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  • 1.
    A. Mouris, Boules
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Information Science and Engineering. KTH Royal Institute of Technology.
    Ghauch, Hadi
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Network and Systems Engineering.
    Thobaben, Ragnar
    Jonsson, B. Lars G.
    KTH, Superseded Departments (pre-2005), Electromagnetic Theory. KTH, Superseded Departments (pre-2005), Electrical Systems. KTH, School of Electrical Engineering and Computer Science (EECS), Electrical Engineering, Electromagnetic Engineering.
    Multi-tone Signal Optimization for Wireless Power Transfer in the Presence of Wireless Communication Links2020In: IEEE Transactions on Wireless Communications, ISSN 1536-1276, E-ISSN 1558-2248Article in journal (Refereed)
    Abstract [en]

    In this paper, we study optimization of multi-tone signals for wireless power transfer (WPT) systems. We investigate different non-linear energy harvesting models. Two of them are adopted to optimize the multi-tone signal according to the channel state information available at the transmitter. We show that a second-order polynomial curve-fitting model can be utilized to optimize the multi-tone signal for any RF energy harvester design. We consider both single-antenna and multi-antenna WPT systems. In-band co-existing communication links are also considered in this work by imposing a constraint on the received power at the nearby information receiver to prevent its RF front end from saturation. We emphasize the importance of imposing such constraint by explaining how inter-modulation products, due to saturation, can cause high interference at the information receiver in the case of multi-tone signals. The multi-tone optimization problem is formulated as a non-convex linearly constrained quadratic program. Two globally optimal solution approaches using mixed-integer linear programming and finite branch-and-bound techniques are proposed to solve the problem. The achieved improvement resulting from applying both solution methods to the multi-tone optimization problem is highlighted through simulations and comparisons with other solutions existing in the literature.

  • 2. Abedifar, V.
    et al.
    Furdek, Marija
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Muhammad, Ajmal
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Eshghi, M.
    Wosinska, Lena
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Optical Network Laboratory (ON Lab).
    Routing, modulation format, spectrum and core allocation in SDM networks based on programmable filterless nodes2018In: Optics InfoBase Conference Papers, Optics Info Base, Optical Society of America, 2018Conference paper (Refereed)
    Abstract [en]

    An RMSCA approach based on binary particle swarm optimization is proposed for programmable filterless SDM networks, aimed at minimizing core and spectrum usage. Nearoptimal resource consumption.

  • 3.
    Aguilar, Xavier
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Performance Monitoring, Analysis, and Real-Time Introspection on Large-Scale Parallel Systems2020Doctoral thesis, monograph (Other academic)
    Abstract [en]

    High-Performance Computing (HPC) has become an important scientific driver. A wide variety of research ranging for example from drug design to climate modelling is nowadays performed in HPC systems. Furthermore, the tremendous computer power of such HPC systems allows scientists to simulate problems that were unimaginable a few years ago. However, the continuous increase in size and complexity of HPC systems is turning the development of efficient parallel software into a difficult task. Therefore, the use of per- formance monitoring and analysis is a must in order to unveil inefficiencies in parallel software. Nevertheless, performance tools also face challenges as a result of the size of HPC systems, for example, coping with huge amounts of performance data generated.

    In this thesis, we propose a new model for performance characterisation of MPI applications that tackles the challenge of big performance data sets. Our approach uses Event Flow Graphs to balance the scalability of profiling techniques (generating performance reports with aggregated metrics) with the richness of information of tracing methods (generating files with sequences of time-stamped events). In other words, graphs allow to encode ordered se- quences of events without storing the whole sequence of such events, and therefore, they need much less memory and disk space, and are more scal- able. We demonstrate in this thesis how our Event Flow Graph model can be used as a trace compression method. Furthermore, we propose a method to automatically detect the structure of MPI applications using our Event Flow Graphs. This knowledge can afterwards be used to collect performance data in a smarter way, reducing for example the amount of redundant data collected. Finally, we demonstrate that our graphs can be used beyond trace compression and automatic analysis of performance data. We propose a new methodology to use Event Flow Graphs in the task of visual performance data exploration.

    In addition to the Event Flow Graph model, we also explore in this thesis the design and use of performance data introspection frameworks. Future HPC systems will be very dynamic environments providing extreme levels of parallelism, but with energy constraints, considerable resource sharing, and heterogeneous hardware. Thus, the use of real-time performance data to or- chestrate program execution in such a complex and dynamic environment will be a necessity. This thesis presents two different performance data introspec- tion frameworks that we have implemented. These introspection frameworks are easy to use, and provide performance data in real time with very low overhead. We demonstrate, among other things, how our approach can be used to reduce in real time the energy consumed by the system.

    The approaches proposed in this thesis have been validated in different HPC systems using multiple scientific kernels as well as real scientific applica- tions. The experiments show that our approaches in performance character- isation and performance data introspection are not intrusive at all, and can be a valuable contribution to help in the performance monitoring of future HPC systems.

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  • 4.
    Andreozzi, Emilio
    et al.
    Univ Naples Federico II, Dept Elect Engn & Informat Technol DIETI, Naples, Italy.;Ist Clin Sci Maugeri IRCCS, Dept Bioengn, Telese Terme Inst, Telese Terme, BN, Italy..
    Carannante, Ilaria
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    D'Addio, Giovanni
    Ist Clin Sci Maugeri IRCCS, Dept Bioengn, Telese Terme Inst, Telese Terme, BN, Italy..
    Cesarelli, Mario
    Univ Naples Federico II, Dept Elect Engn & Informat Technol DIETI, Naples, Italy.;Ist Clin Sci Maugeri IRCCS, Dept Bioengn, Telese Terme Inst, Telese Terme, BN, Italy..
    Balbi, Pietro
    Ist Clin Sci Maugeri IRCCS, Lab Computat Neurophysiol, Telese Terme Inst, Telese Terme, BN, Italy..
    Phenomenological models of Na(V)1.5. A side by side, procedural, hands-on comparison between Hodgkin-Huxley and kinetic formalisms2019In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 17493Article in journal (Refereed)
    Abstract [en]

    Computational models of ion channels represent the building blocks of conductance-based, biologically inspired models of neurons and neural networks. Ion channels are still widely modelled by means of the formalism developed by the seminal work of Hodgkin and Huxley (HH), although the electrophysiological features of the channels are currently known to be better fitted by means of kinetic Markov-type models. The present study is aimed at showing why simplified Markov-type kinetic models are more suitable for ion channels modelling as compared to HH ones, and how a manual optimization process can be rationally carried out for both. Previously published experimental data of an illustrative ion channel (Na(V)1.5) are exploited to develop a step by step optimization of the two models in close comparison. A conflicting practical limitation is recognized for the HH model, which only supplies one parameter to model two distinct electrophysiological behaviours. In addition, a step by step procedure is provided to correctly optimize the kinetic Markov-type model. Simplified Markov-type kinetic models are currently the best option to closely approximate the known complexity of the macroscopic currents of ion channels. Their optimization can be achieved through a rationally guided procedure, and allows to obtain models with a computational burden that is comparable with HH models one.

  • 5.
    Apanasevic, Tatjana
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS.
    Markendahl, Jan
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Mobile ticketing services in the Northern Europe: Critical business model issues2018In: Internet of Things Business Models, Users, and Networks, 2017 / [ed] Morten Falch, Copenhagen, Denmark: IEEE, 2018, p. 1-8Conference paper (Refereed)
    Abstract [en]

    Started as SMS ticketing, today, mobile ticketing services become a platform for combined mobility solutions that integrate mobile ticketing, bike renting, car sharing, and parking payment services. Mobile ticketing services provide a number of benefits for public transport companies and passengers, however, in some Northern European countries, the share of mobile ticket sales does not exceed 10 percent. In this paper, we analyse business models of three types of mobile ticketing services (SMS, in-app, and “Be-In Be-Out” (BIBO)) in order to identify factors that negatively affect wider penetration of mobile ticketing. In order to do so, we use STOF (Service, Technology, Organisation, and Finance) model. The research reveals that there are a number of challenges related to service, technology, and finance domains of mobile ticketing. Due to this, with the help of price policy, many public transport companies push choices of their customers towards use of plastic travel card.

  • 6.
    Aronsson, Sanna
    et al.
    FOI Swedish Defence Research Agency, Stockholm, Sweden.
    Artman, Henrik
    FOI Swedish Defence Research Agency, Stockholm, Sweden.
    Brynielsson, Joel
    KTH, Superseded Departments (pre-2005), Numerical Analysis and Computer Science, NADA. KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS. FOI Swedish Defence Research Agency, Stockholm, Sweden.
    Lindquist, Sinna
    FOI Swedish Defence Research Agency, Stockholm, Swedena.
    Ramberg, Robert
    Stockholm University, Stockholm, Sweden.
    Design of simulator training: a comparative study of Swedish dynamic decision-making training facilities2019In: Cognition, Technology and WorkArticle in journal (Refereed)
    Abstract [en]

    Simulator training is becoming increasingly important for training of time-critical and dynamic situations. Hence, how simulator training in such domains is planned, carried out and followed up becomes important. Based on a model prescribing such crucial aspects, ten decision-making training simulator facilities have been analyzed from an activity theoretical perspective. The analysis reveals several conflicts that exist between the training that is carried out and the defined training objectives. Although limitations in technology and organization are often alleviated by proficient instructors, it is concluded that there is a need for a structured approach to the design of training to be able to define the competencies and skills that ought to be trained along with relevant measurable training goals. Further, there is a need for a pedagogical model that takes the specifics of simulator training into account. Such a pedagogical model is needed to be able to evaluate the training, and would make it possible to share experiences and make comparisons between facilities in a structured manner.

