468 research outputs found
Relating quantitative soil structure metrics to saturated hydraulic conductivity
No full textSoil structure affects saturated hydraulic conductivity (Ks) by creating highly conductive macropores that preferentially transmit soil water. In this study, we explore the relationship between Ks and macropores in an Oxyaquic Vertic Argiudoll in northeastern Kansas. Macropores were quantified from an excavation wall using multistripe laser triangulation (MLT) scanning. Soil water contents were measured at four depths within a soil lysimeter installed within 2 meters of the MLT-scanned soil profile and adjacent to an Ameriflux tower monitoring precipitation, air temperature, and solar radiation. Selected hydraulic properties of soil horizons within the lysimeter were optimized to water content data using a Markov chain Monte Carlo technique in combination with the mobile-immobile water (MIM) model in HYDRUS-1D. Estimates of Ks varied between 4198 cm d-1 in the A horizon and 0.6 cm d-1 in a 2Btss2 horizon with strongly expressed wedge structure. Approximately 87% of the variation in Ks was explained by the geometric mean of the widths of pores quantified with the MLT technique and modified by the coefficient of extensibility (COLE). The use of COLE allows the widths of the macropores obtained at dry conditions to be approximated at saturation. Two models that predict Ks from either texture or water retention data resulted in Ks estimates that were similar to each other, but significantly lower than Ks values predicted with MIM in horizons where structural pores dominate water flow. This technique shows a great deal of promise in better understanding and predicting the relationship of soil structure to water flow.Peer reviewe
Modelling the role of doping elements in metal oxides for photocatalytic organic wastewater treatment
No full textThe thesis presents research on visible light-harvesting photocatalysts for wastewater treatment, with a specific focus on the design of an advanced photocatalyst capable of efficiently generating electron-hole (e- -h+) pairs and harnessing a broader range of the visible light spectrum. To achieve this, first principles computational modelling is employed to quantify the impact of chemical modifications on the structural and electronic properties of the photocatalysts. The primary focus of the thesis revolves around modelling the photocatalytic degradation of methylene blue (MB) molecules using metal oxides. Notably, the research encompasses the exploration of thin film metal oxide (MO) photocatalysts through density functional theory (DFT) modelling, unravelling the intricate processes of organic molecule adsorption and subsequent degradation mechanisms. The successful modelling of undoped and Cu-doped CaWO4 thin films serves as a pioneering milestone in this field. By comprehensively examining the interactions of MB-loaded thin films, this research promises profound insights into the photocatalytic mechanisms crucial for wastewater treatment techniques, with significant implications for industries such as pharmaceuticals, cosmetics, food, and energy harvesting. In terms of structure, the thesis consists of eight chapters. Chapters 1–3 provide the necessary background, the research aims and objectives, and an overview of the modelling methods employed in the project. Chapters 4 and 5 delve into the modelling of doping bulk metal oxides with transition metals (TMs). Chapter 6 focuses on the modelling of doping metal oxide thin films using metal ions. Chapter 7 centres around the modelling of the interaction between methylene blue and the metal oxide thin film. Lastly, Chapter 8 offers concluding remarks summarising the key findings and implications of the research. Chapter 1 is a general introduction to the thesis and the PhD project. Chapter 2 presents the aim, research questions and objectives of the project. Chapter 3 presents the principles of density functional theory (DFT) and an overview of its related applications. The general methodology used throughout the thesis is given here. Chapter 4 presents the computational modelling results of the effect of Zn2+ and La3+ ions on the photocatalytic properties of bulk anatase TiO2 regarding the chemical modification of doping or co-doping the metal oxide. The chapter interprets the impact of dopants (such as Zn2+ and La3+) in TiO2 such as the electronic band structure, relative stability, and photocatalytic activities. The optimal doping concentration was predicted. It was found that the Zn2+-La3+ co doped TiO2 system, which has a composition of 6.25 at.% Zn and 2.08 at.