Nonlinear Model-Based Control of Unstable Wells

This paper illustrates the potential of nonlinear model-based control applied for stabilization of unstable flow in oil wells. A simple empirical model is developed that describes the qualitative behavior of the downhole pressure during severe riser slugging. A nonlinear controller is designed by an integrator backstepping approach, and stabilization for open-loop unstable pressure setpoints is demonstrated. The proposed backstepping controller is shown in simulations to perform better than PI and PD controllers for low pressure setpoints, and is in addition easier to tune. Operation at a low pressure setpoint is desirable since it corresponds to a high production flow rate. The simulation results are presented to illustrate the effectiveness of proposed control scheme

LEGO Mindstorms og MATLAB; anvendt matematikk/fysikk og programmering i skjønn forening

Ved å kombinere LEGO Mindstorms og MATLAB kan studenter introduseres for programmering på en måte som i stor grad er prosjektbasert og som innebærer såkalt studentaktiv læring. Denne artikkel beskriver hvordan Universitetet i Stavanger benytter denne kombinasjonen for data- og elektrostudenter i første semester som en del av Ingeniørfaglig innføringsemne. Det blir også beskrevet hvordan studentene blir organisert i grupper og hvilke forutsetninger som må til for at én faglig ansvarlig skal kunne veilede 160 studenter og gi faglige tilbakemeldinger til samtlige. Videre beskrives hvordan det tilrettelegges for å oppnå individuell læring i gruppearbeidet. Programmeringen er knyttet opp mot praktiske anvendelser fra fysikken som gjør bruk av anvendt matematikk i form av blant annet numerisk integrasjon, filtrering og numerisk derivasjon. Dette åpner for mange motiverende prosjekter som studentene har stor glede av å gjennomføre

Variable setpoint as a relaxing component in physiological control

Setpoints in physiology have been a puzzle for decades, and especially the notion of fixed or variable setpoints have received much attention. In this paper, we show how previously presented homeostatic controller motifs, extended with saturable signaling kinetics, can be described as variable setpoint controllers. The benefit of a variable setpoint controller is that an observed change in the concentration of the regulated biochemical species (the controlled variable) is fully characterized, and is not considered a deviation from a fixed setpoint. The variation in this biochemical species originate from variation in the disturbances (the perturbation), and thereby in the biochemical species representing the controller (the manipulated variable). Thus, we define an operational space which is spanned out by the combined high and low levels of the variations in (1) the controlled variable, (2) the manipulated variable, and (3) the perturbation. From this operational space, we investigate whether and how it imposes constraints on the different motif parameters, in order for the motif to represent a mathematical model of the regulatory system. Further analysis of the controller's ability to compensate for disturbances reveals that a variable setpoint represents a relaxing component for the controller, in that the necessary control action is reduced compared to that of a fixed setpoint controller. Such a relaxing component might serve as an important property from an evolutionary point of view. Finally, we illustrate the principles using the renal sodium and aldosterone regulatory system, where we model the variation in plasma sodium as a function of salt intake. We show that the experimentally observed variations in plasma sodium can be interpreted as a variable setpoint regulatory system.publishedVersio

Homeostatic controllers compensating for growth and perturbations

Cells and organisms have developed homeostatic mechanisms which protect them against a changing environment. How growth and homeostasis interact is still not well understood, but of increasing interest to the molecular and synthetic biology community to recognize and design control circuits which can oppose the diluting effects of cell growth. In this paper we describe the performance of selected negative feedback controllers in response to different applied growth laws and time dependent outflow perturbations of a controlled variable. The approach taken here is based on deterministic mass action kinetics assuming that cell content is instantaneously mixed. All controllers behave ideal in the sense that they for stepwise perturbations in volume and a controlled compound A are able to drive A precisely back to the controllers’ theoretical set-points. The applied growth kinetics reflect experimentally observed growth laws, which range from surface to volume ratio growth to linear and exponential growth. Our results show that the kinetic implementation of integral control and the structure of the negative feedback loop are two properties which affect controller performance. Best performance is observed for controllers based on derepression kinetics and controllers with an autocatalytic implementation of integral control. Both are able to defend exponential growth and perturbations, although the autocatalytic controller shows an offset from its theoretical set-point. Controllers with activating signaling using zero-order or bimolecular (antithetic) kinetics for integral control behave very similar but less well. Their performance can be improved by implementing negative feedback structures having repression/ derepression steps or by increasing controller aggressiveness. Our results provide a guide what type of feedback structures and integral control kinetics are suitable to oppose the dilution effects by different growth laws and time dependent perturbations on a deterministic level.publishedVersio

Identifiability and Kalman Filter Parameter Estimation Applied to Biomolecular Controller Motifs

In this paper we apply Augmented Extended Kalman filters (AEKFs) to performparameter estimation in two different biological controller motifs under both noise-free andnoisy conditions. Based on measurements of the two states of the controller motifs, we showthat under both noise conditions it is possible to estimate all 5 and 6 parameters, respectively,which is in accordance with previously published results that investigated the theoretical conceptof structural identifiability. We further investigate how the level of process/measurement noiseand the initial estimates of both the parameters and states in the AEKFs affect the estimationperformance, and the results indicate that the degree of non-linearity affects filter performance

A Model of Aerobic and Anaerobic Metabolism in Cancer Cells – Parameter Estimation, Simulation, and Comparison with Experimental Results

We present a mathematical model of metabolism in cancer cells that is capable of describing both aerobic oxidative metabolism and anaerobic fermentation metabolism, and how cancer cells shift between these metabolic states when exposed to different substrates and different enzymatic inhibitors. The model is designed to be used in combination with experimental data gathered with an Agilent Seahorse XF metabolic analyzer. The model is parameterized in a manual tuning procedure to fit experimental data, and validated against experimental data from another setup, to which the model shows good conformity. We also investigate the structural identifiability of the model. The results indicate that the model is structurally identifiable, and that it can thus be uniquely parameterized, using the following 5 measurements: extracellular concentrations of glucose, glutamine and lactate, proton production rate (a Seahorse XF analyzer measurement) and oxygen consumption rate

Vernepleierens rolle i eldreomsorgen. Hvordan kan vernepleierens kompetanse bidra i det tverrfaglige arbeidet på somatisk avdeling på sykehjem?

I vår oppgave ønsker vi å belyse: Hvordan kan vernepleierens kompetanse bidra i det tverrfaglige samarbeidet på somatisk avdeling på sykehjem? Ved bruk av kvalitativ metode har vi samlet informasjon ved hjelp av dybdeintervju. Informantene var to vernepleiere og to sykepleiere, hvor alle jobbet på somatisk avdeling på sykehjem. Informantene var enige om at det i dagens eldreomsorg er for lite fokus på miljøarbeid, og at vernepleierens kompetanse bør være en del av det tverrfaglige samarbeidet. I drøftingsdelen forsøker vi å underbygge resultatene fra intervjuene med relevant teori om tverrfaglig samarbeid, miljøarbeid, ensomhet og depresjon. Konklusjonen viser at det er lite fokus på miljøarbeid på somatisk avdeling på sykehjem og at et godt tverrfaglig team gir det beste tjenestetilbudet til pasienten