  • 7.
    Artho, Cyrille
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Banzai, K.
    Department of Computer Science, The University of Tokyo, Tokyo, Japan.
    Gros, Q.
    Polytech Nantes, University of Nantes, Nantes, France.
    Rousset, G.
    Polytech Nantes, University of Nantes, Nantes, France.
    Ma, L.
    Faculty of Information Science and Electrical Engineering, Kyushu University, Fukuoka, Japan.
    Kitamura, T.
    Institute of Information Technology Research, National Institute of Advanced Industrial Science and Technology, Osaka, Japan.
    Hagiya, M.
    Department of Computer Science, The University of Tokyo, Tokyo, Japan.
    Tanabe, Y.
    Department of Library, Archival, and Information Studies, Tsurumi University, Yokohama, Japan.
    Yamamoto, Mitsuharu
    Department of Mathematics and Informatics, Chiba University, Chiba, Japan.
    Model-based testing of Apache ZooKeeper: Fundamental API usage and watchers2019In: Software Testing Verification and Reliability, article id e1720Article in journal (Refereed)
    Abstract [en]

    In this paper, we extend work on model‐based testing for Apache ZooKeeper, to handle watchers (triggers) and improve scalability. In a distributed asynchronous shared storage like ZooKeeper, watchers deliver notifications on state changes. They are difficult to test because watcher notifications involve an initial action that sets the watcher, followed by another action that changes the previously seen state.

    We show how to generate test cases for concurrent client sessions executing against ZooKeeper with the tool Modbat. The tests are verified against an oracle that takes into account all possible timings of network communication. The oracle has to verify that there exists a chain of events that triggers both the initial callback and the subsequent watcher notification. We show in detail how the oracle computes whether watch triggers are correct and how the model was adapted and improved to handle these features. Together with a new search improvement that increases both speed and accuracy, we are able to verify large test setups and confirm several defects with our model.

  • 8.
    Ashraf, Adnan
    et al.
    Abo Akad Univ, Fac Sci & Engn, Turku, Finland..
    Majd, Amin
    Abo Akad Univ, Fac Sci & Engn, Turku, Finland..
    Troubitsyna, Elena
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Online Path Generation and Navigation for Swarms of UAVs2020In: Scientific Programming, ISSN 1058-9244, E-ISSN 1875-919X, Vol. 2020, article id 8530763Article in journal (Refereed)
    Abstract [en]

    With the growing popularity of unmanned aerial vehicles (UAVs) for consumer applications, the number of accidents involving UAVs is also increasing rapidly. Therefore, motion safety of UAVs has become a prime concern for UAV operators. For a swarm of UAVs, a safe operation cannot be guaranteed without preventing the UAVs from colliding with one another and with static and dynamically appearing, moving obstacles in the flying zone. In this paper, we present an online, collision-free path generation and navigation system for swarms of UAVs. The proposed system uses geographical locations of the UAVs and of the successfully detected, static, and moving obstacles to predict and avoid the following: (1) UAV-to-UAV collisions, (2) UAV-to-static-obstacle collisions, and (3) UAV-to-moving-obstacle collisions. Our collision prediction approach leverages efficient runtime monitoring and complex event processing (CEP) to make timely predictions. A distinctive feature of the proposed system is its ability to foresee potential collisions and proactively find best ways to avoid predicted collisions in order to ensure safety of the entire swarm. We also present a simulation-based implementation of the proposed system along with an experimental evaluation involving a series of experiments and compare our results with the results of four existing approaches. The results show that the proposed system successfully predicts and avoids all three kinds of collisions in an online manner. Moreover, it generates safe and efficient UAV routes, efficiently scales to large-sized problem instances, and is suitable for cluttered flying zones and for scenarios involving high risks of UAV collisions.

  • 9.
    Asif, Rizwan
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for Autonomous Systems, CAS.
    Löffel, Hendrik Jan
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for Autonomous Systems, CAS.
    Assavasangthong, Vorapol
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for Autonomous Systems, CAS.
    Martinelli, Giulio
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for Autonomous Systems, CAS.
    Gajland, Phillip
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Rodríguez Gálvez, Borja
    KTH, School of Electrical Engineering and Computer Science (EECS), Intelligent systems, Information Science and Engineering.
    Aerial path planning for multi-vehicles2019In: Proceedings - IEEE 2nd International Conference on Artificial Intelligence and Knowledge Engineering, AIKE 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, p. 267-272, article id 8791733Conference paper (Refereed)
    Abstract [en]

    Unmanned Aerial Vehicles (UAV) are a potential solution to fast and cost efficient package delivery services. There are two types of UAVs, namely fixed wing (UAV-FW) and rotor wing (UAV-RW), which have their own advantages and drawbacks. In this paper we aim at providing different solutions to a collaborating multi-agent scenario combining both UAVs types. We show the problem can be reduced to the facility location problem (FLP) and propose two local search algorithms to solve it: Tabu search and simulated annealing.

  • 10.
    Aurell, Erik
    KTH, School of Electrical Engineering and Computer Science (EECS), Computational Science and Technology (CST). Aalto Univ, Dept Comp Sci, FIN-00076 Aalto, Finland.;Aalto Univ, Dept Appl Phys, FIN-00076 Aalto, Finland.
    Characteristic functions of quantum heat with baths at different temperatures2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, no 6, article id 062117Article in journal (Refereed)
    Abstract [en]

    This paper is about quantum heat defined as the change in energy of a bath during a process. The presentation takes into account recent developments in classical strong-coupling thermodynamics and addresses a version of quantum heat that satisfies quantum-classical correspondence. The characteristic function and the full counting statistics of quantum heat are shown to be formally similar. The paper further shows that the method can be extended to more than one bath, e.g., two baths at different temperatures, which opens up the prospect of studying correlations and heat flow. The paper extends earlier results on the expected quantum heat in the setting of one bath [E. Aurell and R. Eichhorn, New .J Phys. 17, 065007 (2015); E. Aurell, Entropy 19, 595 (2017)].

  • 11.
    Aurell, Erik
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    On Work and Heat in Time-Dependent Strong Coupling2017In: Entropy, ISSN 1099-4300, E-ISSN 1099-4300, Vol. 19, no 11, article id UNSP 595Article in journal (Refereed)
    Abstract [en]

    This paper revisits the classical problem of representing a thermal bath interacting with a system as a large collection of harmonic oscillators initially in thermal equilibrium. As is well known, the system then obeys an equation, which in the bulk and in the suitable limit tends to the Kramers-Langevin equation of physical kinetics. I consider time-dependent system-bath coupling and show that this leads to an additional harmonic force acting on the system. When the coupling is switched on and switched off rapidly, the force has delta-function support at the initial and final time. I further show that the work and heat functionals as recently defined in stochastic thermodynamics at strong coupling contain additional terms depending on the time derivative of the system-bath coupling. I discuss these terms and show that while they can be very large if the system-bath coupling changes quickly, they only give a finite contribution to the work that enters in Jarzynski's equality. I also discuss that these corrections to standard work and heat functionals provide an explanation for non-standard terms in the change of the von Neumann entropy of a quantum bath interacting with a quantum system found in an earlier contribution (Aurell and Eichhorn, 2015).

  • 12.
    Aurell, Erik
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computational Science and Technology (CST).
    Dominguez, Eduardo
    Univ Havana, Dept Theoret Phys, Grp Complex Syst & Stat Phys, Havana, Cuba..
    Machado, David
    Univ Havana, Dept Theoret Phys, Grp Complex Syst & Stat Phys, Havana, Cuba..
    Mulet, Roberto
    Univ Havana, Dept Theoret Phys, Grp Complex Syst & Stat Phys, Havana, Cuba..
    Exploring the diluted ferromagnetic p-spin model with a cavity master equation2018In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 97, no 5, article id 050103Article in journal (Refereed)
    Abstract [en]

    We introduce an alternative solution to Glauber multispin dynamics on random graphs. The solution is based on the recently introduced cavity master equation (CME), a time-closure turning the, in principle, exact dynamic cavity method into a practical method of analysis and of fast simulation. Running CME once is of comparable computational complexity as one Monte Carlo run on the same problem. We show that CME correctly models the ferromagnetic p-spin Glauber dynamics from high temperatures down to and below the spinoidal transition. We also show that CME allows an alternative exploration of the low-temperature spin-glass phase of the model.

  • 13.
    Aurell, Erik
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computational Science and Technology (CST).
    Montana, Federica
    KTH, Centres, Nordic Institute for Theoretical Physics NORDITA.
    Thermal power of heat flow through a qubit2019In: Physical review. E, ISSN 2470-0045, E-ISSN 2470-0053, Vol. 99, no 4, article id 042130Article in journal (Refereed)
    Abstract [en]

    In this paper we consider the thermal power of a heat flow through a qubit between two baths. The baths are modeled as a set of harmonic oscillators initially at equilibrium, at two temperatures. Heat is defined as the change of energy of the cold bath, and thermal power is defined as expected heat per unit time, in the long-time limit. The qubit and the baths interact as in the spin-boson model, i.e., through qubit operator sigma(z). We compute thermal power in an approximation analogous to a "noninteracting blip" (NIBA) and express it in the polaron picture as products of correlation functions of the two baths, and a time derivative of a correlation function of the cold bath. In the limit of weak interaction we recover known results in terms of a sum of correlation functions of the two baths, a correlation functions of the cold bath only, and the energy split.

