| 1. |
- Moparthi, Satish Babu
(författare)
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Biophysical studies of protein folding upon interaction with molecular chaperones
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Proteins are biological macromolecules that serve all functions in cells. Every protein consists of a sequence of amino acids that is folded into a three‐dimensional structure to maintain the unique information it contains and to allow the protein to perform its specific actions. Improper folding caused by mutations in the amino acid sequence or environmental stress can lead to protein aggregation and ultimately to protein conformational disorders such as Parkinson’s disease and other dreadful diseases. Nature has developed special classes of protein guards called foldases and chaperones that can increase folding efficiency in the crowded intracellular milieu by preventing protein aggregation. The present research was aimed to elucidate how chaperones and foldases interact with their target proteins during folding. Special attention was focused on refolding kinetics and dynamic remodulation of site‐specific labeled cysteine variants of the protein human carbonic anhydrase (HCA II) upon interaction with the PPIase cyclophilin18 (Cyp18) and the chaperonin GroEL. Part of the work also compared properties of the group I chaperonin GroEL and the group II chaperonin TRiC, considering how they mediate structural alterations uponinteraction with the cytoskeletal target protein β‐actin. These interactions were studied by various fluorescence techniques, including fluorescence resonance energy transfer (FRET) and fluorescence anisotropy.Refolding of HCA II is an extremely complicated process that involves very fast and slow folding events, and research has shown that Cyp18 enhances the slow rate‐limiting cistrans proline isomerization steps during the refolding process. Furthermore, the active‐site mutant Cyp18R55A has been reported to posses only about 1% catalytic efficiency when acting on short chromogenic peptide substrates. However, we found that Cyp18R55A is as efficient as the wild‐type Cyp18 in accelerating HCA II refolding. We also noted that Cyp18 enhanced the final yield of the severely destabilized HCA IIH107N, and HCA IIH107F mutants by rescuing transient molten globule intermediates from misfolding as a result of condensation of hydrophobic patches at very early stages of the folding process. These findings led to the conclusion that Arg 55, located in the active site of Cyp18, is not required for prolyl cistrans isomerization of protein substrates, and that Cyp18 can function as both a folding catalyst and a chaperone during HCA II folding.Studies have demonstrated that sequestering of protein substrates by the chaperonin GroEL alone results in binding‐induced unfolding of aggregation‐prone molten globule intermediates. It was previously assumed that the co‐chaperonin GroES does not play an independent role in folding. However, based on FRET measurements, we found that GroEL alone stretches the protein substrate as an early event, and also that GroES alone can transiently remodulate the structure of the molten globule intermediate during the refolding process. In addition, GroES acts in i concert with GroEL to exert additive transient stretchng effects on the protein core, and it reverses the unfoldase activity of the GroEL termini, leading to compaction of the structure to attain the more constrained native state.Earlier investigations have shown that partially folded β‐actin binds to both GroEL and the TRiC chaperonin. However, only TRiC guides correct folding of β‐actin, whereas the GroEL–β‐actin interaction is non‐productive. Homo‐FRET measurements on β‐actin mutants labeled with fluorescein during interaction with GroEL and TRiC indicated that interplay with both the chaperonins lead to binding‐induced unfolding and dynamic remodulation of β‐actin. More specifically, the interaction with TRiC resulted in considerable expansion of the entrance of the ATP‐binding cleft of β‐actin by effecting specific modulation of the β‐actin sub‐domains followed by the formation of a compressed state (native‐like) during release from TriC. Conformational rearrangements of β‐actin by GroEL on the other and were ore modest. β‐actin remained rather compact in the complex and consequently did not lead to the native‐like state ven in the encapsulated cis‐cavity when capped by GroES.
