The Beijing 325 m meteorological tower stands as a pivotal research platform for exploring atmospheric boundary layer physics and atmospheric chemistry.With a legacy spanning 45 years,the tower has played a crucial ro...The Beijing 325 m meteorological tower stands as a pivotal research platform for exploring atmospheric boundary layer physics and atmospheric chemistry.With a legacy spanning 45 years,the tower has played a crucial role in unraveling the complexities of urban air pollution,atmospheric processes,and climate change in Beijing,China.This review paper provides a comprehensive overview of the measurements on the tower over the past two decades.Through long-term comprehensive observations,researchers have elucidated the intricate relationships between anthropogenic emissions,meteorological dynamics,and atmospheric composition,shedding light on the drivers of air pollution and its impacts on public health.The vertical measurements on the tower also enable detailed investigations into boundary layer dynamics,turbulent mixing,and pollutant dispersion,providing invaluable data for validating chemical transport models.Key findings from the tower’s research include the identification of positive feedback mechanisms between aerosols and the boundary layer,the characterization of pollutant sources and transport pathways,the determination of fluxes of gaseous and particulate species,and the assessment of the effectiveness of pollution control measures.Additionally,isotopic measurements have provided new insights into the sources and formation processes of particulate matter and reactive nitrogen species.Finally,the paper outlines future directions for tower-based research,emphasizing the need for long-term comprehensive measurements,the development of innovative tower platforms,and integration of emerging technologies.展开更多
In chemical science,the vertical ionization potential(VIP)is a crucial metric for understanding the electronegativity,hardness and softness of chemical material systems as well as the electronic structure and stabilit...In chemical science,the vertical ionization potential(VIP)is a crucial metric for understanding the electronegativity,hardness and softness of chemical material systems as well as the electronic structure and stability of molecules.Ever since the last century,the model chemistry composite methods have witnessed tremendous developments in computing the thermodynamic properties as well as the barrier heights.However,their performance in realm of the vertical electron processes of molecular systems has been rarely explored.In this study,we for the first time benchmarked the model chemistry composite methods(e.g.,CBS-QB3,G4 and W1BD)in comparison with the commonly used Koopmans's theorem(KT),electron propagator theory(e.g.,OVGF,D2,P3 and P3+)and CCSD(T)methods in calculating the VIP for up to 613 molecular systems with available experimental measurements.The large-scale test calculations strongly showed that the CBS-QB3 model chemistry composite technique can be well recommended to calculate VIP from the perspectives of accuracy,economy and applicability.Notably,the VIP values of up to 7 molecules were identified to have the absolute errors of larger than 0.3 e V at all calculation levels,which have strong hints that their VIP experimental values should be re-investigated.展开更多
Recent advances in high-pressure technologies and large-scale experimental and computational facilities have enabled scientists,at an unprecedented rate,to discover and predict novel states and materials under the ext...Recent advances in high-pressure technologies and large-scale experimental and computational facilities have enabled scientists,at an unprecedented rate,to discover and predict novel states and materials under the extreme pressure-temperature conditions found in deep,giant-planet interiors.Based on a well-documented body of work in this field of high-pressure research,we elucidate the fundamental principles that govern the chemistry of dense solids under extreme conditions.These include:(i)the pressure-induced evolution of chemical bonding and structure of molecular solids to extended covalent solids,ionic solids and,ultimately,metallic solids,as pressure increases to the terapascal regime;(ii)novel properties and complex transition mechanisms,arising from the subtle balance between electron hybridization(bonding)and electrostatic interaction(packing)in densely packed solids;and(iii)new dense framework solids with high energy densities,and with tunable properties and stabilities under ambient conditions.Examples are taken primarily fromlow-Z molecular systems that have scientific implications for giant-planet models,condensed materials physics,and solid-state core-electron chemistry.展开更多
An ocean biogeochemistry model was developed and incorporated into a global ocean general circulation model （LICOM） to form an ocean biogeochemistry general circulation model （OBGCM）. The model was used to study t...An ocean biogeochemistry model was developed and incorporated into a global ocean general circulation model （LICOM） to form an ocean biogeochemistry general circulation model （OBGCM）. The model was used to study the natural carbon cycle and the uptake and storage of anthropogenic CO2 in the ocean. A global export production of 12.5 Pg C yr-1 was obtained. The model estimated that in the pre-industrial era the global equatorial region within ~15~ of the equator released 0.97 Pg C yr-1 to the atmosphere, which was balanced by the gain of CO2 in other regions. The post-industrial air sea CO2 flux indicated the oceanic uptake of CO2 emitted by human activities. An increase of 20-50 ~mol kg-1 for surface dissolved inorganic carbon （DIC） concentrations in the 1990s relative to pre-industrial times was obtained in the simulation, which was consistent with data-based estimates. The model generated a total anthropogenic carbon inventory of 105 Pg C as of 1994, which was within the range of estimates by other researchers. Various transports of both natural and anthropogenic DIC as well as labile dissolved organic carbon （LDOC） were estimated from the simulation. It was realized that the Southern Ocean and the high-latitude region of the North Pacific are important export regions where accumulative air-sea CO2 fluxes are larger than the DIC inventory, whereas the subtropical regions are acceptance regions. The interhemispheric transport of total natural carbon （DIC＋LDOC） was found to be northward （0.11 Pg C yr-1）, which was just balanced by the gain of carbon from the atmosphere in the Southern Hemisphere.展开更多
