System Theoretic Point Of View Research Articles

Actuator Anomaly Detection in Linear Parabolic Distributed Parameter Cyber-Physical Systems

Distributed parameter cyber-physical systems (DPCPSs) are characterized by two features: 1) they exhibit spatio-temporal (distributed parameter) dynamics and 2) there exist cyber components in the form of communication channels between the physical plant and control system. DPCPSs are vulnerable to anomalies such as nonmalicious physical faults and malicious cyber-attacks. Although the safety and security aspects of CPSs modeled by ordinary differential equations (ODEs) have been extensively explored during the past decade, security of DPCPSs has not received its due attention despite its safety-critical nature. In this work, we explore anomaly diagnostics in DPCPSs from a system theoretic viewpoint. Specifically, we focus on DPCPSs modeled by linear parabolic partial differential equations (PDEs) subject to physical faults and cyber-attacks in the actuation channel. First, we explore the detectability of malicious anomalies (i.e., cyber-attacks) and derive conditions for stealthy attacks in the context of output-feedback-based monitoring. Such stealthy attacks essentially illustrate the fundamental limitations of feedback-based monitoring algorithms given perfect adversarial knowledge. Subsequently, focusing on the anomalies that are detectable, we develop a design framework for anomaly detection algorithms based on output injection observers. Such detection algorithm explicitly considers the conflicting objectives of robustness to uncertainties and sensitivity to anomalies in their design. Finally, theoretical analysis and simulation studies are performed to illustrate the effectiveness of the proposed approach.

Opinion Formation in Online Public Debates Structured in Information Cascades: A System-Theoretic Viewpoint

Online information cascades (tree-like structures formed by posts, comments, likes, replies, etc.) constitute the spine of the public online information environment, reflecting its various trends, evolving with it and, importantly, affecting its development. While users participate in online discussions, they display their views and thus contribute to the growth of cascades. At the same time, users’ opinions are influenced by cascades’ elements. The current paper aims to advance our knowledge regarding these social processes by developing an agent-based model in which agents participate in a discussion around a post on the Internet. Agents display their opinions by writing comments on the post and liking them (i.e., leaving positive assessments). The result of these processes is dual: on the one hand, agents develop an information cascade; on the other hand, they update their views. Our purpose is to understand how agents’ activity, openness to influence, and cognitive constraints (that condition the amount of information individuals are able to proceed with) affect opinion dynamics in a three-party society. More precisely, we are interested in what opinion will dominate in the long run and how this is moderated by the aforementioned factors, the social contagion effect (when people’ perception of a message may depend not only on the message’s opinion, but also on how other individuals perceive this object, with more positive evaluations increasing the probability of adoption), and ranking algorithms that steer the order in which agents learn new messages. Among other things, we demonstrated that replies to disagreeable opinions are extremely effective for promoting your own position. In contrast, various forms of like activity have a tiny effect on this issue.

Expressivity of Hidden Markov Chains vs. Recurrent Neural Networks From a System Theoretic Viewpoint

Expressivity of Hidden Markov Chains vs. Recurrent Neural Networks From a System Theoretic Viewpoint

BIFURCATIONS OF TRAVELLING WAVE SOLUTIONS IN THREE MODIFIED CAMASSA-HOLM EQUATIONS

<abstract> This paper studies traveling wave solutions of three modified Camassa-Holm equations posed by Anco and Recio in 2019. The corresponding traveling system is a singular system of second class. The bifurcations of traveling wave solutions in the parameter space are investigated from a dynamical systems theoretical point of view. The existence of solitary wave solution, periodic wave solution and so-called $M$-shape-solution are proved. </abstract>

