Data driven bike fitting

During bike fitting sessions, the optimal cyclist’ position is determined. Finding this ‘optimal’ cycling position is often a time-consuming and labor-intensive process, i.e., a standard bike fitting procedure takes at least two hours when done by an expert bike fitter. The best position is a combination of comfort, performance and injury prevention [1,2,3,4]. To date, however, bike fitting suffers from expert ‘subjectivity’ as there is no consensus among bike fitters on which parameters to focus on. In order to examine this hypothesis about expert subjectivity, a reproducible test methodology is currently under development to perform and evaluate a bike fit by a group of independent experts in Flanders. Results of these tests will be discussed during the presentation. To solve the expert subjectivity problem, and to improve the overall fitting process, we started a research project to develop a methodology to perform automatic bike fitting based on novel data-driven decision-making processes. The data is provided by the Bioracer Motion mo-cap system (shown in Figure 1), which consists of 2 arrays of high-speed IR cameras which capture positional data of the active infrared markers which are placed on the cyclists’ body. Up till now, mainly feature engineering techniques were studied and evaluated on the Bioracer Motion datasets. Preliminary experiments focusing on saddle height optimization already show the feasibility of the proposed methodology. Saddle height is a determining factor in knee injuries [5,6,7] and the outputted power [8]. However, it is important to mention that saddle height optimization is only a small step in the bike fitting process [9]. In these experiments our methodology was to compare three different bike configurations (i.e., saddle too high, too low and the 'optimal' position) for different pairs of markers. An example of these spatio-temporal comparisons is shown in Figure 2. This graph shows the relation between the crank angle and the right knee Z speed over time. A good feature to track would be the occurrence of the minimum with regard to the crank angle. If the saddle is in a position that is too high, for example, the minimum occurs at a particularly lesser crank angle. Several of these kind of features are evaluated on the Bioracer Motion dataset. The lesser false positives, the higher the weight of this feature. In the end, a series of 8 features (focusing on the left/right foot and knee movement in X/Y direction) are fed into a weighted feature sum, based on which the saddle height correction is suggested. This methodology results in a 100% correct saddle height up to an accuracy of 5mm for a test set of 40 fits. Future work will include other optimizations (i.e. saddle setback, handlebar drop, ... ) and evaluate machine learning techniques to determine new features. The final goal of our project is to have a fully autonomous bike fitting system, which can fit a cyclist with sufficient accuracy in a short period of time. This system will have a significant impact on the cycling world, as less knowledge will be required to successfully fit cyclists

Meervoud in Vlaamse gebarentaal: onderzoeksrapport 2011

In dit rapport worden de resultaten besproken van het onderzoek naar meervoud in Vlaamse Gebarentaal. Hoe dit onderzoek werd opgevat en uitgevoerd, staat beschreven in Rapport onderzoeksmethodologie meervoudsvorming in Vlaamse Gebarentaal (Heyerick & Van Braeckevelt, 2008). Deze tekst schetst eerst kort wat al gekend was over meervoud in VGT, waarna de resultaten van het huidige onderzoek uitvoerig worden besproken. Deze bespreking bevat een overzicht van welke manieren om meervoud uit te drukken voorkwamen in de geanalyseerde data, hoe deze met elkaar gecombineerd kunnen worden en wat de gebarenvolgorde is. Dit rapport zet de meest gebruikte meervoudsmechanismen in VGT op een rij met oog voor regionale variatie. Het onderzoek belicht ook de fonologische restricties die spelen bij de keuze voor een bepaalde manier van meervoudsvorming. Zo blijken de fonologische kenmerken van een gebaar invloed te hebben op welke meervoudsvorming een gebaar wel of niet kan aannemen. Extra aandacht gaat hierbij naar de parameters articulatieplaats en beweging. Naast het gebruik van meervoudsmechanismen, kan men in VGT ook op een andere manier uitdrukken dat er meer dan één van hetzelfde is. Het gaat hier dan niet meer om zuivere meervoudsvorming. Hoe gebaarders dit doen in VGT wordt voor de volledigheid ook in dit rapport opgenomen. Ten slotte worden de meest opvallende bevindingen met betrekking tot meervoud in VGT overzichtelijk samengevat in het besluit van dit rapport

The need for data-driven bike fitting : data study of subjective expert fitting

The number of cyclists is growing rapidly, for commuting but also as a sport. With this growth, there has been an increasing interest in cycling position. Trainers, athletes and bike vendors acknowledged this and started to perform bike fits. As these experts have different backgrounds and varying levels of expertise, it was hypothesised that this could have an influence on the outcome in terms of the advised position. In this research three cyclists were bike fitted by nine different bike fitting studios. It was hypothesised that, as different bike fitters use varying techniques and have different experience levels, the cyclist would be advised a different optimal position by these different bike fitters. The preconceived hypothesis was confirmed as the range of advised positions in both saddle height and setback was up to 3 cm. Data-driven bike fitting can help bring down these considerable differences amongst fitters and will be discussed in the last chapter

