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  • 251.
    Elmgren Frykberg, Gunilla
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Rehabilitation Medicine.
    Thierfelder, Tomas
    Åberg, Anna Cristina
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Geriatrics.
    Halvorsen, Kjartan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Borg, Jörgen
    Hirschfeld, Helga
    Impact of stroke on anterior–posterior force generation prior to seat-off during sit-to-walk2012In: Gait & Posture, ISSN 0966-6362, E-ISSN 1879-2219, Vol. 35, no 1, p. 56-60Article in journal (Refereed)
  • 252.
    Elmgren Frykberg, Gunilla
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Rehabilitation Medicine.
    Åberg, Anna Cristina
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Geriatrics.
    Halvorsen, Kjartan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Borg, Jörgen
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Rehabilitation Medicine.
    Hirschfeld, Helga
    Karolinska Institutet, Department of Neurobiology, Care Sciences and Society, Division of Physiotherapy.
    Temporal coordination of the sit-to-walk task in subjects with stroke and in controls2009In: Archives of Physical Medicine and Rehabilitation, ISSN 0003-9993, E-ISSN 1532-821X, Vol. 90, no 6, p. 1009-1017Article in journal (Refereed)
    Abstract [en]

    Objectives: To explore events and describe phases for temporal coordination of the sit-to-walk (STW) task, within a semistandardized set up, in subjects with stroke and matched controls. In addition, to assess variability of STW phase duration and to compare the relative duration of STW phases between the 2 groups.

    Design: Cross-sectional.

    Setting: Research laboratory.

    Participants: A convenience sample of persons with hemiparesis (n=10; age 50–67y), more than 6 months after stroke and 10 controls matched for sex, age, height, and body mass index.

    Interventions: Not applicable.

    Main Outcome Measures: Relative duration of STW phases, SE of measurement in percentage of the mean, and intraclass correlation coefficients (ICCs).

    Results: Four STW phases were defined: rise preparation, transition, primary gait initiation, and secondary gait initiation. The subjects with stroke needed 54% more time to complete the STW task than the controls did. ICCs ranged from .38 to .66 and .22 to .57 in the stroke and control groups, respectively. SEs of measurement in percentage of the mean values were high, particularly in the transition phase: 54.1% (stroke) and 50.4% (controls). The generalized linear model demonstrated that the relative duration of the transition phase was significantly longer in the stroke group.

    Conclusions: The present results extend existing knowledge by presenting 4 new phases of temporal coordination of STW, within a semistandardized set-up, in persons with stroke and in controls. The high degree of variability regarding relative STW phase duration was probably a result of both the semistandardized set up and biological variability. The significant difference in the transition phase across the 2 groups requires further study.

  • 253.
    Eriksson Crommert, Martin
    et al.
    Univ Orebro, Fac Med & Hlth, SE-70182 Orebro, Sweden.;Swedish Sch Sport & Hlth Sci GIH, Stockholm, Sweden..
    Halvorsen, Kjartan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control. KTH Royal Inst Technol, Sch Technol & Hlth, Stockholm, Sweden..
    Ekblom, Maria M.
    Swedish Sch Sport & Hlth Sci GIH, Stockholm, Sweden.;Karolinska Inst, Dept Neurosci, Stockholm, Sweden..
    Trunk Muscle Activation at the Initiation and Braking of Bilateral Shoulder Flexion Movements of Different Amplitudes2015In: PLOS ONE, E-ISSN 1932-6203, Vol. 10, no 11, article id e0141777Article in journal (Refereed)
    Abstract [en]

    The aim of this study was to investigate if trunk muscle activation patterns during rapid bilateral shoulder flexions are affected by movement amplitude. Eleven healthy males performed shoulder flexion movements starting from a position with arms along sides (0 degrees) to either 45 degrees, 90 degrees or 180 degrees. EMG was measured bilaterally from transversus abdominis (TrA), obliquus internus (OI) with intra-muscular electrodes, and from rectus abdominis (RA), erector spinae (ES) and deltoideus with surface electrodes. 3D kinematics was recorded and inverse dynamics was used to calculate the reactive linear forces and torque about the shoulders and the linear and angular impulses. The sequencing of trunk muscle onsets at the initiation of arm movements was the same across movement amplitudes with ES as the first muscle activated, followed by TrA, RA and OI. All arm movements induced a flexion angular impulse about the shoulders during acceleration that was reversed during deceleration. Increased movement amplitude led to shortened onset latencies of the abdominal muscles and increased level of activation in TrA and ES. The activation magnitude of TrA was similar in acceleration and deceleration where the other muscles were specific to acceleration or deceleration. The findings show that arm movements need to be standardized when used as a method to evaluate trunk muscle activation patterns and that inclusion of the deceleration of the arms in the analysis allow the study of the relationship between trunk muscle activation and direction of perturbing torque during one and the same arm movement.

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  • 254.
    Evestedt, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Parameter and state estimation using audio and video signals2005Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The complexity of industrial systems and the mathematical models to describe them increases. In many cases point sensors are no longer sufficient to provide controllers and monitoring instruments with the information necessary for operation. The need for other types of information, such as audio and video, has grown. Suitable applications range in a broad spectrum from microelectromechanical systems and bio-medical engineering to papermaking and steel production.

    This thesis is divided into five parts. First a general introduction to the field of vision-based and sound-based monitoring and control is given. A description of the target application in the steel industry is included.

    In the second part, a recursive parameter estimation algorithm that does not diverge under lack of excitation is studied. The focus is on the stationary properties of the algorithm and the corresponding Riccati equation.

