System Theoretic Approach Research Articles

Systems-Theoretic Approaches to Design Biological Networks with Desired Functionalities.

The deduction of design principles for complex biological functionalities has been a source of constant interest in the fields of systems and synthetic biology. A number of approaches have been adopted, to identify the space of network structures or topologies that can demonstrate a specific desired functionality, ranging from brute force to systems theory-based methodologies. The former approach involves performing a search among all possible combinations of network structures, as well as the parameters underlying the rate kinetics for a given form of network. In contrast to the search-oriented approach in brute force studies, the present chapter introduces a generic approach inspired by systems theory to deduce the network structures for a particular biological functionality. As a first step, depending on the functionality and the type of network in consideration, a measure of goodness of attainment is deduced by defining performance parameters. These parameters are computed for the most ideal case to obtain the necessary condition for the given functionality. The necessary conditions are then mapped as specific requirements on the parameters of the dynamical system underlying the network. Following this, admissible minimal structures are deduced. The proposed methodology does not assume any particular rate kinetics in this case for deducing the admissible network structures notwithstanding a minimum set of assumptions on the rate kinetics. The problem of computing the ideal set of parameter/s or rate constants, unlike the problem of topology identification, depends on the particular rate kinetics assumed for the given network. In this case, instead of a computationally exhaustive brute force search of the parameter space, a topology-functionality specific optimization problem can be solved. The objective function along with the feasible region bounded by the motif specific constraints amounts to solving a non-convex optimization program leading to non-unique parameter sets. To exemplify our approach, we adopt the functionality of adaptation, and demonstrate how network topologies that can achieve adaptation can be identified using such a systems-theoretic approach. The outcomes, in this case, i.e., minimum network structures for adaptation, are in agreement with the brute force results and other studies in literature.

Effects of Cyber Attacks on AC and High-Voltage DC Interconnected Power Systems with Emulated Inertia

The high penetration of renewable energy resources and power electronic-based components has led to a low-inertia power grid which would bring challenges to system operations. The new model of load frequency control (LFC) must be able to handle the modern scenario where controlled areas are interconnected by parallel AC/HVDC links and storage devices are added to provide virtual inertia. Notably, vulnerabilities within the communication channels for wide-area data exchange in LFC loops may make them exposed to various cyber attacks, while it still remains largely unexplored how the new LFC in the AC/HVDC interconnected system with emulated inertia would be affected under malicious intrusions. Thus, in this article, we are motivated to explore possible effects of the major types of data availability and integrity attacks—Denial of Service (DoS) and false data injection (FDI) attacks—on such a new LFC system. By using a system-theoretic approach, we explore the optimal strategies that attackers can exploit to launch DoS or FDI attacks to corrupt the system stability. Besides, a comparison study is performed to learn the impact of these two types of attacks on LFC models of power systems with or without HVDC link and emulated inertia. The simulation results on the the exemplary two-area system illustrate that both DoS and FDI attacks can cause large frequency deviations or even make the system unstable; moreover, the LFC system with AC/HVDC interconnections and emulated inertia could be more vulnerable to these two types of attacks in many adversarial scenarios.

A systems-theoretic approach to hazard identification of marine systems with dynamic autonomy

Autonomous marine systems may switch between various operational modes with different levels of autonomy (LoA), due to a rapidly changing environment and the complex nature of tasks. The dynamic autonomy brings an additional layer of complexity to ensuring safe marine operations, but this functionality is not sufficiently considered in current risk analysis methods. Hence, this paper proposes an approach to hazard identification based on the system theoretic process analysis (STPA) that includes unsafe transitions between different LoA in systems. A case study of a remotely operated vehicle (ROV) with four operational modes with different LoAs is used to illustrate the approach. The results show that the proposed approach contributes to: 1) communicating a shift of responsibilities among human operator and system controller in different operational modes by specifying how the allocation of the responsibility between human operators and the controller changes, and what updated process model of the operator and the controller are to ensure a successful transition; 2) refining safety constraints to be more concrete to improve system design, and operational procedures and 3) identifying triggering events for marine system modes’ transitions to handle environmental interaction systematically and sufficiently.

