Information cells and information cell mixture models for concept modelling

By combining the prototype theory and random set theory interpretations of vague concepts, a novel structure named information cell and a combined structure named information cell mixture model are proposed to represent the semantics of vague concepts. An information cell L _i on the domain Ω has a transparent cognitive structure ‘L _i =about P _i ’ which is mathematically formalized by a 3-tuple 〈P _i ,d _i ,δ _i 〉 comprising a prototype set P _i (⊆Ω), a distance function d _i on Ω and a density function δ _i on [0,+∞). An information cell mixture model on domain Ω is actually a set of weighted information cells L _i s. A positive neighborhood function of the information cell mixture model is introduced in this paper to reflect the belief distribution of positive neighbors of the underlying concept. An information cellularization algorithm is also proposed to learn the information cell mixture model from a training data set, which is a direct application of the k-means and EM algorithms. Information cell mixture models provide some tools for information coarsening and concept modelling, and have potential applications in uncertain reasoning and classification.     

Quasilinear nonuniformly parabolic system modelling chemotaxis

A system of quasilinear nonuniformly parabolic equations modelling chemotaxis and taking into account the volume filling effect is studied under no-flux boundary conditions. The proof of the existence of global-in-time solution is given.     

A microcomputer system for simulation modelling

Microcomputers are now widely used for discrete-event simulation work in Operational Research. An inexpensive microcomputer system for simulation modelling is presented. Based on an Apple II, it allows the programmer to develop three-phase activity based interactive models in Ucsd Pascal. Use is made of disc emulation for the provision of simultaneously available pictorial displays and the extension of fast access on-line memory for the development of large simulations.Use of a microcomputer speeds development time and gives the user a transportable computer dedicated to the simulation. Pascal facilitates the development of readable portable simulations.The simulation of a conveyer belt system demonstrates the simplicity and flexibility of the pictorial display. A practical study in the Health Service (modelling the treatment of chronic renal failure) illustrates that the package may be used to simulate a real and complex system.     

Simulation modelling and analysis of a border security system

Border control is vital to the security of a nation and its citizens. All countries look at measures to improve the security of their borders. But increasing security can bring a substantial financial burden. In this study, we analyze the border security problem of Turkey using a simulation approach. Our main objective is to find more efficient ways of improving border control and security along Turkey’s land borders. To achieve this, we examine the structure of the border security system and its major elements, examine the relationships between performance measures, and assess the effectiveness of security elements on each system performance measure. We also look into the issues of planned changes and additional resources, and we evaluate new alternative system designs. The results of simulation experiments are analyzed by statistical methods.     

Dynamic modelling and input-energy comparison for the elevator system

The elevator system driven by a permanent magnet synchronous motor (PMSM) is studied in this paper. The mathematical model of the elevator system includes the electrical and mechanical equations, and the dimensionless forms are derived for the purpose of practicable upward and downward movement. In this paper, the trapezoidal, cycloidal, five-degree (5-D) and seven-degree (7-D) polynomial and industry trajectories are designed and compared numerically in various motion and the absolute input energies. From numerical simulations, it is found that the trapezoidal trajectory consumes the minimum energy; the 7-D polynomial trajectory consumes the maximum one. The less end-point constraints are required, the less energy is consumed. Finally, the proposed sliding mode controller (SMC) is employed to demonstrate the robustness and well tracking control performance numerically.     

Power system modelling for emergency state simulation

A physically based mathematical model for an electric power system is developed to provide an adequate test bed for the testing and evaluation of slow speed dynamics emergency state control strategies. This model incorporates all the major components of the system, includes explicit representations for all the major physical variables and control, and is capable of simulating a wide variety of emergency contingencies. The dependence of the overall power system's behavior on the response characteristics of mechanical prime movers and the limitations placed on the overall system's response by absolute power and power rate capability constraints of the prime movers are described. Certain stochastic aspects of the system's behavior as well as the mechanisms governing cascading failures, which have characterized many major power system collapses in recent years, are introduced; and problems concerning the control of electric power systems under emergency state operating conditions are identified. Simulations are presented to demonstrate the behavior of the system under normal and emergency operating conditions and to show the importance of tie-line interconnection, especially to a region that is importing power from the rest of the system, as well as the effects of governor control action, initial pressure limiter and generation schedule prior to disturbances.     

