| 1. |
- Alfredsson, Lars-Inge, 1964-
(författare)
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VLSI Architectures and Arithmetic Operations with Application to the Fermat Number Transform
- 1996
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The properties of arithmetic operations in Fermat integer quotient rings 2m+1, where m = 2t, are investigated. The arithmetic operations considered are mainly those involved in the computation of the Fermat number transform. We consider some ways of representing the binary coded integers in such rings and investigate VLSI architectures for arithmetic operations, with respect to the different element representations. The VLSI architectures are mutually compared with respect to area (A) and time (T) complexity and area-time performance (AT2). The VLSI model chosen is a linears witch-level RC model.In the polar representation, the nonzero elements of a field are represented by the powers of a primitive element of the field. In the thesis we particularly investigate the properties of arithmetic operations and their corresponding VLSI architectureswith respect to the polar representation of the elements of Fermat prime fields. Somenew results regarding the applicability of the Fermat number transform when usingthe polar representation are also presented.
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| 2. |
- Almeida, Rosimary, 1960-
(författare)
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Severity of illness versus severity of disease : definitions and applications
- 1996
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Outcome assessment should consist of two basic steps - "selection of a meaningful outcome" and "determination of what caused the outcome". The latter step requires comparisons, and therefore information about the initial status of the patients. Severity ratings attempt to group patients with similar initial status so that outcome comparisons are meaningful. They are consequently an essential ingredient in outcome assessment.This thesis aims at expanding the knowledge about outcome measurement focusing on the severity of a case with regard to definitions and applications of severity measures. Further, theoretical knowledge is integrated with practical needs for outcome assessment and methodology is developed for modelling the use of resources and interpreting the association between different severity measures.As with illness and disease, severity of illness and severity of disease are interchangeable terms in medical literature. Based on a holistic theory of health, these terms were differentiated. Severity of a case was described by two basic components - severity of disease and severity of illness. Essentially, severity of illness concerns suffering and disability, and severity of disease concerns risk of death, risk of suffering and risk of disability. These definitions were the core of a set of criteria for classifying severity measures or outcome measures.The role of a disease severity score in explaining resources use (e.g., intensity of technology utilization and length of hospital stay) in a neonatal intensive care unit was investigated. A disease severity score based on the death risk of the initial diagnosis was found to be an indicator of intensity of therapeutic technology together with gestational age and Apgar score. However, it does not show statistical significance to explain length of stay, which was explained by intensity of diagnostic technology and birthweight.The demand for patient classification systems (standard systems to describe a patient's condition) on a national and local level was investigated. There is little experience in the use of these systems, but at the same time there is a demand from the nurse managers for standard measures of a patient's need for care.There is still little knowledge about the association between severity of illness and severity of disease. This association was studied for patients with ulcerative colitis using data analysis techniques for dimension reduction such as cluster analysis, homogeneity analysis and non linear principal components analysis. A non linear relationship between illness and disease severity measures was found. The overall clinical judgement of disease activity was more related to illness patterns than symptoms or endoscopy and laboratory findings. In addition, the two measures of illness severity (Sickness Impact Profile and Rating Form for Inflammatory Bowel Disease Patient Concerns) were found to represent complementary information about a patient's illness experience. This illustrates the importance of conceptual knowledge in the selection process of an illness measure for outcome evaluations. These findings also reinforce the need for the development of systems to support interpretation of these kinds of complex associations, as traditional statistics have been shown to be of limited value under these circumstances.
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| 3. |
- Alvandpour, Atila, 1960-
(författare)
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Power Estimation and Low Power CMOS Circuit Techniques
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The increasing power consumption due to the high integration rate of VLSI digital CMOS circuits has become a major concern. Many important design issues and parameters are strongly dependent on the power dissipation and the accuracy of its estimated value during the design exploration. Among these issues we identify particularly the operation time per battery pack, the computational capacity and performance of the mobile electronic products, as well as more general aspects such as circuit reliability, cost for packaging and power supplies. In this thesis, some issues on power estimation and development of low-power circuit techniques, aimed for medium and high speed operations, are addressed.The complex impact of Miller capacitance on power and performance of digital CMOS circuits is investigated. Significant enhancements in characterization and modeling of the Miller effects compared to the existing conclusions, which are based on simplified rules, are achieved.A novel estimation technique for the relatively involved average short-circuit power consumption has been developed. Compared to the existing, time-consuming technique, the proposed technique provides a fast estimation with a reasonable accuracy, and has a potential to be used for real measurement.A significant portion of the total power consumption in VLSI circuits is due to the capacitance of the interconnections, however, estimating the interconnect length and its RC property at early stages in a large-scale top-down design flow is a hard task. Existing, simplified interconnection length estimation techniques are unacceptably inaccurate and unable to give a useful feedback during the design verification and simulation.A new design-sensitive interconnection length estimation technique and a corresponding algorithm has been developed. The technique has the unique quality to estimate the length of each interconnection separately, and therefore detects and localizes most of the potentially long interconnects. The result of the estimation can directly be used to add the important RC properties of the interconnects to the power estimators or circuit simulators, consequently yielding a significant increase in estimation accuracy.An investigation on generic low-power circuit techniques aimed for main-stream design styles has been made and various suggestions are proposed. The result has later been used to adapt the design of cell libraries to low power requirements.High fan-in dynamic gates can result in lower power consumption, fewer logic levels and very compact layout. Two major disadvantages, which reduce the practical use of such wide gates, are the relatively long propagation delay and the large leakage currents, which are due to the increasing subthreshold current in today's and future submicron devices. For speeding up the wide gates, new and simple sensing elements are proposed, which results in faster gates and lower power consumption compared to the alternative solutions. The issues related to large subthreshold leakage currents is also addressed and a leakage-tolerant multi-phase keeper circuit is presented. The new keeper holds the dynamic output of the wide domino gates statically, with a greater driving strength than that in the conventional solution. Furthermore, an increase in robustness is achieved without any significant delay penalty.Large capacitive loads resulting from long on-chip interconnects and the corresponding driver-receiver circuits can consume a significant portion of the total power consumption of a CMOS chip. A low-power, high-speed and robust driver-receiver circuit is proposed. The new bus architecture utilizes a precharge-to-low interconnect and a fast and simple level converter as receiver, which together reduce the power consumption up to 70% below that of a conventional precharged bus architecture without any delay penalty.
