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| 4. |
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| 5. |
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| 7. |
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| 8. |
- Aly, Gharib, et al.
(författare)
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Dynamical behavior of mixer settlers II: Models and identification
- 1972
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Ingår i: Journal of Applied Chemistry and Biotechnology. - : Wiley. - 0375-9210. ; 22:11, s. 1165-1184
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Tidskriftsartikel (refereegranskat)abstract
- Mathematical models explaining the dynamics of the mixer-settler unit are investigated. It is shown that the static model is inadequate in this context and a two-part dynamic model is proposed.
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| 9. |
- Andersson, Mikael, et al.
(författare)
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Admission control of the Apache web server
- 2004
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Ingår i: Seventeenth Nordic Teletraffic Seminar, NTS 17, Fornebu, Norway, 25-27 August 2004. - 8242305951
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Konferensbidrag (refereegranskat)abstract
- Web sites are exposed to high rates of incoming requests. The servers may become overloaded during temporary traffic peaks when more requests arrive than the server is designed for. An admission control mechanism rejects some requests whenever the arriving traffic is too high and thereby maintains an acceptable load in the system. This paper presents how admission control mechanisms can be designed with a combination of queueing theory and control theory. In this paper we model an Apache web server as a G/G/1-system and then design a PI-controller, commonly used in automatic control, for the server. The controller has been implemented as a module inside the Apache source code. Measurements from the laboratory setup show how robust the implemented controller is, and how it correspond to the results from the theoretical analysis.
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| 10. |
- Barros, P R, et al.
(författare)
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Frequency domain sensitivity shaping in pole placement control
- 1998
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Konferensbidrag (refereegranskat)abstract
- In this paper the frequency domain sensitivity shaping of pole placement controllers is discussed. The sensitivity function is shaped in order to improve robustness and disturbance attenuation, and it is done with the use of controller overparametrization. A design example shows the capabilities of the method. The computation is done by a weighted least squares procedure which is suitable for adaptive control.
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| 11. |
- Barros, P. R., et al.
(författare)
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Frequency domain sensitivity shaping using overparametrized controllers
- 1997
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Ingår i: IEEE Xplore : Proceedings of the 36th IEEE Conference on Decision and Control - Proceedings of the 36th IEEE Conference on Decision and Control. - 0780341872 ; , s. 2716-2721
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Konferensbidrag (refereegranskat)abstract
- A frequency domain, weighted least squares, sensitivity function shaping procedure is presented. Pole placement is used as the basic servo design procedure. Controller overparametrization gives the degree of freedom for shaping the sensitivity function. A benchmark design example shows the capabilities of the method. The computation is simple making the design suitable for adaptive control.
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| 12. |
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| 13. |
- Bexell, Göran, et al.
(författare)
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"Ge forskningen mer resurser"
- 2003
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Ingår i: Sydsvenska dagbladet. - 1104-0068.
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Tidskriftsartikel (populärvet., debatt m.m.)
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| 14. |
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| 15. |
- Borisson, Ulf, et al.
(författare)
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An Industrial Application of a Self-Tuning Regulator
- 1974
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Ingår i: 4th IFAC/IFIP International Conference on Digital Computer Applications to Process Control. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783540066200 ; 93
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Konferensbidrag (refereegranskat)abstract
- An implementation of a self-tuning regulator is described. The regulator algorithm consists of two steps. Firstly the parameters of a model of the process are estimated in real time using the method of least squares. Secondly a minimum variance regulator based on the estimated parameters is computed at each sampling interval. Implementation of the algorithm on a process computer is discussed. Questions concerning program structure and storage requirements are considered. Results from the moisture content control on a paper machine are presented. The experiences are very good concerning the start-up behaviour as well as the stationary behaviour of the self-tuning regulator.
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| 16. |
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| 17. |
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| 18. |
- Fabri, Simon G, et al.
