30 research outputs found
Evolutionary trade-offs between reproduction and dispersal in populations at expanding range boundaries
During recent climate warming, some species have expanded their ranges northwards to keep track of climate changes. Evolutionary changes in dispersal have been demonstrated in these expanding populations and here we show that increased dispersal is associated with reduced investment in reproduction in populations of the speckled wood butterfly, Pararge aegeria. Evolutionary changes in flight versus reproduction will affect the pattern and rate of expansion at range boundaries in the future, and understanding these responses will be crucial for predicting the distribution of species in the future as climates continue to warm
Optical bistability involving planar metamaterial with broken structural symmetry
We report on a bistable light transmission through a planar metamaterial
composed of a metal pattern of weakly asymmetric elements placed on a nonlinear
substrate. Such structure bears the Fano-like sharp resonance response of a
trapped-mode excitation. The feedback required for bistability is provided by
the coupling between the strong antiphased trapped-mode-resonance currents
excited on the metal elements and the intensity of inner field in the nonlinear
substrate.Comment: 4 pages, 4 figure
"Slow" light in metamaterials
We demonstrate that propagation of microwave pulses can be significantly affected by the presence of a planar fish-scale metamaterial, which is at least 30 times thinner than the wavelength. In the resonant band of the fish-scale structure, a spectrally narrow pulse (18 ns) can be significantly delayed (by 5.6 ns) as if propagating through an 84 cm thick dielectric (epsilon=3.77), while a short pulse (220 ps) will split in two roughly equal pulses propagating with subluminal and superluminal velocity respectively. We also interpret the response of the metamaterial in terms of effective material parameters
Two-oscillator model of trapped-modes interaction in a nonlinear bilayer fish-scale metamaterial
We discuss the similarity between the nature of resonant oscillations in two
nonlinear systems, namely, a chain of coupled Duffing oscillators and a bilayer
fish-scale metamaterial. In such systems two different resonant states arise
which differ in their spectral lines. The spectral line of the first resonant
state has a Lorentzian form, while the second one has a Fano form. This
difference leads to a specific nonlinear response of the systems which
manifests itself in appearance of closed loops in spectral lines and bending
and overlapping of resonant curves. Conditions of achieving bistability and
multistability are found out.Comment: 14 pages, 6 figure
Transmission enhancement in loss-gain multilayers by resonant suppression of reflection
Using the transfer-matrix approach and solving time-domain differential
equations, we analyze the loss compensation mechanism in multilayer systems
composed of an absorbing transparent conductive oxide and dielectric doped with
an active material. We reveal also another regime with the possibility of
enhanced transmission with suppressed reflection originating from the resonant
properties of the multilayers. For obliquely incident and evanescent waves,
such enhanced transmission under suppressed reflection turns into the
reflectionless regime, which is similar to that observed in the PT-symmetric
structures, but does not require PT symmetry. We infer that the reflectionless
transmission is due to the full loss compensation at the resonant wavelengths
of the multilayers.Comment: 12 pages, 10 figure
Asymmetric transmission of light through a planar chiral metamaterial
We report that normal incidence transmission of circularly polarized light through lossy anisotropic planar chiral meta-material is asymmetric for opposite directions. The new effect is fundamentally distinct from conventional gyrotropy of bulk chiral media and the Faraday Effect
Enhancement of absorption bistability by trapping light planar metamaterial
We propose to achieve a strong bistable response of a thin layer of a
saturable absorption medium by involving a planar metamaterial specially
designed to bear a high-Q trapped-mode resonance in the infrared region.Comment: 11 pages, 4 figure