Light-confining nanoporous anodic alumina microcavities by apodized stepwise pulse anodization

This study presents an innovative approach to fabricate nanoporous anodic alumina optical microcavities (NAA-μCVs) with enhanced quality factor and versatile optical properties. An apodization strategy using a logarithmic negative function is applied to a stepwise pulse anodization process in order to engineer the effective medium of NAA so that it confines light efficiently. The architecture of these light-trapping photonic crystals is composed of two highly reflecting mirrors with an asymmetrically apodized effective medium. Various anodization parameters such as the anodization time, anodization period, current density offset, and pore-widening time are systematically modified to assess their effect on the optical properties of NAA-μCVs in terms of the quality factor and position of the resonance band. We demonstrate that this fabrication approach enables the generation of NAA-μCVs with a high quality factor (∼113) and well-resolved and tunable resonance bands across the spectral regions, from UV to near-IR, through manipulation of the anodization parameters. These results represent a comprehensive rationale for the development of high-quality NAA-μCVs with enhanced light-confining capabilities, providing new opportunities for further fundamental and applied research across a broad range of fields and disciplines such as photonics and optical sensing.Cheryl Suwen Law, Yee Lim, Raeanne M. Macalincag, Andrew D. Abell, and Abel Santo

The impact of working memory load on task execution and online plan adjustment during multitasking in a virtual environment

Three experiments investigated the impact of working memory load on online plan adjustment during a test of multitasking in young, nonexpert, adult participants. Multitasking was assessed using the Edinburgh Virtual Errands Test (EVET). Participants were asked to memorize either good or poor plans for performing multiple errands and were assessed both on task completion and on the extent to which they modified their plans during EVET performance. EVET was performed twice, with and without a secondary task loading a component of working memory. In Experiment 1, articulatory suppression was used to load the phonological loop. In Experiment 2, oral random generation was used to load executive functions. In Experiment 3, spatial working memory was loaded with an auditory spatial localization task. EVET performance for both good- and poor-planning groups was disrupted by random generation and sound localization, but not by articulatory suppression. Additionally, people given a poor plan were able to overcome this initial disadvantage by modifying their plans online. It was concluded that, in addition to executive functions, multiple errands performance draws heavily on spatial, but not verbal, working memory resources but can be successfully completed on the basis of modifying plans online, despite a secondary task load

Integrating surface plasmon resonance and slow photon effects in nanoporous anodic alumina photonic crystals for photocatalysis

This study explores the potential of gold-coated titania-functionalized nanoporous anodic alumina distributed Bragg reflectors (Au-TiO2-NAA-DBRs) as platforms to enhance photocatalytic reactions by integrating “slow photons” and surface plasmon resonance (SPR). The photocatalytic degradation rate of methylene blue – a model organic compound with a well-defined absorption band in the visible spectral region – by these composite photonic crystals (PCs) upon visible-NIR light irradiation is used as an indicator to identify coupling effects between the “slow photon” effect and SPR. Our study demonstrates that the photocatalytic enhancement in Au-TiO2-NAA-DBRs is strongly associated with “slow photon” effect, while the contribution of SPR to the overall photocatalytic enhancement is weak due to the localized generation of surface plasmons on the top surface of the composite PC structure. Photocatalytic enhancement is optimal when the characteristic photonic stopband of these PCs partially overlaps with the absorption band of methylene blue, which results in edges being positioned away from the absorption maximum of the organic dye. The overall photocatalytic degradation for methylene blue is also correlated to the type of noble metal coating and the geometric features of the PC structures. These results establish a rationale for further development of noble metal-coated NAA-based hybrid plasmonic–photonic crystal photocatalyst platforms to optimally integrate “slow photons” and SPR for enhancing the efficiency of photocatalytic reactions and other light harvesting applications.Siew Yee Lim, Cheryl Suwen Law, Lina Liu, Marijana Markovic, Andrew D. Abell and Abel Santo

Breakdown of superfluidity of an atom laser past an obstacle

The 1D flow of a continuous beam of Bose-Einstein condensed atoms in the presence of an obstacle is studied as a function of the beam velocity and of the type of perturbing potential (representing the interaction of the obstacle with the atoms of the beam). We identify the relevant regimes: stationary/time-dependent and superfluid/dissipative; the absence of drag is used as a criterion for superfluidity. There exists a critical velocity below which the flow is superfluid. For attractive obstacles, we show that this critical velocity can reach the value predicted by Landau's approach. For penetrable obstacles, it is shown that superfluidity is recovered at large beam velocity. Finally, enormous differences in drag occur when switching from repulsive to attractive potential.Comment: 15 pages, 6 figure

