| 1. |
- Larsby, Birgitta, 1950-
(författare)
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Different neurophysiological methods for studying the vestibular system : evaluation of old methods and development of a new test procedure
- 1980
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Different methods were used to study the physiology and anatomy of the vestibular system. 1) A primary vestibular cortical area in the cat was located and tested for somatosensory inflow by recordings of vestibular evoked potentials and extracellular single unit activity. 2) The enzyme horseradish peroxidase was used as a retrograde anatomical tracer to identify thalamo-cortical vestibular pathways. 3) Vestibular disturbances aused by the industrial solvents methylchloroform and styrene were recorded by electro-oculography. Positional nystagmus was seen above a concentration of 75 ppm of methylchloroform and 40 ppm of styrene in blood. 4) A clinical vestibular rotatory test procedure is described and evaluated in an animal model before and after unilateral labyrinthectomy. A long time reduction in gain is seen at higher rotational frequencies and a trend that serves to define the side of a peripheral lesion is superimposed on the oscillatory eye movements after unilateral vestibular damage.
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| 2. |
- Lövsund, Per, 1948-
(författare)
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Biological effects of alternating magnetic fields with special reference to the visual system
- 1980
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aims of the present investigation were to contribute to more knowledge of the interaction between extremely low frequency magnetic fields and excitable tissue and to widen the basic understanding of the mechanisms behind these effects. The human visual system and the frog retina were used as model systems.In order to ensure that industrial magnetic flux densities and frequencies were employed in the laboratory studies, the magnetic field levels in the welding and electrosteelindustries at the site ordinarily occupied by the operator were first measured. These processes usually generated fields with a frequency of 50 Hz and a magnetic flux density of 01-10 mT. In the laboratory magnetic fields (0-40 mT, 10-50Hz) were used to induce visual light phenomena, so-called magnetophosphenes, in volunteers. The threshold values for these phosphcnes were detennined as functions of magnetic field frequency as well as of colour and intensity of the background illumination. Maximum field sensitivity occurred at a frequency of approximately 20-30 Hz. With broad spectrum light the threshold flux density was about 10-12 mT. The thresholds were found to be dependent upon the intensity and the spectral distribution of the background light. During dark-adaptation the magnetic field sensitivity decreased. In certain respects volunteers with normal colour vision differed from colour defective ones as far as threshold values are concerned. Possible mechanisms for generation of magnetophosphenes are discussed. The threshold values for magnetophosphenes (0-40 mT) and electrophosphenes (0-0.3 mA) were compared under otherwise identical experimental conditions. In both broad spectrum and monochromatic background lighting the two types of phosphenes had a concurring sensitivity maximum at 20Hz. At higher frequencies there were significant differences in the threshold values. Applying electric current stimulation in different directions did not give rise to any great differences with regard to threshold values within the frequency range 10-30Hz. Frog retinas were exposed to magnetic fields (0-80 mT, 20-30 Hz). The electrical activity in the retina induced by the fields was registered from the ganglion cell layer with the aid of microelectrode technique, whereby a threshold value was obtained at approximately 20 mT and a sensitivity maximum was found at 20 Hz. The magnetic field response occurred within approximately 5 ms, while the light stimulus response occurred only after an average of approximately 85 ms. The latency from light stimulus to response in the ganglion cell layer was significantly prolonged if the preparation was simultaneously and continuously exposed to a magnetic field. Magnetic stimuli similar to light stimuli only induced a response upon 'on', 'off or 'on/off and not during continuous stimulation. Cells which were on-cells during light stimulation became off-cells during magnetic stimulation and vice versa. Addition of Na-aspartate or CoCl2 extinguished simultaneously the response both to light and to magnetic field stimuli. The results indicate that magnetophosphenes are generated in the retina and in the same channels that normally propagate signals induced by light.