% La, exhibit notable absorption activity within the visible light range of 400 to 540 nm. This behaviour can be attributed to the limited influence of La-4f orbitals on the band edge levels. Chapter 5 presents the computational modelling results of the chemically modified bulk CaWO4 that are doped using Cu2+ cations. The modelling results of the photocatalytic properties of the modified bulk CaWO4 (e.g. absorption spectra), thermostability, and electronic properties (such as density of states (DOS), charge density difference (CDD), electronic band structure) are analysed to understand how and why Cu2+ doping could have such influence. Chapter 6 presents the computational modelling results of doping the CaWO4 thin film using Cu2+, focusing on the electronic and photocatalytic properties. Interestingly, the CaWO4 thin film at the (101) exposed surface effectively decreases the bandgap value by 0.39 eV when compared to the corresponding bulk material. Chapter 7 presents the computational modelling results of the interaction between methylene blue (MB) and undoped and Cu-doped CaWO4 thin films, in relation to the MB absorption and oxidation behaviour as well as the electronic properties of the oxide. Moreover, to examine the electrochemical potential of the thin-film, the adsorption of small molecules such as O2, H2, and H2O on the Ca terminated surface of CaWO4 was analyzed using the computational method. The work on the adsorption of MB with various orientations on CaWO4 surface revealed several new findings for the first time, including (i) the MB molecule would react strongly to the surface of the oxide in the presence of Ca2+ ions due to the charge transfer from the reduced surface to the oxidized molecule, (ii) doping the (101) surface of CaWO4 thin film with a low concentration of Cu-cation can effectively improve the oxidation of MB without compromising surface Ca's reduction, and (iii) doping the (101) surface of CaWO4 thin film with a high concentration of Cu2+ cation can inhibit MB oxidation while promoting surface Ca2+'s partial oxidation on the CaWO4 thin film. Chapter 8 presents the comprehensive conclusions of the project as well as specific answers to the research questions
Computational modelling of linear friction welding of Inconel 718
No full textLinear friction welding (LFW) is a solid-state joining technique that involves the rapid reciprocating motion of two workpieces under large compressive pressure, in order to generate friction heat and plastically deformed material at the contacting surfaces of workpieces. It is an advanced joining technology used for manufacturing and repairing complex assemblies like blade integrated disks (blisks) of aeroengines. LFW can avoid fusion welding defects such as hot cracking, pores, pin holes, solute segregation and solidification structures because it does not involve the remelting of weld material. In practical terms, it can be very difficult to use experimental methods to characterise some phenomena and processes such as the evolution of stress, strain, strain rate and microstructure of welds during the LFW. These challenges have motivated high demand for computational modelling of LFW, which can be used to not only predict these phenomena and processes but also explain or interpret the relationship between heat transfer, deformation of weld, and material microstructural evolution during the LFW. This research enabled the integrated computational modelling of the LFW process for the manufacture of Inconel 718 (IN718) alloy welds by sequentially (one-way) coupling a thermomechanical sub-model with two different microstructural sub-models. The thermomechanical sub-model of the integrated computational modelling involved two-dimensional and three-dimensional (2D and 3D) computations developed for two deformable IN718 workpieces. The thermomechanical sub-model employed Hooke’s law for material elasticity and the strain-compensated Arrhenius constitutive model for material plasticity. One microstructural sub-model formulated the process of dissolution of the δ phase of IN718 by using the time-temperature equivalence method. The other microstructural sub-model formulated the dynamic recrystallization of the primary γ grains during the LFW by using the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model. The integrated computational modelling was implemented within the general-purpose finite element software package Abaqus in conjunction with related custom-written subroutines. On the scale of the overall weld, the integrated computational modelling predicted the macroscopic processes of flash formation, axial shortening, and the evolution of displacement, temperature, stress, strain and strain rate of IN718 during the LFW. The integrated computational modelling also predicted the volume fraction of the δ phase, the volume fraction of recrystallized γ grains, and the average size of γ grains of the weld. The integrated computational modelling was verified by comparing its modelling results of weld temperature, axial shortening, formation of flash, volume fraction of the δ phase and average size of γ grains of the weld to related experimental results of other researchers. The integrated modelling was subsequently used for optimising the LFW process parameters and determining the process windows of the LFW of IN718. By systematically analysing the influence of 10 to 20 different sets of LFW process parameters (using different combinations of friction pressure, oscillation frequency and oscillation amplitude), the friction pressure was identified as the most influential process parameter determining the weld temperature, axial shortening, dissolution of the δ phase and the DRX of γ grains during the LFW of IN718. It is the first time that such integrated computational modelling has been developed for LFW of an alloy. With regard to the contribution to the body of knowledge, the integrated computational modelling provided insight into the relationship and interaction between heat transfer, deformation of weld, and material microstructural evolution during the LFW of IN718. With regard to the contribution to the industry, this project’s integrated computational modelling developed an effective and efficient tool that can be directly used by the manufacturing industry to design and/or optimise its process parameters for LFW of IN718
