Attribute-based encryption with keyword search(ABEKS)is a novel cryptographic paradigm that can be used to implementfine-grained access control and retrieve ciphertexts without disclosing the sensitive information.It i...Attribute-based encryption with keyword search(ABEKS)is a novel cryptographic paradigm that can be used to implementfine-grained access control and retrieve ciphertexts without disclosing the sensitive information.It is a perfect combination of attribute-based encryption(ABE)and public key encryption with keyword search(PEKS).Nevertheless,most of the existing ABEKS schemes have limited search capabilities and only support single or simple conjunctive keyword search.Due to the weak search capability and inaccurate search results,it is difficult to apply these schemes to practical applications.In this paper,an effi-cient expressive ABEKS(EABEKS)scheme supporting unbounded keyword uni-verse over prime-order groups is designed,which supplies the expressive keyword search function supporting the logical connectives of“AND”and“OR”.The proposed scheme not only leads to low computation and communica-tion costs,but also supports unbounded keyword universe.In the standard model,the scheme is proven to be secure under the chosen keyword attack and the cho-sen plaintext attack.The comparison analysis and experimental results show that it has better performance than the existing EABEKS schemes in the storage,com-putation and communication costs.展开更多
The service performance of the turbine blade root of an aero-engine depends on the microstructures in its superficial layer.This work investigated the surface deformation structures of turbine blade root of single cry...The service performance of the turbine blade root of an aero-engine depends on the microstructures in its superficial layer.This work investigated the surface deformation structures of turbine blade root of single crystal nickel-based superalloy produced under different creep feed grinding conditions.Gradient microstructures in the superficial layer were clarified and composed of a severely deformed layer(DFL)with nano-sized grains(48–67 nm)at the topmost surface,a DFL with submicron-sized grains(66–158 nm)and micron-sized laminated structures at the subsurface,and a dislocation accumulated layer extending to the bulk material.The formation of such gradient microstructures was found to be related to the graded variations in the plastic strain and strain rate induced in the creep feed grinding process,which were as high as 6.67 and 8.17×10^(7)s^(−1),respectively.In the current study,the evolution of surface gradient microstructures was essentially a transition process from a coarse single crystal to nano-sized grains and,simultaneously,from one orientation of a single crystal to random orientations of polycrystals,during which the dislocation slips dominated the creep feed grinding induced microstructure deformation of single crystal nickel-based superalloy.展开更多
Silencing phytochrome A1 gene (PHYA1) by RNA interference in Upland cotton (Gossypium hirsutum L. cv. Coker 312) had generated PHYA1 RNAi lines with improved fiber quality (longer, stronger and finer fiber). To reveal...Silencing phytochrome A1 gene (PHYA1) by RNA interference in Upland cotton (Gossypium hirsutum L. cv. Coker 312) had generated PHYA1 RNAi lines with improved fiber quality (longer, stronger and finer fiber). To reveal molecular mechanisms that govern fiber development with positive fiber traits, a study of global gene expression profiling of 10-DPA fibers in a PHYA1 RNAi line and its parent Coker 312 was conducted by high-throughput RNA sequencing. A comparative analysis of transcriptomes between the two lines had identified 142 genes that were differentially expressed in the 10-DPA fiber of the RNAi line. Gene Ontology analysis showed that these differentially expressed genes were mainly involved in metabolic pathways, heterocyclic/organic cyclic compound binding and multiple enzyme activities, and cell structures which were reported to play important roles in fiber development. Twenty-eight KEGG pathways were mapped for the 142 genes, and the pathways related to glycolysis/gluconeogenesis and pyruvate metabolism were the most abundant and followed by cytochrome P450-involved pathways, suggesting that fiber improvement could be through the regulation of proteins involved in cytochrome P450 pathways. Genes encoding WRKY transcription factors, sucrose synthase, xyloglucan endotransglucosylase hydrolase, udp-glucuronate: xylan alpha-glucuronosyltransferase, and genes involved in lipid metabolism and ABA/brassinosteroid signal transduction pathways were found differentially expressed in the RNAi line. These genes have direct impacts on cotton fiber quality. The results of this study elucidate molecular signatures and possible mechanisms of fiber improvement in the background of PHYA1 RNAi in cotton and should help for future fine-tuning and programming of cotton fiber development.展开更多
