| 1. |
- Garulli, Andrea, et al.
(author)
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Robust Finite-Frequency H2 Analysis of Uncertain Systems
- 2011
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Reports (other academic/artistic)abstract
- In many applications, design or analysis is performed over a finite frequency range of interest. The importance of the H2/robust H2 norm highlights the necessity of computing this norm accordingly. This paper provides different methods for computing upper bounds on the robust finite-frequency H2 norm for systems with structured uncertainties. An application of the robust finite-frequency H2 norm for a comfort analysis problem of an aero-elastic model of an aircraft is also presented.
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| 2. |
- Garulli, Andrea, et al.
(author)
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Robust finite-frequency H2 analysis of uncertain systems with application to flight comfort analysis
- 2013
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In: Control Engineering Practice. - : Elsevier. - 0967-0661 .- 1873-6939. ; 21:6, s. 887-897
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Journal article (peer-reviewed)abstract
- In many applications, design or analysis is performed over a finite-frequency range of interest. The importance of the H2 norm highlights the necessity of computing this norm accordingly. This paper provides different methods for computing upper bounds of the robust finite-frequency H2 norm for systems with structured uncertainties. An application of the robust finite-frequency H2 norm for a comfort analysis problem of an aero-elastic model of an aircraft is also presented.
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| 3. |
- Gutiérrez Pérez, Cristina, 1972, et al.
(author)
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High frequency of cognitive dysfunction before stroke in the elderly
- 2011
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In: International Journal of Geriatric Psychiatry. - : Wiley. - 1099-1166 .- 0885-6230. ; 26:6, s. 622-629
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Journal article (peer-reviewed)abstract
- Objectives We examined cognitive functions before and in acute phase of stroke studying frequency and profile of cognitive impairment and relationships between cognitive status.MethodsSeventy-four patients with early phase after stroke and 49 healthy controls were included and examined using the Mini-Mental State Examination (MMSE) and a battery of neuropsychological tests. Cognitive status before stroke-onset was investigated using Cognitive Impairment Questionnaire.ResultsCognitive impairments were present in 96% of patients after stroke onset using the battery of neuropsychological tests and in 39% of patients using the MMSE, but in only 9% of controls. Seventy-six percent exhibited reduced executive function and 75% reduced psychomotor tempo. Cognitive dysfunction was present in 52% before stroke onset without any impact on the frequency of impairment in the various cognitive areas in early phase after stroke.ConclusionsCognitive impairment is frequent before the onset of stroke among older people and may partially explain the very high frequency of cognitive impairment observed after stroke onset.
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| 4. |
- Hansson, Anders, et al.
(author)
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Maximum Likelihood Estimation of Gaussian Models with Missing Data : Eight Equivalent Formulations
- 2011
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Reports (other academic/artistic)abstract
- In this paper we derive the maximum likelihood problem for missing data from a Gaussian model. We present in total eight different equivalent formulations of the resulting optimization problem, four out of which are nonlinear least squares formulations. Among these formulations are also formulations based on the expectation-maximization algorithm. Expressions for the derivatives needed in order to solve the optimization problems are presented. We also present numerical comparisons for two of the formulations for an ARMAX model.
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| 5. |
- Hansson, Anders, et al.
(author)
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Maximum Likelihood Estimation of Gaussian Models with Missing Data : Eight Equivalent Formulations
- 2012
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In: Automatica. - : Elsevier. - 0005-1098 .- 1873-2836. ; 48:9, s. 1955-1962
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Journal article (peer-reviewed)abstract
- In this paper we derive the maximum likelihood problem for missing data from a Gaussian model. We present in total eight different equivalent formulations of the resulting optimization problem, four out of which are nonlinear least squares formulations. Among these formulations are also formulations based on the expectation-maximization algorithm. Expressions for the derivatives needed in order to solve the optimization problems are presented. We also present numerical comparisons for two of the formulations for an ARMAX model.
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| 6. |
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| 7. |
- Wallin, Hans Petter, et al.
(author)
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Sound and vibration
- 2010. - 2., rev. uppl.
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Book (other academic/artistic)
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| 8. |
- Wallin, Ragnar, et al.
(author)
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A Unified Approach to Identification of Linear SISO Models Subject to Missing Output Data and Missing Input Data
- 2011
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Reports (other academic/artistic)abstract
- When output data is missing in a system identification scenario, it is not the Euclidean norm of the prediction error vector per se that should be minimized. Doing so will almost always yield biased parameter estimates. Two algorithms for estimation of the parameters, which can handle both missing output data and missing input data, are presented. The criterion minimized in the algorithms is the Euclidean norm of the prediction error vector scaled by a particular function of the covariance matrix of the observed output data. The algorithms yield a maximum likelihood estimate of the parameters under certain conditions.
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| 9. |
- Wallin, Ragnar, et al.
(author)
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Applications of IQC-Based Analysis Techniques for Clearance
- 2012
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In: Optimization Based Clearance of Flight Control Laws. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 9783642226267 - 9783642226274 ; , s. 277-297
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Book chapter (peer-reviewed)abstract
- Results for stability analysis of the nonlinear rigid aircraft model and comfort and loads analysis of the integral aircraft model are presented in this chapter. The analysis is based on the theory for integral quadratic constraints and relies on linear fractional representations (LFRs) of the underlying closed-loop aircraft models. To alleviate the high computational demands associated with the usage of IQC based analysis to large order LFRs, two approaches have been employed aiming a trade-off between computational complexity and conservatism. First, the partitioning of the flight envelope in several smaller regions allows to use lower order LFRs in the analysis, and second, IQCs with lower computational demands have been used whenever possible. The obtained results illustrate the applicability of the IQCs based analysis techniques to solve highly complex analysis problems with an acceptable level of conservativeness.
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| 10. |
- Wallin, Ragnar, et al.
(author)
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Maximum likelihood estimation of linear SISO models subject to missing output data and missing input data
- 2014
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In: International Journal of Control. - : Taylor and Francis: STM, Behavioural Science and Public Health Titles. - 0020-7179 .- 1366-5820. ; 87:11, s. 2354-2364
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Journal article (peer-reviewed)abstract
- In this paper we describe an approach to maximum likelihood estimation of linear single input single output (SISO) models when both input and output data are missing. The criterion minimised in the algorithms is the Euclidean norm of the prediction error vector scaled by a particular function of the covariance matrix of the observed output data. We also provide insight into when simpler and in general sub-optimal schemes are indeed optimal. The algorithm has been prototyped in MATLAB, and we report numerical results that support the theory.
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