<p>The present work highlights some aspects of ski base sliding friction and ski base structure. Ski base structure causes speed differences that range from negligible to almost 10% of the skier speed. The great speed difference under som snow conditions makes the choice of the best structure an important issue for competition skiers and an interesting aspect to understand the physical processes that control friction against snow.</p><p>The thesis discusses and explains ski base sliding friction by use of tribology, impact and compaction resistances, electrical charging and electrostatic pressures. The optimum ski base structure roughness varies under different snow conditions according to the generated frictional water film thickness under the ski and the roughness of the snow surface. Thick water films correspond to course ski base structures, while it is advantageous to use finer ski bae structures and increase the water film thickness when th water film is thin. The possible increase of water film thickness along the ski implies an increase of the ski base structure roughness along the ski. Impact and compaction resistances are important when the snow hardness is below a certain limit, and when the water film thickness is low relative to the roughness of the ski base structure and the snow surface. The dry friction process is dominated and characterized electrically by accumulaltion of electrostatic charge in the ski base contact points. The frictional water film inititates discharge of potential differences between ski and snow due to the much higher electrical conductivity of water relative to snow. When the air gap volumes between the water film and the ski base structure, and the water film and the snow surface get small, the electrostatic pressures in the air gaps increase, and suction or drag may start occuring. The wet friction process is characterised electrically by electrolytic behavior. Further research is necassary in order to increase the knowledge and understanding of the simultaneous processes of mass, impulse, energy, electrical and chemical balances between the two interacting surfaces in relative motion during friction.</p><p>A Ski base Structure Analyser (SSA) utilising laser technology has been developed to analyse the detailed structure of a stone-fround ski base. The SSA displays the measured surface as an image with 739x570 pixels, where each pixel can have a grey level value from 0 to 255. The value of each pixel is proportional to the height at the corresponding point of the measured surface. In the period between 1995 and 1998 almost 1700 ski base structure measurements were performed on more than 350 skis. It was found that ski pairs ground with the "same" structure at two different times are not necassarily equal if no quality control of the ski base structure and the stone grinding process has been performed. On several competition ski pairs higher structure roughness (up to 84%) was revealed on the forebody than the afterbody of the ski. The work has resulted in develoment of ski base structures with increased roughness along the ski, developed and extreme optimisation of the best structures, and improvement of the frinding diamonds used to set the grinding stone. further, it has given ski technicians and competition skiers confidence in that optimum structures can be reproduced. The ski base structure roughness can be divided into four categories: fine (arithmetic mean roughness 1-4 µm), medium (arithmetic mean roughness 4-7 µm), course ( arithmetic mean roughness 7-10 µm) and very coarse ( arithmetic mean roughness higher than 10 µm) that correspond to dry to moist, moist, moist to wet, and wet to very wet snow conditions, respectively. </p><p>A structure test series consisting of ten ski pairs with eight different structures has been ground and quality-controlled. Accurate sliding tests showed that ski pairs with arithmetic mean structure roughness ≤ 5.4 µm were best under snow conditions with snow humidity ≤ 0.6%, snow temperatures below zero and new snow. A ski pair with arithmetic mean structure roughness equal to 9.3 µm was best under snow conditions with snow humidity between approximatly 0.3 and 4.0 %, snow hardness higher than 4.1x10⁴ Pa and transformed snow types. Under snow conditions with snow humidity higher than approximately 4%, a structure with arithmetic mean roughness 12.7 µm was best. Coarser sructures were relatively better than finer structures at high speeds compared to low speeds, thus implying an increase in the water film thickness and optimum structure roughness with speed. A decrease of the structure roughness along the ski was unfortunate under most snow conditions.