Soil bacterial community assembly during succession

Understanding the contribution of ecological processes structuring microbial communities and predicting their dynamics are ongoing challenges in ecology. To address these challenges, this thesis focused on the interplay of selection, dispersal and ecological drift mediating soil bacterial community assembly during succession. The results revealed a higher temporal turnover of RNA-inferred communities in comparison with DNA-inferred communities, as RNA-inferred communities were more closely associated with selection driven by environmental variations than DNA-inferred communities. Greater attention was also given to members of the rare biosphere (i.e., a collection of low abundance taxa in a community) due to their high diversity and relevance for ecosystem functioning. The findings show that the rare biosphere of soil bacterial communities was composed of different types of rarity. In particular, selection driven by stringent environmental conditions explains the prevalence of permanently rare taxa, whereas selection driven by environmental variations explains the dynamics of conditional rare taxa. Furthermore, this thesis investigated the influence of dispersal through sea water inundation on soil bacterial communities from the early and late stages of succession and found that a stronger influence of sea water inundation on the rare biosphere of soil bacteria communities at the early successional stage rather than the late stage. Altogether, this thesis provides microbial ecologists with more insights on how bacterial communities are assembled during ecological succession, and how the bacterial rare biosphere is structured by a dynamic interplay of quantifiable ecological processes

The Design of Tribological Composites for Multifunctional Applications: Model Development and Topology Optimization

As a result of the significant economic and environmental burdens caused by wear, extensive research has been conducted to understand, predict, and control wear to achieve desired performance and lifetimes for tribological systems. Sliding interfaces in many tribological systems must also be multifunctional, prompting the need to optimize for a range of properties and processes. Composites serve as great multifunctional candidates for targeted properties and performance: including mechanical, thermal, electrical, and chemical. However, current material selection and design processes for tribological composites are often trial-and-error, time-consuming and involve significant material and energy waste. This dissertation presents a new design framework that can direct and accelerate the development of tribological composites for combined wear and thermal performance. The framework integrates three main components: (i) wear models that can predict the evolution of key metrics (surface topography, material loss, contact pressure and temperatures) (ii) wear experiments that are used to evaluate and validate the wear models and (iii) topology optimization tools that control the spatial arrangement of materials in tribological composites to achieve target multifunctional performance. In particular, existing wear models are improved and enhanced for the design of rotary and linear wear systems. One of the major contributions is the development of a thermomechanical wear model that includes frictional heat generation and transfer, along with temperature-dependent wear rates. The model developments are incorporated into several topology optimization protocols, and for the first time, a framework to design tribological composites for enhanced frictional heat dissipation is presented. The material distribution within bi-material composites is optimized to minimize temperatures at sliding interfaces while maintaining target wear performance

Research on forming quality of poly-wedge pulley spinning

As an important power transmission part, pulleys are widely used in automobile industry, agricultural machinery, pumps and machines. A near-net forming process for six-wedge belt pulleys manufacturing was put forward. For this purpose, the required tooth shape and size can be formed directly by spinning without machining. The whole manufacturing procedures include blanking, drawing and spinning. The spinning procedure includes five processes, performing, drumming, thickening, toothing and finishing. The forming defects occurred during each forming processes of poly-wedge pulley spinning, such as the drumming failure, flanged opening-end, folded side-wall, insufficient bottom size, flashed opening-end, cutting-off bottom, are introduced, and the factors influencing the defects are analyzed. The corresponding preventive measures are put forward

Convex (L,M)(L,M)-fuzzy remote neighborhood operators

summary:In this paper, two kinds of remote neighborhood operators in $(L, M)$-fuzzy convex spaces are proposed, which are called convex $(L,M)$-fuzzy remote neighborhood operators. It is proved that these two kinds of convex $(L,M)$-fuzzy remote neighborhood operators can be used to characterize $(L, M)$-fuzzy convex structures. In addition, the lattice structures of two kinds of convex $(L,M)$-fuzzy remote neighborhood operators are also given

