In recent years,polarization remote sensing has garnered increasing attention,particularly within the realm of meteorology.To accurately simulate polarization information,the vector discrete-ordinate radiative transfe...In recent years,polarization remote sensing has garnered increasing attention,particularly within the realm of meteorology.To accurately simulate polarization information,the vector discrete-ordinate radiative transfer(VDISORT)model developed earlier by the community is further enhanced to an advanced version(referred to as A-VDISORT)through an improved ocean surface reflection.The Fresnel reflection matrix,which includes wind-generated roughness and shading effects,is served by an ocean bidirectional reflection distribution function(BRDF).The simulation from AVDISORT is compared with SCIATRAN for a Rayleigh scattering atmosphere,and the influence of water-leaving radiance is analyzed by the PSTAR(Polarized System for Transfer of Atmospheric Radiation) model.For GaoFen-5 Directional Polarimetric Camera(DPC) observations with polarization and multi-angle information,clear-sky pixel recognition over the ocean is first carried out.The DPC reflectance of clear conditions is normalized and compared with the observations.It is shown that A-VDISORT has a high simulation accuracy with a bias of –0.0053.The difference between simulation and observation exhibits a standard normal probability distribution function.展开更多
为解决路侧毫米波雷达数据分布不均匀、噪点较多,导致雷达在多目标跟踪方面准确性下降的问题,本文在密度峰值聚类(density peaks clustering,DPC)算法的基础上,提出一种适用于毫米波雷达数据改进的DPC算法。该方法结合匈牙利匹配算法和...为解决路侧毫米波雷达数据分布不均匀、噪点较多,导致雷达在多目标跟踪方面准确性下降的问题,本文在密度峰值聚类(density peaks clustering,DPC)算法的基础上,提出一种适用于毫米波雷达数据改进的DPC算法。该方法结合匈牙利匹配算法和无迹卡尔曼滤波算法(unscented Kalman filter,UKF),实现77 GHz毫米波雷达在不同车流密度路面上的跟踪验证。实验结果表明:改进后的DPC算法能够在大幅度提高毫米波雷达数据聚类精度的同时,有效提高多目标跟踪算法的跟踪精度。展开更多
Aiming at mitigating the high risks associated with conventional explosive blasting,this study developed a safe directional fracturing technique,i.e.instantaneous expansion with a single fracture(IESF),using a coal-ba...Aiming at mitigating the high risks associated with conventional explosive blasting,this study developed a safe directional fracturing technique,i.e.instantaneous expansion with a single fracture(IESF),using a coal-based solid waste expanding agent.First,the mechanism of directional fracturing blasting by the IESF was analyzed,and the criterion of directional crack initiation was established.On this basis,laboratory experiments and numerical simulations were conducted to systematically evaluate the directional fracturing blasting performance of the IESF.The results indicate that the IESF presents an excellent directional fracturing effect,with average surface undulation differences ranging from 8.1 mm to 22.7 mm on the fracture surfaces.Moreover,during concrete fracturing tests,the stresses and strains in the fracturing direction are measured to be 2.16-3.71 times and 8 times larger than those in the nonfracturing direction,respectively.Finally,the IESF technique was implemented for no-pillar mining with gob-side entry retaining through roof cutting and pressure relief in an underground coal mine.The IESF technique effectively created directional cracks in the roof without causing severe roadway deformation,achieving an average cutting rate and maximum roadway deformation of 94%and 197 mm,respectively.These on-site test results verified its excellent directional rock fracturing performance.The IESF technique,which is safe,efficient,and green,has considerable application prospects in the field of rock mechanics and engineering.展开更多
针对间歇采样转发干扰产生的假目标和目标高速运动产生的多普勒频移导致雷达脉压性能急剧下降的问题,提出一种高多普勒容限的线性调频离散相位编码(linear frequency modulation-discrete phase coding,LFM-DPC)复合调制相干波形集设计...针对间歇采样转发干扰产生的假目标和目标高速运动产生的多普勒频移导致雷达脉压性能急剧下降的问题,提出一种高多普勒容限的线性调频离散相位编码(linear frequency modulation-discrete phase coding,LFM-DPC)复合调制相干波形集设计方法。在一定多普勒频移范围内,以最小化未转发信号自模糊函数旁瓣能量以及未转发信号与转发信号互模糊函数能量建立优化模型,并设计一种基于KKT(Karush-Kuhn-Tucker)最优性条件的迭代算法对模型求解。仿真实验表明,相比于遗传算法和单一调制的LFM和DPC信号,基于KKT最优性条件的交替迭代优化算法优化的LFM-DPC波形集有更好的抗间歇采样转发干扰性能。展开更多
Interval-valued pre-aggregation functions are a hot topic in the research of aggregation functions and have received considerable attention in recent years.As a special class of interval-valued pre-aggregation functio...Interval-valued pre-aggregation functions are a hot topic in the research of aggregation functions and have received considerable attention in recent years.As a special class of interval-valued pre-aggregation functions,(light)interval-valued pre-t-norms were initially proposed by Wang and Hu,but their properties were not further discussed by the authors.The main purpose of this paper is to study in depth the properties and generation of(light)intervalvalued pre-t-norms.Firstly,several properties of(light)interval-valued pre-t-norms and their relationship with(light)pre-t-norms are presented.Then,two different generation methods for(light)interval-valued pre-t-norms are introduced.Finally,it demonstrates a specific application of(light)interval-valued pre-t-norms in constructing interval-valued directional monotonic fuzzy implications,namely,using the(light)interval-valued pre-t-norm IT,interval-valued fuzzy negations IN,and(light)interval-valued pre-t-conorm IS to construct interval-valued QL-directional monotonic operations.展开更多
