Synergistic Dual Dynamic Bonds in Covalent Adaptable Networks

Covalent adaptable networks(CANs),comprising polymer networks crosslinked by dynamic covalent bonds(DCBs),have garnered considerable attention as sustainable materials.Mastering the stress relaxation of CANs is essential for controlling their viscoelastic properties.An unexpected acceleration of stress relaxation has been observed in CANs containing dual dynamic bonds.The dynamic behavior of the second dynamic bonds can accelerate stress relaxation and lower the relaxation activation energy of dual dynamic CANs compared to analogous CANs that rely on only one type of DCB.These findings complement current approaches that utilize catalysts or adjust network parameters.In this minireview,we summarize the synergistic acceleration effects in various CANs containing dual dynamic bonds.We classify these effects based on the second dynamic bonds,including noncovalent bonds,mechanical bonds,and the second DCBs.We also discuss the mechanisms behind this synergy.Finally,we highlight the challenges and offer perspectives on harnessing the synergistic effects of these dual dynamic systems to expand the chemistry and applications of CANs.

Sulfur and carbon co-doped g-C_(3)N_(4)microtubes with enhanced photocatalytic H2 production activity

Metal-free graphitic carbon nitride(g-C_(3)N_(4))has captured significant attention as a low-cost and efficient hydrogen production photocatalyst through.Effectively regulating the microstructure and accelerating the separation of photogenerated carriers remain crucial strategies for promoting the photocatalytic performance of this material.Herein,a novel sulfur–carbon co-doped g-C_(3)N_(4)(SCCN)hierarchical microtubules filled with abundant nanosheets inside by thermal polymerization is reported.Numerous nanosheets create abundant pores and cavities inside the SCCN microtubes,thereby increasing the specific surface area of g-C_(3)N_(4)and providing sufficient reactant attachment sites.Besides,the hierarchical structure of SCCN microtubules strengthens the reflection and scattering of light,and the utilization of visible light is favorably affected.More importantly,co-doping S and C has greatly improved the photocatalytic performance of graphitic carbon nitride,optimized the band gap structure and enhanced the photogenerated carrier splitting.Consequently,the SCCN exhibits a remarkable photocatalytic H_(2)evolution rate of 4868μmol/(g·h).This work demonstrates the potential of multi-nonmetal doped g-C_(3)N_(4)as the ideal photocatalyst for H2 evolution.

紧耦合旋涡环缝式雾化器的初级液体雾化机理研究

为了初步探究紧耦合旋涡环缝式雾化器在真实条件下的液体雾化过程,本文在对旋涡环缝式雾化器气体单相流场特性分析的基础上对金属熔体破碎后形成的并不再继续破碎的雾化液滴在旋流场中的飞行轨迹进行基于离散相模型的数值模拟.研究结果表明:在雾化室内导液管前端中心孔液滴源位置处,自距气流场中心轴线距离越远的液滴源进入旋流场中的雾化液滴在导液管前端径向铺展范围越大.自雾化室内导液管前端中心孔液滴源进入旋流场中的雾化液滴其直径越大则在导液管前端沿径向铺展的范围越小.气流场中的回流区域和雾化液滴自身动能对雾化液滴在旋流场中的飞行轨迹有很大的影响,并且旋涡环缝式雾化器对金属熔体存在两种破碎模式,即波动破碎模式和膜状破碎模式.模拟结果可为旋涡环缝式雾化器在真实液体雾化过程中雾化模式的分类提供参考.

Forest status assessment in China with SDG indicators based on high-resolution satellite data

To assess the status and change trend of forest in China,an indicator framework was developed using SDG sub-indicators.In this paper,we propose an improved methodology and a set of workflows for calculating SDG indicators.The main modification include the use of moderate and high spatial resolution satellite data,as well as state-of-the-art machine learning techniques for forest cover classification and estimation of forest above-ground biomass(AGB).This research employs GF-1 and GF-2 data with enhanced texture information to map forest cover,while time series Landsat data is used to estimate forest AGB across the whole territory of China.The study calculate two SDG sub-indicators:SDG_(15.1.1) for forest area and SDG_(15.2.1) for sustainable forest management.The evaluation results showed that the total forest area in China was approximately 219 million hectares at the end of 2021,accounting for about 23.51%of the land area.The average annual forest AGB from 2015 to 2021 was estimated to be 105.01Mg/ha,and the overall trend of forest AGB change in China was positive,albeit with some spatial differences.

