A STUDY OF SCULLING SWIMMING PROPULSIVE PHASES AND THEIR RELATIONSHIP WITH HIP VELOCITY

The purpose of this study was to identify the effect of sculling propulsive arm actions in displacement on the intra-cycle velocity of the hip. Four phases were defined (based on hand movements) prior to the development of the study: inward, pronation, outward and supination. A group of 9 international synchronized swimmers participated in the study. A displacement of 15 m was recorded using a velocimeter and underwater video cameras (bottom and sagittal views). Mean cycle velocity 0.548m/s, duration 0.828s, sculling frequency 1.220 sculling length 0,455 m and percentage of phase duration: inward (38.6%), pronation (10.3%), outward (33.5%) and supination (17.6%) were obtained. The mean body velocities were similar in the phases, while the durations where significantly different. The sculling propulsive action helps body displacement in the inward, outward and supination phases; while the pronation had a reduced contribution. Reversal stroke actions help to support the hand fixed it the water while the arm muscles are contracted helping the next propulsive phases (inward or outward) to move the hand an body forward

Variable stars in the open cluster NGC 6791 and its surrounding field

Aims: This work presents a high--precision variability survey in the field of the old, super metal-rich open cluster NGC 6791. Methods: The data sample consists of more than 75,000 high-precision CCD time series measurements in the V band obtained mainly at the Canada-France-Hawaii Telescope, with additional data from S. Pedro Martir and Loiano observatories, over a time span of ten nights. The field covers an area of 42x28 arcmin^2. Results: We have discovered 260 new variables and re-determined periods and amplitudes of 70 known variable stars. By means of a photometric evaluation of the membership in NGC 6791, and a preliminary membership based on the proper motions, we give a full description of the variable content of the cluster and surrounding field in the range 16<V<23.5. Accurate periods can be given for the variables with P<4.0 d, while for ones with longer periods the limited time-baseline hampered precise determinations. We categorized the entire sample as follows: 6 pulsating, 3 irregular, 3 cataclysmic, 89 rotational variables and 61 eclipsing systems; moreover, we detected 168 candidate variables for which we cannot give a variability class since their periods are much longer than our time baseline. Conclusions: On the basis of photometric considerations, and of the positions of the stars with respect to the center of the cluster, we inferred that 11 new variable stars are likely members of the cluster, for 22 stars the membership is doubtful and 137 are likely non-members. We also detected an outburst of about 3 mag in the light curve of a very faint blue star belonging to the cluster and we suggest that this star could be a new U Gem (dwarf nova) cataclysmic variable.Comment: 24 pages, 19 Figures, A&A accepte

Compte rendu : Catherine Roth, La nation entre les lignes

Le titre ambivalent de cet ouvrage est un reflet fidèle de sa double vocation théorique et empirique. En effet, avant la lecture du sous-titre, on peut bien penser qu’il s’agit d’un essai sur certains aspects du concept de nation (en général), et ce n’est qu’après la lecture de l’ethnonyme et du toponyme que nous nous voyons, en revanche, devant un ouvrage descriptif à vocation fondamentalement ethnographique. La manière dont ces deux aspects de l’ouvrage sont articulés tout au long de ses ce..

Echelle long-slit optical spectroscopy of evolved stars

We present echelle long-slit optical spectra of a sample of objects evolving off the AGB, most of them in the pre-planetary nebula (pPN) phase, obtained with the ESI and MIKE spectrographs at Keck-II and Magellan-I, respectively. The total wavelength range covered with ESI (MIKE) is ~3900 to 10900 A (~3600 to 7200A). In this paper, we focus our analysis mainly on the Halpha profiles. Prominent Halpha emission is detected in half of the objects, most of which show broad Halpha wings (up to ~4000 km/s). In the majority of the Halpha-emission sources, fast, post-AGB winds are revealed by P-Cygni profiles. In ~37% of the objects Halpha is observed in absorption. In almost all cases, the absorption profile is partially filled with emission, leading to complex, structured profiles that are interpreted as an indication of incipient post-AGB mass-loss. All sources in which Halpha is seen mainly in absorption have F-G type central stars, whereas sources with intense Halpha emission span a larger range of spectral types from O to G. Shocks may be an important excitation agent of the close stellar surroundings for objects with late type central stars. Sources with pure emission or P Cygni Halpha profiles have larger J-K color excess than objects with Halpha mainly in absorption, which suggests the presence of warm dust near the star in the former. The two classes of profile sources also segregate in the IRAS color-color diagram in a way that intense Halpha-emitters have dust grains with a larger range of temperatures. (abridged)Comment: 68 pages, 14 figures, accepted for publication in ApJS (abstract abridged

