| 61. |
- Larsson, Ulf
(författare)
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On robot control with feedback from optronic sensors
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The problem studied in this thesis is control of robots using information from optronic sensors. With a laser range sensor onboard the robot the relative distance to an object can be measured. This allows the robot to operate in a partial unknown environment. One complication with non-contact sensors is the assiciation problem, i.e. finding the correspondence between the measured signals and each object in an unstructured workspace. This problem is addressed in the algorithms presented for using measurements. The approach is model based with respect to sensor errors, uncertainty in association and robot dynamics. Results includes: * The range weighted Hough transform (RWHT) was developed as a robust algorithm for extracting plane surfaces in scans made by a range measuring laser. The peaks in the RWHT are used during navigation of mobile robots and for automatic generation of maps. * A modelling study is made toward improving mobile robot performance using rate gyros. The main limitation seems to be an unknown lateral velocity. The special kinematic for navigating articulated vehicles is also studied. * An hydraulic arm, without joint angle encoders, is controlled with feedback from measured directions to retro-reflectors. An eye-in-hand range camera is studied with respect to gripping and for reducing vibration. Considering the fast development in computing and laser based sensing there is a large potential for novel application like robots in contaminated areas, in mining, in forests etc. The model-based approach in well suited for industrial requirements on predictable properties and self-monitoring of control and information systems.
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| 62. |
- Lehto, Niklas
(författare)
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Dislocations in silicon
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The topic of this thesis is theoretical studies of the electrical and structural properties in the elemental semiconductor silicon. Because of the numerous and powerful applications of semiconductors, e.g., rectifiers, transistors, solar cells and lasers, they have been the focus of huge amounts of research. Electronic devices necessitate use of almost pure semiconductor materials, normally in the form of a single crystal. In this crystal an accurately measured amount, usually extremely small, of a foreign dopant has been included to control its electrical properties. The properties of a device may be distributed by unwanted defects. Dislocations are examples of defects that degrade the performance of an electronic device, and they may even cause breakdown. This is due to the influence of dislocations on density, mobility and, most importantly, lifetime of the electrical carriers in the material. In newer semiconductor materials, such as III-V compounds, Si-Ge alloys, heterostructures and strained layers, dislocations cause problems. Dislocations in silicon are amenable more than most other solids to many different characterisation techniques and theoretical approaches. Therefore, a thorough understanding of dislocations in silicon is valuable, and an important milestone in the longer journey towards a comprehensive description of dislocations in all semiconductors. This thesis presents theoretical calculations focused on dislocations and some dislocation-related defects in silicon. Firstly, the electronic states of intrinsic stacking faults bounded by dislocations are investigated. Such stacking faults are one constituent part of commonly occurring extended dislocations in silicon. Secondly, the electronic and atomic structure of vacancies interacting with dislocations is investigated. This is important since vacancies are gettered by dislocations. Finally dislocation- dislocation interaction and its effects on the core structure of the so- called 90* partial dislocation are investigated. In order to study dislocation-dislocation interactions, a new and self-constitent method to apply periodic boundary conditions is introduced.
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| 63. |
- Lei, Bingqiang
(författare)
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The silicon nitride reaction-bonding process
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The so called Reaction-Bonded Silicon Nitride (RBSN) materials are usually produced through the chemical reaction of silicon powder compacts in a nitriding atmosphere. This nitriding reaction is strongly exothermic and much heat is generated, which may cause to overheating, even melting of the powder compacts so to hinder the further reaction due to the reduction of specific area of the powder compacts, especially when the nitridation involves a rather large mass of silicon. The commercial process of reaction-bonded silicon nitride is usually slow and energy consuming. In order to optimise the production process and to achieve better properties of the materials obtained, mechanism of the enhanced nitridation needs to be further understood. In this thesis, a brief overview is presented of the current state of knowledge concerning the so called Reaction-Bonded Silicon Nitride (RBSN), including relevant crystallography, thermodynamics and kinetics on gas-solid reactions. The work concerns the reaction of silicon powder compacts with a nitrogen atmosphere. The kinetics and mechanisms of the nitridation process of silicon powder compacts have been studied by means of experiment and modelling. The majority of experiments have been carried out on pilot scale batches of silicon powder compacts in nitrogen environment. The XRD, HTXRD (high temperature X-ray diffraction) and SEM have been used to study the kinetics and mechanisms of the nitridation process. The experimental work has confirmed the existence of two reaction rate maxima at two different temperatures and has revealed the effects of selected process variables on these reactions, and explanation for the second reaction regions has been given in terms of possible reaction mechanism. The effect of the auxiliary gases (hydrogen, argon and helium, which were added to the nitriding atmosphere in order to minimise the overheating of the powder compacts) on the nitridation process has been discussed, relating with the sizes of the powder compact and the amount of silicon mass in the nitridation. Based on the understanding of the nitridation process, an advanced computer program that can monitor the gas pressure and temperature and can control the rate of reaction by tailoring both the supply of nitrogen gas and heating rate according to the instantaneous nitridation rate has developed. The nitridation has been investigated by high temperature X-ray diffraction and in situ information of the reaction kinetics and mechanism has been obtained. The insights obtained have formed the foundation for the creation of two theoretical models, one being a quantitative description of the solid-gas reaction as a complex combination of reaction steps, concerning the multiple reaction steps and many factors such as the changes of the specific area of the particle, the corporation of reaction and sintering and the volumetric change due to the reaction, etc.; and the other predicting the development of internal stresses arising when a reaction product forms on particle surface in a solid/gas reaction.
