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61.
  • Al-Taie, Laith (författare)
  • Performance of Clay Liners in Near-Surface Repositories in Desert Climate
  • 2014
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Wars in Iraq (1991 and 2003) generated various types of hazardous waste (HW) in the form of soil contaminated by depleted uranium (DU). Other HW emanated from destroyed army vehicles and remnants of Iraqi nuclear facilities holding various types and amounts of chemical and radioactive material. The negative impact of the various wastes on the health conditions of the population was reported from different parts of Iraq, showing an enhanced frequency of cancer and abnormally born infants. For isolating the wastes, which represent low-level and short-lived intermediate level radioactive wastes, near-surface repositories (NSR) are proposed since they represent the least expensive way of solving future problems with sufficient safety. Internationally, the timeframe of the containment of such wastes is designated to be 300 years. Site selection affects and largely controls the selection of a suitable design the aim being to minimize or eliminate migration of hazardous elements from the waste to the environment. The formulation of siting criteria is the first vital step toward the resolution of the problem. Site selection criteria are proposed taking in account three major factors: environmental, geological and socio-economic factors. Accordingly, Iraqi deserts, which make up 60% of Iraq, represent the number one candidate for locating a safe disposal facility, primarily because of the low population, suitable topography, climatic conditions, seismic stability and availability of raw materials. Long-term performance of NSR is directly related to the function of top and bottom liner systems. They should be designed so that they are mutually compatible and combine to effectively isolate the waste. Liners are considered as the main elements of any disposal facility on the ground surface and a properly designed top liner system is of particular importance since it will minimize or eliminate water percolation into the waste body. Compacted clay liners (CCL) should preferably have with a low hydraulic conductivity, which is achievable by proper selection of raw materials, compaction density and construction methods. A further criterion is that they must not soften significantly by expansion on wetting, which puts a limit to the smectite content and density. The liners can consist of native material found near the landfill site, and be used after simple processing, primarily drying and crushing, or be mixed with fillers like silty sand. Since the hydraulic conductivity is the key property of a reliable CCL, relevant experimental determination of the hydraulic conductivity is vital. The common practice in geotechnical laboratories is to apply high hydraulic gradients for getting results quickly but this can lead to non-conservative, incorrect results. The present study involved determination of the hydraulic conductivity of a smectite-rich clay sampled at places within reasonable distance from potential NSR sites. Various hydraulic gradients were applied to samples compacted to several different densities, using two permeants and two filter types. It was concluded that the outflow filter can significantly affect the evaluated conductivity especially when applying high hydraulic gradients. This was partly explained by clogging of outflow filters of conventional fine-porous type by torn-off clay particles at such gradients. A major conclusion was that the gradient in laboratory testing should not exceed 100 m/m.In order to assess the suitability of available raw materials within the Iraqi Deserts, two smectitic soils termed as Green and Red clays were investigated for potential use in CCLs. Both clays are fairly rich in smectite, which calls for mixing them with properly graded silt/sand material from the desert for modifying the expandability. The shear strength, swelling pressure, hydraulic conductivity and creep properties were determined and used for defining criteria for selecting suitable clay-sand ratios. The results showed that 30-50% Green clay mixed with sand and 40-60% Red clay mixed with sand were suitable for constructing top liners with a hydraulic conductivity of 1×10-9 - 1×10-10 m/s. For bottom liners, 70% Green clay mixed with sand and 80% Red clay mixed with sand would be suitable; they were found to have a hydraulic conductivity of 1×10-11 m/s.The long-term performance of CCL is controlled by a number of processes like long periods of extreme dryness and short periods of very heavy rain. The percolation of water through the top liner system of a number of design alternatives were simulated using the code HELP 3.95D and subsequently by the FE program VADOSE/W. For the assumed NSR concept the slope stability of the top liner is essential and it was determined by using FE technique considering various slope angles. The engineering properties, primarily the hydraulic conductivity, swelling pressure and shear strength of 30-50% Green clay mixed with sand were introduced in the simulations. Two initial water contents of the compacted materials were considered representing 1) optimum water content (“wet case”), and 2) air‐dry conditions (“dry case”). Application of the HELP code decided the selection of suitable CCL having a thickness of 0.5 m and inclined by 5.7ᵒ. More detailed analyses with VADOSE/W showed that a mixture at the dry case would bring 0.5 mm (0.5 litre of leaking water per square meter) through CCL in an eight year simulation period. Long-term simulations (up to 300 years) showed that CCL would undergo continuous drying without reaching saturation even in the case of periods of very heavy rain (616 mm) for the wet and dry cases. The slope stability factor for the rather steep angle 30ᵒ was found to be 1.5 for the most critical case representing complete water saturation. In conclusion, the proposed materials and design features are believed to be suitable for practical application.
