ASTROD and ASTROD I -- Overview and Progress

In this paper, we present an overview of ASTROD (Astrodynamical Space Test of Relativity using Optical Devices) and ASTROD I mission concepts and studies. The missions employ deep-space laser ranging using drag-free spacecraft to map the gravitational field in the solar-system. The solar-system gravitational field is determined by three factors: the dynamic distribution of matter in the solar system; the dynamic distribution of matter outside the solar system (galactic, cosmological, etc.) and gravitational waves propagating through the solar system. Different relativistic theories of gravity make different predictions of the solar-system gravitational field. Hence, precise measurements of the solar-system gravitational field test all these. The tests and observations include: (i) a precise determination of the relativistic parameters beta and gamma with 3-5 orders of magnitude improvement over previous measurements; (ii) a 1-2 order of magnitude improvement in the measurement of G-dot; (iii) a precise determination of any anomalous, constant acceleration Aa directed towards the Sun; (iv) a measurement of solar angular momentum via the Lense-Thirring effect; (v) the detection of solar g-mode oscillations via their changing gravity field, thus, providing a new eye to see inside the Sun; (vi) precise determination of the planetary orbit elements and masses; (viii) better determination of the orbits and masses of major asteroids; (ix) detection and observation of gravitational waves from massive black holes and galactic binary stars in the frequency range 0.05 mHz to 5 mHz; and (x) exploring background gravitational-waves.Comment: 17 pages, 6 figures, presented to The Third International ASTROD Symposium on Laser Astrodynamics, Space Test of Relativity and Gravitational-Wave Astronomy, Beijing, July 14-16, 2006; International Journal of Modern Physics D, in press (2008

A new spin source to search for scalar-pseudoscalar couplings at short range

We describe the design and performance of a new source of polarized spins that can be employed in experiments that search for macroscopic interactions between particles with intrinsic spin. In this article we concentrate on the analysis of the performance of the spin source in generating putative scalar-pseudoscalar forces. We outline two methods of calculating the magnitude of such forces and compare the predictions of the models. We discuss the manufacture of the spin source and the measurements that we have carried out in order to place upper limits on systematic effects that would limit the sensitivity of such searches. We have shown, in a recent article to Physical Review Letters [G. D. Hammond, C. C. Speake, C. Trenkel, and A. Pulido-Patón, Phys. Rev. Lett. 98, 081101 (2007)], that the combination of the spin source together with the torque sensitivity of our torsion balance improves constraints on the coupling strength of macroscopic scalar-pseudoscalar interactions by 10 orders of magnitude at a range of 1 mm. This paper further supports that work and provides a detailed description and characterization of the spin source

Shrub encroachment of Iberian dehesas: implications on total forage productivity

The Iberian dehesa, a grazed Mediterranean open woodland, is an outstanding example of a silvopastoral system. Shrub encroachment has been proposed as an effective method to facilitate natural tree regeneration and ensure the sustainability of silvopastoral systems. At the same time, shrubs can affect both pasture understory and tree overstory production. The effects of varying intensities of shrub encroachment on the productivity of four forage components of this system—pasture, acorns, shrub browse and tree browse—were tested and the overall metabolisable energy (ME) under different scenarios of vegetation structure was calculated. Two common shrub species with contrasting plant architectures and ecological functions were studied as models: Cistus ladanifer and Retama sphaerocarpa. Cistus negatively affected acorn, tree browse and pasture production, whereas Retama positively affected pasture and browse production and was neutral for acorn production. The highest ME values were found when tree cover was ca. 70 % and C. ladanifer cover was low or R. sphaerocarpa cover was medium. The authors recommend conserving and promoting patched three-layered plots in Iberian dehesas and similar extensive silvopastoral systems where certain shrub species could simultaneously encourage the sustainability of these systems and reinforce (with R. sphaerocarpa) or maintain (with C. ladanifer) their productivity.Spanish Ministry of Science and Innovation (AGL2006-09435/FOR) and the Regional Government of Extremadura (PRI07C044).http://link.springer.com/journal/104572016-08-31hb201