158,769 research outputs found
Mutualism supports biodiversity when the direct competition is weak
A key question of theoretical ecology is which properties of ecosystems favour their stability and help maintaining biodiversity. This qu estion recently reconsid- ered mutualistic systems, generating intense controversy about the role of mutu- alistic interactions and their network architecture. Here we show analytically and verify with simulations that reducing the effective intersp ecific competition and the propagation of perturbations positively influences struct ural stability against envi- ronmental perturbations, enhancing persistence. Notewor thy, mutualism reduces the effective interspecific competition only when the direct interspecific competition is weaker than a critical value. This critical competition i s in almost all cases larger in pollinator networks than in random networks with the same connectance. Highly connected mutualistic networks reduce the propagation of e nvironmental perturba- tions, a mechanism reminiscent of MacArthur’s proposal tha t ecosystem complexity enhances stability. Our analytic framework rationalizes p revious contradictory re- sults, and it gives valuable insight on the complex relation ship between mutualism and biodiversity
Global helioseismology (WP4.1): From the Sun to the stars & solar analogs
Sun-as-a star observations put our star as a reference for stellar
observations. Here, I review the activities in which the SPACEINN global
seismology team (Working Package WP4.1) has worked during the past 3 years. In
particular, we will explain the new deliverables available on the SPACEINN
seismic+ portal. Moreover, special attention will be given to surface dynamics
(rotation and magnetic fields). After characterizing the rotation and the
magnetic properties of around 300 solar-like stars and defining proper metrics
for that, we use their seismic properties to characterize 18 solar analogues
for which we study their surface magnetic and seismic properties. This allows
us to put the Sun into context compared to its siblings.Comment: Proceedings of the SPACEINN/TASC2/KASC9 meeting. 7 pages, 6 figure
Light Collimation and Focussing by a Thin Flat Metallic Slab
We present experimental and theoretical work showing that a flat metallic
slab can collimate and focus light impinging on the slab from a punctual
source. The effect is optimised when the radiation is around the bulk, not at
the surface, plasma frequency. And the smaller the imaginary part of the
permittivity is, the better the collimation. Experiments for Ag in the visible
as well as calculations are presented. We also discuss the interesting case of
the Aluminium whose imaginary part of the permittivity is very small at the
plasma frequency in UV radiation. Generalization to other materials and
radiations are also discussed.Comment: 6 pages, 3 figures. To be published on Optics Lette
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