84,719 research outputs found
An empirical evaluation of four variants of a universal species-area relationship
The Maximum Entropy Theory of Ecology (METE) predicts a universal
species-area relationship (SAR) that can be fully characterized using only the
total abundance (N) and species richness (S) at a single spatial scale. This
theory has shown promise for characterizing scale dependence in the SAR.
However, there are currently four different approaches to applying METE to
predict the SAR and it is unclear which approach should be used due to a lack
of empirical evaluation. Specifically, METE can be applied recursively or a
non-recursively and can use either a theoretical or observed species-abundance
distribution (SAD). We compared the four different combinations of approaches
using empirical data from 16 datasets containing over 1000 species and 300,000
individual trees and herbs. In general, METE accurately downscaled the SAR
(R^2> 0.94), but the recursive approach consistently under-predicted richness,
and METEs accuracy did not depend strongly on using the observed or predicted
SAD. This suggests that best approach to scaling diversity using METE is to use
a combination of non-recursive scaling and the theoretical abundance
distribution, which allows predictions to be made across a broad range of
spatial scales with only knowledge of the species richness and total abundance
at a single scale.Comment: main text: 20 pages, 2 tables, 3 figure
Tunable Localization and Oscillation of Coupled Plasmon Waves in Graded Plasmonic Chains
The localization (confinement) of coupled plasmon modes, named as gradons,
has been studied in metal nanoparticle chains immersed in a graded dielectric
host. We exploited the time evolution of various initial wavepackets formed by
the linear combination of the coupled modes. We found an important interplay
between the localization of plasmonic gradons and the oscillation in such
graded plasmonic chains. Unlike in optical superlattices, gradient cannot
always lead to Bloch oscillations, which can only occur for wavepackets
consisting of particular types of gradons. Moreover, the wavepackets will
undergo different forms of oscillations. The correspondence can be applied to
design a variety of optical devices by steering among various oscillations.Comment: Sumitted to Journal of Applied Physic
Giant enhanced optical nonlinearity of colloidal nanocrystals with a graded-index host
The effective linear and third-order nonlinear optical properties of metallic
colloidal crystal immersed in a graded-index host fluid are investigated
theoretically. The local electric fields are extracted self-consistently based
on the layer-to-layer interactions, which are readily given by the Lekner
summation method. The resultant optical absorption and nonlinearity enhancement
show a series of sharp peaks, which merge in a broadened resonant band. The
sharp peaks become a continuous band for increasing packing density and number
of layers. We believe that the sharp peaks arise from the in-plane dipolar
interactions and the surface plasmon resonance, whereas the continuous band is
due to the presence of the gradient in the host refractive index. These results
have not been observed in homogeneous and randomly-dispersed colloids, and thus
would be of great interest in optical nanomaterial engineering.Comment: Submitted to Applied Physics Letter
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