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- Uppman, Hannes
(författare)
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On Some Combinatorial Optimization Problems : Algorithms and Complexity
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is about the computational complexity of several classes of combinatorial optimization problems, all related to the constraint satisfaction problems.A constraint language consists of a domain and a set of relations on the domain. For each such language there is a constraint satisfaction problem (CSP). In this problem we are given a set of variables and a collection of constraints, each of which is constraining some variables with a relation in the language. The goal is to determine if domain values can be assigned to the variables in a way that satisfies all constraints. An important question is for which constraint languages the corresponding CSP can be solved in polynomial time. We study this kind of question for optimization problems related to the CSPs.The main focus is on extended minimum cost homomorphism problems. These are optimization versions of CSPs where instances come with an objective function given by a weighted sum of unary cost functions, and where the goal is not only to determine if a solution exists, but to find one of minimum cost. We prove a complete classification of the complexity for these problems on three-element domains. We also obtain a classification for the so-called conservative case.Another class of combinatorial optimization problems are the surjective maximum CSPs. These problems are variants of CSPs where a non-negative weight is attached to each constraint, and the objective is to find a surjective mapping of the variables to values that maximizes the weighted sum of satisfied constraints. The surjectivity requirement causes these problems to behave quite different from for example the minimum cost homomorphism problems, and many powerful techniques are not applicable. We prove a dichotomy for the complexity of the problems in this class on two-element domains. An essential ingredient in the proof is an algorithm that solves a generalized version of the minimum cut problem. This algorithm might be of independent interest.In a final part we study properties of NP-hard optimization problems. This is done with the aid of restricted forms of polynomial-time reductions that for example preserves solvability in sub-exponential time. Two classes of optimization problems similar to those discussed above are considered, and for both we obtain what may be called an easiest NP-hard problem. We also establish some connections to the exponential time hypothesis.
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| 2. |
- Alaie, Iman
(författare)
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Adulthood Outcomes of Child and Adolescent Depression : From Mental Health to Social Functioning
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Depression is a common mental disorder affecting people across the lifespan, with first onset frequently occurring in the teenage years. The disorder is costly to society and constitutes one of the leading causes of disability in youths and adults worldwide. Research demonstrates that depression in childhood or adolescence is linked to adverse adult consequences, including mental health problems, physical health issues, various social difficulties, and economic hardships. While the specific factors and mechanisms associated with these long-term adversities are not well understood, previous studies point to the relevance of considering the heterogeneity in early-life depression.The overarching aim of this doctoral thesis was to shed more light on long-term outcomes of childhood and adolescent depression across multiple life domains. This work made use of extensive follow-up data gathered in Sweden and USA, as part of two community-based longitudinal cohort studies of depressed and nondepressed youths prospectively followed into adulthood. In the Uppsala Longitudinal Adolescent Depression Study, participants were interviewed around age 16 (n=631) and age 31 (n=409). Using linkage to nationwide population-based registries, participants were followed up around age 40 (n=576). In the Great Smoky Mountains Study, participants were interviewed at repeated occasions in childhood and adolescence (n=1,420), and at further follow-ups in adulthood extending up to age 30 (n=1,336).Findings from this work suggest that childhood/adolescent depression can have long-lasting associations with a broad spectrum of adverse outcomes. First, the risk of adult depression is known to be elevated among those exposed to depression in early life; however, depressed youths experiencing major conflicts with parents may be at an additionally increased risk of subsequent depression recurrence. Second, early-life depression was found to be associated with higher levels of adult psychiatric disorders, and also with worse health, criminal, and social functioning, even when accounting for a multitude of potential confounders. Third, early-life depression was predictive of poor labor market outcomes, especially for those with persistent depression. This link was partially mediated by the course of depression. Fourth, the welfare burden associated with early depression amounted to considerable public expenditures in adulthood, particularly for those with persistent depression or comorbid psychiatric conditions such as anxiety and disruptive behavior disorders.The adverse long-term consequences in the wake of early-life depression underscore the importance of prevention and treatment approaches that are both efficacious and cost-effective. Such targeted efforts may have the potential to avert later ill-health, impairment, and possibly also economic disadvantage.
