The sintering, microstructural analysis and mechanical properties of two β' MgSiAlON ceramics

This work describes the preparation and the determination of some properties of two magnesium SiAlON ceramics, one with a low substitution level and one with a high substitution level ' phase. Each had a specific amount of spinel as second phase which would form on sintering or after a post-sintering heat-treatment. The work was undertaken because (a) the improvement in the properties of pressureless-sintered yttrium SiAlON ceramics was not as high as anticipated and (b) by applying the knowledge gained with the widely researched yttrium system to the MgSiAlON ceramic system, the properties of the magnesium system may be further improved. Under consideration in this thesis were the sintering of these ceramics and some sintering reactions are proposed. Also discussed is the effect on the microstructure of heating the ceramic in both oxidising and inert atmospheres. Some mechanical properties were determined, including fracture toughness and hardness testing at ambient temperature, and creep testing at upto 1300^oC. It was expected that MgSiAlONs would be easier to sinter due to the lower ternary oxide eutectic temperature and from a sintering view-point the high z materials do offer an alternative system to the yttrium system by being easier to sinter, but the low z material was as difficult to sinter as the yttrium system. Whilst the MgSiAlONs that were produced in this project were generally out-performed, encouraging results were obtained for the high z material in oxidation resistance. Low z material had the highest fracture toughness and hardness - both of which increased by heat-treatment. It is proposed that alterations to this heat-treatment would improve matters and would form a useful area for future work

A new earthquake catalogue for Bulgaria and the conterminous Balkan high hazard region

A new homogenous earthquake catalogue covering Bulgaria and the surrounding Balkan area has been created with intention of performing a consistent seismic hazard assessment across the region. In keeping with modern requirements of cataloguing seismicity, this catalogue has been made homogenous as far as possible with regards to magnitude, which has been provided on any of four different reported scales for each event; mb, Ms, Mw and ML. A key historical catalogue for the region has been used to represent the early instrumental period of earthquake recording (1900 to 1963), whilst data have been obtained from the International Seismological Centre (ISC), National Earthquake Information Center (NEIC) and National Observatory of Athens (NOA) to cover the instrumental period of earthquake recording (1964 to 2004). ISC data have also been used to develop a new mb→Ms magnitude conversion equation for the catalogued region. Application of this new magnitude conversion relation, in combination with other selected magnitude scale correlations, ensures reported magnitudes can be systematically rendered onto homogenized Ms and Mw scales for all earthquakes. This catalogue contains 3681 events with homogenized magnitudes ≥4.0 Mw, for the time interval 1900 to 2004 (inclusive), located in the region bounded by 39°–45° N, 19°–29° E, at focal depths of 0.0 km to 401.0 km and in a magnitude range 4.0≤Mw≤7.2. Selected large magnitude (M≥6.0 Ms) earthquakes have had their reported magnitudes reassessed – and adjusted if necessary – in light of work by other authors. Applied statistical approaches aimed at determining the lower threshold to magnitude completeness suggest this catalogue is complete down to a homogenized surface-wave magnitude of 4.6 Ms

An FPGA implementation of the simplex algorithm

Published versio

HATS-8b: A Low-Density Transiting Super-Neptune

HATS-8b is a low density transiting super-Neptune discovered as part of the HATSouth project. The planet orbits its solar-like G-dwarf host (V = 14.03 ± 0.10, T_(eff) = 5679 ± 50 K) with a period of 3.5839 days. HATS-8b is the third lowest-mass transiting exoplanet to be discovered from a wide-field ground-based search, and with a mass of 0.138 ± 0.019 M_J it is approximately halfway between the masses of Neptune and Saturn. However, HATS-8b has a radius of 0.873_(-0.075)^(+0.123) R_J, resulting in a bulk density of just 0.259 ± 0.091 g cm^(-3). The metallicity of the host star is super-solar ([Fe/H] = 0.210 ± 0.080), providing evidence against the idea that low-density exoplanets form from metal-poor environments. The low density and large radius of HATS-8b results in an atmospheric scale height of almost 1000 km, and in addition to this there is an excellent reference star of nearly equal magnitude at just 19" separation in the sky. These factors make HATS-8b an exciting target for future atmospheric characterization studies, particularly for long-slit transmission spectroscopy

