| 71. |
- Albing, Malin
(författare)
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Contributions to process capability indices and plots
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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.
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| 72. |
- Alerby, Eva
(författare)
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Att fånga en tanke : en fenomenologisk studie av barns och ungdomars tänkande kring miljö
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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.
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| 73. |
- Alhalaweh, Amjad
(författare)
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Pharmaceutical cocrystals : formation mechanisms, solubility behaviour and solid-state properties
- 2012
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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.
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| 74. |
- Alhashimi, Anas, 1978-
(författare)
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Statistical Sensor Calibration Algorithms
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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).
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| 75. |
- AlHayali, Amani
(författare)
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In vitro-solubility and supersaturation behavior of supersaturating drug delivery systems
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 76. |
- Ali, Ammar
(författare)
-
Three Dimensional Hydro-Morphological Modeling of Tigris River
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The River Tigris is a major river in Iraq. It divides Baghdad, the capital of Iraq, in two parts. The reach of the river within Baghdad is about 60 km long. The climate change within the region and the construction of hydraulic structures upstream of Baghdad has reduced the water discharge of the river by 44%. Despite the fact that huge volumes of sediment have been trapped in the constructed headwater reservoirs, substantial changes have occurred in the topography of the Tigris River within Baghdad City and the number of depositions is increasing. The debris of the destroyed bridges from the wars of 1991 and 2003 and their subsequent reconstruction have contributed to the development of these depositions. As a consequence, the ability of the river to carry the peak flood waters has been reduced. This has led to a potential increase of flooding in parts of the city. To predict the maximum flood capacity for the river, the bathymetric survey that was conducted for 50 km of the Tigris River by the Ministry of Water Resources in 2008 has been used with the one-dimensional flow model “HEC-RAS”. Calibration of the model was carried out using field measurements for water levels along the last 15 km of the reach, and the water level observations at the Sarai Baghdad gauging station for the last 10 years were used to validate the model. The model showed a significant reduction in the river’s capacity compared with what the river had carried during the floods of 1971 and 1988. This result agrees with previous surveys conducted on the same reach indicating that the ability of the river to convey high water has decreased. To overcome this problem, dredging operations started along most of the Tigris River inside Baghdad City to remove many islands and side bars, as well as cleaning water intakes. An examination for the dredging plan currently in progress and two additional proposed plans was conducted using the ‘HEC-RAS’ model for the 50 km long river reach to investigate whether the designed flooding capacity of the river can be recovered and how much it can be improved. Comparing the historical records of water level and discharge for the last three decades, some improvement of flood capacity was achieved. Cautions about the water intakes should be considered to maintain their functionalities with the expected drop in water levels due to dredging operations. Bathymetric and land surveys were conducted for the northern Tigris River reach (18 km length) in Baghdad, producing 180 cross sections. A riverbed topography map was established from these cross sections. Sediment transport rates and bed composition were investigated by collecting three different types of sediment samples at the quartiles of 16 cross sections along this reach. The Helley-Smith sampler was used to collect 288 bedload samples, a suction pump was used to collect 212 suspended load samples from different depths. The Van Veen grab was used to collect 46 bed material samples. The velocity profiles and the water discharges were measured using ADCP at the sampling sections. Bed sediment compositions were investigated by analysing the collected bed material samples. It was noticed that fine sand dominated the riverbed (90.74%). The average median size within the reach was 2.49 phi (0.177mm) whilst the mean size was 2.58 phi (0.16mm). In addition, the sediments were moderately sorted, fine skewed and leptokurtic. The size of the bed sediment relatively decreased compared to older investigations due to the decrease of the competence of the river. The bed elevation had increased compared to previous surveys. It was noticed that dredging operations and obstacles (e.g. fallen bridges and islands) disturbed the flow of the river and the sediment characteristics in several sites. Bedload rates were computed using the weights of the collected bedload samples. The spatial distribution of sampling cross sections took into consideration the variance of river topography where 7 meanders, 2 islands and several bank depositions characterize the geometry of the river reach. Twenty bedload predictors were applied to the same reach. The annual transported quantities of the bedload were estimated to be 36 and 50 thousand tons in 2009 and 2013 respectively. The total load discharge rate in the northern reach of the Tigris River was computed using the sediment concentrations of the collected suspended load samples after adding the bedload rate at each of the sampling cross sections. The results indicated that the suspended load is the dominant mode in the total load with a minimum percentage of 93.5%. The total load ranged from 29.1 to 190.3 kg/s. A total load rating curve of the power function was established. The associated errors from using the proposed rating curve are within reassuring levels and less than the errors produced from most of the other twenty-two total load formulas, which were applied to the same reach. The scattering of the results from the other formulas can be attributed to the spatial variance in the topography of the riverbed. According to the final results obtained, it is recommended to use the proposed procedure for establishing a spatial total load rating curve to estimate sediment rates for morphologically complicated rivers. The annual transported quantities of the total load were estimated at 2.47 and 4.23 million tons for 2009 and 2013 respectively. The three-dimensional morphodynamic model (Simulation of Sediment movements In water Intakes with Multiblock option - SSIIM) was used to simulate the velocity field and the water surface profile along the northern reach of the Tigris River using the findings of the current bathymetric survey of the river. The model was calibrated for the water levels, the velocity profiles and the sediment concentration profiles using different combinations of parameters and algorithms, those available in the model. The set of parameters that gave a minimum root mean square error (RMSE) was used for the validation process using another set of field measurements. The calibration and the validation results showed good agreement with field measurements, and the model was used to predict the future changes in river hydro-morphology for a period of 14 months. The results of the future predictions showed increases in depositions on the shallow part of the cross section having lower velocity and, on the other hand, the river deepens the incised route to fit its current hydrologic condition leaving the former wide section as a floodplain for the newer river. The net deposition/erosion rate was 67.44 kg/s in average and the total deposition quantity was 2.12 million tons annually. The locations of depositions are compatible with those of the river in the real world. An expansion in the size of current islands was predicted. An indication of the potential threats of the river banks’ collapse and the bridge piers’ instability was given by high erosion along the thalweg line.Keywords: Flood capacity, Dredging, HEC-RAS, Bathymetric survey, Bed sediment, Bedload, Total load, Helley-Smith sampler, Sediment transport, ADCP, Prediction formulas, 3-D morphodynamic model, Bed changes, SSIIM, underfit river, regulated river, Tigris River, Baghdad.