Under the grand economic vision of opening up and cooperation among countries,the world economy is gradually recovering,and economic and trade exchanges between countries are increasing,which is an important sign of s...Under the grand economic vision of opening up and cooperation among countries,the world economy is gradually recovering,and economic and trade exchanges between countries are increasing,which is an important sign of sound economic development.At the same time,we need the joint efforts of all countries to move towards the goal of mutual benefit and common development.We should fully develop one of the"one belt one road"in the economic construction.At the same time,we need to deepen economic cooperation,improve the investment and financing system and credit system,and China International Finance is particularly important.International financial cooperation is one of the difficulties things and“One belt one road”is the same.The financial market's influence on the economic outflow of funds is not to be ignored.Based on this background,one will take the"one belt one road"as the starting point to explore the problems of international financial cooperation.展开更多
Yielding behaviors of waxy crude oil is one of the key issues of flow assurance challenges. The yielding of waxy crude under constant stress is actually a creep process of strain accumulation to structural failure,to ...Yielding behaviors of waxy crude oil is one of the key issues of flow assurance challenges. The yielding of waxy crude under constant stress is actually a creep process of strain accumulation to structural failure,to describe the process completely and accurately is the basis of numerical simulation of restart process of the pipeline. The creep and yield behaviors of two gelled waxy crudes were investigated experimentally under different constant applied stresses. The results clearly show that the creep process of waxy crude is related to the applied stress and time. The greater the applied stress, and the longer the loaded time, the more obvious the nonlinear features. Based on the fractional calculus theory, a fractional viscous element was developed to describe the decelerated and steady creep process of gelled waxy crude. On the basis of the damage theory, an elastic damage element was proposed to describe the accelerated creep after the yielding. According to the idea of mechanical analogy, a nonlinear creep model was established by a fractional viscous element, an elastic damaged element, and an elastic element in series, which can accurately describe the whole creep and yielding process of gelled waxy crude.展开更多
A chromosome substitution line, CS-B25, was developed by the substitution of chromosome pair 25 of Gossypium hirsutum TM-1 with the homologous pair of chromosome 25 from G. barbadense, a double haploid Pima 3-79 line....A chromosome substitution line, CS-B25, was developed by the substitution of chromosome pair 25 of Gossypium hirsutum TM-1 with the homologous pair of chromosome 25 from G. barbadense, a double haploid Pima 3-79 line. CS-B25 has improved fiber traits compared to its parent TM-1. To explore the molecule mechanisms underlying improved fiber traits, deep sequencing of total RNA was used to compare gene expression in fibers of CS-B25 and TM-1 at 10 days post anthesis (10-DPA). A total of 1872 differentially expressed genes (DEGs) were detected between the two lines, with 1175 up-regulated and 697 down-regulated in CS-B25. Gene Ontology (GO) enrichment analysis of the expression data by Generally Applicable Gene-set Enrichment (GAGE) and ReviGO indicated that the most prevalent Biological Process GO terms associated with DEGs included DNA-templated transcription, response to oxidative stress, and cellulose biosynthesis. Enriched Molecular Function GO terms included structural constituents of cytoskeleton, peroxidase activity, cellulose synthase (UDP-forming) activity, and transcription regulatory region sequence-specific DNA binding factors. GAGE was also used to find enriched KEGG pathways, and the highly represented pathways were Biosynthesis of Amino Acids, Starch and Sucrose Metabolism, Phenylpropanoid Biosynthesis, Protein Processing in Endoplasmic Reticulum, and Plant Hormone Signal Transduction. Many of the identified DEGs are involved in cytoskeleton and cell wall metabolism. The results of gene expression data have provided new insight into the molecular mechanisms of fiber development during the fiber elongation stage and would offer novel candidate genes that may be utilized in cotton fiber quality improvement.展开更多