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| 3. |
- Edin, Emil, 1987-
(författare)
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Computational Insights into Atomic Scale Wear Processes in Cemented Carbides
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- As Ti-alloys become more and more utilized the need for efficient and robust manufacturing of Ti-alloy components increase in importance. Ti-alloys are more difficult to machine than e.g. steel, mainly due to their poor thermal conductivity leading to rapid tool wear. The atomic scale processes responsible for this wear is not well understood. Here the focus is turned to the effects of C diffusion out of the tools as a source of the observed wear. A combination of Density Functional Theory (DFT) making use of Harmonic Transition State Theory (HTST), classical Molecular Dynamics (MD) and kinetic Monte Carlo (kMC) is used to investigate C diffusion into and within experimentally observed WC/W interfaces that exists as a consequence of the C depletion. Further, tools are built and used to evaluate interface parameters for large sets of interfaces within the WC/W system to determine which are energetically preferred. The results from the DFT study show stable interfaces with large differences in activation energy between the two most prominent surfaces found in WC materials, namely the basal and prismatic surfaces. Within the WC/W interfaces the diffusion barriers are similar between the two. The classical MD simulations support the view of stable interfaces at the early stages of C depletion. As C is removed this picture shifts to one in which the diffusion barriers are substantially decreased and the difference between the basal and the prismatic interfaces vanish pointing to a process which starts out slow but accelerates as C is continually removed. From the kMC simulations the overall diffusion pre-factor and activation energy is estimated to be D0=1.8x10-8 m2/s and dE=1.24 eV for the investigated [10-10]-I/[100] interface, the kMC simulations also confirm previous results indicating that the diffusion is restricted to the interface region. The investigation and screening of properties for WC/W interfaces show a preference for the W terminated [10-10]-I/[110] and [0001]/[110] interface combinations based on the interfacial energy.
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| 4. |
- Ssegonja, Richard, et al.
(författare)
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Depressive disorders in adolescence, recurrence in early adulthood, and healthcare usage in mid-adulthood : A longitudinal cost-of-illness study
- 2019
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Ingår i: Journal of Affective Disorders. - : ELSEVIER. - 0165-0327 .- 1573-2517. ; 258, s. 33-41
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Tidskriftsartikel (refereegranskat)abstract
- Background: Depression in adolescence is associated with increased healthcare consumption in adulthood, but prior research has not recognized the heterogeneity of depressive disorders. This paper investigated the additional healthcare usage and related costs in mid-adulthood for individuals with adolescent depression, and examined the mediating role of subsequent depression in early adulthood.Methods: This study was based on the Uppsala Longitudinal Adolescent Depression Study, initiated in Sweden in the early 1990s. Depressive disorders were assessed in adolescence (age 16-17) and early adulthood (age 19-30). Healthcare usage and related costs in mid-adulthood (age 31-40) were estimated using nationwide population-based registries. Participants with specific subtypes of adolescent depression (n = 306) were compared with matched non-depressed peers (n = 213).Results: Women with persistent depressive disorder (PDD) in adolescence utilized significantly more healthcare resources in mid-adulthood. The association was not limited to psychiatric care, and remained after adjustment for individual and parental characteristics. The total additional annual cost for a single age group of females with a history of PDD at a population level was estimated at 3.10 million USD. Depression recurrence in early adulthood mediated the added costs for psychiatric care, but not for somatic care.Limitations: Primary health care data were not available, presumably resulting in an underestimation of the true healthcare consumption. Estimates for males had limited precision due to a relatively small male proportion.Conclusions: On a population level, the additional healthcare costs incurred in mid-adulthood in females with a history of adolescent PDD are considerable. Early treatment and prevention should be prioritized.
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