Performance analysis of switching systems

Performance analysis is an important aspect in the design of dynamic (control) systems. Without a proper analysis of the behavior of a system, it is impossible to guarantee that a certain design satisfies the system’s requirements. For linear time-invariant systems, accurate performance analyses are relatively easy to make and as a result also many linear (controller) design methods have appeared in the past. For nonlinear systems, on the other hand, such accurate performance analyses and controller design methods are in general not available. A main reason hereof is that nonlinear systems, as opposed to linear time-invariant systems, can have multiple steady-state solutions. Due to the coexistence of multiple steady-state solutions, it is much harder to define an accurate performance index. Some nonlinear systems, i.e. the so-called convergent nonlinear systems, however, are characterized by a unique steady-state solution. This steady-state solution may depend on the system’s input signals (e.g. reference signals), but is independent of the initial conditions of the system. In the past, the notion of convergent systems has already been proven to be very useful in the performance analysis of nonlinear systems with inputs. In this thesis, new results in the field of performance analysis of nonlinear systems with inputs are presented, based on the notion of convergent systems. One part of the thesis is concerned with the question "how to analyse the performance for a convergent system?" Since the behavior of a convergent system is independent of the initial conditions (after some transient time), simulation can be used to find the unique steady-state solution that corresponds to a certain input signal, but this can be very time-consuming. In this thesis, a computationally more efficient approach is presented to estimate the steady-state performance of harmonically forced Lur’e systems, in terms of nonlinear frequency response functions (nFRFs). This approach is based on the method of harmonic linearization. It provides both a linear approximation of the nFRF and an upper bound on the error between this linear approximation and the true nFRF. It is shown in several examples that the approximation of the nFRF is accurate, and that it provides more detailed information on the considered system than the often used ‘L2 gain’ performance index. An additional observation that is made, is that the method of harmonic linearization can sometimes be ‘misleading’ for Lur’e systems with a saturation-like nonlinearity: for the case that the harmonic balance equation has a unique solution, it is shown that the corresponding nonlinear system can have multiple distinct steady-state solutions. Another part of the thesis is concerned with the question "under what conditions is a system with inputs guaranteed to be convergent?" In particular two types of systems were investigated: switched linear systems and Lur’e systems with a saturation nonlinearity and marginally stable linear part. For the switched linear systems, it is assumed that the dynamics of all the separate linear modes are given. For this setting, it was investigated if it is possible to find a switching rule (which defines when to switch between the available modes) such that the closed-loop system is convergent. Both a state-based, an observer-based, and a time-based switching rule are presented that guarantee a convergent system, assuming some conditions on the linear dynamics are met. The second type of systems that are discussed, are Lur’e systems with a saturation nonlinearity and marginally stable linear part. For this type of systems, the goal was to find sufficient conditions under which the closed-loop system is convergent. Because of the marginally stable linear part, however, a quadratically convergent system cannot be obtained. Instead, sufficient conditions are discussed that guarantee uniform convergency of the system. The obtained theory is shown to be also applicable to a class of anti-windup systems with a marginally stable plant. For this class of systems, the results of the convergency-based performance analysis are compared with the analysis results of existing anti-windup methods. It is shown that the convergency-based performance analysis can in some cases provide more detailed information on the steady-state behavior of the system. The results of uniform convergency for anti-windup systems are shown to be also applicable in the field of production and inventory control of discrete-event manufacturing systems. Since a manufacturing machine has a certain production capacity and cannot produce at a negative rate, it can be seen as an integrator plant (input: production rate, output: amount of finished products) preceded by a saturation function. For this marginally stable plant, a controller was constructed in such a way that the closed-loop system is uniformly convergent. The controller was also implemented in the discrete-event domain and the results from discrete-event simulations were compared with those of continuous-time simulations. Similarly, the controller was also applied for the production and inventory control of a line of four manufacturing machines. For both the single machine and the line of four machines, the resulting controlled discrete-event systems are shown to have the desired tracking properties. Besides these theoretical and numerical results, also experimental results are presented in this thesis. By means of an electromechanical construction, several experimental results were obtained, and used to validate the theoretical results for both the switched linear systems and the anti-windup systems