Ultra-high temperature ceramic(UHTC)nanowires are potential reinforcement materials due to it combines the perfect properties of bulk materials and unique geometric properties of one-dimensional(1D)nanostructures.Thus...Ultra-high temperature ceramic(UHTC)nanowires are potential reinforcement materials due to it combines the perfect properties of bulk materials and unique geometric properties of one-dimensional(1D)nanostructures.Thus,developing 1D nanomaterials that have excellent morphology and structure retention in ultra-high temperature environments is of prime importance to bring their outstanding performance into full play.Herein,we report the novel solid solution((Hf_(0.5)Ta_(0.5))C)ceramic nanowires,which could not only maintain morphological and structural stability at 1900°C but also exhibit 1D nanostructures under oxyacetylene scouring and ablation at 2300°C.The morphology evolution of nanowires obeys the Rayleigh instability mechanism,and the internal structure and element distribution of nanowires remain unchanged even if the surface atoms are rearranged.The fascinating nanowires are demonstrated to have great potential as ideal reinforcement materials of composite materials and toughening phases of ceramics that are applied in ultra-high temperature environments,as well as excellent performance enhancement phases of functional materials.Our work may provide new insights into the development of ceramic nanowires and widen their applications.展开更多
In recent years,high-entropy metal carbides(HECs)have attracted significant attention due to their exceptional physical and chemical properties.The combination of excellent performance exhibited by bulk HEC ceramics a...In recent years,high-entropy metal carbides(HECs)have attracted significant attention due to their exceptional physical and chemical properties.The combination of excellent performance exhibited by bulk HEC ceramics and distinctive geometric characteristics has paved the way for the emergence of one-dimensional(1D)HECs as novel materials with unique development potential.Herein,we successfully fabricated novel(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C nanowires derived via Fe-assisted single-sourced precursor pyrolysis.Prior to the synthesis of the nanowires,the composition and microstructure of(Ti,Zr,Hf,Nb,Ta)-containing precursor(PHECs)were analyzed,and divinylbenzene(DVB)was used to accelerate the conversion process of the precursor and contribute to the formation of HECs,which also provided a partial carbon source for the nanowire growth.Additionally,multi-branched,single-branched,and single-branched bending nanowires were synthesized by adjusting the ratio of PHECs to DVB.The obtained single-branched(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C nanowires possessed smooth surfaces with an average diameter of 130–150 nm and a length of several tens of micrometers,which were a single-crystal structure and typically grew along the[11¯1]direction.Also,the growth of the(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C nanowires was in agreement with top-type vapor–liquid–solid mechanism.This work not only successfully achieved the fabrication of HEC nanowires by a catalyst-assisted polymer pyrolysis,but also provided a comprehensive analysis of the factors affecting their yield and morphology,highlighting the potential application of these attractive nano-materials.展开更多
Creep feed profile grinding of the fir-tree blade root forms of single crystal nickel-based superalloy was conducted using microcrystalline alumina abrasive wheels in the present study. The grinding force and the surf...Creep feed profile grinding of the fir-tree blade root forms of single crystal nickel-based superalloy was conducted using microcrystalline alumina abrasive wheels in the present study. The grinding force and the surface quality in terms of surface topography, subsurface microstructure,microhardness and residual stress obtained under different grinding conditions were evaluated comparatively. Experimental results indicated that the grinding force was influenced significantly by the competing predominance between the grinding parameters and the cross-sectional root workpiece profile. In addition, the root workpiece surface, including the root peak and valley regions, was produced with the large difference in surface quality due to the nonuniform grinding loads along the root workpiece profile in normal section. Detailed results showed that the surface roughness, subsurface plastic deformation and work hardening level of the root valley region were higher by up to25%, 20% and 7% in average than those obtained in the root peak region, respectively, in the current investigation. Finally, the superior parameters were recommended in the creep feed profile grinding of the fir-tree blade root forms. This study is helpful to provide industry guidance to optimize the machining process for the high-valued parts with complicated profiles.展开更多