Columnar grains offer considerable advantages in terms of microstructure for resisting high-temperature low-cycle fatigue. In additive manufacturing, the formation of fine columnar grains is common. However, post-heat...Columnar grains offer considerable advantages in terms of microstructure for resisting high-temperature low-cycle fatigue. In additive manufacturing, the formation of fine columnar grains is common. However, post-heat treatment often transforms these grains into equiaxed grains. This study aimed to tailor the grain morphology by controlling the precipitation of carbides. By balancing the restraining effects of carbide pinning and grain growth, we achieved carbide-assisted in situ-directional recrystallization. This process preserved the columnar grains created via laser powder bed fusion, even after high-temperature heat treatment. The approach emphasizes promoting the longitudinal growth of columnar grains while preventing their broadening. Additionally, we characterized the evolution of carbides and γ′ precipitates and examined their role in nucleation and growth during recrystallization. This study supports the viability of carbide-assisted in situ-directional recrystallization in additive manufacturing alloys, introducing an innovative strategy for microstructure customization. The implementation of carbon stabilization (CS) treatment to control the carbide distribution led to a 40 % improvement in the creep life at 900 ℃ and 150 MPa.展开更多
Microporosity formed in the solidification process of Al alloys is detrimental to the alloy properties.A two-dimensional cellular automaton(CA)model was developed to simulate the microstructure and microporosity forma...Microporosity formed in the solidification process of Al alloys is detrimental to the alloy properties.A two-dimensional cellular automaton(CA)model was developed to simulate the microstructure and microporosity formation in Al-Cu alloys,considering variations in Cu content and solidification rate.The results indicate that the Cu content primarily influences the growth of microporosity.To validate the model,directional solidification experiments were conducted on Al-Cu alloys with varing Cu contents and withdrawal rates.The experimental results of dendrites and microporosity characteristics agree well with the predictions from the developed model,thus confirming the validity of the model.The alloy’s liquidus temperature,dendrite morphology,and hydrogen saturation solubility arising from different Cu contents have significant effects on microporosity morphology.The withdrawal rate primarily affects the nucleation of hydrogen microporosity by altering cooling rates and dendritic growth rates,resulting in different microporosity characteristics.展开更多
Surface recrystallization(RX) is a typical grain defect observed in directionally solidified(DS) Ni-based superalloys. Most studies have focused on the RX behavior and its impact on the mechanical properties of single...Surface recrystallization(RX) is a typical grain defect observed in directionally solidified(DS) Ni-based superalloys. Most studies have focused on the RX behavior and its impact on the mechanical properties of single-crystal(SC) superalloys, with limited research on its influence on the high-temperature mechanical properties of DS superalloys. This study systematically investigated the effect of RX on the high-temperature tensile properties of a DS DZ409 superalloy. The results show that at 650℃, the yield strength decreases almost linearly with an increase in RX fraction. A significant reduction in elongation is observed as the RX fraction increases from 0% to 4.9%. However, beyond this point, further increase in RX fraction leads to minimal changes in elongation. At 950℃, both yield strength and elongation decrease as the RX fraction increases from 0% to 4.9%. At 650℃, fractures in the RX DS superalloys exhibit a mixed mode of transgranular and intergranular cleavage fracture, while at 950℃, it features a combination of ductile and intergranular dimple fractures. The failure mechanism of the RX DS superalloy is associated with the introduction of transverse grain boundaries(GBs) during RX. In the early stages of tensile testing at intermediate and high temperatures, cracks can easily initiate at these GBs. Subsequently, the cracks propagate along the GBs into the DS matrix, ultimately leading to failure of the DS superalloy.展开更多
