| 1. |
- Sannel, A. Britta K., 1968-
(author)
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Temporal and spatial dynamics in subarctic peat plateaus and thermokarst lakes
- 2010
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Doctoral thesis (other academic/artistic)abstract
- Permafrost peatlands are widespread at high northern latitudes and are important soil organic carbon reservoirs. A future warming in these areas, as suggested by global climate models, can cause thawing and increased ground subsidence (thermokarst), resulting in changes in surface hydrology and ecosystem functioning. The aim of this thesis is to increase our knowledge of temporal and spatial dynamics in subarctic peat plateaus with interspersed thermokarst lakes in order to better understand how these ecosystems respond to climate change. Detailed plant macrofossil and carbon/nitrogen ratio analyses of two peat plateaus located in the continuous and northern discontinuous permafrost zones in west-central Canada show that permafrost conditions have been stable since permafrost developed around 5600–4500 cal yr BP. Peat plateaus act as carbon sinks over time. The lack of wet phases since the plateaus formed, despite several local fires, suggests that this type of peatlands have been negligible as methane sources throughout most of their history, representing a negative net radiative forcing on climate. Thermokarst lakes are common features in peat plateaus across the northern permafrost region. A time-series analysis of aerial photographs and high resolution satellite images in three peat plateau/thermokarst lake complexes along a climatic and permafrost gradient shows that where the mean annual air temperature (MAAT) is below -5ºC and ground temperatures are -2ºC or colder, only minor changes in thermokarst lake extent have occurred from the mid 1970s until the mid 2000s. During the same time interval extensive lake drainage and new lake formation has taken place where the MAAT is ca -3ºC and the ground temperature is close to 0ºC. In a future progressively warmer and wetter climate, permafrost degradation can cause significant impacts on landscape pattern and greenhouse gas exchange also in the vast peat plateaus presently experiencing stable permafrost conditions.
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| 2. |
- Ingvander, Susanne, 1979-
(author)
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Snow particle size investigations using digital image analysis - implications for ground observations and remote sensing of snow
- 2011
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Doctoral thesis (other academic/artistic)abstract
- During the past century climate warming has caused rapid changes in the Cryosphere. This has increased the need to accurately monitor rates of change in snow and ice in remote or sparsely populated areas where environmental observing capacity is limited. Monitoring snow cover requires understanding of the snow pack and the snow surface attributes. Snow particle size is an important parameter for characterization of snow pack properties. The size and shape of the snow particles affects the snow/air-ratio which in turn affect how energy is reflected on the snow surface. This governs the snow pack energy balance by changing the albedo or backscattering properties of the snow. Both the albedo and the snow particle size can be quantified by remote sensing. However, the snow particle size estimated by remote sensing, also called the optically equivalent particle size, represents only an approximation of the true or physical particle size of snow. Thus, there is demand for methods that relate both parameters and help to improve the interpretation of remote sensing data of snow at higher spatial and temporal scales. To address this demand the aim of this dissertation thesis is to improve existing sampling methods of the physical snow particle size to retrieve high-resolution, spatial and temporal data sets for validation of remote sensing data. A field sampling method based on object-oriented analysis of digital images was developed that allows measurements of various snow particle size parameters such as length, width, area, specific surface area and shape. The method generates a continuous snow particle size distribution that supports the detailed statistical characterization of a large number of samples. The results show its possibility to compare data from different existing methods. The sampling method was applied in field sites in Antarctica and in northern Sweden, to characterize the spatial variability in the physical snow particle size and to estimate correlations between various remote sensing products and the observed physical snow particle size. The results of the presented studies show that more detailed measurements of snow particle size in the field at higher temporal and spatial scales can improve the interpretation of active and passive satellite retrieved data.