A shadow- eliminated vegetation index (SEVI) for removal of self and cast shadow effects on vegetation in rugged terrains

The effect of terrain shadow, including the self and cast shadows, is one ofthe main obstacles for accurate retrieval of vegetation parameters byremote sensing in rugged terrains. A shadow- eliminated vegetation index(SEVI) was developed, which was computed from only red and nearinfrared top-of-atmosphere reflectance without other heterogeneous dataand topographic correction. After introduction of the conceptual modeland feature analysis of conventional wavebands, the SEVI was constructedby ratio vegetation index (RVI), shadow vegetation index (SVI) andadjustment factor (f (Δ)). Then three methods were used to validate theSEVI accuracy in elimination of terrain shadow effects, including relativeerror analysis, correlation analysis between the cosine of solar incidenceangle (cosi) and vegetation indices, and comparison analysis between SEVIand conventional vegetation indices with topographic correction. Thevalidation results based on 532 samples showed that the SEVI relativeerrors for self and cast shadows were 4.32% and 1.51% respectively. Thecoefficient of determination between cosi and SEVI was only 0.032 and thecoefficient of variation (std/mean) for SEVI was 12.59%. The results indicatethat the proposed SEVI effectively eliminated the effect of terrain shadowsand achieved similar or better results than conventional vegetation indiceswith topographic correction.

Generation of ready to use (RTU) products over China based on Landsat series data

Earth observation community has entered into the era of big data.Family of Landsat sensors have collected massive medium resolution satellite images,which are valuable for long-term land surface monitoring.In order to significantly reduce the magnitude of data processing for remote sensing data users,Landsat-based Ready to Use(RTU)products have been produced.Main RTU products,including orthorectified products,land surface reflectance,land surface temperature,large-area mosaic image,and standard image map products,are described.The resulting Landsat RTU products are hosted on the RSGS earth observation data sharing web site for free download(http://ids.ceode.ac.cn/rtu/).These new products will provide consistent,standardized,multi-decadal image data for robust land cover change detection and monitoring across the Earth sciences.In the coming years,CASEarth DataBank system will be constructed,which is an intelligent data service platform for providing not only the RTU products from multi-source satellite data,but also big earth data analysis methods.

Monitoring vegetation dynamics in East Rennell Island World Heritage Site using multi-sensor and multi-temporal remote sensing data

East Rennell of Solomon Island is the first natural site under customary law to be inscribed on UNESCO’s World Heritage List.Potential threats due to logging,mining and agriculture led to the site being declared a World Heritage in Danger in 2013.For East Rennell World Heritage Site(ERWHS)to‘shed’its‘Danger’status the management must monitor forest cover both within and outside of ERWHS.We used satellite data from multiple sources to track forest cover changes for the entire East Rennell island since 1998.95%of the island is still covered by undisturbed forests;annual average normalized difference vegetation index(NDVI)for the whole island was above 0.91 in 2015.However,vegetation cover in the island has been slowly decreasing,at a rate of–0.0011 NDVI per year between 2000 and 2015.This decrease less pronounced inside ERWHS compared to areas outside.While potential threats due to forest clearing outside ERWHS remain the forest cover change from 2000 to 2015 has been below 15%.We suggest ways in which the Government of Solomon Islands could use our data as well as unmanned air vehicles and field surveys to monitor forest cover change and ensure the future conservation of ERWHS.

Thermo-responsive topological metamorphosis in covalent-and-supramolecular polymer architectures

Topological metamorphosis represents a powerful approach to modulate the properties of polymers.However,it still remains a major challenge to achieve the tunability of bulk mechanical properties via topological transformation in supramolecular polymer systems.Herein,we couple the covalent polymer and supramolecular polymer in a single system—referred to as covalent-and-supramolecular polymer(CSP)—to realize a thermo-responsive macromolecular metamorphosis.The CSP is able to topologically switch from grafted polymer to cross-linked network by taking advantage of synergistic dynamic covalent interactions and host–guest interactions.Benefiting from the topologically structural transformation,brittleness intrinsically evolves into toughness in our CSP architectures with minimum change of their molecular compositions from furan–maleimide to anthracene–maleimide linkers.Our work demonstrates that supramolecular polymers are a promising platform to design smart materials not only due to their inherent stimuli-responsive properties but also because of their abilities in determining bulk mechanical properties of polymers with alterable topological structures.