CONSTANS(CO)and CONSTANS-LIKE(COL)transcription factors are known to regulate a series of cellular processes,including the transition from vegetative growth to flower development in plants.However,their role in regula...CONSTANS(CO)and CONSTANS-LIKE(COL)transcription factors are known to regulate a series of cellular processes,including the transition from vegetative growth to flower development in plants.However,their role in regulating the fruit chlorophyll content is poorly understood.In this study,SlCOL1,the tomato(Solanum lycopersicum)ortholog of Arabidopsis CONSTANS,was shown to play key roles in controlling fruit chlorophyll.The suppression of SlCOL1 expression led to a reduction in the chlorophyll content of immature green fruit,while the overexpression of SlCOL1 increased it.An analysis of protein-protein interactions indicated that SlCOL1 forms a complex with GOLDEN2-LIKE(GLK2),which promotes the stability of its protein.The overexpression of SlCOL1in the glk2 null mutation background of tomato failed to promote chlorophyll accumulation in the immature green fruit,which suggests that GLK2 is required for the function of SlCOL1 in regulating chlorophyll content.These results shed new light on the mechanisms used by COL1 and GLK2 to regulate fruit development and chlorophyll accumulation in tomato.展开更多
Background: Children with seasonal influenza infection cause a significant burden of disease each year in the pediatric clinic. Influenza A and B viruses are the major types responsible for illness. A better understan...Background: Children with seasonal influenza infection cause a significant burden of disease each year in the pediatric clinic. Influenza A and B viruses are the major types responsible for illness. A better understanding of the periodicity facilitates the prevention and control of influenza in children. Objective: This study aims to analyze the epidemiological patterns and subtype characterization of influenza viruses among children in Shenzhen, China. Methods: Influenza samples were collected by nasopharyngeal swabs from influenza like illness patients in Shenzhen Children’s Hospital from January 2016 to December 2018. The positive cases and influenza subtypes were determined by gold labeled antigen detection and reverse transcriptase polymerase chain reaction. The influenza periodicity and age, subtype distribution as well as the association between climate parameters and different influenza subtypes were analyzed by SPSS 22.0. Results: The influenza positive rate during 2016-2018 was 21.0%, with a highest positive rate in the year 2018. The positive rate varied by month, season, and year describing a sequence of peaks presenting primarily in all year including spring, summer and winter. The characteristics of influenza peak were different in each year, with a spring peak in 2016 and a summer plus a winter-spring peaks in 2017 and 2018. In addition, influenza B exhibited a winter-spring seasonal pattern while influenza A displayed a more variable seasonality, highlighting influenza B rather than influenza A which had a negative association with climate parameters. Influenza-positive cases were older than influenza-negative cases (P P Conclusion: Influenza activity in children from Shenzhen typically displays both winter-spring and summer peaks. Influenza A epidemic occurred separately or co-circulated with influenza B, with a winter-spring pattern for influenza B and a much more variable seasonality for influenza A. Influenza B had a negative association with climate parameters. In addition, hospitalization with influenza often occurs in younger individuals infected with influenza A.展开更多
Water-based lubrication is an effective method to achieve superlubricity,which implies a friction coefficient in the order of 10−3 or lower.Recent numerical,analytical,and experimental studies confirm that the surface...Water-based lubrication is an effective method to achieve superlubricity,which implies a friction coefficient in the order of 10−3 or lower.Recent numerical,analytical,and experimental studies confirm that the surface force effect is crucial for realizing water-based superlubricity.To enhance the contribution of the surface force,soft and plastic materials can be utilized as friction pair materials because of their effect in increasing the contact area.A new numerical model of water-based lubrication that considers the surface force between plastic and elastic materials is developed in this study to investigate the effect of plastic flow in water-based lubrication.Considering the complexity of residual stress accumulation in lubrication problems,a simplified plastic model is proposed,which merely calculates the result of the dry contact solution and avoids repeated calculations of the plastic flow.The results of the two models show good agreement.Plastic deformation reduces the local contact pressure and enhances the function of the surface force,thus resulting in a lower friction coefficient.展开更多
The micro crack of aluminum sheet during cold rolling lubricated with emulsions is investigated. Experi-ments show that micro cracks occur after cold rolling process and this is attributed to various parameters, for i...The micro crack of aluminum sheet during cold rolling lubricated with emulsions is investigated. Experi-ments show that micro cracks occur after cold rolling process and this is attributed to various parameters, for instance, the thin oxide film formed at the sheet surface. The micro crack spacing thus becomes an important parameter which deserves more concerns. The aspect ratio of these micro cracks is then analyzed theoreti-cally, which takes into consideration of the oxide fracture process. The good agreement between the obser-vations and the theoretical predictions validates the analysis. The approach can shed some new lights on the mechanical process of aluminium sheet during cold rolling.展开更多