We proposed a new technique route of directional solidification for the manufacture of super slab.A 7-t laboratory-scale thick slab was casted and characterised for trial.To further understand the process,the evolutio...We proposed a new technique route of directional solidification for the manufacture of super slab.A 7-t laboratory-scale thick slab was casted and characterised for trial.To further understand the process,the evolution of the multiple physical fields during the directional solidification was simulated and verified.Similar to the convectional ingot casting,a negative segregated cone of equiaxed grains was formed at the bottom,and a seriously positive segregated region was formed beneath the top surface of the slab.Specific measures on the lateral walls,base plate,and free surface were strongly recommended to ensure that the slab is relatively directionally casted.A water-cooling copper base plate accelerates the solidification rate and the columnar growth along the vertical direction.It inhibits the sedimentation of equiaxed grains and enlarges the columnar zone.Based on the simulation analysis,it can be concluded that the directional solidification technique route is promising to manufacture super slab with lower segregation level,and less porosities and inclusions.展开更多
Pneumatic down-the-hole hammer, serving as rock-breaking tool, possesses appeal for directional drilling due to its high rate of penetration. However, corresponding experimental studies on existing hammers for directi...Pneumatic down-the-hole hammer, serving as rock-breaking tool, possesses appeal for directional drilling due to its high rate of penetration. However, corresponding experimental studies on existing hammers for directional drilling have rarely been reported, and a model for evaluating their output performance is absent. This study proposes a novel structure of self-rotating pneumatic hammer(NSH)with a built-in rotational mechanism, which converts partial impact energy of the piston to rotate the drill bit and, consequently, enables dual functions of impact and rotate drill bit. The energy is converted via a screw key-groove mechanism, and the wedge-shaped teeth mechanism ensures that the drill bit rotates clockwise during the piston moves downward. The computational fluid dynamics method is applied to simulate the dynamic response of airflow and piston during the operation of Φ127NSH.Meanwhile, a test bench is established to record data concerning chamber pressure and piston displacement, as well as recording its operational status and rock fragmentation during drilling into granite. The results showed that the maximum error between simulated and experimental data is 8.2%.The Φ127NSH successfully achieves dual impact and rotary drilling functions, and granite smoothly feeds and forms a continuous shear rock zone. In addition, the effects of torque load, engagement distance in rotation sleeves, and well deviation angle towards the performance of NSH were studied in detail. The designed Φ127NSH operates at an impact velocity of 3.98 m/s, impact frequency of 12.55 Hz, and rotational speed of 29.51 r/min under a mass-flow rate of 0.18 kg/s, torque load of 400 N·m, engagement distance of 40 mm, and well deviation angle of 0°. The torque load adversely affects the NSH output performance. Increasing the engagement distance improves impact performance while reducing rotational performance. The performance variation of the NSH is minimal when drilling directional wells with varying deviation angles.展开更多
Let X be a real uniformly convex and uniformly smooth Banach space and C a nonempty closed and convex subset of X.Let Π_(C):X→C denote the generalized metric projection operator introduced by Alber in[1].In this pap...Let X be a real uniformly convex and uniformly smooth Banach space and C a nonempty closed and convex subset of X.Let Π_(C):X→C denote the generalized metric projection operator introduced by Alber in[1].In this paper,we define the Gâteaux directional differentiability of Π_(C).We investigate some properties of the Gâteaux directional differentiability of Π_(C).In particular,if C is a closed ball,or a closed and convex cone(including proper closed subspaces),or a closed and convex cylinder,then,we give the exact representations of the directional derivatives of Π_(C).By comparing the results in[12]and this paper,we see the significant difference between the directional derivatives of the generalized metric projection operator Π_(C) and the Gâteaux directional derivatives of the standard metric projection operator PC.展开更多
The directional annealing technique is widely used to prepare columnar grains or single crystals.To investigate the effect of hot zone temperature and temperature gradient on the growth of columnar crystals,Ti43Al all...The directional annealing technique is widely used to prepare columnar grains or single crystals.To investigate the effect of hot zone temperature and temperature gradient on the growth of columnar crystals,Ti43Al alloys were heat treated by the directional annealing technique and their mechanical properties were tested.The results show that columnar grains with a maximum size of 22.29 mm can be obtained at a hot zone temperature of 1,350℃ and a temperature gradient of 8 K·mm^(-1).During the directional annealing process,Ti43Al alloys are heated toαsingle-phase domain to start the phase transformation.Columnar grains with a microstructure of fully lamellar colonies are obtained at different hot zone temperatures and temperature gradients.The distribution of the orientation difference for theα2 phase was found to be more random,suggesting that the growth of the columnar crystals may be stochastic in nature.Tensile testing results show that the strength and elongation of directional annealed Ti43Al alloy at 1,400℃-8 K·mm^(-1) are 411.23 MPa and 2.29%,and the remaining directional annealed alloys show almost plasticity.展开更多