    The third part compares the parameter estimation algorithm to a number of well-known estimation techniques, such as the Normalized Least Mean Squares and the Kalman filter. The benchmark for the comparison is an acoustic echo cancellation application. When the input is insufficiently exciting, the studied method performs best of all considered schemes.

    The fourth part of the thesis concerns an experimental application of vision-based estimation. A water model is used to simulate the behaviour of the steel bath in a Linz–Donawitz steel converter. The water model is captured from the side by a video camera. The images together with a nonlinear model is used to estimate important process parameters, describing the heat and mass transport in the process. The estimation results are compared to those obtained by previous researchers and the suggested approach is shown to decrease the estimation error variance by 50%.

    The complexity of the parameter estimation procedure by means of optimization makes the computation time large. In the final part, the time consumption of the estimation is decreased by using a smaller number of data points. Three ways of choosing the sampling points are considered. An observer-based approach decreases the computation time significantly, with an acceptable loss of accuracy of the estimates.

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  • 255.
    Evestedt, Magnus
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Parameter and State Estimation with Information-rich Signals2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The complexity of industrial systems and the mathematical models to describe them increases. In many cases, point sensors are no longer sufficient to provide controllers and monitoring instruments with the information necessary for operation. The need for other types of information, such as audio and video, has grown. These are examples of information-rich signals for which suitable applications range in a broad spectrum from micro-electromechanical systems and bio-medical engineering to paper making and steel production.

    Recursive parameter estimation algorithms are employed to identify parameters in a mathematical model from measurements of input and output signals. For accurate parameter estimation, the input signal must be persistently exciting, i.e. such that important features of the modelled system are reflected in the output over a sufficient period of time.

    The Stenlund-Gustafsson (SG) algorithm, a Kalman filter based method for recursive parameter estimation in linear regression models, that does not diverge under lack of excitation, is studied. The stationary properties of the algorithm and the corresponding Riccati equation are formulated in terms of the excitation space spanned by the regressor vectors.

    Furthermore, it is shown that the Riccati equation of the studied algorithm can be solved element-wise. Convergence estimates for the elements of the solution to the Riccati equation are provided, directly relating convergence rate to the signal-to-noise ratio in the regression model. An element-wise form of the parameter update equation is also given, where the connection to specific elements of the solution to the Riccati equation is apparent.

    The SG-algorithm is employed for two applications with audio signals. One is in an acoustic echo cancellation setting where its performance is shown to match that of other well-known estimation techniques, such as the normalized least mean squares and the Kalman filter. When the input is not sufficiently exciting, the studied method performs best of all considered schemes.

    The other application is the Linz-Donawitz (LD) steel converter. The converter consists of a vessel with molten metal and foam is produced to facilitate chemical reactions. A common problem, usually referred to as slopping, arises when the foam rises above the limits of the vessel and overflows. A warning system is designed, based on the SG-algorithm and change detection methods, to give alarms before slopping occurs. A black-box model relates different sensor values of which one is the microphone signal picked up in the area above the converter. The system detected slopping correctly in 80% of the blows in field studies at SSAB Oxelösund.

    A practical example of a vision-based system is provided by cavity form estimation in a water model of the steel bath. The water model is captured from the side by a video camera. The images together with a non-linear model are used to estimate important process parameters, related to the heat and mass transport in the LD-converter.

