Magnetic interactions and possible structural distortion in kagome FeGe from first-principles study and symmetry analysis

Based on density functional theory and symmetry analysis, we present a comprehensive investigation of electronic structure, magnetic properties and possible structural distortion of magnetic kagome metal FeGe. We estimate the magnetic parameters including Heisenberg and Dzyaloshinskii-Moriya (DM) interactions, and find that the ferromagnetic nearest-neighbor $J_{1}$ dominates over the others, while the magnetic interactions between nearest kagome layers favors antiferromagnetic. The N\'{e}el temperature $T_{N}$ and Curie-Weiss temperature $\theta _{CW}$ are successfully reproduced, and the calculated magnetic anisotropy energy is also in consistent with the experiment. However, these reasonable Heisenberg interactions and magnetic anisotropy cannot explain the double cone magnetic transition, and the DM interactions, which even exist in the centrosymmetric materials, can result in this small magnetic cone angle. Unfortunately, due to the crystal symmetry of the high-temperature structure, the net contribution of DM interactions to double cone magnetic structure is absent. Based on the experimental $2\times 2\times 2$ supercell, we thus explore the subgroups of the parent phase. Group theoretical analysis reveals that there are 68 different distortions, and only four of them (space group $P622$ or $P6_{3}22$) without inversion and mirror symmetry thus can explain the low-temperature magnetic structure. Furthermore, we suggest that these four proposed CDW phases can be identified by using Raman spectroscopy. Since DM interactions are very sensitive to small atomic displacements and symmetry restrictions, we believe that symmetry analysis is an effective method to reveal the interplay of delicate structural distortions and complex magnetic configurations

Machine Learning Empowered Thin Film Acoustic Wave Sensing

Thin film based surface acoustic wave (SAW) technology has been extensively explored for physical, chemical and biological sensors. However, these sensors often show inferior performance for a specific sensing in complex environments, as they are affected by multiple influencing parameters and their coupling interferences. To solve these critical issues, we propose a methodology to extract critical information from the scattering parameter and combine machine learning method to achieve multi-parameter decoupling. We used AlScN film-based SAW device as an example, in which highly c-axis orientated and low stress AlScN film was deposited on silicon substrate. The AlScN/Si SAW device showed a Bode quality factor value of 228 and an electro-mechanical coupling coefficient of ~2.3. Two sensing parameters (i.e., ultraviolet or UV and temperature) were chosen for demonstration and the proposed machine-learning method was used to distinguish their influences. Highly precision UV sensing and temperature sensing were independently achieved without their mutual interferences. This work provides an effective solution for decoupling of multi-parameter influences and achieving anti-interference effects in thin film based SAW sensing

Fungi and cercozoa regulate methane-associated prokaryotes in wetland methane emissions

Wetlands are natural sources of methane (CH4) emissions, providing the largest contribution to the atmospheric CH4 pool. Changes in the ecohydrological environment of coastal salt marshes, especially the surface inundation level, cause instability in the CH4 emission levels of coastal ecosystems. Although soil methane-associated microorganisms play key roles in both CH4 generation and metabolism, how other microorganisms regulate methane emission and their responses to inundation has not been investigated. Here, we studied the responses of prokaryotic, fungal and cercozoan communities following 5 years of inundation treatments in a wetland experimental site, and molecular ecological networks analysis (MENs) was constructed to characterize the interdomain relationship. The result showed that the degree of inundation significantly altered the CH4 emissions, and the abundance of the pmoA gene for methanotrophs shifted more significantly than the mcrA gene for methanogens, and they both showed significant positive correlations to methane flux. Additionally, we found inundation significantly altered the diversity of the prokaryotic and fungal communities, as well as the composition of key species in interactions within prokaryotic, fungal, and cercozoan communities. Mantel tests indicated that the structure of the three communities showed significant correlations to methane emissions (p < 0.05), suggesting that all three microbial communities directly or indirectly contributed to the methane emissions of this ecosystem. Correspondingly, the interdomain networks among microbial communities revealed that methane-associated prokaryotic and cercozoan OTUs were all keystone taxa. Methane-associated OTUs were more likely to interact in pairs and correlated negatively with the fungal and cercozoan communities. In addition, the modules significantly positively correlated with methane flux were affected by environmental stress (i.e., pH) and soil nutrients (i.e., total nitrogen, total phosphorus and organic matter), suggesting that these factors tend to positively regulate methane flux by regulating microbial relationships under inundation. Our findings demonstrated that the inundation altered microbial communities in coastal wetlands, and the fungal and cercozoan communities played vital roles in regulating methane emission through microbial interactions with the methane-associated community