The directional explosion behavior of finite volume water confined within nanochannels holds considerable potential for applications in precision nanofabrication and bioengineering.However,precise control of nanoscale...The directional explosion behavior of finite volume water confined within nanochannels holds considerable potential for applications in precision nanofabrication and bioengineering.However,precise control of nanoscale mass transfer remains challenging in nanofluidics.This study examined the dynamic evolution of water clusters confined within a single-end-opened carbon nanotube(CNT)under pulsed electric field(EF)excitation,with a particular focus on the structural reorganization of hydrogen bond(H-bond)networks and dipole orientation realignment.Molecular dynamics simulations reveal that under the influence of pulsed EF,the confinedwatermolecules undergo cooperative restructuring to maximize hydrogen bond formation through four independent motions during deformation,such as waving,spinning,axial slipping,and radial migration.In this process,the dynamic fracture and recombination of the hydrogen bond network generate an instantaneous high pressure,and drive a unidirectional explosion along the CNT axis.A smaller CNT diameter or a reduced water volume under the same EF conditions leads to a stronger explosion.In contrast,in a wider CNT,the water cluster expands axially and forms a cylindrical shell whose thickness gradually decreases as the axial expansion slows.These insights offer precise control strategies for nanofluidic systems in nanofabrication or bioengineering applications,where finite volume water serves as a programmable nanoscale energy transfer medium.展开更多
Customizing the frequency range of electromagnetic wave(EMW)absorbing materials,especially for low-frequency,is a key research focus for 5G/6G and stealth applications.However,achieving precise low-frequency tuning re...Customizing the frequency range of electromagnetic wave(EMW)absorbing materials,especially for low-frequency,is a key research focus for 5G/6G and stealth applications.However,achieving precise low-frequency tuning remains challenging due to unpredictable parameter variations in practical design.Here,a constant-permeability-based electromagnetic parameter inversion method predicts the required complex permittivity range for multilayer MXene’s effective microwave absorption in the target low-frequency band.Since traditional modulation methods are plagued by electromagnetic parameter fluctuations,this study regulated the dielectric response by adjusting the embedding amount of small-sized iron nanoparticles(Fe NPs)with stable permeability.Under this guidance,multilayer MXene/Fe NPs(MTF)are prepared by embedding small-sized Fe NPs on the MXene surface via electrostatic self-assembly and in-situ reduction.The introduction of Fe NPs increased charge carriers’concentration and strengthened the interface effect,resulting in a significant increase in the real part of the complex permittivity(ε')compared with that of multi-layer MXene(7.13-8.89),reaching the predicted range of the real part of the low-frequency complex permittivity(13.12-15.16,14.34-16.81,and 15.29-18.12).Experimental results show that the MTF has a small error in the frequency of the minimum reflection loss(RLmin)compared to the predicted value(error percentage of 4.69%),along with an in-situ enhancement of the effective absorption bandwidth(EAB)(325.00%growth).Thus,MTF exhibits enhanced low-frequency absorption,with MTF-2 achieving−46.3 dB RLmin at 4.64 GHz(4.35 mm)and 2.24 GHz EAB at 3.8 mm.This work offers a strategy for accurate prediction and regulation of absorption bands over a wide range.展开更多
The ability of cyborg locusts to achieve directional movement in complex outdoor environments is critical for search and rescue missions.Currently,there is a lack of research on motion control for cyborg locusts in ou...The ability of cyborg locusts to achieve directional movement in complex outdoor environments is critical for search and rescue missions.Currently,there is a lack of research on motion control for cyborg locusts in outdoor settings.In this study,we developed cyborg locusts capable of performing directional locomotion in intricate outdoor environments,including jumping over obstacles,climbing slopes,traversing narrow pipelines,and accurately reaching predetermined targets along specified routes.We designed a miniature electrical backpack(10 mm×10 mm,0.75 g)capable of receiving stimulus parameters(frequency,duty ratio,and stimulation time)via Bluetooth commands from mobile phones.Electrical stimulation of locust sensory organs,such as the antennae and cercus,induced turning and jumping behaviors.Experi-mental testing of locust movement control was conducted under outdoor conditions with a short electrical stimulation interval.Results showed a positive correlation between locust turning angles and electrical stimulation parameters within a specified range,with an average jumping height exceeding 10 cm.Additionally,the success rate of locust turning and jumping behaviors correlated positively with the interval time between electrical stimulations.Adjusting these intervals during forward crawling phases increased the likelihood of the locusts jumping again.In conclusion,this study success-fully achieved directional locomotion control of cyborg locusts outdoors,providing insights and references for advancing search and rescue capabilities.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.U2142212)National Key R&D Program of China(Grant No.2019QZKK,Qinghai Tibet KeKao)the National Natural Science Foundation of China(Grant No.U2242211)。
