport assignments, with respect to maintenance. A sub-goal is to minimize costs for vehicle break downs and the costs for maintenance actions. The maintenance planner takes as input customer preferences and maintenance task deadlines where the existing expert rule for the component has been replaced by a predictive model. Using machine learning, operational data have been used to train a predictive random forest model that can estimate the probability that a vehicle will have a breakdown given its operational data as input. The route optimization takes predicted vehicle health into consideration when optimizing routes and assignment allocations. The random forest model satisfactory predicts failures, the maintenance planner successfully computes consistent and good maintenance plans, and the route optimizer give optimal routes within tens of seconds of operation time. The model, the maintenance planner, and the route optimizer have been integrated into a demonstrator able to highlight the usability and feasibility of the suggested approach.

  • 5.
    Brodin, Jane
    Stockholm University, The Stockholm Institute of Education, Department of Human Development, Learning and Special Education .
    Communication and assistive technology for persons with mental retardation1997In: Advancement of assistive technology / [ed] G. Anogianakis, C. Bühler, M. Soede, Amsterdam: IOS Press, 1997, p. 81-84Chapter in book (Other academic)
  • 6.
    Brown, Barry
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    The Social Life of Autonomous Cars2017In: Computer, ISSN 0018-9162, E-ISSN 1558-0814, Vol. 50, no 2, p. 92-96Article in journal (Refereed)
    Abstract [en]

    Until the day comes when all vehicles are fully autonomous, self-driving cars must be more than safe and efficient, they must also understand and interact naturally with human drivers. The web extras include videos demonstrating "rude" behavior by Tesla's Autopilot system, www.youtube.com/watch?v=el4OdwtgzNk; a human driver confused by self-driving technology, www.youtube.com/watch?v=Uj-rK8V-rik; and aggressive driving prompted by self-driving technology, www.youtube.com/watch?v=FbSQm3YaAzA.

  • 7. Cardoso, G.
    et al.
    Stadler, M.
    Siddiqui, Afzal
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences. University College London, UK.
    Marnay, C.
    DeForest, N.
    Barbosa-Povoa, A.
    Ferrao, P.
    Microgrid reliability modeling and battery scheduling using stochastic linear programming2013In: Electric power systems research, ISSN 0378-7796, E-ISSN 1873-2046, Vol. 103, p. 61-69Article in journal (Refereed)
    Abstract [en]

    This paper describes the introduction of stochastic linear programming into Operations DER-CAM, a tool used to obtain optimal operating schedules for a given microgrid under local economic and environmental conditions. This application follows previous work on optimal scheduling of a lithium-iron-phosphate battery given the output uncertainty of a 1 MW molten carbonate fuel cell. Both are in the Santa Rita Jail microgrid, located in Dublin, California. This fuel cell has proven unreliable, partially justifying the consideration of storage options. Several stochastic DER-CAM runs are executed to compare different scenarios to values obtained by a deterministic approach. Results indicate that using a stochastic approach provides a conservative yet more lucrative battery schedule. Lower expected energy bills result, given fuel cell outages, in potential savings exceeding 6%.

  • 8. Conti, Maurizio
    et al.
    Eriksson, Lars
    Stockholm University, Faculty of Science, Department of Physics.
    Westerwoudt, Victor
    Estimating Image Quality for Future Generations of TOF PET Scanners2013In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 60, no 1, p. 87-94Article in journal (Refereed)
    Abstract [en]

    Images taken with time-of-flight (TOF) positron emission tomography (PET) scanners are of improved quality compared to equivalent non-TOF images. This improvement is dependent on the scanner time resolution. The present generation of commercial TOF scanners has a time resolution in the range of 500-600 ps full width half maximum. In this work we investigate how the image characteristics will improve for future generations of TOF PET. We performed a Geant4 simulation of a 30-cm uniform cylinder containing hot spheres, with time resolution ranging from 600 to 200 ps. Data were reconstructed using TOF filtered back projection (FBP) and TOF ordered subsets expectation maximization (OSEM), with nonTOF reconstruction as a reference. Images were compared in terms of contrast recovery and variance in the image. The TOF gain was evaluated for both reconstruction methods. The TOF gain was also evaluated vs. counts in the scan, in order to understand the behavior of such gain at very low statistics. Using TOF FBP, it was shown that the TOF gain can be used as a sensitivity amplifier, reducing (according to the expected TOF gain) the number of counts necessary to produce an image of the same characteristics. Some limitations in the TOF gain were observed at very low counts, particularly if using iterative methods.

  • 9.
    Cunningham, Miriam
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Technology-Enhanced Learning in Kenyan Universities2016In: IEEE technology & society magazine, ISSN 0278-0097, E-ISSN 1937-416X, Vol. 35, no 3, p. 28-35Article in journal (Refereed)
    Abstract [en]

    This article discusses some of the findings of a study that bridges an existing knowledge gap by focusing on identifying influences on the wider adoption and uptake of TEL techniques by HEIs in Nairobi. In this context, TEL techniques can encompass e-learning, blended learning, using massive open online courses (MOOCs), or an entirely online course delivery. This study examines why HEIs are using TEL, perceived benefits and challenges of using TEL from an institutional and instructor perspective, and the impact of policies. The findings have important research, practical, societal, and policy making implications for educational delivery on a continent with a rapidly growing population. Findings will assist decision making, inform policy creation, and provide useful foundational reference material for further comparative research in Africa. The lessons learned will also assist tertiary level institutions across the African continent that wish to plan for wider TEL adoption, or to implement TEL in a more effective manner, by considering common challenges that could limit adoption.

  • 10.
    Elly Amani, Gamukama
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Larsson, Aron
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Popov, Oliver
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Mugisha, Joseph Y. T.
    Group Decision Evaluation of Internet Services in the Context of DevelopmentManuscript (preprint) (Other academic)
    Abstract [en]

    The paper presents group decision assessment for the Internet services in the context of development (ISCD). The assessment is achieved through the use of a decision model whose fundamental goal is to provide a systematic approach for addressing the problem of misalignments among the Internet stakeholders’ objectives. The modelling of the problem is approached from the perspectives of delivering/receiving the Internet services that maximizes the respective stakeholders’ objectives. Based on the AHP theory, it structures the problem into four hierarchies with three aspects of consideration as (a) services relevance in context of development, (b) services delivery mechanism convergence to IP Infrastructure and (c) services commensurability to traffic classes’ requirements. An assessment of the aggregated individually derived final priorities (AIP) reveals that for aligning the stakeholders’ objectives at local level, end users should first strive to implement the Internet components/applications that can cause high impact to their transactions/business, followed by those services/applications that can “empower” them to fulfil their goals. While at global level, the affordability of recurring subscriptions for Internet access, end user terminal equipment cost, and coverage rage/penetration are the key issues that the policy makers should address in view of achieving the ISCD objectives. Finally the paper includes strategic options for the best course of action in aligning the stakeholders’ objectives.