Mathematical modelling of a diesel common-rail system

In diesel common-rail systems, the exact knowledge of the injection pressure is important to accurately control the injected diesel mass and thus the combustion process. This paper focuses on the mathematical modelling of the hydraulic and mechanical components of a common-rail system in order to describe the dynamics of the diesel rail pressure. Based on this model, an average model is derived to reduce the model complexity and to allow for a fast calculation of the mass flow into the rail for different crank shaft revolution speeds and openings of the fuel metering unit. The main purpose of this average model is to serve as a basis for a model-based (non-linear) controller design. The stationary accuracy of the models is validated by means of measurement data.     

Discrete-event modelling of an urban transportation system

The modelling of an urban transportation system is addressed. The transportation network is modelled as an oriented graph in which nodes represent single-mode or intermodal stations, integrating different transportation services. Its characteristics make it suitable to model the network as a Discrete Event System. In introducing the model proposed, attention is paid to the definition of all its components, but particular care is necessary for the identification of the probability distributions of the stochastic variables. The validation procedure performed to check the reliability of the model is described in detail. Some numerical results about a case study are presented and discussed.     

Mathematical modelling of a quasi-linear feedback system

This paper develops a method for system identification of a two input-one output quasi-linear system modelling the dynamics of a non-linear element of a feedback system. The identification method, which may be performed in either the time domain or the frequency domain, is designed to use normal operating records without the need to introduce special test inputs.     

A switched system approach to dynamic race modelling

The paper presents and analyses some nonlinear continuous-time dynamic models of social systems whose members, groups or individuals, may change partners and/or opponents at any time, according to a greedy criterion. The main structural properties of these models, which belong to the class of positive switching systems, are investigated with particular regard to the existence of solutions, their positivity, boundedness and asymptotic behaviour. Simulations show how the cooperative or hostile attitudes of the participants affect their yield.     

Emergency and on-demand health care: modelling a large complex system

This paper describes how system dynamics was used as a central part of a whole-system review of emergency and on-demand health care in Nottingham, England. Based on interviews with 30 key individuals across health and social care, a ‘conceptual map’ of the system was developed, showing potential patient pathways through the system. This was used to construct a stock-flow model, populated with current activity data, in order to simulate patient flows and to identify system bottle-necks. Without intervention, assuming current trends continue, Nottingham hospitals are unlikely to reach elective admission targets or achieve the government target of 82% bed occupancy. Admissions from general practice had the greatest influence on occupancy rates. Preventing a small number of emergency admissions in elderly patients showed a substantial effect, reducing bed occupancy by 1% per annum over 5 years. Modelling indicated a range of undesirable outcomes associated with continued growth in demand for emergency care, but also considerable potential to intervene to alleviate these problems, in particular by increasing the care options available in the community.     

Travelling waves in a reaction-diffusion system modelling fungal mycelia

We discuss travelling-wave solutions of a system of coupledreaction—diffusion equations used by the authors to describethe macroscopic behaviour of fungal mycelia. Such systems havebeen used in a multitude of applications; and, in particular,Merkin and Needham (1990, Proc. R. Soc. Lond. A 430, 315–45)have studied a certain formulation as a model for generic isothermalchemical reactions. We show that an alternative analysis providesmore complete results in ascertaining the conditions under whichtravelling-wave solutions exist and that it allows a wider rangeof parameter values to be considered; this is essential to theapplication considered in the present case. Numerical investigationsof travelling-wave solutions and the related initial-value problemare included to motivate and extend the analysis.     