文摘In recent years,polarization remote sensing has garnered increasing attention,particularly within the realm of meteorology.To accurately simulate polarization information,the vector discrete-ordinate radiative transfer(VDISORT)model developed earlier by the community is further enhanced to an advanced version(referred to as A-VDISORT)through an improved ocean surface reflection.The Fresnel reflection matrix,which includes wind-generated roughness and shading effects,is served by an ocean bidirectional reflection distribution function(BRDF).The simulation from AVDISORT is compared with SCIATRAN for a Rayleigh scattering atmosphere,and the influence of water-leaving radiance is analyzed by the PSTAR(Polarized System for Transfer of Atmospheric Radiation) model.For GaoFen-5 Directional Polarimetric Camera(DPC) observations with polarization and multi-angle information,clear-sky pixel recognition over the ocean is first carried out.The DPC reflectance of clear conditions is normalized and compared with the observations.It is shown that A-VDISORT has a high simulation accuracy with a bias of –0.0053.The difference between simulation and observation exhibits a standard normal probability distribution function.
基金supported by the National Natural Science Foundation of China(Grant No.52404155)State Key Laboratory of Mining Disaster Prevention and Control(Shandong University of Science and Technology)+1 种基金Ministry of Education(Grant No.JMDPC202402)supported by the opening project of State Key Laboratory of Explosion Science and Safety Protection(Beijing Institute of Technology).The opening project number is KFJJ24-20M.
文摘Aiming at mitigating the high risks associated with conventional explosive blasting,this study developed a safe directional fracturing technique,i.e.instantaneous expansion with a single fracture(IESF),using a coal-based solid waste expanding agent.First,the mechanism of directional fracturing blasting by the IESF was analyzed,and the criterion of directional crack initiation was established.On this basis,laboratory experiments and numerical simulations were conducted to systematically evaluate the directional fracturing blasting performance of the IESF.The results indicate that the IESF presents an excellent directional fracturing effect,with average surface undulation differences ranging from 8.1 mm to 22.7 mm on the fracture surfaces.Moreover,during concrete fracturing tests,the stresses and strains in the fracturing direction are measured to be 2.16-3.71 times and 8 times larger than those in the nonfracturing direction,respectively.Finally,the IESF technique was implemented for no-pillar mining with gob-side entry retaining through roof cutting and pressure relief in an underground coal mine.The IESF technique effectively created directional cracks in the roof without causing severe roadway deformation,achieving an average cutting rate and maximum roadway deformation of 94%and 197 mm,respectively.These on-site test results verified its excellent directional rock fracturing performance.The IESF technique,which is safe,efficient,and green,has considerable application prospects in the field of rock mechanics and engineering.
文摘针对间歇采样转发干扰产生的假目标和目标高速运动产生的多普勒频移导致雷达脉压性能急剧下降的问题,提出一种高多普勒容限的线性调频离散相位编码(linear frequency modulation-discrete phase coding,LFM-DPC)复合调制相干波形集设计方法。在一定多普勒频移范围内,以最小化未转发信号自模糊函数旁瓣能量以及未转发信号与转发信号互模糊函数能量建立优化模型,并设计一种基于KKT(Karush-Kuhn-Tucker)最优性条件的迭代算法对模型求解。仿真实验表明,相比于遗传算法和单一调制的LFM和DPC信号,基于KKT最优性条件的交替迭代优化算法优化的LFM-DPC波形集有更好的抗间歇采样转发干扰性能。
基金the National Natural Science Foundation of China(Grant No.12171294)。
文摘Interval-valued pre-aggregation functions are a hot topic in the research of aggregation functions and have received considerable attention in recent years.As a special class of interval-valued pre-aggregation functions,(light)interval-valued pre-t-norms were initially proposed by Wang and Hu,but their properties were not further discussed by the authors.The main purpose of this paper is to study in depth the properties and generation of(light)intervalvalued pre-t-norms.Firstly,several properties of(light)interval-valued pre-t-norms and their relationship with(light)pre-t-norms are presented.Then,two different generation methods for(light)interval-valued pre-t-norms are introduced.Finally,it demonstrates a specific application of(light)interval-valued pre-t-norms in constructing interval-valued directional monotonic fuzzy implications,namely,using the(light)interval-valued pre-t-norm IT,interval-valued fuzzy negations IN,and(light)interval-valued pre-t-conorm IS to construct interval-valued QL-directional monotonic operations.
