| 1. |
- Antonsson, Stefan, 1979-
(författare)
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Strategies for improving kraftliner pulp properties
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A large part of the world paper manufacturing consists of production of corrugated board components, kraftliner and fluting, that are used in many different types of corrugated boxes. Because these boxes are stored and transported, they are often subjected to changes in relative humidity. These changes together with mechanical loads will increase the deformation of the boxes compared to the case where the same loads are applied in a static environment. This enlarged creep due to the changes in relative humidity is called mechano-sorptive or accelerated creep. Mechano-sorptive creep forces producers to use high safety factors when designing boxes, and therefore, this is one of the key properties of kraftliner boards. Different strategies to decrease mechano-sorptive creep, and to simultaneously gain more knowledge about the causes for this phenomenon in paper, are the aim of this work. Derivatised and underivatised black liquor lignins, a by-product produced in pulp mills in large quantities, have been used together with biomimetic methods, to modify the properties of kraftliner pulp. Furthermore, the properties of kraftliner pulp have been compared to other pulps in order to evaluate the influence of fibre morphological factors, such as fibre width and shape factor, on the mechano-sorptive creep. In addition the influence of the chemical composition of the kraftliner pulp has been evaluated both by means of treating a kraftliner pulp with chlorite and xylanase and by producing pulps with different chemical composition. By using lignin and biomimetic methods, to create radical coupling reactions, it has been shown that it is possible to increase the wet strength of kraftliner pulp sheets. This method of treating the pulp showed, however, no significant effects on the mechano-sorptive creep. The addition of an apolar suberin-like lignin derivative, which has been shown to be possible to produce from natural resources, did show a positive effect on mechano-sorptive creep properties, but at the expense of stiffness properties in constant climate. Different pulps were compared with a kraftliner pulp and it was observed that the ratio between tensile stiffness and hygroexpansion can be used to estimate the mechano-sorptive creep properties. The hardwood kraft pulps investigated had lower hygroexpansion, probably due to more slender and straighter fibres, and higher tensile stiffness, probably due to lower lignin content. As the lignin content was varied by different methods in kraft pulps, it was observed that increased lignin content gives an increased hygroexpansion and decreased tensile stiffness as well as an increased mechano-sorptive creep. There were also indications of increased mechano-sorptive creep due to higher xylan content.
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| 2. |
- Farouq, Shiraz, 1980-
(författare)
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Towards large-scale monitoring of operationally diverse thermal energy systems with data-driven techniques
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The core of many typical large-scale industrial infrastructures consists of hundreds or thousands of systems that are similar in their basic design and purpose. For instance, District Heating (DH) utilities rely on a large network of substations to deliver heat to their customers. Similarly, a factory may require a large fleet of specialized robots for manufacturing a certain product. Monitoring these systems is important for maintaining the overall efficiency of industrial operations by detecting various problems due to faults and misconfiguration. However, this can be challenging since a well-understood prior model for each system is rarely available.In most cases, each system in a fleet or network is fitted with a set of sensors to measure its state at different time intervals. Typically, a data-driven model for each system can be used for their monitoring. However, not all factors that can influence the operation of each system in a fleet have an associated sensor. Moreover, sufficient data instances of normal, atypical, and faulty behavior are rarely available to train such a model. These issues can impede the effectiveness of a system-level data-driven model. Alternatively, it can be assumed that since all the systems in a fleet are working on a similar task, they should all behave in a homogeneous manner. Any system that behaves differently from the majority is then considered an outlier. It is referred to as a global or fleet-level model. While the approach is simple, it is less effective in the presence of non-stationary working conditions. Hence, both system-level and fleet-level modeling approaches have their limitations.This thesis investigates system-level and fleet-level models for large-scale monitoring of systems. It proposes to rely on an alternative way, referred to as a reference-group based approach. Herein, the operational monitoring of a target system is delegated to a reference-group, which consists of systems experiencing a comparable operating regime along with the target system. Thus, the definition of a normal, atypical, or faulty operational behavior in a target system is described relative to its reference-group. This definition depends on the choice of the selected anomaly detection model. In this sense, if the target system is not behaving operationally in consort with the systems in its reference-group, then it can be inferred that this is either due to a fault or because of some atypical operation arising at the target system due to its local peculiarities. The application area for these investigations is the large-scale operational monitoring of thermal energy systems: network of DH substations and fleet of heat-pumps.The current findings indicate three advantages of a reference-group based approach. The first is that the reference operational behavior of a target system in the fleet does not need to be predefined. The second is that it provides a basis for what a target system’s operational behavior should have been and what it is. In this respect, each system in the reference-group provides evidence about a particular behavior during a particular period. It can be very useful when the description of a normal, atypical, and faulty operational behavior is not available. The third is that it can detect atypical and faulty operational behavior quickly compared to fleet-level models of anomaly detection.