(författare)
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Dual adaptive extremum control of Hammerstein models
- 2015
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Ingår i: International Journal of Control. - : Informa UK Limited. - 0020-7179 .- 1366-5820. ; 88:6, s. 1271-1286
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Tidskriftsartikel (refereegranskat)abstract
- A novel dual adaptive controller for extremum control of stochastic and uncertain nonlinear Hammerstein systems is proposed. The design is based on the innovations dual control cost function originally developed for conventional adaptive control of linear systems. However, the design process is extensively modified and developed so as to cater for the extremum control scenario. This is a more challenging problem because the reference input is itself a nonlinear function of the unknown system parameters, rather than an independent and predefined external reference signal. As in all dual adaptive schemes, it leads to a control law that balances out the need for caution, due to parameter uncertainty, with the conflicting requirement of probing that acts to quickly reduce parameter uncertainty. The proposed controller’s performance is analysed through extensive Monte Carlo simulation trials and compared with several other non-dual adaptive extremum controllers. It is shown that the novel extremum innovations dual controller is superior to other types of adaptive control systems that are based on a certainty equivalence assumption. In addition, a novel statistical measure is introduced that yields a more objective evaluation of the Monte Carlo simulation results.
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| 19. |
- Gäfvert, Magnus, et al.
(författare)
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On the Effect of Transient Data-Errors in Controller Implementations
- 2003
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Ingår i: Proceedings of the 2003 American Control Conference, vols 1-6. - 0743-1619. - 0780378962 ; 4, s. 3411-3416
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Konferensbidrag (refereegranskat)abstract
- Computer-level faults leading to data errors in computations arepredicted to occur increasingly frequent in future microprocessors.This work discusses the impact of such errors on closed-loopperformance in implementations of digital control systems. A method torender a control system more robust to data errors by introducingartificial signal limits and then combine them with an anti-windupscheme is presented and exemplified. Accepted for publication.
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| 20. |
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| 21. |
- Hagander, Per, et al.
(författare)
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A Self-Tuning Filter for Fixed-Lag Smoothing
- 1976
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Konferensbidrag (refereegranskat)abstract
- The problem of estimating a discrete-time stochastic signal which is corrupted by additive white measurement noise is discussed. How the stationary solution to the fixed-lag smoothing problem can be obtained is shown. The first step is to construct an innovation model for the process. It is then shown how the fixed-lag smoother can be determined from the polynomials in the transfer function of the innovation model. In many applications, the signal model and the characteristics of the noise process are unknown. It is shown that it is possible to derive an algorithm which on-line finds the optimal fixed-lag smoother, a self-tuning smoother. The self-tuning smoother consists of two parts: an on-line estimation of the parameters in the one-step ahead predictor of the measured signal, and a computation of the smoother coefficients by simple manipulation of the predictor parameters. The smoother has good transient, as well as good asymptotic, properties.
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| 22. |
- Hagander, Per, et al.
(författare)
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A Self-Tuning Filter for Fixed-Lag Smoothing
- 1977
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Ingår i: IEEE Transactions on Information Theory. - 0018-9448. ; 23:3, s. 377-384
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Tidskriftsartikel (refereegranskat)abstract
- The problem of estimating a discrete-time stochastic signal which is corrupted by additive white measurement noise is discussed. How the stationary solution to the fixed-lag smoothing problem can be obtained is shown. The first step is to construct an innovation model for the process. It is then shown how the fixed-lag smoother can be determined from the polynomials in the transfer function of the innovation model. In many applications, the signal model and the characteristics of the noise process are unknown. It is shown that it is possible to derive an algorithm which on-line finds the optimal fixed-lag smoother, a self-tuning smoother. The self-tuning smoother consists of two parts: an on-line estimation of the parameters in the one-step ahead predictor of the measured signal, and a computation of the smoother coefficients by simple manipulation of the predictor parameters. The smoother has good transient, as well as good asymptotic, properties.
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| 23. |
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| 24. |
- Karlsson, Magnus, et al.
(författare)
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Evaluation of models for the steam supply system to improve control of the paper dryer
- 2003
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Ingår i: Proceedings TAPPI 2003 Spring Technical Conference.
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Konferensbidrag (refereegranskat)abstract
- The possibility of reducing the transient times at grade changes in paper production and machine start-ups on the paper machines has highlighted the need for increased knowledge of the steam supply system. Models in this area have been presented in previous work and it is of interest to compare these models with each other and evaluate them against experimental data. This paper reports on the results obtained from measurements on an industrial paper dryer. Step responses as well as the dynamic changes caused by new set points for the control system are examined. The two models are derived from different disciplines and comparison between these will be presented. The first model will provide estimations of the heat transfer coefficients in the condensate layer as well as the coefficient between the cylinder and the paper. This model is based on physical properties and first principles. The second model is a linear process model, written in the Laplace operator as a transfer function. This model is based on input-output data, a black box model, where the input and the output are the experimental data from the paper machine.
