| 1. |
- Hansson, Jörgen, et al.
(författare)
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Clearance of Flight Control Laws for Time-Varying Parameters
- 2003
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In this article exponential stability of the closed loop for the Saab AB VEGAS model controlled by a gain-scheduled linear fractional transformation controller is investigated for time-varying Mach-number. The analysis is based on parameter-dependent Lyapunov-functions which are obtained by investigating feasibility of linear matrix inequalities.
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| 2. |
- Hansson, Lars Jörgen, et al.
(författare)
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Vitrectomy for retained lens fragments in the vitreous after phacoemulsification.
- 2002
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Ingår i: Journal of Cataract and Refractive Surgery. - 1873-4502. ; 28:6, s. 1007-1011
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Tidskriftsartikel (refereegranskat)abstract
- PURPOSE: To assess the visual results, retinal detachment (RD) rate, incidence of glaucoma, and intraocular lens (IOL) placement after vitrectomy for removal of retained lens fragments in the vitreous after phacoemulsification. SETTING: Department of Ophthalmology, University Hospital of Lund, Lund, Sweden. METHODS: This retrospective noncomparative interventional case series included all cases of pars plana vitrectomy for removal of retained lens fragments from January 1997 through January 2000. RESULTS: Sixty-six eyes of 65 patients had pars plana vitrectomy with removal of the lens material over the 3-year period. Visual acuity on presentation was 0.1 or worse in 36 eyes (54%). Visual acuity after vitrectomy was 0.5 or better in 35 eyes (53%). The postoperative visual acuity was worse than 0.1 in 14 eyes (21%). Twenty-seven (56%) of the 48 eyes operated on within 1 week and 8 (44%) of the 18 eyes operated on later achieved a visual acuity of 0.5 or better. Twelve eyes (80%) that had secondary posterior chamber IOL implantation achieved an acuity of 0.5 or better. An RD occurred in 7 eyes (11%). CONCLUSIONS: There was no statistically significant difference in outcomes between those having vitrectomy the first few days after cataract surgery and those having it later, although there was a trend toward better results when the vitrectomy was done sooner. Secondary IOL implantation resulted in a good visual outcome. Retinal detachment was the most severe complication.
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| 3. |
- Lindgren, Markus, 1975-
(författare)
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Measurement and Simulation Based Techniques for Real-Time Systems Analysis
- 2000
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rigorous methods for design and implementation of safety critical real-time systems are vital to avoid loss of human lives and/or severe economic losses. Unfortunately, many of these systems are designed and evaluated using ad-hoc techniques. There are, on the other hand, relatively well developed theories for modeling and analysis of timing and reliability. These theories are, however, seldom applied in industry for system development, mainly because of the simplifying model assumptions and lack of appropriate tool support.This thesis presents two new methods aimed to narrow the gap between research results and industrial practice in evaluation and design of real-time systems.The first contribution is a technique that can be used to derive worst-case execution time estimates for real-time software by measurments on the target system. Such estimates are essential when verifying if a system fulfills its timing requirements. The second contribution is a simulation based technique that can be used to evaluate timing aspects of distributed real-time systems, as well as calculating reliability estimates of these systems. Such estimates are essential in determining if a system meets its requirements sufficiently well. Compared to existing analytical methods for execution time analysis and schedulability analysis, which analyze models of the hardware, the starting point for both these methods are real target systems, rather than an abstract model with limited correspondance to reality.The presented initial case-studies give clear evidence that the proposed methods have potential of being both applicable and useful.
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| 4. |
- Ståhl Gunnarsson, Karin, et al.
(författare)
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Clearance of Flight Control Laws using Linear Fractional Transformations
- 2004
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Ingår i: Proceedings of the 2004 AIAA Guidance, Navigation and Control Conference and Exhibit. - Reston, Virigina : American Institute of Aeronautics and Astronautics. - 9781624100734
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Konferensbidrag (refereegranskat)abstract
- The problem of flight clearance of linear stability requirements in the complete flight evelope is studied. The approach is to use mu-analysis of linear fractional transformations description of the system dynamics augmented with an uncertainty model of the clearance criteria. Two methods to derive the linear fractional transformations are used and compared: the Trends and Bands method and rational approximations. The two approaches are applied to a UAV demostrator model. The resulting models are analyzed by mu-sensitivites in order to demonstrate how this can be used to reduce the order of the linear fractional transformations description. A number of algorithms to compute upper and lower bounds on mu are also compared. Results from applying the clearance criteria to the UAV demonstrator model are given.
