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- Christiansson, Anna-Karin, 1947-, et al.
(author)
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Low order sampled-data H∞ control
- 2003
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In: Decision and Control, 2003. Proceedings. 42nd IEEE Conference on. ; 3, s. 2308 - 2313
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Conference paper (peer-reviewed)abstract
- A method for obtaining low order sampled-data H∞ controllers is presented. The method is mainly based on a parametric static feedback controller for a plant that is augmented with the controller dynamics. The design of a full-order controller is a convex problem, while the optimisation problem for lower order controllers is non convex. The proposed method starts with design of a full-order sampled-data controller using Riccati equations. Then this controller is reduced by an ordinary model reduction technique, and the reduced controller is used as an initial value for an iterative procedure using linear matrix inequalities (LMIs) in the search for an optimal controller. The matrix inequalities are in fact linear in either the Lyapunov matrix or the static controller matrix, why the solution to the non convex problem fundamentally is given by a bilinear matrix inequality (BMI). The order of the controller is reduced until the closed loop performance degrades too much. Simulations are shown for the control of a time delayed SISO-plant where the controller order can be reduced from 8th to 3rd order. Results are also shown from control of a MIMO-model of a jet engine where the reduction is successful from 15th to 4th order. It is argued that the non convexity is handled efficiently since the procedure uses a model reduction of the full-order controller as initial value.
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| 10. |
- Christiansson, Anna-Karin, 1947-, et al.
(author)
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Sampled-data H∞ˆž-control for time-varying hybrid systems
- 2001
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In: Dynamics of continuous, discrete and impulsive systems. - 1201-3390 .- 1918-2538. ; 8:4b, s. 427-444
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Journal article (peer-reviewed)abstract
- This paper presents sampled-data H∞ˆž-control of linear mixed continuous-time and discrete-time systems, including a mix of continuous-time and discrete-time performance signals and disturbances. However, neither continuous-time control signals nor continuous-time measurements are included. The sampling may well be multirate, i.e. different signals may be sampled by different rates, as long as a periodic pattern is repeated over the period, consisting of a number of sampling steps. In fact, the results are applicable even to arbitrary linear time-varying systems. The sampled-data system is discretised such that the continuous-time performance is reflected in the discretised or "lifted" system. This lifted system is combined with discrete-time updates at the sampling instants to achieve the sampled-data controller. The "hold-states" case is presented as a special application, when there is also a hold circuit at the controller output. The continuous-time Riccati equations with discrete-time updates then can be replaced by one discrete-time static feedback and filter Riccati equation respectively, which also reflect the intersample behaviour. Furthermore, convergence results between the discretised Riccati solutions and the corresponding continuous-time solutions are shown, when the sampling interval decreases towards zero. Simulations are shown when the results are applied to the control of a MIMO jet-engine model.
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| 11. |
- Christiansson, Anna-Karin, 1947, et al.
(author)
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Sampled-Data H-infinity-Control for Time-Varying Hybrid Systems
- 2001
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In: Dynamics of Continuous, Discrete and Impulsive Systems Series B: Applications and Algorithms. - 1492-8760. ; 8:4, s. 427-444
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Journal article (peer-reviewed)abstract
- This paper presents sampled-data H-infinity-control of linear mixed continuous-time and discrete-time systems, including a mix of continuous-time and discrete-time performance signals and disturbances. However, neither continuous-time control signals nor continuous-time measurements are included. The sampling may well be multirate, i.e. different signals may be sampled by different rates, as long as a periodic pattern is repeated over the period, consisting of a number of sampling steps. In fact, the results are applicable even to arbitrary linear time-varying systems.The sampled-data system is discretised such that the continuous-time performance is reflected in the discretised or "lifted" system. This lifted system is combined with discrete-time updates at the sampling instants to achieve the sampled-data controller. The "hold-states" case is presented as a special application, when there is also a hold circuit at the controller output. The continuous-time Riccati equations with discrete-time updates then can be replaced by one discrete-time static feedback and filter Riccati equation respectively, which also reflect the intersample behaviour.Furthermore, convergence results between the discretised Riccati solutions and the corresponding continuous-time solutions are shown, when the sampling interval decreases towards zero, Simulations are shown when the results are applied to the control of a MIMO jet-engine model.
