A behavioral approach to linear exact modeling

The behavioral approach to system theory provides a parameter-free framework for the study of the general problem of linear exact modeling and recursive modeling. The authors present the solution of the (continuous-time) polynomial-exponential time series modeling problem. Both recursive and nonrecursive solutions are provided and classified according to properties like complexity and controllability. It is shown, in particular, that recursive modeling corresponds to updating by means of a cascade inter-connection of systems. As a special case, the solution of several other problems, such as rational interpolation, realization, and modeling of arbitrary discrete-time time series, is obtained     

Corroles as receptors in liquid membrane electrodes and their potentiometric response towards salicylic acid

Here, we report on the application of corroles as analytically active compounds in liquid membrane electrodes (ISE) that are sensitive towards salicylic acid and salicylate.The potentiometric signals generated by corrole-incorporated ISEs strongly depend on the pH of the aqueous sample solution and the membrane composition, such as the presence of lipophilic sites. Corrole incorporating ISEs are characterised by a low detection limit (4.0 × 10⁻⁵ M) and a wide linear range (4.0 × 10⁻⁵ to 5.3 × 10⁻³ M). Also, they are free from interference versus other organic anions.The mechanism of the generation of the potentiometric signals of corrole incorporating ISEs in the presence of salicylate anion, as well salicylic acid, will be discussed.     

Synthesis of dissipative systems using quadratic differentialforms: part II

For pt.1 see ibid., p.53-69 (2002). The authors discuss several important special cases of the problem solved in Part I. These are: disturbance attenuation and passivation, the full information case, the filtering problem, and the case that the to-be-controlled plant is given in input-state-output representation. An interesting aspect is the notion of full information, which we define in terms of the observability of the to-be-controlled variables from the control variables. When the system is given in state space form, we obtain conditions for the existence of a controller that renders a system dissipative in terms of two coupled algebraic Riccati inequalities. The controller turns out to be a feedback system with a transfer function that is proper, but, in general, not strictly proper. Another issue that we study in this paper is feedback implementability. We find conditions under which, in the context of synthesis of dissipative systems, a controlled behavior can implemented by a feedback controller     

Uncertainty Matters: Computer Models at the Science–Policy Interface

The use of computer models offers a general and flexible framework that can help to deal with some of the complexities and difficulties associated with the development of water management plans as prescribed by the Water Framework Directive. However, despite the advantages modelling presents, the integration of information derived from models into policy is far away from being trivial or the norm. Part of the difficulties of this integration is rooted in the lack of confidence policy makers have on the incorporation of modelling information into policy formulation. In this paper we examine the reasons for this apparent lack of confidence and explore how some tools, presently in use, address this problem. We conclude that public confidence in models is highly dependent on the way uncertainties are addressed and suggest possible directions of action to improve the current situation. Four real case studies illustrate how computer models have been used in The Netherlands for carrying out management plans at regional and national scale. We suggest that the solution to integrate modelling information into policy formulation lies on both the modelling and the policy-making communities.     

A criterion for atomicity revisited

Concurrent and reactive programs are specified by their behaviours in the presence of a nondeterministic environment. In a natural way, this gives a specification (ARW) of an atomic variable in the style of Abadi and Lamport. Several implementations of atomic variables by lower level primitives are known. A few years ago, we formulated a criterion to prove the correctness of such implementations. The proof of correctness of the criterion itself was based on Lynch’s definition of atomicity by serialization points. Here, this criterion is reformulated as a specification HRW in the formal sense. Simulations from HRW to ARW and vice versa are constructed. These now serve as a constructive proof of correctness of the criterion. Eternity variables are used in the simulation from HRW to ARW. We propose so-called gliding simulations to deal with the problems that appear when occasionally the concrete implementation needs fewer steps than the abstract specification.     

Polymerization of liquid propylene with a fourth‐generation Ziegler–Natta catalyst: Influence of temperature,hydrogen, monomer concentration,and prepolymerization method on powder morphology

Liquid propylene was polymerized in a 5‐L autoclave batch reactor using a commercially available TiCl₄/MgCl₂/Al(ethyl)₃/DCPDMS Ziegler–Natta catalyst, with a phthalate ester as internal electron donor. The powders from these polymerizations were characterized using laser diffraction particle size distribution (PSD) analysis, scanning electron microscopy (SEM), and bulk density measurements. These characteristics were analyzed as a function of the process conditions, including hydrogen and monomer concentration, polymerization temperature, and the prepolymerization method. It was shown that polymerization temperature influences the powder morphology to a large extent. At low temperatures, high‐density particles were obtained, showing regular shaped particle surfaces and low porosities. With increasing temperature, the morphology gradually was transferred into a more open structure, with irregular surfaces and poor replication of the shape of the catalyst particle. When using a prepolymerization step at a relatively low temperature, the morphology obtained was determined by this prepolymerization step and was independent from conditions in main polymerization. The morphology obtained was the same as that observed after a full polymerization at temperature. Even when using a short polymerization at an increasing temperature, the morphology was strongly influenced by the initial conditions. The effect of variation in hydrogen concentration supported the conclusion that the initial polymerization rate determines the powder morphology. In the absence of hydrogen, high bulk densities, and regularly shaped particles were obtained, even at high temperatures. With increasing hydrogen concentration, the reaction rates increased rapidly, and with that changed the morphology. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1421–1435, 2003