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| 25. |
- Karlsson, Magnus, et al.
(författare)
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Reducing Moisture Transients in the Paper-Machine Drying Section with the Mid-ranging Control Technique
- 2005
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Ingår i: Nordic Pulp & Paper Research Journal. - : Walter de Gruyter GmbH. - 0283-2631 .- 2000-0669. ; 20:2, s. 150-155
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Tidskriftsartikel (refereegranskat)abstract
- A new control strategy using feedback control has been developed for the multi-cylinder paper dryer configuration to reduce moisture transients in the drying section. The air system in the blow boxes was used to control the fast moisture transients in the paper machine. The new control system was combined with a previously developed physical model and was then compared with a conventional moisture control system. The comparison concerned the ability to restore the moisture ratio for two different dynamic changes, a moisture disturbance and a paper grade change. By combining the conventional steam control loop with an air loop, it was possible to significantly decrease the transient of the moisture disturbance.
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| 26. |
- Kihl, Maria, et al.
(författare)
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Analysis of admission control mechanisms using non-linear control theory
- 2003
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Ingår i: Proceedings of the 8th IEEE International Symposium on Computers and Communication. Vol. 2. - 076951961X ; , s. 1306-1311
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Konferensbidrag (refereegranskat)abstract
- All service control nodes can be modelled as a server system with one or more servers processing incoming requests. In this paper we show how non-linear control theory may be used when analyzing admission control mechanisms for server systems. Two models are developed, one linear and one non-linear. We show that, due to the non-linearities appearing in a real server system, linear control theory is sufficient when designing controllers for these systems. With non-linear analysis, however, the dynamics of a server system may be analysed and taken care of by choosing the controller parameters appropriately.
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| 27. |
- Kihl, Maria, et al.
(författare)
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Control-theoretic Analysis of Admission Control Mechanisms for Web Server Systems
- 2008
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Ingår i: World Wide Web. - : Springer Science and Business Media LLC. - 1386-145X .- 1573-1413. ; 11:1, s. 93-116
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Tidskriftsartikel (refereegranskat)abstract
- Web sites are exposed to high rates of incoming requests. The servers may become overloaded during temporary traffic peaks when more requests arrive than the server is designed for. An admission control mechanism rejects some requests whenever the arriving traffic is too high and thereby maintains an acceptable load in the system. This paper presents how admission control mechanisms can be designed with a combination of queueing theory and control theory. In this paper we model an Apache web server as a GI/G/1-system and then design a PI-controller, commonly used in automatic control, for the server. The controller has been implemented as a module inside the Apache source code. Measurements from the laboratory setup show how robust the implemented controller is, and how it corresponds to the results from the theoretical analysis.
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| 28. |
- Kihl, Maria, et al.
(författare)
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Control theoretic modelling and design of admission control mechanisms for server systems
- 2004
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Ingår i: NETWORKING 2004, Networking Technologies, Services, and Protocols; Performance of Computer and Communication Networks; Mobile and Wireless Communications / Lecture Notes in Computer Science. - 1611-3349 .- 0302-9743. - 9783540219590 ; 3042, s. 1366-1371
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Konferensbidrag (refereegranskat)abstract
- The admission control mechanism is an important part of many communication systems. In this paper we investigate load control mechanisms for server systems, that is systems that may be modelled as queueing systems. We show how control theory can be used when designing controllers for a G/G/1-system. We design a PI-controller for the system and compare the steady-state and transient behavior of this controller with the behavior of a static controller.
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| 29. |
- Kihl, Maria, et al.
