| 1371. |
- Stenström, Christer
(författare)
-
Modelling of fracture toughness using peridynamics : A Study of J-integral, essential work and homogenisation
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fracture toughness is one of the most important properties of a material. Being able toaccurately estimate the energy that goes into forming new crack surfaces is essential for the development of new materials, quality assurance, structural monitoring and failure analysis. Fracture toughness parameters are routinely determined by mechanical testing and are often used in numerical tools. Furthermore, fracture toughness is a common property in material specification. Numerical simulation of fracture toughness can reduce the need of mechanical testing and is sometimes the only viable alternative when mechanical testing is not an option, for example in component optimisation and in the assessment of operational structural components. However, complex fracture is a challenge in material modelling, which comes from that a material body is assumed to remain continuous in classical continuum mechanics. Classical continuum mechanics is formulated assuming a continuous body and that spatial derivatives are defined. However, this is not the case at cracks and other dis continuities. Complementing continuum mechanics with supplementary procedures for modelling discontinues can also add further challenges. Besides, the assumption of locality, that each material point only interacts with is immediate neighbouring points, becomes invalid for nanoscale geometries. Thus, fracture cannot easily be modelled. An alternative is therefore of interest. Peridynamics is a nonlocal extension of continuum mechanics with the constitutive model formulated as an integro-differential equation. The advantages of using an integral expression are foremost that long-range forces can be handled and that the theory is valid even in the presence of discontinuities, such as cracks, allowing unguided modelling of fracture. Since damage is introduced to the constitutive model of peridynamics, there is no requirement of supplementary procedures that can add further complications. Due to its nonlocal formulation, the method is also capable of capturing nano-effects. However, the use and reporting of fracture toughness parameters in peridynamics is a routine in its infancy as the method is under development.In this thesis, two fracture toughness methods, the classical J-integral and the essential work of fracture (EWF), are studied with peridynamics. Also, as the nonlocality of peri dynamics give rise to certain boundary effects, e.g. on crack faces, homogenisation is a part of the study. The thesis consists of two parts; an introductory summary with discussion and conclu sions, followed by a series of appended papers. The first paper concerns application of Rice's J-integral on displacement derivatives formulation in peridynamics with comparison to an exact analytical stress-strain-displacement specimen solution. The next two papers concerns homogenisation of a peridynamic bar, to remove the end effects, arisen from the nonlocality of peridynamics, to obtain an elastic behaviour exact to a classical continuum mechanics bar. The fourth paper is an implementation of the J-area integral into peridynamics, with study of various discretisation methods. Thereafter, in the last paper, Rice's J-integral and the nonlocal peridynamic J-integral are compared on various specimens, followed by an extension of the research to study EWF with peridynamics for the first time. The study includes a novel automated calibration at the interparticle bond level to simulate nonlinear elastic behaviour, which subsequently is complemented with softening and used for EWF modelling. As a part of introducing the peridynamic J-integral, the study also includes a proof of path independence.Major findings of the study includes:• The classical J-integral on a displacement derivative formulation gives accurateestimations of fracture toughness in peridynamics.• The peridynamic lD bar can be homogenised to obtain a linear elastic behaviour identical to that of an corresponding continuum mechanics body.• The bond calibration method gives a nonlinear elastic peridynamic model that can accurately recover an experimentally obtained stress-strain response. Up to the start of material softening, the nonlinear elastic model recovered the experimentally obtained stress-strain response of two very different materials; a lower-ductility martensitic-bainitic steel and a higher-ductility bainitic steel.• The nonlinear elastic model were able to match very well the experimentally measured EWF for the higher-ductility bainitic steel.• The J-integral value obtained from the peridynamic model, matched the experimentally obtained EWF value for the higher-ductility bainitic steel.
