| 1331. |
- Simonsson, Peter
(författare)
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Buildability of concrete structures : processes, methods and material
- 2011
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The causes for the slow development of the construction industry is often attributed the traditional ”peculiarities of construction“, including such factors as one-of-a-kind products, temporary organisation, and on-site production. However, signs of new thinking are becoming apparent in the construction industry in Sweden that emphasise change. Globalization and increased competition are factors for change. The possible future shortage of available qualified workers, demand for shorter construction times and calculated higher risks for projects are also catalysers for the implementation of new and alternative solutions. Still, new production methods and construction ideas are rarely introduced in construction projects, with low or no productivity increase of the industry as a result. Within the scope of this thesis work, the combination of creating buildability during the design phase and utilizing the philosophies of lean construction during the construction phase has been adapted to improve civil engineering concrete construction work. Several full scale projects have been studied and a questionnaire survey has been performed. In order to be able to introduce changes such as prefabricated reinforcement solutions, left concrete form systems and Self-Compacting Concrete (SCC) as a mean to increase productivity at site, there is a need to create projects that are buildable and able to be constructed, i.e. constructions that we know in advance are practically feasible and productive. All involved participants throughout the whole project are therefore responsible for creating buildability in the project. The case studies show that the potential increase in productivity can be vast. The introduction of prefabricated rebar sections, e.g. rebar carpets and rebar cages, decreases time spent on fixing reinforcement with up to 80%. The use of SCC potentially saves 65% on time spent during casting. Both methods improve the working environment substantially. However, the introduction of new methods also put demands on properly planned, communicated and managed construction operations on-site. Thus, the use of Buildability in the design can promote new solutions together with Lean Construction philosophies in management of these alternatives are suitable tools in changing the construction industry. Buildability deals with creating design for “ease of construction” whilst Lean construction focus on planning of a productive flow of work tasks and resources for the selected production methods. The combination of buildability in the “design for” part and lean construction philosophy in the “ease of construction” part within one of the most accepted definitions of buildability i.e. “the extent to which the design of a building facilitates ease of construction” will be able to encourage an increase in productivity at construction sites. This is possible if important factors are considered and utilised sufficiently. Some of these important factors highlighted in this thesis work are: • early project involvement of contractor, to increase construction knowledge during design, a result from the questionnaire survey; • design projects in 3D and create adequate virtual work instructions for workers to study prior to performing the work task, a result from full scale studies; • plan the construction work tasks and material supply thoroughly using lean tools, a result from full scale studies; • make sure adequate attention is spent on the working environment early in a project, this will result in workers feeling confident in a safe work environment, a result from full scale studies. The thesis corroborates the conclusion that, if these factors are considered and encouraged there is a potential for improvement of productivity at site, enhanced quality of finished structures as well as lowered costs for constructing structures in the future.
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| 1332. |
- Simu, Kajsa
(författare)
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The construction site manager's impact on risk management performance
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Risk management in construction is traditionally based on the experience and individual judgements made by site managers, especially in smaller projects. The site managers in construction should also be regarded as key individuals, with a prevailing picture of being tough and possibly also risk prone in their behaviour .This study follows up a previous study by the researcher which found that the management system itself does not have such a large influence on the way risks are managed at a construction site. The construction site manager, as an individual, is regarded as having a greater impact on the project performance related to risk. The question raised in this study is therefore what individual impact the site managers have on the effects of risk management. To be able to answer this question, it is also important to determine the extent to which it is possible to measure the effects of risk management at construction site level. The results of this study present a model for measuring the effects of risk management on site and at individual level in a construction project, using specific indicators. These indicators are related to profit, safety, quality performance and predictability. Further, this model has been tested using authentic data from a construction company. These data do not reveal strong correlations between the chosen indicators and, as a result, reliance on profit is dominant. The individual impact on risk management performance focuses on two aspects of the character of an individual; personality and background information, such as education, age and experience. Personality traits measured by the PAPI test reveal three significant traits that correlate to economic performance on site. They are need for change, need to be forceful and social harmoniser. None of these traits was, however, found to be related to risk management performance. Moreover, the characteristic personality of construction site managers is compared with that of managers from the general labour market to see whether there are any significant differences that could help to explain the prevailing picture of the character of construction site managers. The most powerful difference is the trait of need for change, indicating that construction site managers are more conservative than other managers. In this comparison, it is not possible to assign attributes to site managers as being more risk prone than other managers. Instead, a picture emerges of individuals who focus on details, are keen on following routines and also have a work pace indicating stress tolerance. The conclusions from this study are that there are indicators that ought to work as indicators of risk management performance, but the amount of data required to find significant correlations needs to be vast. It is also concluded from this study that, due to the site managers' aversion to change, they remain at the less demanding rule-based level of problem solving instead of moving up to the more time-consuming, knowledge-based level of problem solving. It is also concluded that site managers from construction are not more risk prone than managers from the general labour market. The final conclusion is that the individual impact on the effects of risk management is fairly small. There are other issues, possibly related to organisational context, that have a greater impact.
