The need for energy efficiency in wireless communication is prevalent in all areas, but to an even greater extent in low-power and lossy networks that rely on resource-constrained devices. This degree project seeks to address the problem of modelling the battery lifetime of a duty-cycled node, participating in a wireless sensor network that is typically used in smart home and building applications. Modelling in MATLAB combined with experimentation are employed to predict the life expectancy and to validate using a hardware implementation. Various scenarios including sleepy end devices in a wireless sensor network are modelled and validated; these range from variable wake-up frequency and packet payload transmission to increasing network contention with the addition of network load. A comprehensive analysis of the main factors contributing to wasteful energy usage is provided in this thesis project, and it can be concluded that the model can estimate the battery lifetime under different testing scenarios with an error less than 5 %. / Det finns ett stort behov av energieffektivitet inom trådlös kommunikation, särskilt inom nätverk med bortfall och låg strömförbrukning där resursbegränsade enheter nyttjas. Det här examensarbetet eftersträvar att lösa problemet med att modellera batterilivslängden hos en sensoranordning med en låg driftcykel, som en del av ett trådlöst sensornätverk avsett för att tillämpas i smarta hus och byggnader. Modellering i MATLAB kombinerat med experimentering används för att förutsäga den förväntade livslängden samt för att validera en hårdvaruimplementering. Flertalet scenarier med sovande noder modelleras och valideras, med allt från variabel uppvakningsfrekvens och paketöverföring till ökande resurskonflikter med ytterligare belastning på nätverket. I detta examensprojekt inkluderas en heltäckande analys av huvudorsakerna till energislöseriet hos enheterna och slutsatsen kan dras att modellen kan beräkna batterilivslängden för olika testscenarier med mindre än 5 % fel.

<p>Left truncation arises because in many situations, failure of a unit is observed only if it fails after a certain period. In many situations, the units under study may not be followed until all of them fail and the experimenter may have to stop at a certain time when some of the units may still be working. This introduces right censoring into the data. Some commonly used lifetime distributions are lognormal, Weibull and gamma, all of which are special cases of the flexible generalized gamma family. Likelihood inference via the Expectation Maximization (EM) algorithm is used to estimate the model parameters of lognormal, Weibull, gamma and generalized gamma distributions, based on left truncated and right censored data. The asymptotic variance-covariance matrices of the maximum likelihood estimates (MLEs) are derived using the missing information principle. By using the asymptotic variances and the asymptotic normality of the MLEs, asymptotic confidence intervals for the parameters are constructed. For comparison purpose, Newton-Raphson (NR) method is also used for the parameter estimation, and asymptotic confidence intervals corresponding to the NR method and parametric bootstrap are also obtained. Through Monte Carlo simulations, the performance of all these methods of inference are studied. With regard to prediction analysis, the probability that a right censored unit will be working until a future year is estimated, and an asymptotic confidence interval for the probability is then derived by the delta-method. All the methods of inference developed here are illustrated with some numerical examples.</p> / Doctor of Philosophy (PhD)