One hundred and ten samples of rainwater were collected for chemical analysis at the summit of Huangshan Mountain, a high-altitude site in East China, from July 2010 to June 2011. The volume-weighted-mean （VWM） pH f...One hundred and ten samples of rainwater were collected for chemical analysis at the summit of Huangshan Mountain, a high-altitude site in East China, from July 2010 to June 2011. The volume-weighted-mean （VWM） pH for the whole sampling period was 5.03. SO2- and Ca2＋ were the most abundant anion and cation, respectively. The ionic concentrations varied monthly with the highest concentrations in winter/spring and the lowest in summer. Evident inter-correlations were found among most ions, indicating the common sources for some species and fully mixing characteristics of the alpine precipitation chemistry. The VWM ratio of [SO]-]/[NO3] was 2.54, suggesting the acidity of rainwater comes from both nitric and sulfuric acids. Compared with contemporary observations at other alpine continental sites in China, the precipitation at Huangshan Mountain was the least polluted, with the lowest ionic concentrations. Trajectories to Huangshan Mountain on rainy days could be classified into six groups. The rainwater with influencing air masses originating in Mongolia was the most polluted with limited effect. The emissions of Jiangxi, Anhui, Zhejiang and Jiangsu provinces had a strong influence on the overall rain chemistry at Huangshan Mountain. The rainwater with influencing air masses from Inner Mongolia was heavily polluted by anthropogenic pollutants.展开更多
The complex of neodymium chloride lower hydrate with diethylammonium diethyldithiocarbamate (D-DDC) was synthesized conveniently in absolute alcohol and dry N_2 atmosphere. The title complex was identified as Et_2NH_2...The complex of neodymium chloride lower hydrate with diethylammonium diethyldithiocarbamate (D-DDC) was synthesized conveniently in absolute alcohol and dry N_2 atmosphere. The title complex was identified as Et_2NH_2[Nd(S_2CNEt_2)_4] by chemical and elemental analyses and the bonding characteristics of which was characterized by IR. The enthalpies of solution of neodymium chloride hydrate and D-DDC in absolute alcohol at 298.15 K and the enthalpies change of liquid-phase reaction of formation for Et_2NH_2[Nd (S_2CNEt_2)_4] at different temperatures were determined by microcalorimetry. On the basis of experimental and calculated results, three thermodynamic parameters (the activation enthalpy, the activation entropy and the activation free energy), the rate constant and three kinetic parameters (the apparent activation energy, the pre-exponential constant and the reaction order) of liquid-phase reaction of formation were obtained. The enthalpy change of the solid-phase title reaction at 298.15 K was calculated by a thermochemical cycle.展开更多
A precise understanding of the redox chemistry of Nm-Mn+(like N4-Fe^(2+))systems is essential for fundamental studies and rational design of Nm-Mn+-based electrocatalysts for the oxygen reduction reaction(ORR).Herein,...A precise understanding of the redox chemistry of Nm-Mn+(like N4-Fe^(2+))systems is essential for fundamental studies and rational design of Nm-Mn+-based electrocatalysts for the oxygen reduction reaction(ORR).Herein,three different iron phthalocyanines(FePcs)adsorbed on carbon nanotubes((NH2)4FePc@CNTs,(t-Bu)4FePc@CNTs,and FePc@CNTs)were evaluated to demonstrate the effect of the electron donating power of the substituents on the Fe^(3+)/Fe^(2+)redox potential of FePc@CNTs and the role of these composites as ORR mediators in alkaline media.The Fe^(3+)/Fe^(2+)redox potential of the FePcs was found to shift towards the cathodic region upon substitution with electron-donating groups.This up-field shift in the eg-orbital leads to a lower overlap between the onset potential of the Fe^(3+)/Fe^(2+)redox couple and that of the ORR,and thus,the ORR activity decreased in the following order based on the substitution of FePc:-H>-t-Bu>-NH2.展开更多
Uranium and molybdenum are important strategic elements. The production of ^(99)Mo and the hydrometallurgical process of uranium ore face difficult problems of separation of uranium and molybdenum.In this study, the f...Uranium and molybdenum are important strategic elements. The production of ^(99)Mo and the hydrometallurgical process of uranium ore face difficult problems of separation of uranium and molybdenum.In this study, the four phenanthroline diamide ligands were synthesized, and extraction and stripping experiments were performed under different conditions to evaluate the potential application of these ligands for separation of U(Ⅵ) over Mo(Ⅵ). With the growth of alkyl chain, the solubility of ligands could be greatly improved, and the separation effect of U(Ⅵ) over Mo(Ⅵ) gradually increased. The SF_(U/Mo) were around 10,000 at 4 mol/L HNO3. Three stripping agents were tested with the stripping efficiency of Na_(2)CO_(3)(5%) > H_(2)O > HNO_(3)(0.01 mol/L). The stripping percentages of the three stripping agents were all close to unity, indicating that the ligands had the potential to be recycled. The chemical stoichiometry of U(Ⅵ) complexes with ligands was evaluated as 1:1 using electrospray ionization mass spectrometry,ultraviolet visible spectroscopy and single-crystal X-ray diffraction. The consistency between theoretical calculation and experimental results further explains the coordination mechanism.展开更多
The paper discusses the advancements and applications of neural networks, specifically ChatGPT, in various fields, including chemistry education and research. It examines the benefits of AI and ChatGPT, such as their ...The paper discusses the advancements and applications of neural networks, specifically ChatGPT, in various fields, including chemistry education and research. It examines the benefits of AI and ChatGPT, such as their ability to process and analyze large amounts of data, create personalized training systems, and offer problem-solving recommendations. The paper delves into practical applications, showcasing how ChatGPT can be utilised to augment chemistry learning. It provides examples of using ChatGPT for creating tests, generating multiple-choice questions, and studying chemistry in general. Concerns are voiced about the ethical and societal impact of AI development. In conclusion, it explores the exciting potential of AI to tackle challenges that may exceed human capabilities alone, paving the way for further exploration and collaboration between humans and intelligent machines.展开更多
The first asymmetry synthesis of glutinone and its three diastereoisomers were carried out in 8 steps and the stereochemistry of this natural product was given out.