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| 3. |
- Nygårds, Mats-Erik, 1944-
(författare)
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Computer-based detection of cardiac arrhythmias : methods and systems
- 1983
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this study was to develop methods and systems which could improve the accuracy or arrhythmia monitoring and analysis of long-term ECGs and eliminate or reduce the need for continuous visual ECG screening. The detection of arrhythmias was based on an automatic classification of heart beats, using waveform features obtained from a basis signals representation. Ventricular fibrillation, a condition in which individual QRS complexes cannot be discerned, was diagnosed from a spectral analysis of the ECG.The methods were put into practice in a computer-based system with the capacity for simultaneous monitoring of eight patients. The accuracy of the system with respect to arrhythmia alarms was studied during ten 24-h periods of clinical routine use, with 55 patients. monitored for a total time of about 1000 h. Seventy percent of the time during which an alarm message should have been present (134 h) a correct alarm was given. An incorrect alarm cause was reported 17% of the time, while 13% of the time no alarm at all was given. The ratio between true and false or incorrect alarms was 3:1.The methods for arrhythmia detection were also utilized in a computer program for offline analysis of long-term ECGs from ambulatory patients. Here, the automatic analysis was combined with a subsequent interactive examination of the analysis results for highest accuracy.
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| 4. |
- Rundquist, Ingemar, 1947-
(författare)
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Cytofluorometry : technique and applications
- 1981
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aims of this investigation were to examine the conditions for rapid fluorescence measurements on cellular material, to improve the performance of measurement systems for microscope fluorometry, and to apply this technique in studies on mast cell biology. Fluorescence fading, a general complication of cytofluorometry, was studied during illumination times in the millisecond range, and a new fading phenomenon characterized by short duration and rapid recovery was described. The findings of the study formed the basis for the construction of two instfurnent systems for microscope fluorometry based on Leitz MPV I and MPV II microscope photometers. Rapid fluorescence measurements were performed by a completely automatic measuring sequence, except forselectionandfocusing of the objects to be measured. Automation was mainly achieved by the integration of computers in the measurement systems, which also resulted in easily interchangeable programdetermined measuring routines and proper data processing and presentation of results. The systems were mainly used for rapid analysis of cell populations. The precision of the measurements was improved by different standardization techniques, and the measuring speed, about 500 cells per h on well prepared specimens, was high enough to permit analysis of relatively large cell populations within a reasonable time.The cytofluorometric technique was applied to studies on the biology of the connective tissue mast cell. Rat peritoneal mast cells were used for this purpose. The proliferation of mast cells was estimated by cytofluorometric measurements of DNA in mast cell populations after staining with the fluorescent dye Hoechst 33258. Formaldehyde-induced fluorescence was used to study the uptake and turnover of dopamine in mast cells in vivo. Measurements of the mast cell content of heparin, a constituent of the mast cell granule matrix, were performed by a combination of microscope fluorometry, which permits visual identification of the cells, and flow cytofluorometry, by which rapid measurements of large populations can be made.
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| 5. |
- Sundqvist, Tommy, 1949-
(författare)
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Probing intestinal permeability in man using different-sized, low-molecular-weight polyethyleneglycols and mathematical modelling
- 1981
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Selective intestinal permeability as reflected by the urinary recovery of low-molecular-weight polyethylene glycols (PEG 400) of dlfferentsizes after oral administration was characterized with a mathematical filter-function. There was relative loss of both large and small PEG molecules on their way from the intestine to the urine. The reduced recovery of the large molecules is explained by selective intestinal absorption, since intravenous instillation abolished the effect. After curve-fitting to the experimental data, the mathematical procedure gives a quantitative measure of the fraction of selective and non-selective passage, and of filter-efficiency at different molecular weights. When applied to patients treated by bypass surgery for morbid obesity the method indicated a less permeable intestine with a reduced effective absorbtive surface area. In patients with rheumatoid arthritis a fasting diet gave a similar effect, which was accompanied by a reduction in disease activity. However, after changing to lactovegetarian diet the intestinal selectivity returned towards the control values, as did the inflammatory indices. Finally, to evaluate the importance of different physiological criteria for the outcome of the PEG 400 absorption test, a mathematical multi-compartment model was constructed and simulated on a computer.