Artificial bandwidth extension of speech signals

Artificial Bandwidth Extension (ABWE) algorithms try to reconstruct frequency components of speech signals which have been lost by coding/transmission. From a system theoretical point of view, this seems to be questionable. However, by exploiting redundancy of speech production as well as psychoacoustic properties of auditory perception, missing parts can subjectively be recovered or at least mimicked to a certain extent. The motivation for ABWE is to bridge the quality gap between the traditional narrowband telephony (200–3400 Hz) and the recent wideband services (HD voice, 50–7000 Hz). An HD terminal which is connected to a traditional phone, may activate ABWE for improving the audio quality and possibly the intelligibility of the received signal. In this contribution, state-of-the-art ABWE algorithms and coding standards including ABWE techniques are reviewed. ABWE algorithms are based on a source-filter model. The three main sub-tasks are to estimate the excitation signal, the spectral envelope and the time domain envelope, given either just the narrowband signal or in addition a few bits of side information. Furthermore, insights with respect to the relative importance of these three components are presented.

Language change as a scientific construct of a probabilistically organized information system

AbstractThe present paper discusses language change from an information and systems theoretical point of view, taking on a diachronic perspective. It is argued that human language has to be regarded as a probabilistically organized information system in which synchronizations of linguistic systems of individuals create unstable (dynamic, ever-changing) collective levels (“language systems”). Therefore, probabilistic organization of language processing on an individual level leads – via bottom-up structure – to probabilistic organization of language systems as a whole. If we thus regard linguistic objects like e.g. a Saussurean sign as generally unstable and defined by probability distributions even from a synchronic point of view, we must understand language change (diachronic developments) as probabilistic as well. Therefore, language change in its “classical sense” (a change in linguistic objects) has to be reinterpreted as a change in probability distribution. Nevertheless, the termlanguage changeand its meaning then still lack exactness regarding some details; so we have to use this term carefully and be aware of its weaknesses. With a close look at language as an information system with both a synchronic as well as a diachronic dimension, we finally have to admit that language change is a scientific construct serving as a – sometimes quite useful – simplification within the linguistic field.

Control of non-minimum phase systems with dead time: a fractional system viewpoint

In this paper, a unified theory is proposed for the fractional control of the non-minimum phase plus dead time systems via the introduction of the fractional filter-PID control and stability inequality. More precisely, three Theorems from a fractional system-theoretic viewpoint are developed. The first Theorem deals with the controller design through the notion of generalised internal model control. That embeds the fractional filter-PID controller coupled with the unified form of the Smith predictor and the inverse compensator. The second Theorem designs a bound on the fractional filter parameter that leads to a stable feedback system. The third Theorem deals with the stability of a fractional quasi-characteristic polynomial of the commensurate order arising from the control of non-minimum phase systems with dead time. Two illustrative second-order plus dead time non-minimum phase systems are presented to test the efficacy of the resulting fractional filter-PID controller that obeys the stability bound. Controller and sensitivity performance indices for the nominal as well as mismatch cases reveal the effectiveness and robustness of the proposed method for enhanced closed-loop performance. Thus, the generalised inverse compensator, the fractional filter-PID controller and the stability inequality in corroboration with numerical simulations demonstrate the better control of non-minimum phase systems with dead time.

On the finite-time boundedness of linear systems

This paper deals with the finite-time boundedness (FTB) of linear time-varying (LTV) systems; in this context, the novel contribution of our work goes in several directions. The first result is a sufficient condition for FTB when the plant input is generated by an exo-system; it is worth noting that constant, norm bounded signals, which most part of the previous literature has considered so far, belong to such class of inputs. To this regard, it is possible to compare our result with the existing literature, which shows that our approach yields less conservative conditions. The second result provided in the paper, is a sufficient condition for FTB when the input belongs to L2, the class of square integrable signals, which have never been considered so far. In both cases, the proposed results require the solution of a feasibility problem constrained by differential linear matrix inequalities (DLMIs). A third contribution of the paper proves that, from the system-theoretic point of view, the obtained FTB conditions can be interpreted in terms of the norm of a suitable input–output operator. As a consequence of this fact, we are able to find alternative and equivalent conditions for FTB, both for the exogenous and the L2 cases, which are based on the solution of differential Lyapunov equations (DLEs), which are much more efficient from the computational point of view. The DLMI-based condition, however, is fundamental to solve the design problem, which is also investigated in the paper. Some examples show that the proposed technique is less conservative with respect to the previous literature, when exogenous inputs are considered, and its effectiveness when L2 signals are considered. Moreover, one example is devoted to show that the analysis approach, based on the solution of DLE, is much more efficient from the computational point of view with respect to the one based on DLMIs; finally the last example investigates the application of the state feedback control technique.