</p><p>Various snow parameters have been registered during measurement campaigns in ski tracks in Norway (1995-98), Hakuba/Japan (1996-98) and Sundance/USA (1999). Specific attention has been paid to snow hardness, snow humidity, snow density, snow grain structure and electrolytic conductivity. Snow hardness between 10⁴and 10⁶Pa is most common in ski tracks, and snow hardness below 10⁵Pa is likely to be present 60% of the time. The mean density of snow in ski tracks (0.50 g/cm³) is considerable higher than typical densities of seasonal snow covers (0.26-0.38 g/cm³) and higher for transformed snow types (0.51-059 g/cm³) than new snow types (0.39-0.43 g/cm³). The snow humidity in a ski track typically ranges between 0 and 12.5%. It is typically less than 2% for snow temperatures below -2 °C and less than 1% for snow temperatures below -7°C. Snow humidities exceeding 4% have only been registered at air temperatures above +1°C. High electrolytic conductivities (61.7 µS/cm and 94.5 µS/cm, respectively) and high levels of Na⁺- and C1^--ions have been registered in melted snow samples from Trondheim and Sundance/Heber due to salt being a major agent during snow nucleation in the snowfalls. These values are approximately 3 times higher than the maximum values found for snow samples from Hakuba (21.9 µS/cm). The electrolytic conductivity of a melted snow sample may indicate the rate of ions introduced th the interface between snow and ski by frictional melting and thereby the rate and ease of discharge between ski and snow through the frictional water film during skiing. </p>

The present work highlights some aspects of ski base sliding friction and ski base structure. Ski base structure causes speed differences that range from negligible to almost 10% of the skier speed. The great speed difference under som snow conditions makes the choice of the best structure an important issue for competition skiers and an interesting aspect to understand the physical processes that control friction against snow. The thesis discusses and explains ski base sliding friction by use of tribology, impact and compaction resistances, electrical charging and electrostatic pressures. The optimum ski base structure roughness varies under different snow conditions according to the generated frictional water film thickness under the ski and the roughness of the snow surface. Thick water films correspond to course ski base structures, while it is advantageous to use finer ski bae structures and increase the water film thickness when th water film is thin. The possible increase of water film thickness along the ski implies an increase of the ski base structure roughness along the ski. Impact and compaction resistances are important when the snow hardness is below a certain limit, and when the water film thickness is low relative to the roughness of the ski base structure and the snow surface. The dry friction process is dominated and characterized electrically by accumulaltion of electrostatic charge in the ski base contact points. The frictional water film inititates discharge of potential differences between ski and snow due to the much higher electrical conductivity of water relative to snow. When the air gap volumes between the water film and the ski base structure, and the water film and the snow surface get small, the electrostatic pressures in the air gaps increase, and suction or drag may start occuring. The wet friction process is characterised electrically by electrolytic behavior. Further research is necassary in order to increase the knowledge and understanding of the simultaneous processes of mass, impulse, energy, electrical and chemical balances between the two interacting surfaces in relative motion during friction. A Ski base Structure Analyser (SSA) utilising laser technology has been developed to analyse the detailed structure of a stone-fround ski base. The SSA displays the measured surface as an image with 739x570 pixels, where each pixel can have a grey level value from 0 to 255. The value of each pixel is proportional to the height at the corresponding point of the measured surface. In the period between 1995 and 1998 almost 1700 ski base structure measurements were performed on more than 350 skis. It was found that ski pairs ground with the "same" structure at two different times are not necassarily equal if no quality control of the ski base structure and the stone grinding process has been performed. On several competition ski pairs higher structure roughness (up to 84%) was revealed on the forebody than the afterbody of the ski. The work has resulted in develoment of ski base structures with increased roughness along the ski, developed and extreme optimisation of the best structures, and improvement of the frinding diamonds used to set the grinding stone. further, it has given ski technicians and competition skiers confidence in that optimum structures can be reproduced. The ski base structure roughness can be divided into four categories: fine (arithmetic mean roughness 1-4 µm), medium (arithmetic