To control the spread of COVID-19,rigorous restrictions have been implemented in China,resulting in a great reduction in pollutant emissions.In this study,we evaluated the air quality in the Yangtze River Delta during...To control the spread of COVID-19,rigorous restrictions have been implemented in China,resulting in a great reduction in pollutant emissions.In this study,we evaluated the air quality in the Yangtze River Delta during the COVID-19 lockdown period using satellite and ground-based data,including particle matter(PM),trace gases,water-soluble ions(WSIs) and black carbon(BC).We found that the impacts of lockdown policy on air quality cannot be accurately assessed using MODIS aerosol optical depth(AOD) data,whereas the tropospheric nitrogen dioxide(NO_(2)) vertical column density can well reflect the influences of these restrictions on human activities.Compared to the pre-COVID period,the PM_(2.5),PM_(10),NO_(2),carbon monoxide(CO),BC and WSIs during the lockdown in Suzhou were observed to decrease by 37.2%,38.3%,64.5%,26.1%,53.3% and 58.6%,respectively,while the sulfur dioxide(SO_(2)) and ozone(O_(3)) increased by 1.5% and 104.7%.The WSIs ranked in the order of NO_(3)~->NH_(4)^(+)>SO_(4)^(2-)>Cl~->Ca^(2+)>K^(+)>Mg^(2+)>Na + during the lockdown period.By comparisons with the ion concentrations during the pre-COVID period,we found that the ions NO 3-,NH 4 +,SO_(4)^(2-),Cl~-,Ca^(2+),K^(+) and Na^(+) decreased by 66.3%,48.8%,52.9%,56.9%,57.9% and 76.3%,respectively,during the lockdown,in contrast to Mg^(2+),which increased by 30.2%.The lockdown policy was found to have great impacts on the diurnal variations of Cl~-,SO_(4)^(2-),Na^(+) and Ca^(2+).展开更多
In this study,the machined surface quality of powder metallurgy nickel-based superalloy FGH96(similar to Rene88DT)and the grinding characteristics of brown alumina(BA)and microcrystalline alumina(MA)abrasive wheels we...In this study,the machined surface quality of powder metallurgy nickel-based superalloy FGH96(similar to Rene88DT)and the grinding characteristics of brown alumina(BA)and microcrystalline alumina(MA)abrasive wheels were comparatively analyzed during creep feed grinding.The infuences of the grinding parameters(abrasive wheel speed,workpiece infeed speed,and depth of cut)on the grinding force,grinding temperature,surface roughness,surface morphology,tool wear,and grinding ratio were analyzed comprehensively.The experimental results showed that there was no significant difference in terms of the machined surface quality and grinding characteristics of FGH96 during grinding with the two types of abrasive wheels.This was mainly because the grinding advantages of the MA wheel were weakened for the difficult-to-cut FGH96 material.Moreover,both the BA and MA abrasive wheeIs exhibited severe tool wear in the form of wheel clogging and workpiece material adhesion.Finally,an analytical model for prediction of the grinding ratio was established by combining the tool wear volume,grinding force,and grinding length.The acceptable errors between the predicted and experimental grinding ratios(ranging from 0.6 to 1.8)were 7.56%and 6.31%for the BA and MA abrasive wheels,respectively.This model can be used to evaluate quantitatively the grinding performance of an alumina abrasive wheel,and is therefore helpful for optimizing the grinding parameters in the creep feed grinding process.展开更多
Fretting wear has an adverse impact on the fatigue life of turbine blade roots.The current work is to comparatively investigate the fretting wear behaviour of the nickel-based superalloy surfaces produced by polishing...Fretting wear has an adverse impact on the fatigue life of turbine blade roots.The current work is to comparatively investigate the fretting wear behaviour of the nickel-based superalloy surfaces produced by polishing and creep-feed profile grinding,respectively,in terms of surface/subsurface fretting damage,the friction coefficient,wear volume and wear rate.Experimental results show that the granulated tribolayer aggravates the workpiece wear,while the flat compacted tribolayer enhances the wear resistance ability of workpiece,irrespective of whether the workpiece is processed by polishing or grinding.However,the wear behaviors of tribolayers are different.For the polished surface,when the normal load exceeds 100 N,the main defects are crack,rupture,delamination and peeling of workpiece materials;the wear mechanism changes from severe oxidative wear to fatigue wear and abrasive wear when the loads increase from 50 to 180 N.As for the ground surface,the main wear mechanism is abrasive wear.Particularly,the ground surface possesses better wear-resistant ability than the polished surface because the former has the lower values in coefficient friction(0.23),wear volume(0.06×10^(6)μm^(3))and wear rate(0.25×10^(-16)Pa^(-1)).Finally,an illustration is given to characterize the evolution of wear debris on such nickel-based superalloy on the ground surface.展开更多
基金supported in part by the National Natural Science Foundation of China under Grant No.61772009the Natural Science Foundation of Jiangsu Province under Grant No.BK20181304.