In the field of perovskite solar cells(PSCs),the research on defects in the buried interface has been relatively limited due to its non-exposure;however,this interface significantly impacts the performance enhancement...In the field of perovskite solar cells(PSCs),the research on defects in the buried interface has been relatively limited due to its non-exposure;however,this interface significantly impacts the performance enhancement of inverted PSCs.This study employs phenylethylammonium chloride(PEACl)molecules as a buffer layer to modify the buried interface of p-i-n structured PSCs,aiming to enhance the uniformity of self-assembled monolayers(SAMs)and facilitate the uniform nucleation and growth of perovskite films on the substrate.Furthermore,the introduction of the PEACl buffer layer effectively passivates defects at the bottom of the perovskite layer and notably enhances the crystal quality of the perovskite film by mitigating residual stress,thereby reducing nonradiative recombination loss.Following these optimizations,the MA-free PSCs treated with PEACl achieve a power conversion efficiency(PCE)of 24.11%,with significant improvements in storage,thermal stability,and operational stability.Particularly noteworthy is the device's performance in an unencapsulated state,whereas after 1,500 hours of continuous light operation stability testing,it retains 97%of its original efficiency.This study not only enriches the systematic understanding of the characteristics of the buried interface in PSCs but also contributes significantly to advancing the commercial production of perovskite photovoltaic technology.展开更多
1-(4-ethylphenyl)-nonane-1,3-dione(0206)is an oil-soluble liquid molecule with rod-like structure.In this study,the chelate(0206-Fe)with octahedral structure was prepared by the reaction of ferric chloride and 1,3-dik...1-(4-ethylphenyl)-nonane-1,3-dione(0206)is an oil-soluble liquid molecule with rod-like structure.In this study,the chelate(0206-Fe)with octahedral structure was prepared by the reaction of ferric chloride and 1,3-diketone.The experimental results show that when using 0206 and a mixed solution containing 60%0206-Fe and 40%0206(0206-Fe(60%))as lubricants of the steel friction pairs,superlubricity can be achieved(0.007,0.006).But their wear scar diameters(WSD)were very large(532µm,370µm),which resulted in the pressure of only 44.3 and 61.8 MPa in the contact areas of the friction pairs.When 0206-Fe(60%)was mixed with PAO6,it was found that the friction coefficient(COF)decreased with increase of 0206-Fe(60%)in the solution.When the ratio of 0206-Fe(60%)to PAO6 was 8:2(PAO6(20%)),it exhibited better comprehensive tribological properties(232.3 MPa).Subsequent studies have shown that reducing the viscosity of the base oil in the mixed solution helped to reduce COF and increased WSD.Considering the COF,contact pressure,and running-in time,it was found that the mixed lubricant(Oil3(20%))prepared by the base oil with a viscosity of 19.7 mPa·s(Oil3)and 0206-Fe(60%)exhibited the best tribological properties(0.007,161.4 MPa,3,100 s).展开更多
Traditional transient angle stability analysis methods do not fully consider the spatial characteristics of the network topology and the temporal characteristics of the time-series disturbance.Hence,a data-driven meth...Traditional transient angle stability analysis methods do not fully consider the spatial characteristics of the network topology and the temporal characteristics of the time-series disturbance.Hence,a data-driven method is proposed in this study,combining graph convolution network and long short-term memory network(GCN-LSTM)to analyze the transient power angle sta-bility by exploring the spatiotemporal disturbance char-acteristics of future power systems with high penetration of renewable energy sources(wind and solar energy)and power electronics.The key time-series electrical state quantities are considered as the initial input feature quantities and normalized using the Z-score,whereas the network adjacency matrix is constructed according to the system network topology.The normalized feature quan-tities and network adjacency matrix were used as the inputs of the GCN to obtain the spatial features,reflecting changes in the network topology.Subsequently,the spa-tial features are inputted into the LSTM network to ob-tain the temporal features,reflecting dynamic changes in the transient power angle of the generators.Finally,the spatiotemporal features are fused through a fully con-nected network to analyze the transient power angle stability of future power systems,and the softmax activa-tion cross-entropy loss functions are used to predict the stability of the samples.The proposed transient power angle stability assessment method is tested on a 500 kV AC-DC practical power system,and the simulation results show that the proposed method could effectively mine the spatiotemporal disturbance characteristics of power sys-tems. Moreover, the proposed model has higher accuracy, higher recall rate, and shorter training and testing times than traditional transient power angle stability algo-rithms.展开更多