A framework to model the STPA hierarchical control structure of an autonomous ship

The demand for risk and safety analysis is becoming greater due to the increased complexity of modern systems such as autonomous ships. Safety is one of the main motivations behind the efforts of multiple organizations to develop autonomous ships. The adoption of an early system-theoretic approach to safety such as System Theoretic Process Analysis (STPA) is an effective way to integrate safety in complex systems. Furthermore, many authors have urged the use of this method to analyse the risks of autonomous vessels in the development phases. Applying STPA requires a description of the system to model the hierarchical control structure and conduct the analysis. At this stage, the functional description of autonomous ships remains limited, which poses a challenge in building the hierarchical control structure. This paper proposes a framework for developing a hierarchical control structure of an autonomous ship. The framework is founded on the principles of the STPA control structure and its five main elements. It makes use of the current shipping operation system, the available information about autonomous ships and the experience of seafarers executing diverse tasks on-board conventional ships. The application of the framework showed that the information provided by the seafarers is essential in developing an initial functional description of an autonomous ship. Furthermore, the results revealed that in addition to the technical aspects of autonomous ships, introducing these vessels into the organizational control structure of current maritime operation also poses challenges that need to be addressed in the earliest design phase.

Hazard analysis for identifying common cause failures of digital safety systems using a redundancy-guided systems-theoretic approach

Replacing the existing aging analog instrumentation and control (I&C) systems with modern safety control and protection, digital technology offers one of the foremost means of performance improvements and cost reductions for the existing nuclear power plants (NPPs). However, the qualification of digital I&C systems remains a challenge, especially considering the issue of software common-cause failures (CCFs), which are difficult to address. With the application and upgrades of advanced digital I&C systems, software CCFs have become a potential threat to plant safety because most redundant designs use similar digital platforms or software in the operating and application systems. With complex designs of multilayer redundancy to meet the single-failure criterion, digital I&C safety systems (e.g., engineered safety-features actuation system [ESFAS]) are of a particular concern in the U.S. Nuclear Regulatory Commission (NRC) licensing procedures. This paper applies a modularized approach to conduct redundancy-guided systems-theoretic hazard analysis for an advanced digital ESFAS with multilevel redundancy designs. Systematic methods and risk-informed tools are incorporated to address both hardware and software CCFs, which provide guidance to eliminate the causal factors of potential single points of failure in the design of digital safety systems in advanced plant designs.

Mechanical system scaling based on output only identification and mass perturbations by state projections

In this article the authors develop a new method for input-output system parametrization based on mechanical output only identification, mass perturbations, and state projections. Based on a brief summary of mechanical model parametrization, the authors develop a central relation of reference and altered structural states based on a general system theoretic approach. By applying a state space description, the novel state projections for system scaling (SP2S) method is defined. The proposed numerical solution based on a least-squares approach follows a reordering by Kronecker product. Very importantly, applied state space parameters can be in general coordinates and the model order is not restricted (for instance to the number of measurement positions). Finally, SP2S is applied and verified based on simulated and real experimental measurements of a laboratory set-up.

Systems-theoretic approach to safety of inland passenger ship operation in Bangladesh

Safety of Passenger vessel operation in Bangladesh is a burning issue that remains uncertain so far. The nation has experienced a number of dreadful accidents involving passenger ships in the past few decades. Furthermore, the accidents involving passenger vessels cover the lion's share of fatality of the overall maritime accidents in Bangladesh. Therefore, the mitigation of the accidents involving the passenger ship will significantly reduce the number of fatalities in Bangladesh. The previous studies conducted on the safety of inland passenger ship were incapable of identifying the underlying causal factors responsible for accidents for being focused on the primary causes of accidents. This study aims to perform a hazard analysis to assess the safety of inland passenger ship operation in Bangladesh by applying the Systems Theoretic Process Analysis (STPA) method. It is revealed that most of the Unsafe Control Actions (UCA) exist in the bridge deck of the passenger ship. Besides, the most contributing category of the causal factor responsible for the occurrence of Unsafe Control Actions (UCA) is the human factor. The causal factors identified by the analysis can easily be comprehended by the stakeholders such as crews of the passenger ship, regulatory bodies, designers and others so that they can avoid the unsafe activities related to the operation of passenger vessels. The effective implementation of the recommended safety requirements can prevent the occurrence of those causal factors and can mitigate the accidents of passenger ships in Bangladesh.