The Moral Complexity of Agriculture: A Challenge for Corporate Social Responsibility

Over the past decades, the modernization of agriculture in the Western world has contributed not only to a rapid increase in food production but also to environmental and societal concerns over issues such as greenhouse gas emissions, soil quality and biodiversity loss. Many of these concerns, for example those related to animal welfare or labor conditions, are stuck in controversies and apparently deadlocked debates. As a result we observe a paradox in which a wide range of corporate social responsibility (CSR) initiatives, originally seeking to reconnect agriculture and society, frequently provoke debate, conflict, and protests. In order to make sense of this pattern, the present paper contends that Western agriculture is marked by moral complexity, i.e., the tendency of multiple legitimate moral standpoints to proliferate without the realistic prospect of a consensus. This contention is buttressed by a conceptual framework that draws inspiration the contemporary business ethics and systems-theoretic scholarship. From the systems-theoretic point of view, the evolution of moral complexity is traced back to the processes of agricultural modernization, specialization, and differentiation, each of which suppresses the responsiveness of the economic and legal institutions to the full range of societal and environmental concerns about agriculture. From the business ethics point of view, moral complexity is shown to prevent the transformation of the ethical responsibilities into the legal and economic responsibilities despite the ongoing institutionalization of CSR. Navigating moral complexity is shown to require moral judgments which are necessarily personal and contestable. These judgments are implicated in those CSR initiatives that require dealing with trade-offs among the different sustainability issues.

On the reduction of 2-D polynomial systems into first order equivalent models

In this paper we propose a novel approach for the reduction of a 2-D rectangular polynomial matrix of arbitrary degree, to first-order matrix pencils of the form $$sE_{1}+zE_{2}+A$$, utilizing the framework of zero coprime equivalence (ZC-E). The proposed approach is in turn employed to derive a series of ZC-E matrix pencils, which can be obtained “by inspection” of the coefficients of the original bivariate polynomial matrix. Improving similar constructions of first order pencils available in the literature, our approach results in matrix pencils whose size increases linearly with the degrees of the indeterminates of the original polynomial matrix. From a system-theoretic point of view, the proposed method, provides the algebraic tools to transform a high order bivariate linear system, into a zero coprime system equivalent first order representation. Notably, one of the proposed transformation techniques gives rise to generalized 2$$-D$$ Roesser models.

Polynomial matrix equivalences: system transformations and structural invariants

Abstract The present article is a survey on linear multivariable systems equivalences. We attempt a review of the most significant forms of system equivalence having as a starting point matrix transformations preserving certain aspects of their spectral structure. From a system theoretic point of view, the need for a variety of forms of polynomial matrix equivalences, arises from the fact that different types of spectral invariants give rise to different types of dynamics of the underlying linear system. A historical perspective of the key results and their contributors is also given.

Social Media, Mass Media and the 'Public Sphere'. Differentiation, Complementarity and Co-Existence

In modern society, ‘the public’ is inevitably a mediated sphere as only media can bridge its spatial, temporal and topical diversity. While this media has traditionally been mass media (one-to-many), the arrival of the Internet has popularised meso media (many-to-many). In that context, the mediated public sphere has undergone significant changes. On the one hand, media theorists emphasise the enabling characteristics of digital media, hoping for an egalitarian public sphere and an empowerment of media users. On the other hand, critics discuss the regulatory attributes of social media platforms, which allow to preformat and to sanction communication more efficiently than ever before. This overview paper discusses the generic relationship between social media and mass media from a systems-theoretical point of view. Further, it addresses the question of whether the social web is in fact on the path to democratising the ‘public sphere’.