On the fractional doubly parabolic Keller-Segel system modelling chemotaxis

This work is concerned with the time-fractional doubly parabolic Keller-Segel system in R^N(N≥1),and we derive some refined results on the large time behavior of solutions which are presupposed to enjoy some uniform boundedness properties. Moreover, the well-posedness and the asymptotic stability of solutions in Marcinkiewicz spaces are studied. The results are achieved by means of an appropriate estimation of the system nonlinearity in the course of an analysis based on Duhamel-type r...     

Nonnegative compartment dynamical system modelling with stochastic differential equations

Compartment models are widely used in various physical sciences and adequately describe many biological phenomena. Elements such as blood, gut, liver and lean tissue are characterized as homogeneous compartments, within which the drug resides for a time, later to transit to another compartment, perhaps recycling or eventually vanishing. We address the issue of compartment dynamical system modelling using multidimensional stochastic differential equations, rather than the classical approach based on the continuous-time Markov chain. Pure-jump processes are employed as perturbation to the deterministic compartmental dynamical system. Unlike with the Brownian motion, noise can be incorporated into both outflows and inter-compartmental flows without violating nonnegativity of the compartmental system, under mild technical conditions. The proposed formulation is easy to simulate, shares various essential properties with the corresponding deterministic ordinary differential equation, such as asymptotic behaviors in mean, steady states and average residence times, and can be made as close to the corresponding diffusion approximation as desired. Asymptotic mean-square stability of the steady state is proved to hold under some assumptions on the model structure. Numerical results are provided to illustrate the effectiveness of our formulation.     

Multi-machine power system state-space modelling for small-signal stability assessments

This work presents a general state-space representation of a multi-machine, multi-order power system model, which may be used to carry out small-signal stability assessments. Computational software coded in MATLAB has been developed in order to find and analyse the solution of an arbitrary number of synchronous generators in the network. Each generator is represented by a pre-defined model. The model choice is tailored to fit the available data for each generator. The software has provisions for conducting power flow solutions and the calculation of the initial state that the generators keep prior to the disturbance. The state-space representation and the equivalent transfer function matrix of the system are generated automatically. Eigenvalue analysis may be carried out using the standard MATLAB functionality. The paper is one of a tutorial nature and in order to check on the sanity of the results given by the new software, two text-book networks have been examined. The results were also compared with those generated using commercial industrial-grade software.     

A reaction-diffusion system modelling the spread of bacterial infections

We investigate a system of reaction-diffusion equations which model the spread of a bacterial infection in a human population. A decoupling technique together with global bifurcation theory is used to study the steady-state solutions of the system. The asymptotic behaviour of solutions is discussed by using sub and subersolutions and the quasimonotonicity of the system.     

A fifth generation numerical modelling system in coastal zone

Nowadays, artificial intelligence (AI) technology is gradually integrated into the numerical modelling system to make the system more intelligent and more user-friendly. The characteristics of the fifth generation numerical modelling are connected with AI applications. The expert system technology as a widely applied AI technology is integrated into our modelling system for coastal water processes with traditional numerical computational tools and the data and graphical pre-processing and post-processing techniques. Five kinds of knowledge bases are built in the system to describe the existing expertise knowledge about model parameters, relations between parameters and physical conditions, various possible selections for parameters and rules of inference. The inference engine is designed to be driven by the confidence of correctness, and the rule base is built with the factor of confidence to link the various relations. The decision tree is designed to drive the inference engine to explore the route of selection procedure of modeling. The decision tree depends on the real problem specifications and can be modified during the dialogue between the system and the user. The forward chaining and backward chaining inference techniques are mixed together in the system to help matching the parameters in the model and the possible selections with sufficiently high confidence. The expert system technology is successfully integrated into the system to provide help for model parameter selection or model selection, and to make the numerical model system more accessible for non-expert users.