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| 4. |
- Andersson, Dick
(författare)
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Conformational Studies of Protein Structure and Dynamics
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The protein folding problem is one of the most important issues to be solved in the field of molecular biology. The subject of this thesis mainly deals with various aspects of the folding process.In Paper I, near-UV CD kinetic measurements on mutants, in which one tryptophan (Trp) residue had been replaced, were performed to probe the development of asymmetric environments around specific Trp residues during the refolding of human carbonic anhydrase II (HCA II). The development of the individual (Trp) CD spectra during refolding was obtained by subtracting the CD spectrum of the mutant lacking one Trp from that of HCA II at different time points. The same method was used for the particular Trp residues to obtain the kinetic CD traces monitored at a specific wavelength (270 nm). Three Trp residues were analyzed, each probing different structural regions of the native structure. The investigated Trp residues develop their native CD bands at different rates, showing that formation of native-like tertiary structure is occurring with varying rates indifferent regions of the protein.The same approach was applied to the extracellular domain of human tissue factor (sTF), which contains four Trp residues (Paper II). The individual Trp CD spectra showed that all four residues contributed to the CD spectrum in almost the entire wavelength region investigated, including the far-UV region. This leads to uncertain predictions of the amounts of various types of secondary structure. Accordingly, the best prediction of secondary sTF structure content was achieved using a hypothetical Trp-free CD spectrum. The kinetic refolding results suggest that the compact asymmetric environments of the individual Trp residues in sTF are formed simultaneously, leading to the conclusion that the native tertiary structure of the whole protein is formed in a cooperative manner.In Paper III, the role of the metal ion cofactor for the refolding of bovine carbonic anhydrase II (BCA II) was studied from the molten globule to the native state. Refolding was possible to achieve by mere addition of the metal ion to the apomolten-globule, because the apoenzyme was less stable than the holoenzyme. The cofactor-effected refolding can be summarized as follows: 1) initially, the metal ion binds to the molten globule; 2) compaction of the metal-binding site region is then induced by the metal ion binding; 3) a functioning active center is formed; 4) finally, the native tertiary structure is generated in the outer parts of the protein.In paper IV the aim was to determine the nature of the tetramer contact of human extracellular superoxide dismutase (hEC-SOD). We chose a strategy in which we mapped the subunit interaction interface by studying effects of twelve different mutations in the N-terminal domain fused to HCA II. The results show that the hydrophobic side of a predicted amphiphatic a-helix (formed by residues 14-32) in the N-terminal domain is essential for the subunit interaction.
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| 5. |
- Andersson, Håkan
(författare)
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Error-Correcting Codes Based on Chaotic Dynamical Systems
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation treats a novel class of error-correcting codes based on chaotic dynamical systems. The codes are defined over a continuous alphabet whereas the information that is to be transmitted belongs to a discrete set of symbols. Simple expressions can be given for the encoders, and the codewords can be described by a parity-check relation. However, the most interesting approach is to view the codewords as orbits of iterated dynamical systems described by integer matrices.Under some rather natural assumptions, the codes are shown to be group codes. The minimum distance is proved to be well-defined and strictly greater than zero. An algorithm for calculating it is also given. Initially, no robust sliding-window encoder inverses exist, but this deficiency is remedied by the introduction of fractal signal sets. The problem of catastrophic encoders is also solved by the introduction of these totally disconnected signal sets.Decoding strategies are discussed, and it is shown why the Viterbi algorithm does not work in higher dimensions for this type of codes. So-called list decoding emerges as a good alternative and its merits are considered. Simulations and comparisons with binary antipodal signaling are performed. The setting of the work is in two dimensions. However, the strength of this code construction is that it easily generalizes to higher dimensions.
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| 6. |
- Andersson, Maria, 1965-
(författare)
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Cooperation in local electricity markets : modelling of technical measures
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents a system analysis for co-operation in local electricity markets including distributors and customers. The purpose of co-operation is to minimise the system cost of local markets by introducing system measures, such as end-use measures and municipal co-generation plants. Co-operation will strengthen the position of local markets in the national as well as future international electricity markets. With end-use measures local markets will achieve flexibility, additional reserve capacity and ability to avoid sudden large costs for peak loads. Biomass-fired cogeneration plants can become of great importance in an international market. In Sweden there is a simultaneous demand for electricity and district heating, many local markets already include district heating systems and there are major forest areas which can contribute with renewable fuel. The system analysis is partly based on the simulation model (INDSIM) and the linear programming model (MODEST). The simulation model has been further developed (STRATO) to include calculation of system costs. Shadow price analysis has been developed in order to study incentives for system measures. Calculation procedures have been developed that describe cooperation between distributor and customer. Six case studies of a selection of real, existing local markets in Sweden are presented. The studies show the potential economical effects of co-operation measured by system costs and shadow prices. Co-operation has been considered between demand- and supply-side, electricity- and district heating systems and also between different time periods. In a typical local market with 90 000 inhabitants, if end use measures are introduced without cooperation the system cost of the distributor will increase by 14 million SEK for a time period of 25 years. If instead end-use measures are introduced in co-operation, together with a biomass-fired cogeneration plant, the system cost of the local market will be reduced by 444 million SEK. Furthermore, the use of biomass in the local market is increased from 36 to 72 % while the use of oil is decreased from 34 to 1%. Another case study of another local market (50 000 inhabitants) shows that end-use measures will reduce the system cost (excluding investment costs) of an industry by 50 % corresponding to 1.3 million SEK for one year. The end-use measures imply reduced power demand during peak load periods in the local market and increased power demand during non- peak load periods.