1,2,3-TrI[Cis-9-Hexadecenoyl](GTM)is a common oiliness additive.In this paper,the anti-wear property of GTM was found poor when it was directly used as lubricating oil for titanium alloy.However,when it was added to w...1,2,3-TrI[Cis-9-Hexadecenoyl](GTM)is a common oiliness additive.In this paper,the anti-wear property of GTM was found poor when it was directly used as lubricating oil for titanium alloy.However,when it was added to water and made into oil-in-water(OW)emulsion,it could play an effective role.The wear volume of titanium alloy sample lubricated by the emulsion was reduced by 75%compared to that lubricated by pure oil.It was difficult to fully uncover the underlying mechanism of these phenomena by experimental methods alone.With the help of molecular simulation method,the changes of GTM in chemical activity and adsorption capacity caused by water medium were revealed on atomic scale.The adsorption energies between GTM and titanium alloy under different temperature were quantitatively calculated.The superior anti-wear performance of the emulsions was related to following three aspects:(1)Water medium enhanced the adsorption capacity of GTM;(2)water medium changed the composition of lubrication film;and(3)the adsorption film in the water medium was less affected by temperature.Based on above results,an approach to predict tribological properties of oiliness additive was proposed.Using this method,the lubrication effects of several oiliness additives were successfully predicted.展开更多
Graphene is a promising material as a lubricant additive for reducing friction and wear.Here,a dispersing method which combines chemical modification of graphene by octadecylamine and dicyclohexylcarbodiimide with a k...Graphene is a promising material as a lubricant additive for reducing friction and wear.Here,a dispersing method which combines chemical modification of graphene by octadecylamine and dicyclohexylcarbodiimide with a kind of effective dispersant has been successfully developed to achieve the remarkable dispersion stability of graphene in base oil.The stable dispersion time of modified graphene(0.5 wt%)with dispersant(1 wt%)in PAO-6 could be up to about 120 days,which was the longest time reported so far.At the same time,the lubricant exhibits a significant improvement of tribological performance for a steel ball to plate tribo-system with a normal load of 2 N.The coefficient of friction between sliding surfaces was~0.10 and the depth of wear track on plate was~21 nm,which decreased by about 44%and 90%when compared to pure PAO-6,respectively.Furthermore,the analysis of the lubricating mechanisms in regard to the sliding-induced formation of nanostructured tribo-film has been contacted by using Raman spectra and TEM.展开更多
In this study,we address the superlubricity behavior of sapphire against ruby(or sapphire against itself)under phosphoric acid solution lubrication.An ultra-low friction coefficient of 0.004 was obtained under a very ...In this study,we address the superlubricity behavior of sapphire against ruby(or sapphire against itself)under phosphoric acid solution lubrication.An ultra-low friction coefficient of 0.004 was obtained under a very high contact pressure,with a virgin contact pressure up to 2.57 GPa.Related experiments have indicated that the load,sliding speed,and humidity of the test environment can affect superlubricity to some degree,so we tested variations in these conditions.When superlubricity appears in this study a thin film is present,consisting of a hydrogen bond network of phosphoric acid and water molecules adsorbed on the two friction surfaces,which accounts for the ultra-low friction.Most significantly,the wear rate of the sapphire and ruby in the friction process is very slow and the superlubricity state is very stable,providing favorable conditions for future technological applications.展开更多
In this work,a super-low friction coefficient of 0.003 was found between a silicon nitride ball and a sapphire plate lubricated by phosphoric acid solution.The wear mainly occurred in the running-in period and disappe...In this work,a super-low friction coefficient of 0.003 was found between a silicon nitride ball and a sapphire plate lubricated by phosphoric acid solution.The wear mainly occurred in the running-in period and disappeared after superlubricity was achieved.The friction coefficient was effectively reduced from 0.3 to 0.003 at a constant speed of 0.076 m/s,accompanied by a 12-nm-thickness film.The lubrication regime was indicated to change from boundary lubrication in the running-in period to elastohydrodynamic lubrication in the superlubricity period,which is also supported by the results of the friction coefficient versus sliding speed.In addition,the experimental results showed good agreement with theoretical calculations based on the elastohydrodynamic lubrication theory,suggesting a significant hydrodynamic effect of phosphoric acid on superlubricity.展开更多
Superlubricity,the state of ultralow friction between two sliding surfaces,has become a frontier subject in tribology.Here,a state-of-the-art review of the phenomena and mechanisms of liquid superlubricity are present...Superlubricity,the state of ultralow friction between two sliding surfaces,has become a frontier subject in tribology.Here,a state-of-the-art review of the phenomena and mechanisms of liquid superlubricity are presented based on our ten-year research,to unlock the secrets behind liquid superlubricity,a major approach to achieve superlubricity.An overview of the discovery of liquid superlubricity materials is presented from five different categories,including water and acid-based solutions,hydrated materials,ionic liquids(ILs),two-dimensional(2D)materials as lubricant additives,and oil-based lubricants,to show the hydrodynamic and hydration contributions