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| 3. |
- Johansson, Mats J., 1958-
(författare)
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Gas Exchange in the Normal Lung : Experimental studies on the effects of positive end-expiratory pressure and body position
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- BACKGROUND: The principal function of the lung is gas exchange requiring adequate ventilation and perfusion at the level of the alveoli. The efficiency of gas exchange is depending on the distributions of regional ventilation (V) and pulmonary blood flow (Q) and their correlation.AIMS: To validate a high-resolution method to quantify regional V and to investigate the combined effect of positive end-expiratory pressure (PEEP) and body position on distributions of regional V and Q in the normal lung with mechanical ventilation. To assess the matching of V and Q by calculating ventilation-perfusion ratio (V/Q) heterogeneity, determining the spatial distribution of V/Q and to investigate the role of nitric oxide (NO) in regional V/Q matching.METHODS: Anesthetized mechanically ventilated sheep were studied in prone or supine position with different levels of PEEP (0, 10 and 20 cmH2O). Measurements of regional V were done by determining the deposition of a wet aerosol of fluorescent microspheres (FMS) with a median mass aerodynamic diameter of 1.1 μm, and validated against Technegas. Radioactive microspheres, 15 μm in diameter, were used for determining regional Q. Nitric oxide synthase (NOS) was inhibited with Nω-nitro-L-arginine methyl ester (L-NAME) to evaluate the role of NO on regional V/Q matching. The right lung was dried at total lung capacity and diced in approx. 1000 regions tracking the spatial location of each region.RESULTS: The deposition of FMS mirrored regional deposition of Technegas and thus regional ventilation well. In prone, with PEEP, only a small dorsal redistribution of V but not of Q was observed. The vertical Q gradient was abolished with PEEP in prone position in conflict with the classical zonal model. In supine position both V and Q were distributed with a unimodal gradient and PEEP displaced the mode further dorsally. V/Q heterogeneity was greater in supine than in prone position with and without PEEP. Furthermore, PEEP generated regions with high V/Q in supine but not in prone position. Inhibition of NOS did not change the V/Q distribution in prone position.CONCLUSION: There were marked differences in redistribution of regional ventilation and regional pulmonary blood flow between prone and supine position when PEEP was applied. NO was not an active mechanism for V/Q matching in normal sheep lungs.
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| 4. |
- Mohammadi, Mohammad
(författare)
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Risk Management in Tunneling Projects : Estimation and Planning
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cost overruns and schedule delays are frequently observed occurrences in the construction of transport infrastructure projects. Such phenomena lead to the mismanagement of significant amounts of both public and private resources.An examination of the literature reveals that uncertainty stands out as one of the potential primary causes of cost overruns and schedule delays. To address the impact of uncertainty on time and cost estimations in transport infrastructure projects, probabilistic approaches can be employed. In this doctoral thesis, first a conceptual risk model has been formulated specifically for the purpose of enhancing time and cost estimations in tunneling projects. This risk model serves as a tool to scrutinize and contrast existing probabilistic time and cost estimation models for tunnel projects, aiming to identify potential areas for improvement. Furthermore, the conceptual model is utilized to delve into the factors influencing the accuracy of subjective assessments regarding the input parameters in time estimation models. It also explores methods for incorporating the role of tunneling phases into the subjective assessment of these input parameters.Then, enhancements and updates are introduced to the existingKTH model for time and cost estimation in tunneling projects. This model primarily targets three main sources of uncertainty: variability in construction performance, geological uncertainties, and the potential incidence of disruptive events. The analysis and improvements related to modelling of construction performance involve three sequential steps. In the first step, the construction process is modeled using the work breakdown structure (WBS), enabling a more realistic assessment of tunneling time. Subsequently, in the second step, PERT distributions are employed to model the uncertainty in the duration of unit activities, compared to the commonly used triangular distributions. The third step involves a detailed examination of a real tunnelling project's data to identify components contributing to construction performance variability for unit activities. This analysis pinpoints three main components: typical performance variability, minor performance delays, and minor machinery delays. These components are integrated into the KTH model, resulting in its further update concerning construction performance variability. A novel approach is introduced into the KTH model by leveraging the Metropolis-Hastings (MH) algorithm within the framework of Markov Chain Monte Carlo (MCMC) simulation to address geological uncertainties along the tunnel route. This method facilitates round-by-round simulation of the tunneling process and allows the model to accommodate uncertainty in the critical path for tunneling projects involving multiple headings. These enhancements aim to improve decision-making processes and mitigate risks associated with schedule delays and cost overruns. Additionally, the magnitude of disruptive events are now modeled as stochastic variables, an improvement on the original version of the KTH model.