    List of papers
    1. Stationary Behavior of an Anti-windup Scheme for Recursive Parameter Estimation under Lack of Excitation
    Open this publication in new window or tab >>Stationary Behavior of an Anti-windup Scheme for Recursive Parameter Estimation under Lack of Excitation
    2006 In: Automatica, Vol. 42, no 1, p. 151-157Article in journal (Refereed) Published
    Identifiers
    urn:nbn:se:uu:diva-96461 (URN)
    Available from: 2007-11-19 Created: 2007-11-19Bibliographically approved
    2. Elementwise Decoupling and Convergence of the Riccati Equation in the SG-algorithm
    Open this publication in new window or tab >>Elementwise Decoupling and Convergence of the Riccati Equation in the SG-algorithm
    Article in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-96462 (URN)
    Available from: 2007-11-19 Created: 2007-11-19Bibliographically approved
    3. Recursive Parameter Estimation by Means of the SG-algorithm
    Open this publication in new window or tab >>Recursive Parameter Estimation by Means of the SG-algorithm
    Article in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-96463 (URN)
    Available from: 2007-11-19 Created: 2007-11-19Bibliographically approved
    4. Windup properties of recursive parameter estimation algorithms in acoustic echo cancellation
    Open this publication in new window or tab >>Windup properties of recursive parameter estimation algorithms in acoustic echo cancellation
    2008 (English)In: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 16, no 11, p. 1372-1378Article in journal (Refereed) Published
    National Category
    Signal Processing
    Identifiers
    urn:nbn:se:uu:diva-96464 (URN)10.1016/j.conengprac.2008.03.006 (DOI)000258989600012 ()
    Available from: 2008-05-05 Created: 2007-11-19 Last updated: 2018-08-17Bibliographically approved
    5. Model-based Slopping Warning in the LD Steel Converter
    Open this publication in new window or tab >>Model-based Slopping Warning in the LD Steel Converter
    Article in journal (Refereed) Submitted
    Identifiers
    urn:nbn:se:uu:diva-96465 (URN)
    Available from: 2007-11-19 Created: 2007-11-19Bibliographically approved
    6. Cavity Shape Dynamical Modelling and Estimation in a Water Model of the Steel Converter Process
    Open this publication in new window or tab >>Cavity Shape Dynamical Modelling and Estimation in a Water Model of the Steel Converter Process
    2007 (English)In: Journal of the Japanese Society for Experimental Mechanics, ISSN 1346-4930, Vol. 7, p. s93-s98Article in journal (Refereed) Published
    National Category
    Computational Mathematics
    Identifiers
    urn:nbn:se:uu:diva-96466 (URN)
    Available from: 2007-11-19 Created: 2007-11-19 Last updated: 2011-03-01Bibliographically approved
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  • 256.
    Evestedt, Magnus
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. Systemteknik.
    Medvedev, Alexander
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. Systemteknik.
    Cavity depth and diameter estimation in the converter process water model2004In: Association for Iron & Steel Technology Conference Proceedings, 2004Conference paper (Other scientific)
  • 257.
    Evestedt, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Medvedev, Alexander
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Cavity Shape Dynamical Modelling and Estimation in a Water Model of the Steel Converter Process2007In: Journal of the Japanese Society for Experimental Mechanics, ISSN 1346-4930, Vol. 7, p. s93-s98Article in journal (Refereed)
  • 258.
    Evestedt, Magnus
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. systemteknik.
    Medvedev, Alexander
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Cavity shape dynamical modelling and estimation in the converter2006In: Proceedings of International symposium on advanced °uid/solid science and technology in experimental mechanics, 2006Conference paper (Refereed)
  • 259.
    Evestedt, Magnus
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. Systemteknik.
    Medvedev, Alexander
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. Systemteknik.
    Gas jet impinging on liquid surface: Cavity shape modelling and video based estimation2005In: Proceedings of the 16th IFAC World Congress, 2005Conference paper (Refereed)
  • 260.
    Evestedt, Magnus
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Medvedev, Alexander
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Gas jet impinging on liquid surface: Cavity shape modelling and video-based estimation2005In: in IFAC World Congress, 2005Conference paper (Refereed)
  • 261.
    Evestedt, Magnus
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Medvedev, Alexander
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Model-based cavity shape estimation in a gas-liquid system with nonuniform image sampling2006In: Proceedings of the 1st international conference on computer vision theory and applications, 2006Conference paper (Refereed)
  • 262.
    Evestedt, Magnus
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. systemteknik.
    Medvedev, Alexander
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. systemteknik.
    Model-based slopping monitoring by change detection2006In: Proceedings of IEEE Conference on Control Applications,, 2006Conference paper (Refereed)
  • 263.
    Evestedt, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Medvedev, Alexander
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Model-based Slopping Warning in the LD Steel Converter Process2009In: Journal of Process Control, ISSN 0959-1524, E-ISSN 1873-2771, Vol. 19, no 6, p. 1000-1010Article in journal (Refereed)
    Abstract [en]

    The most prevalent steel-making process is the basic oxygen steel-making (BOS) process. Problems arise when the layer of foaming slag created on the surface of the molten metal exceeds the height of the vessel and overflows, causing metal loss, process disruption and environmental pollution. This phenomenon is commonly referred to as slopping. A method for automatic slopping detection is described in this contribution. The sound signal from a microphone located in the off-gas funnel is processed to obtain an estimate of the slag level in the converter. A model describing the relationship between off-gas flow rate, pressure and the slag level estimate is updated recursively in time. The output error is fed to a change detector yielding a warning system with three alarm levels indicating the persistence of slopping symptoms. The algorithm was tested on data from 100 heats at SSAB Oxelosund. Slopping was correctly detected in 80% of the blows.

  • 264.
    Evestedt, Magnus
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. Systemteknik.
    Medvedev, Alexander
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. Systemteknik.
    Stationary behavior of an anti-windup scheme for recursive parameter estimation under lack of excitation2006In: Automatica, Vol. 42, no 1, p. 151-157Article in journal (Refereed)
  • 265.
    Evestedt, Magnus
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. Systemteknik.
    Medvedev, Alexander
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. Systemteknik.
    Stationary behaviour of an anti-windup scheme for recursive parameter estimation under lack of excitation2005In: Proceedings of the 16th IFAC World Congress, 2005Conference paper (Refereed)
  • 266.
    Evestedt, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Medvedev, Alexander
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Wigren, Torbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Comparative study of three recursive parameter estimation algorithms with application to acoustic echo cancellation2004In: Proc. Reglermöte, 2004Conference paper (Other academic)
  • 267.
    Evestedt, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Medvedev, Alexander
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Wigren, Torbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Windup properties of recursive parameter estimation algorithms in acoustic echo cancellation2008In: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 16, no 11, p. 1372-1378Article in journal (Refereed)
  • 268.
    Evestedt, Magnus
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Medvedev, Alexander
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Wigren, Torbjörn
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Windup properties of recursive parameter estimation algorithms in acoustic echo cancellation2005Conference paper (Refereed)
  • 269. Falck, Tillmann
    et al.
    Dreesen, Philippe
    De Brabanter, Kris
    Pelckmans, Kristiaan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    De Moor, Bart
    Suykens, Johan A. K.
    Least-Squares Support Vector Machines for the identification of Wiener-Hammerstein systems2012In: Control Engineering Practice, ISSN 0967-0661, E-ISSN 1873-6939, Vol. 20, no 11, p. 1165-1174Article in journal (Refereed)
    Abstract [en]

    This paper considers the identification of Wiener-Hammerstein systems using Least-Squares Support Vector Machines based models. The power of fully black-box NARX-type models is evaluated and compared with models incorporating information about the structure of the systems. For the NARX models it is shown how to extend the kernel-based estimator to large data sets. For the structured model the emphasis is on preserving the convexity of the estimation problem through a suitable relaxation of the original problem. To develop an empirical understanding of the implications of the different model design choices, all considered models are compared on an artificial system under a number of different experimental conditions. The obtained results are then validated on the Wiener-Hammerstein benchmark data set and the final models are presented. It is illustrated that black-box models are a suitable technique for the identification of Wiener-Hammerstein systems. The incorporation of structural information results in significant improvements in modeling performance.

