Aiming at poor efficiency of the traditional materials in low-mid frequency sound absorption and its narrow bandwidth, we present an ultra-broadband acoustic metamaterial that can achieve ...near-perfect continuous absorption within 380 Hz–3600 Hz with a thickness of only 7.2 cm. Its basic cell is constructed by turning the original neck of a Helmholtz resonator into multiple smaller ones, and the neck panel becomes into a micro-perforated panel (MPP). By coupling the characteristics of the cavity’s multi-order resonance and the MPP’s broadband absorption, the cell’s high-order impedances can be tuned to more match that of the air medium. The cell can therefore obtain multiple excellent high-order absorption peaks besides the original one; meanwhile all the peaks can become broader resulting from the larger energy leakage rate. On this basis, a subwavelength 12-cell sample is obtained of which the absorption band is broadened almost 100% by the high-order peaks and has an average absorption coefficient above 90%. Characterized by the extraordinary absorption performance, thin thickness, and easy-fabricated structure, this proposed metamaterial has great potential in noise control engineering applications.
Due to the wet and dynamic environment of the oral cavity, the healing of intraoral wounds, such as tooth extraction wounds, requires stable and firm wound dressings. In clinical practice, cotton ...balls and gauzes, sponge plugs, or sutures are used to treat extraction wounds, but none of these means can continuously isolate the wound from the intraoral environment and facilitate ideal healing conditions. Herein, inspired by the natural extracellular matrix, a family of wound dressings is developed for intraoral wound repair. Infiltrating a ductile long‐chain hydrogel network into a prefabricated, sturdy macromolecular meshwork and in situ crosslinking endowed the composite hydrogel with controllable swelling behaviors and robust mechanical properties. The macromolecular meshwork functioned as the backbone to support the composite and restricts the swelling of the long‐chain hydrogel network. In vitro tests verified that this wound dressing can provide durable protection for intraoral wounds against complex irritations. Furthermore, accelerated wound healing occurred when the wound dressing is applied in vivo on a canine tooth extraction model, due to the effective reduction of acute inflammation. These results suggest that this family of bioinspired hydrogels has great potential for application as intraoral wound dressing.
An extracellular matrix‐mimicking hydrogel wound dressing is designed as tooth extraction adhesive wound dressing for intraoral application. The hydrogel exhibits excellent anti‐swelling efficiency, along with consistent mechanical and adhesive robustness in aqueous environments. In vitro and in vivo tooth extraction models demonstrate the stability of hydrogels as physical and antibacterial barriers for intraoral wounds, leading to continuous protection and effective healing acceleration.
The discussion of sexuality education has a long history in China since the onset of modernisation in the early 20th century. Sexuality education has also existed in China’s educational system for a ...long time but in various forms. However, the discussions regarding students’ experiences and the influence of social stratification in China’s particular social context are still limited. From March to September 2019, the author visited an academic high school (pugao) and a vocational high school (zhigao) in Tianjin, China, to gain first-hand data to understand young people’s sexuality education experiences. In this paper, the author specifically paid attention to China’s social class, a rarely discussed topic in China’s society. She also tried to listen to the voices of young people and schoolteachers and help them to be heard. By presenting the insights from schoolteachers, students, as well as the materials from a nationally approved textbook, the author conducted a thematic analysis about how social class influences young people’s sexuality education experiences in secondary education in China.
Artificial photosynthesis, the biomimetic approach to converting sunlight’s energy directly into chemical fuels, aims to imitate nature by using an integrated system of nanostructures, each of which ...plays a specific role in the sunlight-to-fuel conversion process. Here we describe a fully integrated system of nanoscale photoelectrodes assembled from inorganic nanowires for direct solar water splitting. Similar to the photosynthetic system in a chloroplast, the artificial photosynthetic system comprises two semiconductor light absorbers with large surface area, an interfacial layer for charge transport, and spatially separated cocatalysts to facilitate the water reduction and oxidation. Under simulated sunlight, a 0.12% solar-to-fuel conversion efficiency is achieved, which is comparable to that of natural photosynthesis. The result demonstrates the possibility of integrating material components into a functional system that mimics the nanoscopic integration in chloroplasts. It also provides a conceptual blueprint of modular design that allows incorporation of newly discovered components for improved performance.
In this Perspective, we discuss current challenges in artificial photosynthesis research, with a focus on the benefits of a nanowire morphology. Matching the flux between electrocatalysts and ...light-absorbers, and between individual semiconducting light-absorbers, are two major issues to design economically viable devices for artificial photosynthesis. With the knowledge that natural photosynthesis is an integrated nanosystem, individual building blocks of biomimetic artificial photosynthesis are discussed. Possible research directions are presented under an integrated device design scheme, with examples of our current progress in these areas. Coupling all of the components together, including electrocatalysts, light-absorbers, and charge transport units, is crucial due to both fundamental and practical considerations. Given the advantages of one-dimensional nanostructures, it is evident that semiconductor nanowires can function as essential building blocks and help to solve many of the issues in artificial photosynthesis.