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| 7. |
- Axelsson, Jakob
(författare)
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Analysis and Synthesis of Heterogeneous Real-Time Systems
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During the development of a real-time system the main goal is to find an implementation that satisfies the specified timing constraints. Often, it is most cost-effective to use a heterogeneous solution based on a mixture of different microprocessors and application-specific integrated circuits. There is however a lack of techniques to handle the development of heterogeneously implemented systems, and this thesis therefore presents a novel approach inspired by research in the area of hardware/software codesign. The behaviour of the entire system is specified in a high-level, homogeneous description, independently of how different parts will later be implemented, and a thorough design space exploration is performed at the system level using automatic or semi-automatic synthesis tools which operate on virtual prototypes of the implementation.The objective of the synthesis is to find the least costly implementation which meets all timing constraints, and in order to predict these characteristics of the final system, different analysis methods are needed. The thesis presents an intrinsic analysis which estimates the hardware resource usage of individual tasks, and an extrinsic analysis for determining the effects of resource sharing between several concurrent tasks. The latter is similar to the fixed-priority schedulability analysis used for single-processor systems, but extended to heterogeneous architectures. Since these analysis procedures are applied early in the design process, there are always some discrepancies between the estimated data and the actual characteristics of the final system, and constructive ways of dealing with these inaccuracies are therefore also presented.Several synthesis algorithms are proposed for different aspects of the design. The hardware architecture is assembled from a component library using heuristic search techniques, and three alternative algorithms are evaluated in the thesis. The optimal partitioning of the functionality on an architecture is found using a branch-and-bound algorithm. Finally, a fixed-priority scheduler is instantiated by assigning priorities to the concurrent tasks of the behaviour. Together, the proposed analysis and synthesis methods provide a solid basis for systematic engineering of heterogeneous real-time systems.
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| 8. |
- Bachinger, Thomas
(författare)
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Multisensor arrays : for bioprocess monitoring
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bioprocess engineering, the technology that is focused on the exploitation of the metabolic potential of biological agents, has attracted growing interest throughout the past 50 years from both scientific and industrial communities. The products that have been brought to market range from pharmaceuticals and enzymes to food products and vitamins. The quality of human life has been improved through these efforts in many ways.Despite a strong research effort and the fact that microbial transformations often reach yields close to the theoretical maximum. many bioprocesses still operate at relatively low yields. One of the obstacles in effective operation is the extraction of useful information from the bioprocess. Sensors that acquire real-time information about the cells' state and their interaction with the environment in the bioreactor are seldom available. Hence, the implementation of sophisticated process control is prevented.In this thesis a new approach of non-invasive on-line bioprocess monitoring is evaluated. Chemical multisensor arrays (i.e. electronic noses) are used to extract information from the composition of volatiles emitted from the cell culture. The focus is on two specific areas: (i) monitoring of key variables in the bioreactor environment and (ii) monitoring of cell states and physiological events. The overall concern is, besides the increase of yield and reproducibility, the safety operation of bioprocesses.To cover a comprehensive area of modern bioprocessing, several organisms are investigated under different modes of operation in laboratory- and production scale processes. In repeated batch cultivations of recombinant Escherichia coli it is shown that an electronic nose can monitor biomass and specific growth rate with high accuracy. Glucose and ethanol concentration are monitored in batch cultivations of Saccharomyces cerevisiae. Bioproduct monitoring is presented in production-scale mammalian cell cultivation. The concentration of a therapeutic protein is monitored on-line in this long-term bioprocess thereby also outlining the stability of the sensor technique.In production-scale mammalian cell culture it is possible to follow cell transition states and monitor the reproducibility of the process. The physiological state of the cell population is revealed in laboratory-scale cultivations. It is shown that microbial contamination can be identified earlier than with conventional methods. Finally, the metabolic burden imposed on bacterial cells through strong overexpression of recombinant protein is monitored in fed-batch cultivation.
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| 9. |
- Bellgran, Monica
(författare)
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Systematic Design of Assembly Systems : Preconditions and Design Process Planning
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Efficient assembly systems are necessary to the success of industrial companies where assembly is a strategic core activity. Each assembly system is the result of a unique design process where the available resources and options are utilised in order to suit the specific preconditions of the company and the situation. Designing assembly systems in a systematic way based on a pre-defined structure is advantageous as it improves the chances of achieving the best possible assembly system in a shorter time.In this thesis, a model for analysis of assembly system design is presented, based on the synthesis of empirical findings and a theoretical framework. The analysis model consists of contextual aspects (part 1 ). It further includes an analysis of aspects important to the design process planning activities related to how they should be managed and structured (part 2). The analysis model finally emphasises the design process (part 3) involving preparatory design aspects, and aspects relevant for the design specification activities, i.e. the creation, evaluation and selection of the assembly system proposal.In order to improve the way an assembly system is designed in practice, a method supporting the planning of this design process is also developed. This method development strategy highlights the necessity of the system designers making relevant adaptations by selecting from the pre-defined method structure. The method is presented in a modular form based on a tree structure. In part, the method identifies activities concerning design process management. However, the main part of the method includes the presentation of preparatory design activities and design specification activities.In total, the method comprises eight phases that are further subdivided on two more levels of detail. Besides structuring these design activities, the method also includes parameters that are important when designing assembly systems.