  • 270. Fan, H
    et al.
    Söderström, T
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. AUTOMATIC CONTROL.
    Parameter estimation of continuous-time AR processes using integrated sampling1997In: Proc IEEE Conference on Decision and Control, 1997Conference paper (Refereed)
  • 271. Fan, H
    et al.
    Söderström, T
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. AUTOMATIC CONTROL.
    Mossberg, M
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. AUTOMATIC CONTROL.
    Carlsson, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. AUTOMATIC CONTROL.
    Zou, Y
    Continuous-time AR process parameter estimation from discrete-time data1998In: IEEE International Conference on Acoustics, Speech and Signal Processing: ICASSP '98, 1998Conference paper (Refereed)
  • 272. Fan, H
    et al.
    Söderström, T
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. AUTOMATIC CONTROL.
    Mossberg, M
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. AUTOMATIC CONTROL.
    Carlsson, B
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. AUTOMATIC CONTROL.
    Zou, Y
    Estimation of continuous-time AR process parameters from discrete-time data1999In: IEEE Transactions on Signal Processing, Vol. 47, no 5, p. 1232-1244Article in journal (Refereed)
  • 273. Fan, H
    et al.
    Söderström, T
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. AUTOMATIC CONTROL.
    Zou, Y
    Continuous-time AR process parameter estimation in presence of additive white noise1999In: IEEE Transactions on Signal Processing, Vol. 47, no 12, p. 3392-3398Article in journal (Refereed)
    Abstract [en]

    Most existing work so far on continuous-time AR (CAR) parameter estimation concentrates on the noiseless measurement case. When measurement noise is present, our previous results on CAR parameter estimation need to he revised accordingly. Here we model th

  • 274.
    Fatima, Ghania
    et al.
    Indian Inst Technol Delhi, CARE, New Delhi 110016, India..
    Babu, Prabhu
    Indian Inst Technol Delhi, CARE, New Delhi 110016, India..
    Stoica, Petre
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control.
    Covariance Matrix Estimation Under Positivity Constraints With Application to Portfolio Selection2022In: IEEE Signal Processing Letters, ISSN 1070-9908, E-ISSN 1558-2361, Vol. 29, p. 2487-2491Article in journal (Refereed)
    Abstract [en]

    In this letter we propose a new method to estimate the covariance matrix under the constraint that its off-diagonal elements are non-negative, which has applications to portfolio selection in finance. We incorporate the non-negativity constraint in the maximum likelihood (ML) estimation problem and propose an algorithm based on the block coordinate descent method to solve for the ML estimate. To study the effectiveness of the proposed algorithm, we perform numerical simulations on both synthetic and real-world financial data, and show that our proposed method has better performance than that of a state-of-the-art method.

  • 275.
    Fatima, Ghania
    et al.
    Indian Inst Technol Delhi, CARE, New Delhi 110016, India..
    Babu, Prabhu
    Indian Inst Technol Delhi, CARE, New Delhi 110016, India..
    Stoica, Petre
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control.
    Two New Algorithms for Maximum Likelihood Estimation of Sparse Covariance Matrices With Applications to Graphical Modeling2024In: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 72, p. 958-971Article in journal (Refereed)
    Abstract [en]

    In this paper, we propose two new algorithms for maximum-likelihood estimation (MLE) of high dimensional sparse covariance matrices. Unlike most of the state-of-the-art methods, which either use regularization techniques or penalize the likelihood to impose sparsity, we solve the MLE problem based on an estimated covariance graph. More specifically, we propose a two-stage procedure: in the first stage, we determine the sparsity pattern of the target covariance matrix (in other words the marginal independence in the covariance graph under a Gaussian graphical model) using the multiple hypothesis testing method of false discovery rate (FDR), and in the second stage we use either a block coordinate descent approach to estimate the non-zero values or a proximal distance approach that penalizes the distance between the estimated covariance graph and the target covariance matrix. Doing so gives rise to two different methods, each with its own advantage: the coordinate descent approach does not require tuning of any hyper-parameters, whereas the proximal distance approach is computationally fast but requires a careful tuning of the penalty parameter. Both methods are effective even in cases where the number of observed samples is less than the dimension of the data. For performance evaluation, we test the proposed methods on both simulated and real-world data and show that they provide more accurate estimates of the sparse covariance matrix than the state-of-the-art methods.

  • 276.
    Ferizbegovic, Mina
    et al.
    KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, Div Decis & Control Syst, SE-10044 Stockholm, Sweden..
    Hjalmarsson, Hakan
    KTH Royal Inst Technol, Sch Elect Engn & Comp Sci, Div Decis & Control Syst, SE-10044 Stockholm, Sweden..
    Mattsson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Schön, Thomas B.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Artificial Intelligence.
    Willems' fundamental lemma based on second-order moments2021In: 2021 60th IEEE Conference On Decision And Control (CDC), Institute of Electrical and Electronics Engineers (IEEE) Institute of Electrical and Electronics Engineers (IEEE), 2021, p. 396-401Conference paper (Refereed)
    Abstract [en]

    In this paper, we propose variations of Willems' fundamental lemma that utilize second-order moments such as correlation functions in the time domain and power spectra in the frequency domain. We believe that using a formulation with estimated correlation coefficients is suitable for data compression, and possibly can reduce noise. Also, the formulations in the frequency domain can enable modeling of a system in a frequency region of interest.