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| 6. |
- Tenland, Torsten, 1952-
(författare)
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On laser Doppler flowmetry : methods and microvascular applications
- 1982
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A laser Doppler flowmeter for non-invasive microcirculatory blood flow studies has been developed. The tissue under study is illuminated by laser light (helium-neon laser, output power 2 mW) via an optical fibre and the Doppler shift oflight scattered in moving red cells is analysed. By the use of two photodetectors for detection of the backscattered light, the influences of mode interference and broadband noise from the laser and noise from surrounding light sources have been suppressed. The instrument is designed to give a continuous, stable and linear real-time measure of the flux of red cells (i.e. the number of red cells times their velocity) in the outermost layer (1 mm) of tissue, in which the red cell volume fractions are low or moderate. Linearity, measuring depth and the influence of blood oxygen tension were evaluated in a flow model with optical properties similar to those of human skin. Laser Dopplerflowmetry was found to be versatile for measurements of blood flow in human skin and rat testis and did not influence the flow under study.An extensive study of spatial and temporal variations of human skin blood flow was performed. As it was found that skin blood flow shows wide day-to-day variations and significant differences between adjacent probe sites, earlier reported "normal" values of skin blood flow were seriously questioned. It is proposed that this study can serve as a base for further functional studies.Testicular blood flow in rats was studied in order to evaluate acute effects of stress-linked substances such as adrenaline and noradrenaline. Both substances lowered the blood flow at high doses.Rhythmical variations of blood flow (frequency 5-12 min-1) in human skin and rat testis were observed and found to be in agreement with earlier findings in microscopic studies on other types of tissue. The nature and origin of this rhythmicity point towards a local regulatory mechanism operating also under "steady state" conditions.
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| 7. |
- Armgarth, Mårten, 1955-
(författare)
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Physics of palladium metal-oxide-semiconductor devices
- 1983
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis Palladium gate metal-oxide-semiconductor (PdMOS) devices are used as hydrogen sensors. It is shown that the sensitivity is only partly due to the change of the effective work function of the Pd gate on hydrogen adsorption. Sodium ion drift experiments have shown that hydrogen-sodium interactions occur in PdMOS devices. Hydrogen ions adsorb in the first atomic layers of the silicon dioxide. This is the origin of an instability problem called hydrogen induced drift (HID). The HID can be avoided by the insertion of another insulating material (alumina, silicon nitride or tantalum pentoxide) between the silicon dioxide and the metal gate.A hydrogen induced deterioration of the Pd gate metal has been observed. Blisters in the gate metal are formed due to a hydrogen induced stress in the film. A solution to this problem has been found.The catalytic properties of palladium and platinum gate metals are compared in different hydrogen/oxygen mixtures. PdMOS devices are superior for detection of low hydrogen concentrations, whereas PtMOS devices are more suitable at higher concentrations. High frequency capacitance-voltage measurements have shown that hydrogen induced oxide surface charging occurs in PdMOS devices. It is concluded that the surface charges are protons
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| 8. |
- Bengtsson, Bengt
(författare)
-
On some Control Problems for Queues
- 1982
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis consists of three parts. In the first one, optimal policies are constructed for some singe-line queueing situations. The second part deals with finite-state Markovian decision processes, and in the third part the practical modelling of a more complex problem is discussed and exemplified.The central control object of part I is an M!M/1 queue with fixed arrival rate and controllable service rate. The objective is to minimize the expected long-run average of a cost rate, which isa sum of two functions, associated with the queue length (the holding cost) and the service rate (the service cost), respectively. For the case of a fin ite waiting-room, terminal costs are constructed, such that a solution to the associated dynamic programming (Bellman) equation exists, which is affine in the time parameter. The corresponding optimal control is independent of both time and the length of the control interval. It hasa form which is subsequently used in generali zing into the case of an infinite waiting room. For this case, the analysis res ults in an efficient algorithm, and in several structural results. Assuming essentially only that the holding cost is increasing, it is proved that a monotone optimal policy exists, i.e. that the optimal choice of service rate is an in creasing function of the present queue length. Three variations of the ce ntral problem are also treated in part I. These are the M/M/c problem (for which the above monotonicity result holds only under a stronger condition), the problem of a controllable ar rival rate (with fixed service rate), and the discounted cost problem.In part II, finite-state Markovian decision processes are discussed. A brief and heuristic introduction is given, regarding continuous-time Markov chains, cost structures on these, and the problem of constructing an optimal poli cy. The purpose is to point out the relations to the queueing control problem with finite waiting-room. Counterexamples demonstrate that the approach of part I is not universally applicable.In part 111, a simplified mode! is discussed for a situation where th e customers may reenter the queue after a stochastic delay. It is argued that under heavy-traffic conditions, the influx of reentering customers can be approximated with the output of a linear stochastic system with state-dependent Gaussian noise, whose dynamics depend on the delay distribution. This idea is exemplified with the res ults from a simulated experiment on a telephone station.
