Interaction of flying electromagnetic doughnut with nanostructures

We report on the electromagnetic properties of the single-cycle "flying doughnut" electromagnetic permutations in the context of their interactions with nanoscale objects, such as dielectric and plasmonic nanoparticles

Interrogating nanoparticles with focused doughnuts

The propagation of electromagnetic radiation in free-space is described by the source-free Maxwells equations. In contrast to conventional solutions such as infinite-energy plane waves and Gaussian pulses, there exists a family of exact solutions which represent localised transmission of finite electromagnetic energy [1]. One such solution is known as the Focused Doughnut (FD) pulse a peculiar single-cycle electromagnetic perturbation with a unique toroidal field topology and 3-dimensional, polynomial energy localisation [2]. Here, for the first time we present a comprehensive study of the FD pulse: we investigate the propagation dynamics and interactions of these complex electromagnetic pulses with homogeneous and structured media.The FD pulse exhibits a number of intriguing properties. Its purely single-cycle nature results in an ultra-broadband frequency spectrum and a well defined spatial-chirp. In fact, the spatial dependence of the pulse is inseparable from its temporal dependence. In addition, the toroidal topology of the pulse gives rise to significant longitudinal field components at the pulse that hold potential for particle acceleration applications [2]. Although the FD pulse has remained a theoretical curiosity since its first prediction, successful experimental realisation could lead to its use in a variety of settings, such as microscopy, communications, directed energy transfer, spectroscopy, and particle trapping and acceleration. Further interest in the FD pulse stems from the burgeoning field of toroidal electrodynamics, owing to the topological similarities between the FD pulse and the near-field configuration of the toroidal dipole excitation [3].The intriguing light-matter interactions of the FD pulse are examined from several perspectives. We present a full evaluation of the transformations the FD pulse undergoes due to interactions with dielectric and metallic interfaces. This has revealed the unusual behaviour of both the TE and TM pulses under reflection, with respect to the reversal of the azimuthal and radial field components. Furthermore, the interactions of FDs with small dielectric and plasmonic particles are considered, where the broadband nature and complex field topology of the pulses is expected to play a significant role in mode excitation. Recent work has demonstrated broad modal excitation within the nanostructures and distinct differences between the interaction with TE and TM pulses. Possible experimental realisations of these complex electromagnetic perturbations resulting from the theoretical/computational treatment presented here will be discussed

Offenders' Crime Narratives across Different Types of Crimes

The current study explores the roles offenders see themselves playing during an offence and their relationship to different crime types. One hundred and twenty incarcerated offenders indicated the narrative roles they acted out whilst committing a specific crime they remembered well. The data were subjected to Smallest Space Analysis (SSA) and four themes were identified: Hero, Professional, Revenger and Victim in line with the recent theoretical framework posited for Narrative Offence Roles (Youngs & Canter, 2012). Further analysis showed that different subsets of crimes were more like to be associated with different narrative offence roles. Hero and Professional were found to be associated with property offences (theft, burglary and shoplifting), drug offences and robbery and Revenger and Victim were found to be associated with violence, sexual offences and murder. The theoretical implications for understanding crime on the basis of offenders' narrative roles as well as practical implications are discussed

Generation of flying electromagnetic doughnuts via spatiotemporal conversion of transverse electromagnetic pulses

We introduce a new class of metamaterials that allow simultaneous spatial and temporal control of electromagnetic waveforms and present for the first time the generation of flying doughnuts, single-cycle pulses of toroidal topology

Micrometer-sized Water Ice Particles for Planetary Science Experiments: Influence of Surface Structure on Collisional Properties

Models and observations suggest that ice-particle aggregation at and beyond the snowline dominates the earliest stages of planet formation, which therefore is subject to many laboratory studies. However, the pressure–temperature gradients in protoplanetary disks mean that the ices are constantly processed, undergoing phase changes between different solid phases and the gas phase. Open questions remain as to whether the properties of the icy particles themselves dictate collision outcomes and therefore how effectively collision experiments reproduce conditions in protoplanetary environments. Previous experiments often yielded apparently contradictory results on collision outcomes, only agreeing in a temperature dependence setting in above ≈210 K. By exploiting the unique capabilities of the NIMROD neutron scattering instrument, we characterized the bulk and surface structure of icy particles used in collision experiments, and studied how these structures alter as a function of temperature at a constant pressure of around 30 mbar. Our icy grains, formed under liquid nitrogen, undergo changes in the crystalline ice-phase, sublimation, sintering and surface pre-melting as they are heated from 103 to 247 K. An increase in the thickness of the diffuse surface layer from ≈10 to ≈30 Å (≈2.5 to 12 bilayers) proves increased molecular mobility at temperatures above ≈210 K. Because none of the other changes tie-in with the temperature trends in collisional outcomes, we conclude that the surface pre-melting phenomenon plays a key role in collision experiments at these temperatures. Consequently, the pressure–temperature environment, may have a larger influence on collision outcomes than previously thought

A new type of optical activity in a toroidal metamaterial

We demonstrate experimentally and numerically the first ever observation of optical activity in a chiral metamaterial that is underpinned by the exotic resonant combination of an electric quadrupole and the elusive toroidal dipole