|
|
| 1372. |
- Stenström, Christer
(författare)
-
Operation and maintenance performance of rail infrastructure : Model and Methods
- 2014
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Congestion of roads and sky, increasing energy costs and a demand to reduce emissions, have created a need to shift transportation from road and air to rail. Consequently, rail utilisation is increasing, adding stress to the rail infrastructure and time constraints to maintenance. At the same time, the performance and capacity of rail infrastructure are expected to be preserved or even improved. Railway performance and capacity can be enhanced by: expanding infrastructure; introducing better technology; and improving the efficiency and effectiveness of operation and maintenance. Performance measurement has shown to improve the efficiency and effectiveness of organisations, but the development and integration of performance measurements are essential. A key issue in performance measurement is the process of collecting, storing and converting data into information and knowledge, i.e. data analysis and presentation. Organisations use various systems and methods to collect and analyse data, but the analysis of the collected data to extract relevant information is often a challenge. With improved data analysis and performance measurement, rail transportation can meet the requirements of performance and capacity. Specifically, maintenance planning and optimisation of preventive maintenance can be made more effective, which can decrease interruptions of train operation, reduce costs and ensure safety.In this thesis, a model for monitoring and analysis of operation and maintenance performance of rail infrastructure is developed. The model includes various methods for analysis of operation and maintenance data. The work aims to facilitate improvements and optimisation of decision-making in railways.The thesis consists of two parts. The first part gives an introductory summary of the subject and research, followed by a discussion of the appended papers, an extension of the research and conclusions. The second part consists of five appended papers. The first paper concerns the development of a model for improving performance measurement of rail infrastructure. The second paper is a study of indicators related to rail infrastructure performance. The three subsequent papers are development of data analysis methods for: operational availability of rail infrastructure, composite indicators and maintenance costs.Keywords: operation and maintenance, indicators, performance measurement, maintenance cost, rail infrastructure, linear assets, preventive maintenance, corrective maintenance, aggregation, composite indicators, cost-benefit analysis, decision support
|
|
| 1373. |
- Sterner, Eva
(författare)
-
Green procurement of buildings: estimation of environmental impact and life-cycle cost
- 2002
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis focuses on environmental impact reduction and life-cycle cost estimations in building procurement. The aim for the work presented in this thesis is to contribute to the understanding of whether costs and environmental impact of a building can be integrated in a, from the users perspective, practical model applied for tender evaluation. The model should also be able to use as a base of evaluating different solutions in the design phase. Specifically this means to: Increase knowledge about integration of economical and environmental aspects from a life-cycle perspective in relation to buildings Provide recommendations for procurement of cost effective and environmental aware buildings In the first part, environmental requirements stipulated by Swedish clients were investigated through a questionnaire survey followed by interviews. The identified requirements were analysed in relation to reduction of environmental impact and productivity. It was found that requirements linked to the construction process, waste reduction and choice of building materials were well represented. Several requirements were obstacles for a more cost-effective construction without benefiting the environment. The environmental impact from operation, as energy use, was however not considered to any larger extent. Energy use is currently considered to be the major source of environmental impact and governmental authorities in Sweden and EU advocate reductions. To encourage a development of innovative solutions in this area, clients should provide the incitements. It is here suggested that the integration of environmental impact assessment with life- cycle cost estimation in tender evaluation provide such incitement. In the second part, a broader understanding of life-cycle cost estimations and the extent of use by clients was established by a questionnaire survey in Sweden and a seminar in Canada. It was found that Swedish clients consider life-cycle cost estimations mainly in design and to a limited extent in procurement. In general the cost elements considered are investment, energy and, maintenance costs. Limitations for a wider uptake were also identified as lack of access to reliable input data and restricted experiences in actual use of the method. The seminar in Canada aimed at collecting information about the integration between theory and practice and the use in environmental design. It was found that in the absence of a formalised life-cycle cost