to liquid superlubricity.The review also discusses four methods to further expand superlubricity by solving the challenge of lubricants that have a high load-carrying capacity with a low shear resistance,including enhancing the hydration contribution by strengthening the hydration strength of lubricants,designing friction surfaces with higher negative surface charge densities,simultaneously combining hydration and hydrodynamic contribution,and using 2D materials(e.g.,graphene and black phosphorus)to separate the contact of asperities.Furthermore,uniform mechanisms of liquid superlubricity have been summarized for different liquid lubricants at the boundary,mixed,and hydrodynamic lubrication regimes.To the best of our knowledge,almost all the immense progresses of the exciting topic,superlubricity,since the first theoretical prediction in the early 1990s,focus on uniform superlubricity mechanisms.This review aims to guide the research direction of liquid superlubricity in the future and to further expand liquid superlubricity,whether in a theoretical research or engineering applications,ultimately enabling a sustainable state of ultra-low friction and ultra-low wear as well as transformative improvements in the efficiency of mechanical systems and human bodies.展开更多
Polyether ether ketone(PEEK)is a widely used material for friction pairs due to its excellent mechanical strength,good wear resistance,and chemical inertness.However,some modifications are necessary when PEEK is used ...Polyether ether ketone(PEEK)is a widely used material for friction pairs due to its excellent mechanical strength,good wear resistance,and chemical inertness.However,some modifications are necessary when PEEK is used as a water-lubricated friction pair.In this study,a novel sulfonation method was developed to design a water-lubricated friction pair with ultralow friction,good wear resistance,and high loading capacity.PEEK powders were sulfonated using ClSO3H and sintered to form bulk plastic.The sulfonated PEEK(SPEEK)plastic exhibited good tribological properties.At a low sliding speed,the friction coefficient was smaller than 0.02 when a 3 wt% NaCl solution was used as the lubricant.The order of magnitude of the wear rate was as low as 10^(-8) mm^(3)/(N·m).The mechanism of friction reduction was mainly hydration lubrication.The negatively charged -SO_(3)^(-) groups on the friction pair can adsorb hydrated Na+cations by electrostatic interactions.These hydrated Na+cations have a high load capacity and low shearing resistance.The ultralow wear mechanism observed in this study is possibly due to ultralow friction properties of the friction pairs prepared through the proposed sulfonation and thermoforming procedures.展开更多
High-temperature solid lubricants play a significant role in the hot metal forming process.However,preparing high-temperature solid lubricant is formidably challenging due to the stern working conditions.Here we succe...High-temperature solid lubricants play a significant role in the hot metal forming process.However,preparing high-temperature solid lubricant is formidably challenging due to the stern working conditions.Here we successfully develop a new type of eco-friendly high-temperature graphite-based solid lubricant by using amorphous silica dioxide,aluminum dihydrogen phosphate,and solid lubricant graphite.The solid lubricating coating exhibits excellent tribological properties with a very low friction coefficient and good wear protection for workpiece at high temperature under the air atmosphere.An array of analytical techniques reveals the existence of solid lubricant graphite in the lubricating coating after the high-temperature friction test.A synergistic effect between the protective surface film and the solid lubricant graphite is proposed to account for such superior lubricating performance.This work highlights the synergistic effect between the protection layer and the lubricant graphite and further provides the insight in designing the high-temperature solid lubricant.展开更多
Hydrogenated amorphous carbon(a-C:H)films are capable of providing excellent superlubricating properties,which have great potential serving as self-lubricating protective layer for mechanical systems in extreme workin...Hydrogenated amorphous carbon(a-C:H)films are capable of providing excellent superlubricating properties,which have great potential serving as self-lubricating protective layer for mechanical systems in extreme working conditions.However,it is still a huge challenge to develop a-C:H films capable of achieving robust superlubricity state in vacuum.The main obstacle derives from the lack of knowledge on the influencing mechanism of deposition parameters on the films bonding structure and its relation to their self-lubrication performance.Aiming at finding the optimized deposition energy and revealing its influencing mechanism on superlubricity,a series of highly-hydrogenated a-C:H films were synthesized with appropriate ion energy,and systematic tribological experiments and structural characterization were conducted.The results highlight the pivotal role of ion energy on film composition,nanoclustering structure,and bonding state,which determine mechanical properties of highly-hydrogenated a-C:H films and surface passivation ability and hence their superlubricity performance in vacuum.The optimized superlubricity performance with the lowest friction coefficient of 0.006 coupled with the lowest wear rate emerges when the carbon ion energy is just beyond the penetration threshold of subplantation.The combined growth process of surface chemisorption and subsurface implantation is the key for a-C:H films to acquire stiff nanoclustering network and high volume of hydrogen incorporation,which enables a robust near-frictionless sliding surface.These findings can provide a guidance towards a more effective manipulation of self-lubricating a-C:H films for space application.展开更多