Limited energy supply is one of the major constraints in wireless sensor networks. A feasible strategy is to aggressively reduce the spatial sampling rate of sensors, that is, the density of the ...measure points in a field. By properly scheduling, we want to retain the high fidelity of data collection. In this paper, we propose a data collection method that is based on a careful analysis of the surveillance data reported by the sensors. By exploring the spatial correlation of sensing data, we dynamically partition the sensor nodes into clusters so that the sensors in the same cluster have similar surveillance time series. They can share the workload of data collection in the future since their future readings may likely be similar. Furthermore, during a short-time period, a sensor may report similar readings. Such a correlation in the data reported from the same sensor is called temporal correlation, which can be explored to further save energy. We develop a generic framework to address several important technical challenges, including how to partition the sensors into clusters, how to dynamically maintain the clusters in response to environmental changes, how to schedule the sensors in a cluster, how to explore temporal correlation, and how to restore the data in the sink with high fidelity. We conduct an extensive empirical study to test our method using both a real test bed system and a large-scale synthetic data set.
To promote the development of multivariate prediction modelling in small sample environments, this paper constructs a new multivariate prediction model named CFDNGBM(r,N) by integrating the marine ...predator algorithm (MPA), the modified conformable fractional-order accumulation operation (MCFAO) and the grey prediction model. In CFDNGBM(r,N), the MCFAO and time-delay polynomial are used to enhance the model prediction performance, the backward difference operation is used to activate the unbiasedness, and the unbiased regularization algorithm is used to estimate the model parameters. In addition, the MPA is used to optimize the hyperparameters in the model. The experimental results show that the CFDNGBM(r,N) outperforms the 12 benchmark algorithms and all the optimization measures are effective, both of which confirm the effectiveness of the proposed methods.
•We propose a new grey multivariate prediction model with strong compatibility.•We propose a modified conformable fractional accumulation operator.•The marine predator algorithm is used to solve the hyperparameters in the model.
Recent investigations of Field Programmable Gate Array (FPGA)-based time-to-digital converters (TDCs) have predominantly focused on improving the time resolution of the device. However, the ...monolithic integration of multi-channel TDCs and the achievement of high measurement throughput remain challenging issues for certain applications. In this paper, the potential of the resources provided by the Kintex-7 Xilinx FPGA is fully explored, and a new design is proposed for the implementation of a high performance multi-channel TDC system on this FPGA. Using the tapped-delay-line wave union TDC architecture, in which a negative pulse is triggered by the hit signal propagating along the carry chain, two time measurements are performed in a single carry chain within one clock cycle. The differential non-linearity and time resolution can be significantly improved by realigning the bins. The on-line calibration and on-line updating of the calibration table reduce the influence of variations of environmental conditions. The logic resources of the 6-input look-up tables in the FPGA are employed for hit signal edge detection and bubble-proof encoding, thereby allowing the TDC system to operate at the maximum allowable clock rate of the FPGA and to achieve the maximum possible measurement throughput. This resource-efficient design, in combination with a modular implementation, makes the integration of multiple channels in one FPGA practicable. Using our design, a 128-channel TDC with a dead time of 1.47 ns, a dynamic range of 360 ns, and a root-mean-square resolution of less than 10 ps was implemented in a single Kintex-7 device.
Electrochemical nitrogen reduction to ammonia (NH3) is proposed as a favored alternative for the Haber-Bosch process since it can be powered by renewable electricity at ambient conditions. In light ...of this, electrochemical nitrogen fixation has gathered increasing attention in the scientific community. This Perspective discusses recent efforts devoted to nitrogen fixation in electrochemical systems operating at low temperatures, and the challenges confronting high selectivity for NH3 production as a result of the competition between the nitrogen reduction reaction and hydrogen evolution reaction. A variety of recent approaches have the potential to overcome this challenge for a selective, efficient, and practical electrochemical reaction for nitrogen fixation.
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Ammonia synthesis from nitrogen gas, currently through the Haber-Bosch process, is indispensable to our society. The energy consumption, environmental impact, and capital expenditure of a Haber-Bosch plant encourage the development of an affordable and renewable strategy of nitrogen reduction into ammonia under mild conditions. The electrochemical nitrogen reduction process is a promising alternative in light of such requirements. However, before such an option can be practically possible, challenges in catalyst selectivity, energy efficiency, and process throughput have to be addressed. Detailed fundamental understanding about the reaction mechanism at the catalytic interface remains largely elusive, while a synergistic effort that integrates chemistry, materials, and even biochemistry are needed to develop a functional ammonia synthetic device driven by renewable electricity at ambient conditions.
Electrocatalytic nitrogen reduction at low temperature is considered as a potential renewable nitrogen fixation strategy, while challenges in catalyst selectivity, energy efficiency, and process throughput remain to be addressed. A variety of recent fundamental, theoretical, and experimental studies integrating chemistry, materials, and biochemistry discussed here aid researchers to realize a selective, efficient, and practical electrochemical reaction for nitrogen fixation in the future.
Lithium metal-based battery is considered one of the best energy storage systems due to its high theoretical capacity and lowest anode potential of all. However, dendritic growth and virtually ...relative infinity volume change during long-term cycling often lead to severe safety hazards and catastrophic failure. Here, a stable lithium–scaffold composite electrode is developed by lithium melt infusion into a 3D porous carbon matrix with “lithiophilic” coating. Lithium is uniformly entrapped on the matrix surface and in the 3D structure. The resulting composite electrode possesses a high conductive surface area and excellent structural stability upon galvanostatic cycling. We showed stable cycling of this composite electrode with small Li plating/stripping overpotential (<90 mV) at a high current density of 3 mA/cm² over 80 cycles.
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