mean roughness 4-7 µm), course ( arithmetic mean roughness 7-10 µm) and very coarse ( arithmetic mean roughness higher than 10 µm) that correspond to dry to moist, moist, moist to wet, and wet to very wet snow conditions, respectively. A structure test series consisting of ten ski pairs with eight different structures has been ground and quality-controlled. Accurate sliding tests showed that ski pairs with arithmetic mean structure roughness ≤ 5.4 µm were best under snow conditions with snow humidity ≤ 0.6%, snow temperatures below zero and new snow. A ski pair with arithmetic mean structure roughness equal to 9.3 µm was best under snow conditions with snow humidity between approximatly 0.3 and 4.0 %, snow hardness higher than 4.1x104 Pa and transformed snow types. Under snow conditions with snow humidity higher than approximately 4%, a structure with arithmetic mean roughness 12.7 µm was best. Coarser sructures were relatively better than finer structures at high speeds compared to low speeds, thus implying an increase in the water film thickness and optimum structure roughness with speed. A decrease of the structure roughness along the ski was unfortunate under most snow conditions. Various snow parameters have been registered during measurement campaigns in ski tracks in Norway (1995-98), Hakuba/Japan (1996-98) and Sundance/USA (1999). Specific attention has been paid to snow hardness, snow humidity, snow density, snow grain structure and electrolytic conductivity. Snow hardness between 104 and 106 Pa is most common in ski tracks, and snow hardness below 105 Pa is likely to be present 60% of the time. The mean density of snow in ski tracks (0.50 g/cm3) is considerable higher than typical densities of seasonal snow covers (0.26-0.38 g/cm3) and higher for transformed snow types (0.51-059 g/cm3) than new snow types (0.39-0.43 g/cm3). The snow humidity in a ski track typically ranges between 0 and 12.5%. It is typically less than 2% for snow temperatures below -2 °C and less than 1% for snow temperatures below -7°C. Snow humidities exceeding 4% have only been registered at air temperatures above +1°C. High electrolytic conductivities (61.7 µS/cm and 94.5 µS/cm, respectively) and high levels of Na+- and C1--ions have been registered in melted snow samples from Trondheim and Sundance/Heber due to salt being a major agent during snow nucleation in the snowfalls. These values are approximately 3 times higher than the maximum values found for snow samples from Hakuba (21.9 µS/cm). The electrolytic conductivity of a melted snow sample may indicate the rate of ions introduced th the interface between snow and ski by frictional melting and thereby the rate and ease of discharge between ski and snow through the frictional water film during skiing.

Cardiac fibrosis results from excessive formation of the extracellular matrix by activated cardiac myofibroblasts. Ski, an endogenous repressor of the profibrotic factor transforming growth factor-β1, has been shown to attenuate the myofibroblast phenotype. We demonstrate that Ski regulates rat cardiac myofibroblast’s capacity for ECM remodeling, further solidifying its putative role as an endogenous anti-fibrotic TGF-β1 repressor. We show that Ski overexpression alters matrix metalloproteinase-2 and 9 expression and activity via immunoblotting and zymography. We also observe an attenuation of paxillin, a focal adhesion associated protein, and FAK (Tyr 397) expression by immunoblotting. Additionally, myofibroblast motility is reduced by Ski overexpression via transwell migration and scratch assay. We suggest that Ski may exert multiple effects on adverse ECM remodeling by altering the expression and function of the ECM proteases. The effects of Ski on cell motility also represent a putative mechanism for modulation of myofibroblast function in progression of cardiac fibrosis. / February 2016

North America’s first officially designated backcountry ski area, the Hankin-Evelyn Backcountry Ski Area (Hankin) in northern British Columbia, offers mountain communities seeking alternative recreational amenities an interesting model to emulate. The aim of the research is to explore backcountry ski area design by assessing the quality of both the ski area design elements and the ski experience at Hankin. A case study and a questionnaire were used to gather information about the ski experience and site design. Analysis explores the desired ski experience reported in the questionnaires and the preferred ski area design elements obtained from the case study, direct observations and the questionnaires. Conclusions suggest ski area design elements affect the quality of the ski experience and that backcountry skiers desire a wilderness experience. Findings can be used to inform the design of these unique wilderness recreation areas and expand upon the current knowledge of ski area design.

