Mining evolving data streams for frequent patterns

A data stream is a potentially uninterrupted flow of data. Mining this flow makes it necessary to cope with uncertainty, as only a part of the stream can be stored. In this paper, we evaluate a statistical technique which biases the estimation of the support of patterns, so as to maximize either the precision or the recall, as chosen by the user, and limit the degradation of the other criterion. Theoretical results show that the technique is not far from the optimum, from the statistical standpoint. Experiments performed tend to demonstrate its potential, as it remains robust even under significant distribution drifts.     

Data-driven latent-variable model-based predictive control for continuous processes

A model-based predictive control methodology in the space of the latent variables for continuous processes is presented. Implementing identification and control in the latent variable space eases identification in the case of correlation in the data set, acts as a prefilter reducing the effect of noisy data, and reduces computational complexity. The proposed data-driven LV-MPC approach deals with setting the control horizon different to the prediction horizon, improves Hessian conditioning, and attains offset-free tracking. Additionally, a weighting matrix is introduced in the identification stage so that the performance of the predictor in the near horizon can be enhanced. A MIMO example shows how the proposed methodology can outperform conventional data-driven MPC in terms of computational complexity and reference tracking.     

Air management in a diesel engine using fuzzy control techniques

Air management for diesel engines is a major challenge from the control point of view because of the highly nonlinear behavior of this system. For this reason, linear control techniques are unable to provide the required performance, and nonlinear controllers are used instead. This article discusses two fundamental steps when designing a control system. Firstly, a methodology to identify Takagi–Sugeno (T–S) structures using experimental data is proposed. Secondly, the design of a fuzzy controller in PDC structure (Parallel Distributed Compensation) is presented. The parameters of this controller are obtained from a LMI (Linear Matrix Inequalities) minimization problem.     

Latent variable based model predictive control: Ensuring validity of predictions

This paper presents a methodology to constrain the optimisation problem in LV-MPC so that validity of predictions can be ascertained. LV-MPC is a model-based predictive control methodology implemented in the space of the latent variables and is based on a linear predictor. Provided real processes are non-linear, there is model-process mismatch, and under tight control, the predictor can be used for extrapolation. Extrapolation leads to bad predictions which deteriorates control performance, hence the interest in validity of predictions. In the proposed approach first two validity indicators on predictions are defined. The novelty in the two indicators proposed is they neglect past data, and so validity of predictions is ascertained in terms of future moves which are actually the degrees of freedom in the optimisation. Second, the indicators are introduced in the optimisation as constraints. Provided the indicators are quadratic, recursive optimisation with linearised constraints is implemented. A MIMO example shows how ensuring validity of predictions neglecting past data can improve closed-loop performance, specially under tight control outside the identification region.     

Coplanar perturbation of a crack lying on the mid-plane of a plate

Several groups have studied experimentally the deformation of the front of mode I cracks propagating quasistatically along the interface between bonded plates. The theoretical interpretation of such experiments has always been based up to now on a formula of Rice (ASME J Appl Mech 52:571–579, 1985); this formula provides the first-order variation of the local mode I stress intensity factor resulting from some small, but otherwise arbitrary coplanar perturbation of the front of a semi-infinite crack in an infinite body. To be applicable to bonded plates, this formula requires that the characteristic distance of variation of this perturbation in the direction of the crack front be small compared to all other characteristic dimensions of the problem, and first of all the thickness of the plates. This condition is unfortunately frequently violated in practice. The purpose of this paper is therefore to provide a more exact formula for the variation of the local stress intensity factor, for the specific cracked geometry and boundary conditions used in experiments; this should allow for more accurate theoretical interpretations. This is done in two steps. The first one consists in adapting Rice’s (ASME J Appl Mech 52:571–579, 1985) treatment, applicable to the extreme case of plates of infinite thickness, to the other extreme one of plates of infinitesimal thickness, using the standard Love-Kirchhoff plate theory. An interesting outcome of the analysis is that the distance from the crack front to the boundary of the plate acts as a “cutoff length”, in the sense that when the distance between two points on the crack front gets larger than it, the influence of the crack advance at the first point upon the stress intensity factor at the second diminishes quickly; the plate thickness, however, plays no similar role. The second step consists in supplementing the theoretical expressions applicable to extreme values of the plate thickness with finite element computations providing results for intermediate values. These computations lead to the definition of a simple, approximate but accurate “interpolation formula” for the variation of the local stress intensity factor, applicable to plates of arbitrary thickness.     