62.
  • Alakangas, Lena (författare)
  • Sulphide oxidation, oxygen diffusion and metal mobility in sulphide-bearing mine tailings in Northern Sweden
  • 2006
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Large quantities of sulphide-bearing mining wastes produced from ore processing are deposited throughout the world. Sulphide oxidation in the wastes may release acidic water with high concentrations of metals to the environment. Remediation strategies are usually site specific, since the physical and chemical properties of the wastes vary. Therefore, sulphide oxidation, oxygen diffusion and metal mobility in unoxidised and oxidised, remediated and unremediated wastes have been studied in the present work. The efficiency of different cover systems on unoxidised tailings from Kristineberg, were studied in pilot-scale test cells (5*5*3 m3)under field conditions. Clayey till, sewage sludge, apatite and Trisoplast were used as sealing layers and unspecified till as a protective cover. In one cell tailings were left uncovered. Unoxidised tailings in the test-cells in the initial stage after deposition showed relatively low sulphur release (600- 800 mg/l)in leachate waters, which probably was an effect of high moisture content in the tailings prior to deposition. Near-neutral pH found in the leachates was an effect of neutralisation by carbonate minerals present and lime (Ca(OH)2) added prior to deposition. Similar sulphur concentrations were found also in the uncovered tailings. The sulphide oxidation rate increased with time in the uncovered tailings, and decreased in the covered. The lowest oxygen concentrations were observed below the cover system with sewage sludge, which was the most effective barriar against oxygen in a short-term perspective. The oxygen fluxes through the clayey till and apatite layers were within the same magnitude and varied between 0.5 and 4 mole/year,m2. The Trisoplast layer seemed to have failed as a barrier against oxygen. Tailings studied at field scale at Laver and Kristineberg had oxidised for more than 50 years. The tailings at Kristineberg have high pyrite content (c.25% and 50%) and those at Laver have low grade of pyrrhotite (2-3%). The Laver tailings are unremediated, while at Kristineberg the tailings were remediated in 1996. The transport of metals in the drainage water at Laver decreased during a study period of 8 years. The transport of dissolved sulphur indicated a declining trend of sulphide oxidation rate in the tailings, which was confirmed by oxygen measurements in the tailings and weathering rate estimations. The decline was considered to be natural as a result of the increased distance that oxygen has to travel to reach unoxidised sulphide grains. The major part of the amounts of metals released by sulphide oxidation were secondarily retained in the tailings, and to a small extent in layers cemented by jarosite and Fe-(oxy)hydroxides. Sequential extraction of these layers showed that metals such as Cu and Pb were mostly associated with crystalline Fe-(oxy)hydroxides. Most important retention mechanism was, however, sorption onto minerals surfaces below the oxidation front. The studied Impoundment 1 at Kristineberg was remediated by two different methods; on one part a dry cover consisting of a sealing layer and a protective cover were applied, and the groundwater table was raised and a single dry cover applied on the other part. When the groundwater table was raised in oxidised tailings, secondarily retained metals such as Fe, Mg, Mn, S and Zn were remobilised resulting in increased concentrations in the groundwater. The concentrations declined with time, due to dilution by inflowing uncontaminated water. Decreased concentrations of Fe, Mg, Mn, S and Zn were observed also in the groundwater below the dry cover as the amount of percolating water decreased. The concentrations of trace elements such as Cd, Co, Cr, Cu, Ni and Pb were almost depleted in the groundwater, since these metals were retained within the tailings by mechanisms such as co-precipitation, precipitation and sorption. Analysis of pyrite grains by LA-ICP-SMS showed that pyrite surfaces were important for retention of As and Cu, in particular, but also for Cd and Zn. This study shows that the physico-chemical conditions expressed by pH and redox potential have a large impact on element mobility’s. For example, As was mobilised as a result of remediation, while the concentrations of most metals decreased in the drainage waters.