Creep of (La0.55Sr0.45)0.99Mn1-yGayO3

Steady-state compressive creep was measured in (La0.55Sr0.45)0.99Mn1−yGayO3 at temperatures from 1200 to 1270 °C in air at stresses (σ) from 13 to 40 MPa. The Ga concentration was y = 0, 0.05, and 0.10. Strains to 0.14 were obtained. In the creep equation for strain rate, = An exp(−Q/RT), stress exponents (n) were between 1.3 and 1.7, indicating that diffusional flow is the dominant creep mechanism, and the activation energy (Q) was found to vary from 355 kJ mol−1 for y = 0 to 485 kJ mol−1 for y = 0.10

Full-Folding Optical Potentials for Elastic Nucleon-Nucleus Scattering based on Realistic Densities

Optical model potentials for elastic nucleon nucleus scattering are calculated for a number of target nuclides from a full-folding integral of two different realistic target density matrices together with full off-shell nucleon-nucleon t-matrices derived from two different Bonn meson exchange models. Elastic proton and neutron scattering observables calculated from these full-folding optical potentials are compared to those obtained from `optimum factorized' approximations in the energy regime between 65 and 400 MeV projectile energy. The optimum factorized form is found to provide a good approximation to elastic scattering observables obtained from the full-folding optical potentials, although the potentials differ somewhat in the structure of their nonlocality.Comment: 21 pages, LaTeX, 17 postscript figure

Pulsational instability of yellow hypergiants

Instability of population I (X=0.7, Y=0.02) massive stars against radial oscillations during the post-main sequence gravitational contraction of the helium core is investigated. Initial stellar masses are in the range from 65M_\odot to 90M_\odot. In hydrodynamic computations of self-exciting stellar oscillations we assumed that energy transfer in the envelope of the pulsating star is due to radiative heat conduction and convection. The convective heat transfer was treated in the framework of the theory of time-dependent turbulent convection. During evolutionary expansion of outer layers after hydrogen exhaustion in the stellar core the star is shown to be unstable against radial oscillations while its effective temperature is Teff > 6700K for Mzams=65M_\odot and Teff > 7200K for mzams=90M_\odot. Pulsational instability is due to the \kappa-mechanism in helium ionization zones and at lower effective temperature oscillations decay because of significantly increasing convection. The upper limit of the period of radial pulsations on this stage of evolution does not exceed 200 day. Radial oscillations of the hypergiant resume during evolutionary contraction of outer layers when the effective temperature is Teff > 7300K for Mzams=65M_\odot and Teff > 7600K for Mzams=90M_\odot. Initially radial oscillations are due to instability of the first overtone and transition to fundamental mode pulsations takes place at higher effective temperatures (Teff > 7700K for Mzams=65M_\odot and Teff > 8200K for Mzams=90M_\odot). The upper limit of the period of radial oscillations of evolving blueward yellow hypergiants does not exceed 130 day. Thus, yellow hypergiants are stable against radial stellar pulsations during the major part of their evolutionary stage.Comment: 20 pages, 7 gigures. Accepted for publication in Astronomy Letter

Deformación plástica de compuestos mullita/óxido de itrio

Los compuestos a partir de mullita (3Al2 O3 .2SiO2 ) presentan unas magníficas propiedades mecánicas y térmicas. Las mismas características que hacen de la mullita resistente a la deformación plástica, dificultan su densificación. El óxido de itrio es uno de los aditivos más utilizados para reducir la temperatura de sinterización de la mullita. Adicionalmente la presencia de silicatos vítreos (en este caso Y2 Si2 O7 ) incrementan la ductilidad. En esta investigación se han usado muestras de mullita con diversas cantidades de Y2 O3 (0%, 5% y 9% en peso). Los detalles sobre el procesado y caracterización de los compuestos han sido objeto de una publicación previa. Se ha estudiado comparativamente la ductilidad de estos materiales mediante experimentos de deformación en compresión a alta temperatura. Los ensayos se han desarrollado entre 1300 y 1400ºC, en atmósfera de aire, cubriendo un rango de tensiones de compresión entre 0.69 y 34.4 MPa.Mullite (3Al2 O3 .2SiO2 ) based composites have excellent mechanical and thermal properties. The same characteristics that give mullite good resistance to plastic deformation also make its sintering difficult. Yttria is one of the most commonly used additives to reduce sintering temperatures in mullite. Additionally vitreous silicates (Y2 Si2 O7 ) could improve ductility. In this work we have used mullite samples with various amounts of Y2 O3 (0, 5 and 9 wt.%). Details of processing and characterization of these composites have been the subject of a previous publication. We have compared the ductility of these composites by means of compressive deformation tests at elevated temperatures. Creep tests were performed at temperatures between 1300 and 1400ºC, in air, in a stress range of 0.69 to 34.5 MPa