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| 10. |
- Bengtsson, Per
(författare)
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Microstructural, Residual Stress, and Thermal Shock Studies of Plasma Sprayed ZrO2-Based Thermal Barrier Coatings
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thermal barrier coatings (TBCs), with a thickness of 0.4 mm, are today extensively used on the hot parts of both stationary and flying jet engines. The purpose of the TBC is to protect the underlying material from high temperatures and severe thennal shock. To increase the efficiency of a jet engine, higher turbine inlet temperatures and higher pressure ratios are sought. Consequently, materials with increased insulating properties will be required and a way to achieve this is to use thicker coatings. However, standard production procedures of thick TBCs (> 1 mm) result in coatings with an insufficient thernal shock life. The aim of this work is to develop a thick thermal barrier coating withan acceptable thernal shock life.In the present thesis, parts of the microstructure, the residual stress state, and their correlation to process parameters in thick thermal barrier coatings are described. Further, an optimised coating structure is developed to increase the thermal shock resistance of a burner can, coated with a 1.8 mm thick TBC. The studied thermal barrier coatings, plasma sprayed onto a nickel-based substrate material, consist of a bond coating and a top coating. The bond coating material is an MCrAlY alloy and the top coating material is made of Zr02, partially stabilised with 8 wt.% Y203. The spraying of the coatings is perforned at Volvo Aero Corporation. Residual stresses in the samples were measured with a layer removal technique and the stresses were compared to modelled stresses from a finite element model.Tensile stresses in the order of 150 MPa were measured in the bond coating, after the bond coating deposition. These stresses remained after the spraying of the top coating, where low stresses varying from -15 to 10 MPa were found, dependent on spraying conditions. The low stresses were a result of stress relaxation by microcrack formation. The compressive top coating stresses were found in samples where the substrate temperature was high at the end of the topcoating spraying. This gave a large temperature difference when cooling to room temperature, and due to different thermal expansion coefficients between the substrate and the top coating, more compressive stresses resulted. Good agreement between modelled and measured residual stresses was obtained. Columnar grains were found in the solidified droplets (splats) of the top coating. Between the splats, horizontally oriented delaminations were found. Top coatings sprayed at a high substrate temperature or a high passage thickness showed the columnar grains to extend through the thickness of each lamella. This decreased the density of horizontal delaminations. The density of vertical microcracks was also found to decrease as the substrate temperature increased. This was confirmed from the modelling, where the top coating inelastic strain showed the same behaviour.Also, a segmentation crack network was found in top coatings sprayed with a high substrate temperature or a high passage thickness. The thermal shock performance of a burner can containing a 1.8 mm thick segmented top coating was compared to a can sprayed according to standard procedures. Within 35 thernal shock cycles, the standard burner can contained cracks which were considered to be unsafe for the integrity of the can. No such cracks were found in the segmented structure after 1000 cycles.The study shows that thick thermal barrier coatings on real components can be used in jet engines provided that the correct structure is chosen.
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| 11. |
- Bergman, Niclas
(författare)
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Recursive Bayesian Estimation : Navigation and Tracking Applications
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Recursive estimation deals with the problem of extracting information about parameters, or states, of a dynamical system in real time, given noisy measurements of the system output. Recursive estimation plays a central role in many applications of signal processing, system identification and automatic control. In this thesis we study nonlinear and non-Gaussian recursive estimation problems in discrete time. Our interest in these problems stems from the airborne applications of target tracking, and autonomous aircraft navigation using terrain information.In the Bayesian framework of recursive estimation, both the sought parameters and the observations are considered as stochastic processes. The conceptual solution to the estimation problem is found as a recursive expression for the posterior probability density function of the parameters conditioned on the observed measurements. This optimal solution to nonlinear recursive estimation is usually impossible to compute in practice, since it involves several integrals that lack analytical solutions.We phrase the application of terrain navigation in the Bayesian framework, and develop a numerical approximation to the optimal but intractable recursive solution. The designed point-mass filter computes a discretized version of the posterior filter density in a uniform mesh over the interesting region of the parameter space. Both the uniform mesh resolution and the grid point locations are automatically adjusted at each iteration of the algorithm. This Bayesian point-mass solution is shown to yield high navigation performance in a simulated realistic environment.Even though the optimal Bayesian solution is intractable to implement, the performance of the optimal solution is assessable and can be used for comparative evaluation of suboptimal implementations. We derive explicit expressions for the Cramér-Rao bound of general nonlinear filtering, smoothing and prediction problems. We consider both the cases of random and nonrandom modeling of the parameters. The bounds are recursively expressed and are connected to linear recursive estimation. The newly developed Cramér-Rao bounds are applied to the terrain navigation problem, and the point-mass filter is verified to reach the bound in exhaustive simulations.The uniform mesh of the point-mass filter limits it to estimation problems of low dimension. Monte Carlo methods offer an alternative approach to recursive estimation and promise tractable solutions to general high dimensional estimation problems. We provide a review over the active field of statistical Monte Carlo methods. In particular, we study the particle filters for recursive estimation. Three different particle filters are applied to terrain navigation, and evaluated against the Cramér-Rao bound and the point-mass filter. The particle filters utilize an adaptive grid representation of the filter density and are shown to yield a performance equal to the point-mass method.A Markov Chain Monte Carlo (MCMC) method is developed for a highly complex data association problem in target tracking. This algorithm is compared to previously proposed methods and is shown to yield competitive results in a simulation study.
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| 12. |
- Bergquist, Bjarne
(författare)
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Statistical approaches to PM steel process improvements
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Increased performance:cost ratios for PM steel components is vital if current growth rate of market shares of such components versus competing technology is to be sustained. Both performance and cost of components are affected by variation of component properties. This work focuses on variation; where major variation sources lie and measures to circumvent problems that could be taken.A design-of-experiments approach was used to identify the most important green compact variations and interactions of a Fe-P alloy. The results show that the highest impact energies are obtained for high green densities, and without graphite addition. It is concluded that sintered density is the reason for the observed impact energies. Variation sources controlling phosphorus content and added graphite content are of concern since they affect the dimensional stability. Prospects for a robust sintering operation of same alloy is investigated. The objective is to find a setting of the variables investigated to maintain high tensile strength and proof stress without loss of dimensional stability, tensile elongation or impact energy. In the study, an endothermic sintering atmosphere was better for the robustness of the tested properties. A mechanism for the occasionally brittle behavior of the system is concluded to be loss of grain boundary cohesion due to decarburization.Possibilities for improved particle size distribution of water atomized powder are studied experimentally and by simulations. The most important variable for all studied responses is water pressure. Higher melt temperatures reduce particle size due to decreased viscosity. Large sulfur additions reduce particle size and this is an effect of reduced surface tension. Narrower size distributions were obtained for powder atomized with aluminum additions and for increased melt temperatures. A model for particle size for water atomization is presented and used in simulations.