63.
  • Alam, Md. Minhaj (författare)
  • Laser welding and cladding the effects of defects on fatigue behaviour
  • 2012
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The thesis focuses on weld defects in laser processed materials (for laser welding, laser hybrid arc welding and laser cladding) and their effect on the fatigue life of components. Component properties were studied with particular emphasis on the macro and micro surface geometry, weld defects and clad defects. The influence of these defects on fatigue life was analyzed by; the nominal and effective notch stress method, fatigue life prediction using Linear Elastic Fracture Mechanics (LEFM), fatigue testing, metallurgical analysis, fractography, elastic and elastic-plastic Finite Element Analysis (FEA). A simplified Computational Fluid Dynamics (CFD) analysis was also carried out to better understand the formation of undercuts during the welding process. The main objective is to gain an understanding of the impact of laser weld and clad defects on the fatigue behaviour of components.In the first two papers, fatigue testing involving the bending of laser hybrid arc welded eccentric fillet joints was carried out. Based on measurements of the weld surface geometry the crack initiation location and the crack propagation path were studied, experimentally and in conjunction with FE stress analysis. The competing criteria of throat depth and stress raising by the weld toe radii and by the surface ripples are explained, showing that the topology of surface ripples can be critical to fatigue behaviour. LEFM analysis was conducted to study the effect of Lack of Fusion (LOF) on fatigue life. Cracking starts and propagates preferentially from the lower toe of the top surface for this eccentric weld, even in cases of LOF. In the third paper two-dimensional linear elastic FEA was carried out for laser welding of a high strength steel beam. The impact of the geometrical aspects of joint design and of the weld root geometry on the fatigue performance was studied. Critical geometrical aspects were classified and then studied by FE-analysis with respect to their impact on the fatigue behaviour. In the fourth paper the melt pool flow behaviour during the laser hybrid arc welding process was analyzed by CFD simulation. The melt velocity behind the keyhole was measured from high speed imaging as a starting value for the simulation. It was found that a high speed flow in the thin topmost layer of the melt transferred its momentum to an underlying flow which is faster than the welding speed and this delays the lifting of the depressed melt.In the fifth and sixth papers FEA of different macro stress fields and of stress raisers produced by defects was studied in laser clad surfaces for four different fatigue load conditions. Defects were categorized into zero-, one- and two-dimensional types. Pores intersecting or just beneath the surface initiated fatigue cracking, accompanied by two circular buckling patterns. For a four-point bending load involving a surface pore on a spherical rod, the critical range of azimuthal angle was identified to be 55º. The performance of as-clad surfaces was found to be governed by the sharpness of surface notches. Planar defects like hot cracks or LOF are most critical if oriented vertically, transverse to the bar axis. A generalized theory was established, showing that the combination of the macro stress field with the defect type, position and orientation, determines whether it is the most critical stress raiser.
64.