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| 3. |
- Jansson, Daniel, 1986-
(author)
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Identification Techniques for Mathematical Modeling of the Human Smooth Pursuit System
- 2015
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Doctoral thesis (other academic/artistic)abstract
- This thesis proposes nonlinear system identification techniques for the mathematical modeling of the human smooth pursuit system (SPS) with application to motor symptom quantification in Parkinson's disease (PD). The SPS refers to the complex neuromuscular system in humans that governs the smooth pursuit eye movements (SPEM). Insight into the SPS and its operation is of importance in a wide and steadily expanding array of application areas and research fields. The ultimate purpose of the work in this thesis is to attain a deeper understanding and quantification of the SPS dynamics and thus facilitate the continued development of novel commercial products and medical devices. The main contribution of this thesis is in the derivation and evaluation of several techniques for SPS characterization. While attempts to mathematically model the SPS have been made in the literature before, several key aspects of the problem have been previously overlooked.This work is the first one to devise dynamical models intended for extended-time experiments and also to consider systematic visual stimuli design in the context of SPS modeling. The result is a handful of parametric mathematical models outperforming current State-of-the-Art models in terms of prediction accuracy for rich input signals. As a complement to the parametric dynamical models, a non-parametric technique involving the construction of individual statistical models pertaining to specific gaze trajectories is suggested. Both the parametric and non-parametric models are demonstrated to successfully distinguish between individuals or groups of individuals based on eye movements.Furthermore, a novel approach to Wiener system identification using Volterra series is proposed and analyzed. It is exploited to confirm that the SPS in healthy individuals is indeed nonlinear, but that the nonlinearity of the system is significantly stronger in PD subjects. The nonlinearity in healthy individuals appears to be well-modeled by a static output function, whereas the nonlinear behavior introduced to the SPS by PD is dynamical.
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| 4. |
- Jansson, Peter M., 1965-
(author)
-
Våldets onda cirklar : En explorativ undersökning av mäns barndomsupplevelser, maskuliniteter, känslor, våld samt terapeutiska interventioner mot våld
- 2016
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Doctoral thesis (other academic/artistic)abstract
- Avhandlingens överordnade syfte är att utforska möjligheterna för ett integrerat forskningsperspektiv på mäns våld samt exemplifiera hur sådan forskning kan bedrivas. Det konkreta syftet är att öka kunskapen om hur våldsamma mäns barndomsupplevelser, socialisation, maskulinitetskonstruktion och emotioner kan relateras till deras våld mot andra män, mot sig själva och mot kvinnor samt till hur terapeutiska interventioner mot våld kan analyseras och utvecklas i korrespondens med denna kunskap. Med vetenskapsteoretiska utgångspunkter hämtade från den kritiska realismen och ekologiska metoder relaterar studien forskning från olika skolbildningar till varandra; - psykologisk: om barndomserfarenheter och socialisation, socialpsykologisk: om emotioner och interaktion samt sociologisk: om social klass, könsmaktsstrukturer och hegemonisk maskulinitet. Detta genomförs för att kunna få tillgång till kunskap om hur olika faktorer samverkar vid mäns våld.I studie I och II studerades möjligheterna att undersöka de sociala banden mellan terapeut/terapi och klient inom terapeutiska behandlingar mot våld. I studie I operationaliserades indikatorer på emotionerna stolthet och skam och i studie II testades dessa på terapeuter inom en KBT-orienterad terapi. I studie IIIundersöktes män i olika maskulinitetspositioner, där urvalet för den ena gruppen hämtades ur populationen män dömda till terapi för våld och missbruk och den andra ur populationen män som organiserat arbetade för jämlikhet och mot våld mot kvinnor. I studien jämfördes de båda gruppernas förhållningssätt till faktorer som i tidigare forskning relaterats till våld och våld mot kvinnor. I studie IVundersöktes våldsdömda mäns karriärer fram till deras nuvarande position som våldsbejakande kriminella i avsikt att öka kunskapen om det samspel mellan faktorer som i olika situationer leder fram till deras våld mot andra män, sig själva och kvinnor. Samtliga empiriska studier använde kvalitativa metoder för datainsamling och analys. I studie IV användes individuella intervjuer och biografisk analys, I studie II ochIII användes gruppintervjuer samt deduktiv innehållsanalys. I studie I, den teoretiska reviewartikeln, utgjorde sociologisk, socialpsykologisk och psykologisk teoribildning empiri.Avhandlingen visar att det finns fler fördelar är nackdelar med ett nivåövergripande perspektiv. Nivåintegrerande studier försvåras av att de kräver en komplex metodologi för att kunna hantera samverkan mellan faktorer bakom våld på olika nivåer men ger å andra sidan en mer holistisk