| 1. |
- Brannmark, Cecilia, et al.
(författare)
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Mass and Information Feedbacks through Receptor Endocytosis Govern Insulin Signaling as Revealed Using a Parameter-free Modeling Framework
- 2010
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Ingår i: Journal of Biological Chemistry. - : American Society for Biochemistry and Molecular Biology. - 0021-9258 .- 1083-351X. ; 285:26, s. 20171-20179
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Tidskriftsartikel (refereegranskat)abstract
- Insulin and other hormones control target cells through a network of signal-mediating molecules. Such networks are extremely complex due to multiple feedback loops in combination with redundancy, shared signal mediators, and cross-talk between signal pathways. We present a novel framework that integrates experimental work and mathematical modeling to quantitatively characterize the role and relation between coexisting submechanisms in complex signaling networks. The approach is independent of knowing or uniquely estimating model parameters because it only relies on (i) rejections and (ii) core predictions (uniquely identified properties in unidentifiable models). The power of our approach is demonstrated through numerous iterations between experiments, model-based data analyses, and theoretical predictions to characterize the relative role of co-existing feedbacks governing insulin signaling. We examined phosphorylation of the insulin receptor and insulin receptor substrate-1 and endocytosis of the receptor in response to various different experimental perturbations in primary human adipocytes. The analysis revealed that receptor endocytosis is necessary for two identified feedback mechanisms involving mass and information transfer, respectively. Experimental findings indicate that interfering with the feedback may substantially increase overall signaling strength, suggesting novel therapeutic targets for insulin resistance and type 2 diabetes. Because the central observations are present in other signaling networks, our results may indicate a general mechanism in hormonal control.
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| 2. |
- Glad, Torkel, 1947-
(författare)
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Dealing with Inequalities in Polynomial Models
- 2012
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Ingår i: Proceedings of the 16th IFAC Symposium on System Identification. - 9783902823069 ; , s. 936-940
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Konferensbidrag (refereegranskat)abstract
- It is described how set membership identification and model rejection for polynomial models can be described using polynomial inequalities and inequations. Using difference algebra methods these problems can be reduced to a form based on so called autoreduced sets. It is shown that these descriptions generalize state space descriptions. It is also discussed how special forms of autoreduced sets can make calculations based on interval methods easier to implement.
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| 3. |
- Lyzell, Christian, et al.
(författare)
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Difference Algebra and System Identification
- 2011
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Ingår i: Automatica. - : Elsevier. - 0005-1098 .- 1873-2836. ; 47:9, s. 1896-1904
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Tidskriftsartikel (refereegranskat)abstract
- The framework of differential algebra, especially Ritts algorithm, has turned out to be a useful tool when analyzing the identifiability of certain nonlinear continuous-time model structures. This framework provides conceptually interesting means to analyze complex nonlinear model structures via the much simpler linear regression models. One difficulty when working with continuous-time signals is dealing with white noise in nonlinear systems. In this paper, difference algebraic techniques, which mimic the differential-algebraic techniques, are presented. Besides making it possible to analyze discrete-time model structures, this opens up the possibility of dealing with noise. Unfortunately, the corresponding discrete-time identifiability results are not as conclusive as in continuous time. In addition, an alternative elimination scheme to Ritts algorithm will be formalized and the resulting algorithm is analyzed when applied to a special form of the NFIR model structure.
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| 4. |
- Simon, Daniel, et al.
(författare)
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Reference Tracking MPC using Terminal Set Scaling
- 2012
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Ingår i: Proceedings of the 51st IEEE Conference on Decision and Control. - Linköping : Linköping University Electronic Press. - 9781467320658 - 9781467320641 ; , s. 4543-4548
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A common assumption when proving stability of linear MPC algorithms fort racking applications is to assume that the desired setpoint is located farinto the interior of the feasible set. The reason for this is that the terminal state constraint set which is centered around the setpoint must be contained within the feasible set. In many applications this assumption can be severly limiting since the terminal set is relatively large and therefore limits how close the setpoint can be to the boundary of the feasible set. We present simple modifications that can be performed in order to guarantee stability and convergence to setpoints located arbitrarily close to the boundary of the feasible set. The main idea is to introduce a scaling variable which dynamically scales the terminal state constraint set and therefore allowsa setpoint to be located arbitrarily close to the boundary. In addition to this the concept of pseudo setpoints are used to gain the maximum possible region of attraction and to handle infeasible references. Recursive feasibility and convergence to the desired setpoint, or its closest feasible alternative, is proven and a motivating example of controlling an agile fighter aircraftis given.
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| 5. |
- Tidefelt, Henrik, et al.
(författare)
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A Relaxation of the Strangeness Index
- 2010
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- A new index closely related to the strangeness index of a differential-algebraic equation is presented.Basic properties of the strangeness index are shown to be valid also for the new index. The definitionof the new index is conceptually simpler than that of the strangeness index, hence making it potentiallybetter suited for both practical applications and theoretical developments.
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