Computational Explorations of Enhanced Nonlinearities and Quantum Optical Effects in Photonic Nanostructures

In this thesis, we present a comprehensive theoretical analysis and computataional study of optical nonlinearities in the graphene-based and silicon-based metamaterials. The novel numerical methods and corresponding results described in this work give a significant impact on our understanding of surface plasmon resonance in artificial optical materials, which facilitates the design and fabrication of new photonic devices with enhanced nonlinear optical functionalities. // Two generic nonlinear metasurfaces are elaborated in this dissertation, namely, graphene-based metasurfaces and silicon-based metasurfaces. Employing a novel homogenization technique, the effective second-order susceptibility of graphene metasurfaces is calculated, which can be enhanced by more than two orders of magnitude as compared to the intrinsic value of graphene sheet. There is excellent agreement between the predictions of the homogenization method and those based on rigorous numerical solutions of Maxwell equations. Moreover, we also illustrate that the effective Raman susceptibilities of silicon-based metasurfaces can be enhanced by 3 to 4 orders of magnitude as compared to the intrinsic value of silicon. Even though the homogenization method for silicon-based metasurfaces is not as accurate as graphene-based, this result still gives a qualitative analysis on the effective Raman susceptibility of silicon-based metasurfaces. // Additionally, the optical nonlinearity is utilized to design a two-mode quantum waveguide made of coupled silicon photonic crystal nanocavities in the last part of the thesis. Finally, we also explore the implications of our work to the development of new active photonic nano devices with new or improved functionalities

Large enhancement of the effective second-order nonlinearity in graphene metasurfaces

Using a powerful homogenization technique, one- and two-dimensional graphene metasurfaces are homogenized both at the fundamental frequency (FF) and second harmonic (SH). In both cases, there is excellent agreement between the predictions of the homogenization method and those based on rigorous numerical solutions of Maxwell equations. The homogenization technique is then employed to demonstrate that, owing to a double-resonant plasmon excitation mechanism that leads to strong, simultaneous field enhancement at the FF and SH, the effective second-order susceptibility of graphene metasurfaces can be enhanced by more than three orders of magnitude as compared to the intrinsic second-order susceptibility of a graphene sheet placed on the same substrate. In addition, we explore the implications of our results on the development of new active nanodevices that incorporate nanopatterned graphene structures.Comment: 11 pages, 12 figure

Market share competition in the Chinese online game industry.

This study investigates the impacts of pricing innovations and other non-pricing dimensions on the market share competition of dominant Chinese online game companies. The empirical context of my research is the strategic behaviour of online game operators (i.e. the companies who operate online games) in the Chinese online game market – the most active market in the world with strong network effects. According to the literature review, previous pricing studies have focused mainly on the evaluation of traditional pricing theories and their limited validity for the information economy. Velu (2005) pointed out how dominant firms in a market with strong network effects adopt business innovations to sustain their market dominance. This study first investigates the validity of Velu‟s theory and then aims to develop and expand the theory of pricing practice by discussing how dominant companies integrate pricing and other non-pricing dimensions during market share competition. With the application of an analytical synthesis, this study covers large parts of the traditional economy and information economy literature by linking the concepts of „within‟ and „across‟ theories of pricing and competition. It finally brings together different theories and adopts Bouwman and MacInnes‟ virtual web idea as an original conceptual framework to give an insight into how the pricing process and other internal and external factors impact differently on the market share competition. The study adopts a descriptive multiple-case study strategy including five dominant Chinese online game companies and employs qualitative data collected from 64 interviewees and reliable secondary data from documentations and archival records.The findings suggest that, instead of devoting all their efforts to pricing innovation, the companies have turned to an exploration of their internal resources to enhance their competitiveness. Superficially, as an influential external factor, government regulations have constrained the operation of imported games. The study also discusses two internal themes that influence each company‟s competitive strength. They are: how to deal with the exodus of talent and how to handle strategic alliance management. There seems to be no previous research concerning the relationship between pricing innovation and market dominance within a new economy‟s service sector. As a consequence, this research should provide insights into this academic blind spot and rationalize the diversity of strategic theory within the specific industry

Biomass-derived three-dimensional porous N-doped carbonaceous aerogel for efficient supercapacitor electrodes

Functionalized carbonaceous materials with hierarchical structure and developed porosity are highly desired in energy storage and conversion fields. In this work, a facile and scalable hydrothermal methodology was established to synthesise three-dimensional (3D) N-doped carbonaceous aerogels using biomass-based starting materials and polypyrrole as N-source. The effect of different calcination temperatures on the structural properties, type and content of N-species and electrochemical performance of the 3D N-doped carbonaceous aerogels were uncovered. Thanks to the combinatorial effect of the appropriate N content and porous structure, the obtained samples exhibited excellent electrochemical performance, in particular, an outstanding specific capacitance of 281.0 F g-1 achieved on the sample calcined at 600 °C. This methodology offers a new fabrication strategy to prepare nanoscale carbonaceous materials with desirable morphology and hierarchical architecture of great potentials for the applications in energy fields

Differential Actions of Ethanol and Trichloroethanol at Sites in the M3 and M4 Domains of the NMDA Receptor GluN2A (NR2A) Subunit

Background and purpose:  Alcohol produces its behavioural effects in part due to inhibition of N-methyl-d-aspartate (NMDA) receptors in the CNS. Previous studies have identified amino acid residues in membrane-associated domains 3 (M3) and 4 (M4) of the NMDA receptor that influence ethanol sensitivity. In addition, in other alcohol-sensitive ion channels, sedative-hypnotic agents have in some cases been shown to act at sites distinct from the sites of ethanol action. In this study, we compared the influence of mutations at these sites on sensitivity to ethanol and trichloroethanol, a sedative-hypnotic agent that is a structural analogue of ethanol. Experimental approach:  We constructed panels of mutants at ethanol-sensitive positions in the GluN2A (NR2A) NMDA receptor subunit and transiently expressed these mutants in human embryonic kidney 293 cells. We used whole-cell patch-clamp recording to assess the actions of ethanol and trichloroethanol in these mutant NMDA receptors. Key results:  Ethanol sensitivity of mutants at GluN2A(Ala825) was not correlated with any physicochemical measures tested. Trichloroethanol sensitivity was altered in two of three ethanol-insensitive mutant GluN2A subunits: GluN2A(Phe637Trp) in M3 and GluN2A(Ala825Trp) in M4, but not GluN2A(Met823Trp). Trichloroethanol sensitivity decreased with increasing molecular volume at Phe637 or increasing hydrophobicity at Ala825 and was correlated with ethanol sensitivity at both sites. Conclusions and implications:  Evidence obtained to date is consistent with a role of GluN2A(Ala825) as a modulatory site for ethanol and trichloroethanol sensitivity, but not as a binding site. Trichloroethanol appears to inhibit the NMDA receptor in a manner similar, but not identical to, that of ethanol