Low Temperature Synthesis and Characterisation of Novel Complex Carbide- and Boride-Based Materials

This thesis work dealt with four novel types of carbide- and boride-based materials which are considered to be candidate materials for a variety of important applications. They were synthesized by using a low temperature “universally” applicable molten salt synthesis technique, and characterised systematically. In the first part of this thesis work, phase pure well-dispersed Al8B4C7 particles with the average size of about 200 nm were synthesized from Al, B4C and C after firing in NaCl-NaF at 1250 °C for 6 h. Under the optimal condition, Al initially diffused rapidly through the molten salt onto the surface of C to form Al4C3, and also diffused through the salt rapidly onto the surface of B4C and reacted with it to form Al3BC and AlB2. B from the decomposition of AlB2 and Al3BC also slightly dissolved in the salt, diffused onto the surface of Al4C3 formed earlier (from the Al-C reaction and decomposition of Al3BC), and reacted with it to form Al8B4C7. Compared to the conventional synthesis techniques, the synthesis temperature in the present case was about 500 oC lower, which was attributable to the great accelerating-effect of the molten salt containing NaF. In the second part of this thesis work, molybdenum aluminum boride (MoAlB) fine powders were synthesized from Al, B and Mo in molten NaCl. The effects of key processing parameters on the phase evolution and morphology of product powder were investigated and the relevant reaction mechanisms discussed. As-prepared MoAlB 2 particles exhibited three different morphologies: rounded particles (1~3 μm), plate-like particles (<5 μm in diameter) and columnar crystals with various lengths (up to 20 μm) and diameters (up to 5 μm), resultant from different reaction routes. The optimal synthesis condition for synthesis of phase pure MoAlB was: using 1.4 times excessive Al and firing at 1000 oC for 6 h. This synthesis temperature was much lower than required by other synthesis techniques. Under the optimal condition, Mo initially reacted with Al and B, forming respectively Al8Mo3 and MoB which further reacted with excessive Al to form MoAlB and Al-rich Al-Mo phases (such as Al4Mo). The latter further reacted with the residual B and form secondary MoAlB. The molten salt played an important role in the whole synthesis process by improving the mixing between the reactant species and facilitating their diffusion processes. The third part of this thesis work deals with nanocarbon supported tungsten carbide nanocatalysts for hydrogen generation. By using WO3, Mg and C as starting materials and KCl as reaction media, tungsten carbides (WC with W2C) nanoparticles (< 5 nm) were in-situ formed/anchored on nanosized carbon black (CB) and carbon nanotube (CNT). Owing to this special hybrid structure, both the exposed surface area of active species and the electrical conductivity of the catalysts were increased effectively, making the catalysts perform considerably better in HER than pure WC and WC based catalysts prepared via other conventional routes. WC nanocrystals in-situ formed/anchored on CNTs showed small overpotential (90 mV), low Tafel slope (69 mV dec-1), high current density (93.4 and 28 mA cm-2 at 200 and 300 mV, respectively) and excellent stability 3 (remaining stable even after 3000 cycles). Such a performance is one of the best among those of WC based electrocatalysts developed to date. We demonstrate here significantly improved HER performances of inexpensive tailored WC materials, along with a facile synthesis strategy which could be also readily extended to prepare a range of other types of mono-dispersed nanocatalysts for more potential applications. In the final part of this thesis work, novel 2D SiC nanosheet (SNS), ZrC nanosheet (ZNS), and SiC- and ZrC-coated graphite nanoplatelets were successfully prepared at relatively low temperatures. The effects of processing parameters such as firing temperature, time, and salt on the reaction/synthesis processes were examined, and the relevant mechanisms proposed. In all the cases, Si or Zr slightly dissolved in the molten salt and diffused rapidly through it onto the surface of graphite nanoplatelet, and then reacted in-situ to form SiC or ZrC which retained the morphology and size of the original graphite nanoplatelet, i.e., a template growth mechanism had functioned in all the cases and the original graphite nanoplatelet acted as the template. In the initial stage, as no barrier layer was built up on the surface of the graphite nanoplatelet, so the reaction was rapid. However, with the enhancement in the reaction extent, more and more carbide product would be formed, leading to the formation of a carbide barrier layer the remaining graphite nanoplatelet. Then, the reaction process would be controlled by the diffusion process of the metal and/or carbon. Nevertheless, as the molten salt medium could improve the mixing between the metal and the graphite nanoplatelet, and accelerate the diffusion process of the metal dissolved in it, the overall reaction still remained very 4 rapid, as verified by the much lowered synthesis temperature, especially in the case of ZrC formation where Zr has a sufficiently “high” solubility in the molten salt (1250 and < 850 oC respectively in the cases of SiC and ZrC formation). By controlling the ratio between the metal and graphite nanoplatelet, both carbide nanosheets and carbide-coated graphite nanoplatelet/graphene nanosheets could be readily synthesized

A Critical Commentary on Block 2011: "David Friedman and Libertarianism: a Critique" and a Comparison with Lester [2000] 2012's Responses to Friedman