基金supported by the National Key Research and Development Program of China(Grant No.2019YFA0705300)the National Natural Science Foundation of China(Grant No.51974057)the Fundamental Research Funds for the Central Universities。
文摘Columnar grains offer considerable advantages in terms of microstructure for resisting high-temperature low-cycle fatigue. In additive manufacturing, the formation of fine columnar grains is common. However, post-heat treatment often transforms these grains into equiaxed grains. This study aimed to tailor the grain morphology by controlling the precipitation of carbides. By balancing the restraining effects of carbide pinning and grain growth, we achieved carbide-assisted in situ-directional recrystallization. This process preserved the columnar grains created via laser powder bed fusion, even after high-temperature heat treatment. The approach emphasizes promoting the longitudinal growth of columnar grains while preventing their broadening. Additionally, we characterized the evolution of carbides and γ′ precipitates and examined their role in nucleation and growth during recrystallization. This study supports the viability of carbide-assisted in situ-directional recrystallization in additive manufacturing alloys, introducing an innovative strategy for microstructure customization. The implementation of carbon stabilization (CS) treatment to control the carbide distribution led to a 40 % improvement in the creep life at 900 ℃ and 150 MPa.
基金financially supported by the National Natural Science Foundation of China(Grant No.51875211)the Beijing Natural Science Foundation(Grant No.L223001)。
文摘Microporosity formed in the solidification process of Al alloys is detrimental to the alloy properties.A two-dimensional cellular automaton(CA)model was developed to simulate the microstructure and microporosity formation in Al-Cu alloys,considering variations in Cu content and solidification rate.The results indicate that the Cu content primarily influences the growth of microporosity.To validate the model,directional solidification experiments were conducted on Al-Cu alloys with varing Cu contents and withdrawal rates.The experimental results of dendrites and microporosity characteristics agree well with the predictions from the developed model,thus confirming the validity of the model.The alloy’s liquidus temperature,dendrite morphology,and hydrogen saturation solubility arising from different Cu contents have significant effects on microporosity morphology.The withdrawal rate primarily affects the nucleation of hydrogen microporosity by altering cooling rates and dendritic growth rates,resulting in different microporosity characteristics.
基金supported by the National Science and Technology Major Project(No.HT-J2019-VI-0020-0136)the National Youth Talent Support Program,and the Fundamental Research Funds for the Central Universities(No.xtr072024004).
文摘Surface recrystallization(RX) is a typical grain defect observed in directionally solidified(DS) Ni-based superalloys. Most studies have focused on the RX behavior and its impact on the mechanical properties of single-crystal(SC) superalloys, with limited research on its influence on the high-temperature mechanical properties of DS superalloys. This study systematically investigated the effect of RX on the high-temperature tensile properties of a DS DZ409 superalloy. The results show that at 650℃, the yield strength decreases almost linearly with an increase in RX fraction. A significant reduction in elongation is observed as the RX fraction increases from 0% to 4.9%. However, beyond this point, further increase in RX fraction leads to minimal changes in elongation. At 950℃, both yield strength and elongation decrease as the RX fraction increases from 0% to 4.9%. At 650℃, fractures in the RX DS superalloys exhibit a mixed mode of transgranular and intergranular cleavage fracture, while at 950℃, it features a combination of ductile and intergranular dimple fractures. The failure mechanism of the RX DS superalloy is associated with the introduction of transverse grain boundaries(GBs) during RX. In the early stages of tensile testing at intermediate and high temperatures, cracks can easily initiate at these GBs. Subsequently, the cracks propagate along the GBs into the DS matrix, ultimately leading to failure of the DS superalloy.
基金the National Natural Science Foundation of China(No.52074182)Joint Funds of the National Natural Science Foundation of China(No.U23A20612).