Portfolio assessment: production and reduction of complexity

Over the last two decades, the education system has witnessed a shift from summative, product-oriented assessment towards formative, process-oriented assessment. Among the different learning and assessment initiatives introduced in the slipstream of this paradigmatic turn, the portfolio seems to have become one of the most popular. By redescribing the portfolio from a systems theoretical point of view, this article discusses established expectations of the portfolio in relation to transparency in learning, reflexivity and self-assessment. It shows that the majority of the literature deals with what questions, and that the portfolio is expected to handle a number of challenges with regard to the documentation of learning processes and achievements as well as the conditioning of learning activities. Descriptions of how the portfolio works are sparse. Based on systems theory, the paper adopts a how perspective: How does the portfolio redescribe learning? How does it scaffold and organise communication? One conclusion is that systems theory allows us to redescribe the portfolio as a teaching technology, which, by scaffolding both reflection and reflexivity, produces particular conditions for the stimulation and observation of learning, thus increasing the complexity of observation of learning.

Keeping Systems at Work

This article discusses the reliability of electricity supply and the management of its uncertainties from a systems theoretical point of view. We begin by outlining recent Science and Technology Studies (STS) literature about energy systems, infrastructures and practices concerning their use and argue that many current discussions hold promise in two directions: one concerns the brittleness and uncertainty of the electricity system that is seen as an ongoing achievement, the other is about broader structuring factors and contexts that should also be acknowledged when researching such systems. With an aim of developing this two-part focus, the paper advances systems theoretical considerations about the electricity infrastructure and proposes an analysis tool to study the necessary reductions of complexity of the infrastructure in two emblematic settings. The sites are infrastructure control rooms on the one hand and households on the other hand. The article concludes by discussing the different reductions of complexity by electricity users and electricity experts through using the theoretical point of view presented in the article.

Modelling and Estimation for Finite State Reciprocal Processes

A reciprocal equation is a kind of descriptor linear discrete-index stochastic system which is well known be satisfied (pathwise) by all Gaussian reciprocal processes. From a system-theoretic point of view, it is a kind of `noncausal' linear system, in the sense that the solution of it cannot be determined by only an `initial' condition, indeed requiring the `terminal' state as well, besides all the `input' function between initial and terminal states. Also, nice properties are known of a reciprocal equation, such as the equivalence of it with a couple of ordinary (causal) dynamic systems running in opposite directions. For these reasons, here we assume a reciprocal equation as the target of stochastic realization for the class of finite state reciprocal processes, also named reciprocal chains. The central result of the present paper is showing that any canonical reciprocal chain, i.e. valued in the canonical base of \REALRN , N being the cardinality of the set of chain's states, satisfies (pathwise) a reciprocal equation in a N2 dimensional canonical variable, or in other word a quadratic reciprocal equation, named `Augmented state reciprocal model' (ASRM). Also, for a partially observed reciprocal chain, a linear-optimal smoother is derived. All the results here presented are based upon the idea that a reciprocal chain is a `combination' of Markov bridges, to this purpose other forms, besides the ASRM, are presented in order to make clear the meaning of this `combination', as well as to prove that the linear smoother can be actually implemented as N smoothers all operating independently on each Markov bridge component.

