A COMPOSITE MODEL FOR THE SIMULATION OF SKIING TECHNIQUES

INTRODUCTION In this work we present a model for skiing technique analysis and simulation: it consists of a man model, an equipment model and a contact (ski-snow) model. Such a model is the basis for a deeper understanding of the interaction between skier and equipment and its use will be profitable in various applications such as: equipment optimisation and technique improvement. Moreover this simulation technique can be profitably used for teaching the basic principles of skiing. MATERIAL AND METHODS To build our model we combined the methods used for multibody systems dynamic analysis (man model with finite element techniques (ski model). The human body model consists of 3D chains of rigid bodies: according to the "sophistication" of the simulation we use 16 segments, with 39'internal d.0.f (full man model), or 7 segments, with 6 internal d.0.f . To describe rigid body dynamics and kinematics (man model) we adopt a method based on homogeneous matrices (Casolo 1995): both the absolute and the relative position, velocity and acceleration are described by 4x4 matrices, as well as the inertial properties and the external loads. This approach allows to embed both the linear and angular terms in the same formalism. To derive the equation of motion a Lagrangian approach was adopted, leading to this expression: Mq+C(cf.q.t) = Fl(q.q,t) +Ft(q,q) where M is the mass matrix, C contain the weight, the centrifugal and Coriolis effect, Ft contains joint torques, F2 represent the action exchanged with ski through the bindings and the vector q contains joints laws of motion. The model can be used to perform direct and inverse dynamics analysis of skiing, since it allows the input of joint torques and/or joint relative movements, that can be experimental data or can be generated by scratch, by a law of motion preprocessor. Skis are modelled with Finite Element techniques. The internal structure of a ski is quite complex: different material, with complex arrangement, are employed giving rise to properties (stiffness, damping and mass) which can be determined by experimental measures or by complex FE analysis. These properties can be quite well reproduced by means of a simplified model consisting of 3D beam elements . Some geometrical features, such as camber and sidecut, can be easily reproduced. Ski equations of motion, in matrix form, are: M9+ q v r e l + Kq&f = F,,I +Fnlon-ski f F.+.ki - cn,,wn where M, C, K are, respectively, the ski mass, damping and stiffness matrices. The ski load consists of three terms: weight, action exerted by the skier through the bindings and the contact action exerted by the snow. A simple contact model has been also developed, based on the assumption that the snow reacts both to ski deepening, sliding and skidding. This simple model can take into account, for example, the effect of ski vibration on the ski-snow interaction. RESULTS Some simulations have been performed to test model capabilities: we analysed the effect of ski torsional stiffness, as well as the amount of sidecut, on skier trajectory during traverse and turns. The model is also used to simulate the aerial phase of a free-style jump and the following landing phase. In all of these cases simulation can be an useful tool for predicting the effect of changing joint movements (i.e varying skiing technique) and equipment characteristics. A sensitivity analysis can be a first step toward a technique and equipment optimisation. References Casolo F., Legnani G., Righettini P., Zappa B. "A homogeneous matrix approach to 3D kinematics and dynamics", TMM (in press)

Relationships between population traits, nonstructural carbohydrates, and elevation in alpine stands of Vaccinium myrtillus

Premise: Despite great attention given to the relationship between plant growth and carbon balance in alpine tree species, little is known about shrubs at the treeline. We hypothesized that the pattern of main nonstructural carbohydrates (NSCs) across elevations depends on the interplay between phenotypic trait plasticity, plant\u2013plant interaction, and elevation. Methods: We studied the pattern of NSCs (i.e., glucose, fructose, sucrose, and starch) in alpine stands of Vaccinium myrtillus (above treeline) across an elevational gradient. In the same plots, we measured key growth traits (i.e., anatomical stem features) and shrub cover, evaluating putative relationships with NSCs. Results: Glucose content was positively related with altitude, but negatively related with shrub cover. Sucrose decreased at high altitude and in older populations and increased with higher percentage of vascular tissue. Starch content increased at middle and high elevations and in stands with high shrub cover. Moreover, starch content was negatively related with the number of xylem rings and the percentage of phloem tissue, but positively correlated with the percentage of xylem tissue. Conclusions: We found that the increase in carbon reserves across elevations was uncoupled from plant growth, supporting the growth limitation hypothesis, which postulates NSCs accumulate at high elevation as a consequence of low temperature. Moreover, the response of NSC content to the environmental stress caused by elevation was buffered by phenotypic plasticity of plant traits, suggesting that, under climate warming conditions, shrub expansion due to enhanced plant growth would be pronounced in old but sparse stands

Density functional investigations of defect induced mid-gap states in graphane

We have carried out ab initio electronic structure calculations on graphane (hydrogenated graphene) with single and double vacancy defects. Our analysis of the density of states reveal that such vacancies induce the mid gap states and modify the band gap. The induced states are due to the unpaired electrons on carbon atoms. Interestingly the placement and the number of such states is found to be sensitive to the distance between the vacancies. Furthermore we also found that in most of the cases the vacancies induce a local magnetic moment.Comment: 15 page

Transient Effects of Snow Cover Duration on Primary Growth and Leaf Traits in a Tundra Shrub

