1,721,530 research outputs found
Perceptual-motor planning and performance in dynamical postural control
No full textLo scopo principale di questa dissertazione è di comprendere in maniera più approfondita il controllo dinamico della postura nel movimento umano. In particolare, qui ci approcciamo al problema prendendo in considerazione differenti compiti motori e analizzando differenti popolazioni in tre studi diversi. Nel primo viene presa in considerazione l’azione motoria della salita delle scale. In questo esperimento le popolazioni testate erano giovani ed anziani e lo scopo principale era di comprendere se ci sono differenti strategie posturali e percettive sia durante la pianificazione che durante l’esecuzione del movimento a causa della diminuzione del livello di capacità motorie. Gli altri due studi invece focalizzano più l’attenzione sullo sviluppo degli aggiustamenti posturali, prima e durante l’azione motoria, quando le capacità motorie raggiungono livelli ottimali di prestazione. In questi ultimi due casi le popolazioni prese in considerazione erano atleti di alto livello in cui essi primeggiano nell’azione da loro eseguita nell’esperimento, per cui di conseguenza lo scopo di questi studi era di spiegare come l’alta prestazione emerge in specifiche sinergie muscolari causate dall’esperienze motoria degli atleti. Anche se i tre esperimenti hanno in comune il controllo dinamico della postura, differenti modelli teorici del controllo motorio ispirano ciascuno di essi. Da una parte ci riferiamo al concetto di “equifinalità” formulata da Nicolay Bernstein (1967) e al concetto di “affordance” formulata da J.J. Gibson (1979). Queste due idee prese insieme ispirano il primo studio presentato. Dall’altra parte, la legge formulata da Paul Fitts (1954) ispira gli ultimi due esperimenti. Nel’introduzione presenteremo in sequenza queste idee e i loro relativi modelli: per prima l’equifinalità, seguendo l’affordance e poi la legge di Fitts. Per cui questi tre concetti teorici verranno applicati al controllo dinamico della postura, e un capitolo finale affronterà i modo dettagliato l’argomento riguardante il controllo posturale. Successivamente verranno presentati i tre esperimenti.The main aim of this dissertation is to obtain a deeper understanding about the dynamics of postural control in human movement. In particular here we approach the problem by including several motor tasks and by testing different populations in three separate studies. The first one deals with the action of climbing stairs. In this experiment the populations tested were old and young adults and the main aim was to reveal whether there are different perceptive/motor postural strategies either for planning as well as for executing the action due to the decrease of the level of motor skill. The other two studies instead focalize more the attention on the development of postural adjustments, before and during the action performance, when the level of motor skill reaches its optimality. In these latter two cases the populations tested were elite athletes performing actions in which they excel, and as a consequence the aim of these studies was to reveal how excellence merges from the developments of specific muscular synergies due to practice. Even though the three experiments share issues related to the dynamics of postural control, different models and theoretical frameworks inspire each one. On the one hand, we refer to the concept of movement “equifinality” formulated by Nicolay Bernstein (1967) and to the concept of “affordance” formulated by J.J. Gibson (1979). These two ideas taken together inspired the first study presented. On the other hand, the law formulated by Paul Fitts (1954) inspired the latter two experiments. In the introduction we will present in sequence these ideas and their relative models: first equifinality, followed by affordance, and then Fitts’ law. Since these three theoretical concepts are applied to the dynamics of postural control, a final chapter will discuss more in depth issues related to the control of posture. Then the three experiments will be presented
Characterization of a silica supported rhodium catalyst via hydrogen chemisorption, temperature programmed desorption and isotopic exchange measurements
No full textProduction of synthetic gasoline and diesel fuels by alternative processes using natural gas, coal and biomass: process simulation and economic analysis
No full textPrediction of vapor-liquid equilibrium for polymer solutions by a group-contribution Redlich-Kwong-Soave equation of state
No full textThe aim of this work is to apply a group-contribution cubic equation of state to vapor-liquid equilibria calculations of polymer-solvent mixtures. The model is based on a Redlich-Kwong-Soave equation of state with Huron-Vidal mixing rules where infinite-pressure activity coefficients are predicted by a UNIFAC-type model. An original procedure for estimating the equation-of-state parameters of the polymer is developed: experimental activity data of solvents in banary systems with the same polymer are used to fit parameter b (actually, b/MW) of the polymer, so that only one value of polymer density is needed to calculate parameter a at the temperature of interest. To show the potential of the proposed approach, a table of parameter b values is provided for six polymers, and several examples are presented both for nearly athermal and for polar polymer solutions. The model is able to correlate equilibrium pressure and solvent activities of the data base with good accuracy. The proposed method is then applied to predict solvent activities of systems not included in the fitting procedure with satisfactory results in all cases
Coupling between punch efficacy and body stability for elite karate
No full textCoupling between punch efficacy and body stability for elite
karate
Dimensional analysis and ground reaction forces for stair climbing: effects of age and task difficulty
No full textAltered perception–action capability is often associated with falls and diminished self-efficacy in olderpeople. This study evaluated and compared perception–action capability in stair-climbing performanceof 18 healthy volunteers assigned to two age groups (mean age, 26.3 ! 4.3 years and 66.4 ! 4.7 years,respectively). The experimental set-up included 14 stairs (50 cm wide, 60 cm deep, riser height 35–90 cm)positioned at the edge of a force platform. The task was to climb the stair with the greatest riser heightsubjects thought they could climb without outside support or use of hands. Dimensional and dynamic datawere collected and analyzed to reveal the invariant relationships that sustain action preparation andexecution. All subjects chose the same proportion between stair height and distance covered before mountingthe stair, as expressed by the invariant angle (a). While the geometric invariant relationship was picked up asa visual guide prior to action, there was a dynamic invariance in the forces applied during actual execution. Toestablish whether the invariance still held in extreme cases, two perturbed conditions were introduced inwhich stair distances were changed, forcing subjects to execute a foot-strike, either very far from or near tothe stair, before climbing it, so as to reveal any significant adaptations the climber would undertake to avoidslips or falls. Older and younger subjects applied appropriate visual and motor guidance by scaling their motorcapabilities to the environmental dimensions
The fitts’ law and the anticipatory postural adjustment
No full textThe fitts’ law and the anticipatory postural adjustmen
The speed-accuracy trade-off effects on the gait initiation planning
No full textThe speed-accuracy trade-off effects on the gait initiation plannin
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