This analysis of the multi-model aerosol optical depth (AOD) in eastern China using the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) datasets shows that the global models underestimate the ...This analysis of the multi-model aerosol optical depth (AOD) in eastern China using the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) datasets shows that the global models underestimate the AOD by 33% and 44% in southern and northern China, respectively, and decrease the relative humidity (RH) of the air in the surface layer to 71%–80%, which is less than the RH of 77%–92% in reanalysis meteorological datasets. This indicates that the low biases in the RH partially account for the errors in the AOD. The AOD is recalculated based on the model aerosol concentrations and the reanalysis humidity data. Improving the mean value of the RH increases the multi-model annual mean AOD by 45% in southern China and by 33% in June–August in northern China. This method of improving the AOD is successful in most of the ACCMIP models, but it is unlikely to be successful in GISS-E2-R, in which the plot of its AOD efficiency against RH strongly deviates from the rest of the models. The effect of the improvement in the modeled RH on the AOD depends on the concentration of aerosols. The shape error in the frequency distribution of the RH is likely to be more important than the error in the mean value of the RH, but this requires further research.展开更多
3D printing technology enhances the combustion characteristics of hybrid rocket fuels by enabling complex geometries. However, improvements in regression rates and energy properties of monotonous 3D printed fuels have...3D printing technology enhances the combustion characteristics of hybrid rocket fuels by enabling complex geometries. However, improvements in regression rates and energy properties of monotonous 3D printed fuels have been limited. This study explores the impact of poly(vinylidene fluoride) and polydopamine-coated aluminum particles on the thermal and combustion properties of 3D printed hybrid rocket fuels. Physical self-assembly and anti-solvent methods were employed for constructing composite μAl particles. Characterization using SEM, XRD, XPS, FTIR, and μCT revealed a core-shell structure and homogeneous elemental distribution. Thermal analysis showed that PVDF coatings significantly increased the heat of combustion for aluminum particles, with maximum enhancement observed in μAl@PDA@PVDF(denoted as μAl@PF) at 6.20 k J/g. Subsequently, 3D printed fuels with varying pure and composite μAl particle contents were prepared using 3D printing. Combustion tests indicated higher regression rates for Al@PF/Resin composites compared to pure resin, positively correlating with particle content. The fluorocarbon-alumina reaction during the combustion stage intensified Al particle combustion, reducing residue size. A comprehensive model based on experiments provides insights into the combustion process of PDA and PVDF-coated droplets. This study advances the design of 3D-printed hybrid rocket fuels, offering strategies to improve regression rates and energy release, crucial for enhancing solid fuel performance for hybrid propulsion.展开更多
Purpose–The brake pipe system was an essential braking component of the railway freight trains,but the existing E-type sealing rings had problems such as insufficient low-temperature resistance,poor heat stability an...Purpose–The brake pipe system was an essential braking component of the railway freight trains,but the existing E-type sealing rings had problems such as insufficient low-temperature resistance,poor heat stability and short service life.To address these issues,low-phenyl silicone rubber was prepared and tested,and the finite element analysis and experimental studies on the sealing performance of its sealing rings were carried out.Design/methodology/approach–The low-temperature resistance and thermal stability of the prepared lowphenyl silicone rubber were studied using low-temperature tensile testing,differential scanning calorimetry,dynamic thermomechanical analysis and thermogravimetric analysis.The sealing performance of the lowphenyl silicone rubber sealing ring was studied by using finite element analysis software abaqus and experiments.Findings–The prepared low-phenyl silicone rubber sealing ring possessed excellent low-temperature resistance and thermal stability.According to the finite element analysis results,the finish of the flange sealing surface and groove outer edge should be ensured,and extrusion damage should be avoided.The sealing rings were more susceptible to damage in high compression ratio and/or low-temperature environments.When the sealing effect was ensured,a small compression ratio should be selected,and rubbers with hardness and elasticity less affected by temperature should be selected.The prepared low-phenyl silicone rubber sealing ring had zero leakage at both room temperature(RT)and�508C.Originality/value–The innovation of this study is that it provides valuable data and experience for the future development of the sealing rings used in the brake pipe flange joints of the railway freight cars in China.展开更多
A sp^(2) carbon-conjugated covalent organic framework (BDATN) was modified through γ-ray radiation reduction and subsequent acidification with hydrochloric acid to yield a novel functional COF (named rBDATN-HCl) for ...A sp^(2) carbon-conjugated covalent organic framework (BDATN) was modified through γ-ray radiation reduction and subsequent acidification with hydrochloric acid to yield a novel functional COF (named rBDATN-HCl) for Cr(Ⅵ) removal.The morphology and structure of rBDATN-HCl were analyzed and identified by SEM,FTIR,XRD and solid-state13C NMR.It is found that the active functional groups,such as hydroxyl and amide,were introduced into BDATN after radiation reduction and acidification.The prepared rBDATN-HCl demonstrates a photocatalytic reduction removal rate of Cr(Ⅵ) above 99%after 60min of illumination with a solid-liquid ratio of 0.5 mg/mL,showing outstanding performance,which is attributed to the increase of dispersibility and adsorption sites of r BDATN-HCl.In comparison to the cBDATN-HCl synthesized with chemical reduction,rBDATN-HCl exhibits a better photoreduction performance for Cr(Ⅵ),demonstrating the advantages of radiation preparation of rBDATN-HCl.It is expected that more functionalized sp^(2) carbon-conjugated COFs could be obtained by this radiation-induced reduction strategy.展开更多
A metal-free,visible-light-induced strategy has been developed for the diborylation of gem-dibromoalkanes.This reaction enables the construction of structurally diverse alkyl gem-diboronates at room temperature via vi...A metal-free,visible-light-induced strategy has been developed for the diborylation of gem-dibromoalkanes.This reaction enables the construction of structurally diverse alkyl gem-diboronates at room temperature via visible-light-induced C—Br bond activation using B2cat2 as the boron source.Through a tandem in-situ dibromination/diborylation process,a onepot transformation from aldehydes to alkyl gem-diboronates has been achieved.Additionally,sunlight irradiation has been demonstrated as a viable alternative for inducing this reaction,enabling gram-scale synthesis with practical applicability.展开更多