Nonlinear Dynamics, Switching Kinetics and Physical Realization of the Family of Chua Corsage Memristors

This article reviews the nonlinear dynamical attributes, switching kinetics, bifurcation analysis, and physical realization of a family of generic memristors, namely, Chua corsage memristors (CCM). CCM family contains three 1-st order generic memristor dubbed as 2-lobe, 4-lobe, and 6-lobe Chua corsage memristors and can be distinguished in accordance with their asymptotic stable states. The 2-lobe CCM has two asymptotically stable equilibrium states and regarded as a binary memory device. In contrast, the versatile 4-lobe CCM and 6-lobe CCM are regarded as a multi-bit-per-cell memory device as they exhibit three and four asymptotic stable states, respectively, on their complex and diversified dynamic routes. Due to the diversified dynamic routes, the CC memristors exhibit a highly nonlinear DC V-I curve. Unlike most published highly-nonlinear DC V-I curves with several disconnected branches, the DC V-I curves of CCMs are contiguous along with a locally active negative slope region. Moreover, the DC V-I curves and parametric representations of the CCMs are explicitly analytical. Switching kinetics of the CCM family can be demonstrated with universal formulas of exponential state trajectories xn(t), time period tfn, and applied minimum pulse amplitude VA and width Δw. These formulas are regarded universal as they can be applied to any piecewise linear dynamic routes for any DC or pulse input and with any number of segments. When local activity, and bifurcation and chaos theorems are employed, CMMs exhibit unique stable limit cycles spawn from a supercritical Hopf bifurcation along with static attractors. In addition, the nonlinear circuit and system theoretic approach is applied to explain the asymptotic stability behavior of CCMs and to design real memristor emulators using off-the-shelf circuit components.

A systems-theoretic analysis of low-level human motor control: application to a single-joint arm model.

Continuous control using internal models appears to be quite straightforward explaining human motor control. However, it demands both, a high computational effort and a high model preciseness as the whole trajectory needs to be converted. Intermittent control shows great promise for avoiding these drawbacks of continuous control, at least to a certain extent. In this contribution, we study intermittency at the motoneuron level. We ask: how many different, but constant muscle stimulation sets are necessary to generate a stable movement for a specific motor task? Intermittent control, in our perspective, can be assumed only if the number of transitions is relatively small. As application case, a single-joint arm movement is considered. The muscle contraction dynamics is described by a Hill-type muscle model, for the muscle activation dynamics both Hatze's and Zajac's approach are considered. To actuate the lower arm, up to four muscle groups are implemented. A systems-theoretic approach is used to find the smallest number of transitions between constant stimulation sets. A method for a stability analysis of human motion is presented. A Lyapunov function candidate is specified. Thanks to sum-of-squares methods, the presented procedure is generally applicable and computationally feasible. The region-of-attraction of a transition point, and the number of transitions necessary to perform stable arm movements are estimated. The results support the intermittent control theory on this level of motor control, because only very few transitions are necessary.

Using a systems-theoretic approach to analyze safety in radiation therapy-first steps and lessons learned

Radiation therapy is an important technique to treat cancer. Due to the high occupational risks involved, the process is subject to severe safety regulations and standards. However, these standards do not mandate the usage of a particular hazard analysis method. The de facto methods currently used are the reliability theory-based Fault Tree Analysis (FTA) and Healthcare Failure Mode and Effects Analysis (HFMEA). Systems Theoretic Process Analysis (STPA) is a new, essentially different hazard analysis method, based on systems theory. Although successfully applied in many industries, there are only a few reports on STPA implementation in radiation therapy.This paper contributes to filling this gap with a preliminary assessment of STPA applied to a mature Intensity Modulated Radiation Therapy (IMRT) process. The analysis was conducted by a team consisting of two experts in radiation therapy and one software systems engineer, with little domain knowledge. 142 potentially unsafe control actions were identified and compared with the results of an earlier HFMEA. The main lesson we have learned is that a graphical, system-wise modeling of the analyzed process, although challenging for beginners, is a powerful instrument to catch the same and even other, new hazards. A causal analysis of a subset of these newly found hazards has led to meaningful and valuable risk mitigation measures. These results suggest considering STPA as a viable option for safety analysis in radiation therapy. We expect that this top-down, well-structured way of analysis can especially be advantageous for safety assessment in early design phases, when an HFMEA is not possible yet, because most of system’s implementation and behavior is still unknown.