Polymer electrolyte membrane (PEM) fuel cell (FC) stacks require elastomeric gaskets for each cell to keep the reactant gases within their respective regions[1]. If any gasket degrades or fails, the reactant gases can leak or mix with each other directly during operation or standby, affecting the overall operation and performance of the FC. The elastomeric gaskets used as FC seals are exposed to a range of environmental conditions, and concurrently, subjected to mechanical compression between the bipolar plates forming the cell. The combination of mechanical stress and environmental exposure may result in degradation of the seal material[2] over a period of time. In order to address the durability and make reliability predictions, the long-term stability of the gaskets in FC assemblies is critical. The aim of this study is to investigate the performance of elastomeric seals in a simulated FC environment in the presence of mechanical stresses. The overall scope of the study includes mechanical and viscoelastic properties characterization, and lifetime durability predictions based on an accelerated characterization approach. With the help of finite element analysis software, ABAQUS, a fixture was designed to perform strain-based accelerated characterization of seal material in air, deionized (DI) water, 50v/50v ethylene glycol/water solution, and 0.1M sulfuric acid solution. Dogbone samples were strained to different levels in the custom fixture and submerged in liquid solutions at 90°C and in air at 90°C and 120°C. It was observed that mechanical properties such as tensile strength, strain to break, 100% modulus, crosslink density, and tensile set degrade due to aging and the extent of change (increase or decrease) depends significantly on the strain level on the specimen. Trouser tear tests were conducted on reinforced specimens in air and deionized water (DI) to evaluate the tear resistance of an elastomeric seal material intended for proton exchange membrane fuel cells. Plots relating the crack growth rate with tearing energy were obtained at various temperatures and provided significant insight into the rate and temperature dependence of the tearing strength of the seal material. Stick-slip crack propagation was observed at all temperatures and loading rates, although the behavior was suppressed significantly at low loading rates and high temperatures. Crack growth rate versus tearing energy data at different temperatures was shifted to construct a master curve and an estimate on the threshold value of tear energy was obtained which may be helpful in designing components where material tear is of concern. Strain energy release rate (SERR) value, calculated using the J-integral approach for a pre-existing crack in ABAQUS, was used to estimate the crack growth rate in a given seal cross-section to predict lifetime. In order to assess the viscoelastic behavior and to investigate the long term stress relaxation behavior of the seal material, compression stress relaxation (CSR) tests were performed on molded seals, called as SMORS, over a range of environmental conditions using a custom-designed fixture. The effect of temperature and environment was evident on material property changes and presented in terms of momentary properties and stress relaxation behavior. Various mechanisms involved in material degradation, chain scission and crosslinking, were suggested and insights were gained into how cure state and level of antidegradants in a material dictate the material behavior during the first phase of environmental exposure leading to change in material properties. Ring samples made of silicone were also tested using the fixture to obtain insight additional into material degradation due to aging. Results presented from testing on SMORS showed a lot more variation in data as compared to neat silicone rings due to the complexity involved in making SMORS. For understanding the deformation behavior of an elastomeric seal and its sealing performance, finite element characterization of seal cross-section was carried out on O-ring and SMORS cross-section. The effect of a seal's layout on distribution and magnitude of contact stresses and contact width was investigated for the O-ring and the information obtained thereby helped to analyze a complex assembly such as SMORS, where several interfaces and boundary conditions are involved. Stress/strain profiles were generated to visualize their concentration and distribution in the seal cross-section. Frictionless and rough interfacial conditions between seal material and platens were assumed and it was found that its effect on contact width and peak contact pressure was insignificant. Results obtained from FEA on SMORS were validated through comparison with contact mechanics approach and experimental data and it was found that Lindley's equation correlates well with experimental data whereas ABAQUS overestimates the load values at a given compression. Lindley's approach may be used to develop contact pressure profiles that may help estimate peak contact pressure at a given time so leaking can be avoided. / Ph. D.

This dissertation aims to develop methods for statistical predictions based on various types of data from different areas. We focus on applications from reliability and spatial epidemiology. Chapter 1 gives a general introduction of statistical predictions. Chapters 2 and 3 investigate the photodegradation of an organic coating, which is mainly caused by ultraviolet (UV) radiation but also affected by environmental factors, including temperature and humidity. In Chapter 2, we identify a physically motivated nonlinear mixed-effects model, including the effects of environmental variables, to describe the degradation path. Unit-to-unit variabilities are modeled as random effects. The maximum likelihood approach is used to estimate parameters based on the accelerated test data from laboratory. The developed model is then extended to allow for time-varying covariates and is used to predict outdoor degradation where the explanatory variables are time-varying. Chapter 3 introduces a class of models for analyzing degradation data with dynamic covariate information. We use a general path model with random effects to describe the degradation paths and a vector time series model to describe the covariate process. Shape restricted splines are used to estimate the effects of dynamic covariates on the degradation process. The unknown parameters of these models are estimated by using the maximum likelihood method. Algorithms for computing the estimated lifetime distribution are also described. The proposed methods are applied to predict the photodegradation path of an organic coating in a complicated dynamic environment. Chapter 4 investigates the Lyme disease emergency in Virginia at census tract level. Based on areal (census tract level) count data of Lyme disease cases in Virginia from 1998 to 2011, we analyze the spatial patterns of the disease using statistical smoothing techniques. We also use the space and space-time scan statistics to reveal the presence of clusters in the spatial and spatial/temporal distribution of Lyme disease. Chapter 5 builds a predictive model for Lyme disease based on historical data and environmental/demographical information of each census tract. We propose a Divide-Recombine method to take advantage of parallel computing. We compare prediction results through simulation studies, which show our method can provide comparable fitting and predicting accuracy but can achieve much more computational efficiency. We also apply the proposed method to analyze Virginia Lyme disease spatio-temporal data. Our method makes large-scale spatio-temporal predictions possible. Chapter 6 gives a general review on the contributions of this dissertation, and discusses directions for future research. / Ph. D.