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| 77. |
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| 78. |
- Alizadeh, Morteza, 1987-
(författare)
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Architectural Aspects of Identification in Decentralized Systems
- 2024
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High-level systems need identification techniques, where higher security and scalability are considered requirements. Identification plays a significant role in systems where smart electronic devices increase in zero trust and open environments like decentralized systems. Also, decentralization has emerged as one of the most exciting domains in recent years, again after the first Internet was invented. Besides, decentralization in identification systems has gained popularity worldwide since cryptocurrencies became part of businesses. Distributed Ledger Technology (DLT) and Distributed Hash Tables (DHT) can be appropriate decentralized solutions that improve identification to be much more secure, scalable, and trustworthy.The decentralized nature of DLT and DHT ensures no single point of failure, making them highly resilient to attacks. Blockchain as a DLT solution can help devices communicate with each other securely and trustably by storing an immutable history of transactions, providing an additional layer of security to identification systems. DHT senable applications to keep files and information immutable in a decentralized manner. DHTs ensure that the data is replicated across multiple nodes, making it highly resilient to data loss. Moreover, mitigating high storage costs without memory limitations is the target of these technologies. In this context, a decentralized system paradigm that combines systems with DLT and DHTs can be highly beneficial.This thesis argues for such a paradigm, and the contributions include introducing the term decentralized networks and architectures and demonstrating the feasibility of using blockchain as a DLT solution in real-world scenarios. These scenarios can be applied to the Internet of Things (IoT) or other Peer to Peer networked systems. We explore different architectures in various systems and analyze the interaction in blockchain. This thesis contributes to developing decentralized identification systems that provide users’ trust in an open environment. It presents the challenges associated with decentralized identification, including registry and storage issues, and proposes solutions using DLT and DHT. The immutability of DLT and DHTs provides fast and secure solutions for decentralized identification systems. In particular, we show that a DHT-based architecture is feasible to maintain decentralization while avoiding memory constraints. However, there is still room for improvement in terms of performance. Our investigation shows that combining DHTs with blockchain in decentralized identifiers improves performance.By concealing blocks in the private blockchain, we show that query performance is better than other DHT and public blockchain-based solutions without concealed information. Moreover, our results show that DHT performs better than the public blockchain for scenarios with many records.These findings highlight the importance of selecting the appropriate technology for decentralized identification systems, considering the specific use case and the number of records to be stored.We also consider different decentralized identification systems and platforms built based on the recommendation of W3C Decentralized Identifiers (DIDs). We found low-efficiency issues using this technology, resulting from leveraging public DLT in the data registry part of DIDs. That model has searching time problems if the DLT grows. Finally, this thesis helps to analyze these issues and find better solutions. By choosing the right technology, we can ensure that decentralized identifiers are efficient, secure, and scalable, which enables users to trust them in an open environment.
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| 79. |
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| 80. |
- Alkebro, Jesper
(författare)
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Multiphase oxide ceramics in the alumina-yttria system
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As a means of creating dispersed multiphase oxide structures, high-energy milling has been used for pre-treating alumina-yttria powder mixtures before pressing and sintering. Processing was performed in a planetary ball mill with steel or alumina milling tools and measured effects of the treatment have served as data for a modeling study. Subsequent phase development and sintering during heat treatment of the milled powders have been examined. Two compositions likely to result in a minority phase dispersed in another phase in equilibrium were selected and subjected to the milling treatment. The two constituent powders were homogenously mixed and defects were injected into the crystal structures which were gradually destroyed. Subsequently, depending on milling parameters, there was either amorphization of the sample or formation of yttrium aluminum perovskite, an intermediate phase of the alumina-yttria system. Alumina milling tools exhibited a higher milling efficiency, but they were prone to chipping which lead to massive contamination. Steel milling tools were worn in a more controlled manner and the total amount of contamination was much lower. In heat treatment milled powders easily attained phase equilibrium and there was no metastable behavior noted. Transformation temperatures fell as a function of milling time but for longer milling times the effects of prolonged processing decreased. Sintering properties were also improved resulting in higher final density and lower sintering temperatures. Iron contamination from steel milling tools was suspected to be detrimental for the final solidification and to cause large porosity, but when oxidized the effect is inversed leading to very good densification in argon atmosphere. Relative densities as high as 96% were measured after sintering 1 h in 1500°C, but the process was sensitive to the environment resulting in poor sintering for oxidizing (air) or reducing (argon in graphite furnace) atmospheres. A dispersion of a second phase in the dominant matrix phase was observed but further improvement of the process should be needed to make it finer. The grain size could be estimated to be around 5 µm from fracture surface images.
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