基金supported by grants from the National Natural Science Foundation of China(32360766,32072595 and 32202512)the Earmarked Fund for CARS(CARS-23-A13)。
文摘CONSTANS(CO)and CONSTANS-LIKE(COL)transcription factors are known to regulate a series of cellular processes,including the transition from vegetative growth to flower development in plants.However,their role in regulating the fruit chlorophyll content is poorly understood.In this study,SlCOL1,the tomato(Solanum lycopersicum)ortholog of Arabidopsis CONSTANS,was shown to play key roles in controlling fruit chlorophyll.The suppression of SlCOL1 expression led to a reduction in the chlorophyll content of immature green fruit,while the overexpression of SlCOL1 increased it.An analysis of protein-protein interactions indicated that SlCOL1 forms a complex with GOLDEN2-LIKE(GLK2),which promotes the stability of its protein.The overexpression of SlCOL1in the glk2 null mutation background of tomato failed to promote chlorophyll accumulation in the immature green fruit,which suggests that GLK2 is required for the function of SlCOL1 in regulating chlorophyll content.These results shed new light on the mechanisms used by COL1 and GLK2 to regulate fruit development and chlorophyll accumulation in tomato.
文摘Background: Children with seasonal influenza infection cause a significant burden of disease each year in the pediatric clinic. Influenza A and B viruses are the major types responsible for illness. A better understanding of the periodicity facilitates the prevention and control of influenza in children. Objective: This study aims to analyze the epidemiological patterns and subtype characterization of influenza viruses among children in Shenzhen, China. Methods: Influenza samples were collected by nasopharyngeal swabs from influenza like illness patients in Shenzhen Children’s Hospital from January 2016 to December 2018. The positive cases and influenza subtypes were determined by gold labeled antigen detection and reverse transcriptase polymerase chain reaction. The influenza periodicity and age, subtype distribution as well as the association between climate parameters and different influenza subtypes were analyzed by SPSS 22.0. Results: The influenza positive rate during 2016-2018 was 21.0%, with a highest positive rate in the year 2018. The positive rate varied by month, season, and year describing a sequence of peaks presenting primarily in all year including spring, summer and winter. The characteristics of influenza peak were different in each year, with a spring peak in 2016 and a summer plus a winter-spring peaks in 2017 and 2018. In addition, influenza B exhibited a winter-spring seasonal pattern while influenza A displayed a more variable seasonality, highlighting influenza B rather than influenza A which had a negative association with climate parameters. Influenza-positive cases were older than influenza-negative cases (P P Conclusion: Influenza activity in children from Shenzhen typically displays both winter-spring and summer peaks. Influenza A epidemic occurred separately or co-circulated with influenza B, with a winter-spring pattern for influenza B and a much more variable seasonality for influenza A. Influenza B had a negative association with climate parameters. In addition, hospitalization with influenza often occurs in younger individuals infected with influenza A.
基金National Natural Science Foundation of China(Grant No.51925506)National Key R&D Program of China(Grants No.2020YFA0711003).
文摘Water-based lubrication is an effective method to achieve superlubricity,which implies a friction coefficient in the order of 10−3 or lower.Recent numerical,analytical,and experimental studies confirm that the surface force effect is crucial for realizing water-based superlubricity.To enhance the contribution of the surface force,soft and plastic materials can be utilized as friction pair materials because of their effect in increasing the contact area.A new numerical model of water-based lubrication that considers the surface force between plastic and elastic materials is developed in this study to investigate the effect of plastic flow in water-based lubrication.Considering the complexity of residual stress accumulation in lubrication problems,a simplified plastic model is proposed,which merely calculates the result of the dry contact solution and avoids repeated calculations of the plastic flow.The results of the two models show good agreement.Plastic deformation reduces the local contact pressure and enhances the function of the surface force,thus resulting in a lower friction coefficient.
文摘The micro crack of aluminum sheet during cold rolling lubricated with emulsions is investigated. Experi-ments show that micro cracks occur after cold rolling process and this is attributed to various parameters, for instance, the thin oxide film formed at the sheet surface. The micro crack spacing thus becomes an important parameter which deserves more concerns. The aspect ratio of these micro cracks is then analyzed theoreti-cally, which takes into consideration of the oxide fracture process. The good agreement between the obser-vations and the theoretical predictions validates the analysis. The approach can shed some new lights on the mechanical process of aluminium sheet during cold rolling.