  • 11.
    Eriksson, Lars
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Conti, M.
    Melcher, C. L.
    Zhuravleva, M.
    Eriksson, M.
    Rothfuss, H.
    LuYAP/LSO Phoswich Detectors for High Resolution Positron Emission Tomography2013In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 60, no 1, p. 194-196Article in journal (Refereed)
    Abstract [en]

    The spatial resolution in positron emission tomography (PET) can be improved by the addition of depth-of-interaction (DOI) information. This can be achieved by using the phoswich approach in which depth identification relies on differences in scintillation decay time and pulse shape discrimination techniques. In this paper we have looked at a special phoswich combination LuAP/LSO or LuYAP/LSO. This combination of scintillators is especially interesting since LuAP and LuYAP have emission in the excitation band of LSO, which may have an impact on the timing resolution of the detector. As will be shown in this paper, the phoswich concept based on these two scintillators can be utilized, however, with some limitations. This paper is an extension of our previous phoswich investigation [3].

  • 12.
    Everitt, Tom
    et al.
    Stockholm University, Faculty of Science, Department of Mathematics.
    Lattimore, Tor
    Hutter, Marcus
    Free Lunch for Optimisation under the Universal Distribution2014In: 2014 IEEE Congress on Evolutionary Computation (CEC), New York: IEEE Computer Society, 2014, p. 167-174Conference paper (Refereed)
    Abstract [en]

    Function optimisation is a major challenge in computer science. The No Free Lunch theorems state that if all functions with the same histogram are assumed to be equally probable then no algorithm outperforms any other in expectation. We argue against the uniform assumption and suggest a universal prior exists for which there is a free lunch, but where no particular class of functions is favoured over another. We also prove upper and lower boundson the size of the free lunch.

  • 13.
    Gamukama, Elly A.
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Popov, Oliver B.
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    A Social Welfare Approach in Increasing the Benefits from the Internet in Developing Countries2011In: International Journal on Network Security, ISSN 2152-5064, Vol. 2, no 4, p. 29-33Article in journal (Refereed)
    Abstract [en]

    The paper examines the Internet usage and itsmarket environment in developing countries under theperceived assumption that the Internet is one of the mostimportant drivers for development. It gives an insight onprocesses’ (both unintended and intended) implications andtheir effects on achieving real Internet benefits in theenvironments where network infrastructures are limited suchas the ones found in the developing regions. A welfare basedapproach is proposed in which the Internet providers and endusersidentify a set of objective that leads them in achievingincreased benefits. Analytical model of the maincharacteristics in the approach is presented and eventuallyshown how the end user bit rate could be regulated based onthe utility bounds that lead general satisfaction to all users.User satisfaction signifies delivery of expected QoS and aswell as willing to pay for such services.

  • 14.
    Gamukama, Elly Amani
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Analytical modelling of Internet provision and usage in context of development through a utility based framework2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Information and communication technology and development (ICTD) is a research area that has broadly captured the attention of the public and the academics in the last two decades. It deals with the interaction and the relations between the humans and the society in general on one side and the technology on the other side. The focus in this thesis is on the computing and communication technology, herein referred to as the “Internet – the IP based technology”, which is seen as one of the enablers for economic and social growth.

    The benefit of the Internet connectivity and usage in inducing and enhancing positive social changes in basic dimensions of human life is generally accepted as one of the most important drivers for development. The success and the inevitability of the Internet in the developed world underline its proliferation and diffusion essential in less developed countries. However, sometimes these processes are being impaired by unintended and intended consequences created by the social dynamics that drives the current information technological innovations and evolutions, stakeholders’ desire of fulfilling one’s utility egos, all coupled with market environments.

    This thesis takes an insight in both unintended and intended implications and their effects on enabling development in the environments where the Internet Protocol (IP) based infrastructures are limited like in Least Developing regions/countries.  The results of this insight study have led in;

    a)      Establishing the basic Internet services that would trigger the exploitation of one’s potential for development.

    This has been achieved through the use of analytical scientific methods to classify Internet traffic characteristics and derive the relevance levels of their corresponding Internet services groups in fostering development.

    b)      Developing a framework that lays down structure guidelines to facilitate Decision Makers especially in least developed countries to make scientifically informed subjective judgements for Internet services in the context of development.

    c)      Designing and developing of the Internet Services in the Context of Developing (ISCD) model that enables the alignment of the apparent divergent/misalignment objectives of Internet stakeholders in the present Internet structure to have their respective maximised intended benefits.

    Empirical testing of the model led in setting strategic options for aligning stakeholders goals in view of the ISCD along two main domains (i) network management policies – that focuses on provisions of services, and (ii) Internet consumption/usage – that focus on services relevance, commensurability to specific requirements as pertains LDCs, and services delivery mechanism convergence to all-IP.

  • 15.
    Gamukama, Elly Amani
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Fairness on the Internet and its Importance in Development Context2008Conference paper (Refereed)
    Abstract [en]

    The notion of fairness with respect to resource sharing among the competing flows is one of the important considerations in network design. This is true in particular for IP networks (which are the foundation of the Internet), where the service model is based on best effort and any possible distortion of it may lead to flow starvation and eventually system imbalances. In fact, fairness should be one of the major objectives both on a network layer and transport layer. This is evident in the case of elastic flows such as TCP, where fairness may have a major impact on congestion resolution. On a network layer, fairness mechanisms combined with scheduling and queuing policies lead to equitable service, which may also induce higher router utilization and hence better network performance. The paper investigates the current trends in understanding and applying the fairness concept on the Internet and hence in heterogeneous networks. Then it studies and examines the extension of the fairness concept in the context of development and developing regions, where both the traditional lack of infrastructure and costly communication services have also affected the penetration of the Internet and more even distribution of its benefits. The key question is whether or not it is plausible to identify a framework for the evaluation of efficiently-fairness tradeoffs that may provide a sound basis for a model of a more equitable access to the Internet to a diversity of users with different needs and financial possibilities representing mainly developing regions and emerging economies.

