Placer gold is frequently reported to assay at overall higher values of fineness than the gold in the rock from which it was liberated. A related phenomenon is the historical discovery of many extremely large gold nuggets (up to 28 lbs) in the southeastern United States that have no apparent source rock. Placer gold grains from the southeastem United States have been examined and found to frequently exhibit the development of nearly pure to pure gold rims around their borders. These gold rims are suggested as a possible cause of the high fineness placer deposits. Formation of very thick rims may also be the cause of the large nuggets. Formation of these gold-enriched rims by the often attributed mechanism of simple silver leaching is disputed on the basis of ineffective mechanisms for the removal of silver from the alloy. Diffusion of silver through the gold at low temperatures proceeds far too slowly to produce the chemical gradients observed in the placer gold grains. Comparison of the complexation capacities of 41 ligands with subsequent modelling of expected complex concentrations in natural stream and stream sediment waters indicates CN⁻ and S² as the most likely functional ligands for the transport and redeposition of supergene gold. Electrolytic refining of placer Au-Ag grains is also a process for forming gold-enriched rims that can operate together with secondary enrichment to produce the observed phenomena. / Master of Science

This thesis addresses the synthesis of a new mix-metal trimetallic nitride template endohedral metallofullerene (TNT-EMF) and the functionalizations of M3N@C80 (M = Sc, Gd, Ho) under the high-speed vibration milling (HSVM) condition. In addition, this thesis discusses the internal motion of the cluster, Sc3N inside three different carbon cages, C68, C78 and C80. Water-soluble derivatives of endohedral metallofullerenes possess a unique potential for medical applications, such as magnetic resonance imaging (MRI) contrast agents, X-ray contrast agents and nuclear medicine. The TNT-EMFs have inherent advantages over other endohedral metallofullerenes, such as M@C60 and M@C82, due to the encapsulation of up to three metal atoms inside the carbon cages. M3N@C80(OH)m(O)n (M = Sc, Gd, Ho) were synthesized under the HSVM condition and characterized by FT-IR, MALDI-TOF and XPS. The relaxivity studies on these water-soluble derivatives have shown that Gd-based metallofullerols have significantly higher relaxivities than commercially used MRI contrast agents (e.g. OmniscanTM) and can be the next generation MRI contrast agent. The Ho containing species has a high R2/R1 ratio compared to other samples showing the potential to be a T2 agent. In contrast to homonuclear M3N clusters, there is a paucity of mixed-metal cluster cases of TNT-EMFs reported to date because the mixed-metal metallofullerenes are difficult to be separated and purified. In this thesis, CeSc2N@C80 was synthesized, separated in pure form and fully characterized. Single-crystal X-ray diffraction shows that CeSc2N@C80 consists of a four atom asymmetric top (CeSc2N) inside a C80 (Ih ) carbon cage and the nitride ion is not located at the center of the carbon cage but is offset by 0.36 Å. The NMR studies, together with the XPS results, show that CeSc2N@C80 is a weakly paramagnetic system with a single buried f electron spin. A new cage isomer of the Sc3N@C80 (D5h) metallofullerene was also isolated from the Ce-Sc mixture and the cage symmetry was confirmed by single-crystal X-ray diffraction. The internal motion of the metal-nitride cluster, Sc3N within the carbon cages (C68, C78 and C80) was studied at various temperatures using 45Sc NMR spectroscopy. The reorientation barriers (presumably dominated by motion internal to the cage) were calculated for these three TNT-EMFs. The preliminary results show that the quadrupole coupling constant of Sc3N@C80 (Ih) is quite close to that of Sc3N@C68. / Master of Science

The servosystems which drive a milling table must be capable of asymptotic tracking and disturbance rejection, and must be robust. The internal model principle is a general method developed by Davison, Desoer and Wonham which achieves asymptotic tracking and disturbance rejection, and is robust. In this thesis, a state-variable control system for the positioning of a milling table is designed by using the internal model principle. The control system is simulated as both a continuous-time system and as a discrete-time system. Results of the simulation indicate that a microprocessor-driven version of the state-variable discrete-time control system is a feasible and practical method of control. / M.S.