  • 14.
    Austrin, Per
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Stanković, Aleksa
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematics (Div.).
    Global cardinality constraints make approximating some MAx-2-CSPS harder2019In: Leibniz International Proceedings in Informatics, LIPIcs, Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing , 2019Conference paper (Refereed)
    Abstract [en]

    Assuming the Unique Games Conjecture, we show that existing approximation algorithms for some Boolean Max-2-CSPs with cardinality constraints are optimal. In particular, we prove that Max-Cut with cardinality constraints is UG-hard to approximate within ≈ 0.858, and that Max-2-Sat with cardinality constraints is UG-hard to approximate within ≈ 0.929. In both cases, the previous best hardness results were the same as the hardness of the corresponding unconstrained Max-2-CSP (≈ 0.878 for Max-Cut, and ≈ 0.940 for Max-2-Sat). The hardness for Max-2-Sat applies to monotone Max-2-Sat instances, meaning that we also obtain tight inapproximability for the Max-k-Vertex-Cover problem.

  • 15.
    Azari, Amin
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Masoudi, Meysam
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Cavdar, Cicek
    KTH, School of Electrical Engineering and Computer Science (EECS), Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Optimized Resource Provisioning and Operation Control for Low-power Wide-area IoT NetworksManuscript (preprint) (Other academic)
    Abstract [en]

    Grant-free radio access is a promising solution for reducing energy consumption and access delay in low power wide-area (LPWA) Internet of Things (IoT) networks. This work is devoted to reliability modeling, battery-lifetime analysis, resource provisioning, and operation control for grantfreeIoT networks. Our modeling captures correlation in devices’locations, benefits from 3D (time/frequency/code) interference analysis, and enables coexistence analysis of multi-type IoT technologies. We derive the interplay amongst density of the access points, communication bandwidth, traffic volume, and quality of service (QoS) of communications. Deriving the interplay enables scalability analysis, i.e. it figures out the required increase in device's energy consumption (or access network’s resources) for compensating the increase in traffic volume or QoS demand. Our major contribution consists in deriving traffic loads and respective exchange rates in which, energy and cost resources of devices and the access network, respectively, could be traded to achieve a given level of QoS. We further indicate operation regions in which scaling a parameter turns from being a friend into a foe. Finally, we present energy- and cost-optimized operation control and resource provisioning strategies, respectively. The simulation results confirm tightness of the analytical expressions, and indicate the usefulness of them in planning and operation control of IoT networks.

  • 16.
    Azari, Amin
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Stefanovic, C.
    Aalborg University..
    Popovski, P.
    Aalborg University..
    Cavdar, Cicek
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    On the Latency-Energy Performance of NB-IoT Systems in Providing Wide-Area IoT Connectivity2019In: IEEE Transactions on Green Communications and NetworkingArticle in journal (Refereed)
    Abstract [en]

    Narrowband Internet-of-Things (NB-IoT) offers a significant link budget improvement in comparison with the legacy networks by introducing different coverage classes, allowing repeated transmissions, and tuning the repetition order based on the path-loss in communications. However, those repetitions necessarily increase energy consumption and latency in the whole NB-IoT system. The extent to which the whole system is affected depends on the scheduling of the uplink and downlink channels. We address this question, not treated previously, by developing a tractable model of NB-IoT connectivity, comprising message exchanges in random-access, control, and data channels. The model is then used to analyze the impact of channel scheduling and interaction of coverage classes on the performance of IoT devices through the derivation of the expected latency and battery lifetime. These results are subsequently employed in determining the optimized operation points, i.e., (i) scheduling of data and control channels for a given set of users and respective coverage classes, or (ii) determining the optimal set of coverage classes and served users per coverage class for a given scheduling strategy. Simulations results show the validity of the analysis and confirm that channel scheduling and coexistence of coverage classes significantly affect latency and battery lifetime performance of NB-IoT devices.

  • 17.
    B. da Silva Jr., Jose Mairton
    et al.
    KTH, School of Electrical Engineering (EES), Network and Systems engineering.
    Skouroumounis, Christodoulos
    University of Cyprus.
    Krikidis, Ioannis
    University of Cyprus.
    Fodor, Gabor
    Fischione, Carlo
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Network and Systems Engineering.
    Energy Efficient Full-Duplex Networks2019In: Green Communications for Energy-EfficientWireless Systems and Networks / [ed] A. Zappone, J. Yang, J. S. Thompson, H. Suraweera, The Institution of Engineering and Technology (IET) , 2019Chapter in book (Refereed)
    Abstract [en]

    As the specifications of the 5th generation of cellular networks mature, the deployment phase is starting up. Hence, peaks of data rates in the order of tens of Gbit/s as well as more energy efficient deployments are expected. Nevertheless, the quick development of new applications and services encourage the research community to look beyond 5G and explore new technological components. Indeed, to meet the increasing demand for mobile broadband as well as internet of things type of services, the research and standardization communities are currently investigating novel physical and medium access layer technologies, including further virtualization of networks, the use of the lower Terahertz bands, even higher cell densification, and full-duplex (FD) communications.

     

    FD has been proposed as one of the enabling technologies to increase the spectral efficiency of conventional wireless transmission modes, by overcoming our prior understanding that it is not possible for radios to transmit and receive simultaneously on the same time-frequency resource. Due to this, we can also refer to FD communications as in-band FD. In-band FD transceivers have the potential of improving the attainable spectral efficiency of traditional wireless networks operating with half-duplex (HD) transceivers by a factor close to two. In addition to the spectral efficiency gains, full-duplex can provide gains in the medium access control layer, in which problems such as the hidden/exposed nodes and collision detection can be mitigated and the energy consumption can be reduced.

     

    Until recently, in-band FD was not considered as a solution for wireless networks due to the inherent interference created from the transmitter to its own receiver, the so-called self-interference (SI). However, recent advancements in antenna and analog/digital interference cancellation techniques demonstrate FD transmissions as a viable alternative to traditional HD transmissions. Given the recent architectural progression of 5G towards smaller cells, higher densification, higher number of antennas and utilizing the millimeter wave (mmWave) band, the integration of FD communications into such scenarios is appealing. In-band FD communications are suited for short range communication, and although the SI remains a challenge, the use of multiple antennas and the transmission in the mmWave band are allies that help to mitigate the SI in the spatial domain and provide even more gains for spectral and energy efficiency. To achieve the spectral and energy efficiency gains, it is important to understand the challenges and solutions, which can be roughly divided into resource allocation, protocol design, hardware design and energy harvesting. Hence, FD communications appears as an important technology component to improve the spectral and energy efficiency of current communication systems and help to meet the goals of 5G and beyond.

     

    The chapter starts with an overview of FD communications, including its challenges and solutions. Next, a comprehensive literature review of energy efficiency in FD communications is presented along with the key solutions to improve energy efficiency. Finally, we evaluate the key aspects of energy efficiency in FD communications for two scenarios: single-cell with multiple users in a pico-cell scenario, and a system level evaluation with macro- and small-cells with multiple users.

  • 18.
    Bahri, Leila
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Software and Computer systems, SCS.
    Girdzijauskas, Sarunas
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Software and Computer systems, SCS.
    Blockchain technology: Practical P2P computing (Tutorial)2019In: Proceedings - 2019 IEEE 4th International Workshops on Foundations and Applications of Self* Systems, FAS*W 2019, Institute of Electrical and Electronics Engineers (IEEE), 2019, p. 249-250, article id 8791982Conference paper (Refereed)
    Abstract [en]

    Blockchain technology comes with the promise to revolutionize the way current IT systems are organized as well as to revise how trust is perceived in the wider society. In spite of the wide attention that cyrpto-currencies (such as Bitcoin) have attracted, Blockchain technology is more likely to make an impact beyond ongoing speculations on cyrpto-currencies. Decentralized identity management, transparent supply-chain systems, and IoT governance and security are only few examples of research challenges for which this technology may hold substantial potential. Blockchain technology has emerged at the intersection of two well established research areas: peer-to-peer (P2P) computing and cryptography. In this tutorial, we provide a general overview of the main components behind this technology, we present the difference between the types of Blockchain available today, and we make a high level discussion on its potentials and limitations as well as possible research challenges.

  • 19.
    Bahri, Leila
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Software and Computer systems, SCS.
    Girdzijauskas, Sarunas
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Software and Computer systems, SCS.
    Trust mends blockchains: Living up to expectations2019In: Proceedings - International Conference on Distributed Computing Systems, 2019, p. 1358-1368Conference paper (Refereed)
    Abstract [en]

    At the heart of Blockchains is the trustless leader election mechanism for achieving consensus among pseudo-anonymous peers, without the need of oversight from any third party or authority whatsoever. So far, two main mechanisms are being discussed: proof-of-work (PoW) and proof-of-stake (PoS). PoW relies on demonstration of computational power, and comes with the markup of huge energy wastage in return of the stake in cyrpto-currency. PoS tries to address this by relying on owned stake (i.e., amount of crypto-currency) in the system. In both cases, Blockchains are limited to systems with financial basis. This forces non-crypto-currency Blockchain applications to resort to "permissioned" setting only, effectively centralizing the system. However, non-crypto-currency permisionless blockhains could enable secure and self-governed peer-to-peer structures for numerous emerging application domains, such as education and health, where some trust exists among peers. This creates a new possibility for valuing trust among peers and capitalizing it as the basis (stake) for reaching consensus. In this paper we show that there is a viable way for permisionless non-financial Blockhains to operate in completely decentralized environments and achieve leader election through proof-of-trust (PoT). In our PoT construction, peer trust is extracted from a trust network that emerges in a decentralized manner and is used as a waiver for the effort to be spent for PoW, thus dramatically reducing total energy expenditure of the system. Furthermore, our PoT construction is resilient to the risk of small cartels monopolizing the network (as it happens with the mining-pool phenomena in PoW) and is not vulnerable to sybils. We evluate security guarantees, and perform experimental evaluation of our construction, demonstrating up to 10-fold energy savings compared to PoW without trading off any of the decentralization characteristics, with further guarantees against risks of monopolization.