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| 5. |
- Grigoriev, Igor, 1984-
(författare)
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Turbulence modeling of compressible flows with large density variation
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this study we highlight the influence of mean dilatation and mean density gradient on the Reynolds stress modeling of compressible, heat-releasing and supercritical turbulent flows.Firstly, the modeling of the rapid pressure-strain correlation has been extended to self-consistently account for the influence of mean dilatation.Secondly, an algebraic model for the turbulent density flux has been developed and coupled to the tensor equationfor Reynolds stress anisotropy via a 'local mean acceleration',a generalization of the buoyancy force.We applied the resulting differential Reynolds stress model (DRSM) and the corresponding explicit algebraic Reynolds stress model (EARSM) to homogeneously sheared and compressed or expanded two-dimensional mean flows. Both formulations have shown that our model preserves the realizability of the turbulence, meaning that the Reynolds stresses do not attain unphysical values, unlike earlier approaches. Comparison with rapid distortion theory (RDT) demonstrated that the DRSM captures the essentials of the transient behaviour of the diagonal anisotropies and gives good predictions of the turbulence kinetic energy.A general three-dimensional solution to the coupled EARSM has been formulated. In the case of turbulent flow in de Laval nozzle we investigated the influence of compressibility effects and demonstrated that the different calibrations lead to different turbulence regimes but with retained realizability. We calibrated our EARSM against a DNS of combustion in a wall-jet flow. Correct predictions of turbulent density fluxes have been achieved and essential features of the anisotropy behaviour have been captured.The proposed calibration keeps the model free of singularities for the cases studied. In addition, we have applied the EARSM to the investigation of supercritical carbon dioxide flow in an annulus. The model correctly captured mean enthalpy, temperature and density as well as the turbulence shear stress. Hence, we consider the model as a useful tool for the analysis of a wide range of compressible flows with large density variation.
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| 6. |
- Hegazy, Eman, 1978-
(författare)
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Sustainable Management of Wire-based Infrastructure : On the Multifaceted Challenges of Infrastructure Management in the Swedish Context
- 2024
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cities, as key players in global sustainable development, are linked to challenges and opportunities driven by urbanization's resource consumption and environmental impacts. This context highlights the critical role of urban infrastructure in fostering sustainability, particularly the role of wire-based infrastructure systems (WBIS). The management, maintenance, and renewal of WBIS are vital to ensuring their long-term efficiency, yet they present challenges across technical, environmental, and societal dimensions. The positioning of these systems beneath urban streets introduces complexities, from accelerated wear to costly excavations, with a wide range of environmental consequences. Beyond the physical implications, the financial, policy, and management practices governing WBIS also contribute to their sustainable development challenges. This study, centered on Linköping's water network in Sweden as a case study, aims to unravel these multifaceted dynamics and answer key research questions regarding the management, challenges, influencing factors, and strategies for improving the maintenance and renewal of urban WBIS. Based on a mixed method approach, the case study utilized both qualitative and quantitative methods, including interviews, workshops, and data analysis. The results highlighted Linköping's UWI challenges, encompassing aging infrastructure, limited renewal rates, and financial constraints. To navigate these challenges, the discussion advocated for a shift towards proactive renewal strategies. The conclusions emphasized the need for an increased funding, strategic planning, proactive coordination among diverse stakeholders, and a balanced approach in budgetary allocations, particularly in considering maintenance and renewal alongside other activities, as crucial for ensuring the longevity and sustainability of the WBIS.
