Heterogeneous enantioselective epoxidation catalyzed by Mn(salen) complexes grafted onto mesoporous materials by phenoxy group

Three chiral Mn(salen) complexes were immobilized into different mesoporous material via phenoxy group by a simplified method and they show high activity and enantioselectivity for asymmetric epoxidation of various substituted unfunctional olefins. The heterogeneous Mn(salen) catalysts show comparable ee values for asymmetric epoxidation of styrene and 6-cyano-2,2-dimethylchromene and much higher ee values for epoxidation of a-methylstyrene (heterogeneous 79.7% ee versus homogeneous 26.4% ee) and cis-beta-methylstyrene (heterogeneous 94.9% ee versus homogeneous 25.3% ee for cis-epoxide) than the homogeneous catalysts. These heterogeneous catalysts also remarkably alter the cis/trans ratio of epoxides for asymmetric epoxidation of cis-beta-methylstyrene (heterogeneous 21 versus homogeneous 0.38). The axial tether group does not make a big effect on ee values and the increase in ee value and change in cis/trans ratio are mainly attributed to the axial immobilization mode and the support effect of heterogeneous catalysts. The catalysts keep constant ee values for the recycle tests of eight times for asymmetric epoxidation of a-methylstyrene. And several possibilities were proposed to elucidate the difference in ee values of heterogeneous catalysts from homogeneous catalysts. (c) 2005 Elsevier B.V. All rights reserved.

Fixed Point vs. First-Order Logic on Finite Ordered Structures with Unary Relations

We prove that first order logic is strictly weaker than fixed point logic over every infinite classes of finite ordered structures with unary relations: Over these classes there is always an inductive unary relation which cannot be defined by a first-order formula, even when every inductive sentence (i.e., closed formula) can be expressed in first-order over this particular class. Our proof first establishes a property valid for every unary relation definable by first-order logic over these classes which is peculiar to classes of ordered structures with unary relations. In a second step we show that this property itself can be expressed in fixed point logic and can be used to construct a non-elementary unary relation.

Working Memory Networks for Learning Multiple Groupings of Temporarily Ordered Events: Applications to 3-D Visual Object Recognition

Working memory neural networks are characterized which encode the invariant temporal order of sequential events that may be presented at widely differing speeds, durations, and interstimulus intervals. This temporal order code is designed to enable all possible groupings of sequential events to be stably learned and remembered in real time, even as new events perturb the system. Such a competence is needed in neural architectures which self-organize learned codes for variable-rate speech perception, sensory-motor planning, or 3-D visual object recognition. Using such a working memory, a self-organizing architecture for invariant 3-D visual object recognition is described that is based on the model of Seibert and Waxman [1].

Accommodating curvature in a highly ordered functionalized metal oxide nanofiber: synthesis, characterization and multi-scale modeling of layered nanosheets

A key element in the rational design of hybrid organic-inorganic nanostructures, is control of surfactant packing and adsorption onto the inorganic phase in crystal growth and assembly. In layered single crystal nanofibers and bilayered 2D nanosheets of vanadium oxide, we show how the chemisorption of preferred densities of surfactant molecules can direct formation of ordered, curved layers. The atom-scale features of the structures are described using molecular dynamics simulations that quantify surfactant packing effects and confirm the preference for a density of 5 dodecanethiol molecules per 8 vanadium attachment sites in the synthesised structures. This assembly maintains a remarkably well ordered interlayer spacing, even when curved. The assemblies of interdigitated organic bilayers on V2O5 are shown to be sufficiently flexible to tolerate curvature while maintaining a constant interlayer distance without rupture, delamination or cleavage. The accommodation of curvature and invariant structural integrity points to a beneficial role for oxide-directed organic film packing effects in layered architectures such as stacked nanofibers and hybrid 2D nanosheet systems.

Application of mesoporous silica for the oral delivery of poorly water-soluble drugs

