Derek Michael Forrester

Shear-mediated contributions to the effective properties of soft acoustic metamaterials including negative index.

Here we show that, for sub-wavelength particles in a fluid, viscous losses due to shear waves and their influence on neighbouring particles significantly modify the effective acoustic properties, and thereby the conditions at which negative acoustic refraction occurs. Building upon earlier single particle scattering work, we adopt a multiple scattering approach to derive the effective properties (density, bulk modulus, wavenumber). We show,through theoretical prediction, the implications for the design of “soft” (ultrasonic) metamaterials based on locally-resonant sub-wavelength porous rubber particles, through selection of particle size and concentration, and demonstrate tunability of the negative speed zones by modifying the viscosity of the suspending medium. For these lossy materials with complex effective properties, we confirm the use of phase angles to define the backward propagation condition in preference to “single-” and “double-negative” designations.

Graphene levitons and anti-levitons in magnetic fields

The leviton is an electron or hole wavepacket that rides the surface of the Fermi sea. When a series of Lorentzian or Gaussian time dependent pulses are applied to an ultracold system a soliton-like excitation with only one electron and no localised hole emerges. Graphene is a unique system where the Fermi surface may arise from a Dirac point and therewith the levitons character may display many interesting features. For example, the leviton formation may be associated with a chiral anomaly, and inside a single potential step an anti-leviton forms. We show that the application of weak magnetic fields may switch on and off the leviton Klein tunnelling. Also, in a moderate field negative refraction arises along a curved trajectory, whereas with a stronger field a new elementary excitation - the levity vortex - in the reflected wavefunction occurs. Herein we describe these phenomena in detail along with a complete explanation of the transmission of graphene levitons at a step potential in terms of the probability densities and a series of phase diagrams and the tunnelling times.

Arrays of coupled chemical oscillators

Oscillating chemical reactions result from complex periodic changes in the concentration of the reactants. In spatially ordered ensembles of candle flame oscillators the fluctuations in the ratio of oxygen atoms with respect to that of carbon, hydrogen and nitrogen produces an oscillation in the visible part of the flame related to the energy released per unit mass of oxygen. Thus, the products of the reaction vary in concentration as a function of time, giving rise to an oscillation in the amount of soot and radiative emission. Synchronisation of interacting dynamical sub-systems occurs as arrays of flames that act as master and slave oscillators, with groups of candles numbering greater than two, creating a synchronised motion in three-dimensions. In a ring of candles the visible parts of each flame move together, up and down and back and forth, in a manner that appears like a “worship”. Here this effect is shown for rings of flames which collectively empower a central flame to pulse to greater heights. In contrast, situations where the central flames are suppressed are also found. The phenomena leads to in-phase synchronised states emerging between periods of anti-phase synchronisation for arrays with different columnar sizes of candle and positioning.

Confinement effects of levitons in a graphene cosmology laboratory

The leviton, a long-lifetime soliton that rides the Fermi sea, is described here for a graphene system with a potential barrier. A full description of the leviton into the barrier is given for different angles of incidence. This is achieved by analysing the probability density of the leviton quasiparticle as a function of time. The transmission of the wavepacket through the oblique barrier occurs with negative refraction for low ratios of leviton energy to gate potential. In moderately strong magnetic fields a levity vortex becomes localised in space outside the barrier forming interior vortex states as it circulates. Also, when the field is switched on with an anti-leviton already formed inside the barrier, the quasiparticle becomes trapped and flows along its channel. Thus, the graphene system with leviton/anti-leviton propagation into and inside a barrier is a metamaterial whereby the direction of the quasiparticle can be controlled at will through the angle of the barrier and timing of switching on and off the magnetic fields. We present this analysis of barrier penetration for the inception of leviton electronics in graphene. The results lead to the possibility to create the graphene systems with levitons to explore cosmological questions such as hidden or “dark” energy conditions and therewith may also give some clues for understanding the discrepancies occurring between observed energy levels in the Universe and that of prediction.

The emergence of quantum capacitance in epitaxial graphene

We found an intrinsic redistribution of charge arises between epitaxial graphene, which has intrinsically n-type doping, and an undoped substrate. In particular, we studied in detail epitaxial graphene layers thermally elaborated on C-terminated

Self-assembled multi-ring formations of glutamine and a possible link to erythema gyratum repens

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Fundamental design paradigms for systems of three interacting magnetic nanodiscs

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Whispering galleries and the control of artificial atoms

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Designing magnetic superlattices that are composed of single domain nanomagnets.

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Localised States of Fabry-Perot Type in Graphene Nano-Ribbons

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