KINEMATICAL AND DYNAMICAL ANALYSIS OF LONG JUMP TAKE-OFF: A FOUR CASES STUDY

INTRODUCTION-The take-off is one of. the most important phases of the long jump. Once there is no available knowledge on kinematic vs. dynamic relationships on the take-of, the purposes of this study were: (i) to analyse the biomechanical variations that occur at take-off; (ii) to establish relationships between kinematic and dynamic variables; (iii) to verify which of the moments of the take-off is more important to the production of the vertical velocity as well as the best result. METHODS~ Subjects for this 4-casesstudy research were well trained jumpers. Each athlete performed 6 trials, all videotaped (JVC-SVHS) in the sagitai plane for kinematical analysis (50 Hz). Simultaneously, dynamic analysis was performed through a Kistler 9218 B force plate (250 Hz). The kinematic parameters studied were: (i) resulting velocity of the center mass (VCM); (ii) horizontal velocity of the center mass (Vx); (iii) vertical velocity of the center mass (Vy); (iv) horizontal velocity of the lead leg knee (VeIK); (v) horizontal velocity of the touchdown foot (VeITd); (vi) loss of horizontal velocity (LVx); (vii) gain of vertical velocity (GVy); (viii) center mass / heel angle in the instants of touchdown and take-off (AngCM-he); (ix) knee angle (AngK); (x) support time (ST); (xi) touchdown distance (TdD); (xii) take-off angle (AngT). The described velocities and angles were determined in the following instants: (i) touchdown; (ii) maximum knee flexion and (iii) take off. The dynamical parameters studied were: fi) vertical impulse (Iz): (ii) maximum vertical force (Fzmax): (iii) time course to achieve maximum vertical force (lH/Fz max); (iv) passive impulse (lzPass}: (v) time course of the passive impulse (lHPass); (vi) active impulse (lzAct); (vii) time course of the active impulse (ßTAct); (viii) horizontal anterior posterior impulse (Iy); (ix) horizontal lateral impulse (Ix) RESULTS-The main results of this study showed that, in all cases, the major loss of the Vx and the major gain of the Vy were observed between the touchdown and the maximum knee flexion We also noticed that the knee of the lead leg has its maximum velocity at the moment of the maximum knee flexion for all subjects. This variables contribute significantly, in all cases, to the increase of the AngK in the take-off instant (psO.05), which is theoretically advantageous to the performance. One other finding was that when the values for AngCM-he in the touchdown and take-off instants were out of the theoretical limits defined by Fischer (1975), a reduced performance was observed. The observation of results also showed: (i) a increased Fzmax was always related with a higher jump length, with a higher % IZPass / IzAct, with a reduction both on ßTAct and ST, despite the correlation analysis did not always provide significant r values. CONCLUSIONS-Long jumpers should pay a special attention to the phase between the touchdown and the maximum knee flexion, where the main production of Vy occurs. There, a reduclion on ST during the take-off should be searched. Attention should also be paid to the values of the AngCM-he during the touchdown. REFERENCES Fischer, R. (1975). Weitsprung. Biomechanische untersuchungen am schweizerischen weitsprungkader mittels filmanalyse und messugen mir der mehrkomponenrenmessplattform. Diplamarbeil in biomechanik, ETH, Zurich

Electrical and thermal properties of polyurethane/carbon nanotubes composites

The aim of this work was to study the effect of dispersing small amounts of CNT on the thermal diffusivity and electrical resistivity of PU/CNT composites. The PU nanocomposites were prepared with 0.5% and 1% weight of CNT. The composites were prepared by dispersion of the CNT in poly(propylene glycol) (PPG) followed by in situ polymerization, by mixing with 4,4′-Methylene di-p-phenyl diisocyanate (MDI). The PPG was characterized by an average molecular weight of 425 g/mol and a hydroxyl value 250 to 276 mg KOH/g. The MDI was characterized by a isocianate value (%NCO value) of 27.9-29.2. It was observed that the thermal diffusivity slightly increased with the addition of the CNT, but the results obtained were within the typical range for polymers (in the order of 10-8 m2/s). The electrical resistivity measured for the composites showed a large decrease after the addition of 0.5% and 1% of CNT. The electrical resistivity decreased 3 and 7 decades (from 109 .m to 106 and 103 .m) for 0.5 and 1% CNT composites, respectively. Thus, the composite bearing 1% of CNT dispersed in the PU presented semiconductor behaviour

