Stellar granulation as seen in disk-integrated intensity. I. Simplified theoretical modeling

The solar granulation is known for a long time to be a surface manifestation of convection. Thanks to the current space-borne missions CoRoT and Kepler, it is now possible to observe in disk-integrated intensity the signature of this phenomena in a growing number of stars. The space-based photometric measurements show that the global brightness fluctuations and the lifetime associated with granulation obeys characteristic scaling relations. We thus aim at providing a simple theoretical modeling to reproduce these scaling relations and subsequently at inferring the physical properties of granulation properties across the HR diagram. We develop a simple 1D theoretical model that enable us to test any prescription concerning the time-correlation between granules. The input parameters of the model are extracted from 3D hydrodynamical models of the surface layers of stars, and the free parameters involved in the model are calibrated with solar observations. Two different prescriptions for representing the eddy time-correlation in the Fourier space are compared: a Lorentzian and an exponential form. Finally, we compare our theoretical prediction with a 3D radiative hydrodynamical (RHD) numerical modeling of stellar granulation (ab-initio approach). Provided that the free parameters are appropriately adjusted, our theoretical model satisfactorily reproduces the shape and the amplitude of the observed solar granulation spectrum. The best agreement is obtained with an exponential form. Furthermore, our theoretical model results in granulation spectra that consistently agree with the these calculated on the basis of the ab-initio approach with two 3D RHD models. Comparison between theoretical granulation spectra calculated with the present model and high precision photometry measurements of stellar granulation is undertaken in a companion paper.Comment: 10 pages, 2 figures, accepted for publication in A&

A COMPARISON OF THREE RACKET SKILLS EXECUTED SY NOVICE AND EXPERIENCED PERFORMERS

INTRODUCTIONT he purpose of this investigation was to compare an adult novice (NOV) with an experienced (EXP) adult performing a badminton deep serve, a racquetball forehand, and a racquetball drive serve. Movements were videotaped by 4cameras at 120 Hz and the 3-D data were analyzed using the PEAK5 motion measurement system. Range of motion (ROM), sequence of motion, and temporal values were assessed on the following angular movements: absolute pelvic (P) and upper torso (UT) rotation, and relative humeral (H), elbow (E), and wist (W) rotation. RESULTS For each skill and performer, the segmental sequence and ROM are presented. This information is followed by the range of lag times (LT) between segments within the sequence and the total time (TT) (backswing to contact)over which the skill occurred. Badminton Serve EXP P(37.4"),UT(69.6"), H(76.3"), W(59.7"), E(16.0°).LT(.02-.I 8s). TT(.23s).NOV UT(30.4"), P(l 3.0°), H(67.0°),W(10.2"), E(34.2").LT(.OI -.14~)T. T(.2Os).Racquetball Forehand EXP H(68.8"),P(57.g0),U T(71. I") , W(ll .go), E(12.8").LT(.02-.1 0s). TT(. II S).NOV P(34.8"), UT(69.2"), W(59.4"),E(8.7"), H(10.7").LT(.03-. 1 3s). TT(.20s).Racquetball Serve U(P P(92.4"),UT(122.0°), H(154.0°), E(75.3"),W(41.8"). LT(.00-. 10s). TT(. 1 8s).NOV P(64.3"), UT(77.g0), W(81 .OO),H(87.0°), E (0.8").LT(.OI -. 14s). TT(. 194.CONCLUSIONS1) Results for the badminton serve indicated the EXP exhibited greater ROM than the NOV for all angles except E. The NOV constrained the W to possibly allow for the greater E movement.2) In the forehand and in the racquetball serve, the NOV constrained the elbow more than the EXP which was consistent with Southard's (1 987) results; however, the great W ROM was inconsistent and appeared to be a last resort to generatevelocity.3) The EXP was more compact performing the forehand than the racquetball serve. During the serve, the lack of initial ball velocity required greater ROM to achieve the goal.4) In all 3 tasks, the EXP displayed essentially the same sequence of propulsive segmental initiation (proximal to distal). The patterns exhibited by the NOV were more simultaneous and the sequences varied for each task. REFERENCES Bird, M., Hills, L., & Hudson, J. L.(1 991 ). Intersegmental coordination: an exploration of context. In C. Tant, P.Patterson, & S. York (Eds.),Biomechanics in Sworts IX: Proceedings of the 9th International Symposium on Biomechanics in Sports (pp. 233-237).Ames, IA: Iowa State University.Southard, D. & Higgins,T,. (1 987).Changing movement patterns: effects of demonstration and practice. Research Quarterlv for Exercise and Sport, 58(1),77-80

