Enhancement of the Properties of Polymer by using Carbon Nanotubes

The outstanding properties of carbon nanotubes (CNTs) have stimulated a large number of researches to explore the potential of using them as reinforcement in polymer composites. Although many studies have reported the enlighten improvement of the materials properties by using CNTs as reinforcement, there are no promising and optimal results have been concluded to date. This thesis aims at studying the mechanical properties on thermoset polymer, Epoxy, by employing a small amount of carbon nanotubes as reinforcement. Two different types of nanotube-based composites are prepared i.e. a raw single-walled carbon nanotube (SWNT) composites and a functionalized single-walled carbon nanotube (FSWNT) composite. Chemical functionalization on SWNTs with carboxyl functional group (COOH) aims at modifying the end caps of nanotubes, so to provide covalent bonding of SWNTs to the polymer matrix during manufacturing of composite systems. Different weight percentages (wt %) of each type of SWNTs are added into the composite system. Standard test methods are performed on these nanotube composite systems and satisfactory results were achieved when the weight percentages of both types of SWNTs increased. Through the comparison between two systems (raw SWNTs and FSWNTs), the FSWNT reinforced composite is found to provide a better improvement on the mechanical properties as compared with the SWNT reinforced system. The integrity of both composite systems is examined by using Scanning Electronic Microscopy (SEM). The SEM images of the composites indicated the derivation in wetting and bonding between the nanotubes (both SWNTs and FSWNTs) and epoxy resin, and the FSWNTs provide an eminent dispersion when compared with the SWNTs in the composite system. Moreover, thermal testings are employed to further investigate the interfacial interaction between the nanotubes and the polymer matrix. xiv Molecular Dynamics (MD) simulations are also carried out to investigate the structural change of a SWNT under different temperature-controlled manufacturing environments. Swivel of the SWNT was noticed as the temperature increased. Such alteration in structure form can provide physical interlocking between SWNT and its surrounding polymer system. Thus, its overall mechanical and thermal properties can be enhanced

On Inter-referential Awareness in Collaborative Augmented Reality

For successful collaboration to occur, a workspace must support inter-referential awareness - or the ability for one participant to refer to a set of artifacts in the environment, and for that reference to be correctly interpreted by others. While referring to objects in our everyday environment is a straight-forward task, the non-tangible nature of digital artifacts presents us with new interaction challenges. Augmented reality (AR) is inextricably linked to the physical world, and it is natural to believe that the re-integration of physical artifacts into the workspace makes referencing tasks easier; however, we find that these environments combine the referencing challenges from several computing disciplines, which compound across scenarios. This dissertation presents our studies of this form of awareness in collaborative AR environments. It stems from our research in developing mixed reality environments for molecular modeling, where we explored spatial and multi-modal referencing techniques. To encapsulate the myriad of factors found in collaborative AR, we present a generic, theoretical framework and apply it to analyze this domain. Because referencing is a very human-centric activity, we present the results of an exploratory study which examines the behaviors of participants and how they generate references to physical and virtual content in co-located and remote scenarios; we found that participants refer to content using physical and virtual techniques, and that shared video is highly effective in disambiguating references in remote environments. By implementing user feedback from this study, a follow-up study explores how the environment can passively support referencing, where we discovered the role that virtual referencing plays during collaboration. A third study was conducted in order to better understand the effectiveness of giving and interpreting references using a virtual pointer; the results suggest the need for participants to be parallel with the arrow vector (strengthening the argument for shared viewpoints), as well as the importance of shadows in non-stereoscopic environments. Our contributions include a framework for analyzing the domain of inter-referential awareness, the development of novel referencing techniques, the presentation and analysis of our findings from multiple user studies, and a set of guidelines to help designers support this form of awareness

Determining The Site Specific Metal Binding and Structural Properties of EF-Hand Protein Using Grafting Approach

Calmodulin is an essential EF-hand protein with a helix-loop-helix calcium binding motif. Understanding Ca(II) dependent activation of calmodulin and other EF-hand proteins is limited by Ca(II)-induced conformational change, multiple and cooperative binding of Ca(II) ions, and interactions between the paired EF-hand motifs. The goal of this research project is to probe key determinants for calcium binding properties and pairing interactions at the site specific level using a grafting approach and high resolution NMR. An individual Ca(II) binding site of the EF-hand motifs of calmodulin was grafted into a non-calcium dependent protein, CD2, to bypass limitations associated with natural EF-hand proteins and peptide fragments. Using high resolution NMR, we have shown that the grafted EF-loop III of calmodulin in the host protein retains its native conformation with a strong loop and β-conformation preference. Grafted ligand residues in the engineered protein are directly involved in binding of Ca(II) and La(III). The NMR studies support our hypothesis that both ligand arrangement and dynamic properties play essential role in tuning Ca(II) binding affinities. Using pulse-field diffusion NMR and protein engineering, we further demonstrated that grafted EF- loop remains as a monomer. Although the EF-loop with flanking helices dimerizes in the presence of Ca(II). Additionally, removal of conserved hydrophobic residues at the flanking helices of the EF-hand motif leads to be monomer in the absence and presence of metal ions. Our results suggest that conserved hydrophobic residues are essential for the pair-paired interaction in the coupled EF-hand protein. We have shown that our developed grafting approach can be applied to probe intrinsic Ca(II) binding affinities of different Ca(II) binding sites

The identification of natural inhibitory compounds against the plasmodium GTP Cyclohydrolase I (GCH1) enzyme

Malaria is a disease caused by protozoan parasites that invade red blood cells causing an infection. Malaria remains a global health problem. The genus Plasmodium infects about a quarter of a billion people annually, resulting in over a million death cases. This can severely affect the public health and socioeconomic development especially in countries with limited resources. Malaria is transmitted by the female Anopheles mosquito. Five species within the Plasmodium genus are known to cause infection in humans; namely Plasmodium falciparum, Plasmodium Ovale, Plasmodium knowlesi, Plasmodium vivax and Plasmodium malariae. The increased resistance by the parasite to the majority of available anti-malarial drugs has raised a great challenge in anti-malarial drug discovery. With the problem of drug resistance on the rise, the need to develop new anti-malarial treatment strategies and identification of alternative metabolic targets for the treatment of malaria is crucial. This study is focused on the Guanosine triphosphate CycloHydrolase I (GCH1) enzyme as a potential drug target. GCH1 is important for the survival of malaria parasites as shown by failed attempts to generate knockout lines in plasmodium falciparum. In this study, sequence and evolutionary analysis were carried out in both the human host and parasite GCH1 enzyme. Accurate 3D models of the parasite GCH1 were built and validated. The resulting models were used for high throughput screening against 623 compounds from the South African Natural Compounds Database (SANCDB; https://sancdb.rubi.ru.ac.za/). The high throughput screening was done to identify possible binding sites as well as hit compounds with high selectivity and binding affinity towards the parasite enzyme, this is followed by molecular dynamics simulations to identify protein-ligand complexes and analyze their stability. In this study, a total of five SANCDB compounds were identified as potential inhibitors: SANC00317, SANC00335, SANC00368, SANC00106, SANC00103 and SANC00286. It was found that GCH1 protein can be a potential anti-malarial drug target as it showed selective binding with the inhibitor compounds. The identified inhibitors showed good selectivity and lower free energy of binding towards the parasite GCH1. Force field parameters of GCH1 active site metal were derived and validated. The development of these force field parameters was important for accurate MD simulations of the protein active site; which will allow for future investigation of interactions and stability of the GCH1 protein-ligand complexes