| 1. |
- Axelsson, Mikael D.
(författare)
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Multi-element analysis of environmental samples using LA-ICP-MS : method developments with emphasis on calibration strategies
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Analytical applications based on the use of laser ablation-inductively coupled plasma-sector field mass spectrometry (LA-ICP-SFMS) have shown great potential for both quantitative and qualitative determination of elements in a variety of materials, although the weak point is finding a suitable calibration approach. The major focus of this work has, therefore, been internal standardisation and calibration. Methods for quantitative and qualitative analysis of geological (coal, ferromanganese concretions, sulphide minerals) and biological (nail and hair) samples have been developed. For coal, two reference materials were analysed after microwave (MW) treatment with different combinations of HNO3, aqua regia, HF and H2O2. Lithium metaborate (LMB) fusion with and without ashing of samples, as well as LA solid sampling on pressed coal pellets were also evaluated. External calibration for LA-ICP-SFMS was conducted using matrix-matched standard dopeds with standard solutions. This approach resulted in good accuracy for 46 out of 47 elements tested in the coal fly ash reference material. The precision was assessed in this work by replicate analyses of coal samples and was found to be, as average values for all elements, 4-5% and 10-15% relative standard deviation (RSD) for procedures involving digestion and LA sampling, respectively. For ferromanganese concretions, improvement of existing sample preparation schemes was necessary in order to expand the element coverage. The optimised and validated (for about 60 elements) method has the potential to replace the multitude of sample preparation and instrumental analytical techniques previously used to determine specific groups of elements in ferromanganese nodules. By using this improved method, it was possible to successfully quantify more than 50 elements by LA-ICP-SFMS using external calibration against matrix-matched standards. The results also show how different LA parameters affect the isotopic response and RSD. For sulphide minerals, LA-ICP-SFMS analysis was performed directly on polished crystalline sections. In sphalerite, a number of major and trace elements were determined by a ‘single-standard’ method using Zn for internal standardisation, together with correction for FeS impurities in the mineral, allowing straightforward quantification without using external methods for the determination of the actual Zn content. Results obtained by this approach were in good agreement with those from using external calibration. In order to evaluate the possibility to use crystalline sections of sphalerite and four other sulphide minerals as in-house standards, an analytical method was developed for multi-elemental analysis of such samples after preparation based on both MW digestion using different acid mixtures and LMB fusion. The performance of the sample preparation and analysis stages was evaluated using powdered pyrite and galena reference materials. It was found possible to use the selected minerals as matrix-matched standards for the determination of about 20 trace and ultra-trace elements by LA-ICP-SFMS. The second group of matrices concerned in this work comprises hair and nail samples. The first part of this study was focused on method validation for the determination of 71 elements by conventional ICP-SFMS analysis after MW-assisted digestion, with special attention paid to the correction of spectral interferences and to accuracy assessment. In the follow up study, the main concern was to evaluate the capabilities of LA-ICP-SFMS for quantitative multi-elemental analysis of hair and nail samples, emphasising the collection of spatially resolved information. Quantification was performed by means of an in-house, multi-element, matrix-matched standard using 32S+ as internal standard. A major conclusion of this thesis is that each sample type is in many respects unique, and therefore demands careful selection of a suitable calibration protocol, in order to ensure that reliable analytical results are delivered. The developed methods will make it possible to quantitatively analyse samples such as geological thin-sections, single sulphide grains, ferromanganese concretions, fingernails and hair. The results also show that LA-ICP-SFMS potentially can be used for obtaining quantitative analyses with good spatial resolution in a variety of materials.