The present work aims to stabilize the room temperature allotropic transition of ammonium nitrate(AN)particles utilizing a microencapsulation technique,which involves solvent/non-solvent in which nitrocellulose(NC)has...The present work aims to stabilize the room temperature allotropic transition of ammonium nitrate(AN)particles utilizing a microencapsulation technique,which involves solvent/non-solvent in which nitrocellulose(NC)has been employed as a coating agent.The SEM micrographs revealed distinct features of both pure AN and NC,contrasting with the irregular granular surface topography of the coated AN particles,demonstrating the adherence of NC on the AN surface.Structural analysis via infrared spectroscopy(IR)demonstrated a successful association of AN and NC,with slight shifts observed in IR bands indicating interfacial interactions.Powder X-ray Diffraction(PXRD)analysis further elucidated the structural changes induced by the coating process,revealing that the NC coating altered the crystallization pattern of its pure form.Thermal analysis demonstrates distinct profiles for pure and coated AN,for which the coated sample exhibits a temperature increase and an enthalpy decrease of the room temperature allotropic transition by 6℃,and 36%,respectively.Furthermore,the presence of NC coating alters the intermolecular forces within the composite system,leading to a reduction in melting enthalpy of coated AN by~39%compared to pure AN.The thermal decomposition analysis shows a two-step thermolysis process for coated AN,with a significant increase in the released heat by about 78%accompanied by an increase in the activation barrier of NC and AN thermolysis,demonstrating a stabilized reactivity of the AN-NC particles.These findings highlight the synergistic effect of NC coating on AN particles,which contributed to a structural and reactive stabilization of both AN and NC,proving the potential application of NC-coated AN as a strategically advantageous oxidizer in composite solid propellant formulations.展开更多
An energetic binder based on hydroxyl-terminated polybutadiene(HTPB),doped with different ratios of nitrocellulose(NC)(10%,20%,30%,and 50%),was developed to study the effect of NC doping on the thermal decomposition b...An energetic binder based on hydroxyl-terminated polybutadiene(HTPB),doped with different ratios of nitrocellulose(NC)(10%,20%,30%,and 50%),was developed to study the effect of NC doping on the thermal decomposition behavior of a composite propellant(CP)comprising ammonium nitrate(AN)as an oxidizer and magnesium(Mg)as a fuel.Optimization of the propellant formulation was conducted using Chemical Equilibrium with Applications-National Aeronautics and Space Administration(CEA-NASA)software,which demonstrated an increase in specific impulse by 12.09 s when the binder contained 50%NC.Fourier-transform infrared spectroscopy(FTIR)analysis confirmed the excellent compatibility between the components,and density measurements revealed an increase of 6.4%with a higher NC content.Morphological analysis using optical microscopy showed that NC doping improved the uniformity and compactness of the surface,reduced cavities,and achieved a more homogeneous particle distribution.Differential scanning calorimetry(DSC)analysis indicated a decrease in the decomposition temperature of the propellant as the NC content increased,while kinetic studies revealed a 48.68%reduction in the activation energy when 50%NC was incorporated into the binder.These findings suggest that the addition of NC enhances combustion efficiency and improves overall propellant performance.This study highlights the potential of the new HTPB-NC energetic binder as a promising approach for advancing solid propellant technology.展开更多
Purpose–To investigate the influence of vehicle operation speed,curve geometry parameters and rail profile parameters on wheel–rail creepage in high-speed railway curves and propose a multi-parameter coordinated opt...Purpose–To investigate the influence of vehicle operation speed,curve geometry parameters and rail profile parameters on wheel–rail creepage in high-speed railway curves and propose a multi-parameter coordinated optimization strategy to reduce wheel–rail contact fatigue damage.Design/methodology/approach–Taking a small-radius curve of a high-speed railway as the research object,field measurements were conducted to obtain track parameters and wheel–rail profiles.A coupled vehicle-track dynamics model was established.Multiple numerical experiments were designed using the Latin Hypercube Sampling method to extract wheel-rail creepage indicators and construct a parameter-creepage response surface model.Findings–Key service parameters affecting wheel–rail creepage were identified,including the matching relationship between curve geometry and vehicle speed and rail profile parameters.The influence patterns of various parameters on wheel–rail creepage were revealed through response surface analysis,leading to the establishment of parameter optimization criteria.Originality/value–This study presents the systematic investigation of wheel–rail creepage characteristics under multi-parameter coupling in high-speed railway curves.A response surface-based parameter-creepage relationship model was established,and a multi-parameter coordinated optimization strategy was proposed.The research findings provide theoretical guidance for controlling wheel–rail contact fatigue damage and optimizing wheel–rail profiles in high-speed railway curves.展开更多
Unmanaged wood waste,particularly in countries like Nepal,presents serious environmental concerns due to open burning and improper disposal,leading to carbon emissions,air pollution and land degradation.This study int...Unmanaged wood waste,particularly in countries like Nepal,presents serious environmental concerns due to open burning and improper disposal,leading to carbon emissions,air pollution and land degradation.This study introduces an environmentally sustainable strategy to upcycle Toona ciliata wood scrap—an abundant and underutilized lignocellulosic biomass—into high performance carbon electrodes for green energy storage applications.Activated carbon(TCWAC)was synthesized via single-step pyrolytic carbonization followed by phosphoric acid activation,yielding a material with high specific surface area,hierarchical porosity,and excellent electrical conductivity.Electrochemical measurements using a three-electrode configuration in 6 M KOH revealed optimized potential windows of -1.0 to -0.2 V(TCWAC),-1.2 to 0 V(TCWAC-Mn),and -1.15 to -0.4 V(TCWAC-Fe).TCWAC exhibited a specific capacitance of 156.3 Fg^(-1)at 1 Ag^(-1),with an energy density of 3.5 Whkg^(-1),and 80.2% capacity retention after 1000 charge-discharge cycles.Composites with MnO_(2)and Fe_(2)O_(3)were also evaluated.TWAC-Mn delivered 489.4 Fg^(-1),25.1 Whkg^(-1),and 99.1% retention,whereas,TWAC-Fe achieved 321.3 Fg^(-1),6.3 Whkg^(-1),and 90.3% retention.The superior performance of MnO_(2)is attributed to its multiple oxidation states,facilitating reversible faradaic redox and enhanced pseudocapacitance.This work offers the first direct,systematic comparison of MnO_(2)and Fe_(2)O_(3)composites on a common biomass-carbon matrix under identical synthesis and testing conditions.The finding provides mechanistic insight into charge storage behaviour and demonstrate a scalable route for converting biomass waste into sustainable electrode materials,contributing to cleaner energy solutions and improved biomass valorization.展开更多
Purpose–Regarding that Ultraviolet radiation,pollutant adsorption,and environmental changes may be the main reasons for the aging and yellowing on windshield rubber in high-speed trains,countermeasures are proposed t...Purpose–Regarding that Ultraviolet radiation,pollutant adsorption,and environmental changes may be the main reasons for the aging and yellowing on windshield rubber in high-speed trains,countermeasures are proposed to solve the aging and yellowing of windshield rubber and reduce the adverse effects caused by rubber yellowing.Design/methodology/approach–Scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS)were used to test the yellowed windshield rubber.Aging tests,including UVaging,natural aging and salt spray aging,were conducted to analyze the effects of aging on the windshield rubber.Different cleaning agents were selected to soak the windshield rubber,and the quality,hardness,and surface appearance of the rubber samples were tested.Findings–After UV aging,antioxidants migrated to the surface of the windshield rubber,but due to oxidation failure,they could not capture free radicals,leading to continued oxidation reactions within the material and resulting in yellowing of the rubber in a short period of time.Originality/value–Cleaning agents have a minimal impact on windshield rubber,UV aging has the greatest impact and natural aging is a gradual and slow deterioration process.Through daily deep cleaning and maintenance with protective agents at regular intervals,the deterioration of windshield rubber yellowing in high-speed trains can be effectively suppressed.展开更多
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB0760200)the National Natural Science Foundation of China(Grant Nos.42330605 and 42377101).