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| 2. |
- Barkefors, Annea
(författare)
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Linear Quadratic Gaussian Controllers for Feedforward Active Noise Control : Pushing Performance and Moving Towards Adaptive Control
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Active noise control is a research area focused on using destructive interference of sound fields to attenuate undesired noise. Methods for active noise control are best suited for low frequency noise, as the complexity of the problem grows rapidly with frequency. Coincidentally, passive means of damping have the opposite quality in that they work better for higher frequencies and become bulky and impractical for low frequencies. Applications for active noise control range from fan noise in ducts, noise-cancelling headphones and noise in cars to propeller induced aircraft cabin noise. In this comprehensive summary, the underlying principles of active noise control are presented and the control problem is discussed. Several aspects of the control system are introduced to give an introduction to the research papers that are the basis of this licentiate thesis. The work behind the thesis is focused on a Multiple-Input Multiple-Output (MIMO) Minimal Mean Square Error (MMSE) Linear Quadratic Gaussian (LQG) feedforward controller. This controller is shown to achieve uniform damping in an extended region in space and push the upper frequency that can be controlled. The influence of different design variables has been investigated, and the properties of the control path analyzed with consideration of its ability to suppress noise of prescribed spectral properties over an extended region. In this context, it has been shown how to use the reproducibility of the primary noise path by the control path as an indication of achievable performance for a given control system. Finally, the controller has been adapted to follow changes in the primary noise statistics, an approach that seems promising to considerably raise the performance of the controller.
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| 3. |
- Fredriksson, Maria
(författare)
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From Customer Satisfaction to Citizen Interaction : a cooperation model for community development based on Total Quality Management
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Current problems with unemployment and the consequences of cut-down in the public sector need appropriate solutions, where private citizens perhaps take on more active roles than today, individually or in groups. The aim with this doctoral thesis is to contribute to one such solution, which is a cooperation model for societal development in local communities, based on Total Quality Management (TQM) and on the participation of many residents. The model is gradually developed with the help of collected experiences and opinions from three stakeholder groups in two different Swedish communities, as well as from general theories and literature. These groups are the quality-project initiators, the community residents and the local politicians. The disposition of the thesis is accordingly. The thesis contains two case studies. The first one concerns the use of TQM as a support of societal development in a local community. The improvement work is conducted within a non-profit organisation built on voluntary engagement. These experiences have then been compared, in the second case study, to the ones in another community where TQM is not used, but where the ambitions are the same. Here the framework for the improvement work is both a non-profit organisation and a for-profit one. The analyses indicate that TQM can be used with success within societal development, even if some of its tools or methodologies are interpreted in new ways, or not used at all. As TQM should be applied with regard to the type of organisation and its purpose, a certain flexibility is both expected and helpful. As far as management is concerned, the leadership needs to be “softer” and more diplomatic when managing unpaid volunteers, as compared to the situation in a commercial enterprise. Another observation is that the societal work is best conducted within groups, defined by situations or activities in life or in the society. An active resident can join a group according to interest. This is a modified version of the “quality circles” inherent to TQM. In a separate, and more theoretical study, the issue of adopting TQM to new sectors in society is discussed. In both the studied societies, there are difficulties to get residents involved or active, which puts into question the mandate with a large community project that aims at improving the quality of life for all residents. There are also difficulties with finding and renewing the leadership, and with communication with, above all, local politicians. Nevertheless, these politicians are in general positive to private initiatives like the ones in the two communities, and consider such projects very important for the future development of rural areas. They think that the experienced weaknesses can be reduced if the improvement work is distinctly defined and organised, if information and communication improve, and if the active residents become more educated about the procedures and limitations of the political governing of the communities. These and other observations of the two communities lead to a model where a cooperation between societal stakeholders develop in three phases; the start-up, the establishment and the continuation of the work. Each phase is discussed separately, and advice is given how to avoid, or meet, various problems that are likely to appear along the way.
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| 4. |
- Saarinen, Linn, 1980-
(författare)
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The Frequency of the Frequency : On Hydropower and Grid Frequency Control
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Variations in the electricity consumption and production connected to the power system have to be balanced by active control. Hydropower is the most important balancing resource in the Nordic system, and will become even more important as the share of variable renewable energy sources increases. This thesis concerns balancing of active power, especially the real-time balancing called frequency control. The thesis starts in a description of the situation today, setting up models for the behaviour of hydropower units and the power system relevant to frequency control, and comparing the models with experiments on several hydropower units and on the response of the Nordic grid. It is found that backlash in the regulating mechanisms in hydropower units have a strong impact on the quality of the delivered frequency control. Then, an analysis of what can be done right now to improve frequency control and decrease its costs is made, discussing governor tuning, filters and strategies for allocation of frequency control reserves. The results show that grid frequency quality could be improved considerably by retuning of hydropower governors. However, clear technical requirements and incentives for good frequency control performance are needed. The last part of the thesis concerns the impact from increased electricity production from variable renewable energy sources. The induced balancing need in terms of energy storage volume and balancing power is quantified, and it is found that with large shares of wind power in the system, the energy storage need over the intra-week time horizon is drastically increased. Reduced system inertia due to higher shares of inverter connected production is identified as a problem for the frequency control of the system. A new, linear synthetic inertia concept is suggested to replace the lost inertia and damping. It is shown that continuously active, linear synthetic inertia can improve the frequency quality in normal operation and decrease wear and tear of hydropower units delivering frequency control.