approach, capital cost were used as the primary basis of comparing design alternatives. In the context of environmental design it was further found particularly important to use life-cycle cost approaches to motivate possible initial cost increases. When the use of life-cycle costing and its limitations were identified the development of the tender evaluation model was performed in two steps. First, the life-cycle cost elements with the largest impact on the total cost were identified through a case study of six buildings. This to simplify the model by reduction of cost elements included. Three of the buildings in the case study were environmentally designed and compared with three similar conventional buildings. Results from the life-cycle cost analyse showed that the environmentally designed buildings were in the same cost range as the conventional buildings in spite these had significantly lower initial costs. A sensitivity analyse was used to examine how the variation in energy prices would impact the result. Second, the environmental impact from energy use was established trough a classification of emissions into environmental impact categories. This showed that the environmentally designed buildings in the case study had a significantly lower impact than the conventional buildings. A method to weigh the categories into one index was applied. The use of life-cycle cost estimations in design, procurement and tender evaluation will provide a better base for performing investment decisions. Reduction of operational energy use will be displayed as economical beneficial and automatically environmental impact reductions are obtained. Clients with higher ambitions for environmental impact reductions can use the tender evaluation model suggested where the two aspects, life-cycle cost estimations and environmental impact assessment are integrated. As these parameters are measured on different scales integration experiences some problems. The solution suggested was to convert the environmental impact to a cost. The translation factor was seen as a factor to promote improvements for further energy reductions, and by doing so a comparison on a single criterion was possible. The model was hypothetically tested using empirics from the six case study buildings. Based on the results and conclusions presented in this thesis a number of general recommendations to clients are given: To motivate energy reductions, reduced costs and environmental impact, clients are recommended to evaluate tenders based on life-cycle cost estimations. By reducing the cost items included in the life-cycle cost model to initial costs and costs for operational energy about 70 to 90 % of the total cost is captured. When stipulating environmental requirements in procurement using to general expressions makes the effectiveness of the requirement questionable as the possibilities of verification are limited. Clearly stipulated preferably measurable requirements should be used. Requirements concerning materials should limited to not using hazardous materials. Other requirements will limit the competition and increase costs.
|
|
| 1374. |
- Steyn, Peter
(författare)
-
Online brand relationship building : Asia pacific perspectives
- 2009
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Information technology is empowering consumers through the availability of information, interactivity of online communication tools, and the connectivity with others. The newly empowered consumer is a co-creator of brand communications and is rapidly developing a sense of co-ownership in brands. Consumers are increasingly imposing themselves on the marketing function leaving many practitioners perplexed and unsure about how to respond. This thesis reports on five studies conducted to address specific challenges to marketers. The proactive marketer needs to respond to the adjustment in the marketing equilibrium by initiating and sustaining a meaningful dialogue with the marketplace. It was found that to initiative online brand communications, bloggers and event sponsorship can be effective means, but both have specific requirements and sponsorship is subject to ambush marketing. Consumers may respond to brands by creating their own online brand content which has a source-effect on online advertising. As consumer's brand communications rely on their relationships with the brand, the use of brands as means of self-expression is investigated.
|
|
| 1375. |
- Stjernberg, Jesper
(författare)
-
Degradation mechanisms in refractory lining materials of rotary kilns for iron ore pellet production
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Iron is one of the most important resources in the lithosphere; 90% of all metal ores extracted are based on iron. Many steps are included in the extraction of iron from ore, with extraction processes varying among different producers. Iron ore pellets are a prepared burden material for ironmaking in the blast furnace or by direct reduction. Such pellets can be sintered in a grate-kiln furnace system, in which the kiln is usually lined with mullite-containing bricks. These bricks degrade by various mechanisms, and need to be replaced regularly, which causes expensive production stops. Materials deposit in chunks on the lining in the kiln. These deposits comprise ~95% hematite with oxides of alkali metals, alkaline earth metals and others, which originate mainly from pellets that have