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| 9. |
- Cederberg, Roger, 1952-
(författare)
-
On the coding, processing and display of binary images
- 1980
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Large amounts of binary or nominally binary images are handled by humans and computers. Thus it is important with effective interaction as well as processing and storage of binary images.The thesis contains four separate parts. Automatic input of handdrawn electrical schematics. A method for storage of binary images.The data structure is suitable for applications with large images, where the access to data and storage efficiency are important An algorithm for segmentation of chain-coded objects. The segmentation is accomplished by a parallel, iterative computation of the curvature. A method for generation of straight lines on a square grid. The method is based on structural properties of the discrete straightline.
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| 10. |
- Emanuelson, Pär, 1949-
(författare)
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Performance enhancement in a well-structured pattern matcher through partial evaluation
- 1980
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Partial evaluation is a technique which can be utilized for the generation of compiled code from the corresponding interpreter. In this work the partial evaluation technique is applied to a pattern match interpreter, in order to achieve the simultaneous goals of a general, well-structured program which is extendible and still make high performance at execution possible. A formal definition of pattern matching is presented, which is the basis for the interpreter. The partial evaluation technique is evaluated with respect to other techniques for implementation of pattern matchers. Control structures for pattern matching such as backtracking, generators, and recursion are presented, and the appropriateness of these for use in partial evaluation is discussed.
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| 11. |
- Hägglund, Sture, 1944-
(författare)
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Contributions to the development of methods and tools for interactive design of applications software
- 1980
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis consists of five research reports dealing with different aspects of the design of interactive application oriented software. A generalized framework for dialogue design is presented and the implementation of customized programming environments, supporting computer utilization for specific applications is discussed. Highlights of our presentation are:Uniform treatment of different kinds of end-user dialogues, especially with respect to irregular or unexpected terminal inputsEmphasis on programming environments instead of language design, promoting (he view of programming as a specification process performed with a data editor.Introduction of an intermediate system level, where a general-purpose programming system is specialized for a given class of applications, through the support of specialized conceptual frameworks and default mechanisms.Promotion of control independence in the sense that the specification of program execution particulars, such as end-user interactions etc., is postponed as long as possible and liable to subsequent change without reprogramming.
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| 12. |
- Jonson, Henrik
(författare)
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A Newton Method for Solving Non-Linear Optimal Control Problems with General Constraints
- 1983
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Optimal control of general dynamic systems under realistic constraints on input signals and state variables is an important problem area in control theory. Many practical control problems can be formulated as optimization tasks, and this leads toa significant demand for efficient numerical solution algorithms.Several such algorithms have been developed, and they are typically derived from a dynamic programming view point. In this thesis a differentapproach is taken. The discretetime dynamic optimization problem is formulated as a static one, with the inputs as free variables. Newton's approach to solving such a problem with constraints, also known as Wilson's method, is then consistently pursued, anda algorithm is developed that isa true Newton algorithm for the problem, at the same time as the inherent structure is utilized for efficient calculations. An advantage with such an approach is that global and local convergence properties can be studied in a familiar framework.The algorithm is tested on several examples and comparisons to other algorithms are carried out. These show that the Newton algorithm performs well and is competitive with other methods. lt handles state variable constraints in a direct and efficient manner, and its practical convergence properties are robust.A general algorithm for !arge scale static problems is also developed in the thesis, and it is tested on a problem with load distribution in an electrical power network.
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| 13. |
- Jungert, Erland, 1942-
(författare)
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Synthesizing database structures from a user oriented data model
- 1980
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In data processing a form (document) is normally a medium for data entry. Forms are mainly user oriented, however, they can also be motivated for other reasons. In this study different properties and motives for use of forms are discussed.It will be demonstrated how user defined form types can be used to generate definitions for consistent and non-redundant databases and also how form types can be interfaced to such databases and provide a query language. It will also be shown that form types can constitute application programs written in a special purpose language. An important feature here is that form types can be used as input in a process for automatic program generation.Discussed is also the extraction of efficient access paths from the user defined form types and the architecture of a form oriented system which make full use of the mentioned properties.
