Speed of gravity and gravitomagnetism

A v_J/c correction to the Shapiro time delay seems verified by a 2002 Jovian observation by VLBI. In this Essay, this correction is interpreted as an effect of the aberration of light in an optically refractive medium which supplies an analog of Jupiter's gravity field rather than as a measurement of the speed of gravity, as it was first proposed by other authors. The variation of the index of refraction is induced by the Lorentz invariance of the weak gravitational field equations for Jupiter in a uniform translational slow motion with velocity v_J=13.5 km/s. The correction on time delay and deflection is due not to the Kerr (or Lense-Thirring) stationary gravitomagnetic field of Jupiter, but to its Schwarzschild gravitostatic field when measured from the barycenter of the solar system.Comment: 6 pags, final published version, Honorable Mention in the 2004 Essay Competition of the Gravity Research Foundation, GR

Flux reversal in a simple random walk model on a fluctuating symmetric lattice

A rather simple random walk model on a one-dimensional lattice is put forward. The lattice as a whole switches randomly between two possible states which are spatially symmetric. Both lattice states are identical, but translated by one site with respect to each other, and consist of infinite arrays of absorbing sites separated by two non-absorbing sites. Exact explicit expressions for the long-time velocity and the effective diffusion coefficient are obtained and discussed. In particular, it is shown that the direction of the steady motion can be reversed by conveniently varying the values of either the mean residence times in the lattice states or the transition rates to the absorbing and non-absorbing sites.Comment: 6 pages, 3 Figures, (to appear in Physical Review E

Sport as a privilege in Spain

The reduction of Physical Education hours in the Spanish curriculum originates from a false premise: families are already aware of the importance of physical activity, and attempt to compensate for the lack of it at school with an extra schedule. It seems then, that there is an assumption that classes that are available after school are only related to physical activity: this is not the case. Furthermore, only those families that are fully aware of the consequences of their children’s inactivity, and who can (and want to) invest in those extra classes and engage in some kind of physical activity after school. But the reality is that Physical activity only is important for some families

Inconsistencies in the application of harmonic analysis to pulsating stars

Using ultra-precise data from space instrumentation we found that the underlying functions of stellar light curves from some AF pul- sating stars are non-analytic, and consequently their Fourier expansion is not guaranteed. This result demonstrates that periodograms do not provide a mathematically consistent estimator of the frequency content for this kind of variable stars. More importantly, this constitutes the first counterexample against the current paradigm which considers that any physical process is described by a contin- uous (band-limited) function that is infinitely differentiable.Comment: 9 pages, 8 figure