With the recent climate warming, tundra ecotones are facing a progressive acceleration of spring snowpack melting and extension of the growing season, with evident consequences to vegetation. Along with summer temperature, winter precipitation has been recently recognised as a crucial factor for tundra shrub growth and physiology. However, gaps of knowledge still exist on long-living plant responses to different snowpack duration, especially on how intra-specific and year-to-year variability together with multiple functional trait adjustments could influence the long-term responses. To fill this gap, we conducted a 3 years snow manipulation experiment above the Alpine treeline on the typical tundra species Juniperus communis, the conifer with the widest distributional range in the north emisphere. We tested shoot elongation, leaf area, stomatal density, leaf dry weight and leaf non-structural carbohydrate content of plants subjected to anticipated, natural and postponed snowpack duration. Anticipated snowpack melting enhanced new shoot elongation and increased stomatal density. However, plants under prolonged snow cover seemed to compensate for the shorter growing period, likely increasing carbon allocation to growth. In fact, these latter showed larger needles and low starch content at the beginning of the growing season. Variability between treatments slightly decreased over time, suggesting a progressive acclimation of juniper to new conditions. In the context of future warming scenarios, our results support the hypothesis of shrub biomass increase within the tundra biome. Yet, the picture is still far from being complete and further research should focus on transient and fading effects of changing conditions in the long term

Drought-induced dieback of Pinus nigra: A tale of hydraulic failure and carbon starvation

Ongoing climate change is apparently increasing tree mortality rates, and understanding mechanisms of drought-induced tree decline can improve mortality projections. Differential drought impact on conspecific individuals within a population has been reported, but no clear mechanistic explanation for this pattern has emerged. Following a severe drought (summer 2012), we monitored over a 3-year period healthy (H) and declining (D) Pinus nigra trees co-occurring in a karstic woodland to highlight eventual individual-specific physiological differences underlying differential canopy dieback. We investigated differences in water and carbon metabolism, and xylem anatomy as a function of crown health status, as well as eventual genotypic basis of contrasting drought responses. H and D trees exploited the same water pools and relied on similar hydraulic strategies to cope with drought stress. Genetic analyses did not highlight differences between groups in terms of geographical provenance. Hydraulic and anatomical analyses showed conflicting results. The hydraulic tracheid diameter and theoretical hydraulic conductivity were similar, but D trees were characterized by lower water transport efficiency, greater vulnerability to xylem conduit implosion and reduced carbohydrate stores. Our results suggest that extreme drought events can have different impacts on conspecific individuals, with differential vulnerability to xylem embolism likely playing a major role in setting the fate of trees under climate change

School self-efficacy is affected by gender and motor skills: findings from an Italian study

Background: Perceived school self-efficacy (SE) is an important variable in students' activities as it affects their motivation and learning. Further, self-efficacy might represent a good predictor of performance, persistence and perseverance. Motor skills and other physical health determinants are extensively debated and linked to cognitive function in children of developmental age. However, inconclusive evidence supports a definitive relationship between perceived school SE and motor skills among schoolchildren. We conducted a cross-sectional study on 6-11-year-old schoolchildren to evaluate the extent by which perceived school SE and physical health determinants were related. Methods: A SE questionnaire and motor performance battery tests were administered to primary school pupils recruited from 154 sampled schools of northwest Italy. Perceived SE at school was assessed via 12 items from the Caprara's questionnaire. Motor performance scores were obtained from motor skill tests: 4 × 10 m shuttle run test, SRT; standing broad jump, SBJ; six-minute walking test, 6MWT. Results: A total of 3,962 children (M = 2,019; F = 1943) were studied and 68% were normal weight. Overall, a 58% of the sample perceived a high SE, while, as to gender differences, a greater percentage of females perceived high levels of school SE with respect to any other level (χ2 = 38.93, p < 0.0001). Results from multinomial logistic regression analysis revealed that: (i) females perceived higher SE compared to males; (ii) children who performed better in SRT and 6MWT showed higher levels of perceived school SE; (iii) no significant effect was registered for the body weight. Alternative strategies are encouraged to enhance SE through physical education: structured interventions might enhance both complex motor skills and high-order cognitive skills, like SE, in young children

The RIBES strategy for ex situ conservation: conventional and modern techniques for seed conservation

The Italian seed bank network (RIBES) aims to improve the quality and safety of the germplasm reserves of native plant species in Italy to ensure the long-term conservation of endangered and/or endemic flora. The strategy includes traditional methods to secure seed conservation. A comprehensive priority list for seed collection is being defined, it was prepared by crossing data of various checklists (red lists, endemics) and will soon be cross-referenced with an updated list of accessions of the whole network. A safety-backup program of duplicates will quickly be implemented to secure the conservation of the most threatened species in at least two seed banks of the network. On the other hand, the RIBES strategy also includes research by applying modern techniques. In collaboration with the Millennium Seed Bank, research on the storage behaviour of seeds and spores through thermal analysis is ongoing to inform conservation. Using the Differential Scanning Calorimetry (DSC), we could evaluate seed lipid properties such as glass transition temperature, melting, crystallization, oxidation behaviour, and thermal stability. Finally, RIBES participates as a co-funder in the LIFE Nature project SEEDFORCE, coordinating 11 seed banks of the network for collecting seeds/spores of 29 threatened species of EU interest