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| 13. |
- Bertilsson, Lars
(författare)
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Molecular Adsorption on Self Assembled Monolayers studied by Surface Acoustic Waves and Infrared Spectroscopy
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Chemical sensors based on the selective absorption of gas/vapors in polymer layers rely on molecular interactions. Details of the mechanisms involved can be obtained by studying the adsorption on well defined model organic surfaces. In this thesis, the adsorption of dimethylmethylphosphonate (DMMP), a model molecule for the nerve gas, sarin, and the influence of humidity on the interaction, have been studied. Well defined organic interfaces were obtained by solution self assembly of long chain co-substituted thiol molecules, SH-(CH2)m-X, on gold surfaces. The interfacial properties are given by the tail group X and the following three different functional groups, -CH3, -OH, -COOH, have been analyzed.In the first paper, the properties of the self assembled monolayers (SAMs) were examined. The monolayers form ordered semi-crystalline layers with the tail groups defining the chemical properties of the interfaces. In mixed monolayers the surface concentration of the OH and CH3 terminated thiols corresponds to that of the preparation solution and no signs of macroscopic phase separation could be observed.The equilibrium adsorption of DMMP was analyzed under sensor conditions by a surface acoustic wave sensor (SAW), sensitive to changes in surface mass, and infrared reflection absorption spectroscopy (IRAS). It was found that DMMP interacts with hydrogen bond donating groups and that the lone pair electrons of the P=O oxygen is the main interacting part of the molecule. Both the temperature programmed desorption of DMMP adsorbed at 100 K and the SAW results from room temperature measurements indicate that the strongest interaction is on the -COOH surface followedby -OH and -CH3. For the -OH surface there is also a surface coverage dependent in the strength of interaction.The influence of humidity on the interaction was studied as DMMP was allowed to adsorb at different levels of relative humidity. For the -OH surface, an increase in the DMMP coverage proportional to the relative humidity was observed both with the SAW and with IRAS. A closer examination, however, revealed that a loss of water occurred during adsorption of DMMP. The conclusion from this experiment is that SAW results and other mass sensitive devices must be corrected if competing adsorption takes place. For the -COOH surface, low humidities tend to increase the DMMP coverage but at higher humidities a clear loss was registered by IRAS and the SAW sensor even after compensation for changes in water coverage. As water is present, the increased interaction can be explained by hydrogen bonding to free OH of the water. On the -COOH surface, the adsorption sites become blocked by water, which is more tightly bound on this surface. In the mixed (OH / CH3) monolayers water vapor starts to influence the DMMP adsorption above a critical concentration of OH groups of 0.6. This is also the OH concentration above which total wetting with DMMP occurs.The well defined organic monolayers formed by solution self-assembly was found to be suitable for interaction studies of the hydrogen bond accepting DMMP molecule and the influence of humidity on the interaction. The complementary information resulting from the chosen analytical techniques can be used for both qualitative and quantitative evaluation of the adsorption. For example, an optimal composition for the mixed (OH/CH3) SAM has been identified, where the number of adsorption sites and the interaction is sufficiently high, and the influence from humidity still low.
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| 14. |
- Borga, Magnus, 1965-
(författare)
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Learning Multidimensional Signal Processing
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The subject of this dissertation is to show how learning can be used for multidimensional signal processing, in particular computer vision. Learning is a wide concept, but it can generally be defined as a system’s change of behaviour in order to improve its performance in some sense.Learning systems can be divided into three classes: supervised learning, reinforcement learning and unsupervised learning. Supervised learning requires a set of training data with correct answers and can be seen as a kind of function approximation. A reinforcement learning system does not require a set of answers. It learns by maximizing a scalar feedback signal indicating the system’s performance. Unsupervised learning can be seen as a way of finding a good representation of the input signals according to a given criterion.In learning and signal processing, the choice of signal representation is a central issue. For high-dimensional signals, dimensionality reduction is often necessary. It is then important not to discard useful information. For this reason, learning methods based on maximizing mutual information are particularly interesting.A properly chosen data representation allows local linear models to be used in learning systems. Such models have the advantage of having a small number of parameters and can for this reason be estimated by using relatively few samples. An interesting method that can be used to estimate local linear models is canonical correlation analysis (CCA). CCA is strongly related to mutual information. The relation between CCA and three other linear methods is discussed. These methods are principal component analysis (PCA), partial least squares (PLS) and multivariate linear regression (MLR). An iterative method for CCA, PCA, PLS and MLR, in particular low-rank versions of these methods, is presented.A novel method for learning filters for multidimensional signal processing using CCA is presented. By showing the system signals in pairs, the filters can be adapted to detect certain features and to be invariant to others. A new method for local orientation estimation has been developed using this principle. This method is significantly less sensitive to noise than previously used methods.Finally, a novel stereo algorithm is presented. This algorithm uses CCA and phase analysis to detect the disparity in stereo images. The algorithm adapts filters in each local neighbourhood of the image in a way which maximizes the correlation between the filtered images. The adapted filters are then analysed to find the disparity. This is done by a simple phase analysis of the scalar product of the filters. The algorithm can even handle cases where the images have different scales. The algorithm can also handle depth discontinuities and give multiple depth estimates for semi-transparent images.
