Sections of Coxeter Orbihedra

We study sections of high dimensional polytopes whose vertices form the orbit of a Coxeter group, and create “scans”of such polytopes in order to graphically visualise them for educational and public engagement purposes

Hydrological aspects of the Mesoscale Alpine Programme: finding from field experiments and simulations

Proc. International Conference on Alpine Metorology, Zagreb 23-27 Ma

Influence of natural surfactants on short wind waves in the coastal Peruvian waters

Results from measurements of wave slope statistics during the R/V Meteor M91 cruise in the coastal upwelling regions off the coast of Peru are reported. Wave slope probability distributions were measured with an instrument based on the reflection of light at the water surface and a method very similar to the Cox and Munk (1954b) sun glitter technique. During the cruise, the mean square slope (mss) of the waves was found to be very variable, despite the limited range of encountered wind speeds. The Cox and Munk (1954b) parameterization for clean water is found to overestimate mss, but most measurements fall in the range spanned by their clean water and slick parameterizations. The observed variability of mss is attributed to the wave damping effect of surface films, generated by increased biological production in the upwelling zones. The small footprint and high temporal resolution of the measurement allows for tracking abrupt changes in conditions caused by the often patchy structure of the surface films

The Digital Image Correlation technique applied to the deformation behavior of welded sheet joints

The existence of a welded zone generally influences the local strain and stress distribution especially in case of welding defects. A method able to measure the local deformability can hence give many important information about the real stress and strain fields useful to improve the welded structure design. In this experimental work, some new generation automotive steels have been considered, because of the well known welding problems due to their unstable microstructural condition. Such materials, known as Q&P steels and available only as thin sheets, require a suitable quenching process able to give high mechanical resistance and satisfying deformability. Some sheet samples were welded by electron beam technique, because it is able to reduce the width of the heat affected zone where the main microstructural changes are concentrated. From such samples, tensile specimens were machined. During the tensile tests, the deformations were measured both by a traditional extensometer and by a 3D Digital Image Correlation (3D DIC) technique. A preliminary investigation of the melted and the heat affected zones resulted in small dimensions (about 10 mm) and hence the measuring setup has been optimized in order maximize the achievable measuring resolution minimizing the resulting uncertainty. This result can be achieved by a pattern generated by a suitable software and by an accurate preparation of the surface where the pattern will be deposited on

Simple uncertainty frameworks for selecting weighting schemes and interpreting multimodel ensemble climate change experiments

Future climate change projections are often derived from ensembles of simulations from multiple global circulation models using heuristic weighting schemes. This study provides a more rigorous justification for this by introducing a nested family of three simple analysis of variance frameworks. Statistical frameworks are essential in order to quantify the uncertainty associated with the estimate of the mean climate change response. The most general framework yields the “one model, one vote” weighting scheme often used in climate projection. However, a simpler additive framework is found to be preferable when the climate change response is not strongly model dependent. In such situations, the weighted multimodel mean may be interpreted as an estimate of the actual climate response, even in the presence of shared model biases. Statistical significance tests are derived to choose the most appropriate framework for specific multimodel ensemble data. The framework assumptions are explicit and can be checked using simple tests and graphical techniques. The frameworks can be used to test for evidence of nonzero climate response and to construct confidence intervals for the size of the response. The methodology is illustrated by application to North Atlantic storm track data from the Coupled Model Intercomparison Project phase 5 (CMIP5) multimodel ensemble. Despite large variations in the historical storm tracks, the cyclone frequency climate change response is not found to be model dependent over most of the region. This gives high confidence in the response estimates. Statistically significant decreases in cyclone frequency are found on the flanks of the North Atlantic storm track and in the Mediterranean basin

COMPUTER SIMULATION IN SPORT DIDACTICS AND COACHING

Modern athletics and gymnastics are characterized by very complex exercises whose mechanics Is very often difficult to understand by intuition so t h a t some problems may arise in teaching ,and coaching. Moreover, many exercises include an aerial phase composed of different sub-phases; while learning, they are experimented separately by the athlete who rebuilds the whole exercise afterwards: a difficult coaching item concerns. for example. the variations of the movements which allow t o obtain the same sub-phases once they are linked in the full exercise, since the initial conditions of each sub-phase are in fact different. This kind of reasons gave recently impulse t o the development of computer simulation systems, especially oriented to sport biomechanics for teachers and coaches. BACKGROUND Starting from the Denavit(l975) approach to the kinematics of multi-body chains. which is based on the adoption of 4x4 matrices to define the relative position of bodies in 3D space. we introduced a set of six 4x4 special matrices. Our main goal is to face coherently. with the same matrix approach, the whole question of the mathematical analysis and synthesis of human motion: from the position analysis to the direct and inverse dynamics. Three out of those matrices are related t o kinematics (generalized position, velocity and acceleration matrices). while the other ones deal with dynamics (generalized action, momentum and Inertia matrices); all of them feature both linear and rotational components (eg.:linear and angular velocity; forces and couples; momentum and angular momentum). The structure and the properties of those matrices easily allow t o build computer programs for 3D direct and inverse dynamics of human motion. in which the equation structure is quite simple and clear. and efficient for computer handling. APPLICATIONS The system of programs f o r the simulation of sport exercises developed in our Department in connection with the University of Brescia. consists of a set of cooperating modules, each performing a particular task; the basic modules are: SPACE-LIB: a library of routines to perform the operations Involving the described matrices; ANTHROPM: to compute geometrical parameters and to build the Inertia matrix from as many data as they are available; DY-MAN: the main module. for the solution of the direct dynamic problem: from the knowledge of the relative motion of body segments and the external forces applied it calculates the athlete's body trajectory and orientation during an hypothetical exercise; GRAPIIMAN: a graphic 3D post-processor for dy_man output. This kind of software can help to solve some of the teaching problems described in the introduction, showing for instance to the athlete the effect of hypothetical variations of limbs’ movement on the whole body motion. It can also be very useful to plan complex athletic exercises without exposing the athlete to the danger of the preliminary set-up phase

