Tensile-Strained Self-Assembly: Tunable Nanomaterials for Infrared Optoelectronics and Quantum Optics

Discovered recently, tensile-strained quantum dots are optically active, defect-free nanostructures. Large tensile strains allow us to tailor band structures for applications from tunable infrared emitters to entangled photon sources. I will discuss the history, current state-of-the-art, and future directions of this rapidly expanding research field

Strain-Driven Growth of GaAs(111) Quantum Dots with Low Fine Structure Splitting

Symmetric quantum dots (QDs) on (111)-oriented surfaces are promising candidates for generating polarization-entangled photons due to their low excitonic fine structure splitting(FSS). However, (111) QDs are difficult to grow. The conventional use of compressive strain to drive QD self-assembly fails to form 3D nanostructures on (111) surfaces. Instead, we demonstrate that (111) QDs self-assemble under tensile strain by growing GaAs QDs on an InP(111)A substrate. Tensile GaAs self-assembly produces a low density of QDs with a symmetric triangular morphology. Coherent, tensile QDs are observed without dislocations, and the QDs luminescence at room temperature. Single QD measurements reveal low FSS with a median value of 7.6 μeV, due to the high symmetry of the (111) QDs. Tensile self-assembly thus offers a simple route to symmetric (111) QDs for entangled photon emitters

Quantum Dot Growth on (111) and (110) Surfaces Using Tensile-Strained Self-Assembly

The self-assembly of epitaxial quantum dots on (001) surfaces, driven by compressive strain, is a widely used tool in semiconductor optoelectronics. In contrast, the growth of quantum dots on (111) and (110) surfaces has historically been a significant challenge. In most cases the strain relaxes rapidly via dislocation nucleation and glide before quantum dots can form. In this paper, we discuss a method for the reliable and controllable self-assembly of quantum dots on both (111) and (110) surfaces, where tensile strain is now the driving force. By showing that tensile-strained self-assembly is applicable to several material systems, we demonstrate the versatility of this technique. We believe that tensile-strained self-assembly represents a powerful tool for heterogeneous materials integration, and nanomaterial development, with future promise for band engineering and quantum optics applications

Conglomeration: an investigation into the incidence and significance amongst FTSE100 companies since 1993

This research created a database of financial and non-financial information extracted from DataStream, annual reports and accounts, company websites and other reputable sources to investigate the incidence of conglomeration amongst the largest, by market capitalisation, companies, both industrial/manufacturing and service, that comprised the London Stock Exchange FTSE100 index at the end of 1993, 1998 and 2003. Categorising companies according to the 4-category Rumelt-based scheme used in previous UK research by Channon (1973, 1978) and Whittington & Mayer (2000), this research has found support for the contention, based on anecdotal evidence, that conglomeration amongst the FTSE100 has declined, especially between 1998 and 2003. Rather than confirming the evolutionary flow of companies through the Model of Corporate Development from single business to conglomerate strategies, the research shows more companies to have retreated to greater focus than advanced to wider diversification. Furthermore, the breadth of activities pursued by conglomerates fell through the research period and there was also an increase in diversified companies with a core activity generating more than 50% of their turnover. Whilst acknowledging that several conglomerates were created by strong business personalities including Lords Hanson and White at Hanson and Sir Owen Green at BTR, no strong relationships were found between corporate governance and diversification. The enhancement of corporate governance Best Practice resulted in improvements across all companies. Finally, this research suggests performance is not a primary driver of the trend towards focus but that financial/market and regulatory, especially competition authority, factors led to changes in diversification through a mixture of divestment, demerger, capital reduction/downsizing, acquisitions and internationalisation. The Model of Corporate Development has become multi-directional with movements influenced by generic, industry specific and company specific factors. There is also an inherent trade-off across diversification categories in the potential level of risk, growth, scale and scope benefits

Two Departments, Two Models of Interdisciplinary Peer Learning

On graduation, teacher candidates (TCs) are typically underprepared to teach science, particularly physical science, whereas physics graduates frequently lack training in teaching or effective communication. In response, we created two models for interdisciplinary peer learning where TCs were paired with either graduate or undergraduate physics students. In both models, physics students teach TCs content knowledge relevant to a given area of either classical or quantum physics, which TCs then use to design and implement a short lesson for K-5 students. Overall, both models were successful, with the two sets of students reporting benefits in each case. Affordances for TCs included increased confidence to teach physical science and an appreciation for collaboration with experts. Physics students described increased awareness of the complexities of communicating science to general audiences and stronger community with their classmates. Students from both groups cited insufficient project time as a constraint, whereas physics students found it challenging to align their project and coursework. In moving away from traditional lecture, these interdisciplinary collaborations also benefitted us as instructors, giving us new perspectives on teaching. In light of our findings we propose improvements to these proof-of-concept models to enable their future scale-up and replication in other disciplines

The integrated dynamic land use and transport model MARS

Cities worldwide face problems like congestion or outward migration of businesses. The involved transport and land use interactions require innovative tools. The dynamic Land Use and Transport Interaction model MARS (Metropolitan Activity Relocation Simulator) is part of a structured decision making process. Cities are seen as self organizing systems. MARS uses Causal Loop Diagrams from Systems Dynamics to explain cause and effect relations. MARS has been benchmarked against other published models. A user friendly interface has been developed to support decision makers. Its usefulness was tested through workshops in Asia. This paper describes the basis, capabilities and uses of MARS

Genomic signatures of host-associated divergence and adaptation in a coral-eating snail, Coralliophila violacea (Kiener, 1836).

The fluid nature of the ocean, combined with planktonic dispersal of marine larvae, lowers physical barriers to gene flow. However, divergence can still occur despite gene flow if strong selection acts on populations occupying different ecological niches. Here, we examined the population genomics of an ectoparasitic snail, Coralliophila violacea (Kiener 1836), that specializes on Porites corals in the Indo-Pacific. Previous genetic analyses revealed two sympatric lineages associated with different coral hosts. In this study, we examined the mechanisms promoting and maintaining the snails' adaptation to their coral hosts. Genome-wide single nucleotide polymorphism (SNP) data from type II restriction site-associated DNA (2b-RAD) sequencing revealed two differentiated clusters of C. violacea that were largely concordant with coral host, consistent with previous genetic results. However, the presence of some admixed genotypes indicates gene flow from one lineage to the other. Combined, these results suggest that differentiation between host-associated lineages of C. violacea is occurring in the face of ongoing gene flow, requiring strong selection. Indeed, 2.7% of all SNP loci were outlier loci (73/2,718), indicative of divergence with gene flow, driven by adaptation of each C. violacea lineage to their specific coral hosts