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| 1333. |
- Sin, Jorge Rituerto
(författare)
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Investigation of the corrosion and tribocorrosion behaviour of metallic biomaterials
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Metals are commonly used in various biomedical applications due to their excellent mechanical properties, such as high strength, ductility and toughness.However, the main drawback of metallic biomaterials is their high reactivity, which makes them especially susceptible to corrosion when exposed to aqueous environments such as body fluids. In addition to the corrosiveness of body fluids, metallic biomaterials canbe exposed to mechanical loading and wear. The combined effect of corrosion and wear, also known as tribocorrosion, can lead to enhanced release ofmetallic ions and particles into the surrounding fluids and tissue, which can cause different adverse biological reactions and limit the lifetime of metallicimplants. The overall goal of this study was to investigate the tribocorrosion behaviourof different metallic biomaterials. Firstly, the corrosion and tribocorrosionresistance of a novel candidate material, hafnium, have been studied and compared with titanium. Secondly, the tribocorrosion behaviour of Cobalt-Chromium-Molybdenum alloys has been investigated.The study of the corrosion and tribocorrosion behaviour of hafnium and titanium revealed that both metals form a stable oxide layer that provides highprotection to corrosion. Although the oxide layer can be damaged due to frettingand wear, it rapidly reforms when the mechanical damage ceases. However,hafnium showed a tendency to suffer from pitting, especially when the material was subjected to fretting, which could be a major drawback that mightlimit the application of hafnium in biomedical applications.The behaviour of CoCrMo alloys was also investigated. The analysis of the repassivation kinetics of CoCrMo revealed that a second order exponentialdecay can be used to model the current transient after wear damage. This suggests that the repassivation process can be divided in two phases, first thedepassivated area is rapidly recovered by an oxide layer; then, the thickness of the oxide film grows and stabilises. In addition, it was observed that thechemical composition of the environment can affect not only the corrosion but also the tribological performance of the system. This work has provided an insight into the degradation processes and the parameters affecting the corrosion and tribocorrosion behaviour of different metals in simulated body fluids.
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| 1334. |
- Singh, Maneesh
(författare)
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Studies on the cement-bonded briquettes of iron and steel plant by-products as burden material for blast furnaces
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During the various stages of iron and steel production a number of iron bearing by-products are generated. These by-products can be made into cement- bonded agglomerates for use as burden material for blast furnaces. In order to improve the quality of agglomerates, the effect of various processing parameters on the properties of cement-bonded briquettes has been studied. It has been found that the room-temperature properties of briquettes depend upon various processing parameters like solid / water ratio, vibration time, briquetting force, compression time and particle size distribution of the raw material. The study has also shown that the strength of briquettes decreases after heating in a nitrogen environment and after reduction. The strength of briquettes can be increased by increasing the amount of pre-reduced / flaky components, increasing the amount of cement and decreasing the particle size of the raw material. Under certain reducing conditions, the cement-bonded briquettes exhibit a tendency to swell catastrophically. This happens especially during the reduction of wustite to iron at 950oC using CO as the reducing gas. The briquettes that contain coarse pellet-fines particles are specially prone to swelling since the pellet-fines contains a large percentage of under-fired and weak fraction of the pellets. This swelling can be controlled by grinding the raw material finely, increasing the cement content, and adding calcium oxide / magnesia / silica or alumina to the cement. A model to describe the swelling process has also been propounded.
