1,912 research outputs found
The congruence of Wolstenholme and generalized binomial coefficients related to Lucas sequences
Using generalized binomial coefficients with respect to fundamental Lucas
sequences we establish congruences that generalize the classical congruence of
Wolstenholme and other related stronger congruences.Comment: 23 page
On deriving p-mode parameters for inclined solar-like stars
Thanks to their high quality, new and upcoming asteroseismic observations -
with CoRoT, Kepler, and from the ground... - can benefit from the experience
gained with helioseismology. We focus in this paper on solar-like oscillations,
for which the inclination of the rotation axis is unknown. We present a
theoretical study of the errors of p-mode parameters determined by means of a
maximum-likelihood estimator, and we also analyze correlations and biases. We
have used different, complementary approaches: we have performed either
semi-analytical computation of the Hessian matrix, fitting of single mean
profiles, or Monte Carlo simulations. We give first analytical approximations
for the errors of frequency, inclination and rotational splitting. The
determination of the inclination is very challenging for the common case of
slow rotators (like the Sun), making difficult the determination of a reliable
rotational splitting. Moreover, due to the numerous correlations, biases - more
or less significant - can appear in the determination of various parameters in
the case of bad inclination fittings, especially when a locking at 90 degrees
occurs. This issue concerning inclination locking is also discussed.
Nevertheless, the central frequency and some derived parameters such as the
total power of the mode are free of such biases.Comment: 9 pages, 6 figures, to appear in A&
Mode visibilities in radial velocity and intensity Sun-as-a-star helioseismic measurements
We analyze more than 5000 days of Sun-as-a-star radial velocity GOLF and
intensity VIRGO observations to measure the visibilities of the l=0, 1, 2, and
3 modes and the m-amplitude ratios of the l=2 and 3 modes in the solar acoustic
spectrum. We provide observational values that we compare to theoretical
predictions.Comment: SOHO 24 / GONG 2010 conference, to be published in JPC
Magnetic activity cycles in solar-like stars: The cross-correlation technique of p-mode frequency shifts
Aims. We aim studying the use of cross-correlation techniques to infer the
frequency shifts induced by changing magnetic fields in the p-mode frequencies
and provide precise estimation of the error bars. Methods. This technique and
the calculation of the associated errors is first tested and validated on the
Sun where the p-mode magnetic behaviour is very well known. These validation
tests are performed on 6000-day time series of Sun-as-a-star observations
delivered by the SoHO spacecraft. Errors of the frequency shifts are quantified
through Monte Carlo simulations. The same methodology is then applied to three
solar-like oscillating stars: HD 49933, observed by CoRoT, as well as KIC
3733735 and KIC 7940546 observed by Kepler. Results. We first demonstrate the
reliability of the error bars computed with the Monte Carlo simulations using
the Sun. From the three analyzed stars we confirm the presence of a magnetic
activity cycle with this methodology in HD 49933 and we unveil seismic
signature of on going magnetic variations in KIC 3733735. Finally, the third
star, KIC 7940546, seems to be in a quiet regime.Comment: Paper accepted in A&A. 7 pages and 11 figure
Who benefits from training and R&D: The firm or the workers? A study on panels of French and Swedish firms
The present paper offers a novel study of the effects of intangible assets on wages and productivity. Training, R&D, and physical capital are all taken into account, and their joint effects examined. We use panels of firms in order to control for unobserved fixed effects and the potential endogeneity of training and R&D, and have been able to obtain data for two different countries, France and Sweden, in order to explore the effects of institutional or national specificity. The estimation of productivity and wage equations allows us to show how the benefits of investment in physical capital, R&D and training are shared between the firm and the workers. Although the workers obtain significant benefits, the study shows that the firm obtains the largest return on the investments it makes. This is true not only for physical capital and R&D, but also for training. It suggests that firms can rationally invest in training and that the issue of under-investment in training should be re-examined.Training, R&D, productivity, wages
Gravito-inertial waves in a differentially rotating spherical shell
The gravito-inertial waves propagating over a shellular baroclinic flow
inside a rotating spherical shell are analysed using the Boussinesq
approximation. The wave properties are examined by computing paths of
characteristics in the non-dissipative limit, and by solving the full
dissipative eigenvalue problem using a high-resolution spectral method.
Gravito-inertial waves are found to obey a mixed-type second-order operator and
to be often focused around short-period attractors of characteristics or
trapped in a wedge formed by turning surfaces and boundaries. We also find
eigenmodes that show a weak dependence with respect to viscosity and heat
diffusion just like truly regular modes. Some axisymmetric modes are found
unstable and likely destabilized by baroclinic instabilities. Similarly, some
non-axisymmetric modes that meet a critical layer (or corotation resonance) can
turn unstable at sufficiently low diffusivities. In all cases, the instability
is driven by the differential rotation. For many modes of the spectrum, neat
power laws are found for the dependence of the damping rates with diffusion
coefficients, but the theoretical explanation for the exponent values remains
elusive in general. The eigenvalue spectrum turns out to be very rich and
complex, which lets us suppose an even richer and more complex spectrum for
rotating stars or planets that own a differential rotation driven by
baroclinicity.Comment: 33 pages, 14 figures, accepted for publication in Journal of Fluid
Mechanic
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