Improving Discharge Process at the University of Wisconsin Hospital: A System-Theoretic Method

This paper introduces a system-theoretic approach to improve inpatient discharge process at the University of Wisconsin (UW) Hospital. The complex hospital discharge process is modeled by a stochastic process with parallel subprocesses, splits, merges, and reworks. Then, a stochastic analysis method is introduced to evaluate the performance of discharge. Specifically, the waiting and service times are characterized by gamma distributions, and an efficient algorithm is presented to aggregate the multiple interacting subprocesses and calculate the mean, variability, and discharge-time performance, i.e., the probability to discharge a patient within a desired or given time interval. High accuracy in performance evaluation is obtained by using such a method. To improve the discharge process at UW Hospital, bottleneck and what-if analyses are carried out and improvement recommendations are discussed.

A System Theoretic Investigation of Cortisol Dysregulation in Fibromyalgia Patients with Chronic Fatigue.

Fibromyalgia Syndrome (FMS) and Chronic Fatigue Syndrome (CFS) are complex medical conditions with similar symptoms such as anxiety, fatigue, depression, headaches, muscle aches and joint pain. The etiology of both these syndromes is unknown. The objective of this study is to characterize FMS, both in the presence and in the absence of CFS, by analyzing variations in cortisol secretion patterns, timings, amplitudes, and the number of the underlying pulses as well as infusion and clearance rates. The comparison is performed against matched healthy control subjects. We estimate the hormonal secretory events by deconvolving cortisol data using a two-step coordinate descent approach. The first step implements a sparse recovery approach to infer the amplitudes and the timings of the cortisol secretion events from limited cortisol hormone data. The main advantage of this method is estimating the cortisol secretory events using a system theoretic approach. The second step is to estimate the physiological system parameters (i.e. infusion and clearance rates). This approach has been verified on healthy individuals previously. Our results show that the clearance rate of cortisol by the liver is relatively lower in patients as compared to the matched healthy individuals. This suggests that there is a relatively higher accumulation of serum cortisol in patients when compared to matched healthy subjects.

Ensemble Controllability of Cellular Oscillators

Many diseases including cancer, Parkinson’s disease and heart diseases are caused by loss or malfunction of regulatory mechanism of an oscillatory system. Successful treatment of these diseases might involve recovering the healthy behavior of the oscillators in the system, i.e., achieving synchrony or a desired distribution of the oscillators on their periodic orbit. In this letter, we consider the problem of controlling the distribution of a population of cellular oscillators described in terms of phase models. Different practical limitations on the observability and controllability of cellular states naturally lead to an ensemble control formulation in which a population-level feedback law for achieving a desired distribution is sought. A systems theoretic approach to this problem leads to Lyapunov- and LaSalle-like arguments, from which we develop our main contribution, novel necessary and sufficient conditions for the controllability of phase distributions in terms of the Fourier coefficients of the phase response curve. Since our treatment is based on a rather universal formulation of phase models, the results and methods proposed in this letter are readily applicable to the control of a wide range of other types of oscillating populations, such as circadian clocks, and spiking neurons.

