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- Andersson, Torbjörn
(författare)
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Concepts and Algorithms for Non-Linear System Identifiability
- 1994
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recently, commutative algebra and differential algebra have come to use as mathematical tools for solving problems in automatic control. We will use these tools to answer questions regarding identifiability for models given as a set of differential polynomials. A constructive algorithm, Ritt's algorithm, has been modified for this specific situation. Furthermore, comparisons between Ritt's algorithm and Buchberger's algorithm, to answer the identifiability question when the model structures are given in state space form, are performed. The basic problem is that the computational complexity rapidly increases with the problem size. We examine various ways to simplify the computations in this respect, but it must also be stressed that the complexity increase is inherent in the problem.In identification from a deterministic point of view an algorithm is said to be robustly convergent if the true system is regained when the noise level tends to zero. In this thesis we introduce a concept close to this performance measure; robust global identifiability. A model structure, i.e., a smoothly parameterized set of models, is said to be robustly globally identifiable if there exist an identification algorithm such that the true parameters are regained when the noise level tends to zero. In this thesis we show that global identifiability implies robust global identifiability when the considered model structure is a characteristic set of differential polynomials. This means that any model structure with parameters, that can be uniquely estimated from data has this robustness property.Finally, a method for estirnation of residence time in continuous flow systems with varying dynamics is discussed. By resampling, i.e., choosing time instants different from the given sampling instants, and interpolation between measured data points, we obtain a continuous fl.ow system with constant residence time expressed in a new resampled time vector. We assume that the fiow patterns in the systems are invariant. The new data set is then used for identification of parameters in a chosen model structure. From the identified model, the residence time is readily calculated and a procedure for that is briefly described. The presented method is readily extended to enable use in recursive identification. In that case the modified recursive identification method is an improvement of the tracking ability compared to an ordinary recursive routine.
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- Aron, Frédéric, et al.
(författare)
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A design approach for DSP integrated circuits
- 1993
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents a design approach for digital signal processing integrated circuits. In the first part, we present the different steps of DSP integrated circuit design. Then, we discuss the various methods used at each level and propose a well structured methodology for layout design.In the second part, the implementation of a tool responding to the requirements issued from part one is discussed. We introduce the object-oriented paradigm used and discuss the expected benefits. The emphasis is there on the application of the theoretical requirements and their mapping into object-oriented structures.
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- Axelsson, Caroline
(författare)
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Direct Fourier methods in 3D-reconstruction from cone-beam data
- 1994
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The problem of 3D-reconstruction is encountered in both medical and industrial applications of X-ray tomography. It would seem natural to recover volume data by just repeating 2D-reconstructions slice-by-slice. However, 2D fan-beam exposure is wasting most of the photons on the collimator and such a procedure is inefficient in terms of data acquisition. Fast scanning with acceptable signal-to-noise ratio requires cone-beam exposure.A method able to utilize a complete set of projections complying with Tuy's condition was proposed by Grangeat. His method is mathematically exact and consists of two distinct phases. In phase 1 cone-beam projection data are used to produce the derivative of the Radon transform. In phase 2, after interpolation, the Radon transform data are used to reconstruct the three-dimensional object function.To a large extent our method is an extension of the Grangeat method. Our aim is to reduce the computational complexity, i.e. to produce a faster method. The most taxing procedure during phase 1 is computation of line-integrals in the detector plane. By applying the direct Fourier method in reverse for this computation, we reduce the complexity of phase 1 from O(N4 ) to O(N3logN). Phase 2 can be performed either as a straight 3D-reconstruction or as a sequence of two 2D-reconstructions in vertical and horizontal planes, respectively. Direct Fourier methods can be applied for the 2D- and for the 3D-reconstruction, which reduces the complexity of phase 2 from O(N4) to O(N31ogN) as well. In both cases, linogram techniques are applied.For 3D-reconstruction the inversion formula contains the second derivative filter instead of the well-known ramp-filter employed in the 2D-case. The derivative filter is more well-behaved than the 2D ramp-filter. This implies that less zeropadding is necessary which brings about a further reduction of the computational efforts.The method has been verified by experiments on simulated data. The image quality is satisfactory and independent of cone-beam angles. For a 5123 volume we estimate that our method is ten times faster than Grangeat's method.
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- Babic, Ankica, 1960-
(författare)
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Medical knowledge extraction. Applications of data analysis methods
- 1992
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis we explore and discuss some important methods for knowledge extraction from meclical data. This is done in relation to, and for the purpose of design and development of decision support systems, which could be population specific.To test data and extract knowledge, we use univariate and multivariate statistical methods, the rough sets theory and probabilistic artificial intelligence approaches. These methods are used to estimate characteristics of patient groups, disease profiles and other features relevant for medical problems. In particular, we apply them to clifferentiate among patient groups, develop patient models and derive decision rules. Our experience refers to two medical domains (patients with diagnosed and non-diagnosed, but suspected liver disease and patients with duodenal ulcer surgery).Extracted knowledge can be used both in clinical practice and health care programs, as well as in computer based decision support systems to adjust them to various clinical environments.
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- Bjurstam, Peter, 1959-
(författare)
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Skärkrafter vid fräsning : teori och verklighet
- 1994
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with the machining method milling and the forces affecting the tool during a milling operation. A survey of different tool geometries and conditions of the tool engagement during a machining process is presented. The general cutting theory and the equations used to estimate the load are explored. For practical use this simplified approach may be enough but when a more precise calculation of the load condition are required, i.e for process control or research when the varying chip thickness must be taken into consideration, the general theory is not adequate.As a result of the research work an accurate mathematical model and a computer software has been developed at the Division of Production Engineering. The model calculates the cutting forces acting on the tool during one revolution. The stepsize is one degree. The forces are expressed according to a coordinate system with its origin in the center of the tool. In order to evaluate the software the calculated values have been compared with real forces recorded during machining. The reliability of the equipment and of the developed model has been verified.Different ways for further development of the software have also been investigated. These developments are based on tool life studies made at the Division. One of the applications presented in the thesis is related to the working material. Equations for calculation of the material parameters needed are developed and the structure for a new computer software for the calculations is shown. The presented results can simplify the development of adaptive control modules and improve process planning routines associated with numerical programming of machine tools.
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- Boye, Johan
(författare)
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Dependency-based groundness analysis of functional logic programs
- 1993
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The object of study in this thesis is a class of functional logic programs, where the functions are implemented in an external functional or imperative language. The contributions are twofold:Firstly, an operational semantics is formally defined. The key idea is that non-ground function calls selected for unification are delayed and retained in form of constraints until their arguments become ground. With this strategy two problems arise: (1) Given a program P and an initial goal, will any delayed unifications remain unresolved after computation? (2) For every function call f(X) in P, find a safe evaluation point for f(X), i.e. a point in P where X always will be bound to a ground term, and thus f(X) can be evaluated.Secondly, we present a static groundness analysis technique which enables us to solve problems (1) and (2) in a uniform way. The analysis method is dependency-based, exploiting analogies between logic programs and attribute grammars.
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