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| 5. |
- Tayamon, Soma, 1985-
(författare)
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Nonlinear System Identification and Control Applied to Selective Catalytic Reduction Systems
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The stringent regulations of emission levels from heavy duty vehicles create a demand for new methods for reducing harmful emissions from diesel engines. This thesis deals with the modelling of the nitrogen oxide (NOx) emissions from heavy duty vehicles using a selective catalyst as an aftertreatment system, utilising ammonia (NH3) for its reduction. The process of the selective catalytic reduction (SCR) is nonlinear, since the result of the chemical reactions involved depends on the load operating point and the temperature.The purpose of this thesis is to investigate different methods for nonlinear system identification of SCR systems with control applications in mind. The main focus of the thesis is on finding suitable techniques for effective NOx reduction without the need of over dosage of ammonia. By using data collected from a simulator together with real measured data, new black-box identification techniques are developed. Scaling and convergence properties of the proposed algorithms are analysed theoretically. Some of the resulting models are used for controller development using e.g. feedback linearisation techniques, followed by validation in a simulator environment. The benefits of nonlinear modelling and control of the SCR system are highlighted in a comparison with control based on linear models of the system. Further, a multiple model approach is investigated for simultaneous control of NOx and tailpipe ammonia. The results indicate an improvement in terms of ammonia slip reduction in comparison with models that do not take the ammonia slip into account. Another approach to NOx reduction is achieved by controlling the SCR temperature using techniques developed for LPV systems. The results indicate a reduction of the accumulated NOx.
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| 6. |
- Brus, Linda, 1977-
(författare)
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Nonlinear Identification and Control with Solar Energy Applications
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nonlinear systems occur in industrial processes, economical systems, biotechnology and in many other areas. The thesis treats methods for system identification and control of such nonlinear systems, and applies the proposed methods to a solar heating/cooling plant. Two applications, an anaerobic digestion process and a domestic solar heating system are first used to illustrate properties of an existing nonlinear recursive prediction error identification algorithm. In both cases, the accuracy of the obtained nonlinear black-box models are comparable to the results of application specific grey-box models. Next a convergence analysis is performed, where conditions for convergence are formulated. The results, together with the examples, indicate the need of a method for providing initial parameters for the nonlinear prediction error algorithm. Such a method is then suggested and shown to increase the usefulness of the prediction error algorithm, significantly decreasing the risk for convergence to suboptimal minimum points. Next, the thesis treats model based control of systems with input signal dependent time delays. The approach taken is to develop a controller for systems with constant time delays, and embed it by input signal dependent resampling; the resampling acting as an interface between the system and the controller. Finally a solar collector field for combined cooling and heating of office buildings is used to illustrate the system identification and control strategies discussed earlier in the thesis, the control objective being to control the solar collector output temperature. The system has nonlinear dynamic behavior and large flow dependent time delays. The simulated evaluation using measured disturbances confirm that the controller works as intended. A significant reduction of the impact of variations in solar radiation on the collector outlet temperature is achieved, though the limited control range of the system itself prevents full exploitation of the proposed feedforward control. The methods and results contribute to a better utilization of solar power.
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| 7. |
- Brus, Linda
(författare)
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Recursive black-box identification of nonlinear state-space ODE models
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nonlinear system identification methods is a topic that has been gaining interest over the last years. One reason is the many application areas in controller design and system development. However, the problem of modeling nonlinear systems is complex and finding a general method that can be used for many different applications is difficult.This thesis treats recursive identification methods for identification of systems that can be described by nonlinear ordinary differential equations. The general model structure enables application to a wide range of processes. It is also suitable for usage in combination with many nonlinear controller design methods.The first two papers of the thesis illustrates how a recursive prediction error method (RPEM) can be used for identification of an anaerobic digestion process and a solar heating system. In the former case the model complexity is significantly reduced compared to a semi-physical model of the system, without loosing much in model performance. In the latter case it is shown that it is possible to reach convergence even for a small data set, and that the resulting model is of comparable quality as a previously published grey-box model of the same system.The third paper consists of a convergence analysis of the studied RPEM. The analysis exploits averaging analysis using an associated ordinary differential equation, and formulates conditions for convergence to a minimum of the criterion function. Convergence to a true parameter set is also illustrated by an example.The fourth, and last, paper of this thesis addresses the problem of finding suitable initial parameters e.g. for the RPEM. With a potentially non-convex criterion function the choice of initial parameters becomes decisive for whether the algorithm converges to the global optimum, or a local one. The suggested initialization algorithm is a Kalman filter based method. Experiments using a simulated example show that the Kalman based method can, under beneficial circumstances, be used for initialization of the RPEM. The result is further supported by successful identification experiments of a laboratory scale cascaded tanks process, where the Kalman based method was used for initialization.