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| 1335. |
- Sirkka, Marianne
(författare)
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Hållbart förbättringsarbete med fokus på arbetsterapi och team : Möjligheter och utmaningar
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hälso-och sjukvården (HoS) har skyldighet att bedriva en evidensbaserad verksamhet baserad på bästa tillgängliga vetenskapliga kunskap, professionens expertkunnande, patienternas erfarenheter och tillgängliga resurser. Förbättringsarbeten pågår för att uppnå bästa möjliga HoS men kunskapen om hur hållbara förbättringar uppnås är fortfarande begränsad. Det övergripande syftet med denna avhandling var att bidra till ökad kunskap om möjligheter och utmaningar vid långsiktigt förbättringsarbete med fokus på arbetsterapi och team. Avhandlingens fyra delarbeten baseras på studier av långsiktiga förbättringsarbeten vid två olika enheter. Studie I syftade till att beskriva utvecklingen av ett långsiktigt förbättringsarbete som baserades på en arbetsterapeutisk praxis modell, Occupational Therapy Intervention Process Model (OTIPM). Data utgjordes av olika typer av dokument (435sidor) från 2001-2013 som var relaterade till förbättringsarbetet och analyserades med mönsterjämförelser (pattern matching). I Studie II var syftet attutforska arbetsterapeuters erfarenheter av ett långsiktigt förbättringsarbete. Data utgjordes av semistrukturerade intervjuer med 19 arbetsterapeuter i tre fokusgrupper år 2006 och uppföljande fokusgruppsintervjuer år 2011. Materialet analyserades med kvalitativ innehållsanalys. Studie III syftade till att identifiera stödjande och hindrande element vid långsiktigt förbättringsarbete med stöd av det implementeringsteoretiska ramverket, Promotion Action on Research Implementation in Health Services (PARiSH). Data från fokusgruppintervjuer analyserades först med manifest innehållsanalys med ramverket som raster och vidare med en latent innehållsanalys. Studie IV syftade till att utforska ett tvärprofessionellt teams erfarenheter av att implementera en teamorienterad och evidensbaserad behandlingsmodell Mentaliseringsbaserad terapi (MBT). Data utgjordes av återkommande fokusgruppsintervjuer som analyserades med en metod för jämförelseav kvalitativ data, inspirerad av Grounded Theory. Resultatet av studie I visar på sju olika faser i det långsiktiga förbättringsarbetet. Faserna representerar tre huvudmönster i processen och beskriver olika tillvägagångssätt för omorientering, etablering och långsiktig hållbarhet. I studie II beskrivs det långsiktiga förbättringsarbetet som en resa mot en hållbar ochevidensbaserad praktik. Resultatet visar på en förändringsresa med tre sammanflätade perspektiv; 1) omvandla tankar och handlingar genom återkommande kollegial reflektion, 2) hantera den upplevda dubbelheten av förändring, 3) utveckla en ömsesidigt professionell kultur. I studie III framkommer att samtliga element i ramverket PARiSH (evidens, kontext och facilitering) hade övervägande höga värden vilket indikerar en lyckad implementering. Vidare framkommer att den nya professionsinriktade kunskapen ansågs ha hög evidens. Den starka kollegiala kulturenvärderades högt och underlättade fortsatt förbättringsarbete trots olika utmaningar och stressmoment över tid. Resultatet av Studie IV beskriver implementeringen av den evidensbaserade och teamorienterade modellen, MBT som en interdisciplinär process med teoretiska, praktiska, emotionella och reflekterande komponenter. Det interprofessionella teamarbetet identifierades som en drivkraft för hållbar implementering och den reflekterande komponenten framstod som avgörande för utvecklingen av det interdisciplinära teamarbetet. Avhandlingen som helhet visar att hållbart förbättringsarbete inom arbetsterapi och team förutsätter a) ett reflekterande kollegialt förhållningssätt som ökar förmågan att hantera utmaningar i förbättringsarbetet, b) en i vardagsarbetet integrerad struktur förlångsiktigt förbättringsarbete med regelbunden avsatt tid och allokeradfaciliteringsfunktion, c) rutiner för att kontinuerligt hantera professionell kunskap från vetenskap och beprövad erfarenhet, d) ett strategiskt ledarskap och en gemensam kultur som håller drivkraften att förbättra levande över tid.Nyckelord: arbetsterapi, evidensbaserad praktik, hållbart förbättringsarbete,implementeringsteorier, MBT, OTIPM, PARiSH. hållbart förbättringsarbete, implementeringsteorier, MBT, OTIPM, PARiSH.
