Imitation jumps in ski jumping: Technical execution and relationship to performance level     

Gertjan Ettema  Steinar Braaten  Jørgen Danielsen  Birk Eirik Fjeld 《Journal of sports sciences》2020,38(18):2155-2160

ABSTRACT

Imitation jumps are frequently used in training for ski jumping. Yet, the dynamics of these jumps differ considerably. Thus, the relevance of imitation jumps for ski jumping performance is not elucidated. The aim of this study was to investigate the relationship between the technical execution of imitation jumps and ski jumping performance level. We compared the imitation jumps of 11 ski jumpers of different performance levels using a Spearman correlation transform of time traces of the kinetics (measured using force cells and motion capture) of imitation jumps. The kinetic aspects that were related to performance centred on the moment arm of ground reaction force to the centre of mass before the onset of the push-off, angular momentum early in push-off, thigh angle during the main period of push-off and vertical velocity towards the end of push-off. We propose that the thigh angle may be a key element allowing high development of linear momentum while preparing for appropriate aerodynamic position. Furthermore, the findings suggest that the kinetic development prior to (and during) push-off is more important than the kinematic end state at take-off.  相似文献   

Removal of Organic Acids from Indoor Air in Museum Storage Rooms by Active and Passive Sorption Techniques     

Signe Hjerrild Smedemark  Morten Ryhl-Svendsen  Jørn Toftum 《文物保护研究》2020,65(5):251-261

ABSTRACT

Adsorbent materials can be used for the removal of organic acids from air in storage rooms with heritage collections. The organic acid removal efficiency of two commercially available activated carbon air-filters were tested in situ in two unoccupied stores with densely packed collections. One filter was designed for outdoor type pollutants (Filter A), while the other was designed for organic acids in indoor air (Filter B). Furthermore, the acetic acid removal efficiency of a desiccant silica gel rotor used for dehumidification was measured in a laboratory at different relative humidity levels. Finally, passive removal of acetic acid by silica gel and unfired clay brick were tested in a chamber, and for clay brick at room level as well. Filter B had the highest removal efficiency. The removal efficiency of both filter types depended on the airflow and the filter performance varied considerably in situ from the values reported from standard laboratory tests. Increasing the filter airflow reduced the removal efficiency from 77% and down to 7% for Filter A, and from 92% to 24% for Filter B. There was almost no effect of active air filtration on the concentration of organic acids when this was measured in the middle and in the corner of the storage rooms away from the ventilation inlets. The desiccant dehumidifier removed 98–100% of the acetic acid from the air, independently of the relative humidity. The desiccant rotor will, however, only be running when there is a need for dehumidification and as a result will only periodically remove pollutants. The high acid removal efficiency by dry silica gel was furthermore demonstrated in a chamber test. A clay brick wall in a test room established a concentration gradient across the room and reduced the concentration of organic acids by 56% compared to close to the emission source.  相似文献   

Research and teaching in the universities of Denmark: Does such an interplay really exist?   总被引：1，自引：0，他引：1  

Jens-Jørgen Jensen 《Higher Education》1988,17(1):17-26

The unity of research and teaching is an ingrained principle in university policy in Denmark, but this principle has also been subjected to increasing criticism. This article presents an investigation, consisting of about 50 interviews with teachers from higher educational institutions in Denmark, aiming at the illumination of this issue. According to the conclusions of this investigation it is the basic experience of the teachers that an important interplay exists between research and teaching of the individual teacher, and that almost none would prefer to work in a pure research institution. At the same time the teachers have some crucial reservations. Firstly it can be difficult to administer this twofold task. Secondly the interrelationships are dependent on several factors, the most important of which is the level of teaching and the disciplinary context. This latter factor is explained by differences pertaining to the very nature of varying disciplines - demonstrated and analyzed with reference to Thomas Kuhn and Basil Bernstein. Finally, the importance of the interrelationships between research and teaching for higher educational and research policies in broader perspective is discussed.  相似文献   

A Portable Tool for the Evaluation of Microclimate Conditions within Museum Enclosures,Transit Frames,and Transport Cases     

Marianne Odlyha  Jonathon M. Slater  Terje Grøntoft  Slawomir Jakiela  Michal Obarzanowski  David Thickett 《文物保护研究》2018,63(5):407-410

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User Experiences with Editorial Control in Online Newspaper Comment Fields     

Anders Sundnes Løvlie  Karoline Andrea Ihlebæk  Anders Olof Larsson 《Journalism Practice》2018,12(3):362-381

This article investigates user experiences with editorial control in online newspaper comment fields following the public backlash against online comments after the 2011 terror attacks in Norway. We analyze data from a survey of online news consumers focusing on experiences and attitudes towards editorial control set against a spectrum between “interventionist” and “noninterventionist” positions. Results indicate that interventionist respondents rate the quality of online comments as poor, whereas noninterventionist respondents have most often experienced being the target of editorial control measures and feel that editorial control has intensified after the terror attacks. We conclude that newspapers should pay attention to the different needs of participants when devising strategies for editorial control. Media professionals should also consider changes to increase the transparency of moderation practices.  相似文献   