  • Alander, Sara (författare)
  • Offentliga storkök i det gröna folkhemmet diffrakterade berättelser om hållbar utveckling
  • 2007
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Det är nu 20 år sedan Brundtlandskommissionens rapport kom ut, och begreppet hållbar utveckling fick sin stora spridning och inter¬nationella uppmärksamhet. Nu, våren 2007, är begreppet inte omdiskuterat på samma sätt som det en gång var, idag är det i stället begrepp som ”klimathotet” som debatteras och får rubriker. Hållbar utveckling har blivit ett bärande begrepp i internationella överenskommelser och det finns också en allt mer akut medvetenhet om att hållbar utveckling fordrar omställningar och förändring av många av de förhållanden och förhållningssätt vi i västvärlden tar för givna. I de dokument som oftast pekas ut som ursprunget till aktualiseringen av hållbar utveckling, Brundtland¬rapporten och Agenda 21, framgår att hållbar utveckling vilar på tre ben; ekologiskt, ekonomiskt och socialt. I avhandlingen fokuseras offentliga sektorns storhushåll som i runda tal serverar 2 600 000 måltider varje dag, knappt 2 100 000 av dessa i grund-, gymnasie- och förskolor (Sundström 2000). Särskilt studeras den måltids¬produktion som sker i samband med skol- och förskoleverksamhet, en verksamhet som de flesta i Sverige i dag på något sätt berörs av. Hållbar måltidsproduktion förutsätter hållbara teknologier och hållbar teknologianvändning och -utveckling, med hänsyn till alla tre dimensionerna av hållbarhet. Hur hållbar utveckling kan relateras till teknologi¬användning inom offentliga sektorns måltidsproduktion har därför undersökts med hjälp av feministisk teknovetenskap. Forskningsfrågorna är: Vilka förutsättningar ger och kräver teknologianvändning i den offentliga sektorns storköks¬verksamhet? Hur rimmar dessa med socio¬kulturell, ekonomisk och ekologisk hållbarhet? För att kunna besvara dessa frågor har avhandlingen ytterligare ett syfte; att, med natur- och teknikvetenskapligt språkbruk experimentera med Donna Haraways figuration "diffraktion" som metodologi och därigenom uppmärksamma den mångfald av kunskaper och röster som är nödvändiga för att skapa hållbarhet som beaktar alla tre aspekterna av hållbar utveckling. I analyserna spelar också "situerade kunskaper" stor roll. Avhandlingens empiri består av deltagande observationer i kommunala storkök, intervjuer med kostchefer samt ledare av projekt för hållbar utveckling i offentliga sektorns måltidsproduktion och dokument. Med hjälp av feministisk teknovetenskap har jag kunnat visa på hur djupt involverad offentliga sektorns måltidsverksamhet är i teknologiska system som både fungerar småskaligt i varje enhet i verksamheten men också hur den är sammanlänkad i de storskaliga infrastrukturella systemen i vårt samhälle. Med feministisk forsknings¬metodologisk ansats har jag också visat på hur hållbar utveck¬ling kan förstås inom offentliga sektorns storköksverksamhet samt vad som kan krävas för att strävan efter hållbar utveckling ska bli lyckosam.I avhandlingsarbetet har jag rört mig mellan en fokusering på teknologiers funktioner och konsekvenser, särskilt med fokus på hållbar utveck¬ling, hanteringen av dem i förändringssammanhang och hur den teknologi¬intensiva måltids¬verk¬samheten i skolor och förskolor har betydelse för arbetet för hållbar utveckling men då inte endast som en följd av att verksamheten direkt blir föremål för resurseffektivisering. I den människotäta verksamhet som offentliga sektorns måltidsproduktion utgör är faktorer som omsorg, hälsa och välbefinnande starkt närvarande. Faktorer som är betydelsefulla för hållbar utveckling med hänsyn till alla dess dimensioner. I begreppet teknovetenskap ligger att kunskapsproduktionen och teknologi¬utvecklingen i dag äger rum i komplexa och utspridda sammanhang där universitet, företag och andra aktörer i samhället, till exempel offentliga sektorn, deltar och påverkar vägvalen, lokalt, nationellt och internationellt. Mot den bakgrunden är det väsentligt att överskrida de gränser som vi ofta drar upp mellan teknologi, vetenskap, politik och samhälle och i stället försöka visa på hur dessa länkas samman i användningen och utvecklingen av teknologi, något som är en nödvändighet för den förändringsaspekt som utmärker feministisk teknovetenskap och som feministiska vetenskapsstudier ofta syftar till. Min fokusering på hur materiella-diskursiva praktiker med en mångfald av apparaturer som teknologier, maskiner, människor, livsmedel, beräknade näringsrekommenda¬tioner etc är djupt involverade i det mer abstrakta som värderingar, skolarbete, inlärningsförmåga, sinnesintryck, förebilder… kan inspirera till ökat engagemang i de senare när förändringar och utveckling av teknologier är på gång. Avhandlingens experimenterade kan beskrivas som samtal mellan policies om hållbar utveckling, offentliga sektorns storkök som praktik, och feministisk teknovetenskap. Dessa samtal ger nya perspektiv som kan ge nya möjligheter i skapandet av hållbar utveckling.
