Microstructure and crystallography of abalone shells

Biominerals are biogenic mineralized products comprising both mineral and organic components. Calcium-bearing minerals comprise about 50% of biominerals with the most common being polymorphs of calcium carbonate, e.g. calcite and aragonite. Abalone (Haliotis asinina Linnaeus, 1758; Haliotis rufescens Swainson, 1822 and Haliotis gigantea Gmelin, 1791) are marine snails, belonging to the Phylum Mollusca, class Gastropoda, family Haliotidae, genus Haliotis. They can be easily recognized by the row of apertures, which are closed, half-closed and open ones, along the spiral ridges and towards the shell longitudinal growth direction of the dorsal margin. This study considers the microstructure and crystallography of three species of abalone shells, Haliotis asinina from Australia, Haliotis rufescens from America and Haliotis gigantea from Japan; as well as the aperture infill of H. asinina. The microstructure and crystallography are analysed through Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction (EBSD) respectively. Abalone shells all have an outer prismatic and an inner nacreous layer. It is confirmed that the shell of H. asinina is comprised of aragonite in both prismatic and nacreous layers, with c-axis orientation of crystals throughout the prismatic and nacreous layers of shell. Towards the prismatic-nacreous interface, crystallographic alignment of prismatic layer becomes much more tightly constrained. In nacre, crystallographic continuity persists across several laminae. Along the longitudinal shell growth direction (from posterior part to anterior), there is a trend of gradually thickening tablets towards the shell interior. In addition to this trend from exterior to interior, the tablets formed at the anterior are thicker than those formed earlier at the posterior. It is also confirmed that the nacreous layer in H. rufescens and H. gigantea is aragonite. The prismatic layer of H. rufescens shell is composed of calcite, the c-axis of which is normal to the shell surface. The prismatic layer of H. gigantea shell consists of calcite and aragonite, the c-axis of aragonite is normal to the shell surface and that of calcite is parallel to the shell surface. In these three species, there is higher crystallographic constraint in the nacreous layer than in the prisms. Furthermore, the crystallographic continuity of the nacreous layer persists across as many as 40~50 laminae. H. asinina is about 800 µm thick, H. rufescens is the thinnest at around 600~700 µm and H. gigantea shell is the thickest at about 1 mm. Comparing the three species, the prismatic layer to the shell thickness of three species, the calcite prismatic layer (H. rufescens) takes up about 50% of the shell thickness compared with aragonite prismatic layer (H. asinina) of about 20~30%, and the prismatic layer with calcite and aragonite (H. gigantea) is between the two at over 30% of total shell thickness. Aperture infill of H. asinina is also composed of aragonite with both prismatic and nacreous layers. The crystallographic orientation of infill prismatic layer is parallel to the shell surface unlike that of the shell where the crystallographic orientation of the prismatic layer is perpendicular to the shell surface. There is a prism-like layer between aperture infill and the shell. The contact with the shell always occurs within the nacreous shell layer. Aperture infill grows on this prism-like layer and the growth rate of aperture infill is in- keeping with that of the shell growth rate. When individuals reach six months and older, shell growth and aperture infill occur at approximately the same speed

Numerical simulation of two-phase cross flow in the gas diffusion layer microstructure of proton exchange membrane fuel cells

The cross flow in the under-land gas diffusion layer (GDL) between 2 adjacent channels plays an important role on water transport in proton exchange membrane fuel cell. A 3-dimensional (3D) two-phase model that is based on volume of fluid is developed to study the liquid water-air cross flow within the GDL between 2 adjacent channels. By considering the detailed GDL microstructures, various types of air-water cross flows are investigated by 3D numerical simulation. Liquid water at 4 locations is studied, including droplets at the GDL surface and liquid at the GDL-catalyst layer interface. It is found that the water droplet at the higher-pressure channel corner is easier to be removed by cross flow compared with droplets at other locations. Large pressure difference Δp facilitates the faster water removal from the higher-pressure channel. The contact angle of the GDL fiber is the key parameter that determines the cross flow of the droplet in the higher-pressure channel. It is observed that the droplet in the higher-pressure channel is difficult to flow through the hydrophobic GDL. Numerical simulations are also performed to investigate the water emerging process from different pores of the GDL bottom. It is found that the amount of liquid water removed by cross flow mainly depends on the pore's location, and the water under the land is removed entirely into the lower-pressure channel by cross flow