förståelse av fenomenet i fråga. Resultaten visar att integrerande perspektiv kan minska risken för ekologiska felslut och ökar förståelsen av komplex samverkan mellan faktorer bakom mäns våld, något som kan komma att bidra till kunskapsutvecklingen inom våldsterapiområdet. Den teoretiska reviewartikeln (studie I) exemplifierade hur teoretiskt och metodologiskt driven forskning om sociala band kan göras pragmatiskt tillämpbar av terapeuter inom våldbehandlingar. Den tillämpade studien av en KBT-terapi (studie II) gav exempel på hur operationaliserade indikatorer på stolthet och skam kan användas praktiskt för att bestämma kvalitén på det sociala bandet mellan terapeut och klient. Den studerade KBT-terapin innehöll som förväntat både skam- och stolthetskapande moment vilket utgör värdefulla utgångspunkter för vidare forskning. Jämförelsen mellan män i idealtypiskt motsatta maskulinitetspositioner (studie III) visade att både gruppen av män som arbetar mot våld mot kvinnor och männen dömda till behandling mot våld, bär på ambivalenta attityder gentemot våld och våld mot kvinnor. Jämförelsen visade vidare att gruppernas maskulinitetskonstruktioner och attityder till våld korresponderar med grupperingarnas olika tillgång till ekonomiska, sociala och kulturella resurser. Den biografiskt fokuserade kvalitativa studien av män i våldsbehandling (studie IV) undersökte explorativt hur karriären fram till våldskriminell kan se ut och hur barndomsupplevelser, socialisation, maskulinitet och emotioner hos enskilda våldsverkande män kan tänkas ha samverkat med varandra när våld äger rum. Resultaten visade att de män som vittnar om utsatthet för allvarligt våld i barndomen är mer skambenägna och vid kränkningar från andra tenderar att omedvetet och utan föregående känslor av skam direkt reagera med aggressioner och våld mot båda könen. Övriga män var visserligen skambenägna men beskrev en mer kontrollerad våldsreaktion. Två män som blivit brutalt fysiskt mobbade i grundskolan, berättade om ett mer kontrollerat våld. En preliminär hypotes är att männen kan ha lärt sig att kognitivt, för att undslippa fortsatt mobbing, ta kontrollen över processen där skamkänslor ersätts med aggressioner. Föräldrarnas personliga problem tillsammans med deras bristande sociala kontroll och omsorg antogs ha ett samband med flera av männens skolproblem, deras umgänge med avvikande ungdomar, deras senare svårigheter med att kunna försörja sig med konventionella medel samt deras våldskarriärer.
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| 5. |
- Mercer, Andrew, 1972-
(author)
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Studies in Glacier Mass Balance : Measurement and its errors
- 2018
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Doctoral thesis (other academic/artistic)abstract
- The study of the surface mass balance of valley glaciers has a long history but one that is dogged by uncertainty and errors, and uncertainty about those errors. These problems are acknowledged by the glaciological community and have been examined and formalised in several publications. The latest of these stems from a workshop organised by the World Glacier Monitoring Service, the results of which are presented in the first paper of this thesis. The paper examines two common methods and some of their associated errors, with the aim of unifying them and providing more robust data sets. New methodologies, such as ground penetrating radar (GPR), are used in the second paper herein to provide richer and alternative data sources for approaching measurement problems related to snow depth and, to some degree, snow density. The third paper is concerned with both technical survey issues and glaciological definitions when surveys of glacier surfaces are performed for use in mass balance calculation. Many of these issues are common to remote sensing methods and ground based surveys but the paper attempts to make this commonality more explicit. Whilst the first three papers concern themselves with the act of measurement and calculation the fourth paper considers errors brought about by logistical constraints restricting the timing of surveys. Such errors are technically avoidable to a large degree but inevitable in practice. In the case presented here the error is one of unobserved accumulation, falling late in the season, after the last survey. By modelling expected ablation from minimal data, such as temperature, and comparing this with measured mass balance an estimate of unobserved accumulation is made.Also contained in this work is an assessment of glacier front surveys, specifically those performed by the Tarfala Research Station. Such surveys are assumed to act as a monitor of glacier response to climate change and are assumed to be a large scale proxy of mass balance but the resolution of the response as well as the resolution of survey methods indicates that the frequency of such surveys should be reduced and that remote sensing methods may be more effective.Common to all glaciological field surveys is the relative sparsity of data rendering error analysis and many statistical methods ineffective but new technologies such as Lidar, Global Navigation Satellite System, GPR and remote sensing indicate a way forward and the potential for future work to deliver detailed and reliable data.