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| 14. |
- Knutsson, Hans
(författare)
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Filtering and reconstruction in image processing
- 1982
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Image processing is a broad field posing a wide range of problems. The Work presented in this dissertation is mainly concerned with filter design subject to different criteria and constraints.The first part describes the development of a new radiographic reconstruction method designated Ectomography. The method is novel in that it allows reconstruction of an arbitrarily thick layer of an object using limited viewing angle.The subject of the second part is estimation and filtering of local image information. Quadrature filters are designed enabling accurate orientation and frequency estimates. The extracted information is shown to provide a good basis for efficient image enhancement and coding procedures.
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| 15. |
- Ljung, Stefan
(författare)
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Fast Algorithms for Integral Equations and Least Squares Identification Problems
- 1983
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work is concerned with fast algorithms for integral equations and least squares identification problems.The presentation is divided into three parts. In the first part a fast algorithm for solving systems oflinear equations with a matrix that is alm ost Toeplitz is derived and applied to Fredholm integral equations with stationary kernels. The algorithm is investigated numerically with simulations. Also some areas, where this kind of integral equations arise ha ve been considered. A summary of applications is given in part two. In particular, image restoration problems and boundary element methods from stress analysis have been treated in this respect.In the third part a fast algorithm for computing the gain vector for recursive least squares estimation schemes is the main issue. A comparison to conventional, square root and lattice algorithms is established. The investigation aims at deciding whether the algorithms are stable by performing a simple step response technique. All computations are assumed to be ideal, i. e. the arithmetic operations are performed exactly. An error is then introduced in important quantities ofthe algorithm and the propagation ofthis error is studied as function of time and forgetting factor. The study is. both theoretical and experimental. I fan algorithm tums out to be exponentially stable, a simple mode! for estimating the discrepancy of the computed quantities from the exact ones is performed.The fast algorithms of parts one and three are apparently different. However, there is an immediate interrelation between them. The introduction includes a discussion around this topic.
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| 16. |
- Magnusson, Lennart, 1946-
(författare)
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Cyclic behaviour of carburized steel
- 1980
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The fatigue properties of carburized low alloyed steel have been investigated. The tests in axial fatigue showed that surface carbon below 0.8% and low amounts of retained austenite are advantageous. In bending fatigue the effects of tempering and of surface condition were studied. It was found that internal oxidation in the as-quenched surface deteriorates the fatigue properties considerably. Tempering has slightly adverse effect on the fatigue limit. Large grain size proved to have more serious consequences on the core properties than the presence offerrite. At surfaces, fatigue cracks initiate at stress concentrating defects or at grain boundaries of prior austenite. Sub-surface cracks initiate at slag inclusions or at concentrated slip in large grains. Low cycle fatigue properties of homogenous high carbon steel containing retained austenite showed a significant dependence on initial strain direction. The stress-strain properties found were used in computer calculations of the residual stress state in a carburized cylinder. The residual stresses, which are of great importance for the properties of case-hardened components, are redistributed due to plastic deformation. This was predicted by calculations and experimentally verified.
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| 17. |
- Millnert, Mille
(författare)
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Identification and Control of Systems Subject to Abrupt Changes
- 1982
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many different recursive identification methods for time varying systems have been suggested in the literature. An assumption that the variations in the system parameters are slow is common for almost all the methods. When using the methods on systems with faster variations one is forced to compromise between alertness to parameter variations on one hand and noise sensitivity on the other. The topic ofthe thesis is to investigate how such a compromise can be avoided fora certain class of systems.The systems considered are such that their dynamic changes between some different typical modes. As an example one can think of the different "flight cases" of a supersonic aircraft. The philosophy behind the approach taken in the thesis is that the observations of such a system can be separated into different sets corresponding to the different states of the system. The parameters ofthe different modes can then be estimated from the separated data sets.Technically, this parallel modelling is achieved by describing the system parameters as the realizations of a Markov-chain. An estimation algorithm for time varying systems based on this parallel modet approach is given in the thesis.The behaviour of the algorithm is analysed and problems connected to it are illustrated through simulations. The analysis and the simulations show that a major problem is the initialization of the algorithm without sufficient a priori information. Based on the analysis a procedure is given that makes it possible to use the algorithm with a minimum of a priori information.It is further shown how this recursive identification algorithm can be utilized for adaptive control. As an illustration of this, the method is used for adaptive control of a mode! of a cold rolling mill.