A system dynamics approach in modeling organizational tradeoffs in safety management

AbstractThe mining industry is still ranked highly amongst the economic sectors with the highest fatality rates. Earlier approaches to safety have attributed this to the lack of a comprehensive safety management system that employs effective safety barriers. A system theoretic approach to safety provides a better basis for looking deeper into the interaction of technical, workplace and organizational factors, their magnitude of effects, and their time characteristics. This study presents a system dynamics model of safety and production that looks deeper into their organizational tradeoffs. A safety model integrates aspects of safety culture, worker motivation, and human reliability in an effort to examine how risk evolves over time. Additional models of task management and human resources are developed to trace the interactions between safety and production as well as to examine alternative job designs that can reduce risk. The simulation model has been tested for a number of step to increase production demands and the impact on safety over the course of 5 years.HIGHLIGHTS A methodology has been developed for modeling safety management based on system dynamics. The system dynamics model integrates safety with other organizational processes, such as production and human resources management. System dynamics allow explicit modeling of decision tradeoffs between organizational processes. Emphasis has been given on the evolution of risk over a large period of time where hidden problems may materialize later in the future.

Cybersafety: A System-theoretic Approach to Identify Cyber-vulnerabilities & Mitigations in Industrial Control Systems

Recent cyber-physical attacks, such as Stuxnet, Triton etc., have invoked an ominous realization about the lethality of such attacks and the vulnerability of critical infrastructure, including power, gas and water distribution systems. Traditional IT security-biased protection methods that narrowly focus on improving cyber hygiene are largely impotent in the face of targeted attacks by advanced cyber-adversaries. Thus, there is an urgent need to analyze the safety and security of critical infrastructure systems in an integrated, holistic fashion that leverages the physics of the cyber-physical system. System-Theoretic Accident Model & Processes (STAMP) offers a powerful, holistic, structured framework to analyze complex systems; hitherto, STAMP has been used extensively to perform safety analyses but an integrated safety and cyber-security analysis of industrial control systems (ICS) has not been published. This paper uses an actual electrical generation and distribution system of an archetypal industrial facility to demonstrate the application of a STAMP-based method – we call Cyber-safety – to identify and mitigate cyber-related vulnerabilities in ICS. The key contribution of this work is to differentiate the additional steps required to perform a holistic cyber-security analysis for an ICS of significant size and complexity and to present the analysis in a robust and structured format such that it can be emulated to analyze larger systems with many interdependent subsystems.

A Systems Theoretic Approach to Safety Analysis in Medical Cyber Physical Systems

The concept of a Cyber-Physical System (CPS) has been gaining traction as a promising new field of study in recent years. It integrates digital processing and data transfer with the real environment. Healthcare, aircraft, automobiles, chemicals, civil infrastructure, energy, manufacturing, transportation, and biological systems are just a few of the many applications of cyber-physical systems. Medical Safe, context-aware, and interconnected networks of medical equipment are what we call Medical Cyber-Physical Systems (MCPS). More and more hospitals are installing these systems in order to give their patients with round-the-clock, high-quality treatment. Systems theory is an umbrella term for the study of how various parts of a system interact to provide a unified whole. Bio-electronic systems (implantable medical devices) are a common kind of MCPS. Bionic ear and eye implants, deep brain stimulators for neurological disorders, and bionic arms for amputees are all examples of computer-based bio-electronic systems designed to replace impaired human body parts. There is a lot of work being done to boost the efficiency of bionic systems so that they can operate at near 100% efficiency, at cheap cost, and in smaller, safer packages. Avoiding risks to property and human life caused by uncontrolled interactions in implanted devices of CPS makes the design of bug-free and safe medical device software in MCPS both crucial and difficult.

Toward Resilience as a Tradable Parameter During Conceptual Trade Studies

Methodologies are required to model, evaluate, and analyze the resilience of system architectures at the conceptual design level to support needs evaluations, policy development, or study of social decisions. The primary objective of this paper was to develop a generalized resilience analysis model for the characterization of multistate engineered systems subject to disruptions to support system design selection during trade studies. Each design variant within the tradespace is modeled using continuous time Markov chains that simulate the transient response of each design variant subject to a user-defined disruption. The operating condition of the multistate system is characterized by a finite number of machine states. Each design variant's utility response is generated as a function of the system's machine state response to the disruption. Resilience capacities and capabilities are generated to populate trade studies. A case study consisting of an unmanned surface vessel provides a system theoretic approach to illustrate the concepts presented within this paper and demonstrates the ability of this methodology to aid decision maker's selection of resilient system architectures. Use of an analytical framework serves as a unifying foundation for incorporating resilience behaviors of multistate engineered systems into early stage design considerations.