文摘Attribute-based encryption with keyword search(ABEKS)is a novel cryptographic paradigm that can be used to implementfine-grained access control and retrieve ciphertexts without disclosing the sensitive information.It is a perfect combination of attribute-based encryption(ABE)and public key encryption with keyword search(PEKS).Nevertheless,most of the existing ABEKS schemes have limited search capabilities and only support single or simple conjunctive keyword search.Due to the weak search capability and inaccurate search results,it is difficult to apply these schemes to practical applications.In this paper,an effi-cient expressive ABEKS(EABEKS)scheme supporting unbounded keyword uni-verse over prime-order groups is designed,which supplies the expressive keyword search function supporting the logical connectives of“AND”and“OR”.The proposed scheme not only leads to low computation and communica-tion costs,but also supports unbounded keyword universe.In the standard model,the scheme is proven to be secure under the chosen keyword attack and the cho-sen plaintext attack.The comparison analysis and experimental results show that it has better performance than the existing EABEKS schemes in the storage,com-putation and communication costs.
基金This work was financially supported by the National Nat-ural Science Foundation of China(Nos.51921003,51775275 and 51905363)the Natural Science Foundation of Jiangsu Province(No.BK20190940)+1 种基金the National Major Science and Technology Projects of China(No.2017-VII-0002-0095)the Six Talents Summit Project in Jiangsu Province(No.JXQC-002).
文摘The service performance of the turbine blade root of an aero-engine depends on the microstructures in its superficial layer.This work investigated the surface deformation structures of turbine blade root of single crystal nickel-based superalloy produced under different creep feed grinding conditions.Gradient microstructures in the superficial layer were clarified and composed of a severely deformed layer(DFL)with nano-sized grains(48–67 nm)at the topmost surface,a DFL with submicron-sized grains(66–158 nm)and micron-sized laminated structures at the subsurface,and a dislocation accumulated layer extending to the bulk material.The formation of such gradient microstructures was found to be related to the graded variations in the plastic strain and strain rate induced in the creep feed grinding process,which were as high as 6.67 and 8.17×10^(7)s^(−1),respectively.In the current study,the evolution of surface gradient microstructures was essentially a transition process from a coarse single crystal to nano-sized grains and,simultaneously,from one orientation of a single crystal to random orientations of polycrystals,during which the dislocation slips dominated the creep feed grinding induced microstructure deformation of single crystal nickel-based superalloy.
文摘Silencing phytochrome A1 gene (PHYA1) by RNA interference in Upland cotton (Gossypium hirsutum L. cv. Coker 312) had generated PHYA1 RNAi lines with improved fiber quality (longer, stronger and finer fiber). To reveal molecular mechanisms that govern fiber development with positive fiber traits, a study of global gene expression profiling of 10-DPA fibers in a PHYA1 RNAi line and its parent Coker 312 was conducted by high-throughput RNA sequencing. A comparative analysis of transcriptomes between the two lines had identified 142 genes that were differentially expressed in the 10-DPA fiber of the RNAi line. Gene Ontology analysis showed that these differentially expressed genes were mainly involved in metabolic pathways, heterocyclic/organic cyclic compound binding and multiple enzyme activities, and cell structures which were reported to play important roles in fiber development. Twenty-eight KEGG pathways were mapped for the 142 genes, and the pathways related to glycolysis/gluconeogenesis and pyruvate metabolism were the most abundant and followed by cytochrome P450-involved pathways, suggesting that fiber improvement could be through the regulation of proteins involved in cytochrome P450 pathways. Genes encoding WRKY transcription factors, sucrose synthase, xyloglucan endotransglucosylase hydrolase, udp-glucuronate: xylan alpha-glucuronosyltransferase, and genes involved in lipid metabolism and ABA/brassinosteroid signal transduction pathways were found differentially expressed in the RNAi line. These genes have direct impacts on cotton fiber quality. The results of this study elucidate molecular signatures and possible mechanisms of fiber improvement in the background of PHYA1 RNAi in cotton and should help for future fine-tuning and programming of cotton fiber development.
