| 1. |
- Aleman, Soo, et al.
(författare)
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Health check-ups and family screening allow detection of hereditary hemochromatosis with less advanced liver fibrosis and survival comparable with the general population
- 2011
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Ingår i: Scandinavian Journal of Gastroenterology. - : Informa UK Limited. - 0036-5521 .- 1502-7708. ; 46:9, s. 1118-1126
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Tidskriftsartikel (refereegranskat)abstract
- Objective. The information concerning the morbidity and mortality of hereditary hemochromatosis is based primarily on clinical cohorts of symptomatic patients. The major aim of this study was to analyze the long-term prognosis for Swedish patients with this condition, with respect to both clinical features and survival, in relation to the route by which the disease was detected. Patients and methods. 373 patients with hemochromatosis detected through routine health checkups (n = 153), family screening (n = 44), symptoms of arthralgia (n = 23), investigation of other diseases/symptoms (n = 108) or signs of liver disease (n = 45) were monitored for a mean period of 11.9 +/- 5.8 years. The degree of liver fibrosis and survival were analyzed. Results. Overall survival among these patients was not significantly different from that of a matched normal population. The patients diagnosed through health check-ups and family screening were detected at an earlier age and had the highest rate of survival. Liver biopsy at the time of diagnosis revealed cirrhosis in 9% of those detected through the health check-ups and 5% in the case of family screening, compared with 13% for the group with arthralgia, 17% for other diseases/symptoms and 42% for liver disease. Conclusion. Health check-ups and family screening allow detection of hereditary hemochromatosis at an earlier age and with less advanced liver fibrosis, although a few of these patients have already developed cirrhosis. Our study indicates that iron indices should be included in health check-ups, and if abnormal, should lead to further investigation.
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| 2. |
- Almér, Stefan, 1975-
(författare)
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Control and Analysis of Pulse-Modulated Systems
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The thesis consists of an introduction and four appended papers. In the introduction we give an overview of pulse-modulated systems and provide a few examples of such systems. Furthermore, we introduce the so-called dynamic phasor model which is used as a basis for analysis in two of the appended papers. We also introduce the harmonic transfer function and finally we provide a summary of the appended papers. The first paper considers stability analysis of a class of pulse-width modulated systems based on a discrete time model. The systems considered typically have periodic solutions. Stability of a periodic solution is equivalent to stability of a fixed point of a discrete time model of the system dynamics. Conditions for global and local exponential stability of the discrete time model are derived using quadratic and piecewise quadratic Lyapunov functions. A griding procedure is used to develop a systematic method to search for the Lyapunov functions. The second paper considers the dynamic phasor model as a tool for stability analysis of a general class of pulse-modulated systems. The analysis covers both linear time periodic systems and systems where the pulse modulation is controlled by feedback. The dynamic phasor model provides an $\textbf{L}_2$-equivalent description of the system dynamics in terms of an infinite dimensional dynamic system. The infinite dimensional phasor system is approximated via a skew truncation. The truncated system is used to derive a systematic method to compute time periodic quadratic Lyapunov functions. The third paper considers the dynamic phasor model as a tool for harmonic analysis of a class of pulse-width modulated systems. The analysis covers both linear time periodic systems and non-periodic systems where the switching is controlled by feedback. As in the second paper of the thesis, we represent the switching system using the L_2-equivalent infinite dimensional system provided by the phasor model. It is shown that there is a connection between the dynamic phasor model and the harmonic transfer function of a linear time periodic system and this connection is used to extend the notion of harmonic transfer function to describe periodic solutions of non-periodic systems. The infinite dimensional phasor system is approximated via a square truncation. We assume that the response of the truncated system to a periodic disturbance is also periodic and we consider the corresponding harmonic balance equations. An approximate solution of these equations is stated in terms of a harmonic transfer function which is analogous to the harmonic transfer function of a linear time periodic system. The aforementioned assumption is proved to hold for small disturbances by proving the existence of a solution to a fixed point equation. The proof implies that for small disturbances, the approximation is good. Finally, the fourth paper considers control synthesis for switched mode DC-DC converters. The synthesis is based on a sampled data model of the system dynamics. The sampled data model gives an exact description of the converter state at the switching instances, but also includes a lifted signal which represents the inter-sampling behavior. Within the sampled data framework we consider H-infinity control design to achieve robustness to disturbances and load variations. The suggested controller is applied to two benchmark examples; a step-down and a step-up converter. Performance is verified in both simulations and in experiments.
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| 3. |
- Almér, Stefan, et al.
(författare)
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Dynamic phasor analysis of a class of PWM systems
- 2015
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Ingår i: 2007 European Control Conference, ECC 2007. - : IEEE. - 9783952417386 ; , s. 1940-1947
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Konferensbidrag (refereegranskat)abstract
- The paper makes use of the so-called dynamic phasor model for stability and performance analysis of a class of PWM systems. The dynamic phasor model allows for the state to be represented in the frequency domain where a harmonic Lyapunov function is defined. The analysis covers both periodically switched systems and non-periodic systems where the switching is controlled by feedback.
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| 4. |
- Almér, Stefan, et al.