  • 16.
    Gamukama, Elly Amani
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Larsson, Aron
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Popov, Oliver
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Mugisha, J. Y. T.
    The Decision Model for the Internet Services in the Context of Development2015In: Procedia Computer Science, ISSN 1877-0509, E-ISSN 1877-0509, Vol. 55, p. 622-631Article in journal (Refereed)
    Abstract [en]

    The Internet Services in the Context of Development (ISCD) model is structured in four levels of hierarchy based on the Analytical Hierarchy Processes (AHP) theory. The model provides a formal approach of establishing the relative importance of Internet services in the context of fostering national development. This paper presents the fundamental conceptsof themodel. Pairwise Comparisons (PCs) technique the cornerstone of the AHP theory is used as the baseline technique for measuring the intensity of preference between the Internet traffic classes (therein their respective services they deliver to end users) in the process of formulating the judgment matrix. The ISCD model is modelled to process data obtained from a group of individual decision makers that are independent from each other. Hence decision makers are weighted in the process of aggregating their priority vectors and the normalized weighted geometric mean method (NWGMM) is used to compute the group's priority vector, which is the final output of the model.

  • 17.
    Gamukama, Elly Amani
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Popov, Oliver
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    The Level of Scientific Methods Use in Computing Research Programs2008Conference paper (Refereed)
    Abstract [en]

    The research investigates the level to whichscientists’ use scientific methods in computing researchprograms. Data was collected from a representative sample ofresearchers in the field. The findings show that the presentresearch programs are more driven by the market forces.Innovations come up as a consequence of satisfying themarket calls but not necessarily a result of advancement inbasic science. Researchers’ investigations are driven by threecharacteristics; proof of performance, concept and existence.Also noted from the study, some researchers lack a cleardistinction between the methods. They tend to mix methods intheir research programs as longer as the industry acceptstheir outcome artifact. Consequently, there is lack of a clearcurriculum to instill such methodological concepts at graduatelevel in some of the computing schools.

  • 18.
    Giannoulis, Constantinos
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Kabilan, Vandana
    A Method for VVA Tailoring: The REVVA Generic Process Tailoring Case Study2007Conference paper (Refereed)
  • 19.
    Giannoulis, Constantinos
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Svee, Eric-Oluf
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Zdravkovic, Jelena
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Capturing Consumer Preference in System Requirements Through Business Strategy2013In: International Journal of Information System Modeling and Design, ISSN 1947-8186, E-ISSN 1947-8194, Vol. 4, no 4, p. 1-26Article in journal (Refereed)
    Abstract [en]

    A core concern within Business-IT alignment is coordinating strategic initiatives and plans with Information Systems (IS). Substantial work has been done on linking strategy to requirements for IS development, but it has usually been focused on the core value exchanges offered by the business, and thus overlooking other aspects that influence the implementation of strategy. One of these, consumer preferences, has been proven to influence the successful provisioning of the business's customer value proposition, and this study aims to establish a conceptual link between both strategy and consumer preferences to system requirements. The core contention is that reflecting consumer preferences through business strategy in system requirements allows for the development of aligned systems, and therefore systems that better support a consumer orientation. The contribution of this paper is an approach to establish such alignment, with this being accomplished through the proposal of a consumer preference meta-model mapped to a business strategy meta-model further linked to a system requirements technique. The validity of this proposal is demonstrated through a case study carried out within an institution of higher education in Sweden.

  • 20.
    Giannoulis, Constantinos
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Zdravkovic, Jelena
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    A Design Science Perspective on Business Strategy Modeling2014In: Enterprise, Business-Process and Information Systems Modeling: 15th International Conference, BPMDS 2014, 19th International Conference, EMMSAD 2014, Held at CAiSE 2014, Thessaloniki, Greece, June 16-17, 2014. Proceedings / [ed] Ilia Bider, Khaled Gaaloul, John Krogstie, Selmin Nurcan, Henderik A. Proper, Rainer Schmidt, Pnina Soffer, Springer Berlin/Heidelberg, 2014, p. 424-438Conference paper (Refereed)
    Abstract [en]

    An important topic in the modeling for IS development concerns quality of obtained models, especially when these models are to be used in global scopes, or as references. So far, a number of model quality frameworks have been established to assess relevant criteria such as completeness, clarity, modularity, or generality. In this study we take a look at how a research process contributes to the characteristics of a model produced during that process. For example: what should be observed; what research methods should be selected and how should they be applied; what kind of results should be expected; how they should be evaluated, etc. We report a result on this concern by presenting how we applied Design Science Research to model business strategy.

  • 21.
    Golod, Taras
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Iovan, Adrian
    Stockholm University, Faculty of Science, Department of Physics.
    Krasnov, Vladimir M.
    Stockholm University, Faculty of Science, Department of Physics.
    Single Abrikosov vortices as quantized information bits2015In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 6, article id 8628Article in journal (Refereed)
    Abstract [en]

    Superconducting digital devices can be advantageously used in future supercomputers because they can greatly reduce the dissipation power and increase the speed of operation. Non-volatile quantized states are ideal for the realization of classical Boolean logics. A quantized Abrikosov vortex represents the most compact magnetic object in superconductors, which can be utilized for creation of high-density digital cryoelectronics. In this work we provide a proof of concept for Abrikosov-vortex-based random access memory cell, in which a single vortex is used as an information bit. We demonstrate high-endurance write operation and two different ways of read-out using a spin valve or a Josephson junction. These memory cells are characterized by an infinite magnetoresistance between 0 and 1 states, a short access time, a scalability to nm sizes and an extremely low write energy. Non-volatility and perfect reproducibility are inherent for such a device due to the quantized nature of the vortex.

  • 22. Golov, Nikolay
    et al.
    Rönnbäck, Lars
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Big Data normalization for massively parallel processing databases2017In: Computer Standards & Interfaces, ISSN 0920-5489, E-ISSN 1872-7018, Vol. 54, no 2, p. 86-93Article in journal (Refereed)
    Abstract [en]

    High performance querying and ad-hoc querying are commonly viewed as mutually exclusive goals in massively parallel processing databases. Furthermore, there is a contradiction between ease of extending the data model and ease of analysis. The modern 'Data Lake' approach, promises extreme ease of adding new data to a data model, however it is prone to eventually becoming a Data Swamp - unstructured, ungoverned, and out of control Data Lake where due to a lack of process, standards and governance, data is hard to find, hard to use and is consumed out of context. This paper introduces a novel technique, highly normalized Big Data using Anchor modeling, that provides a very efficient way to store information and utilize resources, thereby providing ad-hoc querying with high performance for the first time in massively parallel processing databases. This technique is almost as convenient for expanding data model as a Data Lake, while it is internally protected from transforming to Data Swamp. A case study of how this approach is used for a Data Warehouse at Avito over a three-year period, with estimates for and results of real data experiments carried out in HP Vertica, an MPP RDBMS, is also presented. This paper is an extension of theses from The 34th International Conference on Conceptual Modeling (ER 2015) (Golov and Ronnback 2015) [1], it is complemented with numerical results about key operating areas of highly normalized big data warehouse, collected over several (1-3) years of commercial operation. Also, the limitations, imposed by using a single MPP database cluster, are described, and cluster fragmentation approach is proposed.