65.
  • Alberg, Henrik (författare)
  • Simulation of welding and heat treatment modelling and validation
  • 2005
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • Many aerospace components with complex geometry are fabricated from smaller parts using joining techniques such as welding. Welding and the heat treatment which usually follows, can result in unwanted deformation and stresses. Expensive materials, tight geometrical tolerances and the need to decrease product and manufacturing development time, cost and associated risks have motivated the development of models and methods for the simulation of manufacturing processes. The work presented concerns methodologies and modelling techniques for the simulation of welding and heat treatment of fabricated aircraft-engine components. The aim of the work was to develop modelling practices to enable the use of finite element analysis for the prediction of deformation, residual stresses and material properties such as microstructure during and after welding and heat treatment. Achieving this aim has required investigation of geometrical discretisation, modelling of boundary conditions and material behaviour for these processes. The case study components were made of a martensitic stainless steel, Greek Ascoloy. Phase evolutions models and models for rate-independent, rate-dependent, and creep were used as the material models in the welding and heat treatment simulations. The work also includes discussion of numerical considerations in material modelling. A toolbox for evaluation of constitutive models and to obtain material parameters for the plasticity models was developed. The heat transfer coefficient is an important parameter for describing energy transfer between the component and a gas. Due to the complexity of the gas flow in the heat treatment furnace during cooling, a method using computational fluid dynamics was developed to obtain an approximate distribution of the heat transfer coefficient. Due to the impact that modelling and simulation predictions can have, the creditability of the computational results are of great concern to engineering designers, managers and other affected by decisions based on these predictions. In this work, a validation methodology for welding and post weld heat treatment models was developed. The model used for welding simulations gives results with the accuracy required for predicting deformation and residual stresses at all stages of the product and manufacturing development process. The heat treatment model predicts deformations and residual stresses resulting from stress relief heat treatment of sufficient accuracy to be used in the concept and preliminary stages of product and manufacturing development. The models and methodology have been implemented, tested and are in use at Volvo Aero.
66.
  • Albing, Malin (författare)
  • Contributions to process capability indices and plots
  • 2008
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • This thesis presents contributions within the field of process capability analysis. Process capability analysis deals with how to assess the capability of processes. Based on process capability analysis one can determine how the process performs relative to its product requirements or specifications. An important part within process capability analysis is the use of process capability indices. This thesis focuses on process capability indices and process capability plots. The thesis consists of six papers and a summary. The summary gives a background to the research area, a short overview of the six papers, and some suggestions for future research. The thesis summary also consists of some new results, not presented in any of the appended papers. In paper I, the frequency and use of process capability analysis, together with statistical process control and design of experiments, within Swedish companies hiring alumni students are investigated. We also investigate what motivates organisations to implement or not implement these statistical methods, and what is needed to increase the use. In papers II-III we generalize the ideas with process capability plots and propose two graphical methods, for deeming a process capable at a given significance level, when the studied quality characteristic is assumed to be normally distributed. In paper II we derive estimated process capability plots for the case when the specification interval is one-sided. In paper III we derive elliptical safety region plots for the process capability index Cpk and its one-sided correspondences. The proposed graphical methods are helpful to determine if it is the variability, the deviation from target, or both that need to be reduced to improve the capability. In papers IV-VI we propose a new class of process capability indices designed for the situation with an upper specification limit, a target value zero, and where the studied quality characteristic has a skewed, zero- bound distribution with a long tail towards large values. The proposed class of indices is simple and possesses properties desirable for process capability indices. The results in papers IV-VI are also valid for the situation with a target value, not equal to zero but equal to a natural lower limit of the quality characteristic. Three estimators of the proposed class of indices are studied and the asymptotic distributions of these estimators are derived. We also consider decision procedures, based on the estimated indices, suitable for deeming the process capability at a given significance level. The new results in the summary combines the ideas from paper II with the results in papers IV-VI and a graphical method for the class of indices proposed in IV-VI are derived.
67.