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| 14. |
- Jolma, A, et al.
(author)
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Multiplexed massively parallel SELEX for characterization of human transcription factor binding specificities
- 2010
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In: Genome research. - : Cold Spring Harbor Laboratory. - 1549-5469 .- 1088-9051. ; 20:6, s. 861-873
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Journal article (peer-reviewed)abstract
- The genetic code—the binding specificity of all transfer-RNAs—defines how protein primary structure is determined by DNA sequence. DNA also dictates when and where proteins are expressed, and this information is encoded in a pattern of specific sequence motifs that are recognized by transcription factors. However, the DNA-binding specificity is only known for a small fraction of the ∼1400 human transcription factors (TFs). We describe here a high-throughput method for analyzing transcription factor binding specificity that is based on systematic evolution of ligands by exponential enrichment (SELEX) and massively parallel sequencing. The method is optimized for analysis of large numbers of TFs in parallel through the use of affinity-tagged proteins, barcoded selection oligonucleotides, and multiplexed sequencing. Data are analyzed by a new bioinformatic platform that uses the hundreds of thousands of sequencing reads obtained to control the quality of the experiments and to generate binding motifs for the TFs. The described technology allows higher throughput and identification of much longer binding profiles than current microarray-based methods. In addition, as our method is based on proteins expressed in mammalian cells, it can also be used to characterize DNA-binding preferences of full-length proteins or proteins requiring post-translational modifications. We validate the method by determining binding specificities of 14 different classes of TFs and by confirming the specificities for NFATC1 and RFX3 using ChIP-seq. Our results reveal unexpected dimeric modes of binding for several factors that were thought to preferentially bind DNA as monomers.
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| 15. |
- Medvedev, Alexander, et al.
(author)
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A systematic synthesis of a neural network-based smoother
- 1992
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In: Proceedings of the 1992 IEEE International Symposium on Intelligent Control. - New York : IEEE Communications Society. - 0780305469 ; , s. 147-151
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Conference paper (peer-reviewed)abstract
- A feedforward neural network (FNN) implementation of a finite-memory smoother (FMS) is proposed. For a linear time-invariant dynamic system with measurement and process white noise, a single-layer FNN with delayed inputs is found to possess the same structure as the FMS designed by the least-squares method. The FNN-based FMS features definite speed advantages over conventional approaches and intrinsically finite process memory. Due to its parallel structure and absence of state vector integration, the FNN suffices for real-time applications. A numerical example illustrates the design procedure
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| 16. |
- Medvedev, Alexander, et al.
(author)
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Continuous finite-memory deadbeat observer
- 1992
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In: Proceedings of the 1992 American Control Conference. - : IEEE Communications Society. - 0780302109 ; , s. 1800-1806
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Conference paper (peer-reviewed)abstract
- A significant class of model-based control approaches uses Kalman filters or Luenberger observers to estimate the plant state vector. Infinite dynamic observer memory inflicts a phenomenon generally referred to as divergence. To overcome this drawback, a structure that intrinsically has finite process memory and does not need state vector integration is proposed in this paper. The observer uses a finite number of delayed input/output measurements to reconstruct the state vector with zero error being provided with a process history over its largest time-delay. This property resembles the deadbeat observer performance for discrete time systems. Moreover, the largest time-delay value puts a natural limit to the observer memory. The Luenberger observer analogy proved to be a useful tool for the observer analysis and paves the way toward observer optimization.
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| 19. |
- Pang, Peter T. H., et al.