  • 23.
    Hidvegi, Attila
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Eriksson, Daniel
    Stockholm University, Faculty of Science, Department of Physics.
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    A Small Portable Test System for the TileCal Digitizer System2008Conference paper (Refereed)
    Abstract [en]

    The hadronic Tile Calorimeter (TileCal) of the ATLAS detector at LHC has a digitization, pipeline and readout system composed of nearly 2000 boards [1][2], developed and maintained by Stockholm University. Prior to now a rather complex test system been used to verify the functionality of the boards. However this system was developed nearly 10 years ago and now difficult to maintain due to several already obsolete components. A new, simpler, more reliable, and portable test system was therefore initiated. Its components have been chosen to reduce problems with obsolescence, and to allow easy migration to new platforms over the lifetime of the digitizer system.

  • 24.
    Hidvegi, Attila
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Eriksson, Daniel
    Stockholm University, Faculty of Science, Department of Physics.
    Cederwall, Bo
    Stockholm University, Faculty of Science, Department of Physics.
    Silverstein, Samuel
    Stockholm University, Faculty of Science, Department of Physics.
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    A High-Speed Data Acquisition System for Segmented Ge-Detectors2007In: Nuclear Science Symposium Conference Record. IEEE, 2007, Vol. 1, p. 536-537Conference paper (Refereed)
    Abstract [en]

    When using segmented Ge-detectors for gamma ray tracking it is necessary to determine the segment pulse shapes with high accuracy. A high-speed data acquisition system with many channels, high precision and with high sampling rate is required. There are also many other applications for such a system. Our system uses high performance FPGAs (Xilinx Virtex-V [2]) to cope with the data rates delivered by the high speed ADC chosen (Atmel 2Gsps, 10 bits) and to make all the data processing onboard in real time. Each board contains four such ADCs, which can either handle four channels up to full speed, or achieve higher sampling rates with interleaving. The boards can communicate with each other over different types of high-speed communication links. Control and monitoring is implemented with embedded processors. The processed result will be transmitted over Ethernet to final storage. The project introduces many challenging issues: signal integrity, ADC performance, interfacing ADCs to the FPGA, synchronisation of ADCs across the entire system, implementing flexible processing algorithms, high speed interconnection between boards and managing the significant heat generation. This is an ongoing project with interesting potentials for the future.

  • 25.
    Hidvegi, Attila
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Eriksson, Daniel
    Stockholm University, Faculty of Science, Department of Physics.
    Cederwall, Bo
    Stockholm University, Faculty of Science, Department of Physics.
    Silverstein, Samuel
    Stockholm University, Faculty of Science, Department of Physics.
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    A High-Speed Data Acquisition System for Segmented Ge-Detectors2006In: Nuclear Science Symposium Conference Record. IEEE, 2006, Vol. 1, p. 999-1001Conference paper (Refereed)
    Abstract [en]

    When using segmented Ge-detectors for gamma ray tracking it is necessary to determine the segment pulse shapes with high accuracy. A high-speed data acquisition system with many channels, high precision and with high sampling rate is required. To find the optimum performance, we are investigating what can be achieved by a system with extremely high sampling rates, 10 bits @2 GS/s. There are many other applications for such a system. Higher sampling rates usually mean lower bit resolution of the ADC, but with oversampling we expect to achieve a very good energy and time resolution. The system uses high performance FPGAs (Xilinx Virtex-IV) to cope with the data rates delivered by the high speed ADCs and to make all the data processing onboard in real time. Control and monitoring is implemented in an embedded soft processor. This processor is also in charge of the offboard gigabit Ethernet communication. The final system will consist of several separate boards, each with a number of input channels that will have to communicate with each other in real time over a high-speed communication link. The processed result will be transmitted over Ethernet to final storage. The project introduces many challenging issues, which are being addressed in turn with different prototype designs. These issues are: the ADC performance, interfacing the ADCs to the FPGA, implementing the flexible processing algorithms and high speed interconnection between the boards.

  • 26.
    Hidvegi, Attila
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gessler, Patrick
    Deutsches Elektronen-Synchrotron (DESY).
    Rehlich, Kay
    Deutsches Elektronen-Synchrotron (DESY),.
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    An Advanced FPGA Based Phase-Lock-Loop System as an Alternative Solution for the XFEL Timing System2009In: Nuclear Science Symposium Conference Record (NSS/MIC), 2009 IEEE, 2009, p. 1871-1872Conference paper (Refereed)
    Abstract [en]

    The European XFEL project requires a high-speed, very precise clock and timing distribution over large distances. A prototype system which fulfils current requirements that uses high-end components has just been completed and is being tested. However, the system is quite complicated and the boards are very complex, being designed using the small micro-TCA form factor. A way to simplify the system, and perhaps reduce cost, would be to implement an Advanced PLL in the programmable logic of an FPGA, which then would control an external VCO. By doing so several major issues could be resolved at the same time, while making more use of the advanced features of modern FPGAs. Such a system could be an alternative solution to the complex part of the Timing and Triggering System for XFEL.

  • 27.
    Hidvegi, Attila
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gessler, Patrick
    Deutsches Elektronen-Synchrotron (DESY).
    Rehlich, Kay
    Deutsches Elektronen-Synchrotron (DESY),.
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Timing and Triggering System Prototype for the XFEL Project2010In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 58, no 4, p. 1852-1856Article in journal (Refereed)
    Abstract [en]

    The European X-ray Free Electron Laser (XFEL) [1] at DESY in Hamburg will begin operating in the next few years, enabling new, ground-breaking research opportunities. The entire system requires very precise clock and trigger distribution, synchronous with the 1.3 GHz system RF-frequency, over distances of more than 3.4 km. The new experiment demanded features that other commercial solutions could not yet provide. Researchers at Stockholm University and DESY have developed a prototype for the timing system of XFEL. It has been decided that XFEL will use modern ATCA and Micro-TCA systems because of their advanced features and reliability. The timing system has been adapted to the Micro-TCA bus standard and also follows the new upcoming xTCA for physics standard. The prototype is fully functional and complete. It will serve as a platform for future development of the whole timing system. This paper describes the hardware design and some test results using the prototype board.

