A “mixed” small gain and passivity theorem in the frequency domain

We show that the negative feedback interconnection of two causal, stable, linear time-invariant systems, with a “mixed” small gain and passivity property, is guaranteed to be finite-gain stable. This “mixed” small gain and passivity property refers to the characteristic that, at a particular frequency, systems in the feedback interconnection are either both “input and output strictly passive”; or both have “gain less than one”; or are both “input and output strictly passive” and simultaneously both have “gain less than one”. The “mixed” small gain and passivity property is described mathematically using the notion of dissipativity of systems, and finite-gain stability of the interconnection is proven via a stability result for dissipative interconnected systems.     

Cooperation without deliberation: A minimal behavior-based approach to multi-robot teams

While terminology and some concepts of behavior-based robotics have become widespread, the central ideas are often lost as researchers try to scale behavior to higher levels of complexity. “Hybrid systems” with model-based strategies that plan in terms of behaviors rather than simple actions have become common for higher-level behavior. We claim that a strict behavior-based approach can scale to higher levels of complexity than many robotics researchers assume, and that the resulting systems are in many cases more efficient and robust than those that rely on “classical AI” deliberative approaches. Our focus is on systems of cooperative autonomous robots in dynamic environments. We will discuss both claims that deliberation and explicit communication are necessary to cooperation and systems that cooperate only through environmental interaction. In this context we introduce three design principles for complex cooperative behavior—minimalism, statelessness and tolerance—and present a RoboCup soccer system that matches the sophistication of many deliberative soccer systems while exceeding their robustness, through the use of strict behavior-based techniques with no explicit communication.     

On uniform observation of nonuniformly observable systems

In [4,7,9,12], classes of nonlinear systems are considered for which observers can be designed. Although observability of nonlinear systems is known to be dependent on the input, the proposed observers have the property that the estimation error decays to zero irrespective of the input. In the first part of this paper, it is shown that this phenomenon follows from a common property of these systems: for all of them, the “unobservable states” with respect to some input, are in some sense “stable” (in the linear case, these systems are called detectable), and for this reason, a reduced order observer can be designed. In the second part is given a more general class of nonlinear systems for which such an observer can be designed.     

Information - organization - decision: Some strange loops

Acceptance of the theoretical foundations of Management Information Systems (MIS) has remained surprisingly high in the past twenty years, whereas information processing technologies have been improving at an incredible rate. This stability appears to be because the MIS model is based on the cybernetic model of organizations. We see, however, a conceptual crisis due in the development of more and more complex information systems and increased questioning of the deficiencies of organizational models based on cybernetic theory. This is particularly highlighted by the problems encountered in introducing the “bounded rationality paradigm” of H.A. Simon into the model.In this paper, we propose a new model that should be better adapted to contempory technology. This model allows both order and disorder to be included, while incorporating the concept of “organizational memory,” to improve the representation of a complex organizational information system with an action and process aspect.     

A framework for specifying and verifying the behaviour of open systems

Coding no longer represents the main issue in developing software applications. It is the design and verification of complex software systems that require to be addressed at the architectural level, following methodologies which permit us to clearly identify and design the components of a system, to understand precisely their interactions, and to formally verify the properties of the systems. Moreover, this process is made even more complicated by the advent of the “network-centric” model of computation, where open systems dynamically interact with each other in a highly volatile environment. Many of the techniques traditionally used for closed systems are inadequate in this context.We illustrate how the problem of modeling and verifying behavioural properties of open system is addressed by different research fields and how their results may contribute to a common solution. Building on this, we propose a methodology for modeling and verifying behavioural aspects of open systems. We introduce the IP-calculus, derived from the π-calculas process algebra so as to describe behavioural features of open systems. We define a notion of partial correctness, acceptability, in order to deal with the intrinsic indeterminacy of open systems, and we provide an algorithmic procedure for its effective verification.     

Performing a course material enhancement process with asynchronous interactive online system

Online systems have come to be heavily used in education, particularly for online learning and collecting information not otherwise readily available. Most e-learning systems, including interactive learning systems, have been designed to “push” course materials to students but rarely to “collect” or “pull” ideas from them. The interactive mechanisms in proposed instructional design models, however, prevent many potential designers from improving course quality, even though some believe that the learning experience and the comments of students are important for enhancing course materials. As well, students could actually contribute to instructional design.This paper presents a course material enhancement process that elicits ideas from students by encouraging students to modify course materials. This process had been tested on different higher education programs, both graduate and undergraduate. It aims to understand which programs’ students have a higher willingness to participate in this work and if they can benefit from this process. To facilitate this research, an asynchronous interaction system, teacher digital assistant (TDA), was designed for teachers to receive responses, recommendations, and modified materials from students at any time. The major advantage of this process is that it could embed students’ thoughts into the course material to improve the curriculum, which can benefit future students.     

Variable structure exponential stabilization of chained systems based on the extended nonholonomic integrator

In this paper, a new variable structure control strategy for exponentially stabilizing chained systems is presented based on the extended nonholonomic integrator model, the discontinuous coordinate transformation and the “reaching law method” in variable structure control design. The proposed approach converts the stabilization problem of an n-dimensional chained system into the pole-assignment problem of an (n−3)-dimensional linear time-invariant system and consequently simplifies the stabilization controller design of nonholonomic chained systems.     