文摘Under the grand economic vision of opening up and cooperation among countries,the world economy is gradually recovering,and economic and trade exchanges between countries are increasing,which is an important sign of sound economic development.At the same time,we need the joint efforts of all countries to move towards the goal of mutual benefit and common development.We should fully develop one of the"one belt one road"in the economic construction.At the same time,we need to deepen economic cooperation,improve the investment and financing system and credit system,and China International Finance is particularly important.International financial cooperation is one of the difficulties things and“One belt one road”is the same.The financial market's influence on the economic outflow of funds is not to be ignored.Based on this background,one will take the"one belt one road"as the starting point to explore the problems of international financial cooperation.
基金the financial support from the National Natural Science Foundation of China (No.52174066)。
文摘Yielding behaviors of waxy crude oil is one of the key issues of flow assurance challenges. The yielding of waxy crude under constant stress is actually a creep process of strain accumulation to structural failure,to describe the process completely and accurately is the basis of numerical simulation of restart process of the pipeline. The creep and yield behaviors of two gelled waxy crudes were investigated experimentally under different constant applied stresses. The results clearly show that the creep process of waxy crude is related to the applied stress and time. The greater the applied stress, and the longer the loaded time, the more obvious the nonlinear features. Based on the fractional calculus theory, a fractional viscous element was developed to describe the decelerated and steady creep process of gelled waxy crude. On the basis of the damage theory, an elastic damage element was proposed to describe the accelerated creep after the yielding. According to the idea of mechanical analogy, a nonlinear creep model was established by a fractional viscous element, an elastic damaged element, and an elastic element in series, which can accurately describe the whole creep and yielding process of gelled waxy crude.
文摘A chromosome substitution line, CS-B25, was developed by the substitution of chromosome pair 25 of Gossypium hirsutum TM-1 with the homologous pair of chromosome 25 from G. barbadense, a double haploid Pima 3-79 line. CS-B25 has improved fiber traits compared to its parent TM-1. To explore the molecule mechanisms underlying improved fiber traits, deep sequencing of total RNA was used to compare gene expression in fibers of CS-B25 and TM-1 at 10 days post anthesis (10-DPA). A total of 1872 differentially expressed genes (DEGs) were detected between the two lines, with 1175 up-regulated and 697 down-regulated in CS-B25. Gene Ontology (GO) enrichment analysis of the expression data by Generally Applicable Gene-set Enrichment (GAGE) and ReviGO indicated that the most prevalent Biological Process GO terms associated with DEGs included DNA-templated transcription, response to oxidative stress, and cellulose biosynthesis. Enriched Molecular Function GO terms included structural constituents of cytoskeleton, peroxidase activity, cellulose synthase (UDP-forming) activity, and transcription regulatory region sequence-specific DNA binding factors. GAGE was also used to find enriched KEGG pathways, and the highly represented pathways were Biosynthesis of Amino Acids, Starch and Sucrose Metabolism, Phenylpropanoid Biosynthesis, Protein Processing in Endoplasmic Reticulum, and Plant Hormone Signal Transduction. Many of the identified DEGs are involved in cytoskeleton and cell wall metabolism. The results of gene expression data have provided new insight into the molecular mechanisms of fiber development during the fiber elongation stage and would offer novel candidate genes that may be utilized in cotton fiber quality improvement.
基金supported by the National Natural Science Foundation of China(Nos.52130205 and 51727804)the National Key R&D Program of China(No.2021YFA0715803)Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(CX2022010).
文摘Ultra-high temperature ceramic(UHTC)nanowires are potential reinforcement materials due to it combines the perfect properties of bulk materials and unique geometric properties of one-dimensional(1D)nanostructures.Thus,developing 1D nanomaterials that have excellent morphology and structure retention in ultra-high temperature environments is of prime importance to bring their outstanding performance into full play.Herein,we report the novel solid solution((Hf_(0.5)Ta_(0.5))C)ceramic nanowires,which could not only maintain morphological and structural stability at 1900°C but also exhibit 1D nanostructures under oxyacetylene scouring and ablation at 2300°C.The morphology evolution of nanowires obeys the Rayleigh instability mechanism,and the internal structure and element distribution of nanowires remain unchanged even if the surface atoms are rearranged.The fascinating nanowires are demonstrated to have great potential as ideal reinforcement materials of composite materials and toughening phases of ceramics that are applied in ultra-high temperature environments,as well as excellent performance enhancement phases of functional materials.Our work may provide new insights into the development of ceramic nanowires and widen their applications.