Numerical steady state analysis of electronic circuits driven by multi-tone signals

Contents Characteristics of analogue circuits such as intermodulation distortion and transfer characteristics can often be received from the steady state behavior. This paper presents a unified approach for the simulation of non-autonomous circuits with multi-tone excitation. The steady state is here regarded as the solution of a partial differential-algebraic equation. A suitable numerical method for its solution is a variational method with trigonometric basis functions. The Harmonic Balance technique based either on the multi-dimensional Fourier transformation or the Artificial Frequency Map technique can be interpreted as a special variant of this method.

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Numerische Berechnung des eingeschwungenen Zustands elektronischer Schaltungen bei einer Mehrton-Erregung

Übersicht Die Eigenschaften analoger Schaltungen, die etwa Intermodulationsverzerrungen und Übertragungscharakteristiken beschreiben, lassen sich häufig im eingeschwungenen Zustands ermitteln. Dieser Beitrag stellt ein vereinheitlichtes Verfahren zur Simulation von nicht-autonomen Schaltungen bei einer Mehrton-Erregung vor. Der eingeschwungene Zustand wird als spezielle Lösung einer partiellen Algebro-Differentialgleichung formuliert. Zur numerischen Berechnung eignen sich Variationsverfahren mit trigonometrischen Ansatzfunktionen. Interessant ist, daß das Verfahren der Harmonischen Balance, sowohl basierend auf einer mehrdimensionalen Fouriertransformation als auch basierend auf einer Transformation auf ein künstliches Hilfsspektrum, als spezielle Variante dieses Ansatzes angesehen werden kann.

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This paper is dedicated to Professor Dr. rer. nat. Walter L. Engl, RWTH Aachen, on the occasion of his 70th birthday.     

Dietary non-extractable condensed tannins as indigestible compounds: Effects on faecal weight,and protein and fat excretion

The possible degradation of non-extractable condensed tannins (NECT) within the intestinal tract and their effect on faecal weight and composition was studied. Two groups of male Wistar rats were fed either a NECT-free control diet, or a diet containing 100 g carob pod concentrate kg^?1 (53 g NECT kg^?1 dry matter) for 5 weeks. A slight effect of NECT on growth rate was observed in the fifth week. The NECT diet did not affect food intake. Significant increases of total faecal output as well as water, nitrogen and fat excretion were observed. NECT were not degraded in the intestinal tract, since they were quantitatively recovered in faeces (98 ± 1%). Since the usual spectrophotometric methods gave contradictory results on NECT levels in the diet and faeces, an alternative method based on Klason lignin residues was used.     

Knee osteoarthritis after meniscectomy: prevalence of radiographic changes after twenty-one years, compared with matched controls

Aggrecan, a large aggregating proteoglycan, is one of the major structural components of cartilage. Its core protein contains three glubular domains and two glycosaminoglycan-attachment domains. These domains play various roles to maintain cartilage structure and function. An N-terminal globular domain binds hyaluronan and link protein to form huge aggregates. The chondroitin sulfate (CS) chains attach to the CS domain and provide a hydrated, viscous gel that absorbs compressive load. Two autosomal recessive chondrodysplasias, cartilage matrix deficiency (cmd) in mice and nanomelia in chicken are both caused by aggrecan gene mutations. Cmd homozygotes die shortly after birth, while the heterozygotes are born normal. However, cmd heterozygotes develop late onset of spinal disorder, which suggests aggrecan as a candidate gene predisposing individuals to spinal problems. Nanomelia is a useful model to elucidate intracellular trafficking of proteoglycans. Further studies on aggrecan will lead to prophylaxis and treatment of joint destructive diseases such as osteoarthrosis and to elucidation of cartilage development, which is essential for skeletal formation.