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| 18. |
- Oskarsson, Östen, 1946-
(författare)
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Mechanisms of modifiability in large software systems
- 1982
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Large software systems are often characterized by a continuing evolution, where a large number of people are involved in maintaining and extending the system. Software modifiability is a critical issue in such system evolution. It is desirable that the basic design is modifiable, and that subsequent evolution maintains this modifiability. This thesis is an investigation of the mechanisms behind the exhibited modifiability and lack of modifiability in a large commercial software system during a part of its evolution.First, the relation between modifiability and different types of modularizations are discussed, and a dichotomy of software modularizations Is proposed. As a measure of modifiability at system level, i.e. disregarding the internal modifiability of modules, we use the number of modules which are influenced by the implementation of a certain system change. The implementation of each requirement in one release of the system is examined, and the underlying causes of good and bad modifiability are explained. This results in a list of factors which were found to Influence the modifiability.
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| 19. |
- Reboh, René, 1944-
(författare)
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Knowledge engineering techniques and tools for expert systems
- 1981
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Techniques and tools to assist in several phases of the knowledge-engineering process for developing an expert system are explored.A sophisticated domain-independent network editor is described that uses knowledge about the representational and computational formalisms of the host consultation system to watch over the knowledge-engineering process and to give the knowledge engineer a convenient environment for developing, debugging, and maintaining the knowledge base.We also illustrate how partial matching techniques can assist in maintaining the consistency of the knowledge base (in form and content) as it grows, and can support a variety of features that will enhance the interaction between the system and the user and make a knowledge-based consultation system behave more intelligently.Although these techniques and features are illustrated in terms of the Prospector environment it will be clear to the reader how these techniques can be applied in other environments.
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| 20. |
- Riklund, Rolf G.
(författare)
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Cluster model of disordered systems : application to doped semiconductors and a simple model polymer
- 1982
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis we study with an extended cluster model calculation the combined effect of disorder and electron-electron interaction on the electronic structure of doped semiconductors and a simple model polymer chain. First a one-band model using a Hartree calculation is compared to other authors result for the impurity band using less realistic Hamiltonians. Secondly a two-band model using a Hartree-Fock calculation is presented. Thecalculated concentration depende nce of the electronic specific heat shows good agreement with the experimental findings. A modified Hartree-Fock scheme is then presented with the upper Hubbard band properly placed. Here it is shown that below the metal-nonmetal transition the one-particle wavefunctions are localized on statistically distributed clusters of impurity atoms. In the last part a stereo-irregular chain of h ydrogen atoms which simulates a model polymer is studied within the modified Hartree-Fock scheme. A detailed study of the localization properties of the wavefunctions is given with a combination of the information extracted from the inverse participation ratio and the moment ana lysis.
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| 21. |
- Söderberg, Dennis, 1953-
(författare)
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Computer assisted evaluation of gas sensors : theory and applications
- 1982
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The application of a low cost computer as program control in a laboratory experimental situation is valuable for the evaluation of a complex measurement problem. The first step in a computer assisted evaluation is to design the experimental methods and construct the apparatus. The second step is to evaluate the results obtained by the use of the experimental system. The scientist does not need to take part himself in the experiment and has thus no possibility to influence the results of the investigation during this part of the investigation. his is positive in the name of objectivity.This thesis contains a description of a computer system, the computer programs and measurement techniques applied to the evaluation of a solid state gas sensor. The sensor studied is a palladium-silicon dioxide-silicon structure with large sensitivity and selectivity for hydrogen in air. This is due to a "channel" open for hydrogen atoms only to reach the palladium-oxide interface, where they give rise to a voltage drop. Through the use of the computer assisted evaluation of the gas induced changes of the surface and interface potential it was possible to propose a model for the catalytic reactions between hydrogen and oxygen on the palladium surface. Three discrete modes of the short term behavior of the sensor were identified, and described by a physical model which incorporate a competion between hydrogen and oxygen for adsorption sites on the metal surface. This had probably not been possible without the use of computer assisted evaluation.It was shown that in porous palladium films also other species than hydrogen atoms reach the palladium-oxide interface. It was thus possible to detect other gases, like carbon monoxide, with a porous metal gate.The gas sensor was originally developed as a hydrogen sensor to be used in air. In the thesis it is shown that the non-porous palladium gate gas sensor is also very useful as an oxygen sensor in an oxygen free background. This application is interesting for the analysis of the oxygen content in e.g. blood or in an inert (food) storage atmosphere.