  • 28.
    Hidvegi, Attila
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Gessler, Patrick
    Deutsches Elektronen-Synchrotron (DESY).
    Rehlich, Kay
    Deutsches Elektronen-Synchrotron (DESY),.
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Rydström, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    A System for Distributing High-Speed Synchronous High-Precision Clock and Trigger Data over Large Distances2008In: Nuclear Science Symposium Conference Record, 2008. NSS '08. IEEE, 2008, p. 2581-2584Conference paper (Refereed)
    Abstract [en]

    The distribution of precise timing throughout the European X-ray Free Electron Laser project [1] (XFEL) and its triggering system is a very challenging part of the system design. ADCs in data acquisition systems and DACs in control systems will require very high precision clocks. The clocks need to be synchronous to each other, both in frequency and phase, with a jitter performance better than 5 ps (RMS). At some high-speed ADCs it might even need a precision down to 0.1ps. The frequencies that must be available are the main 1.3 GHz and some frequencies below, which are all derived from the main frequency. The phase needs to be adjustable to allow synchronization between separate devices.

  • 29.
    Högås, Marcus
    et al.
    Stockholm University, Faculty of Science, Department of Physics. SP Technical Research Institute of Sweden, Sweden.
    Rydler, Karl-Erik
    Stenarson, Jörgen
    Yhland, Klas
    Analytic Solution of the Magnetic Field and Inductance in a Coaxial Short Circuit2015In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 64, no 6, p. 1582-1587Article in journal (Refereed)
    Abstract [en]

    In this paper, the analytic solution of the magnetic field and the inductance in a coaxial short circuit is derived from Maxwell's equations with the appropriate boundary conditions on the short circuit. Helmholtz equation is thus derived for the magnetic field and is solved by a mode matching technique. By integrating the absolute square of the magnetic field the inductance is obtained. The solution is discussed in the light of earlier approximations and solutions and is evaluated both theoretically and through measurements.

  • 30.
    Hörnstein, Jonas
    et al.
    Institute for System and Robotics (ISR), Instituto Superior Técnico, Lisbon, Portugal.
    Gustavsson, Lisa
    Stockholm University, Faculty of Humanities, Department of Linguistics, Phonetics.
    Santos-Victor, José
    Institute for System and Robotics (ISR), Instituto Superior Técnico, Lisbon, Portugal.
    Lacerda, Francisco
    Stockholm University, Faculty of Humanities, Department of Linguistics, Phonetics.
    Multimodal language acquisition based on motor learning and interaction2010In: From Motor Learning to Interaction Learning in Robots / [ed] Olivier Sigaud & jan Peters, Springer Berlin/Heidelberg, 2010, p. 467-489Chapter in book (Other academic)
    Abstract [en]

    In this work we propose a methodology for language acquisition in humanoid robots that mimics that in children. Language acquisition is a complex process that involves mastering several different tasks, such as producing speech sounds, learning how to group different sounds into a consistent and manageable number of classes or speech units, grounding speech, and recognizing the speech sounds when uttered by other persons. While it is not known to which extent those abilities are learned or written in our genetic code, this work aims at two intertwined goals: (i) to investigate how much of linguistic structure that can be derived directly from the speech signal directed to infants by (ii) designing, building and testing biological plausible models for language acquisition in a humanoid robot. We have therefore chosen to avoid implementing any pre-programmed linguistic knowledge, such as phonemes, into these models. Instead we rely on general methods such as pattern matching and hierarchical clustering techniques, and show that it is possible to acquire important linguistic structures directly from the speech signal through the interaction with a caregiver. We also show that this process can be facilitated through the use of motor learning.

  • 31. Ivanov, S. A.
    et al.
    Bush, A. A.
    Hudl, Matthias
    Stockholm University, Faculty of Science, Department of Physics.
    Stash, A. I.
    Andre, G.
    Tellgren, R.
    Cherepanov, V. M.
    Stepanov, A. V.
    Kamentsev, K. E.
    Tokunaga, Y.
    Taguchi, Y.
    Tokura, Y.
    Nordblad, P.
    Mathieu, R.
    Spin and dipole order in geometrically frustrated mixed-valence manganite Pb3Mn7O152016In: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 27, no 12, p. 12562-12573Article in journal (Refereed)
    Abstract [en]

    The structural, magnetic, and dielectric properties of Pb3Mn7O15 have been investigated using high-quality single crystals. Pb3Mn7O15 adopts a pseudo-hexagonal orthorhombic structure, with partially filled Kagom, layers connected by ribbons of edge-sharing MnO6 octahedra and intercalated Pb cations. There are 9 inequivalent sites in the structure for the Mn ions, which exist both as Mn3+ and Mn4+. Pb3Mn7O15 undergoes an antiferromagnetic transition below T-N similar to 67 K, with significant geometric frustration. Neutron powder diffraction on crushed single crystals allowed us to determine the low-temperature antiferromagnetic magnetic structure. We discuss the magnetic interaction pathways in the structure and possible interplay between the structural distortions imprinted by the lone-electron pair of Pb2+ cations and Mn3+/Mn4+ charge ordering.

  • 32.
    Jalali, Amin
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Aspect-Oriented Business Process Management2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Separation of concerns has long been considered an effective and efficient strategy to deal with complexity in information systems.One sort of concern, like security and privacy, crosses over other concerns in a system. Such concerns are called cross-cutting concerns.As a result, the realization of these concerns is scattered through the whole system, which makes their management difficult.

    Aspect Orientation is a paradigm in information systems which aims to modularize cross-cutting concerns.This paradigm is well researched in the programming area, where many aspect-oriented programming languages have been developed, e.g., AspectJ.It has also been investigated in other areas, such as requirement engineering and service composition.In the Business Process Management (BPM) area, Aspect Oriented Business Process Modeling aims to specify how this modularization technique can support encapsulating cross-cutting concerns in process models.However, it is not clear how these models should be supported in the whole BPM lifecycle.In addition, the support for designing these models has only been limited to imperative process models that support rigid business processes.Neither has it been investigated how this modularization technique can be supported through declarative or hybrid models to support the separation of cross-cutting concerns for flexible business processes.

    Therefore, this thesis investigates how aspect orientation can be supported over the whole BPM lifecycle using imperative aspect-oriented business process models. It also investigates how declarative and hybrid aspect-oriented business process models can support the separation of cross-cutting concerns in the BPM area.This thesis has been carried out following the design science framework, and the result is presented as a set of artifacts (in the form of constructs, models, methods, and instantiations) and empirical findings.