Varieties of alternatives
No full textThis dissertation concerns two focus particles (jiu, dou) and wh-expressions (shenme ‘what’, na geren ‘which person’) in Mandarin Chinese. These items are systematically ‘ambiguous’ and have played important roles in various aspects of Mandarin grammar. An idea based on alternatives and varieties of alternatives in particular – following Chierchia’s 2013 analysis of the polarity system – is pursued to account for the systematic ambiguities. Unambiguous semantics of jiu, dou and wh-expressions is maintained and ‘ambiguity’ explained through varieties of alternatives interacting with other independently motivated aspects of the structure they occur in. A better understanding of a large array of phenomena that involve these items – exhaustivity, distributivity, questions and conditionals – is achieved.Ph.D.Includes bibliographical referencesby Mingming Li
Review of Particle-Based Computational Methods and Their Application in the Computational Modelling of Welding, Casting and Additive Manufacturing
No full textA variety of particle-based methods have been developed for the purpose of computationally modelling processes that involve, for example, complex topological changes of interfaces, significant plastic deformation of materials, fluid flow in conjunction with heat transfer and phase transformation, flow in porous media, granular flow, etc. Being different from the conventional methods that directly solve related governing equations using a computational grid, the particle-based methods firstly discretize the continuous medium into discrete pseudo-particles in mathematics. The methods then mathematically solve the governing equations by considering the local interaction between neighbouring pseudo-particles. Such solutions can reflect the overall flow, deformation, heat transfer and phase transformation processes of the target materials at the mesoscale and macroscale. This paper reviews the fundamental concepts of four different particle-based methods (lattice Boltzmann method—LBM, smoothed particle hydrodynamics—SPH, discrete element method—DEM and particle finite element method—PFEM) and their application in computational modelling research on welding, casting and additive manufacturing
EFFICIENT DIFFERENTIATION OF FUNCTIONAL DOPAMINERGIC NEURONS FROM HESCS FOR PARKINSON'S DISEASE
No full textPh.DDOCTOR OF PHILOSOPH
Process modelling and experimental validation of residual stress in metal additive manufacturing
No full textAdditive Manufacturing (AM) is an increasingly attractive advanced manufacturing technology that manufactures three-dimensional (3D) components, usually in a layer-by-layer manner, as opposed to subtractive or formative processes. Comparing with the traditional metal manufacturing techniques, AM has unrivalled capability for manufacturing complex structures and customised metal parts on an industrial scale and thus industries such as medical-device and aviation are adopting AM as a manufacturing method. However, the layer-by-layer approach, as well as indeed the continuous fine melt pool tracing process at each layer, leads to a complex sequence of repeated localised heating, melting, cooling and solidification steps. At any given time in a metal AM process, a microscale volume of the material will be exposed to rapid heating, whilst other regions will either be molten, solidifying, or cooling and solidified. As a result of this, the thermal residual stress (RS) within AM parts is intricate and is considered to be limiting a wider uptake of metal AM in industry. AM RS and the prediction thereof, is the focus of this thesis. Finite element modelling (FEM) is capable of simulating aspects of the multi-physics AM process, but when applied to complete AM processes and parts, conventional FEM techniques accrue prohibitive computational expenses and thus are generally applied to simulating basic phenomena on small single components in basic AM representations. This thesis aims to build thermo-mechanical models for AM, to improve RS predictive capability and then inform RS mitigation strategies in additively manufactured metal components. In this content, coupled thermo-mechanical FEM capabilities for multi-processes, multi-laser beam and multi-part build were developed. Powder bed fusion (PBF) is the most popular and widely used method to additively manufacture 3D metallic components. Ti-6Al-4V titanium alloy is one of the most popular metallic materials for PBF due to its favourable properties and is therefore utilised in this thesis. A novel computationally-efficient thermo-mechanical coupled laser beam powder bed fusion (PBF-LB) process model for part-scale