Yes / In previous decades, the perception of Japan¿s employment practices has been strongly intertwined with its economic fortunes. From the 1970s, Japan¿s employment practices came to be seen as one of the cornerstones of its economic success. However, this perception changed, albeit with a substantial delay, when the economy proved incapable of returning to its former path of growth after the `bubble¿ burst at the end of the 1980s. Like so many of its economic institutions, the employment practices became the subject of substantial criticism in a debate on the revitalisation of Japan¿s economy. This study takes its position within this debate by discussing the likelihood, character, and economic consequences of change. Environmental changes, like the ageing of the population and the substantial decrease in economic growth, require Japanese firms to adapt their human resource management. However, the embeddedness of national practices limits the scope of firms to make these adjustments; and change is determined by the dialectics between their strategies and existing practices. The firm, as an institution, thus experiences the impact of both the embedded employment practices and the economic impact of environmental changes. Accordingly, it is at the centre of this study. Theories of the firm are used to discuss the contribution of employment practices on efficiency, capabilities, and competitive strength. Case-studies from four different industries ¿ automobile, electronics, construction, and retailing ¿ describe the adaptations made by individual firms. Subsequently, these findings constitute the basis for a discussion of industry-specific employment practices and provide an answer to whether developments such as the rise in performance-based pay and labour mobility have altered the logic of Japanese employment practices.

The paradigm change in automotive power electronics towards wide bandgap semiconductor devices poses new challenges and requirements for the die-related packaging technologies as well as the assessment of reliability and lifetime. Here, the use of sintered silver for the die-related packaging in particular has proven promising. However, the empirical lifetime models for power modules developed over many years are not suitable any more. A holistic Physics-of-Failure approach can provide remedy as it allows for a significant reduction of testing time via finite element simulations. This approach requires a detailed understanding of the relevant failure mechanisms as well as an electrical, thermal and mechanical characterisation of the involved materials. A failure analysis of the complete power module revealed that the top-side sinter layer connecting the copper foil to the semiconductor die is prone to degradation. Therefore, the core of this work is the mechanical characterisation of porous sintered silver and, in particular, the primary and secondary creep behaviour. A newly developed creep model which - for the first time - takes load reversal for primary creep into account is implemented with a subroutine. This allows for lifetime simulations within a Physics-of-Failure framework resulting in a first lifetime model on module level for a complex automotive power module employing sintered silver.

The purpose of this thesis is to predict the lifespan of a battery using a predictive model, utilizing data from early cycles. The goal is to minimize both time and costs for the company by reducing the number of cycles needed for testing. Currently, the company tests a diverse set of batteries, which is both time and resource-consuming. To investigate which data-driven predictive model should be used by the company to predict battery capacity at XX cycles, a thorough literature study has been conducted. In summary, a variety of variables from specific cycles have been calculated based on inspiration from Fei et al. (2021), Severson et al. (2019), Enholm et al. (2022) and an internal project from the company. Following this, two different predictive models, Gaussian Process Regression and Ordinary Least Squared Regression, are applied and compared.  Based on the obtained results, Gaussian Process Regression had a slight better results but a significantly higher complexity compared to Ordinary Least Squared Regression. Therefore, the data-driven model that should be implemented at the company is an Ordinary Least Squared Regression with variables related to different phases during a cycle. This result is primarily based on the varying degrees of complexity of the models. / Syftet med detta examensarbete är att med hjälp av en datadriven prediktionsmodell kunna prediktera livslängden på ett batteri genom att använda data från tidiga cykler. Målet är att minimera både tid och kostnader för företaget genom att minska antalet cykler som behövs för testning. I dagsläget testar företaget en mängd batterier vilket både är tids- samt resurskrävande. För att undersöka vilken datadriven prediktionsmodell som bör användas av företaget för att prediktera batteriekapacitet vid XX cykler har en gedigen litteraturstudie utförts. Sammanfattningsvis har en mängd variabler av de mätningar som finns från specifika cykler beräknats utifrån inspiration från Fei med flera (2021), Severson med flera (2019), Enholm med flera (2022) samt ett internt projekt från företaget. Efter detta applicerades och jämfördes två olika prediktionsmodeller: Gaussian Process Regression och Ordinary Least Squared Regression.  Baserat på de erhållna resultaten hade Gaussian Process Regression något bättre resultat men en betydligt högre komplexitet jämfört med Ordinary Least Squared Regression. Därför är den datadrivna modell som bör implementeras på företaget en Ordinary Least Squared Regression med variabler relaterade till olika faser under en cykel. Detta resultat grundar sig framför allt i olika grad av komplexitet hos modellerna.