Placer ore minerals are commonly intergrown with "relict" phases that coexisted with the ore mineral in the original lode deposit. Studying these relict phases can yield important information about the nature, and formation of the lode deposit. This type of study can be useful in areas with poor exposure, areas that are remote, or areas where discretion is important. Analysis of the heavy mineral suite of stream sediments from the Brush Creek area shows no correlation between the heavy minerals and the gold. However, analysis of the relict phases intergrown with the gold grains yields important results. Placer gold grains recovered from streams draining the Brush Creek deposit, in southwestern Virginia, contain relict quartz, orthoclase, ilmenite and mica. Textures, and fluid inclusion composition and character in the relict quartz, indicate that the gold mineralization post dated the mylonitization associated with the Fries ductile deformation zone, which hosts the gold mineralization. The relict orthoclase is interpreted to be adularia, which is common in low-temperature, hydrothermal environments. The intergrowth textures of the gold and ilmenite show that the ilmenite was present in the country rocks prior to gold mineralization, and was not, therefore, cogenetic with the gold. The relict mica was not positively identified, but is believed to be chlorite, which is consistent with the proposed low temperature mineralization. The textures of the relict phases indicate that gold mineralization occurs in late, brittle fractures, with little or no significant alteration. The study of the relict phases intergrown with the alluvial gold grains has yielded information that otherwise could only have been obtained by more advanced, but also much more expensive, exploration techniques. / Master of Science

The main interest of this thesis consists of the study and implementation of postprocessors to adapt the toolpath generated by a Computer Aided Manufacturing (CAM) system to a complex robotic workcell of eight joints, devoted to the rapid prototyping of 3D CAD-defined products. It consists of a 6R industrial manipulator mounted on a linear track and synchronized with a rotary table. To accomplish this main objective, previous work is required. Each task carried out entails a methodology, objective and partial results that complement each other, namely: - It is described the architecture of the workcell in depth, at both displacement and joint-rate levels, for both direct and inverse resolutions. The conditioning of the Jacobian matrix is described as kinetostatic performance index to evaluate the vicinity to singular postures. These ones are analysed from a geometric point of view. - Prior to any machining, the additional external joints require a calibration done in situ, usually in an industrial environment. A novel Non-contact Planar Constraint Calibration method is developed to estimate the external joints configuration parameters by means of a laser displacement sensor. - A first control is originally done by means of a fuzzy inference engine at the displacement level, which is integrated within the postprocessor of the CAM software. - Several Redundancy Resolution Schemes (RRS) at the joint-rate level are compared for the configuration of the postprocessor, dealing not only with the additional joints (intrinsic redundancy) but also with the redundancy due to the symmetry on the milling tool (functional redundancy). - The use of these schemes is optimized by adjusting two performance criterion vectors related to both singularity avoidance and maintenance of a preferred reference posture, as secondary tasks to be done during the path tracking. Two innovative fuzzy inference engines actively adjust the weight of each joint in these tasks. / Andrés De La Esperanza, FJ. (2011). Postprocesamiento CAM-ROBOTICA orientado al prototipado y mecanizado en células robotizadas complejas [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/10627

Yes / Natural rubber (NR) and crosslinked polyethylene (XLPE) waste streams were devulcanized by solid state shear milling (S3M), producing a fine powder that may be more easily reprocessed. Understanding devulcanization and the nature of decrosslinked thermoset materials is of utmost importance for turning these waste steams into functional products. It was found that the devulcanized powders contained significant concentrations of radicals, which may be active in the subsequent revulcanization process. The produced devulcanized powders were converted into recyclable thermoplastic vulcanizates (TPVs) by twin screw extrusion. Reprocessing of these powders into value-added products is an important step in recycling and the use of extrusion allows for high throughput and industrial viability. Herein, we demonstrate that the optimal conditions for reprocessing are dependent upon the particle size of the devulcanized powder. Furthermore, dynamic vulcanization is affected by the nature of these recyclate powders. The successfully prepared TPVs showed similar properties to virgin materials, with a high elongation to failure. Therefore, the conversion of waste rubber into the rubber phase of a TPV shows significant promise in moving towards sustainable products, providing the revulcanization step can be well controlled. / EPSRC and NSFC for their funding of this work through the Joint UK-China Low Carbon Manufacturing Grant, Grant number EP/S018573/1.