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| 2. |
- Bérube, Andrew Patrick
(författare)
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Investigating the streaming potential phenomenon using electric measurements and numerical modelling with special reference to seepage monitoring in embankment dams
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A three-dimensional finite element computer program has been developed to numerically model the streaming potential phenomenon. The program can in fact calculate and display the primary and secondary potential distributions for any two coupled flows in a three dimensional domain. For streaming potentials, the primary flow is hydraulic and the secondary flow is electrical. The program operates in three separate stages. The program first determines the hydraulic potential distribution in the ground based on hydraulic conductivity values and the hydraulic driving forces, such as the pressure drop through an embankment dam. The program then calculates the geometry and magnitude of the electric current sources based on the fluid flow and cross-coupling conductivity values. Finally the electric potential distribution is solved for using these current sources and the electric conductivity distribution. Additionally, the program can incorporate external current sources, which can be used to simulate resistivity measurements in a model. The model domain can take any three-dimensional shape and can be divided into elements as desired. The individual elements can be assigned separate hydraulic, electric and cross-coupling conductivity values, creating an inhomogeneous anisotropic domain with three separate conductivity distributions. Four different types of finite element are available to choose from; two- and three-dimensional versions of isoparametric elements with either linear or quadratic interpolating polynomials. The program has been made fully graphical, allowing the user quick and easy access to information at any particular point of the domain. In order to provide a better picture of the streaming potentials in earth dams and the potential of the SP method for dam safety monitoring, SP investigations were performed on a number of embankment dams. Electric resistivity measurements were also performed on some of the dams to compliment the SP data. The resistivity data was found to be of considerable assistance for interpreting the SP measurements as well as for simulating real dam conditions with the modelling program. Three hydro-electric dams of different size on the Luleå River in northern Sweden were studied together with several dams built by mining companies for containing mine tailing reservoirs. A number of potential seepage areas were identified in several of the investigated dams.
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| 3. |
- Bhongsuwan, Tribop
(författare)
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Research in rock magnetism and palaeomagnetism of recent sediments and palaeozoic to tertiary rocks in Thailand
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Rock magnetic and palaeomagnetic studies have been performed on sediments and Palaeozoic to Tertiary rocks in Thailand. The first part of the thesis includes an environmantal study based on the magnetic properties of recent sediments in one of southern Thailands largest water reservoirs, the Songkla Lake. Sediment from 21 cores collected from different parts of the lake were investigated. From the correlation with age determinations of the sediments, the sedimentation velocities could be determined and related to different parts of the lake. In an attempt to put Thailand and its geological evolution into a plate tectonic context rock magnetic and palaeomagnetic studies were performed on rock from different blocks in southern and northern Thailand. The results show that large parts of Thailand have been remagnetized due to the intrusions of Permian-Triassic granites, and that rock have been deformed in relation with a collition between Asia and India. The plate tectonic analysis shows a clear tectonic contrast between the Shan Thai and Indochina Blocks, a difference that can be related to a collition between Asia and India during the Cenozoic. The study also demonstrates that northeast Thailand, which forms a part of the Indochina Block, has been attached to the South China Block during late Jurrasic time. The presented model of the tectonic evolution for this part of Thailand supports to a large extent earlier presented geological models.
