This dissertation focuses on the synthetic exploratory synthesis of molybdenum chalcogenides and rare earth metal-rich ternary tellurides as a part of an effort to produce molecular building blocks of molybdenum chalcogenide clusters and to explore their structural relationships with solid state cluster networks. The tightly cross-linked Mo3nSe3n+2(n = 2, 3, ...∞) clusters and chain compounds react with alkali metal cyanide or cyanide salt mixtures at temperatures of 450-675 °C to yield reduced, cyanide-terminated molybdenum chalcogenide clusters that are thermodynamically stable. At temperatures of 650-675 °C, linear chain compounds I6[Mo6Se8(CN)4(CN)2/2] (MI = K, Cs) were prepared from reactions of Mo6Se8 or elemental starting materials, Mo and Se with excess molten cyanide (KCN, CsCN). These are the first known compounds to feature linking of Mo6Se8 clusters via cyanide bridges. Magnetic susceptibility and EPR measurements indicate that there is one unpaired electron per cluster. A new reduced molecular octahedral complex, Na8[Mo6Se8(CN)6]•20H2O was prepared by the reduction of [Mo6Se8(CN)6]7-with Zn in an aqueous NaCN solution. Single crystal structure was determined. Cyclic voltammetric measurements in basic aqueous media show multiple reversible redox waves corresponding to [Mo6Se8(CN)6]6-/7-, [Mo6Se8(CN)6]7-/8-, [Mo6Se8(CN)6]8-/9-redox couples with half-wave potentials of E1/2 = -0.442 V, -0.876 V, and 11.369 V respectively versus the standard hydrogen electrode (SHE). UV-Vis studies support the presence of the reduced cluster compound. New reduced molecular tetrahedral complexes, K7Na[Mo4Se4(CN)12]•5H2O•MeOH, Na4Cs7[Mo4Se4(CN)12]Cl3, Na8[Mo4Se4(CN)12], and Na4K4[Mo4Se4(CN)12]•12H2O were prepared. Preparation of Na8[Mo4Se4(CN)12] is an improved method for the synthesis of the Mo4Se4 core. Half-wave potentials of E1/2 for the [Mo4Se4(CN)12]6-/7-and [Mo4Se4(CN)12]7-/8-couples are 0.233 V, and -0.422 V respectively versus SHE. The molecular cubane clusters [Mo4Se4(CN)12]7-/8-play an essential role in the process by which the discrete [Mo6Se8(CN)6]6-and [Mo6Se8(CN)6]are excised from the CN-linked chain compound, K6Mo6Se8(CN)5. A new rare-earth telluride compound with the empirical composition of Gd4NiTe2 was synthesized from a high-temperature solid-state reaction. Gd4MTe2 (M = Ni) crystallizes in the orthorhombic space group Pnma. This unprecedented structure consists of a cluster condensation of Ni-centered gadolinium tricapped trigonal prisms along the rectangular faces of the trigonal prism such that the Ni atoms act as two of the caps to the trigonal prisms.

No description available.

The planting of native species is a common strategy for the conservation of biodiversity; it not only allows for the restoration of degraded habitat both within conservation reserves and the matrix lands between reserves, it supplements the populations of the floral species which are planted. These supplemental populations may play an important role in providing demographic security for rare species. However, the conservation of rare species depends on more than simply maintaining adequate numbers of the species: the diversity within the species must also be conserved. Although maintaining genetic diversity is increasingly a concern for formal species recovery efforts, there has been very little research done about the diversity within plantings by non-state actors. This research was undertaken to address this knowledge gap by studying the provenances of planted rare species and the activities of those who collect and grow these plants. This research was undertaken in the Carolinian zone of southern Ontario, a region with a large number of rare plant species and a large human population. Part of this study utilized semi-structured interviews with commercial seed collectors, commercial native plant growers, and non-commercial, hobbyist growers. A variety of factors limited the diversity with the seeds collected by commercial collectors. Due to difficulty in accessing information about the natural occurrences of rare species, collectors typically collected from the same, limited number of source plants. Trespassing on private property or protected lands was common to access these seed sources, although their preference for easily accessible, reliably fecund source plants on flat, mowed sites also meant that horticultural specimens were also desired. Many of these biases were passed on to commercial growers when the seed was sold by the commercial collectors. Commercial growers shared many collection practices with commercial collectors, creating similar restrictions on the diversity within their collections. However, further limitations in diversity were also created by the growers’ establishment of small populations of seed plants and by the trading of seeds and plants between growers. One boutique grower was a dominant source of seeds and plants in these trades. The limitations in the diversity within these rare species were passed onto those who purchased and planted them. This study also focused on enthusiastic native plant hobbyists and found that they not only purchased plants but collected and grew their own plants. They also traded with other hobbyists. Much of the information about where to collect seed or plants, as well as much of the seed or plants traded between hobbyists, originated with a key individual. Thus, this champion hobbyist plays a significant role in the character of planted examples of rare plant species and the genetics of the champion’s plants are heavily represented with other planted occurrences. The practices of commercial seed collectors, growers and native plant hobbyists create biases which limit the diversity within plantings of rare species. Although these plantings provide demographic security for these species, they do not represent the diversity within their remnant “wild” populations. Thus, important questions must be raised about the conservation value of these plantings. Since many of the practices of seed collectors and growers are also used when growing more common species, the diversity within plantings of these species should also be suspect. Although the lack of diversity within common species may not threaten the regional survival of the species in the short term, it may impact the ultimate success of restoration projects.