Blurred Boundaries or Conflicting Epistemologies     

Nina Grønlykke Mollerup 《Journalism Practice》2017,11(1):48-61

In this article, I discuss how information activists and journalists in Egypt claimed to acquire knowledge about the world, looking particularly at the period of 2012 and 2013, during which the Supreme Council of the Armed Forces and Mohammed Morsi in turn were leading the country. Taking a point of departure in anthropological fieldwork with information activists and journalists in Egypt, I show that information activists and journalists often had very similar practices and goals, which at times made the boundaries very blurry. Yet I argue that there was a significant distinction between the epistemologies of information activists and journalists. Information activists claimed to acquire knowledge about events from being part of them, whereas journalists claimed to acquire knowledge about events from observing them without taking part. Relatedly, information activists and journalists had significantly different relationships with their audiences.  相似文献   

Protection or Participation?     

Anna Grøndahl Larsen 《Journalism Practice》2017,11(7):893-908

Children’s status as a particularly vulnerable group in society implies a journalistic obligation to shed light on children’s stories and listen to their perspectives, but their vulnerable position also means they deserve protection from potentially harmful news coverage. Based on a close-reading of two extensively covered news serials concerning irregular migrant children facing deportation, and on in-depth interviews with journalists, editors, and key actors working on behalf of irregular migrant children, the present article sheds light on how journalists balance competing, ethical, professional, and organizational concerns when reporting on issues concerning children. The article shows that while journalists say they are aware of the ethical aspects concerning extensive media exposure of young children, they justify the reporting by foregrounding children as innocent victims of the immigration system and by highlighting the journalistic obligation of shedding light on the wrongdoings of this system. The potential burden of media exposure is relativized as less harmful than the alternative—deportation. Theoretically, the article contributes to the literature on children in the news media, human-interest stories and journalism, and the role of journalism reporting vulnerable groups.  相似文献   

I The human cost of French University expansion     

Frédéric Gaussen 《Minerva》1973,11(3):372-386

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Effects of two physical education programmes on health- and skill-related physical fitness of Albanian children     

J. Jarani  A. Grøntved  F. Muca  A. Spahi  D. Qefalia  K. Ushtelenca 《Journal of sports sciences》2016,34(1):35-46

This study aims to evaluate the effectiveness of two school-based physical education (PE) programmes (exercise-based and games-based) compared with traditional PE, on health- and skill-related physical fitness components in children in Tirana, Albania.

Participants were 378 first-grade (6.8 years) and 389 fourth-grade (9.8 years) children attending four randomly selected schools in Tirana. Twenty-four school classes within these schools were randomly selected (stratified by school and school grade) to participate as exercise group (EG), games group (GG) and control group (CG). Both EG and GG intervention programmes were taught by professional PE teachers using station/circuit teaching framework while CG referred to traditional PE school lessons by a general teacher. All programmes ran in parallel and lasted 5 months, having the same frequency (twice weekly) and duration (45 min). Heart rate (HR) monitoring showed that intensity during PE lessons was significantly higher in the intervention groups compared with control (P < 0.001). Both PE exercise- and games programmes significantly improved several health- and skill-related fitness indicators compared with traditional PE lessons (e.g. gross motor skill summary score: 9.4 (95% CI 7.9; 10.9) for exercise vs. control and 6.5 (95% CI 5.1; 8.1) for games vs. control, cardiorespiratory fitness: 2.0 ml O₂ · min^?1 · kg^?1 (95% CI 1.5; 2.4) for exercise vs. control and 1.4 ml O₂ · min^?1 · kg^?1 (95% CI 1.0; 1.8) for games vs. control). Furthermore, compared to games-based PE, exercise-based PE showed more positive changes in some gross motor coordination skills outcomes, coordination skills outcomes and cardiorespiratory fitness. The results from this study show that exercise- and games-based PE represents a useful strategy for improving health- and skill-related physical fitness in Albanian elementary school children. In addition, the study shows that exercise-based PE was more effective than games-based PE in improving gross motor function and cardiorespiratory fitness.  相似文献   

Non-circular chainring improves aerobic cycling performance in non-cyclists     

Frédérique Hintzy  Nicolas Horvais 《European Journal of Sport Science》2016,16(4):427-432

Non-circular chainrings alter the crank velocity profile over a pedalling cycle. The aim of this study was to investigate the effect of this altered crank velocity profile on the aerobic performance compared to a circular chainring (CC). Ten male non-cyclists performed two incremental maximal tests at 80?rpm on a cycle ergometer: one with a circular (Shimano) and the other with a non-circular chainring Osymetric^® (Somovedi), at least 50?h apart. Each test started with a workload of 100?W lasting 3?min. During the first 12?min, the workload was increased by 30?W every 3?min. Thereafter, the workload was increased by 30?W every 2?min until exhaustion. The power output, the intra-cycle crank angular velocity and the physiological parameters were monitored continuously, averaged over the last 30?s of each increment and at exhaustion, and compared for the two chainrings. Results showed a higher maximal aerobic power attained with the non-circular chainring (362.6?±?37.9 vs. 338.8?±?32.6?W, p?相似文献