| 1. |
- Kuzmin, Leonid, 1958-
(författare)
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Investigation of the most essential factors influencing ski glide
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- There are many different parameters of a ski running surface (material, roughness, hydrophobicity, etc.). All the parameters have an influence on ski glide, some more and some less. Furthermore, some parameters with only minor relevance are commonly declared as critical, while truly critical parameters, as far as we know, never been investigated. In this thesis, we try to identify and structure the different stages of ski running surface preparation. In our experiments, we have applied well-established, commonly used treatments parallel with alternative preparations. The unexpected result of our experiments is that the treatments commonly used today are not as good as alternative treatments, namely; stone grinding and glide wax application are far from an optimal ski treatment if minimising friction over a given distance is the major goal.
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| 2. |
- Lund Ohlsson, Marie
(författare)
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New methods for movement technique development in cross-country skiing using mathematical models and simulation
- 2009
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Licentiate Thesis is devoted to the presentation and discussion of some new contributions in applied mathematics directed towards scientific computing in sports engineering. It considers inverse problems of biomechanical simulations with rigid body musculoskeletal systems especially in cross-country skiing. This is a contrast to the main research on cross-country skiing biomechanics, which is based mainly on experimental testing alone. The thesis consists of an introduction and five papers. The introduction motivates the context of the papers and puts them into a more general framework. Two papers (D and E) consider studies of real questions in cross-country skiing, which are modelled and simulated. The results give some interesting indications, concerning these challenging questions, which can be used as a basis for further research. However, the measurements are not accurate enough to give the final answers. Paper C is a simulation study which is more extensive than paper D and E, and is compared to electromyography measurements in the literature. Validation in biomechanical simulations is difficult and reducing mathematical errors is one way of reaching closer to more realistic results. Paper A examines well-posedness for forward dynamics with full muscle dynamics. Moreover, paper B is a technical report which describes the problem formulation and mathematical models and simulation from paper A in more detail. Our new modelling together with the simulations enable new possibilities. This is similar to simulations of applications in other engineering fields, and need in the same way be handled with care in order to achieve reliable results. The results in this thesis indicate that it can be very useful to use mathematical modelling and numerical simulations when describing cross-country skiing biomechanics. Hence, this thesis contributes to the possibility of beginning to use and develop such modelling and simulation techniques also in this context.
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| 3. |
- Algervik, Robert, 1981-
(författare)
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Embedding Theorems for Mixed Norm Spaces and Applications
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis is devoted to the study of mixed norm spaces that arise in connection with embeddings of Sobolev and Besov type spaces. The work in this direction originates in a paper due to Gagliardo (1958), and was continued by Fournier (1988) and by Kolyada (2005). We consider fully anisotropic mixed norm spaces. Our main theorem states an embedding of these spaces into Lorentz spaces. Applying this result, we obtain sharp embedding theorems for anisotropic fractional Sobolev spaces and anisotropic Sobolev-Besov spaces. The methods used are based on non-increasing rearrangements and on estimates of sections of functions and sections of sets. We also study limiting relations between embeddings of spaces of different type. More exactly, mixed norm estimates enable us to get embedding constants with sharp asymptotic behaviour. This gives an extension of the results obtained for isotropic Besov spaces $B_p^\alpha$ by Bourgain, Brezis, and Mironescu, and for Besov spaces $B^{\alpha_1,\dots,\alpha_n}_p$ by Kolyada. We study also some basic properties (in particular the approximation properties) of special weak type spaces that play an important role in the construction of mixed norm spaces and in the description of Sobolev type embeddings.
