Algorithms for additive clustering of rectangular data tables

The overlapping additive clustering model or principal cluster model is a model for two-way two-mode object by variable data that implies an overlapping clustering of the objects and a set of profiles (characteristic variable values for each cluster). The model values of the variables of an object are the sum of the profiles of its corresponding clusters. In the associated data analysis the data matrix at hand is approximated by an overlapping additive clustering model of a prespecified rank by minimizing a least squares loss function. Recently an algorithm has been proposed for this purpose. This algorithm is a sequential fitting strategy, also called the method of principal clusters (PCL). Theoretical and empirical evidence that the PCL algorithm may have problems in revealing the true structure underlying a data set will be presented. As a way out, three new algorithms to fit the principal cluster model to empirical data will be presented: two of an alternating least squares (ALS) type, orthogonally combined with two different starting strategies, and one based on simulated annealing (SA). In a simulation study it is demonstrated that all three new algorithms outperform the existing PCL algorithm. The amount of objects that belong to more than one cluster (the overlap) is further found to have a considerable influence on the algorithmic performance of the ALS algorithms, with low amounts of overlap requiring a different starting strategy than high ones. As a consequence, for the analysis of real data sets in practice, a hybrid approach will be presented consisting of one of the ALS algorithms initialized by means of the two starting strategies under study.     

The relation between event processing and the duration of emotional experience.

An emotional experience can last for only a couple of seconds up to several hours or even longer. In the present study, we examine to which extent covert intrapersonal actions (cognitions both related and unrelated to the emotion-eliciting stimulus) as well as overt interpersonal actions (social sharing) account for this variability in emotion duration. Participants were asked to report the duration of their anger, sadness, joy, and gratitude episodes on a daily basis during five days. Furthermore, information was collected with regard to their cognitions during the episodes and their social sharing behavior. Discrete-time survival analyses revealed that for three of the four emotions under study, stimulus-related cognitions with the same valence as the emotion lead to a prolongation of the episode; in contrast, both stimulus-related and stimulus-unrelated cognitions with a valence opposite to the emotion lead to a shortening. Finally, for the four emotions under study, social sharing was associated with a prolongation. The findings are discussed in terms of a possible process basis underlying the time dynamics of negative as well as positive emotions. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Decentralized control design of interconnected chains of integrators: A case study

We develop a constructive decentralized control design procedure for a class of systems that may be loosely described as chained integrators which are dynamically coupled. The design method is inspired by nested saturation control ideas and formulated by applying the singular perturbation theory. We demonstrate that the proposed design provides a Lyapunov function for an associated closed loop system from which semi-global stability may be deduced. Using the proposed idea, we design a semi-globally stabilizing control law for a four degree of freedom spherical inverted pendulum.     

Observability limits for networked oscillators

Inspired by the neuro-scientific problem of predicting brain dynamics from electroencephalography (EEG) measurements of the brain’s electrical activity, this paper presents limitations on the observability of networked oscillators sensed with quantised measurements. The problem of predicting highly complex brain dynamics sensed with relatively limited amounts of measurement is abstracted to a study of observability in a network of oscillators. It is argued that a low-dimensional quantised measurement is in fact, by itself, an exceptionally poor observer for a large-scale oscillator network, even for the case of a completely connected graph. The main rational is based on (i) an information-theoretic argument based on ideas of entropy in measure preserving maps, (ii) a linear deterministic observability argument, and (iii) a linear stochastic approach using Kalman filtering. For prediction of brain network activity, the findings indicate that the classic EEG signal is just not precise enough to be able to provide reliable prediction and tracking in a clinical setting in view of the complexity of underlying neural dynamics.     

Two scale high gain adaptive control

Simple adaptive controllers based on high gain output feedback suffer a lack of robustness with respect to bounded disturbances. Existing modifications achieve boundedness of all solutions but introduce solutions that, even in the absence of disturbances, do not achieve regulation. In this paper a new modification that achieves the desired robustness without the side‐effect of undesirable solutions is proposed. The modification features two data‐driven stability indicators. Intuitively, the first indicator drives the ‘closed‐loop poles’ to the closed right half plane while the latter provides fine‐tuning that prevents persistent imaginary axis poles and their associated undesired behaviour. Copyright © 2004 John Wiley & Sons, Ltd.     

