239 research outputs found
KINEMATIC AND DYNAMIC ANALYSIS OF THE ROWER'S GESTURE ON CONCEPT II ERGOMETER
INTRODUCTION : Biomechanics Studies of rowing, remain most of the time global and consider the gesture as an indivisible whole (classification in style(DAL MONTE 89), coefficient of efficiency(ZATSIORSKY 91), peak of force on the handle (HARTMANN 93)). We plan to consider the gesture as the result of an elementary movements succession(movement of legs, movement of the trunk, movement of arms). Therefore the evaluation of the gesture efficiency depends on the study organization of these movements. The method used was the morphological analysis of kinematic and dynamic variable. An original experimental device has been elaborated. It consists of an optoelectronic system and a Concept II ergometer with of force and torque transducers. The population was a group of three rowers : a beginner, a regional level rower and a female rower of French team. After a period of warming of few minutes, the experimentation consisted in rowing during 20 minutes. The order was to row the furthest possible. The acquisition has been carried out for the first 5minutes.RESULTS : The first results show, for the three subjects, that the developed force on the handle cancels each other out before the end of the propulsion. This corresponds to a inefficiency phase of the gesture of the rower. A thorough morphological analysis shows that this phase is synchronized with a fall of the speed of the handle. Nevertheless, during this phase, the elbow angular speed is maximal. Consequently. During this phase, the contribution of arm is inefficient. The rower does not manageto increase the speed of the handle anymore. In addition, a comparative analysis between the three rowers is presented. It is based on inter-limb angular variable study and on effort delivered by the feet and the hands. The angular variable analysis shows a movement stereotyped for skilled rower. This confirmed that the expert's gestures are an automatism. Moreover, the increase of the force, applied on the feet strechers, carried out by the female rower, during the recovery, was delated, comparatively with the others rowers. The female rower controls her recovery. As this force does not make the boat further, the analysis of this variable shows as inefficient phase for the beginner and the regional rower. CONCLUSION : Kinematic and dynamic analysis of the rower gesture allowed to find 2 ineffective phases : the first during the end of the propulsion and the second during the end of the recovery. REFERENCES :DAL MONTE 89 : Dal Monte A,, Komor A.,Rowing and Sculling Mechanics, Article, Biomechanics of sport, Vaughan C.L.,ISBN : 0-8493-6820-0, 1989ZATSIORSKY 91 : Zatsiorsky V., YakuninN., Mechanics and Biomechanics of Rowing : TO review, International Newspaper of sport biomechanics, p229-281, 1991HARTMANN 93 : Hartmann U., Mader A.,Wasser K., Klauer I., Peak Forces,Velocity, and Power During Five and Maximal Ten Rowing Ergometer Strokesby World Class Female and Pain Rowers, Int J. Sport Med, Flight 14, Supl.1, p 42-545,199
Economic analysis of deforestation in Mexico
This paper uses panel analyses to estimate relationships for agricultural planted area and beef cattle numbers at the state level in Mexico during the periods 1970-85, in order to determine the main factors affecting forest land conversion. Of the key policy variables, maize and fertilizer prices appear to be the main influences on the expansion of planted area, whereas beef prices and credit disbursement influence cattle numbers. Population growth also affects both livestock and agricultural activities, and income per capita is positively correlated with cattle expansion. These estimated relationships are used to examine the effects both of agricultural and livestock sectoral policy changes and of trade liberalization in Mexico resulting from the North American Free Trade Agreement (NAFTA). To avoid any unintended impacts of NAFTA on Deforestation, it may be necessary for Mexico to make complementary investments in Land improvements, especially for existing cultivation on rain fed land
La construction d’une démarche interdisciplinaire à partir de l’émergence de la céréaliculture biologique en Camargue: le projet CEBIOCA
La céréaliculture biologique apparait comme une alternative aux modes de production conventionnels, pour un nombre croissant d'agriculteurs de Camargue. Le programme CEBIOCA cherche à appuyer le développement de ce prototype d'agriculture en favorisant l'élaboration de pratiques agricoles pertinentes, la production de matériel végétal adapté et la mesure des impacts de la conversion à l'AB. Un groupe de travail interdisciplinaire, associant génétique, agronomie, malherbologie, écologie et sociologie s'est constitué à l'occasion de la réponse à l'appel d'offre CIAB et au cours de la première phase de fonctionnemet qui est présenté ici. Malgré certaines lacunes ou faiblesses dans la construction interdiciplinaire, les résultats font entrevoir des perspectives prometteuses,dans un contexte plus favorable, à condition que les partenariats scientifiques et professionnles soient renforcés
Obstacles, levers and impacts of organic farming development in Camargue
We are presenting an analysis of the obstacles and levers for the development of organic cropping systems in Camargue, documented with a multicriteria analysis of scenarios of organic farming (OF) development. This communication is built using results from on-farm agronomic monitoring, stakeholders and farmers’ interviews and the use of models for integrated assessment of scenarios. At the farm level, the obstacles are related to identification of profitable cropping systems and rotations that include enough rice, conversion being therefore risky as impacting financial management and requiring a labour reorganisation. At the regional level, the constraints are related to the absence of advisory services for technical issues, and to the lack of coordination among the different stakeholders, to the low incentive of the public policies to convert, and to a relatively opaque organization of the supply chains. At the regional level, we analysed the consequences of two scenarios related to OF development on criteria such as the rice surface area, the quantity and quality of water, energy consumption or the employment generated. These results are expected to contribute to the definition of an action plan about OF development by the local stakeholders
Microtubule-associated protein 6 mediates neuronal connectivity through Semaphorin 3E-dependent signalling for axonal growth.