文摘The Beijing 325 m meteorological tower stands as a pivotal research platform for exploring atmospheric boundary layer physics and atmospheric chemistry.With a legacy spanning 45 years,the tower has played a crucial role in unraveling the complexities of urban air pollution,atmospheric processes,and climate change in Beijing,China.This review paper provides a comprehensive overview of the measurements on the tower over the past two decades.Through long-term comprehensive observations,researchers have elucidated the intricate relationships between anthropogenic emissions,meteorological dynamics,and atmospheric composition,shedding light on the drivers of air pollution and its impacts on public health.The vertical measurements on the tower also enable detailed investigations into boundary layer dynamics,turbulent mixing,and pollutant dispersion,providing invaluable data for validating chemical transport models.Key findings from the tower’s research include the identification of positive feedback mechanisms between aerosols and the boundary layer,the characterization of pollutant sources and transport pathways,the determination of fluxes of gaseous and particulate species,and the assessment of the effectiveness of pollution control measures.Additionally,isotopic measurements have provided new insights into the sources and formation processes of particulate matter and reactive nitrogen species.Finally,the paper outlines future directions for tower-based research,emphasizing the need for long-term comprehensive measurements,the development of innovative tower platforms,and integration of emerging technologies.
基金funded by the National Natural Science Foundation of China(Nos.22073069,21773082)Science Research Project of Hebei Education Department(No.QN2024255)。
文摘In chemical science,the vertical ionization potential(VIP)is a crucial metric for understanding the electronegativity,hardness and softness of chemical material systems as well as the electronic structure and stability of molecules.Ever since the last century,the model chemistry composite methods have witnessed tremendous developments in computing the thermodynamic properties as well as the barrier heights.However,their performance in realm of the vertical electron processes of molecular systems has been rarely explored.In this study,we for the first time benchmarked the model chemistry composite methods(e.g.,CBS-QB3,G4 and W1BD)in comparison with the commonly used Koopmans's theorem(KT),electron propagator theory(e.g.,OVGF,D2,P3 and P3+)and CCSD(T)methods in calculating the VIP for up to 613 molecular systems with available experimental measurements.The large-scale test calculations strongly showed that the CBS-QB3 model chemistry composite technique can be well recommended to calculate VIP from the perspectives of accuracy,economy and applicability.Notably,the VIP values of up to 7 molecules were identified to have the absolute errors of larger than 0.3 e V at all calculation levels,which have strong hints that their VIP experimental values should be re-investigated.
基金The present study has been performed in support of the NSF(Grant No.DMR 1701360),DOE-NNSA(Grant No.DENA0003342),ARO(Grant No.W911NF-17-1-0468),DARPA(Grant No.W31P4Q-12-1-0009),and ADD in Korea.
文摘Recent advances in high-pressure technologies and large-scale experimental and computational facilities have enabled scientists,at an unprecedented rate,to discover and predict novel states and materials under the extreme pressure-temperature conditions found in deep,giant-planet interiors.Based on a well-documented body of work in this field of high-pressure research,we elucidate the fundamental principles that govern the chemistry of dense solids under extreme conditions.These include:(i)the pressure-induced evolution of chemical bonding and structure of molecular solids to extended covalent solids,ionic solids and,ultimately,metallic solids,as pressure increases to the terapascal regime;(ii)novel properties and complex transition mechanisms,arising from the subtle balance between electron hybridization(bonding)and electrostatic interaction(packing)in densely packed solids;and(iii)new dense framework solids with high energy densities,and with tunable properties and stabilities under ambient conditions.Examples are taken primarily fromlow-Z molecular systems that have scientific implications for giant-planet models,condensed materials physics,and solid-state core-electron chemistry.
基金supported by the National Basic Research Program of China("973 program",Grant No.2010CB951802)the National Natural Science Foundation of China(Grant Nos.40730106,41105087,and 41075091)
文摘An ocean biogeochemistry model was developed and incorporated into a global ocean general circulation model （LICOM） to form an ocean biogeochemistry general circulation model （OBGCM）. The model was used to study the natural carbon cycle and the uptake and storage of anthropogenic CO2 in the ocean. A global export production of 12.5 Pg C yr-1 was obtained. The model estimated that in the pre-industrial era the global equatorial region within ~15~ of the equator released 0.97 Pg C yr-1 to the atmosphere, which was balanced by the gain of CO2 in other regions. The post-industrial air sea CO2 flux indicated the oceanic uptake of CO2 emitted by human activities. An increase of 20-50 ~mol kg-1 for surface dissolved inorganic carbon （DIC） concentrations in the 1990s relative to pre-industrial times was obtained in the simulation, which was consistent with data-based estimates. The model generated a total anthropogenic carbon inventory of 105 Pg C as of 1994, which was within the range of estimates by other researchers. Various transports of both natural and anthropogenic DIC as well as labile dissolved organic carbon （LDOC） were estimated from the simulation. It was realized that the Southern Ocean and the high-latitude region of the North Pacific are important export regions where accumulative air-sea CO2 fluxes are larger than the DIC inventory, whereas the subtropical regions are acceptance regions. The interhemispheric transport of total natural carbon （DIC＋LDOC） was found to be northward （0.11 Pg C yr-1）, which was just balanced by the gain of carbon from the atmosphere in the Southern Hemisphere.