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| 7. |
- Höglund, Linda, 1974-
(författare)
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Growth and characterisation of InGaAs-based quantum dots-in-a-well infrared photodetectors
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents results from the development of quantum dot (QD) based infrared photodetectors (IPs). The studies include epitaxial growth of QDs, investigations of the structural, optical and electronic properties of QD-based material as well as characterisation of the resulting components.Metal-organic vapour phase epitaxy is used for growth of self-assembled indium arsenide (InAs) QDs on gallium arsenide (GaAs) substrates. Through characterisation by atomic force microscopy, the correlation between size distribution and density of quantum dots and different growth parameters, such as temperature, InAs deposition time and V/III-ratio (ratio between group V and group III species) is achieved. The V/III-ratio is identified as the most important parameter in finding the right growth conditions for QDs. A route towards optimisation of the dot size distribution through successive variations of the growth parameters is presented.The QD layers are inserted in In0.15Ga0.85As/GaAs quantum wells (QWs), forming so-called dots-in-a-well (DWELL) structures. These structures are used to fabricate IPs, primarily for detection in the long wavelength infrared region (LWIR, 8-14 μm).The electron energy level schemes of the DWELL structures are revealed by a combination of different experimental techniques. From Fourier transform photoluminescence (FTPL) and FTPL excitation (FTPLE) measurements the energy level schemes of the DWELL structures are deduced. Additional information on the energy level schemes is obtained from tunneling capacitance measurements and the polarization dependence studies of the interband transitions. From tunneling capacitance measurements, the QD electron energy level separation is confirmed to be 40-50 meV and from the polarization dependence measurements, the heavy hole character of the upper hole states are revealed.Further characterisation of the IPs, by interband and intersubband photocurrent measurements as well as dark current measurements, is performed. By comparing the deduced energy level scheme of the DWELL structure and the results of the intersubband photocurrent measurements, the origin of the photocurrent is determined. The main intersubband transition contributing to the photocurrent is identified as the QD ground state to a QW excited state transition. Optical pumping is employed to gain information on the origin of an additional photocurrent peak observed only at temperatures below 60 K. By pumping resonantly with transitions associated with certain quantum dot energy levels, this photocurrent peak is identified as an intersubband transition emanating from the quantum dot excited state. Furthermore, the detector response is increased by a factor of 10, when using simultaneous optical pumping into the quantum dots states, due to the increasing electron population created by the pumping. In this way, the potentially achievable responsivity of the detector is predicted to be 250 mA/W.Significant variations of photocurrent and dark currents are observed, when bias and temperature are used as variable parameters. The strong bias and temperature dependence of the photocurrent is attributed to the escape route from the final state in the QW, which is limited by tunneling through the triangular barrier. Also the significant bias and temperature dependence of the dark current could be explained in terms of the strong variation of the escape probability from different energy states in the DWELL structure, as revealed by interband photocurrent measurements. These results are important for the future optimisation of the DWELL IP.Tuning of the detection wavelength within the LWIR region is achieved by means of a varying bias across the DWELL structure. By positioning the InAs quantum dot layer asymmetrically in a 8 nm wide In0.15Ga0.85As/GaAs quantum well, a step-wise shift in the detection wavelength from 8.4 to 10.3 μm could be achieved by varying the magnitude and polarity of the applied bias. These tuning properties could be essential for applications such as odulators and dual-colour infrared detection.
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| 8. |
- Johansson, Stefan, 1963-
(författare)
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Design for Participation and Inclusion will Follow : Disabled People and the Digital Society
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Digitalization is rapidly taking over all aspects of society, but still there are parts of the population who have to struggle for access to, and to be able to use, the digital resources. Design processes and outcomes in the form of artefacts, that takes accessibility into account, is key to participation. This gives the designer a central role in providing for a more equal participation of all, in the digital society. The work in this thesis contributes to a better understanding of the prerequisites for participation in the digital society, and in the design processes to accomplish this, by presenting research done together with three communities: people with cognitive impairments, people with mental health issues and homeless people.The overall question has been How can participation in the digital society be understood? We have investigated the nature of difficulties or enabling factors for people with impairments, people with mental health issues and homeless people, when using the internet. We have also investigated possible digital divides within the groups, and how they can be explained.Ontologically, the work is based on an assumption that knowledge is to be found in a dialectic interplay between the material world and how we interpret what is going on in this world. The underlying epistemological assumption is that data has to be empiric, and critically interpreted in dialogue between members of the communities, which are being researched, and other stakeholders. This work draws on the idea of emancipation and that research can be liberating.The work also takes on a pragmatic stance. We have used adapted versions of Emancipatory Participatory Research, and of Participatory and Value Sensitive Design, thus making them accessible to people with cognitive impairments, people with mental health issues or homeless people. We have tested and adapted methods for sampling of rare populations, to enhance the quality of quantitative studies of how people with impairments and people with mental health issues have access to, and are using, the internet.In our research, we have found fourteen prerequisites, all of which need to be in place to provide for participation. To promote participation, we need a toolbox of methods and accessible tools. Finally, to analyse what is going on we need an analytical model which allows for analysis on multiple levels and from multiple perspectives.As a result, I here propose, define and position a framework for researching and understanding participation in the digital society, based on three parts: Guidelines, Ethics and Statistics. Guidelines can be understood as the theories, the regulations, the standards, etc. that inform our thinking. Ethics guide us in the right direction. Statistics make progress or lack of progress visible.The conclusion is: if we plan for participation - by improved statistic survey sampling methods, a participatory approach to collaborative research and in using research methods in an accessible and emancipatory way – inclusion will follow.