Ultra High Molecular Weight Polyethylene (UHMWPE) has been used as a ski sole material for many years due to its good tribological properties, good wear resistance and low friction coefficient. Recent studies have showed improved performance on wear rate and hydrophobicity with nanoparticle reinforced UHMWPE. In this study, different kinds of nano-composite UHMWPE’s were tested on snow to investigate if they are suitable as a ski sole material and to find the type of nano-composite UHMWPE that has the greatest potential. Further, the mechanisms of hydrophobicity and its influence on the friction level were examined. The friction coefficient was measured in a ski test rig and simple demonstrations under a microscope were made to simulate how water is dragged along the ski sole in contact with wet snow. Mechanical properties were measured with a CSM Nanoindentation Instrument and surface topography was examined in a Wyko Optical Profiler. The cross-linked UHMWPE material showed the lowest friction coefficient on snow. The hydrophobic demonstrations, together with the ski test results, questions the suggestion that high hydrophobicity enhances the ski glide. Nanoindentation was proved to give valuable data for mechanical properties, but it should be questioned whether it is a good technique for comparing different nano-composite UHMWPE materials. The ski tests show the importance of the characteristics of snow.

En Amérique du Nord, près de 90 % des stations de ski alpin possèdent au moins un parc à neige. Les parcs à neige sont des zones de pratique délimitées de la station où le terrain est profilé et où se trouvent généralement des modules qui favorisent l’exécution de manœuvres acrobatiques. Par exemple, des modules de type saut, rail, boîte, table, champignon et demilune peuvent y être aménagés. Quoique certains bénéfices soient associés à la réalisation de manœuvres acrobatiques dans les parcs à neige, par exemple l’apprentissage d’habiletés motrices complexes, des coûts socioéconomiques importants sont liés à cette pratique. D’ailleurs, de récentes études ont démontré que la probabilité de subir une blessure sévère est plus élevée dans les parcs à neige que sur les pistes régulières. Les facteurs de risque de blessure dans les parcs à neige pourraient être associés aux participants, à l’équipement utilisé, à l’environnement physique et à l’environnement social. La présente thèse de doctorat a comme but principal d’améliorer les connaissances en lien avec la prévention des blessures subies dans les parcs à neige des stations de ski alpin. À cet effet, cette recherche utilise comme cadre de référence les cinq phases de l’approche utilisée en santé publique : 1) surveillance; 2) identification des facteurs de risque et de protection; 3) conception et sélection des interventions; 4) implantation de programmes et de politiques; et 5) évaluation et suivi. De prime abord, dans le cadre de la thèse, une revue systématique de la littérature portant sur les facteurs de risque ainsi que sur les stratégies de prévention a été réalisée. Entre autres, les résultats démontrent que : 1) comparée aux pistes régulières, la sévérité des blessures est plus importante dans les parcs; 2) les modules favorisant une importante hauteur d’envol ou des manœuvres aériennes représentent le principal facteur de risque de blessure; 3) aucune des études publiées et qui ont été répertoriées n’a évalué l’efficacité des stratégies de prévention. Néanmoins, certains auteurs soutiennent que l’optimisation de l’environnement physique des parcs serait une stratégie intéressante pour prévenir les blessures. Dans l’optique que la qualité des parcs à neige pourrait être associée au risque de blessure, la seconde étude avait pour but de concevoir et de valider un instrument de mesure de la qualité des modules. A posteriori, l’instrument pourrait être utilisé pour étudier l’association entre la qualité des modules et le risque de blessure. Dans le même ordre d’idées, l’Association des stations de ski du Québec (ASSQ) a implanté en 2006 un guide de recommandations pour l’optimisation de la qualité des parcs à neige et des modules. Bien que l’adoption des recommandations du guide soit susceptible de prévenir les blessures, aucune évidence scientifique ne démontre que les recommandations sont respectées dans les parcs à neige des stations de ski alpin du Québec. À l’aide de l’instrument de mesure conçu lors de l’étude précédente, il a été possible d’évaluer la conformité des modules en lien avec les recommandations du guide de l’ASSQ. Selon les observations, le niveau de conformité des modules était élevé (91 %). L’effet d’une stratégie de prévention sur les blessures a aussi été étudié dans le cadre de cette thèse. À la saison 2007-2008, les gestionnaires de deux stations de ski du Québec ont décidé de retirer les sauts des parcs à neige. Les gestionnaires d’une