基金supported by funds from the Scientific Research Projects of High-level Talents of the Department of Human Resources and Social Security of Anhui Province (Grant No.2009Z019)the State Key Laboratory of Atmospheric Boundary Physics and Atmospheric Chemistry (Grant No.LAPC-KF-201105)
文摘One hundred and ten samples of rainwater were collected for chemical analysis at the summit of Huangshan Mountain, a high-altitude site in East China, from July 2010 to June 2011. The volume-weighted-mean （VWM） pH for the whole sampling period was 5.03. SO2- and Ca2＋ were the most abundant anion and cation, respectively. The ionic concentrations varied monthly with the highest concentrations in winter/spring and the lowest in summer. Evident inter-correlations were found among most ions, indicating the common sources for some species and fully mixing characteristics of the alpine precipitation chemistry. The VWM ratio of [SO]-]/[NO3] was 2.54, suggesting the acidity of rainwater comes from both nitric and sulfuric acids. Compared with contemporary observations at other alpine continental sites in China, the precipitation at Huangshan Mountain was the least polluted, with the lowest ionic concentrations. Trajectories to Huangshan Mountain on rainy days could be classified into six groups. The rainwater with influencing air masses originating in Mongolia was the most polluted with limited effect. The emissions of Jiangxi, Anhui, Zhejiang and Jiangsu provinces had a strong influence on the overall rain chemistry at Huangshan Mountain. The rainwater with influencing air masses from Inner Mongolia was heavily polluted by anthropogenic pollutants.
文摘The complex of neodymium chloride lower hydrate with diethylammonium diethyldithiocarbamate (D-DDC) was synthesized conveniently in absolute alcohol and dry N_2 atmosphere. The title complex was identified as Et_2NH_2[Nd(S_2CNEt_2)_4] by chemical and elemental analyses and the bonding characteristics of which was characterized by IR. The enthalpies of solution of neodymium chloride hydrate and D-DDC in absolute alcohol at 298.15 K and the enthalpies change of liquid-phase reaction of formation for Et_2NH_2[Nd (S_2CNEt_2)_4] at different temperatures were determined by microcalorimetry. On the basis of experimental and calculated results, three thermodynamic parameters (the activation enthalpy, the activation entropy and the activation free energy), the rate constant and three kinetic parameters (the apparent activation energy, the pre-exponential constant and the reaction order) of liquid-phase reaction of formation were obtained. The enthalpy change of the solid-phase title reaction at 298.15 K was calculated by a thermochemical cycle.
文摘A precise understanding of the redox chemistry of Nm-Mn+(like N4-Fe^(2+))systems is essential for fundamental studies and rational design of Nm-Mn+-based electrocatalysts for the oxygen reduction reaction(ORR).Herein,three different iron phthalocyanines(FePcs)adsorbed on carbon nanotubes((NH2)4FePc@CNTs,(t-Bu)4FePc@CNTs,and FePc@CNTs)were evaluated to demonstrate the effect of the electron donating power of the substituents on the Fe^(3+)/Fe^(2+)redox potential of FePc@CNTs and the role of these composites as ORR mediators in alkaline media.The Fe^(3+)/Fe^(2+)redox potential of the FePcs was found to shift towards the cathodic region upon substitution with electron-donating groups.This up-field shift in the eg-orbital leads to a lower overlap between the onset potential of the Fe^(3+)/Fe^(2+)redox couple and that of the ORR,and thus,the ORR activity decreased in the following order based on the substitution of FePc:-H>-t-Bu>-NH2.
基金supported by the National Natural Science Foundation of China(Nos.U1967216,22076188,U20B2019,21876174)the National Science Fund for Distinguished Young Scholars(No.21925603).
文摘Uranium and molybdenum are important strategic elements. The production of ^(99)Mo and the hydrometallurgical process of uranium ore face difficult problems of separation of uranium and molybdenum.In this study, the four phenanthroline diamide ligands were synthesized, and extraction and stripping experiments were performed under different conditions to evaluate the potential application of these ligands for separation of U(Ⅵ) over Mo(Ⅵ). With the growth of alkyl chain, the solubility of ligands could be greatly improved, and the separation effect of U(Ⅵ) over Mo(Ⅵ) gradually increased. The SF_(U/Mo) were around 10,000 at 4 mol/L HNO3. Three stripping agents were tested with the stripping efficiency of Na_(2)CO_(3)(5%) > H_(2)O > HNO_(3)(0.01 mol/L). The stripping percentages of the three stripping agents were all close to unity, indicating that the ligands had the potential to be recycled. The chemical stoichiometry of U(Ⅵ) complexes with ligands was evaluated as 1:1 using electrospray ionization mass spectrometry,ultraviolet visible spectroscopy and single-crystal X-ray diffraction. The consistency between theoretical calculation and experimental results further explains the coordination mechanism.
文摘The paper discusses the advancements and applications of neural networks, specifically ChatGPT, in various fields, including chemistry education and research. It examines the benefits of AI and ChatGPT, such as their ability to process and analyze large amounts of data, create personalized training systems, and offer problem-solving recommendations. The paper delves into practical applications, showcasing how ChatGPT can be utilised to augment chemistry learning. It provides examples of using ChatGPT for creating tests, generating multiple-choice questions, and studying chemistry in general. Concerns are voiced about the ethical and societal impact of AI development. In conclusion, it explores the exciting potential of AI to tackle challenges that may exceed human capabilities alone, paving the way for further exploration and collaboration between humans and intelligent machines.
基金We are grateful for financial support from the National Natural Science Foundation of China (Grant No. 29732060)
文摘The first asymmetry synthesis of glutinone and its three diastereoisomers were carried out in 8 steps and the stereochemistry of this natural product was given out.
基金jointly supported by the National Key Research and Development Program of China [grant number2016YFE0201400]the Basic Research Program of the State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry,Institute of Atmospheric Physics,Chinese Academy of Sciences [grant number 7-082999]
文摘This analysis of the multi-model aerosol optical depth (AOD) in eastern China using the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) datasets shows that the global models underestimate the AOD by 33% and 44% in southern and northern China, respectively, and decrease the relative humidity (RH) of the air in the surface layer to 71%–80%, which is less than the RH of 77%–92% in reanalysis meteorological datasets. This indicates that the low biases in the RH partially account for the errors in the AOD. The AOD is recalculated based on the model aerosol concentrations and the reanalysis humidity data. Improving the mean value of the RH increases the multi-model annual mean AOD by 45% in southern China and by 33% in June–August in northern China. This method of improving the AOD is successful in most of the ACCMIP models, but it is unlikely to be successful in GISS-E2-R, in which the plot of its AOD efficiency against RH strongly deviates from the rest of the models. The effect of the improvement in the modeled RH on the AOD depends on the concentration of aerosols. The shape error in the frequency distribution of the RH is likely to be more important than the error in the mean value of the RH, but this requires further research.
