Doctor of Philosophy

dissertationGuided ion beam mass spectrometry is used to study the kinetic energy dependence of the reactions of the third-row transition metal ions of hafnium, tantalum, tungsten, and osmium. For Hf+ and Os+, the reaction with H2 and its isotopic analogue, D2 , are performed. The corresponding state-specific reaction cross sections are analyzed for endothermic formation of MH+ and MD+ to give 0 K bond dissociation energies (in eV) of D0(Hf+-H) = 2.11 ± 0.08 and D0(Os+-H) = 2.45 ± 0.10. Results from the reaction of the metal ions with HD provide insight into the reaction mechanism and indicate that Hf+ reacts according to a statistical mechanism while Os+ via a direct reaction. These results are also compared to their first-row and second-row congeners. Theoretical calculations are performed to compare calculated bond energies with experimental bond energies as well as provide electronic structures of species and potential energy surfaces for reaction. For the ions Hf+, Ta+, and W+, reactions with CO and O2 are performed. Reactions with O2 are exothermic and provide an upper bound for the M+-O BDE, while the endothermic cross sections measured for CO provide 0 K bond energies (in eV) of D0(Hf-C) = 3.19 ± 0.03, D0(Ta+-C) = 3.79 ± 0.04, D0(W+-C) = 4.76 ± 0.09, D0(Hf-O) = 6.91 ± 0.11, D0 (Ta+-O) = 7.10 ± 0.12, and D0(W+-O) = 6.77 ± 0.07. Additionally, collision-induced dissociation studies are done for the metal oxides and dioxides of Ta+ and W+ and provide 0 K threshold energies (in eV) of E0(Ta+-O) = 7.01 ± 0.12, E0(W+-O) = 6.72 ± 0.10, Eo(OTa+-O) = 6.08 ± 0.12, and Eo(OW+-O) = 5.49 ± 0.09, which in these cases can also be equated with the 0 K bond energies. Additionally, theoretical calculations are performed to discuss the nature of bonding in the MC+, MO+, and MO2+ species. Calculated BDEs are compared to experimental results and electronic structures of species as well as potential energy surfaces for reaction are provided

Learning generative texture models with extended Fields-of-Experts

We evaluate the ability of the popular Field-of-Experts (FoE) to model structure in images. As a test case we focus on modeling synthetic and natural textures. We find that even for modeling single textures, the FoE provides insufficient flexibility to learn good generative models – it does not perform any better than the much simpler Gaussian FoE. We propose an extended version of the FoE (allowing for bimodal potentials) and demonstrate that this novel formulation, when trained with a better approximation of the likelihood gradient, gives rise to a more powerful generative model of specific visual structure that produces significantly better results for the texture task

Guided ion beam and theoretical study of the reactions of Hf+ with H2, D2, and HD

Journal ArticleThe kinetic energy dependences of reactions of the third-row transition metal cation Hf+ with H2, D2, and HD were determined using a guided ion beam tandem mass spectrometer. A flow tube ion source produces Hf+ in its 2D (6s25d1) electronic ground state level. Corresponding state-specific reaction cross sections are obtained. The kinetic energy dependences of the cross sections for the endothermic formation of HfH+ and HfD+ are analyzed to give a 0 K bond dissociation energy of D0 (Hf+-H)=2.11±0.08 eV. Quantum chemical calculations at several levels of theory performed here generally overestimate the experimental bond energy but results obtained using the Becke-half-and-half-LYP functional show good agreement. Theory also provides the electronic structures of these species and the reactive potential energy surfaces. Results from the reactions with HD provide insight into the reaction mechanisms and indicates that Hf+ reacts via a statistical mechanism. We also compare this third-row transition metal system with the first-row and second-row congeners, Ti+ and Zr+, and find that Hf+ has a weaker M+-H bond. As most third-row transition metal hydride cation bonds exceed their lighter congeners, this trend is unusual but can be understood using promotion energy arguments

Automated Image Analysis of Offshore Infrastructure Marine Biofouling

Supplementary Materials: The following are available online at www.mdpi.com/2077-1312/6/1/2/s1 Acknowledgments: This project was funded by the Natural Environmental Research Council (NERC) project No.: NE/N019865/1. The authors would like to thank Melanie Netherway and Don Orr, from our project partner (company requested to remain anonymous) for the provision of survey footage and for supporting the project. In addition, many thanks to Oscar Beijbom, University California Berkley for providing guidance and support to the project. Additional thanks to Calum Reay, Bibby Offshore; George Gair, Subsea 7; and Alan Buchan, Wood Group Kenny for help with footage collection and for allowing us to host workshops with them and their teams, their feedback and insights were very much appreciated.Peer reviewedPublisher PD