Landscape visualizations: Applications and requirements of 3D visualization software for environmental planning

This paper presents the findings of an investigation into the role and use of landscape visualization software for landscape and environmental planning in Germany. It examines the challenges and requirements of 3D visualization technology and its potential for application in landscape and environmental planning. Relevant literature and comparable surveys are reviewed in order to determine the current state of affairs, and the general and international relevance of the results is assessed.In 2000, a survey of user requirements for 3D landscape simulation software, including the demand for specific features, was conducted within the framework of a feasibility study for a visualization tool. As part of the German-wide survey, comprehensive questionnaires were sent to 1044 respondents from a pool of private landscape planning consultancies, freelance landscape architects, and public planning and environmental authorities.The survey showed that 3D landscape visualization has a positive image in Germany, both among user and non-user groups of visualization tools. Twenty-eight percent of private consultancies and freelance landscape architects, as well as 7% of public authorities, stated that they already used 3D simulation software. Those respondents who did not use 3D simulation software cited insufficient computer equipment, lack of technical expertise of planners and cost-related aspects as reasons for not yet having adopted the technology. “Ease of learning” and “interoperability” are deemed to be the most important features of 3D simulation software, whereas factors such as “high interactivity”, “representability of ecological processes” and “photo-realism” are, surprisingly, regarded as much less important.Users of 3D visualization software are particularly concerned by insufficient representation of plants and habitats in simulations. Looking to the future, the vast majority of respondents (91%) expect increased benefits for landscape planning from 3D visualization software, are convinced of the advantages of the technology, and are eager to integrate 3D landscape visualizations into their working practices.     

Aggregation of a class of interconnected, linear dynamical systems

In this paper, we introduce the notion of a “meaningful” average of a collection of dynamical systems as distinct from an “ensemble” average. Such a notion is useful for the study of a variety of dynamical systems such as traffic flow, power systems, and econometric systems. We also address the associated issue of the existence and computation of such an average for a class of interconnected, linear, time invariant dynamical systems. Such an “average” dynamical system is not only attractive from a computational perspective, but also represents the average behavior of the interconnected dynamical systems. The problem of analysis and control of heirarchical, large scale control systems can be simplified by approximating the lower level dynamics of such systems with such an average dynamical system.     

Critical success factors revisited: success and failure cases of information systems for senior executives

The literature suggests the existence of critical success factors (CSFs) for the development of information systems that support senior executives. Our study of six organizations gives evidence for this notion of CSFs. The study further shows an interesting pattern, namely that companies either “get it right”, and essentially succeed on all CSFs, or “get it completely wrong”, that is, fall short on each of the CSFs. Among the six cases for which data were collected through in-depth interviews with company executives, three organizations seemed to manage all the CSFs properly, while two others managed all CSFs poorly. Only one organization showed a mixed scorecard, managing some factors well and some not so well. At the completion of the study, this organization could neither be judged as a success, nor as a failure. This dichotomy between success and failure cases suggests the existence of an even smaller set of “meta-success” factors. Based on our findings, we speculate that these “meta-success” factors are “championship”, “availability of resources”, and “link to organization objectives”.     

Validating for Liveness in Hidden Adversary Systems

Multi-stream interactive systems can be seen as “hidden adversary” systems (HAS), where the observable behaviour on any interaction channel is affected by interactions happening on other channels. One way of modelling HAS is in the form of a multi-process I/O automata, where each interacting process appears as a token in a shared state space. Constraints in the state space specify how the dynamics of one process affects other processes. We define the “liveness criterion” of each process as the end objective to be achieved by the process. The problem now for each process is to achieve this objective in the face of unforeseen interferences from other processes. In an earlier paper, it was proposed that this uncertainty can be mitigated by collaboration among the disparate processes. Two types of collaboration philosophies were also suggested: altruistic collaboration and pragmatic collaboration. This paper addresses the HAS validation problem where processes collaborate altruistically.     

Optimal design of two interconnected enzymatic bioreactors

This paper deals with the optimal design of two interconnected continuous stirred bioreactors in which a single enzymatic reaction occurs. The term “optimal” should be understood here as the minimum of the total volume of the reactors required to perform a given conversion rate, given a quantity of matter to be converted per time unit. In determining the optimal volume, it is considered that the input flow may be distributed among the tanks and also that a recirculation loop may be used. The optimal design problem is solved for a wide class of kinetics functions including, in particular, the well-known Michaelis–Menten kinetics function. The analysis of the optimal configurations is investigated, and it is shown that the concept of “Steady State Equivalent Biological System” (SSEBS) first introduced by Harmand et al. [AIChE J., in press] for microbial reactions only applies to enzymatic systems which have non-monotonic kinetics. In addition, a stability as well as a sensitivity analysis of the optimal configurations are performed.     

