Effect of spatial nonlocality on the density functional band gap

We show that for a large class of exchange-correlation functionals the local exchange-correlation potential obtained within an optimized effective potential severely underestimates the band gap. On the other hand, the corresponding nonlocal potential obtained from a generalized Kohn-Sham scheme provides a much better description of the band gap, in good agreement with experiments. These results strongly indicate that a local exchange-correlation potential, however good the exchange-correlation approximation, cannot capture the delicate interplay between correlation effects and spatial localization in the KS band structure, unless the (cumbersome) contribution from the derivative discontinuity of the exchange-correlation energy functional is considered.

Electromagnetic pulse compression and energy localization in quantum plasmas

The evolution of the intensity of a relativistic laser beam propagating through a dense quantum plasma is investigated, by considering different plasma regimes. A cold quantum fluid plasma and then a thermal quantum description(s) is (are) adopted, in comparison with the classical case of reference. Considering a Gaussian beam cross-section, we investigate both the longitudinal compression and lateral/longitudinal localization of the intensity of a finite-radius electromagnetic pulse. By employing a quantum plasma fluid model in combination with Maxwell's equations, we rely on earlier results on the quantum dielectric response, to model beam-plasma interaction. We present an extensive parametric investigation of the dependence of the longitudinal pulse compression mechanism on the electron density in cold quantum plasmas, and also study the role of the Fermi temperature in thermal quantum plasmas. Our numerical results show pulse localization through a series of successive compression cycles, as the pulse propagates through the plasma. A pulse of 100 fs propagating through cold quantum plasma is compressed to a temporal size of approximate to 1.35 attosecond and a spatial size of approximate to 1.08 10(-3) cm. Incorporating Fermi pressure via a thermal quantum plasma model is shown to enhance localization effects. A 100 fs pulse propagating through quantum plasma with a Fermi temperature of 350 K is compressed to a temporal size of approximate to 0.6 attosecond and a spatial size of approximate to 2.4 10(-3) cm. (c) 2010 Elsevier B.V. All rights reserved.

Metamaterial as a controllable template for nanoscale field localization

We report that subwavelength localization of light in the near-field of a double-periodic photonic metamaterial may be efficiently controlled by the polarization and wavelength of the incident radiation. A dramatic variation in the periodic near-field landscapes, including a transition from a pattern of isolated subwavelength plasmon hot-spots to a blurred, low contrast pattern, accompanied by a change in the pattern's symmetry has been observed in the proximity of an aluminum nanowire "fish-scale" nanostructure. Hot-spots as small as 0.23 lambda have been achieved and their position has been controlled by tuning the wavelength of incident light across the dipole absorption resonance of the metamaterial. A simple switch of the polarization state can lead to a spatial period doubling in the landscape pattern.

Spatial Distribution of Soil Geochemistry in Geoforensics

Two common scenarios in Geoforensics (definition in text) are considered: the provenance, or localization of unknown samples and the question of sample variability at scenes of crime/alibi locations. Both have been discussed in forensic and soil science publications, but mostly within a theoretical or non-forensic context. These previous publications provide context for the two case study scenarios (one actual, one based on a range of criminal casework) that consider provenance and variability. A challenging scientific question in geoforensics is the provenance question: ‘where may this sample have come from?’ A question the Tellus data can assist in answering. The question of variation between samples maybe less of a challenge, yet variation between a suspect sample within a scene of crime requires detailed sampling. Variation on a larger (tens to hundreds of kilometres) scale may provide useful intelligence on where a sample came from. To summarise, databases such as Tellus and TellusBorder may be used as effective tools to assist in the search for the origin of displaced soil and sediment

Sound Art and Spatial Practices: Situating Sound Installation Art Since 1958

This dissertation examines the emergence and development of sound installation art, an under-recognized tradition that has developed between music, architecture, and media art practices since the late 1950s. Unlike many musical works, which are concerned with organizing sounds in time, sound installations organize sounds in space; they thus necessitate new theoretical and analytical models that take into consideration the spatial situated-ness of sound. Existing discourses on “spatial sound” privilege technical descriptions of sound localization. By contrast, this dissertation examines the ways in which concepts of space are socially, culturally, and politically construed, and how spatially-organized sound works reflect and resist these different constructions. Using an interdisciplinary methodology of critical spatial analysis and critical studies in music, this dissertation explores such topics as: conceptions of acoustic space in postwar Western art music, architecture, and media theory; the development of sound installation art in relation to philosophies of everyday life and social space; the historical links between musical performance, conceptual art, and sound sculpture; the body as a site for sound installations; and sonicspatial strategies that confront politics of race and gender. Through these different investigations, this dissertation proposes an “ontopological” model for considering sound: a critical model of analysis and reception that privileges an understanding of sound in relation to ontologies of space and place.