Surface-effect corrections for solar-like oscillations using 3D hydrodynamical simulations

The space-borne missions have provided us with a wealth of high-quality observational data that allows for seismic inferences of stellar interiors. This requires the computation of precise and accurate theoretical frequencies, but imperfect modeling of the uppermost stellar layers introduces systematic errors. To overcome this problem, an empirical correction has been introduced by Kjeldsen et al. (2008, ApJ, 683, L175) and is now commonly used for seismic inferences. Nevertheless, we still lack a physical justification allowing for the quantification of the surface-effect corrections. We used a grid of these simulations computed with the CO$^5$BOLD code to model the outer layers of solar-like stars. Upper layers of the corresponding 1D standard models were then replaced by the layers obtained from the horizontally averaged 3D models. The frequency differences between these patched models and the 1D standard models were then calculated using the adiabatic approximation and allowed us to constrain the Kjeldsen et al. power law, as well as a Lorentzian formulation. We find that the surface effects on modal frequencies depend significantly on both the effective temperature and the surface gravity. We further provide the variation in the parameters related to the surface-effect corrections using their power law as well as a Lorentzian formulation. Scaling relations between these parameters and the elevation (related to the Mach number) is also provided. The Lorentzian formulation is shown to be more robust for the whole frequency spectrum, while the power law is not suitable for the frequency shifts in the frequency range above $\nu_{\rm max}$.Comment: 11 pages, 14 figures, 4 tables; accepted for publication in Astronomy & Astrophysic

Time scale, objectivity and irreversibility in quantum mechanics

It is argued that setting isolated systems as primary scope of field theory and looking at particles as derived entities, the problem of an objective anchorage of quantum mechanics can be solved and irreversibility acquires a fundamental role. These general ideas are checked in the case of the Boltzmann description of a dilute gas.Comment: 13 pages, latex, no figures, to appear in the Proceedings of the XXI International Colloquium on Group Theoretical Methods in Physics, 1996 (Goslar, Germany

Quantum measurement problem and cluster separability

A modified Beltrametti-Cassinelli-Lahti model of measurement apparatus that satisfies both the probability reproducibility condition and the objectification requirement is constructed. Only measurements on microsystems are considered. The cluster separability forms a basis for the first working hypothesis: the current version of quantum mechanics leaves open what happens to systems when they change their separation status. New rules that close this gap can therefore be added without disturbing the logic of quantum mechanics. The second working hypothesis is that registration apparatuses for microsystems must contain detectors and that their readings are signals from detectors. This implies that separation status of a microsystem changes during both preparation and registration. A new rule that specifies what happens at these changes and that guarantees the objectification is formulated and discussed. A part of our result has certain similarity with 'collapse of the wave function'.Comment: 31 pages, no figure. Published versio

Direct control of the tunnel splitting in a one-electron double quantum dot

Quasi-static transport measurements are employed on a laterally defined tunnel-coupled double quantum dot. A nearby quantum point contact allows us to track the charge as added to the device. If charged with only up to one electron, the low-energy spectrum of the double quantum dot is characterized by its quantum mechanical interdot tunnel splitting. We directly measure its magnitude by utilizing particular anticrossing features in the stability diagram at finite source-drain bias. By modification of gate voltages defining the confinement potential as well as by variation of a perpendicular magnetic field we demonstrate the tunability of the coherent tunnel coupling.Comment: High resolution pdf file available at http://www2.nano.physik.uni-muenchen.de/~huettel/research/anticrossing.pd