No description available.

Two sets of nanostructured Zinc Oxide (ZnO) thin films doped with varying nominal concentrations of rare earth (RE) ions were prepared by pulsed laser deposition (PLD). One set was doped with europium ions (ZnO:Eu³⁺) while the other was doped with erbium ions (ZnO:Er³⁺). The nominal concentration of RE ions ranged from 0.025 to 5 atomic %. The produced films were structurally, morphologically and optically characterised using different techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL), combined excitation and emission spectroscopy (CEES) and X-ray photoelectron spectroscopy (XPS). All films were found to possess a single-crystal hexagonal structure and were strongly oriented along the c-axis. However, the crystallinity of the investigated films seemed to deteriorate as the concentration of the rare earth ions increased. This deterioration is assumed to be due to the local distortion of the ZnO structure (host material) caused by the insertion of the relatively large RE ions, hence inducing structural stresses. Importantly, XRD measurements showed that no other crystalline phases related to europium or erbium, such as Eu₂O₃ or Er₂O₃, were observed. Surprisingly, the ZnO lattice constant (c) tended to become smaller as more RE³⁺ ions were added to the films. An explanation is offered whereby this observation can be taken as further evidence that Zn²⁺ ions were successfully substituted by RE³⁺ ions. Interestingly, doping ZnO films with RE³⁺ ions of a nominal concentration of ≥ 0.5 at.% or higher exhibited a drastic effect on the optical properties of the host matrix (ZnO) in which the near band edge luminescence characteristic of pure ZnO completely disappeared. According to SEM images, morphological changes also occur as dopant concentrations increase. Well-defined grains (crystallites) were clearly seen in films doped with ˂ 0.5 at.% of RE ions. However, these grains became hardly distinguishable at higher RE ion concentrations. Typical intra-4f shell transitions of RE³⁺ ions were observed when these ions were non-resonantly excited with UV radiation, indicating that energy had been efficiently transferred from ZnO to the rare earth ions. A plausible physical mechanism for this energy transfer is proposed. The radiative optical centres of rare earth ions were studied by CEES. In these experiments, both sets of films exhibited multiple optical sites. ZnO:Eu³⁺ thin films were found to have two distinct optical sites with differing site symmetries, whereas up to four optical sites were detected in the ZnO:Er³⁺ films.

Retinoic acid (RA) has been recognized as a chemotherapeutic agent for various malignances such as lung, skin as well as cervical cancers. It binds to retinoid receptors heterodimers and consequently activates several RA-responsive genes which are involved in many biological processes including vertebrate development, bone growth, vision, haematopoiesis, cell growth, differentiation and apoptosis. These genes are under the control of numerous regulators to ensure their timely ordered activities. Among these regulators, we focused here on the 26S proteasome and ubiquitination. It has been reported that the activity of the ubiquitin/proteasome system (UPS) plays a fundamental role in retinoic acid receptor (RAR)-regulated transactivation. The mechanisms underlying this role, however, remain to be established. Chromatin immunoprecipitation (ChIP) assays in our study demonstrated that the 26S proteasome activity is important for preserving the occupancy of a TATA box-containing RA-responsive promoters by liganded retinoid receptors and thus by their coactivators. Additionally, by using coimmunoprecipitation assays and by measuring the half-life of retinoid receptors, we found that the non-proteolytic function of the proteasome is required for ligand-dependent association between DNA-free RAR-α and both DNA-free RXR-α and coactivators. Moreover, using immunofluorescent staining and in vivo ubiquitination assays, a proteasome inhibition-dependent cytoplasmic localization of RAR-α as well as ligand-enhanced ubiquitination and stabilization of RAR-α were shown. Our findings therefore, define novel mechanisms by which the UPS controls RAR-regulated genes. Furthermore, we shed new light on the regulators of retinoid receptors ubiquitination and subcellular localization.