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| 15. |
- Brandt, Jan
(författare)
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On constitutive modelling of the compaction and sintering of cemented carbides
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The common manufacturing procedure for components of cemented carbide is a closed die cold compaction of a powder and a subsequent sintering of the compact to full density and strength.Major problems with the manufacturing process are the possible fracturing on ejection from the tooling and the distortion in the final shape. It is beneficial to perform the design iterations in the form of computer simulations, provided such simulations predict at least the final shape with good accuracy. This thesis concerns the development of computer simulation tools for both the compaction and the sintering.A constitutive model for the compaction based on elasto-plasticity has been developed. The model has a compactness tensor that measures the directionality of the deformation history and a two-dimensional hardening parameter set. The model represents the deformation induced anisotropy in the form ofa kinematic hardening combined with an isotropic hardening, and uses a flow rule that emanates from a non-associated flow potential.Furthermore, a continuum model of the sintering with and without loading has been developed, based on a micromechanical model of the sintering without loading. The model is visco-elastic with the capillary forces represented bya sintering stress. The model parameters evolve with temperature, relative density and rate of temperature. The author presented a rationale for deciding, in which mechanism the rate of temperature influence belongs.The models were implemented in the explicit FE-program LS-DYNA2D and verified against several experimental compaction and sintering tests. Finally, the models have been verified by the simulation of the complete compaction and sintering process of an industrial tool piece. The agreement between simulation and measurement in final shape is good. The convergence of the simulation concept is also demonstrated.
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| 16. |
- Bröms, Per
(författare)
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Polymer Light Emitting Devices : A study on how the electrode-polymer interface affects the performance of polymer light emitting devices
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The research reported in this thesis is concerned with a new type of semiconductor device that can be realised by using thin films of semiconducting polymers, or conjugated polymers. In this thesis only one family of these conjugated polymers is studied, namely poly-(para-phenylene vinylene) and derivatives thereof.This thesis focuses on how a change in the interface conditions between electrodes and polymer affects the performance of the devices. Especially on how low workfunction metals, e.g. calcium, magnesium interact with poly-(para-phenylene vinylene), and derivatives thereof. Those low workfunction metals are often used as the negative electrode for polymer light emitting devices. This type of light emitting device is described in this thesis and the issues off charge injection and transport is discussed in detail. Also the difference between the ideal theoretical models and real life system is in focus.Studies of different types of degradation mechanisms in the polymer light emitting devices are also included. The degradation of the polymer material due to low energy electrons from the thermal electron beam evaporator during fabrication has been studied in detail. Also included is an investigation and comparison of used and unused polymer light emitting devices that has been done with the help of sputtered depth profile analysis with surface sensitive Auger spectrometry.
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| 17. |
- Cai, Hongming, 1956-
(författare)
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Single fibre laser Doppler flowmetry for skeletal muscle perfusion measurements : methodological developments and clinical applications
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Measurements of microvascular blood flow in skeletal muscle by using the laser Doppler flowmetry (LDF) technique were first reported in 1979. The introduction of the single fibre technique in 1987 increased the possibilities of studying muscle perfusion under various physiological conditions without causing major tissue trauma.On-line processing of the LDF- and rms-EMG-signals made possible interpretation of the relationship between the perfusion and the activity of the muscle. Percutaneous single fibre LDF and bipolar surface electromyography (EMG) of the upper portion of trapezius muscle were performed continuously during a 10-minute long series of alternating periods of static contractions and rest, each of a one-minute duration. Regression analyses showed positive correlation between LDF and rms-EMG, as well as LDF and degree of arm elevation. Microcirculation in the trapezius muscle and the supraspinatus were measured simultaneously by continuous LDF during stepwise increased contractions related to the EMG too. Blood flow increased significantly in both muscles during increased shoulder torque. The blood flow in the trapezius muscle increased significantly at increased rms-EMG. But, no significant increase in muscle blood flow occurred in the supraspinatus muscle which thus seems to be more prone to develop ischemia during strenuous static work.A PC-based signal processor with a digital signal processing board was developed for evaluation of the different fibre tips' optic characters and laser Doppler algorithm, as well as for presentation of the laser Doppler measurement results. The Doppler signal power spectral density and corresponding flux values were visualized on the computer screen continuously in real-time. The single fibre technique has been further developed with the aim of improving the signal quality by modifying the geometry of the fibre tip and increasing the light wavelength, since the small monitored tissue volume in the muscle tissue by single fibre LDF is its drawback. The modified fibre tips, sphere and "pear" type, probes showed a higher flow sensitivity than did the flat end type. An infrared laser diode with the wavelength of 750 nm was used in the new optical module. These improvements were interpreted as being related mostly to a larger, strongly irradiated tissue volume in front of the fibre. The results were evaluated theoretically with ray tracing simulations and experimentally with the mechanical and flow models. The modified fibre with the new signal processor for monitoring blood flow has been successfully used in intramuscular measurements.
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| 18. |
- Chen, Fang, 1963-
(författare)
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Thermal Responses of the Hand to Convective and Contact Cold : with and without Gloves
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Many outdoor working tasks and some indoor working tasks still require the worker to perform them in a cold condition. To cope with cold condition, warm clothing is usually applied. Nowadays, the thermal protection of clothing is sufficient but the extremities are still not very well protected. It is very difficult to provide sufficient thermal protection to the hand, that does not decrease the hand performance. In the literature review of this thesis, the most important factors and topics related to the cooling of the hand and fingers are summarized.The issue of cold contact is still not sufficiently studies. How fast the skin may cool down to a dangerous level and how many factors may influence the contact cooling was not clear. There are five empirical studies concerned with cold surface contact by bare and gloved hand which are summarized in the thesis. The experimental studies of contact cooling of the bare finger and gloved finger were carried out in a small climate chamber. Many factors which may possibly influence the contact cooling were considered. These factors include: contact force; surface temperature; material property; surface mass; the thermal situation of the whole body and the morphology of the fingers.For the technical determination of the thermal resistance of the gloves, a mini hot plate was developed according to the EN 511 (36) and ISO 5085 (72) standards. The error from doubledetermination was less than 4%.The skin temperature (Tsk) was the dependent measurement for all of the studies. It varied on the different points of the hand. The measurement points and the location for measuring the Tsk is critical. Tsk and cold induced-vasodilatation showed a very local phenomenon. For unequal cooling (such as contact), the contact Tsk is critical and needs to be considered separately.The results indicated, that a modified Newtonian cooling curve with two time constants provided the best regression function for the contact Tsk of bare hand contact on cold surfaces and it may also be possible to describe the contact Tsk of a gloved hand.