Ti-6Al-4V components were developed. The influences of resolution, energy input and heating step time and cooling step time were characterised, which provide guidelines for the ‘layer scaling’ technique in PBF-LB process modelling for macroscale component. The results indicate that the ‘layer scaling’ method was effective when scaling up to 4 times the physical layer thickness and scaling the cooling step time. To validate the developed thermo-mechanical PBF-LB prediction model, RS measurement was performed by synchrotron high energy X-ray diffraction on parts with different heights and manufactured by different scanning strategies. The computational modelling results of directional stresses were compared with the experimental measurements. To improve the production rate of metal PBF, multi-laser beam powder bed fusion (PBF-MLB) technology has been proposed as the next generation of PBF-LB technology. Thus, a computational multi-laser beam model was developed and presented in a study on RS in PBF-MLB. To investigate the optimum multi-laser scanning strategies in PBF-MLB, the influence of twelve different scanning strategies on temperature, the final resulting RS, and the z- (build) direction deflection by dual laser beams were investigated. The prediction indicates that the more laser beams are employed in PBF-MLB manufacturing, the lower RS and deflection resulted. The four-laser beam PBF-MLB build can mitigate RS by 9.39 % compared to the single laser beam PBF-LB. Most of the existing FEM is focused on single part manufacturing, which is inconsistent with the practical multi-part (full build plate) printing observed in industry. Therefore, multi-part build process PBF-LB model was developed by the layer-by-layer modelling method for mitigating RS of the manufactured parts. Effects of the number of parts per build and part spacing on temperature and RS were investigated on prism sample in PBF-LB. It was found that RS decreased with the number of parts per build and RS of four-part build was 94 % of the single part build. The final studies within this thesis apply the computational techniques to the electron beam variety of PBF (PBF-EB), to another metal AM process- directed energy deposition (DED), and to a new titanium alloy Ti2448 and aluminium alloy. The predicted temperature evolution during PBF-EB was indirectly compared to microstructure evolution of material performed by collaborators. Preheating temperature of the base plate was shown to be a key factor to reduce RS in PBF-LB. To interpret the in-situ RS characterisation of practical DED, process modelling of a thin trapezoidal plate was performed by using a bead-by-bead modelling method. The higher the numbers of layers fabricated in DED, the higher the temperature of the part during the manufacturing process, giving a 21.93 % lower temperature gradient and hence lower RS. The computational DED process modelling proved to be an effective tool to investigate temperature and RS state evolutions in macroscale components. This work reveals further insights into AM RS mechanics and will inform metal AM part designers and process operators of optimum process configuration in order to minimise RS of metal parts in AM.2022-08-1
Visualization studies on evidence-based medicine domain knowledge (series 2): structural diagrams of author networks.
No full textOBJECTIVE: To investigate the output of evidence-based medicine (EBM) researchers in China and elsewhere by examining the EBM domains they work within and the networks that exist among them; using visualization methods to analyze these relationships. This maps the current situation and helps with the identification of areas for future growth. METHODS: We used co-citation matrixes with Pathfinder networks and hierarchical clustering algorithms, and constructed a co-author matrix which were analyzed with a whole network approach. The analyzed matrixes were visualized with the UCINET program. RESULTS: Much of the development of EBM has been centered around three authors, David Sackett, Gordon Guyatt and L Manchikanti, within three different clusters. The main authors of EBM articles in China were divided into nine academic domains. The relations among core authors of articles indexed by the Science Citation Index (SCI) was loose. There was a stronger co-authorship network among core authors in the Chinese literature, with three groups and 21 cliques. Nine distinct academic communities appeared to have formed around Li Youping, Liu Ming and Zhang Mingming. CONCLUSION: The EBM literature contains several key clusters, with universities in high-income countries being the source of the majority of articles. Outside China, McMaster University in Canada, the original home of EBM, is the dominant producer of EBM publications. In China, Sichuan University is the main source of EBM publications. The EBM cooperation network in China is comprised of three major groups, the largest and most productive in this sample is led by Li Youping with Liu Ming, Zhang Mingming, Li Jing, Wang Li, Wu Taixiang, and Liu Guanjian as central members
Weighted spiking neural P systems with structural plasticity working in sequential mode based on maximum spike number
No full text- …