基金funded by the National Natural Science Foundation of China(Grant No.06101213)the National Natural Science Foundation of China(Grant No.22105160).
文摘3D printing technology enhances the combustion characteristics of hybrid rocket fuels by enabling complex geometries. However, improvements in regression rates and energy properties of monotonous 3D printed fuels have been limited. This study explores the impact of poly(vinylidene fluoride) and polydopamine-coated aluminum particles on the thermal and combustion properties of 3D printed hybrid rocket fuels. Physical self-assembly and anti-solvent methods were employed for constructing composite μAl particles. Characterization using SEM, XRD, XPS, FTIR, and μCT revealed a core-shell structure and homogeneous elemental distribution. Thermal analysis showed that PVDF coatings significantly increased the heat of combustion for aluminum particles, with maximum enhancement observed in μAl@PDA@PVDF(denoted as μAl@PF) at 6.20 k J/g. Subsequently, 3D printed fuels with varying pure and composite μAl particle contents were prepared using 3D printing. Combustion tests indicated higher regression rates for Al@PF/Resin composites compared to pure resin, positively correlating with particle content. The fluorocarbon-alumina reaction during the combustion stage intensified Al particle combustion, reducing residue size. A comprehensive model based on experiments provides insights into the combustion process of PDA and PVDF-coated droplets. This study advances the design of 3D-printed hybrid rocket fuels, offering strategies to improve regression rates and energy release, crucial for enhancing solid fuel performance for hybrid propulsion.
基金supported by the Science and Technology Research and Development Plan of the China State Railway Group Company Limited(No.Q2023J012).
文摘Purpose–The brake pipe system was an essential braking component of the railway freight trains,but the existing E-type sealing rings had problems such as insufficient low-temperature resistance,poor heat stability and short service life.To address these issues,low-phenyl silicone rubber was prepared and tested,and the finite element analysis and experimental studies on the sealing performance of its sealing rings were carried out.Design/methodology/approach–The low-temperature resistance and thermal stability of the prepared lowphenyl silicone rubber were studied using low-temperature tensile testing,differential scanning calorimetry,dynamic thermomechanical analysis and thermogravimetric analysis.The sealing performance of the lowphenyl silicone rubber sealing ring was studied by using finite element analysis software abaqus and experiments.Findings–The prepared low-phenyl silicone rubber sealing ring possessed excellent low-temperature resistance and thermal stability.According to the finite element analysis results,the finish of the flange sealing surface and groove outer edge should be ensured,and extrusion damage should be avoided.The sealing rings were more susceptible to damage in high compression ratio and/or low-temperature environments.When the sealing effect was ensured,a small compression ratio should be selected,and rubbers with hardness and elasticity less affected by temperature should be selected.The prepared low-phenyl silicone rubber sealing ring had zero leakage at both room temperature(RT)and�508C.Originality/value–The innovation of this study is that it provides valuable data and experience for the future development of the sealing rings used in the brake pipe flange joints of the railway freight cars in China.
基金supported by the National Natural Science Foundation of China(No.U2067212)the National Science Fund for Distinguished Young Scholars(No.21925603).
文摘A sp^(2) carbon-conjugated covalent organic framework (BDATN) was modified through γ-ray radiation reduction and subsequent acidification with hydrochloric acid to yield a novel functional COF (named rBDATN-HCl) for Cr(Ⅵ) removal.The morphology and structure of rBDATN-HCl were analyzed and identified by SEM,FTIR,XRD and solid-state13C NMR.It is found that the active functional groups,such as hydroxyl and amide,were introduced into BDATN after radiation reduction and acidification.The prepared rBDATN-HCl demonstrates a photocatalytic reduction removal rate of Cr(Ⅵ) above 99%after 60min of illumination with a solid-liquid ratio of 0.5 mg/mL,showing outstanding performance,which is attributed to the increase of dispersibility and adsorption sites of r BDATN-HCl.In comparison to the cBDATN-HCl synthesized with chemical reduction,rBDATN-HCl exhibits a better photoreduction performance for Cr(Ⅵ),demonstrating the advantages of radiation preparation of rBDATN-HCl.It is expected that more functionalized sp^(2) carbon-conjugated COFs could be obtained by this radiation-induced reduction strategy.
文摘A metal-free,visible-light-induced strategy has been developed for the diborylation of gem-dibromoalkanes.This reaction enables the construction of structurally diverse alkyl gem-diboronates at room temperature via visible-light-induced C—Br bond activation using B2cat2 as the boron source.Through a tandem in-situ dibromination/diborylation process,a onepot transformation from aldehydes to alkyl gem-diboronates has been achieved.Additionally,sunlight irradiation has been demonstrated as a viable alternative for inducing this reaction,enabling gram-scale synthesis with practical applicability.
文摘The present work aims to stabilize the room temperature allotropic transition of ammonium nitrate(AN)particles utilizing a microencapsulation technique,which involves solvent/non-solvent in which nitrocellulose(NC)has been employed as a coating agent.The SEM micrographs revealed distinct features of both pure AN and NC,contrasting with the irregular granular surface topography of the coated AN particles,demonstrating the adherence of NC on the AN surface.Structural analysis via infrared spectroscopy(IR)demonstrated a successful association of AN and NC,with slight shifts observed in IR bands indicating interfacial interactions.Powder X-ray Diffraction(PXRD)analysis further elucidated the structural changes induced by the coating process,revealing that the NC coating altered the crystallization pattern of its pure form.Thermal analysis demonstrates distinct profiles for pure and coated AN,for which the coated sample exhibits a temperature increase and an enthalpy decrease of the room temperature allotropic transition by 6℃,and 36%,respectively.Furthermore,the presence of NC coating alters the intermolecular forces within the composite system,leading to a reduction in melting enthalpy of coated AN by~39%compared to pure AN.The thermal decomposition analysis shows a two-step thermolysis process for coated AN,with a significant increase in the released heat by about 78%accompanied by an increase in the activation barrier of NC and AN thermolysis,demonstrating a stabilized reactivity of the AN-NC particles.These findings highlight the synergistic effect of NC coating on AN particles,which contributed to a structural and reactive stabilization of both AN and NC,proving the potential application of NC-coated AN as a strategically advantageous oxidizer in composite solid propellant formulations.