(författare)
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Performance Modelling and Control of Server Systems using Non-linear Control Theory
- 2003
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Ingår i: Providing quality of service in heterogeneous environments : proceedings of the 18th International Teletraffic Congress, ITC-18, Berlin, Germany, 31 August - 5 September 2003 (Teletraffic science and engineering ; vol. 5). - 0444514554 ; 5A-B, s. 1151-1160
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Konferensbidrag (refereegranskat)abstract
- All service control nodes, for example SCPs, HLRs, and MSCs, are constructed as a server system with one or more servers that process incoming requests. Since service control nodes are sensitive to overload, admission control mechanisms are often implemented. In this paper, we model and analyse admission control mechanisms for server systems with control theoretic methods. We develop a nonlinear stochastic control theoretic model of a GI/G/1-system. Further, we show that this model can be used to design admission control mechanisms that behave well in the “real” system, that is the queuing system. We develop two types of controllers for the system, one PI-controller and one RST-controller, both commonly used in automatic control. Also, we discuss some of the limitations of previous work in this area, in which only deterministic and linear models have been used.
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| 30. |
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| 31. |
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| 32. |
- Li, Zheng, et al.
(författare)
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Minimum Variance Prediction for Linear Time-Varying Systems
- 1997
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Ingår i: Automatica. - 0005-1098. ; 33:4, s. 607-618
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Tidskriftsartikel (refereegranskat)abstract
- A minimum variance predictor is developed using pseudocommutation for linear time-varying systems described by an autoregressive moving average model.
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| 33. |
- Li, Zheng, et al.
(författare)
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Minimum Variance Prediction for Linear Time-Varying Systems
- 1994
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Ingår i: IFAC Proceedings Volumes. ; 27:8
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Konferensbidrag (refereegranskat)abstract
- In this paper we study the problem of minimum variance prediction for linear time-varying systems. We consider the standard time-varying autoregression moving average (ARMA) model and develop a predictor which guarantees minimum variance prediction for a large class of linear time-varying systems. The predictor is developed based on a pseudocommutation technique for dealing with noncommutativity of linear time-varying operators in a transfer operator framework. We also show connections between this input-output predictor and the Kalman predictor via an example.
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| 34. |
- Lindoff, Bengt, et al.
(författare)
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Analysis of Approximations to Dual Control
- 1999
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Ingår i: International Journal of Adaptive Control and Signal Processing. - 0890-6327. ; 13, s. 593-620
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Tidskriftsartikel (refereegranskat)abstract
- The dual control problem for time-varying or non-linear systems is inherently analytically and computationally untractable due to the demand of alternating minimizations and mean value computations. Hence, it has to be approached using approximations leading to suboptimal dual control. The core of the successful approximative controller is its ability to be able to consider future changes in the development of the parameters. This paper presents an analysis of the dual-control concept, and a comparison between a number of suboptimal controllers. The analytical comparisons are based on a reformulation of the dual-control problem. The reformulation makes it possible to interpret and understand the nature of the different approximations to dual control, in particular the Adaptive Predictive Controller (APC) and the Active Suboptimal Dual Controller (ASOD). Furthermore, it makes the origin of the computational problems encountered more clear, and suggests new alternatives for approximation. The analysis is carried through on relatively simple examples and is illustrated with simulations. The performance of the controllers when applied to more complicated time-varying systems is illustrated with simulations as well.
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| 35. |
- Lindoff, Bengt, et al.
(författare)
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Analysis of suboptimal dual control
- 1998
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Konferensbidrag (refereegranskat)abstract
- A reformulation of the dual control problem makes it possible to interpret and understand the nature of different approximations to dual control, in particular the Adaptive Predictive Controller (APC) and the Active Suboptimal Dual Controller (ASOD). The analysis makes the origin of the computational problems more clear, and suggests new alternatives for approximations.
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| 36. |
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| 37. |
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| 38. |
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| 39. |
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| 40. |
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| 41. |
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| 42. |
- Ljung, Lennart, 1946-, et al.
(författare)
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On a Stabilizing Property of Adaptive Regulators
- 1976
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Ingår i: Proceedings of the 4th IFAC Symposium on Identification and System Parameter Estimation. - 9780444851130 ; , s. 380-388
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Konferensbidrag (refereegranskat)
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| 43. |
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| 49. |
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| 50. |
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Master's Theses in Automatic Control 1977-1978
- 1979
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report contains abstracts of master thesis (examensarbete) made at the Department of Automatic Control, Lund, during the academic year 77/78. During this year 16 theses were made by 23 students. The theses are written in Swedish with an English abstract.
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