The objective of this thesis was to improve the dissolution rate of the poorly waters-soluble drug, fenofibrate by processing it with a high surface area carrier, mesoporous silica. The subsequent properties of the drug – silica composite were studied in terms of drug distribution within the silica matrix, solid state and release properties. Prior to commencing any experimental work, the properties of unprocessed mesoporous silica and fenofibrate were characterised (chapter 3), this allowed for comparison with the processed samples studied in later chapters. Fenofibrate was a highly stable, crystalline drug that did not adsorb moisture, even under long term accelerated storage conditions. It maintained its crystallinity even after SC-CO2 processing. Its dissolution rate was limited and dependent on the characteristics of the particular in vitro media studied. Mesoporous silica had a large surface area and mesopore volume and readily picked up moisture when stored under long term accelerated storage conditions (75% RH, 40 oC). It maintained its mesopore character after SC-CO2 processing. A variety of methods were employed to process fenofibrate with mesoporous silica including physical mixing, melt method, solvent impregnation and novel methods such as liquid and supercritical carbon dioxide (SC-CO2) (chapter 4). It was found that it was important to break down the fenofibrate particulate structure to a molecular state to enable drug molecules enter into the silica mesopores. While all processing methods led to some increase in fenofibrate release properties; the impregnation, liquid and SC-CO2 methods produced the most rapid release rates. SC-CO2 processing was further studied with a view to optimising the processing parameters to achieve the highest drug-loading efficiency possible (chapter 5). In this thesis, it was that SC-CO2 processing pressure had a bearing on drug-loading efficiency. Neither pressure, duration or depressurisation rate affected drug solid state or release properties. The amount of drug that could be loaded onto to the mesoporous silica successfully was also investigated at different ratios of drug mass to silica surface area under constant SC-CO2 conditions; as the drug – silica ratio increased, the drug-loading efficiency decreased, while there was no effect on drug solid state or release properties. The influence of the number of drug-loading steps was investigated (chapter 6) with a view to increasing the drug-loading efficiency. This multiple step approach did not yield an increase in drug-loading efficiency compared to the single step approach. It was also an objective in this chapter to understand how much drug could be loaded into silica mesopores; a method based on the known volume of the mesopores and true density of drug was investigated. However, this approach led to serious repercussions in terms of the subsequent solid state nature of the drug and its release performance; there was significant drug crystallinity and reduced release extent. The impact of in vitro release media on fenofibrate release was also studied (chapter 6). Here it was seen that media containing HCl led to reduced drug release over time compared to equivalent media not containing HCl. The key findings of this thesis are discussed in chapter 7 and included: 1. Drug – silica processing method strongly influenced drug distribution within the silica matrix, drug solid state and release. 2. The silica surface area and mesopore volume also influenced how much drug could be loaded. It was shown that SC-CO2 processing variables such as processing pressure (13.79 – 41.37 MPa), duration time (4 – 24 h) and depressurisation rate (rapid or controlled) did not influence the drug distribution within the SBA- 15 matrix, drug solid state form or release. Possible avenues of research to be considered going forward include the development and application of high resolution imaging techniques to visualise drug molecules within the silica mesopores. Also, the issues surrounding SBA-15 usage in a pharmaceutical manufacturing environment should be addressed.

Reasoning with sorted-pareto dominance and other qualitative and partially ordered preferences in soft constraints

In decision making problems where we need to choose a particular decision or alternative from a set of possible choices, we often have some preferences which determine if we prefer one decision over another. When these preferences give us an ordering on the decisions that is complete, then it is easy to choose the best or one of the best decisions. However it often occurs that the preferences relation is partially ordered, and we have no best decision. In this thesis, we look at what happens when we have such a partial order over a set of decisions, in particular when we have multiple orderings on a set of decisions, and we present a framework for qualitative decision making. We look at the different natural notions of optimal decision that occur in this framework, which gives us different optimality classes, and we examine the relationships between these classes. We then look in particular at a qualitative preference relation called Sorted-Pareto Dominance, which is an extension of Pareto Dominance, and we give a semantics for this relation as one that is compatible with any order-preserving mapping of an ordinal preference scale to a numerical one. We apply Sorted-Pareto dominance to a Soft Constraints setting, where we solve problems in which the soft constraints associate qualitative preferences to decisions in a decision problem. We also examine the Sorted-Pareto dominance relation in the context of our qualitative decision making framework, looking at the relevant optimality classes for the Sorted-Pareto case, which gives us classes of decisions that are necessarily optimal, and optimal for some choice of mapping of an ordinal scale to a quantitative one. We provide some empirical analysis of Sorted-Pareto constraints problems and examine the optimality classes that result.