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| 4. |
- Bodin, Ulf
(författare)
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Quality issues in Internet packet forwarding
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis addresses quality issues in Internet Protocol (IP) packet forwarding. In IP networks, queue mechanisms and scheduling can be used to construct multiple forwarding behaviors. Thereby, both relative and independent services can be offered to Internet users. Independent services offer forwarding qualities known beforehand. Users are assumed to explicitly request admission to an independent service from their network provider. With relative services, users switch between these services to find one that provides an appealing balance between forwarding quality and cost. The thesis makes contributions to three research areas related to forwarding quality in IP networks; differentiating forwarding mechanisms, admission control for differentiated services, and forwarding quality in radio networks carrying Internet traffic. It contributes to the first research area with definitions of three recommendations related to offering loss-rate differentiation (i.e., multiple drop precedence levels). These recommendations are; (1) the total forwarding quality at congested links should not be degraded due to actions taken to create loss-rate differentiation, (2) traffic at high drop precedence levels should always be given a useful share of available forwarding resources, and (3) users should be able to predict the change in loss-rates when switching between drop precedence levels. We specify and evaluate properties of queue mechanisms following these recommendations. Also, as a contribution to the first research area, a new set of forwarding behaviors is specified and analyzed. These forwarding behaviors are suitable for rate-adaptive and delay-sensitive applications with limited loss-tolerance. Applications needing loss-free forwarding of specific packets can be said to have limited loss tolerance. We define and evaluate a scheduling mechanism creating these forwarding behaviors that can be implemented efficiently. The contribution to the second research area is a mechanism for admission control giving assurances on loss-rates to rate varying applications is defined. With this mechanism, dynamic per-link admission thresholds are used to limit committed aggregate rates. To allow for high link utilization through statistical multiplexing we specify a method to adjust these thresholds using low impact traffic monitoring mechanisms commonly available in legacy routers. In radio networks carrying IP traffic, radio transmissions can be scheduled differently to balance spectrum utilization and the forwarding quality provided. Also, parameters settings can be used to optimize the forwarding quality in radio networks for certain transport protocols and applications. This thesis analyses delay spikes experienced by IP traffic in cellular radio networks. We evaluate two different radio-block scheduling mechanisms’ impact on two versions of the Transmission Control Protocol (TCP) (i.e., TCP Sack and TCP Eifel). The evaluation contributes to the third research area by revealing basic dependencies between scheduling, interference, and congestion control mechanisms implemented by TCP. Finally, the thesis contributes to the third research area by proposing extensions to the Internet architecture for inter-layer communication. These extensions allow applications and transport protocols to exchange information with radio link layers. Such information exchange can be used to improve the forwarding quality and to customize data and transport features for current radio conditions.
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| 5. |
- Byström, Johan
(författare)
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Some mathematical and engineering aspects of the homogenization theory
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted to some problems connected to the theory of homogenization of partial differential operators. The thesis consists of an elementary introduction and five different parts, A-E. In the introduction we give an elementary presentation of the basic ideas in the homogenization theory. Moreover, the introduction also serves as an overview of the field and points out where the results contained in this thesis fit in. The first part, Part A, consists of two papers with a complementary appendix and deals some purely theoretical parts of homogenization theory. Part B consists of one paper dealing with bounds of the homogenized operator. The third part, Part C, consists of two papers concerning some computational aspects of homogenization. Part D consists of two papers which show how the theoretical results from the homogenization theory can be practically used in composites engineering. Finally, Part E consists of two papers presented at international conferences, which consider some further mathematical and engineering aspects of the homogenization method.
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| 6. |
- Carlsson, Erik
(författare)
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Sulphide-rich tailings remediated by soil cover : evaluation of cover efficiency and tailings geochemistry, Kristineberg, northern Sweden
