Deep morphological neural networks

Mathematical morphology is a theory and technique applied to collect features like geometric and topological structures in digital images. Determining suitable morphological operations and structuring elements for a give purpose is a cumbersome and time-consuming task. In this paper, morphological neural networks are proposed to address this problem. Serving as a non-linear feature extracting layers in deep learning frameworks, the efficiency of the proposed morphological layer is confirmed analytically and empirically. With a known target, a single-filter morphological layer learns the structuring element correctly, and an adaptive layer can automatically select appropriate morphological operations. For high level applications, the proposed morphological neural networks are tested on several classification datasets which are related to shape or geometric image features, and the experimental results have confirmed the tradeoff between high computational efficiency and high accuracy

Design and Dynamic Analysis of a Novel Subsea Shuttle Tanker

PhD thesis in Offshore technologyUnderwater pipelines, tanker ships, and liquefied gas carriers have traditionally been employed to transport hydrocarbons between offshore oil and gas facilities and onshore locations. However, both methods come with limitations. Underwater pipelines are costly to install and maintain, while the operation of tanker ships and liquefied gas carriers is heavily dependent on weather conditions, rendering them impractical in severe sea states. As an alternative, a pioneering subsea shuttle tanker (SST) system was proposed as an alternative for offshore transportation. The SST was designed to function at a constant speed and depth beneath the ocean surface, specifically designed for transporting liquid carbon dioxide from existing onshore/offshore sites where carbon dioxide is captured or temporarily stored, to subsea wells for reservoir injection. Nonetheless, the potential applications of the SST extend to being a versatile freight carrier, capable of transporting diverse cargoes such as subsea tools, hydrocarbons, chemicals, and even electricity. This PhD project unfolds in two phases: design and dynamic analysis. In the design phase, a baseline design for the SST was formulated based on existing literature. This comprehensive design encompasses critical aspects of SST design and operation, including structural design, hydrostatic stability computations, resistance and propulsion estimations, operational scenarios, and offloading methodologies. Challenges inherent to CO2 SST transportation were scrutinised, involving thermodynamic properties, purity considerations, and hydrate formation of CO2 during various vessel-transportation states. These aspects were explored in relation to cargo sizing, material selection, and energy consumption. The second phase revolves around dynamic analysis, centred on the derived baseline SST. A manoeuvring model for the SST was constructed as a foundation. Hydrodynamic derivatives were calculated using semi-empirical formulas. Subsequently, the SST’s capability to maintain position during the offloading process was evaluated. A linear quadratic regulator was employed to address the SST’s stationkeeping challenge in stochastic currents, ensuring the vessel remains stationary during offloading. The model was further extended to explore the station-keeping under extreme current conditions, utilising probabilistic methods to predict maximum and minimum depth excursions. These predictions offer valuable insights for cost-effective SST design and operational decision-making. The study then delved into the SST’s recoverability under undesired malfunctions through the establishment of a safety operating envelope (SOE). This envelope considered potential submersible malfunctions, such as partial flooding, jam-to-rise, and jam-to-dive incidents. By identifying feasible speed and depth ranges from an operational safety perspective, the SOE contributes to a reduction in the designed collapse depth, leading to cost savings in materials and enhanced payload capacity. Furthermore, computational fluid dynamics (CFD) analysis was conducted to predict pressure, skin friction, drag, and lift forces affecting the SST. This included scenarios of the SST’s near-wall voyage and hovering. Collectively, the original contributions of this thesis encompass the conceptual design, application of control systems and dynamic analysis of the SST. These contributions pave the way for future exploration in the development of commercial submarine concepts and diverse ocean space utlisation strategies