基金supported by the Fundamental Research Funds for the Central Universities(2024YJS192)the National Natural Science Foundation of China(62174011)。
文摘In the field of perovskite solar cells(PSCs),the research on defects in the buried interface has been relatively limited due to its non-exposure;however,this interface significantly impacts the performance enhancement of inverted PSCs.This study employs phenylethylammonium chloride(PEACl)molecules as a buffer layer to modify the buried interface of p-i-n structured PSCs,aiming to enhance the uniformity of self-assembled monolayers(SAMs)and facilitate the uniform nucleation and growth of perovskite films on the substrate.Furthermore,the introduction of the PEACl buffer layer effectively passivates defects at the bottom of the perovskite layer and notably enhances the crystal quality of the perovskite film by mitigating residual stress,thereby reducing nonradiative recombination loss.Following these optimizations,the MA-free PSCs treated with PEACl achieve a power conversion efficiency(PCE)of 24.11%,with significant improvements in storage,thermal stability,and operational stability.Particularly noteworthy is the device's performance in an unencapsulated state,whereas after 1,500 hours of continuous light operation stability testing,it retains 97%of its original efficiency.This study not only enriches the systematic understanding of the characteristics of the buried interface in PSCs but also contributes significantly to advancing the commercial production of perovskite photovoltaic technology.
基金supported by the National Key R&D Program of China(No.2020YFA0711003)the National Natural Science Foundation of China(No.51925506),and the XPLORER PRIZE.
文摘1-(4-ethylphenyl)-nonane-1,3-dione(0206)is an oil-soluble liquid molecule with rod-like structure.In this study,the chelate(0206-Fe)with octahedral structure was prepared by the reaction of ferric chloride and 1,3-diketone.The experimental results show that when using 0206 and a mixed solution containing 60%0206-Fe and 40%0206(0206-Fe(60%))as lubricants of the steel friction pairs,superlubricity can be achieved(0.007,0.006).But their wear scar diameters(WSD)were very large(532µm,370µm),which resulted in the pressure of only 44.3 and 61.8 MPa in the contact areas of the friction pairs.When 0206-Fe(60%)was mixed with PAO6,it was found that the friction coefficient(COF)decreased with increase of 0206-Fe(60%)in the solution.When the ratio of 0206-Fe(60%)to PAO6 was 8:2(PAO6(20%)),it exhibited better comprehensive tribological properties(232.3 MPa).Subsequent studies have shown that reducing the viscosity of the base oil in the mixed solution helped to reduce COF and increased WSD.Considering the COF,contact pressure,and running-in time,it was found that the mixed lubricant(Oil3(20%))prepared by the base oil with a viscosity of 19.7 mPa·s(Oil3)and 0206-Fe(60%)exhibited the best tribological properties(0.007,161.4 MPa,3,100 s).
基金supported by the National Key R&D Program of China“Response-driven Intelligent Enhanced Analysis and Control for Bulk Power System Stability”(No.2021YFB2400800 and No.SGSDDKOOWJJS 2200092).
文摘Traditional transient angle stability analysis methods do not fully consider the spatial characteristics of the network topology and the temporal characteristics of the time-series disturbance.Hence,a data-driven method is proposed in this study,combining graph convolution network and long short-term memory network(GCN-LSTM)to analyze the transient power angle sta-bility by exploring the spatiotemporal disturbance char-acteristics of future power systems with high penetration of renewable energy sources(wind and solar energy)and power electronics.The key time-series electrical state quantities are considered as the initial input feature quantities and normalized using the Z-score,whereas the network adjacency matrix is constructed according to the system network topology.The normalized feature quan-tities and network adjacency matrix were used as the inputs of the GCN to obtain the spatial features,reflecting changes in the network topology.Subsequently,the spa-tial features are inputted into the LSTM network to ob-tain the temporal features,reflecting dynamic changes in the transient power angle of the generators.Finally,the spatiotemporal features are fused through a fully con-nected network to analyze the transient power angle stability of future power systems,and the softmax activa-tion cross-entropy loss functions are used to predict the stability of the samples.The proposed transient power angle stability assessment method is tested on a 500 kV AC-DC practical power system,and the simulation results show that the proposed method could effectively mine the spatiotemporal disturbance characteristics of power sys-tems. Moreover, the proposed model has higher accuracy, higher recall rate, and shorter training and testing times than traditional transient power angle stability algo-rithms.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51925506 and 52205203).