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| 64. |
- Lindgren, Per
(författare)
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Applications of decision diagrams in digital circuit design
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Design methodology of digital circuits is a rapidly changing field. In the last 20 years, the number of transistors on a single chip has increased from thousands to tens of millions. This sets new demands on the design tools involved, their ability to capture specifications on a high level, and finally synthesize them into hardware implementations. The introduction of Decision Diagrams (DDs) has brought new means towards solving many of the problems raised by the increasing complexity of todays designs. In this thesis, we study their use in VLSI CAD and develop a number of novel applications. Incomplete specifications are inherent to the functionality of almost all digital circuits. We present a design methodology providing a common basis between design validation and logic synthesis, namely the semantics of Kleenean Strong Ternary Logic. This is called upon as commonly used design methodologies, based e.g. on VHDL are shown to put design correctness in jeopardy. By an extension of DDs, we can efficiently represent and manipulate incompletely specified functions. The method presented, not only guarantees correctness of the final circuit, but also offers potential towards expressing and utilizing incompleteness in ways other methodologies are incapable of. The increasing density and speed of todays target technologies also changes the conditions for logic synthesis; e.g., traditional quality measures based on gate delays are becoming less accurate as delays caused by interconnections are raising their heads. To address this problem we propose methodologies allowing quality measures of the final circuit to be foreseen and considered throughout the whole synthesis process. In general this is a very hard task. We approach the problem by limiting our synthesis methodologies to those rendering regular layouts (Such as computational arrays and lattices). The regularity allows us to predict properties of the final circuit and at the same time, ensure design criteria to be met, e.g., path delays and routability of the final circuit. In this thesis, we develop new design methodologies and their algorithms. By our experimental results, they are shown to offer significant improvements to both state of the art two-level and multi-level based tools in the area of layout driven synthesis. Our minimization methods are based on Pseudo Kronecker Decision Diagrams (PKDDs) which are the most general type of ordered bitlevel diagrams for switching functions. In the thesis we elaborate on the properties of PKDDs and Ternary PKDDs (TPKDDs) and develop an efficient minimization method based on local variable exchange for TPKDDs. Furthermore, the problem of PKDD minimization is discussed and a number of different strategies are introduced and evaluated; the potential compactness of PKDDs is confirmed. The thesis spans from validation and verification of high-level specifications all the way down to layout driven synthesis, combining logic minimization, mapping and routing to the target architecture at hand. We conclude our work to offer new means towards solving many of the crucial problems occurring along the design process of modern digital circuits.
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| 65. |
- Lindgren, Åsa
(författare)
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Road construction materials as a source of pollutants
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals mainly with road construction materials, particularly in cases where they may contribute polluting substances. The complexity of the measuring and evaluation of some pollutants with respect to sampling and chemical analysis is considered. Field measurements showed that, on the basis of their chemical composition, large amounts of the solids accumulated in the snow along a rural highway could be attributable to asphalt wear. The elements in the winter- accumulated solids were measured and tested with regard to leaching. Adsorption characteristics were tested for Zn, Cu, Cd and Pb on two different minerals. Through material analyses, PAH were found in bituminous binders and in tyre rubber. Asphalt was tested for leaching. Conventional road construction materials were compared with blast furnace slag in a field study. The slag was chemically and physically characterised.
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| 66. |
- Lindhagen, Johan
(författare)
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Notch sensitivity and bridging laws in glass mat composites
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The fracture behaviour of polymeric random glass mat reinforced composites was investigated. Such materials exhibit very large damage zones with fibre bridging. The damage zone sizes are often comparable with the specimen dimensions, which precludes the use of linear elastic frac-ture mechanics (LEFM). Instead, methods based on crack bridging concepts were applied. Ma- terials with different matrix and different reinforcement structures were studied. The investiga-tions covered measurements of notch sensitivity, microscopic studies, measurements of fracture energy and bridging laws by a DCB test, speckle measurements, and finite element modeling. The materials were found to exhibit low notch sensitivities. At low temperature the notch sen-sitivity decreased further. Differences in notch sensitivity were explained based on mi-cromechanical observations. The investigated materials had softening bridging laws. Based on the measured bridging laws notch sensitivities were predicted and a good correlation with the experimental observations was obtained.
