Transformation Optics with Photonic Band Gap Media

We introduce a class of optical media based on adiabatically modulated, dielectric-only, and potentially extremely low-loss, photonic crystals. The media we describe represent a generalization of the eikonal limit of transformation optics (TO). The foundation of the concept is the possibility to fit frequency isosurfaces in the k-space of photonic crystals with elliptic surfaces, allowing them to mimic the dispersion relation of light in anisotropic effective media. Photonic crystal cloaks and other TO devices operating at visible wavelengths can be constructed from optically transparent substances like glasses, whose attenuation coefficient can be as small as 10 dB/km, suggesting the TO design methodology can be applied to the development of optical devices not limited by the losses inherent to metal-based, passive metamaterials.Comment: 4 pages, 4 figure

Using the UM dynamical cores to reproduce idealised 3D flows

We demonstrate that both the current (New Dynamics), and next generation (ENDGame) dynamical cores of the UK Met Office global circulation model, the UM, reproduce consistently, the long-term, large-scale flows found in several published idealised tests. The cases presented are the Held-Suarez test, a simplified model of Earth (including a stratosphere), and a hypothetical tidally locked Earth. Furthermore, we show that using simplifications to the dynamical equations, which are expected to be justified for the physical domains and flow regimes we have studied, and which are supported by the ENDGame dynamical core, also produces matching long-term, large-scale flows. Finally, we present evidence for differences in the detail of the planetary flows and circulations resulting from improvements in the ENDGame formulation over New Dynamics.Comment: 34 Pages, 23 Figures. Accepted for publication in Geoscientific Model Development (pre-proof version

Competition and cooperation in one-dimensional stepping stone models

Cooperative mutualism is a major force driving evolution and sustaining ecosystems. Although the importance of spatial degrees of freedom and number fluctuations is well-known, their effects on mutualism are not fully understood. With range expansions of microbes in mind, we show that, even when mutualism confers a distinct selective advantage, it persists only in populations with high density and frequent migrations. When these parameters are reduced, mutualism is generically lost via a directed percolation process, with a phase diagram strongly influenced by an exceptional DP2 transition.Comment: 8 pages, 4 figure

Polarimetric Properties of the Crab Pulsar between 1.4 and 8.4 GHz

New polarimetric observations of the Crab pulsar at frequencies between 1.4 and 8.4 GHz are presented. Additional pulse components discovered in earlier observations (Moffett & Hankins 1996, astro-ph/9604163) are found to have high levels of linear polarization, even at 8.4 GHz. No abrupt sweeps in position angle are found within pulse components; however, the position angle and rotational phase of the interpulse do change dramatically between 1.4 and 4.9 GHz. The multi-frequency profile morphology and polarization properties indicate a non-standard origin of the emission. Several emission geometries are discussed, but the one favored locates sites of emission both near the pulsar surface and in the outer magnetosphere.Comment: 20 pages, 7 postscript figures, uses aaspp4 Latex style. To appear in Volume 522 of The Astrophysical Journa

Multiplet Structure below Threshold in Appearance-Potential Spectra—Lanthanum N4,5

We present the N4,5 appearance-potential spectrum of La. Structure exists at energies lower than the threshold energy for transitions terminating at the Fermi level. Several similarities between optical absorption spectra and our results are discussed. These results contradict the simple model usually used to interpret appearance-potential spectra and emphasize the need for a new theory

Predicting polarization enhancement in multicomponent ferroelectric superlattices

Ab initio calculations are utilized as an input to develop a simple model of polarization in epitaxial short-period CaTiO3/SrTiO3/BaTiO3 superlattices grown on a SrTiO3 substrate. The model is then combined with a genetic algorithm technique to optimize the arrangement of individual CaTiO3, SrTiO3 and BaTiO3 layers in a superlattice, predicting structures with the highest possible polarization and a low in-plane lattice constant mismatch with the substrate. This modelling procedure can be applied to a wide range of layered perovskite-oxide nanostructures providing guidance for experimental development of nanoelectromechanical devices with substantially improved polar properties.Comment: 4 pages, submitted to PR

Effects of experience on voluntary intake of supplements by cattle

Experiments examined the effects of prior experience of young cattle on their voluntary intake of supplements, and variability among animals in intake of supplements. Variability was measured using supplement labelled with lithium salts. Experiment 1 examined the effects of offering a concentrate supplement to calves before and/or after weaning on their subsequent intake of the same supplement and of a loose mineral mix supplement. Experience of the concentrate supplement increased acceptance and reduced variability in intake of the loose mineral mix supplement. However, neither voluntary intake (mean is 105 g DM/head.day) nor variability in intake of loose mineral mix supplement was affected by prior experience. Experiments 2 and 3 examined variability in intake of loose mineral mix supplement by weaners in larger groups or offered molasses–urea supplement, respectively. Experiment 4 examined the effects of provision of supplements and/or exposure to human activity and handling on subsequent intake of loose mineral mix supplement. Supplementing grazing weaners with concentrates had a transient effect by increasing voluntary intake of loose mineral mix supplement, but increased exposure to supplements, and human activity and handling while held in yards after weaning had no effects. Variability among animals in intake of loose mineral mix supplement (CV is 52–103%) tended to be greater than with the concentrate or molasses-based supplements (CV is 23–43%), irrespective of previous experience. There were fewer than 1% non-eaters of concentrate supplement and 0–7% non-eaters of loose mineral mix supplement. In experiment 5, prior experience of loose mineral mix supplements increased intake of such supplements by weaners during weeks 1 and 2 but not from weeks 3 to 9. In experiment 6, intake of loose mineral mix supplement by adult cattle was not affected by their experience as weaners of a similar supplement. In conclusion, although prior experience of supplements by young cattle sometimes increased their initial acceptance and voluntary intake of supplements, longer-term intake of supplements was not affected