Agricultural drought,characterized by insufficient soil moisture crucial for crop growth,poses significant chal lenges to food security and economic sustainability,particularly in water-scarce regions like Senegal.Thi...Agricultural drought,characterized by insufficient soil moisture crucial for crop growth,poses significant chal lenges to food security and economic sustainability,particularly in water-scarce regions like Senegal.This study addresses this issue by developing a comprehensive geospatial monitoring system for agricultural drought using the Regional Hydrologic Extremes Assessment System(RHEAS).This system,with a high-resolution of 0.05°,effectively simulates daily soil moisture and generates the Soil Moisture Deficit Index(SMDI)-based agricultural drought monitoring.The SMDI derived from the RHEAS has effectively captured historical droughts in Senegal over the recent 30 years period from 1993 to 2022.The SMDI,also provides a comprehensive understanding of regional variations in drought severity(S),duration(D),and frequency(F),through S-D-F analysis to identify key drought hotspots across Senegal.Findings reveal a distinct north-south gradient in drought conditions,with the northern and central Senegal experiencing more frequent and severe droughts.The study highlights that Senegal experiences frequent short-duration droughts with high severity,resulting in extensive spatial impact.Addition ally,increasing trends in drought severity and duration suggest evolving climate change effects.These findings emphasize the urgent need for sustainable interventions to mitigate drought impacts on agricultural productiv ity.Specifically,the study identifies recurrent and intense drought hotspots affecting yields of staple crops like maize and rice,as well as cash crops like peanuts.The developed high-resolution drought monitoring system for Senegal not only identifies hotspots but also enables prioritizing sustainable approaches and adaptive strategies,ultimately sustaining agricultural productivity and resilience in Senegal’s drought-prone regions.展开更多
A refractory high entropy alloy Ti_(62)Nb_(12)Mo_(12)Ta_(12)W_(2)was prepared by mechanical alloying and spark plasma sintering.The microstructure and mechanical properties of the Ti_(62)Nb_(12)Mo_(12)Ta_(12)W_(2)allo...A refractory high entropy alloy Ti_(62)Nb_(12)Mo_(12)Ta_(12)W_(2)was prepared by mechanical alloying and spark plasma sintering.The microstructure and mechanical properties of the Ti_(62)Nb_(12)Mo_(12)Ta_(12)W_(2)alloy were analyzed.The experimental results show that the microstructure of the alloy is composed of two BCC phases,an FCC precipitated phase,and the precipitated phase which is a mixture of TiC,TiN and TiO.The alloy exhibits good room temperature compressive properties.The plasticity of the sample sintered at 1550℃can reach 10.8%,and for the sample sintered at 1600℃,the yield strength can be up to 2032 MPa,in the meantime the plasticity is 9.4%.The alloy also shows high strength at elevated temperature.The yield strength of the alloy exceeds 420 MPa at 900℃,and value of which is still above 200 MPa when the test temperature reaches 1000℃.Finally,the compressive yield strength model at room temperature is constructed.The prediction error of the model ranges from−7.9%to−12.4%,expressing fair performance.展开更多
Refractory high-entropy alloys(RHEAs),composed of multiple refractory elements,such as Nb,Mo,Ta,W,Ti,Zr,Hf,in nearor non-equiatomic ratios,have recently emerged as promising structural materials for extreme environmen...Refractory high-entropy alloys(RHEAs),composed of multiple refractory elements,such as Nb,Mo,Ta,W,Ti,Zr,Hf,in nearor non-equiatomic ratios,have recently emerged as promising structural materials for extreme environments due to their high melting points,excellent high-temperature mechanical properties,and superior micro structural stability.Compared to conventional HEAs based on elements like Ni,Fe,or Cr,RHEAs offer enhanced elevated-temperature performance but face challenges including segregation during solidification,relatively poor room-temperature ductility,and,most important,high-temperature oxidation.展开更多
W-containing refractory high-entropy alloys(RHEAs)are promising for elevated-temperature applications,while the complexity of dendritic microstructure poses challenges in achieving controllable machining performance.I...W-containing refractory high-entropy alloys(RHEAs)are promising for elevated-temperature applications,while the complexity of dendritic microstructure poses challenges in achieving controllable machining performance.In this work,the controllability of sinking electrical discharge machining(EDM)performance on dendritic-structured(TiVCr)_(95)W_(5)and(FeVCr)_(95)W_(5)RHEAs was evaluated using a mathematical model that expresses the relationship between discharge parameters and machining performance.A superior controllability of the material removal rate and surface roughness(Ra)was obtained by the high accuracy and good predictability of the model,with the R^(2)value close to 1 and a predicted error for Ra below 5%.This was attributed to the stable removal behavior of the dendritic microstructure.Melting was the primary removal mechanism for both dendrites and inter-dendrites.The W element can stabilize the removal behavior of constituent elements.No obvious compositional variation was observed within the crater formed in dendrites.As more W diffused into inter-dendrites,the variation of Cr and V in inter-dendrites reduced from approximately 20.0%to less than 2.0%.Similar melting removal mechanisms led to an analogous relationship between the machining performance and processing conditions of the two RHEAs.Compared to the relatively high surface roughness achieved by wire-EDM,the optimized Ra values of 0.329 and 0.728μm for(TiVCr)_(95)W_(5)and(FeVCr)_(95)W_(5),respectively,demonstrated the superiority of sinking EDM for RHEAs.The present findings have confirmed the superior controllable sinking EDM performance for W-containing RHEAs,providing useful guidance for the processing of W-containing RHEAs in practical applications.展开更多
基金supported by the NASA(Grant No.80NSSC21K0403)USAID Kansas State University subcontract KSU-A20-0163-S035 with Michigan State University.