Some Remarks on the Controllability of Sampled-Data Systems

This paper raises the question of controllability (or more precisely, reachability) of sampled-data systems, i.e., systems composed of a continuous-time plant controlled by a digital controller. The question is formulated from the continuous-time perspective, and the study is carried out in a functional analytic framework. The novelty of the study lies in the infinite-dimensionality of the underlying physical state signals which comes from the fact that the plant actually evolves over a temporal continuum. Different concepts of controllability related directly to the continuous-time behavior of sampled-data systems are introduced, namely exact, approximate, and null controllability. It is shown that the two former notions never occur in sampled-data systems, while the latter notion is a generic property for these systems. Some facts regarding the fundamental input/output structure of sampled-data systems from the control viewpoint are drawn from these results. The spectrum distribution of sampled-data feedback systems is also characterized, and its connection to the controllability properties is pointed out. By way of contrast, the system-theoretic viewpoint adopted in this paper departs from the finite-dimensional state-space system approach which has been taken at the outset in the lifting framework, and in which the pure discrete-time state of the “stroboscopic” model is chosen as the state of the hybrid sampled-data systems. Such a choice for a minimal finite-dimensional state space is justified by the external (input/output) treatment of sampled-data systems. We stress the fact that this paper is situated entirely at the internal level and takes a closer look into the internal continuous-time dynamics of sampled-data systems.

A system-theoretical approach to selective grid coarsening of reservoir models

From a system-theoretical point of view and for a given configuration of wells, there are only a limited number of degrees of freedom in the input–output dynamics of a reservoir system. This means that a large number of combinations of the state variables (pressure and saturation values) are not actually controllable and observable from the wells, and accordingly, they are not affecting the input–output behavior of the system. In an earlier publication, we therefore proposed a control-relevant upscaling methodology that uniformly coarsens the reservoir. Here, we present a control-relevant selective (i.e. non-uniform) coarsening (CRSC) method, in which the criterion for grid size adaptation is based on ranking the grid block contributions to the controllability and observability of the reservoir system. This multi-level CRSC method is attractive for use in iterative procedures such as computer-assisted flooding optimization for a given configuration of wells. In contrast to conventional flow-based coarsening techniques our method is independent of the specific flow rates or pressures imposed at the wells. Moreover the system-theoretical norms employed in our method provide tight upper bounds to the ‘input–output energy’ of the fine and coarse systems. These can be used as an a priori error-estimate of the performance of the coarse model. We applied our algorithm to two numerical examples and found that it can accurately reproduce results from the corresponding fine-scale simulations, while significantly speeding up the simulation.

On optimal control theory in marine oil spill management: A Markovian decision approach

Most evaluations of ecological effects of petroleum contamination have related impacts to effects on the supply of products and services of importance to human cultures. In order to facilitate the decision making process in the event of crude oil spills into marine environments, this paper treats marine oil spill problem from a system-theoretic point of view using the state variable description of Markovian decision process and operational research formalism.

La teoría de la diferenciación funcional en el horizonte de sus críticas

The theory of functional differentiation can be regarded as one of the oldest concepts in the field of the theory of society. Nevertheless, in sociology there is not complete agreement about basic theoretical figures and diagnoses amongst those who use the concept. This contribution uses several criticisms of Niklas Luhmann's theory of society as an opportunity to make clear the lines of theoretical conflict, to comment on this discourse from a systems theoretical point of view, and to line out some adjustments and supplementation with regard to some theoretical problems. In particular the contribution deals with the question of the unity of society, with the question of selective differentiation of functional subsystems, and with an integration of the problem of social inequality into a systems theoretical theory of society.

A Fault Diagnosis and Security Framework for Water Systems

Water resources management is a key challenge that will become even more crucial in the years ahead. From a system-theoretic viewpoint, there is a need to develop rigorous design and analysis tools for control, fault diagnosis and security of water distribution networks. This work develops a mathematical framework suitable for fault diagnosis and security in water systems; in addition it investigates the problem of determining a suitable set of locations for sensor placement in large-scale drinking water distribution networks such that contaminant detection is optimized. This work contributes to the research by presenting a problem formulation were the state-space representation of the propagation and reaction dynamics is coupled with the impact dynamics describing the “damage” caused by a contamination of the water distribution network. We propose a solution methodology for the sensor-placement problem by considering several risk-objectives, and by utilizing various optimization and evolutionary computation techniques. To illustrate the methodology, we present results of a simplified and a real water distribution network.