disintegrated, but also from fly-ash from the burner fuel used to heat the kiln.This study investigated the interaction of deposit materials with refractory lining bricks in kilns during the sintering process in iron ore pellet production. Results are obtained from laboratory scale experiments, and from samples collected from industrial kilns, both in-situ and during production stops. Refractory/deposit compatibility tests were performed in a laboratory furnace at various temperatures, for different holding times, and in a number of atmospheres. Deposit materials collected from three commercial lining bricks in production kilns were analysed in both powder and solid forms. Deliberate additions of alkali species (carbonates of potassium and sodium) were made in order to evaluate their influence on degradation mechanisms.Analysis using scanning electron microscopy, QEMSCAN (quantitative evaluation of minerals by scanning electron microscopy), x-ray diffraction, differential scanning calorimetry, thermogravimetry and in-situ mass spectrometry confirmed that alkali additions in the deposit materials dissolve mullite in the liner bricks, which accelerates degradation. Phases such as nepheline (Na2O·Al2O3·2SiO2), kalsilite (K2O·Al2O3·2SiO2), leucite (K2O·Al2O3·4SiO2) and potassium β-alumina (K2O·11Al2O3) were formed. Moreover, it was observed that potassium penetrates deeper into the lining material, and in larger amounts, than sodium, both on the laboratory scale and in industrial furnaces. Formations of alkalicontaining phases such as the feldspathoid minerals kalsilite and nepheline are coupled with an expansion in the lining material, observed by dilatometry, which causes structural spalling that appears as cracks in some of the refractory/deposit compatibility tests. Grains of hematite with sizes between 50-100 μm remain on the original surface of the brick, whereas micrometer-scale hematite migrates through capillary infiltration (in pores, brick joints and cracks) and diffusion, and appears in finer grains deeper in the lining material. The degradation mechanisms of the bricks in an iron ore pellet producing kiln are shown to involve these chemical reactions in combination with thermomechanical stresses. Recommendations are given regarding the choice of materials, the design of refractory liners in the kilns to extend the time between production stops necessary for repair.
|
|
| 1376. |
- Stocks, Mikael
(författare)
-
Modeling, analysis, state and parameter estimation of faulty induction machines
- 2006
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis covers a broad range of subjects pertaining to induction machines, faulty as well as healthy ones. Firstly, a completely new and unconventional methodology for deriving simplest possible, yet sufficiently accurate, mathematical models for induction machines with general electrical faults is presented. Examples of common faults covered are inter-turn short circuit and increased resistance in one or more stator phases. Some common rotor faults treated in the thesis are broken rotor bars and broken end rings. Another fault that is encompassed by the modeling approach is diminished air-gap in front of one or more stator and/or rotor phases. Although straightforward to consider, it is unlikely in practice that more than one fault would occur at a time. Therefore, the modeling technique is explicitly used for arriving at two different models, where it is assumed that there is an electrical fault in either one stator phase or in one rotor phase. Interestingly, complexity of the resulting models is comparable to that of conventional models for healthy induction machines. The two models are validated against data collected from real-life induction machines with faults on purpose imposed upon them, with excellent agreement between the simulated and measured signals. Secondly, system properties of the two derived models, such as dissipativity, observability and controllability, are analyzed. It is shown that neither a stator nor a rotor fault alters these system attributes, except for very special cases. Furthermore, when a healthy induction machine is subject to a constant load and a perfectly balanced stator voltage source, it is proven that the rotor speed cannot be stabilized if the voltage has a spectral content comprising more than two distinct frequencies. Thirdly, the two developed models are used for state and parameter estimation in induction machines. Two kinds of observers are designed. The first one aims at robust stator flux estimation for healthy induction machines. It is shown that exponential convergence of the estimation error can be guaranteed, at a rate independent of the rotor speed. Therefore, the design possesses robustness against disturbance in rotor speed measurements, however with an upper bound on attainable performance. The second observer methodology provides a generalized linear-quadratic optimal framework for linear complex-valued time-varying systems, where an arbitrary, possibly time-varying, guaranteed convergence rate can be assigned. The methodology is thereafter used in a new parameter estimation scheme, both for healthy induction machines and those subject to stator faults, in order to estimate all electrical parameters on-line, under very mild assumptions. Specifically, the scheme can be used for fault detection. Simulations validating the methodology are provided.