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The efficiency of soil cover as a method of remediation of sulphide-rich tailings has been studied at an impoundment at the Kristineberg mine, Northern Sweden. Two variations of soil cover were used in the remediation. The major part of the impoundment was covered with a 1.0 m layer of till where the groundwater table was shallow. In combination with the removal of the water dividing ditches surrounding the impoundment, saturation of the tailings as well as the till cover was achieved. In areas with a deeper groundwater it was not possible to saturate the tailings by means of this method. Instead, a sealing layer consisting of a 0.3 m compacted clayey till, acting as an oxygen diffusion barrier, situated underneath a 1.5 m protective cover was used. Field studies at the impoundment cover pore-water extraction and solid-sample collection at five locations. Solid tailings were subject to sequential extractions in the laboratory. Open groundwater pipes for measuring groundwater levels as well as BAT® groundwater pipes for geochemical sampling of the groundwater were installed over the entire impoundment. At a location in the area with the sealing layer, tension lysimeters were installed in a profile in the vadose zone down to the unoxidised tailings. Nearby, one oxygen diffusion lysimeter and one water infiltration lysimeter were installed below 1.5, 1.0, and 0.3 m of protective till cover, respectively. The sealing layer has been investigated in the laboratory with respect to its susceptibility to the effects of freezing and thawing. The solid samples from the tailings revealed that in some areas, the sulphide oxidation prior to the remediation had been intense. In other areas, with a shallower pre-remediation groundwater table, the oxidation seemed to have ceased upon reaching it. In the area with water- saturated tailings increased pore water concentrations around and below the oxidation zone were visible, due to release of secondarily retained elements. Elements with peaks at this level were As, Cd, Co, Cr, Cu, Mo, Ni, Pb, and Zn. However, compared with pre-remediation data the concentrations are generally lowered, indicating that sulphide oxidation has slowed down. Sequential extraction of the solid tailings samples showed that a large part of the elements below the oxidation front, in the secondary enrichment layer, are relatively mobile and are released within the adsorbed, or the amorphous iron (oxy)hydroxide fractions. This was the case for elements such as Fe, As, Ba, Cd, Co, Cr, Cu, Ni, and Zn. The continuous measurements performed in the groundwater pipes show that elements released by raising the groundwater table are transported out of the impoundment, and that the overall water quality is constantly improving due to the inflow of uncontaminated groundwater from the adjacent hill slope. A model for the water transport has been developed and prediction of the future behaviour of the impoundment is proposed. The tension lysimeter measurements show that infiltrating water and diffusing oxygen cause remobilisation of metals around the oxidation front. However, most of these metals are retained again prior to reaching the groundwater table. The mass flow caused by this mobilisation is very small compared to that of the laterally flowing groundwater. Mobilised elements are Fe, S, Si, Al, Cd, Co, Hg, Mg, Mn, Mo, Ni, Pb, and Zn. The freeze/thaw laboratory experiments stress that the compaction degree is very important for achieving a hydraulic conductivity low enough for the requirements of a sealing layer. If a high enough compaction degree is obtained, the corresponding hydraulic conductivity is very low, approximately 5x10-10 m/s with the clayey till used at the study site. The freeze/thaw experiments also revealed that when properly compacted the clayey till is sensitive to frost penetration, leading to an increase of hydraulic conductivity, up to ~10-8 m/s. Oxygen diffusion measurements indicate that the effective diffusion through the sealing layer is low for all three different protective till-cover thicknesses, and so is the water infiltration. However, during the field measurements, no frost penetration into the sealing layer was monitored.
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| 7. |
- Ecke, Frauke
(författare)
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Effects of landscape patterns on small mammal abundance
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Several studies indicate a long-term decline in the numbers of voles in northern Fennoscandia. Altered land use and forest management practices have been proposed as possible causes of the decline. This doctorial thesis aimed to identify, on different spatial scales, landscape patterns that are important for the abundance of small mammals and that might be related to the decline. General trends and aspects of spatial habitat modelling were reviewed. Trapping data from three large extent monitoring programs were related to habitat factors on different spatial scales. For these analyses, a broad range of statistical and GIS (geographic information system) related methods was applied. On the microscale (trapping station, extent <= 10 m) and mesoscale (transect, length 90 m), structural habitat factors such as coarse and fine woody debris, umbrella vegetation and structural complexity of the forest floor were identified as important factors influencing small mammal abundance. Small mammal densities were related to the percentage landcover of vegetation types on the micro-, meso-, macro- (subarea/landscape, 1 x 1, 2.5 x 2.5 and 2 x 5 km) and regional scale (overall study area, 20 x 20 - 80 x 80 km). The spatial continuity (non- fragmentation) of old-growth pine forest patches on the landscape scale was positively related to the abundance of C. rufocanus, the species that showed the most pronounced long-term decline in numbers. The results of this thesis strongly suggest that altered land use might indeed be involved in the decline in numbers of voles in managed forest areas in northern Fennoscandia. To reveal and test responses of small mammals to changes in landscape patterns in more detail, this work proposes further application of large scale approaches. These approaches, e.g. the GIS-based prediction of the areas with currently high abundance of C. rufocanus can be tested by field sampling of the type applied in this thesis. Such approaches should consider the key aspects identified in the reviews on GIS-based habitat modelling, e.g. reconciling the scale of the population dynamics of small mammals with the scale (resolution and extent) of the input data, the application of different modelling approaches and the performance of sensitivity analysis.