Instantiating deformable models with a neural net

Deformable models are an attractive approach to recognizing objects which have considerable within-class variability such as handwritten characters. However, there are severe search problems associated with fitting the models to data which could be reduced if a better starting point for the search were available. We show that by training a neural network to predict how a deformable model should be instantiated from an input image, such improved starting points can be obtained. This method has been implemented for a system that recognizes handwritten digits using deformable models, and the results show that the search time can be significantly reduced without compromising recognition performance. © 1997 Academic Press

GTM through time

The standard GTM (generative topographic mapping) algorithm assumes that the data on which it is trained consists of independent, identically distributed (iid) vectors. For time series, however, the iid assumption is a poor approximation. In this paper we show how the GTM algorithm can be extended to model time series by incorporating it as the emission density in a hidden Markov model. Since GTM has discrete hidden states we are able to find a tractable EM algorithm, based on the forward-backward algorithm, to train the model. We illustrate the performance of GTM through time using flight recorder data from a helicopter

SuperGaN: Synthesis of NbTiN/GaN/NbTiN Tunnel Junctions

Nb-based circuits have broad applications in quantum-limited photon detectors, low-noise parametric amplifiers, superconducting digital logic circuits, and low-loss circuits for quantum computing. The current state-of-the-art approach for superconductor-insulator-superconductor (SIS) junction material is the Gurvitch trilayer process based on magnetron sputtering of Nb electrodes with Al-Oxide or AlN tunnel barriers grown on an Al overlayer. However, a current limitation of elemental Nb-based circuits is the low-loss operation of THz circuits operating above the 670 GHz gap frequency of Nb and operation at higher temperatures for projects with a strict power budget, such as space-based applications. NbTiN is an alternative higher energy gap material and we have previously reported on the first NbTiN/AlN/NbTiN superconducting-insulating-superconducting (SIS) junctions with an epitaxially grown AlN tunnel barrier. One drawback of a directly grown tunnel barrier compared to thermal oxidation or plasma nitridation is control of the barrier thickness and uniformity across a substrate, leading to variations in current density (Jc). Semiconductor barriers with smaller barrier heights enable thicker tunnel barriers for a given Jc. GaN is an alternative semiconductor material with a closed-packed Wurtzite crystal structure similar to AlN and it can be epitaxially grown as a tunnel barrier using the Reactive Bias Target Ion Beam Deposition (RBTIBD) technique. This work presents the preliminary results of the first reported high-quality NbTiN/GaN/NbTiN heterojunctions with underdamped SIS I(V) characteristics.Comment: Presented at the 16th EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVIT

Guided ion beam and theoretical study of the reactions of Os + with H 2, D 2, and HD

Journal ArticleReactions of the third-row transition metal cation Os+ with H2, D2, and HD to form OsH+ (OsD+) were studied using a guided ion beam tandem mass spectrometer. A flow tube ion source produces Os+ in its 6D (6s15d6) electronic ground state level. Corresponding state-specific reaction cross sections are obtained. The kinetic energy dependences of the cross sections for the endothermic formation of OsH+ and OsD+ are analyzed to give a 0 K bond dissociation energy of D0(Os+?H) = 2.45 ? 0.10 eV. Quantum chemical calculations are performed here at several levels of theory, with B3LYP approaches generally overestimating the experimental bond energy whereas results obtained using BHLYP and CCSD(T), coupled-cluster with single, double, and perturbative triple excitations, levels show good agreement. Theory also provides the electronic structures of these species and the potential energy surfaces for reaction. Results from the reactions with HD provide insight into the reaction mechanism and indicate that Os+ reacts via a direct reaction. We also compare this third-row transition metal system with the first-row and second-row congeners, Fe+ and Ru+, and find that Os+ reacts more efficiently with dihydrogen, forming a stronger M+? H bond. These differences can be attributed to the lanthanide contraction and relativistic effects

Conformation of the Transmembrane Domain of the Anthrax Toxin Receptor

Restauració dels vitrallsFoto final, plafó a6, cara interna, amb llum a través. Geomètric