  • Alerby, Eva (författare)
  • Att fånga en tanke en fenomenologisk studie av barns och ungdomars tänkande kring miljö
  • 1998
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • This thesis attempts to clarify the way in which young people think about our envíronment, based on their experiences as the starting point. The aim is to make the thinking of people available and to interpret the meaning of these thoughts, whose content comprises the environment. The theoretical roots of the study are to be found within the phenomenology of the lifeworld. I also use the phenomenological method as a type of analysis method to use as inspiration when analysing the empirical material. The children and young people who are included in the study are between the ages of 7 and 16. The data collection is based on two partial studies. In one partial study, empirical material is analysed consisting of the production of drawings by 105 children and young people with attached oral comments, and in the other partial study interviews which were conducted with 16 children and young people are analysed. These two studies are partially connected and partially dependent on one another. The drawing study is aimed at developing an understanding of the thinking of the children and young people and also forms the basis for the selection of subjects for the interview study. The interview study for its part is aimed at further deepening the understanding of the thinking process and the interviews took place on two occations with each person. In the drawing analysis four themes of thoughts were crystallised which focus on: the good world, the bad world, the dialectics between the good and bad world, and symbols and actions promoting the environment. In the interview analysis eight themes emerged of thoughts which focus on: pragmatic perspectives, emotional perspectives, future and visionary perspectives, philosophical perspectives, aesthetic perspectives and romantic perspectives. It can be stated that the results which emerged in the form of the thinking of the children and young people on the environment reflect their thinking as having many nuances. If these many-faceted thoughts are to be taken seriously it is necessary in the teaching and learning situation to take into account the thinking of young citizens. Teaching and learning situations should therefore create time and room for conversation and thinking. This is to stimulate the growing power which the experiences of young people have, experiences which are in turn requirements for thinking: thinking which is constituted by beeing-in-the-world.
68.
  • Alhalaweh, Amjad (författare)
  • Pharmaceutical cocrystals formation mechanisms, solubility behaviour and solid-state properties
  • 2012
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The primary aim of pharmaceutical materials engineering is the successful formulation and process development of pharmaceutical products. The diversity of solid forms available offers attractive opportunities for tailoring material properties. In this context, pharmaceutical cocrystals, multicomponent crystalline materials with definite stoichiometries often stabilised by hydrogen bonding, have recently emerged as interesting alternative solid forms with potential for improving the physical and biopharmaceutical properties of a drug substance. There are, however, gaps in our understanding of the screening, scale-up and formulation operations required for effective use of cocrystals in drug product development. The objective of this thesis was to improve fundamental understanding of the formation mechanisms, solution behaviour and solid-state properties of pharmaceutical cocrystals. The solution chemistry and solubility behaviour of a diverse set of cocrystals were studied. It was found that the thermodynamic stability regions of the cocrystals and their components were defined by the phase solubility diagrams. Spray drying was introduced as a new method of preparing cocrystals; the formation mechanisms are illustrated. The cocrystals were more soluble than the respective drugs alone and the solubility-pH profiles were able to be predicted by mathematical models using a eutectic point determination approach. The cocrystal solubility was pH-dependent and could be engineered by the choice of coformers; this is valuable information for designing robust formulations. The solubility advantage of cocrystals was retained by the use of excipients that imparted kinetic and thermodynamic stability. The retention of drug-coformer association in processed cocrystals has been revealed, introducing a novel concept with potential implications for solid dosage form development. The final study demonstrated that the structure of the crystals and the particle engineering processes affected the solidstate and bulk particle properties of the cocrystals.This thesis contributes to the field of pharmaceutical science by advancing our understanding of crystallization processes and formulation development, thus enabling pharmaceutical cocrystals into drug products.
69.