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| 19. |
- Coradeschi, Silvia, 1968-
(författare)
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Anchoring symbols to sensory data
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Intelligent agents embedded in physical environments need the ability to connect, or anchor, the symbols used to perform abstract reasoning to the physical entities which these symbols refer to. Anchoring must deal with indexical and objective references, definite and indefinite identifiers, and a temporary impossibility to perceive physical entities. Furthermore it needs to rely on sensor data which is inherently affected by uncertainty, and to deal with ambiguities. In this thesis, we outline the concept of anchoring and its functionalities. Moreover we define the general structure for an anchoring module and we present an implementation of the anchoring functionalities in two different domains: an autonomous airborne vehicle for traffic surveillance and a mobile ground vehicle performing navigation.
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| 20. |
- Csaba, Gabor
(författare)
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Modelling Microslip Friction Damping and its Influence on Turbine Blade Vibrations
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A common failure mode for turbomachinery is high-cycle fatigue of compressor and turbine blades, due to high dynamic stresses caused by blade vibration resonance within the operating range of the machinery. A large number of engine shut-downs can be explained by blade failure caused by resonance vibration or flutter. One method of reducing the dynamic stress is to increase the damping by use of dry friction in general, and specially a device called a friction damper. It is a well-know fact that friction dampers may reduce the vibratory blade response at resonance. There is, however, a lack of theoretical models that can predict the performance of an actual damper.This thesis concerns theoretical modelling, analysis and optimization of friction dampers. Two models have been developed, one, named the Bar model, is a development of an existing damper model, the other, named the Brush model, is a new design. Both models have the ability to account for microslip in the contact between blade and damper.Dynamic systems with Coulomb friction, i.e. friction dampers, give rise to nonlinear differential equations. These can be solved either through numerical integration in the time domain or by linearizing the force-displacement relationship of the damper. Partly new theory for linearization and a numeric version of the Bar model have been developed. This results in forced response analysis being computed faster and more efficiently than before.The Bar model is relatively simple, yet complete enough to show the most important properties of a microslip friction interface. The model was used to optimize the weight of a new commercially used damper. Comparing simulations with spin-pit tests with a completely bladed disk shows good qualitative agreement, but it was not possible to see if the right weight had been predicted because the rotor could not be excited up to the design point.The Bar model allows only for slip motion in one direction, while the Brush model permits relative motion between blade and damper in all six degrees of freedom. The variables for the contact model are defined by damper geometry and material data, except coefficient of friction and a constant for the tangential stiffness, which have to be defined by measurements or a more advanced contact model. This type of complicated friction damper model has not previously been presented. Simulations and experiments have been compared for hysteresis curves and forced vibration analysis of a simplified blade-damper-blade system. The agreement is qualitatively good, although the results gave some questions that need more research.
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| 21. |
- Dalfors, Joakim
(författare)
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Photoluminescence studies of the electronic structure in some III-V quantum structures
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Semiconductor compound materials from groups III and V in the periodic table have attracted much interest during recent years, due to promising properties for optoelectronic devices such as lasers and light emitting diodes. Most of these devices are fabricated from quantum well (QW) structures. This thesis is based on optical studies on quantum wells and modulation doped heterostructures in some important III-V material systems: InGaAs/lnP, InGaN/GaN and GaN/AlGaN. The experimental investigations involve photoluminescence (PL), PL excitation (PLE) and time-resolved PL spectroscopy. Simple theoretical models have been used in some cases to compare with and identify experimental data.In the InGaAs/lnP material system, the dependence of the electronic structure on both In content (and thereby built-in strain) and well width has been studied by means of Fourier transform (FT) PL and FTPLE for a set of QW samples. The reduced effective masses for the same set of samples have been determined by applying external magnetic fields and fitting the experimental data to Landau levels. Similar experiments have also been performed on a set of modulation doped heterostructures, where a self-consistent calculation enabled peak identification as well as a suggestion for a probable potential profile.Electronic structure and optical transitions have been studied in a modulation doped GaN/AlGaN QW and compared to calculations based on a simple model. Also, the recombination processes involved in the PL from InGaN/GaN multi QW samples have been investigated. The In content and the growth condition for the barriers were varied. In a set of Si doped samples with different doping concentrations, the screening of the strain induced piezoelectric field was studied.