New perspectives in decision support for port planning

The Decision-Support-System (DSS) to be presented within this paper is based on research done at the department of Computer Science of the Technical University of Berlin. Among the research conducted at the subdepartment for Applied Computer Science, the project “Determination of the Capacity of Ports” was one point of focus in the years 1980–1985. Findings of this research work as well as practical experiences helped in underpinning the knowledge of the decision processes in seaports; all this contributed to the development of a practice-oriented DSS. All parts of the system, including the data base, were programmed in SIMULA and implemented on the IBM 4381-2 of the Technical University of Berlin. Before the system is applied in an actual problem situation, all parts of the system, particularly the integrated simulation model, will have to be validated. Not until this validation has been done, will the decision makers have sufficient confidence regarding the decision support of this system. This validation is still being worked on. Further research is focused on the application of the DSS for similar decision problems in other traffic and transportation systems.     

Ascertaining Mathematical Theorems

Whereas to most logicians, the word “theorem” refers to any statement which has been shown to be true, to mathematicians, the word “Theorem” is, relatively speaking, rarely applied, and denotes something far more special. In this paper, we examine some of the underlying reasons behind this difference in terminology, and we show how this discrepancy might be exploited, in order to build a computer system which automatically selects the latter type of “Theorems” from amongst the former. Indeed, we have begun building the automated discovery system MATHsAiD, the design of which is based upon our research. We provide some preliminary results produced by this system, and compare these results to Theorems appearing in various mathematics textbooks.     

Swing-up and stabilization of a cart–pendulum system under restricted cart track length

This paper describes the swing-up and stabilization of a cart–pendulum system with a restricted cart track length and restricted control force using generalized energy control methods. Starting from a pendant position, the pendulum is swung up to the upright unstable equilibrium configuration using energy control principles. An “energy well” is built within the cart track to prevent the cart from going outside the limited length. When sufficient energy is acquired by the pendulum, it goes into a “cruise” mode when the acquired energy is maintained. Finally, when the pendulum is close to the upright configuration, a stabilizing controller is activated around a linear zone about the upright configuration. The proposed scheme has worked well both in simulation and a practical setup and the conditions for stability have been derived using the multiple Lyapunov functions approach.     

Overrun handling approaches for overload-prone soft real-time systems

Traditional overrun handling approaches for real-time systems enforce some isolation property at the job or task level. This paper shows that by “relaxing” task isolation, it is possible to efficiently deal with overruns in soft real-time systems with highly variable task execution times and proposes Randomized Dropping (RD), a novel overrun handling mechanism. RD is able to bound task overruns in a probabilistic manner, thus providing “soft” task isolation. The paper shows how to combine RD with priority-driven and rate-based scheduling algorithms, and how to analyze the resulting system. Performance evaluation and comparison between simulation and analytical results are discussed.     

A hypothetical application of the Statistical Modeling and Estimation of Reliability Functions for Software (SMERFS) to Knowledge-Based Systems (KBSs)

Software reliability models are applied to conventional software to compute several important quantities. Two of these are the rate at which software fails and the number of software faults remaining in software. The software failure rate and the number of faults remaining in software are measures of software trustworthiness or reliability. Software reliability models, however, have never been applied to knowledge-based systems to determine these quantities. This paper reports a hypothetical application of the Statistical Modeling and Estimation of Reliability Functions for Software (SMERFS) to knowledge-based systems. SMERFS, developed by the Naval Surface Warfare Center (NSWC), contains a representative set of software reliability models “chosen for their performance in comparative studies and their ability to handle data collected from various testing environments.”     

A distributed approach for fault detection and diagnosis based on Time Petri Nets

This paper proposes an algorithm for the model based design of a distributed protocol for fault detection and diagnosis for very large systems. The overall process is modeled as different Time Petri Net (TPN) models (each one modeling a local process) that interact with each other via guarded transitions that becomes enabled only when certain conditions (expressed as predicates over the marking of some places) are satisfied (the guard is true). In order to use this broad class of time DES models for fault detection and diagnosis we derive in this paper the timing analysis of the TPN models with guarded transitions. In this paper we also extend the modeling capability of the faults calling some transitions faulty when operations they represent take more or less time than a prescribed time interval corresponding to their normal execution. We consider here that different local agents receive local observation as well as messages from neighboring agents. Each agent estimates the state of the part of the overall process for which it has model and from which it observes events by reconciling observations with model based predictions. We design algorithms that use limited information exchange between agents and that can quickly decide “questions” about “whether and where a fault occurred?” and “whether or not some components of the local processes have operated correctly?”. The algorithms we derive allow each local agent to generate a preliminary diagnosis prior to any communication and we show that after communicating the agents we design recover the global diagnosis that a centralized agent would have derived. The algorithms are component oriented leading to efficiency in computation.     

Model predictive control for perturbed max-plus-linear systems

Model predictive control (MPC) is a popular controller design technique in the process industry. Conventional MPC uses linear or nonlinear discrete-time models. Recently, we have extended MPC to a class of discrete event systems that can be described by a model that is “linear” in the (max,+) algebra. In our previous work, we have only considered MPC for the deterministic noise-free case without modeling errors. In this paper, we extend our previous results on MPC for max-plus-linear systems to cases with noise and/or modeling errors. We show that under quite general conditions the resulting optimization problems can be solved very efficiently.