885 research outputs found
Consistency of performance in the Tkatchev release and re-grasp on high bar
No full textThe Tkatchev on the high bar is a release and re-grasp skill in which the gymnast rotates in a direction during flight opposite to that of the preceding swing. Since the release window is defined as the time during which the gymnast has appropriate linear and angular momentum to ensure the bar can be re-grasped, it was speculated that the release windows for this skill would be smaller than for dismounts which are less constrained. One senior male gymnast competing at national level performed 60 Tkatchev trials. A four-segment planar simulation model of the gymnast and high bar was used to determine the release windows in 10 successful and 10 unsuccessful performances of the Tkatchev recorded using a Vicon motion analysis system. Model parameters were optimised to obtain a close match between simulations and recorded performances in terms of rotation angle (1°), bar displacements (0.01 m) and release velocities (1%). Each matched simulation was used to determine the time window around the actual point of release for which the model had appropriate release parameters to complete the Tkatchev successfully. The release windows for the successful trials were small compared to those of dismounts. The unsuccessful trials were associated with later release and later timing of the actions at the shoulders and hips
Functional phases and angular momentum characteristics of Tkatchev and Kovacs
No full textUnderstanding the technical requirements and underlying biomechanics of complex release and re-grasp skills on high bar allows coaches and scientists to develop safe and effective training programmes. The aim of this study was to examine the differences in the functional phases between the Tkatchev and Kovacs skills and to explain how the angular momentum demands are addressed. Images of 18 gymnasts performing 10 Tkatchevs and 8 Kovacs at the Olympic Games were recorded (50 Hz), digitised and reconstructed (3D Direct Linear Transformation). Orientation of the functional phase action, defined by the rapid flexion to extension of the shoulders and extension to flexion of the hips as the performer passed through the lower vertical, along with shoulder and hip angular kinematics, angular momentum and key release parameters (body angle, mass centre velocity and angular momentum about the mass centre and bar) were compared between skills. Expected differences in the release parameters of angle, angular momentum and velocity were observed and the specific mechanical requirement of each skill were highlighted. Whilst there were no differences in joint kinematics, hip and shoulder functional phase were significantly earlier in the circle for the Tkatchev. These findings highlight the importance of the orientation of the functional phase in the preceding giant swing and provide coaches with further understanding of the critical timing in this key phase
RAZVOJ PRVIN NA DROGU GLEDE NA JAPONSKE VIRE
No full textMore recently a total of 800 elements have been recorded in the Gymnastics Code of Points. However few of theses elements made gymnastics history. As such we wonder by whom, when or where these various elements are performed. The purpose of this study was to collate data elements on the Horizontal Bar (HB) in men’s artistic gymnastics and to suggest new elements in the future. The method of study was undertaken by bibliographic analysis. This article refers mainly to journals that were published by the Japan Gymnastic Association, and a list that was made regarding the occurrence of new elements on HB in Men’s artistic gymnastics. From the analysis, the author gatherd data regarding various elememts that were performed. For example, Swing forward and vault backward straddle to hang (Tkatchev) was performed by Tkatchev A. in the 1979 World cup. A Tkatchev stretch was performed by Liukin V. and Nishikawa D. in the 1988 Seoul Olympics. In conclusion, developments of HB elements are greatly influenced by the improvement of apparatus, rules of the era. In the near future, directions of new occurring elements on the HB may add twists to the existing elements.V današnjem pravilniku FIG za ocenjevanje v moški orodni telovadbi je okoli 800 prvin. Za malo teh prvin se natančno ve, kdaj so bile prvič izvedene, kdo jih je prvič izvedel in kje jih je izvedel. Namen članka je bil raziskati pojavnost prvin na drogu z namenom predvideti nove prvine. Uporabljena je bila bibliografska metoda. V članku so predvsem uporabljeni japonski viri, izdani s strani Japonske telovadne zveze in narejen je bil seznam glede na čas pojavitve posamezne nove prvine. Upoštevane so bile različne izvedbe posameznih prvin, npr. Tkačev je izvedel iz predkoleba skok nazaj raznožno v ponovni prijem leta 1979 na svetovnem pokala. Prvič sta stegnjenega Tkačeva izvedla Ljukin in Nišikava na olimpijskih igrah leta 1988 v Seulu. Napredek na drogu so omogočili predvsem razvoj orodja in razvoj prvin. V prihodnosti lahko predvsem pričakujemo prvine z dodanimi obrati
Quelques questions de la théorie de la croissance et de la condensation des bulles dans les chambres à bulles
No full text
First measurement of the rate K-L(0)->pi mu nu gamma RID C-6551-2009 RID A-4071-2012
No full textIn a preliminary version of the NA48 experiment at the CERN SPS, in which an iron-scintillator sandwich calorimeter was used as a photon detector, the ratio of K-L --> pi mu nu gamma and K-L --> pi mu nu decays was measured. The branching ratio BR(K-L --> pi mu nu gamma,E-gamma*greater than or equal to 30 MeV)/(K-L --> pi mu nu) is found to be (2.08+/-0.17(-0.21)(+0.16)x10(-3), where the first error is statistical and the second systematic. The result is in agreement with theoretical predictions. (C) 1998 Elsevier Science B.V
Measurement of the decay rate and form factor parameter alpha(K*) in the decay K-L -> e(+)e(-)gamma
No full textThe decay rate of the neutral K meson K-L --> e(+)e(-)gamma has been measured with the NA48 detector at the CERN SPS. A total of 6864 events has been observed with an estimated background of 10 events. The branching ratio is Gamma(K-L --> e(+)e(-)gamma)/Gamma(K-L --> all) = (1.06 +/- 0.02(stat) +/- 0.02(sys) +/- 0.04(calc)) X 10(-5). The parameter alpha(K*) describing the relative strength of the two contributing amplitudes to this decay through intermediate pseudoscalar or vector mesons was measured to be alpha(K*) = -0.36 +/- 0.06(stat) +/- 0.02(sys). (C) 1999 Published by Elsevier Science B.V. All rights reserved
Determination of ǀVcb☐from the semileptonic decay B0 → D*-l+ν
No full textSemileptonic decays B→ D*-l+νX were selected from a sample of 3.1 million hadronic Z decays collected by the DELPHI detector at LEP. A topological search for semileptonic B decays to resonant and non-resonant D*-π+ states was performed and the ratio of the branching fractions: Br(B → D*-l+νX)/Br(B → D*-+νX) + Br(B0 → + D*-l+ν) = 0.19 ± 0.10(stat) ± 0.06(syst) was determined. Taking into account this contribution, the differential decay width of B0 → D*-l+ν was measured as a function of the momentum transfer from the B to the D*- in two separate analyses, using exclusive and inclusive methods of D*- reconstruction. The distributions were fitted over the full momentum transfer range to extract the product of {pipe}Vcb{pipe} times the normalization of the decay form factor F(q2max): F(q2max){pipe}Vcb{pipe} = (35.4 ± 1.9(stat) ± 2.4(syst)) · 10-3. The value of {pipe}Vcb{pipe} was computed using theoretical calculations of F(q2max), giving: {pipe}Vcb{pipe} = (38.9 ± 2.0(stat) ± 2.6(syst) ± 1.7(theory)) · 10-3. The total branching fraction Br(B0 → D*-l+ν) was determined to be: Br(130, D*-l+v) = (5.52 ± 0.17(stat) ± 0.68(syst))%. © Springer-Verlag 1996
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