Structure and properties of metal nanoparticles on carbon nanostructures

The work presented in the thesis describes the preparation and characterisation of nanoparticle-carbon nanotube composite structures by transmission electron microscopy (TEM) and their applications in catalysis and biomedicine. Identical location TEM (IL-TEM) was utilised for the first time to study the nanoscale structure of composites of catalytic metallic nanoparticles and hollow carbon nanotubes in macroscale, liquid-phase, preparative reactions. IL-TEM analysis of palladium nanoparticles confined within graphitised nanofibres (GNF) indicated that the catalytic nanoparticles undergo changes in mean size and size-dependent migrations within the internal channel of GNF under the conditions of Suzuki-Miyaura reactions. IL-TEM analysis of copper nanoparticles in GNF showed dissolution and reprecipitation of the nanoparticles into strand-like nanostructures under the conditions of the “click” reaction, indicating the pseudo-homogeneous mechanism of this catalysed chemical transformation. A series of metal nanoparticle-GNF catalysts were subject to a range of elevated temperatures and gaseous environments and the corresponding structure-function relationships explored. A copper nanoparticle-GNF catalyst was applied in the industrially-significant water-gas shift reaction (WGSR) and compared to a commercially available, metal oxide-supported catalyst. The commercial catalyst exhibited minimal and expected changes in composition under the WGSR and generally remained stable with no changes in mean size or shape of catalytic nanoparticles. In contrast, the structure and composition of both the catalytic nanoparticles and the GNF substrate was found to significantly change in the novel nanoparticle-GNF catalyst. The effect of pre-treatment temperatures and gaseous environments on the composition and structure of three separate palladium, gold and copper nanoparticle-GNF systems was appraised, evidencing clear structure-function relationships between the size and/or composition of the catalysts at the nanoscale with their catalytic properties (selectivity and/or activity) at the macroscale. Molecule-nanotube interactions were studied towards the development of an effective controlled drug release system. The uptake and release of a chemotherapeutic agent, doxorubicin, from carbon, boron nitride and titania nanotubes, and their corresponding gold nanoparticle composites, was studied. No release of doxorubicin was observed for any structure, even with a plasmonic heating-induced release mechanism for the gold nanoparticle-nanotube composites, due to the strength of the host-guest interaction between the drug and the nanotubes

Loss of solutions in shear banding fluids in shear banding fluids driven by second normal stress differences

Edge fracture occurs frequently in non-Newtonian fluids. A similar instability has often been reported at the free surface of fluids undergoing shear banding, and leads to expulsion of the sample. In this paper the distortion of the free surface of such a shear banding fluid is calculated by balancing the surface tension against the second normal stresses induced in the two shear bands, and simultaneously requiring a continuous and smooth meniscus. We show that wormlike micelles typically retain meniscus integrity when shear banding, but in some cases can lose integrity for a range of average applied shear rates during which one expects shear banding. This meniscus fracture would lead to ejection of the sample as the shear banding region is swept through. We further show that entangled polymer solutions are expected to display a propensity for fracture, because of their much larger second normal stresses. These calculations are consistent with available data in the literature. We also estimate the meniscus distortion of a three band configuration, as has been observed in some wormlike micellar solutions in a cone and plate geometry.Comment: 23 pages, to be published in Journal of Rheolog

Modelling the electric field applied to a tokamak

The vector potential for the Ohmic heating coil system of a tokamak is obtained in semi-analytical form. Comparison is made to the potential of a simple, finite solenoid. In the quasi-static limit, the time rate of change of the potential determines the induced electromotive force through the Maxwell-Lodge effect. Discussion of the gauge constraint is included.Comment: 13 pages, 7 figures, final versio

The Sagnac Phase Shift suggested by the Aharonov-Bohm effect for relativistic matter beams

The phase shift due to the Sagnac Effect, for relativistic matter beams counter-propagating in a rotating interferometer, is deduced on the bases of a a formal analogy with the the Aharonov-Bohm effect. A procedure outlined by Sakurai, in which non relativistic quantum mechanics and newtonian physics appear together with some intrinsically relativistic elements, is generalized to a fully relativistic context, using the Cattaneo's splitting technique. This approach leads to an exact derivation, in a self-consistently relativistic way, of the Sagnac effect. Sakurai's result is recovered in the first order approximation.Comment: 18 pages, LaTeX, 2 EPS figures. To appear in General Relativity and Gravitatio

Models of core reconstruction for the 90-degree partial dislocation in semiconductors

We compare the models that have been proposed in the literature for the atomic structure of the 90-degree partial dislocation in the homopolar semiconductors, silicon, diamond, and germanium. In particular, we examine the traditional single-period and our recently proposed double-period core structures. Ab-initio and tight-binding results on the core energies are discussed, and the geometries are compared in light of the available experimental information about dislocations in these systems. The double-period geometry is found to be the ground-state structure in all three materials. We address boundary-conditions issues that have been recently raised about these results. The structures of point excitations (kinks, solitons, and kink-soliton complexes) in the two geometries are also reviewed.Comment: 9 pages, with 3 postscript figures embedded. Uses REVTEX and epsf macros. Also available at http://www.physics.rutgers.edu/~dhv/preprints/rn_eds/index.htm

Mechanisms explaining transitions between tonic and phasic firing in neuronal populations as predicted by a low dimensional firing rate model

Several firing patterns experimentally observed in neural populations have been successfully correlated to animal behavior. Population bursting, hereby regarded as a period of high firing rate followed by a period of quiescence, is typically observed in groups of neurons during behavior. Biophysical membrane-potential models of single cell bursting involve at least three equations. Extending such models to study the collective behavior of neural populations involves thousands of equations and can be very expensive computationally. For this reason, low dimensional population models that capture biophysical aspects of networks are needed. \noindent The present paper uses a firing-rate model to study mechanisms that trigger and stop transitions between tonic and phasic population firing. These mechanisms are captured through a two-dimensional system, which can potentially be extended to include interactions between different areas of the nervous system with a small number of equations. The typical behavior of midbrain dopaminergic neurons in the rodent is used as an example to illustrate and interpret our results. \noindent The model presented here can be used as a building block to study interactions between networks of neurons. This theoretical approach may help contextualize and understand the factors involved in regulating burst firing in populations and how it may modulate distinct aspects of behavior.Comment: 25 pages (including references and appendices); 12 figures uploaded as separate file

The reactivity of lattice nitrogen within the Ni2Mo3N and NiCoMo3N phases

In this study, the reactivity of bulk lattice nitrogen within the filled β-Mn structured Ni2Mo3N phase has been investigated by application of powder neutron diffraction and heterolytic nitrogen isotopic exchange measurements. In contrast to Co3Mo3N, despite the similarity in the N immediate local environment comprising NMo6 octahedra, its reactivity is found to be limited and this lower reactivity was maintained upon the introduction of a significant proportion of cobalt to yield its filled β-Mn structured CoNiMo3N quaternary nitride counterpart