A computer aided machining system for the manufacture of three-dimensional surfaces

Includes bibliographical references.This thesis describes the design of a computerised system for machining three-dimensional surfaces, more specifically "sculptured surfaces", using an IBM PC and a Bridgeport 3 axis Computer Numerically Controlled (CNC) Milling Machine. There was a twofold objective to the project: To design and develop a milling system; To provide a teaching tool for undergraduate students who wish to further their studies in the concepts of Computer Aided Design and Manufacture (CAD/CAM). Five broad areas are covered: 1. The development of a mathematical algorithm to approximate a sculptured surf ace represented by a set, of surface datapoints in the form of XYZ coordinates. 2. The development of an algorithm to calculate the toolpath to machine the sculptured surface. 3. The development of an algorithm to display the surface and toolpath in three dimensions on the computer screen. 4. The development of an algorithm (the postprocessor) which translates the toolpath into a program suitable for use with the CNC milling machine. 5. The development of a communications algorithm for the direct transmission of the CNC program from the IBM microcomputer to the memory of the CNC computer

Accurate measurement of absolute experimental inelastic mean free paths and EELS differential cross-sections

Methods are described for measuring accurate absolute experimental inelastic mean free paths and differential cross-sections using DualEELS. The methods remove the effects of surface layers and give the results for the bulk materials. The materials used are VC0.83,TiC0.98,VN0.97and TiN0.88but the method should be applicable to a wide range of materials. The data were taken at 200 keVusing a probe half angle of 29mradand a collection angle of 36mrad. The background can be subtracted from under the ionisation edges, which can then be separated from each other. This is achieved by scaling Hartree-Slater calculated cross-sections to the edges in the atomic regions well above the threshold. The average scaling factors required are 1.00 for the non-metal K-edges and 1.01 for the metal L-edges (with uncertainties of a few per cent). If preliminary measurements of the chromatic effects in the post-specimen lenses are correct, both drop to 0.99. The inelastic mean free path for TiC0.98 was measured as 103.6±0.5 nm compared to the prediction of 126.9 nm based on the widely used Iakoubovskii parameterisation

Doctor of Philosophy

dissertationIn this work, single molecule fluorescence microscopy techniques are used to investigate the role of electrostatics in deoxyribonucleic acid (DNA) hybridization, and in the interactions of DNA and colloidal particles with charged surfaces. Single molecule total internal reflection fluorescence (TIRF) microscopy provides the sensitivity and interfacial specificity needed to probe electrostatic interactions in the microscopic electrical double-layer region between charged molecules and surfaces. Image analysis has been developed to quantitatively detect single molecule spots in TIRF images by sampling their diffraction-limited point-spread function by multiple pixels on the imaging sensor. By detecting spots with multiple pixels above an intensity threshold, single molecules can be located with signal-to-noise ratios as low as 2.5, minimizing false positive and false negative probabilities. Single molecule imaging was used to monitor the time-course of individual complementary strand DNA hybridization events. Target single stranded DNA (ssDNA) was immobilized at an interface, and its absolute surface density and association constant were determined from the binding isotherm of fluorescently labeled complimentary strand probe ssDNA. Dissociation rate constants of the DNA duplex were determined from the dissociation times, and association rates were calculated from the association constant and the dissociation rate assuming a two-state binding model. From the dependence of association constants, association rates, and dissociation rates on ionic strength, an Eyring model was used to determine the electrostatic contribution to the free energy of the transition state and the fully hybridized double-helix. The electrostatic interactions between large DNA plasmids and a potential-controlled indium tin oxide (ITO) semiconductor surface were investigated by measuring DNA populations and diffusion near the semiconductor surface as a function of applied potential. DNA populations increased exponentially with positive applied potentials, while maintaining free-solution-like diffusion coefficients and no surface adsorption. A Boltzmann model indicates that interfacial DNA has a net charge less than one electron equivalent, suggesting that much of its charge is screened by counterions. Similar accumulation with increasing positive applied potential was observed with 100 nm carboxylate-polystyrene colloidal particles. These colloidal particles were used to investigate shifts in surface charge of the ITO-aqueous interface induced by photoexcitation of charge carriers in the semiconductor

Adsorption models of hybridization and post-hybridisation behaviour on oligonucleotide microarrays

Analysis of data from an Affymetrix Latin Square spike-in experiment indicates that measured fluorescence intensities of features on an oligonucleotide microarray are related to spike-in RNA target concentrations via a hyperbolic response function, generally identified as a Langmuir adsorption isotherm. Furthermore the asymptotic signal at high spike-in concentrations is almost invariably lower for a mismatch feature than for its partner perfect match feature. We survey a number of theoretical adsorption models of hybridization at the microarray surface and find that in general they are unable to explain the differing saturation responses of perfect and mismatch features. On the other hand, we find that a simple and consistent explanation can be found in a model in which equilibrium hybridization followed by partial dissociation of duplexes during the post-hybridization washing phase.Comment: 26 pages, 6 figures, some rearrangement of sections and some additions. To appear in J.Phys.(condensed matter

Investigating the Role of Hydration and DNA Dynamic Alterations in DNA Recognition by A Heterocyclic Diamidine

Target recognition by DNA-binding ligands, such as drugs, occurs in an aqueous environment, in which water (near unit mole fraction, ~55 M) dominates every solute. A quantitative account of how water molecules are disposed in DNA/ligand binding is indispensable for understanding the driving forces that confer high-affinity and selectivity. We are investigating the DNA sequence selectivity of a model DNA minor groove-binding heterocyclic diamidine, DB1976, which shows therapeutic activity in acute myeloid leukemia, systemic fibroses, and obesity-related liver disorders in vivo. The DNA minor groove is richly populated with water molecules. Studies based on explicit-solvent MD simulation have shown distinct DNA dynamics upon drug-DNA complexes. We have cooperated the role of hydration and conformational dynamics in contributing to drug selectivity. Moving forward, our goal is to evaluate the structure-hydration relationships of designed diamidines to site-specific and nonspecific DNA as part of their biophysical characterization as potential therapeutic agents

Bonding and adjoining technology: A compilation

This compilation covers NASA and AEC developed techniques covering bonding, brazing, and joining methods and technology