    The artifacts support modeling, analysis, implementation/configuration, enactment, monitoring, adjustment, and mining cross-cutting concerns while supporting business processes using Business Process Management Systems. Thus, it covers the support for the management of these concerns over the whole BPM lifecycle. The use of these artifacts and their application shows that they can reduce the complexity of process models by separating different concerns.

  • 33.
    Jalali, Amin
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Foundation of Aspect Oriented Business Process Management2012Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Reducing the complexity in information systems is a main concern on which researchers work. Separation of concerns, also known as the principle of ‘divide and conquer’, has long time been a strategy for dealing with complexity. Two examples of the application of this principle in the area of information system design are the break out the data management into Database Management Systems(DBMSs) and the separation of the business logic from the application logic into Business Process Management Systems (BPMSs). However, separation of cross-cutting concerns from the core-concern of a business process is not yet supported in the Business Process Management (BPM) area. Aspect Oriented principle recommends such a separation. When looking into the business process, several concerns, such as security and privacy, can be identified. Therefore, a formal model that provides a foundation for enabling BPMSs to support separation of concerns in BPM area is needed. This thesis provides a formal model for dealing with separation of concerns in the BPM area. Implementing this model in BPMSs would facilitate the design and implementation of business processes with a lower level of complexity, which in turn would reduce the costs associated with BPM projects. The thesis starts with a literature review on aspect orientation both in programming and in the BPM areas. Based on this study, a list of requirements for an Aspect Oriented Service for BPMSs is compiled. Then a formal model for such a service, fulfilling a set of these requirements, is designed using Coloured Petri Nets and implemented in CPN Tools. The model is evaluated through the execution of a number of scenarios. The solution is also validated through an industrial case study. The results of the case study are presented the direction for future work outlined. The case study demonstrates that separation of concerns through aspect orientation does indeed reduce the complexity of business process models.

  • 34.
    Jalali, Amin
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Service Oriented Modularization using Coloured Petri Nets2012Conference paper (Other (popular science, discussion, etc.))
    Abstract [en]

    Modelling service oriented systems using Coloured Petri Nets usually results in cluttered nets which are hard to understand and modify. This complexity is a result of many interactions among services. This paper presents a method for designing service oriented models using coloured petri nets.This method results us in less complex nets which could be extended easier.The validation of the method is given through demonstrating its impact on defining operational semantics of a service.

  • 35.
    Jalali, Amin
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Supporting Enactment of Aspect Oriented Business Process Models: an approach to separate cross-cutting concerns in action2013Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Coping with complexity in Information Systems and Software Engineering is an important issue in both research and industry. One strategy to deal with this complexity is through a separation of concerns, which can result in reducing the complexity, improving the re-usability, and simplifying the evolution.Separation of concerns can be addressed through the Aspect Oriented paradigm. Although this paradigm has been well researched in the field of programming, it is still in a preliminary stage in the area of Business Process Management. While some efforts have been made to propose aspect orientation for business process modeling, it has not yet been investigated how these models should be implemented, configured, run, and adjusted.Such a gap has restrained the enactment of aspect orientated business process models in practice.Therefore, this research enables the enactment of such models to support the separation of cross-cutting concerns in the entire business process management life-cycle.It starts by defining the operational semantics for the Aspect Oriented extension of the Business Process Model and Notation.The semantics specifies how such models can be implemented and configured, which can be used as a blueprint to support the enactment of aspect oriented business process models.The semantics is implemented in the form of artifacts, which are then used in a banking case study to investigate the current modeling technique.This investigation revealed new requirements, which should be considered in aspect oriented modeling approaches.Thus, the current modeling notation has been extended to include new requirements.The extended notation has been formalized, and investigated through re-modeling the processes in the case study. The results from this investigation show the need to refine the separation rules to support the encapsulation of aspects based on different business process perspectives. Therefore, the new refinement is proposed, formalized, and implemented.The implementation is then used as a prototype to evaluate the result through a case study.

  • 36. Jia, Tiekun
    et al.
    Wang, Xiaofeng
    Wang, Weimin
    Wang, Yujiang
    Liao, Guihua
    Xiong, Yan
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK), Inorganic and Structural Chemistry.
    Facile Synthesis of Porous SnO(2) Spherical-Like Aggregates and Their Gas Sensing Property2011In: Integrated Ferroelectrics, ISSN 1058-4587, E-ISSN 1607-8489, Vol. 128, p. 30-36Article in journal (Refereed)
    Abstract [en]

    Porous spherical-like aggregates synthesis of SnO(2) crystals was achieved via a hydrothermal process in the mixed solvents of water and ethanol. The products were characterized by powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy and Raman measurements. Morphological characterization showed that porous spherical-like aggregates were composed of short nanorods. Three main peaks broadening and shifting to high wavenumber in Raman spectrum implied that the components of the products had a smaller size. The result of the gas sensing measurement indicated that porous spherical-like aggregates had excellent ethanol gas sensing property compared to that of nanoparticles.

  • 37.
    Johansson, Anna-Lena
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Logic program synthesis using schema instantiation in an interactive environment1995Doctoral thesis, monograph (Other academic)
  • 38.
    Juell-Skielse, Gustaf
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Improving Organizational Effectiveness through Standard Application Packages and IT Services2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Today, the design, use and distribution of standard application packages are changing due to the emergence of service orientation. In the private sector, Enterprise Resource Planning (ERP) systems are extended to include IT services. In the public sector, standard application packages are integrated with IT services which are often referred to as e-Government. E-Government can be extended with mobile technology to add mobility to public processes, so called m-Government.

    The problem addressed in this thesis is how to improve organizational effectiveness through the use of standard application packages and IT services. The objectives are to:

    • ­Develop a model for explaining the level of adoption of extended ERP among small and medium sized companies.  
    • ­Identify implications and design patterns of business models for service oriented ERP.
    • ­Establish principles for the design of local government m-services.
    • ­Develop a method for benefits evaluation of information systems with integrated services.

    The thesis contributes with theory for analyzing, explaining and predicting how the use of standard application packages as well as IT services affects organizational effectiveness. To practice, it provides new concepts that can change the perceptions and mental models that IS-professionals, such as management consultants, use in their professional lives. In particular, it provides implications, design principles, a model and a method for the use of services in conjunction with standard application packages in public and private sector organizations.

    For future research it is suggested to investigate how service orientation affects implementation methods for standard application packages and to investigate the requirements of completely integrated e-Government on e-services, business models and back-office systems.