文摘An energetic binder based on hydroxyl-terminated polybutadiene(HTPB),doped with different ratios of nitrocellulose(NC)(10%,20%,30%,and 50%),was developed to study the effect of NC doping on the thermal decomposition behavior of a composite propellant(CP)comprising ammonium nitrate(AN)as an oxidizer and magnesium(Mg)as a fuel.Optimization of the propellant formulation was conducted using Chemical Equilibrium with Applications-National Aeronautics and Space Administration(CEA-NASA)software,which demonstrated an increase in specific impulse by 12.09 s when the binder contained 50%NC.Fourier-transform infrared spectroscopy(FTIR)analysis confirmed the excellent compatibility between the components,and density measurements revealed an increase of 6.4%with a higher NC content.Morphological analysis using optical microscopy showed that NC doping improved the uniformity and compactness of the surface,reduced cavities,and achieved a more homogeneous particle distribution.Differential scanning calorimetry(DSC)analysis indicated a decrease in the decomposition temperature of the propellant as the NC content increased,while kinetic studies revealed a 48.68%reduction in the activation energy when 50%NC was incorporated into the binder.These findings suggest that the addition of NC enhances combustion efficiency and improves overall propellant performance.This study highlights the potential of the new HTPB-NC energetic binder as a promising approach for advancing solid propellant technology.
基金sponsored by the National Natural Science Foundation of China(Grant No.52405443)the Technology Research and Development Plan of China Railway(Grant No.N2023G063)the Fund of China Academy of Railway Sciences Corporation Limited(Grant No.2023YJ054).
文摘Purpose–To investigate the influence of vehicle operation speed,curve geometry parameters and rail profile parameters on wheel–rail creepage in high-speed railway curves and propose a multi-parameter coordinated optimization strategy to reduce wheel–rail contact fatigue damage.Design/methodology/approach–Taking a small-radius curve of a high-speed railway as the research object,field measurements were conducted to obtain track parameters and wheel–rail profiles.A coupled vehicle-track dynamics model was established.Multiple numerical experiments were designed using the Latin Hypercube Sampling method to extract wheel-rail creepage indicators and construct a parameter-creepage response surface model.Findings–Key service parameters affecting wheel–rail creepage were identified,including the matching relationship between curve geometry and vehicle speed and rail profile parameters.The influence patterns of various parameters on wheel–rail creepage were revealed through response surface analysis,leading to the establishment of parameter optimization criteria.Originality/value–This study presents the systematic investigation of wheel–rail creepage characteristics under multi-parameter coupling in high-speed railway curves.A response surface-based parameter-creepage relationship model was established,and a multi-parameter coordinated optimization strategy was proposed.The research findings provide theoretical guidance for controlling wheel–rail contact fatigue damage and optimizing wheel–rail profiles in high-speed railway curves.
文摘Unmanaged wood waste,particularly in countries like Nepal,presents serious environmental concerns due to open burning and improper disposal,leading to carbon emissions,air pollution and land degradation.This study introduces an environmentally sustainable strategy to upcycle Toona ciliata wood scrap—an abundant and underutilized lignocellulosic biomass—into high performance carbon electrodes for green energy storage applications.Activated carbon(TCWAC)was synthesized via single-step pyrolytic carbonization followed by phosphoric acid activation,yielding a material with high specific surface area,hierarchical porosity,and excellent electrical conductivity.Electrochemical measurements using a three-electrode configuration in 6 M KOH revealed optimized potential windows of -1.0 to -0.2 V(TCWAC),-1.2 to 0 V(TCWAC-Mn),and -1.15 to -0.4 V(TCWAC-Fe).TCWAC exhibited a specific capacitance of 156.3 Fg^(-1)at 1 Ag^(-1),with an energy density of 3.5 Whkg^(-1),and 80.2% capacity retention after 1000 charge-discharge cycles.Composites with MnO_(2)and Fe_(2)O_(3)were also evaluated.TWAC-Mn delivered 489.4 Fg^(-1),25.1 Whkg^(-1),and 99.1% retention,whereas,TWAC-Fe achieved 321.3 Fg^(-1),6.3 Whkg^(-1),and 90.3% retention.The superior performance of MnO_(2)is attributed to its multiple oxidation states,facilitating reversible faradaic redox and enhanced pseudocapacitance.This work offers the first direct,systematic comparison of MnO_(2)and Fe_(2)O_(3)composites on a common biomass-carbon matrix under identical synthesis and testing conditions.The finding provides mechanistic insight into charge storage behaviour and demonstrate a scalable route for converting biomass waste into sustainable electrode materials,contributing to cleaner energy solutions and improved biomass valorization.
文摘Purpose–Regarding that Ultraviolet radiation,pollutant adsorption,and environmental changes may be the main reasons for the aging and yellowing on windshield rubber in high-speed trains,countermeasures are proposed to solve the aging and yellowing of windshield rubber and reduce the adverse effects caused by rubber yellowing.Design/methodology/approach–Scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS)were used to test the yellowed windshield rubber.Aging tests,including UVaging,natural aging and salt spray aging,were conducted to analyze the effects of aging on the windshield rubber.Different cleaning agents were selected to soak the windshield rubber,and the quality,hardness,and surface appearance of the rubber samples were tested.Findings–After UV aging,antioxidants migrated to the surface of the windshield rubber,but due to oxidation failure,they could not capture free radicals,leading to continued oxidation reactions within the material and resulting in yellowing of the rubber in a short period of time.Originality/value–Cleaning agents have a minimal impact on windshield rubber,UV aging has the greatest impact and natural aging is a gradual and slow deterioration process.Through daily deep cleaning and maintenance with protective agents at regular intervals,the deterioration of windshield rubber yellowing in high-speed trains can be effectively suppressed.