  • 277.
    Ferizbegovic, Mina
    et al.
    KTH Royal Inst Technol, Div Decis & Control Syst, Stockholm, Sweden..
    Mattsson, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Schön, Thomas B.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Artificial Intelligence.
    Hjalmarsson, Håkan
    KTH Royal Inst Technol, Div Decis & Control Syst, Stockholm, Sweden..
    Bayes Control of Hammerstein Systems2021In: IFAC PapersOnLine, Elsevier BV Elsevier, 2021, Vol. 54, no 7, p. 755-760Conference paper (Refereed)
    Abstract [en]

    In this paper, we consider data driven control of Hammerstein systems. For such systems a common control structure is a transfer function followed by a static output nonlinearity that tries to cancel the input nonlinearity of the system, which is modeled as a polynomial or piece-wise linear function. The linear part of the controller is used to achieve desired disturbance rejection and tracking properties. To design a linear part of the controller, we propose a weighted average risk criterion with the risk being the average of the squared L2 tracking error. Here the average is with respect to the observations used in the controller and the weighting is with respect to how important it is to have good control for different impulse responses. This criterion corresponds to the average risk criterion leading to the Bayes estimator and we therefore call this approach Bayes control. By parametrizing the weighting function and estimating the corresponding hyperparameters we tune the weighting function to the information regarding the true impulse response contained in the data set available to the user for the control design. The numerical results show that the proposed methods result in stable controllers with performance comparable to the optimal controller, designed using the true input nonlinearity and true plant.

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  • 278. Ferrari, Riccardo M. G.
    et al.
    Teixeira, André M. H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    A switching multiplicative watermarking scheme for detection of stealthy cyber-attacks2021In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 66, no 6, p. 2558-2573Article in journal (Refereed)
    Abstract [en]

    This article addresses the detection of stealthy attacks on sensor measurements. Inspired in authentication schemes with weak cryptographic guarantees, we propose a watermarking approach to validate the data and its source. In particular, we propose a multiplicative scheme, where the sensor outputs are watermarked by a bank of filters, then transmitted through the possibly unsecured communication network. The original measurement data are finally reconstructed by a watermark remover. To allow the detection of replay attacks, the watermarking filters are devised as hybrid switching systems, whose parameters are assumed to be unknown to the adversary. Design rules are provided, guaranteeing that the nominal closed-loop performance is not deteriorated by the watermarking scheme and ensuring robust stability with mismatched filter parameters. Moreover, we design a switching protocol with no communication overhead to allow the watermarking filters to synchronously update their parameters. The detectability properties of cyber-attacks are analyzed, and the results are illustrated through numerical examples for replay and data injection attacks.

  • 279. Ferrari, Riccardo M. G.
    et al.
    Teixeira, André M. H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Detection of Cyber-Attacks: A Multiplicative Watermarking Scheme2021In: Safety, Security and Privacy for Cyber-Physical Systems / [ed] Ferrari, Riccardo M.G.; Teixeira, André M. H., Springer Publishing Company, 2021, 486, p. 173-201Chapter in book (Other academic)
    Abstract [en]

    This chapter addresses the problem of detecting stealthy data injection attacks on sensor measurements in a networked control system. A multiplicative watermarking scheme is proposed, where the data from each sensor is post-processed by a time-varying filter called watermark generator. At the controller’s side, the watermark is removed from each channel by another filter, called the watermark remover, thus reconstructing the original signal. The parameters of each remover are matched to those of the corresponding generator, and are supposed to be a shared secret not known by the attacker. The rationale for time-varying watermarks is to allow model-based schemes to detect otherwise stealthy attacks by constantly introducing mismatches between the actual and the nominal dynamics used by the detector. A specific model-based diagnosis algorithm is designed to this end. Under the proposed watermarking scheme, the robustness and the detectability properties of the model-based detector are analyzed and guidelines for designing the watermarking filters are derived. Distinctive features of the proposed approach, with respect to other solutions like end-to-end encryption, are that the scheme is lightweight enough to be applied also to legacy control systems, the absence of side-effects such as delays, and the possibility of utilizing a robust controller to operate the closed-loop system in the event of the transmitter and receiver losing synchronization of their watermarking filters. The results are illustrated through numerical examples.

  • 280. Ferrari, Riccardo M. G.
    et al.
    Teixeira, André M. H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Introduction to the Book2021In: Safety, Security and Privacy for Cyber-Physical Systems / [ed] Ferrari, Riccardo M.G.; Teixeira, André M. H., Springer, 2021, p. 1-8Chapter in book (Other academic)
    Abstract [en]

    In this introductory chapter, we illustrate the book’s motivation and objective. In particular, the book takes its raison d’être from the need for protecting Cyber-Physical Systems (CPSs) against threats originating either in the cyber or in the physical domain. Exploring the concepts of safety, security, and privacy for CPSs thus emerged as the natural goal to reach. In order to better support this objective and to help the reader to navigate the book contents, a taxonomy of the above-mentioned concepts is introduced, based on a set of three triads, including the well-known Confidentiality, Integrity, and Availability triad which was introduced in the Information Technology security literature.