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| 1336. |
- Sjöberg, Erik
(författare)
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Zeolite Membranes for Production of Biofuels
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- To deal with the increasing demand of renewable fuels, more efficient processes for the production of biofuels are needed. Zeolite membranes have the potential to improve many existing processes that could be used for production of biofuels. Methanol is a potential biofuel that may be produced from synthesis gas in an equilibrium limited reaction. The production of methanol from synthesis gas could be improved by use of a membrane reactor, which could increase the conversion of synthesis gas to methanol per pass in the reactor. Methanol and several other biofuels can be prepared by first gasifying biomass to synthesis gas. Synthesis gas produced from biomass usually contains significantamounts of carbon dioxide that must be removed before methanol synthesis. However, commercial processes for carbon dioxide removal are very energy intense, and a membrane process could also improve this process and offer lower energy costs and less complicated and more compact equipment.In the present work, silicalite-1 and ZSM-5 membranes (NaZSM-5 and BaZSM-5) were successfully prepared on graded α-aluminasupports and evaluated for removal of carbon dioxide and hydrogen sulfide from synthesis gas. Both synthesis gas prepared from pure gas from gas cylinders and synthesis gas obtained from a black liquor pilot plant gasifier were used. The separations were performed at industrial relevant conditions, i.e. high pressures. It was found that the carbon dioxide fluxes were very high for carbon dioxide separation from synthesis gas free from water and hydrogen sulfide prepared from gas cylinders. Carbon dioxide fluxes up to 657 kg m-2 h-1 were observedfor a binary mixture of carbon dioxide and hydrogen. The high flux was a result of a thin membrane film, an open graded support, and ahigh pressure gradient over the membrane. A CO2/H2separation factor of 32.1 was observed at 2 ˚C and the selectivity was controlled by carbon dioxide adsorption, blocking the transport of hydrogen. The differences in carbon dioxide separation performance, observed for the different evaluated membranes, were likely due to differences in the carbon dioxide adsorption isotherms. The silicalite-1 membrane had a more favourable adsorption isotherm compared to the ZSM-5 membranes at these conditions, which resulted in larger difference in fractional surface loading between feed and permeate side of the membrane. It was also found that the carbon dioxide flux and separation factor decreased substantially when carbon dioxide and hydrogen sulfide was separated from synthesis gas derived from black liquor also containing water and hydrogen sulfide. This was probably an effect of competitive adsorption of hydrogen sulfide and water, which are probably blocking carbon dioxide molecules from permeating through the membrane. Furthermore, all-zeolite membranes (membranes consisting of both zeolite film and zeolite support) were prepared and evaluated for removal of carbon dioxide from synthesis gas in the present work. The membranes were carbon dioxide selective, but quite brittle, which made testing difficult. The zeolite supports used for all-zeolite membranes were prepared by collaborating researchers as an attempt to reduce crack formation in zeolite membranes, since the thermal expansion mismatch between the zeolite film and the membrane support will be minimized using this approach. Mathematical models of a traditional methanol synthesis process and two alternative membrane processes were also developed in the present work. Recorded experimental permeation data for a ZSM-5membrane was used as input to the models. The estimated performance of the traditional process was compared with a membrane reactor process (MRP) and a membrane module process (MMP). The mathematical model indicated that the MRP is the best alternative, since it enabled one pass operation, due to the highest conversion per pass. The MMP is however better from a practical point of view compared to the MRP since membrane and catalyst is separated and the membrane and reactor can be operated at their optimal respective temperatures and the membrane and catalyst can be replaced independently. By adding more membrane modules, the performance of the MMP will approach that of the MRP, to the price of higher complexity of the process.