|
|
| 1377. |
- Strandberg, Agnes
(författare)
-
En del i helheten : En studie av kontextualiserad grammatikundervisning i gymnasieskolan
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Det övergripande syftet med avhandlingen är att bidra med kunskap om grammatikundervisning i svenskämnet genom en design där forskare och lärare tillsammans skapar, iscensätter och utvärderar kontextualiserad grammatikundervisning i gymnasieskolans svenskundervisning, samt att belysa på vilka sätt en sådan undervisning kan användas och förstås. Shulmans (1986; 1987) teoretisering av lärares ämnesdidaktiska kunskapsbas (PCK), samt hans begreppsapparat om undervisning, används som teoretiskt ramverk i avhandlingens ramberättelse. Avhandlingen består av fyra vetenskapliga artiklar där designstudien undersöks utifrån olika perspektiv. Det empiriska material som ligger till grund för avhandlingen är vetenskapliga artiklar publicerade i engelskspråkiga tidskrifter, ljudinspelade fokusgruppsamtal med de sex deltagande lärarna, videoinspelningar av de deltagande elevernas metalingvistiska aktiviteter, observationsanteckningar av forskaren samt en elevenkät. Resultaten visar på vilka sätt kontextualiserad grammatikundervisning med målet att utveckla elevers metalingvistiska förståelse, lämpligen kan ta sig uttryck och användas genom följande samverkande designelement: induktiva arbetssätt, diskussioner, visualiseringar och integrering. Vidare visar resultaten vilka strategier som elever använder sig av när de analyserar syntaktiska egenskaper i ett skönlitterärt textutdrag, samt vilka pedagogiska möjligheter och utmaningar som applicerandet av dessa kan generera. I avhandlingen synliggörs också att användningen av autentiska texter i grammatikundervisningen kan möjliggöra kopplingar mellan olika språkliga nivåer, så som grammatik och pragmatik. Mot bakgrund av den komplexitet som kännetecknar autentiska texter visar studien emellertid att de också kan försvåra representationen av ett grammatiskt fenomen och i förlängningen representationen av språkets hierarkiska uppbyggnad. Med utgångspunkt i avhandlingens sammanförda resultat diskuteras vikten av och komplexiteten med grammatikundervisningens kontextualisering och dess relation till det skolgrammatiska arvet från ett teoretiskt och praktiskt perspektiv. I ljuset av lärares ämnesdidaktiska kunskaper och praktikens villkor indikerar resultaten slutligen betydelsen av att rekapitulera vad grammatikundervisning är och kan vara inom ramen för förstaspråksundervisningen i allmänhet och svenskundervisningen i synnerhet.
|
|
| 1378. |
- Strandberg, Carola, 1981-
(författare)
-
Through the Looking Glass : An Identity-Based View of Place Branding
- 2023
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Places of today face intense global competition for crucial resources. Attracting visitors and retaining residents is vital especially for post-industrial cities and rural places facing a loss of traditional industrial jobs, and urbanization and centralization of the population and economy. To attract resources and target groups like tourists and residents, place managers and authorities are increasingly turning to place branding. A recent stream of literature has adopted an identity-based view of place branding building on an understanding that like the formation of the place itself is an open-ended process, constantly renegotiated and socially constructed so is that of place branding. It depicts place branding as an identity construction process, an ongoing process of multilogue between different place stakeholders involved as active participants in the co-creation of the place brand experience, expression, and communication. In this light, effective place branding strategies must be based on a brand identity that reflects the perceptions of its stakeholders, communicated to and with key stakeholders. This highlights the need for place managers to understand place stakeholders’ perceptions to be able to mirror, articulate and reinforce them in the brand identity and place brand communication. There is however a lack of focus in extant research on the perspective of residents, a primary stakeholder group. Furthermore, questions remain regarding the drivers behind this process, especially regarding the role of person–place bonds in relation to place-related behavioral outcomes.Therefore, the purpose of this thesis was: To investigate place-related identity concepts within an identity-based view of place branding. The current research sought to deepen the understanding of the identity-based view by 1) developing the understanding of how place-related identity aspects can be leveraged to influence the place-related behavioral intentions of key place stakeholders, focusing specifically on residents as a primary stakeholder group, and 2) to contribute to further conceptual