(author)
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An updated nuclear-physics and multi-messenger astrophysics framework for binary neutron star mergers
- 2023
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In: Nature Communications. - 2041-1723. ; 14:1
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Journal article (peer-reviewed)abstract
- The multi-messenger detection of the gravitational-wave signal GW170817, the corresponding kilonova AT2017gfo and the short gamma-ray burst GRB170817A, as well as the observed afterglow has delivered a scientific breakthrough. For an accurate interpretation of all these different messengers, one requires robust theoretical models that describe the emitted gravitational-wave, the electromagnetic emission, and dense matter reliably. In addition, one needs efficient and accurate computational tools to ensure a correct cross-correlation between the models and the observational data. For this purpose, we have developed the Nuclear-physics and Multi-Messenger Astrophysics framework NMMA. The code allows incorporation of nuclear-physics constraints at low densities as well as X-ray and radio observations of isolated neutron stars. In previous works, the NMMA code has allowed us to constrain the equation of state of supranuclear dense matter, to measure the Hubble constant, and to compare dense-matter physics probed in neutron-star mergers and in heavy-ion collisions, and to classify electromagnetic observations and perform model selection. Here, we show an extension of the NMMA code as a first attempt of analyzing the gravitational-wave signal, the kilonova, and the gamma-ray burst afterglow simultaneously. Incorporating all available information, we estimate the radius of a 1.4M⊙ neutron star to be R = 11.98+0.35−0.40 km.
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| 20. |
- Schulenberg, T., et al.
(author)
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European supercritical water cooled reactor
- 2011
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In: Nuclear Engineering and Design. - : Elsevier BV. - 0029-5493 .- 1872-759X. ; 241:9, s. 3505-3513
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Journal article (peer-reviewed)abstract
- The High Performance Light Water Reactor (HPLWR), how the European Supercritical Water Cooled Reactor is called, is a pressure vessel type reactor operated with supercritical water at 25 MPa feedwater pressure and 500 degrees C average core outlet temperature. It is designed and analyzed by a European consortium of 10 partners and 3 active supporters from 8 Euratom member states in the second phase of the HPLWR project. Most emphasis has been laid on a core with a thermal neutron spectrum, consisting of small fuel assemblies in boxes with 40 fuel pins each and a central water box to improve the neutron moderation despite the low coolant density. Peak cladding temperatures of the fuel rods have been minimized by heating up the coolant in three steps with intermediate coolant mixing. The containment design with its safety and residual heat removal systems is based on the latest boiling water reactor concept, but with different passive high pressure coolant injection systems to cause a forced convection through the core. The design concept of the steam cycle is indicating the envisaged efficiency increase to around 44%. Moreover, it provides the constraints to design the components of the balance of the plant. The project is accompanied by numerical studies of heat transfer of supercritical water in fuel assemblies and by material tests of candidate cladding alloys, performed by the consortium and supported by additional tests of the Joint Research Centre of the European Commission. Besides the scientific and technical progress, the HPLWR project turned out to be most successful in training the young generation of nuclear engineers in the technologies of light water reactors. More than 20 bachelor or master theses and more than 10 doctoral theses on HPLWR technologies have been submitted at partner organizations of this consortium since the start of this project.
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| 21. |
- Tirri, M E, et al.
(author)
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Two-photon excitation in fluorescence polarization receptor-ligand binding assay
- 2005
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In: Journal of Biomolecular Screening. - : Elsevier BV. - 1087-0571. ; 10:4, s. 314-319
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Journal article (peer-reviewed)abstract
- Fluorescence polarization is one of the most commonly used homogeneous assay principles in drug discovery for screening of potential lead compounds. In this article, the fluorescence polarization technique is combined with 2-photon excitation of fluorescence. Theoretically, the use of 2-photon excitation of fluorescence increases the volumetric sensitivity and polarization contrast of fluorescence polarization assays. The work in this report demonstrates these predictions for an estrogen receptor ligand binding assay.
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| 22. |
- Toivonen, Hannu T., et al.
(author)
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Damping of harmonic disturbances in sampled-data systems—parameterization of all optimal controllers
- 2003
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In: Automatica. - 0005-1098 .- 1873-2836. ; 39:1, s. 75-80
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Journal article (peer-reviewed)abstract
- Optimal damping of harmonic disturbances of known frequencies is studied for sampled-data systems. A sampled-data output feedback controller is designed to minimize the intersample variations of the controlled variable. The set of all stabilizing optimal controllers is obtained in terms of the Youla parameterization and a set of interpolation conditions at the disturbance frequencies, which ensure that the stationary cost is minimized.