  • 281.
    Fransson, Emma
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Women's and Children's Health, Obstetrics and Reproductive Health Research. Department of Microbiology, Tumor and Cell Biology, Centre for Translational Microbiome Research, Karolinska Institutet, 171 77, Stockholm, Sweden.
    Karalexi, Maria
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Women's and Children's Health, Obstetrics and Reproductive Health Research. Department of Hygiene and Epidemiology, School of Medicine, University of Ioannina, 45110, Ioannina, Greece.
    Kimmel, Mary C.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Women's and Children's Health, Obstetrics and Reproductive Health Research. Department of Psychiatry, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27514, USA.
    Bränn, Emma
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Women's and Children's Health, Obstetrics and Reproductive Health Research.
    Kollia, Natasa
    Department of Nutrition and Dietetics, School of Health Science and Education, Harokopio University, 17676, Athens, Greece.
    Tas, Auke
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience.
    van Zoest, Vera
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Nordling, Eira
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Women's and Children's Health.
    Skalkidou, Alkistis
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Women's and Children's Health, Obstetrics and Reproductive Health Research.
    Papadopoulos, Fotis
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Sciences, Psychiatry.
    Differentiated mental health patterns in pregnancy during COVID-19 first two waves in Sweden: a mixed methods study using digital phenotyping2022In: Scientific Reports, E-ISSN 2045-2322, Vol. 12, no 1, article id 21253Article in journal (Refereed)
    Abstract [en]

    To utilize modern tools to assess depressive and anxiety symptoms, wellbeing and life conditions in pregnant women during the first two waves of the COVID-19 pandemic in Sweden. Pregnant women (n = 1577) were recruited through the mobile application Mom2B. Symptoms of depression, anxiety and wellbeing were assessed during January 2020–February 2021. Movement data was collected using the phone’s sensor. Data on Google search volumes for “Corona” and Covid-related deaths were obtained. Qualitative analysis of free text responses regarding maternity care was performed. Two peaks were seen for depressive symptoms, corresponding to the two waves. Higher prevalence of anxiety was only noted during the first wave. A moderating effect of the two waves in the association of depression, anxiety, and well-being with Covid deaths was noted; positive associations during the first wave and attenuated or became negative during the second wave. Throughout, women reported on cancelled healthcare appointments and worry about partners not being allowed in hospital. The association of mental health outcomes with relevant covariates may vary during the different phases in a pandemic, possibly due to adaptation strategies on a personal and societal/healthcare level. Digital phenotyping can help healthcare providers and governmental bodies to in real time monitor high-risk groups during crises, and to adjust the support offered.

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  • 282.
    Frisk, Mikael
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Nilsson, Albin
    Inertial sensor and ultra-wideband sensor fusion: Precision positioning of robot platform2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    In order to determine the orientation and position of an object it is common to measure linear and angular motion with an inertial sensor. To further improve the positioning an ultra-wideband sensor can be used simultaneously and integrated in the final solution with sensor fusion. This study has evaluated an ultra- wideband sensor, and also integrated it with a pre- existing solution for positioning using inertial sensors, in order to determine if the solution is viable for positioning of an autonomous robot platform for use in industrial environments. The results of the evaluation shows that the ultra- wideband sensor would work well in the intended environments but that further tests are needed to establish behavior in none- line-of-sight conditions. The results from the sensor fusion show that the integration of the two sensors yields a result that is better than either of the sensors working alone. The main issue with the current solution is a low sampling rate of the ultra-wideband sensor. A list of other suggested improvements is provided. 

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    Inertial sensor and ultra- wideband sensor fusion
  • 283.
    Frykberg, Gunilla
    et al.
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Neuroscience, Rehabilitation Medicine.
    Åberg, Anna Cristina
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Public Health and Caring Sciences, Geriatrics.
    Thierfelder, Tomas
    Department of Energy and Technology, Swedish University of Agricultural Sciences, Uppsala.
    Halvorsen, Kjartan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Hirschfeld, Helga
    Department of Neurobiology, Care Sciences and Society, Division of Physiotherapy, Karolinska Institutet.
    Borg, Jörgen
    Department of Clinical Sciences, Rehabilitation Medicine, Karolinska Institutet.
    Locomotor coordination during the sit-to-walk transfer is different in subjects with stroke and controlsManuscript (preprint) (Other academic)
    Abstract [en]

    Objectives: To describe and to compare coordination of centre of mass (COM) horizontal and vertical momenta, and fluidity during the sit-to-walk (STW) transfer in subjects with stroke and in matched controls.

    Design: Cross-sectional.

    Setting: Research laboratory.

    Participants: Ten subjects with stroke in the post-acute phase (> 6 months) and ten control subjects, matched for sex, age, height and weight, were recruited through a convenience sample.

    Interventions: Not applicable.

    Main Outcome Measures: Magnitudes and timing of COM peak horizontal and peak vertical momenta, scores on the Fluidity Scale (FS) and values of the Fluidity Index (FI).

    Results: The stroke subjects generated significantly less COM peak horizontal and peak vertical momenta. Latencies from STW-onset and seat-off to the peaks differed significantly between the two groups. The subjects with stroke displayed significantly lower scores on the FS as well as lower percentages of the FI.

    Conclusions: While rising to walk, scaling and timing parameters of COM horizontal and vertical momenta differed significantly between subjects with stroke and matched controls. This atypical motor strategy needs to be further investigated before it is possible to make clinical recommendations.