A Numerical Investigation of Bio-inspired Scaffolds and Surface Textures

Synthetic scaffolds are widely used as implants to repair bone fracture. Without a proper design, scaffolds could pose significant health risks to the patient and fail to heal the bone properly. A good synthetic scaffold needs to have high porosity and large pore size to allow new bone cells to form on it. However, a scaffold with higher porosity and larger pore size tends to have reduced mechanical strength. Thus, it is important to find a structural design which allows the implant to have a high porosity and large pore size while retaining high strength. In this research, a 3D-printable bio-inspired structure based on the unit cell of hydroxyapatite (HAp), along with several other common scaffold structures, were designed and tested using a multiscale approach. Those structures are tested under different loading conditions to find the stress levels. HAp material properties are extracted from the density functional theory calculations, and the effect of porosity on the material properties are modeled based on empirical relations by utilizing the density as the scaling factor. The results show that the HAp-inspired scaffold could have up to 70% lower stress level when compared to other common scaffold designs，such as round or square pores scaffolds, under the same loading condition. Due to substitutions during aging, the scaffolds made of apatite can be significantly different from stoichiometric HAp. Hence, this study is also extended to test the HAp-inspired scaffold with varying anionic and cationic substitutions, including Mg2+, Zn2+, and CO32-. Furthermore, the surface texture of synthetic scaffolds has also become an important research subject in the last decade. Studies have found that surface texture can alter surface properties, such as cell adhesion, protein adsorption, and coefficient of friction, of a biomaterial. In this study, two of very promising 3D-printable bio-inspired surface textures are studied for their stress reaction under a loading condition. Some advice that could lead to a structurally stronger surface texture design is concluded. This study will provide an insight into a better scaffold design based on bio-inspired structures and the effects of substitutions on HAp scaffolds

Food Environment and Childhood Obesity

This thesis examines whether children\u27s food environment, especially food stores that have fresh produce, affects obesity prevalence among elementary school children in the state of Arkansas. Misclassified food outlet types in the Dun and Bradstreet commercial data set were first corrected and then food environment measures were computed and aggregated to geographic regions corresponding to school attendance areas. After applying classical panel estimation, it was found that the fixed effects model fit the data best. Results indicate that an additional supermarket within a one-mile radial of the census neighborhood block center will bring down childhood obesity prevalence by 0.58 percent, whereas associations between densities of supermarkets within farther buffers and children\u27s overweight status were not found. In addition, distance from neighborhood block center to closest supermarkets did not seem to play a role in determining children\u27s BMI, nor did presence of dollar, convenience and drug stores. Finally, fixed effects models incorporating spatial lags and spatial errors were estimated. Results showed no significant spatial effects

The Moderating Effects of Network Centrality between IT Initiatives and Firm Performance: An Empirical Study

The IS research community has accumulated a criticalmass of studies on IT business value, but the questions of howand why IT creates business values remain understudied. In thisstudy, we focus on the role of network centrality and conjecturethat network centrality moderates the effects of IT initiatives onfirm performance. We collected data of 26 public companiescross 19 industries over a period of 1994-2008 (15 years) andconducted a multiple-level analysis. The results of data analysisshow that IT initiatives are significantly, positively related to firmperformance only in the high network centrality situation

A REPRESENTATION THEOREM FOR MATERIAL TENSORS OF TEXTURED THIN SHEETS WITH WEAK PLANAR ANISOTROPY

Herein we consider material tensors that pertain to thin sheets or thin films, which we model as two-dimensional objects. We assume that the thin sheet in question carries a crystallographic texture characterized by an orientation distribution function defined on the rotation group SO(3), which is almost transversely-isotropic about the sheet normal so that mechanical and physical properties of the thin sheet have weak planar-anisotropy. We present a procedure by which a special orthonormal basis can be determined in each tensor subspace invariant under the action of the orthogonal group O(2). We call members of such special bases irreducible basis tensors under O(2). For the class of thin sheets in question, we derive a representation formula in which each tensor in any given tensor subspace Z is written as the sum of a transversely-isotropic term and a linear combination of orthonormal irreducible basis tensors in Z, where the coefficients are given explicitly in terms of texture coefficients and undetermined material parameters. In addition to the general representation formula, we present also the specialized form for subspaces of tensor products of second-order symmetric tensors, a type commonly found in mechanics of materials