In the context of the Belt and Road Initiative (BRI) and the opening-up of its frontier areas, China possesses regional advantages known as the “golden corner and silver edge”. Local governments at ...all levels should leverage their geographical and resource strengths, while the country as a whole can systematically and proactively plan the development of an overland frontier economic belt. The formation of a “One Belt” along China’s overland frontier regions as well as the establishment of a “One Belt, Multiple Points” pearl chain comprising towns at the frontier-road intersection, highlights great potentials for frontier development and embodies China’s bigger strategy of constructing a “frontier economic belt”.
Since the early nineteenth century, it has been known that an electric potential can be generated by driving an ionic liquid through fine channels or holes under a pressure gradient. More recently, ...it has been reported that carbon nanotubes can generate a voltage when immersed in flowing liquids, but the exact origin of these observations is unclear, and generating electricity without a pressure gradient remains a challenge. Here, we show that a voltage of a few millivolts can be produced by moving a droplet of sea water or ionic solution over a strip of monolayer graphene under ambient conditions. Through experiments and density functional theory calculations, we find that a pseudocapacitor is formed at the droplet/graphene interface, which is driven forward by the moving droplet, charging and discharging at the front and rear of the droplet. This gives rise to an electric potential that is proportional to the velocity and number of droplets. The potential is also found to be dependent on the concentration and ionic species of the droplet, and decreases sharply with an increasing number of graphene layers. We illustrate the potential of this electrokinetic phenomenon by using it to create a handwriting sensor and an energy-harvesting device.
Extracellular polymeric substances (EPS) are present both outside of the cells and in the interior of microbial aggregates, and account for a main component in microbial aggregates. EPS can influence ...the properties and functions of microbial aggregates in biological wastewater treatment systems, and specifically EPS are involved in biofilm formation and stability, sludge behaviors as well as sequencing batch reactors (SBRs) granulation whereas they are also responsible for membrane fouling in membrane bioreactors (MBRs). EPS exhibit dual roles in biological wastewater treatments, and hence the control of available EPS can be expected to lead to changes in microbial aggregate properties, thereby improving system performance. In this review, current updated knowledge with regard to EPS basics including their formation mechanisms, important properties, key component functions as well as sub-fraction differentiation is given. EPS roles in biological wastewater treatments are also briefly summarized. Special emphasis is laid on EPS controlling strategies which would have the great potential in promoting microbial aggregates performance and in alleviating membrane fouling, including limitation strategies (inhibition of quorum sensing (QS) systems, regulation of environmental conditions, enzymatic degradation of key components, energy uncoupling etc.) and elevation strategies (enhancement of QS systems, addition of exogenous agents etc.). Those strategies have been confirmed to be feasible and promising to enhance system performance, and they would be a research niche that deserves further study.
•EPS are of importance for microbial aggregates in biological wastewater treatments.•EPS control can cause changes in microbial aggregates and system performance.•EPS elevation has great potential in promoting microbial aggregates performance.•EPS limitation has great potential in alleviating membrane fouling in MBRs.
Dielectrics with ultralow permittivity within 2 times that of air, excellent mechanical performance, and high thermal stability are highly attractive to many applications. However, since the finding ...of silica aerogels in the 1930s, no alternative ultralight porous dielectric with density below 10 mg/cm3 has been developed. Here we present three-dimensional hierarchical boron nitride foam with permittivity of 1.03 times that of air, density of 1.6 mg/cm3, and thermal stability up to 1200 °C obtained by chemical vapor deposition on a nickel foam template. This BN foam exhibits complete recovery after cyclic compression exceeding 70% with permittivity within 1.12 times that of air. Gathering all these exceptional characters, the BN foam should create a breakthrough development of flexible ultralow-permittivity dielectrics and ultralight materials.
Coating is the most widely applied technology to improve surface properties of substrates, and nanotechnology has been playing an important role in enhancing the coating performance. However, the ...tunability of surface properties by a single atomic layer remains poorly understood. Here we demonstrate that a chemical vapor deposited hexagonal boron nitride (h-BN) monolayer of large area and high quality can serve as a perfect coating to significantly improve friction, oxidation and electric resistance of the substrates. The exceptional low friction and insulation of h-BN monolayer coating facilitate the characterization of the h-BN film vividly by atomic force microscopy, showing the h-BN monolayer consists of domains with size within a few micrometers. This excellent coating performance together with the exceptional high thermal and chemical stability make the h-BN monolayer a promising coating material.