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| 6. |
- Sannel, A. Britta K., 1968-
(author)
-
Holocene dynamics in subarctic peat plateaus of west-central Canada : Vegetation succession, peat accumulation and permafrost history
- 2007
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Licentiate thesis (other academic/artistic)abstract
- Dynamics in vegetation, permafrost and peat and net carbon accumulation rates throughout the Holocene have been studied in two subarctic peat plateaus of west-central Canada through plant macrofossil analysis, geochemical analyses and AMS radiocarbon dating. Peatland formation at the studied sites began around 6600-5900 cal yr BP as a result of paludification of upland forests. Permafrost aggradation probably occurred 5600-4500 cal yr BP when Sphagnum fuscum became established and rootlet layers started to appear. Alternating layers of Sphagnum fuscum and rootlet peat throughout most of the peat profiles are indicating relatively dry surface conditions, suggesting that permafrost conditions have remained stable since the peat plateau stages were initiated. Local fires have occurred in the peatlands, but most fires did not cause degradation of the permafrost. However, lower peat and net carbon accumulation rates are recorded from rootlet layers containing charcoal. The long-term peat and net carbon accumulation rates for both studied peat profiles are 0,30-0,31 mm/yr and 12,5-12,7 gC/m2yr. Accumulation rates are variable depending on peat plateau stage. Peat accumulation rates are in general 4-5 times higher in S. fuscum than in rootlet stages, and net carbon accumulation rates are 3-4 times higher. Therefore even though Sphagnum peat makes up a majority of the peat profile depth, rootlet peat stages can represent most of the time since the peatland was initiated. The gross stratigraphy and plant macrofossil analyses show that there have been no wet phases, indicating permafrost collapse, since the peat plateau stages were initiated. This suggests that subarctic peat plateaus with alternating Sphagnum fuscum and rootlet peat layers have been acting as long-term net carbon sinks, accumulating carbon which has been incorporated into the permafrost, throughout most of the Holocene. High and stable carbon/nitrogen ratios throughout most of the profiles suggest that decomposition has not occurred in the perennially frozen peat. Since the peat plateaus are characterized by no decay in the permafrost and dry surface conditions, methane emissions are negligible from these ecosystems. In a future warmer climate carbon that has been stored under permafrost conditions can be remobilized. The warming may cause drier surface conditions resulting in increased emissions of carbon dioxide or, alternatively, permafrost collapse resulting in wetter surface conditions and increased methane emissions.
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| 7. |
- Andersson, Anders, 1983-
(author)
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Distributed Moving Base Driving Simulators : Technology, Performance, and Requirements
- 2019
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Doctoral thesis (other academic/artistic)abstract
- Development of new functionality and smart systems for different types of vehicles is accelerating with the advent of new emerging technologies such as connected and autonomous vehicles. To ensure that these new systems and functions work as intended, flexible and credible evaluation tools are necessary. One example of this type of tool is a driving simulator, which can be used for testing new and existing vehicle concepts and driver support systems. When a driver in a driving simulator operates it in the same way as they would in actual traffic, you get a realistic evaluation of what you want to investigate. Two advantages of a driving simulator are (1.) that you can repeat the same situation several times over a short period of time, and (2.) you can study driver reactions during dangerous situations that could result in serious injuries if they occurred in the real world. An important component of a driving simulator is the vehicle model, i.e., the model that describes how the vehicle reacts to its surroundings and driver inputs. To increase the simulator realism or the computational performance, it is possible to divide the vehicle model into subsystems that run on different computers that are connected in a network. A subsystem can also be replaced with hardware using so-called hardware-in-the-loop simulation, and can then be connected to the rest of the vehicle model using a specified interface. The technique of dividing a model into smaller subsystems running on separate nodes that communicate through a network is called distributed simulation.This thesis investigates if and how a distributed simulator design might facilitate the maintenance and new development required for a driving simulator to be able to keep up with the increasing pace of vehicle development. For this purpose, three different distributed simulator solutions have been designed, built, and analyzed with the aim of constructing