and operational clarity regarding the elusive concept of place identity and related concepts underlying this process. Drawing on identity-based place branding literature in combination with identity, congruity, and attachment theory four research questions (RQs) were formulated: RQ1: How can the identity perspectives expressed in residents’ place image be characterized? RQ2: What is the relationship between place image, place attachment, self-congruity, and positive place word-of-mouth (WOM) across different stakeholder groups? RQ3: What is the relationship between place image, place attachment, self-congruity, and likelihood to stay in a place across cities of different sizes? RQ4: How can the concept of place identity be measured? To answer the research questions four studies were conducted, one qualitative, two quantitative and one conceptual, the results from each study presented in a research paper. In response to RQ1 the qualitative study highlights the different identity perspectives manifested by residents when describing their place perceptions. The place identity perspectives expressed in residents’ place image descriptions evidence both subject identity perspectives - through personal and social identity perspectives, and object identity perspectives – in terms of person, people/social (in-/out) group, and place object identity perspectives. These perspectives influence the content of place image descriptions both in terms of what residents describe – in terms of object identity, and how they describe it – depending on which identity lens is applied and from whose point of view. The results highlight the need for priming to activate a specific stakeholder identity when gathering place image perceptions and designing place branding campaigns.Quantitative findings in response to RQ2 applicable across two cities of different size indicate that affective place image influences positive WOM and that this relationship is mediated by place attachment for both residents and visitors. Interestingly, while the connection between affective place image and place attachment is stronger for residents, the connection between place attachment and positive WOM is significant also for visitors. Contrary to previous studies, the findings suggest that self-congruity with residents’ image may not offer sufficient symbolic value to inspire WOM behavior. Results however support that self-congruity plays a mediating role between affective place image and place attachment which is stronger for visitors than for residents. The findings highlight the need to successfully reflect the self-concept of key stakeholders in communication messages to strengthen emotional brand connections and consequently WOM behavior. When targeting residents, communication is best centered around aspects reflecting the place’s identity while, additionally, communication reflecting residents’ image may be targeted towards visitors to increase the probability of positive WOM.Findings concerning RQ3 show a positive relationship between place image and residents’ likelihood to stay, mediated by place attachment. The relationship between place image and place attachment is mediated by resident self-congruity. Implications include that perceived resident image fit may not offer any direct influence on residents’ likelihood to stay but is important to instill place attachment which impacts resident retention. Implications highlight the multifaceted nature of place self-congruity, the importance of careful consideration of constructs when operationalizing identification with a place, and that place attachment should not be used to measure residents’ likelihood to stay. Future research is encouraged to include images of both place and place consumers when studying residents’ place self-congruity. Implications highlight the capacity for place branding policies supporting inclusive community practices to unify and retain residents. Results from the conceptual study related to RQ4 show a range of elements and sub-dimensions relevant to measure the place identity/identification construct. Findings show how different labels have been applied to identify what appears to be conceptually equivalent constructs and vice-versa. A framework is presented of the cognitive, affective, and conative and evaluative elements of place identity/identification including their sub-dimensions. Results highlight the need to exert stringency when applying the terms in research and to carefully define and delineate concepts when gathering data and reporting results.Further theoretical and managerial contributions and suggestions for future research are discussed in the final chapter of the thesis. The four papers are presented as Appendices, three of which have been published and the fourth is being revised to be submitted for review in a scholarly journal.