  • 20.
    Bahuguna, Jyotika
    et al.
    Aix Marseille Univ, Inst Syst Neurosci, Marseille, France..
    Sahasranamam, Ajith
    Ongil Pvt Ltd, Singapore, Singapore..
    Kumar, Arvind
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Uncoupling the roles of firing rates and spike bursts in shaping the STN-GPe beta band oscillations2020In: PloS Computational Biology, ISSN 1553-734X, E-ISSN 1553-7358, Vol. 16, no 3Article in journal (Refereed)
    Abstract [en]

    The excess of 15-30 Hz (beta-band) oscillations in the basal ganglia is one of the key signatures of Parkinson's disease (PD). The STN-GPe network is integral to generation and modulation of beta band oscillations in basal ganglia. However, the role of changes in the firing rates and spike bursting of STN and GPe neurons in shaping these oscillations has remained unclear. In order to uncouple their effects, we studied the dynamics of STN-GPe network using numerical simulations. In particular, we used a neuron model, in which firing rates and spike bursting can be independently controlled. Using this model, we found that while STN firing rate is predictive of oscillations but GPe firing rate is not. The effect of spike bursting in STN and GPe neurons was state-dependent. That is, only when the network was operating in a state close to the border of oscillatory and non-oscillatory regimes, spike bursting had a qualitative effect on the beta band oscillations. In these network states, an increase in GPe bursting enhanced the oscillations whereas an equivalent proportion of spike bursting in STN suppressed the oscillations. These results provide new insights into the mechanisms underlying the transient beta bursts and how duration and power of beta band oscillations may be controlled by an interplay of GPe and STN firing rates and spike bursts. Author summary The STN-GPe network undergoes a change in firing rates as well as increased bursting during excessive beta band oscillations during Parkinson's disease. In this work we uncouple their effects by using a novel neuron model and show that presence of oscillations is contingent on the increase in STN firing rates, however the effect of spike bursting on oscillations depends on the network state. In a network state on the border of oscillatory and non-oscillatory regime, GPe spike bursting strengthens oscillations. The effect of spike bursting in the STN depends on the proportion of GPe neurons bursting. These results suggest a mechanism underlying a transient beta band oscillation bursts often seen in experimental data.

  • 21.
    Balliu, Musard
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Bastys, Iulia
    Chalmers Univ Technol, Dept Comp Sci & Engn, Gothenburg, Sweden..
    Sabelfeld, Andrei
    Chalmers Univ Technol, Dept Comp Sci & Engn, Gothenburg, Sweden..
    Securing IoT Apps2019In: IEEE Security and Privacy, ISSN 1540-7993, E-ISSN 1558-4046, Vol. 17, no 5, p. 22-29Article in journal (Refereed)
    Abstract [en]

    Users increasingly rely on Internet of Things (IoT) apps to manage their digital lives through the overwhelming diversity of IoT services and devices. Are the IoT app platforms doing enough to protect the privacy and security of their users? By securing IoT apps, how can we help users reclaim control over their data?

    Download full text (pdf)
    fulltext
  • 22.
    Balliu, Musard
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Dam, Mads
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Guanciale, Roberto
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    InSpectre: Breaking and Fixing Microarchitectural Vulnerabilities by Formal Analysis.Manuscript (preprint) (Other academic)
    Abstract [en]

    The recent Spectre attacks has demonstrated the fundamental insecurity of current computer microarchitecture. The attacks use features like pipelining, out-of-order and speculation to extract arbitrary information about the memory contents of a process. A comprehensive formal microarchitectural model capable of representing the forms of out-of-order and speculative behavior that can meaningfully be implemented in a high performance pipelined architecture has not yet emerged. Such a model would be very useful, as it would allow the existence and non-existence of vulnerabilities, and soundness of countermeasures to be formally established. In this paper we present such a model targeting single core processors. The model is intentionally very general and provides an infrastructure to define models of real CPUs. It incorporates microarchitectural features that underpin all known Spectre vulnerabilities. We use the model to elucidate the security of existing and new vulnerabilities, as well as to formally analyze the effectiveness of proposed countermeasures. Specifically, we discover three new (potential) vulnerabilities, including a new variant of Spectre v4, a vulnerability on speculative fetching, and a vulnerability on out-of-order execution, and analyze the effectiveness of three existing countermeasures: constant time, Retpoline, and ARM's Speculative Store Bypass Safe (SSBS).

    Download full text (pdf)
    fulltext
  • 23.
    Balliu, Musard
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Merro, Massimo
    University of Verona.
    Pasqua, Michele
    University of Verona.
    Friendly Fire: Cross-App Interactions in IoT Platforms2020In: https://www.cambridge.org/core/what-we-publish/textbooks#, 2020Conference paper (Refereed)
    Abstract [en]

    IoT platforms enable users to connect various smart devices and online services viareactive apps running on the cloud. These apps, often developed by third-parties, performsimple computations on data triggered by external information sources and actuate theresults of computation on external information sinks. Recent research shows that unin-tended or malicious interactions between the dierent (even benign) apps of a user cancause severe security and safety risks. These works leverage program analysis techniquesto build tools for unveiling unexpected interference across apps for specic use cases.We propose a calculus that models the behavioral semantics of a system of apps ex-ecuting concurrently, and use it to dene desirable semantic policies in the security andsafety context of IoT apps. To demonstrate the usefulness of our framework, we denestatic mechanisms for enforcing cross-app security and safety, and prove them sound withrespect to our semantic conditions. Finally, we leverage real-world apps to validate thepractical benets of our policy framework.

    Download full text (pdf)
    fulltext
  • 24.
    Barbette, Tom
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    Katsikas, Georgios P.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    Maguire Jr., Gerald Q.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS, Radio Systems Laboratory (RS Lab).
    Kostic, Dejan
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS.
    RSS++: load and state-aware receive side scaling2019In: Proceedings of the 15th International Conference on emerging Networking EXperiments and Technologies / [ed] ACM, Orlando, FL, USA: Association for Computing Machinery (ACM), 2019Conference paper (Refereed)
    Abstract [en]

    While the current literature typically focuses on load-balancing among multiple servers, in this paper, we demonstrate the importance of load-balancing within a single machine (potentially with hundreds of CPU cores). In this context, we propose a new load-balancing technique (RSS++) that dynamically modifies the receive side scaling (RSS) indirection table to spread the load across the CPU cores in a more optimal way. RSS++ incurs up to 14x lower 95th percentile tail latency and orders of magnitude fewer packet drops compared to RSS under high CPU utilization. RSS++ allows higher CPU utilization and dynamic scaling of the number of allocated CPU cores to accommodate the input load, while avoiding the typical 25% over-provisioning. RSS++ has been implemented for both (i) DPDK and (ii) the Linux kernel. Additionally, we implement a new state migration technique, which facilitates sharding and reduces contention between CPU cores accessing per-flow data. RSS++ keeps the flow-state by groups that can be migrated at once, leading to a 20% higher efficiency than a state of the art shared flow table.

    Download full text (pdf)
    RSSPP
  • 25.
    Barbette, Tom
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    Tang, Chen
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Yao, Haoran
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Kostic, Dejan
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    Maguire Jr., Gerald Q.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS.
    Papadimitratos, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS.
    Chiesa, Marco
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    A High-Speed Load-Balancer Design with Guaranteed Per-Connection-Consistency2020In: 17th USENIX Symposium on Networked Systems Design and Implementation / [ed] USENIX Association, Santa Clara, CA, USA, 2020, p. 667-683Conference paper (Refereed)
    Abstract [en]

    Large service providers use load balancers to dispatch millions of incoming connections per second towards thousands of servers. There are two basic yet critical requirements for a load balancer: uniform load distribution of the incoming connections across the servers and per-connection-consistency (PCC), i.e., the ability to map packets belonging to the same connection to the same server even in the presence of changes in the number of active servers and load balancers. Yet, meeting both these requirements at the same time has been an elusive goal. Today's load balancers minimize PCC violations at the price of non-uniform load distribution.

    This paper presents Cheetah, a load balancer that supports uniform load distribution and PCC while being scalable, memory efficient, resilient to clogging attacks, and fast at processing packets. The Cheetah LB design guarantees PCC for any realizable server selection load balancing mechanism and can be deployed in both a stateless and stateful manner, depending on the operational needs. We implemented Cheetah on both a software and a Tofino-based hardware switch. Our evaluation shows that a stateless version of Cheetah guarantees PCC, has negligible packet processing overheads, and can support load balancing mechanisms that reduce the flow completion time by a factor of 2–3×.

    Download full text (pdf)
    cheetah.pdf
  • 26.
    Bastys, Iulia
    et al.
    Chalmers University of Technology.
    Balliu, Musard
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Rezk, Tamara
    INRIA Sophia-Antipolis.
    Sabelfeld, Andrei
    Chalmers University of Technology.
    Clockwork: Tracking Remote Timing Attacks2020Conference paper (Refereed)
    Download full text (pdf)
    fulltext
  • 27. Baumann, Christoph
    et al.
    Schwarz, Oliver
    Dam, Mads
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    On the verification of system-level information flow properties for virtualized execution platforms2019In: Journal of Cryptographic Engineering, ISSN 2190-8508, Vol. 9, no 3, p. 243-261Article in journal (Refereed)
    Abstract [en]

    The security of embedded systems can be dramatically improved through the use of formally verified isolation mechanisms such as separation kernels, hypervisors, or microkernels. For trustworthiness, particularly for system-level behavior, the verifications need precise models of the underlying hardware. Such models are hard to attain, highly complex, and proofs of their security properties may not easily apply to similar but different platforms. This may render verification economically infeasible. To address these issues, we propose a compositional top-down approach to embedded system specification and verification, where the system-on-chip is modeled as a network of distributed automata communicating via paired synchronous message passing. Using abstract specifications for each component allows to delay the development of detailed models for cores, devices, etc., while still being able to verify high-level security properties like integrity and confidentiality, and soundly refine the result for different instantiations of the abstract components at a later stage. As a case study, we apply this methodology to the verification of information flow security for an industry-scale security-oriented hypervisor on the ARMv8-A platform and report on the complete verification of guest mode security properties in the HOL4 theorem prover.