distributed simulators, including external hardware, where the simulation achieves the same degree of realism as with a traditional driving simulator. One of these simulator solutions has been used to create a parameterized powertrain model that can be configured to represent any of a number of different vehicles. Furthermore, the driver's driving task is combined with the powertrain model to monitor deviations. After the powertrain model was created, subsystems from a simulator solution and the powertrain model have been transferred to a Modelica environment. The goal is to create a framework for requirement testing that guarantees sufficient realism, also for a distributed driving simulation.The results show that the distributed simulators we have developed work well overall with satisfactory performance. It is important to manage the vehicle model and how it is connected to a distributed system. In the distributed driveline simulator setup, the network delays were so small that they could be ignored, i.e., they did not affect the driving experience. However, if one gradually increases the delays, a driver in the distributed simulator will change his/her behavior. The impact of communication latency on a distributed simulator also depends on the simulator application, where different usages of the simulator, i.e., different simulator studies, will have different demands. We believe that many simulator studies could be performed using a distributed setup. One issue is how modifications to the system affect the vehicle model and the desired behavior. This leads to the need for methodology for managing model requirements. In order to detect model deviations in the simulator environment, a monitoring aid has been implemented to help notify test managers when a model behaves strangely or is driven outside of its validated region. Since the availability of distributed laboratory equipment can be limited, the possibility of using Modelica (which is an equation-based and object-oriented programming language) for simulating subsystems is also examined. Implementation of the model in Modelica has also been extended with requirements management, and in this work a framework is proposed for automatically evaluating the model in a tool.
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| 8. |
- Andersson, Anders
(author)
-
Extensions for Distributed Moving Base Driving Simulators
- 2017
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Licentiate thesis (other academic/artistic)abstract
- Modern vehicles are complex systems. Different design stages for such a complex system include evaluation using models and submodels, hardware-in-the-loop systems and complete vehicles. Once a vehicle is delivered to the market evaluation continues by the public. One kind of tool that can be used during many stages of a vehicle lifecycle is driving simulators.The use of driving simulators with a human driver is commonly focused on driver behavior. In a high fidelity moving base driving simulator it is possible to provide realistic and repetitive driving situations using distinctive features such as: physical modelling of driven vehicle, a moving base, a physical cabin interface and an audio and visual representation of the driving environment. A desired but difficult goal to achieve using a moving base driving simulator is to have behavioral validity. In other words, \A driver in a moving base driving simulator should have the same driving behavior as he or she would have during the same driving task in a real vehicle.".In this thesis the focus is on high fidelity moving base driving simulators. The main target is to improve the behavior validity or to maintain behavior validity while adding complexity to the simulator. One main assumption in this thesis is that systems closer to the final product provide better accuracy and are perceived better if properly integrated. Thus, the approach in this thesis is to try to ease incorporation of such systems using combinations of the methods hardware-in-the-loop and distributed simulation. Hardware-in-the-loop is a method where hardware is interfaced into a software controlled environment/simulation. Distributed simulation is a method where parts of a simulation at physically different locations are connected together. For some simulator laboratories distributed simulation is the only feasible option since some hardware cannot be moved in an easy way.Results presented in this thesis show that a complete vehicle or hardware-in-the-loop test laboratory can successfully be connected to a moving base driving simulator. Further, it is demonstrated that using a framework for distributed simulation eases communication and integration due to standardized interfaces. One identified potential problem is complexity in interface wrappers when integrating hardware-in-the-loop in a distributed simulation framework. From this aspect, it is important to consider the model design and the intersections between software and hardware models. Another important issue discussed is the increased delay in overhead time when using a framework for distributed simulation.