  • 39.
    Juell-Skielse, Gustaf
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Enquist, Håkan
    School of Business, Economics and Law, University of Gothenburg.
    Implications of ERP as Service2011Conference paper (Refereed)
    Abstract [en]

    In this paper we present implications for using and delivering Enterprise Resource Planning as services (ERP-as-a-service). The objective is to construct a framework of opportunities and challenges for users and suppliers of ERP-as-a-service. The framework is based on a combination of literature study and field study and includes approximately 80 implications. New implications, not found in literature, were identified in the field study. Examples of new implications include: more focus on IT-value; simplified phasing of implementation and improved supplier brand. For future research it is suggested that the framework is tested in a larger setting and that implications are prioritized for certain industries and types of business models.

  • 40.
    Juell-Skielse, Gustaf
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Perjons, Erik
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    VAMEE: A Value Aware Method for Evaluating Inclusive E-Government Initiatives2011In: The Practice of Enterprise Modeling / [ed] Johannesson, P., Krogstie, J., Opdahl, A., Heidelberg: Springer , 2011, p. 97-111Chapter in book (Refereed)
    Abstract [en]

    The growing use of ICT solutions for improving the public sector has created a need for valuating e-government initiatives. A number of methods for this purpose have been developed, but they are typically restricted to analyzing the benefits and costs of only one single actor. There is, therefore, a need for methods that take a broader view and take into account entire networks of actors. This paper proposes a novel method, called VAMEE, the purpose of which is to produce a well-grounded and easily understandable valuation of an e-government initiative that takes into consideration the benefits, costs, and interrelationships of all actors concerned. The basis of the proposed method is a combination of enterprise modeling techniques, in particular goal modeling and value modeling, with an established method for cost benefit analysis (i.e. Peng). VAMEE is designed to be inclusive, easily understandable, and visual. These properties of the method will support accurate and unbiased valuations as well as improved innovation in the development of e-government initiatives.

  • 41.
    Kajko-Mattsson, Mira
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Upfront corrective maintenance at the front-end support level2005In: Managing corporate information systems evolution and maintenance / [ed] Khaled M. Khan, Yan Zhang, Hershey, PA: Idea Group Publishing, 2005, p. 75-107Chapter in book (Other academic)
    Abstract [en]

    This chapter presents the process of upfront corrective maintenance at the front-end support level. The chapter is logically divided into two parts. The first part introduces the domain of the upfront corrective maintenance process, and presents its current status practiced in the industry. It first describes the process, places it within a global virtual IT enterprise and explains its role within the enterprise. It then puts the process in the context of a total front-end support process, the process performing a multitude of diverse types of support activities. Finally, it lists the problems encountered by the front-support organisations today. The second part provides a glimpse into Corrective Maintenance Maturity Model (CM3): Upfront Maintenance, a process model specialized in upfront corrective maintenance. It describes its process phases, maturity levels, and collaboration with the CM3: Problem Management model, a problem management process model at the back-end support level. The goal of this chapter is to provide a detailed insight of the process of upfront corrective maintenance.

  • 42.
    Karokola, Geoffrey Rwezaura
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    A Framework for Securing e-Government Services: The Case of Tanzania2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    e-Government services are becoming one of the most important and efficient means by which governments (G) interact with businesses (B) and citizens (C). This has brought not only tremendous opportunities but also serious security challenges. Critical information assets are exposed to current and emerging security risks and threats. In the course of this study, it was learnt that e-government services are heavily guided and benchmarked by e-Government maturity models (eGMMs). However, the models lack built-in security services, technical as well as non-technical; leading to lack of strategic objectives alignment between e-government services and security services. Information security has an important role in mitigating security risks and threats posed to e-government services. Security improves quality of the services offered.

    In light of the above, the goal of this research work is to propose a framework that would facilitate government organisations to effectively offer appropriate secure e-government services. To achieve this goal, an empirical investigation was conducted in Tanzania involving six government organizations. The investigations were inter-foiled by a sequence of structural compositions resulting in a proposition of a framework for securing e-government services which integrates IT security services into eGMMs. The research work was mainly guided by a design science research approach complemented in parts by systemic-holistic and socio-technical approaches.

    The thesis contributes to the empirical and theoretical body of knowledge within the computer and systems sciences on securing e-government structures. It encompasses a new approach to secure e-government services incorporating security services into eGMMs. Also, it enhances the awareness, need and importance of security services to be an integral part of eGMMs to different groups such as researched organizations, academia, practitioners, policy and decision makers, stakeholders, and the community.

  • 43. Kotsifakos, Alexios
    et al.
    Karlsson, Isak
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Papapetrou, Panagiotis
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Athitsos, Vassilis
    Gunopulos, Dimitrios
    Embedding-based subsequence matching with gaps-range-tolerances: a Query-By-Humming application2015In: The VLDB journal, ISSN 1066-8888, E-ISSN 0949-877X, Vol. 24, no 4, p. 519-536Article in journal (Refereed)
    Abstract [en]

    We present a subsequence matching framework that allows for gaps in both query and target sequences, employs variable matching tolerance efficiently tuned for each query and target sequence, and constrains the maximum matching range. Using this framework, a dynamic programming method is proposed, called SMBGT, that, given a short query sequence Q and a large database, identifies in quadratic time the subsequence of the database that best matches Q. SMBGT is highly applicable to music retrieval. However, in Query-By-Humming applications, runtime is critical. Hence, we propose a novel embedding-based approach, called ISMBGT, for speeding up search under SMBGT. Using a set of reference sequences, ISMBGT maps both Q and each position of each database sequence into vectors. The database vectors closest to the query vector are identified, and SMBGT is then applied between Q and the subsequences that correspond to those database vectors. The key novelties of ISMBGT are that it does not require training, it is query sensitive, and it exploits the flexibility of SMBGT. We present an extensive experimental evaluation using synthetic and hummed queries on a large music database. Our findings show that ISMBGT can achieve speedups of up to an order of magnitude against brute-force search and over an order of magnitude against cDTW, while maintaining a retrieval accuracy very close to that of brute-force search.

  • 44.
    Lacerda, Francisco
    et al.
    Stockholm University, Faculty of Humanities, Department of Linguistics.
    House, DavidHeldner, MattiasStockholm University, Faculty of Humanities, Department of Linguistics.Gustafson, JoakimStrömbergsson, SofiaWlodarczak, MarcinStockholm University, Faculty of Humanities, Department of Linguistics.
    Interspeech 2017: Situated interaction: Book of abstracts2017Conference proceedings (editor) (Refereed)
  • 45.
    Lansner, Anders
    et al.
    Stockholm University, Faculty of Science, Numerical Analysis and Computer Science (NADA). Royal Institute of Technology, Sweden.
    Benjaminsson, Simon
    Nexa: A scalable neural simulator with integrated analysis2012In: Network: Computation in Neural Systems, ISSN 0954-898X, Vol. 23, no 4, p. 254-271Article in journal (Refereed)
    Abstract [en]

    Large-scale neural simulations encompass challenges in simulator design, data handling and understanding of simulation output. As the computational power of supercomputers and the size of network models increase, these challenges become even more pronounced. Here we introduce the experimental scalable neural simulator Nexa, for parallel simulation of large-scale neural network models at a high level of biological abstraction and for exploration of the simulation methods involved. It includes firing-rate models and capabilities to build networks using machine learning inspired methods for e.g. self-organization of network architecture and for structural plasticity. We show scalability up to the size of the largest machines currently available for a number of model scenarios. We further demonstrate simulator integration with online analysis and real-time visualization as scalable solutions for the data handling challenges.