(författare)
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Dynamic Phasor Analysis of Periodic Systems
- 2009
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Ingår i: IEEE Transactions on Automatic Control. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9286 .- 1558-2523. ; 54:8, s. 2007-2012
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Tidskriftsartikel (refereegranskat)abstract
- The paper considers stability analysis of linear time-periodic (LTP) systems based on the dynamic phasor model (DPM). The DPM exploits the periodicity of the system by expanding the system state in a Fourier series over a moving time window. This results in an L-2-equivalent representation in terms of an infinite-dimensional LTI system which describes the evolution of time varying Fourier coefficients. To prove stability, we consider quadratic time-periodic Lyapunov candidates. Using the DPM, the corresponding time-periodic Lyapunov inequality can be stated as a finite dimensional inequality and the Lyapunov function can be found by solving a linear matrix inequality.
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| 5. |
- Almér, Stefan, et al.
(författare)
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Dynamic Phasor Analysis Of Pulse-Modulated Systems
- 2012
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Ingår i: SIAM Journal of Control and Optimization. - : Society for Industrial & Applied Mathematics (SIAM). - 0363-0129 .- 1095-7138. ; 50:3, s. 1110-1138
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Tidskriftsartikel (refereegranskat)abstract
- This paper considers stability and harmonic analysis of a general class of pulse-modulated systems. The systems are modeled using the dynamic phasor model, which explores the cyclic nature of the modulation functions by representing the system state as a Fourier series expansion defined over a moving time window. The contribution of the paper is to show that a special type of periodic Lyapunov function can be used to analyze the system and that the analysis conditions become tractable for computation after truncation. The approach provides a trade-off between complexity and accuracy that includes standard state space averaged models as a special case. The paper also shows how the dynamic phasor model can be used to derive a frequency domain input-to-state map which is analogous to the harmonic transfer function.
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| 6. |
- Almér, Stefan, et al.
(författare)
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Dynamic phasor analysis of pulse-modulated systems
- 2007
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Ingår i: Proceedings Of The 46th IEEE Conference On Decision And Control, Vols 1-14. - 9781424414970 ; , s. 3938-3945
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Konferensbidrag (refereegranskat)abstract
- The paper considers stability analysis of a general class of pulse modulated systems in a phasor dynamic framework. The dynamic phasor model exploits the cyclic nature of the modulation functions by representing the system dynamics in terms of a Fourier series expansion defined over a moving time-window. The contribution of the paper is to show that a special type of periodic Lyapunov function can be used to analyze the system and that the analysis conditions become tractable for computation after truncation. The approach provides a trade-off between complexity and accuracy that includes standard state space averaged models as a special case.
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| 7. |
- Almér, Stefan, et al.
(författare)
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Global stability analysis of DC-DC converters using sampled-data modeling
- 2004
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Ingår i: PROCEEDINGS OF THE 2004 AMERICAN CONTROL CONFERENCE, VOLS 1-6. - 0780383354 ; , s. 4549-4554
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Konferensbidrag (refereegranskat)abstract
- The paper presents stability analysis of a class of pulse-width modulated (PWM) systems which incorporates many different DC-DC converters. Two types of pulse-width modulation (digital and analog control) are considered. A procedure is developed for systematic search for Lyapunov functions. The state space is partitioned in such a way that stability is verified if a set of coupled Linear Matrix Inequalities (LMIs) is feasible. Global stability is considered as well as the computation of local regions of attraction.
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| 8. |
- Almer, Sven, 1938-, et al.
(författare)
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Handläggning av svårt skov av ulcerös kolit. In: Löfberg R (ed): Inflammatorisk tarmsjukdom.
- 2010
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Ingår i: Läkartidningen. - 0023-7205 .- 1652-7518. ; 106:45, s. 62-75
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Tidskriftsartikel (refereegranskat)abstract
- Patienter med svårt skov av ulcerös kolit bör vårdas på sjukhus och handläggas av gastroenterolog och kolorektal kirurg i nära samarbete.Skovets svårighetsgrad kan underskattas, varför noggrann bedömning av inflammationens utbredning och svårighetsgrad enligt validerade kriterier är viktigt.Intravenös behandling med kortikosteroider är en av hörnstenarna i den akuta behandlingen.Patienter som inte förbättras på denna behandling, bör erbjudas medicinsk »rescue-behandling« eller kolektomi.Infliximab har visats vara en effektiv rescue-behandling och kan minska behovet av kolektomi inom de första 3 månaderna och upp till 3 år.
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| 9. |
- Almér, Stefan, et al.
(författare)
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Harmonic analysis of pulse-width modulated systems
- 2009
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098 .- 1873-2836. ; 45:4, s. 851-862
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Tidskriftsartikel (refereegranskat)abstract
- The paper considers the so-called dynamic phasor model as a basis for harmonic analysis of a class switching systems. The analysis covers both periodically switched systems and non-periodic systems where the switching is controlled by feedback. The dynamic phasor model is a powerful tool for exploring cyclic properties of dynamic systems. It is shown that there is a connection between the dynamic phasor model and the harmonic transfer function of a linear time periodic system and this connection is used to extend the notion of harmonic transfer function to describe periodic solutions of non-periodic systems.
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| 10. |
- Almér, Stefan, et al.
(författare)
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Harmonic Lyapunov functions in the analysis of periodically switched systems
- 2006
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Ingår i: PROCEEDINGS OF THE 45TH IEEE CONFERENCE ON DECISION AND CONTROL, VOLS 1-14. - 9781424401703 ; , s. 2759-2764
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Konferensbidrag (refereegranskat)abstract
- The dynamic phasor model of a time-periodic system is used to derive a stability test involving a harmonic Lyapunov function. This reveals a new interpretation of the harmonic Lyapunov function with an appealing time-domain representation. Most importantly, it indicates that the ideas behind the harmonic Lyapunov equation can be generalized to include cyclic switching systems that have different pulse form in each period.
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