Redox interactions of Tc(VII), U(VI), and Np(V) with microbially reduced biotite and chlorite

Technetium, uranium, and neptunium are contaminants that cause concern at nuclear facilities due to their long half-life, environmental mobility, and radiotoxicity. Here we investigate the impact of microbial reduction of Fe(III) in biotite and chlorite and the role that this has in enhancing mineral reactivity toward soluble TcO4 -, UO2 2+, and NpO2 +. When reacted with unaltered biotite and chlorite, significant sorption of U(VI) occurred in low carbonate (0.2 mM) buffer, while U(VI), Tc(VII), and Np(V) showed low reactivity in high carbonate (30 mM) buffer. On reaction with the microbially reduced minerals, all radionuclides were removed from solution with U(VI) reactivity influenced by carbonate. Analysis by X-ray absorption spectroscopy (XAS) confirmed reductive precipitation to poorly soluble U(IV) in low carbonate conditions and both Tc(VII) and Np(V) in high carbonate buffer were also fully reduced to poorly soluble Tc(IV) and Np(IV) phases. U(VI) reduction was inhibited under high carbonate conditions. Furthermore, EXAFS analysis suggested that in the reaction products, Tc(IV) was associated with Fe, Np(IV) formed nanoparticulate NpO2, and U(IV) formed nanoparticulate UO2 in chlorite and was associated with silica in biotite. Overall, microbial reduction of the Fe(III) associated with biotite and chlorite primed the minerals for reductive scavenging of radionuclides: this has clear implications for the fate of radionuclides in the environment

Actors and networks or agents and structures: towards a realist view of information systems

Actor-network theory (ANT) has achieved a measure of popularity in the analysis of information systems. This paper looks at ANT from the perspective of the social realism of Margaret Archer. It argues that the main issue with ANT from a realist perspective is its adoption of a `flat' ontology, particularly with regard to human beings. It explores the value of incorporating concepts from ANT into a social realist approach, but argues that the latter offers a more productive way of approaching information systems

Electrochemical engineering of nanoporous materials for photocatalysis: fundamentals, advances, and perspectives

Photocatalysis comprises a variety of light-driven processes in which solar energy is converted into green chemical energy to drive reactions such as water splitting for hydrogen energy generation, degradation of environmental pollutants, CO₂ reduction and NH3 production. Electrochemically engineered nanoporous materials are attractive photocatalyst platforms for a plethora of applications due to their large effective surface area, highly controllable and tuneable light-harvesting capabilities, efficient charge carrier separation and enhanced diffusion of reactive species. Such tailor-made nanoporous substrates with rational chemical and structural designs provide new exciting opportunities to develop advanced optical semiconductor structures capable of performing precise and versatile control over light–matter interactions to harness electromagnetic waves with unprecedented high efficiency and selectivity for photocatalysis. This review introduces fundamental developments and recent advances of electrochemically engineered nanoporous materials and their application as platforms for photocatalysis, with a final prospective outlook about this dynamic field.Siew Yee Lim, Cheryl Suwen Law, Lina Liu, Marijana Markovic, Carina Hedrich, Robert H. Blick, Andrew D. Abell, Robert Zierold, and Abel Santo

The institutional shaping of management: in the tracks of English individualism

Globalisation raises important questions about the shaping of economic action by cultural factors. This article explores the formation of what is seen by some as a prime influence on the formation of British management: individualism. Drawing on a range of historical sources, it argues for a comparative approach. In this case, the primary comparison drawn is between England and Scotland. The contention is that there is a systemic approach to authority in Scotland that can be contrasted to a personal approach in England. An examination of the careers of a number of Scottish pioneers of management suggests the roots of this systemic approach in practices of church governance. Ultimately this systemic approach was to take a secondary role to the personal approach engendered by institutions like the universities of Oxford and Cambridge, but it found more success in the different institutional context of the USA. The complexities of dealing with historical evidence are stressed, as is the value of taking a comparative approach. In this case this indicates a need to take religious practice as seriously as religious belief as a source of transferable practice. The article suggests that management should not be seen as a simple response to economic imperatives, but as shaped by the social and cultural context from which it emerges