A Stackelberg game theoretic model for optimizing product family architecting with supply chain consideration

Planning of an optimal product family architecture (PFA) plays a critical role in defining an organization's product platforms for product variant configuration while leveraging commonality and variety. The focus of PFA planning has been traditionally limited to the product design stage, yet with limited consideration of the downstream supply chain-related issues. Decisions of supply chain configuration have a profound impact on not only the end cost of product family fulfillment, but also how to design the architecture of module configuration within a product family. It is imperative for product family architecting to be optimized in conjunction with supply chain configuration decisions. This paper formulates joint optimization of PFA planning and supply chain configuration as a Stackelberg game. A nonlinear, mixed integer bilevel programming model is developed to deal with the leader–follower game decisions between product family architecting and supply chain configuration. The PFA decision making is represented as an upper-level optimization problem for optimal selection of the base modules and compound modules. A lower-level optimization problem copes with supply chain decisions in accordance with the upper-level decisions of product variant configuration. Consistent with the bilevel optimization model, a nested genetic algorithm is developed to derive near optimal solutions for PFA and the corresponding supply chain network. A case study of joint PFA and supply chain decisions for power transformers is reported to demonstrate the feasibility and potential of the proposed Stackelberg game theoretic joint optimization of PFA and supply chain decisions

How the rural infrastructure construction drives rural economic development through rural living environment governance—case study of 285 cities in China

With deepening of rural revitalization strategy, rural infrastructure construction plays an important role in local economic development and living environment governance. Based on the mediation model, this paper takes case study of 285 cities in China from 2017 to 2022 as samples, constructs the explanatory variable, the explained variable and the mediator variable by entropy method, empirically analyzes the impact of rural infrastructure construction on rural living environment governance and rural economic development, as well as the mediation role played by rural living environment governance. It is found that there is a significant positive impact between rural infrastructure construction and rural economic development, and rural infrastructure construction can promote economic development through rural living environment governance. Further analysis show that the impact of rural infrastructure construction on rural economic development presents heterogeneity, and the impacts of rural infrastructure construction on local economic development and on local economic development through living environment governance in the eastern and central China is stronger than that in the western China. After controlling a series of variables related to rural infrastructure construction, and performing endogeneity tests and robustness tests such as tail-shrinkage regression and principal component analysis, the regression results are still robust. This paper firstly provides scientific empirical evidence for the hypothesis that rural infrastructure construction promotes local economic development through rural living environment governance, and secondly confirms the necessity of strengthening rural infrastructure construction in China to promote rural revitalization, providing a policy basis for scientific decision-making, and finally finds an important way out to solve the problem of unbalanced economic development in rural areas to some extent

Cloning and Characterization of a Pyrethroid Pesticide Decomposing Esterase Gene, \u3cem\u3eEst3385\u3c/em\u3e, from \u3cem\u3eRhodopseudomonas palustris\u3c/em\u3e PSB-S

Full length open reading frame of pyrethroid detoxification gene, Est3385, contains 963 nucleotides. This gene was identified and cloned based on the genome sequence of Rhodopseudomonas palustris PSB-S available at the GneBank. The predicted amino acid sequence of Est3385 shared moderate identities (30–46%) with the known homologous esterases. Phylogenetic analysis revealed that Est3385 was a member in the esterase family I. Recombinant Est3385 was heterologous expressed in E. coli, purified and characterized for its substrate specificity, kinetics and stability under various conditions. The optimal temperature and pH for Est3385 were 35 °C and 6.0, respectively. This enzyme could detoxify various pyrethroid pesticides and degrade the optimal substrate fenpropathrin with a Km and Vmax value of 0.734 ± 0.013 mmol·l−1 and 0.918 ± 0.025 U·µg−1, respectively. No cofactor was found to affect Est3385 activity but substantial reduction of enzymatic activity was observed when metal ions were applied. Taken together, a new pyrethroid degradation esterase was identified and characterized. Modification of Est3385 with protein engineering toolsets should enhance its potential for field application to reduce the pesticide residue from agroecosystems