基金supported by the National Key R&D Program of China(Grant No.2021YFA0715803)the National Natural Science Foundation of China(Grant Nos.52293373 and 52130205)ND Basic Research Funds of Northwestern Polytechnical University(Grant No.G2022WD).
文摘In recent years,high-entropy metal carbides(HECs)have attracted significant attention due to their exceptional physical and chemical properties.The combination of excellent performance exhibited by bulk HEC ceramics and distinctive geometric characteristics has paved the way for the emergence of one-dimensional(1D)HECs as novel materials with unique development potential.Herein,we successfully fabricated novel(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C nanowires derived via Fe-assisted single-sourced precursor pyrolysis.Prior to the synthesis of the nanowires,the composition and microstructure of(Ti,Zr,Hf,Nb,Ta)-containing precursor(PHECs)were analyzed,and divinylbenzene(DVB)was used to accelerate the conversion process of the precursor and contribute to the formation of HECs,which also provided a partial carbon source for the nanowire growth.Additionally,multi-branched,single-branched,and single-branched bending nanowires were synthesized by adjusting the ratio of PHECs to DVB.The obtained single-branched(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C nanowires possessed smooth surfaces with an average diameter of 130–150 nm and a length of several tens of micrometers,which were a single-crystal structure and typically grew along the[11¯1]direction.Also,the growth of the(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))C nanowires was in agreement with top-type vapor–liquid–solid mechanism.This work not only successfully achieved the fabrication of HEC nanowires by a catalyst-assisted polymer pyrolysis,but also provided a comprehensive analysis of the factors affecting their yield and morphology,highlighting the potential application of these attractive nano-materials.
基金financial support for this work by the National Natural Science Foundation of China (No. 51775275)the Funding of Jiangsu Innovation Program for Graduate Education of China (KYCX170245)+2 种基金the Funding for Outstanding Doctoral Dissertation in NUAA of China (BCXJ17-04)the Fundamental Research Funds for the Central University of China (No. NP2018110)the National Science and Technology Major Project and the Six Talents Summit Project in Jiangsu Province of China (No.JXQC-002)。
文摘Creep feed profile grinding of the fir-tree blade root forms of single crystal nickel-based superalloy was conducted using microcrystalline alumina abrasive wheels in the present study. The grinding force and the surface quality in terms of surface topography, subsurface microstructure,microhardness and residual stress obtained under different grinding conditions were evaluated comparatively. Experimental results indicated that the grinding force was influenced significantly by the competing predominance between the grinding parameters and the cross-sectional root workpiece profile. In addition, the root workpiece surface, including the root peak and valley regions, was produced with the large difference in surface quality due to the nonuniform grinding loads along the root workpiece profile in normal section. Detailed results showed that the surface roughness, subsurface plastic deformation and work hardening level of the root valley region were higher by up to25%, 20% and 7% in average than those obtained in the root peak region, respectively, in the current investigation. Finally, the superior parameters were recommended in the creep feed profile grinding of the fir-tree blade root forms. This study is helpful to provide industry guidance to optimize the machining process for the high-valued parts with complicated profiles.
基金supported by the National Natural Science Foundation of China (Nos.91644224,41805096)the National Key Research and Development Program of China (No.2016YFA0602003)+1 种基金the China Postdoctoral Science Foundation (No.2018M640169)the Natural Science Research Project for Universities of Jiangsu Province,China (No.18KJB170011)。
文摘To control the spread of COVID-19,rigorous restrictions have been implemented in China,resulting in a great reduction in pollutant emissions.In this study,we evaluated the air quality in the Yangtze River Delta during the COVID-19 lockdown period using satellite and ground-based data,including particle matter(PM),trace gases,water-soluble ions(WSIs) and black carbon(BC).We found that the impacts of lockdown policy on air quality cannot be accurately assessed using MODIS aerosol optical depth(AOD) data,whereas the tropospheric nitrogen dioxide(NO_(2)) vertical column density can well reflect the influences of these restrictions on human activities.Compared to the pre-COVID period,the PM_(2.5),PM_(10),NO_(2),carbon monoxide(CO),BC and WSIs during the lockdown in Suzhou were observed to decrease by 37.2%,38.3%,64.5%,26.1%,53.3% and 58.6%,respectively,while the sulfur dioxide(SO_(2)) and ozone(O_(3)) increased by 1.5% and 104.7%.The WSIs ranked in the order of NO_(3)~->NH_(4)^(+)>SO_(4)^(2-)>Cl~->Ca^(2+)>K^(+)>Mg^(2+)>Na + during the lockdown period.By comparisons with the ion concentrations during the pre-COVID period,we found that the ions NO 3-,NH 4 +,SO_(4)^(2-),Cl~-,Ca^(2+),K^(+) and Na^(+) decreased by 66.3%,48.8%,52.9%,56.9%,57.9% and 76.3%,respectively,during the lockdown,in contrast to Mg^(2+),which increased by 30.2%.The lockdown policy was found to have great impacts on the diurnal variations of Cl~-,SO_(4)^(2-),Na^(+) and Ca^(2+).