des stations les ont réintégrés lors de la saison 2013-2014. Cette modification de l’environnement physique était une occasion unique pour étudier la stratégie passive de prévention des blessures. Les résultats de cette étude suggèrent que le retrait des modules de type saut diminuerait le risque de blessures sévères alors que leur réintroduction augmenterait le risque de blessures sévères chez les skieurs alpins et les surfeurs des neiges. La présente thèse de doctorat porte sur la prévention des blessures subies dans les parcs à neige des stations de ski alpin du Québec. Bien que la littérature scientifique montre l’importance des blessures subies dans les parcs à neige, peu d’études s’intéressent aux stratégies visant à prévenir ce type de blessures. Les résultats des études conduites dans le cadre de cette thèse améliorent les connaissances en cette matière. / In North America, more than 90 % of the ski areas in operation have at least one terrain park.Terrain parks are specific areas of the slopes designed to accommodate acrobatic manoeuvreson features such as rails, boxes, kickers, mushrooms, tables, jumps, quarter-pipes and halfpipes. Although the practice of skiing and snowboarding in terrain parks is associated withsome benefits, including learning new complex motor skills, there are also potential risks.There is evidence that terrain park injuries are more likely to be severe than injuries sustainedon regular slopes. Risk factors for terrain park injuries can be associated with participants,equipment use, physical environment, and social environment.This doctoral thesis aims to improve knowledge on the prevention of terrain park injuriessustained in alpine ski areas. The public health approach to injury prevention was used as aframework for this thesis. It is composed of five steps: 1) Surveillance; 2) Identifying riskand protective factors; 3) Selecting and designing interventions; 4) Programs and policiesimplementation; 5) Evaluation and monitoring. First of all, we conducted a systematic reviewto identify risk factors for injury and prevention strategies aiming to reduce the risk of injuriessustained in terrain parks. Among others, results showed that: 1) compared to regular slopes,injuries sustained in terrain parks are more likely to be severe; 2) features that promoteacrobatic manoeuvres or large drops to the ground represent the main risk factor for terrainpark injuries; 3) no published study retrieved in our systematic review assessed injuryprevention strategies. Although no intervention has been tested, some authors suggest thatthe optimization of the physical environment of terrain parks could prevent injuries. Thisassociation has been observed in playground injuries.Then, since some studies have suggested that the quality of terrain park features could beassociated with the risk of injury, we decided to develop and validate an evaluation tool thatassesses the quality of terrain park features in Québec ski areas. To our knowledge, no suchinstrument exists to assess the quality of features in terrain parks. A posteriori, the instrumentcould be used to examine the association between the quality of terrain park features and therisk of injury. Likewise, in order to optimize the quality of terrain parks, the Québec SkiAreas Association (QSAA) implemented a guide in 2006 in Québec ski areas. The guide provides recommendations on the design, construction, and maintenance of terrain parkfeatures. Although it could contribute to preventing injuries, there is no scientific evidencethat terrain park features in Québec ski areas are compliant with the recommendations fromthe guide. Using the instrument designed in the previous study, we assessed the complianceof terrain park features with the recommendations of the QSAA guide. According to ourobservations, the features compliance level was high (91 %).As part of the thesis, the effect of an injury prevention strategy has also been studied. Duringthe 2007-2008 season, the administrators of two Québec ski areas decided to remove jumpsfrom their terrain parks. Jumps were reintroduced later in one ski area during the 2013-2014season. The decision of the administrators to remove and reintroduce man-made jumps fromtheir terrain parks provided a unique opportunity for research. Our results suggest thatremoving jumps from terrain parks could reduce the risk of severe injuries (protective effect)whereas reintroducing them could increase the risk of severe injuries (harmful effect) inalpine skiers and snowboarders.This thesis provides relevant information on the prevention of injuries sustained in terrainparks. Although epidemiological studies agree on the severity of injuries in terrain parks, fewstudies explore injury prevention strategies. Studies conducted during the project willcontribute to improving knowledge of key stakeholders in order to prevent terrain parkinjuries.

