2 research outputs found
Exceptional points in optical systems: A resonant-state expansion study
Exceptional points (EPs) in open optical systems are rigorously studied using
the resonant-state expansion (RSE). A spherical resonator, specifically a
homogeneous dielectric sphere in a vacuum, perturbed by two point-like defects
which break the spherical symmetry and bring the optical modes to EPs, is used
as a worked example. The RSE is a non-perturbative approach encoding the
information about an open optical system in matrix form in a rigorous way, and
thus offering a suitable tool for studying its EPs. These are simultaneous
degeneracies of the eigenvalues and corresponding eigenfunctions of the system,
which are rigorously described by the RSE and illustrated for perturbed
whispering-gallery modes (WGMs). An exceptional arc, which is a line of
adjacent EPs, is obtained analytically for perturbed dipolar WGMs. Perturbation
of high-quality WGMs with large angular momentum and their EPs are found by
reducing the RSE equation to a two-state problem by means of an orthogonal
transformation of a large RSE matrix. WGM pairs of opposite chirality away from
EPs are shown to have the same chirality at EPs. This chirality can be observed
in circular dichroism measurements, as it manifested itself in a
squared-Lorentzian part of the optical spectra, which we demonstrate here
analytically and numerically in the Purcell enhancement factor for the
perturbed dipolar WGMs.Comment: 24 pages. 13 figures (3 in Appendix). To be submitted in Physical
Review A. Authors: K S Netherwood (primary author), H Riley (initial concept
work), E A Muljarov (theme leader
Access to Mutualistic Endosymbiotic Microbes: An Underappreciated Benefit of Group Living
The original publication is available at www.springerlink.com A central question in behavioral ecology has been why animals live in groups. Previous theories about the evolution of sociality focused on the potential benefits of decreased risk of predation, increased foraging or feeding efficiency, and mutual aid in defending resources and/or rearing offspring. This paper argues that access to mutualistic endosymbiotic microbes is an underappreciated benefit of group living and sets out to reinvigorate Troyer’s hypothesis that the need to obtain cellulolytic microbes from conspecifics influenced the evolution of social behavior in herbivores and to extend it to nonherbivores. This extension is necessary because the benefits of endosymbionts are not limited to nutrition; endosymbionts also help protect their hosts from pathogens. When hosts must obtain endosymbionts from conspecifics, they are forced to interact. Thus, complex forms of sociality may be more likely to evolve when hosts must repeatedly obtain endosymbionts from conspecifics than when endosymbionts can be obtained either directly from the environment, are vertically transmitted, or when repeated inoculations are not necessary. Observations from a variety of taxa are consistent with the ideas that individuals benefit from group living by gaining access to endosymbionts and the complexity of social behavior is associated with the mode of acquisition of endosymbionts. Ways to test this theory include (a) experiments designed to examine the effects of endosymbionts on host fitness and how endosymbionts are obtained and (b) using phylogenetic analyses to examine endosymbiont-host coevolution with the goal of determining the relationship between the mode of endosymbiont acquisition and host sociality