Comparative Study of the Response of Kinematical Variables from the Hip and the Center of Mass in Butterfliers

The aim of this study was to compare the intracyclic variation of kinematical variables from the hip and the center of mass (CM) with the purpose to assess if the analysis of kinematical variables of the hip might replace the study of the kinematical variables of the CM. Seven Portuguese male swimmers of national and intemational levei were studied. Each swimmer performed 3 sets of3x25 meters, at a constant velocity and as close as possible to the maximum, using exclusively frontal inspiration cycles, lateral inspiration cycles and non-inspiratory cycles in each set. Two pairs of cameras were used to create "dual media" images. Another cam era was set behind an underwater window in the endwall. One last camera was placed above the water surface. The study comprised the analysis of complete stroke cycles in buttert1y using the "Ariel Performance Analysis System" from Ariel Dynamics Inc. Some of the correlations between the maximal vertical amplitude of displacement of the hip and the CM didn't present significant values. AlI the correlations between the horizontal velocity and horizontal acceleration of the hip and the CM were significant in all breathing models. However, only one swimmer presented in both cases r>=O.95. So, apparently, the hip does not represent properly the intracyclic variations ofthe kinematical variables ofthe CM.info:eu-repo/semantics/publishedVersio

Análise de solos coesos do litoral Norte da Bahia utilizando a granulometria a laser.

Uma das características mais conspícuas dos solos dos Tabuleiros Costeiros é a coesão manifestada em horizontes subsuperficiais (horizontes coesos). Alguns autores defendem que a gênese dos horizontes coesos está relacionada a iluviação de argila muito fina, enquanto que outros relatam a importância da boa distribuição granulométrica. Visando contribuir para o entendimento dos horizontes coesos, foram realizados estudos em três perfis de solos utilizando um granulômetro a laser. O trabalho não comprovou a relação entre a translocação de argila muito fina e os horizontes coesos, contudo sugere que a boa distribuição granulométrica e a argiluviação favoreceram a constituição e evolução da coesão

A ÉTICA DE EMMANUEL LÉVINAS E A AUSÊNCIA DE ALTERIDADE NA INSTITUIÇÃO DAS GATED COM-MUNITIES: QUEM OU O QUE ESTÁ POR DETRÁS DOS MUROS?

Objetivou-se com este trabalho analisar a ordenação do solo urbano reconhecida no Brasil como Loteamentos Fechados (Gated Communities) e seus aspectos sociais e filosóficos, no que concerne ao fechamento dos muros e o isolamento social provocado por tal atitude. A doutrina jurídica estrangeira foi utilizada como marco para explanação do fenômeno e os conflitos que o mesmo provoca em diversos países. Também, a obra de Emmanuel Lévinas sobre a Ética da Alteridade, o que auxiliou o presente trabalho a comprovar, através de um fundamento filosófico, a ausência do outro e do caráter altero nos processos de formação das comunidades fechadas.

Measuring performance in agri‐food supply chains: A case study of a Portuguese company

Organizations seek to create value, increase competitiveness, reduce costs, share information and strengthen relationships between the various actors in the chain. In this sense, it is of the utmost importance that tools be developed which define objectives, monitor processes and document the performance of the supply chains. The Performance Measurement Systems (PMS) have come about to aid decision support, bringing together relevant Key Performance Indicators (KPis) which are fundamental for decision makers when deciding the best strategies for increasing supply chain competitiveness. In this study a PMS was developed collating a range of KPIs that seek to help in the continuous improvement of the agri-food supply chain. A case study allowed a PMS model to be designed incorporating the experiences of professionals in the area and subsequent tests to be made of its applicability, its outputs and its usefulness for decision support in a Portuguese plant.info:eu-repo/semantics/publishedVersio