Abstract 2D materials have attracted much interest over the past decade in nanoelectronics. However, it was believed that the atomically thin layered materials are not able to show memristive effect in vertically stacked structure, until the recent discovery of monolayer transition metal dichalcogenide (TMD) atomristors, overcoming the scaling limit to sub-nanometer. Herein, the nonvolatile resistance switching (NVRS) phenomenon in monolayer hexagonal boron nitride (h-BN), a typical 2D insulator, is reported. The h-BN atomristors are studied using different electrodes and structures, featuring forming-free switching in both unipolar and bipolar operations, with large on/off ratio (up to 107). Moreover, fast switching speed (\textless15 ns) is demonstrated via pulse operation. Compared with monolayer TMDs, the one-atom-thin h-BN sheet reduces the vertical scaling to ≈0.33 nm, representing a record thickness for memory materials. Simulation results based on ab-initio method reveal that substitution of metal ions into h-BN vacancies during electrical switching is a likely mechanism. The existence of NVRS in monolayer h-BN indicates fruitful interactions between defects, metal ions and interfaces, and can advance emerging applications on ultrathin flexible memory, printed electronics, neuromorphic computing, and radio frequency switches.
Three-dimensional numerical simulation is performed to study the formation mechanism and influencing factors of droplets in a microfluidic flow-focusing device (MFFD). Three types of liquid-liquid two-phase flow patterns include squeezing, dripping and jetting. Through the level-set method, the two-phase interface is tracked and the process of droplet generation is obtained. The key factors influencing droplet formation size and frequency are studied in MFFD. The results show that the formation of droplets is divided into three stages: Filling stage, Necking stage and Detachment stage, respectively. The formation of droplets is mainly that the continuous phase has flow-focusing effect on the dispersed phase. The flow rate ratio of two phases, the viscosity of the continuous phase and interfacial tension between two phases are the key factors that influence droplet size and frequency. As the flow rate ratio increases, the droplet size becomes larger and the frequency decreases. As the viscosity of the continuous phase increases, the size of the droplets becomes smaller and the frequency increases. When the two-phase interfacial tension becomes larger, the size of the droplets becomes larger and the frequency decreases.
In response to the ongoing challenges for health care and human motion monitoring, this work proposes a three-electrode multi-module sensor (TEMS) integrating proximity feedback, compression sensing and stretching perception. With the assist of the porous carbon nanotubes (CNTs)-polydimethylsiloxane (PDMS) patch in optimized parameters, the unification of the device's out-of-plane non-contact sensing and in-plane contact segmental detection is realized. Besides, coordinated with a set of symmetrically patterned Ag nanowires (NWs) electrodes with specified initial conductivity, the device is highly-sensitive to two-dimensional strains and qualified for recognizing the horizontal tension strain as small as 0.077% and the vertical pressure exerted by a piece of scrip (0.18 Pa) in fast response (millisecond level). The anti-interference ability of the signals is ensured by the PDMS encapsulation and regional stiffness of the device. Furthermore, the simplified fabrication process based on PDMS doping/modification is suitable for human skin-attachable applications, especially as the accurate differentiation of similar motions and the time-phased judgment of continuous movements through collaboration among acquisition results.
In recent years, many researches focus on sound source localization based on neural networks, which is an appealing but difficult problem. In this paper, a novel time-domain end-to-end method for sound source localization is proposed, where the model is trained by two strategies with both cross entropy loss and mean square error loss. Based on the idea of multi-task learning, CNN is used as the shared hidden layers to extract features and DNN is used as the output layers for each task. Compared with SRP-PHAT, MUSIC and a DNN-based method, the proposed method has better performance.
Managing reactive nitrogen (N-r) to achieve a sustainable balance between production of food, feed and fiber, and environmental protection is a grand challenge in the context of an increasingly affluent society. Here, we propose a novel framework for national nitrogen (N) assessments enabling a more consistent comparison of the uses, losses and impacts of N-r between countries, and improvement of N-r management for sustainable development at national and regional scales. This framework includes four key components: national scale N budgets, validation of N fluxes, cost-benefit analysis and N-r, management strategies. We identify four critical factors for Nr management to achieve the sustainable development goals: N use efficiency (NUE), N-r recycling ratio (e.g., ratio of livestock excretion applied to cropland), human dietary patterns and food waste ratio. This framework was partly adopted from the European Nitrogen Assessment and now is successfully applied to China, where it contributed to trigger policy interventions toward improvements for future sustainable use of N-r. We demonstrate how other countries can also benefit from the application our framework, in order to include sustainable N-r management under future challenges of growing population, hence contributing to the achievement of some key sustainable development goals (SDGs).