Syfte: Studiens syfte är att undersöka svenska och amerikanska företagsmäklares inställning till kundkapitalet och dess värderingsmodeller. Studien syftar även till att finna konsekvenser som en explicit redovisning av kundkapitalet skulle ha på företagsvärderingar.   Tidigare forskning: Centrala modeller i studien är Customer Lifetime Value, Customer Equity, Customer Profitability och Multi-Period Excess Earnings Model. Tidigare forskning hittas i Edvinsson och Malone (1997), Gupta et al (2004), Villanueva och Hanssens (2007), Wiesel et al., (2006) samt Hofstedes forskning om nationella dimensioner.    Metod: Studien använder metodtriangulering. Huvudsaklig primärdata genereras ur webbaserade enkäter som skickas till svenska och amerikanska företagsmäklare. Vidare utförs tre semi-strukturerade intervjuer med representanter från KPMG, Deloitte och UC. Ett chi-tvåtest utformas för att se om det finns ett samband mellan nationalitet och företagsmäklares inställning till att beakta kundkapitalet.   Slutsats: 72 procent av de deltagande företagsmäklarna och samtliga intervjupersoner anser att det är viktigt att värdera kundkapitalet. Trots detta är det endast 38 procent av enkätrespondenterna som svarar att de beaktar kundkapitalet vid värdering av kundbaserade företag. En jämförelse mellan nationaliteterna visar att svenska företagsmäklare är mer positiva till de ”nya” kundvärderingsmodellerna, främst Customer Equity och Customer Profitability. De är också mer benägna att använda dessa. Amerikanska företagsmäklare tenderar istället att använda den traditionella Multi-Period Excess Earnings Method. / Purpose: The purpose of this thesis is to investigate Swedish and American business appraisers’ attitude towards customer capital and its valuation models. This thesis also aims to find consequences that an explicit accounting of customer capital would have on business valuations.  Previous Research: Central models in this study are Customer Lifetime Value, Customer Equity, Customer Profitability and Multi-Period Excess Earnings Method. Previous research is found in Edvinsson and Malone (1997), Gupta et al., (2004), Villanueva and Hanssens (2007), Wiesel et al., (2006) and Hofstedes research regarding cultural dimensions. Method: This study uses a triangulation of methods. The main primary data is generated through internet-based questionnaires which was sent to Swedish and American business appraisers. Furthermore, three semi-structured interviews are conducted with representatives from KPMG, Deloitte and UC. A chi-Squared test is made to see if there is any relationship between nationality and business appraisers’ attitude towards taking heed of the customer capital. Conclusion:  72 per cent of the participated business appraisers and all interviewees think that it is important to value customer capital. Despite this, there are only 38 per cent of the survey respondents who say that they account for customer capital when valuing customer-based companies. A comparison between the nationalities show that Swedish business appraisers are more positive towards the “new” customer valuation models such as Customer Equity and Customer Profitability. They are also more inclined to use these. American business appraisers tend to use the more traditional Multi-Period Excess Earnings Method.

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The evolution of extra-group paternity (EGP) is a contentious issue in evolutionary biology. This thesis examines the factors and adaptive benefits driving EGP in a high-density, group-living population of European badgers (Meles meles). To improve power to assign parentage, I isolated and characterised 21 new polymorphic microsatellite markers. I genotyped 83% of 1410 badger trapped 1987‒2010 using 35 autosomal microsatellite markers. Maternity and paternity were assigned at 80% confidence ca. 82% of individuals. 48% of paternities were extra-group, where 85% were attributable to neighbouring-group males and EGP was detected in 47% of litters; thus badger social group do not correspond with a breeding unit. I tested whether indirect genetic benefits explain these high EGP rates. (1) ‘Good-gene-as-heterozygosity Hypothesis’: Paternal heterozygosity, but not maternal or an individual’s own heterozygosity, associated positively with first-year survival probability. Under benign environmental conditions, cubs fathered by more heterozygous males had a higher first year survival probability. Despite this correlation, the EGP rate per litter correlated with neither average nor maximum within-group heterozygosity of candidate fathers. (2) Fitness benefit Hypothesis: Extra-group offspring (EGO) had lower first-year survival probability and lived 1.3 years less than within-group offspring (WGO). Female WGO produced more litters and offspring over their lifetime than female EGO, whereas male EGO produced more offspring than male WGO. (3) Inbreeding avoidance hypothesis: The EGP rate within a litter increased with greater average pair-wise relatedness between mothers and within-group candidate fathers. No inbreeding depression on first-year survival probability was detected, but small sample sizes limited statistical power. Socio-ecologically, at the litter level, EGP correlated negatively with the number of within-group candidate fathers, and positively with neighbouring-group candidate fathers. In conclusion, EGP in badgers may reduce inbreeding and be maintained in the population through a sex-specific antagonistic selection and indirect genetic benefits may occur when the total fitness benefits of producing extra-group sons outweigh the costs of producing extra-group daughters. These indirect genetic benefits only partially explain the evolution of promiscuity in European badgers, highlighting that evolutionary factors underlying promiscuity remain unclear.