    Download full text (pdf)
    fulltext
  • 28. Beckert, B.
    et al.
    Bormer, T.
    Gocht, Stephan
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Herda, M.
    Lentzsch, D.
    Ulbrich, M.
    Using Relational Verification for Program Slicing2019In: 17th International Conference on Software Engineering and Formal Methods, SEFM 2019, Springer Verlag , 2019, p. 353-372Conference paper (Refereed)
    Abstract [en]

    Program slicing is the process of removing statements from a program such that defined aspects of its behavior are retained. For producing precise slices, i.e., slices that are minimal in size, the program’s semantics must be considered. Existing approaches that go beyond a syntactical analysis and do take the semantics into account are not fully automatic and require auxiliary specifications from the user. In this paper, we adapt relational verification to check whether a slice candidate obtained by removing some instructions from a program is indeed a valid slice. Based on this, we propose a framework for precise and automatic program slicing. As part of this framework, we present three strategies for the generation of slice candidates, and we show how dynamic slicing approaches – that interweave generating and checking slice candidates – can be used for this purpose. The framework can easily be extended with other strategies for generating slice candidates. We discuss the strengths and weaknesses of slicing approaches that use our framework.

  • 29.
    Beckman, Claes
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS.
    5G and its Implication for Rail2019In: Train Communicatins Systems 2019: The WiFi on trains conference, London, 2019Conference paper (Other (popular science, discussion, etc.))
  • 30.
    Belic, Jovana
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Automatic detection of exudates in retinal images2010Conference paper (Refereed)
    Abstract [en]

    Nowadays, automatic detection of different diseases plays an important role in early and reliable diagnosis, which leads to faster recovery and significant reduction in health care costs. One such disease is diabetic retinopathy, which is induced by diabetes and is manifested through the gradual loss of eye blood vessels. Exudates are a form of diabetic retinopathy, and the idea of this paper was developing the program which would be used for automatic recognition of places that are potentially exudates in retinal images. The program was made in MatLab and three different methods were used. Also, a method for detection of blind spots was developed, concerning importance of it for appropriate detection of exudates.

  • 31. Bernstein, A.
    et al.
    Na Nongkai, Danupon
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Distributed exact weighted all-pairs shortest paths in near-linear time2019In: Proceeding STOC 2019 Proceedings of the 51st Annual ACM SIGACT Symposium on Theory of Computing, Association for Computing Machinery (ACM), 2019, p. 334-342Conference paper (Refereed)
    Abstract [en]

    In the distributed all-pairs shortest paths problem (APSP), every node in the weighted undirected distributed network (the CONGEST model) needs to know the distance from every other node using least number of communication rounds (typically called time complexity). The problem admits (1 + o(1))-approximation Θ (n)time algorithm and a nearly-tight Ω (n) lower bound [Nanongkai, STOC’14; Lenzen and Patt-Shamir PODC’15]. For the exact case, Elkin [STOC’17] presented an O(n5/3 log2/3 n) time bound, which was later improved to Õ(n5/4) in [Huang, Nanongkai, Saranurak FOCS’17]. It was shown that any super-linear lower bound (in n) requires a new technique [Censor-Hillel, Khoury, Paz, DISC’17], but otherwise it remained widely open whether there exists a Õ(n)-time algorithm for the exact case, which would match the best possible approximation algorithm. This paper resolves this question positively: we present a randomized (Las Vegas) Õ(n)-time algorithm, matching the lower bound up to polylogarithmic factors. Like the previous Õ(n5/4) bound, our result works for directed graphs with zero (and even negative) edge weights. In addition to the improved running time, our algorithm works in a more general setting than that required by the previous Õ(n5/4) bound; in our setting (i) the communication is only along edge directions (as opposed to bidirectional), and (ii) edge weights are arbitrary (as opposed to integers in (1, 2, . . ., poly(n))). The previously best algorithm for this more difficult setting required Õ(n3/2) time [Agarwal and Ramachandran, ArXiv’18] (this can be improved to Õ(n4/3) if one allows bidirectional communication). Our algorithm is extremely simple and relies on a new technique called Random Filtered Broadcast. Given any sets of nodes A, B ⊆ V and assuming that every b ∈ B knows all distances from nodes in A, and every node v ∈ V knows all distances from nodes in B, we want every v ∈ V to know DistThroughB(a,v) = minb∈B dist(a,b) + dist(b,v) for every a ∈ A. Previous works typically solve this problem by broadcasting all knowledge of every b ∈ B, causing super-linear edge congestion and time. We show a randomized algorithm that can reduce edge congestions and thus solve this problem in Õ(n) expected time.

  • 32.
    Bhattacharya, Sayan
    et al.
    Univ Warwick, Coventry, W Midlands, England..
    Henzinger, Monika
    Univ Vienna, Vienna, Austria..
    Na Nongkai, Danupon
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    A New Deterministic Algorithm for Dynamic Set Cover2019In: 2019 IEEE 60TH ANNUAL SYMPOSIUM ON FOUNDATIONS OF COMPUTER SCIENCE (FOCS 2019), IEEE COMPUTER SOC , 2019, p. 406-423Conference paper (Refereed)
    Abstract [en]

    We present a deterministic dynamic algorithm for maintaining a (1 + epsilon) f-approximate minimum cost set cover with O(f log(Cn)/epsilon(2)) amortized update time, when the input set system is undergoing element insertions and deletions. Here, n denotes the number of elements, each element appears in at most f sets, and the cost of each set lies in the range [1/C, 1]. Our result, together with that of Gupta et al. [STOC'17], implies that there is a deterministic algorithm for this problem with O(f log(Cn)) amortized update time and O(min(log n, f))-approximation ratio, which nearly matches the polynomial-time hardness of approximation for minimum set cover in the static setting. Our update time is only O(log(Cn)) away from a trivial lower bound. Prior to our work, the previous best approximation ratio guaranteed by deterministic algorithms was O(f(2)), which was due to Bhattacharya et al. [ICALP'15]. In contrast, the only result that guaranteed O(f)-approximation was obtained very recently by Abboud et al. [STOC'19], who designed a dynamic algorithm with (1+epsilon) f-approximation ratio and O(f(2) log n/E) amortized update time. Besides the extra O(f) factor in the update time compared to our and Gupta et al.'s results, the Abboud et al. algorithm is randomized, and works only when the adversary is oblivious and the sets are unweighted (each set has the same cost). We achieve our result via the primal-dual approach, by maintaining a fractional packing solution as a dual certificate. This approach was pursued previously by Bhattacharya et al. and Gupta et al., but not in the recent paper by Abboud et al. Unlike previous primal-dual algorithms that try to satisfy some local constraints for individual sets at all time, our algorithm basically waits until the dual solution changes significantly globally, and fixes the solution only where the fix is needed.

  • 33.
    Bhatti, Muhammad Khurram
    et al.
    Informat Technol Univ, Embedded Comp Lab, 346-B Ferozpur Rd, Lahore, Pakistan..
    Oz, Isil
    Izmir Inst Technol, Comp Engn Dept, Izmir, Turkey..
    Amin, Sarah
    Informat Technol Univ, Embedded Comp Lab, 346-B Ferozpur Rd, Lahore, Pakistan..
    Mushtaq, Maria
    Informat Technol Univ, Embedded Comp Lab, 346-B Ferozpur Rd, Lahore, Pakistan..
    Farooq, Umer
    Dhofar Univ, Dept Elect & Comp Engn, Salalah 211, Oman..
    Popov, Konstantin
    SICS, Isafjordsgatan 22, S-16429 Kista, Sweden..
    Brorsson, Mats
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Software and Computer systems, SCS.
    Locality-aware task scheduling for homogeneous parallel computing systems2018In: Computing, ISSN 0010-485X, E-ISSN 1436-5057, Vol. 100, no 6, p. 557-595Article in journal (Refereed)
    Abstract [en]

    In systems with complex many-core cache hierarchy, exploiting data locality can significantly reduce execution time and energy consumption of parallel applications. Locality can be exploited at various hardware and software layers. For instance, by implementing private and shared caches in a multi-level fashion, recent hardware designs are already optimised for locality. However, this would all be useless if the software scheduling does not cast the execution in a manner that promotes locality available in the programs themselves. Since programs for parallel systems consist of tasks executed simultaneously, task scheduling becomes crucial for the performance in multi-level cache architectures. This paper presents a heuristic algorithm for homogeneous multi-core systems called locality-aware task scheduling (LeTS). The LeTS heuristic is a work-conserving algorithm that takes into account both locality and load balancing in order to reduce the execution time of target applications. The working principle of LeTS is based on two distinctive phases, namely; working task group formation phase (WTG-FP) and working task group ordering phase (WTG-OP). The WTG-FP forms groups of tasks in order to capture data reuse across tasks while the WTG-OP determines an optimal order of execution for task groups that minimizes the reuse distance of shared data between tasks. We have performed experiments using randomly generated task graphs by varying three major performance parameters, namely: (1) communication to computation ratio (CCR) between 0.1 and 1.0, (2) application size, i.e., task graphs comprising of 50-, 100-, and 300-tasks per graph, and (3) number of cores with 2-, 4-, 8-, and 16-cores execution scenarios. We have also performed experiments using selected real-world applications. The LeTS heuristic reduces overall execution time of applications by exploiting inter-task data locality. Results show that LeTS outperforms state-of-the-art algorithms in amortizing inter-task communication cost.

