Functionalization, growth and applications of single wall carbon nanotubes

Because of their remarkable structural, mechanical and electrical properties, carbon nanotubes, and especially single wall carbon nanotubes (SWNTs), represent one of the most widely investigated materials today in the emerging field of nanotechnology. The development of oriented growth of SWNTs critical for applications, novel approaches for the creation of functional SWNTs, and applications of both as-prepared and chemically functionalized SWNTs for electrochemically-induced hydrogen storage, in-situ formation of new polymer and ceramic nanocomposites with SWNTs, and the fabrication and study for the first time, to the best of our knowledge, of a SWNT-based biofuel cell and self-powered biosensor, are the thrusts of the research discussed in this thesis. Introduction to the science and the potential applications of carbon nanotubes are presented in Chapters 1 to 2 of the thesis, and an overview of the methods used in this work is discussed in Chapter 3. Chapters 4 to 6 discuss the results of the work performed. Spin-coating deposition of a polymer-chelated catalyst precursor on conductive silicon wafers developed for the oriented growth of SWNTs, is discussed in Chapter 4. Oriented growth of SWNTs was obtained using chemical vapor deposition with alcohol as the carbon source. For application in biofuel cells and biosensors (discussed in the final segment), the oriented SWNTs on silicon were functionalized with selected redox enzymes to form the fuel cell and sensor electrodes. In initial tests, a substantial open circuit cell voltage of 200 mV, and analyte-sensitive direct electron transfer, were observed from the fabricated biofuel cell and biosensor devices, respectively. Environmentally friendly, rapid and efficient microwave-induced chemical functionalization of SWNTs was achieved for the first time in the course of this work and is described in Chapter 5 of the thesis. The microwave radiation assisted technique has brought down the functionalization time from days using typical chemical methods, such as refluxing, to the order of minutes. Chemical functionalizations by the microwave method achieved include amidation, 1 ,3-dipolar cycloaddition and nitration, with the latter providing SWNTs that are very soluble in water and alcohol. Both microwave-induced and supercritical carbon dioxide approaches were also used to prepare and study the formation of ceramic (silicon carbide, SiC) and polymer (polymethyl methacrylate, PMMA) nanocomposites with SWNTs, respectively. Electrochemically-induced functionalization of SWNTs by nitro groups and enzymes has been studied in some detail, whereas electrochemical hydrogen storage for fuel cell operation using pristine and functionalized SWNTs as the storage medium has also been studied in this work and discussed in Chapter 6 of this thesis. Strong evidence for electrochemically-induced hydrogen uptake approaching 3 wt % based on thermogravimetric measurements has been obtained on SWNT nanopaper membranes on which the nitrogen-containing conducting polymer, polyaniline, was deposited. A summary of the work performed and suggestions for future work are provided in Chapter 7. The schematic molecular structures of the more complex molecules, polymers and enzymes used in this work (except those shown in the tables) are shown schematically in Appendix A

Probabilistic assessments of the seismic stability of slopes : improvements to site-specific and regional analyses

textEarthquake-induced landslides are a significant seismic hazard that can generate large economic losses. Predicting earthquake-induced landslides often involves an assessment of the expected sliding displacement induced by the ground shaking. A deterministic approach is commonly used for this purpose. This approach predicts sliding displacements using the expected ground shaking and the best-estimate slope properties (i.e., soil shear strengths, ground water conditions and thicknesses of sliding blocks), and does not consider the aleatory variability in predictions of ground shaking or sliding displacements or the epistemic uncertainties in the slope properties. In this dissertation, a probabilistic framework for predicting the sliding displacement of flexible sliding masses during earthquakes is developed. This framework computes a displacement hazard curve using: (1) a ground motion hazard curve from a probabilistic seismic hazard analysis, (2) a model for predicting the dynamic response of the sliding mass, (3) a model for predicting the sliding response of the sliding mass, and (4) a logic tree that incorporates the uncertainties in the various input parameters. The developed probabilistic framework for flexible sliding masses is applied to a slope at a site in California. The results of this analysis show that the displacements predicted by the probabilistic approach are larger than the deterministic approach due to the influence of the uncertainties in the slope properties. Reducing these uncertainties can reduce the predicted displacements. Regional maps of seismic landslide potential are used in land-use planning and to identify zones that require detailed, site-specific studies. Current seismic landslide hazard mapping efforts typically utilize deterministic approaches to estimate rigid sliding block displacements and identify potential slope failures. A probabilistic framework that uses displacement hazard curves and logic-tree analysis is developed for regional seismic landslide mapping efforts. A computationally efficient approach is developed that allows the logic-tree approach to be applied for regional analysis. Anchorage, Alaska is used as a study area to apply the developed approach. With aleatory variability and epistemic uncertainties considered, the probabilistic map shows that the area of high/very high hazard of seismic landslides increases by a factor of 3 compared with a deterministic map.Civil, Architectural, and Environmental Engineerin

Sequential emitter identification method based on D-S evidence theory

This paper proposes a novel sequential identification method for enhancing the anti-jamming performance and for accurate recognition rate of the emitters’ individual identification in the complicated environment. The proposed method integrates the D-S evidence theory and features extraction that can get the utmost out of features of information systems and decrease the influence of uncertain factors in the signal processing. Firstly, selected features are extracted from intercepted signals. Then, the proposed self-adaptive fusing rule based on the decision vector is utilized to fuse the evidences that are transformed by features and the previous fusing information. Finally, recognition results can be obtained by judgment rules. The simulation analysis demonstrates that self-adaptive fusing rule can achieve a great balance between computational efficiency and accurate identifying rate. While comparing with other identifying methods, the proposed sequential identifying method can provide more accurate and stable recognition results, which makes the utmost care and use of existing information

Form factors of Ω−\Omega^- in a covariant quark-diquark approach

The electromagnetic and gravitational form factors of $\Omega^-$, a spin-3/2 hyperon composed of three $s$ quarks, are calculated by using a covariant quark-diquark approach. The model parameters are determined by fitting to the form factors of the lattice QCD calculations. Our obtained electromagnetic radii, magnetic moment, and electric-quadrupole moment are in agreement with the experimental measurements and some other model calculations. Furthermore, the mass and spin distributions of $\Omega^-$ from the gravitational form factors are also displayed. It is found that the mass radius is smaller than its electromagnetic ones. Finally, the interpretations of the energy density and momentum current distribution are also discussed

Form factors of decuplet baryons in a covariant quark-diquark approach

The electromagnetic and gravitational form factors of decuplet baryons are systematically studied with a covariant quark-diquark approach. The model parameters are firstly discussed and determined through comparison with the lattice calculation results integrally. Then, the electromagnetic properties of the systems including electromagnetic radii, magnetic moments, and electric-quadrupole moments are calculated. The obtained results are in agreement with experimental measurements and the results of other models. Finally, the gravitational form factors and the mechanical properties of the decuplet baryons, such as mass radii, energy densities, and spin distributions, are also calculated and discussed.Comment: 19 pages, 27 figure