Effects of simple indoles, noradrenaline, nicotine, and tyramine on action potential and contractility of the isolated guinea-pig papillary muscle

1. Simultaneous recordings of both the transmembrane action potential and the contractions were made in isolated electrically driven papillary muscles of the guinea pig in order to compare the effects of 6-methoxyindole (6-MOI), 3-methylindole (3-MI) and 5-methylindole (5-MI) with those of noradrenaline (1.2 - 10(-6) M), nicotine (2 - 10(-5) M), and tyramine (5.8 - 10(-6) M). 2. Noradrenaline, nicotine, tyramine and 6-MOI (5.4 - 10(-4) M) enhanced the contractility whilst 3-MI (3.8 and 7.8 - 10(-4) M) and 5-MI (1.9 and 3.8 - 10(-4) M) had only irregular effects. The active compounds shortened and time-to-peak tension and increased the rate of relaxation. 3. The duration of the action potential was prolonged by noradrenaline, nicotine, and tyramine, but shortened by 3-MI, 5-MI, and 6-MOI. 4. The results showed that the effect of drugs on the action potential are not necessarily linked to those on contractility.     

Non-linear stable inversion-based output tracking control for a spherical inverted pendulum

We design an exact output tracking control law for a four degree of freedom spherical inverted pendulum based on the non-linear stable inversion tool proposed by Devasia et al. (1989). The pendulum is a slim cylindrical beam attached to a horizontal plane via a universal joint; the joint is free to move in the plane under the influence of a planar force. The upright position is an unstable equilibrium of the uncontrolled system because of gravity. The objective is to design a controller so that the pendulum can be steered to track some smooth desired translational trajectories while keeping the pendulum tightly around the upright position. The design proceeds in three steps: 1. identification of the internal dynamics; 2. feedforward control design for achievable trajectories; 3. feedback design to stabilize the achievable trajectories. The computer simulations show that the proposed controller can deliver excellent tracking performance.     

Simultaneous analysis of coupled data blocks differing in size: A comparison of two weighting schemes

Research questions in several research domains imply the simultaneous analysis of different blocks of information that pertain to the same research objects. In personality psychology, for example, to study the relation between individual differences in behavior and cognitive-affective units that can account for these differences, two types of information pertaining to the same set of persons need to be analyzed simultaneously: (1) information about the situation-specific behavior profile of these persons, and (2) information about the cognitive-affective units these persons exhibit. When dealing with such coupled data blocks (i.e., different N-way N-mode data blocks that have one or more modes in common) it often happens that one data block is much larger in size than the other(s). In this case, the question arises whether the data entries or the data blocks should be considered as the units of information, in order to disclose the true structure underlying the coupled data blocks. To answer this question, two weighting schemes are compared that are obtained by applying weights in the overall objective function that is to be optimized in the data analysis, with each weight indicating the extent to which the corresponding data block influences the integrated analysis. In a simulation study it is showed that weighting the different data blocks such that each data entry influences the analysis to the same extent (i.e., data entries as units of information) outperforms a weighting scheme in which each data block has an equal influence on the analysis (i.e., data blocks as units of information). This superior performance is demonstrated for two global models for coupled data consisting of a three-way three-mode data block and a two-way two-mode data block that have one mode in common: (1) a multiway multiblock component model for coupled real-valued data, and (2) a simultaneous clustering model for coupled binary data.     

On the choice of dither in extremum seeking systems: A case study

We discuss how the choice of dither (excitation signal) affects the performance of extremum seeking using a benchmark situation: a static scalar map; and a simple scalar extremum seeking scheme. Our comparisons are based on the performance of the system with different dithers in terms of three performance indicators: the speed of convergence, domain of attraction and accuracy (i.e. the ultimate bound on trajectories). Our analysis explicitly shows how the dither shape affects each of these performance indicators. Our study suggests that the practitioners using extremum seeking control should consider the dither shape as an important design parameter. Computer simulations support our theoretical findings.