Optimal design of water treatment processes

Predicted water shortages assign water treatment a leading role in improving water resources management. One of the main challenges associated with the processes remains early stage design of techno-economically optimised purification. This work addresses the current gap by undertaking a whole-system approach of flowsheet synthesis for the production of water at desired purity at minimum overall cost. The optimisation problem was formulated as a mixed-integer non-linear programming model. Two case studies were presented which incorporated the most common commercial technologies and the major pollution indicators, such as chemical oxygen demand, dissolved organic carbon, total suspended solids and total dissolved solids. The results were analysed and compared to existing guidelines in order to examine the applicability of the proposed approach

Structures And Properties Of Junctions In Two-Dimensional Materials

Conventional bulk material junctions are the key components in fabricating devices such as field-effect transistors, photovoltaic cells and light-emiiting diodes. Extensive effort has been made to improve their performance and fabricate new promising junctions. Over the past two decades, the 2-dimensional (2D) materials have attracted great interests because of their promising electronic and mechanical properties. They also provide new opportunities to fabricate novel 2D junctions to build 2D nano devices. These 2D junctions can be fabricated by stacking two 2D monolayers together to form vertical junctions, or by connecting two materials within one monolayer to form lateral junctions. Recent studies show that these 2D junctions have promising novel properties and good performance in various devices. The goal of this dissertation is to deepen understanding of the structure of these 2D junctions and look for new ways to tune their properties for various applications. In particular, we investigate the structures of vertical and lateral 2D junctions by calculating the generalized stacking fault energy in bilayer 2D materials and the heterophase interface energy in lateral transition metal dichalcogenide (TMD) junctions. Moreover, we investigate the effects of alloying, twisting and lattice misfit on the band structure of TMD vertical junctions. We prove that the heterojunction of Type I band alignment with preferred direct bandgap can be achieved within a large composition region and a wide range of twist angles. The work of this dissertation provides a deeper understanding of the structures of 2D junctions, and provides new opportunities and methods to fabricate novel 2D nano-devices

Necessity and Feasibility of Developing Low Carbon Agriculture in Xuzhou City

According to the characteristics of low carbon economy and low carbon agriculture at home and abroad, and combining with actual situations of agricultural development in Xuzhou City, the necessity of developing low carbon agriculture in Xuzhou City is analyzed by the perspectives of its agricultural production conditions, agricultural modernization, comprehensive competitive power, ecological civilization and low carbon economy. Simultaneously, the feasibility of developing low carbon agriculture in the city is discussed through low carbon technology, rural land management model, agricultural input channel, agriculture-related scientific research system, agricultural research transformation mechanism and rural personnel training program to provide some references for promoting the rapid and sound development of low carbon agriculture in Xuzhou City

Bimorph Dual-Electrode ScAlN PMUT with Two Terminal Connections

This paper presents a novel bimorph Piezoelectric Micromachined Ultrasonic Transducer (PMUT) fabricated with 8-inch standard CMOS-compatible processes. The bimorph structure consists of two layers of 20% scandium-doped aluminum nitride (Sc0.2Al0.8N) thin films, which are sandwiched among three molybdenum (Mo) layers. All three Mo layers are segmented to form the outer ring and inner plate electrodes. Both top and bottom electrodes on the outer ring are electrically linked to the center inner plate electrodes. Likewise, the top and bottom center plate electrodes are electrically connected to the outer ring in the same fashion. This electrical configuration maximizes the effective area of the given PMUT design and improves efficiency during the electromechanical coupling process. In addition, the proposed bimorph structure further simplifies the device’s electrical layout with only two-terminal connections as reported in many conventional unimorph PMUTs. The mechanical and acoustic measurements are conducted to verify the device’s performance improvement. The dynamic mechanical displacement and acoustic output under a low driving voltage (1 Vpp) are more than twice that reported from conventional unimorph devices with a similar resonant frequency. Moreover, the pulse-echo experiments indicate an improved receiving voltage of 10 mV in comparison with the unimorph counterpart (4.8 mV). The validation of device advancement in the electromechanical coupling effect by using highly doped ScAlN thin film, the realization of the proposed bimorph PMUT on an 8-inch wafer paves the path to production of next generation, high-performance piezoelectric MEMS