文摘We proposed a new technique route of directional solidification for the manufacture of super slab.A 7-t laboratory-scale thick slab was casted and characterised for trial.To further understand the process,the evolution of the multiple physical fields during the directional solidification was simulated and verified.Similar to the convectional ingot casting,a negative segregated cone of equiaxed grains was formed at the bottom,and a seriously positive segregated region was formed beneath the top surface of the slab.Specific measures on the lateral walls,base plate,and free surface were strongly recommended to ensure that the slab is relatively directionally casted.A water-cooling copper base plate accelerates the solidification rate and the columnar growth along the vertical direction.It inhibits the sedimentation of equiaxed grains and enlarges the columnar zone.Based on the simulation analysis,it can be concluded that the directional solidification technique route is promising to manufacture super slab with lower segregation level,and less porosities and inclusions.
基金supported by the Natural Science Foundation of Jilin Province(YDZJ202101ZYTS143).
文摘Pneumatic down-the-hole hammer, serving as rock-breaking tool, possesses appeal for directional drilling due to its high rate of penetration. However, corresponding experimental studies on existing hammers for directional drilling have rarely been reported, and a model for evaluating their output performance is absent. This study proposes a novel structure of self-rotating pneumatic hammer(NSH)with a built-in rotational mechanism, which converts partial impact energy of the piston to rotate the drill bit and, consequently, enables dual functions of impact and rotate drill bit. The energy is converted via a screw key-groove mechanism, and the wedge-shaped teeth mechanism ensures that the drill bit rotates clockwise during the piston moves downward. The computational fluid dynamics method is applied to simulate the dynamic response of airflow and piston during the operation of Φ127NSH.Meanwhile, a test bench is established to record data concerning chamber pressure and piston displacement, as well as recording its operational status and rock fragmentation during drilling into granite. The results showed that the maximum error between simulated and experimental data is 8.2%.The Φ127NSH successfully achieves dual impact and rotary drilling functions, and granite smoothly feeds and forms a continuous shear rock zone. In addition, the effects of torque load, engagement distance in rotation sleeves, and well deviation angle towards the performance of NSH were studied in detail. The designed Φ127NSH operates at an impact velocity of 3.98 m/s, impact frequency of 12.55 Hz, and rotational speed of 29.51 r/min under a mass-flow rate of 0.18 kg/s, torque load of 400 N·m, engagement distance of 40 mm, and well deviation angle of 0°. The torque load adversely affects the NSH output performance. Increasing the engagement distance improves impact performance while reducing rotational performance. The performance variation of the NSH is minimal when drilling directional wells with varying deviation angles.
文摘Let X be a real uniformly convex and uniformly smooth Banach space and C a nonempty closed and convex subset of X.Let Π_(C):X→C denote the generalized metric projection operator introduced by Alber in[1].In this paper,we define the Gâteaux directional differentiability of Π_(C).We investigate some properties of the Gâteaux directional differentiability of Π_(C).In particular,if C is a closed ball,or a closed and convex cone(including proper closed subspaces),or a closed and convex cylinder,then,we give the exact representations of the directional derivatives of Π_(C).By comparing the results in[12]and this paper,we see the significant difference between the directional derivatives of the generalized metric projection operator Π_(C) and the Gâteaux directional derivatives of the standard metric projection operator PC.
基金supported by the National Natural Science Foundation of China(Grant Nos.52074229,52371035)the Key R&D Plan of Sichuan Province(Grant No.SC2022A1C01J)the State Key Lab of Advanced Metals and Materials(Grant No.2020-ZD05).
文摘The directional annealing technique is widely used to prepare columnar grains or single crystals.To investigate the effect of hot zone temperature and temperature gradient on the growth of columnar crystals,Ti43Al alloys were heat treated by the directional annealing technique and their mechanical properties were tested.The results show that columnar grains with a maximum size of 22.29 mm can be obtained at a hot zone temperature of 1,350℃ and a temperature gradient of 8 K·mm^(-1).During the directional annealing process,Ti43Al alloys are heated toαsingle-phase domain to start the phase transformation.Columnar grains with a microstructure of fully lamellar colonies are obtained at different hot zone temperatures and temperature gradients.The distribution of the orientation difference for theα2 phase was found to be more random,suggesting that the growth of the columnar crystals may be stochastic in nature.Tensile testing results show that the strength and elongation of directional annealed Ti43Al alloy at 1,400℃-8 K·mm^(-1) are 411.23 MPa and 2.29%,and the remaining directional annealed alloys show almost plasticity.
基金The Start-up Research Fund from Shenzhen,the Natural Science Foundation of Guangdong(Grant Nos.2024A1515010821,2025A1515011727)the Shenzhen Development and ReformCommission(Grant No.XMHT20220103004).