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| 1337. |
- Sjöberg, Frank
(författare)
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The Zipper duplex method in very high-speed digital subscriber lines
- 2000
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis deals with different aspects of digital subscriber lines (DSL). Over the years several DSL techniques for high-speed communication on the telephone access network have evolved that gradually have allowed higher data rates. In this thesis we focus on the latest technique, called Very high-speed Digital Subscriber Line (VDSL), which is intended to offer bit-rates up to 50-60 Mbits/s on ordinary twisted-pair wires. The major part of this thesis concerns a novel scheme called the Zipper duplex method, which is introduced herein. Zipper has been proposed as duplex method for VDSL, and represents one of the two leading proposals in the North American (ANSI T1E1.4), the European (ETSI TM6), and in the International (ITU SG15/Q4) standardization groups. The key advantages with the Zipper duplex method are superior flexibility, high duplex efficiency and compatibility with existing services. It is based on discrete multitone (DMT) modulation and uses different DMT-tones in the up- and the downstream directions. The method relies on an additional cyclic extension, a cyclic suffix, to ensure orthogonality between signals in opposite directions. Best performance is achieved when all transmitters in the access network are synchronized, but Zipper can also operate in an asynchronous mode. However the asynchronous mode comes with some bit-rate performance loss and this performance loss tends to increase with wire-length. So we have developed a method for self-synchronizing all Zipper-modems that guarantees best possible performance for long wires. This method uses the correlation present in DMT-signals, due to the cyclic extension, to estimate the other users' frame-offset relative to their own. It then adjusts the frame-timing accordingly. Problems with near-far far-end crosstalk (FEXT) in the upstream can severely limit the performance of modems on long wires. In this thesis we propose a bandwidth efficient power allocation method called the multi-rate power back-off. This method creates a spectrally shaped transmit power spectral density (PSD) that results in higher bit-rates for all users compared to using a flat transmit PSD. By incorporating target bit-rates, a system operator can better control the bit rate distribution among the users, and the FEXT is kept at a minimum since no user is allowed to use more transmit power than necessary to achieve the desired target rate. The unshielded wires in the access network are quite susceptible to radio frequency interference (RFI). We introduce an efficient digital RFI-cancellation method that operates in the frequency domain for modems using DMT-modulation. By deriving a parameterized model of the narrowband RFI-signal and measuring the RFI-signal on a few unmodulated DMT-tones, the RFI can be extrapolated to the other tones and cancelled. Simulations show that it is sufficient with two parameters and two measurement tones to almost completely eliminate the RFI. Impulse noise that originates from telephone activity can be very harmful to VDSL. The use of a system margin together with Reed-Solomon coding and interleaving have been proposed to handle the impulse noise. In this thesis we study the effect of impulse noise on DMT-based VDSL systems, and present a robust detection and erasure scheme that can reduce the interleaving depth required to cope with the strongest impulses.
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| 1338. |
- Sjöberg, Jonny
(författare)
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Analysis of large scale rock slopes
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The objective of this work was to (1) increase the knowledge of the behavior of large scale rock slopes, (2) improve the ability to estimate rock mass strength for such slopes, and (3) develop an improved design methodology for forward design of large scale slopes in open pit mining. A fourth objective included the application of the results to the Aitik open pit in northern Sweden. A large number of case studies were collected into a database and empirical design guidelines were developed. A procedure for determining the strength of large scale slopes was developed, based on the Hoek-Brown failure criterion. Failure mechanisms of high slopes were studied using numerical modeling. The procedure for strength estimation and the modeling methodology, were applied to selected case studies-this enabled verification of the design methodology. Finally, the design methodology was applied to the Aitik open pit mine, and slope design recommendations given.
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| 1339. |
- Sjöblom, Margareta
(författare)
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Health promotion through the lifespan - the phenomenon of the inner child reflected in childhood events - experienced by children, adults and older persons
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In spite of the fact that we are living longer lives, we still have to face challenges in our society like mental ill-health and stress-related conditions. However, human experiences may give insight on how to overcome challenges like these, by using a health-promoting perspective focusing on salutogenic aspects of health and well-being. The overall aim of this thesis was to describe and gain more knowledge about the phenomenon of the inner child reflected in human beings’ experiences of childhood in connection to health and well-being in the present and through the life course. The thesis consists of three data collections and four studies, and they are all based on a qualitative approach. A total of 53 human beings aged 9 to 91 participated. Open-ended interviews (I – III) were conducted to explore the participants’ lived experiences of childhood. The schoolchildren were also asked to create a drawing to support their narrations about playing (I). A hermeneutical phenomenological approach was used to analyse the data (I – III). A secondary analysis of the data from the three hermeneutical phenomenological studies was performed (IV). The comprehensive understanding of all studies (I-IV) was about meeting the challenges in our society of mental ill-health and stress-related conditions. The findings suggest that the participants by practicing self-knowledge to be the best they can be are turning challenges into life lessons. The findings illuminate how human beings are influenced by the inner child throughout the lifespan. Experiences during childhood have an impact on how we act in relation to the next generation, in our choice of profession, and in the promotion of health. The notion of “test-driving life” was about the participants trying to manoeuvre through life with experiences of supportive relationships and safe surroundings, and also of the opposite. Using a health promotion perspective focusing on salutogenic aspects of health and wellbeing, human experiences during the lifespan may give insight on how to overcome challenges in life increasing health literacy – an area in need of further research. The phenomenon of the inner child may further the discussion of health promotion.
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| 1340. |
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