文摘1,2,3-TrI[Cis-9-Hexadecenoyl](GTM)is a common oiliness additive.In this paper,the anti-wear property of GTM was found poor when it was directly used as lubricating oil for titanium alloy.However,when it was added to water and made into oil-in-water(OW)emulsion,it could play an effective role.The wear volume of titanium alloy sample lubricated by the emulsion was reduced by 75%compared to that lubricated by pure oil.It was difficult to fully uncover the underlying mechanism of these phenomena by experimental methods alone.With the help of molecular simulation method,the changes of GTM in chemical activity and adsorption capacity caused by water medium were revealed on atomic scale.The adsorption energies between GTM and titanium alloy under different temperature were quantitatively calculated.The superior anti-wear performance of the emulsions was related to following three aspects:(1)Water medium enhanced the adsorption capacity of GTM;(2)water medium changed the composition of lubrication film;and(3)the adsorption film in the water medium was less affected by temperature.Based on above results,an approach to predict tribological properties of oiliness additive was proposed.Using this method,the lubrication effects of several oiliness additives were successfully predicted.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51527901 and 51335005)。
文摘Graphene is a promising material as a lubricant additive for reducing friction and wear.Here,a dispersing method which combines chemical modification of graphene by octadecylamine and dicyclohexylcarbodiimide with a kind of effective dispersant has been successfully developed to achieve the remarkable dispersion stability of graphene in base oil.The stable dispersion time of modified graphene(0.5 wt%)with dispersant(1 wt%)in PAO-6 could be up to about 120 days,which was the longest time reported so far.At the same time,the lubricant exhibits a significant improvement of tribological performance for a steel ball to plate tribo-system with a normal load of 2 N.The coefficient of friction between sliding surfaces was~0.10 and the depth of wear track on plate was~21 nm,which decreased by about 44%and 90%when compared to pure PAO-6,respectively.Furthermore,the analysis of the lubricating mechanisms in regard to the sliding-induced formation of nanostructured tribo-film has been contacted by using Raman spectra and TEM.
基金supported by the National Key Basic Research and Development Program(973)of China(2013CB934200)Foundation for the Supervisor of Beijing Excellent Doctoral Dissertation(20111000305)the National Natural Science Foundation of China(NSFC)(Nos.51321092,51027007).
文摘In this study,we address the superlubricity behavior of sapphire against ruby(or sapphire against itself)under phosphoric acid solution lubrication.An ultra-low friction coefficient of 0.004 was obtained under a very high contact pressure,with a virgin contact pressure up to 2.57 GPa.Related experiments have indicated that the load,sliding speed,and humidity of the test environment can affect superlubricity to some degree,so we tested variations in these conditions.When superlubricity appears in this study a thin film is present,consisting of a hydrogen bond network of phosphoric acid and water molecules adsorbed on the two friction surfaces,which accounts for the ultra-low friction.Most significantly,the wear rate of the sapphire and ruby in the friction process is very slow and the superlubricity state is very stable,providing favorable conditions for future technological applications.
基金supported by the National Key Basic Research(973)Program of China(No.2013CB934200)the National Natural Science Foundation of China(Nos.51222507,51335005,51321092).
文摘In this work,a super-low friction coefficient of 0.003 was found between a silicon nitride ball and a sapphire plate lubricated by phosphoric acid solution.The wear mainly occurred in the running-in period and disappeared after superlubricity was achieved.The friction coefficient was effectively reduced from 0.3 to 0.003 at a constant speed of 0.076 m/s,accompanied by a 12-nm-thickness film.The lubrication regime was indicated to change from boundary lubrication in the running-in period to elastohydrodynamic lubrication in the superlubricity period,which is also supported by the results of the friction coefficient versus sliding speed.In addition,the experimental results showed good agreement with theoretical calculations based on the elastohydrodynamic lubrication theory,suggesting a significant hydrodynamic effect of phosphoric acid on superlubricity.