Serial clustering of extratropical cyclones in a multi-model ensemble of historical and future simulations

This study has investigated serial (temporal) clustering of extra-tropical cyclones simulated by 17 climate models that participated in CMIP5. Clustering was estimated by calculating the dispersion (ratio of variance to mean) of 30 December-February counts of Atlantic storm tracks passing nearby each grid point. Results from single historical simulations of 1975-2005 were compared to those from historical ERA40 reanalyses from 1958-2001 ERA40 and single future model projections of 2069-2099 under the RCP4.5 climate change scenario. Models were generally able to capture the broad features in reanalyses reported previously: underdispersion/regularity (i.e. variance less than mean) in the western core of the Atlantic storm track surrounded by overdispersion/clustering (i.e. variance greater than mean) to the north and south and over western Europe. Regression of counts onto North Atlantic Oscillation (NAO) indices revealed that much of the overdispersion in the historical reanalyses and model simulations can be accounted for by NAO variability. Future changes in dispersion were generally found to be small and not consistent across models. The overdispersion statistic, for any 30 year sample, is prone to large amounts of sampling uncertainty that obscures the climate change signal. For example, the projected increase in dispersion for storm counts near London in the CNRMCM5 model is 0.1 compared to a standard deviation of 0.25. Projected changes in the mean and variance of NAO are insufficient to create changes in overdispersion that are discernible above natural sampling variations

Future changes in atmospheric rivers and their implications for winter flooding in Britain

Within the warm conveyor belt of extra-tropical cyclones, atmospheric rivers (ARs) are the key synoptic features which deliver the majority of poleward water vapour transport, and are associated with episodes of heavy and prolonged rainfall. ARs are responsible for many of the largest winter floods in the mid-latitudes resulting in major socioeconomic losses; for example, the loss from United Kingdom (UK) flooding in summer/winter 2012 is estimated to be about $1.6 billion in damages. Given the well-established link between ARs and peak river flows for the present day, assessing how ARs could respond under future climate projections is of importance in gauging future impacts from flooding. We show that North Atlantic ARs are projected to become stronger and more numerous in the future scenarios of multiple simulations from five state-of-the-art global climate models (GCMs) in the fifth Climate Model Intercomparison Project (CMIP5). The increased water vapour transport in projected ARs implies a greater risk of higher rainfall totals and therefore larger winter floods in Britain, with increased AR frequency leading to more flood episodes. In the high emissions scenario (RCP8.5) for 2074–2099 there is an approximate doubling of AR frequency in the five GCMs. Our results suggest that the projected change in ARs is predominantly a thermodynamic response to warming resulting from anthropogenic radiative forcing

A multimodel assessment of future projections of North Atlantic and European extratropical cyclones in the CMIP5 climate models

The response of North Atlantic and European extratropical cyclones to climate change is investigated in the climate models participating in phase 5 of the Coupled Model Intercomparison Project (CMIP5). In contrast to previous multimodel studies, a feature-tracking algorithm is here applied to separately quantify the re- sponses in the number, the wind intensity, and the precipitation intensity of extratropical cyclones. Moreover, a statistical framework is employed to formally assess the uncertainties in the multimodel projections. Under the midrange representative concentration pathway (RCP4.5) emission scenario, the December–February (DJF) response is characterized by a tripolar pattern over Europe, with an increase in the number of cyclones in central Europe and a decreased number in the Norwegian and Mediterranean Seas. The June–August (JJA) response is characterized by a reduction in the number of North Atlantic cyclones along the southern flank of the storm track. The total number of cyclones decreases in both DJF (24%) and JJA (22%). Classifying cyclones according to their intensity indicates a slight basinwide reduction in the number of cy- clones associated with strong winds, but an increase in those associated with strong precipitation. However, in DJF, a slight increase in the number and intensity of cyclones associated with strong wind speeds is found over the United Kingdom and central Europe. The results are confirmed under the high-emission RCP8.5 scenario, where the signals tend to be larger. The sources of uncertainty in these projections are discussed

HIGH JUMP DIRECT DYNAMIC SIMULATION

INTRODUcrION High jumps are composed of a complex sequence of movements whose single contribution to the whole body motion cannot be intuitively predicted. While most of the movements are well learned by the elite athletes in order to reach the result, few are not effective or negative from the mechanical point of view and are probably performed for an erroneous feeling of their effects. The direct dynamic simulation of jumping can be useful in order to more fully understand the mechanics of high jump techniques; to explain to the athletes the consequences of some errors; and to test possible evolution of the exercise. When the external forces and the relative movements of the limbs are known, the calculation of the whole body trajectory and orientation is a direct dynamic problem