Spectral filtering as a method of visualising and removing striped artefacts in digital elevation data

Spectral filtering was compared with traditional mean spatial filters to assess their ability to identify and remove striped artefacts in digital elevation data. The techniques were applied to two datasets: a 100 m contour derived digital elevation model (DEM) of southern Norway and a 2 m LiDAR DSM of the Lake District, UK. Both datasets contained diagonal data artefacts that were found to propagate into subsequent terrain analysis. Spectral filtering used fast Fourier transformation (FFT) frequency data to identify these data artefacts in both datasets. These were removed from the data by applying a cut filter, prior to the inverse transform. Spectral filtering showed considerable advantages over mean spatial filters, when both the absolute and spatial distribution of elevation changes made were examined. Elevation changes from the spectral filtering were restricted to frequencies removed by the cut filter, were small in magnitude and consequently avoided any global smoothing. Spectral filtering was found to avoid the smoothing of kernel based data editing, and provided a more informative measure of data artefacts present in the FFT frequency domain. Artefacts were found to be heterogeneous through the surfaces, a result of their strong correlations with spatially autocorrelated variables: landcover and landsurface geometry. Spectral filtering performed better on the 100 m DEM, where signal and artefact were clearly distinguishable in the frequency data. Spectrally filtered digital elevation datasets were found to provide a superior and more precise representation of the landsurface and be a more appropriate dataset for any subsequent geomorphological applications

Coherent generation of symmetry-forbidden phonons by light-induced electron-phonon interactions in magnetite

Symmetry breaking across phase transitions often causes changes in selection rules and emergence of optical modes which can be detected via spectroscopic techniques or generated coherently in pump-probe experiments. In second-order or weakly first-order transitions, fluctuations of the order parameter are present above the ordering temperature, giving rise to intriguing precursor phenomena, such as critical opalescence. Here, we demonstrate that in magnetite (Fe$_3$O$_4$) light excitation couples to the critical fluctuations of the charge order and coherently generates structural modes of the ordered phase above the critical temperature of the Verwey transition. Our findings are obtained by detecting coherent oscillations of the optical constants through ultrafast broadband spectroscopy and analyzing their dependence on temperature. To unveil the coupling between the structural modes and the electronic excitations, at the origin of the Verwey transition, we combine our results from pump-probe experiments with spontaneous Raman scattering data and theoretical calculations of both the phonon dispersion curves and the optical constants. Our methodology represents an effective tool to study the real-time dynamics of critical fluctuations across phase transitions

Attosecond streaking of photoelectron emission from disordered solids

Attosecond streaking of photoelectrons emitted by extreme ultraviolet light has begun to reveal how electrons behave during their transport within simple crystalline solids. Many sample types within nanoplasmonics, thin-film physics, and semiconductor physics, however, do not have a simple single crystal structure. The electron dynamics which underpin the optical response of plasmonic nanostructures and wide-bandgap semiconductors happen on an attosecond timescale. Measuring these dynamics using attosecond streaking will enable such systems to be specially tailored for applications in areas such as ultrafast opto-electronics. We show that streaking can be extended to this very general type of sample by presenting streaking measurements on an amorphous film of the wide-bandgap semiconductor tungsten trioxide, and on polycrystalline gold, a material that forms the basis of many nanoplasmonic devices. Our measurements reveal the near-field temporal structure at the sample surface, and photoelectron wavepacket temporal broadening consistent with a spread of electron transport times to the surface

The old drama and the new: conceptions of the nature of the theatrical experience in the work of William Archer, G.B. Shaw, W.B. Yeats, E.G. Craig and H. Granville-Barker.

PhDTwo opposing philosophical outlooks can be discerned in the thought of the men discussed in this dissertation.. The humanist view, associated with Archer and Barker, sees life as centred solely on man; the religious thinkers, Yeats and Craig, are concerned with man's relationship with a power beyond himself. Shaw is unique in his advocacy of contradictory elements from both philosophies. The humanist thinkers are concerned in art with the communication of information about man; those of the religious party value an indescribable experience communicated by artistic symbols. These two kinds of communication can perhaps be seen in the English theatre of the nineteenth century; the theatre of the early part of the century made use of a traditional language of theatrical symbols, while the later theatres of Irving and the Bancrofts abandoned tradition in favour of new "realistic" portrayals of society and human psychology. Archer illustrates the humanist approach to art in his concern for the moral and psychological information conveyed by the play. In his humanist guise, Shaw emphasizes the need for drama to convey new social and philosophical ideas. For Barker, drama conveys, through the medium of the actor, a special kind of "subjective" truth. Each of the religious theorists seeks symbolic value in a different facet of the theatrical performance;, for Yeats, the religious communication is achieved by the traditional symbols of poetry; for Shaw, in his religious guise, the performer is the prime source of symbolic value; for Craig, purely visual symbols of natural process provide a glimpse of a world untainted by man's egotism. The theories are open to criticism. The humanist theories seem to deny the value of artistic form, while the religious theories seem to seek form without content. All the theories seem to show insufficient respect for the laws of audience psychology