  • 34. Bittar, A.
    et al.
    Velupillai, Sumithra
    KTH, School of Electrical Engineering and Computer Science (EECS), Theoretical Computer Science, TCS. Institute of Psychiatry, Psychology and Neuroscience, King's College London, London, United Kingdom.
    Roberts, A.
    Dutta, R.
    Text classification to inform suicide risk assessment in electronic health records2019In: 17th World Congress on Medical and Health Informatics, MEDINFO 2019, IOS Press, 2019, Vol. 264, p. 40-44Conference paper (Refereed)
    Abstract [en]

    Assessing a patient's risk of an impending suicide attempt has been hampered by limited information about dynamic factors that change rapidly in the days leading up to an attempt. The storage of patient data in electronic health records (EHRs) has facilitated population-level risk assessment studies using machine learning techniques. Until recently, most such work has used only structured EHR data and excluded the unstructured text of clinical notes. In this article, we describe our experiments on suicide risk assessment, modelling the problem as a classification task. Given the wealth of text data in mental health EHRs, we aimed to assess the impact of using this data in distinguishing periods prior to a suicide attempt from those not preceding such an attempt. We compare three different feature sets, one structured and two text-based, and show that inclusion of text features significantly improves classification accuracy in suicide risk assessment. © 2019 International Medical Informatics Association (IMIA) and IOS Press. This article is published online with Open Access by IOS Press and distributed under the terms of the Creative Commons Attribution Non-Commercial License 4.0 (CC BY-NC 4.0).

  • 35.
    Boman, Magnus
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Software and Computer systems, SCS.
    ben Abdesslem, Fehmi
    Forsell, Erik
    Gillblad, Daniel
    Görnerup, Olof
    Isacsson, Nils
    Sahlgren, Magnus
    Kaldo, Viktor
    Learning machines in Internet-delivered psychological treatment2019In: Progress in artificial intelligence, ISSN 2192-6352, Vol. 8, no 4, p. 475-485Article in journal (Refereed)
    Abstract [en]

    A learning machine, in the form of a gating network that governs a finite number of different machine learning methods, is described at the conceptual level with examples of concrete prediction subtasks. A historical data set with data from over 5000 patients in Internet-based psychological treatment will be used to equip healthcare staff with decision support for questions pertaining to ongoing and future cases in clinical care for depression, social anxiety, and panic disorder. The organizational knowledge graph is used to inform the weight adjustment of the gating network and for routing subtasks to the different methods employed locally for prediction. The result is an operational model for assisting therapists in their clinical work, about to be subjected to validation in a clinical trial.

  • 36.
    Boman, Magnus
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Software and Computer systems, SCS.
    Heger, Tobias
    Circles of Impression: External Foresight in Global Enterprises2019In: Futures Thinking and Organizational Policy / [ed] D. A. Schreiber and Z. L. Berge, Cham: Palgrave Macmillan, 2019, p. 179-199Chapter in book (Refereed)
  • 37.
    Brocke, Ekaterina
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Method development for co-simulation of electrical-chemical systems in Neuroscience2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Multiscale modeling and simulation is a powerful approach for studying such phenomena in nature as learning and memory. In computational neuroscience, historically, methods and tools for neuronal modeling and simulations have been developed for studies focused on a single level of the neuronal organization. Once the community realized that the interaction of multiple systems acting at different temporal and spatial scales can lead to emerging properties of the phenomena under study, the interest in and need for models encompassing processes acting at multiple scales of time and space increased. Such models are called multiscale models.

    Multiscale modeling and simulation can be achieved in different ways. One of the possible solutions is to use an already existing foundation of formalisms and methods, and couple existing numerical algorithms and models during a simulation in a co-simulation, i.e. a joint simulation of subsystems. However, there are several obstacles on the way. First, a lack of interoperability of simulation environments makes it non-trivial to couple existing models in a single environment that supports multiscale simulation. Second, there is a decision to make regarding which variables to communicate between subsystems. The communication signal has a significant impact on the behavior of the whole multiscale system. Last but not least, an absence of a theory or general approach for the numerical coupling of existing mathematical formalisms makes the coupling of the numerical solvers a challenging task.

    The main contribution of this thesis is a numerical framework for multiscale co-simulation of electrical and chemical systems in neuroscience. A multiscale model that integrates a subcellular signaling system with the electrical activity of the neuron was developed. The thesis emphasizes the importance of numerically correct and efficient coupling of the systems of interest. Two coupling algorithms, named singlerate and multirate, differ in the rate of communication between the coupling subsystems, were proposed in the thesis. The algorithms, as well as test cases, were implemented in the MATLAB® environment. MATLAB was used to validate the accuracy and efficiency of the algorithms. Both algorithms showed an expected second order accuracy with the simulated electrical-chemical system. The guaranteed accuracy in the singlerate algorithm can be used as a trade-off for efficiency in the multirate algorithm. Thus, both algorithms can find its application in the proposed numerical framework for multiscale co-simulations. The framework exposes a modular organization with natural interfaces and could be used as a basis for the development of a generic tool for multiscale co-simulations.

    The thesis also presents an implementation of a new numerical method in the NEURON simulation environment, with benchmarks. The method can replace the standard discretization schema for the Hodgkin-Huxley type models. It can be beneficial in a co-simulation of large models where the Jacobian evaluation of the whole system becomes a very expensive operation.

    Finally, the thesis describes an extension of the MUlti-SImulation Coordinator tool (MUSIC). MUSIC is a library that is mainly used for co-simulations of spiking neural networks on a cluster. A series of important developments was done in MUSIC as the first step towards multiscale co-simulations. First, a new algorithm and an improvement of the existing parallel communication algorithms were implemented as described in the thesis. Then, a new communication scheduling algorithm was developed and implemented in the MUSIC library and analyzed. The numerical framework presented in the thesis could be implemented with MUSIC to allow efficient co-simulations of electrical-chemical systems.

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  • 38.
    Brocke, Ekaterina
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Djurfeldt, Mikael
    KTH, School of Electrical Engineering and Computer Science (EECS), Centres, Centre for High Performance Computing, PDC.
    Efficient Spike Communication in the MUSIC Framework on a Blue Gene/Q SupercomputerManuscript (preprint) (Other (popular science, discussion, etc.))
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  • 39.
    Brodén, Cyrus
    et al.
    Department of Surgery and Cancer, Imperial College London, St Mary’s Hospital, London, UK2Karolinska Institutet, Department of Clinical Sciences, Danderyd Hospital, Division of Orthopaedics, Stockholm, Sweden.
    Giles, Joshua W.
    Department of Mechanical Engineering, University of Victoria, Victoria, BC, Canada4Mechatronics in Medicine Laboratory, Mechanical Engineering, Imperial College London, London, UK.
    Popat, Ravi
    Department of Bioengineering, Imperial College London, London, UK.
    Fetherston, Shirley
    Department of Radiology, St Mary’s Hospital, Imperial College Healthcare NHS Trust, London, UK.
    Olivecrona, Henrik
    Karolinska Institutet, Sweden.
    Sandberg, Olof
    Sectra, Linköping, Sweden.
    Maguire Jr., Gerald Q.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Communication Systems, CoS.
    Noz, Marilyn E.
    New York University, Department of Radiology.
    Sködenberg, Olof
    Karolinska Institutet, Department of Clinical Sciences, Danderyd Hospital, Division of Orthopaedics, Stockholm, Sweden.
    Emery, Roger
    Department of Surgery and Cancer, Imperial College London, St Mary’s Hospital, London, UK.
    Accuracy and precision of a CT method for assessing migration in shoulder arthroplasty: an experimental study2019In: Acta Radiologica, ISSN 0284-1851, E-ISSN 1600-0455Article in journal (Refereed)
    Abstract [en]

    Background: Radiostereometric analysis (RSA) is the gold standard to measure early implant migration which is a predictive factor for implant survival. Purpose: To validate an alternative computed tomography (CT) technique to measure implant migration in shoulder arthroplasty. Material and Methods: A cadaver proximal humerus and a scapula, which had tantalum beads incorporated within them, were prepared to accept a short-stemmed humeral component and a two-pegged glenoid component of a commercial total shoulder arthroplasty (TSA) system. A five degree of freedom micrometer and goniometer equipped rig was used to translate and rotate the implant components relative to the respective bone to predetermined positions. Double CT examinations were performed for each position and CT motion analysis software (CTMA) was used to assess these movements. The accuracy and precision of the software was estimated using the rig’s micrometers and goniometers as the gold standard. The technique’s effective dose was also assessed. Results: The accuracy was in the range of 0.07–0.23 mm in translation and 0.22–0.71° in rotation. The precision was in the range of 0.08–0.15 mm in translation and 0.23–0.54° in rotation. The mean effective dose for the CT scans was calculated to be 0.27 mSv. Conclusion: In this experimental setting, accuracy, precision, and effective dose of the CTMA technique were found to be comparable to that of RSA. Therefore, we believe clinical studies are warranted to determine if CTMA is a suitable alternative to traditional RSA for migration measurements in TSA.