Structural microtubule associated proteins (MAPs) stabilize microtubules, a property that was thought to be essential for development, maintenance and function of neuronal circuits. However, deletion of the structural MAPs in mice does not lead to major neurodevelopment defects. Here we demonstrate a role for MAP6 in brain wiring that is independent of microtubule binding. We find that MAP6 deletion disrupts brain connectivity and is associated with a lack of post-commissural fornix fibres. MAP6 contributes to fornix development by regulating axonal elongation induced by Semaphorin 3E. We show that MAP6 acts downstream of receptor activation through a mechanism that requires a proline-rich domain distinct from its microtubule-stabilizing domains. We also show that MAP6 directly binds to SH3 domain proteins known to be involved in neurite extension and semaphorin function. We conclude that MAP6 is critical to interface guidance molecules with intracellular signalling effectors during the development of cerebral axon tracts
Study of Tau-pair Production in Photon-Photon Collisions at LEP and Limits on the Anomalous Electromagnetic Moments of the Tau Lepton
Tau-pair production in the process e+e- -> e+e-tau+tau- was studied using
data collected by the DELPHI experiment at LEP2 during the years 1997 - 2000.
The corresponding integrated luminosity is 650 pb^{-1}. The values of the
cross-section obtained are found to be in agreement with QED predictions.
Limits on the anomalous magnetic and electric dipole moments of the tau lepton
are deduced.Comment: 20 pages, 9 figures, Accepted by Eur. Phys. J.
CP asymmetry in in a general two-Higgs-doublet model with fourth-generation quarks
We discuss the time-dependent CP asymmetry of decay in an
extension of the Standard Model with both two Higgs doublets and additional
fourth-generation quarks. We show that although the Standard Model with
two-Higgs-doublet and the Standard model with fourth generation quarks alone
are not likely to largely change the effective from the decay of
, the model with both additional Higgs doublet and
fourth-generation quarks can easily account for the possible large negative
value of without conflicting with other experimental
constraints. In this model, additional large CP violating effects may arise
from the flavor changing Yukawa interactions between neutral Higgs bosons and
the heavy fourth generation down type quark, which can modify the QCD penguin
contributions. With the constraints obtained from processes
such as and , this model can lead to the
effective to be as large as in the CP asymmetry of .Comment: 13 pages, 5 figures, references added, to appear in Eur.Phys.J.
Energy dependence of Cronin momentum in saturation model for and collisions
We calculate dependence of Cronin momentum for and
collisions in saturation model. We show that this dependence is consistent with
expectation from formula which was obtained using simple dimentional
consideration. This can be used to test validity of saturation model (and
distinguish among its variants) and measure dependence of saturation
momentum from experimental data.Comment: LaTeX2e, 12 pages, 8 figure
Search for composite and exotic fermions at LEP 2
A search for unstable heavy fermions with the DELPHI detector at LEP is
reported. Sequential and non-canonical leptons, as well as excited leptons and
quarks, are considered. The data analysed correspond to an integrated
luminosity of about 48 pb^{-1} at an e^+e^- centre-of-mass energy of 183 GeV
and about 20 pb^{-1} equally shared between the centre-of-mass energies of 172
GeV and 161 GeV. The search for pair-produced new leptons establishes 95%
confidence level mass limits in the region between 70 GeV/c^2 and 90 GeV/c^2,
depending on the channel. The search for singly produced excited leptons and
quarks establishes upper limits on the ratio of the coupling of the excited
fermio
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