Deciphering the sources of metals is a prerequisite to establishing genetic models of ore formation, and is of importance for developing exploration models. For most magmatic-hydrothermal deposits, non-magmatic sourced components (e.g., fluids, sulfur and metals) are suggested to have minor or negligible contributions. On the other hand, there is substantial evidence to indicate that external ore-forming components could be crucial for the mineralization of some magmatic-hydrothermal deposits. Here, we conduct a detailed pyrite sulfur and lead isotope study on the Xinqiao stratabound deposit, South China, with the aim of constraining the contributions of ore-forming components from sedimentary rocks and existing mineralization through water-rock interaction. Traditionally, the source of mineralization at Xinqiao is debated. For example, a Cretaceous magmatic-hydrothermal origin was proposed as the sole source of metals. In sharp contrast, a Carboniferous sedimentary sulfide layer as proto-ore, which was enriched later by the Cretaceous magmatic-hydrothermal fluids, is required in a remobilization model. Crystallized pyrite grains from the stratabound orebody (pyl) have a delta S-34 value of 4.09 +/- 1.42 parts per thousand (2 SD), which is similar to that of pyrite grains from the garnet bearing skarn ore (py3). Colloform pyrite ore, which is composed of fine-grained (similar to 500 nm) cubic pyrite grains (py2a), has a delta S-34 value of 0.20 +/- 1.14 parts per thousand. The sulfur isotope composition of pyrite grains from the sandstone hosted quartz-pyrite veins is bimodal with delta S-34 values of 3.28 +/- 6.46 parts per thousand (py4a) and -11.87 +/- 5.43 parts per thousand (py4b). The Pb isotope compositions ((206)/(204)pb approximate to 18.5, (207)/Pb-204 approximate to 15.5) of pyl, py4a and py4b are broadly the same as that of K-feldspar ro from the Cretaceous Jitou diorite, while py2a are more radiogenic ((206)/Pb-204 approximate to 21.5, (207)/(204) Pb approximate to, ro = 18). Our pyrite S and Pb isotope data show no support for the presence of a Carboniferous sedimentary sulfide layer as proto-ore, but instead suggest that leaching sulfur and metals from Permian shales and an unexposed mineralization through water-rock interaction is a vital mechanism for the mineralization at Xinqiao. In line with previous studies, contributions from the late Permian shales are complementary for the stratabound orebody, and recycling existing Mo-Au rich mineralization is key for the formation of sandstone hosted gold rich pyrite-quartz veins. The existing mineralization is not exposed yet, and should be considered in future mineral exploration. Limited sulfur isotope fractionation between pyl, py2 and py3 (0-4 parts per thousand) further indicates a relatively reducing condition during their formation, while significant lower sulfur isotope composition (delta S-34 = 012 parts per thousand) of py4 could imply an oxidizing condition during its formation. Our study highlights that detailed in-situ sulfur and lead isotope analyses under robust geological and petrographic frameworks can tightly constrain the source of ore forming components, yield insights into oxygen fugacity during ore formation, and offer clues for future mineral exploration.
Current technologies could identify the abundance and functions of specific microbes, and evaluate their individual effects on microbial ecology. However, these microbes interact with each other, as well as environmental factors, in the form of complex network. Determination of their combined ecological influences remains a challenge. In this study, we developed a tripartite microbial-environment network (TMEN) analysis method that integrates microbial abundance, metabolic function, and environmental data as a tripartite network to investigate the combined ecological effects of microbes. Applying TMEN to analyzing the microbial-environment community structure in the sediments of Hangzhou Bay, one of the most seriously polluted coastal areas in China, we found that microbes were well-organized into 4 bacterial communities and 9 archaeal communities. The total organic carbon, sulfate, chemical oxygen demand, salinity, and nitrogen-related indexes were detected as crucial environmental factors in the microbial-environmental network. With close interactions with these environmental factors, Nitrospirales and Methanimicrococcu were identified as hub microbes with connection advantage. Our TMEN method could close the gap between lack of efficient statistical and computational approaches and the booming of large-scale microbial genomic and environmental data. Based on TMEN, we discovered a potential microbial ecological mechanism that crucial species with significant influence on the microbial community ecology would possess one or two of the community advantages for enhancing their ecological status and essentiality, including abundance advantage and connection advantage.
This paper presents a tunable 60 GHz band-pass filter, based on a coplanar waveguide (CPW) transmission line, periodically loaded with ferroelectric Hafnium Zirconium Oxide (HZO) variable metal-ferroelectric-metal (MIM) capacitors (varactors), developed for back-end-of-line (BEoL) integration. Derived from the nonlinear capacitance of hafnium zirconium oxide and implementing the method-of-moments simulation, it was shown, that with changing the bias voltage between 0.95 and -3 V, the filter’s center frequency can be tuned between 60.5 and 69,7 GHz, respectively. Hereby, a minimum insertion loss of -3.3 dB is realized. The chip area of the filter is only 0.062 mm 2 , making it the smallest among tunable V-band filters.