文摘Agricultural drought,characterized by insufficient soil moisture crucial for crop growth,poses significant chal lenges to food security and economic sustainability,particularly in water-scarce regions like Senegal.This study addresses this issue by developing a comprehensive geospatial monitoring system for agricultural drought using the Regional Hydrologic Extremes Assessment System(RHEAS).This system,with a high-resolution of 0.05°,effectively simulates daily soil moisture and generates the Soil Moisture Deficit Index(SMDI)-based agricultural drought monitoring.The SMDI derived from the RHEAS has effectively captured historical droughts in Senegal over the recent 30 years period from 1993 to 2022.The SMDI,also provides a comprehensive understanding of regional variations in drought severity(S),duration(D),and frequency(F),through S-D-F analysis to identify key drought hotspots across Senegal.Findings reveal a distinct north-south gradient in drought conditions,with the northern and central Senegal experiencing more frequent and severe droughts.The study highlights that Senegal experiences frequent short-duration droughts with high severity,resulting in extensive spatial impact.Addition ally,increasing trends in drought severity and duration suggest evolving climate change effects.These findings emphasize the urgent need for sustainable interventions to mitigate drought impacts on agricultural productiv ity.Specifically,the study identifies recurrent and intense drought hotspots affecting yields of staple crops like maize and rice,as well as cash crops like peanuts.The developed high-resolution drought monitoring system for Senegal not only identifies hotspots but also enables prioritizing sustainable approaches and adaptive strategies,ultimately sustaining agricultural productivity and resilience in Senegal’s drought-prone regions.
基金support from the Fundamental Research Program of Shanxi Province(202203021211130)the Innovation and Entrepreneurship Training Program for College Students in Shanxi Province(20220119)+1 种基金the Research Project Supported by Shanxi Scholarship Council of China(2023-068)the National Natural Science Foundation of China(Grant No.51801132).
文摘A refractory high entropy alloy Ti_(62)Nb_(12)Mo_(12)Ta_(12)W_(2)was prepared by mechanical alloying and spark plasma sintering.The microstructure and mechanical properties of the Ti_(62)Nb_(12)Mo_(12)Ta_(12)W_(2)alloy were analyzed.The experimental results show that the microstructure of the alloy is composed of two BCC phases,an FCC precipitated phase,and the precipitated phase which is a mixture of TiC,TiN and TiO.The alloy exhibits good room temperature compressive properties.The plasticity of the sample sintered at 1550℃can reach 10.8%,and for the sample sintered at 1600℃,the yield strength can be up to 2032 MPa,in the meantime the plasticity is 9.4%.The alloy also shows high strength at elevated temperature.The yield strength of the alloy exceeds 420 MPa at 900℃,and value of which is still above 200 MPa when the test temperature reaches 1000℃.Finally,the compressive yield strength model at room temperature is constructed.The prediction error of the model ranges from−7.9%to−12.4%,expressing fair performance.
文摘Refractory high-entropy alloys(RHEAs),composed of multiple refractory elements,such as Nb,Mo,Ta,W,Ti,Zr,Hf,in nearor non-equiatomic ratios,have recently emerged as promising structural materials for extreme environments due to their high melting points,excellent high-temperature mechanical properties,and superior micro structural stability.Compared to conventional HEAs based on elements like Ni,Fe,or Cr,RHEAs offer enhanced elevated-temperature performance but face challenges including segregation during solidification,relatively poor room-temperature ductility,and,most important,high-temperature oxidation.
基金supported by Anhui Provincial Natural Science Foundation(No.2308085ME172,2308085QE164)the National Magnetic Confinement Fusion Energy Research&Development(MCF Energy R&D)Program(No.2022YFE03140000)。
文摘W-containing refractory high-entropy alloys(RHEAs)are promising for elevated-temperature applications,while the complexity of dendritic microstructure poses challenges in achieving controllable machining performance.In this work,the controllability of sinking electrical discharge machining(EDM)performance on dendritic-structured(TiVCr)_(95)W_(5)and(FeVCr)_(95)W_(5)RHEAs was evaluated using a mathematical model that expresses the relationship between discharge parameters and machining performance.A superior controllability of the material removal rate and surface roughness(Ra)was obtained by the high accuracy and good predictability of the model,with the R^(2)value close to 1 and a predicted error for Ra below 5%.This was attributed to the stable removal behavior of the dendritic microstructure.Melting was the primary removal mechanism for both dendrites and inter-dendrites.The W element can stabilize the removal behavior of constituent elements.No obvious compositional variation was observed within the crater formed in dendrites.As more W diffused into inter-dendrites,the variation of Cr and V in inter-dendrites reduced from approximately 20.0%to less than 2.0%.Similar melting removal mechanisms led to an analogous relationship between the machining performance and processing conditions of the two RHEAs.Compared to the relatively high surface roughness achieved by wire-EDM,the optimized Ra values of 0.329 and 0.728μm for(TiVCr)_(95)W_(5)and(FeVCr)_(95)W_(5),respectively,demonstrated the superiority of sinking EDM for RHEAs.The present findings have confirmed the superior controllable sinking EDM performance for W-containing RHEAs,providing useful guidance for the processing of W-containing RHEAs in practical applications.