INTERPRETING AND PRUNING COMPUTER VISON BASED NEURAL NETWORKS

Computer vision is a complex subject matter entailing tasks, such as, object detection and recognition, image segmentation, super resolution, image restoration, generated artwork, and many others. The application of these tasks is becoming more fundamental to our everyday lives. Hence, beyond the complexity of said systems, their accuracy has become critical. In this context, the ability to decentralise the computation of the neural networks behind cutting edge computer vision systems has become essential. However, this is not always possible, models are getting larger, and this makes them harder, or potentially impossible to use on consumer hardware. This thesis develops a pruning methodology called “Weight Action Pruning” to reduce the complexity of computer vision neural networks, this method combines sparsity pruning and structured pruning. Sparsity pruning highlights the importance of specific neurons and weights, and structural pruning is then used to remove any redundancies. This process is repeated multiple times and results in a significant decrease in the computing power required to deploy a neural network, reducing inference times and memory requirements. Weight Action Pruning is first applied to deblocking neural networks used in video coding. Pruning these networks with Weight Action Pruning allowed for large computational reductions without significant impacts on accuracy. To further test the validity of Weight Action Pruning on multiple datasets and different network architectures, Weight Action Pruning was tested on the generative adversarial U-Net used in a seminal paper in the field. This work showed that the ability to prune a neural network relies not only on the neural network’s architecture, but also the dataset used to train the model. Weight Action Pruning was then applied to image recognition networks VGG-16 and ResNet-50, this allowed Weight Action Pruning to be directly evaluated against other state of the art pruning methods. It was found that, models that were pruned to a set size had higher accuracies than models that were trained from scratch with the same size. Finally, the impact of pruning a neural network is investigated by analysing weight distribution, saliency maps and other visualizations. It must be noted that Weight Action Pruning comes at a cost at training time, due to the re-training required. Additionally pruning may cause networks to become less robust, as they are optimised by removing the learnt “edge cases”

Lupus-TR-3b: A Low-Mass Transiting Hot Jupiter in the Galactic Plane?

We present a strong case for a transiting Hot Jupiter planet identified during a single-field transit survey towards the Lupus Galactic plane. The object, Lupus-TR-3b, transits a V=17.4 K1V host star every 3.91405d. Spectroscopy and stellar colors indicate a host star with effective temperature 5000 +/- 150K, with a stellar mass and radius of 0.87 +/- 0.04M_sun and 0.82 +/- 0.05R_sun, respectively. Limb-darkened transit fitting yields a companion radius of 0.89 +/- 0.07R_J and an orbital inclination of 88.3 +1.3/-0.8 deg. Magellan 6.5m MIKE radial velocity measurements reveal a 2.4 sigma K=114 +/- 25m/s sinusoidal variation in phase with the transit ephemeris. The resulting mass is 0.81 +/- 0.18M_J and density 1.4 +/- 0.4g/cm^3. Y-band PANIC image deconvolution reveal a V>=21 red neighbor 0.4'' away which, although highly unlikely, we cannot conclusively rule out as a blended binary with current data. However, blend simulations show that only the most unusual binary system can reproduce our observations. This object is very likely a planet, detected from a highly efficient observational strategy. Lupus-TR-3b constitutes the faintest ground-based detection to date, and one of the lowest mass Hot Jupiters known.Comment: 4 pages, 4 figures, accepted for publication in ApJ

Why simheuristics? : Benefits, limitations, and best practices when combining metaheuristics with simulation

Many decision-making processes in our society involve NP-hard optimization problems. The largescale, dynamism, and uncertainty of these problems constrain the potential use of stand-alone optimization methods. The same applies for isolated simulation models, which do not have the potential to find optimal solutions in a combinatorial environment. This paper discusses the utilization of modelling and solving approaches based on the integration of simulation with metaheuristics. These 'simheuristic' algorithms, which constitute a natural extension of both metaheuristics and simulation techniques, should be used as a 'first-resort' method when addressing large-scale and NP-hard optimization problems under uncertainty -which is a frequent case in real-life applications. We outline the benefits and limitations of simheuristic algorithms, provide numerical experiments that validate our arguments, review some recent publications, and outline the best practices to consider during their design and implementation stages

The Lupus Transit Survey For Hot Jupiters: Results and Lessons

We present the results of a deep, wide-field transit survey targeting Hot Jupiter planets in the Lupus region of the Galactic plane conducted over 53 nights concentrated in two epochs separated by a year. Using the Australian National University 40-inch telescope at Siding Spring Observatory (SSO), the survey covered a 0.66 sq. deg. region close to the Galactic Plane (b=11 deg.) and monitored a total of 110,372 stars (15.0<V<22.0). Using difference imaging photometry, 16,134 light curves with a photometric precision of sigma<0.025 mag were obtained. These light curves were searched for transits, and four candidates were detected that displayed low-amplitude variability consistent with a transiting giant planet. Further investigations, including spectral typing and radial velocity measurements for some candidates, revealed that of the four, one is a true planetary companion (Lupus-TR-3), two are blended systems (Lupus-TR-1 and 4), and one is a binary (Lupus-TR-2). The results of this successful survey are instructive for optimizing the observational strategy and follow-up procedure for deep searches for transiting planets, including an upcoming survey using the SkyMapper telescope at SSO.Comment: 27 pages, 9 figures, 4 tables. Accepted for publication in A