| 19661. |
- Ståhl, Göran, et al.
(författare)
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Presence-absence sampling for estimating plant density using survey data with variable plot size
- 2020
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Ingår i: Methods in Ecology and Evolution. - : John Wiley & Sons. - 2041-210X. ; 11:4, s. 580-590
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Tidskriftsartikel (refereegranskat)abstract
- Presence–absence sampling is an important method for monitoring state and change of both individual plant species and communities. With this method, only the presence or absence of the target species is recorded on plots and thus the method is straightforward to apply and less prone to surveyor judgement compared to other vegetation monitoring methods. However, in the basic setting, all plots must be equally large or otherwise it is unclear how data should be analysed. In this study, we propose and evaluate five different methods for estimating plant density based on presence–absence registrations from surveys with variable plot sizes.Using artificial plant population data as well as empirical data from the Swedish National Forest Inventory, we evaluated the performance of the proposed methods. The main analysis was conducted through sampling simulation in artificial populations, whereby bias and variance of density estimators for the different methods were quantified and compared.Both for state and change estimation of plant density, we found that the best method to handle variable plot size was to perform generalized least squares regression, using plot size as an independent variable. Methods where plots smaller than a certain threshold were excluded or their registrations recalculated were, however, almost as good. Using all registrations as if they were obtained from plots with the nominal plot size resulted in substantial bias.Our findings are important for plant population studies in a wide range of environmental monitoring programmes. In these programmes, plots are typically randomly laid out and may be located across boundaries between different land‐use or land‐cover classes, resulting in subplots of variable size. Such splitting of plots is common when large plots are used, for example, with the 100 m2 plots used in the Swedish National Forest Inventory. Our methods overcome problems to estimate plant density from presence–absence data observed in plots that vary in size.
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| 19662. |
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| 19663. |
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| 19664. |
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| 19665. |
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| 19666. |
- Stödberg, Ulf, 1977-, et al.
(författare)
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A municipal implementation of a new learning management system in K-12 schools : The teacher perspective
- 2017
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Ingår i: The Proceedings of the International Conference on Information Communication Technologies in Education 2017. - 9780993288982
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Konferensbidrag (refereegranskat)abstract
- Municipalities continue to seek ways to enhance communication, information and documentation for teachers, students and parents through the implementation of learning management systems in schools. In this paper, the launch of a system for K-12 schools in a municipality in Sweden is studied from the teacher perspective. Survey comments submitted by the teachers (N=470) were analysed using a modified version of Koole’s (2011) Framework for the Rational Analysis of Mobile Education. The findings show possibilities such as communication and documentation, as well as challenges related to usability, access and resistance. Lessons learned regarding the implementation of the system are presented.
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| 19667. |
- Stöggl, R., et al.
(författare)
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Motor abilities and anthropometrics in youth cross-country skiing
- 2015
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Ingår i: Scandinavian Journal of Medicine and Science in Sports. - : Wiley. - 0905-7188 .- 1600-0838. ; 25:1, s. E70-E81
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Tidskriftsartikel (refereegranskat)abstract
- The purposes were to validate whether general motor abilities and anthropometrics are determinants of youth cross-country (XC) skiing performance; evaluate gender-specific differences; and to establish noninvasive diagnostics. Fifty-one youth XC skiers (34 boys; 13.8 +/- 0.6 years and 17 girls; 13.4 +/- 0.9 years) performed motor skill and laboratory tests, and anthropometric data were collected and correlated with XC skiing performance. Anthropometrics and maturity status were related to boys but not to girls XC skiing performance. Push-ups and 20-m sprint were correlated to XC skiing performance in both boys and girls. XC skiing performance of boys was predominantly influenced by upper body and trunk strength capacities (medicine ball throw, push-ups, and pull-ups) and jumping power (standing long and triple jump), whereas XC skiing of girls was mainly influenced by aerobic capacities (3000-m run). Laboratory measures did not reveal greater correlations to XC skiing performance compared with simple test concepts of speed, strength, and endurance. Maturity was a major confounding variable in boys but not girls. Use of noninvasive simple test concepts for determination of upper body strength, speed, and endurance represent practicable support for ski clubs, schools, or skiing federations in the guidance and evaluation of young talent, being aware of the effect of maturity especially in boys.
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| 19668. |
- Stöggl, Thomas, et al.
(författare)
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Automatic classification of the Sub-Techniques (Gears) used in cross-country ski skating employing a mobile phone
- 2014
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Ingår i: Sensors. - : MDPI AG. - 1424-8220. ; 14:11, s. 20589-20601
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Tidskriftsartikel (refereegranskat)abstract
- The purpose of the current study was to develop and validate an automatic algorithm for classification of cross-country (XC) ski-skating gears (G) using Smartphone accelerometer data. Eleven XC skiers (seven men, four women) with regional-to-international levels of performance carried out roller skiing trials on a treadmill using fixed gears (G2left, G2right, G3, G4left, G4right) and a 950-m trial using different speeds and inclines, applying gears and sides as they normally would. Gear classification by the Smartphone (on the chest) and based on video recordings were compared. Formachine-learning, a collective database was compared to individual data. The Smartphone application identified the trials with fixed gears correctly in all cases. In the 950-m trial, participants executed 140 ± 22 cycles as assessed by video analysis, with the automatic Smartphone application giving a similar value. Based on collective data, gears were identified correctly 86.0% ± 8.9% of the time, a value that rose to 90.3% ± 4.1% (P < 0.01) with machine learning from individual data. Classification was most often incorrect during transition between gears, especially to or from G3. Identification was most often correct for skiers who made relatively few transitions between gears. The accuracy of the automatic procedure for identifying G2left, G2right, G3, G4left and G4right was 96%, 90%, 81%, 88% and 94%, respectively. The algorithm identified gears correctly 100% of the time when a single gear was used and 90% of the time when different gears were employed during a variable protocol. This algorithm could be improved with respect to identification of transitions between gears or the side employed within a given gear.
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| 19669. |
- Stöggl, Thomas, 1977-, et al.
(författare)
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Biomechanical determinants of oxygen extraction during cross-country skiing
- 2013
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Ingår i: Scandinavian Journal of Medicine and Science in Sports. - : Wiley. - 0905-7188 .- 1600-0838. ; 23:1, s. e9-e20
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Tidskriftsartikel (refereegranskat)abstract
- To determine the relationship of muscle activation, force production, and cycle characteristics to O2 extraction during high- and lower-intensity double poling (DP), nine well-trained male cross-country skiers performed DP on a treadmill for 3 min at 90% VO2peak followed by 6 min at 70%. During the final minute at each workload, arterial, femoral, and subclavian venous blood were collected for determination of partial pressure of O2, partial pressure of CO2, pH, and lactate. Electromyography (EMG) was recorded from six upper and lower body muscles, leg and pole forces were measured, and cardiorespiratory variables were monitored continuously. O2 extraction was associated with time point of peak pole force (PFpeak), duration of recovery, EMG activity, and lower body use. Arm O2 extraction was lower than in the legs at both intensities (P < 0.001) and was reduced to a lesser extent upon decreasing the workload (P < 0.05). Arm root-mean-square EMG was higher during the poling phase and entire cycle compared with the legs (P < 0.001). Blood lactate was higher in the subclavian than in femoral vein and artery (P < 0.001) and independent of intensity. O2 extraction was correlated to low muscle activation, later PFpeak, prolonged poling time, and extensive dynamic lower body use. Cycle rate and recovery time were associated with O2 extraction during high-intensity exercise only.
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| 19670. |
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