Business value of big data analytics: A systems-theoretic approach and empirical test

Although big data analytics have been widely considered a key driver of marketing and innovation processes, whether and how big data analytics create business value has not been fully understood and empirically validated at a large scale. Taking social media analytics as an example, this paper is among the first attempts to theoretically explain and empirically test the market performance impact of big data analytics. Drawing on the systems theory, we explain how and why social media analytics create super-additive value through the synergies in functional complementarity between social media diversity for gathering big data from diverse social media channels and big data analytics for analyzing the gathered big data. Furthermore, we deepen our theorizing by considering the difference between small and medium enterprises (SMEs) and large firms in the required integration effort that enables the synergies of social media diversity and big data analytics. In line with this theorizing, we empirically test the synergistic effect of social media diversity and big data analytics by using a recent large-scale survey data set from 18,816 firms in Italy. We find that social media diversity and big data analytics have a positive interaction effect on market performance, which is more salient for SMEs than for large firms.

Exact Analysis and Physical Realization of the 6-Lobe Chua Corsage Memristor

A novel generic memristor, dubbed the 6-lobe Chua corsage memristor, is proposed with its nonlinear dynamical analysis and physical realization. The proposed corsage memristor contains four asymptotically stable equilibrium points on its complex and diversified dynamic routes which reveals a 4-state nonlinear memory device. The higher degree of versatility of its dynamic routes reveal that the proposed memristor has a variety of dynamic paths in response to different initial conditions and exhibits a highly nonlinear contiguous DC V-I curve. The DC V-I curve of the proposed memristor is endowed with an explicit analytical parametric representation. Moreover, the derived three formulas, exponential trajectories of state xnt, time period tfn, and minimum pulse amplitude VA, are required to analyze the movement of the state trajectories on the piecewise linear (PWL) dynamic route map (DRM) of the corsage memristor. These formulas are universal, that is, applicable to any PWL DRM curves for any DC or pulse input and with any number of segments. Nonlinear dynamics and circuit and system theoretic approach are employed to explain the asymptotic quad-stable behavior of the proposed corsage memristor and to design a novel real memristor emulator using off-the-shelf circuit components.

The supply and demand of social systems: towards a systems theory of the firm

PurposeThe economic theory of the firm apparently concurs with Niklas Luhmann’s theory of social systems with regard to the primary function of the firm to be complexity reduction, i.e. the alleviation of the cognitive burden on agents whose cognitive capacities are limited. At the same time, however, the theory of the firm ignores the attendant issues of societal sustainability emphasised by Luhmann. The paper aims to fill this gap.Design/methodology/approachTaking a theoretical approach, the paper builds on the conceptual construct of “the complexity-sustainability trade-off”, which combines two contrasting aspects of the relationship between a system and its environment, namely, the precariousness highlighted by Luhmann and the embeddedness highlighted by open systems theory. These themes are respectively reflected in the principles of complexity reduction and environmental dependence which constitute the trade-off.FindingsDrawing inspiration from the classic Marshallian presentation of supply and demand in modern economics, the paper argues that the principles of complexity reduction and critical dependence translate into the demand for and supply of social systems. In the proposed systems-theoretic interpretation of the theory of the firm, demand and supply refer to the imperatives of achieving coordination and securing cooperation within the firm, respectively. Thus, in the theory of the firm, the complexity-sustainability trade-off manifests itself as a trade-off between coordination and cooperation.Originality/valueThe implicit focus of the theory of the firm on complexity reduction disregards the nature, importance and fragility of cooperation in real-world firms. In so doing, it impedes the authors’ understanding of unconventional types of business organisation, such as cooperatives. These defects can be corrected by reorienting the theory of the firm according to the proposed systems-theoretic approach, which holds that firms should not be governed or studied in isolation from their environment, as they too often are – and, accordingly, that apparently anomalous forms of organisation should be taken seriously, as they too often are not.