     

  • 284. Gallo, Alexander J.
    Teixeira, André
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Signals and Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Ferrari, Riccardo M. G.
    Switching Multiplicative Watermark Design against Covert AttacksIn: Article in journal (Refereed)
  • 285.
    Gallo, Alexander J.
    et al.
    Delft Univ Technol, Delft Ctr Syst & Control Mech Maritime & Mat Engn, Delft, Netherlands..
    Coimbatore Anand, Sribalaji
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Signals and Systems.
    Teixeira, André M. H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Ferrari, Riccardo M. G.
    Delft Univ Technol, Delft Ctr Syst & Control Mech Maritime & Mat Engn, Delft, Netherlands..
    Design of multiplicative watermarking against covert attacks2021In: 2021 60th IEEE CConference On Decision And Control (CDC), Institute of Electrical and Electronics Engineers (IEEE), 2021, p. 4176-4181Conference paper (Refereed)
    Abstract [en]

    This paper addresses the design of an active cyber-attack detection architecture based on multiplicative watermarking, allowing for detection of covert attacks. We propose an optimal design problem, relying on the so-called output-to-output l(2)-gain, which characterizes the maximum gain between the residual output of a detection scheme and some performance output. Although optimal, this control problem is non-convex. Hence, we propose an algorithm to design the watermarking filters by solving the problem suboptimally via LMIs. We show that, against covert attacks, the output-to-output l(2)-gain is unbounded without watermarking, and we provide a sufficient condition for boundedness in the presence of watermarks.

  • 286.
    Ganesan, G
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Stoica, P
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Differential detection based on space-time block codes2002In: Wireless Personal Comm, Vol. 21, p. 163-180Article in journal (Refereed)
  • 287.
    Ganesan, G
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Stoica, P
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Differential modulation using space-time block codes2002In: IEEE Sign Process Lett, Vol. 9, p. 57-60Article in journal (Refereed)
  • 288.
    Ganesan, G
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control. DEPARTMENT OF SYSTEMS AND CONTROL.
    Stoica, P
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Space-time block codes: A maximum SNR approach2001In: IEEE TRANSACTIONS ON INFORMATION THEORY, ISSN 0018-9448, Vol. 47, no 4, p. 1650-1656Article in journal (Refereed)
    Abstract [en]

    In a recent work space-time block codes were introduced to obtain coded diversity for a multiple-antenna communication system. In this work, we cast space-time codes in an optimal signal-to-noise ratio (SNR) framework and show that they achieve the maximum SNR and, in fact, they correspond to a generalized maximal ratio combiner. The maximum SNR framework also helps in calculating the distribution of the SNR and in deriving explicit expressions for bit error rates.

    We bring out the connection between the theory of amicable orthogonal designs and space-time codes. Based on this, we give a much simpler proof to one of the main theorems on space-time codes for complex symbols. We present a rate $1/2$ code for complex symbols which has a smaller delay than the code already known. We also present another rate $3/4$ code which is simpler than the one already known, in the sense it does not involve additions or multiplications. We also point out the connection between generalized real designs and generalized orthogonal designs.

  • 289.
    Ganesan, G
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Stoica, P
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Larsson, E
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Diagonally weighted orthogonal space-time block codes2002In: 36th ASILOMAR Conference on Signals, Systems and Computers, Pacific Grove, CA, 2002Conference paper (Refereed)
  • 290. Ganesan, G
    et al.
    Stoica, Peter
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Constructing space-time trellis codes using orthogonal designs2004In: Wireless Personal Communicattions, Vol. 28, p. 1-16Article in journal (Refereed)
  • 291. Ganesan, G
    et al.
    Stoica, Peter
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Larsson, E
    Orthogonal space-time block codes with feedback2004In: Wireless personal Communications, Vol. 28, p. 287-312Article in journal (Refereed)
  • 292.
    Ganesan, Girish
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Designing Space-Time Codes Using Orthogonal Designs2002Doctoral thesis, monograph (Other academic)
    Abstract [en]

    This thesis deals with coding schemes for systems with multiple transmit antennas. The problem of finding optimal transmission schemes for the case when the transmitter knows the channel and the case when the transmitter does not know the channel are considered. Also considered is the case when some partial feedback is possible from the receiver to the transmitter.

    When the transmitter knows the channel perfectly, a beamforming solution is shown to be optimal. To tackle the case where the transmitter does not know the channel perfectly, schemes based on orthogonal designs are proposed that give the best performance under some conditions. A differential detection scheme is also proposed where neither the transmitter nor the receiver has to know the channel. The thesis also considers the concatenation of a conventional (scalar) coding scheme with a space-time modulation scheme and shows how optimum coded diversity can be obtained with this concatenation. An alternative to the concatenation method concatenation of a space-time modulation scheme with a scalar code is to develop space-time trellis codes.

    Orthogonal designs are usually associated with space-time block codes. In this thesis the design of space-time trellis codes based on orthogonal designs is considered. A turbo implementation of the new trellis codes is also proposed.