The synthesis of yttrium phenalenide complexes 129-132 was achieved by salt metathesis reactions between ligand anions and YCI3. Ytterbium phenalenide complexes 133-137 were synthesized by protonolysis reactions between neutral ligands and Yb[N(SiMe3)2]2(THF)2. The solid state structure of (Pni1Bu)2Yb(THF) 136 reveals a unique n3 bonding pattern, however the electrons of the phenalenide ligand remain delocalized even when bonded to the metal center. Mono-alkyl complexes (PCpR)2Y(CH2SiMe3)(THFSiMe3)(THF) 147-149 (R = Me. Ph. H) and bis-alkyl complexes (PCp*)Y(CH2SiMe3)2(THF) 150 and (sCp)Y(CH2SiMe3)2(THF) 152 were synthesized by direct protonolysis reactions between Y(CH2SiMe3)3(THF)2 and neutral ligands. When treated with phenylsilane, complex 148 generated the crowded hydride dimer [(PCpPh)2Y(u-H)]2 161. Complexes 150 and 152 undergo acid-base. metallation. insertion reactions and polymerization of small substrates. A variable temperature `H NMR study of 150 and 152 at low temperature reveals an equilibrium between 150/152-THF and 1501152. The THF-free complexes. 150/152-THF. appear to undergo inversion of a pyramidal ground state structure to generate a C2 symmetric intermediate. The X-ray structures of 136, 147, 150. 152, (sCp)Y(CH2SiMe3)2(bipy) 154, 161. [PCp*Y(CCSiMe3)(THF)]2(u2-CCSiMe3)2] 167, acetylide cluster 169 and bis-(Me3Si)2Cp yttrium chloride dimer 176 were determined and structural features discussed.

The cross-entropy method is an established technique for solving difficult estimation, simulation, and optimisation problems. The method has its origins in an adaptive importance sampling procedure for rare-event estimation published by R. Y. Rubinstein in 1997. In that publication, the adaptive procedure produces a parametric probability density function whose parameters minimise the variance of the associated likelihood ratio estimator. This variance minimisation can also be viewed as minimising a measure of divergence to the minimum-variance importance sampling density over all members of the parametric family in question. Soon thereafter it was realised that the same adaptive importance sampling procedure could be used to solve combinatorial optimisation problems by viewing the set of solutions to the optimisation problem as a rare-event. This realisation led to the debut of the cross-entropy method in 1999, where it was introduced as a modification to the existing adaptive importance sampling procedure, with a different choice of directed divergence measure, in particular, the Kullback-Leibler cross-entropy. The contributions of this thesis are threefold. Firstly, in a review capacity, it provides an up-to-date consolidation of material on the cross-entropy method and its generalisations, as well as a collation of background material on importance sampling and Monte Carlo methods. The reviews are elucidated with original commentary and examples. Secondly, two new major applications of the cross-entropy methodology to optimisation problems are presented, advancing the boundary of knowledge on cross-entropy in the applied arena. Thirdly, two contributions to the methodological front are (a) an original extension of the generalised cross-entropy framework which enables one to construct state- and time-dependent importance sampling algorithms, and (b) a new algorithm for counting solutions to difficult binary-encoded problems.

Bibliography: leaves 111-116 / xi, 170 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, 1984

The cross-entropy method is an established technique for solving difficult estimation, simulation, and optimisation problems. The method has its origins in an adaptive importance sampling procedure for rare-event estimation published by R. Y. Rubinstein in 1997. In that publication, the adaptive procedure produces a parametric probability density function whose parameters minimise the variance of the associated likelihood ratio estimator. This variance minimisation can also be viewed as minimising a measure of divergence to the minimum-variance importance sampling density over all members of the parametric family in question. Soon thereafter it was realised that the same adaptive importance sampling procedure could be used to solve combinatorial optimisation problems by viewing the set of solutions to the optimisation problem as a rare-event. This realisation led to the debut of the cross-entropy method in 1999, where it was introduced as a modification to the existing adaptive importance sampling procedure, with a different choice of directed divergence measure, in particular, the Kullback-Leibler cross-entropy. The contributions of this thesis are threefold. Firstly, in a review capacity, it provides an up-to-date consolidation of material on the cross-entropy method and its generalisations, as well as a collation of background material on importance sampling and Monte Carlo methods. The reviews are elucidated with original commentary and examples. Secondly, two new major applications of the cross-entropy methodology to optimisation problems are presented, advancing the boundary of knowledge on cross-entropy in the applied arena. Thirdly, two contributions to the methodological front are (a) an original extension of the generalised cross-entropy framework which enables one to construct state- and time-dependent importance sampling algorithms, and (b) a new algorithm for counting solutions to difficult binary-encoded problems.