Accurately Determining the Phase Transition Temperature of CsPbI3 via Random-Phase Approximation Calculations and Phase-Transferable Machine Learning Potentials

While metal halide perovskites (MHPs) have shown great potential for various optoelectronic applications, their widespread adoption in commercial photovoltaic cells or photo-sensors is currently restricted, given that MHPs such as CsPbI3 and FAPbI(3) spontaneously transition to an optically inactive non-perovskite phase at ambient conditions. Herein, we put forward an accurate first-principles procedure to obtain fundamental insight into this phase stability conundrum. To this end, we computationally predict the Helmholtz free energy, composed of the electronic ground state energy and thermal corrections, as this is the fundamental quantity describing the phase stability in polymorphic materials. By adopting the random phase approximation method as a wave function-based method that intrinsically accounts for many-body electron correlation effects as a benchmark for the ground state energy, we validate the performance of different exchange-correlation functionals and dispersion methods. The thermal corrections, accessed through the vibrational density of states, are accessed through molecular dynamics simulations, using a phase-transferable machine learning potential to accurately account for the MHPs' anharmonicity and mitigate size effects. The here proposed procedure is critically validated on CsPbI3, which is a challenging material as its phase stability changes slowly with varying temperature. We demonstrate that our procedure is essential to reproduce the experimental transition temperature, as choosing an inadequate functional can easily miss the transition temperature by more than 100 K. These results demonstrate that the here validated methodology is ideally suited to understand how factors such as strain engineering, surface functionalization, or compositional engineering could help to phase-stabilize MHPs for targeted applications

WHO European Childhood Obesity Surveillance Initiative: body mass index and level of overweight among 6-9-year-old children from school year 2007/2008 to school year 2009/2010.

BACKGROUND: The World Health Organization (WHO) Regional Office for Europe has established the Childhood Obesity Surveillance Initiative (COSI) to monitor changes in overweight in primary-school children. The aims of this paper are to present the anthropometric results of COSI Round 2 (2009/2010) and to explore changes in body mass index (BMI) and overweight among children within and across nine countries from school years 2007/2008 to 2009/2010. METHODS: Using cross-sectional nationally representative samples of 6-9-year-olds, BMI, anthropometric Z-scores and overweight prevalence were derived from measured weight and height. Significant changes between rounds were assessed using variance and t-tests analyses. RESULTS: At Round 2, the prevalence of overweight (including obesity; WHO definitions) ranged from 18% to 57% among boys and from 18% to 50% among girls; 6 - 31% of boys and 5 - 21% of girls were obese. Southern European countries had the highest overweight prevalence. Between rounds, the absolute change in mean BMI (range: from -0.4 to +0.3) and BMI-for-age Z-scores (range: from -0.21 to +0.14) varied statistically significantly across countries. The highest significant decrease in BMI-for-age Z-scores was found in countries with higher absolute BMI values and the highest significant increase in countries with lower BMI values. The highest significant decrease in overweight prevalence was observed in Italy, Portugal and Slovenia and the highest significant increase in Latvia and Norway. CONCLUSIONS: Changes in BMI and prevalence of overweight over a two-year period varied significantly among European countries. It may be that countries with higher prevalence of overweight in COSI Round 1 have implemented interventions to try to remedy this situation

WHO European Childhood Obesity Surveillance Initiative: Impact of Type of Clothing Worn during Anthropometric Measurements and Timing of the Survey on Weight and Body Mass Index Outcome Measures in 6–9-Year-Old Children

Background. The World Health Organization European Childhood Obesity Surveillance Initiative (COSI) conducted examinations in 6–9-year-old children from 16 countries in the first two rounds of data collection. Allowing participating countries to adhere to their local legal requirements or adapt to other circumstances required developing a flexible protocol for anthropometric procedures. Objectives. (1) Review intercountry variation in types of clothing worn by children during weight and height measurements, clothes weight adjustments applied, timing of the survey, and duration of data collection; (2) assess the impact of the observed variation in these practices on the children’s weight or body mass index (BMI) outcome measures. Results. The relative difference between countries’ unadjusted and clothes-adjusted prevalence estimates for overweight was 0.3–11.5%; this figure was 1.4–33.3% for BMI-for-age Z-score values. Monthly fluctuations in mean BMI-for-age Z-score values did not show a systematic seasonal effect. The majority of the monthly BMI-for-age Z-score values did not differ statistically within a country; only 1–3 monthly values were statistically different within some countries. Conclusions. The findings of the present study suggest that the built-in flexibility in the COSI protocol concerning the data collection practices addressed in the paper can be kept and thus do not necessitate a revision of the COSI protocol.info:eu-repo/semantics/publishedVersio

