On the oscillations in Mercury's obliquity

One major objective of MESSENGER and BepiColombo spatial missions is to accurately measure Mercury's rotation and its obliquity in order to obtain constraints on internal structure of the planet. Which is the obliquity's dynamical behavior deriving from a complete spin-orbit motion of Mercury simultaneously integrated with planetary interactions? We have used our SONYR model integrating the spin-orbit N-body problem applied to the solar System (Sun and planets). For lack of current accurate observations or ephemerides of Mercury's rotation, and therefore for lack of valid initial conditions for a numerical integration, we have built an original method for finding the libration center of the spin-orbit system and, as a consequence, for avoiding arbitrary amplitudes in librations of the spin-orbit motion as well as in Mercury's obliquity. The method has been carried out in two cases: (1) the spin-orbit motion of Mercury in the 2-body problem case (Sun-Mercury) where an uniform precession of the Keplerian orbital plane is kinematically added at a fixed inclination (S2K case), (2) the spin-orbit motion of Mercury in the N-body problem case (Sun and planets) (Sn case). We find that the remaining amplitude of the oscillations in the Sn case is one order of magnitude larger than in the S2K case, namely 4 versus 0.4 arcseconds (peak-to-peak). The mean obliquity is also larger, namely 1.98 versus 1.80 arcminutes, for a difference of 10.8 arcseconds. These theoretical results are in a good agreement with recent radar observations but it is not excluded that it should be possible to push farther the convergence process by drawing nearer still more precisely to the libration center.Comment: 30 pages, 3 tables, 8 figures, accepted to Icarus (26 Jul 2007

My Evolving Program for Negro Freedom

This autobiographical essay, published in 1944, defines freedom for Negroes and identifies the paths taken by Du Bois to achieve this freedom

Theory of the Mercury's spin-orbit motion and analysis of its main librations

The upcoming space missions, MESSENGER and BepiColombo with onboard instrumentation capable of measuring the rotational parameters stimulate the objective to reach an accurate theory of the rotational motion of Mercury. For obtaining the real motion of Mercury, we have used our relativistic BJV model of solar system integration including the coupled spin-orbit motion of the Moon. We have extended this model by generalizing the spin-orbit couplings to the terrestrial planets, notably Mercury. The updated model is called SONYR (acronym of Spin-Orbit N-BodY Relativistic model). The SONYR model giving an accurate solution of the spin-orbit motion of Mercury permits to analyze the different families of the Hermean rotational librations. The spin-orbit motion of Mercury is characterized by two proper frequencies (namely 15.847 and 1066 years) and its 3:2 resonance presents a second synchronism which can be understood as a spin-orbit secular resonance (278 898 years). By using the SONYR model, we find a new determination of the mean obliquity, namely 1.6 arcminutes. Besides, we identify in the Hermean librations the impact of the uncertainty of the greatest principal moment of inertia (\cmr2) on the obliquity and on the libration in longitude (2.3 mas and 0.45 as respectively for an increase of 1% on the \cmr2 value). These determinations prove to be suitable for providing constraints on the internal structure of Mercury.Comment: 15 pages, 14 figures, 3 tables, accepted version to A&A (4 sept 2003

Effects of perturbing forces on the orbital stability of planetary systems

We consider dynamical effects of additional perturbative forces due to the non-point mass nature of stars and planets: effects such as quadrupolar distortion and tidal friction in the systems of exo-planets. It is shown that these forces should not be neglected while modelling the dynamics of planetary systems, especially taking into account the undefined real masses of the planets due to unknown orbital inclinations and the unsatisfactory application of Keplerian fits to the radial velocity data in multiple planetary systems.Comment: 5 pages, 2 figures, accepted by ApJ Le

Energy Saving Analysis of a Solar Combi-system using Detailed Control Algorithm Modeled with Modelica

AbstractThis paper analyzes the detailed behavior and efficiency of a solar combi-system during a full year based on an existing control algorithm developed by SolisArt Company. Whereas so far simulations are usually done with a simplified control system or black box models, it may be formed conveniently by a detailed algorithm model to control all the system equipments thanks to Modelica language versatility. According to the results, reducing energy demands or increasing solar area lead to higher energy savings and high economy rate between 34 and 70% with 6 collectors. Finally, the developed model can also be used to size and optimize the key components of the system

Decoherence and gravitational backgrounds

We study the decoherence process associated with the scattering of stochastic gravitational waves. We discuss the case of macroscopic systems, such as the planetary motion of the Moon around the Earth, for which gravitational scattering is found to dominate decoherence though it has a negligible influence on damping. This contrast is due to the very high effective temperature of the background of gravitational waves in our galactic environment.Comment: 10 page

The 6 minute walk in idiopathic pulmonary fibrosis: longitudinal changes and minimum important difference

The response characteristics of the 6 minute walk test (6MWT) in studies of idiopathic pulmonary fibrosis (IPF) are only poorly understood, and the change in walk distance that constitutes the minimum important difference (MID) over time is unknown

Regulation of the formin cappuccino is critical for polarity of Drosophilao ocytes

The Drosophila formin Cappuccino (Capu) creates an actin mesh‐like structure that traverses the oocyte during midoogenesis. This mesh is thought to prevent premature onset of fast cytoplasmic streaming which normally happens during late‐oogenesis. Proper cytoskeletal organization and cytoplasmic streaming are crucial for localization of polarity determinants such as osk, grk, bcd, and nanos mRNAs. Capu mutants disrupt these events, leading to female sterility. Capu is regulated by another nucleator, Spire, as well as by autoinhibition in vitro. Studies in vivo confirm that Spire modulates Capu's function in oocytes; however, how autoinhibition contributes is still unclear. To study the role of autoinhibition in flies, we expressed a Capu construct that is missing the Capu Inhibitory Domain, CapuΔN. Consistent with a gain of activity due to loss of autoinhibition, the actin mesh was denser in CapuΔN oocytes. Further, cytoplasmic streaming was delayed and fertility levels decreased. Localization of osk mRNA in early stages, and bcd and nanos in late stages, were disrupted in CapuΔN‐expressing oocytes. Finally, evidence that these phenotypes were due to a loss of autoinhibition comes from coexpression of the N‐terminal half of Capu with CapuΔN, which suppressed the defects in actin, cytoplasmic streaming and fertility. From these results, we conclude that Capu can be autoinhibited during Drosophila oocyte development