  • 40.
    Broman, David
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Software and Computer systems, SCS.
    A vision of miking: Interactive programmatic modeling, sound language composition, and self-learning compilation2019In: SLE 2019 - Proceedings of the 12th ACM SIGPLAN International Conference on Software Language Engineering, co-located with SPLASH 2019, Association for Computing Machinery, Inc , 2019, p. 55-60Conference paper (Refereed)
    Abstract [en]

    This paper introduces a vision of Miking, a language framework for constructing efficient and sound language environments and compilers for domain-specific modeling languages. In particular, this language framework has three key objectives: (i) to automatically generate interactive programmatic modeling environments, (ii) to guarantee sound compositions of language fragments that enable both rapid and safe domain-specific language development, (iii) to include first-class support for self-learning compilation, targeting heterogeneous execution platforms. The initiative is motivated in the domain of mathematical modeling languages. Specifically, two different example domains are discussed: (i) modeling, simulation, and verification of cyber-physical systems, and (ii) domain-specific differentiable probabilistic programming. The paper describes the main objectives of the vision, as well as concrete research challenges and research directions.

  • 41. Brown, N.
    et al.
    Nash, R.
    Gibb, G.
    Prodan, B.
    Kontak, M.
    Olshevsky, V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Chien, Wei Der
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    The Role of Interactive Super-Computing in Using HPC for Urgent Decision Making2019In: 34th International Conference on High Performance Computing, ISC High Performance 2019, Springer , 2019, p. 528-540Conference paper (Refereed)
    Abstract [en]

    Technological advances are creating exciting new opportunities that have the potential to move HPC well beyond traditional computational workloads. In this paper we focus on the potential for HPC to be instrumental in responding to disasters such as wildfires, hurricanes, extreme flooding, earthquakes, tsunamis, winter weather conditions, and accidents. Driven by the VESTEC EU funded H2020 project, our research looks to prove HPC as a tool not only capable of simulating disasters once they have happened, but also one which is able to operate in a responsive mode, supporting disaster response teams making urgent decisions in real-time. Whilst this has the potential to revolutionise disaster response, it requires the ability to drive HPC interactively, both from the user’s perspective and also based upon the arrival of data. As such interactivity is a critical component in enabling HPC to be exploited in the role of supporting disaster response teams so that urgent decision makers can make the correct decision first time, every time.

  • 42.
    Bruce, Neil J.
    et al.
    Heidelberg Inst Theoret Studies, Mol & Cellular Modeling Grp, Schloss Heidelberg, Germany..
    Narzi, Daniele
    Ecole Polytech Fed Lausanne, Inst Sci & Ingn Chim, CH-1015 Lausanne, Switzerland..
    Trpevski, Daniel
    KTH, Centres, Science for Life Laboratory, SciLifeLab. KTH, School of Electrical Engineering and Computer Science (EECS).
    van Keulen, Siri C.
    Ecole Polytech Fed Lausanne, Inst Sci & Ingn Chim, CH-1015 Lausanne, Switzerland.;Stanford Univ, Dept Comp Sci, Stanford, CA 94305 USA..
    Nair, Anu G.
    Univ Zurich, Inst Mol Life Sci, Zurich, Switzerland..
    Rothlisberger, Ursula
    Ecole Polytech Fed Lausanne, Inst Sci & Ingn Chim, CH-1015 Lausanne, Switzerland..
    Wade, Rebecca C.
    Heidelberg Inst Theoret Studies, Mol & Cellular Modeling Grp, Schloss Heidelberg, Germany.;Heidelberg Univ, Ctr Mol Biol ZMBH, DKFZ ZMBH Alliance, Heidelberg, Germany.;Heidelberg Univ, Interdisciplinary Ctr Sci Comp IWR, Heidelberg, Germany..
    Carloni, Paolo
    Rhein Westfal TH Aachen, Dept Phys, Aachen, Germany.;Rhein Westfal TH Aachen, Dept Neurobiol, Aachen, Germany.;Forschungszentrum Julich, Inst Neurosci & Med INM 11, Julich, Germany.;Forschungszentrum Julich, Inst Neurosci & Med INM 9, Julich, Germany.;Forschungszentrum Julich, Inst Adv Simulat IAS 5, Julich, Germany..
    Hällgren Kotaleski, Jeanette
    KTH, Centres, Science for Life Laboratory, SciLifeLab. KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Computational Science and Technology (CST).
    Regulation of adenylyl cyclase 5 in striatal neurons confers the ability to detect coincident neuromodulatory signals2019In: PloS Computational Biology, ISSN 1553-734X, E-ISSN 1553-7358, Vol. 15, no 10, article id e1007382Article in journal (Refereed)
    Abstract [en]

    Author summary Adenylyl cyclases (ACs) are enzymes that can translate extracellular signals into the intracellular molecule cAMP, which is thus a 2nd messenger of extracellular events. The brain expresses nine membrane-bound AC variants, and AC5 is the dominant form in the striatum. The striatum is the input stage of the basal ganglia, a brain structure involved in reward learning, i.e. the learning of behaviors that lead to rewarding stimuli (such as food, water, sugar, etc). During reward learning, cAMP production is crucial for strengthening the synapses from cortical neurons onto the striatal principal neurons, and its formation is dependent on several neuromodulatory systems such as dopamine and acetylcholine. It is, however, not understood how AC5 is activated by transient (subsecond) changes in the neuromodulatory signals. Here we combine several computational tools, from molecular dynamics and Brownian dynamics simulations to bioinformatics approaches, to inform and constrain a kinetic model of the AC5-dependent signaling system. We use this model to show how the specific molecular properties of AC5 can detect particular combinations of co-occuring transient changes in the neuromodulatory signals which thus result in a supralinear/synergistic cAMP production. Our results also provide insights into the computational capabilities of the different AC isoforms. Long-term potentiation and depression of synaptic activity in response to stimuli is a key factor in reinforcement learning. Strengthening of the corticostriatal synapses depends on the second messenger cAMP, whose synthesis is catalysed by the enzyme adenylyl cyclase 5 (AC5), which is itself regulated by the stimulatory G alpha(olf) and inhibitory G alpha(i) proteins. AC isoforms have been suggested to act as coincidence detectors, promoting cellular responses only when convergent regulatory signals occur close in time. However, the mechanism for this is currently unclear, and seems to lie in their diverse regulation patterns. Despite attempts to isolate the ternary complex, it is not known if G alpha(olf) and G alpha(i) can bind to AC5 simultaneously, nor what activity the complex would have. Using protein structure-based molecular dynamics simulations, we show that this complex is stable and inactive. These simulations, along with Brownian dynamics simulations to estimate protein association rates constants, constrain a kinetic model that shows that the presence of this ternary inactive complex is crucial for AC5's ability to detect coincident signals, producing a synergistic increase in cAMP. These results reveal some of the prerequisites for corticostriatal synaptic plasticity, and explain recent experimental data on cAMP concentrations following receptor activation. Moreover, they provide insights into the regulatory mechanisms that control signal processing by different AC isoforms.

  • 43. Buss, S.
    et al.
    Itsykson, D.
    Knop, A.
    Sokolov, Dmitry
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Reordering rule makes OBDD proof systems stronger2018In: Leibniz International Proceedings in Informatics, LIPIcs, Schloss Dagstuhl- Leibniz-Zentrum fur Informatik GmbH, Dagstuhl Publishing , 2018, p. 1-24Conference paper (Refereed)
    Abstract [en]

    Atserias, Kolaitis, and Vardi showed that the proof system of Ordered Binary Decision Diagrams with conjunction and weakening, OBDD(∧, weakening), simulates CP∗ (Cutting Planes with unary coefficients). We show that OBDD(∧, weakening) can give exponentially shorter proofs than dag-like cutting planes. This is proved by showing that the Clique-Coloring tautologies have polynomial size proofs in the OBDD(∧, weakening) system. The reordering rule allows changing the variable order for OBDDs. We show that OBDD (∧, weakening, reordering) is strictly stronger than OBDD(∧, weakening). This is proved using the Clique-Coloring tautologies, and by transforming tautologies using coded permutations and orification. We also give CNF formulas which have polynomial size OBDD(∧) proofs but require superpolynomial (actually, quasipolynomial size) resolution proofs, and thus we partially resolve an open question proposed by Groote and Zantema. Applying dag-like and tree-like lifting techniques to the mentioned results, we completely analyze which of the systems among CP∗, OBDD(∧), OBDD(∧, reordering), OBDD(∧, weakening) and OBDD (∧, weakening, reordering) polynomially simulate each other. For dag-like proof systems, some of our separations are quasipolynomial and some are exponential; for tree-like systems, all of our separations are exponential.

  • 44.
    Bälter, Olle
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Media Technology and Interaction Design, MID.
    Riese, Emma
    KTH, School of Electrical Engineering and Computer Science (EECS), Theoretical Computer Science, TCS.
    Enoksson, Fredrik
    KTH, School of Industrial Engineering and Management (ITM), Learning.
    Hedin, Björn
    KTH, School of Electrical Engineering and Computer Science (EECS), Media Technology and Interaction Design, MID.
    Baltatzis, Alexander
    KTH, School of Electrical Engineering and Computer Science (EECS), Media Technology and Interaction Design, MID.
    Josefsson, Pernilla
    KTH, School of Electrical Engineering and Computer Science (EECS), Media Technology and Interaction Design, MID.
    The Challenge of Identifying the Importance of Drivers and Barriers for Implementation of Technology Enhanced Learning2018In: The 11th Pan-Hellenic and International Conference: ICT in Education, 2018, p. 283-290Conference paper (Refereed)
    Abstract [en]

    The potential of technology enhanced learning (TEL) can have both pedagogical and administrative benefits. In a previous study, we investigated the drivers and barriers for TEL in higher education using Force Field Analysis (FFA). In this follow-up study, we collected new data through a questionnaire to a group of pedagogical developers and at a presentation at a university internal conference for teachers. A Kruskal Wallis test was carried out to test if the groups filling out questionnaire deviated from each other in their ranking. A comparison was also done to the scores in the previous study. As a result of this triangulation, deviations were found between ratings for seven of the 20 identified forces. While the assessments of strengths in FFA is debated, we argue that each group’s view is an important component to understand the situation, and triangulation of data is helpful in understanding the different views.