David Friedman posed a number of libertarian philosophical problems (Friedman 1989). This essay criticizes Walter Block’s Rothbardian responses (Block 2011) and compares them with J C Lester’s critical-rationalist, libertarian-theory responses (Lester [2000] 2012). The main issues are as follows. 1. Critical rationalism and how it applies to libertarianism. 2.1. How libertarianism is not inherently about law and is inherently about morals. 2.2. How liberty relates to property and can be maximized: carbon dioxide and radio waves. 2.3. Applying the theory to flashlights. 2.4. Applying the theory to the probability of imposed risks. 2.5. “Homesteading” or initial acquisition. 2.6 What is “essential” for a “true libertarian.” 2.7. Crime and punishment. 2.8. Extent of punishment. 2.9. The libertarian response to a madman with a gun. 2.10. How contradictions in rights are possible. 2.11. The draft. 3.1. Utilitarian libertarianism and “nose counting”. 3.2. How interpersonal comparisons of utility are possible and utility monsters are not a threat. 3.3. Why it is not utilitarian in practice to kill an innocent prisoner to prevent a riot. 3.4. Why David Friedman should not be forced to give up one of his eyes. 3.5. How utilitarians can be libertarians. Conclusion: a proper theory of liberty combined with critical rationalism offers superior solutions to Friedman’s problems. Appendix: replies to two commentators

Data driven approaches for investigating molecular heterogeneity of the brain

It has been proposed that one of the clearest organizing principles for most sensory systems is the existence of parallel subcircuits and processing streams that form orderly and systematic mappings from stimulus space to neurons. Although the spatial heterogeneity of the early olfactory circuitry has long been recognized, we know comparatively little about the circuits that propagate sensory signals downstream. Investigating the potential modularity of the bulb’s intrinsic circuits proves to be a difficult task as termination patterns of converging projections, as with the bulb’s inputs, are not feasibly realized. Thus, if such circuit motifs exist, their detection essentially relies on identifying differential gene expression, or “molecular signatures,” that may demarcate functional subregions. With the arrival of comprehensive (whole genome, cellular resolution) datasets in biology and neuroscience, it is now possible for us to carry out large-scale investigations and make particular use of the densely catalogued, whole genome expression maps of the Allen Brain Atlas to carry out systematic investigations of the molecular topography of the olfactory bulb’s intrinsic circuits. To address the challenges associated with high-throughput and high-dimensional datasets, a deep learning approach will form the backbone of our informatic pipeline. In the proposed work, we test the hypothesis that the bulb’s intrinsic circuits are parceled into distinct, parallel modules that can be defined by genome-wide patterns of expression. In pursuit of this aim, our deep learning framework will facilitate the group-registration of the mitral cell layers of ~ 50,000 in-situ olfactory bulb circuits to test this hypothesis

NLSC: Unrestricted Natural Language-based Service Composition through Sentence Embeddings

Current approaches for service composition (assemblies of atomic services) require developers to use: (a) domain-specific semantics to formalize services that restrict the vocabulary for their descriptions, and (b) translation mechanisms for service retrieval to convert unstructured user requests to strongly-typed semantic representations. In our work, we argue that effort to developing service descriptions, request translations, and matching mechanisms could be reduced using unrestricted natural language; allowing both: (1) end-users to intuitively express their needs using natural language, and (2) service developers to develop services without relying on syntactic/semantic description languages. Although there are some natural language-based service composition approaches, they restrict service retrieval to syntactic/semantic matching. With recent developments in Machine learning and Natural Language Processing, we motivate the use of Sentence Embeddings by leveraging richer semantic representations of sentences for service description, matching and retrieval. Experimental results show that service composition development effort may be reduced by more than 44\% while keeping a high precision/recall when matching high-level user requests with low-level service method invocations.Comment: This paper will appear on SCC'19 (IEEE International Conference on Services Computing) on July 1

Cellular Automata on Group Sets

We introduce and study cellular automata whose cell spaces are left-homogeneous spaces. Examples of left-homogeneous spaces are spheres, Euclidean spaces, as well as hyperbolic spaces acted on by isometries; uniform tilings acted on by symmetries; vertex-transitive graphs, in particular, Cayley graphs, acted on by automorphisms; groups acting on themselves by multiplication; and integer lattices acted on by translations. For such automata and spaces, we prove, in particular, generalisations of topological and uniform variants of the Curtis-Hedlund-Lyndon theorem, of the Tarski-F{\o}lner theorem, and of the Garden-of-Eden theorem on the full shift and certain subshifts. Moreover, we introduce signal machines that can handle accumulations of events and using such machines we present a time-optimal quasi-solution of the firing mob synchronisation problem on finite and connected graphs.Comment: This is my doctoral dissertation. It consists of extended versions of the articles arXiv:1603.07271 [math.GR], arXiv:1603.06460 [math.GR], arXiv:1603.07272 [math.GR], arXiv:1701.02108 [math.GR], arXiv:1706.05827 [math.GR], and arXiv:1706.05893 [cs.FL