  • Alhashimi, Anas, 1978- (författare)
  • Statistical Sensor Calibration Algorithms
  • 2018
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The use of sensors is ubiquitous in our IT-based society; smartphones, consumer electronics, wearable devices, healthcare systems, industries, and autonomous cars, to name but a few, rely on quantitative measurements for their operations. Measurements require sensors, but sensor readings are corrupted not only by noise but also, in almost all cases, by deviations resulting from the fact that the characteristics of the sensors typically deviate from their ideal characteristics.This thesis presents a set of methodologies to solve the problem of calibrating sensors with statistical estimation algorithms. The methods generally start with an initial statistical sensor modeling phase in which the main objective is to propose meaningful models that are capable of simultaneously explaining recorded evidence and the physical principle for the operation of the sensor. The proposed calibration methods then typically use training datasets to find point estimates of the parameters of these models and to select their structure (particularlyin terms of the model order) using suitable criteria borrowed from the system identification literature. Subsequently, the proposed methods suggest how to process the newly arriving measurements through opportune filtering algorithms that leverage the previously learned models to improve the accuracy and/or precision of the sensor readings.This thesis thus presents a set of statistical sensor models and their corresponding model learning strategies, and it specifically discusses two cases: the first case is when we have a complete training dataset (where “complete” refers to having some ground-truth informationin the training set); the second case is where the training set should be considered incomplete (i.e., not containing information that should be considered ground truth, which implies requiring other sources of information to be used for the calibration process). In doing so, we consider a set of statistical models consisting of both the case where the variance of the measurement error is fixed (i.e., homoskedastic models) and the case where the variance changes with the measured quantity (i.e., heteroskedastic models). We further analyzethe possibility of learning the models using closed-form expressions (for example, when statistically meaningful, Maximum Likelihood (ML) and Weighted Least Squares (WLS) estimation schemes) and the possibility of using numerical techniques such as Expectation Maximization (EM) or Markov chain Monte Carlo (MCMC) methods (when closed-form solutions are not available or problematic from an implementation perspective). We finally discuss the problem formulation using classical (frequentist) and Bayesian frameworks, and we present several field examples where the proposed calibration techniques are applied on sensors typically used in robotics applications (specifically, triangulation Light Detection and Rangings (Lidars) and Time of Flight (ToF) Lidars).
70.
  • AlHayali, Amani (författare)
  • In vitro-solubility and supersaturation behavior of supersaturating drug delivery systems
  • 2018
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The development of new pharmaceutical products has been challenged by the growing number of poorly water-soluble drugs, which often lead to suboptimal bioavailability. Various approaches, such as the use of amor-phous solid dispersions and cocrystals, have been used to improve the solu-bility, and subsequent bioavailability, of these drug molecules. Supersaturat-ing drug delivery systems (SDDSs) have potential for achieving adequate oral drug bioavailability by increasing the drug solubility and creating a su-persaturated state in the gastrointestinal tract. However, there is a need for better understanding of the supersaturation behavior in SDDSs and of the factors affecting supersaturation. The main objective of this thesis was to improve understanding of the supersaturation solubility behavior in SDDSs with a particular focus on rapidly dissolving solid forms (amorphous forms/cocrystals).In the course of the work, a new formulation for ezetimibe using an amorphous solid dispersion was prepared, cocrystals of tadalafil were pre-pared, and oral films of silodosin were formulated for the first time. These new formulations were thoroughly characterized using a number of solid-state and pharmaceutical characterization techniques.The dissolution and supersaturation behavior of the prepared SDDSs were studied. The effects of various factors on the supersaturation and precipita-tion characteristics were investigated. These factors included the preparation method, the temperature of the dissolution medium, the type of dissolution biorelevant medium (gastric/intestinal) used, the permeability of the relevant gastrointestinal membranes, the addition of polymers, and the addition of surfactants. The amorphous solid dispersions, cocrystals and oral films that were prepared represent new drug formulations that provide significantly higher dissolution rates and supersaturated solubility than crystalline drug forms. Solid dispersions prepared by the melting method had better super-saturation properties than those prepared by spray drying. The precipitation kinetics of the solid dispersion were faster at 37 ̊C than at 25 ̊C in bio-relevant media. Implementation of an absorption tool during in vitro evalua-tion of supersaturation levels could improve the prediction accuracy of su-persaturation and precipitation. A better understanding of the effects of ex-cipients on the supersaturation and precipitation behavior of these types of formulation was obtained in this thesis. The improvement in supersaturation solubility obtained by adding polymers and surfactants was not proportional to the amounts of excipient used.This thesis has made notable contributions to the field of pharmaceutical science by advancing our understanding of the supersaturation solubility behavior of the newly prepared SDDSs.
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