基金supported by the National Natural Science Foundation of China(Grant Nos.51775275 and 51921003)National Major Science and Technology Project(Grant No.2017-Ⅶ-0002-0095)+2 种基金Funding for Outstanding Doctoral Dissertation in NUAA(Grant No.BCXJ19-06)the Six Talents Summit Project in Jiangsu Province(Grant No.JXQC-002)Fundamental Research Funds for the Central Universities(Grant No.NP2018110).
文摘In this study,the machined surface quality of powder metallurgy nickel-based superalloy FGH96(similar to Rene88DT)and the grinding characteristics of brown alumina(BA)and microcrystalline alumina(MA)abrasive wheels were comparatively analyzed during creep feed grinding.The infuences of the grinding parameters(abrasive wheel speed,workpiece infeed speed,and depth of cut)on the grinding force,grinding temperature,surface roughness,surface morphology,tool wear,and grinding ratio were analyzed comprehensively.The experimental results showed that there was no significant difference in terms of the machined surface quality and grinding characteristics of FGH96 during grinding with the two types of abrasive wheels.This was mainly because the grinding advantages of the MA wheel were weakened for the difficult-to-cut FGH96 material.Moreover,both the BA and MA abrasive wheeIs exhibited severe tool wear in the form of wheel clogging and workpiece material adhesion.Finally,an analytical model for prediction of the grinding ratio was established by combining the tool wear volume,grinding force,and grinding length.The acceptable errors between the predicted and experimental grinding ratios(ranging from 0.6 to 1.8)were 7.56%and 6.31%for the BA and MA abrasive wheels,respectively.This model can be used to evaluate quantitatively the grinding performance of an alumina abrasive wheel,and is therefore helpful for optimizing the grinding parameters in the creep feed grinding process.
基金financially supported by the National Natural Science Foundation of China(Nos.51921003 and 51775275)National Major Science and Technology Projects of China(No.2017-VII-0002-0095)Six Talents Summit Project in Jiangsu Province(No.JXQC-002)。
文摘Fretting wear has an adverse impact on the fatigue life of turbine blade roots.The current work is to comparatively investigate the fretting wear behaviour of the nickel-based superalloy surfaces produced by polishing and creep-feed profile grinding,respectively,in terms of surface/subsurface fretting damage,the friction coefficient,wear volume and wear rate.Experimental results show that the granulated tribolayer aggravates the workpiece wear,while the flat compacted tribolayer enhances the wear resistance ability of workpiece,irrespective of whether the workpiece is processed by polishing or grinding.However,the wear behaviors of tribolayers are different.For the polished surface,when the normal load exceeds 100 N,the main defects are crack,rupture,delamination and peeling of workpiece materials;the wear mechanism changes from severe oxidative wear to fatigue wear and abrasive wear when the loads increase from 50 to 180 N.As for the ground surface,the main wear mechanism is abrasive wear.Particularly,the ground surface possesses better wear-resistant ability than the polished surface because the former has the lower values in coefficient friction(0.23),wear volume(0.06×10^(6)μm^(3))and wear rate(0.25×10^(-16)Pa^(-1)).Finally,an illustration is given to characterize the evolution of wear debris on such nickel-based superalloy on the ground surface.
基金The National Natural Science Foundation of China (Grant No. 81703768 and 81803400)the Natural Science Foundation of Shandong Province (Grant No. ZR2017MH118 and ZR2018BH045)。