Synthesis and characterization of oxide materials

Nanostructured materials are central to the evolution of future electronics and biomedical applications amongst other applications. This thesis is focused on developing novel methods to prepare a number of nanostructured metal oxide particles and films by a number of different routes. Part of the aim was to see how techniques used in nanoparticle science could be applied to thin film methods to develop functional surfaces. Wet-chemical methods were employed to synthesize and modify the metal oxide nanostructures (CeO2 and SiO2) and their structural properties were characterized through advanced X-ray diffraction, electron microscopy, photoelectron spectroscopy and other techniques. Whilst particulates have uses in many applications, their attachment to surfaces is of importance and this is frequently challenging. We examined the use of block copolymer methods to form very well defined metal oxide particulate-like structures on the surface of a number of substrates. Chapter 2 describes a robust method to synthesize various sized silica nanoparticles. As-synthesized silica nanoparticles were further functionalized with IR-820 and FITC dyes. The ability to create size controlled nanoparticles with associated (optical) functionality may have significant importance in bio-medical imaging. Thesis further describes how non-organic modified fluorescent particles might be prepared using inorganic oxides. A study of the concentrations and distributions of europium dopants within the CeO2 nanoparticles was undertaken and investigated by different microscopic and spectroscopic techniques. The luminescent properties were enhanced by doping and detailed explanations are reported. Additionally, the morphological and structural evolution and optical properties were correlated as a function of concentrations of europium doping as well as with further annealing. Further work using positron annihilation spectroscopy allowed the study of vacancy type defects formed due to europium doping in CeO2 crystallites and this was supported by complimentary UV-Vis spectra and XRD work. During the last few years the interest in mesoporous silica materials has increased due to their typical characteristics such as potential ultra-low dielectric constant materials, large surface area and pore volume, well-ordered and uniform pores with adjustable pores between 2 and 50 nm. A simple, generic and cost-effective route was used to demonstrate the synthesis of 2D mesoporous silica thin films over wafer scale dimensions in chapter 5. Lithographic resist and in situ hard mask block copolymer followed by ICP dry etching were used to fabricate mesoporous silica nanostructures. The width of mesoporous silica channels can be varied by using a variety of commercially available lithographic resists whereas depth of the mesoporous silica channels can be varied by altering the etch time. The crystal structure, morphology, pore arrangement, pore diameters, thickness of films and channels were determined by XRD, SEM, ellipsometry and the results reported. This project also extended work towards the study of the antimicrobial study of nanopatterned silver nanodot arrays formed using the block copolymer approach defined above. Silver nanodot arrays were successfully tested for antimicrobial activity over S. aureus and P. aeruginosa biofilms and results shows silver nanodots has good antimicrobial activity for both S. aureus and P. aeruginosa biofilms. Thus, these silver nanodot arrays shows a potential to be used as a substitute for the resolution of infection complications in many areas.

Formation and characterisation of ordered porous vanadium oxide inverse opal materials for Li-ion batteries

This thesis presents several routes towards achieving artificial opal templates by colloidal self-assembly of polystyrene (PS) or poly(methyl methacrylate) (PMMA) spheres and the use of these template for the fabrication of V2O5 inverse opals as cathode materials for lithium ion battery applications. First, through the manipulation of different experimental factors, several methods of affecting or directing opal growth towards realizing different structures, improving order and/or achieving faster formation on a variety of substrates are presented. The addition of the surfactant sodium dodecyl sulphate (SDS) at a concentration above the critical micelle concentration for SDS to a 5 wt% solution of PMMA spheres before dip-coating is presented as a method of achieving ordered 2D PhC monolayers on hydrophobic Au-coated silicon substrates at fast and slow rates of withdrawal. The effect that the degree of hydrophilicity of glass substrates has on the ordering of PMMA spheres is next investigated for a slow rate of withdrawal under noise agitation. Heating of the colloidal solution is also presented as a means of affecting order and thickness of opal deposits formed using fast rate dip coating. E-beam patterned substrates are shown as a means of altering the thermodynamically favoured FCC ordering of polystyrene spheres (PS) when dip coated at slow rate. Facile routes toward the synthesis of ordered V2O5 inverse opals are presented with direct infiltration of polymer sphere templates using liquid precursor. The use of different opal templates, both 2D and 3D partially ordered templates, is compared and the composition and arrangement of the subsequent IO structures post infiltration and calcination for various procedures is characterised. V2O5 IOs are also synthesised by electrodeposition from an aqueous VOSO4 solution at constant voltage. Electrochemical characterisation of these structures as cathode material for Li-ion batteries is assessed in a half cell arrangement for samples deposited on stainless steel foil substrates. Improved rate capabilities are demonstrated for these materials over bulk V2O5, with the improvement attributed to the shorter Li ion diffusion distances and increased electrolyte infiltration provided by the IO structure.

Increasing Stability of Lithium-Ion Batteries with Ordered Graphene Silicon Negative Electrodes

Currently, lackluster battery capability is restricting the widespread integration of Smart Grids, limiting the long-term feasibility of alternative, green energy conversion technologies. Silicon nanoparticles have great conductivity for applications in rechargeable batteries, but have degradation issues due to changes in volume during lithiation/delithiation cycles. To combat this, we use electrochemical deposition to uniformly space silicon particles on graphene sheets to create a more stable structure. We found the process of electrochemical deposition degraded the graphene binding in the electrode material, severely reducing charge capacity. But, the usage of mechanically mixing silicon particles with grapheme yielded batteries better than those that are commercially available.

Three-machine shop scheduling with partially ordered processing routes

This paper considers the problem of sequencing n jobs in a three-machine shop with the objective of minimising the maximum completion time. The shop consists of three machines, M1,M2 and M_{3}. A job is first processed on M1 and then is assigned either the route (M2,M_{3}) or the route (M_{3},M2). Thus, for our model the processing route is given by a partial order of machines, as opposed to the linear order of machines for a job shop, or to an arbitrary sequence of machines for an open shop. The main result is on O(nlog n) time heuristic, which generates a schedule with the makespan that is at most 5/3 times the optimum value.