|
|
| 1379. |
- Strandkvist, Ida
(författare)
-
Minimisation of Chromium Leaching from Low-Alloy Electric Arc Furnace Slag by Mineral Modifications
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Iron and steel are produced continuously as a vital part of modern life. The largest by-product of metal production is slag. Slag is an essential part of the production of steel since, in the furnace, the molten slag removes impurities from the metal. When the slag which consists of oxides, solidifies minerals form. Slag can then be used in different applications: fertiliser, water purification, cement, concreate and as building material. By using slag, natural resources can be saved. In the electric arc furnace, EAF, scrap is melted to produce steel. The scrap contains chromium which partly distributes to the slag. Unfortunately, excessive leaching of chromium restricts slag usage. Chromium leaching occurs when chromium-containing minerals in slag dissolve. In low-alloy electric arc furnace slag there are three chromium containing minerals: spinel (Mg,Fe)Cr2O4, magnesiowüstite (Mg,Mn,Fe)O and brownmillerite Ca2(Al,Fe)2O5. Of these minerals the spinel has already been determined to be stable. The aim of this thesis is to minimise the chromium leaching of low-alloy EAF slag by modifying the minerals and/or mineralogy in the slag so that the chromium-containing minerals do not dissolve. In addition, it was discovered that ageing of low-alloy electric arc furnace slag may increase the chromium leaching. Autoclave treatment of remelted slag resulted in chromium leaching at the same magnitude as before remelting. Autoclave treatment was performed before the leaching test to determine the chromium leaching of aged slag.Instead of indirectly examining the chromium leaching from magnesiowüstite and brownmillerite by comparing chromium leaching from slag samples, the dissolution properties of the minerals were investigated individually. Dissolution of different compositions of magnesiowüstite and brownmillerite were studied at pH 7 and pH 10 for 40 hours. The conclusion was that increased iron content decreased the dissolution rate of both magnesiowüstite and brownmillerite. Magnesiowüstite (Mg,Fe)O did not dissolve at pH 10 when it contained 60 wt% FeO and did neither dissolve at pH 7 or pH 10 at higher FeO content. According to thermodynamic calculations, the FeO content in the magnesiowüstite can be affected and this was investigated. Laboratory and full-scale experiments showed that the composition of magnesiowüstite in slag could not be correlated to chromium leaching. The conclusion was that magnesiowüstite was not the main mineral leaching chromium.Brownmillerite composition is difficult to control in slag and had a significant impact on the dissolution rate; therefore, brownmillerite in slag should be avoided to minimise leaching of chromium. From thermodynamic calculations two options to avoid brownmillerite formation were identified: decreasing the basicity (CaO/SiO2 ratio) or increasing the cooling rate. Both methods were tested in laboratory scale using low-alloy electric arc furnace slag. When the basicity was decreased by SiO2 addition, the chromium leaching of the slag decreased. The chromium leaching was correlated to the brownmillerite content, the chromium leaching decreased with the decreasing basicity until brownmillerite was no longer be detected by XRD analysis. After that the chromium leaching did not decrease significantly. This indicates a correlation between basicity, brownmillerite and chromium leaching. When cooling of slag was investigated the slower cooling rates increased the chromium leaching and fast cooling rates decreased the chromium leaching. The results were verified by full-scale experiments. Si-sand addition was used to decrease the basicity to 2.2; according to thermodynamic calculations this would prevent brownmillerite formation. The targeted basicity of 2.2 was difficult to achieve, as the basicity varied between batches since the scrap composition and other parameters changed. Batches from other experiments were included for more data. It was seen that the chromium leaching of batches below basicity 2.2 did not reach the same magnitude as the batches above basicity 2.2. The full-scale trials with different cooling methods confirmed that the faster-cooled water-sprayed slag had lower chromium leaching than slag that had cooled by its own.Basicity between 2.0 and 2.2 minimises chromium leaching but decreasing the basicity to specific values in full-scale is challenging. A decrease in basicity is the most efficient method of decreasing chromium leaching, but faster cooling also decreases the chromium leaching.