文摘The directional explosion behavior of finite volume water confined within nanochannels holds considerable potential for applications in precision nanofabrication and bioengineering.However,precise control of nanoscale mass transfer remains challenging in nanofluidics.This study examined the dynamic evolution of water clusters confined within a single-end-opened carbon nanotube(CNT)under pulsed electric field(EF)excitation,with a particular focus on the structural reorganization of hydrogen bond(H-bond)networks and dipole orientation realignment.Molecular dynamics simulations reveal that under the influence of pulsed EF,the confinedwatermolecules undergo cooperative restructuring to maximize hydrogen bond formation through four independent motions during deformation,such as waving,spinning,axial slipping,and radial migration.In this process,the dynamic fracture and recombination of the hydrogen bond network generate an instantaneous high pressure,and drive a unidirectional explosion along the CNT axis.A smaller CNT diameter or a reduced water volume under the same EF conditions leads to a stronger explosion.In contrast,in a wider CNT,the water cluster expands axially and forms a cylindrical shell whose thickness gradually decreases as the axial expansion slows.These insights offer precise control strategies for nanofluidic systems in nanofabrication or bioengineering applications,where finite volume water serves as a programmable nanoscale energy transfer medium.
基金supported by the Chongqing New Youth Innovation Talent Program(No.CSTB2024NSCQ-QCXMX0086)Science and Technology Research Program of Chongqing Municipal Education Commission(No.KJZD-K202300606)+1 种基金National High-end Foreign Experts Introduction Plan(No.G2022035005L)Chongqing Talent Plan of Overall Rationing System Project(No.CQYC202203091156).
文摘Customizing the frequency range of electromagnetic wave(EMW)absorbing materials,especially for low-frequency,is a key research focus for 5G/6G and stealth applications.However,achieving precise low-frequency tuning remains challenging due to unpredictable parameter variations in practical design.Here,a constant-permeability-based electromagnetic parameter inversion method predicts the required complex permittivity range for multilayer MXene’s effective microwave absorption in the target low-frequency band.Since traditional modulation methods are plagued by electromagnetic parameter fluctuations,this study regulated the dielectric response by adjusting the embedding amount of small-sized iron nanoparticles(Fe NPs)with stable permeability.Under this guidance,multilayer MXene/Fe NPs(MTF)are prepared by embedding small-sized Fe NPs on the MXene surface via electrostatic self-assembly and in-situ reduction.The introduction of Fe NPs increased charge carriers’concentration and strengthened the interface effect,resulting in a significant increase in the real part of the complex permittivity(ε')compared with that of multi-layer MXene(7.13-8.89),reaching the predicted range of the real part of the low-frequency complex permittivity(13.12-15.16,14.34-16.81,and 15.29-18.12).Experimental results show that the MTF has a small error in the frequency of the minimum reflection loss(RLmin)compared to the predicted value(error percentage of 4.69%),along with an in-situ enhancement of the effective absorption bandwidth(EAB)(325.00%growth).Thus,MTF exhibits enhanced low-frequency absorption,with MTF-2 achieving−46.3 dB RLmin at 4.64 GHz(4.35 mm)and 2.24 GHz EAB at 3.8 mm.This work offers a strategy for accurate prediction and regulation of absorption bands over a wide range.
基金supported by Postgraduate Research&Practice Innovation Program of Jiangsu Province under Grant KYCX22_0290.
文摘The ability of cyborg locusts to achieve directional movement in complex outdoor environments is critical for search and rescue missions.Currently,there is a lack of research on motion control for cyborg locusts in outdoor settings.In this study,we developed cyborg locusts capable of performing directional locomotion in intricate outdoor environments,including jumping over obstacles,climbing slopes,traversing narrow pipelines,and accurately reaching predetermined targets along specified routes.We designed a miniature electrical backpack(10 mm×10 mm,0.75 g)capable of receiving stimulus parameters(frequency,duty ratio,and stimulation time)via Bluetooth commands from mobile phones.Electrical stimulation of locust sensory organs,such as the antennae and cercus,induced turning and jumping behaviors.Experi-mental testing of locust movement control was conducted under outdoor conditions with a short electrical stimulation interval.Results showed a positive correlation between locust turning angles and electrical stimulation parameters within a specified range,with an average jumping height exceeding 10 cm.Additionally,the success rate of locust turning and jumping behaviors correlated positively with the interval time between electrical stimulations.Adjusting these intervals during forward crawling phases increased the likelihood of the locusts jumping again.In conclusion,this study success-fully achieved directional locomotion control of cyborg locusts outdoors,providing insights and references for advancing search and rescue capabilities.
