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published_or_final_version / Biochemistry / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / abstract / Electrical and Electronic Engineering / Master / Master of Philosophy

published_or_final_version / Real Estate and Construction / Doctoral / Doctor of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

The Best MPhil Thesis in the Faculties of Dentistry, Engineering, Medicine and Science (University of Hong Kong), Li Ka Shing Prize,2008-2009 / published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

The light harvesting systems of photosynthetic organisms harness solar energy by efficient light capture and subsequent transport of the light’s energy to a chemical reaction center. Man-made optical devices could benefit by mimicking these naturally occurring light harvesting processes. Supramolecular organic nanostructures, composed of the amphiphilic carbocyanine dye 3,3’-bis- (2-sulfopropyl)-5,5’,6,6’-tetrachloro-1,1’- dioctylbenzimida-carbocyanine (C8S3), self assemble in aqueous solution to form tubular, double-walled J-aggregates. These J-aggregates have drawn comparisons to light harvesting systems, owing to their optical and structural similarities to the cylindrical chlorosomes (antenna) from green sulfur bacteria. This research utilizes optical spectroscopy and microscopy to study the supramolecular origins of the exciton transitions and fundamental nature of exciton energy transport in C8S3 artificial light harvesting systems. Two J-aggregate morphologies are investigated: well-separated, double-walled nanotubes and bundles of agglomerated nanotubes. Linear dichroism spectroscopy of flow-aligned nanotubes is used to generate the first quantitative, polarized model for the complicated C8S3 nanotube excitonic absorption spectrum that is consistent with theoretical predictions. The C8S3 J-aggregate photophysical properties are further explored, as the Stokes shift, quantum yield, and spectral line broadening are measured as a function of temperature from 77 – 298 K. The temperature-dependent emission ratios of the C8S3 J-aggregate two-band fluorescence spectra reveal that nanotube emission is well described with Boltzmann partitioning between states, while the bundles’ is not. Finally, understanding energy transport in these materials is critical for the proposed use of artificial light harvesting systems in optoelectronic devices. The spatial extent of energy transfer in individual C8S3 J- aggregate structures is directly determined using fluorescence imaging. We find that aggregate structural hierarchy greatly influences exciton transport distances: impressive average exciton migration distances of ~ 150 nm are measured along the nanotubes, while these distances increase to over 500 nm in the bundle superstructures. / text

This thesis presents a first study of the continuum limit of light hadronic physics using a lattice gauge theory simulation with good chiral symmetry. The results are interpreted and extrapolated using both the chiral effective theory and analytic models. Matrix elements of operators of the effective weak Hamiltonian are calculated. The thesis details a combined chiral and continuum extrapolation of two ensemble sets of 2+1 flavour Domain Wall QCD data with inverse lattice spacings around 1.73 and 2.32 GeV. A novel procedure of matching lattice data at unphysical quark masses is used to define the scaling trajectory to the continuum limit. Quantities studied include the pion and kaon masses and decay constants, the average up/down quark mass, the strange quark mass, and the neutral kaon mixing parameter BK. The latter is an important theoretical input to the K band in the unitarity triangle of the CKM matrix. A subset of recent results of ref. [1] in the chiral effective theory needed to perform our fits are re-derived. New methods for the improved determination of the BK matrix element (and other correlation functions), and also for the renormalisation of the relevant four-quark operator for BK are presented.