Thesis (M.S.)--Boston University

Cardiovascular disease is a leading cause of death and a major economic burden in the developed and developing world. Many heart diseases, including post-myocardial infarction, include a fibrotic component with remodeling of the extracellular matrix in the myocardium. Cardiac myofibroblasts are non-myocyte cells derived from relatively quiescent fibroblasts and are the main mediators of collagen remodeling in disease states. TGF-β is recognized as an important contributor to adverse cardiac remodeling in heart disease. In this study we have investigated the role of c-Ski, which is an endogenous TGF-β inhibitor, in controlling/regulating myofibroblast function and phenotype. We have developed an adenoviral overexpression system to study these endpoints using Western blot, immunofluorescence, MTT assay, flow cytometry, procollagen type I amino terminal peptide secretion and qPCR analysis. We observed that the 95 kDa c-Ski form is overexpressed upon virus infection with adenovirus encoding c-Ski and this form of c-Ski is localized to the nucleus. c-Ski expression inhibited cardiac myofibroblast collagen synthesis and secretion as well as contractility. Phosphorylation and translocation of Smad2 into the nucleus was not affected in the presence of c-Ski overexpression. We found that c-Ski overexpression was associated with diminution of the myofibroblastic phenotype with reduced α-smooth muscle actin and extra domain-A fibronectin expression (but not non-muscle myosin heavy chain B expression). c-Ski may reduce cell viability via the induction of apoptosis. Finally, we have elucidated a putative mechanism for c-Ski-mediated reduction of myofibroblast phenotype through the upregulation of the homeodomain protein Meox2. Adenoviral overexpression of Meox2 was associated with a significant reduction of α-smooth muscle actin and extra domain-A fibronectin expression in a similar manner to that of c-Ski overexpression. Thus we have identified c-Ski as being an antifibrotic protein as well as a novel mechanism for modulation of cardiac myofibroblast phenotype, possibly through the induction of Meox2 expression.

Cardiovascular disease is a leading cause of death and a major economic burden in the developed and developing world. Many heart diseases, including post-myocardial infarction, include a fibrotic component with remodeling of the extracellular matrix in the myocardium. Cardiac myofibroblasts are non-myocyte cells derived from relatively quiescent fibroblasts and are the main mediators of collagen remodeling in disease states. TGF-β is recognized as an important contributor to adverse cardiac remodeling in heart disease. In this study we have investigated the role of c-Ski, which is an endogenous TGF-β inhibitor, in controlling/regulating myofibroblast function and phenotype. We have developed an adenoviral overexpression system to study these endpoints using Western blot, immunofluorescence, MTT assay, flow cytometry, procollagen type I amino terminal peptide secretion and qPCR analysis. We observed that the 95 kDa c-Ski form is overexpressed upon virus infection with adenovirus encoding c-Ski and this form of c-Ski is localized to the nucleus. c-Ski expression inhibited cardiac myofibroblast collagen synthesis and secretion as well as contractility. Phosphorylation and translocation of Smad2 into the nucleus was not affected in the presence of c-Ski overexpression. We found that c-Ski overexpression was associated with diminution of the myofibroblastic phenotype with reduced α-smooth muscle actin and extra domain-A fibronectin expression (but not non-muscle myosin heavy chain B expression). c-Ski may reduce cell viability via the induction of apoptosis. Finally, we have elucidated a putative mechanism for c-Ski-mediated reduction of myofibroblast phenotype through the upregulation of the homeodomain protein Meox2. Adenoviral overexpression of Meox2 was associated with a significant reduction of α-smooth muscle actin and extra domain-A fibronectin expression in a similar manner to that of c-Ski overexpression. Thus we have identified c-Ski as being an antifibrotic protein as well as a novel mechanism for modulation of cardiac myofibroblast phenotype, possibly through the induction of Meox2 expression.

Thesis (Ph.D.)--University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on April 29, 2009) Vita. Includes bibliographical references.