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  • 45.
    Bälter, Olle
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Media Technology and Interaction Design, MID.
    Riese, Emma
    KTH, School of Electrical Engineering and Computer Science (EECS), Theoretical Computer Science, TCS.
    Viberg, Olga
    KTH, School of Electrical Engineering and Computer Science (EECS), Media Technology and Interaction Design, MID.
    Effective Feedback for Faster Learning2019In: KTH SoTL 2019, Stockholm: KTH Royal Institute of Technology, 2019Conference paper (Refereed)
    Abstract [en]

    Background and purpose The Open Learning Initiative (OLI) at Carnegie Mellon University and Stanford University showed already in 2008 (Lovett, Meyer & Thille) that by using the OLI methodology, teaching and learning time could be reduced with 50% with maintained results. One key in this methodology is to use online questions with answer-depending feedback. In this workshop we will work with you to formulate OLIinspired questions for your course. Work done/work in progress We have previously worked with online quizzes in several forms (Bälter, Enström & Klingenberg, 2013) and analyzed learning data from OLI courses (Bälter, Zimmaro & Thille, 2018). The online learning material where the questions and feedback is embedded is in campus courses used in flipped classroom settings. In 2017 we ran a pilot of preparatory course in programming based on a Stanford course with OLI methodology in the OpenEdX environment. During the fall semester 2018 questions with answer-depending feedback was added to the course material in an online introductory programming course given in Canvas at KTH. Results/observations/lessons learned While a full implementation of the entire OLI methodology requires infrastructure that is not in place at KTH yet (event handler, analytic engine), the actual learning for the students takes place in the interaction with the questions and their feedback and this part can already be implemented in Canvas at KTH. Take-home message Well-formulated questions with forward focused feedback can dramatically speed up both teaching and 1 2 1 1 2 Page 25 KTH SoTL 2019 (A-K) learning. This workshop brings that speed to your course with practical exercises based on your own course.

  • 46.
    Cabrera Arteaga, Javier
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Monperrus, Martin
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Theoretical Computer Science, TCS.
    Baudry, Benoit
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Software and Computer systems, SCS.
    Scalable comparison of JavaScript V8 bytecode traces2019Conference paper (Refereed)
    Abstract [en]

    The comparison and alignment of runtime traces are essential, e.g., for semantic analysis or debugging. However, naive sequence alignment algorithms cannot address the needs of the modern web: (i) the bytecode generation process of V8 is not deterministic; (ii) bytecode traces are large.

    We present STRAC, a scalable and extensible tool tailored to compare bytecode traces generated by the V8 JavaScript engine. Given two V8 bytecode traces and a distance function between trace events, STRAC computes and provides the best alignment. The key insight is to split access between memory and disk. STRAC can identify semantically equivalent web pages and is capable of processing huge V8 bytecode traces whose order of magnitude matches today's web like https://2019.splashcon.org, which generates approx. 150k of V8 bytecode instructions.

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  • 47.
    Canat, Mert
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Català, Nuria
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Jourkovski, Alexander
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Petrov, Svetlomir
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Wellme, Martin
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Lagerström, Robert
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Network and Systems Engineering.
    Enterprise Architecture and Agile Development: Friends or Foes?2018Conference paper (Refereed)
    Abstract [en]

    Nowadays, both agile development and enterprise architecture are often employed in large organizations. However there is still some confusion if these can and should be used together, and there is not much research about the possible interplay. The aim of this study is to bring new knowledge to the field of enterprise architecture and its relation to agile development. Twelve qualitative interviews with professionals in different roles, such as developers and architects, have been carried out. The participants belong to five different companies and the information obtained from them has been used to compare opinions and stated challenges regarding agile and EA. We found that some common opinions among the interviewees are; 1) agile development and enterprise architecture can be combined, 2) there are clear communication problems among architects, different teams, and project owners, and 3) there is a lack of system and application reusability. © 2018 IEEE.

  • 48.
    Castañeda Lozano, Roberto
    KTH, School of Electrical Engineering and Computer Science (EECS), Software and Computer systems, SCS. RISE SICS (Swedish Institute of Computer Science).
    Constraint-Based Register Allocation and Instruction Scheduling2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Register allocation (mapping variables to processor registers or memory) and instruction scheduling (reordering instructions to improve latency or throughput) are central compiler problems. This dissertation proposes a combinatorial optimization approach to these problems that delivers optimal solutions according to a model, captures trade-offs between conflicting decisions, accommodates processor-specific features, and handles different optimization criteria.

    The use of constraint programming and a novel program representation enables a compact model of register allocation and instruction scheduling. The model captures the complete set of global register allocation subproblems (spilling, assignment, live range splitting, coalescing, load-store optimization, multi-allocation, register packing, and rematerialization) as well as additional subproblems that handle processor-specific features beyond the usual scope of conventional compilers.

    The approach is implemented in Unison, an open-source tool used in industry and research that complements the state-of-the-art LLVM compiler. Unison applies general and problem-specific constraint solving methods to scale to medium-sized functions, solving functions of up to 647 instructions optimally and improving functions of up to 874 instructions. The approach is evaluated experimentally using different processors (Hexagon, ARM and MIPS), benchmark suites (MediaBench and SPEC CPU2006), and optimization criteria (speed and code size reduction). The results show that Unison generates code of slightly to significantly better quality than LLVM, depending on the characteristics of the targeted processor (1% to 9.3% mean estimated speedup; 0.8% to 3.9% mean code size reduction). Additional experiments for Hexagon show that its estimated speedup has a strong monotonic relationship to the actual execution speedup, resulting in a mean speedup of 5.4% across MediaBench applications.

    The approach contributed by this dissertation is the first of its kind that is practical (it captures the complete set of subproblems, scales to medium-sized functions, and generates executable code) and effective (it generates better code than the LLVM compiler, fulfilling the promise of combinatorial optimization). It can be applied to trade compilation time for code quality beyond the usual optimization levels, explore and exploit processor-specific features, and identify improvement opportunities in conventional compilers.

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  • 49.
    Castañeda Lozano, Roberto
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Software and Computer systems, SCS. RISE SICS, Electrum 229, Kista, 164 40, Sweden.
    Carlsson, M.
    Hjort Blindell, Gabriel
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Software and Computer systems, SCS.
    Schulte, Christian
    KTH, School of Electrical Engineering and Computer Science (EECS), Computer Science, Software and Computer systems, SCS. RISE SICS, Electrum 229, Kista, 164 40, Sweden.
    Combinatorial register allocation and instruction scheduling2019In: ACM Transactions on Programming Languages and Systems, ISSN 0164-0925, E-ISSN 1558-4593, Vol. 41, no 3, article id 17Article in journal (Refereed)
    Abstract [en]

    This article introduces a combinatorial optimization approach to register allocation and instruction scheduling, two central compiler problems. Combinatorial optimization has the potential to solve these problems optimally and to exploit processor-specific features readily. Our approach is the first to leverage this potential in practice: it captures the complete set of program transformations used in state-of-the-art compilers, scales to medium-sized functions of up to 1,000 instructions, and generates executable code. This level of practicality is reached by using constraint programming, a particularly suitable combinatorial optimization technique. Unison, the implementation of our approach, is open source, used in industry, and integrated with the LLVM toolchain. An extensive evaluation confirms that Unison generates better code than LLVM while scaling to medium-sized functions. The evaluation uses systematically selected benchmarks from MediaBench and SPEC CPU2006 and different processor architectures (Hexagon, ARM, MIPS). Mean estimated speedup ranges from 1.1% to 10% and mean code size reduction ranges from 1.3% to 3.8% for the different architectures. A significant part of this improvement is due to the integrated nature of the approach. Executing the generated code on Hexagon confirms that the estimated speedup results in actual speedup. Given a fixed time limit, Unison solves optimally functions of up to 946 instructions, nearly an order of magnitude larger than previous approaches. The results show that our combinatorial approach can be applied in practice to trade compilation time for code quality beyond the usual compiler optimization levels, identify improvement opportunities in heuristic algorithms, and fully exploit processor-specific features.

  • 50.
    Castañeda Lozano, Roberto
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Software and Computer systems, SCS. RISE SICS (Swedish Institute of Computer Science).
    Schulte, Christian
    KTH, School of Electrical Engineering and Computer Science (EECS), Software and Computer systems, SCS.
    Survey on Combinatorial Register Allocation and Instruction Scheduling2018In: ACM Computing Surveys, ISSN 0360-0300, E-ISSN 1557-7341Article in journal (Refereed)
    Abstract [en]

    Register allocation (mapping variables to processor registers or memory) and instruction scheduling (reordering instructions to increase instruction-level parallelism) are essential tasks for generating efficient assembly code in a compiler. In the last three decades, combinatorial optimization has emerged as an alternative to traditional, heuristic algorithms for these two tasks. Combinatorial optimization approaches can deliver optimal solutions according to a model, can precisely capture trade-offs between conflicting decisions, and are more flexible at the expense of increased compilation time.

    This paper provides an exhaustive literature review and a classification of combinatorial optimization approaches to register allocation and instruction scheduling, with a focus on the techniques that are most applied in this context: integer programming, constraint programming, partitioned Boolean quadratic programming, and enumeration. Researchers in compilers and combinatorial optimization can benefit from identifying developments, trends, and challenges in the area; compiler practitioners may discern opportunities and grasp the potential benefit of applying combinatorial optimization.

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