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| 8. |
- Ekman, Mats, 1970-
(författare)
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Modeling and Control of Bilinear Systems : Application to the Activated Sludge Process
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis concerns modeling and control of bilinear systems (BLS). BLS are linear but not jointly linear in state and control. In the first part of the thesis, a background to BLS and their applications to modeling and control is given. The second part, and likewise the principal theme of this thesis, is dedicated to theoretical aspects of identification, modeling and control of mainly BLS, but also linear systems. In the last part of the thesis, applications of bilinear and linear modeling and control to the activated sludge process (ASP) are given.
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| 9. |
- Halvarsson, Björn, 1978-
(författare)
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Interaction Analysis in Multivariable Control Systems : Applications to Bioreactors for Nitrogen Removal
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many control systems of practical importance are multivariable. In such systems, each manipulated variable (input signal) may affect several controlled variables (output signals) causing interaction between the input/output loops. For this reason, control of multivariable systems is typically much more difficult compared to the single-input single-output case. It is therefore of great importance to quantify the degree of interaction so that proper input/output pairings that minimize the impact of the interaction can be formed. For this, dedicated interaction measures can be used. The first part of this thesis treats interaction measures. The commonly used Relative Gain Array (RGA) is compared with the Gramian-based interaction measures the Hankel Interaction Index Array (HIIA) and the Participation Matrix (PM) which consider controllability and observability to quantify the impact each input signal has on each output signal. A similar measure based on the norm is also investigated. Further, bounds on the uncertainty of the HIIA and the PM in case of uncertain models are derived. It is also shown how the link between the PM and the Nyquist diagram can be utilized to numerically calculate such bounds. Input/output pairing strategies based on linear quadratic Gaussian (LQG) control are also suggested. The key idea is to design single-input single-output LQG controllers for each input/output pair and thereafter form closed-loop multivariable systems for each control configuration of interest. The performances of these are compared in terms of output variance. In the second part of the thesis, the activated sludge process, commonly found in the biological wastewater treatment step for nitrogen removal, is considered. Multivariable interactions present in this type of bioreactor are analysed with the tools discussed in the first part of the thesis. Furthermore, cost-efficient operation of the activated sludge process is investigated.
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| 10. |
- Samuelsson, Pär, 1973-
(författare)
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Control of Nitrogen Removal in Activated Sludge Processes
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- More stringent requirements on nitrogen removal from wastewater are the motivation for this thesis. In order to improve treatment results and enhance cost-efficient operation of wastewater treatment plants, model based control strategies are presented. A Java based simulator for activated sludge processes (JASS) is presented. The graphical user interface, educational experiences and implemented control strategies are discussed. Controlling the addition of an external carbon source is the next topic discussed. A simple model based feedforward controller is derived and evaluated in a simulation study. The controller attenuates process disturbances quickly. Further, two feedforward controllers for adjusting the aeration volume in activated sludge processes are derived. The aim of the volume control strategies was to efficiently dampen the impact of process disturbances without using an excessively high dissolved oxygen concentration. The simulation results are promising and show that the aeration volume may be a feasible control variable. A linearisation method for static input non-linearities is presented. The method gives essentially the same result as the existing standard method, but possesses some implementational advantages. The method is used to linearise the non-linear oxygen transfer function of an activated sludge process in an application study. Multivariable interactions in a process model describing nitrate removal in an activated sludge process are studied using the well known RGA method as well as a relatively novel tool based on Hankel norms. The results of the analysis are compared to conclusions drawn from common process knowledge and are used to design a multivariable control strategy. It was found that process disturbances may be rejected faster using multivariable control. Finally, the operational costs of the denitrification process are investigated and visualised graphically. Cost optimal regions are found by a numerical grid search. Procedures for controlling the denitrification process in a cost-efficient way are described.
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