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| 8. |
- Grip, Niklas
(författare)
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Wavelet and gabor frames and bases : approximation, sampling and applications
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted to both theoretical and practical aspects of applied mathematics. It consists of three main parts: Part I consists of an application-oriented introduction to the theory of frames and bases for separable Hilbert spaces, as well as an introduction to the main tools used in the remaining Chapters: Time-frequency analysis, Gabor frames and wavelet frames. Part II contain five publications in the fields of approximation theory, sampling and perturbation stability. One paper and one research report consider different estimates of the error (measured in L^p, Besov or Triebel-Lizorkin norm) when a function is projected on certain so-called shift-invariant spaces. This is closely connected to a certain class of wavelet subspace sampling problems (containing the classical Shannon sampling theorem as a special case), prefiltering of the discrete wavelet transform and a certain perturbation stability theorem called the Kadec 1/4-theorem. These are the topics of the three remaining papers in Part II. Chapter 3 contains estimates of the L^p-norm error in certain projections of a function f onto a shift-invariant space V_j, spanned by translated copies of some given function. In Chapter 4, we propose a method which is well-suited for studying irregular sampling problems in such spaces. The main advantage of our method is that it provides an intuitive understanding and relatively simple proofs of some studied problems. The method builds on a study of an equivalent coefficient mapping, which we also use in Chapter 5. There we propose an improved low-complexity approximation of an often neglected prefilter which is needed when the discrete wavelet transform is used for analysis of real-world (i.e., non-discrete) signals. Chapter 6 consists of further results and remarks. First we prove some new results related to Chapter 3, but now the error estimates are measured in other function space norms. Then we conclude Part II with a collection of remarks on some recent proofs of some perturbation theory theorems, including the Kadec 1/4-theorem, which is equivalent to the classical Shannon sampling problem and a special case of the problems studied in Chapter 4. Part III contains one selected publication from each the two practical applications which I have been working with during my years as Ph.D. student: VDSL signal transmission and bearing condition monitoring. The first paper is one of four papers which were included and defended in my licentiate thesis. They describe the solutions to some important problems during the development of a duplex method (called Zipper) for very high speed digital communication in ordinary unshielded telephone copper wires. This was done together with Telia Research and the Division of Signal processing and the end-product (VDSL modems for up to 52 Mbit/s) is currently under development by the French-Italian company ST Microelectronics (former SGS-Thomson). The paper included here describes a patented method for reducing the interference that the unshielded copper wires experience from high-power narrowband radio transmissions, such as radio amateurs. The last paper, finally, is an overview article about bearing condition monitoring. Here the main problem is to find a method for predicting bearing failures by analysis of vibration measurements from rotating machines. The paper contains the main results of a co-operation with (among others) Nåiden Teknik and three forestry combines. We argue that time-frequency analysis based methods are well suited for this task and compare such methods with different old and new methods, using a large number of (mainly industrial environment) test signals.