Quorum sensing (QS) is a communication process between cells, in which bacteria secrete and sense the specific chemicals, and regulate gene expression in response to population density. Quorum ...quenching (QQ) blocks QS system, and inhibits gene expression mediating bacterial behaviors. Given the extensive research of acyl-homoserine lactone (AHL) signals, existences and effects of AHL-based QS and QQ in biological wastewater treatments are being subject to high concern. This review summarizes AHL structure, synthesis mode, degradation mechanisms, analytical methods, environmental factors, AHL-based QS and QQ mechanisms. The existences and roles of AHL-based QS and QQ in biomembrane processes, activated sludge processes and membrane bioreactors are summarized and discussed, and corresponding exogenous regulation strategy by selective enhancement of AHL-based QS or QQ coexisting in biological wastewater treatments is suggested. Such strategies including the addition of AHL signals, AHL-producing bacteria as well as quorum quenching enzyme or bacteria can effectively improve wastewater treatment performance without killing or limiting bacterial survival and growth. This review will present the theoretical and practical cognition for bacterial AHL-based QS and QQ, suggest the feasibility of exogenous regulation strategies in biological wastewater treatments, and provide useful information to scientists and engineers who work in this field.
•Endogenous AHL-based QS and QQ are coexisting in biological wastewater treatments.•Exogenous regulation by selective enhancement of AHL-based QS or QQ is proposed.•Exogenous addition of AHLs or AHL-producing bacteria enhances sludge performance.•Exogenous AHL-based QQ effectively improves membrane flux in MBRs.
An observational study with a 12-year follow-up in the general population reported that the relative risk for mortality associated with an increased body mass index (BMI) declined with age 3. The ...linear trend for hazard ratio with an increase of 1.0 in BMI across age groups was tested by Cox regression analysis with inverse-variance weighted average. ...our data are in concert with the obesity paradox and suggest that age has a modifying effect on the association between BMI and in-hospital mortality.
A three-dimensional sharp interface model is proposed to investigate the self-consistent keyhole and weld pool dynamics in deep penetration laser welding. The coupling of three-dimensional heat ...transfer, fluid flow and keyhole free surface evolutions in the welding process is simulated. It is theoretically confirmed that under certain low heat input welding conditions deep penetration laser welding with a collapsing free keyhole could be obtained and the flow directions near the keyhole wall are upwards and approximately parallel to the keyhole wall. However, significantly different weld pool dynamics in a welding process with an unstable keyhole are numerically found. Many flow patterns in the welding process with an unstable keyhole, verified by x-ray transmission experiments, were successfully simulated and analysed. Periodical keyhole collapsing and bubble formation processes are also successfully simulated and believed to be in good agreement with experiments. The mechanisms of keyhole instability are found to be closely associated with the behaviour of humps on the keyhole wall, and it is found that the welding speed and surface tension are closely related to the formation of humps on the keyhole wall. It is also shown that the weld pool dynamics in laser welding with an unstable keyhole are closely associated with the transient keyhole instability and therefore modelling keyhole and weld pool in a self-consistent way is significant to understand the physics of laser welding.
The finding of power generation from droplets (Yin et al., 2014) 1, based on the moving boundary of electrical double layer, has triggered great research enthusiasm, and a breakthrough in ...instantaneous electric power density was achieved recently by a droplet-based electricity generator (DEG) (Xu et al., 2020) 2. However, the dynamic mechanism for such droplet-based electricity generators remains elusive, impeding optimization of the DEGs for practical applications. Through comprehensive experiments, we developed a dynamic model of surface charge density that can explain the underlying mechanism for the DEGs. The spreading droplet in touch with the top electrode can be equivalently regarded as an additional part of the top electrode, and the change of droplet area causes the change of surface charge density of the top electrode, driving electrons to migrate between the two electrodes. The insight of the dynamic mechanism paves a way for optimal design and practical applications of the DEGs.
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•Direct correspondence between the droplet-induced voltage signal and area change rate dS/dt of the droplet is revealed.•A dynamic model based on experiments is proposed, which provides deep insights of the underlying mechanism for the DEGs.•Variable impacts on the droplet-based electricity generator are quantitatively demonstrated.
A controllable synthesis of two-dimensional crystal monolayers in a large area is a prerequisite for potential applications, but the growth of transition metal dichalcogenide monolayers in a large ...area with spatial homogeneity remains a great challenge. Here we report a novel and efficient method to fabricate large-scale MoS2 monolayers by direct sulfurization of pre-annealed molybdenum foil surfaces with large grain boundaries of more than 50 μm in size at elevated temperatures. Continuous MoS2 monolayers can be formed uniformly by sulfurizing the Mo foils in sulfur vapor at 600 °C within 1 min. At a lower temperature even down to 500 °C, uniform MoS2 monolayers can still be obtained but in a much longer sulfurizing duration. It is demonstrated that the formed monolayers can be nondestructively transferred onto arbitrary substrates by removing the Mo foil using diluted ferric chloride solution and can be successfully fabricated into photodetectors. The results show a novel avenue to efficiently fabricate two-dimensional crystals in a large area in a highly controllable way and should have great potential for the development of large-scale applications of two-dimensional crystals in electrophotonic systems.
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