4 research outputs found
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