|
|
| 1380. |
- Strandkvist, Viktor
(författare)
-
Hand grip strength and postural control among individuals with and without Chronic Obstructive Pulmonary Disease : Epidemiological and motion laboratory studies
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- BackgroundChronic obstructive pulmonary disease (COPD) is estimated to affect approximately 8%–10% of all adults. The disease is considered to be a heterogenic syndrome with systemic effects, in which comorbidities including cardiovascular diseases, muscle dysfunction and fatigue are common. The majority of all individuals with COPD have mild to moderate disease (Global Initiative for Chronic Obstructive Lung Disease (GOLD) 1-2), and only a third are identified by health care, and this under-diagnosis contributes to a lack of knowledge of COPD in the population. COPD is related to skeletal muscle dysfunction, where muscle weakness, frequently assessed with hand grip strength (HGS), is one of the components. Evidence of postural control limitations among individuals with severe or very severe COPD has been emerging during the last decade. These limitations are partly related to muscle weakness, however, research of the other underlying systems of postural control is scarce, and an increased knowledge is of importance for the prevention of falls.AimThe main objective of the thesis was to increase the population-based knowledge about muscle strength, assessed as hand grip strength, and also postural control among individuals with and without COPD. Another objective was to investigate the value of hand grip strength measurements in relation to lower limb muscle strength and postural control among community-dwelling older adults.MethodsPaper I and II are based on the population-based Obstructive Lung disease in Northern Sweden (OLIN) COPD study. All individuals with obstructive lung function impairment (n=993) and an age- and sex-matched group without (n=993) (COPD and non-COPD) were identified after re-examination of population based cohorts during 2002-04. They (n=1,986) have been invited to recurrent examinations including structured interviews and spirometry. Paper I (n=1011) and II (n=831) include data from examinations during 2009-2010 and 2014, respectively, where measurements of HGS (Paper I & II) as well as assessment of fatigue and physical activity (Paper II) were included. Paper III and IV are based on the population-based Balancing Human and Robot (BAHRT) study. Randomly selected individuals over 70 years of age were invited to participate in a study of postural control aspects, in their homes and at the 2 Human Health and Performance Lab- Movement Science, at Luleå University of Technology. The examinations included a structured interview as well as measurements of postural control and sensory and motor systems including HGS, lower limb strength, proprioception, pressure sensitivity, visual acuity, vestibular function and reaction time. Participants in Paper III consisted of communitydwelling individuals over 70 years of age (n=45). Paper IV consisted of individuals with COPD recruited from both the OLIN COPD study as well as the BAHRT-study (n=22), as well as a control group without airway obstruction from the BAHRT-study (n=34).ResultsIn Paper I, there was no differences in mean HGS between the groups with and without COPD. However, HGS was related to disease severity; HGS was lower among those with severe to very severe COPD (GOLD 3-4) compared to nonCOPD, and HGS was associated with forced expiratory volume during 1 second % of predicted value (FEV1 % predicted) in regression models. Five years later, in Paper II, mean HGS was lower in COPD compared to non-COPD. Further, individuals with COPD and clinically relevant fatigue had lower HGS than those without clinically relevant fatigue, significantly so among men and close to among women. There was no clear association between HGS and level of physical activity. In Paper III, there was a strong and valid model showing association between HGS and lower limb strength, where all tested muscle groups were significantly correlated to hand grip strength. The regression model with HGS and postural control was significant, however, the model was weak. In Paper IV, individuals with COPD had worse postural control than those without COPD, significantly so regarding mediolateral amplitude in quiet stance with eyes open on soft/unstable surface, as well as anteroposterior limits of stability. In the COPD group, mediolateral amplitude was related to eye sight and the burden of tobacco smoking assessed as pack-years. Further, muscle strength associated with anteroposterior amplitude in the limits of stability test.ConclusionsIn the population-based OLIN COPD study in 2009-2010, mean HGS was significantly lower among individuals with severe to very severe COPD (GOLD 3-4) than those without COPD. Five years later, mean HGS was lower among all individuals with COPD (GOLD 1-4) compared to those without COPD, which may indicate altered aging process in COPD. HGS was associated to fatigue among individuals with COPD, while there were no associations between HGS and physical activity. HGS is a valid tool for the estimation of lower limb muscle strength among community-dwelling older adults, however, HGS is not 3 appropriate to use as an estimation of postural control. Postural control was impaired among individuals with COPD and different postural control assessments had different demands on the sensory and motor systems. The burden of tobacco smoking and visual acuity might be important for quiet stance trials with visual input, while muscle strength might be important for the more dynamic limits of stability test. Further research regarding the longitudinal aspects of muscle weakness and postural control among individuals with COPD is needed to gain knowledge for appropriate preventive or rehabilitative interventions.
|
|