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| 67. |
- Liu, Wenxin
(författare)
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Surface reactions of natural illites from different origins
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Studies of natural illites from different origins were performed, including surface acid-base properties, determination of total inorganic carbonates, and spectroscopic investigations of chemical and structural nature as well as alterations of surface properties by acid-base titration. Using surface complexation model, the fitting results showed that the acid-base behavior of aqueous illite surfaces was dominated by deprotonation procedure. Acidimetric supernatant as the system blank was more reasonable than the neutral one. In addition, surface complexation or precipitation of hydrous Al-Si species (HAS) influenced the illite surface characteristics. Photoacoustic spectroscopy was a flexible and reproducible method for measurements of carbonate in solids and waters. Spectral information illustrated similarities and discrepancies in chemical composition and structure between the illite samples. The combined spectroscopic evidence confirmed the alterations of surface properties by acid-base titration and the formation of surface HAS.
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| 68. |
- Liu, Xiaoxiong
(författare)
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Evaluation of thermal comfort of head gear : a method to measure heat transfer characteristics
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This study was carried out within the research project "Thermal properties of protective helmets - improvement, validation and standardization of a measurement method" which was a continuation of a research project being carried out since 1992 at the Division of Industrial Ergonomics, Department of Human Work Sciences, Luleå University of Technology, Sweden, with co-operation of the Department of Ergonomics, National Institute for Working, Life (NIWL), Solna, Sweden. A method was developed for measuring the evaporative heat transfer properties of helmets, based on the results of a thorough literature survey. This method has been further improved by building a new sweating head manikin and improving the water (simulated sweat) supply system. Seven different helmets were used in extensive laboratory experiments under various controlled environmental conditions to verify the improvements in the method, and to standardize the measurement procedures. This method was then adapted to measure dry heat transfer properties of helmets. Laboratory tests were conducted with the sweating manikin head under dry conditions (without simulating sweating on the manikin head). The same helmets used in evaporative thermal transfer tests were used in the dry heat loss measurements. Field investigations with human subjects in both hot and cold environments were also carried out to validate the laboratory tests with the method. The results from the laboratory tests showed that the improved method can reveal more detailed information about the evaporative heat transfer from head gear, it is easy to use and control. The field investigation indicated that the subjective results were consistent with the laboratory measurements results in terms of heat transfer. Efforts were made to incorporate the dry heat transfer measurement into the evaporative heat transfer measurement to form a standardized total thermal transfer testing method for head gear thermal evaluations. Further laboratory measurements are proposed to apply this total heat transfer measurement technique to practical tests.
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| 69. |
- Ljungberg, Johan
(författare)
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The geochemical dynamics of mine tailings at Laver and Stekenjokk, Northern Sweden
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents geochemical studies of tailings and waters sampled at two closed mines; the Laver mine in Norrbotten where the tailings have not been remediated, and the Stekenjokk mine in Västerbotten where the tailings have been flooded. Oxidation of sulfide minerals in the tailings at Laver has led to the development of a distinct chemical zonation with an oxidised zone above the unoxidised tailings. Metals released from oxidation and weathering of sulfide minerals are retained within the tailings impoundment. This retention mechanism is today very efficient and only 5-10 % of the released masses of metals reaches the surface water system. Areas of the tailings deposit with shallow groundwater table are at present the main source of metal release. The water column of the water cover at Stekenjokk was sampled four times at various stations. The pond water contains higher concentrations of Ca, S (as sulfate), Cd and Zn than local background. The flow of Ca, S, Cd and Zn to the water column from the pore water of the tailings is an effect of both in-situ oxidation and buffering in the uppermost part of the tailings, and the fact that some parts of the tailings material were oxidised prior to the remediation with water cover. Resuspension of sulfides from the tailings surface itself is insignificant. Flooding as remediation method works well at Stekenjokk.
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| 70. |
- Löfqvist, Torbjörn
(författare)
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Ultrasonic measurement technology for characterization of pulp fibre suspensions
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In the papermaking industry, there is a need for sensors to measure the properties of the fibre suspension that determine important parameters in the finished paper. This lack of on-line sensors hampers the development of advanced process control strategies. Ultrasonic measurement techniques might become useful tool for on-line measure of fibre properties. In general, an acoustic wave, propagating through a suspension, inherently carries information about the physical properties of the suspended material. The presented thesis deals with the fundamental physical processes that governs the propagation of ultrasonic waves in dilute suspensions of paper pulp fibres and water. It also presents a simulation tool capable of simulating all components of a pulse-echo, ultrasonic measurement system, including measurement cell and the fluid under investigation. Experiments are performed in a custom-built measurement cell for low intensity, ultrasonic, pulse-echo measurements. It is investigated both theoretically and experimentally how macroscopic, measurable quantities as speed of sound and attenuation of the ultrasonic pulse are affected by fibre mass fraction, fibre geometry and the physical properties of the fibre material. This knowledge could be applied in using ultrasound to evaluate elastic, or other properties, of fibres in a fibre suspension.
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