Robust Optimization Design of Bolt-Shotcrete Support Structure in Tunnel

The uncertainty of rock and soil parameters is one of the key problems to limit the stability of tunnel support structure. Based on this, a robust optimization design method is proposed to reduce the sensitivity of support system to the uncertainty of rock and soil parameters. By defining the design parameters, noise factors and system response, a robust design system for bolt-shotcrete support structure is established. The non-dominant solutions of system robustness and support cost consist of the Pareto Front, then an knee point recognition method is designed to further filter all non-dominant solutions and determine the only optimal solution. The robust optimization design of the bolt-shotcrete support structure is carried out with a tunnel as the engineering background. The results show that the method can not only improve the stability and adaptability of the supporting structure, but also reduce the economic cost to the greatest extent, which provides a reference for the optimization design of other geotechnical engineering supporting structures

Comparing the influence of assembly processes governing bacterial community succession based on DNA and RNA data

Quantifying which assembly processes structure microbiomes can assist prediction, manipulation, and engineering of community outcomes. However, the relative importance of these processes might depend on whether DNA or RNA are used, as they differ in stability. We hypothesized that. RNA-inferred community responses to (a)biotic fluctuations are faster than those inferred by DNA; the relative influence of variable selection is stronger in RNA-inferred communities (environmental factors are spatiotemporally heterogeneous), whereas homogeneous selection largely influences DNA-inferred communities (environmental filters are constant). To test these hypotheses, we characterized soil bacterial communities by sequencing both 16S rRNA amplicons from the extracted DNA and RNA transcripts across distinct stages of soil primary succession and quantified the relative influence of each assembly process using ecological null model analysis. Our results revealed that variations in α-diversity and temporal turnover were higher in RNA- than in DNA-inferred communities across successional stages, albeit there was a similar community composition; in line with our hypotheses, the assembly of RNA-inferred community was more closely associated with environmental variability (variable selection) than using the standard DNA-based approach, which was largely influenced by homogeneous selection. This study illustrates the need for benchmarking approaches to properly elucidate how community assembly processes structure microbial communities

Unravelling the interplay of ecological processes structuring the bacterial rare biosphere

Most ecological communities harbor many rare species (i.e., the rare biosphere), however, relatively little is known about how distinct ecological processes structure their existence. Here, we used spatiotemporal data on soil bacterial communities along a natural ecosystem gradient to model the relative influences of assembly processes structuring the rare and common biospheres. We found a greater influence of homogeneous selection (i.e., imposed by spatiotemporally constant variables) mediating the assembly of the rare biosphere, whereas the common biosphere was mostly governed by variable selection (i.e., imposed by spatial and/or temporal fluctuating variables). By partitioning the different types of rarity, we found homogeneous selection to explain the prevalence of permanently rare taxa, thus suggesting their persistence at low abundances to be restrained by physiological traits. Conversely, the dynamics of conditionally rare taxa were mostly structured by variable selection, which aligns with the ability of these taxa to switch between rarity and commonness as responses to environmental spatiotemporal variations. Taken together, our study contributes to the establishment of a link between conceptual and empirical developments in the ecology of the soil microbial rare biosphere. Besides, this study provides a framework to better understand, model, and predict the existence and dynamics of microbial rare biospheres across divergent systems and scales

Synthesis of NaYF4:Yb3+, Er3+ upconversion nanoparticles in normal microemulsions

An interface-controlled reaction in normal microemulsions (water/ethanol/sodium oleate/oleic acid/n-hexane) was designed to prepare NaYF4:Yb3+, Er3+ upconversion nanoparticles. The phase diagram of the system was first studied to obtain the appropriate oil-in-water microemulsions. Transmission electron microscopy and X-ray powder diffractometer measurements revealed that the as-prepared nanoparticles were spherical, monodisperse with a uniform size of 20 nm, and of cubic phase with good crystallinity. Furthermore, these nanoparticles have good dispersibility in nonpolar organic solvents and exhibit visible upconversion luminescence of orange color under continuous excitation at 980 nm. Then, a thermal treatment for the products was found to enhance the luminescence intensity. In addition, because of its inherent merit in high yielding and being economical, this synthetic method could be utilized for preparation of the UCNPs on a large scale