  • 293. Garnier, Hugues
    et al.
    Söderström, Torsten
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Yuz, Juan I.
    Editorial special issue on continuous-time model identification2011In: IET Control Theory & Applications, ISSN 1751-8644, Vol. 5, no 7, p. 839-841Article, review/survey (Refereed)
  • 294.
    Gedon, Daniel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Artificial Intelligence.
    Abedsoltan, Amirhesam
    Schön, Thomas B.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Artificial Intelligence.
    Belkin, Mikhail
    Uncertainty Estimation with Recursive Feature MachinesManuscript (preprint) (Other academic)
    Abstract [en]

    In conventional regression analysis, predictions are typically represented as point estimates derived from covariates. The Gaussian Process (GP) offer a kernel-based framework that predicts and additionally quantifies associated uncertainties. However, kernel-based methods often underperform ensemble-based decision tree approaches in regression tasks involving tabular and categorical data. Recently, Recursive Feature Machines (RFMs) were proposed as a novel feature-learning kernel which strengthens the capabilities of kernel machines. In this study, we harness the power RFMs in a probabilistic GP-based approach to enhance uncertainty estimation through feature extraction within kernel methods. We employ this learned kernel for in-depth uncertainty analysis. On tabular datasets, our RFM-based method surpasses other leading uncertainty estimation techniques, including NGBoost and CatBoost-ensemble. Additionally, when assessing out-of-distribution performance, we found that boosting-based methods are surpassed by our RFM-based approach.

  • 295.
    Gedon, Daniel
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Artificial Intelligence.
    Horta Ribeiro, Antônio
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Artificial Intelligence.
    Schön, Thomas B.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Artificial Intelligence.
    No Double Descent in Principal Component Regression: A High-Dimensional AnalysisManuscript (preprint) (Other academic)
    Abstract [en]

    Understanding the generalization properties of large-scale models necessitates incorporating realistic data assumptions into the analysis. Therefore, we consider Principal Component Regression (PCR)---combining principal component analysis and linear regression---on data from a low-dimensional manifold. We present an analysis of PCR when the data is sampled from a spiked covariance model, obtaining fundamental asymptotic guarantees for the generalization risk of this model. Our analysis is based on random matrix theory and allows us to provide guarantees for high-dimensional data. We additionally present an analysis of the distribution shift between training and test data. The results allow us to disentangle the effects of (1) the number of parameters, (2) the data-generating model and, (3) model misspecification on the generalization risk. The use of PCR effectively regularizes the model and prevents the interpolation peak of the double descent. Our theoretical findings are empirically validated in simulation, demonstrating their practical relevance.

  • 296.
    Geng, Li-Hui
    et al.
    Tianjin Univ Technol & Educ, Sch Automat & Elect Engn, Tianjin Key Lab Informat Sensing & Intelligent Co, Tianjin, Peoples R China.
    Ninness, Brett
    Univ Newcastle, Fac Engn & Built Environm, Callaghan, NSW, Australia.
    Wills, Adrian
    Univ Newcastle, Fac Engn & Built Environm, Callaghan, NSW, Australia.
    Schön, Thomas B.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Smoothed State Estimation via Efficient Solution of Linear Equations2017In: IFAC-PapersOnLine, E-ISSN 2405-8963, Vol. 50, no 1, p. 1613-1618Article in journal (Refereed)
    Abstract [en]

    This paper addresses the problem of computing fixed interval smoothed state estimates of a linear time varying Gaussian stochastic system. There already exist many algorithms that perform this computation, but all of them impose certain restrictions on system matrices in order for them to be applicable. This paper develops a new forwards–backwards pass algorithm that is applicable under the mildest restrictions possible - namely that the smoothed state distribtions exists in forms that can be characterised by means and covariances, for which this paper also develops a new necessary and sufficient condition.

  • 297.
    Geng, Li-Hui
    et al.
    Tianjin Key Laboratory of Information Sensing and Intelligent Control, School of Automation and Electrical Engineering, Tianjin University of Technology and Education, Tianjin, China.
    Wills, Adrian George
    School of Engineering, The University of Newcastle, Callaghan, NSW, Australia.
    Ninness, Brett
    Faculty of Engineering and Built Environment, The University of Newcastle, Callaghan, NSW, Australia.
    Schön, Thomas Bo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Artificial Intelligence.
    Smoothed State Estimation via Efficient Solution of Linear Equations2023In: IEEE Transactions on Automatic Control, ISSN 0018-9286, E-ISSN 1558-2523, Vol. 68, no 10, p. 5877-5889Article in journal (Refereed)
    Abstract [en]

    This article addresses the problem of computing fixed-interval smoothed state estimates of a linear time-varying Gaussian stochastic system. There already exist many algorithms that perform this computation, but all of them impose certain restrictions on system matrices in order for them to be applicable, and the restrictions vary considerably between the various existing algorithms. This article establishes a new sufficient condition for the fixed-interval smoothing density to exist in a Gaussian form that can be completely characterized by associated means and covariances. It then develops an algorithm to compute these means and covariances with no further assumptions required. This results in an algorithm more generally applicable than any one of the multitude of existing algorithms available to date.

  • 298. Gershman, A
    et al.
    Stoica, P
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Pesavento, M
    Larsson, E
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Stochastic Cramer-Rao bound for direction estimation in unknown noise fields2002In: IEE Proc Radar Sonar Navig, Vol. 149, p. 2-8Article in journal (Refereed)
  • 299. Gianelli, Christopher
    et al.
    Li, Jian
    Stoica, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    Coherent mimo radar and waveform diversity2015In: Wiley Encyclopedia of Electrical and Electronics Engineering, Hoboken, NJ: John Wiley & Sons, 2015, p. 1-19Chapter in book (Refereed)
  • 300. Gianelli, Christopher
    et al.
    Xu, Luzhou
    Li, Jian
    Stoica, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Systems and Control. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Automatic control.
    One-bit compressive sampling with time-varying thresholds for sparse parameter estimation2016In: Proc. 9th Sensor Array and Multichannel Signal Processing Workshop, Piscataway, NJ: IEEE, 2016Conference paper (Refereed)
3456789 251 - 300 of 1530
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