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| 5. |
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| 6. |
- Amirijoo, Mehdi, et al.
(författare)
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Algorithms for managing QoS for real-time data services using imprecise computation
- 2004
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Ingår i: Real-Time and Embedded Computing Systems and Applications 9th International Conference, RTCSA 2003, Tainan City, Taiwan, February 18-20, 2003. Revised Papers. - Berlin, Heidelberg : Springer Berlin/Heidelberg. - 3540219749 - 9783540219743 ; , s. 136-157
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Bokkapitel (refereegranskat)abstract
- Lately the demand for real-time data services has increased in applications where it is desirable to process user requests within their deadlines using fresh data. The real-time data services are usually provided by a real-time database (RTDB). Here, since the workload of the RTDBs cannot be precisely predicted, RTDBs can become overloaded. As a result, deadline misses and freshness violations may occur. To address this problem we propose a QoS-sensitive approach to guarantee a set of requirements on the behavior of RTDBs. Our approach is based on imprecise computation, applied on both data and transactions. We propose two algorithms to dynamically balance the workload and the quality of the data and transactions. Performance evaluations show that our algorithms give a robust and controlled behavior of RTDBs, in terms of transaction and data quality, even for transient overloads and with inaccurate run-time estimates of the transactions.
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| 7. |
- Amirijoo, Mehdi, 1978-, et al.
(författare)
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Error-Driven QoS Management in Imprecise Real-Time Databases
- 2003
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Ingår i: Euromicro Conference on Real-Time Systems,2003. - Los Alamitos, CA, USA : IEEE Computer Society. ; , s. 63-
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Konferensbidrag (refereegranskat)abstract
- In applications such as web-applications, e-commerce, and engine control, the demand for real-time data services has increased. In these applications, requests have to be processed within their deadlines using fresh data. Since the workload of these systems cannot be precisely predicted, they can become overloaded and as a result, deadline and freshness violations may occur. To address this problem we propose a QoS-sensitive approach based on imprecise computation, applied on transactions and data objects. We propose two algorithms FCS-HEF and FCS-HEDF that give a robust and controlled behavior of RTDBs in terms of transaction and data preciseness, even for transient overloads and with inaccurate run-time estimates of the transactions. Further, performance experiments show that the proposed algorithms outperform a set of baseline algorithms including FCS-EDF, which schedules the transactions using EDF.
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| 8. |
- Amirijoo, Mehdi, 1978-, et al.
(författare)
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Specification and Management of QoS in Imprecise Real-Time Databases
- 2003
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Ingår i: International Database Engineering and Applications Symposium,2003. - Los Alamitos, CA, USA : IEEE Computer Society. ; , s. 192-
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Konferensbidrag (refereegranskat)abstract
- Real-time applications such as e-commerce, flight control, chemical and nuclear control, and telecommunication are becoming increasingly sophisticated in their data needs, resulting in greater demands for real-time data services. Since the workload of real-time databases RTDBs, providing real-time data services, cannot be precisely predicted, they can become overloaded and thereby cause temporal violations, resulting in a damage or even a catastrophe. Imprecise computation techniques address this problem and allow graceful degradation during overloads. In this paper, we present a framework consisting of a model for expressing QoS requirements in terms of data and transaction preciseness, an architecture based on feedback control scheduling, and a set of algorithms implementing different policies and behaviors. Our approach gives a robust and controlled behavior of RTDBs, even for transient overloads and with inaccurate run-time estimates of the transactions. Further, performance experiments show that the proposed algorithms outperform a set of baseline algorithms, including FCS-EDF that schedules the transactions using EDF and feedback control.
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