Thesis (Ph. D.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 168-177).

published_or_final_version / Chemistry / Master / Master of Science

Complex optimization problems are prevalent in various fields of science and engineering. However, many of them belong to a category of problems called NP- hard (nondeterministic polynomial-time hard). On the other hand, due to the powerful capability in solving a myriad of complex optimization problems, metaheuristic approaches have attracted great attention in recent decades. Chemical Reaction Optimization (CRO) is a recently developed metaheuristic mimicking the interactions of molecules in a chemical reaction. With the flexible structure and excellent characteristics, CRO can explore the solution space efficiently to identify the optimal or near optimal solution(s) within an acceptable time. Our research not only designs different versions of CRO and applies them to tackle various NP-hard optimization problems, but also investigates theoretical aspects of CRO in terms of convergence and finite time behavior. We first focus on the problem of task scheduling in grid computing, which involves seeking the most efficient strategy for allocating tasks to resources. In addition to Makespan and Flowtime, we also take reliability of resource into account, and task scheduling is formulated as an optimization problem with three objective functions. Then, four different kinds of CRO are designed to solve this problem. Simulation results show that the CRO methods generally perform better than existing methods and performance improvement is especially significant in large-scale applications. Secondly, we study stock portfolio selection, which pertains to deciding how to allocate investments to a number of stocks. Here we adopt the classical Markowitz mean-variance model and consider an additional cardinality constraint. Thus, the stock portfolio optimization becomes a mixed-integer quadratic programming problem. To solve it, we propose a new version of CRO named Super Molecule-based CRO (S-CRO). Computational experiments suggest that S-CRO is superior to canonical CRO in solving this problem. Thirdly, we apply CRO to the short adjacent repeats identification problem (SARIP), which involves detecting the short adjacent repeats shared by multiple DNA sequences. After proving that SARIP is NP-hard, we test CRO with both synthetic and real data, and compare its performance with BASARD, which is the previous best algorithm for this problem. Simulation results show that CRO performs much better than BASARD in terms of computational time and finding the optimal solution. We also propose a parallel version of CRO (named PCRO) with a synchronous communication scheme. To test its efficiency, we employ PCRO to solve the Quadratic Assignment Problem (QAP), which is a classical combinatorial optimization problem. Simulation results show that compared with canonical sequential CRO, PCRO can reduce the computational time as well as improve the quality of the solution for instances of QAP with large sizes. Finally, we perform theoretical analysis on the convergence and finite time behavior of CRO for combinatorial optimization problems. We explore CRO convergence from two aspects, namely, the elementary reactions and the total system energy. Furthermore, we also investigate the finite time behavior of CRO in respect of convergence rate and first hitting time. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Heterogeneous palladium catalysts for use in Suzuki-type reactions have been prepared using the molecular imprinting technique. Using this technique allows the preparation of a heterogeneous catalyst with uniform active sites which have a metal complex configuration that favours processes in the catalytic cycle, thus enhancing the rate of reaction. It was reasoned, from the general catalytic cycle for palladium cross-couplings, that a bisphosphine complex with a cis ligand geometry would be beneficial. Polymerisable phosphines were synthesised and the cis bisphosphine palladium complexes prepared. The geometry of the complexes was fixed by addition of a bidentate ligand (catechol). The resulting complexes were incorporated into a macroporous polymer framework using the molecular imprinting technique. This produced the heterogeneous palladium catalysts with uniform active sites and known palladium content. The catalysts were ~ested in model Suzuki reactions and were shown to give far superior yields to the homogeneous catalyst and control heterogeneous catalyst (derived from commercial ligand). The favoured square-planar cis-geometry was likely to increase the rate of reductive elimination, which takes place from that conformation. It is also reasonable to imply that the catalytically active palladium(O) species would be strained, being tetrahedral not square-planar, and so the rate of oxidative addition (the slow step in some cases) could also be accelerated. The improved yields shown by the imprinted catalysts for the Suzuki reactions suggest that this is the case.

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