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| 24. |
- Tuovinen, EA, et al.
(author)
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Novel Hemizygous IL2RG p.(Pro58Ser) Mutation Impairs IL-2 Receptor Complex Expression on Lymphocytes Causing X-Linked Combined Immunodeficiency
- 2020
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In: Journal of clinical immunology. - : Springer Science and Business Media LLC. - 1573-2592 .- 0271-9142. ; 40:3, s. 503-514
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Journal article (peer-reviewed)abstract
- Hypomorphic IL2RG mutations may lead to milder phenotypes than X-SCID, named variably as atypical X-SCID or X-CID. We report an 11-year-old boy with a novel c. 172C>T;p.(Pro58Ser) mutation in IL2RG, presenting with atypical X-SCID phenotype. We also review the growing number of hypomorphic IL2RG mutations causing atypical X-SCID. We studied the patient’s clinical phenotype, B, T, NK, and dendritic cell phenotypes, IL2RG and CD25 cell surface expression, and IL-2 target gene expression, STAT tyrosine phosphorylation, PBMC proliferation, and blast formation in response to IL-2 stimulation, as well as protein-protein interactions of the mutated IL2RG by BioID proximity labeling. The patient suffered from recurrent upper and lower respiratory tract infections, bronchiectasis, and reactive arthritis. His total lymphocyte counts have remained normal despite skewed T and B cells subpopulations, with very low numbers of plasmacytoid dendritic cells. Surface expression of IL2RG was reduced on his lymphocytes. This led to impaired STAT tyrosine phosphorylation in response to IL-2 and IL-21, reduced expression of IL-2 target genes in patient CD4+ T cells, and reduced cell proliferation in response to IL-2 stimulation. BioID proximity labeling showed aberrant interactions between mutated IL2RG and ER/Golgi proteins causing mislocalization of the mutated IL2RG to the ER/Golgi interface. In conclusion, IL2RG p.(Pro58Ser) causes X-CID. Failure of IL2RG plasma membrane targeting may lead to atypical X-SCID. We further identified another carrier of this mutation from newborn SCID screening, lost to closer scrutiny.
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| 26. |
- van Meel, Evelien R., et al.
(author)
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Early-life respiratory tract infections and the risk of school-age lower lung function and asthma: a meta-analysis of 150 000 European children
- 2022
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In: European Respiratory Journal. - : EUROPEAN RESPIRATORY SOC JOURNALS LTD. - 0903-1936 .- 1399-3003. ; 60:4
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Journal article (peer-reviewed)abstract
- Background Early-life respiratory tract infections might affect chronic obstructive respiratory diseases, but conclusive studies from general populations are lacking. Our objective was to examine if children with early-life respiratory tract infections had increased risks of lower lung function and asthma at school age. Methods We used individual participant data of 150 090 children primarily from the EU Child Cohort Network to examine the associations of upper and lower respiratory tract infections from age 6 months to 5 years with forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC), FEV1/FVC, forced expiratory flow at 75% of FVC (FEF75%) and asthma at a median (range) age of 7 (4-15) years. Results Children with early-life lower, not upper, respiratory tract infections had a lower school-age FEV1, FEV1/FVC and FEF75% (z-score range: -0.09 (95% CI -0.14- -0.04) to -0.30 (95% CI -0.36- -0.24)). Children with early-life lower respiratory tract infections had a higher increased risk of school-age asthma than those with upper respiratory tract infections (OR range: 2.10 (95% CI 1.98-2.22) to 6.30 (95% CI 5.64-7.04) and 1.25 (95% CI 1.18-1.32) to 1.55 (95% CI 1.47-1.65), respectively). Adjustment for preceding respiratory tract infections slightly decreased the strength of the effects. Observed associations were similar for those with and without early-life wheezing as a proxy for early-life asthma. Conclusions Our findings suggest that early-life respiratory tract infections affect development of chronic obstructive respiratory diseases in later life, with the strongest effects for lower respiratory tract infections.
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