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| 9. |
- Helanow, Christian, 1981-
(author)
-
Basal boundary conditions, stability and verification in glaciological numerical models
- 2017
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Doctoral thesis (other academic/artistic)abstract
- To increase our understanding of how ice sheets and glaciers interact with the climate system, numerical models have become an indispensable tool. However, the complexity of these systems and the natural limitation in computational power is reflected in the simplifications of the represented processes and the spatial and temporal resolution of the models. Whether the effect of these limitations is acceptable or not, can be assessed by theoretical considerations and by validating the output of the models against real world data. Equally important is to verify if the numerical implementation and computational method accurately represent the mathematical description of the processes intended to be simulated. This thesis concerns a set of numerical models used in the field of glaciology, how these are applied and how they relate to other study areas in the same field.The dynamical flow of glaciers, which can be described by a set of non-linear partial differential equations called the Full Stokes equations, is simulated using the finite element method. To reduce the computational cost of the method significantly, it is common to lower the order of the used elements. This results in a loss of stability of the method, but can be remedied by the use of stabilization methods. By numerically studying different stabilization methods and evaluating their suitability, this work contributes to constraining the values of stabilization parameters to be used in ice sheet simulations. Erroneous choices of parameters can lead to oscillations of surface velocities, which affects the long term behavior of the free-surface ice and as a result can have a negative impact on the accuracy of the simulated mass balance of ice sheets.The amount of basal sliding is an important component that affects the overall dynamics of the ice. A part of this thesis considers different implementations of the basal impenetrability condition that accompanies basal sliding, and shows that methods used in literature can lead to a difference in velocity of 1% to 5% between the considered methods.The subglacial hydrological system directly influences the glacier's ability to slide and therefore affects the velocity distribution of the ice. The topology and dominant mode of the hydrological system on the ice sheet scale is, however, ill constrained. A third contribution of this thesis is, using the theory of R-channels to implement a simple numerical model of subglacial water flow, to show the sensitivity of subglacial channels to transient processes and that this limits their possible extent. This insight adds to a cross-disciplinary discussion between the different sub-fields of theoretical, field and paleo-glaciology regarding the characteristics of ice sheet subglacial hydrological systems. In the study, we conclude by emphasizing areas of importance where the sub-fields have yet to unify: the spatial extent of channelized subglacial drainage, to what degree specific processes are connected to geomorphic activity and the differences in spatial and temporal scales.As a whole, the thesis emphasizes the importance of verification of numerical models but also acknowledges the natural limitations of these to represent complex systems. Focusing on keeping numerical ice sheet and glacier models as transparent as possible will benefit end users and facilitate accurate interpretations of the numerical output so it confidently can be used for scientific purposes.
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| 10. |
- Mølmen, Live
(author)
-
Materials Reliability in PEM Fuel Cells
- 2021
-
Licentiate thesis (other academic/artistic)abstract
- As part of the global work towards reducing CO2 emissions, all vehicles needs to be electrified, or fueled by green fuels. Batteries have already revolutionised the car market, but fuel cells are believed to be a key energy conversion system to be able to electrify also heavy duty vehicles. The type of fuel cell commercially available for vehicles today is the polymer electrolyte membrane fuel cell (PEMFC), but for it to be able to take a larger market share, the cost must be reduced while sufficient lifetime is ensured.The PEMFC is a system containing several components, made of different materials including the polymer membrane, noble metal catalyst particles, and metallic bipolar plate. The combination of different materials exposed to elevated temperature, high humidity and low pH make the PEMFC components susceptible to corrosion and degradation.The noble metal catalyst is one of the major contributors to the high cost. In this work, the latest research on new catalyst materials for PEMFCs are overviewed. Furthermore, electrodeposition as a simple synthesis route to test different Pt-alloys for the cathode catalyst in the fuel cell is explored by synthesis of PtNi and PtNiMo. The gas diffusion layer of the PEMFC is used as substrate to reduce the number of steps to form the membrane electrode assembly.In addition to cheaper and more durable materials, understanding of how the materials degrade, and how the degradation affects the other components is crucial to ensure a long lifetime. Finding reliable test methods to validate the lifetime of the final system is necessary to make fuel cell a trusted technology for vehicles, with predictable performance.In this work, commercial flow plates are studied, to see the effect of different load cycles and relative humidities on the corrosion of the plate. Defects originating from production is observed, and the effect of these defects on the corrosion is further analysed. Suggestions are given on how the design and production of bipolar plates should be made to reduce the risk of corrosion in the PEMFC.
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