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| 22. |
- De la Cruz Rodrígues, Pedro
(författare)
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Fatigue and Corrosion Fatigue Fracture of a Plasma Nitrided, Laser Hardened, and Galvanized B-Mn Steel
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fundamental and technological aspects of fatigue and fracture of conventional and advanced material are topics of primary importance to the development of materials science and engineering. Surface treatments have been established to improve the surface properties of material against surface phenomenon such as wear, corrosion, fatigue and corrosion fatigue. This thesis deals with the influence of two modem (plasma nitriding and laser hardening), and one conventional (hot dip galvanizing), surface treatments on the fatigue, corrosion fatigue (in seawater) and fracture of a B-Mn steel. The main approach adopted here focuses the attention on fatigue crack initiation mechanisms.Constant stress amplitude plane reversed bending fatigue tests (R = -1) at room temperature and at a frequency of 47 Hz in air and sea water were conducted using cylindrical untreated and surface treated quenched and tempered (Q&T) steel specimens made of a B-Mn SS2131(∼AISI 15B21H) steel with stress concentration factors of Kt =1.05 and 1.7.S-N curves show that surface treatments improved the fatigue limit by 53 % and 115 % (plasma nitriding), and 18% and 56 % (laser hardening) of smooth and notched Q&T specimens; whereas hot dip galvanizing slightly decrease the air fatigue limit of smooth (-9 %) and notched (-10 %) Q&T specimens. The small cracks formed in the coating during galvanizing could be the cause of this reduction. Compressive stresses and improved strength (hardness) introduced by plasma nitriding and laser hardening play the principal role for the improvement of fatigue strength, subsurface crack nucleation, fish-eye asymmetry, and reduction of stress intensity factors. Plasma nitrided (PN) and laser hardened (LH) materials behaves as composites. Laser process parameters have to be optimised in order to avoid the formation of a damaged area (characterised by a low hardness and low compressive residual stresses) around the overlap zone which promotes the formation of long narrow crack along the edge of the overlap zone causing premature failure.Sea water suppress the fatigue limit and reduces fatigue strength (especially at long lives) of smooth and notched Q&T, PN and LH specimens, but smooth and notched hot dip galvanized (HDG) specimens still exhibit a corrosion fatigue limit (at 2x107 cycles) with values a little lower than the corresponding air fatigue limits. Physical and electrochemical corrosion protection by hot dip galvanizing are the causes for the good corrosion fatigue properties obtained. Plasma nitriding improves the corrosion fatigue resistance of Q&T specimens; it is associated to the good corrosion resistance of ε and -phases, the enhancement of corrosion and fatigue by compressive residual stresses and the consumption of H+ ions during reduction of nitrogen. Mechanisms for nucleation of pits, and corrosion fatigue cracks have been proposed to explain corrosion fatigue strength reduction due to sea water. A derived equation predict well the corrosion fatigue strength of notched specimens from the observed air fatigue strength of smooth specimens.
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| 23. |
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| 24. |
- Drakengren, Thomas
(författare)
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Algorithms and Complexity for Temporal and Spatial Formalisms
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The problem of computing with temporal information was early recognised within the area of artificial intelligence, most notably the temporal interval algebra by Allen has become a widely used formalism for representing and computing with qualitative knowledge about relations between temporal intervals. However, the computational properties of the algebra and related-formalisms are known to be bad: most problems (like satisfiability) are NP-hard. This thesis contributes to finding restrictions (as weak as possible) on Allen's algebra and related temporal formalisms (the point-interval algebra and extensions of Allen's algebra for metric time) for which the satisfiability problem can be computed in polynomial time. Another research area utilising temporal information is that of reasoning about action, which treats the problem of drawing conclusions based on the knowledge about actions having been performed at certain time points (this amounts to solving the infamous frame problem). One paper of this thesis attacks the computational side of this problem; one that has not been treated in the literature (research in the area has focused on modelling only). A nontrivial class of problems for which satisfiability is a polynomial-time problem is isolated, being able to express phenomena such as concurrency, conditional actions and continuous time.Similar to temporal reasoning is the field of spatial reasoning, where spatial instead of temporal objects are the field of study. In two papers, the formalism RCC-5 for spatial reasoning, very similar to Allen's algebra, is analysed with respect to tractable subclasses, using techniques from temporal reasoning.Finally, as a spin-off effect from the papers on spatial reasoning, a technique employed therein is used for finding a class of intuitionistic logic for which computing inference is tractable.
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| 25. |
- Edman, Anders, 1966-
(författare)
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High Data Throughput CMOS Circuits
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis describes some high-performance digital CMOS circuits and the design of these circuits.The goal is to have a higher utilization of standard CMOS processes in order to increase performance of digital circuits. This is done without the use of aggressive processes. The designs are targeted towards very high clock rate and low power consumption.At the high level, the design are adjusted to fit into a low level architecture optimized for high performance. The architecture is also optimized for the high level design. The logic style and the flip-flops are selected for high performance.The digital processing chips presented in this thesis are based on a principle of heavily pipelined uni-directional processing in a data path. The logic is pipelined to a logic depth of one or two gates per pipeline stage. This design method and architecture is used for applications with high throughput processing of data.Two chips are designed for processing of 10 Gb/s SDH (Synchronous Digital Hierarchy) data, for use in fiber optic transmission systems. They include processing for the framer and deframer functions of a SDH regenerator. The 10 Gb/s is internally processed with 16 bits in parallel at a clock rate of 622 MHz. The chips are implemented in standard 0.6-0.8 μm CMOS.A quadrature 350 MHz Direct Digital Frequency Synthesizer is implemented in 0.8 μm CMOS. This DDFS is a high-speed compact implementation with on-chip DIA converters for the four-phase output. It calculates the sine and cosine values with a precision of 8 bits and with a frequency resolution below 1 Hz by using a sparse ROM-table and interpolation.A correlator chip for satellite-based high-performance auto-correlator spectrometers is designed. This chip performs more than 0.5 Tera-Multiply and Accumulate operations per second at a speed of 320 MHz in 1664 multipliers and accumulators. This 58 mm2 chip contains 1.6 million transistors and is implemented in a 0.6 μm process. The power consumption per operation is reduced with more than 5 times compared with other implementations, without any reduction in supply voltage. The internal noise level is reduced by dividing the processing and clock signal distribution into blocks with a clock buffer in between.Finally, two different high-speed multiplexers are presented. A 2.4-Gb/s 4:1 multiplexer and a 4-Gb/s 2:1 multiplexer are implemented in 0.8 μm CMOS. Both multiplexers are designed to be clocked by an external high swing clock.All chips results have been verified by measurements.
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