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| 9. |
- Holmström, Henning
(författare)
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Geochemical processes in sulphidic mine tailings : field and laboratory studies performed in northern Sweden at the Laver, Stekenjokk and Kristineberg mine-sites
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents geochemical, mineralogical and laboratory studies of unremediated and remediated tailings at two abandoned mine sites; at Laver and Stekenjokk and at one active mine site; the Kristineberg mine. At Laver the Cu released from oxidation is enriched in an enrichment zone just below the oxidation front. Other sulphide bound metals seem to be more evenly spread over a greater volume of tailings and are mainly immobilised as a result of adsorption onto mineral surfaces. Adsorption is also important for Cu, but covellite (CuS) formation is more important, due to transformation of pyrrhotite (Fe1-xS). The groundwater within the impoundment at Laver is affected by the breakdown of sulphides during oxidation. Vertical flow of contaminated water is not the cause of groundwater contamination, since the metals are to a large extent retained in the tailings below the oxidation front. Instead, contamination occurs when the advancing oxidation front pushes the secondary enrichments of metals ahead to meet the groundwater table and the metals are released to the groundwater. The release of metals is caused by desorption due to the low pH in this environment. Areas of the tailings deposit with shallow groundwater table are at present the main sources of metal release. There is a seasonal variation in the composition of groundwater, particularly shallow groundwater, caused by changing levels of the groundwater table. Laboratory studies of the tailings from Laver and Stekenjokk using Humidity Cells tests show that the tailings at Laver are more reactive and have a higher oxidation rate compared with the tailings at Stekenjokk. This is probably due to the large carbonate content at Stekenjokk. The oxidation rate of the Stekenjokk tailings decreases with time, probably due to Fe-oxide-hydroxide coatings on sulphide surfaces. High pH conditions can be maintained and low metal concentrations are measured in the leachate waters. Diffusion of metals from the tailings up into the overlying pond water is occurring at Stekenjokk. Oxygen is available down to depths of 16 to 17 mm in the tailings and minor oxidation seems to occur in the uppermost tailings. Due to the oxygen consumption by decomposing organic material the oxidation rate will decrease in the future. An organic layer and a layer rich in Mn- and Fe-oxide-hydroxides have developed on top of the tailings since the flooding. The layers contain higher element versus Ti ratios compared to the underlying tailings, indicating that these layers, to some extent, control the diffusion of elements from the tailings. The suspended phase in the pond contains high metal concentrations and consists mostly of Fe- and Mn-oxyhydroxides precipitated in the pond and detrital material from the surroundings. Sorption of metals onto Fe- and Mn-oxyhydroxides is occurring. The element concentrations in the pond at Stekenjokk therefore seem to be largely controlled by processes controlling the precipitation and dissolution of Mn- and Fe-oxyhydroxides in both the water column and in the surficial tailings. The flooding works well. Pore water and solid tailings in impoundment 1 at the Kristineberg mine contain high contents of metals. Flush out of elements seems to be occurring at some locations due to inflow of surface- and ground water from the surroundings, since the total molar concentrations are much lower in the upper part of the tailings. The pH is high at most depths in the tailings except in and around the former oxidation zone, where the highest heavy metal concentrations also are generally measured. It seems likely that the aim of remediation has been fulfilled, in that oxidation has ceased. However, desorption and remobilization of metals may occur after remediation due to the raised groundwater table.
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| 10. |
- Jonsson, Håkan
(författare)
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The Euclidean traveling salesman problem with neighborhoods and a connecting fence
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- An important class of problems in robotics deals with the planning of paths. In this thesis, we study this class of problems from an algorithmic point of view by considering cases where we have complete knowledge of the environment and each solution must ensure that a point-sized robot capable of moving continuously and turning arbitrarily accomplishes the following: (1) visits a given set of objects attached to an impenetrable simple polygon in the plane, and (2) travels along a path of minimum length over all the possible paths that visit the objects without crossing the polygon. In its general form, this is The (Euclidean) Traveling Salesman Problem with Neighborhoods and a Connecting Fence. We make several contributions. One is an algorithm that computes a shortest watchman path in a rectilinear polygon in time polynomial in the size of the polygon. Each point in the polygon is visible from some point along the computed path, which is a shortest visiting path for a set of convex polygons, each of which is bounded by a chord in the interior of the polygon. For the special case of computing a shortest watchman route, where the end points of the resulting path must coincide, we give a polynomial-time algorithm for general simple polygons. We also give substantially faster and more practical algorithms for computing provably short approximations, that is watchman paths/routes with lengths guaranteed to be at most a constant times longer than the length of a shortest watchman path/route only. To achieve one of these approximations, we develop a linear-time algorithm for computing a constant factor approximation in the case where the convex polygons are impenetrable. For this problem, which is called the Zookeeper's Problem, we show how an exact solution can be computed in linear time when the number of convex polygons is constant. We also present an application of our results to the computation of both exact and approximate solutions to the problem of computing a shortest visiting route for a set of lines in the plane.
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