Genetic algorithm based two-mode clustering of metabolomics data

Metabolomics and other omics tools are generally characterized by large data sets with many variables obtained under different environmental conditions. Clustering methods and more specifically two-mode clustering methods are excellent tools for analyzing this type of data. Two-mode clustering methods allow for analysis of the behavior of subsets of metabolites under different experimental conditions. In addition, the results are easily visualized. In this paper we introduce a two-mode clustering method based on a genetic algorithm that uses a criterion that searches for homogeneous clusters. Furthermore we introduce a cluster stability criterion to validate the clusters and we provide an extended knee plot to select the optimal number of clusters in both experimental and metabolite modes. The genetic algorithm-based two-mode clustering gave biological relevant results when it was applied to two real life metabolomics data sets. It was, for instance, able to identify a catabolic pathway for growth on several of the carbon sources

Grondwateronttrekking en infiltratie te Fikkerdries

Verzoek uitbreiding grondwaterwinning door pompstation Fikkersdries (Betuwe

High mathematics and reading performance:How important are environmental influences?

Earlier findings of international comparisons on school achievement are often interpreted to mean that there is only a small percentage of excellent students in the Netherlands. Inspired by research in behaviour genetics, it was investigated whether Dutch high-scoring children are less sensitive to environmental influences than the non-high-scoring students. To test this, the reading and mathematics scores from high-scoring and non-high-scoring students participating in the Programme for International Student Achievement (PISA) 2012, the Trends in International Mathematics and Science Study (TIMSS) 2011 and the Progress in International Reading and Literacy Study (PIRLS) 2011 were analyzed. Contrary to our expectations, the results suggest that high-scoring children are as sensitive to school influences as are non-high-scoring students, but more sensitive to the influence of individual socioeconomic status

Associations between job demands, job resources and patient-related burnout among physicians: results from a multicentre observational study

Objectives To investigate associations of job demands and resources with patient-related burnout among physicians. Design Multicentre observational study. Setting Fifty medical departments at 14 (academic and non-academic) hospitals in the Netherlands. Participants Four hundred sixty-five physicians (71.6% response rate), comprising 385 (82.8%) medical specialists and 80 (17.2%) residents. Main outcome measures Job demands (workload and bureaucratic demands), job resources (participation in decision making, development opportunities, leader’s inspiration, relationships with colleagues and patients)— measured with the validated Questionnaire of Experience and Evaluation of Work and Physician Worklife Survey— and patient-related burnout, measured using the validated Copenhagen Burnout Inventory. Results Patient-related burnout was positively associated with workload (b=0.36; 95% CI, 0.25 to 0.48; p<0.001) and negatively associated with development opportunities (b=–0.18; 95% CI, –0.27 to –0.08; p<0.001) and relationships with patients (b=–0.12; 95% CI, –0.22 to –0.03; p=0.01). Relationships with patients moderated the association between bureaucratic demands and patient-related burnout (b=–0.15; 95% CI, –0.27 to –0.04; p=0.01). Conclusions Physicians with high workloads and few development opportunities reported higher levels of patient-related burnout. Those with positive patient relationships were less likely to experience patient-related burnout, even in the presence of excessive bureaucracy. Therefore, positive physician–patient relationships may be supported to reduce the likelihood of physicians’ patientrelated burnout. Howeve

Volatilization of fenpropimorph and clopyralid after spraying onto a sugar beet crop

Volatilization rates of pesticides were measured with two micrometeorological methods. For fenpropimorph, the highest rates (1.3-3.0% per hour) were measured in the first hours after application. The rate gradually declined to less than 0.01% per houron the sixth day. Clopyralid had much lower volatilization rates. They were highest (0.1% per hour) on the day after the day of application and declined below the detection limit (less than 0.01% per hour) on the sixth day after application. Rates calculated with the aerodynamic method were slightly higher than those calculated with the Bowen ratio

Volatilization of tri-allate, ethoprophos and parathion measured with four methods after spraying on a sandy soil

At about eleven times after application of tri-allate, ethoprophos and parathion to a sandy soil, their rates of volatilization were determined by the aerodynamic method (AD), the Bowen-ratio method (BR), the theoretical-profile method (TP) and the Box method. The volatilization was highest for tri-allate and lowest for parathion. On the first day after application, the volatilization rate decreased sharply, but thereafter the decrease was more gradual. The differences in volatilization rate as determined with the AD, BR and TP methods were comparatively small. The rates determined with the Box method were mostly lower than those determined with the other methods