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| 4. |
- Henriksnäs, Johanna, 1973-
(författare)
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Helicobacter pylori and Gastric Protection Mechanisms : An in vivo Study in Mice and Rats
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The stomach is frequently exposed to hazardous agents and to resist this harsh environment, several protective mechanisms exist. Of special interest is the gastric pathogen Helicobacter pylori which causes gastritis, ulcers and cancer but the mechanism leading to these diseases are still unclear. However it is very likely that H. pylori negatively influence the protection mechanisms that exist in the stomach. The aims of the present investigation were first to develop an in vivo mouse model in which different protection mechanisms could be studied, and second to investigate the influence of H. pylori on these mechanisms. An in vivo preparation of the gastric mucosa in mice was developed. This preparation allows studies of different gastric mucosal variables and can also be applied for studies in other gastro-intestinal organs. Mice chronically infected with H. pylori, were shown to have a reduced ability of the mucosa to maintain a neutral pH at the epithelial cell surface. This could be due to the thinner inner, firmly adherent mucus gel layer, and/or to defective bicarbonate transport across the epithelium. The Cl-/HCO3- exchanger SLC26A9 was inhibited by NH4+, which also is produced by H. pylori. The mRNA levels of SLC26A9 were upregulated in infected mice, suggesting a way to overcome the inhibition of the transporter. Furthermore, the hyperemic response to acid pH 2 and 1.5 was abolished in these mice. The mechanisms by which the bacteria could alter the blood flow response might involve inhibition of the epithelial iNOS.Water extracts of H. pylori (HPE) reduces the blood flow acutely through an iNOS and nerve-mediated pathway, possibly through the endogenous iNOS inhibitor ADMA. Furthermore, HPE alters the blood flow response to acid as the hyperemic response to acid pH 0.8 is accentuated in mice treated with HPE.
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| 5. |
- Johnson, Tomas, 1979-
(författare)
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Computer-aided Computation of Abelian integrals and Robust Normal Forms
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This PhD thesis consists of a summary and seven papers, where various applications of auto-validated computations are studied. In the first paper we describe a rigorous method to determine unknown parameters in a system of ordinary differential equations from measured data with known bounds on the noise of the measurements. Papers II, III, IV, and V are concerned with Abelian integrals. In Paper II, we construct an auto-validated algorithm to compute Abelian integrals. In Paper III we investigate, via an example, how one can use this algorithm to determine the possible configurations of limit cycles that can bifurcate from a given Hamiltonian vector field. In Paper IV we construct an example of a perturbation of degree five of a Hamiltonian vector field of degree five, with 27 limit cycles, and in Paper V we construct an example of a perturbation of degree seven of a Hamiltonian vector field of degree seven, with 53 limit cycles. These are new lower bounds for the maximum number of limit cycles that can bifurcate from a Hamiltonian vector field for those degrees. In Papers VI, and VII, we study a certain kind of normal form for real hyperbolic saddles, which is numerically robust. In Paper VI we describe an algorithm how to automatically compute these normal forms in the planar case. In Paper VII we use the properties of the normal form to compute local invariant manifolds in a neighbourhood of the saddle.
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| 6. |
- Hansson, Örjan, 1965-
(författare)
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Studying the views of preservice teachers on the concept of function
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis consists of an overview of the subject, where in particular five papers are put into a frame. The research conducted for the thesis concerns the views of preservice teachers on the concept of function. Preservice teachers’ conceptions of the function concept are in particular examined in relation to mathematical statements that can be related to different topics on a variety of levels in mathematics; in this research, concept mapping technique is a research tool of interest. Questions concerning preservice teachers’ conceptions of the significance of functions in mathematics, and the presence of functions in school mathematics, are also considered relevant aspects of their views of functions. The final part of the research study includes an intervention study regarding the concept of function, located to a calculus course as one of the concluding courses in mathematics on the educational programme. There is a range of findings from the study that is summarized and further discussed in the overview part of the thesis. One result, is that preservice teachers in their reasoning show signs of knowledge compartmentalization which is an issue of concern in their development of conceptual frameworks rich in meaningful connections. This might have consequences for their abilities to operate in a constructivist environment and reason with their students from different points of view. The function concepts’ large network of relations to other concepts is frequently omitted in the preservice teachers’ reasoning. One reason for this is that to preservice teachers, properties of functions seem to be results of isolated procedures, associated with operational conceptions rather than structural conceptions of functions. The findings imply that preservice teachers should encounter functions in a variety of context, to develop their views of the concept of function – including frameworks rich of meaningful relations – and realize that the concept of function is one of the underlying concepts of mathematics, and an important concept to introduce to their future students. The preservice teachers’ reflections concerning functions in school mathematics contribute to emphasize the significance of the process of transformation of subject matter knowledge to pedagogical content knowledge. Further results of the research study, and an outline of the implications, are included in the concluding discussion of the overview part of the thesis. The preservice teachers participating in the study are enrolled in a four and a half year teacher preparation program in mathematics and science, grades 4 to 9. The five papers included in the thesis, describe parts of a larger study essentially conducted until the sixth term during the concluding mathematics courses of the program.
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