Papers by Ewaryst Rafajlowicz
Lecture Notes in Computer Science, Dec 31, 2022
Prace Naukowe Instytutu Cybernetyki Technicznej Politechniki Wrocławskiej. Konferencje, 1998
2009 IEEE/SP 15th Workshop on Statistical Signal Processing, Aug 1, 2009
This paper examines a new method for sequential detection of a sudden and unobservable change in ... more This paper examines a new method for sequential detection of a sudden and unobservable change in a sequence of independent observations with completely unspecified distribution functions. A nonparametric detection rule is proposed which relies on the concept of a moving vertically trimmed box. As such, it will be coined as the Vertical Box Control Chart (V-Box Chart). Its implementation requires merely to count the number of data points which fall into the box attached to the last available observation. No a priori knowledge of data distributions is required and proper tuning of the box size provides a quick detection technique. This is supported by establishing statistical properties of the method which explain the role of the tuning parameters used in the V-Box Chart. These theoretical results are verified by simulation studies which indicate that the V-Box Chart may provide quick detection with zero delay for jumps of moderate sizes. Its averaged run length to detection is more favorable than the one for the classical EWMA method. By comparison with the classical Shewhart chart, which was optimized for normal errors, our method provides comparable or better performance. Index Terms-Average run length, change in mean, changepoint, exponential bounds, nonparametric inference. I. INTRODUCTION I N the analysis of observed data, an important problem is to detect an event of a structural change, e.g., a jump in the mean, of a signal. This question of the constancy of model parameters plays a critical role in many problems of signal processing, quality control, fault detection, finance, security, and clinical medicine. This is often referred to as the change-point problem and the issue is to detect the change as quickly as possible. In real applications, however, we observe samples of the discrete time stochastic process which represent the only available information about the true signal. Furthermore,
Mechanical Systems and Signal Processing, Jun 1, 2017
In this work we provide theoretical and numerical results regarding optimal designs of experiment... more In this work we provide theoretical and numerical results regarding optimal designs of experiments with an emphasis on coupled problems like piezoelectrics and poroelastics. The work is motivated by the need of identifying parameters for complex problems from measured data, where it is a priori not clear which data are to choose. We assume a harmonic excitation of the systems and measurements related to different excitation frequencies. Results of optimal experimental designs under harmonic excitations are reviewed and adapted correspondingly, e.g., the D-optimality criterion is extended to the case of multiple fields. The manuscript at hand further reviews techniques to identify parameters and their statistical properties and discusses the previously derived theory for two examples, one coming from piezoelectricity, the other from poroelasticity. For these examples, it is analytically shown that they fit to the previously presented theory. Numerical results discussing the optimal choice of the fields to measure and finding the optimal excitation frequencies finalize this work.
De Gruyter eBooks, Mar 2, 2022
Lecture Notes in Computer Science, 2023
Our aim is to consider a model-based approach to control of image-driven control systems, i.e., t... more Our aim is to consider a model-based approach to control of image-driven control systems, i.e., the systems in which images play the role of system states. As a tool for describing such systems we have selected n × n matrix state equations. For linear, time invariant systems we prove necessary and sufficient controllability and asymptotic stability conditions that can be efficiently verified by considering an accompanying system with n-dimensional states. Furthermore, the existing software can be used for their verification. The approach is illustrated by a semi-discretized heat equation with a control system, which is used to invoke large stresses in a ceramic plate.
Data in Brief, Apr 1, 2021
Automation in Construction, Nov 1, 2020
The aim of the paper is to propose algorithms for suppressing vibrations of massive components of... more The aim of the paper is to propose algorithms for suppressing vibrations of massive components of machinery, e.g., operators' cabins in bucket wheel excavators (BWEs). Repetitive perturbations provide the opportunity to learn a control system to suppress or reduce their influence by applying a repetitive control scheme. A new version of the iterative learning control approach, called iterative learning of optimal control (ILOC), is derived. This approach is able to learn a control signal that approximately minimizes the squared acceleration of a system, e.g., the cabin. The resulting algorithms can be used alone or in parallel with a hybrid version of the classic proportional-derivative (PD) controller. The simulations indicate that the ILOC algorithm provides a large improvement in suppressing quasi-periodic disturbances in comparison to the cases of no control and PD control, while the hybrid version provides even slightly better results. The proposed algorithms are intended to be used with magneto-rheological (MR) dampers as semi-active control devices. Subtle properties of MR dampers, such as their hysteresis, are omitted here.
Systems & Control Letters, Apr 1, 1984
Outliers that can significantly affect data analysis are frequently present in environmental data... more Outliers that can significantly affect data analysis are frequently present in environmental data sets. Most methods suggested for the detection of outliers impose restrictions on the distribution of analysed variables. However, in many environmental areas, the observed variable is influenced by a lot of different factors and its distribution is often difficult to find or cannot be estimated.
Contributions to statistics, 1998
Lecture Notes in Computer Science, 2023
The well known Logan's theorem asserts that, under some assumptions, a one octave bandpass signal... more The well known Logan's theorem asserts that, under some assumptions, a one octave bandpass signal is recoverable, modulo a multiplicative constant, from its zero crossings only. However, such recovery is numerically problematic and the theorem is not applicable to general bandlimited signals. In this paper, we demonstrate that the additional timing information sufficient for recovery of general band limited signals can be provided in the form of the zero crossings of several of its derivatives and propose novel numerically robust algorithms for such timing extraction and for signal reconstruction, both with high fidelity. We tested the proposed algorithms extensively, with both synthetic and audio signals. In particular, we numerically demonstrate that the timing of the zero crossings of a typical speech signal and of its first two derivatives are not sufficient for a numerically robust recovery of such a signal, but that a robust recovery becomes possible by adding the timing of the zero crossings of the third order derivative.
this paper, please contact the author for details: raf@ldhpux.immt.pwr.pl 1 Introduction
Nature Communications, 2021
Disease modelling has had considerable policy impact during the ongoing COVID-19 pandemic, and it... more Disease modelling has had considerable policy impact during the ongoing COVID-19 pandemic, and it is increasingly acknowledged that combining multiple models can improve the reliability of outputs. Here we report insights from ten weeks of collaborative short-term forecasting of COVID-19 in Germany and Poland (12 October–19 December 2020). The study period covers the onset of the second wave in both countries, with tightening non-pharmaceutical interventions (NPIs) and subsequently a decay (Poland) or plateau and renewed increase (Germany) in reported cases. Thirteen independent teams provided probabilistic real-time forecasts of COVID-19 cases and deaths. These were reported for lead times of one to four weeks, with evaluation focused on one- and two-week horizons, which are less affected by changing NPIs. Heterogeneity between forecasts was considerable both in terms of point predictions and forecast spread. Ensemble forecasts showed good relative performance, in particular in ter...
Acta Polytechnica Hungarica
Our aim is to propose a systematics (taxonomy) of data structures that arise in classifying patte... more Our aim is to propose a systematics (taxonomy) of data structures that arise in classifying patterns and images, starting from unrelated vectors and ending with matrix and tensors for storing video sequences. Then, we discuss possibilities of classifying such structures under matrix (tensor) normal distribution assumptions. Finally, we provide a case study of using classifiers for quality control of laser-based additive manufacturing.
this paper, please contact the author for details: raf@ldhpux.immt.pwr.pl 1 Introduction
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Papers by Ewaryst Rafajlowicz