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| 9. |
- Johansson, Stefan, 1963-
(författare)
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Towards a framework to understand mental and cognitive accessibility in a digital context
- 2016
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This digitalization has in many ways contributed to greater inclusion but access to the digital community is not evenly distributed in the population, and we can see that groups of citizens do not feel involved in the transition to a digitalized society, or are not involved as much as they would actually like.The purpose of this thesis is to discuss how designers and developers to a greater extent can be able to take account of accessibility requirements for people with mental and cognitive impairments. The discussion is based on the study “Pilot study on accessibility of electronic communications for persons with mental disabilities”, literature reviews and my experience from almost 25 years of work in the field.The design and development processes I primarily want to highlight are those that produce digital products and services in what we call the mainstream. Mainstream is the society in which we act as citizens have rights and duties, and where we should be able to realize our dreams, wishes and needs, where we find friends, family, education, livelihood and meaningfulness in the activities and the tasks we perform.The persons who participated in the study describe situations where:Design and development processes often fail to meet the need for cognitive simplicity.Many in themselves relatively simple functions, processes and activities can, used together create new and unknown difficulties.Support processes malfunction.Knowledge of user requirements is missing or does not reach out to the people and the processes where this knowledge would be useful.The people also describes that they are never involved in the design- and development processes, and that the knowledge and experience they possess is not being utilized.There is a need for a transfer of knowledge from the areas that produce knowledge today (rehabilitation, assistive technology, special solutions) to the mainstream. There is a need to explore and describe the knowledge and experience persons with mental and cognitive disabilities possesses. There is a need to work closely with persons who have mental and cognitive disabilities directly in mainstream-solutions in order to improve the digital society. Methods seem to be further developed on how to do this cooperation, in research, in innovation and in ordinary societal processes.The thesis presents a proposed framework for the design and development processes to be able to meet accessibility requirements for persons with mental and cognitive disabilities.
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| 10. |
- Krounis, Alexandra
(författare)
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Sliding stability re-assessment of concrete dams with bonded concrete-rock interfaces
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The shear strength of the concrete-rock interface is an important parameter in sliding stability analyses of concrete dams founded on rock and depends, in addition to the normal stress state, on the bonding conditions of the interface; concrete-rock interfaces can be either unbonded, partially bonded or fully bonded.In the Swedish guidelines for dam safety all dam-foundation contacts are treated as unbonded. This has the benefit of eliminating all uncertainties related to the cohesive strength of bonded contacts but it might also lead to unnecessary strengthening of dams. Other national guidelines deal with the uncertainties related to cohesion by applying higher safety factors, mainly determined based on previous experience, when both cohesion and friction are taken into account.The main objective of this project is to study if and how cohesion can be included when evaluating the shear strength of bonded or partially bonded interfaces. To accomplish this, uncertainties associated with cohesion are identified and their influence on the assessed stability is investigated.The results show that the influence on the assessed sliding stability is strongly dependent on the magnitude of the involved uncertainties that might vary significantly for different dams. It is thus questionable if one safety factor applicable for all dams can be established for use in deterministic analyses.Taking into account cohesion when reliability methods are used is somewhat less complicated because of the possibility of directly incorporating the uncertainties in the analysis. The main challenge in such cases is the quantification of the involved uncertainties due to lack of proper data and, in some cases, knowledge. In this thesis, a framework for quantification of parameter uncertainty is suggested and the model error due to brittle failure in combination with spatial variation in cohesion is analysed. Areas that require more research to further refine the analysis are also identified.
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