基金This work is financially supported by the National Key R&D Program of China(No.2018YFB2002204)the National Natural Science Foundation of China(No.51925506)。
文摘Superlubricity,the state of ultralow friction between two sliding surfaces,has become a frontier subject in tribology.Here,a state-of-the-art review of the phenomena and mechanisms of liquid superlubricity are presented based on our ten-year research,to unlock the secrets behind liquid superlubricity,a major approach to achieve superlubricity.An overview of the discovery of liquid superlubricity materials is presented from five different categories,including water and acid-based solutions,hydrated materials,ionic liquids(ILs),two-dimensional(2D)materials as lubricant additives,and oil-based lubricants,to show the hydrodynamic and hydration contributions to liquid superlubricity.The review also discusses four methods to further expand superlubricity by solving the challenge of lubricants that have a high load-carrying capacity with a low shear resistance,including enhancing the hydration contribution by strengthening the hydration strength of lubricants,designing friction surfaces with higher negative surface charge densities,simultaneously combining hydration and hydrodynamic contribution,and using 2D materials(e.g.,graphene and black phosphorus)to separate the contact of asperities.Furthermore,uniform mechanisms of liquid superlubricity have been summarized for different liquid lubricants at the boundary,mixed,and hydrodynamic lubrication regimes.To the best of our knowledge,almost all the immense progresses of the exciting topic,superlubricity,since the first theoretical prediction in the early 1990s,focus on uniform superlubricity mechanisms.This review aims to guide the research direction of liquid superlubricity in the future and to further expand liquid superlubricity,whether in a theoretical research or engineering applications,ultimately enabling a sustainable state of ultra-low friction and ultra-low wear as well as transformative improvements in the efficiency of mechanical systems and human bodies.
基金financially supported by the National Natural Science Foundation of China(Grant No.51925506).
文摘Polyether ether ketone(PEEK)is a widely used material for friction pairs due to its excellent mechanical strength,good wear resistance,and chemical inertness.However,some modifications are necessary when PEEK is used as a water-lubricated friction pair.In this study,a novel sulfonation method was developed to design a water-lubricated friction pair with ultralow friction,good wear resistance,and high loading capacity.PEEK powders were sulfonated using ClSO3H and sintered to form bulk plastic.The sulfonated PEEK(SPEEK)plastic exhibited good tribological properties.At a low sliding speed,the friction coefficient was smaller than 0.02 when a 3 wt% NaCl solution was used as the lubricant.The order of magnitude of the wear rate was as low as 10^(-8) mm^(3)/(N·m).The mechanism of friction reduction was mainly hydration lubrication.The negatively charged -SO_(3)^(-) groups on the friction pair can adsorb hydrated Na+cations by electrostatic interactions.These hydrated Na+cations have a high load capacity and low shearing resistance.The ultralow wear mechanism observed in this study is possibly due to ultralow friction properties of the friction pairs prepared through the proposed sulfonation and thermoforming procedures.
基金The work is financially supported by the National Key Research and Development Program(No.2018 YFB2002204)the National Natural Science Foundation of China(Grant Nos.51925506 and 51527901).
文摘High-temperature solid lubricants play a significant role in the hot metal forming process.However,preparing high-temperature solid lubricant is formidably challenging due to the stern working conditions.Here we successfully develop a new type of eco-friendly high-temperature graphite-based solid lubricant by using amorphous silica dioxide,aluminum dihydrogen phosphate,and solid lubricant graphite.The solid lubricating coating exhibits excellent tribological properties with a very low friction coefficient and good wear protection for workpiece at high temperature under the air atmosphere.An array of analytical techniques reveals the existence of solid lubricant graphite in the lubricating coating after the high-temperature friction test.A synergistic effect between the protective surface film and the solid lubricant graphite is proposed to account for such superior lubricating performance.This work highlights the synergistic effect between the protection layer and the lubricant graphite and further provides the insight in designing the high-temperature solid lubricant.
基金The authors would like to thank Dongzhou ZHAN for technological support during friction experiment.This work was supported by the National Natural Science Foundation of China(Nos.51925506,51975314,51935006,and 51527901).
文摘Hydrogenated amorphous carbon(a-C:H)films are capable of providing excellent superlubricating properties,which have great potential serving as self-lubricating protective layer for mechanical systems in extreme working conditions.However,it is still a huge challenge to develop a-C:H films capable of achieving robust superlubricity state in vacuum.The main obstacle derives from the lack of knowledge on the influencing mechanism of deposition parameters on the films bonding structure and its relation to their self-lubrication performance.Aiming at finding the optimized deposition energy and revealing its influencing mechanism on superlubricity,a series of highly-hydrogenated a-C:H films were synthesized with appropriate ion energy,and systematic tribological experiments and structural characterization were conducted.The results highlight the pivotal role of ion energy on film composition,nanoclustering structure,and bonding state,which determine mechanical properties of highly-hydrogenated a-C:H films and surface passivation ability and hence their superlubricity performance in vacuum.The optimized superlubricity performance with the lowest friction coefficient of 0.006 coupled with the lowest wear rate emerges when the carbon ion energy is just beyond the penetration threshold of subplantation.The combined growth process of surface chemisorption and subsurface implantation is the key for a-C:H films to acquire stiff nanoclustering network and high volume of hydrogen incorporation,which enables a robust near-frictionless sliding surface.These findings can provide a guidance towards a more effective manipulation of self-lubricating a-C:H films for space application.