Yes / Artemether (ARTM) is a very effective antimalarial drug with poor solubility and consequently low bioavailability. Smart nanocrystals of ARTM with particle size of 161±1.5 nm and polydispersity index of 0.172±0.01 were produced in <1 hour using a wet milling technology, Dena® DM-100. The crystallinity of the processed ARTM was confirmed using differential scanning calorimetry and powder X-ray diffraction. The saturation solubility of the ARTM nanocrystals was substantially increased to 900 µg/mL compared to the raw ARTM in water (145.0±2.3 µg/mL) and stabilizer solution (300.0±2.0 µg/mL). The physical stability studies conducted for 90 days demonstrated that nanocrystals stored at 2°C-8°C and 25°C were very stable compared to the samples stored at 40°C. The nanocrystals were also shown to be stable when processed at acidic pH (2.0). The solubility and dissolution rate of ARTM nanocrystals were significantly increased (P<0.05) compared to those of its bulk powder form. The results of in vitro studies showed significant antimalarial effect (P<0.05) against Plasmodium falciparum and Plasmodium vivax. The IC50 (median lethal oral dose) value of ARTM nanocrystals was 28- and 54-fold lower than the IC50 value of unprocessed drug and 13- and 21-fold lower than the IC50 value of the marketed tablets, respectively. In addition, ARTM nanocrystals at the same dose (2 mg/kg) showed significantly (P<0.05) higher reduction in percent parasitemia (89%) against P. vivax compared to the unprocessed (27%), marketed tablets (45%), and microsuspension (60%). The acute toxicity study demonstrated that the LD50 value of ARTM nanocrystals is between 1,500 mg/kg and 2,000 mg/kg when given orally. This study demonstrated that the wet milling technology (Dena® DM-100) can produce smart nanocrystals of ARTM with enhanced antimalarial activities.

Yes / Polymorphism of crystalline drugs is a common phenomenon. However, the number of reported polymorphic cocrystals is very limited. In this work, the synthesis and solid state characterisation of a polymorphic cocrystal composed of sulfadimidine (SD) and 4- aminosalicylic acid (4-ASA) is reported for the first time. By liquid-assisted milling, the SD:4-ASA 1:1 form I cocrystal, the structure of which has been previously reported, was formed. By spray drying, a new polymorphic form (form II) of the SD:4-ASA 1:1 cocrystal was discovered which could also be obtained by solvent evaporation from ethanol and acetone. Structure determination of the form II cocrystal was calculated using high resolution X-ray powder diffraction. The solubility of the SD:4-ASA 1:1 cocrystal was dependent on the pH and predicted by a model established for a two amphoteric component cocrystal. The form I cocrystal was found to be thermodynamically more stable in aqueous solution than form II, which showed transformation to form I. Dissolution studies revealed that the dissolution rate of SD from both cocrystals was enhanced when compared to a physical equimolar mixture and pure SD. / Science Foundation Ireland (SFI) under Grant Number 07/SRC/B1158 and SFI/12/RC/2275.

No / Mechanochemical chemoenzymatic peptide and amide bond formation catalysed by papain was studied by ball milling. Despite the high-energy mixing experienced inside the ball mill, the biocatalyst proved stable and highly efficient to catalyse the formation of α,α- and α,β-dipeptides. This strategy was further extended to the enzymatic acylation of amines by milling, and to the mechanosynthesis of a derivative of the valuable dipeptide L-alanyl-L-glutamine. / We thank RWTH Aachen University for support from the Distinguished Professorship Program funded by the Excellence Initiative of the German federal and state governments. EPSRC, grant no. EP/L019655/1.

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