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| 22. |
- Trulsson, Eva
(författare)
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Adaptive Control based on Explicit Criterion Minimization
- 1983
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A common approach to regulator design is to define an objective function, which is minimized with respect to adjustable regulator parameters. Here we discuss how such objective functions can be minimized online, thus providingadaptive eon tro I. Such an approach has its roots in early contributions to learning systems and it is here further developed and discussed in the light of the recent development in the field.A general algorithm is given and it is then specialized to some concrete examples. One problem when to use this algorithm is that the convergence properties are tied to successful identification of the system dynamics. Therefore an Instrumental Variable identification method based on extra injected noise is analysed and convergence is proved under a boundedness assumption.Special attention is paid to the minimization of quadratic criteria. It is shown that if the regulator is flexible enough the minimum of such a criterion is unique. It is also shown that the self tuning regulator is obtained as a special case of the algorithm, corresponding toa particular quadratic criterion anda particular way of estimating the system dynamics.One specific feature of the algorithm is that it does not utilize specific knowledge about how to calculate the optimal regulator. The algorithm is thus the same for minimum phase as well as for non minimum phase systems.
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| 23. |
- van Overbeek, A J M
(författare)
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On-Line Structure Selection for the Identification of Multivariable Systems
- 1982
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An algorithm is described for the selection of mod el structure for identifying multivariable mode Is of"black box" character. The algorithm receives as "input" a mode I in a given parametrization (= mode I structure). It is then tested whether this parametrization is suitable (well conditioned) for identification purposes. If not, a better one is selected and the transformation of the mode! to the new representation is performed.The test is based upon the properties ofthe Hankel matrix ofthe impulse response ofthe mode I. The relation between the conditioning ofthe Hankel matrix and the conditioning of the identification (minimization) is described.This mode! structure selection algorithm can be used as a block in both an iterative, offline identification procedure, and in recursive, on-line identification. It can be used whenever there is some indication that the parametrization is ill-conditioned. It is discussed how the algorithm can be interfaced with an identification procedure.A complete procedure consisting of an off-line identification algorithm and the model structure selection algorithm is described. Results are given when this com bined algorithm is applied to both simulated and real data.
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| 24. |
- Ödman, Svante, 1948-
(författare)
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On biomedical electrode technology : with special reference to long-term properties and movement-induced noise in surface electrodes
- 1980
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of the present investigation was to improve the quality of surface electrode measurements. Long-term properties of commercially available ECG-electrodes were studied by investigating polarization potentials, electrode impedance, adhesion and skin reactions during a period of 7 days. The most stable polarization potentials were obtained for Ag/AgC1-electrodes and stable electrode impedance were obtained for disposable electrodes with stable adhesion and equipped with an electrode capsule. Unchanged adhesion and mechanical strength were shown by disposable electrodes with large self-adhesive collars.Movement-induced potentials of streaming potential type were studied in various electrode configurations. The geometric design of the electrode was important for reduction of noise generated by the movement of gel. Potential and impedance variations were measured for electrode movements in electrolytes relative to the skin. The impedance variations were small and streaming potentials with a magnitude of up to 10μV were recorded. The deformation potentials generated in the skin dominate the disturbance pattern in surface electrode recordings. Potential and impedance variations studied with varying mechanical stress upon skin showed that the impedance variations did not bring about the potential variations. The size of potential variations in skin and related mechanical stress possess a non-linear relationship which varies between individuals. A non-linear character of the time sequence of stretch potentials was found.The spread of deformation potentials was studied in the skin area around and beneath surface electrodes. When stretching a rectangular skin zone between two plates fixed to the skin the highest potentials were obtained in the zone. The magnitude of the potentials decreased with the distance to the zone. Stretch potentials could be reduced but not geometrically limited by fixing the skin to a rigid electrode collar. The potential spread is a consequence of successively decreasing deformation.
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