An embedded interfacial network stabilizes inorganic CsPbI₃ perovskite thin films

The black perovskite phase of CsPbI(3) is promising for optoelectronic applications; however, it is unstable under ambient conditions, transforming within minutes into an optically inactive yellow phase, a fact that has so far prevented its widespread adoption. Here we use coarse photolithography to embed a PbI(2)-based interfacial microstructure into otherwise-unstable CsPbI(3) perovskite thin films and devices. Films fitted with a tessellating microgrid are rendered resistant to moisture-triggered decay and exhibit enhanced long-term stability of the black phase (beyond 2.5 years in a dry environment), due to increasing the phase transition energy barrier and limiting the spread of potential yellow phase formation to structurally isolated domains of the grid. This stabilizing effect is readily achieved at the device level, where unencapsulated CsPbI(3) perovskite photodetectors display ambient-stable operation. These findings provide insights into the nature of phase destabilization in emerging CsPbI(3) perovskite devices and demonstrate an effective stabilization procedure which is entirely orthogonal to existing approaches

Worldwide trends in body-mass index, underweight, overweight, and obesity from 1975 to 2016: a pooled analysis of 2416 population-based measurement studies in 128·9 million children, adolescents, and adults.

BACKGROUND: Underweight, overweight, and obesity in childhood and adolescence are associated with adverse health consequences throughout the life-course. Our aim was to estimate worldwide trends in mean body-mass index (BMI) and a comprehensive set of BMI categories that cover underweight to obesity in children and adolescents, and to compare trends with those of adults. METHODS: We pooled 2416 population-based studies with measurements of height and weight on 128·9 million participants aged 5 years and older, including 31·5 million aged 5-19 years. We used a Bayesian hierarchical model to estimate trends from 1975 to 2016 in 200 countries for mean BMI and for prevalence of BMI in the following categories for children and adolescents aged 5-19 years: more than 2 SD below the median of the WHO growth reference for children and adolescents (referred to as moderate and severe underweight hereafter), 2 SD to more than 1 SD below the median (mild underweight), 1 SD below the median to 1 SD above the median (healthy weight), more than 1 SD to 2 SD above the median (overweight but not obese), and more than 2 SD above the median (obesity). FINDINGS: Regional change in age-standardised mean BMI in girls from 1975 to 2016 ranged from virtually no change (-0·01 kg/m2 per decade; 95% credible interval -0·42 to 0·39, posterior probability [PP] of the observed decrease being a true decrease=0·5098) in eastern Europe to an increase of 1·00 kg/m2 per decade (0·69-1·35, PP>0·9999) in central Latin America and an increase of 0·95 kg/m2 per decade (0·64-1·25, PP>0·9999) in Polynesia and Micronesia. The range for boys was from a non-significant increase of 0·09 kg/m2 per decade (-0·33 to 0·49, PP=0·6926) in eastern Europe to an increase of 0·77 kg/m2 per decade (0·50-1·06, PP>0·9999) in Polynesia and Micronesia. Trends in mean BMI have recently flattened in northwestern Europe and the high-income English-speaking and Asia-Pacific regions for both sexes, southwestern Europe for boys, and central and Andean Latin America for girls. By contrast, the rise in BMI has accelerated in east and south Asia for both sexes, and southeast Asia for boys. Global age-standardised prevalence of obesity increased from 0·7% (0·4-1·2) in 1975 to 5·6% (4·8-6·5) in 2016 in girls, and from 0·9% (0·5-1·3) in 1975 to 7·8% (6·7-9·1) in 2016 in boys; the prevalence of moderate and severe underweight decreased from 9·2% (6·0-12·9) in 1975 to 8·4% (6·8-10·1) in 2016 in girls and from 14·8% (10·4-19·5) in 1975 to 12·4% (10·3-14·5) in 2016 in boys. Prevalence of moderate and severe underweight was highest in India, at 22·7% (16·7-29·6) among girls and 30·7% (23·5-38·0) among boys. Prevalence of obesity was more than 30% in girls in Nauru, the Cook Islands, and Palau; and boys in the Cook Islands, Nauru, Palau, Niue, and American Samoa in 2016. Prevalence of obesity was about 20% or more in several countries in Polynesia and Micronesia, the Middle East and north Africa, the Caribbean, and the USA. In 2016, 75 (44-117) million girls and 117 (70-178) million boys worldwide were moderately or severely underweight. In the same year, 50 (24-89) million girls and 74 (39-125) million boys worldwide were obese. INTERPRETATION: The rising trends in children's and adolescents' BMI have plateaued in many high-income countries, albeit at high levels, but have accelerated in parts of Asia, with trends no longer correlated with those of adults. FUNDING: Wellcome Trust, AstraZeneca Young Health Programme