古诗里的中华瑰宝之光揭秘

通过借用《华夏诗词藏瑰宝》节目,将脍炙人口的古诗词与化学科学相结合,采用拟人化的方式演绎并讲述诗词中具有神秘光彩的中华瑰宝,揭秘它们发光背后的故事,使读者在趣味阅读中认识这些瑰宝的珍贵之处及蕴含的化学知识。

Insights into grain boundary segregation and solubility limit of Cr in(TiZrNbTaCr)C

Dense(TiZrNbTaCr)C with Cr segregation along grain boundaries(GBs)has been first proposed and fabri-cated by pressureless sintering at 1800-2000℃,utilizing the self-synthesized carbide powders obtained by carbothermal reduction.Cr segregation along GBs is successfully realized as expected via optimizing the initial Cr content.When Cr content is more than 11.12 at.%,Cr addition is excessive and results in Cr-rich second phase formation at triple junctions.To analyze the Cr solubility dependence on tempera-ture and initial Cr content,the Cr content in(TiZrNbTaCr)C grains is investigated by EDS.The solubility limit of Cr in(TiZrNbTaCr)C is about 3.8 at.%at 1900℃.Finally,Vickers hardness of all the samples is measured to assess the mechanical property of(TiZrNbTaCr)C ceramics.The basic understanding of the Cr solubility limit and GB segregation feature in(TiZrNbTaCr)C have been preliminarily clarified,which may pave a potential way to design and tailor microstructure and GB feature of(TiZrNbTaCr)C for the purpose of enhancing its properties in the future.

Effects of cathode potentials and nitrate concentrations on dissimilatory nitrate reductions by Pseudomonas alcaliphila in bioelectrochemical systems

The effects of cathode potentials and initial nitrate concentrations on nitrate reduction in bio- electrochemical systems （BESs） were reported. These factors could partition nitrate reduction between denitrification and dissimilatory nitrate reduction to ammonium （DNRA）. Pseudomonas alcaliphilastrain MBR utilized an electrode as the sole electron donor and nitrate as the sole electron acceptor. When the cathode potential was set from -0.3 to -I.1 V （vs. Ag/AgC1） at an initial nitrate concentration of 100 mg NO^-N/L, the DNRA electron recovery increased from （10.76 ± 1.6）% to （35.06 ± 0.99）%; the denitrification electron recovery decreased from （63.42 ± 1,32）% to （44.33 ± 1.92）%. When the initial nitrate concentration increased from （29.09 ± 0.24） to （490.97 ± 3.49） mg NO3-N/L at the same potential （-0.9 V）, denitrification electron recovery increased from （5.88 ± 1.08）% to （50.19 ±2.59）%; the DNRA electron recovery declined from （48.79 ±1.32）% to （16.02 ± 1.41）%. The prevalence of DNRA occurred at high ratios of electron donors to acceptors in the BESs and denitrification prevailed against DNRA under a lower ratio of electron donors to acceptors. These results had a potential application value of regulating the transformation of nitrate to N2 or ammonium in BESs for nitrate removal.

Fracture behavior dependent on crack-tip shapes in nanoscale crack-defect monolayer boron nitride sheets

Nanoscale defects,including cracks,circular holes,and the triangular-shaped defects,often occur in the growth of boron nitride nanosheets(BNNS).In this study,the fracture behavior of chiral BNNS with different crack-tip shapes and the interactions of nanoscale crack-defects are studied using molecular dynamics(MD)simulations and finite element(FE)analysis.Both MD and FE results indicate that the fracture strength of BNNS with two crack tips(t=2)is significantly higher than that with one crack tip(t=1),in which the difference in zigzag(ZZ)direction is more obvious than that in armchair(AC)direction,mainly due to the fact that the change of bond angles near the crack tips is more substantial in the ZZ direction than those in the AC direction.Our results show that the fracture strength of BNNS strongly depends on crack-tip shapes,chiral angles,the defect-to-crack tip spacing and deflection angles.Checking against the current MD simulations and FE analysis shows the present results are reasonable.This study should be of great importance for enhancing the fracture performance of BNNS by modulating their crack-tip shapes and the interactions of nanoscale crack-defects.

六方氮化硼韧脆转变性能的理论研究

基于六方氮化硼原子间Tersoff势函数,论文建立了手性依赖的六方氮化硼"杆-簧"模型,得到了其在大变形下的非线性力学行为.结果表明六方氮化硼断裂模式从扶手椅型(Armchair,手性角为0°)到锯齿型(Zigzag,手性角为30°)由韧性断裂转变为脆性断裂.通过分析拉伸过程中键长键角变化情况,键角变化所起作用超过键长变化导致韧性断裂,而键长起主导作用时则为脆性断裂.探讨不同手性氮化硼非线性力学行为,获得两种断裂模式的分界点大约为手性角15°.相同条件下,石墨烯在拉伸过程中键长变化起支配作用,而氮化硼除了键长变化的影响之外,键角的变化对整个过程也有着至关重要的作用.最后,与分子动力学模拟结果对比显示论文的理论结果是可靠的.该研究对理解六方氮化硼优异的力学性能及其在微纳器件领域的应用提供了理论支撑.

Single-cell technologies:From research to application

In recent years,more and more single-cell technologies have been developed.A vast amount of single-cell omics data has been generated by large projects,such as the Human Cell Atlas,the Mouse Cell Atlas,the Mouse RNA Atlas,the Mouse ATAC Atlas,and the Plant Cell Atlas.Based on these single-cell big data,thousands of bioinformatics algorithms for quality control,clustering,cell-type annotation,developmental inference,cell-cell transition,cell-cell interaction,and spatial analysis are developed.With powerful experimental single-cell technology and state-of-the-art big data analysis methods based on artificial intelligence,the molecular landscape at the single-cell level can be revealed.

Endogenous Fluorescence Carbon Dots Derived from Food Items

BACKGROUND Fluorescent carbon dots(CDs)are a novel class of carbon-based nanomaterials that were discovered in 2004.However,nobody knew that CDs existed in food items naturally until 2012.Properties of nanosize materials are distinct from those of their bulk materials due to the particle size and accordingly alter their bioavailability and/or biocompatibility.Therefore,the potential health risk of nanoparticles in food has drawn massive attention.Currently,almost all studies regarding the biosafety of nanoparticles in food have mainly focused on engineered nanoparticles used as food additives and have excluded the endogenous nanoparticles in food.Therefore,investigation of the properties of food-borne fluorescent CDs and their potential health risk to humans is of great significance.