  • 46. Li, Andol X.
    et al.
    Lou, Xiaolong
    Hansen, Preben
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Peng, Ren
    On the Influence of Distance in the Interaction With Large Displays2016In: IEEE/OSA Journal of Display Technology, ISSN 1551-319X, E-ISSN 1558-9323, Vol. 12, no 8, p. 840-850Article in journal (Refereed)
    Abstract [en]

    As reported by a recent survey, over half of large display purchases are conducted for productivity purposes, while the remainder are purchased for a variety of purposes such as gaming and advertising. These large displays have advanced visibility, scalability, and accessibility characteristics and thus benefit perceived usability. However, usability issues such as the difficulties in precisely accessing distal information on large displays while on the move are still of concern. Therefore, in this paper, we investigate the influence of moving distance on perceived usability in interactions with large displays. Comparative study results show inconsistent perceived usability throughout a range of distances, which differs from standard usability conventions. Moreover, the results show a correlation between distance and perceived usability in that, as the distance from commonly visited ranges increases, the perceived usability level decreases, and vice versa. The study demonstrates that distance is an effective interaction modality in large-display interactions, although it has weaknesses such as limited input channels.

  • 47. Liu, Zheng
    et al.
    Fujita, Nobuhisa
    Miyasaka, Keiichi
    Han, Lu
    Stevens, Sam M.
    Suga, Mitsuo
    Asahina, Shunsuke
    Slater, Ben
    Xiao, Changhong
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Sakamoto, Yasuhiro
    Anderson, Michael W.
    Ryoo, Ryong
    Terasaki, Osamu
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK). Korea Advanced Institute of Science & Technology (KAIST) .
    A review of fine structures of nanoporous materials as evidenced by microscopic methods2013In: Microscopy, ISSN 2050-5698, Vol. 62, no 1, p. 109-146Article, review/survey (Refereed)
    Abstract [en]

    This paper reviews diverse capabilities offered by modern electron microscopy techniques in studying fine structures of nanoporous crystals such as zeolites, silica mesoporous crystals, metal organic frameworks and yolk-shell materials. For the case of silica mesoporous crystals, new approaches that have been developed recently to determine the three-dimensionally periodic average structure, e. g., through self-consistent analysis of electron microscope images or through consideration of accidental extinctions, are presented. Various structural deviations in nanoporous materials from their average structures including intergrowth, surface termination, incommensurate modulation, quasicrystal and defects are demonstrated. Ibidem observations of the scanning electron microscope and atomic force microscope give information about the zeolite-crystal-growth mechanism, and an energy for unstitching a building-unit from a crystal surface is directly observed by an anatomic force microscope. It is argued how these observations lead to a deeper understanding of the materials.

  • 48.
    Luo, Cuicui
    et al.
    Stockholm University, Faculty of Social Sciences, Stockholm Business School.
    Wu, Desheng
    Stockholm University, Faculty of Social Sciences, Stockholm Business School.
    Wu, Dexiang
    Stockholm University, Faculty of Social Sciences, Stockholm Business School.
    A deep learning approach for credit scoring using credit default swaps2017In: Engineering applications of artificial intelligence, ISSN 0952-1976, E-ISSN 1873-6769, Vol. 65, p. 465-470Article in journal (Refereed)
    Abstract [en]

    After 2007-2008 crisis, it is clear that corporate credit scoring is becoming a key role in credit risk management. In this paper, we investigate the performances of credit scoring models applied to CDS data sets. The classification performance of deep learning algorithm such as deep belief networks with Restricted Boltzmann Machines are evaluated and compared with some popular credit scoring models such as logistic regression, multi-layer perceptron and support vector machine. The performance is assessed using the classification accuracy and the area under the receiver operating characteristic curve. It is found that DBN yields the best performance.

  • 49. Min, Byungjoon
    et al.
    Liljeros, Fredrik
    Stockholm University, Faculty of Social Sciences, Department of Sociology. Institute for Futures Study, Stockholm, Sweden.
    Makse, Hernan A.
    Finding Influential Spreaders from Human Activity beyond Network Location2015In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 10, no 8, article id e0136831Article in journal (Refereed)
    Abstract [en]

    Most centralities proposed for identifying influential spreaders on social networks to either spread a message or to stop an epidemic require the full topological information of the network on which spreading occurs. In practice, however, collecting all connections between agents in social networks can be hardly achieved. As a result, such metrics could be difficult to apply to real social networks. Consequently, a new approach for identifying influential people without the explicit network information is demanded in order to provide an efficient immunization or spreading strategy, in a practical sense. In this study, we seek a possible way for finding influential spreaders by using the social mechanisms of how social connections are formed in real networks. We find that a reliable immunization scheme can be achieved by asking people how they interact with each other. From these surveys we find that the probabilistic tendency to connect to a hub has the strongest predictive power for influential spreaders among tested social mechanisms. Our observation also suggests that people who connect different communities is more likely to be an influential spreader when a network has a strong modular structure. Our finding implies that not only the effect of network location but also the behavior of individuals is important to design optimal immunization or spreading schemes.

  • 50.
    Nyfjord, Jaana
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Kajko-Mattsson, Mira
    Stockholm University, Faculty of Social Sciences, Department of Computer and Systems Sciences.
    Integrating risk management with software development: state of practice2008In: Proceedings of The International MultiConference of Engineers and Computer Scientists 2008 Vol. I / [ed] S. I. Ao, Oscar Castillo, Craig Douglas, David Dagan Feng, Jeong-A Lee, Newswood Limited , 2008, p. 878-884Conference paper (Other academic)
    Abstract [en]

    In this paper, we investigate the state of practice of integrating risk management with software development in 37 software organizations. We do this by using a set of evaluation criteria covering various process integration aspects. Our results recognize that process integration in this domain is still in its infancy. There is a great need for process integration and process integration models within the industry studied.

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